Editing Lanthanide (section)

==Chemistry and compounds==

{{Main article|Lanthanide compounds}}

{| class="wikitable" style="font-size: 95%; text-align: center;"
|-
![[Chemical element]]!![[Lanthanum|La]]!![[Cerium|Ce]]!![[praseodymium|Pr]]!![[neodymium|Nd]]!![[promethium|Pm]]!![[samarium|Sm]]!![[europium|Eu]]!![[gadolinium|Gd]]!![[terbium|Tb]]!![[dysprosium|Dy]]!![[holmium|Ho]]!![[erbium|Er]]!![[thulium|Tm]]!![[ytterbium|Yb]]!![[lutetium|Lu]]
|-
| [[Atomic number]]
|57||58||59||60||61||62||63||64||65||66||67||68||69||70||71
|-
| Ln<sup>3+</sup> electron configuration*<ref name=CottonSA2006/>||4f<sup>0</sup> || 4f<sup>1</sup>||4f<sup>2</sup>|| 4f<sup>3</sup>|| 4f<sup>4</sup>||4f<sup>5</sup>|| 4f<sup>6</sup>|| 4f<sup>7</sup>||4f<sup>8</sup>|| 4f<sup>9</sup>|| 4f<sup>10</sup>||4f<sup>11</sup>||4f<sup>12</sup>|| 4f<sup>13</sup>||
4f<sup>14</sup>
|-
| Ln<sup>3+</sup> radius ([[picometer|pm]])<ref name = "Greenwood&Earnshaw"/> || 103 || 102 || 99|| 98.3|| 97|| 95.8|| 94.7|| 93.8|| 92.3|| 91.2|| 90.1|| 89||88|| 86.8|| 86.1
|-
| Ln<sup>4+</sup> ion color in aqueous solution<ref name="SroorEdelmann2012">{{cite book|last1=Sroor|first1=Farid M.A.|title=Encyclopedia of Inorganic and Bioinorganic Chemistry|last2=Edelmann|first2=Frank T.|year=2012|doi=10.1002/9781119951438.eibc2033|chapter=Lanthanides: Tetravalent Inorganic|isbn=9781119951438}}</ref> || — || Orange-yellow || Yellow || Blue-violet || — || — || — || — || Red-brown || Orange-yellow || — || — || — || — || —
|-
| Ln<sup>3+</sup> ion color in aqueous solution<ref name=CottonSA2006>{{cite book |last=Cotton |first=Simon |year=2006 |title=Lanthanide and Actinide Chemistry|publisher= John Wiley & Sons Ltd}}</ref> || Colorless || Colorless || Green || Violet || Pink || Pale yellow || Colorless || Colorless || V. pale pink || Pale yellow || Yellow || Rose || Pale green || Colorless || Colorless
|-
| Ln<sup>2+</sup> ion color in aqueous solution<ref name = "Greenwood&Earnshaw"/> || — || — || — || — || — || Blood red || Colorless || — || — || — || — || — || Violet-red || Yellow-green || —
|}

<nowiki>*</nowiki> Not including initial [Xe] core

f → f transitions are [[symmetry forbidden]] (or Laporte-forbidden), which is also true of [[transition metal]]s. However, transition metals are able to use [[vibronic coupling]] to break this rule. The valence orbitals in lanthanides are almost entirely non-bonding and as such little effective vibronic coupling takes, hence the spectra from f → f transitions are much weaker and narrower than those from d → d transitions. In general this makes the colors of lanthanide complexes far fainter than those of transition metal complexes. 

{| class="wikitable collapsible" style="margin:1em auto; text-align:center; color: black;"
|+Approximate colors of lanthanide ions in aqueous solution<ref name = "Greenwood&Earnshaw"/><ref name="HOWI1">[[#Holleman|Holleman]], p.&nbsp;1937.</ref><ref name="dtv1">dtv-Atlas zur Chemie '''1981''', Vol. 1, p.&nbsp;220.</ref>
| style="background:#ddd;"| Oxidation state
| 57 || 58 || 59 || 60 || 61 || 62 || 63 || 64 || 65 || 66 || 67 || 68 || 69 || 70 || 71
|-
| +2|| || || || ||
| style="background:#d00; color: white;"| '''Sm<sup>2+</sup>''' || '''Eu<sup>2+</sup>'''
|| || || || ||
| style="background:#d07; color: white;"| '''Tm<sup>2+</sup>'''
| style="background:#cf0;"| '''Yb<sup>2+</sup>''' ||
|-
| +3|| '''La<sup>3+</sup>''' || '''Ce<sup>3+</sup>'''
| style="background:#cf0;"| '''Pr<sup>3+</sup>'''
| style="background:#b0d; color: white;"| '''Nd<sup>3+</sup>'''
| style="background:#d0d; color: white;"| '''Pm<sup>3+</sup>'''
| style="background:#fe0;"| '''Sm<sup>3+</sup>'''
| '''Eu<sup>3+</sup>''' || '''Gd<sup>3+</sup>'''
| style="background:#fee;"| '''Tb<sup>3+</sup>'''
| style="background:#FFFFC5;"| '''Dy<sup>3+</sup>'''
| style="background:#ff0;"| '''Ho<sup>3+</sup>'''
| style="background:#e0d; color: white;"| '''Er<sup>3+</sup>'''
| style="background:#ef0;"| '''Tm<sup>3+</sup>'''
| '''Yb<sup>3+</sup>''' || '''Lu<sup>3+</sup>'''
|-
| +4|| || style="background:#fd0;"| '''Ce<sup>4+</sup>'''
| style="background:#ff0;"| '''Pr<sup>4+</sup>'''
| style="background:#70d; color: white;"| '''Nd<sup>4+</sup>''' || || || ||
| style="background:#d60; color: white;"| '''Tb<sup>4+</sup>'''
| style="background:#fd0;"| '''Dy<sup>4+</sup>''' || || || || ||
|}

===Effect of 4f orbitals===
Viewing the lanthanides from left to right in the periodic table, the seven [[Atomic orbital#Orbitals_table|4f atomic orbital]]s become progressively more filled (see above and {{section link|Periodic table|Electron configuration table}}). The electronic configuration of most neutral gas-phase lanthanide atoms is [Xe]6s<sup>2</sup>4f<sup>''n''</sup>, where ''n'' is 56 less than the atomic number ''Z''. Exceptions are La, Ce, Gd, and Lu, which have 4f<sup>''n''−1</sup>5d<sup>1</sup> (though even then 4f<sup>''n''</sup> is a low-lying excited state for La, Ce, and Gd; for Lu, the 4f shell is already full, and the fifteenth electron has no choice but to enter 5d). With the exception of lutetium, the 4f orbitals are chemically active in all lanthanides and produce profound differences between lanthanide chemistry and [[transition metal]] chemistry. The 4f orbitals penetrate the [Xe] core and are isolated, and thus they do not participate much in bonding. This explains why crystal field effects are small and why they do not form π bonds.<ref name=CottonSA2006/> As there are seven 4f orbitals, the number of unpaired electrons can be as high as 7, which gives rise to the large [[magnetochemistry|magnetic moments]] observed for lanthanide compounds. 

Measuring the magnetic moment can be used to investigate the 4f electron configuration, and this is a useful tool in providing an insight into the chemical bonding.<ref name="BochkarevFedushkin1997">{{cite journal|last1=Bochkarev|first1=Mikhail N.|last2=Fedushkin|first2=Igor L.|last3=Fagin|first3=Anatoly A.|last4=Petrovskaya|first4=Tatyana V.|last5=Ziller|first5=Joseph W.|last6=Broomhall-Dillard|first6=Randy N. R.|last7=Evans|first7=William J.|title=Synthesis and Structure of the First Molecular Thulium(II) Complex: [TmI<sub>2</sub>(MeOCH<sub>2</sub>CH<sub>2</sub>OMe)<sub>3</sub>]|journal=Angewandte Chemie International Edition in English|volume=36|issue=12|year=1997|pages=133–135|doi=10.1002/anie.199701331}}</ref> The [[lanthanide contraction]], i.e. the reduction in size of the Ln<sup>3+</sup> ion from La<sup>3+</sup> (103 pm) to Lu<sup>3+</sup> (86.1&nbsp;pm), is often explained by the poor shielding of the 5s and 5p electrons by the 4f electrons.<ref name=CottonSA2006/>

[[File:Rareearthoxides.jpg|thumb|Lanthanide oxides: clockwise from top center: praseodymium, cerium, lanthanum, neodymium, samarium and gadolinium.]]
The chemistry of the lanthanides is dominated by the +3 oxidation state, and in Ln<sup>III</sup> compounds the 6s electrons and (usually) one 4f electron are lost and the ions have the configuration [Xe]4f<sup>(''n''−1)</sup>.<ref>{{cite web|author=Winter, Mark |url=http://www.webelements.com/lanthanum/atoms.html|title=Lanthanum ionisation energies|publisher=WebElements Ltd, UK|access-date=2 September 2010}}</ref> All the lanthanide elements exhibit the [[oxidation state]] +3. In addition, Ce<sup>3+</sup> can lose its single f electron to form Ce<sup>4+</sup> with the stable electronic configuration of xenon. Also, Eu<sup>3+</sup> can gain an electron to form Eu<sup>2+</sup> with the f<sup>7</sup> configuration that has the extra stability of a half-filled shell. Other than Ce(IV) and Eu(II), none of the lanthanides are stable in oxidation states other than +3 in aqueous solution. 

In terms of reduction potentials, the Ln<sup>0/3+</sup> couples are nearly the same for all lanthanides, ranging from −1.99 (for Eu) to −2.35 V (for Pr). Thus these metals are highly reducing, with reducing power similar to alkaline earth metals such as Mg (−2.36 V).<ref name = "Greenwood&Earnshaw"/>

===Lanthanide oxidation states===
{| class="wikitable collapsible collapsed" style="font-size:95%;"
|+ Ionization energies and reduction potentials of the elements
![[Chemical element]]!![[Lanthanum|La]]!![[Cerium|Ce]]!![[praseodymium|Pr]]!![[neodymium|Nd]]!![[promethium|Pm]]!![[samarium|Sm]]!![[europium|Eu]]!![[gadolinium|Gd]]!![[terbium|Tb]]!![[dysprosium|Dy]]!![[holmium|Ho]]!![[erbium|Er]]!![[thulium|Tm]]!![[ytterbium|Yb]]!![[lutetium|Lu]]
|-
| [[Atomic number]]
|57||58||59||60||61||62||63||64||65||66||67||68||69||70||71
|-
| [[electron configuration]]<br> above [Xe] core||'''4f<sup>0</sup>5d<sup>1</sup>'''6s<sup>2</sup>||'''4f<sup>1</sup>5d<sup>1</sup>'''6s<sup>2</sup>||4f<sup>3</sup>6s<sup>2</sup>||4f<sup>4</sup>6s<sup>2</sup>|| 4f<sup>5</sup>6s<sup>2</sup>||4f<sup>6</sup>6s<sup>2</sup>||4f<sup>7</sup>6s<sup>2</sup>||'''4f<sup>7</sup>5d<sup>1</sup>'''6s<sup>2</sup>||4f<sup>9</sup>6s<sup>2</sup>||4f<sup>10</sup>6s<sup>2</sup>||4f<sup>11</sup>6s<sup>2</sup>||4f<sup>12</sup>6s<sup>2</sup>||4f<sup>13</sup>6s<sup>2</sup>||4f<sup>14</sup>6s<sup>2</sup>||4f<sup>14</sup>5d<sup>1</sup>6s<sup>2</sup>
|-
|E° Ln<sup>4+</sup>/Ln<sup>3+</sup>
|  ||1.72||  3.2|| ||  ||  ||  ||  ||  3.1|| ||  ||  ||  ||  ||
|-
|E° Ln<sup>3+</sup>/Ln<sup>2+</sup>
|  ||  ||  ||−2.6||  ||−1.55||−0.35||  ||  ||−2.5||  ||  ||−2.3||−1.05||
|-
|E° Ln<sup>3+</sup>/Ln           
| −2.38||−2.34||−2.35||−2.32||−2.29||−2.30||−1.99||−2.28||−2.31||−2.29||−2.33||−2.32||−2.32||−2.22||−2.30
|-
|1st Ionization energy<br> (kJ·mol<sup>−1</sup>)
|538||541||522||530||536||542||547||595||569||567||574||581||589||603||513
|-
|2nd Ionization energy<br> (kJ·mol<sup>−1</sup>)
|1067||1047||1018||1034||1052||1068||1085||1172||1112||1126||1139||1151||1163||1175||1341
|-
|1st + 2nd Ionization energy<br> (kJ·mol<sup>−1</sup>)
|1605||1588||1540||1564||1588||1610||1632||1767||1681||1693||1713||1732||1752||1778||1854
|-
|3rd Ionization energy<br> (kJ·mol<sup>−1</sup>)
|1850||1940||2090||2128||2140||2285||2425||1999||2122||2230||2221||2207||2305||2408||2054
|-
|1st + 2nd + 3rd Ionization energy<br> (kJ·mol<sup>−1</sup>)
|3455||3528||3630||3692||3728||3895||4057||3766||3803||3923||3934||3939||4057||4186||3908
|-
|4th Ionization energy<br> (kJ·mol<sup>−1</sup>)
|4819||3547||3761||3900||3970||3990||4120||4250||3839||3990||4100||4120||4120||4203||4370
|}
The ionization energies for the lanthanides can be compared with aluminium. In aluminium the sum of the first three ionization energies is 5139 kJ·mol<sup>−1</sup>, whereas the lanthanides fall in the range 3455 – 4186 kJ·mol<sup>−1</sup>. This correlates with the highly reactive nature of the lanthanides.

The sum of the first two ionization energies for europium, 1632 kJ·mol<sup>−1</sup> can be compared with that of barium 1468.1 kJ·mol<sup>−1</sup> and europium's third ionization energy is the highest of the lanthanides. The sum of the first two ionization energies for ytterbium are the second lowest in the series and its third ionization energy is the second highest. The high third ionization energy for Eu and Yb correlate with the half filling 4f<sup>7</sup> and complete filling 4f<sup>14</sup> of the 4f subshell, and the stability afforded by such configurations due to exchange energy.<ref name=CottonSA2006/> Europium and ytterbium form salt like compounds with Eu<sup>2+</sup> and Yb<sup>2+</sup>, for example the salt like dihydrides.<ref name="Fukai"/> Both europium and ytterbium dissolve in liquid ammonia forming solutions of Ln<sup>2+</sup>(NH<sub>3</sub>)<sub>x</sub> again demonstrating their similarities to the alkaline earth metals.<ref name = "Greenwood&Earnshaw"/>

The relative ease with which the 4th electron can be removed in cerium and (to a lesser extent praseodymium) indicates why Ce(IV) and Pr(IV) compounds can be formed, for example CeO<sub>2</sub> is formed rather than Ce<sub>2</sub>O<sub>3</sub> when cerium reacts with oxygen. Also Tb has a well-known IV state, as removing the 4th electron in this case produces a half-full 4f<sup>7</sup> configuration.

The additional stable valences for Ce and Eu mean that their abundances in rocks sometimes varies significantly relative to the other rare earth elements: see [[cerium anomaly]] and [[europium anomaly]].

===Separation of lanthanides===
The similarity in ionic radius between adjacent lanthanide elements makes it difficult to separate them from each other in naturally occurring ores and other mixtures. Historically, the very laborious processes of [[Cascade (chemical engineering)|cascading]] and [[fractional crystallization (chemistry)|fractional crystallization]] were used. Because the lanthanide ions have slightly different radii, the [[lattice energy]] of their salts and hydration energies of the ions will be slightly different, leading to a small difference in [[solubility]]. Salts of the formula Ln(NO<sub>3</sub>)<sub>3</sub>·2NH<sub>4</sub>NO<sub>3</sub>·4H<sub>2</sub>O can be used. Industrially, the elements are separated from each other by [[solvent extraction]]. Typically an aqueous solution of nitrates is extracted into kerosene containing [[Tributyl phosphate|tri-''n''-butylphosphate]]. The [[stability constants of complexes|strength of the complexes]] formed increases as the ionic radius decreases, so solubility in the organic phase increases. Complete separation can be achieved continuously by use of [[countercurrent exchange]] methods. The elements can also be separated by [[ion-exchange chromatography]], making use of the fact that the [[stability constants of complexes|stability constant]] for formation of [[EDTA]] complexes increases for log K ≈ 15.5 for [La(EDTA)]<sup>−</sup> to log K ≈ 19.8 for [Lu(EDTA)]<sup>−</sup>.<ref name = "Greenwood&Earnshaw"/><ref>Pettit, L. and Powell, K. [http://www.acadsoft.co.uk/scdbase/scdbase.htm SC-database] {{Webarchive|url=https://web.archive.org/web/20170619235720/http://www.acadsoft.co.uk/scdbase/scdbase.htm |date=19 June 2017 }}. Acadsoft.co.uk. Retrieved on 15 January 2012.</ref>

===Coordination chemistry and catalysis===
When in the form of [[coordination complex]]es, lanthanides exist overwhelmingly in their +3 [[oxidation state]], although particularly stable 4f configurations can also give +4 (Ce, Pr, Tb) or +2 (Sm, Eu, Yb) ions. All of these forms are strongly electropositive and thus lanthanide ions are [[HSAB theory|hard Lewis acids]].<ref name="Ortu">{{ cite journal | title = Rare Earth Starting Materials and Methodologies for Synthetic Chemistry | first1 = Fabrizio | last1 = Ortu | journal = [[Chemical Reviews|Chem. Rev.]] | year = 2022 | volume = 122 | issue = 6 | pages = 6040–6116 | doi = 10.1021/acs.chemrev.1c00842 | pmid = 35099940 | pmc = 9007467 }}</ref> The oxidation states are also very stable; with the exceptions of [[SmI2|SmI<sub>2</sub>]]<ref>{{cite journal|last1=Molander|first1=Gary A.|last2=Harris|first2=Christina R.|title=Sequencing Reactions with Samarium(II) Iodide|journal=Chemical Reviews|date=1 January 1996|volume=96|issue=1|pages=307–338|doi=10.1021/cr950019y|pmid=11848755}}</ref> and [[Ceric ammonium nitrate|cerium(IV) salts]],<ref>{{cite journal|last1=Nair|first1=Vijay|last2=Balagopal|first2=Lakshmi|last3=Rajan|first3=Roshini|last4= Mathew|first4=Jessy|title=Recent Advances in Synthetic Transformations Mediated by Cerium(IV) Ammonium Nitrate|journal=Accounts of Chemical Research|date=1 January 2004|volume=37|issue=1|pages=21–30|doi=10.1021/ar030002z|pmid=14730991}}</ref> lanthanides are not used for [[redox]] chemistry. 4f electrons have a high probability of being found close to the nucleus and are thus strongly affected as the [[nuclear charge]] increases across the [[Chemical series|series]]; this results in a corresponding decrease in [[ionic radii]] referred to as the [[lanthanide contraction]].

The low probability of the 4f electrons existing at the outer region of the atom or ion permits little effective overlap between the [[Atomic orbitals|orbitals]] of a lanthanide ion and any binding [[ligand]]. Thus lanthanide [[coordination complex|complexes]] typically have little or no [[covalent bond|covalent]] character and are not influenced by orbital geometries. The lack of orbital interaction also means that varying the metal typically has little effect on the complex (other than size), especially when compared to [[transition metals]]. Complexes are held together by weaker [[ionic bond|electrostatic]] forces which are omni-directional and thus the ligands alone dictate the [[molecular symmetry|symmetry]] and coordination of complexes. [[Steric effects|Steric factors]] therefore dominate, with coordinative saturation of the metal being balanced against inter-ligand repulsion. This results in a diverse range of [[Coordination geometry|coordination geometries]], many of which are irregular,<ref>{{cite journal|last1=Dehnicke|first1=Kurt|last2=Greiner|first2=Andreas|title=Unusual Complex Chemistry of Rare-Earth Elements: Large Ionic Radii—Small Coordination Numbers|journal=Angewandte Chemie International Edition|year=2003|volume=42|issue=12|pages=1340–1354|doi=10.1002/anie.200390346|pmid=12671966}}</ref> and also manifests itself in the highly [[fluxional]] nature of the complexes. As there is no energetic reason to be locked into a single geometry, rapid intramolecular and intermolecular ligand exchange will take place. This typically results in complexes that rapidly fluctuate between all possible configurations.

Many of these features make lanthanide complexes effective [[catalyst]]s. Hard Lewis acids are able to polarise bonds upon coordination and thus alter the electrophilicity of compounds, with a classic example being the [[Luche reduction]]. The large size of the ions coupled with their labile ionic bonding allows even bulky coordinating species to bind and dissociate rapidly, resulting in very high turnover rates; thus excellent yields can often be achieved with loadings of only a few mol%.<ref>{{cite book|last=Aspinall|first=Helen C.|title=Chemistry of the f-block elements|year=2001|publisher=Gordon & Breach|location=Amsterdam [u.a.]|isbn=978-9056993337}}</ref> The lack of orbital interactions combined with the lanthanide contraction means that the lanthanides change in size across the series but that their chemistry remains much the same. This allows for easy tuning of the steric environments and examples exist where this has been used to improve the catalytic activity of the complex<ref>{{cite journal |last1=Kobayashi|first1=Shū|last2=Hamada|first2=Tomoaki|last3=Nagayama|first3=Satoshi|last4=Manabe|first4=Kei |title=Lanthanide Trifluoromethanesulfonate-Catalyzed Asymmetric Aldol Reactions in Aqueous Media|journal=Organic Letters|date=1 January 2001|volume=3|issue=2|pages=165–167|doi=10.1021/ol006830z|pmid=11430025|url=https://figshare.com/articles/journal_contribution/3737823}}</ref><ref>{{cite journal|last1=Aspinall|first1=Helen C.|last2=Dwyer|first2=Jennifer L.|last3=Greeves|first3=Nicholas|last4=Steiner|first4=Alexander
|title=Li<sub>3</sub>[Ln(binol)<sub>3</sub>]·6THF: New Anhydrous Lithium Lanthanide Binaphtholates and Their Use in Enantioselective Alkyl Addition to Aldehydes|journal=Organometallics|date=1 April 1999|volume=18|issue=8|pages=1366–1368|doi=10.1021/om981011s}}</ref><ref>{{cite journal|last1=Parac-Vogt|first1=Tatjana N.|last2=Pachini|first2=Sophia|last3=Nockemann|first3=Peter|last4=VanmHecke|first4=Kristof|last5=Van Meervelt|first5=Luc|last6=Binnemans|first6=Koen|title=Lanthanide(III) Nitrobenzenesulfonates as New Nitration Catalysts: The Role of the Metal and of the Counterion in the Catalytic Efficiency|journal=European Journal of Organic Chemistry|date=1 November 2004|volume=2004|issue=22|pages=4560–4566|doi=10.1002/ejoc.200400475|s2cid=96125063 |url=https://lirias.kuleuven.be/handle/123456789/33568|type=Submitted manuscript}}</ref> and change the [[nuclearity]] of metal clusters.<ref>{{cite journal|last1=Lipstman|first1=Sophia|last2=Muniappan|first2=Sankar|last3=George|first3= Sumod|last4=Goldberg|first4=Israel|title=Framework coordination polymers of tetra(4-carboxyphenyl)porphyrin and lanthanide ions in crystalline solids|journal=Dalton Transactions|date=1 January 2007|issue=30|pages=3273–81|doi=10.1039/B703698A|pmid=17893773}}</ref><ref>{{cite journal|last1=Bretonnière|first1=Yann|last2=Mazzanti|first2=Marinella|last3=Pécaut|first3=Jacques|last4=Dunand|first4=Frank A.|last5=Merbach|first5=André E.|title=Solid-State and Solution Properties of the Lanthanide Complexes of a New Heptadentate Tripodal Ligand: A Route to Gadolinium Complexes with an Improved Relaxation Efficiency|journal=Inorganic Chemistry|date=1 December 2001|volume=40|issue=26|pages=6737–6745|doi=10.1021/ic010591+|pmid=11735486}}</ref>

Despite this, the use of lanthanide coordination complexes as [[Homogeneous catalysis|homogeneous catalysts]] is largely restricted to the laboratory and there are currently few examples them being used on an industrial scale.<ref>{{cite journal|last1=Trinadhachari|first1=Ganala Naga|last2=Kamat|first2=Anand Gopalkrishna|last3=Prabahar|first3=Koilpillai Joseph|last4=Handa|first4=Vijay Kumar|last5=Srinu|first5=Kukunuri Naga Venkata Satya|last6=Babu|first6=Korupolu Raghu|last7=Sanasi|first7=Paul Douglas|title=Commercial Scale Process of Galanthamine Hydrobromide Involving Luche Reduction: Galanthamine Process Involving Regioselective 1,2-Reduction of α,β-Unsaturated Ketone|journal=Organic Process Research & Development|date=15 March 2013|volume=17|issue=3|pages=406–412|doi=10.1021/op300337y}}</ref> Lanthanides exist in many forms other than coordination complexes and many of these are industrially useful. In particular lanthanide [[metal oxide]]s are used as [[heterogeneous catalysis|heterogeneous catalysts]] in various industrial processes.

====Ln(III) compounds====
The trivalent lanthanides mostly form ionic salts. The trivalent ions are [[hsab theory|hard]] acceptors and form more stable complexes with oxygen-donor ligands than with nitrogen-donor ligands. The larger ions are 9-coordinate in aqueous solution, [Ln(H<sub>2</sub>O)<sub>9</sub>]<sup>3+</sup> but the smaller ions are 8-coordinate, [Ln(H<sub>2</sub>O)<sub>8</sub>]<sup>3+</sup>. There is some evidence that the later lanthanides have more water molecules in the second coordination sphere.<ref>{{cite book|last=Burgess|first=J.|title=Metal ions in solution|publisher=Ellis Horwood|location= New York|year=1978|isbn=978-0-85312-027-8}}</ref> Complexation with [[monodentate]] ligands is generally weak because it is difficult to displace water molecules from the first coordination sphere. Stronger complexes are formed with chelating ligands because of the [[chelate effect]], such as the tetra-anion derived from 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid ([[DOTA (chelator)|DOTA]]).

:[[File:Lanthanide nitrates.png|thumb|650px|center|Samples of lanthanide nitrates in their hexahydrate form. From left to right: La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu.]]
{{-}}

====Ln(II) and Ln(IV) compounds====
The most common divalent derivatives of the lanthanides are for Eu(II), which achieves a favorable f<sup>7</sup> configuration. Divalent halide derivatives are known for all of the lanthanides. They are either conventional salts or are Ln(III) "[[electride]]"-like salts. The simple salts include YbI<sub>2</sub>, EuI<sub>2</sub>, and SmI<sub>2</sub>. The electride-like salts, described as Ln<sup>3+</sup>, 2I<sup>−</sup>, e<sup>−</sup>, include LaI<sub>2</sub>, CeI<sub>2</sub> and GdI<sub>2</sub>. Many of the iodides form soluble complexes with ethers, e.g. TmI<sub>2</sub>(dimethoxyethane)<sub>3</sub>.<ref name=Nief>{{cite journal|author=Nief, F. |title=Non-classical divalent lanthanide complexes|journal= Dalton Trans.|year= 2010|volume=39|issue=29|pages= 6589–6598|doi=10.1039/c001280g|pmid=20631944}}</ref> [[Samarium(II) iodide]] is a useful reducing agent. Ln(II) complexes can be synthesized by [[transmetalation]] reactions. The normal range of oxidation states can be expanded via the use of sterically bulky [[cyclopentadienyl ligand]]s, in this way many lanthanides can be isolated as Ln(II) compounds.<ref>{{cite journal|last1=Evans|first1=William J.|title=Tutorial on the Role of Cyclopentadienyl Ligands in the Discovery of Molecular Complexes of the Rare-Earth and Actinide Metals in New Oxidation States|journal=Organometallics|date=15 September 2016|volume=35|issue=18|pages=3088–3100|doi=10.1021/acs.organomet.6b00466|doi-access=free}}{{open access}}</ref>

Ce(IV) in [[ceric ammonium nitrate]] is a useful oxidizing agent. The Ce(IV) is the exception owing to the tendency to form an unfilled f shell. Otherwise tetravalent lanthanides are rare. However, recently Tb(IV)<ref>{{cite journal |title=Molecular Complex of Tb in the +4 Oxidation State< |author1=Palumbo, C.T. |author2=Zivkovic, I. |author3=Scopelliti, R. |author4=Mazzanti, M. |date=2019 |pages=9827–9831 |volume=141 |journal=Journal of the American Chemical Society |doi=10.1021/jacs.9b05337 |pmid=31194529 |issue=25 |s2cid=189814301 |url=http://infoscience.epfl.ch/record/268286/files/Palumbo%20ja-2019-05337d%20manuscriptR1.pdf |archive-url=https://web.archive.org/web/20240423040613/https://infoscience.epfl.ch/record/268286/files/Palumbo%20ja-2019-05337d%20manuscriptR1.pdf |url-status=dead |archive-date=23 April 2024 }}</ref><ref>{{Cite journal|last1=Rice|first1=Natalie T.|last2=Popov|first2=Ivan A.|last3=Russo|first3=Dominic R.|last4=Bacsa|first4=John|last5=Batista|first5=Enrique R.|last6=Yang|first6=Ping|last7=Telser|first7=Joshua|last8=La Pierre|first8=Henry S.|date=21 August 2019|title=Design, Isolation, and Spectroscopic Analysis of a Tetravalent Terbium Complex|journal=Journal of the American Chemical Society|volume=141|issue=33|pages=13222–13233|doi=10.1021/jacs.9b06622|pmid=31352780|osti=1558225|s2cid=207197096|issn=0002-7863|url=https://figshare.com/articles/journal_contribution/9450461 }}</ref><ref>{{cite journal |title= Stabilization of the Oxidation State + IV in Siloxide-Supported Terbium Compounds |author1=Willauer, A.R. |author2=Palumbo, C.T. |author3=Scopelliti, R. |author4=Zivkovic, I. |author5=Douair, I. |author6=Maron, L.  |author7=Mazzanti, M. |date=2020 |pages=3549–3553|volume=59 |journal=Angewandte Chemie International Edition |issue=9 |doi=10.1002/anie.201914733|pmid=31840371 |s2cid=209385870 |url=http://infoscience.epfl.ch/record/275738 }}</ref> and Pr(IV)<ref>{{cite journal |title= Accessing the +IV Oxidation State in Molecular Complexes of Praseodymium. |author1=Willauer, A.R. |author2=Palumbo, C.T. |author3=Fadaei-Tirani, F. |author4=Zivkovic, I. |author5=Douair, I. |author6=Maron, L.  |author7=Mazzanti, M. |date=2020 |pages=489–493|volume=142 |journal=Journal of the American Chemical Society |issue=12 |doi=10.1021/jacs.0c01204|pmid=32134644 |s2cid=212564931 |url=http://infoscience.epfl.ch/record/277306 }}</ref> complexes have been shown to exist.

====Hydrides====
{| class="wikitable collapsible collapsed" style="font-size:95%;"
|-
![[Chemical element]]!![[Lanthanum|La]]!![[Cerium|Ce]]!![[praseodymium|Pr]]!![[neodymium|Nd]]!![[promethium|Pm]]!![[samarium|Sm]]!![[europium|Eu]]!![[gadolinium|Gd]]!![[terbium|Tb]]!![[dysprosium|Dy]]!![[holmium|Ho]]!![[erbium|Er]]!![[thulium|Tm]]!![[ytterbium|Yb]]!![[lutetium|Lu]]
|-
| [[Atomic number]]
|57||58||59||60||61||62||63||64||65||66||67||68||69||70||71
|-
|Metal lattice (RT)
|dhcp ||fcc ||dhcp ||dhcp ||dhcp ||r ||bcc ||hcp ||hcp ||hcp ||hcp||hcp ||hcp ||hcp ||hcp
|-
|Dihydride<ref name="Fukai">{{cite book |last=Fukai |first=Y. |year=2005 |title=The Metal-Hydrogen System, Basic Bulk Properties, 2d edition|publisher=Springer|isbn=978-3-540-00494-3}}</ref>
|LaH<sub>2+x</sub>||CeH<sub>2+x</sub>||PrH<sub>2+x</sub>  ||[[Neodymium(II) hydride|NdH<sub>2+x</sub>]]|| ||SmH<sub>2+x</sub>  ||[[europium hydride|EuH<sub>2</sub>]] o <br> "salt like"||GdH<sub>2+x</sub> ||TbH<sub>2+x</sub> ||DyH<sub>2+x</sub> ||HoH<sub>2+x</sub>  ||ErH<sub>2+x</sub> ||TmH<sub>2+x</sub>   ||[[Ytterbium hydride|YbH<sub>2+x</sub>]] o, ''fcc''<br> "salt like" ||LuH<sub>2+x</sub>
|-
| style="padding-left: 2em" |''Structure''
|[[calcium fluoride|CaF<sub>2</sub>]]||[[calcium fluoride|CaF<sub>2</sub>]]||[[calcium fluoride|CaF<sub>2</sub>]]||[[calcium fluoride|CaF<sub>2</sub>]]||[[calcium fluoride|CaF<sub>2</sub>]]||[[calcium fluoride|CaF<sub>2</sub>]]||*[[lead(II) chloride|PbCl<sub>2</sub>]]<ref name="KohlmannYvon2000">{{cite journal|last1=Kohlmann|first1=H.|last2=Yvon|first2=K.|title=The crystal structures of EuH<sub>2</sub> and EuLiH<sub>3</sub> by neutron powder diffraction|journal=Journal of Alloys and Compounds|volume=299|issue=1–2|year=2000|pages=L16–L20|doi=10.1016/S0925-8388(99)00818-X}}</ref>  ||[[calcium fluoride|CaF<sub>2</sub>]]||[[calcium fluoride|CaF<sub>2</sub>]]||[[calcium fluoride|CaF<sub>2</sub>]]||[[calcium fluoride|CaF<sub>2</sub>]]||[[calcium fluoride|CaF<sub>2</sub>]]||[[calcium fluoride|CaF<sub>2</sub>]]||  ||[[calcium fluoride|CaF<sub>2</sub>]]
|-
| style="padding-left: 2em" |''metal sub lattice''
|''fcc''||''fcc''||''fcc''||''fcc''||''fcc''||''fcc''||''o''||''fcc''||''fcc''||''fcc''||''fcc''||''fcc''||''fcc''||''o'' ''fcc''||''fcc''
|-
|Trihydride<ref name="Fukai"/>
|LaH<sub>3−x</sub>||CeH<sub>3−x</sub> ||PrH<sub>3−x</sub>||[[Neodymium(III) hydride|NdH<sub>3−x</sub>]] ||||SmH<sub>3−x</sub>  ||EuH<sub>3−x</sub><ref name="MatsuokaFujihisa2011">{{cite journal|last1=Matsuoka|first1=T.|last2=Fujihisa|first2=H.|last3=Hirao|first3=N.|last4=Ohishi|first4=Y.|last5=Mitsui|first5=T.|last6=Masuda|first6=R.|last7=Seto|first7=M.|last8=Yoda|first8=Y.|last9=Shimizu|first9=K.|last10=Machida|first10=A.|last11=Aoki|first11=K.|title=Structural and Valence Changes of Europium Hydride Induced by Application of High-Pressure H<sub>2</sub>|journal=Physical Review Letters|volume=107|issue=2|pages=025501|year=2011|doi=10.1103/PhysRevLett.107.025501|pmid=21797616|bibcode=2011PhRvL.107b5501M}}</ref> ||GdH<sub>3−x</sub>||TbH<sub>3−x</sub> ||DyH<sub>3−x</sub> ||HoH<sub>3−x</sub>||ErH<sub>3−x</sub>  ||TmH<sub>3−x</sub> ||||LuH<sub>3−x</sub>
|-
|style="padding-left: 2em" |''metal sub lattice''
|''fcc''||''fcc''||''fcc''||''hcp''||''hcp''||''hcp''||''fcc''||''hcp''||''hcp''||''hcp''||''hcp''||''hcp''||''hcp''||''hcp''||''hcp''
|-
|Trihydride properties<br> transparent insulators <br>(color where recorded)
|red ||bronze to grey<ref name="TellefsenKaldis1985">{{cite journal|last1=Tellefsen|first1=M.|last2=Kaldis|first2=E.|last3=Jilek|first3=E.|title=The phase diagram of the Ce-H<sub>2</sub> system and the CeH<sub>2</sub>-CeH<sub>3</sub> solid solutions|journal=Journal of the Less Common Metals|volume=110|issue=1–2|year=1985|pages=107–117|doi=10.1016/0022-5088(85)90311-X}}</ref> ||PrH<sub>3−x</sub> ''fcc''||NdH<sub>3−x</sub> ''hcp'' ||||golden greenish<ref name="KumarPhilip2002">{{cite journal|last1=Kumar|first1=Pushpendra|last2=Philip|first2=Rosen|last3=Mor|first3=G. K.|last4=Malhotra|first4=L. K.|title=Influence of Palladium Overlayer on Switching Behaviour of Samarium Hydride Thin Films|journal=Japanese Journal of Applied Physics|volume=41|issue=Part 1, No. 10|year=2002|pages=6023–6027|doi=10.1143/JJAP.41.6023|bibcode=2002JaJAP..41.6023K|s2cid=96881388 }}</ref> ||EuH<sub>3−x</sub> ''fcc'' ||GdH<sub>3−x</sub> ''hcp'' ||TbH<sub>3−x</sub> ''hcp''||DyH<sub>3−x</sub> ''hcp'' ||HoH<sub>3−x</sub> ''hcp''||ErH<sub>3−x</sub> ''hcp'' ||TmH<sub>3−x</sub> ''hcp'' ||||LuH<sub>3−x</sub> ''hcp''
|}

Lanthanide metals react exothermically with hydrogen to form LnH<sub>2</sub>, dihydrides.<ref name="Fukai"/> With the exception of Eu and Yb, which resemble the Ba and Ca hydrides (non-conducting, transparent salt-like compounds), they form black, [[pyrophoricity|pyrophoric]], conducting compounds<ref name="Holleman"/> where the metal sub-lattice is face centred cubic and the H atoms occupy tetrahedral sites.<ref name="Fukai"/> Further hydrogenation produces a trihydride which is [[non-stoichiometric compound|non-stoichiometric]], non-conducting, more salt like. The formation of trihydride is associated with and increase in 8–10% volume and this is linked to greater localization of charge on the hydrogen atoms which become more anionic (H<sup>−</sup> hydride anion) in character.<ref name="Fukai"/>

====Halides====

{{See also|Lanthanide chlorides}}

{| class="wikitable collapsible collapsed" style="font-size: 95%; text-align: center;"
|+ Lanthanide halides<ref name = "Greenwood&Earnshaw"/><ref name = "Atwood">{{cite book|title=The Rare Earth Elements: Fundamentals and Applications (eBook)|editor=David A. Atwood|publisher=John Wiley & Sons|date=19 February 2013|isbn=9781118632635}}</ref><ref name="Wells">{{cite book|last1=Wells|first1=A. F.|year=1984|title=Structural Inorganic Chemistry|edition=5th |publisher=Oxford Science Publication|isbn=978-0-19-855370-0}}</ref><ref name="Holleman">[[#Holleman|Holleman]], p. 1942</ref>
![[Chemical element]]!![[Lanthanum|La]]!![[Cerium|Ce]]!![[praseodymium|Pr]]!![[neodymium|Nd]]!![[promethium|Pm]]!![[samarium|Sm]]!![[europium|Eu]]!![[gadolinium|Gd]]!![[terbium|Tb]]!![[dysprosium|Dy]]!![[holmium|Ho]]!![[erbium|Er]]!![[thulium|Tm]]!![[ytterbium|Yb]]!![[lutetium|Lu]]
|-
| [[Atomic number]]
|57||58||59||60||61||62||63||64||65||66||67||68||69||70||71
|-
|'''Tetrafluoride'''
|  ||'''''[[Cerium(IV) fluoride|CeF<sub>4</sub>]]'''''||'''''[[Praseodymium(IV) fluoride|PrF<sub>4</sub>]]'''''||'''''NdF<sub>4</sub>'''''||  ||  ||  ||  ||'''''[[Terbium(IV) fluoride|TbF<sub>4</sub>]]'''''||'''''DyF<sub>4</sub>'''''||  ||  ||   ||  ||
|- style="font-size:85%"
|style="padding-left: 2em" |Color m.p. °C
|  ||white dec||white dec||  ||  ||  ||   ||   ||white dec ||  ||  ||  ||  ||  ||
|- style="font-size:85%"
|style="padding-left: 2em" |Structure C.N.
|||UF<sub>4</sub> 8||UF<sub>4</sub> 8||  ||  ||  ||  ||  ||UF<sub>4</sub> 8||  ||  ||  ||  ||
|-
|'''Trifluoride'''
|'''''[[Lanthanum(III) fluoride|LaF<sub>3</sub>]]'''''||'''''[[Cerium(III) fluoride|CeF<sub>3</sub>]]'''''||'''''[[Praseodymium(III) fluoride|PrF<sub>3</sub>]]'''''||'''''[[Neodymium(III) fluoride|NdF<sub>3</sub>]]'''''||'''''[[Promethium(III) fluoride|PmF<sub>3</sub>]]'''''||'''''[[Samarium(III) fluoride|SmF<sub>3</sub>]]'''''||'''''[[Europium(III) fluoride|EuF<sub>3</sub>]]'''''||'''''[[Gadolinium(III) fluoride|GdF<sub>3</sub>]]'''''||'''''[[Terbium(III) fluoride|TbF<sub>3</sub>]]'''''||'''''[[Dysprosium(III) fluoride|DyF<sub>3</sub>]]'''''||'''''[[Holmium(III) fluoride|HoF<sub>3</sub>]]'''''||'''''[[Erbium(III) fluoride|ErF<sub>3</sub>]]'''''||'''''[[Thulium(III) fluoride|TmF<sub>3</sub>]]'''''||'''''[[Ytterbium(III) fluoride|YbF<sub>3</sub>]]'''''||'''''[[Lutetium(III) fluoride|LuF<sub>3</sub>]]'''''
|- style="font-size:85%"
|style="padding-left: 2em" |Color m.p. °C
|white 1493<ref name="Handbook">{{cite book |last=Perry|first=Dale L.|year=2011|title=Handbook of Inorganic Compounds, Second Edition|page=125|url=https://books.google.com/books?id=SFD30BvPBhoC|location=Boca Raton, Florida|publisher=CRC Press|isbn=978-1-43981462-8|access-date=17 February 2014}}</ref> ||white 1430||green 1395||violet 1374||green 1399||white 1306||white 1276||white 1231||white 1172||green 1154||pink 1143||pink 1140||white 1158||white 1157||white 1182
|- style="font-size:85%"
|style="padding-left: 2em" |Structure C.N.
| LaF<sub>3</sub> 9 || LaF<sub>3</sub> 9|| LaF<sub>3</sub> 9|| LaF<sub>3</sub> 9|| LaF<sub>3</sub> 9 ||YF<sub>3</sub> 8||YF<sub>3</sub> 8||YF<sub>3</sub> 8||YF<sub>3</sub> 8||YF<sub>3</sub> 8||YF<sub>3</sub> 8||YF<sub>3</sub> 8||YF<sub>3</sub> 8||YF<sub>3</sub> 8||YF<sub>3</sub> 8
|-
|'''Trichloride'''
|'''''[[Lanthanum(III) chloride|LaCl<sub>3</sub>]]'''''||'''''[[Cerium(III) chloride|CeCl<sub>3</sub>]]'''''||'''''[[Praseodymium(III) chloride|PrCl<sub>3</sub>]]'''''||'''''[[Neodymium(III) chloride|NdCl<sub>3</sub>]]'''''||'''''[[Promethium(III) chloride|PmCl<sub>3</sub>]]'''''||'''''[[Samarium(III) chloride|SmCl<sub>3</sub>]]'''''||'''''[[Europium(III) chloride|EuCl<sub>3</sub>]]'''''||'''''[[Gadolinium(III) chloride|GdCl<sub>3</sub>]]'''''||'''''[[Terbium(III) chloride|TbCl<sub>3</sub>]]'''''||'''''[[Dysprosium(III) chloride|DyCl<sub>3</sub>]]'''''||'''''[[Holmium(III) chloride|HoCl<sub>3</sub>]]'''''||'''''[[Erbium(III) chloride|ErCl<sub>3</sub>]]'''''||'''''[[Thulium(III) chloride|TmCl<sub>3</sub>]]'''''||'''''[[Ytterbium(III) chloride|YbCl<sub>3</sub>]]'''''||'''''[[Lutetium(III) chloride|LuCl<sub>3</sub>]]'''''
|- style="font-size:85%"
|style="padding-left: 2em" |Color m.p. °C
|white 858||white 817||green 786||mauve 758||green 786||yellow 682||yellow dec||white 602||white 582||white 647||yellow 720||violet 776||yellow 824||white 865||white 925
|- style="font-size:85%"
|style="padding-left: 2em" |Structure C.N.
|UCl<sub>3</sub> 9||UCl<sub>3</sub> 9||UCl<sub>3</sub> 9||UCl<sub>3</sub> 9||UCl<sub>3</sub> 9||UCl<sub>3</sub> 9||UCl<sub>3</sub> 9||UCl<sub>3</sub> 9||PuBr<sub>3</sub> 8 ||PuBr<sub>3</sub> 8||YCl<sub>3</sub> 6||YCl<sub>3</sub> 6||YCl<sub>3</sub> 6||YCl<sub>3</sub> 6||YCl<sub>3</sub> 6
|-
|'''Tribromide'''
|'''''[[Lanthanum(III) bromide|LaBr<sub>3</sub>]]'''''||'''''[[Cerium(III) bromide|CeBr<sub>3</sub>]]'''''||'''''[[Praseodymium(III) bromide|PrBr<sub>3</sub>]]'''''||'''''[[Neodymium(III) bromide|NdBr<sub>3</sub>]]'''''||'''''[[Promethium(III) bromide|PmBr<sub>3</sub>]]'''''||'''''[[Samarium(III) bromide|SmBr<sub>3</sub>]]'''''||'''''[[Europium(III) bromide|EuBr<sub>3</sub>]]'''''||'''''[[Gadolinium(III) bromide|GdBr<sub>3</sub>]]'''''||'''''[[Terbium(III) bromide|TbBr<sub>3</sub>]]'''''||'''''[[Dysprosium(III) bromide|DyBr<sub>3</sub>]]'''''||'''''[[Holmium(III) bromide|HoBr<sub>3</sub>]]'''''||'''''[[Erbium(III) bromide|ErBr<sub>3</sub>]]'''''||'''''[[Thulium(III) bromide|TmBr<sub>3</sub>]]'''''||'''''[[Ytterbium(III) bromide|YbBr<sub>3</sub>]]'''''||'''''[[Lutetium(III) bromide|LuBr<sub>3</sub>]]'''''
|- style="font-size:85%"
|style="padding-left: 2em" |Color m.p. °C
|white 783||white 733||green 691||violet 682||green 693||yellow 640||grey dec||white 770||white 828||white 879||yellow 919||violet 923||white 954||white dec||white 1025
|- style="font-size:85%"
|style="padding-left: 2em" |Structure C.N.
|UCl<sub>3</sub> 9||UCl<sub>3</sub> 9||UCl<sub>3</sub> 9||PuBr<sub>3</sub> 8||PuBr<sub>3</sub> 8||PuBr<sub>3</sub> 8||PuBr<sub>3</sub> 8||   6||  6||   6||  6||  6||  6||   6||   6
|-
|'''Triiodide'''
|'''''[[Lanthanum(III) iodide|LaI<sub>3</sub>]]'''''||'''''[[Cerium(III) iodide|CeI<sub>3</sub>]]'''''||'''''[[Praseodymium(III) iodide|PrI<sub>3</sub>]]'''''||'''''[[Neodymium(III) iodide|NdI<sub>3</sub>]]'''''||'''''[[Promethium(III) iodide|PmI<sub>3</sub>]]'''''||'''''[[Samarium(III) iodide|SmI<sub>3</sub>]]'''''||'''''[[Europium(III) iodide|EuI<sub>3</sub>]]'''''||'''''[[Gadolinium(III) iodide|GdI<sub>3</sub>]]'''''||'''''[[Terbium(III) iodide|TbI<sub>3</sub>]]'''''||'''''[[Dysprosium(III) iodide|DyI<sub>3</sub>]]'''''||'''''[[Holmium(III) iodide|HoI<sub>3</sub>]]'''''||'''''[[Erbium(III) iodide|ErI<sub>3</sub>]]'''''||'''''[[Thulium(III) iodide|TmI<sub>3</sub>]]'''''||'''''[[Ytterbium(III) iodide|YbI<sub>3</sub>]]'''''||'''''[[Lutetium(III) iodide|LuI<sub>3</sub>]]'''''
|- style="font-size:85%"
|style="padding-left: 2em" |Color m.p. °C
|yellow-green 772||yellow 766||green 738||green 784||green 737||orange 850||colorless dec. ||yellow 925 ||brown 957 ||green 978||yellow 994||violet 1015||yellow 1021||white dec||brown 1050
|- style="font-size:85%"
|style="padding-left: 2em" |Structure C.N.
|PuBr<sub>3</sub> 8||PuBr<sub>3</sub> 8||PuBr<sub>3</sub> 8||PuBr<sub>3</sub> 8||  ||BiI<sub>3</sub> 6||BiI<sub>3</sub> 6||BiI<sub>3</sub> 6||BiI<sub>3</sub> 6||BiI<sub>3</sub> 6||BiI<sub>3</sub> 6||BiI<sub>3</sub> 6||BiI<sub>3</sub> 6||BiI<sub>3</sub> 6||BiI<sub>3</sub> 6
|-
|'''Difluoride'''
| || || || || ||'''''[[Samarium(II) fluoride|SmF<sub>2</sub>]]'''''||'''''[[Europium(II) fluoride|EuF<sub>2</sub>]]'''''|| || || ||  ||  || '''''[[Thulium(II) fluoride|TmF<sub>2</sub>]]'''''||'''''YbF<sub>2</sub>'''''||
|- style="font-size:85%"
|style="padding-left: 2em" |Color m.p. °C
|  ||  ||  ||  ||  ||purple 1417||yellow 1416||  ||  ||  ||  ||  ||  ||grey ||
|- style="font-size:85%"
|style="padding-left: 2em" |Structure C.N.
| || || || || ||[[calcium fluoride|CaF<sub>2</sub>]] 8||[[calcium fluoride|CaF<sub>2</sub>]] 8|| || || || || || ||[[calcium fluoride|CaF<sub>2</sub>]] 8||
|-
|'''Dichloride'''
| || || ||'''''[[Neodymium(II) chloride|NdCl<sub>2</sub>]]'''''|| ||'''''[[Samarium(II) chloride|SmCl<sub>2</sub>]]'''''||'''''[[Europium(II) chloride|EuCl<sub>2</sub>]]'''''|| || ||'''''[[Dysprosium(II) chloride|DyCl<sub>2</sub>]]'''''|| || ||'''''[[Thulium(II) chloride|TmCl<sub>2</sub>]]'''''||'''''[[Ytterbium(II) chloride|YbCl<sub>2</sub>]]'''''||
|- style="font-size:85%"
|style="padding-left: 2em" |Color m.p. °C
|  ||  ||  ||green 841||  ||brown 859||white 731||  ||  ||black dec.||  ||  ||green 718||green 720||
|- style="font-size:85%"
|style="padding-left: 2em" |Structure C.N.
| ||  || ||[[lead(II) chloride|PbCl<sub>2</sub>]] 9|| ||[[lead(II) chloride|PbCl<sub>2</sub>]] 9||[[lead(II) chloride|PbCl<sub>2</sub>]] 9|| || ||[[strontium bromide|SrBr<sub>2</sub>]]|| || ||[[strontium iodide|SrI<sub>2</sub>]] 7||[[strontium iodide|SrI<sub>2</sub>]] 7  ||
|-
|'''Dibromide'''
| ||  ||  ||'''''[[Neodymium(II) bromide|NdBr<sub>2</sub>]]'''''||  ||'''''[[Samarium(II) bromide|SmBr<sub>2</sub>]]'''''||'''''[[Europium(II) bromide|EuBr<sub>2</sub>]]'''''||  ||  ||'''''DyBr<sub>2</sub>'''''||  ||  ||'''''TmBr<sub>2</sub>'''''||'''''YbBr<sub>2</sub>'''''||
|- style="font-size:85%"
|style="padding-left: 2em" |Color m.p. °C
|  || ||  ||green 725||  ||brown 669||white 731||  ||  ||black||  ||  ||green ||yellow 673||
|- style="font-size:85%"
|style="padding-left: 2em" |Structure C.N.
|  ||  ||  ||[[lead(II) chloride|PbCl<sub>2</sub>]] 9||  ||[[strontium bromide|SrBr<sub>2</sub>]] 8||[[strontium bromide|SrBr<sub>2</sub>]] 8|| ||  ||[[strontium iodide|SrI<sub>2</sub>]] 7||  ||  ||[[strontium iodide|SrI<sub>2</sub>]] 7||[[strontium iodide|SrI<sub>2</sub>]] 7  ||
|-
|'''Diiodide'''
|'''''[[Lanthanum diiodide|LaI<sub>2</sub>]]'''''<br> metallic||'''''[[Cerium diiodide|CeI<sub>2</sub>]]'''''<br> metallic  ||'''''[[Praseodymium diiodide|PrI<sub>2</sub>]]'''''<br> metallic  ||'''''[[Neodymium(II) iodide|NdI<sub>2</sub>]]'''''<br> high pressure metallic  ||  ||'''''[[Samarium(II) iodide|SmI<sub>2</sub>]]'''''||'''''[[Europium(II) iodide|EuI<sub>2</sub>]]'''''  ||'''''[[Gadolinium diiodide|GdI<sub>2</sub>]]'''''<br> metallic ||  ||'''''DyI<sub>2</sub>'''''||  ||  ||'''''TmI<sub>2</sub>'''''||'''''[[Ytterbium(II) iodide|YbI<sub>2</sub>]]'''''||
|- style="font-size:85%"
|style="padding-left: 2em" |Color m.p. °C
|  ||bronze 808||bronze 758||violet 562||  ||green 520||green 580||bronze 831||  ||purple 721||  ||  ||black 756||yellow 780||Lu
|- style="font-size:85%"
|style="padding-left: 2em" |Structure C.N.
|CuTi<sub>2</sub> 8||CuTi<sub>2</sub> 8||CuTi<sub>2</sub> 8|| SrBr<sub>2</sub> 8 <br>CuTi<sub>2</sub> 8  || ||EuI<sub>2</sub> 7||EuI<sub>2</sub> 7  ||2H-MoS<sub>2</sub> 6|| ||  ||  ||  ||CdI<sub>2</sub> 6  ||CdI<sub>2</sub> 6  ||
|-
|'''Ln<sub>7</sub>I<sub>12</sub>'''
|'''''La<sub>7</sub>I<sub>12</sub>'''''||  ||'''''Pr<sub>7</sub>I<sub>12</sub>'''''||  ||  ||  ||  ||  ||'''''Tb<sub>7</sub>I<sub>12</sub>'''''||  ||  ||  ||  ||  ||
|-
|'''Sesquichloride'''
|'''''La<sub>2</sub>Cl<sub>3</sub>''''' || || || || ||  ||  ||'''''Gd<sub>2</sub>Cl<sub>3</sub>''''' ||'''''Tb<sub>2</sub>Cl<sub>3</sub>'''''|| || || '''''Er<sub>2</sub>Cl<sub>3</sub>''''' || '''''Tm<sub>2</sub>Cl<sub>3</sub>''''' ||  ||'''''Lu<sub>2</sub>Cl<sub>3</sub>'''''
|- style="font-size:85%"
|style="padding-left: 2em" |Structure
| || || || || ||  ||  ||Gd<sub>2</sub>Cl<sub>3</sub>  ||Gd<sub>2</sub>Cl<sub>3</sub>  || || || || ||  ||
|-
|'''Sesquibromide'''
| || || || || ||  ||  ||'''''Gd<sub>2</sub>Br<sub>3</sub>''''' ||'''''Tb<sub>2</sub>Br<sub>3</sub>''''' || ||  ||  ||  ||  ||
|- style="font-size:85%"
|style="padding-left: 2em" |Structure
| || || || || ||  ||  ||Gd<sub>2</sub>Cl<sub>3</sub>  ||Gd<sub>2</sub>Cl<sub>3</sub>  || || || || ||  ||
|-
|'''Monoiodide'''
| '''''LaI'''''<ref name="RyazanovKienle2006">{{cite journal|last1=Ryazanov|first1=Mikhail|last2=Kienle|first2=Lorenz|last3=Simon|first3=Arndt|last4=Mattausch|first4=Hansjürgen|title=New Synthesis Route to and Physical Properties of Lanthanum Monoiodide†|journal=Inorganic Chemistry|volume=45|issue=5|year=2006|pages=2068–2074|doi=10.1021/ic051834r|pmid=16499368}}</ref>|| || || || ||  ||  || || || ||  ||  ||'''''TmI'''''<ref name="TmI">{{cite journal|last1=Fagin|first1=A. A.|last2=Bukhvalova|first2=S. Yu.|last3=Kuropatov|first3=B. A.|last4=Bochkarev|first4=M. N.|title=Monovalent Thulium. Synthesis and Properties of TmI|journal=Russian Journal of Coordination Chemistry|volume=49|year=2023|issue=5 |pages=299–303|doi=10.1134/s1070328423700525|s2cid=258991972 }}</ref>||  ||
|- style="font-size:85%"
|style="padding-left: 2em" |Structure
| NiAs type ||  ||  ||  ||  ||  ||  ||  ||  ||  ||  ||  ||  ||   ||
|}
The only tetrahalides known are the tetrafluorides of [[Cerium(IV) fluoride|cerium]], [[Praseodymium(IV) fluoride|praseodymium]], [[Terbium(IV) fluoride|terbium]], neodymium and dysprosium, the last two known only under matrix isolation conditions.<ref name = "Greenwood&Earnshaw"/><ref>{{cite journal|last1=Vent-Schmidt|first1=T.|last2=Fang|first2=Z.|last3=Lee|first3=Z.|last4=Dixon|first4=D.|last5=Riedel|first5=S.|title=Extending the Row of Lanthanide Tetrafluorides: A Combined Matrix-Isolation and Quantum-Chemical Study.|journal=Chemistry: A European Journal|volume=22|issue=7|year=2016|pages=2406–16|pmid=26786900|doi=10.1002/chem.201504182|hdl=2027.42/137267|hdl-access=free}}</ref>
All of the lanthanides form trihalides with fluorine, chlorine, bromine and iodine. They are all high melting and predominantly ionic in nature.<ref name = "Greenwood&Earnshaw"/> The fluorides are only slightly soluble in water and are not sensitive to air, and this contrasts with the other halides which are air sensitive, readily soluble in water and react at high temperature to form oxohalides.<ref name = "halides handbook">{{cite book |last=Haschke |first=John. M. |editor-first=K. A. Jr. |editor-last=Gschneider |title=Handbook on the Physics and Chemistry of Rare Earths vol 4|pages=100–110 |year=1979|chapter=Chapter 32:Halides |publisher=North Holland Publishing Company|isbn=978-0-444-85216-8}}</ref>

The trihalides were important as pure metal can be prepared from them.<ref name = "Greenwood&Earnshaw"/> In the gas phase the trihalides are planar or approximately planar, the lighter lanthanides have a lower % of dimers, the heavier lanthanides a higher proportion. The dimers have a similar structure to [[aluminium chloride|Al<sub>2</sub>Cl<sub>6</sub>]].<ref name="Kovács2004">{{cite journal|last1=Kovács|first1=Attila|title=Structure and Vibrations of Lanthanide Trihalides: An Assessment of Experimental and Theoretical Data|journal=Journal of Physical and Chemical Reference Data|volume=33|issue=1|year=2004|page=377|doi=10.1063/1.1595651|bibcode=2004JPCRD..33..377K}}</ref>

Some of the dihalides are conducting while the rest are insulators. The conducting forms can be considered as Ln<sup>III</sup> electride compounds where the electron is delocalised into a conduction band, Ln<sup>3+</sup> (X<sup>−</sup>)<sub>2</sub>(e<sup>−</sup>). All of the diiodides have relatively short metal-metal separations.<ref name = "Atwood"/> The CuTi<sub>2</sub> structure of the lanthanum, cerium and praseodymium diiodides along with HP-NdI<sub>2</sub> contain 4<sup>4</sup> nets of metal and iodine atoms with short metal-metal bonds (393-386 La-Pr).<ref name = "Atwood"/> these compounds should be considered to be two-dimensional metals (two-dimensional in the same way that graphite is). The salt-like dihalides include those of Eu, Dy, Tm, and Yb. The formation of a relatively stable +2 oxidation state for Eu and Yb is usually explained by the stability (exchange energy) of half filled (f<sup>7</sup>) and fully filled f<sup>14</sup>. GdI<sub>2</sub> possesses the layered [[Molybdenum disulfide|MoS<sub>2</sub>]] structure, is [[ferromagnetic]] and exhibits colossal [[magnetoresistance]].<ref name = "Atwood"/>

The sesquihalides Ln<sub>2</sub>X<sub>3</sub> and the Ln<sub>7</sub>I<sub>12</sub> compounds listed in the table contain metal [[Cluster chemistry|clusters]], discrete Ln<sub>6</sub>I<sub>12</sub> clusters in Ln<sub>7</sub>I<sub>12</sub> and condensed clusters forming chains in the sesquihalides. Scandium forms a similar cluster compound with chlorine, Sc<sub>7</sub>Cl<sub>12</sub><ref name = "Greenwood&Earnshaw"/> Unlike many transition metal clusters these lanthanide clusters do not have strong metal-metal interactions and this is due to the low number of valence electrons involved, but instead are stabilised by the surrounding halogen atoms.<ref name = "Atwood"/>

LaI and TmI are the only known monohalides. LaI, prepared from the reaction of LaI<sub>3</sub> and La metal, it has a NiAs type structure and can be formulated La<sup>3+</sup> (I<sup>−</sup>)(e<sup>−</sup>)<sub>2</sub>.<ref name="RyazanovKienle2006"/> TmI is a true Tm(I) compound, however it is not isolated in a pure state.<ref name="TmI"/>

====Oxides and hydroxides====
All of the lanthanides form sesquioxides, Ln<sub>2</sub>O<sub>3</sub>. The lighter/larger lanthanides adopt a hexagonal 7-coordinate structure while the heavier/smaller ones adopt a cubic 6-coordinate "C-M<sub>2</sub>O<sub>3</sub>" structure.<ref name="Wells"/> All of the sesquioxides are basic, and absorb water and carbon dioxide from air to form carbonates, hydroxides and hydroxycarbonates.<ref name = "Adachi">Adachi, G.; Imanaka, Nobuhito and Kang, Zhen Chuan (eds.) (2006) ''Binary Rare Earth Oxides''. Springer. {{ISBN|1-4020-2568-8}}</ref> They dissolve in acids to form salts.<ref name=CottonSA2006/>

Cerium forms a stoichiometric dioxide, CeO<sub>2</sub>, where cerium has an oxidation state of +4.  CeO<sub>2</sub> is basic and dissolves with difficulty in acid to form Ce<sup>4+</sup> solutions, from which Ce<sup>IV</sup> salts can be isolated, for example the hydrated nitrate Ce(NO<sub>3</sub>)<sub>4</sub>.5H<sub>2</sub>O.  CeO<sub>2</sub> is used as an oxidation catalyst in catalytic converters.<ref name=CottonSA2006/> Praseodymium and terbium form non-stoichiometric oxides containing Ln<sup>IV</sup>,<ref name=CottonSA2006/> although more extreme reaction conditions can produce stoichiometric (or near stoichiometric) PrO<sub>2</sub> and TbO<sub>2</sub>.<ref name = "Greenwood&Earnshaw"/>

Europium and ytterbium form salt-like monoxides, EuO and YbO, which have a rock salt structure.<ref name=CottonSA2006/> EuO is ferromagnetic at low temperatures,<ref name = "Greenwood&Earnshaw"/> and is a semiconductor with possible applications in [[spintronics]].<ref name = "Nasirpouri">Nasirpouri, Farzad and Nogaret, Alain (eds.) (2011) ''Nanomagnetism and Spintronics: Fabrication, Materials, Characterization and Applications''. World Scientific. {{ISBN|9789814273053}}</ref> A mixed Eu<sup>II</sup>/Eu<sup>III</sup> oxide Eu<sub>3</sub>O<sub>4</sub> can be produced by reducing Eu<sub>2</sub>O<sub>3</sub> in a stream of hydrogen.<ref name = "Adachi"/> Neodymium and samarium also form monoxides, but these are shiny conducting solids,<ref name = "Greenwood&Earnshaw"/> although the existence of samarium monoxide is considered dubious.<ref name = "Adachi"/>

All of the lanthanides form hydroxides, Ln(OH)<sub>3</sub>.  With the exception of lutetium hydroxide, which has a cubic structure, they have the hexagonal UCl<sub>3</sub> structure.<ref name = "Adachi"/> The hydroxides can be precipitated from solutions of Ln<sup>III</sup>.<ref name=CottonSA2006/> They can also be formed by the reaction of the sesquioxide, Ln<sub>2</sub>O<sub>3</sub>, with water, but although this reaction is thermodynamically favorable it is kinetically slow for the heavier members of the series.<ref name = "Adachi"/> [[Fajans' rules]] indicate that the smaller Ln<sup>3+</sup> ions will be more polarizing and their salts correspondingly less ionic.  The hydroxides of the heavier lanthanides become less basic, for example Yb(OH)<sub>3</sub> and Lu(OH)<sub>3</sub> are still basic hydroxides but will dissolve in hot concentrated [[sodium hydroxide|NaOH]].<ref name = "Greenwood&Earnshaw"/>

====Chalcogenides (S, Se, Te)====
All of the lanthanides form Ln<sub>2</sub>Q<sub>3</sub> (Q= S, Se, Te).<ref name=CottonSA2006/> The sesquisulfides can be produced by reaction of the elements or (with the exception of Eu<sub>2</sub>S<sub>3</sub>) sulfidizing the oxide (Ln<sub>2</sub>O<sub>3</sub>) with H<sub>2</sub>S.<ref name=CottonSA2006/> The sesquisulfides, Ln<sub>2</sub>S<sub>3</sub> generally lose sulfur when heated and can form a range of compositions between Ln<sub>2</sub>S<sub>3</sub> and Ln<sub>3</sub>S<sub>4</sub>. The sesquisulfides are insulators but some of the Ln<sub>3</sub>S<sub>4</sub> are metallic conductors (e.g. Ce<sub>3</sub>S<sub>4</sub>) formulated (Ln<sup>3+</sup>)<sub>3</sub> (S<sup>2−</sup>)<sub>4</sub> (e<sup>−</sup>), while others (e.g. Eu<sub>3</sub>S<sub>4</sub> and Sm<sub>3</sub>S<sub>4</sub>) are semiconductors.<ref name=CottonSA2006/> Structurally the sesquisulfides adopt structures that vary according to the size of the Ln metal. The lighter and larger lanthanides favoring 7-coordinate metal atoms, the heaviest and smallest lanthanides (Yb and Lu) favoring 6 coordination and the rest structures with a mixture of 6 and 7 coordination.<ref name=CottonSA2006/> 

Polymorphism is common amongst the sesquisulfides.<ref name="Flahaut handbookvol4">{{cite book |last=Flahaut |first=Jean |editor-first=K. A. Jr. |editor-last=Gschneider |title=Handbook on the Physics and Chemistry of Rare Earths vol 4|pages=100–110 |year=1979|chapter=Chapter 31:Sulfides, Selenides and Tellurides|publisher=North Holland Publishing Company|isbn=978-0-444-85216-8}}</ref> The colors of the sesquisulfides vary metal to metal and depend on the polymorphic form. The colors of the γ-sesquisulfides are La<sub>2</sub>S<sub>3</sub>, white/yellow; Ce<sub>2</sub>S<sub>3</sub>, dark red; Pr<sub>2</sub>S<sub>3</sub>, green; Nd<sub>2</sub>S<sub>3</sub>, light green; Gd<sub>2</sub>S<sub>3</sub>, sand; Tb<sub>2</sub>S<sub>3</sub>, light yellow and Dy<sub>2</sub>S<sub>3</sub>, orange.<ref name="HighPerfPigs">{{cite book |last=Berte |first=Jean-Noel |editor-first=Hugh M. |editor-last=Smith |title=High Performance Pigments|year=2009|chapter= Cerium pigments|publisher= Wiley-VCH|isbn=978-3-527-30204-8}}</ref> The shade of γ-Ce<sub>2</sub>S<sub>3</sub> can be varied by doping with Na or Ca with hues ranging from dark red to yellow,<ref name = "Atwood"/><ref name="HighPerfPigs"/> and Ce<sub>2</sub>S<sub>3</sub> based pigments are used commercially and are seen as low toxicity substitutes for cadmium based pigments.<ref name="HighPerfPigs"/>

All of the lanthanides form monochalcogenides, LnQ, (Q= S, Se, Te).<ref name=CottonSA2006/> The majority of the monochalcogenides are conducting, indicating a formulation Ln<sup>III</sup>Q<sup>2−</sup>(e-) where the electron is in conduction bands. The exceptions are SmQ, EuQ and YbQ which are semiconductors or insulators but exhibit a pressure induced transition to a conducting state.<ref name="Flahaut handbookvol4"/>
Compounds LnQ<sub>2</sub> are known but these do not contain Ln<sup>IV</sup> but are Ln<sup>III</sup> compounds containing polychalcogenide anions.<ref name="HOWI2">[[#Holleman|Holleman]], p.&nbsp;1944.</ref>

Oxysulfides Ln<sub>2</sub>O<sub>2</sub>S are well known, they all have the same structure with 7-coordinate Ln atoms, and 3 sulfur and 4 oxygen atoms as near neighbours.<ref>Liu, Guokui and Jacquier, Bernard (eds) (2006)  ''Spectroscopic Properties of Rare Earths in Optical Materials'', Springer</ref>
Doping these with other lanthanide elements produces phosphors. As an example, [[gadolinium oxysulfide]], Gd<sub>2</sub>O<sub>2</sub>S doped with Tb<sup>3+</sup> produces visible photons when irradiated with high energy X-rays and is used as a [[scintillator]] in flat panel detectors.<ref name="Intmicro">{{cite book |last=Sisniga |first=Alejandro |editor-first=Krzysztof |editor-last= Iniewski|title=Integrated Microsystems: Electronics, Photonics, and Biotechnology|year=2012|chapter= Chapter 15|publisher=CRC Press|isbn=978-3-527-31405-8}}</ref>
When [[mischmetal]], an alloy of lanthanide metals, is added to molten steel to remove oxygen and sulfur, stable oxysulfides are produced that form an immiscible solid.<ref name=CottonSA2006/>

====Pnictides (group 15)====
All of the lanthanides form a mononitride, LnN, with the rock salt structure. The mononitrides have attracted interest because of their unusual physical properties. SmN and EuN are reported as being "[[half metal]]s".<ref name = "Atwood"/> NdN, GdN, TbN and DyN are ferromagnetic, SmN is antiferromagnetic.<ref name="Temmerman handbookvol39">{{cite book |last=Temmerman |first=W. M. |editor-first=K. A. Jr. |editor-last=Gschneider |title=Handbook on the Physics and Chemistry of Rare Earths vol 39|pages=100–110 |year=2009|chapter=Chapter 241: The Dual, Localized or Band‐Like, Character of the 4f‐States|publisher=Elsevier|isbn=978-0-444-53221-3 }}</ref> Applications in the field of [[spintronics]] are being investigated.<ref name = "Nasirpouri"/>
CeN is unusual as it is a metallic conductor, contrasting with the other nitrides also with the other cerium pnictides. A simple description is Ce<sup>4+</sup>N<sup>3−</sup> (e–) but the interatomic distances are a better match for the trivalent state rather than for the tetravalent state. A number of different explanations have been offered.<ref>Dronskowski, R. (2005) ''Computational Chemistry of Solid State Materials: A Guide for Materials Scientists, Chemists, Physicists and Others'', Wiley, {{ISBN|9783527314102}}</ref>
The nitrides can be prepared by the reaction of lanthanum metals with nitrogen. Some nitride is produced along with the oxide, when lanthanum metals are ignited in air.<ref name=CottonSA2006/> Alternative methods of synthesis are a high temperature reaction of lanthanide metals with ammonia or the decomposition of lanthanide amides, Ln(NH<sub>2</sub>)<sub>3</sub>. Achieving pure stoichiometric compounds, and crystals with low defect density has proved difficult.<ref name = "Nasirpouri"/> The lanthanide nitrides are sensitive to air and hydrolyse producing ammonia.<ref name="Holleman"/>

The other pnictides phosphorus, arsenic, antimony and bismuth also react with the lanthanide metals to form monopnictides, LnQ, where Q = P, As, Sb or Bi. Additionally a range of other compounds can be produced with varying stoichiometries, such as LnP<sub>2</sub>, LnP<sub>5</sub>, LnP<sub>7</sub>, Ln<sub>3</sub>As, Ln<sub>5</sub>As<sub>3</sub> and LnAs<sub>2</sub>.<ref name="Hulliger handbookvol4">{{cite book |last=Hulliger |first=F. |editor-first=K. A. Jr. |editor-last=Gschneider |title=Handbook on the Physics and Chemistry of Rare Earths vol 4|pages=100–110 |year=1979|chapter=Chapter 33: Rare Earth Pnictides|publisher=North Holland Publishing Company|isbn=978-0-444-85216-8}}</ref>

====Carbides====
Carbides of varying stoichiometries are known for the lanthanides. Non-stoichiometry is common. All of the lanthanides form LnC<sub>2</sub> and Ln<sub>2</sub>C<sub>3</sub> which both contain C<sub>2</sub> units. 

The dicarbides with exception of EuC<sub>2</sub>, are metallic conductors with the [[calcium carbide]] structure and can be formulated as Ln<sup>3+</sup>C<sub>2</sub><sup>2−</sup>(e–). The C-C bond length is longer than that in [[calcium carbide|CaC<sub>2</sub>]], which contains the C<sub>2</sub><sup>2−</sup> anion, indicating that the antibonding orbitals of the C<sub>2</sub><sup>2−</sup> anion are involved in the conduction band. These dicarbides hydrolyse to form hydrogen and a mixture of hydrocarbons.<ref name = "Greenwood&Earnshawp297">{{Greenwood&Earnshaw2nd|pages=297–299}}</ref> EuC<sub>2</sub> and to a lesser extent YbC<sub>2</sub> hydrolyse differently producing a higher percentage of acetylene (ethyne).<ref name="SpeddingGschneidner1958">{{cite journal|last1=Spedding|first1=F. H.|last2=Gschneidner|first2=K.|last3=Daane|first3=A. H.|title=The Crystal Structures of Some of the Rare Earth Carbides|journal=Journal of the American Chemical Society|volume=80|issue=17|year=1958|pages=4499–4503|doi=10.1021/ja01550a017}}</ref> 

The sesquicarbides, Ln<sub>2</sub>C<sub>3</sub> can be formulated as Ln<sub>4</sub>(C<sub>2</sub>)<sub>3</sub>. These compounds adopt the Pu<sub>2</sub>C<sub>3</sub> structure<ref name = "Atwood"/> which has been described as having C<sub>2</sub><sup>2−</sup> anions in bisphenoid holes formed by eight near Ln neighbours.<ref name="WangLoa2005">{{cite journal|last1=Wang|first1=X.|last2=Loa|first2=I.|last3=Syassen|first3=K.|last4=Kremer|first4=R.|last5=Simon|first5=A.|last6=Hanfland|first6=M.|last7=Ahn|first7=K.|title=Structural properties of the sesquicarbide superconductor La<sub>2</sub>C<sub>3</sub> at high pressure|journal=Physical Review B|volume=72|issue=6|pages=064520|year=2005|doi=10.1103/PhysRevB.72.064520|arxiv=cond-mat/0503597|bibcode=2005PhRvB..72f4520W|s2cid=119330966}}</ref>  The C-C bond is less elongated than in the dicarbides, with the exception of Ce<sub>2</sub>C<sub>3</sub>,<ref name = "Greenwood&Earnshawp297"/> indicating that the delocalized metal electrons do not fill C-C antibonding orbitals.<ref name=CarbideHandbk>{{cite encyclopedia|title=Handbook on the Physics and Chemistry of Rare Earths|volume=15|publisher=Elsevier|year=1991|editor-first1=Karl&nbsp;A.|editor-last1=Gschneider|editor-first2=LeRoy|editor-last2=Eyring|isbn=978-0-444-88966-9|entry=Rare earth carbides|author1=Adachi Gin-ya|author2=Imanaka Nobuhito|author3=Zhang Fuzhong|p=90|ref={{harvid|Adachi|Imanaka|Zhang|1991}}}}</ref>  

Other carbon rich stoichiometries are known for some lanthanides. Ln<sub>3</sub>C<sub>4</sub> (Ho-Lu) containing C, C<sub>2</sub> and C<sub>3</sub> units;<ref name="PoettgenJeitschko1991">{{cite journal|last1=Poettgen|first1=Rainer.|last2=Jeitschko|first2=Wolfgang.|title=Scandium carbide, Sc<sub>3</sub>C<sub>4</sub>, a carbide with C3 units derived from propadiene|journal=Inorganic Chemistry|volume=30|issue=3|year=1991|pages=427–431|doi=10.1021/ic00003a013}}</ref> Ln<sub>4</sub>C<sub>7</sub> (Ho-Lu) contain C atoms and C<sub>3</sub> units<ref>{{cite journal |title=Preparation, Crystal Structure, and Properties of the Lanthanoid Carbides Ln<sub>4</sub>C<sub>7</sub> with Ln: Ho, Er, Tm, and Lu  |journal=Z. Naturforsch. B|year=1996|volume=51|issue=5|pages=646–654|url=http://zfn.mpdl.mpg.de/data/Reihe_B/51/ZNB-1996-51b-0646.pdf|doi=10.1515/znb-1996-0505|last1=Czekalla|first1=Ralf|last2=Jeitschko|first2=Wolfgang|last3=Hoffmann|first3=Rolf-Dieter|last4=Rabeneck|first4=Helmut|s2cid=197308523}}</ref> and Ln<sub>4</sub>C<sub>5</sub> (Gd-Ho) containing C and C<sub>2</sub> units.<ref>{{cite journal|last1=Czekalla|first1=Ralf|last2=Hüfken|first2=Thomas|last3=Jeitschko|first3=Wolfgang|last4=Hoffmann|first4=Rolf-Dieter|last5=Pöttgen|first5=Rainer|title=The Rare Earth Carbides R<sub>4</sub>C<sub>5</sub> with R=Y, Gd, Tb, Dy, and Ho|journal=Journal of Solid State Chemistry|volume=132|issue=2|year=1997|pages=294–299|doi=10.1006/jssc.1997.7461|bibcode=1997JSSCh.132..294C}}</ref>

Metal rich carbides contain interstitial C atoms and no C<sub>2</sub> or C<sub>3</sub> units. These are Ln<sub>4</sub>C<sub>3</sub> (Tb and Lu); Ln<sub>2</sub>C (Dy, Ho, Tm)<ref name="AtojiA1981">{{cite journal|last1=Atoji|first1=Masao|title=Neutron-diffraction study of Ho<sub>2</sub>C at 4–296 K |journal=The Journal of Chemical Physics|volume=74|issue=3|year=1981|page=1893|doi=10.1063/1.441280|bibcode=1981JChPh..74.1893A}}</ref><ref name="AtojiB1981">{{cite journal|last1=Atoji|first1=Masao|title=Neutron-diffraction studies of Tb<sub>2</sub>C and Dy<sub>2</sub>C in the temperature range 4–296 K|journal=The Journal of Chemical Physics|volume=75|issue=3|year=1981|page=1434|doi=10.1063/1.442150|bibcode=1981JChPh..75.1434A}}</ref> and Ln<sub>3</sub>C<ref name = "Atwood"/> (Sm-Lu).  These hydrolyze to [[methane]].{{sfn|Adachi|Imanaka|Zhang|1991|p=98}}

====Borides====
All of the lanthanides form a number of borides. The "higher" borides (LnB<sub>x</sub> where x > 12) are insulators/semiconductors whereas the lower borides are typically conducting. The lower borides have stoichiometries of LnB<sub>2</sub>, LnB<sub>4</sub>, LnB<sub>6</sub> and LnB<sub>12</sub>.<ref name="Mori handbookvol38">{{cite book |last=Mori |first=Takao |editor-first=K. A. Jr. |editor-last=Gschneider |title=Handbook on the Physics and Chemistry of Rare Earths vol 38|pages=105–174 |year=2008|chapter=Chapter 238:Higher Borides| publisher=North Holland|isbn=978-0-444-521439 }}</ref> Applications in the field of [[spintronics]] are being investigated.<ref name = "Nasirpouri"/> The range of borides formed by the lanthanides can be compared to those formed by the transition metals. The boron rich borides are typical of the lanthanides (and groups 1–3) whereas for the transition metals tend to form metal rich, "lower" borides.<ref name = "Greenwood&Earnshawp147">{{Greenwood&Earnshaw2nd|pages=147}}</ref> The lanthanide borides are typically grouped together with the group 3 metals with which they share many similarities of reactivity, stoichiometry and structure. Collectively these are then termed the rare earth borides.<ref name="Mori handbookvol38"/>

Many methods of producing lanthanide borides have been used, amongst them are direct reaction of the elements; the reduction of Ln<sub>2</sub>O<sub>3</sub> with boron; reduction of boron oxide, B<sub>2</sub>O<sub>3</sub>, and Ln<sub>2</sub>O<sub>3</sub> together with carbon; reduction of metal oxide with [[boron carbide]], B<sub>4</sub>C.<ref name="Mori handbookvol38"/><ref name = "Greenwood&Earnshawp147"/><ref name = "Alper">Refractory Materials, Volume 6-IV: 1976, ed. Allen Alper, Elsevier, {{ISBN|0-12-053204-2}}</ref><ref name = "InorgReactvol13">Zuckerman, J. J. (2009) ''Inorganic Reactions and Methods, The Formation of Bonds to Group-I, -II, and -IIIb Elements'', Vol. 13, John Wiley & Sons, {{ISBN|089573-263-7}}</ref> Producing high purity samples has proved to be difficult.<ref name = "InorgReactvol13"/> Single crystals of the higher borides have been grown in a low melting metal (e.g. Sn, Cu, Al).<ref name="Mori handbookvol38"/>

Diborides, LnB<sub>2</sub>, have been reported for Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. All have the same, AlB<sub>2</sub>, [[yttrium borides#YB2 (yttrium diboride)|structure]] containing a graphitic layer of boron atoms. Low temperature ferromagnetic transitions for Tb, Dy, Ho and Er. TmB<sub>2</sub> is ferromagnetic at 7.2 K.<ref name = "Atwood"/>

Tetraborides, LnB<sub>4</sub> have been reported for all of the lanthanides except EuB<sub>4</sub>, all have the same UB<sub>4</sub> [[yttrium borides#YB4 (yttrium tetraboride)|structure]]. The structure has a boron sub-lattice consists of chains of octahedral B<sub>6</sub> clusters linked by boron atoms. The unit cell decreases in size successively from LaB<sub>4</sub> to LuB<sub>4</sub>. The tetraborides of the lighter lanthanides melt with decomposition to LnB<sub>6</sub>.<ref name = "InorgReactvol13"/> Attempts to make EuB<sub>4</sub> have failed.<ref name = "Alper"/> The LnB<sub>4</sub> are good conductors<ref name="Mori handbookvol38"/> and typically antiferromagnetic.<ref name = "Atwood"/>

Hexaborides, LnB<sub>6</sub> have been reported for all of the lanthanides. They all have the CaB<sub>6</sub> [[yttrium borides#YB6 (yttrium hexaboride)|structure]], containing B<sub>6</sub> clusters. They are non-stoichiometric due to cation defects. The hexaborides of the lighter lanthanides (La – Sm) melt without decomposition, EuB<sub>6</sub> decomposes to boron and metal and the heavier lanthanides decompose to LnB<sub>4</sub> with exception of YbB<sub>6</sub> which decomposes forming YbB<sub>12</sub>. The stability has in part been correlated to differences in volatility between the lanthanide metals.<ref name = "InorgReactvol13"/> In EuB<sub>6</sub> and YbB<sub>6</sub> the metals have an oxidation state of +2 whereas in the rest of the lanthanide hexaborides it is +3. This rationalises the differences in conductivity, the extra electrons in the Ln<sup>III</sup> hexaborides entering conduction bands. EuB<sub>6</sub> is a semiconductor and the rest are good conductors.<ref name = "Atwood"/><ref name = "InorgReactvol13"/> [[lanthanum hexaboride|LaB<sub>6</sub>]] and [[cerium hexaboride|CeB<sub>6</sub>]] are thermionic emitters, used, for example, in [[scanning electron microscope]]s.<ref>{{cite book|author=Reimer, Ludwig |title=Image Formation in Low-voltage Scanning Electron Microscopy|url=https://books.google.com/books?id=BbUO-gwN00AC&pg=PR9|year=1993|publisher=SPIE Press|isbn=978-0-8194-1206-5}}</ref>

Dodecaborides, LnB<sub>12</sub>, are formed by the heavier smaller lanthanides, but not by the lighter larger metals, La – Eu. With the exception YbB<sub>12</sub> (where Yb takes an intermediate valence and is a [[Kondo insulator]]), the dodecaborides are all metallic compounds. They all have the UB<sub>12</sub> [[yttrium borides#YB12 (yttrium dodecaboride)|structure]] containing a 3 dimensional framework of cubooctahedral B<sub>12</sub> clusters.<ref name="Mori handbookvol38"/>

The higher boride LnB<sub>66</sub> is known for all lanthanide metals. The composition is approximate as the compounds are non-stoichiometric.<ref name="Mori handbookvol38"/> They all have similar complex [[yttrium borides#YB66|structure]] with over 1600 atoms in the unit cell. The boron cubic sub lattice contains super icosahedra made up of a central B<sub>12</sub> icosahedra surrounded by 12 others, B<sub>12</sub>(B<sub>12</sub>)<sub>12</sub>.<ref name="Mori handbookvol38"/> Other complex higher borides LnB<sub>50</sub> (Tb, Dy, Ho Er Tm Lu) and LnB<sub>25</sub> are known (Gd, Tb, Dy, Ho, Er) and these contain boron icosahedra in the boron framework.<ref name="Mori handbookvol38"/>

====Organometallic compounds====
Lanthanide-carbon [[Sigma bond|σ bonds]] are well known; however as the 4f electrons have a low probability of existing at the outer region of the atom there is little effective [[Atomic orbitals|orbital]] overlap, resulting in bonds with significant [[Ionic bond|ionic]] character. As such organo-lanthanide compounds exhibit [[carbanion]]-like behavior, unlike the behavior in [[transition metal]] [[organometallic]] compounds. Because of their large size, lanthanides tend to form more stable organometallic derivatives with bulky ligands to give compounds such as Ln[CH(SiMe<sub>3</sub>)<sub>3</sub>].<ref>{{cite journal|last=Cotton|first=S. A.|title=Aspects of the lanthanide-carbon σ-bond|journal=Coord. Chem. Rev.|volume=160|pages=93–127|doi=10.1016/S0010-8545(96)01340-9|year=1997}}</ref> Analogues of [[uranocene]] are derived from dilithiocyclooctatetraene, Li<sub>2</sub>C<sub>8</sub>H<sub>8</sub>. Organic lanthanide(II) compounds are also known, such as Cp*<sub>2</sub>Eu.<ref name=Nief/>