Editing Berkelium (section)

==Compounds==
{{main|Berkelium compounds}}

===Oxides===
Two oxides of berkelium are known, with the berkelium [[redox|oxidation]] state of +3 ({{chem2|Bk2O3}}) and +4 ([[Berkelium(IV) oxide|{{chem2|BkO2}}]]).<ref>{{cite journal|last1=Peterson|first1=J.|title=Crystal structures and lattice parameters of the compounds of berkelium I. Berkelium dioxide and cubic berkelium sesquioxide|journal=Inorganic and Nuclear Chemistry Letters|volume=3|pages=327|date=1967|doi=10.1016/0020-1650(67)80037-0|issue=9|last2=Cunningham|first2=B. B.|url=https://escholarship.org/uc/item/5mv047vq}}</ref> {{Not a typo|Berkelium(IV)}} oxide is a brown solid,<ref name="BK_OX">{{cite journal|last1=Baybarz|first1=R. D.|title=The berkelium oxide system|journal=Journal of Inorganic and Nuclear Chemistry|volume=30|pages=1769–1773|date=1968|doi=10.1016/0022-1902(68)80352-5|issue=7}}</ref> while {{Not a typo|berkelium(III)}} oxide is a yellow-green solid with a melting point of 1920&nbsp;°C{{sfn|Holleman|Wiberg|2007|p=1972}}<ref name="BK_OX" /> and is formed from BkO<sub>2</sub> by [[redox|reduction]] with molecular [[hydrogen]]:
:{{chem2|2 BkO2 + H2 → Bk2O3 + H2O}}

Upon heating to 1200&nbsp;°C, the oxide {{chem2|Bk2O3}} undergoes a phase change; it undergoes another phase change at 1750&nbsp;°C. Such three-phase behavior is typical for the actinide [[sesquioxide]]s. {{Not a typo|Berkelium(II)}} oxide, BkO, has been reported as a brittle gray solid but its exact chemical composition remains uncertain.{{sfn|Peterson|Hobart|1984|p=51}}

===Halides===
In [[halide]]s, berkelium assumes the oxidation states +3 and +4.{{sfn|Holleman|Wiberg|2007|p=1969}} The +3 state is the most stable, especially in solutions, while the tetravalent halides {{chem2|BkF4}} and {{chem2|Cs2BkCl6}} are only known in the solid phase.{{sfn|Peterson|Hobart|1984|p=47}} The coordination of berkelium atom in its trivalent fluoride and chloride is tricapped [[Octahedral molecular geometry#Trigonal prismatic geometry|trigonal prismatic]], with the [[coordination number]] of 9. In trivalent bromide, it is bicapped trigonal prismatic (coordination 8) or [[Octahedral molecular geometry|octahedral]] (coordination 6),<ref name="conv" /> and in the iodide it is octahedral.{{sfn|Greenwood|Earnshaw|1997|p=1270}}

{| Class = "wikitable" style ="float:right; text-align: center; text-size:90%"
|-
! Oxidation <br>number
! F
! Cl
! Br
! I
|-
! +4
| {{chem2|BkF4}}<br /> (yellow{{sfn|Greenwood|Earnshaw|1997|p=1270}})
| {{chem2|Cs2BkCl6}}<br />(orange{{sfn|Peterson|Hobart|1984|p=51}})
|
|
|-
! +3
| {{chem2|BkF3}}<br /> (yellow{{sfn|Greenwood|Earnshaw|1997|p=1270}})
| {{chem2|BkCl3}}<br /> (green{{sfn|Greenwood|Earnshaw|1997|p=1270}})<br />{{chem2|Cs2NaBkCl6}}{{sfn|Peterson|Hobart|1984|p=48}}
| {{chem2|BkBr3}}<ref name="conv">{{cite journal|last1=Young|first1=J. P.|last2=Haire|first2=R. G.|last3=Peterson|first3=J. R.|last4=Ensor|first4=D. D.|last5=Fellows|first5=R. L.|title=Chemical consequences of radioactive decay. 1. Study of californium-249 ingrowth into crystalline berkelium-249 tribromide: a new crystalline phase of californium tribromide|journal=Inorganic Chemistry|volume=19|pages=2209|date=1980|doi=10.1021/ic50210a003|issue=8}}</ref><ref>{{cite journal|last1=Burns|first1=J.|title=Crystallographic studies of some transuranic trihalides: 239PuCl3, 244CmBr3, 249BkBr3 and 249CfBr3|journal=Journal of Inorganic and Nuclear Chemistry|volume=37|pages=743|date=1975|doi=10.1016/0022-1902(75)80532-X|issue=3|last2=Peterson|first2=J. R.|last3=Stevenson|first3=J. N.}}</ref><br />(yellow-green{{sfn|Greenwood|Earnshaw|1997|p=1270}})
| {{chem2|BkI3}}<br /> (yellow{{sfn|Greenwood|Earnshaw|1997|p=1270}})
|}

{{Not a typo|Berkelium(IV)}} fluoride ({{chem2|BkF4}}) is a yellow-green ionic solid and is isotypic with [[uranium tetrafluoride]] or [[zirconium tetrafluoride]].{{sfn|Peterson|Hobart|1984|p=48}}<ref name="BKF_3_4" /><ref name="f1">{{cite journal|last1=Keenan|first1=Thomas K.|last2=Asprey|first2=Larned B.|title=Lattice constants of actinide tetrafluorides including berkelium|journal=Inorganic Chemistry|volume=8|pages=235|date=1969|doi=10.1021/ic50072a011|issue=2}}</ref> {{Not a typo|Berkelium(III)}} fluoride ({{chem2|BkF3}}) is also a yellow-green solid, but it has two crystalline structures. The most stable phase at low temperatures is isotypic with [[yttrium(III) fluoride]], while upon heating to between 350 and 600&nbsp;°C, it transforms to the structure found in [[lanthanum trifluoride]].{{sfn|Peterson|Hobart|1984|p=48}}<ref name="BKF_3_4">{{cite journal|last1=Ensor|first1=D.|title=Absorption spectrophotometric study of {{Not a typo|berkelium(III)}} and (IV) fluorides in the solid state|journal=Journal of Inorganic and Nuclear Chemistry|volume=43|pages=1001|date=1981|doi=10.1016/0022-1902(81)80164-9|issue=5|last2=Peterson|first2=J. R.|last3=Haire|first3=R. G.|last4=Young|first4=J. P.}}</ref><ref>{{cite journal|last1=Peterson|first1=J. R.|last2=Cunningham|first2=B. B.|title=Crystal structures and lattice parameters of the compounds of berkelium—IV berkelium trifluoride☆|journal=Journal of Inorganic and Nuclear Chemistry|volume=30|pages=1775|date=1968|doi=10.1016/0022-1902(68)80353-7|issue=7|url=https://escholarship.org/uc/item/1mn5c30t}}</ref>

Visible amounts of [[Berkelium(III) chloride|{{Not a typo|berkelium(III)}} chloride]] ({{chem2|BkCl3}}) were first isolated and characterized in 1962, and weighed only 3 billionths of a [[gram]]. It can be prepared by introducing [[hydrogen chloride]] vapors into an evacuated quartz tube containing berkelium oxide at a temperature about 500&nbsp;°C.<ref name="o1" /> This green solid has a melting point of 600&nbsp;°C,{{sfn|Holleman|Wiberg|2007|p=1969}} and is isotypic with [[uranium(III) chloride]].<ref>{{cite journal|last1=Peterson|first1=J. R.|last2=Cunningham|first2=B. B.|title=Crystal structures and lattice parameters of the compounds of berkelium—IIBerkelium trichloride|journal=Journal of Inorganic and Nuclear Chemistry|volume=30|pages=823|date=1968|doi=10.1016/0022-1902(68)80443-9|issue=3}}</ref><ref>{{cite journal|last1=Peterson|first1=J. R.|last2=Young|first2=J. P.|last3=Ensor|first3=D. D.|last4=Haire|first4=R. G.|title=Absorption spectrophotometric and x-ray diffraction studies of the trichlorides of berkelium-249 and californium-249|journal=Inorganic Chemistry|volume=25|pages=3779|date=1986|doi=10.1021/ic00241a015|issue=21}}</ref> Upon heating to nearly melting point, {{chem2|BkCl3}} converts into an orthorhombic phase.{{sfn|Peterson|Hobart|1984|p=52}}

Two forms of {{Not a typo|berkelium(III)}} bromide are known: one with berkelium having coordination 6, and one with coordination 8.{{sfn|Peterson|Hobart|1984|p=38}} The latter is less stable and transforms to the former phase upon heating to about 350&nbsp;°C. An important phenomenon for radioactive solids has been studied on these two crystal forms: the structure of fresh and aged <sup>249</sup>BkBr<sub>3</sub> samples was probed by [[X-ray crystallography|X-ray diffraction]] over a period longer than 3 years, so that various fractions of berkelium-249 had [[beta decay]]ed to californium-249. No change in structure was observed upon the <sup>249</sup>BkBr<sub>3</sub>—<sup>249</sup>CfBr<sub>3</sub> transformation. However, other differences were noted for <sup>249</sup>BkBr<sub>3</sub> and <sup>249</sup>CfBr<sub>3</sub>. For example, the latter could be reduced with hydrogen to <sup>249</sup>CfBr<sub>2</sub>, but the former could not – this result was reproduced on individual <sup>249</sup>BkBr<sub>3</sub> and <sup>249</sup>CfBr<sub>3</sub> samples, as well on the samples containing both bromides.<ref name="conv" /> The intergrowth of californium in berkelium occurs at a rate of 0.22% per day and is an intrinsic obstacle in studying berkelium properties. Beside a chemical contamination, <sup>249</sup>Cf, being an alpha emitter, brings undesirable self-damage of the crystal lattice and the resulting self-heating. The chemical effect however can be avoided by performing measurements as a function of time and extrapolating the obtained results.{{sfn|Peterson|Hobart|1984|p=47}}

===Other inorganic compounds===
The [[Pnictogen#Compounds|pnictides]] of berkelium-249 of the type BkX are known for the elements [[nitrogen]],<ref name="n1">{{cite journal|last1=Stevenson|first1=J.|last2=Peterson|first2=J.|title=Preparation and structural studies of elemental curium-248 and the nitrides of curium-248 and berkelium-249|journal=Journal of the Less Common Metals|volume=66|pages=201|date=1979|doi=10.1016/0022-5088(79)90229-7|issue=2}}</ref> [[phosphorus]], [[arsenic]] and [[antimony]]. They crystallize in the [[Cubic crystal system|rock-salt structure]] and are prepared by the reaction of either {{Not a typo|berkelium(III)}} hydride ({{chem2|BkH3}}) or metallic berkelium with these elements at elevated temperature (about 600&nbsp;°C) under high vacuum.<ref>{{cite journal|last1=Damien|first1=D.|last2=Haire|first2=R. G.|last3=Peterson|first3=J. R.|title=Preparation and lattice parameters of <sup>249</sup>Bk monopnictides|journal=Journal of Inorganic and Nuclear Chemistry|volume=42|pages=995|date=1980|doi=10.1016/0022-1902(80)80390-3|issue=7}}</ref>

{{Not a typo|Berkelium(III)}} sulfide, {{chem2|Bk2S3}}, is prepared by either treating berkelium oxide with a mixture of [[hydrogen sulfide]] and [[carbon disulfide]] vapors at 1130&nbsp;°C, or by directly reacting metallic berkelium with elemental sulfur. These procedures yield brownish-black crystals.{{sfn|Peterson|Hobart|1984|p=53}}

{{Not a typo|Berkelium(III)}} and {{Not a typo|berkelium(IV)}} hydroxides are both stable in 1 [[Molar concentration|molar]] solutions of [[sodium hydroxide]]. {{Not a typo|Berkelium(III)}} [[phosphate]] ({{chem2|BkPO4}}) has been prepared as a solid, which shows strong [[fluorescence]] under excitation with a green light.{{sfn|Peterson|Hobart|1984|pp=39–40}} Berkelium hydrides are produced by reacting metal with hydrogen gas at temperatures about 250&nbsp;°C.<ref name="n1" /> They are non-stoichiometric with the nominal formula {{chem|BkH|2+''x''}} (0 < ''x'' < 1).{{sfn|Peterson|Hobart|1984|p=53}} Several other salts of berkelium are known, including an oxysulfide ({{chem2|Bk2O2S}}), and hydrated [[Berkelium(III) nitrate|nitrate]] ({{chem|Bk(NO|3|)|3|·4H|2|O}}), chloride ({{chem|BkCl|3|·6H|2|O}}), [[sulfate]] ({{chem|Bk|2|(SO|4|)|3|·12H|2|O}}) and [[oxalate]] ({{chem|Bk|2|(C|2|O|4|)|3|·4H|2|O}}).{{sfn|Peterson|Hobart|1984|p=47}} Thermal decomposition at about 600&nbsp;°C in an [[argon]] atmosphere (to avoid oxidation to {{chem2|BkO2}}) of {{chem|Bk|2|(SO|4|)|3|·12H|2|O}} yields the crystals of {{Not a typo|berkelium(III)}} oxysulfate ({{chem2|Bk2O2SO4}}). This compound is thermally stable to at least 1000&nbsp;°C in inert atmosphere.{{sfn|Peterson|Hobart|1984|p=54}}

===Organoberkelium compounds===
Berkelium forms a trigonal (η<sup>5</sup>–C<sub>5</sub>H<sub>5</sub>)<sub>3</sub>Bk [[metallocene]] complex with three [[Cyclopentadienyl complex|cyclopentadienyl]] rings, which can be synthesized by reacting {{Not a typo|berkelium(III)}} chloride with the molten [[beryllocene]] ({{chem2|Be(C5H5)2}}) at about 70&nbsp;°C. It has an amber color and a density of 2.47&nbsp;g/cm<sup>3</sup>. The complex is stable to heating to at least 250&nbsp;°C, and sublimates without melting at about 350&nbsp;°C. The high radioactivity of berkelium gradually destroys the compound (within a period of weeks).<ref name="o1">{{cite journal|last1=Laubereau|first1=Peter G.|last2=Burns|first2=John H.|title=Microchemical preparation of tricyclopentadienyl compounds of berkelium, californium, and some lanthanide elements|journal=Inorganic Chemistry|volume=9|pages=1091|date=1970|doi=10.1021/ic50087a018|issue=5}}</ref><ref>Christoph Elschenbroich ''Organometallic Chemistry'', 6th Edition, Wiesbaden 2008, {{ISBN|978-3-8351-0167-8}}, pp. 583–584</ref> One cyclopentadienyl ring in (η<sup>5</sup>–C<sub>5</sub>H<sub>5</sub>)<sub>3</sub>Bk can be substituted by chlorine to yield {{chem2|[Bk(C5H5)2Cl]2}}. The optical absorption spectra of this compound are very similar to those of (η<sup>5</sup>–C<sub>5</sub>H<sub>5</sub>)<sub>3</sub>Bk.{{sfn|Peterson|Hobart|1984|pp=41, 54}}

Berkelium also forms Berkelocene, an [[actinocene]] complex, with substituted cyclooctatetraenides.<ref>{{Cite journal |last=Russo |first=Dominic R. |last2=Gaiser |first2=Alyssa N. |last3=Price |first3=Amy N. |last4=Sergentu |first4=Dumitru-Claudiu |last5=Wacker |first5=Jennifer N. |last6=Katzer |first6=Nicholas |last7=Peterson |first7=Appie A. |last8=Branson |first8=Jacob A. |last9=Yu |first9=Xiaojuan |last10=Kelly |first10=Sheridon N. |last11=Ouellette |first11=Erik T. |last12=Arnold |first12=John |last13=Long |first13=Jeffrey R. |last14=Lukens |first14=Wayne W. |last15=Teat |first15=Simon J. |date=2025-02-28 |title=Berkelium–carbon bonding in a tetravalent berkelocene |url=https://www.science.org/doi/10.1126/science.adr3346 |journal=Science |volume=387 |issue=6737 |pages=974–978 |doi=10.1126/science.adr3346}}</ref>