Editing Actinium (section)

==Chemical compounds==
{{Main|Actinium compounds}}
Due to actinium's intense radioactivity, only a limited number of actinium compounds are known. These include: [[Actinium fluoride|AcF<sub>3</sub>]], [[Actinium(III) chloride|AcCl<sub>3</sub>]], [[Actinium(III) bromide|AcBr<sub>3</sub>]], [[Actinium oxyfluoride|AcOF]], [[Actinium(III) oxychloride|AcOCl]], [[Actinium(III) oxybromide|AcOBr]], [[Actinium(III) sulfide|Ac<sub>2</sub>S<sub>3</sub>]], [[Actinium oxide|Ac<sub>2</sub>O<sub>3</sub>]], [[Actinium(III) phosphate|AcPO<sub>4</sub>]] and [[Actinium(III) nitrate|Ac(NO<sub>3</sub>)<sub>3</sub>]]. They all contain actinium in the oxidation state +3.<ref name="bse" /><ref name="j2" /> In particular, the lattice constants of the analogous lanthanum and actinium compounds differ by only a few percent.<ref name="j2" />

{| Class = "wikitable collapsible collapsed" style = "text-align: center"
! Formula
! color
! symmetry
! [[space group]]
! No
! [[Pearson symbol]]
! ''a'' (pm)
! ''b'' (pm)
! ''c'' (pm)
! ''Z''
! density, <br />g/cm<sup>3</sup>
|-
| Ac
| silvery
| ''[[Cubic crystal system|fcc]]''<ref name="ach">{{cite journal |doi=10.1016/0022-1902(61)80369-2 |last1=Farr |date=1961 |first1=J. |pages=42–47 |volume=18 |journal=Journal of Inorganic and Nuclear Chemistry |title=The crystal structure of actinium metal and actinium hydride |last2=Giorgi |first2=A. L. |last3=Bowman |first3=M. G. |last4=Money |first4=R. K.|osti=4397640 }}</ref>
| Fm{{overline|3}}m
| 225
| cF4
| 531.1
| 531.1
| 531.1
| 4
| 10.07
|-
| AcH<sub>2</sub>
|unknown
| cubic<ref name="ach" />
| Fm{{overline|3}}m
| 225
| cF12
| 567
| 567
| 567
| 4
| 8.35
|-
| Ac<sub>2</sub>O<sub>3</sub>
| white<ref name="blueglow" />
| [[Trigonal crystal system|trigonal]]<ref name="aco">{{cite journal |doi=10.1107/S0365110X49001016 |last1=Zachariasen |date=1949 |first1=W. H. |pages=388–390 |volume=2 |journal=Acta Crystallographica |title=Crystal chemical studies of the 5f-series of elements. XII. New compounds representing known structure types |issue=6|doi-access=free |bibcode=1949AcCry...2..388Z }}</ref>
| P{{overline|3}}m1
| 164
| hP5
| 408
| 408
| 630
| 1
| 9.18
|-
| Ac<sub>2</sub>S<sub>3</sub>
| black
| cubic<ref name="acs">{{cite journal |doi=10.1107/S0365110X49000126 |last1=Zachariasen |date=1949 |first1=W. H. |pages=57–60 |volume=2 |journal=Acta Crystallographica |title=Crystal chemical studies of the 5f-series of elements. VI. The Ce2S3-Ce3S4 type of structure|issue=1 |bibcode=1949AcCry...2...57Z |url=http://journals.iucr.org/q/issues/1949/01/00/a00105/a00105.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://journals.iucr.org/q/issues/1949/01/00/a00105/a00105.pdf |archive-date=2022-10-09 |url-status=live }}</ref>
| I{{overline|4}}3d
| 220
| cI28
| 778.56
| 778.56
| 778.56
| 4
| 6.71
|-
| AcF<sub>3</sub>
| white<ref name="m71">Meyer, p. 71</ref>
| [[Hexagonal crystal system|hexagonal]]<ref name="j2" /><ref name="aco" />
| P{{overline|3}}c1
| 165
| hP24
| 741
| 741
| 755
| 6
| 7.88
|-
| AcCl<sub>3</sub>
|white
| hexagonal<ref name="j2" /><ref name="accl">{{cite journal |doi=10.1107/S0365110X48000703 |last1=Zachariasen |date=1948 |first1=W. H. |pages=265–268 |volume=1 |journal=Acta Crystallographica |title=Crystal chemical studies of the 5f-series of elements. I. New structure types |issue=5|doi-access=free |bibcode=1948AcCry...1..265Z }}</ref>
| P6<sub>3</sub>/m
| 165
| hP8
| 764
| 764
| 456
| 2
| 4.8
|-
| AcBr<sub>3</sub>
| white<ref name="j2" />
| hexagonal<ref name="accl" />
| P6<sub>3</sub>/m
| 165
| hP8
| 764
| 764
| 456
| 2
| 5.85
|-
| AcOF
| white<ref name="m87" />
| cubic<ref name="j2" />
| Fm{{overline|3}}m
|
|
| 593.1
|
|
|
| 8.28
|-
| AcOCl
|white
| [[Tetragonal crystal system|tetragonal]]<ref name="j2" />
|
|
|
| 424
| 424
| 707
|
| 7.23
|-
| AcOBr
|white
| tetragonal<ref name="j2" />
|
|
|
| 427
| 427
| 740
|
| 7.89
|-
| AcPO<sub>4</sub>·0.5H<sub>2</sub>O
|unknown
| hexagonal<ref name="j2" />
|
|
|
| 721
| 721
| 664
|
| 5.48
|}

Here ''a'', ''b'' and ''c'' are lattice constants, No is space group number and ''Z'' is the number of [[formula unit]]s per [[unit cell]]. Density was not measured directly but calculated from the lattice parameters.

===Oxides===
{{Main|Actinium(III) oxide}}
[[Actinium oxide]] (Ac<sub>2</sub>O<sub>3</sub>) can be obtained by heating the hydroxide at {{cvt|500|°C}} or the [[oxalate]] at {{cvt|1100|°C}}, in vacuum. Its crystal lattice is [[Isomorphism (crystallography)|isotypic]] with the oxides of most trivalent rare-earth metals.<ref name="j2" />

===Halides===
[[Actinium trifluoride]] can be produced either in solution or in solid reaction. The former reaction is carried out at room temperature, by adding [[hydrofluoric acid]] to a solution containing actinium ions. In the latter method, actinium metal is treated with hydrogen fluoride vapors at {{cvt|700|°C}} in an all-platinum setup. Treating actinium trifluoride with [[ammonium hydroxide]] at {{cvt|900|–|1000|°C}} yields [[oxyfluoride]] AcOF. Whereas lanthanum oxyfluoride can be easily obtained by burning lanthanum trifluoride in air at {{cvt|800|°C}} for an hour, similar treatment of actinium trifluoride yields no AcOF and only results in melting of the initial product.<ref name="j2" /><ref name="m87">Meyer, pp. 87–88</ref>

:AcF<sub>3</sub> + 2 NH<sub>3</sub> + H<sub>2</sub>O → AcOF + 2 NH<sub>4</sub>F

Actinium trichloride is obtained by reacting actinium hydroxide or [[oxalate]] with [[carbon tetrachloride]] vapors at temperatures above {{cvt|960|°C}}. Similarly to the oxyfluoride, actinium [[oxychloride]] can be prepared by hydrolyzing actinium trichloride with [[ammonium hydroxide]] at {{cvt|1000|°C}}. However, in contrast to the oxyfluoride, the oxychloride could well be synthesized by igniting a solution of actinium trichloride in [[hydrochloric acid]] with [[ammonia]].<ref name="j2" />

Reaction of [[aluminium bromide]] and actinium oxide yields [[Actinium(III) bromide|actinium tribromide]]:
:Ac<sub>2</sub>O<sub>3</sub> + 2 AlBr<sub>3</sub> → 2 AcBr<sub>3</sub> + Al<sub>2</sub>O<sub>3</sub>

and treating it with ammonium hydroxide at {{cvt|500|°C}} results in the oxybromide AcOBr.<ref name="j2" />

===Other compounds===
[[Actinium hydride]] was obtained by reduction of actinium trichloride with potassium at {{cvt|300|°C}}, and its structure was deduced by analogy with the corresponding LaH<sub>2</sub> hydride. The source of hydrogen in the reaction was uncertain.<ref>Meyer, p. 43</ref>

Mixing [[monosodium phosphate]] (NaH<sub>2</sub>PO<sub>4</sub>) with a solution of actinium in hydrochloric acid yields white-colored actinium phosphate hemihydrate (AcPO<sub>4</sub>·0.5H<sub>2</sub>O), and heating [[actinium oxalate]] with [[hydrogen sulfide]] vapors at {{cvt|1400|°C}} for a few minutes results in a black [[actinium sulfide]] Ac<sub>2</sub>S<sub>3</sub>. It may possibly be produced by acting with a mixture of [[hydrogen sulfide]] and [[carbon disulfide]] on [[actinium oxide]] at {{cvt|1000|°C}}.<ref name="j2">{{cite journal |doi=10.1021/ja01158a034 |last1=Fried |date=1950 |first1=Sherman |pages=771–775 |volume=72 |journal=Journal of the American Chemical Society |last2=Hagemann |first2=French |last3=Zachariasen |first3=W. H. |title=The Preparation and Identification of Some Pure Actinium Compounds |issue=2|bibcode=1950JAChS..72..771F }}</ref>