Chemical Compounds
Only a limited number of actinium compounds are known including AcF3, AcCl3, AcBr3, AcOF, AcOCl, AcOBr, Ac2S3, Ac2O3 and AcPO4. Except for AcPO4, they are all similar to the corresponding lanthanum compounds and contain actinium in the oxidation state +3. In particular, the lattice constants of the analogous lanthanum and actinium compounds differ by only a few percent.
| Formula | color | symmetry | space group | No | Pearson symbol | a (pm) | b (pm) | c (pm) | Z | density, g/cm3 |
|---|---|---|---|---|---|---|---|---|---|---|
| Ac | silvery | fcc | Fm3m | 225 | cF4 | 531.1 | 531.1 | 531.1 | 4 | 10.07 |
| AcH2 | cubic | Fm3m | 225 | cF12 | 567 | 567 | 567 | 4 | 8.35 | |
| Ac2O3 | white | trigonal | P3m1 | 164 | hP5 | 408 | 408 | 630 | 1 | 9.18 |
| Ac2S3 | cubic | I43d | 220 | cI28 | 778.56 | 778.56 | 778.56 | 4 | 6.71 | |
| AcF3 | white | hexagonal | P3c1 | 165 | hP24 | 741 | 741 | 755 | 6 | 7.88 |
| AcCl3 | hexagonal | P63/m | 165 | hP8 | 764 | 764 | 456 | 2 | 4.8 | |
| AcBr3 | white | hexagonal | P63/m | 165 | hP8 | 764 | 764 | 456 | 2 | 5.85 |
| AcOF | white | cubic | Fm3m | 593.1 | 8.28 | |||||
| AcOCl | tetragonal | 424 | 424 | 707 | 7.23 | |||||
| AcOBr | tetragonal | 427 | 427 | 740 | 7.89 | |||||
| AcPO4ยท0.5H2O | hexagonal | 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 units per unit cell. Density was not measured directly but calculated from the lattice parameters.
Read more about this topic: Actinium
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