Page "Actinium" Paragraph 8

Only a limited number of actinium compounds are known including AcF < sub > 3 </ sub >, AcCl < sub > 3 </ sub >, AcBr < sub > 3 </ sub >, AcOF, AcOCl, AcOBr, Ac < sub > 2 </ sub > S < sub > 3 </ sub >, Ac < sub > 2 </ sub > O < sub > 3 </ sub > and AcPO < sub > 4 </ sub >.

Except for AcPO < sub > 4 </ sub >, 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.