Multiplicity of Se–Se Bond in Selenium-Containing Lanthanide Compounds

Resumo

Using the Voronoi–Dirichlet polyhedra (VDPs), structures of 420 compounds containing 646 coordination polyhedra LnSe_n in the crystal structures have been analyzed, where Ln is any lanthanide from La to Lu. It is shown that the VDP parameters make it possible to determine the valence state of the Ln atoms. It has been determined that selenides contain Ln(II) and Ln(III) atoms which bond 4–10 selenium atoms existing in the form of Se^2– or Se^– ions. The VDPs of the Se atoms are studied; it is found that the Se–Se homoatomic bonds arise only when the electron donor metal atoms are deficient in the composition of crystalline compounds. By using VDP parameters, the dependence of the multiplicity of the Se–Se covalent bond on its length is detected, the efficiency of which is tested on a number of compounds, including Ln polyselenides. Some features of lanthanide compression in selenides are studied.