Crystal-chemical manifestation of the Jahn-Teller effect in the CrXn complexes (X = F, Cl, Br, I)

Crystal chemical analysis of 70 compounds containing the CrXn, (X = F, Cl, Br, I) polyhedra is carried out with the use of Voronoi-Dirichlet polyhedra and the method of intersecting spheres. Despite a varied oxidation state (IV, III, II) of chromium atoms, 114 types of Cr atoms are six-coordinate with respect to the halogen atoms and form, as a rule, the octahedral CrX6 complexes (and only one time, the trigonal prism (CrF6)-F-II). An increase in the oxidation number of chromium atoms is accompanied by a regular decrease in the volume of their VD polyhedra (for the transformation Cr(II) --> Cr(III), by 3.0-4.1 Angstrom(3); for Cr(III) --> Cr(IV), by 0.8 Angstrom(3)). The shortest Cr-Cr distances in the structures of chromium fluoro complexes (3.30 Angstrom) noticeably exceed analogous distances in chloro (3.09 Angstrom), bromo (3.19 Angstrom), or iodo (3.19 Angstrom) complexes. Strong (specific) nonbonded Cr ... Cr interactions occur only in the structures of Cr(II) chlorides and bromides or Cr(II) and Cr(III) iodides containing CrX6 octahedra that share faces to form infinite chains CrX6/2 = [CrX3](-) or dimers 2CrX(3/2)X(3/1) = [Cr2X9](3-).