The Conformations of the Hexaammineruthenium(III) Ion in Simple Salts

Abstract

Single-crystal X-ray diffraction results are presented for six hexaammineruthenium (III) salts, viz. [ Ru (NH₃)₆]₂(SO₄)₃5H₂O, [ Ru (NH₃)₆] CdCl₅, [ Ru (NH₃)₆]ZnCl₅, [ Ru (NH₃)₆]Cl₂SCN, [ Ru (NH₃)₆]₂(S₂O₆)₃.H₂O, and a salt of approximate formula [ Ru (NH₃)₆]₂ [POF₅]₃.4H₂O. The 11 independent cations in these and other published structures do not adopt a single conformation in respect of hydrogen atom disposition. Analysis of the N- Ru -N-H dihedral angles and their correlations strongly suggests that the conformation is random, given the crystallographic site symmetry. The structure with torsional energy calculated at a minimum by ab initio methods is not observed. This suggests that there are only a limited number of interionic geometries feasible in crystallization. Such a limitation suggests that computing crystal structures, with no assumptions as to space group or any other assumption, is not an open-ended problem with excessive alternatives.