Configurations of weak interactions from vibrational perturbations in tetrahedral XY4 molecules or ions

Abstract

Approximate methods are described for estimating changes in stretching force constants due to weak interactions involving tetrahedral molecules or ions from the shifts in their vibration frequencies. These methods are used to discuss published vibrational data for the C_3v species Na[Co(CO)₄] and [(H₁₅C₇)₃HN][GaCl₄] in solution, which are deduced to be apical ion-pairs from the size of the force-constant changes. Approximate formulae are also given for the stretching frequencies of trigonal-planar XY₃ and octahedral XY₆ molecules for stretching-force-constant perturbations which lower their symmetry to C_2v and D_4h respectively.