Configurations of weak interactions from vibrational perturbations in tetrahedral xy4 molecules or ions

TLDR: In this paper, an approximate method for estimating changes in stretching force constants due to weak interactions involving tetrahedral molecules or ions from the shifts in their vibration frequencies is described, which is used to discuss published vibrational data for the C3v species Na[Co(CO)4] and [(H15C7)3HN][GaCl4] in solution.

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 C3v 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 C2v and D4h respectively.