Vibrations of Hydrogen Bonds in Hydrogendisulfito and Hydrogensulfito Complexes

Abstract

Compounds K 3[MX 2(SO 3) 2H/D] (M = Pd, Pt; X = Cl, Br) with very short intramolecular hydrogen bonds O⋯H/D⋯O (bond lengths R(O⋯O) < 240 pm) were studied with IR, Raman, and, partly, inelastic neutron scattering spectrometries at ambient and low temperatures. On this experimental basis, the hydrogen-bond vibrations in the unusual sequence δ(OHO) > γ(OHO) > ν as(OHO) are assigned to bands around 1500, 950, and 750 cm −1, respectively; the latter shows a complex structure (IR spectrum) and abnormal isotope shift with ν H/ν D close to 1. These vibrations are not strictly localized, but couple with modes of the SO 3 ligands. Slow rocking modes of the SO 3 ligands involving protons occur around 350 and 250 cm −1. In contrast, the vibrations of the medium-strong intermolecular hydrogen bonds in [Ru(SO 3H/D) 2(NH/D 3) 4] (R(O⋯O) 268.9 pm) behave normally with ν as(OHO) 2950, δ(OHO) 1240, and γ(OHO) 700 cm −1/100 K, all with isotope shift ratios near 1.35.