Raman spectra of Na3AsS4·8(D, H)2O and Na3SbS4·9(D, H)2O and O-D(H)…S bonds in salt hydrates

Abstract

Raman spectra, measured in the temperature range T =75–295 K, are reported for H₂O, D₂O and isotopically dilute samples of Na₃AsS₄·8(D, H)₂O and Na₃SbS₄·9(D, H)₂O. At T =75 K the uncoupled OD(H) stretching frequencies are observed in the range ν = 2433–2664(3279–3618) cm⁻¹ and ν = 2461–2528(3318–3417) cm⁻¹ for the thioarsenate and the thioantimonate, respectively. Plausible assignments to the distinct crystallographically non‐equivalent OD(H) groups are given.The correlation between the uncoupled OD stretching frequencies and the hydrogen bond distances R_(D…S) of approximately linear OD…S bonds in salt hydrates is discussed. The frequency shifts upon H‐bond formation are shown to depend strongly on the chemical nature of the sulphur proton acceptors.