Infrared study of νOD modes in isotopically dilute (HDO molecules) Na 2Me(XO 4) 2·2H 2O with matrix-isolated X′O 42− guest ions (Me=Mn, Co, Ni, Cu, Zn, Cd, and X=S, Se)

Abstract

The infrared spectra of related compounds with kröhnkite-type chains Na 2Me(XO 4) 2·2H 2O (Me=Mn, Co, Ni, Cu, Zn, Cd, and X=S, Se) containing matrix-isolated X′O 4 2− guest ions and HDO molecules are presented and discussed in the region of the OD stretching modes. The strength of the hydrogen bonds formed in the compounds under study are discussed in terms of the hydrogen bond acceptor strength of the SO 4 2− and SeO 4 2− ions, the respective O w⋯O bond lengths, the metal–water interactions (synergetic effect), the repulsion potential of the lattice (reduced unit-cell volume), the hydrogen bond acceptor capability of the oxygen atoms. The frequencies of the uncoupled ν OD stretches indicate the formation of stronger hydrogen bonds in the selenate series as compared to the respective compounds of the sulfate one due to the stronger hydrogen bond acceptor capability of the SeO 4 2− ions than that of the SO 4 2− ions. The frequency shifts of ν OD corresponding to the guest ions to higher or lower wavenumbers as compared to the parent compounds (i.e. SO 4 2− guest ions in Na 2Me(SeO 4) 2·2H 2O and SeO 4 2− guest ions in Na 2Me(SO 4) 2·2H 2O, respectively) are due to the translatory and rotatory reorientation of the H 2O molecules adjacent to the guest ions.