Infrared study of νOD modes in isotopically dilute (HDO molecules) Na2Me(XO4)2•2H2O with matrix-isolated X′O42- guest ions (Me = Mn, Co, Ni, Cu, Zn, Cd, and X = S, Se)

The infrared spectra of related compounds with krohnkite-type chains Na2Me(XO4)(2).2H(2)O (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 hydrogen bond acceptor strength of the SO42- and SeO42- ions, the respective (OwO)-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 nu(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 capability of the Se 4 ions than that of the 4 ions. The frequency shifts of nu(OD) corresponding to the guest ions to or lower wavenumbers as compared to the parent compounds (i.e. SO42- guest ions in Na2Me(SeO4)(2).2H(2)O and SeO42- guest ions in Na2Me(SO4)(2).2H(2)O; respectively) are due to the translatory and rotatory reorientation of the H2O molecules adjacent to the guest ions. (C) 2002 Elsevier Science B.V. All rights reserved.