Vibrational behavior of the S-O stretches in compounds with krohnkite-type chains Na2Me(SeO4)2.2H2O with matrix-isolated SO42- and Me'2+ guest ions (Me = Mn, Co, Ni, Cu, Zn, Cd)

The infrared spectra of related compounds with krošhnkite-type chains Na2Me(SeO4)2ž2H2O (Me=Mn, Co, Ni, Cu, Zn, Cd) containing matrix-isolated SO42- guest ions are reported and discussed with respect to the S-O stretching modes ?3 and ?1. Due to the low site symmetry C1 of the SO42- guest ions three bands for ?3 and one band for ?1 are seen in all spectra. When SO42- guest ions are incorporated in the triclinic Na2Zn(SeO4)2ž2H2O, Na2Co(SeO4)2ž2H2O and Na2Ni(SeO4)2ž2H2O host lattices the ?3 stretching region resembles a higher local symmetry (A1?E) of the SO42- guest ions than the crystallographic one (i.e. ??ab>??bc instead of ??ab˜??bc, a, b and c being three ?3 components). Hence, the ratio between ??ab and ??bc additionally to ??max (the difference between the highest and the lowest wavenumbered S-O stretching modes) has to be taken into account when the SO42- guest ion distortions are considered (the higher the ratio ??ab/??bc is, the weaker the distortion is). Both the site group splittings of the triplet component ?3 (??ac) and ??max values are an adequate measure for the SO42- guest ion distortion when the guest ions are incorporated in the monoclinic Na2Cu(SeO4)2ž2H2O, Na2Mn(SeO4)2ž2H2O and Na2Cd(SeO4)2ž2H2O (i.e. ??ab˜??bc). In addition to the local potential at the lattice site of the host lattice, the metal environment of the SO42- guest ions reflects on the guest ion distortions. A correlation between the SO42- guest ion distortions and the metal electronic configurations has been found and discussed. Me'2+ guest ions incorporated additionally to the SO42- guest ions in the selenate lattices do not influence practically on the vibrational behavior of the S-O stretches. Œ 2002 Elsevier Science B.V. All rights reserved.