Crystal matrix and crystal double matrix spectroscopy

Abstract

Infrared and Raman spectra of matrix isolated ions in crystalline solids display the normal modes of these units with respect to the symmetry of the respective lattice sites. Hence, they give information on all structure changes of the incorporated entities (energetic distortion), the amount of intramolecular coupling of the respective stretching modes, and symmetry and potential at the host crystal lattice sites. In the case of neat compounds, this information is hidden by collective solid-state effects. Assignment of the modes of matrix isolated guest ions can be performed by Raman single crystal experiments. If two different matrix isolated entities in a crystalline matrix come into contact forming complexes (double matrix spectroscopy) symmetry and frequencies of the modes of the guest ions are additionally changed. In the case of solid hydrates, thus the influence of metal ions and anions on the strength of hydrogen bonds (cooperative, competitive, and synergetic effects) can be analysed in detail. Examples of crystal matrix and crystal double matrix spectroscopic experiments are presented on orthorhombic halates M( XO 3) 2, monoclinic halate monohydrates M( XO 3) 2·H 2O ( M=Sr, Ba, Pb and X=Cl, Br, I), and likewise monoclinic kieserite-type compounds MXO 4·H 2O ( M=Mn, Co, Ni, Zn, and X=S, Se) with matrix-isolated XO 3 −, XO 4 2−, and M 2+ guest ions and HDO guest molecules.