Infrared matrix isolation studies of some alkali metal oxo-anion salts

Williams, Stephen James (1982) Infrared matrix isolation studies of some alkali metal oxo-anion salts. University of Southampton, Doctoral Thesis.

Abstract

This thesis is concerned with the study of molecules present in high temperature vapours and,-in particular, their characterisation using matrix isolation infrared spectroscopy. In the introductory section a brief discussion of the physical methods which may be employed to study high temperature vapours is given. Some aspects of the matrix isolation technique are then outlined and the experimental apparatus used in this work is described. The analysis of matrix isolation infrared spectra is considered and isotopic substitution is shown to be of great assistance both qualitatively and quantitatively. Subsequent chapters describe in detail original work carried out on the molecular species present in the vapour above a series of heated alkali metal carbonates, phosphates, arsenites and antimonites. The principal conclusions are summarised as follows. When the heavier alkali metal carbonates (M = K, Rb, Cs) are heated in vacuo and the products condensed in nitrogen matrices the spectra obtained show the presence of molecular carbonates together with COZ and a number of other features. lb0 enrichment is used to show that matrix isolated K2CO3 has a structure in which one C-0' bond is weaker than the other two. Some possible modes of anion-cation coordination which would, give this result are then discussed. Matrix isolation infrared spectra of the vapour present above a range of alkali metal phosphates (M = Li - Cs) in contact with a suitable reducing agent (Ta, Mo) are assigned to the molecular phosphites, MP02. A C2V structure is proposed for matrix-isolated NaP02 on the basis of the isotopic pattern obtained for the 180 substituted molecule. These results enable the previously conflicting mass spectrometric investigations to be rationalised. Evidence is found for the existence of new high temperature arsenite and antimonite molecules. The infrared matrix isolation spectra of MAsO2 (M = Na, K, Cs) and MSb02 (M = Na, K, Cs) are all very similar, and Cgy structures are suggested for CsAsO2 and KSb02 on the basis of their isotopic substitution patterns. Both substituted molecules show severe intensity and frequency perturbations in the X-0 (X = As, Sb) stretching regions, however these results may be readily interpreted using a simple model.

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