The use of 18O enrichment to determine the mode of co-ordination in MXO3 species via infrared frequency and intensity patterns: the shape of matrix-isolated KNO3

Abstract

This paper describes a new experimental approach to the problem of determining the mode of co-ordination of [XO₃]^n– ions (e.g.[NO₃]^–, [CO₃]^2–). Using the nitrate ion as an example, it is shown, via line diagrams, that a qualitative distinction between monodentate and bidentate binding should be possible simply by noting the number and relative intensities of isotope bands associated with the highest frequency N–O stretching mode in the i.r. spectrum of the ¹⁸O-enriched material. The method is illustrated by reference to the matrix i.r. spectrum of molecular KNO₃, where the initial qualitative conclusion of bidentate co-ordination is confirmed by subsequent force-constant analysis.