Lewis bases, alkali halide salt

Matrix Isolation Studies of Alkali Halide Salt Molecules with Lewis Acids and Bases... 

The matrix isolation technique has been applied, in conjunction with the salt/molecule reaction technique, to model the high temperature gas phase reactions of alkali halide salt molecules. The reactions with Lewis acids such as SiFi, HF and CO2 yielded ion pair products which were quenched into inert matrices for spectroscopic study. Difficulties arising from lattice energy considerations in alkali halide salt reactions are minimized by the initial vaporization of the salt reactant. The reaction of such salt molecules with Lewis bases, including H2O and NH3, yielded complexes similar in nature to transition metal coordination complexes, with binding through the alkali metal cation to the base lone pair. 

Only occasionally have salt molecules been vaporized for use as a reactant toward another species in matrix isolation studies. Devlin (24,25,26) conducted extensive experiments in which salt molecules were vaporized and condensed into argon matrices containing from 1% to 90% H2O or NH3, to study the effects of stepwise solvation of the salt molecule, as a model for solution studies. Margrave (27 ) and Snelson (28) each have used salt molecules as reactants, but most commonly toward another salt molecule to form a mixed salt dimer. The work described below, which was initiated at the University of Virginia and has been continued at the University of Cincinnati, employs alkali halide salt molecules as reactants toward a variety of species, including both Lewis acids and Lewis bases. The initial intent was to react a salt molecule such as NaCl with HCl in an excess of argon to bring... 

Alkali Halide Salt Reactions with Lewis Bases... 

The application of the salt/molecule reaction technique to the study of reactions with Lewis bases such as H2O and NH3 presents the possibility for a different type of interaction which may find some cinalogy in transition metal coordination chemistry. The structure of small complexes such as MX H20 are of considerable interest both experimentally and theoretically. These studies were initiated as a result of the observation of several beinds in the spectrum of alkali halide salts in argon which could not readily be assigned to the isolated salt species. Rather, it was shown that these bands were due to reaction of the salt with impurity H2O, which was always present in these experiments to some degree. A study was then initiated to investigate these beinds, and the nature of the reaction conplex. 

Thus, in the modified Lewis (or Lux-Flood) concept, pure alkali halides represent the highest degree of basicity as the solvent composition changes from alkali halide-rich to alkali halide-deficient melts, the solvent becomes acidic. Acid-base properties of molten halides may be used to explain stabilization of unusually low (or high) oxidation states, the differences in stability of the same oxidation state in related melts, and the effects on coordination observed spectrally for certain metal ions. Or, restating the idea in other terms, the redox potentials depend on melt basicity. Thus, the systematic variation of melt composition is a useful technique in the arsenal of the molten salt electrochemist who is interested in the chemistry of solute species in molten salt solvents. In this respect, it is important to note that variation of temperature may be used to serve the same purpose for example, it has been shown that in neutral chloro-aluminates C1- decreases with temperature. 

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