Kinetic and thermochemical studies of rhenium-halogen compounds

• Main Author: Cartwright, S. J.
• Published: University of Leicester 1975
• Subjects: 546
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.450871

This thesis is concerned with aspects of the solution kinetics and thermochemistry of several binary and complex halides of rhenium. The standard enthalpies of formation of potassium hexachlororhenate(IV), potassium hexabromorhenate(IV), ?-rhenium tetrachloride, rhenium tetrabromide and rhenium oxide tetrachloride have been determined as -1333.1 +/- 5.5, -1036.0 +/- 10.3, -360.7 +/- 15.1, -303.0 +/- 17.2 and -600.1 +/- 16.6 kJ mol-1, respectively. Hence, the Lewis acidities, ?H2X-, of ?-rhenium tetrachloride and rhenium tetrabromide have been estimated as -7.1 and +135.4 kJ mol-1, respectively. ?H2X- is the enthalpy change for the reaction, ReX4 (c) + 2X- (g)?ReX62- (g) The solution enthalpies of the sparingly soluble caesium hexachlororhenate(IV) and caesium hexabromorhenate(IV) have been determined as +88 and +96 kJ mol-1, respectively. Hence, the single-ion hydration enthalpies of the gaseous hexachlororhenate (IV) and hexabromorhenate(IV) anions have been estimated as -846 and -784 kJ mol-1, respectively, and have been compared with estimates for other polyatomic anions. Attempts have been made to correlate the solubility of caesium exachlororhenate(IV) in mixed aqueous solvents with empirical solvent parameters and to estimate transfer parameters for the hexachlororhenate(IV) anion. Metal-ion (Hg2+, Tl3+, Cd2+ and In3+) catalysed aquations of hexachlororhenate(IV) and hexabromorhenate(IV) in acid aqueous solutions have been investigated. A rate law, rate constants and activation parameters have been determined and have been compared with data for similar systems. The possible connection between the effectiveness of the catalysts and the stability constants of their monohalo- complexes has been discussed. The reactions of rhenium pentacarbonyl iodide, bromide and chloride with cyanide ion in methanol-water mixtures all follow a two step consecutive pattern, with the formation of a common product, [Re (CO)4(CN)2]-. Rate laws, rate constants and activation parameters have been determined. The Gibbs free energy of transfer of rhenium pentacarbonyl iodide, from 50 vol.% to 70 vol.% methanol-water, has been estimated as -3.3 kj mol-1. The reactivity trend for the Re(CO)5I/CN- reaction upon change of solvent medium has been discussed in terms of transfer parameters.