Abstract
Vapour pressures over the temperature range 293-405 K, have been measured, for some metal beta-diketonates, using the Knudsen effusion technique. Heats of sublimation have been derived from the vapour pressure/temperature data, by means of the Clausius-Clapeyron relationship, for the following complexes: Be(acac)2 DeltaHsub. = 94 +/- 1kJ.mol-1 Hacac = acetylacetone. A1 (acac)3 DeltaHsub. = 120 +/- 3 kJ.mol-1. Cr(acac)3 DeltaHsub. = 123 +/- 3 kJ.mol-1. Be (tfacac)2 DeltaHsub. = 88 +/- 4 kJ.mol-1 Htfacac = trifluoro-acetylacetone. A1 (tfacac)3 DeltaHsub. = 108 +/- 2 kJ.mol-1. Be(dpm)2 DeltaHsub. = 102 +/- 3 kJ.mol-1 Hdpm=dipivaloylmethane. al(dpm)3 DeltaHsub. =119 +/- kJ.mol-1 These results have been correlated with various properties of the metal complexes, including stereochemistry, crystal packing, molecular polarity and steric effects. The design of the Knudsen effusion apparatus was decided on after a detailed analysis of theoretical and practical aspects of the technique. Heats of solution at 298.15K for Be(acac)2, Be(tfacac)2, Be(dpm)2, Al(acac)3, Al(tfacac)3, Al(dpm)3, Cr(acac)3, Fe(acac)3, Co(acac)3 in carbontetrachloride; Be(acac)2, Be(tfacac)2, Be(dpm)2, Al(tfacac)3, Al(dpm)3 in benzene and Be(acac)2, Be(tfacac)2, A1(tfacac)3 in chloroform have been measured using the LKB-8700 Solution Calorimeter. Heats of solvation were derived from heats of sublimation and solution for the following complexes: [table] Solvation energies have been interpreted in terms of interaction characteristics of both solvents and complexes. The higher solvation energies in chloroform with respect to the other solvents can be attributed to some form of hydrogen bonding.