VAPOR-PRESSURES AND STANDARD MOLAR ENTHALPIES OF SUBLIMATION OF BERYLLIUM(II) AND ALUMINUM(III) BENZOYLACETONATES

The simultaneous torsion and mass-loss effusion technique was used to measure the vapour pressure of crystalline bis(benzoylacetonato)beryll ium (II) - Be(BZAC)(2) - and tris(benzoylacetonato) aluminium(III) - A I(BZAC)(3) -, as a function of temperature, from 415.7 K to 437.6 K an d from 461.9 K to 478.2 K respectively. From the temperature dependenc e of the vapour pressure, the standard molar enthalpies of sublimation , at the mean temperature of the experimental temperature ranges, were derived for both complexes. The mean values obtained from both techni ques are: Be(BZAC)(2), Delta(cr)(g)H(m)(o)(426.6 K)=151.6+/-1.8 kJ mol (-1); AI(BZAC)(3), Delta(cr)(g)H(m)(o)(470.1 K)=186.6+/-2.1 kJ mol(-1) . Using the estimated value of Delta(cr)(g)C(p)(o) -50 J K-1 mol(-1), for both beryllium(Il) and aluminium(III) complexes, the standard mola r enthalpies of sublimation at 298.15 K, were calculated as 158.0+/-1. 8 kJ mol(-1) and 195.2+/-2.1 kJ mol(-1) respectively.