Thermochemistry of Gallium Acetylacetonate.

The standard heat of formation of crystalline gallium acetyl-ncetonate (GaAcac3), has been determined by solution calorimetry. The calorimeter was used to determine the heat of reaction (HR) between gallium tri-chloride and acetylacetone. As this could not be measured directly, perchloric acid (60.4%) was chosen as solvent for each chemical species and the above heat of reaction determined by application of Hess' Law. The standard heat of formation of GaAcac3 was then calculated from the value of HR. The experimental technique involved the measurement of smaller quantities of heat than had previously been met with this particular type of calorimeter. In order to achieve the required accuracy, an investigation of the physical behaviour of the instrumental system was made and several modifications introduced. Two calculation methods have been discussed at some length from the user's viewpoint, and one of them, 'the change in thermistor resistance (R) method has been selected. Results were determined with the aid of a computer, and the programme justified by a series of calorimeter experiments. The value of the standard heat of formation of GaAcac3 was used to estimate both the hemolytic and heterolytic gallium---oxygen bonding energies in this complex. Other subsidiary values calculated include the gas-phase enthalpy of reaction and the enthalpy of atomization. Results have been compared with those for aluminium acetylacetonate, and bond energy relationships between other physical properties suggested