The solid state chemistry of some uranium(IV) and -(VI) complexes

The thermal decomposition of UCl42tmu in an oxygen atmosphere was studied. The decomposition of the single crystals begins at a temperature of approximately 1800C and gives the following exothermic reaction: UCl42tmu(s)+O2(g)-UO2Cl2tmu(s)+tmu(g)+volatile products ΔHr=-270 kJ mol-1. The apparent activation energy calculated for the initial stages of the reaction, which includes the nucleation process, was estimated at 362 kJ mol-1. The growth period is described by a one-dimensional diffusion law (α2 = kt) and the linear rate law (α = kt). The activation energy calculated for the decay period was approximately 203 kJ mol-1. This period is described by the contracting area model. The effect of oxygen on the decomposition reaction was also studied. Isothermal decomposition of UO2Cl22tmu in the solid state yields UO2Cl2tmu. The kinetics follow the contracting area model. The enthalpy of the reaction was estimated as ΔHr=78,7+-0,3 kJ mol-1. The dissociation reaction is accompanied by a structural rearrangement during which a bridged dimeric compound is formed. Heat capacities, Cp and Cp,m values for UO2Cl22tmu and UO2Cl2tmu and the mixtures are reported. The stepwise formation of UO2Cl22tmu in acetone was determined