Structure and energetics of clusters relevant to thorium tetrachloride melts

We study within an ionic model the structure and energetics of neutral and charged molecular clusters which may be relevant to molten ThCl4 and to its liquid mixtures with alkali chlorides, with reference to Raman scattering experiments by Photiadis and Papatheodorou. As stressed by these authors, t he most striking facts for ThCl4 in comparison to other tetrachloride compo unds (and in particular to ZrCl4) are the appreciable ionic conductivity or the pure melt and the continuous structural changes which occur in the mel t mixtures with varying composition. After adjusting our model to data on t he isolated ThCl4 tetrahedral molecule, we evaluate (i) the Th2Cl8 dimer an d the singly charged species obtained from it by chlorine-ion transfer betw een two such neutral dimers; (ii) the ThCl6 and ThCl7 clusters both as char ged anions and as alkali-compensated species; and (iii) various oligomers c arrying positive or negative double charges. Our study shows that the chara cteristic structural properties of the ThCl4 compound and of the alkali-Th chloride systems are the consequence of the relatively high ionic character of the binding, which is already evident in the isolated ThCl4 monomer.