Isolation of thorium benzoate polytypes with discrete ThO8 square antiprismatic units involved in chain-like assemblies

Two thorium benzoate polytypes (I- and II-Th[O2C-C6H5]4) have been identified. The I-type has been hydrothermally (H2O; 210 °C for 20 h) or solvothermally (THF; 130 °C for 36 h) synthesized as a pure phase, from the association of thorium salt (chloride or nitrate) with the monotopic ligand, benzoic acid. The second is obtained from a mixture of thorium chloride and THF in the presence of small amount of water (H2O/Th = 15) after heating at 130 °C for 36 h. For the latter batch, the resulting white powder is composed of a mixture of I and II polytypes. Single-crystal X-ray diffraction analyses revealed that the thorium benzoates consist of the similar assembly of infinite chains of square antiprismatic units (ThO8) linked to each other through four bidentate carboxylates on each square face of the ThO8 moieties. They only differ by the β angle of the monoclinic crystallographic cell, which induces shift of the chain to each other in the I and II forms. Thermogravimetric analysis of I-Th[O2C-C6H5]4 indicated a two step weight loss from 280 up to 465 °C. It is assigned to the decomposition of the organic part together with the possible formation of thorium carbonate. The final residue after 465 °C is thorianite, ThO2.