The polymorphism of CsThF5

Three new polymorphs of cesium thorium pentafluoride, CsThF5, have been synthesized hydrothermally and structurally characterized. Of the structures of three polymorphs of CsThF5 one is described in space group P4/nmm with a = 5.7358(8) and c = 7.4048(15) and two in the space group P21/c: one with a = 8.3600(17), b = 7.5780(15), c = 8.9912(18), β = 116.69(3) and the other with a = 8.4196(17), b = 14.645(3), c = 8.5017(17), β = 102.67(3). Comparison of these materials was made based on their structures and synthesis conditions. The formation of these species and other previously reported metal fluoride species in hydrothermal fluids appears to be dependent upon the concentration of the alkali fluoride mineralizer, pressure, temperature, and reaction time. Differential scanning calorimetry (DSC) studies show that all of the different phases of cesium thorium fluoride transition into the same monoclinic phase of CsThF5 and eventually into the orthorhombic phase of CsTh3F13.

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► Three new polymorphs of CsThF5 have been synthesized hydrothermally.
► The formation of these species is dependent upon multiple experimental factors.
► DSC studies show monoclinic CsThF52 transforms to the monoclinic form 3 at 500 °C.
► Monoclinic form 3 transforms into the hexagonal phase of CsTh3F13 at 650 °C.