High-Temperature Phase Transitions, Spectroscopic
Properties, and Dimensionality Reduction in Rubidium Thorium Molybdate
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Abstract
Four
new rubidium thorium molybdates have been synthesized by high-temperature
solid-state reactions. The crystal structures of Rb<sub>8</sub>Th(MoO<sub>4</sub>)<sub>6</sub>, Rb<sub>2</sub>Th(MoO<sub>4</sub>)<sub>3</sub>, Rb<sub>4</sub>Th(MoO<sub>4</sub>)<sub>4</sub>, and Rb<sub>4</sub>Th<sub>5</sub>(MoO<sub>4</sub>)<sub>12</sub> were determined using
single-crystal X-ray diffraction. All these compounds construct from
MoO<sub>4</sub> tetrahedra and ThO<sub>8</sub> square antiprisms.
The studied compounds adopt the whole range of possible structure
dimensionalities from zero-dimensional (0D) to three-dimensional (3D):
finite clusters, chains, sheets, and frameworks. Rb<sub>8</sub>Th(MoO<sub>4</sub>)<sub>6</sub> crystallizes in 0D containing clusters of [Th(MoO<sub>4</sub>)<sub>6</sub>]<sup>8–</sup>. The crystal structure
of Rb<sub>2</sub>Th(MoO<sub>4</sub>)<sub>3</sub> is based upon one-dimensional
chains with configuration units of [Th(MoO<sub>4</sub>)<sub>3</sub>]<sup>2–</sup>. Two-dimensional sheets occur in compound Rb<sub>4</sub>Th(MoO<sub>4</sub>)<sub>4</sub>, and a 3D framework with channels
formed by thorium and molybdate polyhedra has been observed in Rb<sub>4</sub>Th<sub>5</sub>(MoO<sub>4</sub>)<sub>12</sub>. The Raman and
IR spectroscopic properties of these compounds are reported. Temperature-depended
phase transition effects were observed in Rb<sub>2</sub>Th(MoO<sub>4</sub>)<sub>3</sub> and Rb<sub>4</sub>Th(MoO<sub>4</sub>)<sub>4</sub> using thermogravimetry-differential scanning calorimetry analysis
and high-temperature powder diffraction methods
