Li<sub>13</sub>Mn(SeO<sub>3</sub>)<sub>8</sub>: Lithium-Rich Transition Metal Selenite Containing Jahn–Teller Distortive Cations

A novel lithium-rich transition metal selenite, Li<sub>13</sub>Mn­(SeO<sub>3</sub>)<sub>8</sub>, that is composed of a Jahn–Teller distortive cation, Mn<sup>3+</sup>, in the high spin d<sup>4</sup> state, and a second-order Jahn–Teller (SOJT) distortive lone pair cation, Se<sup>4+</sup>, has been synthesized via hydrothermal and high temperature solid state reactions. The selenite is classified as a molecular compound consisting of MnO<sub>6</sub> octahedra, SeO<sub>3</sub> trigonal pyramids, and Li<sup>+</sup> cations. Considering the Li–O interactions, the structure of Li<sub>13</sub>Mn­(SeO<sub>3</sub>)<sub>8</sub> may be described as a pseudo-three-dimensional framework as well. The title compound is thermally stable up to 500 °C and starts decomposing above the temperature attributable to the volatilization of SeO<sub>2</sub>. While the MnO<sub>6</sub> octahedra in Li<sub>13</sub>Mn­(SeO<sub>3</sub>)<sub>8</sub> exhibit six identical Mn–O bond distances at room temperature due to the dynamic Jahn–Teller effect, a clear elongation of two Mn–O bonds along a specific direction is observed at 100 K. A series of isostructural selenites with different transition metals, i.e., Li<sub>13</sub>M­(SeO<sub>3</sub>)<sub>8</sub> (M = Sc, Cr, and Fe), have been also successfully obtained in phase pure forms using similar synthetic methods. Magnetic properties, spectroscopic characterizations, and local dipole moments calculations for all the synthesized selenites are presented.