We
successfully synthesized a novel fluorinated polyoxomolybdate, K<sub>5</sub>Mo<sub>4</sub>O<sub>14</sub>F, in which the unusual polyanion
[Mo<sub>4</sub>O<sub>14</sub>F]<sup>5–</sup> consists of face-sharing
[Mo<sub>2</sub>O<sub>8</sub>F] bioctahedra linked with [MoO<sub>4</sub>] tetrahedra. This unique structural feature provides the very rare
case that simultaneously violates Pauling’s electrostatic valence
(II) and atomic coordination (IV) rules, as well as the stable tendency
governed by the polyhedral sharing (III) rule. The structural stability
of K<sub>5</sub>Mo<sub>4</sub>O<sub>14</sub>F was confirmed from thermal
experiments over a wide temperature range and further elucidated by
first-principles calculations
