Synthesis of the Single‐Crystalline Form and First‐Principles Calculations of Photomagnetic Copper(II) Octacyanidomolybdate(IV)

A gel crystallization technique was successfully applied in the pioneering preparation of a single‐crystalline form of the three‐dimensional copper(II) octacyanidomolybdate(IV) network, which is a photomagnetic material. This assembly crystallizes with the formula {[Cu II (H 2 O)] 2 [Mo IV (CN) 8 ]} · 2H 2 O in the tetragonal crystal system and reveals a three‐dimensional cyanido‐bridged framework constructed of five‐coordinate square‐pyramidal [Cu II (H 2 O)(NC) 4 ] 2– complexes and [Mo IV (CN) 8 ] 4– ions of square‐antiprismatic geometry. First‐principles calculations by the GGA + U method indicate that the visible‐light absorption band, crucial for the observation of a photomagnetic effect, is interpreted in terms of Mo IV to Cu II charge transfer, which is enabled owing to the accompanying p z  → sp x transition of the nitrogen atoms of the bridging cyanido ligands. The optical transitions in the visible range are anisotropic, and the most efficient light absorption along the [111] direction corresponds to the alignment of the cyanide bridges.