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 {[CuII(H2O)]2[MoIV(CN)8]}·2H2O in the tetragonal crystal system and reveals a three‐dimensional cyanido‐bridged framework constructed of five‐coordinate square‐pyramidal [CuII(H2O)(NC)4]2– complexes and [MoIV(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 MoIV to CuII charge transfer, which is enabled owing to the accompanying pz → spx 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.