The preparation, structure, and magnetic properties of the first three-dimensional framework containing octahedral niobium cyanochloride clusters as building units are reported. Reactions of aqueous solutions of (Me4N)(2)K-2[Nb6Cl12(CN)(6)] (2) with aqueous solutions of MnCl2 result in the precipitation of the compound (Me4N)(2)[MnNb6Cl12(CN)(6)] (3). The structure of 3 was determined from single-crystal X-ray diffraction study (crystal data: cubic, Fm3m (No. 225), a = 15.513(4) Angstrom, V = 3733.2(12) Angstrom(3), Z = 4). Its 3D framework is based on edge-bridged [Nb6Cl12](2+) clusters and Mn2+ ions bridged by cyanide ligands to form a cfc: lattice [MnNb6Cl12(CN)(6)](2-) in which all tetrahedral sites are occupied by the cations (Me4N)(+) which act as charge compensating template. The structure of 3 can be considered as an expansion of the Prussian blue framework in which [Fe(CN)6]4- is replaced by the cluster [Nb6Cl12(CN)(6)](4-). Magnetic susceptibility measurements indicate that Mn2+ is present in a high spin d(5) configuration. No magnetic ordering is observed.