A novel 3D cyanide-bridging mixed-valence copper (I/II) coordination polymer: [CuII(CN)2(DMF)4Cu4I(CN)4]

[CuII(CN)2(DMF)4Cu4I(CN)4], a novel 3D cyanide-bridged mixedvalence CuII/CuI coordination polymer constructs from the interpenetrating double-layers containing the largest 36-membered M-CN-M rings and the strong Cu⋯Cu interactions.