Poly[tetra­amminecopper(II) bis­[tris­([mu]₂-cyanido-[kappa]²C,N)dicuprate(I)]]: a unique Cu^I-Cu^II mixed-valence complex containing anionic cuprous cyanide layers and [Cu(NH₃)₄]²⁺ cations

The title compound, {[Cu(NH₃)₄][Cu(CN)₃]₂}_n, features a Cu^I-Cu^II mixed-valence CuCN framework based on {[Cu₂(CN)₃]^-}_n anionic layers and [Cu(NH₃)₄]²⁺ cations. The asymmetric unit contains two different Cu^I ions and one Cu^II ion which lies on a centre of inversion. Each Cu^I ion is coordinated to three cyanide ligands with a distorted trigonal-planar geometry, while the Cu^II ion is ligated by four ammine ligands, with a distorted square-planar coordination geometry. The inter­linkage between Cu^I ions and cyanide bridges produces a honeycomb-like {[Cu₂(CN)₃]^-}_n anionic layer containing 18-membered planar [Cu(CN)]₆ metallocycles. A [Cu(NH₃)₄]²⁺ cation fills each metallocyclic cavity within pairs of exactly superimposed {[Cu₂(CN)₃]^-}_n anionic layers, but there are no cations between the layers of adjacent pairs, which are offset. Pairs of N-H...N hydrogen-bonding interactions link the N-H groups of the ammine ligands to the N atoms of cyanide ligands.