Cu(Cu0.44Cr4.56)Ge2O12: a close-packed oxide with CuO4 tetrahedra

Acta Crystallogr C. 2007 Apr;63(Pt 4):i21-4. doi: 10.1107/S0108270107005355. Epub 2007 Mar 10.

Abstract

The structure of copper(I,II) pentachromium(III) germanate, Cu(Cu(0.44)Cr(4.56))Ge(2)O(12), contains one Cu position (m2m), one Ge position (m) and three Cr positions (2/m, m and 2). The close-packed structure is described in terms of slabs of edge-sharing Cr(3+)O(6) octahedra and isolated CuO(4) and GeO(4) tetrahedra. These slabs are aligned parallel to the bc plane and are separated from each other by GeO(4) tetrahedra along a. The tetrahedral coordination observed for the Cu(+)/Cu(2+) ions represents an unusual feature of the structure. The Cr-O and Cu-O bond lengths are compared with literature data.