A novel germanate, Cu2Fe2Ge4O13, with a four tetrahedra oligomer

The structure Of Cu2Fe2Ge4O13, previously thought to be CuFeGe2O6, has been determined from single-crystal X-ray diffraction data to be monoclinic, P2(1)/m, a = 12.1050(6), b = 8.5073(4), c = 4.8736(2) Angstrom, beta = 96.145(1)degrees, Z = 2, with R1 = 0.0231 and wR2 = 0.0605. The unique structure has an oligomer of four germanate tetrahedra, cross-linked laterally by square-planar copper ions, joined end-to-end by a zigzag chain of edge-sharing iron oxide octahedra. Running along the a-direction the metal oxide chain consists of alternating Cu-Cu and Fe-Fe dimers. A hypothetical series of homologous structures (Cun-2Fe2GenO3n+1 with n = 3, 4,..., infinity) with different length germanate oligomers is proposed, where as n increases, the infinite chain of the CuGeO3 is approached. In this context, Cu2Fe2Ge4O13 is viewed as being built from blocks of CuGeO3 and the Fe oxide chains. This material has significance to the study of low-dimensional mixed-spin systems. (C) 2003 Elsevier Inc. All rights reserved.