H. Otto, M. Meibohm
1999
Citations
0
Influential Citations
17
Citations
Journal
Zeitschrift Fur Kristallographie
Abstract
For 40 years the copper polysilicate Cu[SiO 3 ], isotypic with the germanate prototype Cu[GeO 3 ], was considered non-existent. Recently however we discovered this compound as a metastable decomposition product of the silicate mineral dioptase, Cu 6 [Si 6 O 18 ]-6 H 2 O. Its orthorhombic unit-cell was refined from Guinier data giving a = 4.6357(6) A, b = 8.7735(11) A and c = 2.8334(4) A. Using powder diffraction data, the crystal structure was determined in the space group Pbmm with Z = 2 formula units, d x = 4.024 g-cm -3 . The reliability factors after least-squares refinement are R F = 0.035 and wR 2 = 0.047. The crystal structure consists of einer single chains of silicate tetrahedra running along [001]. These chains are connected by chains of edge-sharing CuO 4+2 octahedra' with two more distant oxygen neighbours, a result of the Jahn-Teller effect. The interatomic distances were found to be (2×) 1.582(7) A and (2×) 1.640(7) A for Si-O; (4×) 1.941(4) A and (2×) 2.926(7) A for Cu-O. Using this data, the cationic bond valence sums were calculated in accordance with the valencies and found to be 3.96 for Si 4+ , respectively 2.00 for Cu 2+ . The valence angles of ahout 119.5° obtained between silicon atoms and bridging oxygen atoms (ideally 109.47 for the tetrahedral O-Si-O angles and about 139 ° for the Si-O br -Si one) are evidently the topological limits for condensed silicate anions. Being a quasi-onedimensional antiferromagnetic material, the prototype Cu[GeO 3 ] belongs to a few inorganic compounds that exhibit a Spin-Peierls transition. It is expected that Cu[SiO 3 ] will also show magnetic properties of considerable interest.