Cu2Sc2Ge4O13, a novel germanate isotypic with the quasi-1D compound Cu2Fe2Ge4O13 between 100 and 298 K |
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Authors: | G.J Redhammer G Roth |
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Affiliation: | a Institute of Crystallography, Technical University (RWTH)-Aachen, Jägerstrasse 17/19, Aachen D-52056, Germanyb Institute of Mineralogy, University of Salzburg, Hellbrunnerstr. 34, Salzburg A-5020, Austria |
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Abstract: | The germanate compound Cu2Sc2Ge4O13 has been synthesized by solid-state ceramic sintering techniques between 1173 and 1423 K. The structure was solved from single-crystal data by Patterson methods. The title compound is monoclinic, a=12.336(2) Å, b=8.7034(9) Å, c=4.8883(8) Å, β=95.74(2), space group P21/m, Z=4. The compound is isotypic with Cu2Fe2Ge4O13, described very recently. The structure consists of crankshaft-like chains of edge-sharing ScO6 octahedra running parallel to the crystallographic b-axis. These chains are linked laterally by [Cu2O6]8− dimers forming a sheet of metal-oxygen-polyhedra within the a-b plane. These sheets are separated along the c-axis by [Ge4O13]10− units. Cooling to 100 K does not alter the crystallographic symmetry of Cu2Sc2Ge4O13. While the b, c lattice parameter and the unit cell volume show a positive linear thermal expansion (α=6.4(2)×10−6, 5.0(2)×10−6 and 8.3(2)×10−6 K−1 respectively), the a lattice parameter exhibits a negative thermal expansion (α=−3.0(2)×10−6 K−1) for the complete T-range investigated. This negative thermal expansion of a is mainly due to the increase of the Cu-Cu interatomic distance, which is along the a-axis. Average bond lengths remain almost constant between 100 and 298 K, whereas individual ones partly show both significant shortages and lengthening. |
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Keywords: | Germanate compound Structure determination Low temperature Chain structure |
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