| Abstract
| - Two new quasi-infinite heteropolychalcogenidechain compounds,α-CsCu(SxSe4-x)andCsCu(SxSe6-x),have been prepared by hydrothermal synthesis and structurally andphysically characterized. Extended Hückel calculations havebeen used to investigate the distribution of sulfur and selenium overdifferent chalcogenide sites in the structures and the shifting opticalband gaps.
- The Cs−Cu−Q (Q = S, Se) system has been investigated usingcopper metal, cesium chloride, and alkali-metalpolychalcogenide salts under mild hydrothermal reaction conditions.Heteropolychalcogenide salts and mixturesof known polysulfide and polyselenide salts have been used as reagents.The reaction products contain theα-CsCuQ4 and CsCuQ6 structures. Theα-CsCuQ4 phase exhibits a smooth transition in latticeparameters fromthe pure sulfur to the pure selenium phases, based on Vegard's law.The CsCuQ6 phase has been prepared as thepure sulfur analog and a selenium rich analog. The single-crystalstructures of the disordered compoundsα-CsCuS2Se2 (P212121,Z = 4, a = 5.439(1) Å, b =8.878(2) Å, c = 13.762(4) Å) andCsCuS1.6Se4.4 (P1̄,Z = 2, a =11.253(4) Å, b = 11.585(2) Å, c =7.211(2) Å, α = 92.93°, β = 100.94°, γ =74.51°) have been solved usinga correlated-site occupancy model. These disordered structuresdisplay a polychalcogenide geometry in whichthe sulfur atoms prefer positions that are bound to copper. Theoptical absorption spectra of these materials havebeen investigated. The optical band gap varies as a function ofthe sulfur−selenium ratio. Extended Hückelcrystal orbital calculations have been performed to investigate theelectronic structure and bonding in thesecompounds in an attempt to explain the site distribution of sulfur andselenium.
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