Syntheses, crystal structures, and optical properties of K3V0.32Ta0.68S4, K6Nb1.07Ta2.93S22, K6Nb2.97Ta1.03S25, K3Cu3Nb0.98Ta1.02S8, and KCu2Nb0.53Ta0.47S4

The new compounds K3V0.32Ta0.68S4 (1), K6Nb1.07Ta2.93S22 (2), K6Nb2.97Ta1.03S25 (3), K3Cu3Nb0.98Ta1.02S8 (4), and KCu2Nb0.53Ta0.47S4 (5) have been synthesized by the reactive flux method. Their crystal structures were determined by single crystal X-ray diffraction. Crystal data: 1: space group Pnma, a=9.2354(7), b=10.6920(6), c=9.2991(5) A, Z=4; 2: space group P21/c, a=7.6412(4), b=8.7572(5), c=24.5772(14) A, β=98.559(6)o, Z=2; 3: space group P21/n, a=15.7147(10), b=12.9840(9), c=18.2363(12) A, β=104.123(8)o, Z=4; 4: space group C2/c, a=23.5934(19), b=5.5661(2), c=14.2373(12) A, β=120.631(9)o, Z=4; 5: space group Ama2, a=7.4615(4), b=18.2902(16), c=5.5320(6) A, Z=4. The structure of compound 1 is based on discrete tetrahedral MS4 (M=V/Ta) anions, which are separated by K+ cations. The structure of 2 consists of K+ cations and [M 4S22]6- (M=Nb/Ta) anions, in which two M 2S11 building blocks are linked via terminal sulfur ligands. In 3 the complex anion [M 4S25]6- (M=Nb/Ta) is observed which comprises two M 2S11 subunits bridged by a S3 chain. In 4 1∞[Cu3 M 2S8]3- (M=Nb/Ta) anionic chains are found which are formed by corner sharing of CuS4 tetrahedra and edge sharing between CuS4 and MS4 tetrahedra. The structure of 5 consists of [Cu2 MS4]- (M=Nb/Ta) anionic layers separated by K+ cations. The CuS4 and MS4 tetrahedra share edges and corners yielding layers. All compounds were characterized with Raman spectroscopy and the compound 2-5 with UV/vis diffuse reflectance spectroscopy. - Graphical abstract: The five compounds K3V0.32Ta0.68S4, K6Nb1.07Ta2.93S22, K6Nb2.97Ta1.03S25, K3Cu3Nb0.98Ta1.02S8, and KCu2Nb0.53Ta0.47S4 have been prepared in polychalcogenide melts. The structures of these compounds base on discrete tetrahedra [MS4]3- (M=V/Ta), complex [M 4S22]6- and [M 4S25]6- anions comprised of two M 2S11 subunits bridged by a S2 or S3 chain, 1∞[Cu3 M 2S8]3- anionic chains, and 2∞[Cu2 MS4]- (M=Nb/Ta) anionic layers formed by corner sharing and edge sharing between CuS4 and MS4 tetrahedra