Three types of the samarium(III) sulfide selenide Sm2S2-xSe1+x (0.1 <= x <0.2)

Single crystals of Sm2S2-xSe1+x (0-1 less than or equal to x < 0.2) have be en obtained for the first time through the oxidation of KSm2Cl5 with an exc ess of sulfur and selenium in equimolar amounts at 850<degrees>C after seve n days in evacuated silica tubes. They emerged as almost black, in thin lay ers deep red, lath-shaped needles (A and U type, respectively) as well as r ed, bead-shaped polyhedra (C type) of the gross chemical composition Sm2S2S e according to X-ray structure analyses. A much simpler method of synthesis is based on the direct fusion of the elements (samarium, sulfur and seleni um) in appropriate molar ratios (2:2:1) in the presence of NaCl as a flux u nder otherwise analogous conditions (silica tubes, 7 d, 850 degreesC). A-Sm 2S1.82Se1.18 crystallizes orthorhombically (a=753.1(3), b=401.9(1), c=1565. 8(6) pm, Z=4) in the space group Pnma with the alpha -Gd2S3-type structure. Two crystallographic ally different Sm3+ cations are coordinated by eight (Sm1) and seven (Sm2) Ch(2-) anions (S2- and Se-2-) as bi- and monocapped t rigonal prisms, respectively. C-Sm2S1.90Se1.10 adopts the cubic gamma -Ce2S 3-type structure (I (4) over bar 3d; a=858.7(2) pm, Z=5.333) with trigon-do decahedrally coordinated Sm3+ cations (CN=8). Finally, U-Sm2S1.84Se1.16 wit h the orthorhombic U2S3-type structure (Pnma; a=1105.3(6), b=399.2(1), c=10 74.0(5) pm, Z=4) exhibits two crystallographic ally different Sm3+ cations again, which are coordinated by seven (Sm1) and 2 seven phis one (Sm2) Ch(2 -) anions, respectively. The preferential occupation of S2- and Se2- anions at only one in the C-type, but three anionic sites each in the A- and U-ty pe crystal structures of Sm2S2-xSe1+x (0.1 less than or equal to x < 0.2) i s discussed.