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  • Author: Kurt O. Klepp x
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Abstract

The title compound was prepared by reacting a corresponding mixture of Na2Te2 , copper and tellurium at 700 °C. NaCu3Te2 forms crystals of metallic lustre which are rapidly decomposed in humid atmosphere. It crystallizes with a rhombohedral structure, space group R3m, with a = 4.276(3) Å, c = 23.78(1) Å, Z = 3. The crystal structure was determined from diffractometer data and refined to a conventional R of 0.050 for 135 independent reflections.

The atomic arrangement of NaCu3Te2 is based on a c.c.p. array of tellurium atoms with stacking sequence c6 . Na and Cu occupy alternatingly the interstitial layers. Na is in an octahedral coordination (d̄Na-Te : 3.22 Å), the Cu atoms occupy the tetrahedral and the octahedral voids. They are, however, shifted from the centers of these sites, resulting in an 1 + 3 coordination (d̄Cu-Te : 2.70 Å) for Cu on the tetrahedral. and an essentially trigonal coordination (dCu-Te : 2.575 Å) for Cu on the octahedral sites.

NaCu3Te2 shows no closer structural relationships to the other alkali-copper-chalcogenides known so far. However, its crystal structure may be interpreted as an ordered defect derivative structure of the CaCu4P2 -type [1].

Transparent single crystals of Na4Ga2S5 were obtained from a melt of Na2S, Ga and S. Na4Ga2S5 is monoclinic, space group P21/c with a = 7.967(1), b = 6.133(2), c = 19.852(9) Å, β = 91.61(2)°, Ζ = 4. Its crystal structure was refined to a conventional R of 0.033 for 1150 observed reflections.

The structure of Na4Ga2S5 is of a new type. It is characterized by infinite ribbon like thiogallate anions, -, which are built up by GaS4-tetrahedra (mean Ga-S bond length 2.28 A) sharing apices and edges. The four crystallographically independent alkali cations are coordinated to six sulphur atoms in distorted octahedral configurations.

K2Sn2S5 and K2Sn2Se5 were prepared by reacting stoichiometric powdered mixtures of the binary compounds K2S or K2Se with Sn and the corresponding chalcogen at 1070 K, followed by slow cooling of the melt. The two compounds are isostructural and crystallize with the Tl2Sn2S5 structure type, s.g. C 2/c, Z = 4 with a = 11.072(5) Å, b = 7.806(3)Å, c = 11.517(5)Å, β = 108.43(2)° for K2Sn2S5 and a = 11.613(5)Å, b = 8.189(3) Å, c = 11,897(6) Å, β = 108.28(2)° for K2Sn2Se5. The crystal structures were refined to conventional R-factors of 0.032 and 0.031, respectively. Sn-atoms are in a distorted trigonal-bipyramidal chalcogen coordination. The average equatorial bond lengths are Sn -S: 2.427 Å and Sn -Se: 2.552 Å , the axial ones are Sn -S: 2.600 Å and Sn -Se: 2.774 Å.

Abstract

Transparent yellow single crystals of Na4SnSe4 and K4SnSe4 were prepared by reacting stoichiometric powdered mixtures of the binary compounds Na2Se or K2Se, Sn and Se at 850 K. Na4SnSe4 is tetragonal, s.g. P4̄21c, with a = 8.165(2) Å, c = 7.268(2) Å, Z = 2. K4SnSe4 is orthorhombic, s.g. Pnma, with a = 14.714(7) Å, b = 10.323(3) Å, c = 8.248(6) Å, Z = 4. The crystal structures were refined to conventional residuals of 0.058 and 0.031, respectively. Both com pounds are characterized as salts with discrete tetrahedral selenostannate anions. Na4SnSe4 is isostructural with Na4SnS4, K4SnSe4 is of a new type. The observed Sn -Se bond lengths range from 2.494 Å to 2.536 Å.

Fibrous red crystals of the new compound K2TiS3 were obtained by reacting K2S, Ti and S at 1070 K. K2TiS3 is monoclinic, space group C 2/c with a = 11.667(6) Å, b = 8.325(4) Å, c = 6.494(4) Å, β = 9 i.81(4)°, Z = 4. The crystal structure was refined to a conventional residual of 0.070. The atomic arrangement is characterized by pseudo-one-dimensional - -[TiS3]2− chains formed by distorted TiS5 square pyramids sharing opposite edges of their basal planes. The structure - though closely related to that of Cs2TiS3 - is of a new type.

Abstract

Tl2TiS4 is orthorhombic, space group Pbca, with a = 22.176(7), b = 9.484(4), c = 6.3977(9) Å, Z = 8. The crystal structure was solved by direct methods and refined to a conventional R of0.058 for 704 reflections with I ≥3σ(I). The crystal structure is characterized by infinite perthioanions, 1-[TiS 4/2 (S2)2- ], which are separated by Tl+ -cations. The anion chains are built up by distorted octahedra which share two skew edges to form infinite cis-chains running along [001], The two unshared S-atoms of each octahedron are connected via a S -S-single bond of 2.10 Å length. The crystal structure is described as a mixed packing of TI-and S-atoms, composed of puckered TlS2 -layers, in which the Ti-atoms occupy the octahedral interstices. The relationship of the 1-[TiS4 2- -]-chains to the anionic groups of Cs2TiS3 is discussed.

Abstract

Na4GeSe4 was obtained from a stoichiometric melt of Na2Se, Ge and Se at 750 °C. It crystallizes with a new orthorhombic structure, space group Pnma, with a = 28.518(8), b - 9.447(5), c = 7.128(2) Å , Z = 8. The crystal structure was refined to a conventional R of 0.074 for 1236 reflections with I > 3 σ (I) (diffractometer data). It is characterized by discrete GeSe4 4--anions with almost regular tetrahedral geometry. Two independent anions appear in the structure, the mean Ge - Se-bond lengths are 2.345 and 2.353 Å, resp. The Na+-ions are coordinated to 4 -6 chalcogen atoms in the range 2.88-3.28 Å. The structure is composed of mixed cation-anion-slabs, 2 [Na2(GeSe4)2-], which run parallel to the bc-plane and are separated from each other by corrugated 36-layers of Na+-ions.

Abstract The new compound Tl3AgTe2 was prepared by the reaction of Tl5Te3, Ag and Te at 550 °C, followed by slow cooling of the melt. It forms black crystals of metallic lustre which decompose by the influence of humidity. Tl3AgTe2 is monoclinic, space group P21/c, with a = 11.020(5), b = 7.427(2), c = 9.888(3) Å , β = 116.62(4)°, Z = 4. The crystal structure was determined from four-circle diffractometer data and refined to a conventional R of 0.083 for 1015 observed reflections.

Tl3AgTe2 crystallizes with a new structure type, characterized by infinite layers, 2 [AgTe2], running along (100), which are separated from each other by thallium atoms. The layers are built up by pairs of edge sharing AgTe4-tetrahedra linked together by common Te atoms according to 2 [Ag (Te)Te3/3].

The crystal structure is based on an arrangement of distorted c.p. tellurium layers, stacked along [010] (stacking sequence h2). All octahedral voids are occupied by Tl-atoms, Ag-and Tl-atoms are regularly distributed over the tetrahedral sites.

The isostructural compounds K2ZrTe3 and Rb2ZrTe3 were obtained at 1000°C by reacting K2Te and Rb2Te with stoichiometric amounts of Zr and Te. The compounds are monoclinic, mP24, space group P21/c, Z = 4 with a = 9.089(3), b = 14.148(4), c = 6.986(3) Å, β = 105.90( 1)° and a = 9.735(4), b = 14.300(7), c = 6.952(8) Å, β = 108.61(2)°, respectively. The crystal structure was determined from diffractometer data and refined to R = 0.030 for 1452 Fo's for K2ZrTe3 and R = 0.038 for 1131 Fo's for Rb2ZrTe3. The crystal structure is of a new type, characterized by infinite anionic chains, 1 -[ZrTe3]2- built up by octahedra sharing opposite faces which run along [001]. The mean Zr-Te bond lengths are 2.921 and 2.920 Å, respectively. The alkali cations separating the chains are characterized by two different - distorted octahedral and pentagonal bipyramidal - chalcogen environments.

Abstract

The isostructural compounds Tl4TiS4, Tl4SnS4 and Tl4TiSe4 crystallize in the monoclinic system, space group P21/c with a = 8.328, b = 8.191, c = 15.248 Å, β = 104.53°; a = 8.395, b = 8.280, c = 15.398 A, ft = 103.69°, and a = 8.517, b = 8.389, c = 15.672 Å, β = 103.50°, respectively. There are four formula units in the unit cell. The crystal structures were determined and refined from single crystal diffractometer data. They are characterized by isolated tetrahedral thioanions which are connected with each other by Tl+ ions. The mean bond lengths are Ti-S = 2.26 Å, Sn-S = 2.40 Å and Ti -Se = 2.38 Å. The Tl atoms are surrounded by six and seven chalcogen atoms, respectively, in an irregular and polar arrangement, thus indicating stereochemical activity of the lone electron pair of the Tl+ ions. Tl-S distances vary from 2.93 to 3.98 Å, Tl-Se distances from 3.03 to 3.96 Å. The Tl atoms have nearest Tl neighbours at distances ranging from 3.46 to 3.65 Å. The crystal structure can be described as built from pseudotetragonal slabs oriented parallel to (001) which contain the cations and the tetrahedral anions. It is shown that a similar description is valid also for the crystal structures of Tl4GeS4 [1] and Na4SnS4 [2, 3].