The reactions of potassium polysulfides with elemental Nb were investigated with different analytical techniques. The amount of the polysulfide applied has no influence onto product formation, i. e. the ratio K2Sx: Nb is not important. The length of the polsysulfide chain, i. e. the value of x in K2Sx determines what product is formed. In sulfur-poor melts, K3NbS4 is observed. Increasing x to 5 - 6, K4Nb2S11 is formed with a structure containing S22− anions. Finally, applying a melt with x > 6, K6Nb4S25 is found as the product with a crystal structure containing the S52− polysulfide anion. When K2Sx (x < 5) is heated with sulfur in the first step the pentasulfide K2S5 is formed. Immediately after melting of K2S5 a reaction with elemental Nb occurs. The results of FT-IR and X-ray investigations have demonstrated that after oxidation the anion [Nb2S11]4− is formed relatively fast, and after a short time crystalline K4Nb2S11 can be detected. After 24 h the reaction is complete.

Reaction of the ternary transition metal chalcogenide K4Nb2S11 with K2Se5 leads to the formation of the new mixed sulfur selenium compound K4Nb2S8.9Se2.1. Single crystal structure determination proves that the connectivity within the molecular [Nb2S11]4− anion remains intact but distinct sulfur positions are partially substituted by selenium. All S22− anions are selectively exchanged by selenium whereas the S2− anions are not affected. The refinement of the site occupation factors demonstrates that the two sulfur atoms in the S22− anions were non-statistically substituted by the selenium atoms. Furthermore, the partial substitution of S by Se leads to a new structural type for compounds with general formula A4M2Q11 (A=alkali metals, M=Nb, Ta, Q=S, Se). The direct synthesis using a S/Se mixture yields a second compound with composition K4Nb2S9.5Se1.5 showing an exchange pattern within the S22− anions being slightly different from that found in K4Nb2S8.9Se2.1.

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The new compounds K4Nb2S10O and Rb4Nb2S10O have been synthesized by the reaction of potassium or rubidium alkaline polychalcogenides with NbO2, Nb2O5, or mixtures of Nb and NbO. Their structures consist of discrete [Nb(2)Q(11)](4-) anions (Q = O, S) built up of two face-sharing pentagonal bipyramids, which are connected via the alkali metal cations.

The new compounds K4Nb2Se11O and Cs4Nb2Se11O have been synthesized from a K2Sen and Cs2Sen flux, respectively. K4Nb2Se11O crsytallizes in the orthorhombic space group Pbca with lattice parameters a = 15.946(4) Angstrom, b = 13.872(3) Angstrom, c = 18.622(3) Angstrom, V= 4119(2) Angstrom(3), Z = 8. The structure has been refined to a wR(2)(F-2) of 0.1547 for 163 parameters and 4714 reflections. The R-1(F) amounts to 0.0410. Cs4Nb2Se11O crsytallizes in the triclinic space group P-1 with unit cell dimensions a = 12.023(4) Angstrom, b = 14.367(4) Angstrom, c = 14.571(4) Angstrom, alpha = 76.90(2)degrees, beta = 78.43(2)degrees, gamma = 71.89(2)degrees, V = 2307(1) Angstrom(3), ((Z) over bar= 4). Refinement against F resulted in a wR(2) of 0.1075 for 326 parameters and 10542 unique reflections. The R1(F) amounts to 0.0411. The structures of both compounds consist of expanded and interconnected Nb(2)Q(11) units (Q = Se, O) which are built up of two face-sharing pentagonal NbSe6O and NbSe7 bipyramids. In K4Nb2Se11O the Nb2Q11 units are interconnected by Se-3(2-) anions giving rise to infinite anionic (1)(infinity)[Nb2Se11O](4-) chains which are separated by the K+ cations. Cs4Nb2Se11O resembles a mixture of molecular [Nb2Se11O](4-) anions and,(1)(infinity)[Nb2Se11O](4-) infinite anionic chains coexisting in one structure. Both compounds exhibit Se-n(n-) anions with unusual bonding properties. In K4Nb2Se11O, a nearly linear Se-3(4-) anion is found, whereas Cs4Nb2Se11O contains a See fragment which carries six negative charges.

The reaction of K2S5, Cu, Gd, and S in a 2:1:2:4 molar ratio at 450 degrees C yields yellow-orange needle-like cuboids of the new quaternary compound KCuGd2S4. The crystal structure represents a novel three-dimensional structure type of quaternary rare earth chalcogenides with alkali metal. The compound crystallizes in the orthorhombic space group Cmcm (No. 63) with a = 3.9921(1) Angstrom, b = 13.523(3) Angstrom, c=13.802(3) Angstrom, V=745.1(3) Angstrom(3), Z=4. In the structure GdS6 octahedra and CuS4 tetrahedra are joined by common edges and corners forming corrugated layers parallel to (010). The GdS6 octahedra are connected via common edges in the third dimension thus leading to the formation of a three-dimensional tunnel structure. The potassium cations are confined within the pentagonal shaped channels and are surrounded by eight sulfide anions each.

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Needle-shaped, moisture sensitive, yellow crystals of Na3TaS4 were obtained by the reaction of Na2S3, Ta, and 8 at 450 degrees C. The structure was determined by single crystal X-ray diffraction and refined to R1 and wR2 values of 0.0172 and 0.0381, respectively. Na3TaS4 crystallizes with 32 formula units in the orthorhombic space group Fdd2 (No.: 43) with a = 27.113(4), b = 28.326(6) and c = 7.918(1) Angstrom. The structure consists of discrete tetrahedral TaS43- ions and Na+ ions.

The new tetra(alkali metal) ditantalum undecasulfides A(4)Ta(2)S(11) (A = Rb, Cs) were prepared at low temperature via the molten-flux method. The crystal structures consist of well separated A(+) and [Ta2S11](4-) ions. Within the anions, the Ta atoms display a sevenfold coordination by S-2(2-) units and S2- anions; the coordination polyhedra can be described as distorted pentagonal bipyramids. Two such bipyramids share common faces, thus forming the [Ta2S11](4-) anion.

The new quaternary compounds CsAgVS4, K2AgVSe4, Rb2AgVSe4, Rb2AgNbS4, and Cs2AgNbSe4 were prepared using the reactive flux method. In this structure type infinite chains of edge-sharing AgQ(4)- and M(V)Q(4)-tetrahedra are running parallel to the crystallographic a-axis. The chains are separated by alkali cations. A linear relationship between the size of the alkali cation A(+) and the Q-Q interchain distances was found. These compounds are isostructural with the analogous quaternary copper chalcogenides. The optical properties were studied by collecting UV/Vis transmission and reflectance spectra which allowed to derive the optical band gaps. The colours of the vanadium compounds range from black to dark violet with optical band gaps between 1.7 and 1.8 eV. In addition, the behaviour of the samples was studied using polarized light. Under these experimental conditions the niobium compound Rb2AgNbS4 changes its colour from green to red when the direction of the polarization plane is changed by 90 degrees.

The new ternary compound K6Nb4S25 was prepared in molten potassium polysulfide at 350 degrees C. It contains the complex anion [Nb4S25](6-) which is comprised of two Nb2S10-subunits bridged by a S-5(2-) chain. The Nb-centers are coordinated by S in a distorted pentagonal bipyramidal geometry. The S2-, S-2(2-) and S-5(2-)-anions are bound to the Nb-centers so that the polysulfide-anion may be described as [(Nb-2(eta(2),mu-eta(1)-S-2)(eta(2)-S-2)(3) (S)(2))(2)(mu-eta(1)-S-5)](6-). Because the intramolecular S...S contacts are just long enough to accomodate one of the six K+-cations, the [Nb4S25](6-) anion acts like a polydentate ligand.

The new ternary niobium polysulfide K4Nb2S14 was prepared at low temperatures via the reactive flux method. It crystallizes in the monoclinic space group P21/c with unit cell dimensions of a=21.656(2), b=7.8541(9), c=12.455(1) Å, β=99.22(1)° and Z=4. The crystal structure consists of well-separated K+ and [Nb2S14]4− ions. The Nb centers are coordinated by S22− units, S2− and S42− anions. The title compound is the first transition metal polysulfide in which an S42− anion acts as a monodentate ligand. According to the different bridging modes of the ligands [Nb2S14]4− may be described as [Nb2(μ-η2,η1-S2)(η2-S2)3(S)2(η1-S4)]4−. The Nb centers are in a six-fold coordination and the polyhedra may be described as distorted pentagonal pyramids. The Nb–S interatomic distances vary from 2.189 to 2.949 Å. Bond-valence calculations show that the bond valences for these distances range from 0.1 to 1.5. Within the unit cell the anions are stacked parallel to the crystallographic b-axis, and the K+ ions are located between the anions. UV–Vis experiments yield an optical gap of Eg=2.11 eV.

The new ternary gadolinium telluride, CsGdTe4, was prepared via the molten flux method. It is a layer compound containing Te22− tellurium dianions. Layers of Gd centres are sandwiched by Te layers leading to [GdTe4]nn− layers which are separated by Cs cations. Within a [GdTe4]nn− layer, the Gd cations are in a square-antiprismatic coordination of eight Te anions.

The new quaternary one-dimensional chain compounds Rb2CuVS4, K2CuVSe4, Rb2CuNbSe4, Cs2CuNbSe4 and Rb2CuNbS4 were prepared at 350 degrees C. They are isostructural crystallizing in the orthorhombic space group Fddd with Z = 8. The structure consists of infinite linear chains of alternating edge-sharing CuQ(4)- and M(V)Q(4)-tetrahedra (Q = S or Se) running parallel to the [100] direction separated by the alkali metal cations. The alkali cations are in an eightfold coordination of Q(2-) ions. A linear relationship between the size of the alkali cation and the chalcogen interchain distance is observed. The optical properties were studied by measuring the UV/Vis transmission (A(2)CuNbQ(4)) or reflectance (A(2)CuVQ(4)) spectra. The derived optical band gaps ranging between 1.85 (Rb2CuVS4) to 2.82 eV (K2CuNbS4) do not depend on the type of alkali cation. In contrast, substitution of selenium by sulfur shifted the gap to significantly larger values.

Source of material: During our investigations in the system A/NB/Sb/S the compound s-K3SbS4 was obtained under the following conditions. K2S3, Nb, Sb and S, in a 4/1/2/8 ratio, were thoroughly mixed in a dry box. K2S3 was prepared by the reaction of stoichiometric amounts of Κ and S in liquid ammonia under an argon atmosphere. The mixture was then loaded into apyrexglass ampoule which was subsequently evacuated (4x10 mbar) and sealed. The ampoule was heated to 623 Κ for 6 days and afterwards was cooled to roomtemperature with 3K/h. The resulting black-red melt was washed with DMF and dried in vacuum. The product consisted of two components, red crystals of K6Nb4S25 and white transparent crystals of s-K3SbS4-s-K3SbS4 is hygroscopic and must be stored under dry conditions. For X-ray crystal structure determination, a suitable crystal was mounted on a glass fiber and completely covered with glue. Despite these measure the crystal slightly decomposed during

The quaternary sulfides K2AgVS4 and Rb2AgVS4 crystallize as dark violet needle-like crystals with a metallic lustre. Infinite Ag- and V-centered tetrahedra sharing common edges are running parallel to the crystallographic a axis. The chains are separated by K+ or Rb+ ions which are in an eightfold environment. The tetrahedra are occupied in an ordered fashion. The Ag-V interatomic distances amount to 2.904(1) and 2.910(1) Angstrom, respectively, which is significantly larger than the sum of the ionic radii of Ag+ and V5+. Whereas the V-S distances are in the normal range, the average (Ag-S) distances are the shortest reported so far indicating strong covalent bonding between monovalent Ag+ and S2-. In addition, the title compounds represent very rare examples of AgS4 polyhedra with equidistant Ag-S bonds. The geometrical parameters within the tetrahedra chains are only slightly affected when K+ is replaced by the larger Rb+ demonstrating the rigidity of the bonding properties within the tetrahedra. The compounds are isotypic with the quaternary copper sulfide K2CuVS4 and the selenides K(2)CuMSe(4)(M=Nb, Ta).

The ternary potassium vanadium sulfide K3VS4 and the new quaternary compound K2CuVS4 were prepared at low temperatures via the molten flux method. K2CuVS4 is isostructural with the analoguous niobium and tantalum selenides. Infinite chains of edge-sharing copper and vanadium-centered tetrahedra are running parallel to the [100] direction. The chains are separated by K+ ions. The Cu and V atoms occupy the tetrahedra in an ordered fashion. The Cu-V interatomic separation of 2.719 Angstrom is indicative of no significant metal to metal bonding interaction, Originally K3VS4 was synthesized at 800 degrees C. This compound can also be prepared at temperatures as low as 270 degrees C via the reactive flux method.

The new ternary niobium polysulfide K4Nb2S11 was prepared at low temperatures via the molten flux method. The compound crystallizes in the non-centrosymmetric space group Pca2(1). The direction of the polar axis was determined. The crystal structure consists of well-separated K+ and Nb2S114- ions. Within the anions the Nb atoms are coordinated by S-2(2-) units and S2- anions. According to the different bridging modes of the ligands Nb2S114- may be described as Nb-2(mu-S)(mu-eta(2),eta(1)-S-2)(2)(eta(2)-S-2)(2)(S)(2)(4-). Every Nb is in a sevenfold coordination and the polyhedra can be described as strongly distorted pentagonal bipyramids. The Nb-S interatomic bonding distances vary from 2.183 Angstrom to 2.859 Angstrom. Within the unit cell the anions are stacked parallel to the crystallographic b-axis. These stacks are arranged in "lapers" and the K+ ions are located between the layers.