Synthesis and Crystal Structure of Rb6Ta4S22: The First Tantalum Polysulfide Composed of the Dimeric Complex Anion [Ta4S22]6–

The reaction of Rb₂S₃, Ta and S in a 1.3 : 1 : 5.6 molar ratio at 400 °C yields red‐orange crystals of the new ternary compound Rb₆Ta₄S₂₂ being the first tantalum polysulfide containing the dimeric complex anion [Ta₄S₂₂]^6–. The polysulfide anions are composed of two Ta₂S₁₁ subunits which are linked to Ta₄S₂₂ units via terminal sulfur ligands. The Ta⁵⁺ centers are coordinated by S₂^2– and S^2– ligands according to [(Ta₂(μ₂‐η²,η¹‐S₂)₃(η²‐S₂)(S)₂)₂(μ₂‐η¹,η¹‐S₂)]^6–. Every Ta⁵⁺ ion is surrounded by seven sulfur ions forming a strongly distorted pentagonal bipyramid. In the crystal structure the discrete [Ta₄S₂₂]^6– anions are stacked parallel to the crystallographic b‐axis. The Rb⁺ cations are located between these stacks. Rb₆Ta₄S₂₂ crystallizes in the monoclinic space group P2₁/c (No. 14) with a = 11.8253(9) Å, b = 7.9665(4) Å, c = 19.174(2) Å, β = 104.215(9)°, V = 1751.0(2) ų, Z = 2.     

Darstellung,Eigenschaften, röntgenographische und spektroskopische Untersuchung von Tl4Nb2S11 und Tl4Ta2S11

On Polychalcogenides of Thallium with M₂Q₁₁ Groups as a Structural Building Block. I Preparation, Properties, X‐ray Diffractometry, and Spectroscopic Investigations of Tl₄Nb₂S₁₁ and Tl₄Ta₂S₁₁ The new ternary compounds Tl₄Nb₂S₁₁ and Tl₄Ta₂S₁₁ were prepared using Thallium polysulfide melts. Tl₄M₂S₁₁ crystallises isotypically to K₄Nb₂S_8.9Se_2.1 in the triclinic space group P 1 with a = 7.806(2) Å, b = 8.866(2) Å, c = 13.121(3) Å, α = 72.72(2)°, β = 88.80(3)°, and γ = 85.86(2)° for M = Nb and a = 7.837(1) Å, b = 8.902(1) Å, c = 13.176(1) Å, α = 72.69(1)°, β = 88.74(1)°, and γ = 85.67(1)° for M = Ta. The interatomic distances as well as angles within the [M₂S₁₁]^4– anions are similar to those of the previously reported data for analogous alkali metal polysulfides. Significant differences between Tl₄M₂S₁₁ and A₄M₂S₁₁ (A = K, Rb, Cs) are obvious for the shape of the polyhedra around the electropositive elements. The two title compounds melt congruently at 732 K (M = Nb) and 729 K (M = Ta). The optical band gaps were estimated as 1.26 eV for Tl₄Nb₂S₁₁ and as 1.80 eV for the Tantalum compound.     

Dimorphism of K4Ta2S11: Syntheses,Crystal Structures,and Properties of two Alkali Metal Tantalum Sulfides

The new ternary potassium tantalum polysulfide K₄Ta₂S₁₁ crystallizing in the triclinic space group P1 with a = 7.465(2), b = 11.441(3), c = 11.534(3) Å, α = 68.66(2), β = 86.59(2) and γ = 83.09(2)° represents a second modification of the already known orthorhombic form, space group Pca2₁ with a = 13.166(2), b = 7.449(2) and c = 18.000(2) Å. The interatomic distances and angles within the Ta₂S₁₁^4– anions of both forms are very similar, but significant differences are observed for the S…S distances between neighboured anions. Temperature dependent single crystal X‐ray experiments yield thermal expansion coefficients of 9.88(30) and 9.44(4) 10^–5 K^–1 for the triclinic and orthorhombic compound, respectively. The higher density for the orthorhombic form indicates that this modification is the thermodynamical more stable form at low temperatures. This assumption is supported by calculations of the electrostatic contributions to the lattice energies using MAPLE (Madelung part of lattice energy). The lattice energy of the orthorhombic form is about 46 kJ mol^–1 larger than that of the triclinic modification. Small differences are observed in the MIR (Medium Infrared Range) spectra of the two dimorphs which correlate well with the slightly different Ta = S bond lengths within the Ta₂S₁₁^4– anions. The compounds were also characterized using UV/Vis reflectance spectroscopy.     

Octahedral Niobium Thiocyanato Complexes Containing [Nb6Cl9O3] Cluster Core: Syntheses, Crystal Structures and Evidences of NCS Ligand Exchange

Two isomers (cis and trans) of [Nb₆Cl₉O₃(NCS)₆]^5– niobium cluster complexes characterized by an ordered arrangement of oxygen and chlorine ligands over the 12 inner positions in the cluster core were prepared by reaction of Cs₂LaNb₆Cl₁₅O₃ and ScNb₆Cl₁₃O₃ solid state compounds with aqueous solution of potassium thiocyanate. The cis and trans isomers (idealized C _{2 v} and D ₃ symmetry, respectively) crystallize with counter cations and water molecules to form the following salts: Cs_4.75K_0.25[Nb₆Cl₉O₃(NCS)₆] · 5.5H₂O (1) and Cs_2.5K_2.5[Nb₆Cl₉O₃(NCS)₆] · 2H₂O (2), respectively. The trans isomer is ordered in structure 1 (s.g.: C2/c), while in the structure of 2 (s.g.: Pnma), the cis isomer is randomly disordered over two positions that correspond one to each other by a mirror plane. Interestingly, the treatment of thiocyanato complexes cis and trans with hydrochloric acid led to substitution of (NCS)^– ligands by Cl^– and to formation of soluble complexes [Nb₆Cl₉O₃Cl₆]^5–. The cesium salt of trans-[Nb₆Cl₉O₃Cl₆]^5– was crystallized as Cs₅[Nb₆Cl₁₅O₃] · CsCl · 7H₂O (3) and structurally characterized. Indeed, the formation of soluble [Nb₆Cl₉O₃(NCS)₆]^5– intermediates is a necessary step towards the formation of soluble anions.     

Mononuclear Imido Amido Complexes via Exhaustive Ammonolysis of Niobium and Tantalum Pentachloride with tert‐Butyl Amine

Reaction of MCl₅ (M = Nb, Ta) with excess of ^tBuNH₂ in the presence of pyridine leads to formation of mononuclear complexes [M(N^tBu)(NH^tBu)Cl₂Py₂],M = Nb ( 1 ), Ta ( 2 ). These new key compounds are characterized by ¹H, ¹³C NMR spectroscopy, mass spectrometry and elemental analyses. A single crystal structure analysis of [Ta(N^tBu)(NH^tBu)Cl₂Py₂] ( 2 ) reveals, that surprisingly chloro and not pyridine ligands are trans to the strongest π donor ligands [N^tBu]^2? and [NH^tBu]^?.     

A Novel Tantalum Cluster Chalcohalide Ta4S1.5Se7.5I8

Single crystals of Ta₄S_1.5Se_7.5I₈ are obtained by heating Ta, S, Se and I₂ at 300 °C in 4.0:1.0:8.0:4.4 molar ratio. The structure was determined by X-ray analysis and consists of molecular clusters [Ta₄(μ₄-S)(μ₂-Q_axSe_eq)₄I₈] (Q ≈ Se_0.87S_0.13). The tantalum atoms form a square with long Ta…Ta distances (3.26–3.32 Å), with four dichalcogenide ligands bridging the Ta–Ta edges and a sulfur atom capping the square. Each Ta atom has two terminal iodine atoms. Raman spectroscopy study shows the presence of the characteristic absorption band at 396 cm^?1 which is due to the Ta₄–μ₄-S vibrations. Cyclic voltammetry shows that Ta₄S_1.5Se_7.5I₈ in solid state undergoes quasi-reversible one-electron oxidation which is metal-centered.     

A Novel Tantalum Cluster Chalcohalide Ta4S1.5Se7.5I8

Single crystals of Ta₄S_1.5Se_7.5I₈ are obtained by heating Ta, S, Se and I₂ at 300 °C in 4.0:1.0:8.0:4.4 molar ratio. The structure was determined by X-ray analysis and consists of molecular clusters [Ta₄(μ₄-S)(μ₂-Q_axSe_eq)₄I₈] (Q ≈ Se_0.87S_0.13). The tantalum atoms form a square with long Ta…Ta distances (3.26–3.32 Å), with four dichalcogenide ligands bridging the Ta–Ta edges and a sulfur atom capping the square. Each Ta atom has two terminal iodine atoms. Raman spectroscopy study shows the presence of the characteristic absorption band at 396 cm^?1 which is due to the Ta₄–μ₄-S vibrations. Cyclic voltammetry shows that Ta₄S_1.5Se_7.5I₈ in solid state undergoes quasi-reversible one-electron oxidation which is metal-centered.     

Coordination Chemistry of [Nb2(S2)2]4+ Clusters: Preparation and Crystal Structures of K4[Nb2(S2)2(C2O4)4] · 6 H2O and (NH4)6[Nb2(S2)2(C2O4)4](C2O4)

Bis(disulfido)bridged Nb^IV cluster oxalate complexes [Nb₂(S₂)₂(C₂O₄)₄]^4– were prepared by ligand substitution reaction from the aqua ion [Nb₂(μ‐S₂)₂(H₂O)₈]⁴⁺ and isolated as K₄[Nb₂(S₂)₂(C₂O₄)₄] · 6 H₂O ( 1 ), (NH₄)₆[Nb₂(S₂)₂(C₂O₄)₄](C₂O₄) ( 2 ) and Cs₄[Nb₂(S₂)₂(C₂O₄)₄] · 4 H₂O ( 3 ). The crystal structures of 1 and 2 were determined. The crystals of 1 belong to the space group P1, a = 720.94(7) pm, b = 983.64(10) pm, c = 1071.45(10) pm, α = 109.812(1)°, β = 91.586(2)°, γ = 105.257(2)°. The crystals of 2 are monoclinic, space group C2/c, a = 1567.9(2) pm, b = 1906.6(3) pm, c = 3000.9(4) pm, β = 95.502(2)°. The packing in 2 shows alternating layers of cluster anions and of ammonium/uncoordinated oxalates perpendicular to the [1 0 1] direction. Vibration spectra, electrochemistry and thermogravimetric properties of the complexes are also discussed.     

Re‐evaluation of the X‐ray Crystal Structure of [Ta4F20] and the Synthesis and Characterization of a Series of Mixed‐Metal Pentafluorides of Niobium and Tantalum

The direct fluorination of intimately mixed niobium and tantalum powders gives a range of mixed‐metal pentafluorides [Nb_xTa_4‐xF₂₀] (x = 1 2 , 2 3 , 3 4 ) as discreet species isostructural with tantalum pentafluoride (x = 0 1 ). The crystal structures of 1–4 are indistinguishable by X‐ray crystallography. Complex 1 crystallizes in the monoclinic space group C2/m with a = 9.5462(13), b = 14.3578(19), c = 5.0174(7) Å, β = 97.086(2)°, Z = 2. The geometry about the tantalum atom is distorted octahedral with 2 short and 2 slightly longer Ta‐F_terminal, and 2 Ta‐F_bridging distances. The angles at the bridging fluorine atoms are 172.9(5)°.     

Organometallic Niobium and Tantalum Complexes with Primary Phosphine Ligands: Syntheses and Molecular Structures of [Cp*MCl4(PH2R)] (M = Nb,Ta; Cp* = C5Me5;R = But,Ad, Cy,Ph, 2, 4, 6‐Me3C6H2 (Mes))

The reaction of [Cp*MCl₄] (M = Nb, Ta; Cp* = C₅Me₅) with PH₂R in toluene at room temperature gives the primary phosphine complexes [Cp*MCl₄(PH₂R)] [Cp* = C₅Me₅; M = Nb: R = Bu^t ( 1a ), Ad ( 2a ), Cy ( 3a ), Ph ( 4a ), 2, 4, 6‐Me₃C₆H₂ (Mes) ( 5a ); M = Ta: R = Bu^t ( 1b ), Ad ( 2b ), Cy ( 3b ), Ph ( 4b ), Mes ( 5b )] in high yield. 1—5 were characterized spectroscopically (NMR, IR, MS) and by crystal structure determinations. The starting material [Cp*TaCl₄] is monomeric in the solid state, as shown by crystal structure determination.     

Synthesis and Approximated Crystal and Electronic Structure of a Proposed New Tantalum Oxide Nitride Ta3O6N

In the quasibinary system Ta₂O₅/Ta₃N₅ we prepared a new oxide nitride phase, Ta₃O₆N, by the reaction of 1T–TaS₂ with water‐saturated ammonia gas. The determination of the unit cell metric and the crystal structure indicated that Ta₃O₆N is structurally related to the TiNb₂O₇‐type. Quantum‐chemical calculations on DFT level were used to rank the relative stabilities of possible N/O distributions and to provide a plausible structural model of the ground state with a minimum in the total energy. In agreement with Paulings 2nd rule, nitrogen ions prefer sites with high coordination numbers.     

(NH4)3[M2NCl10] (M = Nb,Ta): Synthese,Kristallstruktur und Phasenumwandlung

(NH₄)₃[M₂NCl₁₀] (M = Nb, Ta): Synthesis, Crystal Structure, and Phase Transition The nitrido complexes (NH₄)₃[Nb₂NCl₁₀], and (NH₄)₃[Ta₂NCl₁₀] are obtained in form of moisture-sensitive, tetragonal crystals by the reaction of the corresponding pentachlorides with NH₄Cl at 400 °C in sealed glass ampoules. Both compounds crystallize isotypically in two modifications, a low temperature form with the space group P4/mnc and a high temperature form with space group I4/mmm. In case of (NH₄)₃[Ta₂NCl₁₀] a continuous phase transition occurs between –70 °C and +60 °C. For the niobium compound this phase transition is not yet fully completed at 90 °C. The structure of (NH₄)₃[Nb₂NCl₁₀] was determined at several temperatures between –65 °C und +90 °C to carefully follow the continuous phase transition. For (NH₄)₃[Ta₂NCl₁₀] the structure of the low temperature form was determined at –70 °C, and of the high temperature form at +60 °C. The closely related crystal structures of the two modifications contain NH₄⁺ cations and [M₂NCl₁₀]^3– anions. The anions with the symmetry D_4h are characterized by a symmetrical nitrido bridge M=N=M with distances Nb–N = 184.5(1) pm at –65 °C or 183.8(2) pm at 90 °C, and Ta–N = 184.86(5) pm at –70 °C or 184.57(5) pm at 60 °C.     

Synthesis,Crystal Structure and Magnetism of the New Oxysulfide Ce3NbO4S3

The orange cerium‐niobium‐oxysulfide Ce₃NbO₄S₃ was synthesized by the solid state reaction of CeO₂, Ce‐metal, Nb₂O₅ and sulfur at 1100 °C. The crystal structure has orthorhombic symmetry (space group Pbam, a = 7.055(1), b = 14.571(3), c = 7.627(2) Å, Z = 4) and contains isolated [Nb₂S₄O₆]¹⁰⁻ ions consisting of two strongly distorted, edge sharing NbO₃SS_2/2 octahedra. Niobium is connected to three oxygen and three sulfur atoms. The cerium atoms are eightfold coordinated by oxygen and sulfur atoms. Certain oxygen and sulfur atoms are not connected to niobium, but exclusively surrounded by cerium. By connecting these cation polyhedra, one recognizes layers of polycations perpendicular to the c‐axis. The magnetic susceptibility shows Curie‐Weiss behavior with an effective magnetic moment μ_eff = 2.63(1) μ_B/Ce in agreement with Ce³⁺. A Weiss‐constant θ_p = –12(1) K indicates weak antiferromagnetic coupling. No magnetic ordering was detected above 2 K.     

Tantalum Clusters in Oxidic Matrices — Synthesis,Crystal Structure and Magnetic Properties of Eu1.83Ta15O32

The mixed‐valent oxotantalate Eu_1.83Ta₁₅O₃₂ was prepared from a compressed mixture of Ta₂O₅ and the metals in a sealed Ta ampoule at 1400 °C. The crystal structure was determined by means of single crystal X‐ray diffraction: space group R3¯, a = 777.2(6) pm and c = 3523.5(3) pm, Z = 3, 984 symmetrically independent reflections, 83 variables, R_F = 0.027 for I > 2σ (I). The structure is isotypic to Ba₂Nb₁₅O₃₂. The salient feature is a [Ta(+8/3)₆O₁₂ⁱO₆^a] cluster consisting of an octahedral Ta₆ core bonded to 12 edge‐bridging inner and six outer oxygen atoms. The clusters are arranged to slabs which are sandwiched by layers of [Ta(+5)₃O₁₃] triple octahedra. Additional Ta(+5) and Eu(+2) atoms provide the cohesion of these structural units. Twelve‐fold coordinated Eu(+2) atoms are situated on a triply degenerate position 33 pm displaced from the threefold axis of symmetry. A depletion of the Eu(+2) site from 6 to 5.5 atoms per unit cell reduces the number of electrons available for Ta‐Ta bonding from 15 to 14.67 electrons per cluster. Between 125 and 320 K Eu_1.83Ta₁₅O₃₂ is semi‐conducting with a band gap of 0.23 eV. The course of the magnetization is consistently described with the Brillouin function in terms of a M_mol/(N_Aμ_B) versus B/T plot in the temperature range 5 K — 320 K and at magnetic flux densities 0.1 T — 5 T. At moderate flux densities (< 1 T) the magnetic moment agrees fairly well with the expected value of 7.94 μ_B for free Eu (2+) ions with 4f⁷ configuration in ⁸S_7/2 ground state. Below 5 K, anisotropic magnetization measurements at flux densities B < 1 T point to an onset of an antiferromagnetic ordering of Eu spins within the layers and an incipient ferromagnetic ordering perpendicular to the layers.     

The Cocrystallization of the Cubic [Ta6Br12(H2O)6][CuBr2X2]·10H2O and Triclinic [Ta6Br12(H2O)6]X2·trans‐[Ta6Br12(OH)4(H2O)2]·18H2O (X = Cl,Br, NO3) Phases with the Coexistence of [Ta6Br12]2+ and [Ta6Br12]4+ in the Latter

Cubic [Ta₆Br₁₂(H₂O)₆][CuBr₂X₂]·10H₂O and triclinic [Ta₆Br₁₂(H₂O)₆]X₂·trans‐[Ta₆Br₁₂(OH)₄(H₂O)₂]·18H₂O (X = Cl, Br, NO₃) cocrystallize in aqueous solutions of [Ta₆Br₁₂]²⁺ in the presence of Cu²⁺ ions. The crystal structures of [Ta₆Br₁₂(H₂O)₆]Cl₂·trans‐[Ta₆Br₁₂(OH)₄(H₂O)₂]·18H₂O ( 1 ) and [Ta₆Br₁₂(H₂O)₆]Br₂·trans‐[Ta₆Br₁₂(OH)₄(H₂O)₂]·18H₂O ( 3 )have been solved in the triclinic space group P&1macr; (No. 2). Crystal data: 1 , a = 9.3264(2) Å, b = 9.8272(2) Å, c = 19.0158(4) Å, α = 80.931(1)?, β = 81.772(2)?, γ = 80.691(1)?; 3 , a = 9.3399(2) Å, b = 9.8796(2) Å, c = 19.0494(4) Å; α = 81.037(1)?, β = 81.808(1)?, γ = 80.736(1)?. 1 and 3 consist of two octahedral differently charged cluster entities, [Ta₆Br₁₂]²⁺ in the [Ta₆Br₁₂(H₂O)₆]²⁺ cation and [Ta₆Br₁₂]⁴⁺ in trans‐[Ta₆Br₁₂(OH)₄(H₂O)₂]. Average bond distances in the [Ta₆Br₁₂(H₂O)₆]²⁺ cations: 1 , Ta‐Ta, 2.9243 Å; Ta‐Brⁱ , 2.607 Å; Ta‐O, 2.23 Å; 3 , Ta‐Ta, 2.9162 Å; Ta‐Brⁱ , 2.603 Å; Ta‐O, 2.24 Å. Average bond distances in trans‐[Ta₆‐Br₁₂(OH)₄(H₂O)₂]: 1 , Ta‐Ta, 3.0133 Å; Ta‐Brⁱ, 2.586 Å; Ta‐O(OH), 2.14 Å; Ta‐O(H₂O), 2.258(9) Å; 3 , Ta‐Ta, 3.0113 Å; Ta‐Brⁱ, 2.580 Å; Ta‐O(OH), 2.11 Å; Ta‐O(H₂O), 2.23(1) Å. The crystal packing results in short O···O contacts along the c axes. Under the same experimental conditions, [Ta₆Cl₁₂]²⁺ oxidized to [Ta₆Cl₁₂]⁴⁺ , whereas [Nb₆X₁₂]²⁺ clusters were not affected by the Cu²⁺ ion.     

Crystal Structures of NbOI3 and NbOBr3 – Polar Double Chains in Different Non‐centrosymmetric Structures

NbOI₃ was obtained from a reaction of Nb₂O₅, Nb, and I₂. Single crystals free from disorder were a by‐product from a reaction with additional CsI. The monoclinic crystal structure (C2, a = 14.624(3) Å, b = 3.9905(8) Å, c = 12.602(3) Å, β = 120.4(3)°, Z = 4, R₁(F) = 0.0368, wR₂(F²) = 0.0804) represents a new structure type which is built up by distorted octahedral NbI₄O₂ with unequal O‐atoms in trans‐position. The octahedra are linked to dimers by a common edge of iodine atoms and to double chains by the apical oxygen atoms. A non‐centrosymmetric structure results because the short Nb–O distances point to the same direction and the polar double chains are parallel. The crystal structure of NbOBr₃ (NbOCl₃‐type, , a = 11.635(6) Å, c = 3.953(2) Å, R₁(F) = 0.082, wR₂(F²) = 0.174) shows the same polar double chains but the dimeric units Nb₂Br₆O₂ are orthogonal.     

Structures and Properties of NbOF3 and TaOF3 — with a Remark to the O/F Ordering in the SnF4 Type Structure

Powder samples of NbOF₃ und TaOF₃ were prepared by heating mixtures of NbO₂F and NbF₅ or TaO₂F and TaF₅, respectively, in the corresponding stoichiometric ratio in platinum crucibles under argon atmosphere (180—220 °C). Both oxide fluorides are coulourless with a slight greyish tinge. They are sensitive to moisture and decompose in air at room temperature within hours. Both, NbOF₃ and TaOF₃ crystallize as a variant of the SnF₄ type structure, space group I4/mmm. The structures have been refined from X‐ray powder diffraction data using the Rietveld method (a = 3.9675(1) Å, c = 8.4033(1) Å, R_B = 3.60 %, R_p = 4.58 % for NbOF₃ and a = 3.9448(1) Å, c = 8.4860(1) Å, R_B = 2.07 %, R_p = 2.44 % for TaOF₃). Characteristic building units are sheets of corner sharing MX₆ octahedra which are stacked via van der Waals interactions to a three dimensional framework. The occupancy of the two crystallographic sites for the anions by O and F is discussed on the basis of structure refinements, bond order summations, IR and NMR data and calculations of the Madelung parts of the lattice energy.     

Fluorinated Weakly Coordinating Anions [M(hfip)6]– (M = Nb,Ta): Syntheses,Structural Characterizations and ­Computations

The synthesis, spectroscopic and structural characterisation of a series of [M(hfip)₆]^– (M = Nb, Ta; hfip = O–C(H)(CF₃)₂) salts that are the typical starting materials to introduce these weakly coordinating anions by metathesis reactions into a given system is described. The salts Li[Nb(hfip)₆] and Li[Ta(hfip)₆] formed in 65 to 77 % yield from freshly sublimed MCl₅ and Li[hfip]. By contrast, several attempts to synthesize Li[Sb(hfip)₆] on the similar route (replace NbCl₅ by SbCl₅) failed to yield a pure product. Upon metathesis of the Li‐niobate with AgF in CH₂Cl₂, the pure Ag[Nb(hfip)₆] formed. Mixing Li[Nb(hfip)₆] with an equimolar amount of Cl–CPh₃ in CH₂Cl₂ gave the yellow [CPh₃][Nb(hfip)₆]. Several of the compounds were characterized by X‐ray analysis. Thus, the crystal structures of the Li⁺‐ and Ag⁺‐solvates 1, 2‐C₆H₄F₂{LiNb(hfip)₆}₂, [Li(H₂O)][Ta(hfip)₆], and [Ag(C₆H₅F)][Nb(hfip)₆] as well as that of [CPh₃][Nb(hfip)₆] were solved and are described in this work.