Oxo-Phosphaniminato-Komplexe von Molybdän und Wolfram. Die Kristallstrukturen von [Mo(O)2(NPPh3)2] und [WO(NPPh3)3]2[W6O19]

Oxo-phosphoraneiminato Complexes of Molybdenum and Tungsten. Crystal Structures of [Mo(O)₂(NPPh₃)₂] and [WO(NPPh₃)₃]₂[W₆O₁₉] The dioxo-phosphoraneiminato complexes [Mo(O)₂(NPPh₃)₂] ( 1 ) and [W(O)₂(NPPh₃)₂] ( 2 ) originate from hydrolysis of the nitrido complexes [MN(NPPh₃)₃] (M = Mo, W). They form colourless crystals, which are characterized by IR and NMR spectroscopy as well as by mass spectrometry. According to the crystal structure analysis of 1 (space group Fdd2, Z = 8; lattice dimensions at –83 °C: a = 1953.3(1), b = 3275.8(3), c = 953.4(1) pm) there are monomeric molecules with tetrahedrally coordinated molybdenum atoms. The distances MoO of 171.2 pm and MoN of 185.9 pm correspond to double bonds. In dichloromethane solution 2 undergoes further hydrolysis with colourless crystals of [WO(NPPh₃)₃]₂[W₆O₁₉] ( 3 ) originating, which are characterized crystallographically (space group Pbcn, Z = 4; lattice dimensions at –50 °C: a = 3225.1(6), b = 1803.6(3), c = 1811.9(3) pm). 3 consists of cations [WO(NPPh₃)₃]⁺ with tetrahedrally coordinated tungsten atoms and of the known [W₆O₁₉]^2– anions. The tungsten atoms of the cations show distances WO of 171.8 pm and WN of 182 pm which correspond to double bonds as in 1 .     

Zum chemischen Transport von Wolfram mit HgBr2 – Experimente und Modellrechnungen

On the Chemical Transport of Tungsten using HgBr₂ – Experiments and Thermochemical Calculations Using HgBr₂ as transport agent tungsten migrates in a temperature gradient from the region of higher temperature to the lower temperature (e.g. 1 000 → 900°C). The transport rates were measured for various transport agent concentrations (0.64 ? C(HgBr₂) ? 11.74 mg/cm³; T? = 950°C) and for various mean transport temperatures (800 ? T? ? 1 040°C). Under these conditions tungsten crystals were observed in the sink region. To observe the influence of tungsten dioxide (contamination of the tungsten powder) on the transport behaviour of tungsten, experiments with W/WO₂ as starting materials were performed. According to model calculations the following endothermic reactions are important for the migration of tungsten: In the presence of H₂O or WO₂ other equilibria play a role, too. Using a special “transport balance” we observed a delay of deposition of tungsten (e.g. T? = 800°C; 15 h delay of deposition) with W and W/WO₂ as starting materials. The heterogeneous and homogeneous equilibria will be discussed and an explanation for the non equilibrium transport behaviour of tungsten will be given.     

Synthese und Kristallstruktur von Cs3AuO2

Synthesis and Crystal Structure of Cs₃AuO₂ Bright orange single crystals of Cs₃AuO₂, sensitive to moisture and atmosphere, are obtained by reacting CsAu with a 1 : 1 molar mixture of Cs₂O and CsO₂ (CsAu : Cs₂O : CsO₂ = 3 : 2 : 2) in sealed silver crucibles under argon atmosphere at 380 °C for a period of 6 days. The crystal structure (Pearsoncode mP72, P2₁/n, a = 1019.6(3), b = 1984.3(7), c = 1028.5(4) pm, β = 93.96(1)°, Z = 12, 2562 reflections mit I_o > 2σ(I), R₁ = 0.0662, wR₂ = 0.1660) is characterized by the presence of dumb‐bell‐shaped [O–Au–O]‐moieties (d(Au–O) = 200,8(2) pm), a common feature of oxoaurates(I).     

Ein neues Syntheseverfahren für die Wolframbronze Cs0,29WO3

A Novel Synthetic Access to the Tungsten Bronze Cs_0.29WO₃ and its Crystal Structure The hexagonal tungsten bronze Cs_0.29WO₃ was obtained in form of black, prismatic crystal by the reduction of WO₃ with molten cesium iodide at 700°C. Its crystal structure was determined by X-ray diffraction (399 unique observed reflexions, R = 0.058). Crystal data: a = 741.2(3), c = 760.0(5) pm, space group P6₃22, Z = 6. It corresponds to the known structure of hexagonal tungsten bronzes, having tungsten atoms displaced from the octahedra centres by 11.9 pm and with three different W? O bond lengths (198, 191, 187 pm). The WO₆ octahedra are slightly titled mutually.     

Synthese und Kristallstrukturen der Wolfram(VI)-Alkin-Komplexe [W2(O)(OMe)6(Et?Se?CC?Se?Et)2] und Li[W(OMe)5(Et?Te?CC?Te?Et)]

Synthesis and Crystal Structures of the Tungsten(VI)-alkyne Complexes [W₂(O)(OMe)₆(Et? Se? C?C? Se? Et)₂] and Li[W(OMe)₅(Et? Te? C?C? Te? Et)] The title compounds have been prepared by reactions of lithium methanolate with [WCl₄(Et? Se? C?C? Se? Et)(THF)] and [WCl₄(Et? Te? C?C? Te? Et)(THF)], respectively, in diethylether suspensions. Both complexes were characterized by crystal structure determinations. [W₂(O)(OMe)₆(Et? Se? C?C? Se? Et)₂]: Space group P1 , Z = 2, structure determination with 4 320 observed unique reflections, R = 0.041. Lattice dimensions at ?70°C: a = 949.3, b = 1 225.3, c = 1 285.0 pm, α = 82.48°; γ = 82.44°; β = 81.44°. The tungsten atoms are bridged by three μ₂-O-atoms of the OMe groups; the alkyne ligands are coordinated side-on in a metallacyclopropene-like fashion. Li[W(OMe)₅(Et? Te? C?C? Te? Et)]: Space group P1 , Z = 2, structure determination with 9 381 observed unique reflections, R = 0.038. Lattice dimensions at ?70°C: a = 983.4, b = 1606.9, c = 1971.5 pm, α = 66.09°, β = 84.29°, γ = 79.83°. The lithium ions link the [W(OMe)₅(Et? Te? C?C? Te? Et)]^? anions to a trimeric ion ensemble via the O atoms of three OMe groups of each anion.     

Synthese und Struktur von Cs11[(WN2,5O1,5)2](N3)2, ein Caesiumoxonitridomonowolframat(VI)-azid

Synthesis and Structure of Cs₁₁[(WN_2,5O_1,5)₂](N₃)₂, a Cesium Oxo Nitrido Monotungstate(VI) Azide Cs₁₁[(WN_2,5O_1,5)₂](N₃)₂ results from the reaction of a mixture of CsNH₂, W and WO₃ at 620 °C in autoclaves. It crystallizes monoclinic in the space group C2/m with the lattice parameters a = 12.421(4) Å, b = 11.568(6) Å, c = 10.516(4) Å, β = 118.71(3)° and Z = 4. The crystal structure is built up by isolated tetrahedra [WX₄] with X = N, O, which are connected by cesium cations. Between the cesium ions lie azide ions separated from the anions [WX₄]. The tungsten atoms and azide ions together build up the motif of a distorted arrangement of the CsCl structure type.     

Über Thiomercurate. 3. Zur Kenntnis von Ba[HgS2]

On Thiomercurates. 3. About BaHgS₂ The hitherto unknown carminred BaHgS₂ was prepared by heating binary sulfides [intimate mixtures, Ba:Hg = 1.00:1, in quartz-seales, 600–650°C, 2–3 d (powder), or 700–750°C, 8–10 d (single crystals)]. BaHgS₂ crystallizes orthorhombic with a = 4.21₅, b = 14.38₈, c = 7.33₈ Å, space group Pmc2₁. The new structure was elucidated by diffractometer data (MoKα), 1199 of 1228 independent hkl, R = 8.8, R_W = 9.2% as final result (Parameter see text). Effective Coordination Numbers, ECoN, Mean Fictive Ionic Radii, MEFIR, and the Madelung Part of Lattice Energy, MAPLE are discussed.     

Zur Darstellung und Struktur neuer Modifikationen von CeTa3O9

Preparation and Structure of New CeTa₃O₉ Modifications The modifications M? , O? and P? CeTa₃O₉ could be prepared by chemical transport reactions (T₂ → T₁; T₂ = 1100°C; T₁ = 1000°C) with chlorine as transport agent. M? CeTa₃O₉ crystallizes in the monoclinic space group C 2/m with a = 12.415(1) Å, b = 7.6317(8) Å, c = 6.5976(8) Å, β = 93.31(1)°; Z = 4; R = 4.88%, R_w = 3.67%. The structure consists of two types of Ta? O-polyhedra. Especially remarkable are chains of edge sharing pentagonal TaO₇-bipyramids which are connected by TaO₆-octahedra at opposite sides. Tunnels running along [010] are created by the framework of Ta? O-polyhedra and are filled with Ce in levels of y = 1/2 and y = 0. O? CeTa₃O₉ crystallizes orthorhombically with a = 6.5429(7) Å, b = 7.6491(7) Å, c = 12.583(1) Å and is isostructural to O? LaTa₃O₉ (space group: Pnma). O? CeTa₃O₉ contains the same characteristic structural units namely pentagonal TaO₇-bipyramides and TaO₆-octahedra. The difference between O? and M? CeTa₃O₉ is based on the orientation of the tunnels: in the orthorhombic modification they are arranged zigzag-like, in the latter parallel. Both modifications of CeTa₃O₉ can be irreversibly converted into the well-known perovskite-related P? CeTa₃O₉ structure with a lower density by heating in air to 1200°C.     

Kristallstrukturen von [TiF3(NPPh3)(HNPPh3)]2 und von HNPPh3

Crystal Structures of [TiF₃(NPPh₃)(HNPPh₃)]₂ and of HNPPh₃ The phosphoraneiminato-phosphaneimine complex [TiF₃(NPPh₃)(HNPPh₃)]₂ was obtained by the reaction of TiF₄ with Me₃SiNPPh₃ in boiling dichloromethane. It crystallizes from 1,2-dichloroethane as yellow crystals which include four molecules C₂H₄Cl₂ per dimeric formula unit. Space group P2₁/n, Z = 2, structure solution with 7270 independent reflections, R = 0.060 for reflections with I > 2σ(I). Lattice dimensions at ?50°C: a = 1417.5, b = 1896.9, c = 1586.6 pm, β = 101.22°. The compound forms centrosymmetric dimeric molecules via μ₂-F bridges with TiF distances of 194.6 and 223.3 pm, the longer one being in trans-position to the N atom of the (NPPh₃)^? ligand. Its TiN bond length of 177.7 pm corresponds with a double bond. The TiN bond length of the HNPPh₃ donor molecule of 213.4 pm is typical for a donor acceptor bond. According to the crystal structure determination the phosphaneimine HNPPh₃ forms monomeric molecules without intermolecular hydrogen bridges with a PN bond length of 152.4 pm. Space group P2₁/c, Z = 4, structure solution with 3229 independent reflections, R = 0.062 for reflections with I > 2σ(I). Lattice dimensions at ?70°C: a = 1460.4, b = 928.9, c = 1096.6 pm, β = 93.35°.     

Synthese und Kristallstruktur des tetrameren Nitridokomplexes [Cu(CH3CN)4]2[W4N4Cl14(CH3CN)2]

Synthesis and Crystal Structure of the Tetrameric Nitrido Complex [Cu(CH₃CN)₄]₂[W₄N₄Cl₁₄(CH₃CN)₂] . The title compound has been prepared by the reaction of CuCl with WNCl₃ in acetonitrile solution, forming red, moisture sensitive crystals. They were characterized by IR spectroscopy and by an X-ray structure determination. Space group I2/a, Z = 4, 2 027 observed unique reflections, R = 0.049. Lattice dimensions at -80°C: a = 2 527.0, b = 971.9, c = 2 137.5 pm, β = 106.01°. The compound consists of [Cu(CH₃CN)₄]⁺ ions, which are arranged to form strands, and of anions [W₄N₄Cl₁₄(CH₃CN)₂]^2?, in which the tungsten atoms were located at the vertices of a square and are linked with one another via linear W?N? W bridges. Two of the four tungsten atoms have four chlorine atoms as terminal ligands, the other two tungsten atoms have three chlorine atoms and an acetonitrile molecule as terminal ligands.     

Über den α-NaFeO2-Typ: Zur Kenntnis von NaCrO2 und KCrO2

on the α-NaFeO₂ type: about NaCrO₂ and KCrO₂ Single crystals of NaCrO₂ (“chromic-green”) and KCrO₂ (deep dark green), always hexagonal plates, were prepared for the first time. Homogeneous mixtures of Na₂O resp. K₂O (Na:Cr = 1.1 : 1 resp. K : Cr = 1.1 : 1) and Cr₂O₃ were heated in closed Ni-tubes at 1000°C (1100°C). Heating up and cooling down slowly. Corresponding powder samples were obtained at 500°C (700°C). Four-circle-diffractometer dates were used to derive the structure determining parameter z_o. Madelung part of lattice energy, MAPLE, was calculated.     

Syntheses of Monomeric,Dimeric, and Trimeric Complexes of Tungsten(VI), (V), (IV), and (III) with the 1,4,7-Triazacyclononane (L) Ligand. Crystal Structures of Dimeric [W2L2(μ2?OH)2Br2]Br2 · 2H2O and of Trimeric [W3L3(μ3?0)(μ2-0)3][ZnBr4]2

Reactions of WL(CO)₃ (L = 1, 4, 7-triazacyclononane; C₆H₁₅N₃) with bromine under different conditions afford the monomeric W^VI compound, WO₂LBr₂, or the monomeric W^V complex, WOLBr₃. The former dimerizes in aqueous solution, yielding the [W₂O₅L₂]²⁺ cation. Two diamagnetic isomers of the W^V -dimer, [W₂O₄L₂]²⁺, have been prepared : a yellow form with terminal oxo groups in cis-positions with respect to each other and a red species containing two terminal oxo-groups in trans-positions. The cationic W^IV -trinuclear cluster, [W₃O₄L₃]⁴⁺, has been isolated as the tetrabromozincate(2-) salt and its structure has been determined by single crystal X-ray diffraction. [W₃O₄L₃][ZnBr₄]₂ crystallizes in the monoclinic space group P2₁/c with a = 12.698(2) Å, b = 21.267(6) Å, c = 15.687(7) Å, β = 92.94(3)⁰, and V = 4222 ų, d_ealed. = 2.79 g cm^?3 for Z = 4, and mol wt 1773.2. The structure was solved by direct methods using 7399 unique reflections with I≥ 2.5 σ (I). Final residuals were R₁ = 0.089 and R₂ = 0.096. The structure consists of [W₃L₃O₄]⁴⁺ cations of the M₃X₁₃ cluster type and isolated ZnBr₄^2? anions. Three tungsten atoms occupy the corners of an equilateral triangle bridged by three μ₂-oxo- and one μ₃-oxo-ligands; each tungsten atom has a distorted octahedral environment of three oxygen and three nitrogen atoms. The short W - W distances of 2,52 Å and the diamagnetism indicate metal-metal bonding. The green, diamagnetic binuclear W_III complex, [W₂L₂(μ? OH)₂Br₂]Br₂ · 2 H₂O, has been prepared by reduction of monomeric WLOBr₃ in strongly acidic solution with zinc powder. The complex has been characterized by a single-crystal X-ray diffraction study; it crystallized in the orthorhombic space group Pnnm with a = 13.837(5) Å, b = 11.657(6) Å, c = 7.832 Å, and V = 1263 ų, d_calcd. = 2.67 g cm^?3 for Z = 2, and mol wt 1015.8. The structure was solved by direct methods using 783 unique reflections with I ? 2.5 σ(1). Final residuals were R₁ = 0.062 and R₂ = 0.084. The structure consists of dimeric cations [W₂L₂(μ? OH)₂Br₂]²⁺, bromide anions and molecules of water of crystallization. The tungsten centers are in a distorted octahedral environment of the tridentate N-donor igand, one coordinated bromide and two μ₂-hydroxo bridges (edge sharing), respectively. The bromide ligands are in trans-positions with respect to each other. The four-membered W₂(μ? OH)₂ ring is planar. The W? W distance of 2.477(3) Å together with its diamagnetism imply the presence of a strong metal-metal bond between the tungsten(II1) centers (σ²π²δ²).     

Darstellung,Kristallstruktur und elektronenmikroskopische Untersuchung von UNb6O16 – einem neuen niobreichen Oxid im System U/Nb/O

Preparation, Crystal Structure and Electron Microscopic Investigation of UNb₆O₁₆ – a New Niobium-rich Phase in the System U/Nb/O Powdery UNb₆O₁₆ was produced by heating (1 000°C or 1 100°C; evacuated silica tube) mixed powders of UO₂, NbO₂ and Nb₂O₅ (1:2:2). Single-crystals of UNb₆O₁₆ were obtained by chemical transport in a small temperature gradient (1 000°C → 990°C; transport agent NH₄Cl). The lattice constants are a = 22 339(4) Å; b = 3.7750(6) Å; c = 7.249(3) Å; β = 97.61(3)° and Z = 2. The structure determination (space group C2) let to R = 0.026 (R_w = 0.026). Eight oxygen atoms surround U⁴⁺ like a trans-bis-capped octahedron, Nb⁴⁺ and Nb⁵⁺ are coordinated distorted octahedraly. The structure was checked and the occupation of the positions O8 and O9 was clarified with the program MAPLE4 [3]. A through focus series of high resolution transmission electron microscopic images was obtained which is in acceptable agreement with images calculated on the basis of the multi-slice method.     

Synthese und Kristallstruktur von Pb2P4O12 · 3 H2O

Synthesis and Crystal Structure Determination of Pb₂P₄O₁₂ · 3 H₂O Pb₂P₄O₁₂ · 3 H₂O precipitates at mixing aqueous solutions of Pb(NO₃)₂ and Na₄P₄O₁₂ (25°C). Crystal growth was achieved by applying gel-techniques (Agar-Agar-gel). The crystal structure (P1 , a = 786.4(3), b = 914.4(3), c = 1021.6(3) pm, α = 97.42(2)°, β = 100.63(2)°, γ = 114.92(2)°; Z = 2; 4160 unique diffractometer data, R = 0.05) contains cyclo-tetraphosphate anions with point symmetry D_2d. Lead is coordinated by eight oxygen, the polyhedra deriving from a square antiprism.     

Synthese und Kristallstruktur von [WNCl3 · NC–Ph]4 · 3 CH2Cl2

Synthesis and Crystal Structure of [WNCl₃ · NCPh]₄ · 3 CH₂Cl₂ The adduct of tungsten nitride trichloride with benzonitrile, [WNCl₃ · NCPh]₄, is formed by the reaction of N,N,N'-tris(trimethylsilyl)benzamidine and tungsten hexachloride in CCl₄ solution. It forms red crystal needles and was characterized by its IR spectrum and an X-ray crystal structure determination (1983 unique observed reflexions, R = 0.075). Crystal data: a = 1464.8, b = 1902.6, c = 2033.8 pm, β = 102.27°, space group C2/c, Z = 4. In the [WNCl₃ · NCPh]₄ molecule the tungsten atoms were located at the vertices of a square and are linked with one another via linear W?N? W nitrido bridges with alternating short and long bonds having average lengths of 166 and 211 pm. The N atoms of the benzonitrile ligands are in the positions trans to the W?N bonds at distances of 237 pm.     

AsPh4[W2Cl4(N3S2)3] · CCl4; Synthese und Kristallstruktur

AsPh₄[W₂Cl₄(N₃S₂)₃] · CCl₄; Synthesis and Crystal Structure The title compound was obtained in form of black crystals along with other products by the reaction of H₂S and AsPh₄[WCl₄(N₃S₂)] in dichloromethane and subsequent addition of CCl₄. Its crystal structure was determined by X-ray diffraction (3036 observed reflexions, R = 0.051). Crystal data: triclinic, space group P¯1, Z = 2, a = 1369, b = 1398, c = 1441 pm, α = 64.8, β = 68.02 and γ = 58.1°. The compound consists of AsPh₄^⊕ ions, CCl₄ molecules and [W₂Cl₄(N₃S₂)₃]^? ions. In the latter, one tungsten atom is member of one planar WN₃S₂ ring while the second tungsten atom belongs to two such rings forming a nearly planar S₂N₃WN₃S₂ unit. Two nitrogen atoms of this unit are linked to the other tungsten atom forming a WN₂W ring. Two chloro ligands at each tungsten atom complete the coordination sphere to coordination numbers of six.     

A new route to prepare the mixed oxo-ethylidyne-capped trinuclear tungsten(IV) cluster and the crystal structure of H2Na3[W3O(CCH3)-(O2CCH3)6(H2O)3][H2W12O40]·13.5H2O

The synthesis and the structural characterization of the title compound H₂Na₃[W₃O(CCH₃)-(O₂CCH₃)₆(H₂O)₃][H₂W₁₂O₄₀]·13.5H₂O are described. It is known that the mixed oxo-ethylidynecapped tritungsten cluster can be obtained by Zn dust reduction of Na₂WO₄·2H₂O in acetic anhydride. The title compound has been characterized by X-ray diffraction, UV/VIS and ¹H NMR spectra. The tungsten atoms in the cluster cation and anion are in the oxidation states of W(IV) and W(VI) respectively. The crystal is rhombohedral with the space group R32, a = 17.058 (3)Å, c = 49.665 (9)Å, γ=120°, V=12516(9)ų, Z=6, final R = 0.037 for 2071 reflections with I ≥3σ (I). Both the cluster cation and anion have a C₃ symmetry. The important interatomic distances in angstroms for the cluster cation are: W—W, 2.730(2); W—μ₃?O, 2.00; W—O (carboxy1), 2.12; W—O_t 2.18 (2).     

Struktur des Oxooctathiotriwolframat-Ions W3OS82−

Structure of the Oxooctathiotritungstate Ion W₃OS₈^2? [(ⁿC₄H₉)₄N]₂W₃OS₈ crystallizes with Z = 6 in the monoclinic space group Pc with cell dimensions a = 24.491(5) Å, b = 14.990(5) Å, c = 19.982(5) Å, β = 92.3(2)°. The structure has been determined from single crystal X-ray data by means of Patterson and Fourier syntheses and refined to a final conventional R value of 0.148 using 4032 independent reflexions. The structure of the W₃OS₈^2? ion can be described as consisting of two distorted WS₄ tetrahedra. The third tungsten atom has a distorted quadratic-pyramidal configuration with four sulfur atoms at the base and one oxygen atom at the apex of this polyhedron. The quadratic pyramid is connected with the two tetrahedra by two common S₂ edges.     

Darstellung und Strukturen von Mg‐Komplexen mit α, ω‐Dicarboxylato‐Liganden (Dicarboxylat = Succinat,Glutarat und Suberat)

Syntheses and Structures of Magnesium Complexes with α, ω‐Dicarboxylato Ligands; Dicarboxylate = Succinate, Glutarate, and Suberate Crystals of (Tetraaqua)(succinato)magnesium ( 1 ), (Tetraaqua)(glutarato)magnesium ( 2 ) und (Triaqua)(suberato)magnesium ( 3 ) were obtained by layering an aqueous solution of the respective sodium salt with a solution of MgCl₂ in isopropanol. In 1 a chain structure is realized. Mg(H₂O)₄ units are bridged in trans orientation by α, ω‐bonded succinate groups. 2 contains also chains. Glutarato groups are bonded in a cis fashion to Mg(H₂O)₄ units. They form bridges by using their two α O atoms. 3 represents a layer structure. The basic structural motives are α, α, ω‐bonded suberate, and fac‐Mg(H₂O)₃ units. All three structures contain efficient H bridging systems. The connection between the symmetry of the polymeric groups (chains or layer) and the symmetry of the underlying space groups is discussed. 1 : Space group P2₁/c, Z = 4, lattice constants at 20 °C: a = 7.441(2), b = 14.827(2), c = 7.771(2) Å; β = 99.77(3)°, R1 = 0.052. 2 : Space group C2/c, Z = 8, lattice constants at 20 °C: a = 12.867(2), b = 7.109(1), c = 21.683(3) Å; β = 107.33(2)°; R₁ = 0.032. 3 : Space group P2₁/a, Z = 4, lattice constants at 20 °C: a = 9.174(2), b = 8.071(2), c = 15.960(3) Å; β = 104.29(2)°; R₁ = 0.052.     

Zum chemischen Transport von Verbindungen des Typs LnTa7O19 (Ln = La?Nd) mit einer Bemerkung zur Strukturverfeinerung von NdTa7O19

Chemical Transport Reactions of Compounds LnTa₇O₁₉ (Ln = La? Nd) and Structure Refinement of NdTa₇O₁₉ Crystals of compounds LnTa₇O₁₉ (Ln ? Na? Nd) could be obtained by chemical transport reactions (T₂ → T₁; T₂ = 1100°C, T₁ = 1000°C) using chlorine (p(Cl₂; 298 K) = 1 atm) as transport agent. An increase of transport rate and an improvement of crystal growth was observed if small amounts of vanadium metal were added. Solid state reactions with mixtures of Ln₂O₃/Ta₂O₅ (1:7) in air (T ≈ 1400–1500°C), however, were not succesful because the resulting samples contained LnTa₇O₁₉ with other ternary phases as by-products. NdTa₇O₁₉ crystallizes in the well-known LaTa₇O₁₉-type structure with cell dimensions of a = 6.2229(3) Å, c = 19.939(2) Å and Z = 2. The crystal structure was refined in space groups P6 c2 (R = 3.35%, R_W = 2.67%) and P6₃/mcm (R = 4.75%, R_W = 3.88%). Taking aspects of structural chemistry, x-ray results and MAPLE calculations into account, however, the spacegroup P6 c2 should be preferred.