Li2PtH2, Darstellung und Struktur

Li₂PtH₂, Synthesis and Structure The synthesis of Li₂PtH₂ succeeded in decomposing Li₅Pt₂H₉ at 220°C in an argon atmosphere. X-ray investigations on a powdered sample and elastic neutron diffraction experiments on the deuterated compound led to the complete structure. Li₂PtH₂ crystallizes in the space group Immm with Z = 2. The structure is characterized by [PtH₂]^2? -dumb-bells which are hitherto unknown in platinum compounds. The arrangement of the [PtH₂]^2? -anions and of the lithium cations shows a close relationship to the hydride Li₂PdH₂ which crystallizes tetragonal I-centred.     

Water-rich molybdotellurates: Preparation and crystal structure of Li6[TeMo6O24] · 18 H2O and Li6[TeMo6O24] · Te(OH)6 · 18 H2O

Li₆[TeMo₆O₂₄] · 18 H₂O is triclinic (space group P1 , a = 1 041.7(1), b = 1 058.6(1), c = 1 070.8(1) pm, α = 61.08(1), β = 60.44(1), γ = 73.95(1)°). Single crystal X-ray structure analysis (Z = 1, 295 K, 317 parameters, 3 973 reflections, R_g = 0.0250) revealed an infinite branched chain of edge-sharing Li coordination polyhedra to be the prominent structural feature. One of the four crystallographically independent Li⁺ is coordinated octahedrally. The coordination polyhedra of the remaining Li⁺ are distorted trigonal bipyramids. Only three unique oxygen atoms (O(9), O(10), O(12)) of the centrosymmetric [TeMo₆O₂₄]^6? anion are bound to Li⁺. The further positions in the coordination spheres of the Li⁺ are occupied by water molecules. Intermolecular hydrogen bonds involve mainly oxygen atoms of the [TeMo₆O₂₄]^6? anion as nearly equivalent proton acceptors without regard to their different bonding modes to Te and Mo, respectively. Li₆[TeMo₆O₂₄] · Te(OH)₆ · 18 H₂O crystallizes monoclinically in space group P2₁/n with Z = 4, a = 994.1(3), b = 2 344.8(10), c = 1 764.9(4) pm, and β = 91.36(4)°. Single crystal structure analysis with least squares refinement of 627 parameters (5 900 reflections, 295 K) converged to R_g = 0.0324. There are six unique Li⁺ cations. The coordination polyhedra of Li(1), Li(2), Li(3), and Li(4) are linked by common edges to yield an eight membered centrosymmetric strand. The coordination polyhedra of the remaining two Li⁺ sites (Li(5), Li(6)) are connected to a dimeric unit via a common corner. All oxygen atoms of the Te(OH)₆ molecule are involved in the coordination of Li⁺. However, only three oxygen atoms (O(13), O(18), O(23)) of the [TeMo₆O₂₄]^6? anion which lacks crystallographic symmetry are involved in the coordination of Li⁺. The oxygen atoms of the anion act as proton acceptors in hydrogen bonds of predominantly medium strength. Te(OH)₆ molecules and [TeMo₆O₂₄]^6? anions connected by strong hydrogen bonds form an infinite chain.     

Li6+2x[B10Se18]Sex (x ≈ 2), ein ionenleitendes Doppelsalz

Li_6+2x[B₁₀Se₁₈]Se_x (x ≈ 2), an Ion‐conducting Double Salt Li_6+2x[B₁₀Se₁₈]Se_x (x ≈ 2) was prepared in a solid state reaction from lithium selenide, amorphous boron and selenium in evacuated carbon coated silica tubes at a temperature of 800 °C. Subsequent cooling from 600 °C to 300 °C gave amber colored crystals with the following lattice parameters: space group I2/a (at 173 K); a = 17.411(1) Å, b = 21.900(1) Å, c = 17.820(1) Å, β = 101.6(1)°. The crystal structure contains a well‐defined polymeric selenoborate network of composition ([B₁₀Se₁₆Se_4/2]^6?)_n consisting of a system of edge‐sharing [B₁₀Se₁₆Se_4/2] adamantanoid macro‐tetrahedra forming large channels in which a strongly disorderd system of partial occupied Li⁺ cations and additional disordered Se^2? anions is observed. The crystal structure of the novel selenoborate is isotypic to Li_6+2x[B₁₀S₁₈]S_x (x ≈ 2) [1]. X‐ray and ⁷Li magic‐angle spinning NMR data suggest that the site occupancies of the three crystallographically distinct lithium ions exhibit a significant temperature dependence. The lithium ion mobility has been characterized by detailed temperature dependent NMR lineshape and spin‐lattice relaxation measurements.     

Li47B3P14N42—A Lithium Nitridoborophosphate with [P3N9]12−, [P4N10]10−, and the Unprecedented [B3P3N13]15− Ion

Li₄₇B₃P₁₄N₄₂, the first lithium nitridoborophosphate, is synthesized by two different routes using a Li₃N flux enabling a complete structure determination by single‐crystal X‐ray diffraction data. Li₄₇B₃P₁₄N₄₂ comprises three different complex anions: a cyclic [P₃N₉]¹²⁻, an adamantane‐like [P₄N₁₀]¹⁰⁻, and the novel anion [P₃B₃N₁₃]¹⁵⁻. [P₃B₃N₁₃]¹⁵⁻ is the first species with condensed B/N and P/N substructures. Rietveld refinement, ⁶Li, ⁷Li, ¹¹B, and ³¹P solid‐state NMR spectroscopy, FTIR spectroscopy, EDX measurements, and elemental analyses correspond well with the structure model from single‐crystal XRD. To confirm the mobility of Li⁺ ions, their possible migration pathways were evaluated and the temperature‐dependent conductivity was determined by impedance spectroscopy. With the Li₃N flux route we gained access to a new class of lithium nitridoborophosphates, which could have a great potential for unprecedented anion topologies with interesting properties.     

Mixed‐Valent Europium in the Cubic Thiosilicate Li3Eu6[SiS4]4

In an attempt to synthesize LiEu₃S₃[SiS₄] utilizing elemental europium and sulfur as well as SiS₂ and an excess of LiCl as flux and lithium source, dark red, platelet‐shaped single crystals of Li₃Eu₆[SiS₄]₄ were obtained. This new compound crystallizes in the cubic space group I4 3d (a = 1369.22(5) pm) with four formula units per unit cell. Both the Li⁺ and the Si⁴⁺ cations are surrounded by four sulfide anions. The [SiS₄]^4– tetrahedra show merely a slight trigonal distortion, while the [LiS₄]^7– units are best described as flattened bisphenoids. The europium cations exhibit an eightfold, rather irregular coordination environment by eight S^2– anions and have to be regarded mixed‐valent with a +2:+3 charge‐ratio of 5:1 in order to gain electroneutrality. The lack of an inversion center is caused by the [SiS₄]^4– tetrahedra being stacked exclusively top up along [111] in this acentric crystal structure.     

Quantum-Chemical Investigation of Ionic Association of Lithium Salts LiXF<Subscript>6</Subscript> (X = As,P)

The possibility of formation of various ion clusters for lithium salts LiXF₆ (X = As, P) is studied. The dynamic matrix of the clusters in a gas phase is calculated by numerical and analytical differentiation of the full energy of clusters in the MO LCAO approximation by the Hartree-Fock-Roothaan (HFR) method with the aid of program package PC GAMESS. Stable ionic clusters are ion pairs Li⁺[XF₆]⁻ with bi- and tridentate cation coordination relative to the octahedral anion, ion triplets [XF₆]⁻Li⁺[XF₆]⁻ and Li⁺[XF₆]⁻Li⁺ with bi- and tridentate coordination, and ion dimers { Li⁺[XF₆]⁻}₂ with bidentate coordination. Trimers {Li⁺[XF₆]⁻}₃ and tetramers {Li⁺[XF₆]⁻}₄ in the form of symmetrical ring structures with monodentate coordination are stable only for [AsF₆]⁻. For stable ion species, densities of vibrational states and IR spectra are calculated.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 546–555.Original Russian Text Copyright © 2005 by Popov, Nikiforov, Bushkova, Zhukovskii.     

A rhodium(III) complex of the linear diborazine H3B·NMe2BH2·NMe2H: an intermediate in the dehydrocoupling of H3B·NMe2H

The solid‐state structure of the rhodium complex (dimethylamine–dimethylaminoborane–borane‐κ²H,H′)dihydridobis(triisopropylphosphane‐κP)rhodium(III) tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate, [RhH₂(C₄H₁₈B₂N₂)(C₉H₂₁P)₂](C₃₂H₁₂BF₂₄), is reported. The complex contains the linear diborazine H₃B·NMe₂BH₂·NMe₂H, a kinetically important intermediate in the transition‐metal‐mediated dehydrocoupling of H₃B·NMe₂H, ultimately affording the dimeric amino‐borane [H₂BNMe₂]₂. The structure of the title complex contains a distorted octahedral Rh^III centre, with mutually trans phosphane ligands and cis hydride ligands. The diborazine is bound through two Rh—H—B σ‐bonds and exhibits a gauche conformation with respect to the B—N—B—N backbone.     

catena‐Poly­[[di­aqua­lithium(I)]‐μ‐[9H‐purine‐2,6(1H,3H)‐dionato‐O2:N7]]

In the title compound, [Li(C₅H₃N₄O₂)(H₂O)₂]_n, the coordinate geometry about the Li⁺ ion is distorted tetrahedral and the Li⁺ ion is bonded to N and O atoms of adjacent ligand mol­ecules forming an infinite polymeric chain with Li—O and Li—N bond lengths of 1.901 (5) and 2.043 (6) Å, respectively. Tetrahedral coordination at the Li⁺ ion is completed by two cis water mol­ecules [Li—O 1.985 (6) and 1.946 (6) Å]. The crystal structure is stabilized both by the polymeric structure and by a hydrogen‐bond network involving N—H?O, O—H?O and O—H?N hydrogen bonds.     

Li2H3IO6, eine neue Variante der Molybdänitstruktur

Li₂H₃IO₆, a New Variant of the Molybdenite Structure Li₂H₃IO₆ crystallizes in P6₁ (a = 529.70(8), c = 2 759.6(5) pm; Z = 6). The crystals are twinned by merohedry, described by m ‖ [001] and 2 ? [001]. According to the results of an X-ray structure determination (2 778 diffractometer data, R_w = 0.047), Li₂H₃IO₆ exhibits a layer structure, with oxygen forming a distorted variant of the sulfur partial structure in molybdenite (MoS₂), however, with iodine and lithium in the more (Li) or less (I) distorted octahedral holes. The Li₂IO₆ packages are connected via strong hydrogen bonds along the edges of distorted trigonal prisms.     

Ternäre Lithium-Selten-Erd-Nitrate mit einsamen Nitrationen: Li3[M(NO3)5](NO3) (M = Gd?Lu,Y). Die Kristallstruktur von Li3Er(NO3)6

Ternary Lithium Rare Earth Nitrates with Lonesome Nitrate Ions: Li₃[M(NO₃)₅](NO₃) (M = Gd? Lu, Y). The Crystal Structure of Li₃Er(NO₃)₆ Single crystals of the ternary nitrate Li₃Er(NO₃)₆ are obtained from a solution of “Er(NO₃)₃” in the melt of LiNO₃. In Li₃Er(NO₃)₆ (monoclinic, P2₁/n, Z = 4; a = 776.0(1); b = 748.86(8); c = 2 396(1) pm; β = 90.76(3)°; R1 = 0.0490; wR2 = 0.0792), Er³⁺ is surrounded by five bidentate nitrate ligands yielding the anionic units [Er(NO₃)₅]^2?. These are arranged in the direction of the 2₁ screw axis. Two lonesome NO₃^? ions are in the middle of such a “helix” and are connected by Li⁺ with the anions [Er(NO₃)₅]^2?. The helices are moved against each other by about half of the lattice constant a and are connected by further Li⁺ ions.     

Synthesis and Crystal Structure of the two Lithium Hypersilylcuprates LiCu2[Si(SiMe3)3]3 and [Li7(OtBu)6][Cu2{Si(SiMe3)3}3]

The two hypersilylcuprates LiCu₂Hyp₃ ( 2 ) and [Li₇(O^tBu)₆][Cu₂Hyp₃] ( 3 ) (Hyp = Si(SiMe₃)₃) were synthesized by reactions of unsolvated lithium hypersilanide, LiHyp with hypersilylcopper and CuO^tBu, respectively. Both contain the novel A‐frame trihypersilyldicuprate anion [Cu₂Hyp₃]^–. In the former case a molecular compound is produced containing intimate ion pairs. In the latter case the cuprate anion and the unique large [Li₇(O^tBu)₆]⁺ cation form a salt‐like compound, only sparingly soluble in unpolar solvents. According to NBO analyses the bonding within the trihypersilyldicuprate moiety is best described by interaction of a bridging lewis‐basic hypersilanide anion with two lewis‐acidic hypersilyl copper fragments.     

Ein neues Oxouranat(VI): K2Li4[UO6]. Mit einer Bemerkung über Rb2Li4[UO6] und Cs2Li4UO6

A New Oxouranate(VI): K₂Li₄[UO₆]. With a Remark about Rb₂Li₄[UO₆] and Cs₂Li₄[UO₆] For the first time K₂Li₄UO₆ has been prepared by an exchange reaction of α-Li₆UO₆ with K₂O [K:U = 2.0:1, sealed au-tube; 750°C; 30 d single crystals; 680°C, 10 d powder]. The irregular shaped single crystals, which are of yellow color and sensitive to moisture crystallize in P3 m1 (Z = 1) with a = 619.27(5), c = 533.76(6) pm. The structure determination (PW 1100, AgKα R = 4.80%, R_w = 4.81% for 220 unique reflexions) reveals a new type of structure. The characteristic elements are the isolated group [UO₆] and the C.N. = 12 for K⁺. While Li(1) has a nearly regular square of 4 O^2? as coordination polyhedron, Li(2) is octahedrally surrounded. The Madelung Part of Lattice Energy (MAPLE) is calculated and discussed. In addition to K₂Li₄[UO₆] the new oxides Rb₂Li₄[UO₆] and Cs₂Li₄[UO₆] are prepared as pale yellow powders which are little sensitive to moisture (both: au-tube, 680°C, 10 d). According to powder datas both compounds are isotypic with K₂Li₄[UO₆] [Rb₂Li₄[UO₆]: a = 622.91(5), c = 535.93(6) pm; Cs₂Li₄[UO₆]: a = 626.70(6), c = 539.92(6) pm].     

Ein ungewöhnlicher trimerer Bimetallkomplex mit dem Gerüst [Zr3(μ2-OH)3(μ3-O)Li5] durch Reaktion von Zirconiumorgano- und -hydrido-Komplexen mit Wasser

An Unusual Trimeric Bimetallic Li? Zr Complex with the Backbone [Zr₃(μ₂-OH)₃(μ₃-O)Li₅] by Reaction of Zirconiumorgano and Hydrido Complexes with Water The reaction of compounds of the type [(LZr)(LiH)(L′)]_n and [(LZr)(LiH)(L′)(alkyne)]_n (L: 2,2′-Biphenolato-dianion, L′: thf, Bu₃P, alkyne: Ph? C?C? SiMe₃, CH?CH) with water at 0°C in a thf solution results in the formation of th trimeric bimetallic complex 8 [(L₂Zr)₃(μ₂-OH)₃(μ₃-O)Li₅(thf)₈(H₂O)₅] in 50% yield. The X-ray analysis of 8 shows that a planar six-membered ring Zr₃(μ₂-OH)₃ is formed. In the middle of this ring is a dianionic oxygen atom placed, coordinating to the three L₂Zr centres in a planar μ₃-coordination (bond angles 120,05μ). Five lithium ions stabilize the anionic backbone by bridging the biphenolato chelate ligands, which form seven-membered chelate rings with the atoms. ¹H-, ¹³C-, and ⁷Li-NMR spectra exhibit that the solid state structure remains unchanged in solution (thf).     

Untersuchungen zur Kristallstruktur von Lithium‐dodecahydro‐closo‐dodecaborat aus wäßriger Lösung: Li2(H2O)7[B12H12]

Investigations on the Crystal Structure of Lithium Dodecahydro‐closo‐dodecaborate from Aqueous Solution: Li₂(H₂O)₇[B₁₂H₁₂] By neutralization of an aqueous solution of the acid (H₃O)₂[B₁₂H₁₂] with lithium hydroxide (LiOH) and subsequent isothermic evaporation of the resulting solution to dryness, it was possible to obtain the heptahydrate of lithium dodecahydro‐closo‐dodecaborate Li₂[B₁₂H₁₂] · 7 H₂O (≡ Li₂(H₂O)₇[B₁₂H₁₂]). Its structure has been determined from X‐ray single crystal data at room temperature. The compound crystallizes as colourless, lath‐shaped, deliquescent crystals in the orthorhombic space group Cmcm with the lattice constants a = 1215.18(7), b = 934.31(5), c = 1444.03(9) pm and four formula units in the unit cell. The crystal structure of Li₂(H₂O)₇[B₁₂H₁₂] can not be described as a simple AB₂‐structure type. Instead it forms a layer‐like structure analogous to the well‐known barium compound Ba(H₂O)₆[B₁₂H₁₂]. Characteristic feature is the formation of isolated cation pairs [Li₂(H₂O)₇]²⁺ in which the water molecules form two [Li(H₂O)₄]⁺ tetrahedra with eclipsed conformation, linked to a dimer via a common corner. The bridging oxygen atom (∢(Li‐ O ‐Li) = 112°) thereby formally substitutes Ba²⁺ in Ba(H₂O)₆[B₁₂H₁₂] according to (H₂ O )Li₂(H₂O)₆[B₁₂H₁₂]. A direct coordinative influence of the [B₁₂H₁₂]^2— cluster anions to the Li⁺ cations is not noticeable, however. The positions of the hydrogen atoms of both the water molecules and the [B₁₂H₁₂]^2— units have all been localized. In addition, the formation of B‐H^δ—···^δ+H‐O‐hydrogen bonds between the water molecules and the hydrogen atoms from the anionic [B₁₂H₁₂]^2— clusters is considered and their range and strength is discussed. The dehydratation of the heptahydrate has been investigated by DTA‐TG measurements and shown to take place in two steps at 56 and 151 °C, respectively. Thermal treatment leads to the anhydrous lithium dodecahydro‐closo‐dodecaborate Li₂[B₁₂H₁₂], eventually.     

Zur Kenntnis ‘Kationen-reicher’ Tantalate Über Li7[TaO6]

On Tantalates ‘rich in Cations’ On Li₇[TaO₆] For the first time, colourless single crystals of Li₇[TaO₆] were grown by annealing intimate mixtures of Li₂O and Ta₂O₅ (Li:Ta = 7,7:1) in closed Ni-cylinders (1 000°C, 156 d). [Trigonal-rhomboedral with a = 535.8(1) pm, c = 1 507.3(3) pm, c/a = 2.81/Guinier-Simon-powder data; Z = 3. Space group R3 for the part Li(1)₆TaO₆ and presumably P3 for Li₇TaO₆, including Li(2)]. The crystal structure was solved by four-cycle-diffractometer data [Mo? Kα , 331 from 331 I_o(hkl), R = 1.99%, R_w = 1.96%], parameters see text. The positions of anions correspond to the motif of a hexagonal closest packing of spheres, obviously deformed (with MEFIR of O^2? space filling corresponds to 69.8% instead of expected 73.2%. 1/3 of the octahedron holes are ordered occupied by Ta and Li(2), 1/2 of the tetrahedral holes likewise ordered by Li(1). All polyhedra of coordination of the anions are trigonal prisms. The Madelung Part of Lattice Energy, MAPLE, and Effective Coordination Numbers, ECoN, these calculated via Mean Fictive Ionic Radii, as well as charge distribution ‘CHARDI’ are calculated and discussed.     

Über Oxocobaltate der Alkalimetalle. Zur Kenntnis von Li8CoO6

Oxocobaltates of Alkali Metals. On Li₈CoO₆. Hitherto unknown Li₈CoO₆, rubin- red single crystals, cristallizes according to WEISSENBERG and precession photographs (MoK_α) hexagonal with a = 5.44 Å, c = 10.87 Å; c/a = 2.0; Z = 2, space group C? P6₃cm. Atomic parameters see text. The structure derives from a closest packing of O^2?, ABACA … (The tetrahedral, ?isolated”? groups [CoO₄] show remarkable short distances Co–O (1.66 Å), comparable with [CoO₄] in Li₄CoO₄, being isotypic with Li₄SiO₄. The MADELUNG Part of Lattice Energy is calculated and discussed.     

Synthese et propriétés de conduction ionique des phases Li8−2xCaxCeO6 (0 < x ≤ 0,5) et Li6CaCeO6

The solid solution Li_8−2xCa_xCeO₆ (0 < x ≤ 0,5) and the definite phase Li₆CaCeO₆ have been obtained at 800°C through a study of Li---Ca---Ce---O system. Electrical measurements on the doped phases Li^tetr.₆ [Li_2-2xCa_xCe□]^oct.O₆ show that the conductivity varies slightly with the creation of vacancies in the octahedral layers. This result unambiguously confirms the following diffusion mechanism: the conduction is assumed essentially by lithium ions located in the tetrahedral layers. The compound Li₆CaCeO₆ is isostructural with Li₆In₂O₆. The cell is trigonal, Å, c = 10,603 Å, c/a = 1,058₇, and Z = 6. This new quaternary phase, which belongs to the same structural family of oxides of the type Li₈MO₆, either pure or doped with calcium, may be represented by the formula Li^tetr.₆[Ca Ce□]^oct.O₆. Electrical and structural data are correlated for this compound.     

Synthese und Kristallstruktur eines μ-Methylen-μ-hydrido-dialanats [R2Al(μ-CH2)(μ-H)AlR2]− (R = CH(SiMe3)2)

Synthesis and Crystal Structure of a μ-Methylene-μ-hydrido-dialanate [R₂Al(μ-CH₂)(μ-H)AlR₂]^? (R = CH(SiMe₃)₂) tert-Butyl lithium reacts with the recently synthesized methylene bridged dialuminium compound [(Me₃Si)₂CH]₂Al? CH₂? Al[CH(SiMe₃)₂]₂ 2 in the presence of TMEDA under β-elimination; the thereby formed hydride anion is bound in a chelating manner by both unsaturated aluminium atoms forming a 3c–2e–Al? H? Al bond. The crystal structure of the product shows two independent molecules differing only slightly in bond lengths and angles, but significantly in conformation. While one of the Al₂CH heterocycles deviates little from planarity with a rough C₂ symmetry for the whole anion, the other one is folded with an angle of 21.1° and the arrangement of the substituents is best described by C_s symmetry.     

Li4Ca3Si2N6 and Li4Sr3Si2N6 – Quaternary Lithium Nitridosilicates with Isolated [Si2N6]10– Ions

The isotypic nitridosilicates Li₄Ca₃Si₂N₆ and Li₄Sr₃Si₂N₆ were synthesized by reaction of strontium or calcium with Si(NH)₂ and additional excess of Li₃N in weld shut tantalum ampoules. The crystal structure, which has been solved by single‐crystal X‐ray diffraction (Li₄Sr₃Si₂N₆: C2/m, Z = 2, a = 6.1268(12), b = 9.6866(19), c = 6.2200(12) Å, β = 90.24(3)°, wR₂ = 0.0903) is made up from isolated [Si₂N₆]^10– ions and is isotypic to Li₄Sr₃Ge₂N₆. The bonding angels and distances within the edge‐sharing [Si₂N₆]^10– double‐tetrahedra are strongly dependent on the lewis acidity of the counterions. This finding is discussed in relation to the compounds Ca₅Si₂N₆ and Ba₅Si₂N₆, which also exhibit isolated [Si₂N₆]^10– ions.     

Darstellung und Schwingungsspektren der Komplexe [MBr6]−, [Br5MN3]− und [Br5MNPPh3]− von Niob und Tantal Die Kristallstruktur von PPh4[NbBr6]

Preparation and vibrational spectra of the complexes [MBr₆]^?, [Br₅MN₃]^? and [Br₅MNPPh₃]^? of niobium and tantalum. Cyrstal structure of PPh₄[NbBr₆] The compounds PPh₄[MBr₆] and PPh₄[MBr₅N₃] are obtained by reaction of MBr₅ with PPh₄Br or PPh₄N₃, respectively, in CH₂Cl₂ solution (M ? Nb, Ta). The azido complexes PPh₄[MBr₅N₃] can also be obtained by reactions of the hexabromo complexes with iodine azide. According to its i.r. spectrum the symmetry of the [MBr₆]^? ion is lower than O_h in the solide state. This is corfirmed for PPh₄[NbBr₆] by a crystal structure analysis; it crystallizes in the monoclinic space group B2/b with four formula units in the unit cell and with the lattice constants a = 2301, b = 1777, c = 686 pm and γ = 96,6°. The structure was determined with X-ray diffraction data and was refined to a residual index of R = 0.055. The [NbBr₆]^? ion has the symmetry C_i, the deviations from O_h being small. In the azido complexes [MBr₅N₃]^? the azido groups are covalently linked with the metal. From [NbBr₅N₃]^? and PPh₃ the complex [Br₅Nb?N?PPh₃]^?, is obtained; for the analogous formation of the corresponding Ta complex photochemical activation is necessary. In this way the complex [Cl₅Nb?N?AsPh₃]^? can also be obtained. I.r. spectra of all the compounds are reported and assigned.