A novel Mo(V) diphosphate with an intersecting tunnel structure: Sr(MoO)2(P2O7)2

A novel Mo(V) diphosphate Sr(MoO)₂P₂O₇ has been synthesized. It crystallizes in the space group P2₁/n with a=7.925(1) Å, b=7.739(1) Å, c=9.485(1) Å and β=91.05(1)°. Its original framework consists of MoP₂O₁₁ units built up of one P₂O₇ group sharing two apices with one MoO₆ octahedron. The MoP₂O₁₁ units share corners, forming [MoP₂O₁₀]_∞ chains running along [101]. The assemblage of these chains forms the [Mo₂P₄O₁₆]_∞ intersecting tunnel framework. The Sr²⁺ cations are located at the tunnel intersection, showing a distorted cubic coordination. This structure is compared to those of Ba(MoO)₂P₂O₇ and LiMoOP₂O₇, which are also built up of MoP₂O₁₁ units forming [MoP₂O₁₀]_∞ chains, but with different configurations.     

A Mixed-Valent Molybdenotungsten Monophosphate with a Tunnel Structure: Nax(Mo, W)2O3(PO4)2

A mixed-valent molybdenotungstophosphate, Na_x(Mo, W)₂O₃(PO₄)₂ (x 0.75) has been isolated for the first time. It crystallizes in the space group P 2₁/m with a = 7.200(1) Å, b = 6.369(1) Å, c = 9.123(1) Å, and β = 106.29(1)°. Its structure consists of M₂PO₁₃ units built up of two M O₆ octahedra (M = Mo, W) and one PO₄ tetrahedron sharing their apices as already observed in several molybdenum phosphates. These units share their apices with PO₄ tetrahedra forming [M₂P₂O₁₅]_∞ chains running along . The host lattice [(Mo, W)₂P₂O₁₁]_∞ can be described by the assemblage of such chains or by the assemblage of [MPO₈]_∞ chains running along , in which one PO₄ tetrahedron alternates with one MO₆ octahedron. The tridimensional framework [Mo, WP₂O₁₁]_∞ delimits tunnels running along , occupied by sodium with two kinds of coordination, 6 and 5. The distribution of the different species, in the octahedral sites according to the formulation Na_0.75(Mo^VI_0.42W^VI_0.58)_M1 (Mo^V_0.75W^VI_0.25)₂O₃(PO₄)₂, is discussed.     

Structure and properties of Y5Mo2O12 and Gd5Mo2O12: Mixed valence oxides with structurally equivalent molybdenum atoms

Crystals of Ln₅Mo₂O₁₂ (Ln = Y, Gd) were grown by electrochemical reduction of alkali-molybdate/rare-earth oxide melts at 1075–1100°C. A single crystal of Y₅Mo₂O₁₂, used for structure determination, was found to be monoclinic with a = 12.2376(7) Å, b = 5.7177(8) Å, c = 7.4835(5) Å, β = 108.034(5)°, and Z = 2. Although the structure was refined in space group C2/m, the true space group appears to be P2₁/m. In Y₅Mo₂O₁₂, rutile-like sheets of edge-shared MoO₆ chains linked by YO₆ octahedra are interconnected with YO₇ monocapped trigonal prisms. The Mo atoms in the chains have alternating distances of 2.496 and 3.221 Å and in that respect are similar to MoO₂. However, in contrast to metallic MoO₂ both the Y and Gd compounds are n-type semiconductors with room temperature resistivities of the order of 10³ ohm-cm. Magnetic susceptibility measurements confirm the presence of one unpaired electron per Mo₂ unit. The semiconducting behavior can be explained in terms of an unfavorable bridging oxygen coordination which prevents electron delocalization through metal-oxygen pi bonding as in MoO₂.     

[As(V)As(III)O6]: An uncommon anion group in the crystal structure of K2Cu3(As2O6)2

The crystal structure of K₂Cu₃(As₂O₆)₂ was determined from single-crystal X-ray data by a direct method strategy and Fourier summations [a = 10.359(4) Å, B = 5.388(2)Å, C = 11.234(4) Å, β = 110.48(2)°; space group C2/m; Z = 2; R_w = 0.025 for 1199 reflections up to sin /λ = 0.81 Å⁻¹]. In detail, the structure consists of As(V)O₄ tetrahedra and As(III)O₃ pyramids linked by a common O corner atom to [As(V)As(III)O₆]⁴⁻ groups with symmetry m. The bridging bonds As(V)---O [1.749(3) Å] and As(III)---O [1.838(2) Å] are definitely longer than the other As(V)---O bonds [mean 1.669 Å] and As(III)---O bonds [1.764(2) Å, 2×]. The angle As(V)---O---As(III) is 123.0(1)°. The Cu atoms are [4 + 2]- and [4 + 1]-, and the K atom is [9]-coordinated to oxygen atoms. The As₂O₆ groups and the Cu coordination polyhedra are linked to sheets parallel to (001). These sheets are connected by the K atoms. Single crystals of K₂Cu₃(As₂O₆)₂ suitable for X-ray work were synthesized under hydrothermal conditions.     

[{(NiOH)2Mo10O36(PO4)Ti2}n]: a novel chainlike trimetal heteropolyanion based on pseudo-keggin fragments

A new mixed Mo/Ni/Ti heteropoly compound [C₅H₅NH]₅ [(NiOH)₂Mo₁₀O₃₆(PO₄)Ti₂] has been hydrothermally synthesized and structurally determined by the single-crystal X-ray diffraction. Black prismatic crystals crystallize in the monoclinic system, space group P2(1)/n, a=11.2075(2), b=37.8328(5) c=13.0888(1) Å, β=101.4580(10)°, M=2276.13, V=5439.19(13) ų, Z=4. Data were collected on a Siemens SMART CCD diffractometer at 293(2) K in the range of 1.68<θ<25.09° using the ω-scan technique (λ=0.71073 Å R(F)=0.0872 for 9621 reflections). The title compound contains a trimetal heteropolyanion polymer and “trans-titanium”-bridging pseudo-Keggin fragments linked to a chain.     

Syntheses, crystal structures and spectroscopic properties of KEu[AsS4], K3Dy[AsS4]2 and Rb4Nd0.67[AsS4]2

Three rare earth compounds, KEu[AsS₄] (1), K₃Dy[AsS₄]₂ (2), and Rb₄Nd_0.67[AsS₄]₂ (3) have been synthesized employing the molten flux method. The reactions of A₂S₃ (A = K, Rb), Ln (Ln = Eu, Dy, Nd), As₂S₃, S were accomplished at 600 °C for 96 h in evacuated fused silica ampoules. Crystal data for these compounds are: 1, monoclinic, space group P2₁/m (no. 11), a = 6.7276(7) Å, b = 6.7190(5) Å, c = 8.6947(9) Å, β = 107.287(12)°, Z = 2; 2, monoclinic, space group C2/c (no. 15), a = 10.3381(7) Å, b = 18.7439(12) Å, c = 8.8185(6) Å, β = 117.060(7)°, Z = 4; 3, orthorhombic, space group Ibam (no. 72), a = 18.7333(15) Å, b = 9.1461(5) Å, c = 10.2060(6) Å, Z = 4. 1 is a two-dimensional structure with ²_∞[Eu(AsS₄)]⁻ layers separated by potassium cations. Within each layer, distorted bicapped trigonal [EuS₈] prisms are linked through distorted [AsS₄]³⁻ tetrahedra. Each Eu²⁺ cation is coordinated by two [AsS₄]³⁻ units by edge-sharing and bonded to further two [AsS₄]³⁻ units by corner-sharing. Compound 2 contains a one-dimensional structure with ¹_∞[Dy(AsS₄)₂]³⁻ chains separated by potassium cations. Within each chain, distorted bicapped trigonal prisms of [DyS₈] are linked by slightly distorted [AsS₄]³⁻ tetrahedra. Each Dy³⁺ ion is surrounded by four [AsS₄]³⁻ moieties in an edge-sharing fashion. For compound 3 also a one-dimensional structure with ¹_∞[Nd₀.₆₇(AsS₄)₂]⁴⁻ chains is observed. But the Nd position is only partially occupied and overall every third Nd atom is missing along the chain. This cuts the infinite chains into short dimers containing two bridging [As₄]³⁻ units and four terminal [AsS₄]³⁻ groups. 1 is characterized with UV/vis diffuse reflectance spectroscopy, IR, and Raman spectra.     

Hydrothermal Syntheses, Structures, and Properties of Two New Potassium Vanadium Phosphates: K3(VO) (V2O3) (PO4)2(HPO4) and K3 (VO) (HV2O3) (PO4)2(HPO4)

Two new potassium vanadium phosphates have been prepared and their structures have been determined from analysis of single crystal X-ray data. The two compounds, K₃(VO)(V₂O₃) (PO₄)₂(HPO₄) and K₃(VO)(HV₂O₃)(PO₄)₂(HPO₄), are isostructural, except for the incorporation of an extra hydrogen atom into the nearly identical frameworks. The structures consist of a three-dimensional network of [VO]_n chains connected through phosphate groups to a [V₂O₃] moiety. Magnetic susceptibility experiments indicate that in the case of the di-hydrogen compound, there are no significant magnetic interactions between the three independent vanadium (IV) centers. Crystal data: for K₃(VO)(V₂O₃)(PO₄)₂ (HPO₄), M_r = 620.02, orthorhombic space group Pnma (No. 62), a = 7.023(4) Å, b = 13.309(7) Å, c = 14.294(7) Å, V = 1336(2) ų, Z = 4, R = 5.02%, and R_w = 5.24% for 1238 observed reflections [I > 3σ(I)]; for K₃(VO)(HV₂O₃)(PO₄)₂(HPO₄), M_r = 621.04, orthorhombic space group Pnma (No. 62), a = 6.975(3) Å, b = 13.559(7) Å, c = 14.130(7) Å, V = 1336(1) ų, Z = 4, R = 6.02%, and R_w = 6.34% for 1465 observed reflections [I > 3σ(I)].     

The designed synthesis and characterization of two novel heterometallic trinuclear incomplete cubane-like clusters [(CH3CH2)4N]{(M2CuS4)}(S2C2H4)2(PPh3) (M = Mo, W)

Two novel heterometallic trinuclear incomplete cubane-like clusters [(CH₃CH₂)₄N][{M₂CuS₄}(edt)₂(PPh₃)] (M = Mo, W) have been synthesized by reaction of [(CH₃CH₂)₄N]₂[M₂S₄(edt)₂] (M = Mo, W) with Cu(PPh₃)₂(dtp) [where edt is 1,2-ethane-dithiolato ligand, dtp is S₂P(OCH₂CH₃)₂⁻]. The two crystals are isomorphous in space group P1 (No. 1). The unit cell contains two independent molecules, but the two discrete anions have the same orientation for the PPh₃ ligands along one axis so the space group is undoubtedly non-centrosymmetric. The discrete anion contains two edt ligands and one PPh₃ ligand attached to one incomplete cubane-like cluster core {M₂CuS₄}³⁺ (M = Mo, W). The bond lengths of Mo---Mo[W---W] and the two Mo---Cu[W-Cu] are 2.852(2)[2.844(1)], 2.802(2)[2.765(3)], 2.760(2)[2.762(3)] Å, respectively. The M ₂S₄(edt)₂ (M = Mo, W) moiety remains almost unchanged, except that for the compound 1 the Mo=S double bond length elongates from av. 2.10 to av. 2.165 Å. The title clusters provide a new type of unsymmetric μ₂-bridging sulphido ligand. The incomplete cubane-like cluster core {Mo₂CuS₄}³⁺ of compound 1 is distorted because the two Cu---μ₂---S bond lengths are significantly different (2.313 Å and 2.409 Å), but the core {W₂CuS₄}³⁺ of compound 2 has approximately C_s symmetry. The IR spectra of the two title clusters and two starting materials are assigned.     

Hydrothermal Synthesis and Crystal Structure of [(CH3NH3)1.03K2.97]Sb12S20·1.34H2O

A novel thioantimonate(III) [(CH₃NH₃)_1.03K_2.97]Sb₁₂S₂₀·1.34H₂O was synthesized hydrothermally. It crystallizes in space groupP , witha=11.9939(7) Å,b=12.8790(8) Å,c=14.9695(9) Å,α=100.033(1)°,β=99.691(1)°,γ=108.582(1)°,V=2095.3(2) ų, andZ=2. The structure is determined from single crystal X-ray diffraction data collected at room temperature and refined toR(F)=0.037. In the crystal structure, each Sb(III) atoms has short bonds (2.37–2.58 Å) to three S atoms. The pyramidal [SbS₃] groups share common S atoms forming two types of centrosymmetric [Sb₁₂S₂₀] rings with the same topology. These rings are interconnected by weaker Sb–S bonds (2.92–3.29 Å) into 2-dimensional layers. Adjacent layers are parallel with K⁺and CH₃NH⁺₃ions and H₂O molecules located between them. Variation of bond valence sums calculated for the Sb(III) cations is found to be correlated with the coordination geometry. This is interpreted as due to the stereochemical activity of their lone electron pairs.     

Syntheses and characterization of two oxoborates, (Pb3O)2(BO3)2MO4 (M=Cr, Mo)

Two oxoborates, (Pb₃O)₂(BO₃)₂MO₄ (M=Cr, Mo), have been prepared by solid-state reactions below 700 °C. Single-crystal XRD analyses showed that the Cr compound crystallizes in the orthorhombic group Pnma with a=6.4160(13) Å, b=11.635(2) Å, c=18.164(4) Å, Z=4 and the Mo analog in the group Cmcm with a=18.446(4) Å, b=6.3557(13) Å, c=11.657(2) Å, Z=4. Both compounds are characterized by one-dimensional chains formed by corner-sharing OPb₄ tetrahedra. BO₃ and CrO₄ (MoO₄) groups are located around the chains to hold them together via Pb–O bonds. The IR spectra further confirmed the presence of BO₃ groups in both structures and UV–vis diffuse reflectance spectra showed band gaps of about 1.8 and 2.9 eV for the Cr and Mo compounds, respectively. Band structure calculations indicated that (Pb₃O)₂(BO₃)₂MoO₄ is a direct semiconductor with the calculated energy gap of about 2.4 eV.     

Preparation and Structure of Cerium Titanates Ce2TiO5, Ce2TiO7, and Ce4Ti9O24

Compounds Ce₂TiO₅, Ce₂Ti₂O₇, and Ce₄Ti₉O₂₄ were prepared by heating appropriate mixtures of solids containing Ce⁴⁺ and Ti³⁺ or Ti which were placed in a platinum-silica-ampoule combination at T = 1250°C (3d) under vacuum. The new compounds were characterized by powder patterns. We obtained Ce₂TiO₅ which is isotypic to La₂TiO₅ and crystallizes in the Y₂TiO₅-type (space group Pnma) with a = 10.877(6) Å, b = 3.893(1) Å, c = 11.389(8) Å, Z = 4. Ce₂Ti₂O₇ is isotypic to La₂Ti₂O₇ and crystallizes in the monoclinic Ca₂Nb₂O₇ type (space group P 2₁) with a = 7.776(6) Å, b = 5.515(4) Å, c = 12.999(6) Å, β = 98.36(5), Z = 4. The compound Ce₄Ti₉O₂₄ crystallizes orthorhombic with a = 14.082(4) Å, b = 35.419(8) Å, c = 14.516(4) Å, Z = 16. The new cerium titanate Ce₄Ti₉O₂₄ is isotypic to Nd₄Ti₉O₂₄ (space group Fddd (No. 70)) which represents a novel type of structure.     

β-BaV2(P2O7)2: A New Polymorph of Barium Vanadium (III) Pyrophosphate Characterized by Intersecting Tunnels

Investigation into the synthesis of reduced vanadium phosphate has led to the formation of a new form of the barium vanadium (III) pyrophosphate compound β-BaV₂(P₂O₇)₂. It is a polymorph of the previously known BaV₂(P₂O₇)₂, which is now labeled as the α-phase. The title compound crystallizes in the P-1 (No. 2) space group with a = 6.269(1) Å, b = 7.864(3) Å, c = 6.1592(9) Å, α = 101.34(2)°, β = 105.84(1)°, and γ = 96.51(2)°. The structure consists of corner-shared VO₆ octahedra and PO₄ tetrahedra that are connected in V-O-P-O-V and V-O-P-O-P-O-V bonding arrangements. This interesting three-dimensional framework is characterized by seven types of intersecting tunnels, three of which are occupied by the barium cation, while the others are empty. It is important to know that one of the empty tunnels has a relatively large window with a minimum diagonal distance of 4.41 Å, which facilitates a possible framework for a lithium ion insertion reaction. The barium atom has a 10-coordination sphere, BaO₁₀, in which the oxygen atoms can be viewed as forming two intersecting pseudohexagonal planes. β-BaV₂(P₂O₇)₂ appears to form at a relatively higher temperature than its polymorph, α-BaV₂(P₂O₇)₂. A detailed structural analysis and structural comparison with the α-phase, as well as a brief comparison with SrV₂(P₂O₇)₂, are presented.     

Two mixed valent molybdenophosphates with a tunnel structure closely related to K0.17MoP2O7: Pb2(PbO)2Mo8(P2O7)8 and PbK2Mo8(P2O7)8

Two new mixed valent Mo(III)/Mo(IV) diphosphates containing lead Pb₂(PbO)₂Mo₈(P₂O₇)₈ and PbK₂Mo₈(P₂O₇)₈ have been synthesized. The [Mo₈P₁₆O₅₆]∞ frameworks of these phosphates are closely related to that of K_0.17MoP₂O₇: the MoO₆ octahedra and P₂O₇ groups form two sorts of large eight-sided tunnels. They are occupied in an ordered way by PbO chains and Pb²⁺ cations in Pb₂(PbO)₂Mo₈(P₂O₇)₈ and by K⁺ and Pb²⁺ cations in PbK₂Mo₈(P₂O₇)₈. It results in different symmetries of these two structures, which are tetragonal and monoclinic, respectively, showing the great flexibility of these mixed frameworks, susceptible to accommodate various species with different sizes.     

Synthesis, properties and structures of the two “electron rich” cobalt-sulphur clusters [Co6(μ3-S)8(PEt3)6]

The reaction of hydrogen sulphide with [Co(H₂O)₆](BF₄)₂ and triethylphosphine in the presence of sodium tetraphenylborate or tetrabutylammonium hexafluorophosphate gave the paramagnetic clusters [Co₆(μ₃-S)₈(PEt₃)₆](Y) (Y = BPh₄, (1), PF₆, (2)). These compounds can be easily reduced by sodium napthalenide to the diamagnetic species [Co₆(μ₃-S)₈(PEt₃)₆] · 2C₄H₈O (3). The molecular structures of 1 and 3 have been established by single-crystal X-ray diffraction methods. Crystal data: (1) space group P , a = 19.481(9), b = 15.562(7), c = 12.390(b) Å, α = 92.70(8), β = 94.50(7), γ = 94.10(9)°, Z = 2, (3) space group R , a = 11.780(6) Å, α = 92.50(7)°, Z = 1. Both structures were solved by the heavy atom method and refined by full-matrix least-squares techniques to the conventional R factors values of 0.050 for 1 and 0.044 for 3 on the basis of 4251 and 1918 observed reflections, respectively. The two clusters [Co₆(μ₃-S)₈)(PEt₃)₆]^1+,0 are isostructural, the inner core consisting of an octahedron of cobalt atoms with all the faces symmetrically capped by triply bridging sulphur atoms. Each metal centre is additionally linked to a triethylphosphine group so that each cobalt atom is co-ordinated by four sulphur atoms and one phosphorus in a distorted square pyramidal environment. The addition of one electron whilst leaving unchanged the geometry of the inner framework, induces small changes in the structural parameters, the average Co---Co and Co---P distances being 2.794 (3) and 2.162 (2) Å for 1 and 2.817 (3) and 2.138 (2) Å for 3 respectively. Electrochemistry in non-aqueous solvents shows the electron-transfer sequence

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The tricationic species is stable only in the short time of cyclic voltammetric tests.     

Diamine incorporated compounds derived from polymeric nickel(II) fumarates and oxalates: Crystal structure, spectral and thermal properties of [Ni(en)3](O2CCHCHCO2)·3H2O and [Ni(en)3](O2CCO2)

Lewis-base mediated fragmentation of polymeric nickel(II) fumarate and oxalate are attempted using chelating σ-donor diamines like ethylenediamine (en) and 1,3-diaminopropane (dap) in various conditions which yielded [Ni(en)₃](fum)·3H₂O (1), [Ni(en)₃](ox) (2), [Ni(dap)₂(fum)] (3) and [Ni(dap)(ox)]·2H₂O (4). While 1 and 2 are molecular products each containing octahedral [Ni(en)₃]²⁺ moieties and the anionic dicarboxylate species, 3 and 4 are dap-incorporated polymeric products. The fumarate derivative 1 containing [Ni(en)₃]²⁺ moieties crystallizes in the monoclinic space group C2/c with a = 17.899(4) Å, b = 11.747(2) Å, c = 10.748(2) Å, β = 125.59(3)°, V = 1837.7(6) ų, Z = 4, while the oxalate analogue 2 is seen to be in the trigonal space group P−31c with a = 8.8770(13) Å, b = 8.8770(13) Å, c = 10.482(2) Å, γ = 120°, V = 715.3(2) ų, Z = 2. The octahedral [Ni(en)₃] units in both 1 and 2 are seen to be strongly H-bonded to the dicarboxylate moieties through the coordinated en units leading to a three-dimensional network. However, in 1 the water molecules also take part in the H-bonding and contribute to the overall 3D structure. In both 1 and 2 the crystal packing is done with the [Ni(en)₃]²⁺ units with absolute configuration Λ(δδδ) and its mirror conformer with Δ configuration in exactly equal numbers. Spectral (IR and UV–Visible) and magnetic measurements were carried out and some of the ligand-field parameters like D_q, B and β were evaluated for all the four compounds. These values suggest the presence of octahedrally coordinated nickel(II) in all the four complexes. Spectral data suggest that 3 has the two chelating dap moieties and the fumarate coordinated in η¹ form through both its carboxylate moieties while 4 has one chelating dap and the oxalate moiety coordinated in η⁴-bis-chelating form. Though both 1 and 2 are made of the same type of [Ni(en)₃]²⁺ units their thermograms give entirely different thermal features; 1 showing three clearly successive and step-wise dissociation of each en unit while 2 having a combined loss of two en units in the first thermal step. The relevant thermodynamic and kinetic parameters like E_a and ΔS also could be evaluated for various thermal steps for the compounds 1–4 using Coats–Redfern equation.     

The Crystal Structures of the Strontium Gallates Sr10Ga6O19 and Sr3Ga2O6

The crystal structures of Sr₁₀Ga₆O₁₉ and Sr₃Ga₂O₆ have been characterized using X-ray diffraction techniques. In the case of Sr₁₀Ga₆O₁₉, the structure was determined from a single crystal diffraction data set collected at room conditions and refined to a final R index of 0.061 for 3471 observed reflections (I>2 σ(I)). The compound is monoclinic with space group C12/c1 (a=34.973(4) Å, b=7.934(1) Å, c=15.943(2) Å, β=103.55(1)°, V=4300.7(6) ų, Z=8, D_calc=4.94 g/cm³, μ(MoKα)=32.04 mm⁻¹) and can be classified as an oligogallate. It is the first example of an inorganic compound where six [TO₄]-tetrahedra of only one chemical species occupying the tetrahedral centres are linked via bridging oxygen atoms to form [T₆O₁₉] groups. The hexamers are not linear, but highly puckered. Eleven symmetrically different Sr cations located in planes parallel (100) crosslink between the oligo-groups. They are coordinated by six to eight oxygen ligands. The structure of Sr₃Ga₂O₆ has been refined from powder diffraction data using the Rietveld method (space group Pa , a=16.1049(1), V=4177.1(1) ų, Z=24, D_calc=4.75 g/cm³). The compound is isostructural with tricalcium aluminate and contains highly puckered, six-membered [Ga₆O₁₈]¹⁸⁻ rings. The rings are linked by strontium cations having six to nine nearest oxygen neighbors.     

A novel Mo(V) oligophosphate built up of di- and triphosphate groups: Cs(MoO)4(P2O7)2(P3O10)

A Mo(V) oligophosphate, built up of di and triphosphate groups, Cs(MoO)₄(P₂O₇)₂(P₃O₁₀) has been synthesized for the first time. This compound crystallizes in the triclinic P−1 space group with , , , α=94.534(6)°, β=102.520(6)°, γ=103.663(4)°. This original structure can be described by the association of MoO₆ octahedra, MoP₂O₁₁ units built up of one P₂O₇ group sharing two apices with the same MoO₆ octahedron, and triphosphates groups P₃O₁₀. The resulting tridimensional framework forms large S-shaped tunnels running along c where the Cs⁺ cations are located.     

Niobium Thiobromide, Nb3SBr7, with Triangle Nb3 Cluster: Structure and Bonding

The reaction of Nb, S, and Br₂ in a sealed quartz ampoule at 550°C yielded Nb₃SBr₇. The structure of Nb₃SBr₇ determined by the single-crystal X-ray diffraction method (P3m1, a= 7.1012(6) Å, c = 6.3040(9) Å, V = 275.30(9) ų, Z = 1, d_calc = 5.248(2) g/cm³, R = 0.0395, R_w = 0.0392) consists of one-layer packing of {[Nb₃SBr₃]Br_6/2Br_3/3}²_∞ layers. The molecular orbitals of the model anions [Nb₃Br₁₃]^5- and [Nb₃SBr₁₂]^5-, which involve the triangle Nb₃ cluster with the nearest ligand environment in the structures of Nb₃Br₈ and Nb₃SBr₇, respectively, were calculated by applying the extended Hückel method. The HOMO in [Nb₃Br₁₃]^5- has slightly metal-metal bonding character which is consistent with an Nb-Nb bond length increase from 2.88 Å in a seven-electron Nb₃Br₈ to 2.896(1) Å in a six-electron Nb₃SBr₇. The bonding schemes are in accordance with magnetic properties of Nb₃Br₈, which is paramagnetic, and Nb₃SBr₇, which is diamagnetic.     

Carbomolybdate clusters formed by carbonyl insertion into molybdenum-oxygen bonds. Structural investigation of the [RMo4O15X] core (R = ---C9H4O, X = OCH3; R = ---C14H10, X = ---C7H5O2; R = C14H8, X = ---OH)

[C₄H₉)₄N]₂[Mo₂O₇] reacts with a variety of organic species containing α-diketone groups to give tetranuclear complexes of general composition [RMo₄O₁₅X]³⁻. The complexes [(C₄H₉)₄N]₃[(C₉H₄O)Mo₄O₁₅(OCH₃)] (I), [(C₄H₉)₄N]₃[(C₁₄H₁₀)Mo₄O₁₅(C₆H₅CO₂)] (11) and [(C₄H₉)₄N]₃[(C₁₄H₈)Mo₄O₁₅(OH)] (III) were synthesized from the reactions of dimolybdate with ninhydrin, benzil and phenanthraquinone, respectively. Complex II may also be prepared from dimolybdate and benzoin in acetonitrile-methanol solution, from which it co-crystallizes with the binuclear species [(C₄H₉)₄N]₂[Mo₂O₅(C₆H₅C(O)C(O)C₆H₅)₂] · CH₃CN · CH₃OH (IV). Complexes I–III exhibit the tetranuclear core, previously described for the α-glyoxal derivatives [(C₄H₉)₄N]₃[(HCCH)Mo₄O₁₅X], where X = F⁻ or HCO₂⁻. The ligands may be formally described as diketals, formed by insertion of ligand carbonyl subunits into molybdenum-oxygen bonds. The structures I–III differ most dramatically in the identity and coordination mode of the anionic ligand X⁻ which occupies a position opposite the diketal moiety relative to the [Mo₄O₁₁]²⁺ central cage. Thus, I exhibits a doubly bridging methoxy group in this position, while II possesses a benzoate ligand with an unusual μ₃-O,O′coordination mode. Complex III presents a hydroxy-group unsymmetrically bonded to three of the molybdenum centres. The stereochemical consequences of the various coordination modes are discussed. Crystal data: Compound I, monoclinic space group Pc, a = 24.888(2), b = 12.897(3), c = 24.900(3) Å, β = 101.94(2)°, D_calc = 1.28 g cm⁻¹ for Z = 4. Structure solution and refinement based on 8695 reflections with F_o 6σ(F_o) (Mo-K_α, λ = 0.71073 Å) converged at a conventional discrepancy factor of 0.060. Compound II, orthorhombic space group Pbca, a = 20.426(6), b = 26.916(6), c = 32.147(7) Å, V = 17673.2(20) ų, D_calc = 1.33 g cm⁻³ for Z = 8; 5224 reflections, R = 0.076. Compound III, tetragonal space group I4₁/a, a = b = 48.129(6), c = 13.057(2) Å, V = 30246.2(12) ų, D_calc = 1.35 g cm⁻³ for Z = 16; 5554 reflections, R = 0.053. Compound IV, orthorhombic space group Pnca, a = 16.097(4), b = 16.755(4), c = 25.986(7) Å, V = 7008.1(13) ų, Z = 4, D_calc = 1.18 g cm⁻³ ; 2944 reflections, R = 0.061.     

The use of half-sandwich iridium dithiolate and diselenolate complexes, Cp*Ir(L)(ER)2 (L=CO, PMe3, PPh3; ER=SPh, SePh, SeMe), for the synthesis of heterodimetallic compounds. The molecular structure of Cp*Ir(CO)(μ-SePh)2[Mo(CO)4]

Carbonyl–iridium half-sandwich compounds, Cp*Ir(CO)(EPh)₂ (E=S, Se), were prepared by the photo-induced reaction of Cp*Ir(CO)₂ with the diphenyl dichalcogenides, E₂Ph₂, and used as neutral chelating ligands in carbonylmetal complexes such as Cp*Ir(CO)(μ-EPh)₂[Cr(CO)₄], Cp*Ir(CO)(μ-EPh)₂[Mo(CO)₄] and Cp*Ir(CO)(μ-EPh)₂[Fe(CO)₃], respectively. A trimethylphosphane–iridium analogue, Cp*Ir(PMe₃)(μ-SeMe)₂[Cr(CO)₄], was also obtained. The new heterodimetallic complexes were characterized by IR and NMR spectroscopy, and the molecular geometry of Cp*Ir(CO)(μ-SePh)₂[Mo(CO)₄] has been determined by a single crystal X-ray structure analysis. According to the long Ir…Mo distance (395.3(1) Å), direct metal–metal interactions appear to be absent.