Mo Angle Research Articles

Realizing isotropic negative thermal expansion covering room temperature by breaking the superstructure of ZrV2O7

ZrV2O7 is a well-known isotropic negative thermal expansion (NTE) material. However, the NTE property of ZrV2O7 can only be observed in high temperatures above 375 K. In this paper, we report a facile method to break the superstructure of ZrV2O7 for realizing the NTE property of ZrV2O7 to room temperature by partial substitution of Mo for V atoms. The detailed structure information and the phase transition process are revealed by high-resolution synchrotron x-ray diffraction, neutron powder diffraction, and high pressure Raman spectral analyses. It is found that the incorporation of Mo prompts the V-O2-V/Mo angles to expand from 160° to 180°, which enables the NTE property at room temperature. Different from most open framework structures where NTE is dominated by low energy phonons, here several high energy phonon modes are found to have negative Grüneisen parameters and contribute to the negative thermal expansion.

Effects of doping Fe cations on crystal structure and thermal expansion property of Yb2Mo3O12

Crystal structures and thermal expansion properties of Yb2−xFexMo3O12 (x=0.0, 0.6, 1.0, 1.1, 1.4) solid solutions have been studied by X-ray powder diffraction (XRPD) at different temperatures. Rietveld analysis of the XRPD data shows that Yb2−xFexMo3O12 solid solutions adopt orthorhombic structure and have variable thermal expansion coefficients controlled by the ratio of Yb3+ to Fe3+. Yb2Mo3O12 shows anisotropic negative thermal expansion property, induced by the reductions in average Yb–O–Mo angle and average apparent Mo2–O bond length with increasing temperatures. As more Yb3+ substituted by Fe3+, the linear thermal expansion coefficients of Yb2−xFexMo3O12 increase from negative to positive. A near-zero thermal expansion coefficient of 0.55×10−6K−1 for Yb0.6Fe1.4Mo3O12 is observed in the temperature range of 573–873K

Chemistry-Controlled Structural Relaxation and Enhanced Redox Abilities in Vanadium-Doped Two-Dimensional Semiconductive TeMo5O16 Catalyst

Structure relaxation of monoclinic TeMo5O16 catalyst that exhibits two-dimensional semiconductive character has been controlled by ultralow doping content of vanadium. Its roles in changing the redox abilities of the catalysts are first studied via experimental and theoretical methods. Strong O−Mo···O bond alteration occurs along the b direction both in bulk and on the surface. Meanwhile, the Mo−Mo distances and Mo−O−Mo angles are continuously changed as the degree of structural relaxation increases. As a result, the electron coupling and oxygen covalent bonding are remarkably weakened in the Mo4O18 unit. The redistribution of Mo 4d electrons in the Mo4O18 unit forms the (Mo5+−O−Mo5+)/(Mo6+−O−Mo6+) redox sites as electron donor−acceptor and oxygen reservior. The presence of such redox sites is proved to sharply enhance the redox abilities of the catalysts by surface probe reactions.

High-pressure Raman scattering and x-ray diffraction of phase transitions in MoO3

The high-pressure behavior of molybdenum trioxides (MoO3) has been investigated by angle-dispersive synchrotron x-ray powder diffraction and Raman spectroscopy techniques in a diamond anvil cell up to 43 and 30 GPa, respectively. In the pressure range of up to 43 GPa, structural phase transitions from the orthorhombic α-MoO3 phase (Pbnm) to the monoclinic MoO3-II phase (P21/m), and then to the monoclinic MoO3-III phase (P21/c), occurred at pressures of about 12 and 25 GPa at room temperature, respectively. Our observation of the transition from the orthorhombic α-MoO3 to the monoclinic MoO3-II phase is in disagreement with earlier studies in which the phase transition could not be obtained when only pressure is applied. The changes in the Mo–O distances and O–Mo–O and Mo–O–Mo angles may explain the changes in Raman spectrum. The pressure dependence of the volume of two monoclinic high-pressure phases is described by a third-order Birch–Murnaghan equation of state, which yields a bulk modulus value of B0=143.41(3) GPa with B0′=12, and B0=261.9(3) GPa with B0′=3.5.

Bis(η7-cycloheptatrienyl)tri-μ-hydrido-dimolybdenum(0,I)

In the title compound, [Mo2(η7-C7H7)2(μ-H)3], which displays crystallographic mirror symmetry, two (η7-C7H7)Mo units are linked along the Mo—Mo axis by three bridging hydride ligands. The Mo—Mo distance is 2.5732 (4) Å. The perpendicular distances of the Mo atoms from the C7 planes are 1.5827 (8) and 1.5814 (8) Å, with individual Mo—C bond lengths in the range 2.261 (2)–2.2789 (14) Å. Mo—H distances range from 1.77 (3) to 1.85 (4) Å, with Mo—H—Mo angles of 89 (2) and 92 (1)°.

Tris(tetramethylammonium) tetra-μ2-sulfido-tetrasulfidocopper(I)dimolybdenum(VI)N,N-dimethylformamide solvate

The title compound, (C4H12N)3[CuMo2S8]·C3H7NO, was obtained from the self-assembly of tetra­thio­molybdate, tetra­methyl­ammonium nitrate and cuprous sulfide in dimethyl­formamide (DMF). The asymmetric unit contains three (NMe4)+ cations, one [Mo2S8Cu]3− anion and one DMF solvent mol­ecule, and no obvious inter­actions are observed between these species. The trinuclear anion can be viewed as fused [MoS4Cu]− units sharing a copper center. The geometric parameters of the trivalent anion are comparable to those reported for other related salts including isomorphous anions, namely (NEt4)2(PPh4)[Mo2S8Cu] (a) and (Ph3P=N=PPh3)2(NEt4)[W2S8Cu]·2CH3CN (b). However, the Mo—Cu—Mo angle is found to be 160.24 (3)° for the title salt, while this angle is 162.97 (2)° in (a) and the W—Cu—W angle is 170.3 (2)° in (b), indicating that the largest deviation from linearity is in the title compound.

Desoxo Molybdenum(IV) and Tungsten(IV) Bis(dithiolene) Complexes: Monomer−Dimer Interconversion Involving Reversible Thiol Bridge Formation

Two series of thiol-bridged dimeric desoxo molybdenum(IV) and tungsten(IV) bis(dithiolene) complexes, [Et(4)N](2)[M(IV)(2)(SR)(2)(mnt)(4)] [M = Mo, R = (1) -Ph, (2) -CH(2)Ph, (3) -CH(2)CH(3), (4) -CH(2)CH(2)OH; M = W, R = (1a) -Ph, (2a) -CH(2)Ph, (3a) -CH(2)CH(3), (4a) -CH(2)CH(2)OH] and one monomeric desoxo complex, [Et(4)N](2)[WIV(SPh)(2)(mnt)(2)] (5a) are reported. These complexes are diamagnetic, and crystal structures of each of the complex (except 5a) exhibits a dimeric {M(IV)(2)(SR)(2)} core without any metal-metal bond where each metal atom possesses hexa coordination. The M-SR distance ranges from 2.437 to 2.484 Angstrom in molybdenum complexes and from 2.418 to 2.469 Angstrom in tungsten complexes. These complexes display Mo-S(R)-Mo angles ranging from 92.84 degrees to 96.20 degrees in the case of 1-4 and W-S(R)-W angles ranging from 91.20 degrees to 96.25 degrees in the case of 1a-4a. Interestingly, both the series of Mo(IV) and W(IV) dimeric complexes respond to an unprecedented interconversion between the dimer and the corresponding hexacoordinated monomer upon change of pH. This pH-dependent interconversion establishes the fact that even the pentacoordinated Mo(IV) and W(IV) bis(dithiolene) moieties are forced to dimerize; these can easily be reverted back to the corresponding monomeric complex, reflecting the utility of dithiolene ligand in stabilizing the Mo(IV)/W(IV) moiety in synthesized complexes similar to the active sites present in native proteins.

Synthesis and Characterization of the Oxynitride Y2Mo2O4.5N2.5 Pyrochlore: A Neutron Diffraction and Magnetic Study

Abstract A new molybdenum oxynitride Y2Mo2O4.5N2.5 with cubic pyrochlore structure (a = 10.3350(2) Å, space group Fd3̅m, Z =8) has been synthesized by heating the parent Y2Mo2O7 oxide in flowing ammonia at 898 K. The polycrystalline sample has been characterized by thermal analysis, X-ray and neutron diffraction (NPD), and magnetic susceptibility measurements. The analysis of high resolution NPD data, based on the contrast existing between the scattering lengths of O and N, shows that both atoms are distributed at random at the anion substructure; the refined crystallographic formula implies an oxidation state of +5.25 for Mo cations. The thermogravimetric curve shows a weight gain of 7.5% at 1000 K in air, corresponding to the complete elimination of N2 and oxidation to Mo(VI) oxide, in good agreement with the proposed composition. The magnetic susceptibility exhibits a Pauli-like, temperature-independent term which derives from the partial delocalization of Mo electrons on Mo-(O,N) bands with a broader bandwidth, as a consequence of the significant opening of the Mo-(O,N)-Mo angle and strengthening of the Mo-(O,N) interactions with respect to the parent Y2Mo2O7 oxide. As in this oxide, a reminiscent spin-glass behaviour is observed at low temperature.

Chiral open-framework uranyl molybdates. 2. Flexibility of the U:Mo = 6:7 frameworks: syntheses and crystal structures of (UO 2) 0.82[C 8H 20N] 0.36[(UO 2) 6(MoO 4) 7(H 2O) 2](H 2O) n and [C 6H 14N 2][(UO 2) 6(MoO 4) 7(H 2O) 2](H 2O) m

Two new chiral open-framework uranyl molybdates, (UO 2) 0.82[C 8H 20N] 0.36[(UO 2) 6(MoO 4) 7(H 2O) 2](H 2O) n ( 1) and [C 6H 14N 2][(UO 2) 6(MoO 4) 7(H 2O) 2](H 2O) m ( 2) have been synthesized by hydrothermal methods. The structures of 1 and 2 have been refined using X-ray diffraction data collected at −127 °C. The structure of 1 [orthorhombic, C222 1, a = 12.2303(15), b = 18.966(2), c = 22.392(3) Å, V = 5194.0(11) Å 3] has been refined to R 1 = 0.043 on the basis of 4126 unique observed reflections. The structure of 2 [orthorhombic, C222 1, a = 11.3256(15), b = 19.860(3), c = 23.731(3) Å, V = 5337.8(12) Å 3] has been refined to R 1 = 0.056 on the basis of 3519 unique observed reflections. The structures of 1 and 2 are based upon complex chiral [(UO 2) 6(MoO 4) 7(H 2O) 2] frameworks of corner-sharing UO 7 bipyramids and MoO 4 tetrahedra. In addition to framework U sites, the structure of 1 contains an additional, partially-occupied and disordered U(4) site, located within the framework cavities and coordinated by several disordered anions to form the complex [(UO 2)(H 2O) 5] 2+ cation. The structure of 2 contains disordered DABCO (1,4-diazabicyclo[2.2.2]-octane) molecules. The geometrical parameters of the uranyl molybdate frameworks in the structures of 1 and 2 are significantly different. The a parameter of 1 is about 0.9 Å longer than that of 2, whereas the b and c parameters of 1 are shorter than those of 2 (∼0.9 and 1.3 Å, respectively). This occurs due to the adaptation of the [(UO 2) 6(MoO 4) 7(H 2O) 2] 2− framework to the shape of the complex [(UO 2)(H 2O) 5] 2+ cation in 1. Analysis of the U–O–Mo bond angles of the frameworks indicates the U–O(15)–Mo and U–O(20)–Mo links are the most flexible. The transition from 2 to 1 involves an increase of the U–O(15)–Mo and U–O(20)–Mo angles from 146.7° to 169.0° and from 151° to 171°, respectively.

Pentacarbonyl[diphenyl(perfluorovinyl)phosphine]molybdenum(0)

In the title compound, [Mo{(C2F3)PPh2}(CO)5], the Mo atom occupies the center of a slightly distorted octahedral environment, bound to five carbonyl groups and one phosphine ligand, so that the local symmetry of the Mo(CO)4P portion of the mol­ecule is approximately C4v. The P atom sits in a distorted-tetrahedral environment; the C—P—Mo angles are much larger than the C—P—C angles. The C2F3 group is rotationally disordered by ∼180°.

Crystal structure and magnetic properties of the double perovskite (Sr 2− xCa x)FeMoO 6 (0⩽ x⩽1.0)

We have investigated the crystal structure and magnetic properties of the new series of ordered double perovskite oxides (Sr 2− x Ca x )FeMoO 6 (0⩽ x⩽1.0). A monotonous decrease of the lattice constants ( a and c) has been found with increasing x. Such an effect may also give rise to a distorted structure with Fe–O–Mo angle changing from 180° for x=0 to 162° for x=1.0. The magnetization increases from x=0 to 0.5 and then slightly decreases from x=0.5 to 1.0. Such complex magnetic behavior is strongly correlated to the chemical size effect (corresponding to the internal pressure) in the title compounds.

A molecule based on polyoxometalate acid and crown ether: synthesis and characterization of [(H 3O)(C 20H 24O 6)] 2[HPMo 12O 40]·C 20H 24O 6·3MeCN·H 2O (C 20H 24O 6=dibenzo-18-crown-6)

The new molecule based on 12-molybdophosphate acid and dibenzo-18-crown-6, [(H 3O)(C 20H 24O 6)] 2[HPMo 12O 40]·C 20H 24O 6·3MeCN·H 2O 1, was synthesized in acetonitrile and characterized by elemental analyses, IR, 1H NMR, electrospray mass spectra and single crystal X-ray diffraction, indicating that it contains [(H 3O)(dibenzo-18-crown-6)] + cations, where oxonium ions are out of the planes defined by crown ether oxygen atoms, and disordered PMo 12O 40 3− anions with α-Keggin structure where the crystal has high lattice energy so that it is difficult to dissolve it. The crystallographic disorder averages Mo–Mo distances and Mo–O b/ c –Mo angles between the M 3 triplets and within the M 3 triplet. The interactions between crown ether molecules and oxonium ions are hydrogen-bonding with the O(crown ether)–OH 3 + distances of 2.510(10)–2.783(7) Å. The interactions between [(H 3O)(dibenzo-18-crown-6)] + cations and PMo 12O 40 3− anions are dominantly electrostatic. The electrical conductivity is <10 −7 S.cm −1.

Stereochemistry and electrochemical properties of molybdenum ions incorporated into S-bridged polynuclear structures

The reactions of fac(S)-[M(aet)3] (M = IrIII or RhIII; aet = 2-aminoethanethiolate) with [NH4]2[MoCl5(H2O)] in both anaerobic and aerobic atmospheres gave linear-type S-bridged trinuclear complexes, [MoIV{Ir(aet)3}2]4+1 and [MoIII{Rh(aet)3}2]3+2. Complex 2 was spontaneously oxidized by exposure to air and converted into a novel S-bridged pentanuclear complex, [MoV2O2(μ-O){Rh(aet)3}3]4+3, and the structural change from 2 to 3 was monitored by UV-vis spectroscopy. The crystal structures of 1Br4·4H2O, 2Br3·H2O, and 3Br4·6H2O were determined by X-ray diffraction. In the complex cations 1 and 2, Mo4+ and Mo3+ ions are co-ordinated by the six thiolato sulfur atoms from two fac(S)-[M(aet)3] units and relatively short metal–metal distances (2.7469(7) and 2.860(3) Å) are observed, respectively. In 3 the Mo–O–Mo angle (157.0(4)°) in the Mo2O2(μ-O)4+ core is unique and the core is co-ordinated by the eight thiolato sulfur atoms of three fac(S)-[Rh(aet)3] units. The cyclic voltammograms for 1 and 2 indicate that the oxidation states of the molybdenum ions, which are incorporated into the S-bridged polynuclear structures, and stability of the complexes, depend upon the metal ions in the terminal building blocks, fac(S)-[M(aet)3]. The absorption spectrum of each complex exhibited characteristic intense bands in the visible region, which relate to the molybdenum ions.

Synthesis and Characterisation of a Dioxo-μ-Oxo Molybdenum Dimer: An Unusual case of a μ-Oxo Conformational Equilibrium

A new thiocyanatomolybdenum(VI) dioxo-μ-oxo complex dimer bearing a 4,4′-di-tert-butyl-2,2′-bipyridine ligand (2) is shown to exist in the crystal cell unit as a meso (Mo-O–Mo angle of 180°) and d,l, pair (Mo–O–Mo angle of 155.7°). These conformers are in equilibrium in solution and have been observed clearly by 1H NMR spectroscopy.

A Hetero-Tribridged Dinuclear Molybdenum Compound [Bu4N][Mo2(CO)6(p-Cl-C6H4S)2Br

The title compound, tetra-n-butylammonium μ-bromo-bis(μ-p-chlorobenzenethiolato)bis(tricarbonylmolybdenum)(Mo—Mo), (C16H36N)[Mo2Br(C6H4ClS)2(CO)6], contains a Bu4N+ cation and a [Mo2(CO)6(p-Cl-C6H4S)2Br]− anion. The structure of the anion can be viewed as a cofacial bioctahedral dimer, in which two fac-Mo(CO)3 fragments are bridged by two p-Cl—C6H4S− groups and one Br− ligand. The mean Mo—Br distance is 2.765 (2) Å and the Mo—Br—Mo angle is 62.68 (4)°.

Crystal structure of tetraethylammonium bis(tetracarbonylmolybdenum)-tetrathiotungstate, [Et 4N] 2[(OC) 4MoS 2WS 2Mo(CO) 4] and synthesis, infrared spectra, 95 Mo NMR spectra and cyclic voltammetry of new linear trinuclear Mo(W)–S carbonyl clusters containing mixed-valence metal atoms [(OC) 4MS 2M′SM(CO) 4] 2− (M, M′=Mo or W)

Four trinuclear molybdenum(tungsten)-sulfur carbonyl cluster compounds, [Et 4N] 2[(OC) 4Mo-S 2MoS 2Mo(CO) 4] (1), [Et 4N] 2[(OC) 4WS 2WS 2W(CO) 4] (2), [Et 4N] 2[(OC) 4MoS 2WS 2Mo(CO) 4] (3), [Et 4N] 2[(OC) 4WS 2MoS 2W(CO) 4] (4) have been prepared by both reaction of [M(CO) 4(S 2CNEt 2)] − with M′S 4 2− in MeOH and reaction of MeCN solution of M(CO) 6 with M′S 4 2− in MeOH (M=Mo, W; M′=Mo, W). These complexes has been characterized by routine elemental analysis and spectroscopy and the structures of 1 and 3 have been determined by X-ray crystallography. The structure study reveals that the anion of 3 contains a heteronuclear Mo–W–S trimetallic core, [MoS 2WS 2Mo] 2−, consisting of two perpendicular rhombic MoS 2W units sharing a tungsten atom. The Mo–W bond distances are 3.028(2) and 3.031(2) Å and the Mo–W–Mo angle is 176.04(5)°. The average bond lengths of W–S and Mo–S are 2.21 and 2.54 Å, respectively. The X-ray, structure, IR, CV (cyclic voltammetry) and 95 Mo NMR studies on these four cluster complexes indicated that these cluster complexes possess wide separated oxidation states of metal atoms and exhibit the charge transfer, M L→M HS 4 (M L represents a low-valance metal atom and M H a high valence metal atom), between the two different valence metallic centers in the cluster complexes. It has been found that the charge transfer, M L→M HS 4, in the complexes are: 1>4, 3>2, 1>3, 4>2, 1>2 and 3∼4 implying the electron-donation ability of low-valence metal atoms in the complexes is Mo 0>W 0 and the electron-accepted ability of the high valence metal atoms in the complexes is Mo VI>W VI.

A Triangular [Mo3S7]4+Complex: Tris(diethyldithiocarbamato-S,S')tris(μ2-η2-disulfido)(μ3-sulfido)trimolybdenum(IV)(3Mo—Mo)Diethyldithiocarbamate

In the cluster cation of the title compound, [Mo3S7(Et2NCS2)3](Et2NCS2), three Mo atoms form an approximately equilateral triangle, with Mo–Mo distances ranging from 2.7140 (5) to 2.7277 (5) Å, and Mo—Mo—Mo angles of ca 60°. The triangle is capped by the μ3—S atom, and each Mo—Mo bond is bridged by a disulfido group in μ2-η2 mode. Diethyldithiocarbamate ligands (Et2dtc) are chelated to the Mo atoms with an average S—Mo—S bite angle of 69.98 (1)°. There is a weak S⋯S interaction between the cluster cation and the anion (Et2dtc−).

Substitution of chloride in [PtCl 2(PET 3) 2] by the chiral anionic ligand [Mo(CO) 5(PPhH)] − to give mixed platinum-molybdenum compounds and a 31P∗ 1H∗ NMR analysis of their fluxionality. X-ray crystal structure of [PtCl(PEt 3) 2 (μ-PPhH) ∗Mo(CO) 5∗] and trans-[Pt(PEt 3) 2 (μ-PPH) 2 ∗Mo(CO) 5∗ 2

Deprotonation of the primary phosphine complex [Mo(CO) 5(PPhH 2)] generated [Mo(CO) 5(PPhH)] −, a chiral anionic ligand which reacted readily with cis- or trans-[PtCl 2(PEt 3) 2] via facile nucleophilic substitution of one or both chloride ligands to afford trans-[PtCl(PEt 3) 2(μ-PPhH)∗Mo(CO) 5∗] ( 1) and cis- and trans-[Pt(PEt 3) 2(μ-PPhH) 2∗Mo(CO) 5∗ 2] ( 2), respectively. These are rare examples of heterometallic complexes containing primary phosphido bridges. Compound ( 1) can be described either as the square-planar Pt 11 complex with the anionic ligand PPhH∗Mo(CO) 5∗ − or as the PtMo phosphido-bridged dimer trans-[PtCl(PEt 3) 2(μ-PPhH)∗Mo(CO) 5∗]. As a phosphido-bridged heterobimetallic ( 1) possesses an exceptionally large PtPMo angle [120.9(1) °] reflecting the long PtMo nonbonding interaction (4.5 Å). Compound 2 can correspondingly be described either as a phosphido-bridged PtMo 2 trimer or a square-planar arrangement of two neutral PEt 3 and two anionic PPhH∗Mo(CO) 5∗ ligands at Pt. The low-temperature 31P∗ 1H∗ NMR spectrum of 1 showed several ABXY spin systems together with their associated ABXYM ( M = 195 Pt ) counterparts and variable-temperature studies revealed the dynamic interconversion of several rotametric isomers arising from restricted rotation about the PtPμ bond. The 31P∗ 1H∗ NMR spectrum of trans- 2 shows its two possible RR/SS and meso diastereoisomers, the latter existing in clearly identifiable rotameric forms which interconvert slowly at −75°C. We note very different values between 2J( P P) and 1J( 195 Pt P) for the anionic ligands [PPhH∗Mo(CO) 5∗] − and PEt 3, unattributable to bond length variation but which must reflect reduced s-orbital contribution to the PtP bond of the anionic phosphines PPhH∗Mo(CO) 5∗.

Molybdenum(VI) complex with citric acid: synthesis and structural characterization of 1:1 ratio citrato molybdate K 2Na 4[(MoO 2) 2(cit) 2]·5H 2O

Sodium potassium citrato molybdate K 2Na 4[(MoO 2) 2O(cit) 2]·5H 2O has been prepared by the reaction of potassium trihydrogen citrate and sodium molybdate. Analysis of the crystal structure reveals that the anion of the complex contains a bent (MoO 2)O(MoO 2) core with an MoOMo angle 142°. Each molybdenum has a distorted octahedral coordination and citrato ligands are tridentate to the two molybdenum atoms via the deprotonated hydroxy-, α- and β-carboxyl groups. Principal dimensions are: [MoO(t)] av, 1.706(4); [MoO(b)] av, 1.899(3); [MoO(hydroxy)] av, 1.944(3); [Mo Oα-carboxyl)] av, 2.207(3), and [MoO(β-carboxyl)] av, 2.264(3) Å. The IR, 1H and 13C NMR spectra are in agreement with this structure.

Synthesis and molecular structures of di- and trinuclear molybdenum complexes containing pyridine-2-thiolato (pyS) ligand

Dinuclear complexes [Mo 2(μ-pyS) 2(CO) 4(PPh 3) 2], [Mo 2(μ-pyS) 2(CO) 5(PPh 3)] ( 2) and a trace quality of trinuclear complex [Mo 3( μ-pyS) 3( μ 3-pyS) 2(CO) 6] ( 3) were obtained from the reaction of [Mo(CO) 3(MeCN) 3] with pyridine-2-thione (pySH) and PPh 3 in THF. The crystal structures of 1 · 2C 7H 8 and 3 · C 7H 8 have been determined by X-ray diffraction studies. Crystals of 1 · 2C 7H 8 are monoclinic, space group C2 c and Z = 4, with a = 18.797(3), b = 11.143(4), c = 28.157(7) A ̊ , β = 101.23(2)° . The structure was refined to R = 0.050 and Rw = 0.057 for 3146 observed reflections. Crystals of 3 · C 7H 8 are monoclinic, space group P2 a and Z = 4, with a = 13.912(2), b = 17.161(2), c = 15.577(3) A ̊ , β = 101.17(1)° . The structure was refined to R = 0.046 and Rw = 0.051 for 4357 observed reflections. The molecule of 1 consists of two Mo(CO) 2(PPh 3) fragments linked by an MoMo (2.974(2) Å0 and by two doubly-bridging pyS ligands. The compound 3 contains a bent open geometry of three molybdenum atoms (Mo(1)Mo(2)Mo(3) angle 122.99(3)°) linked by two MoMo bonds (2.943(1) and 2.950(1) Å) and by two doubly- and two triply-bridging pyS ligands.