Bioctahedral Complexes Research Articles

Crystal structure and magnetic properties of a Cs3Nb2I9 bioctahedral complex

A cluster complex Cs3Nb2I9 is obtained by a high-temperature reaction of niobium, iodine, and cesium iodide. Its crystal structure is determined: trigonal space group P63/mmc, a = 8.2463(3) A, c = 19.5419(14) A, V = 1150.84(10) A3, R(F) = 0.0614. The compound obtained is characterized by temperature independent paramagnetism in the temperature range 70–290 K.

Theoretical Study of the Pseudo-Jahn−Teller Effect in the Edge-Sharing Bioctahedral Complex Mo2(DXylF)2(O2CCH3)2(μ2-O)2

A study of the D(2h) to C(2h) pseudo-Jahn-Teller distortion in the edge-sharing bioctahedral complex Mo(2)(DXylF)(2)(O(2)CCH(3))(2)(mu(2)-O)(2) is presented. We have performed extensive density functional theory (DFT) and complete active space self-consistent field (CASSCF) calculations. For both the full target complex and a model derived by replacing xylyl and methyl groups with hydrogens we observe that the central Mo(2)(mu(2)-O)(2) motif displays C(2h) rather than D(2h) symmetry. Analytical CASSCF frequency calculations prove that the rhomboidal distortion of the complex from D(2h) to C(2h) is due to a vibronic mixing of the ground electronic state and a low-lying pidelta* excited state.

Chemistry of Unsaturated Group 6 Metal Complexes with Bridging Hydroxy and Methoxycarbyne Ligands. 1. Synthesis, Structure, and Bonding of 30-Electron Complexes

The new cationic alkoxy and hydroxycarbyne complexes [M2Cp2(μ-COR)(μ-PR‘2)2]BF4 (Cp = η5-C5H5; M = W, R = Me, R‘ = Ph; M = Mo, R = Me and H, R‘ = Et) and [Mo2Cp2(μ-COR)(μ-COR‘)(μ-PCy2)]BF4 (R = Me; R‘ = H, Me, Et) are obtained in high yield by the reaction of the corresponding neutral monocarbonyl precursors with either [Me3O]BF4 or HBF4·OEt2 in dichloromethane. While the methoxycarbyne complexes are stable at room temperature, the analogous hydroxycarbyne species are thermally unstable, and above ca. 253 K they experience a hydrogen migration from oxygen to metal, to give the new hydride carbonyl complexes [Mo2Cp2(H)(μ-PEt2)2(CO)]BF4 and [Mo2Cp2(H)(μ-COMe)(μ-PCy2)(CO)]BF4 as major products. The electronic structure and bonding in some of these face-sharing bioctahedral complexes were studied by means of density functional theory. These calculations allow us to describe the intermetallic interaction present in the carbonyl-bridged 30-electron complexes by a configuration of type σ2δ4, with the δ orbitals being involved in π back-bonding to the carbonyl bridges. Upon methylation of the latter ligands, these δ-bonding orbitals become more delocalized over the Mo2C(carbyne) triangle and constitute the π-bonding component of the metal−carbyne bond. Therefore, a partial reduction of the direct metal−metal overlap occurs upon formation of these methoxycarbyne complexes, which still retain some multiplicity in the corresponding C−O bonds. The topological analysis of the electron density under the AIM scheme supports the above description of the Mo−Mo, Mo−C, and C−O bonds in these complexes.

Mono-, di-, and tri-ruthenium complexes with the ligand 2,2′-dipyridylamide (dpa): insights into the formation of extended metal atom chains

Reactions between Hdpa (2,2′-dipyridylamine) and either RuCl3·xH2O and Ru2(OAc)4Cl produce mono-, di-, and tri-ruthenium complexes under various conditions. The ligand Hdpa and RuCl3·xH2O react in boiling DMF to form the ionic species [Ru(Hdpa)2Cl2]Cl (1). Reaction of Ru2(OAc)4Cl with molten Hdpa leads to scission of the Ru–Ru bond and formation of the vertex-sharing bioctahedral complex Ru2(dpa)3(OAc)0.64Cl1.36 (2). A mixture of both of these species results from the reaction of Ru2(OAc)4Cl with Hdpa and LiCl in refluxing o-dichlorobenzene/EtOH mixtures. This mixture of compounds reacts further with KOBut and n-butanol in refluxing naphthalene to give low yields of the extended metal atom chain (EMAC) complex Ru3(dpa)4Cl2 (I).

An Asymmetric Edge-Sharing Bioctahedral Complex: ( 2-DAniF)MoIII( -DAniF)2( -O,Cl)MoVCl2(DAniF=N,N′-di-p-anisylformamidinate)

A novel asymmetric, edge-sharing bioctahedral complex with formamidinato ligands (η 2-DAniF)Mo(μ-DAniF)2(μ-O,Cl)MoCl2, 1, (DAniF=N,N′-di-p-anisylformamidinate) has been isolated as a byproduct from the preparation of the dimolybdenum(II,III) compound Mo2(DAniF)3Cl2. An X-ray crystallographic study shows that the structure consists of edge-sharing bioctahedra, with the shared edge defined by the vector joining the: μ-O and μ-Cl ligands. Compound 1 is best formulated as a mixed-valent MoIII→MoV compound, the Mo(V) ion being that with the two terminal Cl− ligands. The cyclic voltammogram of 1 shows a reversible reduction at −0.472 V and a reversible oxidation at 1.028 V vs. the Ag/AgCl reference electrode, while the absorption spectrum of 1 reveals an intense low energy absorption at 523 nm (∈ max=12 500) which is attributed to an intervalence charge transfer transition. Crystallographic data for 1 are as follows: a=13.387(1) A, b=15.500(2) A, c=21.855(2) A, β=98.786(2)°, V=4481.8(8) A3, P21/c, R1 (wR2)=0.082 (0.177).

Preparation and crystal structures of dirhenium face-sharing bioctahedral complexes Re 2(μ-SR) 3X 4(PR 3) 2, R=methyl, ethyl or phenyl, and X=Cl or Br

The reactions of Re 2Cl 4(PEt 2Ph) 4, Et=ethyl and Ph=phenyl, with excess methyl disulfide (MeSSMe) and phenyl disulfide (PhSSPh) produce the compounds Re 2(μ-SMe) 3Cl 4(PEt 2Ph) 2 ( 1) and Re 2(μ-SPh) 3Cl 4(PEt 2Ph) 2·acetone ( 2), respectively. Similarly, Re 2Cl 5(PMePh 2) 3 reacts with PhSSPh to yield Re 2(μ-SPh) 3Cl 4(PMePh 2) 2 ( 3) and Re 2Br 4(PEt 2Ph) 4 reacts with either EtSSEt or PhSSPh to produce either Re 2(μ-SEt) 3Br 4(PEt 2Ph) 2 ( 4) or Re 2(μ-SPh) 3Cl 4(PEt 2Ph) 2 ( 5). All of these new Re 2 7+ complexes display one-electron paramagnetism. X-ray crystallographic studies of compounds 1– 4 reveal a common face-sharing bioctahedral structure with three bridging thiolate ligands. The ReRe bond distances (averaging 2.473 Å) are indicative of multiple metal–metal bonds. Compound 1 may also be prepared in low yield by the reaction of Re 2Cl 4(PEt 2Ph) 4 with 2,5-dithiahexane or the reaction of ( n-Bu 4N) 2Re 2Cl 8 with a mixture of MeSSMe and PEt 2Ph.

Cl(3)V(mu-S(CH(3))(2))(3)VCl(3)(2)(-): a first-row, face-shared bioctahedral complex with multiple metal-metal bonding.

Density functional theory calculations have been used to investigate the structure and bonding of the d(3)d(3) bioctahedral complexes X(3)V(mu-S(CH(3))(2))(3)VX(3)(2)(-) (X = F(-), Cl(-), OH(-), SH(-), NH(2)(-)). According to geometry optimizations using the broken-symmetry approach and the VWN+B-LYP combination of density functionals, the halide-terminated complexes have a V-V bond order of approximately 2, while complexes featuring OH(-), SH(-), or NH(2)(-) as terminal ligands exhibit full triple bonding between the vanadium atoms. The tendency toward triple bonding in the latter complexes is consistent with an increased covalency of the vanadium-ligand bonds, and the influence of bond covalency is apparent also in the tendency for V-V bond elongation in the complexes with OH(-) and NH(2)(-) terminal ligands. Detailed examination of the composition of molecular orbitals in all of the thioether-bridged V(II) complexes substantiates the conclusion that the strong antiferromagnetic coupling which we have determined for these complexes (-J > 250 cm(-)(1)) is due to direct bonding between metal atoms rather than superexchange through the bridging ligands. As such, these V(II) complexes comprise the first apparent examples of multiple metal-metal bonding in first-transition-row, face-shared dinuclear complexes and are therefore of considerable structural and synthetic interest.

Factors affecting metal-metal bonding in the face-shared d(3)d(3) bioctahedral dimer systems, MM'Cl(9)(5-) (M, M' = V, Nb, Ta).

Density functional theory (DFT) calculations have been used to investigate the d(3)d(3) bioctahedral complexes, MM'Cl(9)(5-), of the vanadium triad. Broken-symmetry calculations upon these species indicate that the V-containing complexes have optimized metal-metal separations of 3.4-3.5 A, corresponding to essentially localized magnetic electrons. The metal-metal separations in these weakly coupled dimers are elongated as a consequence of Coulombic repulsion, which profoundly influences (and destabilizes) the gas-phase structures for such dimers; nevertheless, the intermetallic interactions in the V-containing dimers involve significantly greater metal-metal bonding character than in the analogous Cr-containing dimers. These observations all show good agreement with existing experimental (solid state) results for the chloride-bridged, face-shared dimers V(2)Cl(9)(5-) and V(2)Cl(3)(thf)(6)(+). In contrast to the V-containing dimers, complexes featuring only Nb and Ta have much shorter intermetallic distances (approximately 2.4 A) consistent with d-electron delocalization and formal metal-metal triple bond formation; again, good agreement is found with available experimental data. Calculations on the complexes V(2)(mu-Cl)(3)(dme)(6)(+), Nb(2)(mu-dms)(3)Cl(6)(2-), and Ta(2)(mu-dms)(3)Cl(6)(2-), which are closely related to compounds for which crystallographic structural data exist, have been pursued and provide an insight into the intermetallic interactions in the experimentally characterized complexes. Analysis of the contributions from d-orbital overlap (E(ovlp)) stabilization, as well as spin polarization (exchange) stabilization of localized d electrons (E(spe)), has also been attempted for the MM'Cl(9)(5-) dimers. While E(ovlp) clearly dominates over E(spe) as a stabilizing factor in those dimers containing only Nb and Ta metal atoms, detailed assessment of the competition between E(ovlp) and E(spe) for V-containing dimers is obstructed by the instability of triply bonded V-containing dimers against Coulombic explosion. On the basis of the periodic trends in E(ovlp) versus E(spe), the V-triad dimers have a greater propensity for metal-metal bonding than do their Cr-triad or Mn-triad counterparts.

Carboxylate and alkyl carbonate coordination at the hydrophobic binding site of redox-active dicobalt amine thiophenolate complexes.

A series of new dicobalt complexes of the permethylated macrocyclic hexaamine dithiophenolate ligand H(2)L(Me) have been prepared and investigated in the context of ligand binding and oxidation state changes. The octadentate ligand is an effective dinucleating ligand that supports the formation of bioctahedral complexes with a central N(3)Co(mu-SR)(2)(mu-X)CoN(3) core structure, leaving a free bridging position X for the coordination of the substrates. The acetato- and cinnamato-bridged complexes [(L(Me))Co(II)(2)(mu-O(2)CMe)](+) (2) and [(L(Me))Co(II)(2)(mu-O(2)CCH=CHPh)](+) (5) were prepared by reaction of the mu-Cl complex [(L(Me))Co(II)(2)(mu-Cl)](+) (1) with the corresponding sodium carboxylates in methanol. The electrochemical properties of these and of the methyl carbonate complex [(L(Me))Co(II)(2)(mu-O(2)COMe)](+) (8) were also investigated. All complexes undergo two stepwise oxidations at ca. E(1)(1/2) = +0.22 and at E(2)(1/2) = ca. +0.60 V vs SCE, affording the mixed-valent complexes [(L(Me))Co(II)Co(III)(mu-O(2)CR)](2+) (3, 6, 9) and the fully oxidized Co(III)Co(III) forms [(L(Me))Co(III)(2)(mu-O(2)CR)](3+) (4, 7, 10), respectively. Compounds 3, 6, 9 and 4, 7, 10 refer to acetato-, cinnamato-, and methylcarbonato species, respectively. The Co(II)Co(III) compounds were prepared by comproportionation of the respective Co(II)(2) and Co(III)(2) compounds. The Co(III)Co(III) species were prepared by bromine oxidation of the Co(II)Co(II) forms. The crystal structures of complexes 2.BPh(4).MeCN, 3.(I(3))(2), 5.BPh(4).2MeCN, 6.(ClO(4))(2).EtOH, 7.(ClO(4))(3).MeCN.(H(2)O)(3), and 9.(ClO(4))(2).(MeOH)(2).H(2)O were determined by single-crystal X-ray crystallography at 210 K. The oxidations occur without gross structural changes of the parent complexes. The Co(II)Co(III) complexes are composed of high-spin Co(II) (d(7)) and low-spin Co(III) (d(6)) ions. The Co(III)Co(III) complexes are diamagnetic. The oxidation reactions affect the binding mode of the substrates. In the Co(II)(2) and Co(II)Co(III) forms the carboxylates bridge the two Co(2+) ions in a symmetric mu-1,3 fashion with uniform C-O bond distances, whereas asymmetric bridging modes, with one short C=O and one long C-O distance, are adopted in the fully oxidized species. This is consistent with the observed shifts in vibrational frequencies for nu(as)(C-O) and nu(s)(C-O) across the series.

Mutual interdependence of spin crossover and metal-metal bond formation in M2Cl9(3-) (M = Fe, Ru, Os).

Broken-symmetry density functional theory is used to examine the coupling between metal ions in the face-shared bioctahedral complexes M2Cl9(3-), M = Fe, Ru, Os. In the ruthenium and osmium systems, the metal ions have low-spin configurations, and strong coupling results in the formation of a metal-metal sigma bond. In contrast, the iron system contains two weakly coupled high-spin FeIII centers, the different behavior being due to the high spin-polarization energy in the smaller Fe atom. At Fe-Fe separations shorter than 2.4 A, however, an abrupt transition occurs and the ground state becomes very similar to that for the heavier congeners (i.e., strongly coupled low-spin FeIII). The intrinsic link between high-spin/low-spin transitions on the individual metal centers and the onset of metal-metal bond formation is traced to the spin-polarization energy, which plays a central role in both processes.

Metalmetal versus metalligand bonding in dimetal compounds with tridentate ligands

Reaction of a ‘VCl 2· nTHF’ solution, prepared by the reduction of VCl 3(THF) 3 with NaBEt 3H in THF, and Lidpa (dpa=the anion of 2,2′-dipyridylamine) in a mixture of THF/toluene at reflux temperature yields the bioctahedral V 2(dpa) 4·THF ( 1) compound. A similar reaction performed in THF at 0°C gave [V 2(dpa) 3(μ-Cl) 2Li 2(THF) 6][BEt 3H] ( 2), in which a dpa ligand adopts a novel ‘doubly-chelating/bridging’ coordination mode. Compound 2 reacts with CH 2Cl 2 giving V 2(dpa) 3Cl 2·2CH 2Cl 2 ( 3), a valence delocalized V(II)⋯V(III) bioctahedral complex. In all three complexes, the formation of four additional metalligand bonds is favored over the formation of a VV bond. The V⋯V separations are 3.038(2), 3.024(2) and 3.091(2) Å for 1– 3, respectively. Crystal data are: compound 1, space group P2/ n, a=13.102(2), b=9.294(2), c=16.510(4) Å, β=98.98(2)°, V=1985.7(6) Å 3 and Z=2; compound 2, space group I2/ a, a=19.4674(8), b=14.390(1), c=24.219(2) Å, β=92.954(7)°, V=6775.4(7) Å 3 and Z=2; compound 3, space group P2 1/ c, a=12.0853(8), b=18.679(2), c=16.709(2), β=109.98(1)°, V=3544.9(6) Å 3 and Z=4.

Oxidative scission of a Mo-Mo quadruple bond.

Two compounds containing the cations Mo2(DPhIP)4n+, n = 1 or 2 and DPhIP = the anion of 2,6-diphenyliminopiperidine, have been obtained by oxidation of the quadruply-bonded Mo2(DPhIP)4 species. The first oxidation process conserves the structure but results in a slight increase of the Mo-Mo distance from 2.114(1) to 2.136(2) A in [Mo2(DPhIP)4](PF6).2CH2Cl2 (1.2CH2Cl2). However, the second oxidation process breaks the dimolybdenum bond, giving a bioctahedral complex, [Mo2(DPhIP)4](BF4)2.5CH3CN.Et2O (2.5CH3CN.Et2O), with Mo...Mo separation of 2.9954(7) A. Crystallographic data for 1.2CH2Cl2 are space group C2/c, a = 17.1891(9) A, b = 17.807(1) A, c = 24.210(2) A, beta = 106.403(4) degrees, Z = 4; for 2.5CH3CN.Et2O, space group P2(1)/n, a = 16.523(5) A, b = 27.418(5) A, c = 18.163(3) A, beta = 93.48(2) degrees, Z = 4.

Involvement of multiply bonded dirhenium complexes in mixed-metal assemblies. Isolation and characterization of a new type of Re4Pd2 cluster.

The Re−Clt bond that is cis to the μ-CO unit in the edge-sharing bioctahedral complex Re2(μ-Cl)(μ-CO)(μ-dppE)2Cl3(CO) (1b; dppE = Ph2PC(CH2)PPh2) is labile toward substitution by anionic and neutral thiocyanate and cyanide containing metal fragments to afford mixed-metal Re4Pd2, Re2W, and Re2Pt assemblies. These products (3−5) retain the ReRe bond of the parent dirhenium(II) complex as demonstrated by the crystal structure of the Re4Pd2 cluster [Re2(μ-Cl)(μ-CO)(μ-dppE)2Cl2(CO)]2(μ-NCS)2[Pd2(μ-SCN)(μ-NCS)Cl2].

Preparation and Structure of Two Ditungsten Compounds Synthesized with the 3,5-Dichlorophenylformamidinate Ligand.

The structure, preparation, and spectroscopy of a W(2)(II, II) paddlewheel complex with four formamidinate ligands is reported. Upon exposure to air and moisture in solution, the W(2)(II, II) core undergoes an oxidative addition reaction to form a W(2)(III, III) edge-sharing bioctahedral (ESBO) complex with two bridging hydroxides. The products, W(2)(&mgr;-DCPF)(4) (1) and W(2)(&mgr;-OH)(2)(&mgr;-DCPF)(2)(eta(2)-DCPF)(2) (2) where DCPF is [(3,5-Cl(2)C(6)H(3))NC(H)N(3,5-Cl(2)C(6)H(3))(-)], were characterized by UV-vis and (1)H NMR spectroscopy. Structural data are presented for W(2)(&mgr;-DCPF)(4) with four bridging formamidinate ligands and W(2)(&mgr;-OH)(2)(&mgr;-DCPF)(2)(eta(2)-DCPF)(2) with the formamidinate ligands in both chelating and bridging positions. Crystallographic data for W(2)(&mgr;-DCPF)(4) (1) and W(2)(&mgr;-OH)(2)(&mgr;-DCPF)(2)(eta(2)-DCPF)(2) (2) are as follows: (1), C(68)H(60)Cl(16)N(8)O(4)W(2), a = 12.6906(3) Å, b = 12.7818(4) Å, c = 13.0450(3) Å, alpha = 109.173(1) degrees, beta = 93.865(1) degrees, gamma = 103.746(1) degrees, triclinic, P&onemacr; (No. 2), and Z = 1 and (2), C(59)H(35)Cl(16)N(8)O(2)W(2), a = 17.1524(1) Å, b = 20.6568(3) Å, c = 19.3959(3) Å, beta = 102.791(1) degrees, monoclinic, C2/c (No. 15), and Z = 4.

Two-electron photoelimination reactions from edge-sharing bioctahedral dimolybdenum(III) complexes

Dimolybdenum(III) edge-sharing bioctahedral (ESBO) complexes, Mo2X6(dtbppm)2 [dtbppm = bis(di(4-tert-butylphenyl)phosphinomethane), X= Cl, Br, I], photoreact when irradiated with near-UV light, cleanly producing the corresponding quadruple metal–metal bonded complexes, Mo2X4(dtbppm)2.

W 2Cl 4(NR 2) 2(PR 3′) 2 molecules—9. New mixed valent W III/W IV face-sharing bioctahedral complexes with chelating bis(diphenylphosphino)propane and dialkylamido ligands

The triply-bonded ditungsten(III) species trans, trans-W 2Cl 4(NBu 2 n ) 2(dppp) ( 1) and a new mixed-valent W III/W IV complex (dppp)ClW( μ-Cl) 3WCl 2(NBu 2 n ) ( 3) have been isolated from the reaction of W 2Cl 4(NBu 2 n ) 2(NHBu 2 n ) 2 with 1,3-bis(diphenylphosphino)propane (dppp). A complex similar to 3, (dppp)ClW(μ-Cl) 3WCl 2(NEt 2) ( 2), has also been prepared. Both 2 and 3 are characterized by a W 2 7+ core and they adopt face-sharing bioctahedral geometry with a chelating dppp ligand. The WW distances in 2 and 3 are both 2.660(1) Å and each of them shows an EPR signal at g = 1.88. The structure of 1 contains a W 2 6+ core with a WW distance of 2.3055(8) Å. It has a bridging dppp ligand and a trans,trans stereochemistry.

Probing the Balance between Localization and Delocalization of the Metal-Based Electrons in Face-Shared Bioctahedral Complexes.

The electronic structures of a variety of metal nonahalides, MM'X(9), with the {d(3)d(3)} configuration are examined using broken-symmetry density functional theory. Complexes containing trivalent ions of the chromium triad and tetravalent ions of the manganese triad are considered, where metal-metal interactions range from strong multiple bonding to weak antiferromagnetic coupling. The division of the metal-based electrons into symmetry-distinct sigma and delta(pi) subsets also gives rise to an intermediate group of complexes, where the sigma electrons are involved in a strong bond, but the delta(pi) subset remain weakly coupled. The balance between localization and delocalization of the metal-based electrons is determined by two distinct factors. The overlap of metal-based orbitals favors delocalization, whereas the high single-ion spin polarization energy associated with an isolated d(3) ion favors localization. Independent estimates of these two factors are made, and their contribution to the observed periodic trends is assessed. On descending a triad, the radial expansion of the d orbitals reduces the single-ion spin polarization energy and also increases overlap between orbitals on adjacent centers. Both factors contribute approximately equally to the increased tendency of the metal-based electrons to delocalize in the heavier congeners. Moving across a period, the greater covalence of the M(IV)-Cl bond in complexes of the manganese triad reduces the spin polarization energy, favoring delocalization. The contracted orbitals of the M(IV) ion, however, reduce the orbital overlap term, favoring localization. Changes in the overlap term dominate, and hence the overall trend is toward greater localization of the metal-based electrons in complexes of the manganese triad.

Multiple Bonds Between Main Group Elements and Transition Metals. 151.1Trioxorhenium(VII) Alkoxide Complexes

The reaction of Me3SiOReO3 with trimethylsilyl ethers Me3SiOR (R = Me, CMe2CMe2OMe, CMe2CMe2OH, CMe2CMe2OSiMe3) yields the trioxorhenium(VII) alkoxide complexes [ReO3(OMe)(MeOH)]2 (1), ReO3(OCMe2CMe2OMe) (2), ReO3(OCMe2CMe2OH) (3), and the glycolate complex (Me3SiO)ReO2(OCMe2CMe2O) (4), respectively. The alkoxides 1−4 have fluxional structures at room temperature in solution on the 17O NMR time scale. The trigonal bipyramidal structure of 2, in the crystal, is static in solution only at −90 °C. The protic hydrogen of 3 can be abstracted by lithium 2,2,6,6-tetramethylpiperidinate to give the ionic complex Li[ReO3(OCMe2CMe2O)] (5). [ReO3(OMe)(MeOH)]2 (1) crystallizes from dichloromethane in the space group P1̄ with unit cell dimensions a = 6.276(3) Å, b = 6.720(3) Å, c = 8.005(4) Å, α = 109.39(3)°, β = 99.48(3)°, γ = 110.31(2)°, V = 238.3 Å3, and Z = 1; the structure was refined to R = 0.050 and Rw = 0.056. ReO3(OCMe2CMe2OMe) (2) crystallizes from toluene in the space group Pbca with unit cell dimensions a = 8.263(2) Å, b = 10.884(3) Å, c = 22.963(5) Å, V = 2065 Å3, and Z = 8; the structure was refined to R = 0.044 and Rw = 0.028. ReO3(OCMe2CMe2OH) (3) crystallizes from dichloromethane in the space group C2/c with unit cell dimensions a = 12.327(5) Å, b = 10.973(3) Å, c = 14.491(6) Å, β = 90.22(2)°, V = 1960 Å3, and Z = 8; the structure was refined to R = 0.047 and Rw = 0.030. (Me3SiO)ReO2(OCMe2CMe2O) (4) crystallizes from n-pentane in the space group P21/c with unit cell dimensions a = 12.042(8) Å, b = 10.782(2) Å, c = 12.485(9) Å, β = 117.44(3)°, V = 1439 Å3, and Z = 4; the structure was refined to R = 0.044 and Rw = 0.044. The edge-sharing bioctahedral complex 1 has bridging methoxy and terminal methanol ligands trans to rhenium−oxygen double bonds. The rhenium centers in compounds 2 and 3 are pentacoordinated and located in a distorted trigonal bipyramidal geometry. The alkoxy function of the alkoxy ligand −OCMe2CMe2OR (R = H, Me) is located in the equatorial plane, and the Lewis base (−OMe, −OH) is bonded trans to an oxygen atom in an axial coordination site. (Me3SiO)ReO2(OCMe2CMe2O) (4) has a similar geometry to 2 and 3 with a trimethylsiloxy ligand trans to an alkoxy function in an axial position.

The evaluation of singlet-triplet separations for [W 2(μ-H)(μ-Cl)Cl 4(μ-dppm) 2] and [W 2(μ-H) 2 (μ-O 2CC 6H 5) 2(P(C 6H 5) 3) 2] based on 31P NMR and crystallographic data

The singlet-triplet separations for the edge-sharing bioctahedral (ESBO) complex W 2(μ-H)(μ-Cl)(Cl 4(μ-dppm) 2 · (THF) 3 ( II) has been studied by 31P NMR spectroscopy. The structural characterization of [W 2(μ-H) 2(μ-O 2CC 6H 5) 2Cl 2(P(C 6H 5) 3) 2] ( I) by single-crystal X-ray crystallography has allowed the comparison of the energy of the HOMOLUMO separation determined using the Fenske-Hall method for a series of ESBO complexes with two hydride bridging atoms, two chloride bridging atoms and the mixed case with a chloride and hydride bridging atom. The complex representing the mixed case, [W 2(μ-H)(μ-Cl)Cl 4(μ-dppm) 2 · (THF) 3] ( II), has been synthesized and the value of −2 J determined from variable-temperature 31P NMR spectroscopy.

Reactions of the dirhenium(II) complexes Re2X4(dppm)2 (X= Cl, Br; dppm = Ph2PCH2PPh2) with isocyanides. Part IX. New isomeric forms of the mixed carbonyl-isocyanide dirhenium(II) Complexes Re2 Cl4(dppm)2(CO)(CNxyl) and [Re2Cl3(dppm)2(CO)(CNxyl)2]O3SCF3 The X-ray crystal structure of [(xyl NC)2ClRe(?-dppm)2ReCl2(CO)] O3SCF3

The monocarbonyl complex Re2Cl4(µ-dppm)2(CO) reacts with xylyl isocyanide in acetonitrile to afford the bioctahedral complex (CO)Cl2Re(µ-dppm)2 ReCl2(CNxyl), 2b. This is a different structural isomer from the edge-sharing bioctahedral complex Cl2Re(µ-Cl)(µ-dppm)2ReCl(CNxyl) or this same stoichiometry which A formed when acetone is be reaction solvent. The complex2b reacts with a further equivalent of xylNC in the presence of TlO3SCF3 in dichloromethane to form a red complex of composition [Re2Cl3(µ-dppm)2 (CO)(CNxyl)2]O3SCF3. 3, which has the open bioctahedral structure [(xylNC)2ClRe(µ-dppm)2ReCl2(CO)]O3SCF3. This is a third isomeric form of this dirhenium cation: the previously isolated green and yellow forms have edge-sharing bioctahedral structures. Crystal data for3 at 295 K: orthorhombic space group Pbca (No. 61) witha=22.654(5) A,b=22.717(4) A,c=27.324(4) A,V= 14061(7) A3, andZ = 8. The structure was refined to R = 0.059 (R, = 0.134 ) for 14164 data. The Re-Re distance is 2.3833(8) A.