Synthesis, characterization, and ligand exchange studies of W(6)S(8)L(6) cluster compounds

Eleven organic Lewis bases were investigated as potential ligands (L) on W(6)S(8)L'(6) clusters by exploring ligand exchange reactions to form W(6)S(8)L(6) clusters. Six new homoleptic W(6)S(8)L(6) cluster complexes were prepared and characterized with L = tri-n-butylphosphine (P(n)Bu(3)), triphenylphosphine (PPh(3)), tert-butylisocyanide ((t)BuNC), morpholine, methylamine (MeNH(2)), and tert-butylamine ((t)BuNH(2)). While partial replacement of ligands occurred with diethylamine (Et(2)NH) and dibutylamine (Bu(2)NH), homoleptic clusters could not be prepared by these exchange reactions. When aniline, tribenzylamine, and tri-tert-butylphosphine were the potential ligands, no exchange was observed. From ligand exchange studies of these ligands and others previously studied, a thermodynamic series of binding free energies for ligands on W(6)S(8)L(6) clusters was established as the following: non-Lewis base solvents, aniline, P(t)()Bu(3), etc. < Et(2)NH, Bu(2)NH < (t)BuNH(2) < morpholine, piperidine < or = (n)BuNH(2), MeNH(2) < or = 4-tert-butylpyridine, pyridine < (t)BuNC < tricyclohexylphosphine (PCy(3)) < PPh(3), P(n)Bu(3) < or = triethylphosphine (PEt(3)). Structures of the new cluster complexes were determined by X-ray crystallography. The new compounds were also characterized by NMR spectroscopy and thermogravimetric analyses (TGA). The W-L bond orders and TGA data qualitatively agree with the thermodynamic series above.     

Synthesis and characterization of oxidized W(6)S(8)L(6) clusters

Cationic [W(6)S(8)L(6)]PF(6) (L = PEt(3) (3), 4-tert-butylpyridine (4)) clusters were successfully synthesized and isolated for the first time by reacting the corresponding neutral W(6)S(8)L(6) (L = PEt(3) (1), 4-tert-butylpyridine (2)) clusters with [Cp(2)Fe]PF(6) as the oxidant. The products 3 and 4 were characterized by NMR spectroscopy, mass spectroscopy, and X-ray crystallography (only for 3) and shown to be the desired oxidized W(6)S(8) clusters with a metal electron count of 19. Magnetic property studies showed that they are paramagnetic compounds with S = (1)/(2). Their chemical properties and stability are also reported. Crystal data for 3.2 THF: space group, R3 (No. 148); a = 13.91170(10) A; c = 32.4106(2) A; Z = 3.     

The Dean-Evans relation in (31)P NMR spectroscopy and its application to the chemistry of octahedral tungsten sulfide clusters

One of the challenges in studying the chemistry of hexanuclear octahedral metal clusters is analyzing the many possible complexes, including stereoisomers, when these complexes consist of mixed axial ligands (two or more). In the case of W(6)S(8)L(6-n)(PR(3))(n)(n = 0-6; L = nonphosphine Lewis base ligands, PR(3) = phosphines) clusters, in situ identification of the 10 possible complexes is possible by (31)P NMR due to P-W-W-P coupling. A linear relation for (31)P NMR shifts (delta((31)P)) of these W(6)S(8)L(6-n)(PR(3))(n) complexes, analogous to the Dean-Evans relation for (19)F NMR shifts of octahedral tin complexes, is found and expressed as delta((31)P) = delta(ref) + pC + qT with two variables (p and q, the number of ligands L in the cis or trans position to PR(3), respectively) with two constants (C and T, characteristic of a given ligand L). (31)P NMR investigation of over 200 complexes in 26 W(6)S(8)L(6-n)(PR(3))(n) systems show that this relation is generally valid for W(6)S(8) clusters. Such a relation helps spectroscopic assignments and demonstrates the trans and cis influence on hexanuclear clusters. Large bulky ligands cause deviations from the linear behavior due to steric effects. With the help of 2-D (31)P NMR spectroscopy, mixtures of W(6)S(8)(PR(3))(6-n)(PR'(3))(n) (n = 0-6) complexes can also be unequivocally interpreted. The Dean-Evans relation is expanded to account for different phosphine ligands. Partial substitution reactions of these W(6)S(8) complexes by phosphines were investigated using (31)P NMR, and four single crystals of mixed-ligand clusters are characterized with X-ray diffraction. In summary, (31)P NMR and other NMR techniques, combined with Dean-Evans relations, are invaluable analytical tools for studying molecular W(6)S(8) cluster chemistry and are likely to be useful for studying other mixed-ligand metal clusters.     

Synthesis and characterization of hydrogen-bonded assemblies of W6S8L6 clusters

Ligand-exchange reactions involving octahedral W6S8 clusters and a family of pyridine-based ligands (isonicotinic acid, isonicotinamide, 4-hydroxypyridine, 4-aminopyridine, 4-pyridineacetamide) have been explored with the goal of preparing compounds that crystallize in hydrogen-bonded arrays. Two new compounds, W6S8(4-pyridineacetamide)6.DMF.4-pyridineacetamide (1) and W6S8(4-aminopyridine)6.4DMF (2), were isolated and characterized by single-crystal X-ray diffraction. Both compounds crystallize in the P2(1)/c space group with a = 16.461(1), b = 33.08(2), c = 13.165(10) A, beta = 103.270(15) degrees for 1 and a = 13.8988(5), b = 13.2791(5), c = 15.6293(6) A, beta = 108.5410(10) degrees for 2. Each compound was further characterized by 1H NMR spectroscopy, elemental (CHN) analysis, and thermogravimetric analysis. Examination of the structures shows that 1 forms a three-dimensional hydrogen-bonded network in which each 4-pyridineacetamide ligand interacts with ligands on neighboring clusters or with the free ligand of crystallization. This is the first hydrogen-bonded network formed from W6S8 clusters. In 2, the amino groups act as hydrogen-bond donors toward DMF molecules of crystallization, but an extended array is not formed. In addition, the binding strengths of these pyridine-based ligands to the W6S8 cluster were studied through quantitative 1H NMR studies of ligand-exchange reactions. A qualitative relationship was found between ligand binding strengths and Hammett substituent constants for this group of ligands.     

A family of octahedral rhenium cluster complexes [Re6Q8(H2O)n(OH)6-n]n-4 (Q=S, Se; n=0-6): structural and pH-dependent spectroscopic studies

The conversions of hexahydroxo rhenium cluster complexes [Re6Q8(OH)6]4- (Q=S, Se) in aqueous solutions in a wide pH range were investigated by chemical methods and spectroscopic measurements. Dependences of the spectroscopic and excited-state properties of the solutions on pH have been studied in detail. It has been found that a pH decrease of aqueous solutions of the potassium salts K4[Re6Q8(OH)6].8H2O (Q=S, Se) results in the formation of aquahydroxo and hexaaqua cluster complexes with the general formula [Re6Q8(H2O)n(OH)6-n]n-4 that could be considered as a result of the protonation of the terminal OH- ligands in the hexahydroxo complexes. The compounds K2[Re6S8(H2O)2(OH)4].2H2O (1), [Re6S8(H2O)4(OH)2].12H2O (2), [Re6S8(H2O)6][Re6S6Br8].10H2O (3), and [Re6Se8(H2O)4(OH)2] (4) have been isolated and characterized by X-ray single-crystal diffraction and elemental analyses and infrared (IR) spectroscopy. In crystal structures of the aquahydroxo complexes, the cluster units are connected to each other by an extensive system of very strong hydrogen bonds between terminal ligands.     

Preparation and properties of the full series of cuboidal clusters [Mo(x)W4-xSe4(H2O)12]n+ (n = 4-6) and their derivatives

Hydrothermal reactions between incomplete cuboidal cluster aqua complexes [M3Q4(H2O)9]4+ and M(CO)6 (M = Mo, W; Q = S, Se) offer easy access to the corresponding cuboidal clusters M4Q4. The complete series of homometal and mixed Mo/W clusters [Mo(x)W4-xQ4(H2O)12]n+ (x = 0-4, n = 4-6) has been prepared. Upon oxidation of the mixed-metal clusters, it is the W atom which is lost, allowing selective preparation of new trinuclear clusters [Mo2WSe4(H2O)9]4+ and [MoW2Se4(H2O)9]4+. The aqua complexes were converted by ligand exchange reactions into dithiophosphato and thiocyanato complexes, and crystal structures of [W4S4((EtO)2PS2)6], [MoW3S4((EtO)2PS2)6], [Mo4Se4((EtO)2PS2)6], [W4Se4((i-PrO)2PS2)6], and (NH4)6[W4Se4(NCS)12]-4H20 were determined. Cyclic voltammetry was performed on [Mo(x)W4-xCO4(H2O)12]n+, showing reversible redox waves 6+/5+ and 5+/4+. The lower oxidation states are more difficult to access as the number of W atoms increases. The [Mo2WSe4(H2O)9]4+ and [MoW2Se4(H2O)9]4+ species were derivatized into [Mo2WSe4(acac)3(py)3]+ and [MoW2Se4(acac)3(py)3]+, which were also studied by CV. When appropriate, the products were also characterized by FAB-MS and NMR (31P, 1H) data.     

W6S8] octahedral tungsten clusters functionalized with thiophene derivatives: toward polymerizable building blocks

The functionalization of octahedral [W(6)S(8)] clusters with a family of phosphino-thiophene ligands has been investigated with the goal of synthesizing extended networks of [W(6)S(8)] units covalently linked to one another through thiophene-conjugated bridges. In addition to new phosphino-thiophene ligands, eight clusters were synthesized and characterized by (1)H and (31)P NMR spectroscopies, elemental analysis, and UV-vis absorption. These clusters are formulated [W(6)S(8)(T-PPh(2))6] (1a), [W(6)S(8)(T-PEt(2))(6)] (1b), [W(6)S(8)(2T-PPh(2))(6)] (2a), [W(6)S(8)(2T-PEt(2))(6)] (2b), [W(6)S(8)(3T-PPh(2))(6)] (3a), [W(6)S(8)(3T-PEt(2))(6)] (3b), [W(6)S(8)((2T)(3)P)(6)] (4), and [W(6)S(8)(2EDOT-PEt(2))(6)] (5) (T = thiophene and EDOT = 3,4-ethylenedioxythiophene). The molecular structure of six of them has been obtained by single-crystal X-ray diffraction analysis. All of them crystallize in the P1 triclinic space group except 3b, which has the P2(1)/c monoclinic symmetry. The redox behavior of both the ligands and the corresponding functionalized clusters has been investigated by cyclic voltammetry. An attempt to electropolymerize these species is also reported.     

Dinuclear copper(I) and copper(I)/silver(I) complexes with condensed dithiolato ligands

The Cu(III) complex Pr 4N[Cu{S 2C=( t-Bu-fy)} 2] ( 1) ( t-Bu-fy = 2,7-di- tert-butylfluoren-9-ylidene) reacts with [Cu(PR 3) 4]ClO 4 in 1:1 molar ratio in MeCN to give the dinuclear complexes [Cu 2{[SC=( t-Bu-fy)] 2S}(PR 3) n ] [ n = 2, R = Ph ( 2a); n = 3, R = To ( 3b); To = p-tolyl]. The analogue of 2a with R = To ( 2b) can be obtained from the reaction of 3b with 1/8 equiv of S 8. Compound 2b establishes a thioketene-exchange equilibrium in solution leading to the formation of [Cu 4{S 2C=( t-Bu-fy)} 2(PTo 3) 4] ( 4b) and [Cu 2{[SC=( t-Bu-fy)] 3S}(PTo 3) 2] ( 5b). Solid mixtures of 4b and 5b in varying proportions can be obtained when the precipitation of 2b is attempted using MeCN. The reactions of 1 with AgClO 4 and PPh 3, PTo 3 or PCy 3 in 1:1:4 molar ratio in MeCN afford the heterodinuclear complexes [AgCu{[SC=( t-Bu-fy)] 2S}(PR 3) 3] [R = Ph ( 6a), To ( 6b), Cy ( 6c)]. Complex 6c dissociates PCy 3 in solution to give the bis(phosphine) derivative [AgCu{[SC=( t-Bu-fy)] 2S}(PCy 3) 2] ( 7c), which undergoes the exchange of [M(PCy 3)] (+) units in CD 2Cl 2 solution to give small amounts of [Cu 2{[SC=( t-Bu-fy)] 2S}(PCy 3) 2] ( 2c) and [Ag 2{[SC=( t-Bu-fy)] 2S}(PCy 3) 2] ( 8c). Complexes 6a and b participate in a series of successive equilibria in solution, involving the dissociation of phosphine ligands and the exchange of [M(PCy 3)] (+) units to give 2a or 3b and the corresponding disilver derivatives [Ag 2{[SC=( t-Bu-fy)] 2S}(PR 3) 2] [R = Ph ( 8a), To ( 8b)], followed by thioketene-exchange reactions to give [AgCu{[SC=( t-Bu-fy)] 3S}(PR 3) 2] [R = Ph ( 9a), To ( 9b)]. Complexes 9a and b can be directly prepared from the reactions of 1 with AgClO 4 and PPh 3 or PTo 3 in 1:1:3 molar ratio in THF. The crystal structures of 3b, 6b, 6c, 7c, and 9a have been solved by single-crystal X-ray diffraction studies and, in the cases of 7c and 9a, reveal the formation of short Ag...Cu metallophilic contacts of 2.8157(4) and 2.9606(6) A, respectively.     

Synthesis, characterization, and substitution chemistry of [Bu4N]2[W6Cl8(OSO2CF3)6]. A versatile precursor for axially substituted clusters containing the (W6Cl8)4+ core

The new cluster [Bu4N]2[W6Cl8(OSO2CF3)6] (1) has been prepared and structurally characterized. This material is an effective precursor for the generation of cluster ions with the general formula [W6C18L6]n (L = Cl-, Br-, I-, NCS-, NCO-, NCSe-, and O=PPh3; n = 2- or 4+). The last three clusters are new. The products have been characterized by IR spectroscopy, NMR spectroscopy, and FAB mass spectrometry. In addition to 1, the products [Bu4N]2[W6C18(NCS)6] (5) and [Bu4N]2[W6C18(NCO)6] (7) were structurally characterized. Crystal data for 1: space group, P2(1/c) (No. 14); a = 11.116(5) A; b = 27.952(1) A; c = 24.516(1) A; beta = 95.182(9) degrees; V = 7586.3(5) A3; Z = 4. Crystal data for 5: space group, P2(1/n) (No. 14); a = 11.3323(9) A; b = 12.3404(9) A; c = 44.583(3) A; beta = 97.089(1) degrees ; V = 6187.1(7) A3; Z = 4. Crystal data for 7: space group, P1 (No. 2); a = 11.8009(8) A; b = 11.9332(8) A; c = 11.9522(8) A; alpha = 77.904(1) degrees; beta = 95.182(9) degrees; gamma = 62.574(1) degrees V = 1450.5(2) A3; Z = 1.     

About the Keggin isomers: crystal structure of [N(C4H9)4]-gamma-[SiMo2W10O40]n- (n= 4 or 6)

The tetrabutylammonium gamma-dodecatungstosilicate has been crystallized in a 6/1 acetonitrile/water solvent. An X-ray single-crystal analysis was carried out on [N(C4H9)4]4-gamma-[SiW12O40] which crystallizes in the orthorhombic system, space group P2(1)2(1)2(1), with a = 19.0881(3) A, b = 21.4435(3) A, c = 26.0799(1) A, V = 10674.9(2) A3, Z = 4, and rho(calcd) = 2.392 g/cm3. The idealized C2v arrangement of the anion results from the rotation of 60 degrees of two trigonal [W3O13] groups in the Keggin anion. Taking as reference the geometrical characteristics of the Keggin anion, it appears that the bond lengths and bonds angles within the four [W3O13] groups are not significantly modified while the mu-oxo junctions between the two rotated groups and those between the two unrotated groups involve more acute and opened W-O-W angles, respectively. The syntheses and 183W NMR characterizations of the mixed gamma-[SiW10Mo2O40]n- compounds corresponding to the oxidized (Mo(VI); n = 4) and to the two electron-reduced (Mo(V); n = 6) anions are reported. Structural analysis by 183W NMR has proved unambiguously that the C2v structure of the gamma-[SiW10O36]8- subunit is retained in both the compounds. The electronic behavior of the series gamma-[SiW10M2E2O36]6- (M = Mo or W; E = O or S) is examined, compared and related to 183W NMR data.     

一些单立方烷化合物MFe_3S_4(S_2CNR_2)_5(M=Mo,W)的~1H NMR研究

本文报道了一些单立方烷化合物MFe_3S_4(S_2CNR_2)_5(M=Mo,W;R_2=Me_2,Et_2,C_4H_8,OC_4H_8,C_5H_(10))的~1H NMR谱研究,结果表明与铁原子相连的配体的α-H产生了相当大的各向同性位移,它随温度升高而减少,基本上服从居里定律。本文还讨论了化合物中的配体间交换反应以及簇骼中金属原子间耦合作用对配体的NMR的影响。     

Cluster-to-metal magnetic coupling: synthesis and characterization of 25-electron [Re6-nOsnSe8(CN)6](5-n)-(n = 1, 2) clusters and (Re6-nOsnSe8[CNCu(Me6tren)]6)9+(n = 0, 1, 2) assemblies

The first face-capped octahedral clusters with 25 metal-based valence electrons are shown to provide versatile building units capable of engaging in magnetic exchange coupling. Reactions of [Re(5)OsSe(8)Cl(6)](3-) and [Re(4)Os(2)Se(8)Cl(6)](2-) with NaCN in a melt of NaNO(3) or KCF(3)SO(3) afford the 24-electron clusters [Re(5)OsSe(8)(CN)(6)](3-) and [Re(4)Os(2)Se(8)(CN)(6)](2-). The 13C NMR spectrum of a 13C-labeled version of the latter species indicates a 1:2 mixture of cis and trans isomers. Cyclic voltammograms of the clusters in acetonitrile display reversible [Re(5)OsSe(8)(CN)(6)](3-/4-), cis-[Re(4)Os(2)Se(8)(CN)(6)](2-/3-), and trans-[Re(4)Os(2)Se(8)(CN)(6)](2-/3-) couples at E(1/2) = -1.843, -0.760, and -1.031 V vs FeCp(2)(0/+), respectively, in addition to other redox processes. Accordingly, reduction of [Re(5)OsSe(8)(CN)(6)](3-) with sodium amalgam and [Re(4)Os(2)Se(8)(CN)(6)](2-) with cobaltocene produces the 25-electron clusters [Re(5)OsSe(8)(CN)(6)](4-) and [Re(4)Os(2)Se(8)(CN)(6)](3-). EPR spectra of these S = 1/2 species in frozen DMF solutions exhibit isotropic signals with g = 1.46 for the monoosmium cluster and g = 1.74 and 1.09 for the respective cis and trans isomers of the diosmium cluster. In each case, results from DFT calculations show the unpaired spin to delocalize to some extent into the pi* orbitals of the cyanide ligands, suggesting the possibility of magnetic superexchange. Reaction of [Re(5)OsSe(8)(CN)(6)](3-) with [Ni(H(2)O)(6)](2+) in aqueous solution generates the porous Prussian blue analogue Ni(3)[Re(5)OsSe(8)(CN)(6)](2).32H(2)O; however, the tendency of the 25-electron clusters to oxidize in water prohibits their use in reactions of this type. Instead, a series of cyano-bridged assemblies, [Re(6-n)Os(n)Se(8)[CNCu(Me(6)tren)](6)](9+) (n = 0, 1, 2; Me(6)tren = tris(2-(dimethylamino)ethyl)amine), were synthesized to permit comparison of the exchange coupling abilities of clusters with 23-25 electrons. As expected, the results of magnetic susceptibility measurements show no evidence for exchange coupling in the assemblies containing the 23- and 24-electron clusters, but reveal the presence of weak ferromagnetic coupling in [Re(4)Os(2)Se(8)[CNCu(Me(6)tren)](6)](9+). Assuming all cluster-Cu(II) exchange interactions to be equivalent, the data were fit to give an estimated coupling strength of J = 0.4 cm(-1). To our knowledge, the ability of such clusters to participate in magnetic exchange coupling has never previously been demonstrated.     

Substitution chemistry of MM quadruply bonded complexes (M = Mo or W) supported by the anion of 2-hydroxy-6-methylpyridine

The compounds M(2)(mhp)(4), where M = Mo or W and mhp is the anion formed from deprotonation of 2-hydroxy-6-methylpyridine, are shown to react with carboxylic acids RCOOH to give an equilibrium mixture of products M(2)(O(2)CR)(n)(mhp)(4-n) where R = 2-thienyl and phenyl. The equilibrium can be moved in favor of M(2)(O(2)CR)(4) by the addition of excess acid or by the favorable crystallization of these products. The latter provides a facile synthesis of the W(2)(O(2)CR)(4) compound where R = 9-anthracene. Reactions involving 2,4,6-triisopropyl benzoic acid, TiPBH, yield M(2)(TiPB)(2)(mhp)(2) compounds as thermodynamic products. Reactions involving Me(3)OBF(4) (1 and 2 equiv.) yield the complexes Mo(2)(mhp)(3)(CH(3)CN)(2)BF(4) and Mo(2)(mhp)(2)(CH(3)CN)(4)(BF(4))(2), respectively. The latter compound has been structurally characterized and shown to have mirror symmetry with two cis mhp ligands: MoMo = 2.1242(5) A, Mo-O = 2.035(2) A, Mo-N(mhp) = 2.161(2) A, and Mo-N(CH(3)CN) = 2.160(3) and 2.170(3) A. Reactions involving Mo(2)(mhp)(3)(CH(3)CN)(2)(2+) and Mo(2)(mhp)(2)(CH(3)CN)(4)(2+) with (n)Bu(4)NO(2)CMe (1 and 2 equiv.) yield the complexes Mo(2)(mhp)(3)(O(2)CMe) and Mo(2)(mhp)(2)(O(2)CMe)(2) which are shown to be kinetically labile to ligand scrambling. Reactions between Mo(2)(mhp)(3)(CH(3)CN)(2)(+)BF(4)(-) (2 equiv.) and [(n)Bu(4)N(+)](2)[O(2)C-X-CO(2)](2-) yielded dimers of dimers [Mo(2)(mhp)(3)](2)(micro-O(2)C-X-CO(2)] where X = nothing, 2,5- or 3,4-thienyl and 1,4-C(6)H(4). Reactions between Mo(2)(mhp)(2)(CH(3)CN)(4)(2+)(BF(4)(-))(2) and tetra-n-butylammonium oxalate and terephthalate yield compounds [Mo(mhp)(2)bridge](n) which by MALDI-TOF MS are proposed to be a mixture of molecular squares (n = 4) and triangles (n = 3) along with minor products of [Mo(2)(mhp)(3)](2)(bridge) and Mo(2)(mhp)(4) that arise from ligand scrambling.     

Resonance Raman Spectra of [M(6)X(8)Y(6)](2)(-) Cluster Complexes (M = Mo, W; X, Y = Cl, Br, I)

Resonance Raman spectra of the cubic metal-halide complexes having the general formula [M(6)X(8)Y(6)](2)(-) (M = Mo or W; X, Y = Cl, Br, or I) are reported. The three totally symmetric fundamental vibrations of these complexes are identified. The extensive mixing of the symmetry coordinates that compose the symmetric normal modes expected in these systems is not observed. Instead the "group-frequency" approximation is valid. Furthermore, the force constants of both the apical and face-bridging metal-halide bonds are insensitive to the identity of either the metal or the halide. Raman spectra of related complexes with methoxy and benzenethiol groups as ligands are reported along with the structural data for [Mo(6)Cl(8)(SPh)(6)][NBu(4)](2). Crystal data for [Mo(6)Cl(8)(SPh)(6)][NBu(4)](2) at -156 degrees C: monoclinic space group P2(1)/c; a = 12.588(3), b = 17.471(5), c = 20.646(2) ?; beta = 118.53(1) degrees, V = 3223.4 ?(3); d(calcd) = 1.664 g cm(-)(3); Z = 2.     

Synthesis and Characterization of Four Consecutive Members of the Five-Member [Fe(6)S(8)(PEt(3))(6)](n)()(+) (n = 0-4) Cluster Electron Transfer Series

The clusters [Fe(6)S(8)(PEt(3))(6)](+,2+) have been shown by other investigators to be formed by the reaction of [Fe(OH(2))(6)](2+) and H(2)S, to contain face-capped octahedral Fe(6)S(8) cores, and to be components of the five-membered electron transfer series [Fe(6)S(8)(PEt(3))(6)](n)()(+) (n = 0-4) estalished electrochemically. We have prepared two additional series members. Reaction of [Fe(6)S(8)(PEt(3))(6)](2+) with iodine in dichloromethane affords [Fe(6)S(8)(PEt(3))(6)](3+), isolated as the perchlorate salt (48%). Reduction of [Fe(6)S(8)(PEt(3))(6)](2+) with Na(Ph(2)CO) in acetonitrile/THF produces the neutral cluster [Fe(6)S(8)(PEt(3))(6)] (65%). The structures of the four clusters with n = 0, 1+, 2+, 3+ were determined at 223 K. The compounds [Fe(6)S(8)(PEt(3))(6)](ClO(4))(3), [Fe(6)S(8)(PEt(3))(6)] crystallize in trigonal space group R&thremacr;c with a = 21.691(4), 16.951(4) ?, c = 23.235(6), 19.369(4) ?, and Z = 6, 3. The compounds [Fe(6)S(8)(PEt(3))(6)](BF(4))(2), [Fe(6)S(8)(PEt(3))(6)](BF(4)).2MeCN were obtained in monoclinic space groups P2(1)/c, C2/c with a = 11.673(3), 16.371(4) ?, b = 20.810(5), 16.796(4) ?, c = 12.438(4), 23.617(7) ?, beta = 96.10(2), 97.98(2) degrees, and Z = 2, 4. [Fe(6)S(8)(PEt(3))(6)](BPh(4))(2) occurred in trigonal space group P&onemacr; with a = 11.792(4) ?, b = 14.350(5) ?, c = 15.536(6) ?, alpha = 115.33(3) degrees, beta = 90.34(3) degrees, gamma = 104.49(3) degrees, and Z = 1. Changes in metric features across the series are slight but indicate increasing population of antibonding Fe(6)S(8) core orbitals upon reduction. Zero-field M?ssbauer spectra are consistent with this result, isomer shifts increasing by ca. 0.05 mm/s for each electron added, and indicate a delocalized electronic structure. Magnetic susceptibility measurements together with previously reported results established the ground states S = (3)/(2) (3+), 3 (2+), (7)/(2) (1+), 3 (0). The clusters [Fe(6)S(8)(PEt(3))(6)](n)()(+) possess the structural and electronic features requisite to multisequential electron transfer reactions. This work provides the first example of a cluster type isolated over four consecutive oxidation states. Note is also made of the significance of the [Fe(6)S(8)(PEt(3))(6)](n)()(+) cluster type in the development of iron-sulfur-phosphine cluster chemistry.     

Direct measurements of rate constants and activation volumes for the binding of H2, D2, N2, C2H4, and CH3CN to W(CO)3(PCy3)2: theoretical and experimental studies with time-resolved step-scan FTIR and UV-vis spectroscopy

Pulsed 355 nm laser excitation of toluene or hexane solutions containing W-L (W = mer,trans-W(CO)3(PCy3)2; PCy3 = tricyclohexylphosphine; L = H2, D2, N2, C2H4, or CH3CN) resulted in the photoejection of ligand L and the formation of W. A combination of nanosecond UV-vis flash photolysis and time-resolved step-scan FTIR (s2-FTIR) spectroscopy was used to spectroscopically characterize the photoproduct, W, and directly measure the rate constants for binding of the ligands L to W to reform W-L under pseudo-first-order conditions. From these data, equilibrium constants for the binding of L to W were estimated. The UV-vis flash photolysis experiments were also performed as a function of pressure in order to determine the activation volumes, DeltaV thermodynamic, for the reaction of W with L. Small activation volumes ranging from -7 to +3 cm3 mol(-1) were obtained, suggesting that despite the crowded W center an interchange mechanism between L and the agostic W...H-C interaction of one of the PCy3 ligands (or a weak interaction with a solvent molecule) at the W center takes place in the transition state. Density functional theory (DFT) calculations were performed at the B3LYP level of theory on W with/without the agostic C-H interaction of the PCy3 ligand and also on the series of model complexes, mer,trans-W(CO)3(PH3)2L (W'-L, where L = H2, N2, C2H4, CO, or n-hexane) in an effort to confirm the infrared spectroscopic assignment of the W-L complexes, to simulate and assign the electronic transitions in the UV-vis spectra, to determine the nature of the HOMO and LUMO of W-L, and to understand the agostic C-H interaction of the ligand vs solvent interaction. Our DFT calculations indicate an entropy effect that favors agostic W...H-C interaction over a solvent sigma C-H interaction by 8-10 kcal mol(-1).     

Preparation and crystal structures of formato complexes of the [MIV3O4]4+ and [MIV3S4]4+ (M = Mo,W) clusters. Convenient precursors to the corresponding aqua complexes

In the aqueous chemistry of molybdenum(IV) and tungsten(IV), trinuclear, incomplete cubane-like, oxo and sulfido clusters of the type [M3E4]4+ (M = Mo, W; E = O, S) play a central role. We here describe how formato complexes of all these cluster cores can be prepared in high yields by crystallization from methanol-water or ethanol-water mixtures. Since potassium and ammonium formate are very soluble in these alcohol-water mixtures, high formate concentrations could be accomplished in the solutions from which the corresponding salts of cluster formato complexes crystallized. The [Mo3O4]4+ compounds could be synthesized without requiring the use of noncomplexing acids in the process. Some [M3E4]4+ compounds were characterized by single-crystal structure determinations. [NH4]3.20[K]0.80[H3O][Mo3O4(HCO2)8][HCO2].H2O was triclinic, space group P1 (No. 2) with a = 11.011(2) A, b = 13.310(2) A, c = 9.993(1) A, alpha = 106.817(7) degrees, beta = 91.651(9) degrees, gamma = 88.340(9) degrees, and two formula units per cell. [K]6[W3S4(HCO2)9][HCO2].2.27H2O.0.73CH3OH was monoclinic, space group C2/m (No. 12) with a = 19.605(6) A, b = 14.458(7) A, c = 13.627(5) A, beta = 118.94(2) degrees, and four formula units per cell. Generally, the nine coordination sites of [M3E4]4+ were occupied either by a mixture of monodentate and mu 2-bridging formato ligands or by monodentate formato ligands only. By dissolution in noncomplexing strong acid, all the formato complexes immediately hydrolyzed to form [M3E4(H2O)9]4+ aqua complexes. This allows, for example, high concentrations of [Mo3S4(H2O)9]4+ in CF3SO3H to be obtained and these solutions to be used for the synthesis of bimetallic clusters containing the cubane-like motif Mo3M'S4.     

Structural characterization of four members of the electron-transfer series [PdII(L)2)2]n (L = o-Iminophenolate derivative; n = 2-, 1-, 0, 1+, 2+). ligand mixed valency in the monocation and monoanion with S = (1)/(2) ground states

The reaction of the ligand 2-(2-trifluoromethyl)anilino-4,6-di-tert-butylphenol, H(2)((1)L(IP)), and PdCl(2) (2:1) in the presence of air and excess NEt(3) in CH(2)Cl(2) produced blue-green crystals of diamagnetic [Pd(II)((1)L(ISQ))(2)] (1), where ((1)L(ISQ))(*)(-) represents the o-iminobenzosemiquinonate(1-) pi radical anion of the aromatic ((1)L(IP))(2-) dianion. The diamagnetic complex 1 was chemically oxidized with 1 equiv of Ag(BF(4)), affording red-brown crystals of paramagnetic (S = (1)/(2)) [Pd(II)((1)L(ISQ))((1)L(IBQ))](BF(4)) (2), and one-electron reduction with cobaltocene yielded paramagnetic (S = (1)/(2)) green crystals of [Cp(2)Co][Pd(II)((1)L(ISQ))((1)L(IP))] (3); ((1)L(IBQ))(0) represents the neutral, diamagnetic quinone form. Complex 1 was oxidized with 2 equiv of [NO]BF(4), affording green crystals of diamagnetic [Pd(II)((1)L(IBQ))(2)](3)(BF(4))(4){(BF(4))(2)H}(2).4CH(2)Cl(2) (5). Oxidation of [Ni(II)((1)L(ISQ))(2)] (S = 0) in CH(2)Cl(2) solution with 2 equiv of Ag(ClO(4)) generated crystals of [Ni(II)((1)L(IBQ))(2)(ClO(4))(2)].2CH(2)Cl(2) (6) with an S = 1 ground state. Complexes 1-5 constitute a five-membered complete electron-transfer series, [Pd((1)L)(2)](n) (n = 2-, 1-, 0, 1+, 2+), where only species 4, namely, diamagnetic [Pd(II)((1)L(IP))(2)](2-), has not been isolated; they are interrelated by four reversible one-electron-transfer waves in the cyclic voltammogram. Complexes 1, 2, 3, 5, and 6 have been characterized by X-ray crystallography at 100 K, which establishes that the redox processes are ligand centered. Species 2 and 3 exhibit ligand mixed valency: [Pd(II)((1)L(ISQ))((1)L(IBQ))](+) has localized ((1)L(IBQ))(0) and ((1)L(ISQ))(*)(-) ligands in the solid state, whereas in [Pd(II)((1)L(ISQ))((1)L(IP))](-) the excess electron is delocalized over both ligands in the solid-state structure of 3. Electronic and electron spin resonance spectra are reported, and the electronic structures of all members of this electron-transfer series are established.     

Dihydrogen complexes of rhodium: [RhH2(H2)x (PR3)2]+ (R = Cy, iPr; x = 1, 2)

Addition of H2 (4 atm at 298 K) to [Rh(nbd)(PR3)2][BAr(F)4] [R = Cy, iPr] affords Rh(III) dihydride/dihydrogen complexes. For R = Cy, complex 1a results, which has been shown by low-temperature NMR experiments to be the bis-dihydrogen/bis-hydride complex [Rh(H)2(eta2-H2)2(PCy3)2][BAr(F)4]. An X-ray diffraction study on 1a confirmed the {Rh(PCy3)2} core structure, but due to a poor data set, the hydrogen ligands were not located. DFT calculations at the B3LYP/DZVP level support the formulation as a Rh(III) dihydride/dihydrogen complex with cis hydride ligands. For R = iPr, the equivalent species, [Rh(H)2(eta2-H2)2(P iPr3)2][BAr(F)4] 2a, is formed, along with another complex that was spectroscopically identified as the mono-dihydrogen, bis-hydride solvent complex [Rh(H)2(eta2-H2)(CD2Cl2)(P iPr3)2][BAr(F)4] 2b. The analogous complex with PCy3 ligands, [Rh(H)2(eta2-H2)(CD2Cl2)(PCy3)2][BAr(F)4] 1b, can be observed by reducing the H2 pressure to 2 atm (at 298 K). Under vacuum, the dihydrogen ligands are lost in these complexes to form the spectroscopically characterized species, tentatively identified as the bis hydrides [Rh(H)2(L)2(PR3)2][BAr(F)4] (1c R = Cy; 2c R = iPr; L = CD2Cl2 or agostic interaction). Exposure of 1c or 2c to a H2 atmosphere regenerates the dihydrogen/bis-hydride complexes, while adding acetonitrile affords the bis-hydride MeCN adduct complexes [Rh(H)2(NCMe)2(PR3)2][BAr(F)4]. The dihydrogen complexes lose [HPR3][BAr(F)4] at or just above ambient temperature, suggested to be by heterolytic splitting of coordinated H2, to ultimately afford the dicationic cluster compounds of the type [Rh6(PR3)6(mu-H)12][BAr(F)4]2 in moderate yield.