X-ray Crystallographic Study of the Ruthenium Blue Complexes [Ru(2)Cl(3)(tacn)(2)](PF(6))(2).4H(2)O, [Ru(2)Br(3)(tacn)(2)](PF(6))(2).2H(2)O, and [Ru(2)I(3)(tacn)(2)](PF(6))(2): Steric Interactions and the Ru-Ru "Bond Length"

X-ray crystal structures are reported for the following complexes: [Ru(2)Cl(3)(tacn)(2)](PF(6))(2).4H(2)O (tacn = 1,4,7-triazacyclononane), monoclinic P2(1)/n, Z = 4, a = 14.418(8) ?, b = 11.577(3) ?, c = 18.471(1) ?, beta = 91.08(5) degrees, V = 3082 ?(3), R(R(w)) = 0.039 (0.043) using 4067 unique data with I > 2.5sigma(I) at 293 K; [Ru(2)Br(3)(tacn)(2)](PF(6))(2).2H(2)O, monoclinic P2(1)/a, Z = 4, a = 13.638(4) ?, b = 12.283(4) ?, c = 18.679(6) ?, beta = 109.19(2) degrees, V = 3069.5 ?(3), R(R(w)) = 0.052 (0.054) using 3668 unique data with I > 2.5sigma(I) at 293 K; [Ru(2)I(3)(tacn)(2)](PF(6))(2), cubic P2(1)/3, Z = 3, a = 14.03(4) ?, beta = 90.0 degrees, V = 2763.1(1) ?(3), R (R(w)) = 0.022 (0.025) using 896 unique data with I > 2.5sigma(I) at 293 K. All of the cations have cofacial bioctahedral geometries, although [Ru(2)Cl(3)(tacn)(2)](PF(6))(2).4H(2)O, [Ru(2)Br(3)(tacn)(2)](PF(6))(2).2H(2)O, and [Ru(2)I(3)(tacn)(2)](PF(6))(2) are not isomorphous. Average bond lengths and angles for the cofacial bioctahedral cores, [N(3)Ru(&mgr;-X)(3)RuN(3)](2+), are compared to those for the analogous ammine complexes [Ru(2)Cl(3)(NH(3))(6)](BPh(4))(2) and [Ru(2)Br(3)(NH(3))(6)](ZnBr(4)). The Ru-Ru distances in the tacn complexes are longer than those in the equivalent ammine complexes, probably as a result of steric interactions.     

Highly electrophilic, 16-electron [Ru(P(OMe)(OH)(2))(dppe)(2)](2+) complex turns H(2)(g) into a strong acid and splits a Si-H bond heterolytically. Synthesis and structure of the novel phosphorous acid complex [Ru(P(OH)(3))(dppe)(2)](2+)

The highly electrophilic, 16-electron, coordinatively unsaturated [Ru(P(OMe)(OH)(2))(dppe)(2)][OTf](2) complex brings about the heterolytic activation of H(2)(g) and spontaneously generates HOTf. In addition, trans-[Ru(H)(P(OMe)(OH)(2))(dppe)(2)](+) and an unprecedented example of a phosphorous acid complex, [Ru(P(OH)(3))(dppe)(2)](2+), are formed. The [Ru(P(OMe)(OH)(2))(dppe)(2)][OTf](2) complex also cleaves the Si-H bond in EtMe(2)SiH in a heterolytic fashion, resulting in the trans-[Ru(H)(P(OMe)(OH)(2))(dppe)(2)](+) derivative.     

Metal(II) hexafluorophosphates(V) (M = Sr, Pb) containing XeF(2)-coordinated metal ions [M(XeF(2))(3)](PF(6))(2), [Pb(3)(XeF(2))(11)](PF(6))(6), and [Sr(3)(XeF(2))(10)](PF(6))(6)

From the system MF(2)/PF(5)/XeF(2)/anhydrous hydrogen fluoride (aHF), four compounds [Sr(XeF(2))(3)](PF(6))(2), [Pb(XeF(2))(3)](PF(6))(2), [Sr(3)(XeF(2))(10)](PF(6))(6), and [Pb(3)(XeF(2))(11)](PF(6))(6) were isolated and characterized by Raman spectroscopy and X-ray single-crystal diffraction. The [M(XeF(2))(3)](PF(6))(2) (M = Sr, Pb) compounds are isostructural with the previously reported [Sr(XeF(2))(3)](AsF(6))(2). The structure of [Sr(3)(XeF(2))(10)](PF(6))(6) (space group C2/c; a = 11.778(6) Angstrom, b = 12.497(6) Angstrom, c = 34.60(2) Angstrom, beta = 95.574(4) degrees, V = 5069(4) Angstrom(3), Z = 4) contains two crystallographically independent metal centers with a coordination number of 10 and rather unusual coordination spheres in the shape of tetracapped trigonal prisms. The bridging XeF(2) molecules and one bridging PF(6)- anion, which connect the metal centers, form complicated 3D structures. The structure of [Pb(3)(XeF(2))(11)](PF(6))(6) (space group C2/m; a = 13.01(3) Angstrom, b = 11.437(4) Angstrom, c = 18.487(7) Angstrom, beta = 104.374(9) degrees, V = 2665(6) Angstrom(3), Z = 2) consists of a 3D network of the general formula {[Pb(3)(XeF(2))(10)](PF(6))(6)}n and a noncoordinated XeF(2) molecule fixed in the crystal structure only by weak electrostatic interactions. This structure also contains two crystallographically independent Pb atoms. One of them possesses a unique homoleptic environment built up by eight F atoms from eight XeF(2) molecules in the shape of a cube, whereas the second Pb atom with a coordination number of 9 adopts the shape of a tricapped trigonal prism common for lead compounds. [Pb(3)(XeF(2))(11)](PF(6))(6) and [Sr(3)(XeF(2))(10)](PF(6))(6) are formed when an excess of XeF(2) is used during the process of the crystallization of [M(XeF(2))(3)](PF(6))(2) from their aHF solutions.     

Characterization of the Lowest Excited States of [Rh(bpy-h(8))(n)(bpy-d(8))(3-n)](3+) by Highly Resolved Emission and Excitation Spectra

Highly resolved emission, excitation, and resonantly line-narrowed spectra, as well as emission decay properties of [Rh(bpy-h(8))(n)(bpy-d(8))(3-n)](3+) (n = 0, 2, 3; bpy = 2,2'-bipyridine) doped into [Zn(bpy-h(8))(3)](ClO(4))(2) are presented for the first time. [Rh(bpy-h(8))(3)](3+) and [Rh(bpy-d(8))(3)](3+) exhibit one low-lying triplet T(1) at 22 757 +/- 1 and 22 818 +/- 1 cm(-1), respectively (blue shift 61 cm(-1)), while [Rh(bpy-h(8))(2)(bpy-d(8))](3+) has two low-lying triplets at 22 757 +/- 1 and 22 818 +/- 1 cm(-1). The well-resolved vibrational satellite structures show, that the equilibrium positions of the triplet and the singlet ground S(0) state are not very different and that the force constants in T(1) are mostly slightly smaller than in S(0). Moreover, the vibrational satellite structure is strongly dominated by vibrational ligand modes, which demonstrates the pipi character of the corresponding transition. However, the occurrence of several very weak vibrational modes of metal-ligand character displays a small influence of the metal ion. This is supported by the emission decay behavior. [Rh(bpy-h(8))(2)(bpy-d(8))](3+) exhibits an emission which is clearly assignable to the protonated ligand(s), even when the deuterated ligand is selectively excited. Obviously, an efficient intramolecular energy transfer from the deuterated to the protonated ligand(s) occurs, presumably mediated by the small Rh(3+) d-admixture. A so-called "dual emission" is not observed. Moreover, a series of spectroscopic properties of the lowest excited state of [Rh(bpy)(3)](3+) (energies of electronic origins, emission decay times, zero-field splittings, structures of vibrational satellites, etc.) is compared to properties of bpy, [Pt(bpy)(2)](2+), [Ru(bpy)(3)](2+), and [Os(bpy)(3)](2+). This comparison displays in a systematic way the increasing importance of the metal d and/or MLCT character for the lowest excited states and thus provides guidelines for an experimentally based classification. In particular, the lowest excited states of [Rh(bpy)(3)](3+) may be ascribed as being mainly of (3)pipi character confined to one ligand in contrast to the situation found for [Ru(bpy)(3)](2+) where these states are covalently delocalized over the whole complex.     

Reactions of [Ru(H(2)O)(6)](2+) with water-soluble tertiary phosphines

In aqueous solutions under mild conditions, [Ru(H(2)O)(6)](2+) was reacted with various water-soluble tertiary phosphines. As determined by multinuclear NMR spectroscopy, reactions with the sulfonated arylphosphines L =mtppms, ptppms and mtppts yielded only the mono- and bisphosphine complexes, [Ru(H(2)O)(5)L](2+), cis-[Ru(H(2)O)(4)L(2)](2+), and trans-[Ru(H(2)O)(4)L(2)](2+) even in a high ligand excess. With the small aliphatic phosphine L = 1,3,5-triaza-7-phosphatricyclo-[3.3.1.1(3,7)]decane (pta) at [L]:[Ru]= 12:1, the tris- and tetrakisphosphino species, [Ru(H(2)O)(3)(pta)(3)](2+), [Ru(H(2)O)(2)(pta)(4)](2+), [Ru(H(2)O)(OH)(pta)(4)](+), and [Ru(OH)(2)(pta)(4)] were also detected, albeit in minor quantities. These results have significance for the in situ preparation of Ru(II)-tertiary phosphine catalysts. The structures of the complexes trans-[Ru(H(2)O)(4)(ptaMe)(2)](tos)(4)x2H(2)O, trans-[Ru(H(2)O)(4)(ptaH)(2)](tos)(4)[middle dot]2H(2)O, and trans-mer-[RuI(2)(H(2)O)(ptaMe)(3)]I(3)x2H(2)O, containing protonated or methylated pta ligands (ptaH and ptaMe, respectively) were determined by single crystal X-ray diffraction.     

Reactions of acetonitrile coordinated to a nitrosylruthenium complex with H2O or CH(3)OH under mild conditions: structural characterization of imido-type complexes

The reaction of cis-[Ru(NO)(CH(3)CN)(bpy)(2)](3+) (bpy = 2,2'-bipyridine) in H(2)O at room temperature proceeded to afford two new nitrosylruthenium complexes. These complexes have been identified as nitrosylruthenium complexes containing the N-bound methylcarboxyimidato ligand, cis-[Ru(NO)(NH=C(O)CH(3))(bpy)(2)](2+), and methylcarboxyimido acid ligand, cis-[Ru(NO)(NH=C(OH)CH(3))(bpy)(2)](3+), formed by an electrophilic reaction at the nitrile carbon of the acetonitrile coordinated to the ruthenium ion. The X-ray structure analysis on a single crystal obtained from CH(3)CN-H(2)O solution of cis-[Ru(NO)(NH=C(O)CH(3))(bpy)(2)](PF(6))(3) has been performed: C(22)H(20.5)N(6)O(2)P(2.5)F(15)Ru, orthorhombic, Pccn, a = 15.966(1) A, b = 31.839(1) A, c = 11.707(1) A, V = 5950.8(4) A(3), and Z = 8. The structural results revealed that the single crystal consisted of 1:1 mixture of cis-[Ru(NO)(NH=C(O)CH(3))(bpy)(2)](2+) and cis-[Ru(NO)(NH=C(OH)CH(3))(bpy)(2)](3+) and the structural formula of this single crystal was thus [Ru(NO)(NH=C(OH(0.5))CH(3))(bpy)(2)](PF(6))(2.5). The reaction of cis-[Ru(NO)(CH(3)CN)(bpy)(2)](3+) in dry CH(3)OH-CH(3)CN at room temperature afforded a nitrosylruthenium complex containing the methyl methylcarboxyimidate ligand, cis-[Ru(NO)(NH=C(OCH(3))CH(3))(bpy)(2)](3+). The structure has been determined by X-ray structure analysis: C(25)H(29)N(8)O(18)Cl(3)Ru, monoclinic, P2(1)/c, a = 13.129(1) A, b = 17.053(1) A, c = 15.711(1) A, beta = 90.876(5) degrees, V = 3517.3(4) A(3), and Z = 4.     

Synthesis and Characterization of a Series of Triethylphosphine-Ligated Pt-Au Cluster Compounds. X-ray Crystal and Molecular Structure of [Pt(AuPEt(3))(9)](NO(3))(3)

The first triethylphosphine-stabilized Pt-Au cluster compounds, [Pt(AuPEt(3))(10)](2+) (2) and [Pt(AuPEt(3))(9)](3+) (3), were prepared by the direct reaction of Pt(PEt(3))(3) with AuPEt(3)NO(3) under a dihydrogen atmosphere. Cluster 2 is the highest-nuclearity homoleptic Pt(AuPR(3))(n)() cluster yet prepared. The reactivity and structures of these clusters are in agreement with the well-established electron-counting arguments. The 18-electron cluster 2 was converted into the 16-electron cluster 3 by oxidation with 2 equiv of ferricinium ion [Fe(eta(5)-C(5)H(5))(2)](+). Cluster 3 was converted into 2 by reduction with H(2) in the presence of [AuPEt(3)](+). Cluster 3 was also observed to cleanly add the 2-electron donors CO and PEt(3) to form the 18-electron clusters [(CO)Pt(AuPEt(3))(9)](3+) (4) and [(PEt(3))Pt(AuPEt(3))(9)](3+) (5), respectively. Single-crystal X-ray diffraction results show that 3 has a flattened, toroidal structure in which the PtAu(9) framework has a Pt-centered, tricapped trigonal prismatic geometry. Crystal data for [Pt(AuPEt(3))(9)](NO(3))(3) is as follows: hexagonal P6(3)/m, a = 15.134(5) ?, c = 23.48(1) ?, V = 4657 ?(3), Z = 2, residuals R = 0.056, and R(w)() = 0.053 for 1489 observed reflections and 81 variables, Mo Kalpha radiation. Compound 3 was found to reversibly add H(2) in solution to form the dihydride cluster [(H)(2)Pt(AuPEt(3))(9)](3+) (6). The equilibrium constant for this addition reaction is 1.1 x 10(3) M(-)(1) (CD(2)Cl(2) solution, 25 degrees C), slightly smaller than that for [Pt(AuPPh(3))(8)](2+). The rate of the addition is also slower than that with [Pt(AuPPh(3))(8)](2+). Cluster 3 is an excellent homogeneous catalyst for H(2)-D(2) equilibration giving a turnover rate for HD production of 0.13 s(-)(1) (nitrobenzene solvent, 30 degrees C, 1 atm). The PEt(3)-containing clusters give similar rates and follow the same general trends previously observed with PPh(3)-ligated clusters. The chemistry of these new clusters is explained by consideration of the steric and electronic properties of the PEt(3) ligand. These new compounds will be useful as models for hydrogen activation by Pt-Au clusters and as precursors for supported Pt-Au catalysts.     

Preparation and characterization of the argentates: [Ag[P(CF(3))(2)](2)](-), [Ag[(micro-P(CF(3))(2))M(CO)(5)](2)](-) (M = Cr, W), and [Ag[(micro-P(C(6)F(5))(2))W(CO)(5)](2)](-): X-ray crystal structure of [K(18-crown-6)][Ag[(micro-P(CF(3))(2))Cr(CO)(5)](2)

The first example of a mononuclear diphosphanidoargentate, bis[bis(trifluoromethyl)phosphanido]argentate, [Ag[P(CF(3))(2)](2)](-), is obtained via the reaction of HP(CF(3))(2) with [Ag(CN)(2)](-) and isolated as its [K(18-crown-6)] salt. When the cyclic phosphane (PCF(3))(4) is reacted with a slight excess of [K(18-crown-6)][Ag[P(CF(3))(2)](2)], selective insertion of one PCF(3) unit into each silver phosphorus bond is observed, which on the basis of NMR spectroscopic evidence suggests the [Ag[P(CF(3))P(CF(3))(2)](2)](-) ion. On treatment of the phosphane complexes [M(CO)(5)PH(CF(3))(2)] (M = Cr, W) with [K(18-crown-6)][Ag(CN)(2)], the analogous trinuclear argentates, [Ag[(micro-P(CF(3))(2))M(CO)(5)](2)](-), are formed. The chromium compound [K(18-crown-6)][Ag[(micro-P(CF(3))(2))Cr(CO)(5)](2)] crystallizes in a noncentrosymmetric space group Fdd2 (No. 43), a = 2970.2(6) pm, b = 1584.5(3) pm, c = 1787.0(4), V = 8.410(3) nm(3), Z = 8. The C(2) symmetric anion, [Ag[(micro-P(CF(3))(2))Cr(CO)(5)](2)](-), shows a nearly linear arrangement of the P-Ag-P unit. Although the bis(pentafluorophenyl)phosphanido compound [Ag[P(C(6)F(5))(2)](2)](-) has not been obtained so far, the synthesis of its trinuclear counterpart, [K(18-crown-6)][Ag[(micro-P(C(6)F(5))(2))W(CO)(5)](2)], was successful.     

Spectroelectrochemical studies on mixed-valence states in a cyanide-bridged molecular square, [Ru(II)(2)Fe(II)(2)(mu-CN)(4)(bpy)(8)](PF6)(4).CHCl(3).H(2)O

A cyanide-bridged molecular square of [Ru(II) (2)Fe(II) (2)(mu-CN)(4)(bpy)(8)](PF(6))(4).CHCl(3).H(2)O, abbreviated as [Ru(II) (2)Fe(II) (2)](PF(6))(4), has been synthesised and electrochemically generated mixed-valence states have been studied by spectroelectrochemical methods. The complex cation of [Ru(II) (2)Fe(II) (2)](4+) is nearly a square and is composed of alternate Ru(II) and Fe(II) ions bridged by four cyanide ions. The cyclic voltammogram (CV) of [Ru(II) (2)Fe(II) (2)](PF(6))(4) in acetonitrile showed four quasireversible waves at 0.69, 0.94, 1.42 and 1.70 V (vs. SSCE), which correspond to the four one-electron redox processes of [Ru(II) (2)Fe(II) (2)](4+) right arrow over left arrow [Ru(II) (2)Fe(II)Fe(III)] (5+) right arrow over left arrow [Ru(II) (2)Fe(III) (2)](6+) right arrow over left arrow [Ru(II)Ru(III)Fe(III) (2)](7+) right arrow over left arrow [Ru(III) (2)Fe(III) (2)](8+). Electrochemically generated [Ru(II) (2)Fe(II)Fe(III)](5+) and [Ru(II) (2)Fe(III) (2)](6+) showed new absorption bands at 2350 nm (epsilon =5500 M(-1) cm(-1)) and 1560 nm (epsilon =10 500 M(-1) cm(-1)), respectively, which were assigned to the intramolecular IT (intervalence transfer) bands from Fe(II) to Fe(III) and from Ru(II) to Fe(III) ions, respectively. The electronic interaction matrix elements (H(AB)) and the degrees of electronic delocalisation (alpha(2)) were estimated to be 1090 cm(-1) and 0.065 for the [Ru(II) (2)Fe(II)Fe(III) (2)](5+) state and 1990 cm(-1) and 0.065 for the [Ru(II) (2)Fe(III) (2)](6+) states.     

Polyoxoanions Derived from [gamma-SiO(4)W(10)O(32)](8-)-Containing Oxo-Centered Dinuclear Chromium(III) Carboxylato Complexes: Synthesis and Single-Crystal Structural Determination of [gamma-SiO(4)W(10)O(32)(OH)Cr(2)(OOCCH(3))(2)(OH(2))(2)](5-)

The previously unknown heteropolyoxometalates [gamma-SiO(4)W(10)O(32)(OH)Cr(2)(OOCR)(2)(OH(2))(2)](5-) (R = H, CH(3)) have been prepared by the reaction of [gamma-SiO(4)W(10)O(32)](8-) with [Cr(OH(2))(6)](3+) in formate or acetate buffer solution. Isolation of these new Cr(III)-substituted polyoxometalates was accomplished both as Cs(+) salts and as the Bu(4)N(+) salt for the acetate-containing anion. The compounds were characterized by elemental analysis, UV/vis, IR, and ESR spectroscopy, and cyclic voltammetry. The single-crystal X-ray structural analysis of (Bu(4)N)(3)H(2)[gamma-SiO(4)W(10)O(32)(OH)Cr(2)(OOCCH(3))(2)(OH(2))(2)].3H(2)O [P2(1)2(1)2(1); a = 17.608(12), b = 20.992(13), c = 24.464(11) ?; Z = 4; R = 0.057 for 6549 observed independent reflections] reveals that the two corner-linked CrO(6) octahedra are additionally bridged by two acetate groups, demonstrating the relationship to the well-studied oxo-centered trinuclear carboxylato complexes of Cr(III).     

2,6-Mes(2)C(6)H(3)](2)Ga(+)Li[Al(OCH(CF(3))(2))(4)](2)(-) (Mes = 2,4,6-Me(3)C(6)H(2)): A compound containing a linear unsolvated two-coordinate gallium cation

The title compound [2,6-Mes(2)C(2)H(3)](2)Ga(+)Li[Al(OCH(CF(3))(2))(4)](2)(-), 1, containing a linear two-coordinate gallium cation, has been obtained by metathesis reaction of [2,6-Mes(2)C(2)H(3)](2)GaCl with 2 equiv of Li[Al(OCH(CF(3))(2))(4)] in C(6)H(5)Cl solution at room temperature. Compound 1 has been characterized by (1)H, (13)C((1)H), (19)F, and (27)Al NMR spectroscopy and X-ray crystallography. Compound 1 consists of isolated [2,6-Mes(2)C(6)H(3)](2)Ga(+) cations and Li[Al(OCH(CF(3))(2))(4)](2)(-) anions. The C-Ga-C angle is 175.69(7) degrees, and the Ga-C distances are 1.9130(14) and 1.9145(16) A. The title compound is remarkably stable, is only a weak Lewis acid, and polymerizes cyclohexene oxide.     

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.     

Synthesis and characterization of the hexagonal prismatic cage [THF[subset or is implied by][PhB(CN)(3)](6)[Cp*Rh](6)](6+)

Condensation of [Cp*Rh(CH(3)NO(2))(n)](2+) and the tricyanoborate [PhB(CN)(3)](-) affords the hexagonal bipyramidal cage [[PhB(CN)(3)](6)[Cp*Rh](6)](6+), demonstrating that tetrahedral tricyanide building blocks can lead to novel cage structures.     

Single- and double-cubane clusters in the multiple oxidation states [VFe(3)S(4)](3+,2+,1+)

A new series of cubane-type [VFe(3)S(4)](z)() clusters (z = 1+, 2+, 3+) has been prepared as possible precursor species for clusters related to those present in vanadium-containing nitrogenase. Treatment of [(HBpz(3))VFe(3)S(4)Cl(3)](2)(-) (2, z = 2+), protected from further reaction at the vanadium site by the tris(pyrazolyl)hydroborate ligand, with ferrocenium ion affords the oxidized cluster [(HBpz(3))VFe(3)S(4)Cl(3)](1)(-) (3, z = 3+). Reaction of 2 with Et(3)P results in chloride substitution to give [(HBpz(3))VFe(3)S(4)(PEt(3))(3)](1+) (4, z = 2+). Reaction of 4 with cobaltocene reduced the cluster with formation of the edge-bridged double-cubane [(HBpz(3))(2)V(2)Fe(6)S(8)(PEt(3))(4)] (5, z = 1+, 1+), which with excess chloride underwent ligand substitution to afford [(HBpz(3))(2)V(2)Fe(6)S(8)Cl(4)](4)(-) (6, z = 1+, 1+). X-ray structures of (Me(4)N)[3], [4](PF(6)), 5, and (Et(4)N)(4)[6] x 2MeCN are described. Cluster 5 is isostructural with previously reported [(Cl(4)cat)(2)(Et(3)P)(2)Mo(2)Fe(6)S(8)(PEt(3))(4)] and contains two VFe(3)S(4) cubanes connected across edges by a Fe(2)S(2) rhomb in which the bridging Fe-S distances are shorter than intracubane Fe-S distances. M?ssbauer (2-5), magnetic (2-5), and EPR (2, 4) data are reported and demonstrate an S = 3/2 ground state for 2 and 4 and a diamagnetic ground state for 3. Analysis of (57)Fe isomer shifts based on an empirical correlation between shift and oxidation state and appropriate reference shifts results in two conclusions. (i) The oxidation 2 --> 3 + e(-) results in a change in electron density localized largely or completely on the Fe(3) subcluster and associated sulfur atoms. (ii) The most appropriate charge distributions are [V(3+)Fe(3+)Fe(2+)(2)S(4)](2+) (Fe(2.33+)) for 1, 2, and 4 and [V(3+)Fe(3+)(2)Fe(2+)S(4)](3+) (Fe(2.67+)) for 3 and [V(2)Fe(6)S(8)(SEt)(9)](3+). Conclusion i applies to every MFe(3)S(4) cubane-type cluster thus far examined in different redox states at parity of cluster ligation. The formalistic charge distributions are regarded as the best current approximations to electron distributions in these delocalized species. The isomer shifts require that iron atoms are mixed-valence in each cluster.     

Simplest homoleptic metal-centered tetrahedrons, [M(OH2)4]2+, in 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid (M = Co, Ni, Cu)

Dissolution of a tetrafluoroborate or perchlorate salt of [M(OH(2))(6)](2+) (M = Co, Ni, Cu) in 1-ethyl-3-methylimidazolium tetraluforoborate ionic liquid ([emim]BF(4)) results in significant solvatochromism and increasing intensity of color. These observations arise from partial dehydration from the octahedral [M(OH(2))(6)](2+) and formation of the tetrahedral [M(OH(2))(4)](2+). This reaction was monitored by the intense absorption band due to the d-d transition in the UV-vis absorption spectrum. The EXAFS investigation clarified the coordination structures around M(2+) {[Co(OH(2))(4)](2+), R(Co-O) = 2.17 ?, N = 4.2; [Cu(OH(2))(4)](2+), R(Cu-O) = 2.09 ?, N = 3.8}. (1)H and (19)F NMR study suggested that both [emim](+) and BF(4)(-) are randomly arranged in the second-coordination sphere of [M(OH(2))(4)](2+).     

A high-pressure iron K-edge x-ray absorption spectral study of the spin-state crossover in (Fe[HC(3,5-(CH(3))(2)pz)(3)](2))I(2) and (Fe[HC(3,5-(CH(3))(2)pz)(3)](2))(BF(4))(2)

The room temperature iron K-edge X-ray absorption near edge structure spectra of (Fe[HC(3,5-(CH(3))(2)pz)(3)](2))I(2) and (Fe[HC(3,5-(CH(3))(2)pz)(3)](2))(BF(4))(2) have been measured between ambient and 88 and 94 kbar, respectively, in an opposed diamond anvil cell. The iron(II) in (Fe[HC(3,5-(CH(3))(2)pz)(3)](2))I(2)undergoes the expected gradual spin-state crossover from the high-spin state to the low-spin state with increasing pressure. In contrast, the iron(II) in (Fe[HC(3,5-(CH(3))(2)pz)(3)](2))(BF(4))(2) remains high-spin between ambient and 78 kbar and is only transformed to the low-spin state at an applied pressure of between 78 and 94 kbar. No visible change is observed in the preedge peak in the spectra of (Fe[HC(3,5-(CH(3))(2)pz)(3)](2))I(2) with increasing pressure, whereas the preedge peak in the spectra of ((e[HC(3,5-(CH(3))(2)pz)(3)](2))(BF(4))(2) changes as expected for a high-spin to low-spin crossover with increasing pressure. The difference in the spin-state crossover behavior of these two complexes is likely related to the unusual behavior of (Fe[HC(3,5-(CH(3))(2)pz)(3)](2))(BF(4))(2) upon cooling.     

Homoleptic, sigma-bonded octahedral [M(CO)(6)](2+) cations of iron(II), ruthenium(II), and osmium(II). Part 1: Syntheses, thermochemical and vibrational characterizations, and molecular structures as [Sb(2)F(11)](-) and [SbF(6)](-) salts. A comprehensive, comparative study

Homoleptic octahedral, superelectrophilic sigma-bonded metal carbonyl cations of the type [M(CO)(6)](2+) (M = Ru, Os) are generated in the Bronsted-Lewis conjugate superacid HF/SbF(5) by reductive carbonylation of M(SO(3)F)(3) (M = Ru, Os) or OsF(6). Thermally stable salts form with either [Sb(2)F(11)](-) or [SbF(6)](-) as anion, just as for the previously reported [Fe(CO)(6)](2+) cation. The latter salts are generated by oxidative (XeF(2)) carbonylation of Fe(CO)(5) in HF/SbF(5). A rationale for the two diverging synthetic approaches is provided. The thermal stabilities of [M(CO)(6)][SbF(6)](2) salts, studied by DSC, range from 180 degrees C for M = Fe to 350 degrees C for M = Os before decarbonylation occurs. The two triads [M(CO)(6)][SbF(6)](2) and [M(CO)(6)][Sb(2)F(11)](2) (M = Fe, Ru, Os) are extensively characterized by single-crystal X-ray diffraction and vibrational and (13)C NMR spectroscopy, aided by computational studies of the cations. The three [M(CO)(6)][SbF(6)](2) salts (M = Fe, Ru, Os) crystallize in the tetragonal space group P4/mnc (No. 128), whereas the corresponding [Sb(2)F(11)](-) salts are monoclinic, crystallizing in space group P2(1)/n (No. 14). In both triads, the unit cell parameters are nearly invariant of the metal. Bond parameters for the anions [SbF(6)](-) and [Sb(2)F(11)](-) and their vibrational properties in the two triads are completely identical. In all six salts, the structural and vibrational properties of the [M(CO)(6)](2+) cations (M = Fe, Ru, Os) are independent of the counteranion and for the most part independent of M and nearly identical. Interionic C...F contacts are similarly weak in all six salts. Metal dependency is noted only in the (13)C NMR spectra, in the skeletal M-C vibrations, and to a much smaller extent in some of the C-O stretching fundamentals (A(1g) and T(1u)). The findings reported here are unprecedented among metal carbonyl cations and their salts.     

Solid-state NMR spectroscopic study of coordination compounds of XeF(2) with metal cations and the crystal structure of [Ba(XeF(2))(5)][AsF(6)](2)

The coordination compounds [Mg(XeF(2))(2)][AsF(6)](2), [Mg(XeF(2))(4)][AsF(6)](2), [Ca(XeF(2))(2.5)][AsF(6)](2), [Ba(XeF(2))(3)][AsF(6)](2), and [Ba(XeF(2))(5)][AsF(60](2) were characterized by solid-state (19)F and (129)Xe magic-angle spinning NMR spectroscopy. The (19)F and (129)Xe NMR data of [Mg(XeF(2))(2)][AsF(6)](2), [Mg(XeF(2)(4)][AsF(6)](2), and [Ca(XeF(2))(2.5)][AsF(6)](2) were correlated with the previously determined crystal structures. The isotropic (19)F chemical shifts and (1)J((129)Xe-(19)F) coupling constants were used to distinguish the terminal and bridging coordination modes of XeF(2). Chemical-shift and coupling-constant calculations for [Mg(XeF(2))(4)][AsF(6)](2) confirmed the assignment of terminal and bridging chemical-shift and coupling-constant ranges. The NMR spectroscopic data of [Ba(XeF(2))(3)][AsF(6)](2) and [Ba(XeF(2))(5)][AsF(6)](2) indicate the absence of any terminal XeF(2) ligands, which was verified for [Ba(XeF(2))(5)][AsF(6)](2) by its X-ray crystal structure. The adduct [Ba(XeF(2))(5)][AsF(6)](2) crystallizes in the space group Fmmm, with a = 11.6604(14) Angstrom, b = 13.658(2) Angstrom, c = 13.7802(17) Angstrom, V = 2194.5(5) Angstrom(3) at -73 degrees C, Z = 4, and R = 0.0350 and contains two crystallographically independent bridging XeF(2) molecules and one nonligating XeF(2) molecule. The AsF(6-) anions in [Mg(XeF(2))(4)][AsF(6)](2), [Ca(XeF(2))(2.5)][AsF(6)](2), [Ba(XeF(2))(3)][AsF(6)](2), and [Ba(XeF(2))(5)][AsF(6)](2) were shown to be fluxional with the fluorines-on-arsenic being equivalent on the NMR time scale, emulating perfectly octahedral anion symmetry.     

Elimination of sulfur from aromatic heterocycles by a water-soluble arene ruthenium cluster: synthesis and molecular structure of [H2S2Ru4(C6H6)4]Cl2

C-S bond cleavage in thiophene, benzothiophene and dibenzothiophene is achieved under biphasic conditions by the water-soluble cluster cation [H(4)Ru(4)(C(6)H(6))(4)](2+) which is converted into the disulfido cluster [H(2)S(2)Ru(4)(C(6)H(6))(4)](2+).     

Spectroscopic and structural characterization of the [Fe(imidazole)(6)](2+) cation

Spectroscopic, structural, and magnetic data are presented for Fe(C(3)H(4)N(2))(6)(NO(3))(2), which facilitate a precise definition of the electronic and molecular structure of the [Fe(Im)(6)](2+) cation. The structure was determined at 120(1) K by X-ray diffraction methods. The salt crystallizes in the trigonal space group R3 with unit-cell parameters a = 12.4380(14) A, c = 14.5511(18) A, and Z = 3. All the imidazole ligands are equivalent with an Fe-N bond distance of 2.204(1) A. Variable-temperature inelastic neutron scattering (INS) measurements identify a cold magnetic transition at 19.4(2) cm(-1) and a hot transition at 75.7(6) cm(-1). The data are interpreted using a ligand field Hamiltonian acting in the weak-field (5)D basis, from which the diagonal trigonal field splitting of the (5)T(2g) (O(h)) term is estimated as approximately 485 cm(-1), with the (5)A(g) (S(6)) component lower lying. High-field multifrequency (HFMF) EPR data and measurements of the magnetic susceptibility are also reported and can be satisfactorily modeled using the energies and wave functions derived from analysis of the INS data. The electronic and molecular structures are related through angular overlap model calculations, treating the imidazole ligand as a weak pi-donor.