Syntheses, structural determination, and electrochemistry of Ru(2)(Fap)(4)Cl and Ru(2)(Fap)(4)(NO)Cl

Ru(2)(Fap)(4)Cl and Ru(2)(Fap)(4)(NO)Cl, where Fap is the 2-(2-fluoroanilino)pyridinate anion, were synthesized, and their structural, electrochemical, and spectroscopic properties were characterized. Ru(2)(Fap)(4)Cl, which was obtained by reaction between Ru(2)(O(2)CCH(3))(4)Cl and molten HFap, crystallizes in the monoclinic space group P2(1)/c, with a = 11.2365(4) A, b = 19.9298(8) A, c = 19.0368(7) A, beta = 90.905(1) degrees, and Z = 4. The presence of three unpaired electrons on the Ru(2)(5+) core and the 2.2862(3) A Ru-Ru bond length for Ru(2)(Fap)(4)Cl are consistent with the electronic configuration (sigma)(2)(pi)(4)(delta)(2)(pi*)(2)(delta*)(1). The reaction between Ru(2)(Fap)(4)Cl and NO gas yields Ru(2)(Fap)(4)(NO)Cl, which crystallizes in the orthorhombic space group Pbca, with a = 10.0468(6) A, b = 18.8091(10) A, c = 41.7615(23) A, and Z = 8. The Ru-Ru bond length of Ru(2)(Fap)(4)(NO)Cl is 2.4203(8) A, while its N-O bond length and Ru-N-O bond angle are 1.164(8) A and 155.8(6) degrees, respectively. Ru(2)(Fap)(4)(NO)Cl can be formulated as a formal Ru(2)(II,II)(NO(+)) complex with a linear Ru-N-O group, and the proposed electronic configuration for this compound is (sigma)(2)(pi)(4)(delta)(2)(pi*)(3)(delta*)(1). The binding of NO to Ru(2)(Fap)(4)Cl leads to some structural changes of the Ru(2)(Fap)(4) framework and a stabilization of the lower oxidation states of the diruthenium unit. Also, IR spectroelectrochemical studies of Ru(2)(Fap)(4)(NO)Cl show that NO remains bound to the complex upon reduction and that the first reduction involves the addition of an electron on the diruthenium core and not on the NO axial ligand.     

Hydrolysis of tin(II) neo-pentoxide: syntheses, characterization, and X-ray structures of [Sn(ONep)(2)](infinity), Sn(5)(mu(3)-O)(2)(mu-ONep)(6), and Sn(6)(mu(3)-O)(4)(mu-ONep)(4) where ONep = OCH(2)CMe(3)

The reaction of [Sn(NMe(2))(2)](2) (1) with 4 equiv of HOCH(2)CMe(3) (HONep) leads to the isolation of [Sn(ONep)(2)](infinity) (2). Each Sn atom is four coordinated with mu-ONep ligands bridging the metal centers; however, if the free electrons of the Sn(II) metal center are considered, each Sn center adopts a distorted trigonal bipyramidal (TBP) geometry. Through (119)Sn NMR experiments, the polymeric compound 2 was found to be disrupted into smaller oligomers in solution. Titration of 2 with H(2)O led to the identification of two unique hydrolysis products characterized by single-crystal X-ray diffraction as Sn(5)(mu(3)-O)(2)(mu-ONep)(6) (3) and Sn(6)(mu(3)-O)(4)(mu-ONep)(4) (4). Compound 3 consists of an asymmetrical molecule that has five Sn atoms arranged in a square-based pyramidal geometry linked by four basal mu-ONep ligands, two facial mu(3)-O, and two facial mu-ONep ligands. Compound 4 was solved in a novel octahedral arrangement of six Sn cations with an asymmetric arrangement of mu(3)-O and mu-ONep ligands that yields two square base pyramidal and four pyramidal coordinated Sn cations. These compounds were further identified by multinuclear ((1)H, (13)C, (17)O, and (119)Sn) solid-state MAS and high resolution, solution NMR experiments. Because of the complexity of the compounds and the accessibility of the various nuclei, 2D NMR experiments were also undertaken to elucidate the solution behavior of these compounds. On the basis of these studies, it was determined that while the central core of the solid-state structures of 3 and 4 is retained, dynamic ligand exchange leads to more symmetrical molecules in solution. Novel products 3 and 4 lend structural insight into the stepwise hydrolysis of Sn(II) alkoxides.     

Synthesis, Molecular Structure, and Vibrational Spectra of mer-Tris(carbonyl)iridium(III) Fluorosulfate, mer-Ir(CO)(3)(SO(3)F)(3)

Addition of carbon monoxide (0.5-2 atm) to iridium(III) fluorosulfate, Ir(SO(3)F)(3), dissolved in HSO(3)F over 4 days and at 60 degrees C, results in the quantitative formation of tris(carbonyl)iridium(III) fluorosulfate Ir(CO)(3)(SO(3)F)(3). Slow evaporation of the solvent produces single crystals of mer-Ir(CO)(3)(SO(3)F)(3). Crystal structure data for mer-Ir(CO)(3)(SO(3)F)(3): monoclinic, space group P2(1)/c, Z = 4, a = 8.476(1) ?, b = 12.868(2) ?, c = 12.588 (1) ?, beta = 108.24(1) degrees, V = 1304.0 ?(3), T = 200 K, R(F)() = 0.022 for 2090 data (I(o) >/= 2.5sigma(I(o))) and 200 variables. Vibrational spectra of the crystalline solid are consistent with a mer-isomer with CO stretching modes at 2249 (A(1)), 2208 (B(1)), and 2198 (A(1)) cm(-)(1) in the IR spectrum. In solution of HSO(3)F, additional CO stretching bands attributed to the fac-isomer are found in the FT-Raman and IR spectra at 2233 (A(1)) and 2157 cm(-)(1) (E). Additional evidence for a mixture of fac- and mer-isomers comes from (19)F NMR spectra. The vibrational spectra suggest strongly reduced iridium to CO pi-back-bonding. The crystal structure reveals significant intra- and intermolecular contacts between the electropositive C atom of the CO groups and O or F atoms of the fluorosulfate groups. Hence mer-tris(carbonyl)iridium(III) fluorosulfate becomes the first thermally stable, structurally characterized, and predominantly sigma-bonded carbonyl derivative of a metal in the +3 oxidation state.     

N,N'-diisopropyl-N'-bis(trimethylsilyl)guanidinate ligand as a supporting coordination environment in yttrium chemistry. Synthesis, structure, and properties of complexes [(Me(3)Si)(2)NC(Ni-Pr)(2)]YCl(2)(THF)(2), [(Me(3)Si)(2)NC(Ni-Pr)(2)]Y(CH(2)SiMe(3))(2)(THF)(2), and [(Me(3)Si)(2)NC(Ni-Pr)(2)]Y[(mu-H)(mu-Et)(2)BEt](2)(THF)

The reaction of anhydrous YCl3 with an equimolar amount of lithium N,N'-diisopropyl-N' '-bis(trimethylsilyl)guanidinate, Li[(Me3Si)2NC(Ni-Pr)2], in tetrahydrofuran (THF) afforded the monomeric monoguanidinate dichloro complex {(Me3Si)2NC(Ni-Pr)2}YCl2(THF)2 (1). Alkylation of complex 1 with 2 equiv of LiCH2SiMe3 in hexane at 0 degrees C yielded the monomeric salt-free dialkyl complex {(Me3Si)2NC(Ni-Pr)2}Y(CH2SiMe3)2(THF)2 (2). The bis(triethylborohydride) complex [(Me3Si)2NC(Ni-Pr)2]Y[(mu-H)(mu-Et)2BEt]2(THF) (5) was prepared by the reaction of complex 1 with 2 equiv of LiBEt3H in a toluene-THF mixture at 0 degrees C. The complexes 1, 2, and 5 were structurally characterized. Complex 2 as well as the systems 2-Ph3B, 2-Ph3B-MAO, and 1-MAO (MAO = methylaluminoxanes) in toluene were inactive in ethylene polymerization, while the product obtained in situ from the reaction of complex 2 with a 2-fold molar excess of PhSiH3 in toluene polymerized ethylene with moderate activity.     

Synthesis and structures of gallium amido imido phenyl clusters (PhGa)(4)(NH(i)Bu)(4)(N(i)Bu)(2) and (PhGa)(7)(NHMe)(4)(NMe)(5)

The phenylgallium-containing clusters constructed with bridging imido and amido ligands, (PhGa)(4)(NH(i)Bu)(4)(N(i)Bu)(2) (1) (51% yield) and (PhGa)(7)(NHMe)(4)(NMe)(5) (2) (31% yield), were synthesized from the room-temperature reactions of bis(dimethylamido)phenylgallium, [PhGa(NMe(2))(2)](2), with isobutylamine and methylamine, respectively. The reaction of [PhGa(NMe(2))(2)](2) in refluxing isobutylamine (85 degrees C) afforded (Ph(2)GaNH(i)Bu)(2) as one of the products, while the reaction of [PhGa(NMe(2))(2)](2) with methylamine at 150 degrees C afforded compound 2 in only 9% yield. Compound 1 possessed an admantane-like Ga(4)N(6) core, whereas compound 2 had a novel Ga(7)N(9) core constructed with both chair- and boat-shaped Ga(3)N(3) rings. The presence of several isomers of compounds 1 and 2 in solution is discussed along the structural similarities with other known gallium-nitrogen clusters and with gallium nitride.     

Synthesis,structure, and magnetic properties of the single-molecule magnet [Ni(21)(cit)(12)(OH)(10)(H(2)O)(10)](16-)

The preparation of two new compounds containing the cluster [Ni(21)(cit)(12)(OH)(10)(H(2)O)(10)](16-) is presented, together with a detailed magnetic investigation of one of the compounds. We found that this cluster shows an unexpected stability and that it exists as different stereoisomers. Compound 1 contains the achiral cluster with a Delta-Lambda configuration, and compound 2 contains a pair of enantiomeric clusters with the configurations Delta-Delta and Lambda-Lambda, respectively. Magnetic measurements of 1 in the millikelvin range were necessary to determine the spin ground state of S = 3, and they also revealed a magnetic anisotropy within the ground state. A frequency-dependent out-of-phase signal was found in alternating current susceptibility measurements at very low temperatures, which indicates a slow relaxation of the magnetization. Thus, individual molecules are acting as single magnetic units, which is a rare phenomenon for nickel clusters. The energy barrier exhibited by compound 1 has been calculated to be 2.9 K.     

Noble gas-actinide compounds: evidence for the formation of distinct CUO(Ar)(4-n)(Xe)(n) and CUO(Ar)(4-n)(Kr)(n) (n = 1, 2, 3, 4) complexes

Laser-ablated U atoms react with CO in excess argon to produce CUO, which gives rise to 852.5 and 804.3 cm-1 infrared absorptions for the triplet state CUO(Ar)n complex in solid argon at 7 K. Relativistic density functional calculations show that the CUO(Ar) complex is stable and that up to four or five argon atoms can complex to CUO. When 1-3% Xe is added to the argon/CO reagent mixture, strong absorptions appear at 848.0 and 801.3 cm-1 and dominate new four-band progressions, which increase on annealing to 35-50 K as Xe replaces Ar in the intimate coordination sphere. Analogous spectra are obtained with 1-2% Kr added. This work provides evidence for eight distinct CUO(Ng)n(Ar)4-n (Ng = Kr, Xe, n = 1, 2, 3, 4) complexes and the first characterization of neutral complexes involving four noble-gas atoms on one metal center.     

Synthesis, crystal structure, and magnetic studies of oxo-centered trinuclear chromium(III) complexes: [Cr(3)(mu(3)-O)(mu(2)-PhCOO)(6)(H(2)O)(3)]NO(3). 4H(2)O.2CH(3)OH, a case of spin-frustrated system, and [Cr(3)(mu(3)-O)- (mu(2)-PhCOO)(2)(mu(2)-OCH(2)CH(3))(2)(bpy)(2)(NCS )(3)], a new type of [Cr(3)O] core

The synthesis, crystal structure, and magnetic properties of two trinuclear oxo-centered carboxylate complexes are reported and discussed: [Cr3(mu3-O)(mu2-PhCOO)6(H2O)3]NO3.4H2O.2CH3OH (1) and [Cr3(mu3-O)(mu2-PhCOO)2(mu2-OCH2CH3)2(bpy)2(NCS)3] (2). For both complexes the crystal system is monoclinic, with space group C2/c for 1 and P1/n for 2. The structure of complex 1 consists of discrete trinuclear cations, associated NO3- anions, and lattice methanol and water molecules. The structure of complex 2 is built only by neutral discrete trinuclear entities. The most important feature of 2 is the unusual skeleton of the [Cr3O] core due to the lack of peripheral bridging ligands along one side of the triangular core, which is unique among the structurally characterized (mu3-oxo)trichromium(III) complexes. Magnetic measurements were performed in the 2-300 K temperature range. For complex 1, in the high-temperature region (T > 8 K), experimental data could be satisfactorily reproduced by using an isotropic exchange model, H = -2J12S1S2 - 2J13S1S3 - 2J23S2S3 (J12 = J13 = J23) with Jij = -10.1 cm(-1), g = 1.97, and TIP = 550 x 10(-6) emu mol(-1). The antisymmetric exchange interaction plays an important role in the magnetic behavior of the system, so in order to fit the experimental magnetic data at low temperature, a new magnetic model was used where this kind of interaction was also considered. The resulting fitting parameters are the following: Gzz = 0.25 cm(-1), delta = 2.5 cm(-1), and TIP = 550 x 10(-6) emu mol(-1). For complex 2, the experimental data could be satisfactorily reproduced by using an isotropic exchange model, H = -2J1(S1S2 + S1S3) - 2J2(S2S3) with J1 = -7.44 cm(-1), J2 = -51.98 cm(-1), and g = 1.99. The magnetization data allows us to deduce the ground term of S = 1/2, characteristic of equilateral triangular chromium(III) for complex 1 and S = 3/2 for complex 2, which is confirmed by EPR measurements.     

Carboxylate-bridged copper(II)-lanthanide(III) complexes [(Cu(3)Ln(2)(oda)(6)(H(2)O)(6)).12H(2)O](n)(Ln = Dy,Ho, Er,Y; oda = oxydiacetate)

The hydrothermal reaction of Ln(2)O(3) (Ln = Dy and Ho), Cu(OAc)(2).2H(2)O, and oxydiacetic acid in the approximate mole ratio of 1:3:8 resulted in the formation of two new members of the isostructural series of polymers formulated as [(Cu(3)Ln(2)(oda)(6)(H(2)O)(6)).12H(2)O](n), crystallizing in the hexagonal crystal system, space group P6/mcc (No. 192). Temperature-dependent magnetic susceptibilities and EPR spectra are reported for the heterometallic compounds Cu-Dy 1, Cu-Ho 2, Cu-Er 3, and Cu-Y 4. The results are discussed in terms of the structure of the compounds, the electronic properties of the lanthanide ions, and the exchange interactions between the magnetic ions.     

Outer-Sphere Electron Transfer in Methylene Chloride: Concentration, Salt, and Temperature Dependences of the Oxidation of beta-Re(2)X(4)(cis-1,2-bis(diphenylphosphino)ethylene)(2) (X = Cl, Br) by [Co(dimethylglyoximate)(3)(BF)(2)]BF(4) and the Oxidation of Re(2)Br(4)(PMe(2)Ph)(4) by [Co(1,2-cyclohexanedione dioximate)(3)(BBu)(2)]BF(4)

The kinetics of the oxidation of beta-Re(2)X(4)(cis-1,2-bis(diphenylphosphino)ethylene)(2) (X = Cl, Br) by the cobalt clathrochelate [Co(dimethylglyoximate)(3)(BF)(2)]BF(4) and the oxidation of Re(2)Br(4)(PMe(2)Ph)(4) by the cobalt clathrochelate [Co(1,2-cyclohexanedione dioximate)(3)(BBu)(2)]BF(4) have been studied by the stopped-flow method as a function of temperature (-85 to -19 degrees C), added Bu(4)NBF(4) (0-0.100 M), and reactant concentration in the low dielectric solvent methylene chloride. For each reaction, approximately 100 different conditions were studied. The observed rate constants were well fit by a mechanism involving separate paths for free ion and the ion-paired Co(III) oxidant. The analysis yielded values for DeltaH() and DeltaS() for each path of each reaction and consistent DeltaH degrees and DeltaS degrees values for the ion-pairing of the cationic reactant and the electrolyte. In addition, temperature-dependent electrochemical measurements in 0.10 M Bu(4)NBF(4) yielded DeltaH degrees and DeltaS degrees for the electron transfer process. This is the first measurement of the homogeneous electron transfer reactivity of the dirhenium complexes, and they showed the expected high reactivity. The most notable result is a very high inhibition (ca. 700-fold) by added salt of only the [Co(dmg)(3)(BF)(2)]BF(4) reactions. We attribute this to a change of rate-controlling step, for the ion-paired path, to one involving anion migration. This appears only to occur when the magnitude of ion-pairing free energy is significantly greater than the magnitude of the free energy change for the electron transfer process.     

Isolation of the novel dirhodium(II/II) thiolate compound Rh(2)(eta(1)-C(6)H(5)S)(2)(mu-C(6)H(5)S)(2)(bpy)(2)

The reaction of the anticancer active compound [Rh(2)(mu-O(2)CCH(3))(2)(bpy)(2)(CH(3)CN)(2)][BF(4)](2) (1) (bpy = 2,2'-bipyridine) with NaC(6)H(5)S under anaerobic conditions yields Rh(2)(eta(1)-C(6)H(5)S)(2)(mu-C(6)H(5)S)(2)(bpy)(2).CH(3)OH (2), which was characterized by UV-visible, IR, and (1)H NMR spectroscopies as well as single-crystal X-ray crystallography. Compound 2 crystallizes as dark red platelets in the monoclinic space group C2/c with cell parameters a = 20.398(4) A, b = 11.861(2) A, c = 17.417(4) A, beta = 108.98 degrees, V = 3984.9(14) A(3), Z = 4. The main structural features are the presence of a [Rh(2)](4+) core with a Rh-Rh distance of 2.549(2) A bridged by two benzene thiolate ligands in a butterfly-type arrangement. The axial positions of the [Rh(2)](4+) core are occupied by two terminal benzene thiolates. Cyclic voltammetric studies of 2 reveal that the compound exhibits an irreversible oxidation at +0.046 V in CH(3)CN, which is in accord with the fact that the compound readily oxidizes in the presence of O(2). The fact that this unusual dirhodium(II/II) thiolate compound is formed under these conditions is an important first step in understanding the metabolism of dirhodium anticancer active compounds with thiol-containing peptides and proteins.     

First example of mu(3)-sulfido bridged mixed-valent triruthenium complex triangle Ru(III)(2)Ru(II)(O,O-acetylacetonate)(3)(mu-O,O,gamma-C-acetylacetonate)(3)(mu(3)-S) (1) incorporating simultaneous O,O- and gamma-C-bonded bridging acetylacetonate units. Synthesis,crystal structure,and spectral and redox properties

The reaction of mononuclear ruthenium precursor [Ru(II)(acac)(2)(CH(3)CN)(2)] (acac = acetylacetonate) with the thiouracil ligand (2-thiouracil, H(2)L(1) or 6-methyl -2-thiouracil, H(2)L(2)) in the presence of NEt(3) as base in ethanol solvent afforded a trinuclear triangular complex Ru(3)(O,O-acetylacetonate)(3)(mu-O,O,gamma-C-acetylacetonate)(3)(mu(3)-sulfido) (1). In 1, each ruthenium center is linked to one usual O,O-bonded terminal acetylacetonate molecule whereas the other three acetylacetonate units act as bridging functions: each bridges two adjacent ruthenium ions through the terminal O,O-donor centers at one end and via the gamma-carbon center at the other end. Moreover, there is a mu(3)-sulfido bridging in the center of the complex unit, which essentially resulted via the selective cleavage of the carbon-sulfur bond of the thiouracil ligand. In diamagnetic complex 1, the ruthenium ions are in mixed valent Ru(III)Ru(III)Ru(II) state, where the paramagnetic ruthenium(III) ions are antiferromagnetically coupled. The single crystal X-ray structure of 1 showed two crystallographically independent C(3)-symmetric molecules, Ru(3)(O,O-acetylacetonate)(3)(mu-O,O,gamma-C-acetylacetonate)(3)(mu(3)-S) (1), in the asymmetric unit. Bond distances of both crystallographically independent molecules are almost identical, but there are some significant differences in bond angles (up to 6 degrees ) and interplanar angles (up to 8 degrees ). Each ruthenium atom exhibits a distorted octahedral environment formed by four oxygen atoms, two from each of the terminal and bridging acetylacetonate units, one gamma-carbon of an adjacent acetylacetonate ligand, and the sulfur atom in the center of the complex. In agreement with the expected 3-fold symmetry of the complex molecule, the (1)H and (13)C NMR spectra of 1 in CDCl(3) displayed signals corresponding to two types of ligand units. In dichloromethane solvent, 1 exhibited three metal center based successive quasireversible redox processes, Ru(III)Ru(III)Ru(III)-Ru(III)Ru(III)Ru(II) (couple I, 0.43 V vs SCE); Ru(III)Ru(III)Ru(IV)-Ru(III)Ru(III)Ru(III) (couple II, 1.12 V); and Ru(III)Ru(III)Ru(II)-Ru(III)Ru(II)Ru(II) (couple III, -1.21 V). However, in acetonitrile solvent, in addition to the three described couples [(couple I), 0.34 V; (couple II), 1.0 V; (couple III), -1.0], one irreversible oxidative response (Ru(III)Ru(III)Ru(IV) --> Ru(III)Ru(IV)Ru(IV) or oxidation of the coordinated sulfide center) appeared at E(pa), 1.50 V. The large differences in potentials between the successive couples are indicative of strong coupling between the ruthenium ions in the mixed-valent states. Compound 1 exhibited a moderately strong charge-transfer (CT) transition at 654 nm and multiple ligand based intense transitions in the UV region. In the Ru(III)Ru(III)Ru(III) (1(+)) state, the CT band was slightly blue shifted to 644 nm; however, the CT band was further blue shifted to 520 nm on two-electron oxidation to the Ru(III)Ru(III)Ru(IV) (1(2+)) state with a reduction in intensity.