Synthesis and crystal and electronic structures of the Na2(Sc4Nb2)(Nb6O12)3 octahedral niobium cluster oxide. Structural correlations between AnBM6L12(Z) series and Chevrel Phases

We report here the synthesis and crystal and electronic structures of the Na(2)(Sc(4)Nb(2))(Nb(6)O(12))(3) niobium oxide whose structure is related to that of Ti(2)Nb(6)O(12). It constitutes a new member of the larger A(n)()BM(6)L(12)(Z) families (A = monovalent cation located in tetrahedral cavities of units, B = monovalent or trivalent cations located in octahedral cavities of units, M = rare earth, Zr, or Nb, Z = interstitial except for M = Nb). The structural relationships between the A(n)BM(6)L(12)(Z) series (M(6)L(i)(12)L(a)(6) unit-based compounds with a M(6)L(i)(6)L(i-a)(6/2)L(a-i)(6/2) cluster framework) and Chevrel Phases (M(6)L(i)(8)L(a)(6) unit-based compounds with a M(6)L(i)(2)L(i-a)(6/2)L(a-i)(6/2) cluster framework) are shown in terms of M(6)L(18) and M(6)L(14) unit packing. Despite a topology similar to that encountered in Chevrel Phases, intercalation properties are not expected in the Nb(6)O(i)(6)O(i-a)(6/2)O(a-i)(6/2) cluster framework-based compounds. Finally, it is shown, from theoretical LMTO calculations, that a semiconducting behavior is expected for a maximum VEC of 14 in the Nb(6)O(i)(6)O(i-a)(6/2)O(a-i)(6/2) cluster framework.     

A new quasi-one-dimensional niobium oxychloride cluster compound Cs2Ti4Nb6Cl18O6: structural effects of ligand combination

The new niobium oxychloride cluster compound, Cs2Ti4Nb6Cl18O6, was obtained by solid-state synthesis techniques in the course of our systematic investigation of metal oxychloride systems aimed at the preparation of low-dimensional cluster compounds. Cs2Ti4Nb6Cl18O6 crystallizes in the trigonal system, with unit cell parameters a= 11.1903(7), c = 15.600(2) A, space group P3bar1c, Z = 2. Its crystal structure was determined by single-crystal X-ray diffraction techniques. The full-matrix least-squares refinement against F(2) converged to R(1) = 0.048 (F(o) > 4sigma(F(o))), wR(2) = 0.069 (all data). The structure is based on an octahedral cluster unit (Nb6Cl(i)6O(i)6)Cl(a)6 in which the six edge-bridging oxide ligands are arranged in two sets of three on opposite sides of the Nb6 octahedron. Ti(3+) ions link the clusters through O(i) and Cl(a) ligands to form linear chains running along the c axis. The location of titanium ions correlates with the arrangement of oxide ligands around the Nb6 metal core. The chains interact with each other through additional Ti(3+) and Cs(+) ions. Interchain interactions are significantly weaker than intrachain interactions, resulting in a quasi-one-dimensional character of the overall structure.     

Electrochemistry of niobium(V) in sulfuric and methanesulfonic acids: formation of the Nb3O2(SO4)6(H2O)(3)(5-) cluster and designed electrochemical generation of "Nb3O2" core clusters by double potential pulse electrolysis

The electrochemical and spectroelectrochemical properties of niobium(V) and the Nb(3)O(2)(SO(4))(6)(H(2)O)(3)(5-) cluster in sulfuric acid and methanesulfonic acid were investigated using cyclic voltammetry, constant potential electrolysis, and spectroelectrochemistry. These chemical systems were suitable to probe the formation of "Nb(3)O(2)" core trinuclear clusters. In 9 M H(2)SO(4) the cluster Nb(3)O(2)(SO(4))(6)(H(2)O)(3)(5-) exhibited a reversible 1-electron reduction peak at E(pc) = -1.30 V vs Hg/Hg(2)SO(4) electrode, as well as a 4-electron irreversible oxidation peak at E(pa) = -0.45 V. Controlled potential reduction at E = -1.40 V produced the green Nb(3.33+) cluster anion Nb(3)O(2)(SO(4))(6)(H(2)O)(3)(6-). In 12 M H(2)SO(4) Nb(V) displayed two reduction peaks at E(pc) = -1.15 V and E(pc) = -1.30 V. It was determined that the first process involves a quasi-reversible 2-electron reduction. After reduction of Nb(V) to Nb(III) the following chemical step involves formation of [Nb(III)](2) dimer, which further reacts with Nb(V) to produce the Nb(3)O(2)(SO(4))(6(H(2)O)(3)(5-) cluster (ECC process). The second reduction peak at E(pc) = -1.30 V corresponds to further 2-electron reduction of Nb(III) to Nb(I). The electrogenerated Nb(I) species also chemically reacts with starting material Nb(V) to produce additional [Nb(III)](2). In 5 M H(2)SO(4), the rate of the second chemical step in the ECC process is relatively slower and reduction of Nb(V) at E = -1.45 V/-1.2 V produces a mixture of Nb(3)O(2)(SO(4))(6)(H(2)O)(3)(5-) and [Nb(III)](2) dimer. [Nb(III)](2) can be selectively oxidized by two 2-electron steps at E = -0.65 V to Nb(V). However, if the oxidation is performed at E = -0.86 V, the product is Nb(3)O(2)(SO(4))(6)(H(2)O)(3)(5-). A double potential pulse electrolysis waveform was developed to direct the reduction of Nb(V) toward selective formation of the Nb(3)O(2)(SO(4))(6)(H(2)O)(3)(5-) cluster. Proper application of dc-voltage pulses alternating between E(1) = -1.45 V and E(2) = -0.86 V yields only the target trinuclear cluster. Analogous double potential pulse electrolysis of Nb(V) in methanesulfonic acid generates the "Nb(3)O(2)" core cluster Nb(3)O(2)(CH(3)SO(3))(6)(H(2)O)(3)(+).     

Soluble mu-Fi bridged niobium clusters: synthesis and crystal structures of (Et4N)6[Nb6Fi6Bri6(NCS)a6]Br2 and Cs1.6K2.4[Nb6Fi6Ii6(NCS)a6

Two new anions [Nb(6)F(i)(6)X(i)(6)(NCS)(a)(6)](4-)(X = Br, I) based on octahedral niobium clusters with edge-bridging F ligands have been prepared by reaction of Cs(3)Nb(6)F(6)Br(12) and Cs(4)Nb(6)F(8.5)I(9.5) with aqueous solution of KSCN. The anions were isolated as (Et(4)N)(6)[Nb(6)F(6)Br(6)(NCS)(6)]Br(2) (1)and Cs(1.6)K(2.4)[Nb(6)F(6)I(6)(NCS)(6)] (2) salts.     

Synthesis and characterization of open-framework niobium silicates: Rb2(Nb2O4)(Si2O6).H2O and the dehydrated phase Rb2(Nb2O4)(Si2O6)

A new niobium(V) silicate, Rb(2)(Nb(2)O(4))(Si(2)O(6)).H(2)O, has been synthesized by a high-temperature, high-pressure hydrothermal method and characterized by single-crystal X-ray diffraction, thermogravimetric analysis, and solid-state NMR spectroscopy. It crystallizes in the tetragonal space group P4(3)22 (No. 95) with a = 7.3431(2) A, c = 38.911(3) A, and Z = 8. Its structure contains tetrameric units of the composition Nb(4)O(18), which share corners to form a layer of niobium oxide. The Nb-O layer is a slice of the pyrochlore structure. Neighboring Nb-O layers are linked by vierer single-ring silicates generating eight-ring and six-ring channels running parallel to <100> directions, in which the Rb(+) cations and water molecules reside. The tantalum analogue was prepared and characterized by powder X-ray diffraction. Upon heating to 500 degrees C, Rb(2)(Nb(2)O(4))(Si(2)O(6)).H(2)O loses lattice water molecules, while the framework structure is retained to give the anhydrous compound Rb(2)(Nb(2)O(4))(Si(2)O(6)), whose structure was also characterized by single-crystal X-ray diffraction. The dehydrated sample absorbs water reversibly, as indicated by powder X-ray diffraction. Rb(2)(Nb(2)O(4))(Si(2)O(6)) crystallizes in the tetragonal space group I4(1) (No. 80) with a = 10.2395(6) A, c = 38.832(3) A, and Z = 16.     

Synthesis and characterization of Mo(6) chalcobromides and cyano-substituted compounds built from a novel [(Mo(6)Br(i)(6)Y(i)(2))L(a)(6)](n)()(-) discrete cluster unit (Y(i) = S or Se and L(a) = Br or CN)

The syntheses, crystal structures determined by single-crystal X-ray diffraction, and characterizations of new Mo(6) cluster chalcobromides and cyano-substituted compounds with 24 valence electrons per Mo(6) cluster (VEC = 24), are presented in this work. The structures of Cs(4)Mo(6)Br(12)S(2) and Cs(4)Mo(6)Br(12)Se(2) prepared by solid state routes are based on the novel [(Mo(6)Br(i)(6)Y(i)(2))Br(a)(6)](4)(-) (Y = S, Se) discrete units in which two chalcogen and six bromine ligands randomly occupy the inner positions, while the six apical ones are fully occupied by bromine atoms. The interaction of these two compounds with aqueous KCN solution results in apical ligand exchange giving the two first Mo(6) cyano-chalcohalides: Cs(0.4)K(0.6)(Et(4)N)(11)[(Mo(6)Br(6)S(2))(CN)(6)](3).16H(2)O and Cs(0.4)K(0.6)(Et(4)N)(11)[(Mo(6)Br(6)Se(2))(CN)(6)](3).16H(2)O. Their crystal structures, built from the original [(Mo(6)Br(i)(6)Y(i)(2))(CN)(a)(6)](4)(-) discrete units, will be compared to those of the two solid state precursors and other previously reported Mo(6) cluster compounds. Their redox properties and (77)Se NMR characterizations will be presented. Crystal data: Cs(4)Mo(6)Br(12)S(2), orthorhombic, Pbca (No. 61), a = 11.511(5) A, b = 18.772(5) A, c = 28.381 A (5), Z = 8; Cs(4)Mo(6)Br(12)Se(2), Pbca (No. 61), a = 11.6237(1) A, b = 18.9447(1) A, c = 28.4874(1) A, Z = 8; Cs(0.4)K(0.6)(Et(4)N)(11)[(Mo(6)Br(6)S(2))(CN)(6)](3).16H(2)O, Pm-3m (No. 221), a = 17.1969(4) A, Z = 1; Cs(0.4)K(0.6)(Et(4)N)(11)[(Mo(6)Br(6)Se(2))(CN)(6)](3).16H(2)O, Pm-3m (No. 221), a = 17.235(5) A, Z = 1.     

Molecular precursors for ferroelectric materials: synthesis and characterization of Bi2M2(mu-O)(sal)4(Hsal)4(OEt)2 and BiM4(mu-O)4(sal)4(Hsal)3(O(i)Pr)4 (sal = O2CC6H4O,Hsal = O2CC6H4OH) (M = Nb,Ta)

Reactions between triphenyl bismuth, salicylic acid, and niobium or tantalum ethoxide have been explored. Four new coordination complexes incorporating bismuth and the group 5 metals niobium or tantalum have been synthesized and characterized spectroscopically, by elemental analysis, and by single crystal X-ray diffraction. The new complexes are Bi(2)M(2)(mu-O)(sal)(4)(Hsal)(4)(OEt)(2) (1a, M = Nb; 1b, M = Ta) and BiM(4)(mu-O)(4)(sal)(4)(Hsal)(3)(O(i)Pr)(4) (sal = O(2)CC(6)H(4)-2-O, Hsal = O(2)CC(6)H(4)-2-OH) (2a, M = Nb; 2b, M = Ta). Complexes 1a and 1b are isomorphous, as are 2a and 2b. The thermal and hydrolytic decomposition of 1a has been explored by DT/TGA and powder X-ray diffraction, while scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) were used to characterize the morphology and composition of the oxides. The heterobimetallic molecules are completely converted to the amorphous bimetallic oxide by heating to 500 degrees C in air. Decomposition of 1a or 1b at 650 degrees C produces the metastable high temperature form of BiNbO(4) as the major crystalline oxide phase. Heating samples of 1a to 850 degrees C favors conversion of the materials to the low temperature phase as well as disproportionation into Bi(5)Nb(3)O(15) and Nb(2)O(5). Thermal decomposition of 1a and 1b produces porous oxides, while hydrolytic decomposition of the complexes has been shown to produce nanometer scale bimetallic oxide particles. The potential of the complexes to act as single-source precursors for ferroelectric materials is considered.     

The first coordination polymers and hydrogen bonded networks containing octahedral Nb6 clusters and alkaline earth metal complexes

Three novel coordination polymers built of octahedral niobium cyanochloride clusters [Nb6Cl12(CN)6] and alkaline earth metal complexes have been prepared by reaction of aqueous solutions of (Me4N)4Nb6Cl18 and KCN with solutions of alkaline earth metal salts and 1,10-phenanthroline (phen) (1:2 molar ratio) in H2O/EtOH. The structures of [Ca(phen)2(H2O)3]2[Nb6Cl12(CN)6] x (phen)(EtOH)1.6 (1), [Ca(phen)2(H2O)2]2[Nb6Cl12(CN)6] x (phen)2 x 4H2O (2), and [Ba(phen)2(H2O)]2[Nb6Cl12(CN)6] (3) were determined by single-crystal X-ray diffraction. The three compounds were found to crystallize in the monoclinic system (space group Pn) with a = 11.5499(6) A, b = 17.5305(8) A, c = 21.784(1) A, beta = 100.877(1) degrees for 1; triclinic system (P1) with a = 12.609(4) A, b = 13.262(4) A, c = 16.645(5) A, alpha = 69.933(6) degrees, beta = 68.607(6) degrees, gamma = 63.522(5) degrees for 2; and a = 16.057(1) A, b = 16.063(1) A, c = 16.061(1) A, alpha = 86.830(1) degrees, beta = 64.380(1) degrees, gamma = 67.803(1) degrees for 3. Compounds 1 and 2 are built of cluster anions [Nb6Cl12(CN)6]4- trans-coordinated by two Ca2+ complexes via CN ligands to form neutral macromolecular units [Ca(phen)2(H2O)3]2[Nb6Cl12(CN)6] in 1 and [Ca(phen)2(H2O)2]2[Nb6Cl12(CN)6] in 2. Water of coordination and cyanide ligands form hydrogen bonded 3D and 2D frameworks for 1 and 2, respectively. The structure of 3 consists of [Nb6Cl12(CN)6]4- cluster anions and [Ba(phen)2(H2O)]2+ complexes linked through bridging cyanide ligands to form a neutral three-dimensional framework in which each barium complex is bound to three neighboring Nb6 clusters and each Nb6 cluster is linked to six Ba complexes.     

Host-guest complexes [(H4L)(SiF6)2-4H2O] and [(H4L)(GeF6)2 4H2O] (L =meso-5,7,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane)

Synthesis and X-ray structure analysis of host-guest complexes [(H₄L)(SiF₆)₂-4H₂O] (I) and [(H₄L)(GeF₆)₂-4H₂O] (II) are reported (L = meso-5,7,7,12,12,14-hexamethyl-l,4,8,11-tetraazacyclo-tetradecane). The crystals of both compounds are triclinic with close unit cell parameters. I: a = 9.576(3), b= 9.217(3), c= 8.334(2) å, α= 105.66(2), Ω= 83.68(2), α = 105.38(2)? II: a= 9.627(3), b = 9.358(3), c.= 8.497(4) A, a= 106.02(2), Ω = 83.74(2), α= 106.06(2)?. The structural units of the crystals are the (H₄L)⁴⁺ cations, the hexafluorosilicate (or hexafluowgemanate) anions, and the water molecules linked by a system of H bonds. The macrocycle in the complexes has C₁ symmetry. In the inorganic anions, the silicon as well as germanium atom is surrounded by an octahedron of six fluorine atoms.

     

Heterobimetallic bismuth-transition metal salicylate complexes as molecular precursors for ferroelectric materials. Synthesis and structure of Bi(2)M(2)(sal)(4)(Hsal)(4)(OR) (4) (M = Nb,Ta; R = CH(2)CH(3), CH(CH(3))(2)), Bi(2)Ti(3)(sal)(8)(Hsal)(2), and Bi(2)Ti(4)(O(i)Pr)(sal)(10)(Hsal) (sal = O(2)CC(6)H(4)-2-O; Hsal = O(2)CC(6)H(4)-2-OH)

The reactions between triphenylbismuth, salicylic acid, and the metal alkoxides M(OCH(2)CH(3))(5) (M = Nb, Ta) or Ti[OCH(CH(3))(2)](4) have been investigated under different reaction conditions and in different stoichiometries. Six novel heterobimetallic bismuth alkoxy-carboxylate complexes have been synthesized in good yield as crystalline solids. These include Bi(2)M(2)(sal)(4)(Hsal)(4)(OR)(4) (M = Nb, Ta; R = CH(2)CH(3), CH(CH(3))(2)), Bi(2)Ti(3)(sal)(8)(Hsal)(2), and Bi(2)Ti(4)(O(i)Pr)(sal)(10)(Hsal) (sal = O(2)CC(6)H(4)-2-O; Hsal = O(2)CC(6)H(4)-2-OH). The complexes have been characterized spectroscopically and by single-crystal X-ray diffraction. Compounds of the group V transition metals contain metal ratios appropriate for precursors of ferroelectric materials. The molecules exhibit excellent solubility in common organic solvents and good stability against unwanted hydrolysis. The nature of the thermal decomposition of the complexes has been explored by thermogravimetric analysis and powder X-ray diffraction. We have shown that the complexes are converted to the corresponding oxide by heating in an oxygen atmosphere at 500 degrees C. The mass loss of the complexes, as indicated by thermogravimetric analysis, and the resulting unit cell parameters of the oxides are consistent with the formation of the desired heterobimetallic oxide. The complexes decomposed to form the bismuth-rich phases Bi(4)Ti(3)O(12) and Bi(5)Nb(3)O(15) as well as the expected oxides BiMO(4) (M = Nb, Ta) and Bi(2)Ti(4)O(11).     

Synthesis, structure, and characterization of two new layered mixed-metal phosphates, BaTeMO4(PO4) (M = Nb5+ or Ta5+

Two new isostructural mixed-metal phosphates, BaTeMO(4)(PO(4)) (M = Nb(5+) or Ta(5+)), have been synthesized as bulk phase powders and single crystals by standard solid-state techniques using BaCO(3), TeO(2), Nb(2)O(5) (or Ta(2)O(5)), and NH(4)H(2)PO(4) as reagents. The materials have novel layered crystal structures consisting of [M(5+)O(6/2)](-) corner-sharing octahedral chains that are connected to [Te(4+)O(4/2)](0) polyhedra and [P(5+)O(2/1)O(2/2)](-) tetrahedra. The Ba(2+) cations reside between the layers and maintain charge balance. The Te(4+) cations are in asymmetric coordination environments attributable to their lone pairs. The Nb(5+) distorts along the local C(4) direction of its octahedron resulting in a "short-long-short-long" Nb-O-Nb bond motif. The Nb(5+) cation displaces away from the oxide ligands that are bonded to Te(4+) or P(5+) cations, attributable to the structural rigidity of the TeO(4) and PO(4) polyhedra. Thus, the TeO(4) and PO(4) polyhedra support and reinforce the intraoctahedral distortion observed within the NbO(6) octahedra. Infrared and Raman spectroscopy, thermogravimetric analysis, and ion-exchange experiments are also presented. Crystal data: BaTeNbO(4)(PO(4)), orthorhombic, space group Pbca (No. 61), with a = 6.7351(9) A, b = 7.5540(10) A, c = 27.455(4) A, V = 1396.8(3) A(3), and Z = 8; BaTeTaO(4)(PO(4)), orthorhombic, space group Pbca (No. 61), with a = 6.734(2) A, b = 7.565(3) A, c = 27.435(9) A, V = 1372.6(8) A(3), and Z = 8.     

Hydrothermal Synthesis, Structure, and Solid State (19)F NMR Study of ULM-17: (H(3)O)(2)[V(4)(HPO(4))(PO(4))(3)O(6)F](2)[NC(7)H(14)](6)

(H(3)O)(2)[V(4)(HPO(4))(PO(4))(3)O(6)F](2)[NC(7)H(14)](6) (labeled ULM-17) has been hydrothermally synthesized (150 degrees, 24 h, autogeneous pressure). It is monoclinic (space group P2(1)/c (No. 14)) with a = 21.4747(6) ?, b = 17.7223(5) ?, c = 20.1616(6) ?, beta = 94.329(1) degrees, and Z = 4. The structure consists in the hexagonal close packing of discrete hydronium cations, protonated quinuclidine and molecular anions [V(4)(HPO(4))(PO(4))(3)O(6)F](4)(-) (1) The structure presents two kinds of octameric anions built up from the tetrahedral arrangement of V(V)O(5)F octahedra sharing edges and vertices, capped by phosphorus tetrahedra. The stability of the solid is ensured via strong hydrogen bonds between the oxygens of the polyanions and the hydrogens of both hydronium and quinuclidinium cations. The particuliar location of fluorine at the center of the molecular anion 4-fold coordinated by V(V) was studied by solid state NMR.     

The Osmium(VIII) Oxofluoro Cations OsO(2)F(3)(+) and F(cis-OsO(2)F(3))(2)(+): Syntheses, Characterization by (19)F NMR Spectroscopy and Raman Spectroscopy, X-ray Crystal Structure of F(cis-OsO(2)F(3))(2)(+)Sb(2)F(11)(-), and Density Functional Theory Calculations of OsO(2)F(3)(+), ReO(2)F(3), and F(cis-OsO(2)F(3))(2)(+)

Osmium dioxide tetrafluoride, cis-OsO(2)F(4), reacts with the strong fluoride ion acceptors AsF(5) and SbF(5) in anhydrous HF and SbF(5) solutions to form orange salts. Raman spectra are consistent with the formation of the fluorine-bridged diosmium cation F(cis-OsO(2)F(3))(2)(+), as the AsF(6)(-) and Sb(2)F(11)(-) salts, respectively. The (19)F NMR spectra of the salts in HF solution are exchange-averaged singlets occurring at higher frequency than those of the fluorine environments of cis-OsO(2)F(4). The F(cis-OsO(2)F(3))(2)(+)Sb(2)F(11)(-) salt crystallizes in the orthorhombic space group Imma. At -107 degrees C, a = 12.838(3) ?, b = 10.667(2) ?, c = 11.323(2) ?, V = 1550.7(8) ?(3), and Z = 4. Refinement converged with R = 0.0469 [R(w) = 0.0500]. The crystal structure consists of discrete fluorine-bridged F(cis-OsO(2)F(3))(2)(+) and Sb(2)F(11)(-) ions in which the fluorine bridge of the F(cis-OsO(2)F(3))(2)(+) cation is trans to an oxygen atom (Os-O 1.676 ?) of each OsO(2)F(3) group. The angle at the bridge is 155.2(8) degrees with a bridging Os---F(b) distance of 2.086(3) ?. Two terminal fluorine atoms (Os-F 1.821 ?) are cis to the two oxygen atoms (Os-O 1.750 ?), and two terminal fluorine atoms of the OsO(2)F(3) group are trans to one another (1.813 ?). The OsO(2)F(3)(+) cation was characterized by (19)F NMR and by Raman spectroscopy in neat SbF(5) solution but was not isolable in the solid state. The NMR and Raman spectroscopic findings are consistent with a trigonal bipyramidal cation in which the oxygen atoms and a fluorine atom occupy the equatorial plane and two fluorine atoms are in axial positions. Density functional theory calculations show that the crystallographic structure of F(cis-OsO(2)F(3))(2)(+) is the energy-minimized structure and the energy-minimized structures of the OsO(2)F(3)(+) cation and ReO(2)F(3) are trigonal bipyramidal having C(2)(v)() point symmetry. Attempts to prepare the OsOF(5)(+) cation by oxidative fluorination of cis-OsO(2)F(4) with KrF(+)AsF(6)(-) in anhydrous HF proved unsuccessful.     

Synthesis, characterization, and hydrolysis of aluminum(III) compounds bearing the C6F5-substituted beta-diketiminate HC[(CMe)(NC6F5)]2 (L) ligand

A series of Al(III) compounds containing the C6F5-substituted beta-diketiminate ligands LAlMeCl (2), LAlMe2 (3), LAlMeI (4), and LAlBr2 (5) (L = HC[(CMe)(NC6F5)]2) were synthesized and characterized. The hydrolysis of 2 and 4 in the presence of 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene as the hydrogen halide acceptor both lead to (LAlMe)2(mu-O) (6), a methylalumoxane derivative, which is the first hydrolysis product with the general formula of (RAlMe)(n)O. A comparison of the hydrolysis products of 2 and 4 with that of L'AlMeCl (L' = HC[(CMe)(NAr)]2, Ar = 2,6-iPr2C6H3) shows that with the C6F5-substituted beta-diketiminate ligand, it was not possible to generate LAlMe(OH). This is obviously due to the stronger Br?nsted acidity of the proton and the smaller size of the C6F5 group in this compound compared to that of the corresponding 2,6-iPr2C6H3 derivative.     

Reactions of the Dirhenium(II) Complexes Re(2)X(4)(dppm)(2) (X = Cl, Br; dppm = Ph(2)PCH(2)PPh(2)) with Isocyanides. 10.(1) Synthesis and Characterization of the Complex [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(2)(CNXyl)]O(3)SCF(3) and Several Isomeric Forms of [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(CNXyl)(2)]Y (Y = PF(6), O(3)SCF(3))

The reactions of the unsymmetrical, coordinatively unsaturated dirhenium(II) complexes [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(CNXyl)]Y (XylNC = 2,6-dimethylphenyl isocyanide; Y = O(3)SCF(3) (3a), PF(6) (3b)) with XylNC afford at least three isomeric forms of the complex cation [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(CNXyl)(2)](+). Two forms have very similar bis(&mgr;-halo)-bridged edge-sharing bioctahedral structures of the type [(CO)BrRe(&mgr;-Br)(2)(&mgr;-dppm)(2)Re(CNXyl)(2)]Y (Y = O(3)SCF(3) (4a/4a'), PF(6) (4b/4b')), while the third is an open bioctahedron [(XylNC)(2)BrRe(&mgr;-dppm)(2)ReBr(2)(CO)]Y (Y = O(3)SCF(3) (5a), PF(6) (5b)). While the analogous chloro complex cation [Re(2)Cl(3)(&mgr;-dppm)(2)(CO)(CNXyl)(2)](+) was previously shown to exist in three isomeric forms, only one of these has been found to be structurally similar to the bromo complexes (i.e. the isomer analogous to 5a and 5b). The reaction of 3a with CO gives the salt [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(2)(CNXyl)]O(3)SCF(3) (7), in which the edge-sharing bioctahedral cation [(XylNC)BrRe(&mgr;-Br)(&mgr;-CO)(&mgr;-dppm)(2)ReBr(CO)](+) has an all-cis arrangement of pi-acceptor ligands. The Re-Re distances in the structures of 4b', 5a, and 7 are 3.0456(8), 2.3792(7), and 2.5853(13) ?, respectively, and accord with formal Re-Re bond orders of 1, 3, and 2, respectively. Crystal data for [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(CNXyl)(2)](PF(6))(0.78)(ReO(4))(0.22).CH(2)Cl(2) (4b') at 295 K: monoclinic space group P2(1)/n (No. 14) with a = 19.845(4) ?, b = 16.945(5) ?, c = 21.759(3) ?, beta = 105.856(13) degrees, V = 7038(5) ?(3), and Z = 4. The structure was refined to R = 0.060 (R(w) = 0.145) for 14 245 data (F(o)(2) > 2sigma(F(o)(2))). Crystal data for [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(CNXyl)(2)]O(3)SCF(3).C(6)H(6) (5a) at 173 K: monoclinic space group P2(1)/n (No. 14) with a = 14.785(3) ?, b = 15.289(4) ?, c = 32.067(5) ?, beta = 100.87(2) degrees, V=7118(5) ?(3), and Z = 4. The structure was refined to R = 0.046 (R(w) = 0.055) for 6962 data (I > 3.0sigma(I)). Crystal data for [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(2)(CNXyl)]O(3)SCF(3).Me(2)CHC(O)Me (7) at 295 K: monoclinic space group P2(1)/n (No. 14) with a = 14.951(2) ?, b = 12.4180(19) ?, c = 40.600(5) ?, beta = 89.993(11) degrees, V = 7537(3) ?(3), and Z = 4. The structure was refined to R = 0.074 (R(w) = 0.088) for 6595 data (I > 3.0sigma(I)).     

Composition Space of the (CuO, (1)/(2)Nb(2)O(5))/(HF)(x)().pyridine/H(2)O System. Structure and Synthesis of [pyH(+)](2)[CuNb(2)(py)(4)O(2)F(10)](2-) and CuNb(py)(4)OF(5)

Single crystals of [pyH(+)](2)[CuNb(2)(py)(4)O(2)F(10)](2)(-) and CuNb(py)(4)OF(5) were synthesized in a (HF)(x)().pyridine/pyridine/water solution (150 degrees C, 24 h, autogeneous pressure) using CuO and Nb(2)O(5) as reagents. The compound [pyH(+)](2)[CuNb(2)(py)(4)O(2)F(10)](2)(-) contains clusters of [CuNb(2)(py)(4)O(2)F(10)](2)(-) anions linked through N-H(+).F hydrogen bonds to the [pyH(+)] cations. In contrast CuNb(py)(4)OF(5) is a unidimensional compound consisting only of chains, perpendicular to the c axis, of alternating [Cu(py)(4)(O/F)(2/2)](0.5+) and [NbF(4)(O/F)(2/)(2)](0.5)(-) octahedra. The chains change direction between the [110] and [1&onemacr;0] every c/2. Crystal data for [pyH(+)](2)[CuNb(2)(py)(4)O(2)F(10)](2)(-): tetragonal, space group I4(1)22 (No. 98),with a = 11.408(3) ?, c = 30.36(1) ?, and Z = 4. Crystal data for CuNb(py)(4)OF(5): monoclinic, space group C2/c (No. 15), with a = 10.561(3) ?, b = 13.546(6) ?, c = 16.103(4) ?, beta = 97.77(2) degrees, and Z = 4.     

Excited-state properties of Rh(2)(O(2)CCH(3))(4)(L)(2) (L = CH(3)OH, THF, PPh(3), py)

The photophysical properties of Rh(2)(O(2)CCH(3))(4)(L)(2) (L = CH(3)OH, THF = tetrahydrofuran, PPh(3) = triphenylphosphine, py = pyridine) were explored upon excitation with visible light. Time-resolved absorption shows that all the complexes possess a long-lived transient (3.5-5.0 micros) assigned as an electronic excited state of the molecules, and they exhibit an optical transition at approximately 760 nm whose position is independent of axial ligand. No emission from the Rh(2)(O(2)CCH(3))(4)(L)(2) (L = CH(3)OH, THF, PPh(3), py) systems was detected, but energy transfer from Rh(2)(O(2)CCH(3))(4)(PPh(3))(2) to the (3)pipi excited state of perylene is observed. Electron transfer from Rh(2)(O(2)CCH(3))(4)(PPh(3))(2) to 4,4'-dimethyl viologen (MV(2+)) and chloro-p-benzoquinone (Cl-BQ) takes place with quenching rate constants (k(q)) of 8.0 x 10(6) and 1.2 x 10(6) M(-1) s(-1) in methanol, respectively. A k(q) value of 2 x 10(8) M(-1) s(-1) was measured for the quenching of the excited state of Rh(2)(O(2)CCH(3))(4)(PPh(3))(2) by O(2) in methanol. The observations are consistent with the production of an excited state with excited-state energy, E(00), between 1.34 and 1.77 eV.     

Zn6[MeN(CH2CO2)(CH2PO3)](6)(Zn)]4- anion: the first example of the oxo-bridged Zn6 octahedron with a centered Zn(II) cation

Hydrothermal reactions of N-(phosphonomethyl)-N-methylglycine, MeN(CH(2)CO(2)H)(CH(2)PO(3)H(2)) (H(3)L), with zinc(II) acetate resulted in the formation of a novel zinc carboxylate-phosphonate, [Zn(6)L(6)(Zn)][Zn(H(2)O)(6)](2) x 22H(2)O (1). The structure of 1 contains a heptanuclear zinc phosphonate cluster anion, [Zn(6)L(6)(Zn)](4-), in which seven zinc(II) cations form an unusual Zn(6)(Zn) centered octahedron with six of its Zn(3) triangle faces each further capped by a phosphonate group. The Zn(II) cations of the Zn(6) octahedron are five-coordinated whereas the centered Zn(II) cation is octahedrally coordinated. Packing of these cluster anions creates micropores occupied by the hydrated zinc(II) cations as well as lattice water molecules. The structural skeleton of 1 is retained after the removal of the lattice water molecules.     

High hydride count rhodium octahedra, [Rh6(PR3)6H12][BArF4]2: synthesis, structures, and reversible hydrogen uptake under mild conditions

A new class of transition metal cluster is described, [Rh(6)(PR(3))(6)H(12)][BAr(F)(4)](2) (R = (i)Pr (1a), Cy (2a); BAr(F)(4) = [B{C(6)H(3)(CF(3))(2)}(4)](-)). These clusters are unique in that they have structures exactly like those of early transition metal clusters with edge-bridging pi-donor ligands rather than the structures expected for late transition metal clusters with pi-acceptor ligands. The solid-state structures of 1a and 2a have been determined, and the 12 hydride ligands bridge each Rh-Rh edge of a regular octahedron. Pulsed gradient spin-echo NMR experiments show that the clusters remain intact in solution, having calculated hydrodynamic radii of 9.5(3) A for 1a and 10.7(2) A for 2a, and the formulation of 1a and 2a was unambiguously confirmed by ESI mass spectrometry. Both 1a and 2a take up two molecules of H(2) to afford the cluster species [Rh(6)(P(i)Pr(3))(6)H(16)][BAr(F)(4)](2) (1b) and [Rh(6)(PCy(3))(6)H(16)][BAr(F)(4)](2) (2b), respectively, as characterized by NMR spectroscopy, ESI-MS, and, for 2b, X-ray crystallography using the [1-H-CB(11)Me(11)](-) salt. The hydride ligands were not located by X-ray crystallography, but (1)H NMR spectroscopy showed a 15:1 ratio of hydride ligands, suggesting an interstitial hydride ligand. Addition of H(2) is reversible: placing 1b and 2b under vacuum regenerates 1a and 2a. DFT calculations on [Rh(6)(PH(3))(6)H(x)()](2+) (x = 12, 16) support the structural assignments and also show a molecular orbital structure that has 20 orbitals involved with cluster bonding. Cluster formation has been monitored by (31)P{(1)H} and (1)H NMR spectroscopy, and mechanisms involving heterolytic H(2) cleavage and elimination of [HP(i)Pr(3)](+) or the formation of trimetallic intermediates are discussed.