Ligand Substitution Reactions at the Nickel of [Mo(3)NiS(4)(H(2)O)(10)](4+) with Two Water Soluble Phosphines, CO, Br(-), I(-), and NCS(-) and the Inertness of the 1,4,7-Triazacyclononane (L) Complex [Mo(3)(NiL)S(4)(H(2)O)(9)](4+)

Comparisons (25 degrees C) are made of substitution reactions, X replacing H(2)O, at the tetrahedral Ni of the heterometallic sulfido cuboidal cluster [Mo(3)NiS(4)(H(2)O)(10)](4+), I = 2.00 M (LiClO(4)). Stopped-flow formation rate constants (k(f)/M(-)(1) s(-)(1)) for six X reagents, including two water soluble air-stable phosphines, 1,3,5-triaza-7-phosphaadamantane PTA (119) and tris(3-sulfonatophenyl)phosphine TPPTS(3)(-) (58), and CO (0.66), Br(-) (14.6), I(-) (32.3), and NCS(-) (44) are reported alongside the previous value for Cl(-) (9.4). A dependence on [H(+)] is observed with PTA, which gives an unreactive form confirmed by NMR as N-protonated PTA (acid dissociation constant K(a) = 0.61 M), but in no other cases with [H(+)] in the range 0.30-2.00 M. The narrow spread of rate constants for all but the CO reaction is consistent with an I(d) dissociative interchange mechanism. In addition NMR studies with H(2)(17)O enriched solvent are too slow for direct determination of the water-exchange rate constant indicating a value <10(3) s(-)(1). Equilibrium constants/M(-)(1) for 1:1 complexing with the different X groups at the Ni are obtained for PTA (2040) and TPPTS(3)(-) (8900) by direct spectrophotometry and from kinetic studies (k(f)/k(b)) for Cl(-) (97), Br(-) (150), NCS(-) (690), and CO (5150). No NCS(-) substitution at the Ni is observed in the case of the heterometallic cube [Mo(3)Ni(L)S(4)(H(2)O)(9)](4+), with tridentate 1,4,7-triazacyclononane(L) coordinated to the Ni. Substitution of NCS(-) for H(2)O, at the Mo's of [Mo(3)NiS(4)(H(2)O)(10)](4+) and [Mo(3)(NiL)S(4)(H(2)O)(9)](4+) are much slower secondary processes, with k(f) = 2.7 x 10(-)(4) M(-)(1) s(-)(1) and 0.94 x 10(-)(4) M(-)(1) s(-)(1) respectively. No substitution of H(2)O by TPPTS(3)(-) or CO is observed over approximately 1h at either metal on [Mo(3)FeS(4)(H(2)O)(10)](4+), on [Mo(4)S(4)(H(2)O)(12)](5+) or [Mo(3)S(4)(H(2)O)(9)](4+).     

Interconversion and Reactivity of Two Heterometallic Tin-Containing Cuboidal Clusters from [Mo(3)S(4)(H(2)O)(9)](4+): X-ray Structure of the Single Cube with an Mo(3)SnS(4) Core

The Mo(3)SnS(4)(6+) single cube is obtained by direct addition of Sn(2+) to [Mo(3)S(4)(H(2)O)(9)](4+). UV-vis spectra of the product (0.13 mM) in 2.00 M HClO(4), Hpts, and HCl indicate a marked affinity of the Sn for Cl(-), with formation of the more strongly yellow [Mo(3)(SnCl(3))S(4)(H(2)O)(9)](3+) complex complete in as little as 0.050 M Cl(-). The X-ray crystal structure of (Me(2)NH(2))(6)[Mo(3)(SnCl(3))S(4)(NCS)(9)].0.5H(2)O has been determined and gives Mo-Mo (mean 2.730 ?) and Mo-Sn (mean 3.732 ?) distances, with a difference close to 1 ?. The red-purple double cube cation [Mo(6)SnS(8)(H(2)O)(18)](8+) is obtained by reacting Sn metal with [Mo(3)S(4)(H(2)O)(9)](4+). The double cube is also obtained in approximately 50% yield by BH(4)(-) reduction of a 1:1 mixture of [Mo(3)SnS(4)(H(2)O)(10)](6+) and [Mo(3)S(4)(H(2)O)(9)](4+). Conversely two-electron oxidation of [Mo(6)SnS(8)(H(2)O)(18)](8+) with [Co(dipic)(2)](-) or [Fe(H(2)O(6)](3+) gives the single cube [Mo(3)SnS(4)(H(2)O)(12)](6+) and [Mo(3)S(4)(H(2)O)(9)](4+) (up to 70% yield), followed by further two-electron oxidation to [Mo(3)S(4)(H(2)O)(9)](4+) and Sn(IV). The kinetics of the first stages have been studied using the stopped-flow method and give rate laws first order in [Mo(6)SnS(8)(H(2)O)(18)](8+) and the Co(III) or Fe(III) oxidant. The oxidation with [Co(dipic)(2)](-) has no [H(+)] dependence, [H(+)] = 0.50-2.00 M. With Fe(III) as oxidant, reaction steps involving [Fe(H(2)O)(6)](3+) and [Fe(H(2)O)(5)OH](2+) are implicated. At 25 degrees C and I = 2.00 M (Li(pts)) k(Co) is 14.9 M(-)(1) s(-)(1) and k(a) for the reaction of [Fe(H(2)O)(6)](3+) is 0.68 M(-)(1) s(-)(1) (both outer-sphere reactions). Reaction of Cu(2+) with the double but not the single cube is observed, yielding [Mo(3)CuS(4)(H(2)O)(10)](5+). A redox-controlled mechanism involving intermediate formation of Cu(+) and [Mo(3)S(4)(H(2)O)(9)](4+) accounts for the changes observed.     

Anionic Halomolybdate(III) Chemistry. Tetrahydrofuran Loss from [MoX(3)Y(THF)(2)](-) (X, Y = Cl, Br, I), Preparation and Properties of [Mo(3)X(12)](3)(-) (X = Br, I), and Crystal Structure of the Edge-Sharing Trioctahedral [PPh(4)](3)[Mo(3)I(12)

By interaction of MoX(3)(THF)(3) with [Cat]X in THF, the salts [Cat][MoX(4)(THF)(2)] have been synthesized [X = I, Cat = PPh(4), NBu(4), NPr(4), (Ph(3)P)(2)N; X = Br, Cat = NBu(4), PPh(4) (Ph(3)P)(2)N]. Mixed-halide species [MoX(3)Y(THF)(2)](-) (X, Y = Cl, Br, I) have also been generated in solution and investigated by (1)H-NMR. When the tetraiodo, tetrabromo, and mixed bromoiodo salts are dissolved in CH(2)Cl(2), clean loss of all coordinated THF is observed by (1)H-NMR. On the other hand, [MoCl(4)(THF)(2)](-) loses only 1.5 THF/Mo. The salts [Cat](3)[Mo(3)X(12)] (X = Br, I) have been isolated from [Cat][MoX(4)(THF)(2)] or by running the reaction between MoX(3)(THF)(3) and [Cat]X directly in CH(2)Cl(2). The crystal structure of [PPh(4)](3)[Mo(3)I(12)] exhibits a linear face-sharing trioctahedron for the trianion: triclinic, space group P&onemacr;; a = 11.385(2), b = 12.697(3), c = 16.849(2) ?; alpha = 76.65(2), beta = 71.967(12), gamma = 84.56(2) degrees; Z = 1; 431 parameters and 3957 data with I > 2sigma(I). The metal-metal distance is 3.258(2) ?. Structural and magnetic data are consistent with the presence of a metal-metal sigma bond order of (1)/(2) and with the remaining 7 electrons being located in 7 substantially nonbonding orbitals. The ground state of the molecule is predicted to be subject to a Jahn-Teller distortion, which is experimentally apparent from the nature of the thermal ellipsoid of the central Mo atom. The [Mo(3)X(12)](3)(-) ions reacts with phosphines (PMe(3), dppe) to form products of lower nuclearity by rupture of the bridging Mo-X bonds.     

Preparation and Properties of the Corner-Shared Double Cube [Mo(6)BiS(8)(H(2)O)(18)](8+) as a Derivative of [Mo(3)S(4)(H(2)O)(9)](4+) in Aqueous Acidic Solutions

The reaction of [Mo(3)S(4)(H(2)O)(9)](4+) with Bi(III) in the presence of BH(4)(-) (rapid), or with Bi metal shot (3-4 days), gives a heterometallic cluster product. The latter has been characterized as the corner-shared double cube [Mo(6)BiS(8)(H(2)O)(18)](8+) by the following procedures. Analyses by ICP-AES confirm the Mo:Bi:S ratio as 6:1:8. Elution from a cation-exchange column by 4 M Hpts (Hpts = p-toluenesulfonic acid), but not 2 M Hpts (or 4 M HClO(4)), is consistent with a high charge. The latter is confirmed as 8+ from the 3:1 stoichiometries observed for the oxidations with [Co(dipic)(2)](-) or [Fe(H(2)O)(6)](3+) yielding [Mo(3)S(4)(H(2)O)(9)](4+) and Bi(III) as products. Heterometallic clusters [Mo(6)MS(8)(H(2)O)(18)](8+) are now known for M = Hg, In, Tl, Sn, Pb, Sb, and Bi and are a feature of the P-block main group metals. The color of [Mo(6)BiS(8)(H(2)O)(18)](8+) in 2.0 M Hpts (turquoise) is different from that in 2.0 M HCl (green-blue). Kinetic studies (25 degrees C) for uptake of a single chloride k(f) = 0.80 M(-)(1) s(-)(1), I = 2.0 M (Hpts), and the high affinity for Cl(-) (K > 40 M(-)(1)) exceeds that observed for complexing at Mo. A specific heterometal interaction of the Cl(-) not observed in the case of other double cubes is indicated. The Cl(-) can be removed by cation-exchange chromatography with retention of the double-cube structure. Kinetic studies with [Co(dipic)(2)](-) and hexaaqua-Fe(III) as oxidants form part of a survey of redox properties of this and other clusters. The Cl(-) adduct is more readily oxidized by [Co(dipic)(2)](-) (factor of approximately 10) and is also more air sensitive.     

Synthesis and reactivity of W3Te74+ clusters and chalcogen exchange in the M3Q7 (M = Mo, W; Q = S, Se, Te) cluster family

Heating WTe(2), Te, and Br(2) at 390 degrees C followed by extraction with KCN gives [W(3)Te(7)(CN)(6)](2-). Crystal structures of double salts Cs(3.5)K{[W(3)Te(7)(CN)(6)]Br}Br(1.5).4.5H(2)O (1), Cs(2)K(4){[W(3)Te(7)(CN)(6)](2)Cl}Cl.5H(2)O (2), and (Ph(4)P)(3){[W(3)Te(7)(CN)(6)]Br}.H(2)O (3) reveal short Te(2)...X (X = Cl, Br) contacts. Reaction of polymeric Mo(3)Se(7)Br(4) with KNCSe melt gives [Mo(3)Se(7)(CN)(6)](2-). Reactions of polymeric Mo(3)S(7)Br(4) and Mo(3)Te(7)I(4) with KNCSe melt (200-220 degrees C) all give as final product [Mo(3)Se(7)(CN)(6)](2)(-) via intermediate formation of [Mo(3)S(4)Se(3)(CN)(6)](2-)/[Mo(3)SSe(6)(CN)(6)](2-) and of [Mo(3)Te(4)Se(3)(CN)(6)](2-), respectively, as was shown by ESI-MS. (NH(4))(1.5)K(3){[Mo(3)Se(7)(CN)(6)]I}I(1.5).4.5H(2)O (4) was isolated and structurally characterized. Reactions of W(3)Q(7)Br(4) (Q = S, Se) with KNCSe lead to [W(3)Q(4)(CN)(9)](5-). Heating W(3)Te(7)Br(4) in KCNSe melt gives a complicated mixture of W(3)Q(7) and W(3)Q(4) derivatives, as was shown by ESI-MS, from which E(3)[W(3)(mu(3)-Te)(mu-TeSe)(3)(CN)(6)]Br.6H(2)O (5) and K(5)[W(3)(mu(3)-Te)(mu-Se)(3)(CN)(9)] (6) were isolated. X-ray analysis of 5 reveals the presence of a new TeSe(2-) ligand. The complexes were characterized by IR, Raman, electronic, and (77)Se and (125)Te NMR spectra and by ESI mass spectrometry.     

Coordination chemistry of novel scorpionate ligands based on 3-cyclohexylpyrazole and 3-cyclohexyl-4-bromopyrazole

The ligands [hydrotris(3-cyclohexylpyrazol-1-yl)borate, [Tp(Cy)](-), tetrakis(3-cyclohexylpyrazol-1-yl)borate, [pz(o)Tp(Cy)](-), and hydrotris(3-cyclohexyl-4-bromopyrazol-1-yl)borate, [Tp(Cy,4Br)](-) were synthesized and characterized as their Tl(I) derivatives. They were converted to a variety of tetrahedral LMX and octahedral LML' complexes, as well as to the dinuclear nickel carbonate complex [Ni(Tp(Cy))](2)(CO(3)), 4, and the compound Ni[Tp(Cy,4Br)][pz(Cy,4Br)](3)(H)(2), 5. The structures of Co[Tp(Cy)]Cl, 1, Co[Tp(Cy,4Br)]Cl, 2, Co[Tp(Cy,4Br)]NCS, 3, [Ni(Tp(Cy))](2)(CO(3)), 4, Ni[Tp(Cy,4Br)][pz(Cy,4Br)](3)(H)(2), 5, and Mo[Tp(Cy)](CO)(2)(eta(3)-methallyl), 6, were determined by X-ray crystallography. The structures of paramagnetic heteroleptic complexes Co[Tp(Cy)][Tp], Co[Tp(Cy)][Tp], Co[Tp(Cy,4Br)][Tp], and Co[Tp(Cy,4Br)][Tp] were established by NMR. The homoleptic compounds Co[Tp(Cy)](2) and Co[Tp(Cy,4Br)](2) rearrange thermally to Co[Tp(Cy)](2) and to Co[Tp((Cy,4Br))](2), respectively, containing one 5-cyclohexyl group/ligand.     

QTAIM analysis of the bonding in Mo-Mo bonded dimolybdenum complexes

A number of local and integral topological parameters of the electron density of relevant bonding interactions in the binuclear molybdenum complexes [Mo(2)Cl(8)](4-), [Mo(2)(μ-CH(3)CO(2))(4)], [Mo(2)(μ-CF(3)CO(2))(4)], [Mo(2)(μ-CH(3)CO(2))(4)Br(2)](2-), [Mo(2)(μ-CF(3)CO(2))(4)Br(2)](2-), [Mo(2)(μ-CH(3)CO(2))(2)Cl(4)](2-), [Mo(2)(μ-CH(3)CO(2))(2)(μ-Cl)(2)Cl(4)](2-), and [Mo(2)(μ-Cl)(3)Cl(6)](3-) have been calculated and interpreted under the perspective of the quantum theory of atoms in molecules (QTAIM). These data have allowed a comparison between related but different atom-atom interactions, such as different Mo-Mo formal bond orders, ligand-unbridged versus Cl-bridged, CH(3)CO(2)-bridged, and CF(3)CO(2)-bridged Mo-Mo interactions, and Mo-Cl(terminal) and Mo-Cl(bridge) versus Mo-Br and Mo-O interactions. Calculations carried out using nonrelativistic and relativistic approaches afforded similar results.     

Synthesis, Structure, and Reactivities of [eta(2)-P(7)M(CO)(4)](3)(-), [eta(2)-HP(7)M(CO)(4)](2)(-), and [eta(2)-RP(7)M(CO)(4)](2)(-) Zintl Ion Complexes Where M = Mo, W

Ethylenediamine (en) solutions of [eta(4)-P(7)M(CO)(3)](3)(-) ions [M = W (1a), Mo (1b)] react under one atmosphere of CO to form microcrystalline yellow powders of [eta(2)-P(7)M(CO)(4)](3)(-) complexes [M = W (4a), Mo (4b)]. Compounds 4 are unstable, losing CO to re-form 1, but are highly nucleophilic and basic. They are protonated with methanol in en solvent giving [eta(2)-HP(7)M(CO)(4)](2)(-) ions (5) and are alkylated with R(4)N(+) salts in en solutions to give [eta(2)-RP(7)M(CO)(4)](2)(-) complexes (6) in good yields (R = alkyl). Compounds 5 and 6 can also be prepared by carbonylations of the [eta(4)-HP(7)M(CO)(3)](2)(-) (3) and [eta(4)-RP(7)M(CO)(3)](2)(-) (2) precursors, respectively. The carbonylations of 1-3 to form 4-6 require a change from eta(4)- to eta(2)-coordination of the P(7) cages in order to maintain 18-electron configurations at the metal centers. Comparative protonation/deprotonation studies show 4 to be more basic than 1. The compounds were characterized by IR and (1)H, (13)C, and (31)P NMR spectroscopic studies and microanalysis where appropriate. The [K(2,2,2-crypt)](+) salts of 5 were characterized by single crystal X-ray diffraction. For 5, the M-P bonds are very long (2.71(1) ?, average). The P(7)(3)(-) cages of 5 are not displaced by dppe. The P(7) cages in 4-6 have nortricyclane-like structures in contrast to the norbornadiene-type geometries observed for 1-3. (31)P NMR spectroscopic studies for 5-6 show C(1) symmetry in solution (seven inequivalent phosphorus nuclei), consistent with the structural studies for 5, and C(s)() symmetry for 4 (five phosphorus nuclei in a 2:2:1:1:1 ratio). Crystallographic data for [K(2,2,2-crypt)](2)[eta(2)-HP(7)W(CO)(4)].en: monoclinic, space group C2/c, a = 23.067(20) ?, b = 12.6931(13) ?, c = 21.433(2) ?, beta = 90.758(7) degrees, V = 6274.9(10) ?(3), Z = 4, R(F) = 0.0573, R(w)(F(2)) = 0.1409. For [K(2,2,2-crypt)](2)[eta(2)-HP(7)Mo(CO)(4)].en: monoclinic, space group C2/c, a = 22.848(2) ?, b = 12.528(2) ?, c = 21.460(2) ?, beta = 91.412(12) degrees, V = 6140.9(12) ?(3), Z = 4, R(F) = 0.0681, R(w)(F(2)) = 0.1399.     

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.     

Preparation,structures, and redox and emission characteristics of the isothiocyanate complexes of hexarhenium(III) clusters [Re6(mu3-E)8(NCS)6]4- (E = S,Se)

Hexarhenium(III) complexes with terminal isothiocyanate ligands, [(n-C(4)H(9))(4)N](4)[Re(6)(mu(3)-S)(8)(NCS)(6)] (1) and (L)(4)[Re(6)(mu(3)-Se)(8)(NCS)(6)] (L(+) = PPN(+) (2a), (n-C(4)H(9))(4)N(+) (2b)), have been prepared by three different methods. Complex 1 was prepared by the reaction of [(n-C(4)H(9))(4)N](4)[Re(6)(mu(3)-S)(8)Cl(6)] with molten KSCN at 200 degrees C, while 2b was obtained by refluxing the chlorobenzene-DMF (2:1 v/v) solution of [Re(6)(mu(3)-Se)(8)(CH(3)CN)(6)](SbF(6))(2) and [(n-C(4)H(9))(4)N]SCN. The [Re(6)(mu(3)-Se)(8)(NCS)(6)](4)(-) anion was also obtained from a mixture of Cs(2)[Re(6)(mu(3)-Se)(8)Br(4)] and KSCN in C(2)H(5)OH by a mechanochemical activation at room temperature for 20 h and isolated as 2a. The X-ray structures of 1 and 2a.4DMF have been determined (1, C(70)H(144)N(10)S(14)Re(6), monoclinic, space group P2(1)/n (No. 14), a = 14.464(7) A, b = 22.059(6) A, c = 16.642(8) A, beta = 113.62(3) degrees, V = 4864(3) A(3), Z = 2; 2a.4DMF, C(162)H(144)N(14)O(4)P(8)S(6)Se(8)Re(6), triclinic, space group P1 (No. 2), a = 15.263(2) A, b = 16.429(2) A, c = 17.111(3) A, alpha = 84.07(1) degrees, beta = 84.95(1) degrees, gamma = 74.21(1) degrees, V = 4098.3(8) A(3), Z = 1). All the NCS(-) ligands in both complexes are coordinated to the metal center via nitrogen site with the Re-N distances in the range of 2.07-2.13 A. The redox potentials of the reversible Re(III)(6)/Re(III)(5)Re(IV) process in acetonitrile are +0.84 and +0.70 V vs. Ag/AgCl for [Re(6)(mu(3)-S)(8)(NCS)(6)](4)(-) and [Re(6)(mu(3)-Se)(8)(NCS)(6)](4)(-), respectively, which are the most positive among the known hexarhenium complexes with six terminal anionic ligands. The complexes show strong red luminescence with the emission maxima (lambda(max)/nm), lifetimes (tau(em)/micros), and quantum yields (phi(em)) being 745 and 715, 10.4 and 11.8, and 0.091 and 0.15 for 1 and 2b, respectively, in acetonitrile. The data reasonably well fit in the energy-gap plots of other hexarhenium(III) complexes. The temperature dependence of the emission spectra and tau(em) of 1 and [(n-C(4)H(9))(4)N](4)[Re(6)(mu(3)-S)(8)Cl(6)] are also reported.     

Substitution and derivatization reactions of a water soluble iron(II) complex containing a self-assembled tetradentate phosphine ligand

Facile substitution reactions of the two water ligands in the hydrophilic tetradentate phosphine complex cis-[Fe{(HOCH2)P{CH2N(CH2P(CH2OH)2)CH2}2P(CH2OH)}(H2O)2](SO4) (abbreviated to [Fe(L1)(H2O)2](SO4), 1) take place upon addition of Cl-, NCS-, N3(-), CO3(2-) and CO to give [Fe(L1)X2] (2, X = Cl; 4, X = NCS; 5, X=N3), [Fe(L1)(kappa2-O(2)CO)], 6 and [Fe(L1)(CO)2](SO4), 7. The unsymmetrical mono-substituted intermediates [Fe(L1)(H2O)(CO)](SO(4)) and [Fe(L(1))(CO)(kappa(1)-OSO(3))] (8/9) have been identified spectroscopically en-route to 7. Treatment of 1 with acetic anhydride affords the acylated derivative [Fe{(AcOCH2)P{CH2N(CH2P(CH2OAc)2)CH2}2P(CH2OAc)}(kappa2-O(2)SO2)] (abbreviated to [Fe(L2)(kappa2-O(2)SO2)], 10), which has increased solubility over 1 in both organic solvents and water. Treatment of 1 with glycine does not lead to functionalisation of L1, but substitution of the aqua ligands occurs to form [Fe(L(1))(NH(2)CH(2)CO(2)-kappa(2)N,O)](HSO(4)), 11. Compound 10 reacts with chloride to form [Fe(L(2))Cl(2)] 12, and 12 reacts with CO in the presence of NaBPh4 to form [Fe(L2)Cl(CO)](BPh4) 13b. Both of the chlorides in 12 are substituted on reaction with NCS- and N3(-) to form [Fe(L2)(NCS)2] 14 and [Fe(L2)(N3)2] 15, respectively. Complexes 2.H2O, 4.2H2O, 5.0.812H2O, 6.1.7H2O, 7.H2O, 10.1.3CH3C(O)CH3, 12 and 15.0.5H2O have all been crystallographically characterised.     

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.     

(Eta-C5H4R)Fe(CO)2X], X = Cl, Br, I, NO3, CO2Me and [(eta-C5H4R)Fe(CO)3]+, R = (CH2)nCO2Me (n = 0-2), and CO2CH2CH2OH: a new group of CO-releasing molecules

A new group of CO-releasing molecules, CO-RMs, based on cyclopentadienyl iron carbonyls have been identified. X-Ray structures have been determined for [(eta-C(5)H(4)CO(2)Me)Fe(CO)(2)X], X = Cl, Br, I, NO(3), CO(2)Me, [(eta-C(5)H(4)CO(2)Me)Fe(CO)(2)](2), [(eta-C(5)H(4)CO(2)CH(2)CH(2)OH)Fe(CO)(2)](2) and [(eta-C(5)H(4)CO(2)Me)Fe(CO)(3)][FeCl(4)]. Half-lives for CO release, (1)H, (13)C, and (17)OC NMR and IR spectra have been determined along with some biological data for these compounds, [(eta-C(5)H(4)CO(2)CH(2)CH(2)OH)Fe(CO)(3)](+) and [[eta-C(5)H(4)(CH(2))(n)CO(2)Me]Fe(CO)(3)](+), n = 1, 2. More specifically, cytotoxicity assays and inhibition of nitrite formation in stimulated RAW264.7 macrophages are reported for most of the compounds analyzed. [(eta-C(5)H(5))Fe(CO)(2)X], X = Cl, Br, I, were also examined for comparison. Correlations between the half-lives for CO release and spectroscopic parameters are found within each group of compounds, but not between the groups.     

A family of diruthenium compounds with dianionic tridentate ligands of N-(2-pyridyl)-2-oxy-5-R-benzylaminate (R = H, Me, Cl, Br, NO(2)): isolation, structure determination, and electrochemistry

The ligand substitution reaction of Ru(2)(O(2)CCH(3))(4)Cl with 5-substituted N-(2-pyridyl)-2-oxy-5-R-benzylaminate (R = H, Me, Cl, Br, NO(2)) resulted in a family of anionic diruthenium species of [Ru(2)(O(2)CCH(3))(2)(R-salpy)(2)](-) that were isolated by using Na(+)- or K(+)-18-crown-6-ether as the countercation: [A(18-crown-6)(S)(x)()][Ru(2)(O(2)CCH(3))(2)(R-salpy)(2)] (A = Na(+), K(+); S = solvent; R = H, 1; Me, 2; Cl, 3; Br, 4; NO(2), 5). All compounds were structurally characterized by X-ray crystallography. The structural features of the anionic parts are very similar among the compounds: two acetate and two R-salpy(2)(-) ligands are, respectively, located around the Ru(2) unit in a trans fashion, where the R-salpy(2)(-) ligand acts as a tridentate ligand having both bridging and chelating characters to form the M-M bridging/axial-chelating mode. Compounds 1 and 5 with K(+)-18-crown-6-ether have one-dimensional chain structures, the K(+)-18-crown-6-ether interacting with phenolate oxygens of the [Ru(2)(O(2)CCH(3))(2)(R-salpy)(2)](-) unit to form a repeating unit, [.K.O-Ru-Ru-O.], whereas 2-4 are discrete. Cyclic voltammetry and differential pulse voltammetry revealed systematic redox activities based on the dimetal center and the substituted ligand, obeying the Hammett law with the reaction constants per substituent, rho, for the redox processes being 127 mV for Ru(2)(5+)/Ru(2)(4+), 185 mV for Ru(2)(6+)/Ru(2)(5+), 92 mV for Ru(2)(7+)/Ru(2)(6+), and 179 mV for R-salpy(-)/R-salpy(2)(-). For 3, the singly oxidized and reduced species, Ru(2)(6+) and Ru(2)(4+), respectively, generated by bulk controlled-potential electrolyses were finally monitored by spectroscopy. The singly oxidized species can also be slowly generated by air oxidation.     

Syntheses of chromium pentacarbonyl derivatives of arsenic(V) and antimony(V). contrasting chemical reactivity with organic halogen derivatives

We have synthesized a new series of chromium-group 15 dihydride and hydride complexes [H(2)As(Cr(CO)(5))(2)](-) (1) and [HE(Cr(CO)(5))(3)](2)(-) (E = As, 2a; E = Sb, 2b), which represent the first examples of group 6 complexes containing E-H fragments. The contrasting chemical reactivity of 2a and 2b with organic halogen derivatives is demonstrated. The reaction of 2a with RBr (R = PhCH(2), HC triple bond CCH(2)) produces the RX addition products [(R)(Br)As(Cr(CO)(5))(2)](-) (R = PhCH(2), 3; R = C(3)H(3), 4), while the treatment of 2b with RX (RX = PhCH(2)Br or HC triple bond CCH(2)Br, CH(3)(CH(2))(5)C(O)Cl) forms the halo-substituted complexes [XSb(Cr(CO)(5))(3)](2-) (X = Br, 5; X = Cl, 6). Moreover, the dihaloantimony complexes [XX'Sb(Cr(CO)(5))(2)](-) can be obtained from the reaction of 2b with the appropriate organic halides. In this study, a series of organoarsenic and antimony chromium carbonyl complexes have been synthesized and structurally characterized and the role of the main group on the formation of the resultant complexes is also discussed.     

Substitution reactions of [Fe(4)S(4)Cl(4)](2-) with Bu(t)NC or Et(2)NCS(2)(-): trapping intermediates and detecting new pathways

Kinetic studies on the substitution reaction between [Fe(4)S(4)Cl(4)](2-) and Bu(t)NC or Et(2)NCS(2)(-) are reported. The binding of small molecules and ions to Fe-S clusters is a fundamental step in substitution reactions but can be difficult to follow directly because these reactions are rapid and often associated with small spectroscopic changes. A novel kinetic method is reported which allows the time course of molecule and ion binding to Fe-S clusters to be followed by monitoring the lability of the cluster. Using a stopped-flow, sequential-mix apparatus, [Fe(4)S(4)Cl(4)](2-) and L (L = Et(2)NCS(2)(-) or Bu(t)NC) are rapidly mixed, and after a known time (delta) the resulting solution is mixed with a solution of PhS(-). The thiolate substitutes for the chloro ligands on the cluster, in a reaction which is easy to follow because of the large change in the visible absorption spectrum. The rate of this substitution is extremely sensitive to whether L is bound to the cluster or not. By correlation of delta with the rate of the reaction with PhS(-), the time course of the reaction between [Fe(4)S(4)Cl(4)](2-) and L can be mapped out. In studies where L = Bu(t)NC this technique has allowed the detection of an intermediate ([Fe(4)S(4)Cl(4)(CNBu(t))](2-)) which cannot be detected spectrophotometrically. In further studies, the substitution reactions of [Fe(4)S(4)Cl(4)](2-) with PhS(-), Et(2)NCS(2)(-), or Bu(t)NC are all perturbed by the addition of Cl(-). In all cases a common pathway for substitution is evident, but with Et(2)NCS(2)(-) an additional, slower pathway becomes apparent under conditions where the common pathway is completely inhibited by Cl(-).     

Coordination site-dependent cation binding and multi-responsible redox properties of Janus-head metalloligand, [Mo(V)(1,2-mercaptophenolato)3

The redox-active fac-[Mo(V)(mp)(3)](-) (mp: o-mercaptophenolato) bearing asymmetric O- and S-cation binding sites can bind with several kinds of metal ions such as Na(+), Mn(II), Fe(II), Co(II), Ni(II), and Cu(I). The fac-[Mo(V)(mp)(3)](-) metalloligand coordinates to Na(+) to form the contact ion pair {Na(+)(THF)(3)[fac-Mo(V)(mp)(3)]} (1), while a separated ion pair, n-Bu(4)N[fac-Mo(V)(mp)(3)] (2), is obtained by exchanging Na(+) with n-Bu(4)N(+). In the presence of asymmetric binding-sites, the metalloligand reacts with Mn(II)Cl(2)·4H(2)O, Fe(II)Cl(2)·4H(2)O, Co(II)Cl(2)·6H(2)O, and Ni(II)Cl(2)·6H(2)O to afford UV-vis-NIR spectra, indicating binding of these guest metal cations. Especially, for the cases of the Mn(II) and Co(II) products, trinuclear complexes, {M(H(2)O)(MeOH)[fac-Mo(V)(mp)(3)](2)}·1.5CH(2)Cl(2) (3·1.5CH(2)Cl(2) (M = Mn(II)), 4·1.5CH(2)Cl(2) (M = Co(II))), are successfully isolated and structurally characterized where the M are selectively bound to the hard O-binding sites of the fac-[Mo(V)(mp)(3)](-). On the other hand, a coordination polymer, {Cu(I)(CH(3)CN)[mer-Mo(V)(mp)(3)]}(n) (5), is obtained by the reaction of fac-[Mo(V)(mp)(3)](-) with [Cu(I)(CH(3)CN)(4)]ClO(4). In sharp contrast to the cases of 1, 3·1.5CH(2)Cl(2), and 4·1.5CH(2)Cl(2), the Cu(I) in 5 are selectively bound to the soft S-binding sites, where each Cu(I) is shared by two [Mo(V)(mp)(3)](-) with bidentate or monodentate coordination modes. The second notable feature of 5 is found in the geometric change of the [Mo(V)(mp)(3)](-), where the original fac-form of 1 is isomerized to the mer-[Mo(V)(mp)(3)](-) in 5, which was structurally and spectroscopically characterized for the first time. Such isomerization demonstrates the structural flexibility of the [Mo(V)(mp)(3)](-). Spectroscopic studies strongly indicate that the association/dissociation between the guest metal ions and metalloligand can be modulated by solvent polarity. Furthermore, it was also found that such association/dissociation features are significantly influenced by coexisting anions such as ClO(4)(-) or B(C(6)F(5))(4)(-). This suggests that coordination bonds between the guest metal ions and metalloligand are not too static, but are sufficiently moderate to be responsive to external environments. Moreover, electrochemical data of 1 and 3·1.5CH(2)Cl(2) demonstrated that guest metal ion binding led to enhance electron-accepting properties of the metalloligand. Our results illustrate the use of a redox-active chalcogenolato complex with a simple mononuclear structure as a multifunctional metalloligand that is responsive to chemical and electrochemical stimuli.     

Precursors to water-soluble dinitrogen carriers. Synthesis of water-soluble complexes of iron(II) containing water-soluble chelating phosphine ligands of the type 1,2-bis(bis(hydroxyalkyl)phosphino)ethane

The reactions of the water-soluble chelating phosphines 1,2-bis(bis(hydroxyalkyl)phosphino)ethane (alkyl = n-propyl, DHPrPE; n-butyl, DHBuPE; n-pentyl, DHPePE) with FeCl(2).4H(2)O and FeSO(4).7H(2)O were studied as routes to water-soluble complexes that will bind small molecules, dinitrogen in particular. The products that form and their stereochemistry depend on the solvent, the counteranion, and the alkyl chain length on the phosphine. In alcoholic solvents, the reaction of FeCl(2).4H(2)O with 2 equiv of DHBuPE or DHPePE gave trans-Fe(L(2))(2)Cl(2). The analogous reactions in water with DHBuPE and DHPePE gave only cis products, and the reaction of FeSO(4).7H(2)O with any of the phosphines gave only cis-Fe(L(2))(2)SO(4). These results are interpreted as follows. The trans stereochemistry of the products from the reactions of FeCl(2).4H(2)O in alcohols is suggested to be the consequence of the trans geometry of the Fe(H(2)O)(4)Cl(2) complex, i.e., substitution of the water molecules by the phosphines retains the geometry of the starting material. The formation of cis-Fe(DHPrPE)(2)Cl(2) is an exception to this result because the coordination of two -OH groups forms two six-membered rings, as shown in the X-ray structure of the molecule. DHBuPE and DHPePE reacted with FeSO(4).7H(2)O in water to initially yield cis-Fe(P(2))(2)SO(4) compounds, but subsequent substitution reactions occurred over several hours to give sequentially trans-Fe(DHBuPE)(2)(H(2)O)(SO(4)) and then trans-[Fe(DHBuPE)(2)(H(2)O)(2)]SO(4). The rate constants and activation reactions for these aquation reactions were determined and are consistent with dissociatively activated mechanisms. The cis- and trans-Fe(L(2))(2)X (X = (Cl)(2) or SO(4)) complexes react with N(2), CO, and CH(3)CN to yield trans complexes with bound N(2), CO, or CH(3)CN. The crystal structures of the cis-Fe(DHPrPE)(2)SO(4), trans-Fe(DHPrPE)(2)(CO)SO(4), trans-Fe(DHBuPE)(2)Cl(2), trans-[Fe(DHBuPE)(2)(CO)(Cl)][B(C(6)H(5))(4)], trans-Fe(DMeOPrPE)(2)Cl(2), trans-Fe(DMeOPrPE)(2)Br(2), and trans-[Fe(DHBuPE)(2)Cl(2)]Cl complexes are reported. As expected from using water-soluble phosphines, the complexes reported herein are water soluble (generally greater than 0.5 M at 23 degrees C).     

(S)-(2-(2'-Pyridyl)ethyl)cysteamine and (S)-(2-(2'-pyridyl)ethyl)-d,l-homocysteine as ligands for the "fac-[M(CO)(3)](+)" (M = Re, (99m)Tc) core

The reaction of fac-[NEt(4)](2)[Re(CO)(3)Br(3)] with (S)-(2-(2'-pyridyl)ethyl)cysteamine, L(1), in methanol leads to the formation of the cationic fac-[Re(CO)(3)(NSN)][Br] complex, 1, with coordination of the nitrogen of the pyridine, the sulfur of the thioether, and the nitrogen of the primary amine. When fac-[NEt(4)](2)[Re(CO)(3)Br(3)] reacts with the homocysteine derivative (S)-(2-(2'-pyridyl)ethyl)-d,l-homocysteine, L(2), the neutral fac-Re(CO)(3)(NSO) complex, 2, is produced with coordination of the nitrogen of the primary amine, the sulfur of the thioether, and the oxygen of the carboxylate group, while the pyridine ring remains uncoordinated. The analogous technetium-99m complexes, 1' and 2', were also prepared quantitatively by the reaction of L(1) and L(2) with the fac-[(99m)Tc(CO)(3)(H(2)O)(3)](+) precursor at 70 degrees C in water. Given that both (S)-(2-(2'-pyridyl)ethyl)cysteamine and homocysteine can be easily N- or S-derivatized by a bioactive molecule of interest, both the NSN or NSO ligand systems could be used to develop target-specific radiopharmaceuticals for diagnosis and therapy.     

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.