Enhancing the stability of trinickel molecular wires and switches: Ni(3)(6+)/Ni(3)(7+)

This paper describes in detail four new compounds that contain extended metal atom chains (EMACs) of three nickel atoms wrapped by either di(2-pyridyl)amide (dpa) or the new homologous ligand with an ethyl group at the para position of each pyridyl group, depa, and compares them to the precursor Ni(3)(dpa)(4)Cl(2) (1) and the oxidized and rather unstable Ni(3)(dpa)(4)(PF(6))(3) (2). The new molecules are Ni(3)(depa)(4)Cl(2) (3), Ni(3)(depa)(4)(PF(6))(3) (4), [Ni(3)(dpa)(4)(CH(3)CN)(2)](PF(6))(2) (5), and [Ni(3)(depa)(4)(CH(3)CN)(2)](PF(6))(2) (6). These compounds are fully described as to preparation, elemental composition, structure, infrared spectra, (1)H NMR spectra (where possible), electrochemistry, magnetic susceptibility, and an EPR spectrum for 4. The effects of (a) introducing the ethyl substituents on the ligands, (b) replacing axial anions by neutral axial ligands, and (c) oxidizing the Ni(3) chains are reported and discussed. The point of major interest is how oxidation profoundly alters the electronic structure of the EMAC.     

Electron delocalization in nickel metallic wires: a DFT investigation of Ni(3)(dpa)(4)Cl(2) and [Ni(3)(dpa)(4)](3+) (dpa = dipyridylamide) and extension to higher nuclearity chains

The electronic structure of Ni(3)(dpa)(4)Cl(2) (1) has been investigated within the framework of the density functional theory (DFT), using two types of exchange-correlation functionals and various basis sets. The "broken-symmetry" approach proposed by Noodleman for the characterization of electronic states displaying an antiferromagnetic coupling has been applied to 1. All calculations lead to the conclusion that the ground state results from an antiferromagnetic coupling between the terminal Ni atoms, both displaying a high-spin electronic configuration. The central Ni atom is in a low-spin configuration, but is involved in a superexchange interaction connecting the two magnetic centers. These results are in agreement with the assignments recently proposed by the group of F. A. Cotton on the basis of magnetic measurements. It is shown that the ground state electronic configuration calculated for 1 provides the trinickel framework with some delocalized sigma bonding character. The observed geometry of 1 is accurately reproduced by the broken-symmetry solution. The doublet ground state assigned to the oxidized species [Ni(3)(dpa)(4)](3+) (2) and the dramatic contraction of the coordination sphere of the terminal metals observed upon oxidation are also confirmed by the calculations. However, the formal Ni-Ni bond order is not expected to increase in the oxidized species. The contraction of the Ni-Ni distance in 2 is shown to result in part from the vanishing of the important trans influence originating in the axial ligands, and for the rest from a more efficient shielding of the metal nuclear charge along the Ni-Ni-Ni axis. The conclusions deduced from the analysis of the bonding in 1 and 2 can be extended to their homologues with higher nuclearity. More specifically, it is predicted that the single occupancy of the most antibonding sigma orbital, extending over the whole metal framework, will provide the (Ni(p))(2)(p)(/(2)(p)(+1)+) chains with some delocalized bonding character and, possibly, with electrical conduction properties.     

M(rac-N-benzyl Asp)(H2O)] (M = Co, Ni): noncentrosymmetric coordination polymeric chains with racemic chiral ligands

The hydrothermal reaction of fumaric acid, benzylamine, and metal salts yielded M[(rac-N-benzyl-Asp)(H(2)O)] (M = Co, Ni), 1 and 2, and Ni[(rac-N-benzyl-Asp)(H(2)O)(3)]·H(2)O 3. Under mild hydrothermal conditions, Michael addition of benzylamine to fumaric acid led to the formation of a racemic mixture of N-benzyl aspartic acid enantiomers. The noncentrosymmetric structures of 1 and 2 consist of one-dimensional polymeric chains in which metal cations are bridged by d- and l-N-benzyl aspartate anions alternating along the chain. The centrosymmetric structure of 3 is composed of discrete Ni[(rac-N-benzyl-Asp)(H(2)O)(3)] units that are connected by hydrogen bonds into layers. The single layers are homochiral but are hydrogen bonded to similar homochiral layers that contain the N-benzyl aspartate with the opposite handedness. Compounds 1 and 2 showed second harmonic generation (SHG), and their magnetic and thermodynamic properties are described.     

Convergent synthesis of 10 nm aryleneethynylene molecular wires by an iterative regioselective deprotection/Sonogashira coupling protocol

[structure: see text] The synthesis of a new series of rigid-rod aryleneethynylene derivatives of up to ca. 10 nm molecular length (compounds 16 and 17) is reported using iterative Pd-mediated Sonogashira coupling methodology combined with regioselective removal of the different protecting groups (namely, trimethylsilyl and 2-hydroxyprop-2-yl groups) from the terminal alkyne units. Additionally, the TMS-acetylene unit has been cleanly deprotected to afford a terminal alkyne in the presence of a cyanoethylsulfanyl group. Some of these molecular wires are functionalized with terminal protected thiophenol units for attachment to metal surfaces (compounds 16 and 17). Internal electron-acceptor units have been incorporated into their structures, namely, 9-[di(4-pyridyl)methylene]fluorene (compound 17) or fluorenone (compounds 19-22). Optical absorption and photoluminescence spectra reveal a red shift in the value of lambda(max) with increasing molecular length, which approaches saturation at an effective conjugation length of ca. 15-20 pi-units in the molecules, where each phenyl ring or a triple bond is counted as one pi-unit.     

Oxidation reaction of [Ni(1,4,7-triazacyclononane)(2)](2+) by [Fe(o-phenanthroline)(3)](3+) in aqueous acidic solution at elevated pressures: determination of the activation and reaction volumes for the Ni(iii)/(ii) couple

The reaction volume corresponding to the self-exchange process of the [Ni(tacn)(2)](3+/2+) couple was determined in aqueous acidic solution. Theoretical equations on the basis of the Mean Spherical Approximation were proposed for the estimation of reaction volumes for M(n+/(n- 1)+) couples in solution, and the calculated reaction volumes were compared with the experimentally estimated values. The activation volume for the [Ni(tacn)(2)](3+/2+) couple was determined in the acidic condition from the cross reaction of [Ni(tacn)(2)](2+) and [Fe(o-phen)(3)](3+) at elevated pressures. The agreement of the experimentally estimated activation volume for the [Ni(tacn)(2)](3+/2+) couple, -8.2 +/- 2.4 cm(3) mol(-1), with the theoretically calculated value, -7.5 cm(3) mol(-1), within the allowed uncertainty (+/-1 cm(3) mol(-1)) indicates that the electron self-exchange reaction of this redox couple obeys the Marcusian behavior in aqueous acidic solution.     

The versatility of molecular ruthenium catalyst RuCl(COD)(C5Me5)

This review reports the contribution of the catalyst precursor RuCl(COD)C₅Me₅, and of the Rennes team, for the selective transformation of alkynes to generate high value chemicals with atom economy reactions. Ruthenium activation processes are discussed. Are successively presented (i) the cross-oxidative coupling of alkyne and allyl alcohol to generate γ,δ-unsaturated aldehydes, (ii) the head-to-head dimerisation of alkynes in the presence of carboxylic acids, via a mixed Fischer-Schrock type biscarbene-ruthenium complex, to give functional dienes, and that of propargyl alcohols, via cyclobutadienyl-ruthenium intermediate, to produce cyclobutene derivatives, (iii) the addition of diazoalkanes to alkynes leading to functional dienes via double carbene addition and (iv) the reaction of diazoalkanes to enynes leading to new bicyclo[3.1.0]hexane compounds. Most of the above catalytic reactions involve carbene-ruthenium catalytic species of type Cp*(Cl)Ru(biscarbene) or Cp*(Cl)RuCHR.     

配合物Ni(C14H10N2O3)(C5H5N)的合成和晶体结构

A novel nickel(Ⅱ) complex with 2,4-dihydroxybenzalidene benzoylhydrazone and pyridine ligands, Ni(C₁₄H₁₀N₂O₃)(C₅H₅N), has been synthesized and characterized by elemental analysis and IR. The crystal structure of the title complex has been determined by single crystal X-ray diffraction techniques. The crystal belongs to orthorhombic, space group Pbca. The cell parameters are: a=1.580 20(19) nm, b=1.362 18(16) nm, c=1.616 50(19) nm, and V=3.479 5(7) nm³, Z=8, D_c=1.497 Mg·m^-3, μ(MoKα)=1.139 mm^-1, F(000)=1 616, R=0.032 9 and wR=0.077 0 for 2 772 observed reflections (I>2σ(I)) out of 3810 unique ones. The nickel(Ⅱ) ion lies in a distorted square-planar environment composed of two oxygen atoms, one nitrogen atom of tridentate acyhydrazone schiff base ligand and one nitrogen atom of the pyridine ligand. The analysis of the crystal structure indicates that the complex has a one-dimensional chain structure, which is formed by intermolecular hydrogen bonds. CCDC: 244668.     

The extraordinary ability of guanidinate derivatives to stabilize higher oxidation numbers in dimetal units by modification of redox potentials: structures of Mo(2)(5+) and Mo(2)(6+) compounds

Full characterization of the first homologous series of dimolybdenum paddlewheel compounds having electronic configurations of the types sigma(2)pi(4)delta(x), x = 2, 1, 0, and Mo-Mo bond orders of 4, 3.5, and 3, respectively, has been accomplished with the guanidinate-type ligand hpp (hpp = the anion of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine). Essentially quantitative oxidation of Mo(2)(hpp)(4), 1, by CH(2)Cl(2) gives Mo(2)(hpp)(4)Cl, 2. The halide in 2 can be replaced by reaction with TlBF(4) to produce Mo(2)(hpp)(4)(BF(4)), 3. Further oxidation of 2 by AgBF(4) produces Mo(2)(hpp)(4)ClBF(4), 4. The change from bond order 4 (in 1) to 3.5 in Mo(2)(hpp)(4)Cl is accompanied by an increase in the Mo-Mo bond length of 0.061 to 2.1280(4) A. A further increase of 0.044 A in the Mo-Mo distance to 2.172(1) A is observed as the bond order decreases to 3 in 4. At the same time, the Mo-N distances decrease smoothly as the oxidation state of the Mo atoms increases. Electrochemical studies have shown two chemically reversible processes at very negative potentials, E(1)(1/2)= -0.444 V and E(2)(1/2)= -1.271 V versus Ag/AgCl. These correspond to the processes Mo(2)(6+/5+) and Mo(2)(5+/4+), respectively. The latter potential is displaced by over 1.5 V relative to those of the Mo(2)(formamidinate)(4) compounds and the first one has never been observed in such complexes. Thus, in surprising contrast to previously observed behavior of the dimolybdenum unit, when it is surrounded by the very basic guanidinate ligand hpp, there is an extraordinary stabilization of the higher oxidation numbers of the molybdenum atoms.     

Ge(7)O(13)(OH)(2)F(3)](3)(-).Cl(-).2[Ni(dien)(2)](2+): the first chainlike germanate templated by a transition metal complex

The first chainlike germanate, [Ge(7)O(13)(OH)(2)F(3)](3)(-).Cl(-).2[Ni(dien)(2)](2+), has been solvothermally synthesized by using Ni(dien)(2)(2+) cations as the template and characterized by IR, SEM, TGA, powder X-ray diffraction (PXRD), energy-dispersive X-ray analysis (EDXA), elemental analysis, and single-crystal X-ray diffraction, respectively. This compound crystallized in the monoclinic space group P2/nwith a = 8.8904(2) A, b = 17.4374(3) A, c = 13.2110(3) A, beta = 101.352(1) degrees, V = 2007.97(7) A(3), and Z = 2. Interestingly, the structure contains two types of chiral mer-[Ni(dien)(2)](2+) cations and two types of chiral chains, one left-handed and the other right-handed, which lead to a racemic compound. The orderly separation of achiral s-fac-[Ni(dien)(2)](2+) and chiral mer-[Ni(dien)(2)](2+) isomers was found in the structure. The structure is stabilized by N-H.O(F, Cl) hydrogen bonds.     

Ab initio molecular dynamics study on the electron capture processes of protonated methane (CH5+)

Electron capture dynamics of protonated methane (CH5(+)) have been investigated by means of a direct ab initio molecular dynamics (MD) method. First, the ground and two low-lying state structures of CH5 (+) with eclipsed Cs , staggered Cs and C2v symmetries were examined as initial geometries in the dynamics calculation. Next, the initial structures of CH5 (+) in the Franck-Condon (FC) region were generated by inclusion of zero point energy and then trajectories were run from the selected points on the assumption of vertical electron capture. Two competing reaction channels were observed: CH5 (+) + e (-)--> CH4 + H (I) and CH5 (+) + e (-) --> CH3 + H2 (II). Channel II occurred only from structures very close to the s- Cs geometry for which two protons with longer C-H distances are electronically equivalent in CH5 (+). These protons have the highest spin density as hydrogen atoms following vertical electron capture of CH5 (+) and are lost as H2. On the other hand, channel I was formed from a wide structural region of CH5 (+). The mechanism of the electron capture dynamics of CH5 is discussed on the basis of the theoretical results.     

Synthesis and characterization of {Ni(NO)}10 and {Co(NO)2}10 complexes supported by thiolate ligands

Nitric oxide is an important molecule in biology and modulates a variety of physiological and pathophysiological processes. Some of its regulatory functions are exerted through interactions with redox-active elements, including iron, nickel, cobalt, and sulfur. Metalloenzymes containing [ nFe- nS] ( n = 2 or 4) clusters can be activated or inactivated by reaction with NO, affording dinitrosyl iron complexes. Studies of the NO chemistry of small-molecule iron thiolate complexes have provided insight into these biological processes and suggested probable intermediates. To explore this chemistry from a different perspective, we prepared nickel and cobalt thiolate complexes and investigated their reactions with NO and related compounds. We report here the first examples of anionic complexes containing {Ni(NO)} (10) and {Co(NO) 2} (10) units, the reactivity of which suggests possible intermediates in the interconversion of iron thiolate nitrosyl compounds. Our results demonstrate new chemistry involving NO and simple complexes of nickel and cobalt supported by thiolates, which have been known for more than 30 years. The use of mass balance methodology was key to their discovery. Among the novel complexes reported are (Et 4N) 2[Ni(NO)(SPh) 3] ( 2), from (Et 4N) 2[Ni(SPh) 4] ( 1) and NO, (Et 4N) 2[Ni 2(NO) 2(mu-SPh) 2(SPh) 2] ( 3), from 1 and NO (+) or 2 and Me 3O (+), (Et 4N)[Co(NO) 2(SPh) 2] ( 5), from (Et 4N) 2[Co(SPh) 4] ( 4) and NO, and [Co 3(NO) 6(mu-SPh) 3] ( 6), from 5 and Me 3O (+). In the syntheses of 2 and 5, NO could be replaced by the convenient solid Ph 3CSNO.     

Chemistry of vinylidene complexes: IV. Synthesis and the crystal and molecular structure of (η5-C5H5)MnOs3(μ2-CHCHPh)(μ-H)(μ-CO)(CO)11, an unusual heterometallic cluster

By the reaction of Cp(CO)₂MnCCHPh (I) with H₂Os₃(CO)₁₀ (II) the tetranuclear mixed-metal complex CpMnOs₃(μ₂-CHCHPh)(μ-H)(μ-CO)(CO)₁₁ (III) was prepared. An X-ray study of the structure of III showed that it is a spiked, tetranuclear cluster with the Mn atom linked to one of the vertices of the osmium triangle; the MnOs bond is bridged by CO and CHCHPh groups, the latter being σ-bonded to Os and η²-coordinated by Mn. In the course of the formation of III, hydrogenation and n-π rearrangement of the initial phenylvinylidene ligand take place. In solution, complex III readily eliminates the [CpMn(CO)₂] fragment to give triosmium clusters containing unsaturated organic ligands: HOs₃(μ₂-CHCHPh)(CO)₁₀, H₂Os₃(μ₃-CHCPh)(CO)₉, and H₂Os₃(μ₃-CCHPh)(CO)₉.     

The molecular structure of a three-coordinate palladium(II)-styrene complex [Pd(η5-C5H5)(PEt3)(styrene)]BF4

The molecular structure of a three-coordinate palladium(II)-styrene complex, [Pd(η⁵-C₅H₅)(PEt₃)(styrene)]BF₄ has been determined by means of X-ray diffraction. The crystal belongs to the monoclinic system, space group P2₁/c, with four formula units in a cell of dimensions: a 10.229(3), b 11.262(3), c 18.760(5) Å and β 103.77(2)°. The structure was solved by the heavy atom method, and refined by the least-squares procedure to R = 0.050 for 3635 observed reflections. The palladium atom is surrounded by the cyclopentadienyl group, the triethylphosphine ligand and the olefinic bond of styrene in the cationic complex. In the palladiumstyrene bonding, the olefinic bond is inclined by 77.3° to the coordination plane defined by the Pd and P atoms and the center of the cyclopentadienyl ring (PdC(1) 2.176(6), PdC(2) 2.234(5) and C(1)C(2) 1.369(8) Å).     

Comparative study of NS(2)(S-aryl) pyridine-based dithia-containing ligands with different substituent groups. Reactivity toward Cu(II) and Ru(II)

Ligands LX of the type NS(2) with S-aryl substituents which incorporate the unit 2,6-bis(thiomethyl)pyridine modified with functional groups bonded to the aromatic moieties, either on the phenyl or on the pyridine, are produced. Electron-withdrawing groups, 3-chloro and 4-nitro, that reduce the pyridine basicity have been introduced. Methoxy or methoxycarbonyl substituents have been incorporated on the thiophenyl moieties. The comparative results from the reaction of these ligands with Cu(ClO(4))(2).6H(2)O and [RuCl(2)(PPh(3))(3)] have revealed that their coordination capacity has not been greatly modified as a result of the introduced groups. Complexes of general formulas [Cu(LX)][ClO(4)](2), except for L5, and [RuCl(2)(LX)(PPh(3))], have been obtained, respectively. The electronic characteristics of these complexes have been studied by cyclic voltammetry experiments. The structures of 2,6-bis[(2'-methoxycarbonyl)phenylthio-methyl]-4-nitropyridine (L5) and [RuCl(2)(L5)(PPh(3))].2CCl(4) have been characterized by single-crystal X-ray diffraction methods.     

Replacement of CO group by other ligands in (CO)3MnC5H4Ni(PPh3)C5H5-π

Russian Chemical Bulletin - One of the carbonyl groups inπ-cyclopentadienyl(triphenylphosphine)-σ-(π-cyclopentadienylmanganese tricarbonyi)nickel was replaced by triphenylphosphine...     

Photochromism of dihydroindolizines. Part XVI: first attempts toward molecular wires comprising photochromic dihydro 5-azaindolizines and π-extended ethynyl and butadiynyl oxadiazole derivatives

Eight new photochromic dihydro 5-azaindolizines (DHAIs) linked with 2,5-diaryl-1,3,4-oxadiazole (OXD) derivatives containing terminal ethynes and butadiyne substituents on the fluorene part of the DHAI skeleton are synthesized via palladium-mediated coupling reaction pathways. Irradiation of the DHAI-OXD derivatives with polychromatic light affords red- and green-colored betaines.     

Novel oxovanadium phosphate tubule incorporating 2,2-bipyridine ligands: hydrothermal synthesis and crystal structure of [(V(IV)O)(3)(mu(5)-PO(4))(2)(2,2'-bpy)(mu-OH(2))].1/3H(2)O

The novel tubular framework of [(V(IV)O)(3)(mu(4)-PO(4))(2)(2,2'-bpy)(mu-OH(2))].1/3H(2)O, which was synthesized from hydrothermal reaction, possesses some attractive structural features: (i) O=V(IV)O(4)(OH(2)) octahedra and PO(4) tetrahedra linked together by corner-sharing and face-sharing into a cylinder-shaped channel including 6 water molecules per cell unit, and (ii) (VO)(2,2'-bpy) groups regularly arranged around the tube, so that the 2,2-bpy ligands constitute an organic shell around an aqueous polar channel.     

Crystal and molecular structure of (η5-trimethylsilylcyclopentadienyl)(η4-tetraphenylcyclobutadiene)cobalt

The structure of (η⁵-trimethylsilylcyclopentadienyl)(η⁴-tetraphenylcyclobutadiene)cobalt, ((CH₃)₃SiC₅H₄)Co((C₆H₅)₄C₄), has been determined by single crystal X-ray diffraction techniques using three-dimensional data collected on an automatic diffractometer. The crystals are monoclinic, space group P2₁/c, with lattice parameters a 11.551(1), b 16.352(6), c 18.324(2) », β 122.85(1)° with four molecules in the unit cell. The structure consists of discrete molecules in which a cobalt atom is sandwiched between the η⁵-cyclopentadienyl (Cp) and the η⁴-cyclobutadience (Cb) ligands bonded to the metal in the hapto mode. The perpendicular distances Co?(Cp) and Co?(Cb) of 1.688 and 1.699 », respectively, as well as the dihedral angle of 6.9° between the two rings and the distortions of their side groups, indicate steric interactions within the molecule. The Cb ring is planar within 0.015 » and has a rectangular shape with edges of 1.480(5) and 1.463(3) ». The Cp ring, which is planar to within 0.005 », appears to be highly distorted by the trimethylsilyl group, which induces a lengthening of the C—C distances involving the substituted carbon atom (1.440(7) ») and a narrowing of the corresponding bond angle (105.3(2)°).