Donald M. Baird

Structural Characterization of bis(arylimino)isoindoline Complexes of Dimolybdenum

Abstract The complexes [Mo2(OAc)3(BAII)], where BAII is either bis(pyridylimino) isoindoline or bis(4,6-dimethylpyridylimino)isoindoline, have been synthesized. A detailed interpretation of their 1H NMR spectra has been made. The structure of the bis(pyridylimino)isoindoline derivative has been determined by X-ray analysis to facilitate the assignment of the resonance lines in the NMR spectra. The complex is triclinic belonging to the space group P1 with a = 8.241(3), b = 12.274(4), c = 15.390(6) A, V = 1490.1(9) A3 and Dcalc = 1.66 g cm−3. The final R value was 0.058. The structure consists of a quadruply bonded dimolybdenum unit which is bound to three bridging acetates and one bridging BAII ligand. The BAII ligand is bound to one molybdenum by an imino nitrogen and to the other molybdenum by the isoindoline nitrogen and a pyridyl nitrogen. The pyridyl nitrogen is bound in a position approximately co-axial with the metal-metal bond. The MoMo bond distance is 2.109(1) A.

Spectroscopic studies of ZnWO4 single crystals

Abstract The luminescence properties of colored and color-free ZnWO 4 single crystals are reported. Two emission bands are observed for the colored sample in the blue-green and near infrared regions. Only the blue-green band is observed for the color-free sample. The decay times of these emission bands are presented, and the assignments of these bands are discussed.

Complexes of the I,3-Bis(2-Arylimino) Benz (F) Isoindoline Ligand Including the Crystal Structure of the Cu(II)-Acetate Complex

Abstract The new BA1I ligand l,3-bis(2-pyridylimino)benz(f) isoindoline, NBAII, has been synthesized and Zn(II), Ni(II) and Cu(II) complexes with the formula (NBAII)MX (where X = OAc− for Cu(II) and Ni(II) and X = Cl− for Pd(II)) have been prepared. The ligand and complexes have been characterized by 1H-NMR spectroscopy, infrared spectroscopy and electronic absorption spectroscopy. The NBAII ligand can accommodate both planar and distorted tetrahedral geometries in these cases. The quadruply-bonded complex (NBAII)Mo2(OAc)3 has also been prepared. It was found to exhibit an unusual bonding mode for the NBAII ligand. The molecular structure of the Cu(II) compound was determined by single crystal x-ray diffraction techniques: (NBAII)Cu(OAc) crystallizes in the centrosymmetric space group C2/m with a = 20.256(4) A, b = 16.166(3) A, c = 7.915(2) A, α = 90°, β = 94.83(2) °, γ = 90°, V = 2583(1) A and Z = 4. The structure of this complex is compared to that of (B AII)Cu(OAc) which has been used as a model for th...

Trends in δ → δ* Energies and Intensities in Bis(arylimino)isoindoline Complexes of Dimolybdenum

Abstract It has been found that the δ → δ* band in the electronic absorption spectra of a series of bis(arylimino)isoindoline dimolybdenum complexes, Mo2(BAII)(OAc)3, follows three trends. First, as the energy of the band decreases across the series its intensity increases. Second, as electron-releasing groups are added to the aryl portion of the ligand the energy of the band increases, while addition of electron-releasing groups decreases its energy. Third, as the parent aryl group becomes a better π-acceptor the bands energy decreases. These three trends are taken to indicate that the energy of the δ → °* band in this series of compounds is determined by mixing of a ligand-to-metal charge-transfer transition with the original δ → δ* transition.

Ligand Effects on the δ → δ* Band Energies and Intensities in a Series of Diimine Complexes of Dimolybdenum

Abstract The complexes Mo 2 X 4 (diimine) 2 (X = Cl, Br, I and diimine = 2,2′-bipyridine, 4,4′-dimethyl-2,2′-bipyridine, 2,2′-bipyrazine, 3,3′-bipyridazine, 2,2′-bipyrimidine, 1,10-phenanthroline and 4,7-diphenyl-1,10-phenanthroline) have been prepared by reaction of Mo 2 (OAc) 4 with (CH 3 ) 3 SiX in the presence of excess diimine. The product complexes apparently contain non-bridged quadruple molybdenum—molybdenum bonds. Each molybdenum is coordinated to a bidentate diimine and two halogen atoms. Electronic absorption and electrochemical studies have shown that shifts in the energy of the δ → δ * band are affected by the mixing of this transition with a metal-to-ligand charge transfer transition, probably a δ → π * transition. It was also found that the compounds Mo 2 X 4 (diimine) 2 react slowly with oxygen to form Mo 2 O 4 Cl 4 (diimine) 2 and then MoO 2 Cl 2 (diimine). The crystal and molecular structure of MoO 2 Cl 2 (4,4′-dimethyl-2,2′bipyridine), determined by a three-dimensional X-ray diffraction study, is reported.

Mechanism of an Oxygen Atom Transfer Reaction Involving an Oxo-bridged Mo(V) Complex

Abstract The kinetics of the oxygen atom transfer reaction Mo 2 O 3 I 2 (dtc) 2 (THF) 2 (1) + pyridine- N -oxide= 2MoO 2 I(dtc) + pyridine was investigated in methylene chloride solution using a variety of substituted pyridine- N -oxides. This is the first kinetics study of the reaction of an oxobridged Mo(V) complex participating in an oxo-transfer reaction. Reactions were studied using pseudo-first-order conditions of excess N -oxide. These reactions were characterized by saturation kinetics in which 1 reversibly forms a Mo 2 O 3 4+ - N -oxide precursor complex that generates products via irreversible breaking of an MoO b bond to give two equivalents of MoO 2 2+ complex and the appropriate pyridine derivative. A considerable group effect was observed (two orders of magnitude) when substituents on the pyridine- N -oxides were varied, with electron releasing substituents slowing the rate of reaction. This observation is used to support a proposed mechanism by which the rate of MoO b bond breaking in the precursor complex is determined by the NO bond strength of the substrate N -oxide.

Dissociation of Solvent Molecules from Mo2O3I2(dtc)2(solv)2 in Solutions of Non-Coordinating Solvents

Abstract Mo 2 O 3 I 2 (dtc) 2 (THF) 2 reacts with solvents in various ways depending on their coordinating ability. With weakly coordinating solvents the coordinatively unsaturated Mo 2 O 3 I 2 (dtc) 2 results because the THF molecules have been removed. With moderately coordinating solvents the THF is replaced by solvent molecules resulting in Mo 2 O 3 I 2 (dtc) 2 (solv) 2 . However, NMR and electronic absorption studies indicate that in CH 2 Cl 2 and CHCl 3 solution the coordinated solvent molecules from the Mo 2 O 3 I 2 (dtc) 2 (solv) 2 species are dissociated. With the strongly coordinating solvent pyridine a complex results which has no MoO bonds.

Revrsed Phase High Performance Liquid Chromatographic Analysis of Triphenylphosphine in a Reaction Mixture

Abstract An isocratic reversed phase high performance liquid chromatographic method is described for monitoring concentrations of triphenylphosphine (TPP) and other compounds involved in an oxygen-transfer reaction catalyzed by a molybdenum complex. Using an inexpensive octadecylsilane column and a mobile phase consisting of aqueous acetonitrile, good separations and linear chromatographic responses were achieved for solutions of TPP, pyridine and each of their oxides in the mobile phase with concentrations in the range of 0.0012 – 0.12 grams/100 mL. No evidence for TPP precipitation was observed during the analysis of supersaturated solutions containing TPP at concentrations as high as 0.27 grams/100 mL. Chromatograms of more concentrated TPP solutions exhibited a second peak corresponding in retention time to TPP-oxide. Contrary to the interpretation of a similar effect in a previous study, evidence is presented indicating that this second peak is not the result of decomposition of TPP to its oxide, but...