Wayne H. Pearson

A comparison of the gas, solution, and solid state coordination environments for the copper(II) complexes of a series of aminopyridine ligands of varying coordination number

Abstract The synthesis and characterization of the copper(II) complexes of a series of aminopyridine ligands that range from tri- to heptadentate is described. The ligands include the tripod ligand tris(2-((2-pyridylmethyl)amino)ethyl)amine, TREN-pyr, and the following linear ligands: (2-pyridylmethyl)(2-(2-(2-((2-pyridylmethyl)amino)ethyl)amino)ethyl)amine, TRIEN-pyr; bis(2-((2-pyridylmethyl)amino)ethyl)amine, DIEN-pyr; (2-pyridylmethyl)(2-((2-pyridylmethyl)amino)ethyl)amine, EN-pyr; bis(2-pyridylmethyl)amine, AM-pyr; and methyl(2-((-pyridylmethyl)amino)ethyl)amine, MeEN-pyr. The following methods were used to determine the binding geometries of the Cu(II) complexes in the solid, solution, and gas phases: magnetic susceptibility measurements, absorption spectroscopy, EPR spectroscopy, electrochemistry, and analyzing the gas phase ion-molecule reactions in a mass spectrometer. The solid state structures for the TRIEN-pyr and DIEN-pyr complexes were determined by X-ray crystallography. [Cu(TRIEN-pyr)](BF 4 ) 2 crystallized in the octahedral system, space group Pbca , with a =9.4107(7), b =17.536(13), c =30.132(6) A, and Z =8 ( R =0.064, R w =0.060). [Cu(DIEN-pyr)](BF 4 ) 2 crystallized in the octahedral system, space group Pbca , with a =29.137(5), b =14.829(3), c =9.850(1) A, and Z =8 ( R =0.071, R w =0.066). The coordination numbers of the Cu(II) complexes in this study are dependent on the denticity of the ligand. The complexes with AM-pyr, MeEN-pyr and TRIEN-pyr appear to be six-coordinate, DIEN-pyr to be five-coordinate and the EN-pyr to be four-coordinate in the solid state. The TREN-pyr complex was isolated as a dimer in the solid state but appears to be a tetragonally distorted monomeric complex in the solution and gas phases. For all of the complexes except DIEN-pyr, the coordination sphere appears to be independent of the phase of the complex. The Cu(II) DIEN-pyr complex appears to be five-coordinate in the solid phase, a mixture of four- and five-coordinate in the solution phase, and predominately four-coordinate in the gas phase.

New Dicarboxylic Acid Bipyridine Ligand for Ruthenium Polypyridyl Sensitization of TiO2

An ambidentate dicarboxylic acid bipyridine ligand, (4,5-diazafluoren-9-ylidene) malonic acid (dfm), was synthesized for coordination to Ru(II) and mesoporous nanocrystalline (anatase) TiO(2) thin films. The dfm ligand provides a conjugated pathway from the pyridyl rings to the carbonyl carbons of the carboxylic acid groups. X-ray crystal structures of [Ru(bpy)(2)(dfm)]Cl(2) and the corresponding diethyl ester compound, [Ru(bpy)(2)(defm)](PF(6))(2), were obtained. The compounds displayed intense metal-to-ligand charge transfer (MLCT) absorption bands in the visible region (ε > 11,000 M(-1) cm(-1) for [Ru(bpy)(2)(dfm)](PF(6))(2) in acetonitrile). Significant room temperature photoluminescence, PL, was absent in CH(3)CN but was observed at 77 K in a 4:1 EtOH:MeOH (v:v) glass. Cyclic voltammetry measurements revealed quasi-reversible Ru(III/II) electrochemistry. Ligand reductions were quasi-reversible for the diethyl ester compound [Ru(bpy)(2)(defm)](2+), but were irreversible for [Ru(bpy)(2)(dfm)](2+). Both compounds were anchored to TiO(2) thin films by overnight reactions in CH(3)CN to yield saturation surface coverages of 3 × 10(-8) mol/cm(2). Attenuated total reflection infrared measurements revealed that the [Ru(bpy)(2)(dfm)](2+) compound was present in the deprotonated carboxylate form when anchored to the TiO(2) surface. The MLCT excited states of both compounds injected electrons into TiO(2) with quantum yields of 0.70 in 0.1 M LiClO(4) CH(3)CN. Micro- to milli-second charge recombination yielded ground state products. In regenerative solar cells with 0.5 M LiI/0.05 M I(2) in CH(3)CN, the Ru(bpy)(2)(dfm)/TiO(2) displayed incident photon-to-current efficiencies of 0.7 at the absorption maximum. Under the same conditions, the diethylester compound was found to rapidly desorb from the TiO(2) surface.

Instability of 15-electron Cp☆MoCl2L (L = 2-electron donor) derivatives. X-ray structure of Cp☆MoCl2(PMe2Ph)2 and [Cp☆MoCl2(PMe2Ph)2]AlCl4

Abstract The complex Cp★MoCl2(PMe2Ph)2 (Cp★ = η5C5Me5) has been obtained in good yield from Cp☆MoCl4, PMe2Ph2, and Na in the appropriate stoichiometric ratio, and it is also obtained by a ligand redistribution process after reduction of Cp☆MoCl3- (PMe2Ph) with Na. This compound is oxidized by the CH2Cl2 solvent in the presence of AlCl3 to afford the salt [Cp☆MoCl2(PMe2Ph)2AlCl4. Both compounds have been characterized crystallographically and by 1H-NMR spectroscopy. The reasons for the instability of 15-electron Cp☆MoCl2L complexes are discussed. The 1H-NMR resonance data for Cp ☆ MoCl 2 L 2 ( L = PMe 3 , PMe 2 Ph ) and [Cp☆MoCl2(PMe2Ph)2]+ are also discussed.

2,4,6-Tris-(4-fluoro-phen-yl)-2-(1-pyrid-yl)-boroxine.

Crystals of the title compound, C23H17B3F3NO3, were obtained unintentionally by slow evaporation of a chloroform solution of the preformed boroxine–pyridine adduct. The molecule contains three fluoro-substituted benzene rings, each bonded to one of the three B atoms of a six-membered boroxine ring. A pyridyl ring is also bound to one of the B atoms through a Lewis acid–base interaction. The binding of the pyridyl substituent causes the otherwise planar boroxine ring to twist, resulting in a maximum torsion angle within the ring of 17.6 (2)°.

Synthesis and characterization of nickel-group bis(dithiocroconate) complexes and dicyanomethylene-substituted analogues

Two series of nickel-group metal bis(dithiolene) complexes with ligands 4,5-disulfanylcyclopent-4-ene-1,2,3-trionate (L1) and 2-dicyanomethylene-4,5-disulfanylcyclopent-4-ene-1,3-dionate (L2) have been prepared and characterized: [NBu4n]2[M(Li)2](M = Ni, Pd or Pt; i= 1 or 2). Oxidation of the dianion complexes yielded paramagnetic monoanions with ESR spectra indicative of a delocalized b3g HOMO (highest occupied molecular orbital), like that previously found for comparable bis(dithiolene) complexes. The intense low-energy visible absorptions and multiple, reversible reductions exhibited by the dianions likewise suggest that the LUMO (lowest unoccupied molecular orbital) is a ligand-based au(π*) orbital, rather than the b1g(dxy) orbital as commonly found for such complexes. The stabilization of the ligand-based LUMO in this case is attributed to the strongly electron-withdrawing character of the ligand substituents. Iodination of [NBu4n]2[Pd(L2)2] in CH2Cl2 solution yielded the novel iodine inclusion compound [NBun4]2[Pd(L2)2]·I2, which crystallizes in space group P with Z= 1, a= 10.792(3), b= 13.995(5), c= 10.737(3)A, α= 105.48(1), β= 115.15(1) and γ= 76.51(2)° at 25 °C. The I2 molecules are associated with the complex anions through short [3.1696(9)A] S ⋯ I contacts; however, the observed I–I distance [2.7354(4)A] indicates that the degree of charge transfer associated with this interaction is small.

cis-3,3-Dimethyl-3,3a,4,5,6,6a-hexa-hydro-1H-cyclo-penta-[c]furan-1,6-dione.

The bicyclic molecule of the title compound, C9H12O3, contains two five-membered rings with different functional groups, viz. a ketone and an ester. Both rings assume an envelope conformation. The mean planes of these functional groups form a dihedral angle of 60.7 (1)°. The crystal structure exhibits weak intermolecular C—H⋯O interactions, which link the molecules into zigzag chains extended in the [010] direction. The unit cell contains a racemic mixture of enantiomers.

2,5-Dioxopyrrolidin-1-yl 2-methyl-prop-2-enoate.

In the title compound, C8H9NO4, the pyrrolidine ring (r.m.s. deviation 0.014 Å) is almost normal to the mean plane of the propenoate group (r.m.s deviation 0.028 Å), making a dihedral angle of 86.58 (4)°. In the crystal, molecules are linked via pairs of weak C—H⋯O hydrogen bonds, forming inversion dimers which stack along the c axis.