Joseph A. Connor

Binuclear 2,2′-bipyrimidine complexes derived from chromium, molybdenum and tungsten carbonyls

Abstract Reaction of 2,2′-bipyrimidine (bpym) with [Mo(CO)4(diene)] gives [Mo(CO)4(bpym)], which will react with [M(CO)4(diene)] to form [MoM(CO)8(bpym)] (M = Cr, Mo, W). The bipyrimidine complexes are characterised by microanalysis and spectroscopy (IR, 1H and 13C NMR, UV/vis). Reduction of [Mo2(CO)8(bpym)] produces an anion in which the unpaired electron is localised on the bridging bpym ligand.

Crystal and molecular structures of tetracarbonyl(3,3′-dimethyl-2,2′-bipyridine)-chromium(0) and -molybdenum(0) benzene solvates and the unsolvated tungsten(0) analogue

Abstract The crystal structures of the complexes of 3,3-dimethyl- 2,2′-bipyridine (L), cis-[W(CO)4L], cis-[MO(CO)4L] · C4H6 and cis-[Cr(CO)4L] · C6H6 have been determined by X-ray diffraction. These structures show that repulsion between the methyl groups is principally responsible for the geometric distortion in each complex. Within the ligand, L, the two pyridine rings suffer distortion, in opposite directions, to pseudo-boat conformations so as to optimize metal—nitrogen binding. The benzene solvent molecules are arranged in a layer structure alternating with units of the metal complex. The metal complex molecule is beyond van der Waals contact with the benzene solvent molecule in each case.

Substituted 2,2′-bipyridines as ligands. preparation and characterization of 4,4′-disubstituted 2,2′-bipyridine derivatives of the hexacarbonyls of chromium, molybdenum and tungsten

The preparation of cis-[M(CO)4(biL)] (M = Cr, Mo, W; biL is 4,4′X2-2,2′-Bipyridine; X = NMe2, NH2, OMe, CMe3, Me, H, Ph, CHCHPh, Cl, CO2H, CO2Me, NO2) is reported. The ligands and complexes are characterized by spectroscopy (IR, electronic absorption and emission, NMR (1H, 13C, 15N, 95Mo)) and microanalysis. The variations observed in the spectroscopic properties of these complexes are strongly correlated with electronic substitutent parameters of the group X. This is most apparent in the lowest energy (visible) absoprtion which changes by ca. 0.8 eV between the extremes of donor and of acceptor substituent used.

Capacity of siderophore — producing alkalophilic bacteria to accumulate iron, gallium and aluminum

SummaryThe ability of alkalophilic bacteria to remove iron, gallium and aluminium from culture media is reported. Of six bacterial strains grown in the presence of iron, gallium or aluminium (10 μM), five were able to accumulate iron or gallium, but only two depleted the aluminium stock. A comparison of gallium removal under low (< 1 gmM) or high (10 gmM) iron conditions showed that two isolates accumulated gallium only under low-Fe conditions. One isolate, a coryneform bacterium, was able to grow in the presence of 1, 10 and 100 mg gallium/l, but growth and siderophore production were affected at high gallium concentration. Similar concentrations of gallium were accumulated from cultures initially containing 1 or 100 mg gallium/l.

Electronic spectra and electrochemistry of disubstituted 2,2′-bipyridinetetracarbonylmolybdenum complexes. Solvent and substituent effects

Abstract Electronic absorption spectra of cis -[Mo(CO) 4 ( n,n ′-X 2 -bipy)] ( n = 4, X = NMe 2 , NH 2 , OMe, CMe 3 , Me, H, Ph, CH:CHPh, CO 2 H, Cl, CO 2 Me, NO; n =5, X = Me, CO 2 H) have been measured at ambient temperature in a variety of solvents of different polarity. Emission spectra from glasses containing the complexes at 77 K have also been measured. The influence of the substituent X on the spectroscopic properties is correlated with the Hammett parameters, σ p (X) and σ p + (X). The effect of solvent is correlated with the Taft-Kamlet parameter, π ★ , indicating charge redistribution along the permanent dipole axis of the complex. The oxidation and reduction potentials in solution are simply related to the electronic effect of the substituent group, X, and are relatively independent of the solvent. The influence of the metal on these properties is not significant.

Low temperature pyrolysis products of chromium, molybdenum and tungsten hexacarbonyls

Abstract The Group 6 metal hexacarbonyls have often been investigated as precursors in chemical vapour deposition processes. The solid products, obtained by thermal decomposition of the vapours of the compounds below 300°C, have been re-examined. Under these conditions, all three carbonyls produce a metallic phase with a face-centred cubic structure, distinct from the body-centred cubic structure of the pure metals. Microanalysis shows that the materials contain roughly equimolar amounts of carbon and oxygen. Pyrolysis of 18 O-labelled Mo(CO) 6 has demonstrated that the oxygen derives from the CO ligand of the precursors. Evidence that the pyrolysis products are insterstial oxycarbides is presented; their response to annealing treatment is described.

Bipyridinedicarbonitrile complexes of molybdenum and tungsten

Abstract The preparation of cis -[Mo(CO) 4 (biL)] (biL denotes 2,2′-bipyridine- x,x ′-dicarbonitrile, x,x ′ = 4,5) is reported. Reaction of these complexes with [W(CO) 5 (THF)] produces [MoW 2 (CO) 14 (biL)]. The synthesis of [W 2 CO) 10 (biL)] (biL, x,x ′ = 5) is also reported. The ligands and complexes have been characterised by spectroscopy (IR, electronic absorption, NMR) and microanalysis. The synthesis of biL is significantly assisted by ultrasonification.

Novel tetra- and hexa-dentate ligands from 6,6′-dicyano-2,2′-bipyridine

A simple, direct route from 2,2′-bipyridine to 6,6′-dicyano-2,2′-bipyridine and its conversion to the 6,6′-dithiocarboxamide and various novel tetra- and hexa-dentate ligands such as the 6,6′-bis(4-methylthiazol-2-yl) and 6,6′-bis[4-(2-pyridyl)thiazol-2-yl] derivatives have been established. Diaqua[6,6′-bis(4-methylthiazol-2-yl)-2,2′-bipyridine]zinc(II) bis(trifluoromethanesulfonate) has been prepared and its crystal structure determined. The tetra-heterocyclic ligand is planar, binding through two bipyridine nitrogen atoms and, more weakly, through two thiazolyl nitrogen atoms to zinc(II) which is in a distorted octahedral environment.

Isolation of bacteria producing siderophores under alkaline conditions

SummaryThe isolation of bacteria producing siderophores under alkaline conditions is reported. Enrichment cultures initiated with samples from a number of alkaline environmental sources yielded 80 isolates. From this group selections were made on the basis of growth at high pH and the gallium-binding capacity of the siderophores. It was found that some isolates grew well and high concentrations of siderophore were detected whereas others grew well in the presence of much lower concentrations of siderophore. The effect of iron, gallium and aluminium on growth and siderophore production in batch culture was investigated for six isolates. The presence of iron greatly decreased the siderophore concentration in these cultures, whereas the response to added gallium or aluminium was dependent upon the isolate.

Oxidation of 1,10-phenanthroline by tetraoxomanganate(VI) and (VII). Preparation, structure and properties of 1H-cyclopenta[2,1-b:3,4-b′]dipyridine-2,5-dione

Oxidation of 1,10-phenanthroline with tetraoxomanganate(VI) gave good yields of ketone 3 and the previously unknown dione 5, formed by the unusual further oxidation of 3 at the 2 position of a pyridine ring. In contrast, use of the tetraoxomanganate(VII) gave the bipyridine diacid 2(69%), ketone 3(20%) and only a trace of the dione 5. The X-ray crystal structure of the anion of 5 indicates that the negative charge is located mainly on the 2-O rather than 5-O atom, with some delocalisation into the pyridine ring.