John F. Richardson

New tripodal Cu(II) complexes containing imidazole ligands

Abstract A new class of imidazole containing tripodal ligands has been synthesized containing from 0–3 imidazole pendants. Copper(II) complexes of the formulas [Cu(L)Cl] + and [Cu(L)(1-MeIm)] 2+ have been prepared and studied by UV-Vis and EPR spectroscopies and cyclic voltammetry. The X-ray crystal structures of [Cu(bipa)Cl] + and [Cu(tmima)Cl] + have been determined. Electrochemical and electronic spectral data suggest that the donor strengths of the tripods decrease in the following order: tpa > bpia > bipa > tmima. Results from EPR suggest that the complexes with tmima are more distorted than those of tpa.

Synthesis and characterization of ruthenium, rhenium and titanium formate, acetate and trifluoroacetate complexes. Correlation of IR spectral properties and bonding types

Abstract New formate ( 1 – 3 ; 4b , 6 and 7 ), acetate ( 8 , 9) and trifluoroacetate ( 12 , 13 and 15 ) complexes have been synthesized and characterized by elemental analysis and by IR and 1 H and 13 C NMR spectroscopies. New data or new synthetic procedures are provided for several known complexes ( 4a , 5 , 19 , 11 and 14 ). X-ray structural data for cis -Ru(bpy) 2 (CO)(OCHO)(PO 2 F 2 ) ( 4b ) clearly identify the η 1 -bound formate ligand bound to an octahedral ruthenium center and the data for fac -Re(CO) 3 (PPh 3 (OCOMe) ( 9 ) show an η 2 -bound acetate ligand bound to an octahedral rhenium center. Infrared spectral data for four types of formate complexes, three bonding types of acetates and the two known types of trifluoroacetate ligands are discussed. Comparisons of the v OCO bands for the carboxylate ligands in all of the complexes show that these bands are useful in identifying the bonding type of each carboxylate ligand.

Synthesis and properties of a binuclear (μ-oxo) diiron(III) complex containing a tripodal polybenzimidazole ligand

Several iron(III) complexes of the polybenzimidazole ligand tris((benzimidazol-2-yl)methyl)amine(ntb) have been synthesized and characterized. The μ-oxo bridged dinuclear complex, [Fe 2 O(ntb) 2 Cl 2 ](PF 6 ) 2 ·4THF, has been isolated and structurally characterized by X-ray crystallography. The complex crystallizes in the triclinic space group P with one complex molecule per unit cell. The cell dimensions are a =13.758(3), b =13.913(2), c =11.526(1) A, α=110.52(1), β=90.56(2), γ=60.65(2)° and V =1765.2 A 3 . The structure refined to a final agreement factor ( R ) of 0.057 using 5092 reflections with 1>3σ( I ). The complex is a centrosymmetric dimer and the coordination environment around each iron(III) center is pseudooctahedral. One benzimidazole pendant is bonded trans to the bridging oxo group, while the other benzimidazole pendants, the tertiary amine nitrogen atom and Cl − ion are bonded cis to the oxo ligand. The FeOFe bridging angle is 180°, as required by the crystallographically imposed center of symmetry. The FeFe separation is 3.610(1) A. A mononuclear form of complex 1 , [Fe(ntb)Cl 2 ](PF 6 ) 0.5 (Cl) 0.5 ( 2 ), has been prepared and shown to form 1 in aqueous ethanol solutions containing NEt 4 Cl. Compounds 1 and 2 can be used to prepare compound 3 which contains a μ-oxo-μ-acetato bridged core structure, [Fe 2 O(ntb) 2 (OAc)](ClO 4 ) 3 . Compound 3 was recrystallized from an acetonitrile solution containing THF. The dinuclear complex 1 exhibits antiferromagnetic exchange with a J value of −100 cm −1 . The room temperature solution effective magnetic moments for compounds 1 (μ eff =2.0) and 3 (μ eff =1.85 BM) are consistent with antiferromagnetically coupled diiron(III) complexes and indicate that the μ-oxo bridged structure is retained in solution. The room temperature effective magnetic moment of compound 2 is 5.9 BM. The electronic spectra of compounds 1–3 are similar to those observed for related complexes. The cyclic voltammetry of compound 1 indicates that the dinuclear complex can stabilize redox levels higher than +3. Compound 2 exhibits a single one electron redox process at E 1/2 =0.468 V NHE. The proton NMR spectra of compounds 1 and 3 confirm the stability of the μ-oxo bridged structures in solution. Inequivalent benzimidazole NH proton signals are observed for compounds 1 and 3 , consistent with the X-ray crystal structure of 1 .

Synthesis, structure and properties of a N3 tridentate bis-imidazolyl ligand with copper(II)

The synthesis of a new tridentate ligand, bis[2-(1-methylimidazolyl)methyl] amine, [B-MIMA], is described. The compound has been characterized by 1 H and 13 C NMR spectroscopy and mass spectrometry, and forms complexes with various copper(II) salts. Crystallographic studies have been completed on the blue product from the reaction of B-MIMA with copper(II) acetate, [Cu(B-MIMA)(CH 3 COO)](ClO 4 ) ( 6 ). Crystal data for 6 are: triclinic, P 1, a = 5.176(2), b = 8.489(3), c = 10.066(3) A, α = 95.09(5), β = 95.72(3), γ = 102.37(4), V = 427.1 A and Z = 1. The structure was solved using the Patterson method which revealed the position of the copper atom and successive difference Fourier syntheses which revealed the location of the remaining atoms. The atom positions were refined by least-squares methods producing a final agreement factor of R = 0.021 and R w = 0.029 for 1897 observed reflections. The structure consists of a polymeric acetate bridged network of distorted square-pyramidal copper(II) ions. The five coordinate geometry around each metal ion is a result of the bonding of three nitrogen atoms from the B-MIMA ligand and two oxygen atoms from different acetate ions. The acetate ions act as bidentate ligands bridging different copper ions and the resulting extended bridging network extends out the crystallograhic a axis. Spectroscopic, magnetic and electrochemical properties of the complex are described and compared with related compounds. The solution spectroscopic properties of 6 suggest that the square-pyramidal geometry of the metal ion in the solid-state is not retained in solution.

Campylobacteriosis outbreak associated with consumption of undercooked chicken liver pâté in the East of England, September 2011: identification of a dose-response risk.

SUMMARY A foodborne outbreak with 49 cases (22 culture positive for Campylobacter sp.) following a wedding party in the East of England was investigated. A retrospective cohort study identified an association between consumption of chicken liver pâté and infection with Campylobacter jejuni/coli. There was a statistically significant association between dose (amount of chicken liver pâté eaten) and the risk of disease [‘tasted’: odds ratio (OR) 1·5, 95% confidence interval (CI) 0·04–∞; ‘partly eaten’: OR 8·4, 95% CI 1·4–87·5; ‘most or all eaten’: OR 36·1, 95% CI 3·3–2119). The local authority found evidence that the preparation of chicken livers breached Food Standards Agencys guidelines. This epidemiological investigation established a clear dose–response relationship between consumption of chicken liver pâté and the risk of infection with Campylobacter. The continuing need to raise public awareness of the risk to human health posed by undercooked chicken liver is evident.

Bis-1,2,3-thiaselenazolyl radicals and their σ-bonded dimers

Resonance stabilized bis-1,2,3-thiaselenazolyl radicals associate in the solid state to afford Se–Se σ-bonded dimers.

Synthesis, crystal structure and properties of (1,3-(bis(N-methylimidazolimine)propan-2-ol)Cu(II)•perchlorate

Abstract The synthesis, crystal structure and physical properties of a mononuclear Cu(II) complex of 1,3-bis(N-methylimidazolimine)propan-2-ol is described. The complex crystallizes in the triclinic space group P 1 with a = 11.343(5), b = 11.770(4), c = 8.452(2) A, α = 109.71(2)°, β = 91.25(2)°, γ = 98.24(3)°, V = 1048.4 A3 and Z = 2. The structure of the complex is a distorted square pyramid consisting of the N4 basal plane resulting from coordination of the 1,3-bis(N-methylimidazolimine)propan-2-ol ligand and a weak coordinated apical water molecule. The complex displays quasireversible electrochemical behavior in both aqueous and acetonitrile solutions. In addition, the complex has been studied by UV-Vis and EPR spectroscopies.

Synthesis, X-ray structure and properties of a new nitrite-bound copper(II) complex with 2-(3,5- dimethylpyrazol-1-ylmethyl)pyridine in a CuN4(O) coordination

Abstract Synthesis and characterization of a nitrite-bound copper(II) compound [CuL4)2(ONO)]ClO4 have been achieved (L4 = 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine]. The bidentate ligand L4 provides a pyridine and a pyrazole donor site; however, they are separated by a methylene spacer. The complex has been structurally characterized and it belongs to only a handful of complexes having nitrito-bound mononuclear copper(II) centre. The metal atom has a distorted square pyramidal geometry with the copper atom displaced from the equatorial plane by 0.25 A. In MeCN solution the green complex exhibits a broad ligand-field transition at 655 nm with a shoulder at 675 nm and in dichloromethane-toluene glass (80 K) it exhibits an EPR spectral feature characteristic of the unpaired electron in the dx2−y2 orbital. Variable-temperature (80–300 K) magnetic susceptibility measurements in the solid state as well as room temperature measurement in MeCN solution reveal mononuclear magnetically dilute copper(II) centre. When examined by cyclic voltammetry (MeCN solution) it displays electrochemically irreversible CuIICuI response [cathodic peak potential, Epc (V vs saturated calomel electrode (SCE)): −0.32]. An oxidative response is observed at 1.14 V, probably due to bound-nitrite oxidation and is partially removed to generate a solvated complex at the electrode surface. The latter species gives rise to reversible CuIICuI redox response [ E 1 2 = 0.41 V vs SCE ].

Room temperature dissolution of metal powders by thiourea: a novel route to transition metal isothiocyanate complexes

Abstract A new synthetic route to isothiocyanate containing materials is presented. Five isothiocyanate 4-methylpyridine (γ-picoline) compounds were prepared by refluxing metal powders (Fe, Co, Ni and Cu) with thiourea in γ-picoline. The isothiocyanate ligand is generated in situ by the isomerization of thiourea to NH4+SCN− at reflux temperatures. The complexes [Fe(NCS)2(pic)4]·pic (1), [Co(NCS)2(pic)4]·pic (2), [Ni(NCS)2(pic)4] (3), [Cu(NCS)2(pic)4]·2/3pic·1/3H2O (4), [Cu(NCS)(pic)2]x (5) (where pic=γ-picoline) were characterized by X-ray crystallography; the structural data for compounds 1–3 and 5 are presented.

Covalent alternatives for the elusive iminophosphonium cation. Crystal structures of PCl(NPri2)2NPh·AlCl3 and P(NPri2)2[NPh(SO2CF3)]O

Reactions between diaminoiminophosphinic chlorides and the chloride-abstracting agents AlCl3 and Ag(SO3CF3) have been comprehensively examined as potential routes to the three-co-ordinate iminophosphonium cation. However, bis(dialkylamino)(phenylimino)phosphinic chlorides react to give the covalent phosphoryl systems PCl(NR2)2NPh·AlCl3 and P(NR2)2[NPh(SO2CF3)]O respectively, in quantitative yield. The AlCl3 complexes are also prepared quantitatively from the reaction of P(NPri2)2+AlCl4– with PhN3(Staudinger reaction). All compounds have been comprehensively characterised and the structures of the isopropyl derivatives confirmed by X-ray crystallography. Crystal data: PCl(NPri2)2NPH·AlCl3, space group P21, a= 8.719(2), b= 15.553(2), c= 9.509(2)A, β= 102.73(2)°, Z= 2, R= 0.029; P(NPri2)2[NPh(SO2CF3)]O, space group P21/n, a= 10.594(3), b= 13.222(2), c= 17.084(3)A, β= 97.71(2)°, Z= 4, R= 0.048. The results indicate that the three-co-ordinate diaminoiminophosphonium cation is thermodynamically unstable with respect to the observed alternative covalent structures, and that steric shielding is responsible for the stability of the analogous diaminomethylenephosphonium cation.