Re(I)(tricarbonyl) complexes with the 2-(2-pyridyl)-N-methyl-benzimidazole, 2-(2-pyridyl)benzoxazole and 2-(2-pyridyl)benzothiazole ligands - syntheses, structures, electrochemical and spectroscopic studies

The reactions of Re(CO)₅Cl with the chelating ligands 2-(2-pyridyl)-N-methylbenzimidazole, 2-(2-pyridyl)benzoxazole and 2-(2-pyridyl)benzothiazole afforded neutral fac-Re(CO)₃(L)Cl and ionic complexes with structures confirmed by means of X-ray measurements. UV-vis absorption and emission properties have been studied at room and 77 K temperatures in order to determine the nature of the lowest electronically excited states. Electrochemical behaviour of the investigated fac-Re(CO)₃(L)Cl and complexes has been studied using cyclic and square-wave voltammetry. Preliminary results from the electrogenerated chemiluminescence studies of the ionic and the neutral fac-Re(CO)₃(MPBI)Cl complexes are briefly presented.     

Interaction of gold(I) with thiosulfate-sulfite mixed ligand systems

The system was studied at 25 °C and at I = 0.1 M NaClO₄ using hydrodynamic voltammetry, gold potentiometry, UV-Vis spectrophotometry and Raman spectroscopy. The presence of two mixed-ligand species, Au(S₂O₃)(SO₃)³⁻ and , was detected from the Raman experiments and supported by the gold potentiometric experiments. The stepwise formation constant, log K_11r, for the reaction was found to be 1.1 (r = 1) and 4.8 (r = 2) from the hydrodynamic voltammetric experiments.     

In situ alkylation of 4,4′-bipyridine in hydrothermal synthesis of one-dimensional copper(I) bromide compounds

Hydrothermal reaction of CuBr₂, 4,4′-bipyridine and ethanol/methanol generated two copper (I) bromide complexes with in situ alkylated 4,4′-bipyridium, namely [C₁₄H₁₈N₂][Cu₅Br₇] (1) and [C₁₂H₁₄N₂][Cu₄Br₆] (2). The structure of 1 consists of chains and N,N′-diethyl-4,4′-bipyridinium. The underlying structural motif in of 1 is the Cu₅Br capped square pyramid, which is different from the Cu₅Br₂ pentagonal bipyramidal structural motif in various documented anions. The in 1 contains untypical μ₅-bromide, with which five copper atoms forms a capped square pyramid rather than a pentagonal pyramid as predicted by Subramanian and Hoffmann. Compound 2 is isostructural with [C₁₂H₁₄N₂][Cu₄Cl₆] reported by Willett, and consists of chains and N,N′-dimethyl-4,4′-bipyridinium. The chain is composed of alternating Cu₆Br₆ and Cu₂Br₆ units.     

Dinuclear gold(III) pyrazolato complexes - Synthesis, structural characterization and transformation to their trinuclear gold(I) and gold(I/III) analogues

The reaction of AuCl₃py with Na(pz∗) (pz∗ = pyrazolato, or substituted pyrazolato anion) yields stable dinuclear [cis-Au^IIICl₂(μ-pz∗)]₂ complexes. In the presence of a base, the latter undergo reduction with concomitant transformation of the dinuclear -structure to trinuclear Au^I, Au^III (containing trans Au^IIICl₂-centres) and species.     

Oxomolybdenum(III, IV and V) complexes of thiofunctional ligands

Reaction of [MoO₂(acac)₂] with (S is a thioether, S′ a thiophenolate function) yielded the compound Li₇(thf)₁₇{MoO}₈ · 10thf · hexane, where {MoO}₈ represents one 1, three (2, linked, via the oxo group, to [Li(thf)₃]⁺) and two (3a, linked by two [Li(thf)₂]⁺).A mixed-valent variant of 3, (3b, with an additional[Li(thf)₃]⁺ attached to S′), was also identified. The compounds model features pertinent to oxo-transferases containing the molybdopterin cofactor.     

Kinetics and mechanism of the oxidation of oxalic acid by tetrachloroaurate(III) ion

The oxidation of oxalic acid by tetrachloroaurate(III) ion in 0.005 ? [HClO₄] ? 0.5 mol dm⁻³ is first order in and a fractional order in [oxalic acid], the reactive entities being AuCl₃(OH)⁻ and ions. The pseudo first-order rate, k_obs, with respect to [Au(III)], is retarded by increasing [H⁺] and [Cl⁻]. The retardation by H⁺ ion is caused by the dissociation equilibrium . A mechanism in which a substitution complex, is formed from AuCl₃(OH)⁻ and ions prior to its rate limiting disproportionation into products is suggested. The rate limiting constant, k, has been evaluated and its activation parameters are reported. The equilibrium constant K₁ for the formation of the substitution complex and its thermodynamic parameters are also reported.     

Crystal structures and magnetic properties of Ni-bisdithiolene complexes with decamethylmetallocenium cations

Three new compounds of formula (1), (2), and (3) have been synthesised, and structurally and magnetically characterised (dmit²⁻ = 1,3-dithiol-2-thione-4,5-dithiolato; dmid²⁻ = 1,3-dithiol-2-one-4,5-dithiolato). Their structural features and magnetic behaviours are compared with those of and . The result of this is that the interactions between the Ni(dmit)₂ units in 1 are of ferromagnetic-type, as suggested previously for . The change from acetonitrile to acetone when going from to 2 results in stronger ferromagnetic intermolecular interactions. This better cooperativity is due to a significant increase of the number of contacts between the various moieties within the . On the contrary, the inclusion of larger solvents such as benzonitrile in this type of complexes results in a totally different structural arrangement, which leads to an antiferromagnetic behaviour for 3.     

Mononuclear cobalt(II) carboxylate complexes: Synthesis, molecular structure and selective oxygenation study

Some cobalt carboxylate (both mononuclear as well as binuclear) complexes have been prepared by using hindered hydrotris(3,5-diisopropyl-1-pyrazolyl)borate (Tp^iPr2) as supporting ligand. The reaction of [Tp^iPr2Co(NO₃)] (2) with sodium benzoate resulted in the formation of acetonitrile coordinated complex [Tp^iPr2Co(OBz)(CH₃CN)] (3) whereas the reaction of 2 with sodium fluorobenzoate gave coordinately unsaturated five coordinate complex of the type [Tp^iPr2Co(F-OBz)] (4). The oxidation of compound 4 in the presence of 3,5-diisopropylpyrazole resulted in the formation of a unique compound (5) where only one methine carbon of isopropyl group on pyrazole ring of hydrotris(3,5-diisopropyl-1-pyrazolyl)borate oxidized and coordinated with cobalt center. In compound 5, the binding behavior of fluorobenzoate also changes from bidentate to monodentate and the nonbonded oxygen atom formed intramolecular hydrogen bond with the hydrogen atom of the NH fragment of the coordinated . X-ray crystallography and IR studies confirmed the existence of hydrogen bonding in complex 5. The pyrazolato bridged binuclear cobalt(II) complex (6) was prepared by the reaction of hydrated cobalt(II) nitrate, 3,5-diisopropylpyrazole and sodium nitrobenzoate where, each cobalt is four coordinate. The X-ray structure of 6 showed that the NH fragment of terminally coordinated formed intramolecular hydrogen bonding with nonbonded oxygen atom of monodentately coordinated nitrobenzoate.     

Applicability of new spin trap agent, 2-diphenylphosphinoyl-2-methyl-3,4-dihydro-2H-pyrrole N-oxide, in biological system

Electron spin resonance using spin-trapping is a useful technique for detecting direct reactive oxygen species, such as superoxide (). However, the widely used spin trap 2,2-dimethyl-3,4-dihydro-2H-pyrrole N-oxide (DMPO) has several fundamental limitations in terms of half-life and stability. Recently, the new spin trap 2-diphenylphosphinoyl-2-methyl-3,4-dihydro-2H-pyrrole N-oxide (DPhPMPO) was developed by us. We evaluated the biological applicability of DPhPMPO to analyze in both cell-free and cellular systems. DPhPMPO had a larger rate constant for and formed more stable spin adducts for than DMPO in the xanthine/xanthine oxidase (X/XO) system. In the phorbol myristate acetate-activated neutrophil system, the detection potential of DPhPMPO for was significantly higher than that of DMPO (k_DMPO = 13.95 M⁻¹ s⁻¹, k_DPhPMPO = 42.4 M⁻¹ s⁻¹). These results indicated that DPhPMPO is a potentially good candidate for trapping in a biological system.     

Alkyl dehydrogenation in iridium tri-cyclopentyl phosphines

The iridium cyclooctadiene complex incorporating a tricyclopentyl phosphine ligand (PCyp₃), Ir(η²:η²-C₈H₁₂)(PCyp₃)Cl, has been prepared. Removal of the chloride from this complex using in CH₂Cl₂/arene solvent results in dehydrogenation (C-H activation followed by β-H transfer) of one of the alkyl phosphine rings and formation of the complexes (X = H, F) which contain a hybrid phosphine-alkene ligand. These complexes are formed alongside another product (5-20% yield) that has been identified as , which can be prepared in high yield by an alternative, and slightly modified, route. This complex is with a minor isomer that has been tentatively identified as , which results from allylic C-H activation of cyclooctadiene. Addition of H₂ to and its isomer in arene solvent (C₆H₅X, X = F, H) forms the dihydrido η⁶-arene Ir(III) complexes . In contrast, hydrogenation in CH₂Cl₂ alone results in the formation of in which the anion is now acting as a ligand through one of its aryl rings. The fluorobenzene complex can be cleanly converted to by addition of the hydrogen acceptor tert-butylethene (tbe).     

A new Cu(4,5-diazafluoren-9-one)-capped Keggin derivative: Hydrothermal synthesis and crystal characterization

A new α-Keggin POM derivative (1) (DF = 4,5-diazafluoren-9-one) has been prepared under hydrothermal conditions and characterized by single-crystal X-ray diffraction, elemental analysis, IR, XPS spectra, thermogravimetric analysis and cyclic voltammetry. In compound 1, the polyoxoanion cluster is decorated by a single capping {Cu(DF)}²⁺ subunit via four bridging oxygen atoms on a {Mo₄O₄} pit. The isolated copper dimer unit acts as counter cation, in which the organic ligand DF exhibits a rare coordination mode. Furthermore, the capped Keggin polyoxoanions are fused together via the copper dimers through the weak Cu ? O interactions to form chains. Hybrid 1 was used as a solid bulk modifier to fabricate a carbon paste electrode (1-CPE) by direct mixing. The electrochemical and electrocatalytic behaviors of the 1-CPE have been studied in detail.