P.S. Zacharias

Catalytic and magnetic properties of a new series of binuclear copper(II) complexes

Abstract Binuclear copper(II) complexes of ligands derived from condensation of 2,6- diformyl-4-methylphenol with various aromatic mono- and diamines have been synthesized. Complexes derived from monoamines have the Cu 2 LCl 3 composition and those from diamines have the Cu 2 L′Cl 2 composition, where L and L′ represent the ligands. Analytical data, conductance and spectral studies support these formulations. Cu 2 LCl 3 complexes are chloro-bridged, as evidenced by two intense IR bands centred around 300 and 320 cm −1 . Magnetic susceptibility measurements show that Cu 2 LCl 3 complexes have low μ eff f values indicating magnetically interacting copper(II) centres and Cu 2 L′Cl 2 complexes have non-interacting copper(II) centres. Cu 2 LCl 3 complexes undergo single-step quasi-reversible reduction at - 0.62 V vs SCE. Catalysis of Cu 2 LCl 3 complexes for the oxidation of 3,5-di- t-butylcatechol (3,5-DTBC) and ascorbic acid by dioxygen is studied.

Studies on dinuclear metal complexes of macrocyclic ligands with varying chelate ring size

Abstract Dinuclear Cu (II) , Ni (II) and Co (II) complexes of macrocyclic Schiff-base ligands of 2,6-difornyl-4-methyphenol with α,ω-diamines have been synthesized and characterized. The effect of chelate ring size and saturation of azomethine groups of these ligands on stability, structure and electrochemical properties of the metal complexes has been investigated. Catalytic activity of the metal complexes in the oxidation reaction of 3,5-di-tert-butylcatechnol to 3,5-di-tert-butylquinone by molecular oxygen is reported

Synthesis and characterization of Cp∗Rh (III) and Ir (III) polypyridyl complexes:: fluxional behaviour of Rh (III) complexes and molecular structure of [Cp∗Rh (Ph-terpy)Cl]BF4 complex (Cp∗=η5− (C5Me5))

Abstract Reaction of [Cp ∗ M( μ -Cl)Cl] 2 (Cp ∗ = η 5 - (C 5 Me 5 ), MRh, Ir) with 4′-phenyl-2,2′: 6′, 2″ terpyridine (Ph-terpy), L 1 and 1,4-bis (2,2′: 6′, 2″-terpyridin-4′-yl)benzene (diterpy), L 2 results in the formation of cationic complexes by the cleavage of halide bridge. These complexes, [Cp ∗ RhL 1 Cl]BF 4 , (1), [ (Cp ∗ RhCl) 2 L 2 ] (BF 4 ) 2 , (2), [Cp ∗ IrL 1 Cl]BF 4 , (3) and [ (Cp ∗ IrCl) 2 L 2 ] (BF 4 ) 2 , (4) are characterised by various spectral methods. Ph-terpy coordinates the metal ion in a bidentate fashion to form mononuclear complexes while diterpy bridges two metal ions to form dinuclear complexes. Complex (1) is crystallographically characterised. In solution Rh (III) complexes show fluxional behavior.

Identification of Cu(II)/Cu(III) couples in binuclear copper(II) complexes

Abstract A new series of binuclear copper(II) complexes were synthesised and studied by magnetic, spectral, ESR and cyclic voltammetry methods. The μeff values per copper atom correspond to the values observed for mononuclear copper(II) complexes. ESR spectral data in solution indicate weak interactions resulting from the electron delocalisation through the ligand system. Two nearly reversible red-ox couples are identified at + 0.50 V and + 0.75 V vs SCE. They correspond to Cu(II)αCu(III) red-ox processes, successively occurring at the two copper sites in the binuclear complexes.

Synthesis and molecular structure of [CpRu(PPh3)(Phterpy-N,N′)]Cl complex: Hdentate nature of phterpy and diterpy

Abstract Ligand displacement reactions of the complex [CpRu(PPh3)2Cl] were investigated with N3 terdentate ligands, 4′-phenyl-2,2′:6,2″-terpyridine (Phterpy) and 1,4-bis(2,2′:6″,2″-terpyridin-4-yl)benzene (diterpy). The [CpRu(PPh3)2Cl] reacted with these ligands to form stable complexes of the type [CpRu(PPh3)(Phterpy)]X (X  Cl−, PF6−) and [{CpRu(PPh3)}(diterpy){Ru(PPh3)Cp}]X2 (X  Cl−, PF6−) respective ligands coordinate in a bidentate fashion. The X-ray crystal structure of the former complex was determined showing octahedral geometry about the metal center assuming the cyclopentadienyl ligand occupying three coordination sites and Phterpy acts as a bidentate ligand.

Electrochemical reversibility of the CuI–Cu0 couple in bis[2,9-di(o-substituted phenyl)-1,10-phenanthroline]-copper(I) complexes. Stability of the corresponding copper(0) species

Copper(I) complexes of 1,10-phenanthroline disubstituted at the 2,9 positions or monosubstituted at the 2 position by phenyl moieties having ortho substituents have been prepared and investigated by spectral and electrochemical methods. The bis[2,9-di(o-substituted phenyl)-1,10-phenanthroline]-copper(I) complexes, where Cul is surrounded by two disubstituted phenanthroline units, undergo reversible electrochemical reduction at about –1.72 V vs. saturated calomel electrode, whereas bis[2-(o-substituted phenyl)-1,10-phenanthroline]copper(I) complexes, where Cul is surrounded by two monosubstituted phenanthroline units, undergo quasireversible/irreversible electrochemical reduction at about –1.68 V. The electrochemical reversibility of the former complexes is related to the dual effect of stabilization of copper(0) species and the steric involvement of the ortho substituents on the phenyl ring.

Synthesis, characterization and catalytic activity of dinuclear iron(III) and ruthenium(III) complexes

Abstract A number of dinuclear iron(III) and ruthenium(III) complexes from dinucleating ligands have been synthesised and characterized. The iron(III) complexes of dinucleating triazene-1-oxide ligands (type 1) catalyse the epoxidation of alkenes with iodosyl benzene as an oxidant. The catalytic activity of iron(III) complexes of dinucleating Schiff base ligands (type 2) could not be studied due to insolubility. Ruthenium(III) complexes of both types of ligands catalyse epoxidation reactions.

Cyclic voltammetric studies of copper(II) amino acid complexes: electrochemical evidence for the generation of copper(I) complex as an intermediate

Abstract The reduction of the title complexes is studied by cyclic voltammetry in aqueous media. It proceeds through a one-electron process generating the corresponding copper(I) amino acid complexes. The reduced copper(I) species undergo chemical reactions generating Cu(O) at the mercury electrode. The unreacted fraction of the copper(I) species is re-oxidised to the copper(II) complexes. The Cu(O) generated undergo a two-electron oxidation to Cu2+ at less cathodic potentials which get reduced to Cu(O) subsequently. pH-dependence of these complexes is also investigated.

Characterization of simple photoresponsive systems and their applications to metal ion transport

Some new photoresponsive azobenzenes (1–5) have been synthesized and characterized. On irradiation at 330 nm these systems undergo conversion from the E to the Z form to a varying extent which depends upon the nature and position of substitution on the azobenzene rings. They revert back to the E form on thermal isomerization in the dark. Photochemical equilibria have been studied and compared in acetonitrile and o-dichlorobenzene; E forms are stabilized more in o-dichlorobenzene than in acetonitrile. Two of the molecules (1 and 4) show enhanced transport of Cu2+ ions across a liquid membrane on irradiation.

Cyclic voltammetric studies of copper(II) dipeptide complexes. Evidence for copper(I) dipeptide complexes in aqueous media

Abstract The reduction of the title complexes was studied by cyclic voltammetry in aqueous media. It proceeds through a one-electron process generating intermediate copper(I) dipeptide complexes. The copper(I) dipeptide complexes are found to be short-lived and undergo transformations eventually generating Cu 0 at the mercury electrode. The unchanged fraction of the copper(I) species is re-oxidised to the copper(II) complexes. The Cu 0 generated undergoes a two-electron oxidation at a more anodic potential than the copper(I) complexes. pH-dependence of the title complexes is also investigated by cyclic voltammetry.