Manindranath Bera

Structure and properties of a new double-stranded tetranuclear [CuII2]2 helicate

A novel double-stranded tetranuclear helicate composed of a pair of [CuII2] dimers has been prepared and characterized by exploiting the flexibility, chelating ability and bridging potential of a hexadentate bis-oximate ligand.

Imidazolidine ring as a reduced heterocyclic spacer in a new all-N-donor μ-bis(bidentate) Schiff base ligand: Synthesis, characterization and electron transfer properties of imidazolidine-bridged dicopper complexes

Low-temperature stoichiometric Schiff base reaction in air in 3:1 mole ratio between benzaldehyde and triethylenetetramine (trien) in methanol yields a novel tetraaza μ-bis (bidentate) acyclic ligand L. It was characterized by elemental analysis, IR, EI mass and NMR (1H and13C) spectra. The formation of a five-membered imidazolidine ring from the ethylenediamine backbone as a spacer-cumbridging unit gives rise to a new type of imidazolidine-bridged ligand. A geometric optimisation was made of the synthesized ligand and its complexes by the method of molecular mechanics (MM2) method in order to establish the stable conformations. This hitherto unknown tetraaza acyclic ligand affords new cationic dicopper(I/I) and dicopper(II/II) complexes in good yield. Dicopper(II/II) complex displays weakd-d transition bands in the visible region, while dicopper(I/I) complex displays strong MLCT band in the same region. Both the dinuclear complexes are of non-intimate nature and show interesting solution electrochemical behaviour. EPR spectral study of μ-bis (imidazolidino) bridged dicopper(II/II) complex also supports the non-communicative nature of the two copper centres within the same molecule

Dicopper(II/II) complexes of an amine phenol hexadentate ligand showing μ-bis(tridentate) coordination: EPR spectral model of binuclear CuA centre of nitrous oxide reductase

A new family of binuclear Cu(II)–Cu(II) complexes with a hexadentate Schiff base ligand containing imine-phenol end groups has been studied as an EPR spectral model of the binuclear CuA centre of nitrous oxide reductase. The complexes have been characterised by elemental analysis, solution electrical conductivities, IR, UV-vis, EPR spectral, magnetic studies and geometrical optimisation by molecular mechanics (MM2) method.

Synthesis, characterisation and activity in catalytic epoxidation of olefins of new dinuclear nickel(II) complexes

Two new dinuclear nickel(ll) compounds of formula [Nill2(μ-L1)2](CIO4)2·MeCN (1·MeCN) and [NiII2(μ-L2)2](CIO4)2 (2) where HL1 and HL2 stand for 3-(2-(dimethylamino)ethylimino)butan-2-one oxime and 1-(2-(dimethylamino)ethyl-imino)-1-phenylpropan-2-one oxime respectively, have been synthesised. Single crystal X-ray analyses of the complexes reveal that the nickel(ll) ions are in square-planar N3O environments and form six-membered (NiNO)2 metallacycles. Cyclic voltammetric measurements of 1·MeCN and 2 in MeCN solution show quasirreversible one-electron oxidations at E1/2 = 0.566 V and 0.603 V (vs Fc+/Fc), respectively, attributed to NiIIINiII/NiII2 redox couples. Additional reversible NiIII2/NiIIINiII redox responses were observed at relatively higher potential near E1/2 = 0.832 V and 0.850 V (vs Fc+/Fc), respectively, for 1·MeCN and 2. Complexes 1·MeCN and 2 display intense charge-transfer bands at ∼390 and ∼345 nm in the visible region. Chemical oxidation of complex 1·MeCN by sodium hexachloroiridate(IV) hexahydrate generates red Ni2III species with characteristic new bands at ∼520 and 427 nm in the visible region as well as the characteristic EPR signals at 77 K with g⊥ > gII. Similar phenomena were observed for complex 2 upon chemical oxidation. The dinickel(ll) complexes are catalytically active for epoxidation of olefins using iodosylbenzene as the terminal oxidant.