Panthapally S. Zacharias

First structurally characterized optically active mononuclear Mn(IV) complex: synthesis, crystal structure and properties of [MnIVL2]{H2L = S-(−)-2-[(2-hydroxy-1-phenylethylimino)methyl]phenol}

The reaction of Mn(CH3COO)2·4H2O with H2L {H2L = S-(−)-2-[(2-hydroxy-1-phenylethylimino)methyl]phenol} in the presence of air afforded dark brown crystals of [MnIVL2], 1. Compound 1 crystallizes in the monoclinic chiral C2 space group. Crystals of 1 were further characterized by elemental analysis, room temperature magnetic moment determination, IR, UV-visible and EPR spectroscopy, cyclic voltammetry and circular dichroism (CD) studies. Cyclic voltammetry reveals a quasi-reversible redox wave corresponding to the Mn(IV)/Mn(III) couple. The EPR spectrum at liquid nitrogen temperature consists of a strong signal at g ∼ 4 and a weak but resolved response at g ∼ 2. The CD spectrum of 1 exhibits a negative band, such as shown by the enantiopure ligand H2L. Complex 1 was found to catalyze the oxidation of olefins using iodosobenzene as the oxidant in acetonitrile solutions.

Synthesis and characterization of a chiral dimeric copper(II) complex: Crystal structure of [Cu2(μ-Cl)2(HL)2]·H2O(H2L = S-(−)-2-[(2-hydroxy-1-phenyl-ethylimino)-methyl]-phenol)

Synthesis and characterization of an optically active binuclear dichloro-bridged copper(II) complex [Cu2(μ-Cl)2(HL)2]·H2O 1 (H2L = S-(−)-2-[(2-hydroxy-1-phenyl-ethylimino)-methyl]-phenol) of a Schiff-base derived from salicylaldehyde and (S)-(+)-2-phenylglycinol are described. Compound 1 crystallizes in the orthorhombic chiral P212121 space group with Z = 4, a = 10·21(2), b = 11·574(3), c = 25·364(9). Each copper shows square pyramidal geometry with O2NCl2 coordination and the Cu2Cl2 core geometry adopts a butterfly shape. Crystals of 1 were further characterized by elemental analysis, IR, UV-visible and EPR spectroscopy and circular dichroism (CD) studies.

New optically active hexaaza triphenolic macrocycles: synthesis, molecular structure and crystal packing features

3 + 3 Condensed optically active hexaaza triphenolic macrocyles 1 and 2 are synthesised and characterised; molecular and close packing structures of macrocycle 2 are discussed.

A chiral Mn(IV) complex and its supramolecular assembly: Synthesis, characterization and properties

The open air reaction of the chiral Schiff base ligand H2L, prepared by the condensation of L-phenylalaninol and 5-bromosalicylaldehyde, with MnII(CH3COO)2.4H2O yielded dark brown complex [MnIV L2]·0·5 DMF (1). Compound 1 was characterized by elemental analysis, IR, UV-visible, CD and EPR spectroscopy, cyclic voltammetry and room temperature magnetic moment determination. Single-crystal X-ray analysis revealed that compound 1 crystallises in the monoclinicP21 space group with six mononuclear [MnIV L2] units in the asymmetric unit along with three solvent DMF molecules. In the crystal structure, each Mn(IV) complex, acting as the building unit, undergoes supramolecular linking through C-H...0 bonds leading to an intricate hydrogen bonding network.

Copper(II) complexes of entwined 2,9-di(o-substituted phenyl)-1,10-phenanthroline type ligands and intramolecular quenching in copper(I) complexes

SummaryCu11 complexes of 1,10-phenanthroline, disubstituted at the 2 and 9 positions or monosubstituted at the 2 position by phenyl moieties possessingortho substituents, were prepared and investigated by spectroscopic and electrochemical methods. The electronic spectral d-d band position varies from 14 500 to 13 200 cm−1. E.s.r. g‖ values are between 2.256 to 2.283 and A‖ between 164 to 117×10−4 cm−1. Thebis[2,9-di(o-substituted phenyl)-1,10-phenanthroline]Cu11 complexes undergo reversible one-electron electrochemical reduction (Cu11/Cu1) in the +0.536 to +0.825 V potential range versus s.c.e., whereas thebis[2-mono(o-substituted phenyl)-1,10-phenanthroline]Cu11 complexes undergo reduction in the +0.360 to +0.405 V range; the redox couple is found to be quasireversible. Emission studies on copper(I) complexes show that onlybis[2,9-di(o-tolyl)-1,10-phen]Copper(I) complex exhibits emission properties. Emission behaviour of other structurally similar compounds is explored.

Synthesis and structural characterisation of Fe(II) and Cu(I) complexes of a new tetrafunctional N-donor ligand with dodecahedral or tetrahedral binding domains

The tetrafunctional N-donor ligand 1 is able to form homoleptic complex cations with dodecahedral ([Fe{C12H6N2(CHNC6H4 SMe)2}2]2+2) or tetrahedral ([Cu2{C12H6N2(CHNC6 H4SMe)2}2]2+3) binding domains.

Nickel(II) complexes of tridentate anthracene based Schiff bases: syntheses, properties and crystal structures

The crystal and molecular structures of Ni(II) complexes with two tridentate anthracene-containing Schiff bases are reported. The Schiff bases were prepared by condensation of 9-anthraldehyde with diethylenetriamine (adien) and with dipropylenetriamine (adipn). Complexes synthesized from Ni(O2CCH3)2·4H2O and the ligands (1 : 1 mol ratio) crystallize from methanol as [Ni(adien)(O2CCH3)2(H2O)] (1) and [Ni(adipn)(O2CCH3)2]·2CH3OH (2·2CH3OH) in space groups P21/n and P212121, respectively. In 1, the distorted octahedral N3O3 coordination sphere around the metal ion is formed by the meridional N3-donor adien, two mutually trans unidentate acetates and one water molecule. The N3O3 coordination sphere constituted by the N3-donor adipn, one unidentate acetate and one bidentate acetate in 2 can be best described as trigonal bipyramidal. The secondary amine-N of adipn, the O-atom of the unidentate acetate and the midpoint of the two O-atoms of the bidentate acetate occupy the three equatorial positions and two imine-N atoms of adipn lie in axial sites. In the crystal lattice, molecules of 1 exist as discrete dimers due to intermolecular hydrogen bonding and π–π interactions. In contrast, self-assembly of 2 via intermolecular π–π interactions leads to a one-dimensional supramolecular structure.

Enantiospecific inclusion of chiral 1,2-dichloroethane rotamers in the crystal lattice of chiral square-pyramidal Cu(II) complexes with perfectly polar alignment of guest and host molecules

The inclusion compounds, [CuL(1)2(H2O)].(P)-C2H4Cl2 and [CuL(2)2(H2O)].(M)-C2H4Cl2(HL1 = N-(2-hydroxy-5-nitrobenzyl)-(R)-alpha-methylbenzylamine and HL2 = N-(2-hydroxy-5-nitrobenzyl)-(S)-alpha-methylbenzylamine), crystallise in the non-centrosymmetric space group C2; intermolecular hydrogen bonding leads to a perfectly polar alignment of both host and guest molecules with enantioselectivity.

Photoinduced fluorescence changes on E–Z isomerisation in azobenzene derivatives

New fluorosensors based on azobenzene derivatives have been synthesised, characterised and their photophysical properties investigated. Compounds 2a and 2b undergo E→Z photoisomerisation on irradiation at ≈330 nm accompanied by fluorescence enhancement. Z→E isomerisation in the dark is accompanied by a decrease in the fluorescence intensity. These are the first reported examples of fluorescence enhancement on E→Z isomerisation across a NN bond. Protonation of the azo groups in 2a and 2b is also accompanied by fluorescence enhancement. The origin of the fluorescence enhancement in the cis isomer is explained on the basis of the inhibition of photoinduced electron transfer due to the nonplanar geometry of this isomer, which reduces the effective conjugation of the nitrogen lone pair electrons with the π electrons of the fluorophore.

Spectral and Mössbauer studies of some iron(III) high spin complexes

Some new iron(III) complexes of triazene 1-oxides are synthesised and characterised by analysis, magnetic, electronic and Mössbauer spectra. They are found to be high spin Fe3+ systems.