A compact general theory for the effect of Heisenberg spin exchange on ESR linewidths and saturation parameters is detailed. The effects of Heisenberg exchange on the linewidths of the tetracyanoethylene anion (TCNE-) radical and the di-tert-butyl nitroxide (DTBN) radical in both dimethoxyethane (DME) and tetrahydrofuran (THF) are investigated. From comparative studies of linewidth as a function of temperature and of radical concentration, TCNE-in DME is shown to undergo strong exchange with a secondorder rate constant of 4.1±0.6X10 9 M-I· sec-I at 15°C. The TCNE-radical in THF exhibits an anomalous concentration-dependent linewidth effect when compared to the theory and to the experiments employing DME as the solvent. The uncharged DTBN radical shows similar spin-exchange properties in both solvents. Possible mechanisms for the anomalous linewidth effect are discussed. The effect of spin exchange on the saturation parameters of the TCNE-radical in DME is investigated in detail, and the experimental results are shown to agree, within experimental error, with the theory developed. Electron-nuclear dipolar and electron-electron dipolar relaxation effects are discussed in terms of their (small) contributions to the experimentally determined relaxation times. Present address:

Carboxamide based gelator molecule used for the detection of iron by turning off the aggregate-induced emission and selective sensing anion by either switching off or switching on the emission property of the metallogel.

The spin-density distributions in the 1,4-benzosemiquinone and 2,5-dioxy-1,4-benzosemiquinone ions have been estimated by measuring the proton and 13C splittings and using reasonable choices for the values of the sigma—pi parameters which relate the splittings to the spin densities for C–C and C–H bonds. The determination of the signs as well as the magnitudes of the 13C splittings was required to obtain the spin densities. With QCHH=−27.0 G in the relation aiH=QCHHρi π between proton splitting aiH and carbon-atom—pi-electron spin density ρiπ, the sigma—pi parameters for the 13C splitting at a carbonyl position were found to be QCOC=17.7 G and QOCC=−27.1 G. The values of QCOC and QOCC depend on the value assumed for QCHH. Contrary to earlier predictions made on the basis of molecular orbital calculations, the sign of the 13C splitting from the 2 position of the p-benzosemiquinone ion was found to be negative. This discrepancy results because the MO calculations were performed so as to reproduce proton splittings rather than the entire spin-density distribution, a procedure that is insensitive to the spin densities on the carbonyl carbon and oxygen atoms. New MO calculations were performed to fit the spin densities at all the positions in the radical. The results show that calculations fitted to proton splittings alone are inadequate for predicting spin densities at ``blind'' positions such as those at the carbon and oxygen atoms of a carbonyl group, or the nitrogen and oxygen atoms of a nitro group. Carbon-13 splittings were also observed in the anthrasemiquinone ion in both ethanol and 1,2-dimethoxyethane (DME) solutions. The sign of the 9-position 13C splitting changes from +0.70 G in ethanol to −0.47 G in DME solution. By using the sigma—pi parameters for the carbonyl group carbon atom, the spin densities were determined for this radical and MO calculations performed to reproduce the spin-density distributions. The variation of the splittings in the p-benzosemiquinone ion with solvent composition could be accounted for quantitatively by using the newly determined sigma—pi parameters.

Four new mononuclear Ni(ii) complexes [Ni(L(1))]ClO4 (), [Ni(L(2))]ClO4(), [Ni(SCN)3(CH3OH)(aminoethylpiperazineH)] (), and [Ni(DMSO)4(aminoethylpiperazineH)](ClO4)3()have been synthesized from two Schiff base ligands [L(1) = 1-phenyl-3-((2-(piperidin-4-yl)ethyl)imino)but-1-en-1-ol and L(2) = 4-((2-(piperazin-1-yl)ethyl)imino)pent-2-en-2-ol] by exploiting the flexibility of the piperazinyl moiety. Structural analysis reveals that and are square planar complexes with piperazine rings in boat conformations whereas hydrolysis of Schiff bases (L(1) and L(2)) occurs during formation of octahedral complexes ( and ) with piperazine rings in chair conformations. Screening tests were conducted to quantify the binding ability of complexes (, and ) towards DNA, BSA and HSA and it was found that square planar complexes ( and ) showed more effective binding properties over octahedral complex (). Furthermore, enzyme kinetic studies reflect that square planar complexes ( and ) are also effective in mimicking catecholase like activities over octahedral complex (). Among all the complexes, was found to be the most promising molecule among the series due to its large binding affinity towards different bio-macromolecules and higher T.O.N in the catechol oxidation reaction.