Archana Tiwari

Effect of Geometrical Distortion on the Electronic Structure: Synthesis and Characterization of Monoradical-Coordinated Mononuclear Cu(II) Complexes

Ligand H3Sami(Mixed(tBu)) was composed of two different compartments, a redox-active 2-aminophenol and a salen salicylidene. Both compartments were linked via a benzyl linker. The ligand reacted with CuCl2·2H2O under air in the presence of Et3N and provided the corresponding monoradical-coordinated mononuclear Cu(II) complex (1). Complex 1, in solution, reacted with air and provided complex 2 via ligand-centered oxygenation at the benzyl-CH2 position. Both complexes were characterized via IR, mass spectrometry, X-ray single-crystal diffraction, variable-temperature magnetic susceptibility, cyclic voltammograms (CVs), and UV-vis/NIR spectroscopic techniques. X-ray crystallographic analyses clearly showed almost equally distorted square planar geometry around the Cu(II) atom in both complexes. However, the bending of the radical-containing C6 ring compared to the N1-Cu1-O1 plane was different in both complexes. While complex 1 was paramagnetic and showed a ferromagnetic coupling between the d(x(2)-y(2)) magnetic orbital of Cu(II) ion and the p(z) orbital of coordinated π-radical, complex 2 was diamagnetic by experiencing a strong antiferromagnetic coupling between the two magnetic orbitals. UV-vis/NIR spectra of the complexes were dominated by charge-transfer transitions. CVs of the complexes showed two reversible one-electron oxidations and one reversible one-electron reduction. E(1/2)(ox2) and E(1/2)(red1) potentials were different in both complexes, while E(1/2)(ox1) values were almost the same and the process corresponded to the formation of phenoxyl radical. Theoretical studies were also performed to understand the magnetic coupling phenomena, and TD-DFT calculations were employed for the assignment of charge-transfer absorption bands.

Solid-state valence tautomeric octahedral {CoII[(BQ-N-Cat)]2}0 complex formation via ligand-centered phenolic C–O bond breaking and Co–O bond making

Ligand H4LO(AP/AP) underwent ligand-centered C-O bond cleavage during a complexation reaction with Co(ii)-salt. The thus formed octahedral {CoII[(BQ-N-Cat)]2}0 complex showed valence tautomerization in the solid state. While the process was triggered by the presence of lattice solvent, the nature of the solvent molecule has less effect on the process.

Effects of swift heavy ion-irradiation on mica- and coal-based rocks of Lower Himalayas in Sikkim, India

Naturally occurring mica schist and coal sedimentary sequence in Sikkimese Himalaya were collected and investigated by two micro-techniques: scanning electron microscopy/energy dispersive spectrometry and Raman spectroscopy. They were applied to identify the constituents and the structure of the minerals before and after swift heavy ion irradiation. Vibrational data and the constituents of abundantly found mica schist and coal-based rock were acquired at room temperature and were compared with those reported for their analogues in the previous reports.

Optical Characterization of Medicinal Plants’ Extracts Used for the Treatment of Diabetes

The fluorescence and absorption spectroscopy on the medicinal plants’ extracts used for the cure of diabetes in Eastern Himalayan region viz. Darjeeling and Sikkim are presented. The extracts from the seeds of Totola (Oroxylum indicum Vent.) and fruits of Harra (Terminalia chebula Retz.) and Barra (Terminalia belerica Roxb.) are studied using thin layer chromatography and atomic absorption spectroscopy. The results are compared with those of commercially prepared polyherbal formulations from Totola, Harra and Barra viz. Dashmool Kwath, Haritaki Churna and Triphala Churna.