Monisha Bose

Nuclear magnetic resonance studies of N14 bonded to carbon

Abstract Chemical shifts of N14 resonances in aza-aromatics as well as substituted aromatics and aliphatics have been investigated and attempts to correlate shifts with electronic structure have been made. Effects of conjugation and hyperconjugation, as well as charge-transfer interaction were evaluated. The effect of relaxation on line-widths is discussed from symmetry considerations. Further, equilibrium in the pyridine-pyridinium system has been studied by focussing the N14 resonance.

Solid solutions of Li3VO4Li4GeO4 as solid electrolytes: NMR and related studies

Abstract It has been shown from NMR and conductivity studies of Li 3 VO 4 Li 4 GeO 4 solid solution that the activation energy is insensitive to change of composition over a wide range while it is highly sensitive to moisture. This effect has been significantly brought out in NMR studies as revealed in the ultimate disappearance of the NMR line due to penetration of the moisture within the grains.

NMR studies of the mixed conductor LixV2O5

Abstract A systematic NMR study of 51 V and 7 Li in the mixed conductor Li x V 2 O 5 is presented. The paramagnetic effect in the β bronze with the highest σ is very much evident, whereas it is much subdued in the intercalates. LiV 2 O 5 interecalate shows a second order quadrupolar effect in contrast to first order effects in both intercalates and bronzes with x ∼0.4.

59Co NMR studies of the spin-state equilibria in rare-earth cobaltites

Abstract Hyperfine interaction parameters reveal differences in the nature of spin-state equilibria in the lighter and heavier rare-earth cobaltites; the crystal-field parameter is lower in the lighter cobaltites. Temperature variation of the quadrupolar coupling constant is also more marked in the lighter rare-earth cobaltites, with NdCoO 3 showing evidence for a structural phase transition.

Dynamics of the Lisicon system from 7Li NMR

Abstract T 1 measurements in the Lisicon system conform to BPP mechanism due to Li + diffusion at higher temperatures. Quadrupolar satellites are observed in FT spectra of both Lisicon and ZRA at 500K. At 666K, e 2 qQ vanishes for Lisicon but exists for the ZRA (e 2 qQ/h ∼ 40.5 KHz). Finally FID indicates that T 2 involves two different processes, one arising from mobile Li ions and the other from the frame-work Li.

Solvent effects in the N.M.R. spectra of aza-aromatics

Solvent effects on proton chemical shifts in a number of substituted pyridines have been investigated. The systems chosen were asymmetric 3 and 4 spin systems, which were analysed by the ‘Effective Larmor Frequency Method’ of Pople and Schaefer. The chemical shifts were then investigated in a number of solvents ranging from the non-polar n-hexane to the highly polar water. The shifts could be qualitatively interpreted on the basis of Buckinghams theory. The rather interesting but anomalous shifts obtained on dilution with water have been explained on the basis of the highly ordered water structure around the solute molecule.

Hyperfine interaction in the mixed conductor γ LiV2O5

Transferred hyperfine interaction effects as studied from51v NMR in γ LiV2O5 (bronze) between the non-magnetic V5+ and paramagnetic V4+ lead to differing non-integral valences (neither 5+ nor 4+) on these sites at room temperature and below. However, at high temperatures exchange between two sites leads to a single mixed-valence state. d-d (V4+ −V4+) pairing along with relaxation effects show up in the low temperature spectra. Though susceptibility remains almost constant from 300–100K, there is considerable narrowing as well as intensification of the lines.