Taro Isobe

ESR studies of the spin-exchange interaction within parallel planar copper (II) dimers in frozen solutions

Abstract The temperature variations of the ESR spectral intensity of the triplet dimers over the range 1.6 to 4.2 K indicated that the spin-exchange interaction within the parallel planar dimers, which had been reported to be ferromagnetic in crystal, is antiferromagnetic (1.5–2.5 cm −1 ) in frozen solutions.

Proton Hyperfine Splittings in the ESR of Some Alkylphosphine Dimeric Radicals

The triplet splittings due to protons were observed for the ESR of the dimeric cation radicals of P(CH3)3, P(CH2CH3)3, and PH(CH3)2; they were formed by the γ irradiation of the rigid CH2Cl2 solutions of these alkylphosphines at 77 K. The observed proton hyperfine splittings for the dimer-cation radicals, [(CH3)3P–P(CH3)3]+ and [(CH3CH2)3P–P(CH2CH3)3]+, were assigned to the hyperfine interaction with two of the methyl and with two of the methylene protons respectively, while those for the [(CH3)2HP–PH(CH3)2]+ radical were assigned to the hyperfine interaction with the two P–H protons. In the former two radicals, the rotations of the methyl and the ethyl groups are restricted. The conformations of the methyl and the ethyl groups have been estimated on the basis of the observed proton hyperfine splittings. The P–H protons of the [(CH3)2HP–PH(CH3)2]+ radical have an extremely large isotropic coupling constant of 58 G; it may be attributed to the direct interaction with the unpaired electron in the anti-bondi...

Electron spin resonance studies of cation radicals of some alkylphosphines

The effect of alkyl substitution on the geometry of the phosphine cation radical has been investigated by e.s.r. spectroscopy. It is shown by the use of Huheeys electronegativity parameters that the geometry of the alkylphosphine cation radicals is related to the electronegativity of the alkyl groups as in other trigonal radicals. The effects of methyl substitution on the geometry of AlH–3 and SiH3 are also discussed in terms of Huheeys electronegativity parameters. It is shown, further, that there is a correlation between the 31P hyperfine coupling constants of the alkylphosphine cation radicals and 31P n.m.r. chemical shifts for the respective neutral molecules.

An improved insertion‐type liquid‐helium Dewar for X‐band ESR spectroscopy

A liquid‐helium Dewar in conjunction with the X‐band room‐temperature cavity is reported. The Dewar consists of a fourfold silvered Pyrex glass tube graded to fourfold unsilvered clear fused quartz fingers. A full charge (250 ml) of liquid helium has given about 10 h of operation.

Nuclear magnetic resonance studies of low-spin complexes of cobalt(II) with Schiff bases. NN′-1,1-dimethylethylenebis(salicylideneiminato)cobalt(II) in pyridine

Isotropic paramagnetic proton n.m.r. shifts have been measured for the low-spin title complex in [2H5]pyridine. The temperature dependence of the shifts shows large deviations from the Curie law. The deviation is interpreted in term of the effects of temperature-dependent ligand field on mixing of excited electronic configurations with the ground state. The contact shifts evaluated from the isotropic shifts are shown to arise from spin delocalization through both σ and π orbitals. the latter having a smaller contribution than the former. The pattern of the contact shift is explained by the ground-state configuration of CoII where the unpaired electron is primarily in the dz2 orbital, and by the non-planar structure of the complex.

Electron spin relaxation of methyl radicals in alkali metal acetates

Abstract The hyperfine splitting constant of the methyl radical, produced by the γ-irradiation of alkali metal acetates, decreases from that found in caesium acetate in the order potassium, sodium and lithium. Electron spin relaxation is also affected by the presence of alkali metals, showing some correlation with the changes in the hyperfine splitting constants. It is estimated that the intramolecular anisotropic dipolar interaction between the unpaired electron and the magnetic moment of the protons may be a major mechanism contributing to the electron spin relaxation, and that the variation in T1T2 values among the metal acetate systems may be attributed to the freedom of molecular motion of the methyl radicals in the metal acetates.

Formation of naphthalene anion by the reaction of 4-phenyl-1,3-dioxan with sodium–potassium alloy

The reaction of 4-phenyl-1,3-dioxan with sodium–potassium alloy produced the naphthalene radical anion.

High-spin quadridentate salicylaldehyde Schiff base complexes of cobalt(II) in N-heterocyclic solvents

E.s.r. and magnetic susceptibility studies of the title complexes show that an appreciable amount of the high-spin base di-adduct is formed in N-heterocyclic solvents such as pyridine and its methyl derivatives.