Leo Burlamacchi

Electron spin relaxation of manganese (II) in solution

Abstract The electron spin resonance of Mn(II)in liquids and its implication as a paramagnetic probe are discussed. A motional model is proposed to account for

Electron spin relaxation and hyperfine line shape of manganese (II) in mixed‐solvent systems

The X‐band ESR line shape of the six hyperfine components of manganese (II) has been investigated both in pure and in mixed solvents. The procedure used by Luckhurst and Pedulli [G. R. Luckhurst and G. F. Pedulli, Mol. Phys. 22, 931 (1971)] to account for the removal of the spin degeneracy by the nonsecular terms in the spin Hamiltonian has been used to compute the line shape as a function of (D:D) and of τc. In mixed solvents, large deviations from the theoretical line shape are due to the presence of differently coordinated complexes. A criterion for the determination of the selective solvation has been established.

Electron spin relaxation as a tool for studying the dynamics in the outer solvation sphere of 6S spin state ions

The apparently homogeneous E.S.R. spectra of solution manganous ions are interpreted in terms of a sum of degenerate lorentzian lineshapes with different widths. The existence of a distribution of linewidths instead of a single linewidth, is interpreted assuming that the electron spin relaxation is dominated by rotation of a static zero-field splitting tensor caused by slow configurational changes of the ionic environment, including first and second solvation spheres. Typical configurational lifetimes of the second solvation sphere were found to be τ k ∼ 10-9 s. Details of the ionic structure and dynamics are discussed.

Electron spin resonance of the Mn2+ ion in the study of the mobility of water adsorbed on silica gel and γ-alumina

The electron spin relaxation of Mn2+ in supercooled water adsorbed on silica gel and γ-alumina has been investigated. The correlation time for the modulation of the zero-field splitting tensor has been evaluated from the temperature and frequency dependence of the e.s.r. linewidth: τc= 1.4 ± 0.3 × 10–12 s at 25 °C has been extrapolated for bulk water solution. In the capillary adsorbed water, lineshape analysis suggests the existence of a distribution of crystal-field sites. The rate of interchange among differently relaxing sites is < 109 s–1. This suggests a long-range solid-water interaction which slows the mobility of water molecules up to 15–20 A from the surface.

An electron spin resonance study of the interactions of olefins with Na and K molybdates

Abstract The ESR spectra and the catalytic activity of sodium and potassium molybdates have been investigated. In agreement with the structural analogies with the bismuth molybdate catalysts active in olefin oxidation, formation of the Mo(V) ESR signal is observed when they are placed in contact with 1-butene or propene. However, the catalytic activity was almost nil. The catalytic inactivity has been explained as due to the difficulty of reoxidation by gaseous oxygen. The failure of a partner with red-ox properties, such as Bi(III) or Fe(III), and the higher stability of the reduced centers have been suggested to be responsible for the difficulty of reoxidation.

Electron spin resonance study of the freezing properties of water adsorbed on γ-alumina

The e.s.r. spectrum of the manganese(II) ion has been investigated in bulk water and in water adsorbed on γ-alumina. The high mobility of the e.s.r. detectable ions shows that the water filling large pores in γ-alumina has the same viscosity as bulk water. On cooling, the viscosity of adsorbed water increases continuously even below the homogeneous nucleation temperature (–40°C), leading to the formation of an amorphous glass.

The motional model in the electron spin relaxation of large Mn(II) complexes: Rotational or fluctuational process?

Abstract The solution ESR spectra of Mn(II) bound to ATP have been analyzed at three microwave frequencies. The liquid-type relaxation process induced by rapid fluctuations of the crystal-field symmetry does not account for the frequency dependence of the linewidth. The ESR lineshapes are better explained in terms of a static distribution of crystalfield sites which induces field dependent inhomogeneous broadening.

Electron spin resonance and catalytic measurements of the oxidation of olefins on cadmium molybdate catalyst

The formation of the e.s.r. single absorption line at g= 2.003 previously observed on bismuth molybdates and MoO3 catalysts during interaction with olefins, has been investigated with CdMoO4. The signal is formed only by interaction of adsorbed olefins with adsorbed oxygen and arises from an ill-defined radical located on the catalyst surface. The easy oxidation of this radical under usual catalytic conditions suggests that it may be an intermediate in a pathway of non-selective oxidation of olefins. Comparison between catalytic and e.s.r. results suggests that adsorbed molecular oxygen is active in this oxidation.

Electron spin resonance of manganous ion in methanol glass

Abstract The distribution of the zero-field splitting sites experienced by the Mn2+ ion in frozen methanol is investigated from the electron spin resonance lineshape at low magnetic field.

Molecular Dynamics in Water Solutions Adsorbed on Porous Solids Studied By ESR of Paramagnetic Probes

The electron spin resonance of Mn(H2O)2+ 6 and of Cu(H2O)2+ 6 ions was used to investigate the mobility and the freezing properties of water adsorbed on silica gel samples with pore diameters of 4, 6, 20, and 100 nm. The lineshape analysis of the esr spectra shows that the first two or three layers of water molecules are strongly immobilized even at room temperature, while at least the first ten layers from the surface do not freeze at any low temperature. Beyond this limit, the water seems to behave like normal water.