Electron spin relaxation of copper(II) complexes in glassy solution between 10 and 120 K

The temperature dependence, between 10 and 120 K, of electron spin-lattice relaxation at X-band was analyzed for a series of eight pyrrolate-imine complexes and for ten other copper(II) complexes with varying ligands and geometry including copper-containing prion octarepeat domain and S100 type proteins. The geometry of the CuN4 coordination sphere for pyrrolate-imine complexes with R=H, methyl, n-butyl, diphenylmethyl, benzyl, 2-adamantyl, 1-adamantyl, and tert-butyl has been shown to range from planar to pseudo-tetrahedral. The fit to the recovery curves was better for a distribution of values of T1 than for a single time constant. Distributions of relaxation times may be characteristic of Cu(II) in glassy solution. Long-pulse saturation recovery and inversion recovery measurements were performed. The temperature dependence of spin-lattice relaxation rates was analyzed in terms of contributions from the direct process, the Raman process, and local modes. It was necessary to include more than one process to fit the experimental data. There was a small contribution from the direct process at low temperature. The Raman process was the dominant contribution to relaxation between about 20 and 60 K. Debye temperatures were between 80 and 120 K. For samples with similar Debye temperatures the coefficient of the Raman process tended to increase as gz increased, as expected if modulation of spin-orbit coupling is a major factor in relaxation rates. Above about 60 K local modes with energies in the range of 260-360 K (180-250 cm-1) dominated the relaxation. For molecules with similar geometry, relaxation rates were faster for more flexible molecules than for more rigid ones. Relaxation rates for the copper protein samples were similar to rates for small molecules with comparable coordination spheres. At each temperature studied the range of relaxation rates was less than an order of magnitude. The spread was smaller between 20 and 60 K where the Raman process dominates, than at higher temperatures where local modes dominate the relaxation. Spin echo dephasing time constants, Tm, were calculated from two-pulse spin echo decays. Near 10 K Tm was dominated by proton spins in the surroundings. As temperature was increased motion and spin-lattice relaxation made increasing contributions to Tm. Near 100 K spin-lattice relaxation dominated Tm.     

Electron spin relaxation of triarylmethyl radicals in fluid solution

Electron spin relaxation times of a Nycomed triarylmethyl radical (sym-trityl) in water, 1:1 water:glycerol, and 1:9 water:glycerol were measured at L-band, S-band, and X-band by pulsed EPR methods. In H(2)O solution, T(1) is 17+/-1 micros at X-band at ambient temperature, is nearly independent of microwave frequency, and exhibits little dependence on viscosity. The temperature dependence of T(1) in 1:1 water:glycerol is characteristic of domination by a Raman process between 20 and 80 K. The increased spin-lattice relaxation rates at higher temperatures, including room temperature, are attributed to a local vibrational mode that modulates spin-orbit coupling. In H(2)O solution, T(2) is 11+/-1 micros at X-band, increasing to 13+/-1 micros at L-band. For more viscous solvent mixtures, T(2) is much shorter than T(1) and weakly frequency dependent, which indicates that incomplete motional averaging of hyperfine anisotropy makes a significant contribution to T(2). In water and 1:1 water:glycerol solutions continuous wave EPR linewidths are not relaxation determined, but become relaxation determined in the higher viscosity 1:9 water:glycerol solutions. The Lorentzian component of the 250-MHz linewidths as a function of viscosity is in good agreement with T(2)-determined contributions to the linewidths at higher frequencies.     

Electron spin relaxation rates for nitridochromium(V) tetratolylporphyrin and nitridochromium(V) octaethylporphyrin in Frozen solution

T ₁ andT _m for nitridochromium(V) tetratolylporphyrin and nitridochromium(V) octaethylporphyrin were measured by saturation recovery and electron spin echo EPR, respectively, between 10 and 130 K. The temperature dependence of 1/T ₁ was similar to that observed previously for chromium(V) complexes of hydroxycarboxylic acids. The spin lattice relaxation rate was faster in the perpendicular plane (the porphyrin plane) than normal to this plane. 1/T _m was orientation dependent with the fastest rates observed for orientations intermediate between the principal axes. The orientation dependence of 1/T _m increased with increasing temperature and decreasing rigidity of the matrix, and is attributed to molecular motion.     

Electron spin relaxation in solutions of manganese (II) ions

Measurements of the neutron scattering static structure factor S(Q) are reported for orthobaric liquid fluorine at 77K for an incident wavelength of 1·2Å. The observed S(Q) and the atom-atom correlation function are discussed and compared with those of other halogens and oxygen. From the d(r) pair distribution function it is shown that liquid fluorine has a coordination number of first neighbours more similar to liquid oxygen than halogens. The number of atoms in the first and second coordination shell is in good agreement with a close-packed arrangement of atoms.     

Electron spin relaxation of copper(II) ions in diamagnetic crystals

The electron spin-lattice and spin-spin phase relaxation measurements of Cu²⁺ ions in various crystals are reviewed and discussed. Examples of the Debye temperature determination from a wide temperature range measurements of the spin-lattice relaxation time T₁ are shown. An influence of the Jahn-Teller dynamics on T₁ is presented. The phase relaxation described by the phase memory time T_M is affected by temperature due to the spin packet width modulation by molecular motions. The T_M is anisotropic in crystals and can be different for different hyperfine lines of an EPR spectrum.     

Nuclear spin relaxation in solution of paramagnetic complexes with large transient zero-field splitting

A theory for paramagnetic relaxation enhancement (PRE) in systems with S> 1 at low magnetic field is developed for the case when the fluctuations of zero-field splitting (ZFS) in the molecular frame are larger than the averaged ZFS. The validity limits of the new theory are discussed, and its performance is evaluated by comparisons with the general slow-motion approach. The relevance of the new approach for the proton PRE in aqueous solution of Ni(II) is discussed.     

Electronic structure and spin relaxation of Fe(III) in LiNbO3

Crystal field parameter have been determined from EPR spectra (77K) of LiNbO₃Fe(III). Anomalous line shapes are described phenomenologically and saturation studies are compared with calculations using a second order dynamic spin-hamiltonian H. Mössbauer spectra of LiNbO₃Fe(III) have been interpreted by means of simulations using Liouville superoperators including a static fine-and a hyperfine spin-hamiltonian and H. Calculations have been performed using an effective spin of 1/2, the supermatrix with dimension 288 and a reduced formalism (supermatrix with dimension 96).     

Electron spin relaxation in pseudo-Jahn-Teller low-symmetry Cu(II) complexes in diaqua(L-aspartate)Zn(II).H(2)O crystals.

Low-temperature (4-55 K) pulsed EPR measurements were performed with the magnetic field directed along the z-axis of the g-factor of the low-symmetry octahedral complex [(63)Cu(L-aspartate)(2)(H2O)2] undergoing dynamic Jahn-Teller effect in diaqua(L-aspartate)Zn(II) hydrate single crystals. Spin-lattice relaxation time T(1) and phase memory time T(M) were determined by the electron spin echo (ESE) method. The relaxation rate 1/T(1) increases strongly over 5 decades in the temperature range 4-55 K. Various processes and mechanisms of T(1)-relaxation are discussed, and it is shown that the relaxation is governed mainly by Raman relaxation processes with the Debye temperature Theta(D)=204 K, with a detectable contribution from disorder in the doped Cu(2+) ions system below 12 K. An analytical approximation of the transport integral I(8) is given in temperature range T=0.025-10Theta(D) and applied for computer fitting procedures. Since the Jahn-Teller distorted configurations differ strongly in energy (delta(12)=240 cm(-1)), there is no influence of the classical vibronic dynamics mechanism on T(1). Dephasing of the ESE (phase relaxation) is governed by instantaneous diffusion and spectral diffusion below 20 K with resulting rigid lattice value 1/T(0)(M)=1.88 MHz. Above this temperature the relaxation rate 1/T(M) increases upon heating due to two mechanisms. The first is the phonon-controlled excitation to the first excited vibronic level of energy Delta=243 cm(-1), with subsequent tunneling to the neighbor potential well. This vibronic-type dynamics also produces a temperature-dependent broadening of lines in the ESEEM spectra. The second mechanism is produced by the spin-lattice relaxation. The increase in T(M) is described in terms of the spin packets forming inhomogeneously broadened EPR lines.     

Electron spin echo modulation and relaxation in polythiophene

Electron spin echo measurements on neutral poly (thiophene) show a clear modulation of the spin-echo decay. Analysis of the modulation and its Fourier transformed (ω) power spectrum indicates that the wave function of the spin defect is extended over ～ 25 proton nuclei. The functional behavior of the longitudinal relaxation, T₁, versus temperature is very similar to that observed previously for (CH)_x, although T₁ values for poly (thiophene) are significantly longer.     

Electron spin relaxation via vibronic level of rhodium(II) hexacyanide complex in KCl crystal

Electron spin-lattice relaxation rates for the low-spin [Rh(CN)(6)](4-) complex in KCl were measured by the inversion recovery and saturation recovery techniques, in the range of 5 to 30 K. Angular variation experiments indicate that electron spin-lattice relaxation times present axial symmetry. The data fit very well to a relaxation process involving localized anharmonic vibration modes, also responsible for the g tensor temperature dependence.     

Electron spin-lattice relaxation rates for high-spin Fe(III) complexes in glassy solvents at temperatures between 6 and 298 K

The temperature dependence of spin-lattice relaxation rates was analyzed for four high-spin nonheme iron proteins between 5 and 20 K, for three high-spin iron porphyrins between 5 and 118 K, and for four high-spin heme proteins between 5 and 150 to 298 K. For the nonheme proteins the zero-field splittings, D, are less than 0.7 cm(-1), and the relaxation is dominated by the Orbach and Raman processes. For the iron porphyrins and heme proteins D is between 4 and 12 cm(-1) and the relaxation is dominated by the Orbach process between about 5 and 100 K and by a local mode at higher temperatures. The relaxation rates for the heme proteins in glassy matrices extrapolated to values at room temperature that are similar to values obtained by NMR relaxivity in fluid solution. This similarity suggests that for high-spin Fe(III) heme proteins with effective intramolecular spin-lattice relaxation processes, the additional motional freedom gained when a relatively large protein goes from glassy solid to liquid solution at room temperature has little impact on spin-lattice relaxation.     

Electron spin relaxation in very diluted CdMnTe quantum wells

Electron spin dephasing is studied by time-resolved Kerr rotation in n-type modulation-doped CdMnTe quantum wells with very dilute Mn content. We find good agreement between measured and calculated electron spin relaxation times, considering relaxation induced by fluctuating exchange field created by the Mn spins, and taking into account inhomogeneous heating of the Mn spins by laser pulses.     

Synthesis, characterization and relaxivity of DTPA double alkyl esters heterocyclic gadolinium(III) complexes

The DTPA ligand modified by heterocyclic compound and linked through double alkyl ester covalent bond was synthesized by acylation reaction between diethylenetriamine pentaacetic (DTPA) bisanhydride and a novel heterocyclic compound. The corresponding paramagnetic Gd(III) complex was gained by the reaction of the DTPA ligand with GdCl3.6H2O. The structure of the ligand and its Gd(III) complex was characterized by elemental analysis, FTIR and 1H NMR, and the longitudinal relaxivity (R1) was measured. Besides, the magnetic resonance imaging of the new Gd(III) complex in vitro was studied. The result suggested that the stability of the complex was well, and when the Gd(III) quantity was identical, the R1 of the Gd(III) complex (5.12 mmol x L(-1) x s(-1)) was higher than the clinical magnetic resonance imaging contrast agent Gd-DTPA (3.64 mmol x L(-1).     

Ising-like model study of size dependence relaxation in spin crossover complexes

In this paper we present a theoretical study of size effects during relaxation in spin transition solids. The systems are described using an Ising-like model consisting of molecules having two energy levels and fictitious spin values of +1, (HS) and −1 (LS). We compare relaxation in various 2D or 3D systems (rectangular, hexagonal or cubic) and we realise an exhaustive analysis of the parameters that influence the relaxation in small size samples. The differences between homogenous and inhomogeneous systems reflected on the shapes of relaxation curves are discussed and analysed.     

Electron spin relaxation studies of impurity iron ions in ferroelectric lithium niobate

The nuclear hyperfine structure of dilute impurity iron ions in ferroelectric lithium niobate is investigated via⁵⁷Fe Mössbauer effect (ME). The ME spectra exhibit typical slow electron spin relaxation effects associated with Fe³⁺ ions in the⁶S_5/2 state, which are analysed using spin-Hamiltonian formalism. For Fe³⁺ ions, the principal axis of EFG tensor is found to be parallel to the crystallographic c-axis. The strong external magnetic field of 47 KOe is used to study magnetic and crystal field effects on the ME hyperfine structure.     

Electron spin resonance and antiferromagnetic resonance of single crystals of yttrium doped with gadolinium

The nonlinear interaction of oscillation modes is investigated on the basis of Lagrangian formalism. Equations describing the changes of the bound mode amplitudes versus time, are obtained. It is shown that the energy transformation between different modes is of a periodic nature: if in the initial moment of time an appreciable part of the energy is contained, for example, in them-th mode, then after a period of timeTt (called a time of nonlinear interaction) the energy will be transformed to then-th mode. Expressions forT _t for cases with the interaction of two and three modes are obtained. As a particular case the process of nonlinear interaction of the electron “transverse” and “longitudinal” oscillations in the highfrequency hybrid resonance region of a “weakly” inhomogeneous plasma was investigated.     

Electron spin resonance in manganese-doped BSCCO (2212) crystals

The electron spin resonance (ESR) spectra of undoped and manganese-doped BSCCO (2212) crystals (nominal composition Bi₂Sr₂CaCu_2–x Mn_xO_y, where x=0.1) are compared. Zh. Tekh. Fiz. 67, 137–138 (October 1997)