Electron and nuclear spin relaxation in S = ½ paramagnetic transition-metal complexes

1977 ◽  
Vol 30 (8) ◽  
pp. 1635 ◽  
Author(s):  
DM Doddrell ◽  
DT Pegg ◽  
MR Bendall ◽  
AK Gregson
Keyword(s):  
Transition Metal ◽  
Metal Complexes ◽  
Transition Metal Complexes ◽  
Spin Relaxation ◽  
Nuclear Spin ◽  
Magnetic Transition ◽  
Nuclear Spin Relaxation ◽  
Relaxation Processes ◽  
Electron Spin Relaxation ◽  
Van Vleck

Nuclear spin relaxation in some S = 1/2 paramagnetic transition-metal complexes is considered. If rotational reorientation dominates the electron and nuclear spin relaxation processes current theoretical treatments of spin relaxation provide an adequate description of the spin relaxation. However, there are many complexes where other time processes appear to be important. It is suggested that dynamic Jahn- Teller effects may be operative in Ru(acac)3. ��� It is shown that the rotational Van Vleck mechanism is effectively the same relaxation mechanism as the so-called ?g-tensor? process. Although the Van Vleck mechanism is a useful reformulation of the same problem, it appears that this mechanism or any other rotationally induced electron spin relaxation process cannot adequately describe the nuclear relaxation times in a variety of para-magnetic transition-metal complexes.

Intramolecular reorientation, an electron spin relaxation process in solutions of discrete paramagnetic transition-metal complexes

1978 ◽  
Vol 31 (11) ◽  
pp. 2355 ◽  
Author(s):  
DM Doddrell ◽  
DT Pegg ◽  
MR Bendall ◽  
AK Gregson
Keyword(s):  
Transition Metal ◽  
Metal Complexes ◽  
Temperature Dependence ◽  
Transition Metal Complexes ◽  
Spin Relaxation ◽  
Electron Spin ◽  
Potential Energy Profile ◽  
Methyl Proton ◽  
Electron Spin Relaxation ◽  
Time Modulation

Time modulation of the g-tensor by intramolecular reorientation between structurally equivalent molecular arrangements is postulated to dominate electron spin relaxation in solutions of some paramagnetic transition-metal complexes. The process is treated theoretically and it is shown that the resulting electron spin relaxation time depends on the correlation time for intramolecular reorientation. The temperature dependence of the nuclear T1 thus yields information concerning the potential energy profile for intramolecular reorientation. Experimental results on the field dependence of the temperature dependence of T1 of the methyl proton in Ru(acac)3 are in accord with the theory.

Frequency dependence of nuclear spin relaxation in paramagnetic transition-metal complexes

1976 ◽  
Vol 29 (9) ◽  
pp. 1885 ◽  
Author(s):  
DT Pegg ◽  
DM Doddrell
Keyword(s):  
Transition Metal ◽  
Metal Complexes ◽  
Frequency Dependence ◽  
Transition Metal Complexes ◽  
Spin Relaxation ◽  
Nuclear Spin ◽  
Relaxation Times ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Zero Field

Proton spin-lattice relaxation times have been determined as a function of magnetic field strength (H0) for a series of paramagnetic transition-metal complexes chosen so that, for some, the electron spin relaxation times (te) fall in the Redfield limit (te � tr) while for others te << tr being the rotational correlation time. When te � tr dominates the nuclear relaxation and the experimental results can be readily explained by Redfield theory. When te << tr current theory predicts the nuclear T1 values to get longer as H0 decreases. This is not observed experimentally. This can only be explained by using non-Redfield relaxation theory and by assuming the spacings of the electron-nuclear spin energy levels are not dominated by H0. It is shown that, although the trace of the zero-field splitting tensor is zero TrD = 0 because TrD is averaged by tr when te < tr the value of Dzz is important in determining the energy-level spacings. By this approach the frequency dependence can be explained. Experimentally, it is shown that a Phase Alternating Pulse Sequence (PAPS) is required to measure T1. The problem originates from interference from transverse magnetization. A density matrix theory of the PAPS sequence is presented.

Electron and nuclear spin relaxation in paramagnetic transition-metal complexes with S = 1. The effects of a non-zero average zero-field splitting on the spin energy levels

1978 ◽  
Vol 31 (3) ◽  
pp. 475 ◽  
Author(s):  
DT Pegg ◽  
DM Doddrell
Keyword(s):  
Transition Metal Complexes ◽  
Spin Relaxation ◽  
Energy Levels ◽  
Nuclear Spin Relaxation ◽  
Zero Field ◽  
Zero Field Splitting ◽  
Field Splitting ◽  
Electron Spin Relaxation ◽  
Spin Lattice ◽  
Splitting Constant

The effects of a non-zero average zero-field splitting on electron spin relaxation in paramagnetic (S = 1) complexes is treated theoretically. The spin-lattice interaction is postulated to be a simple scalar P(t). S process with correlation time Ti. This process is assumed not to modulate the zero-field splitting which, however, is modulated by the molecular tumbling. The frequency dependence of the nuclear relaxation time (Tl) now depends on the magnitude of the zero-field splitting constant (D), and, for large values of D, the value of T1 is independent of the applied field strength.

Nuclear spin relaxation in paramagnetic complexes of S=1: Electron spin relaxation effects

1999 ◽  
Vol 111 (13) ◽  
pp. 5795-5807 ◽  
Author(s):  
Ivano Bertini ◽  
Jozef Kowalewski ◽  
Claudio Luchinat ◽  
Tomas Nilsson ◽  
Giacomo Parigi
Keyword(s):  
Spin Relaxation ◽  
Electron Spin ◽  
Nuclear Spin ◽  
Nuclear Spin Relaxation ◽  
Electron Spin Relaxation ◽  
Relaxation Effects ◽  
Paramagnetic Complexes
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