Spin relaxation of quadrupolar nuclei in T_d-oxo-complexes

Abstract

The relaxation rates R ₁ and R ₂ of quadrupolar nuclei M in T_d -oxocomplexes MO ₄ ^n- (M ≡ ^35,36,37Cl, ^79,81Br, ^95,97Mo, ^50,51V, ^99,101Ru, ⁵⁵Mn, ⁵³Cr, ⁹⁹Tc, ¹⁸⁷Re) in solution have been measured for the temperature range -60 to +100°C. The R ₁ temperature dependence for some nuclei was found to show a minimum. The spin-lattice relaxation of the M nuclei is determined only by the quadrupole mechanism and a model of this relaxation mechanism for the central nuclei in T_d -complexes has been given. The EFG is due to internal vibrations of the polyatomic ions and to the external charged particles in solution. The presence of the minimum in R ₁ ^Q(T) is caused by Boltzmann factors which depend on the relations between ħω₁ (vibrational energies) and the energy of diffusive motion of the complex.