Slow-motion theory of nuclear spin relaxation in paramagnetic low-symmetrycomplexes: A generalization to high electron spin

The slow-motion theory of nuclear spin relaxation in paramagnetic low-symme try complexes is generalized to comprise arbitrary values of S. We describe the effects of rhombic symmetry in the static zero-field splitting (ZFS) a nd allow the principal axis system of the static ZFS tensor to deviate from the molecule-fixed frame of the nuclear-electron dipole-dipole tensor. We show nuclear magnetic relaxation dispersion (NMRD) profiles for different i llustrative cases, ranging from within the Redfield limit into the slow-mot ion regime with respect to the electron spin dynamics. We focus on S = 3/2 and compare the effects of symmetry-breaking properties on the paramagnetic relaxation enhancement (PRE) in this case with that of S = 1, which we hav e treated in a previous paper. We also discuss cases of S = 2, 5/2, 3, and 7/2. One of the main objectives of this investigation, together with the pr evious papers, is to provide a set of standard calculations using the gener al slow-motion theory, against which simplified models may be tested. (C) 2 000 Academic Press.