Microdynamic motion of tetrahedral clusters studied by 59Co and 99Ru NMR relaxations

Abstract

The microdynamic motions of the clusters A[MCo3(CO)12] (A = H, NEt4; M = Fe, Ru) and HFeCo3(CO)9[P(OCH3)3]3 have been studied for the first time using 59Co NMR spectroscopy. The chemical shift anisotropies and the quadrupolar coupling constants known from solid state NMR results allow a direct determination of the correlation times in solution by measuring the relaxation times at different temperatures. Most of the clusters behave as rigid spherical rotors with an activation energy nearly equal to that of the solvents. The phosphite derivative is a good example of the case where the mechanical properties are spherical although the shape is not spherical. From the 99Ru relaxation time measurements, the quadrupolar coupling constant of this nucleus is deduced.