MICRODYNAMIC MOTION OF TETRAHEDRAL CLUSTERS STUDIED BY CO-59 AND RU-99 NMR RELAXATIONS

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 th e first time using Co-59 NMR spectroscopy. The chemical shift anisotro pies and the quadrupolar coupling constants known from solid state NMR results allow a direct determination of the correlation times in solu tion by measuring the relaxation times at different temperatures. Most of the clusters behave as rigid spherical rotors with an activation e nergy nearly equal to that of the solvents. The phosphite derivative i s a good example of the case where the mechanical properties are spher ical although the shape is not spherical. From the Ru-99 relaxation ti me measurements, the quadrupolar coupling constant of this nucleus is deduced.