LONGITUDINAL NUCLEAR-RELAXATION IN AN A(2) SPIN SYSTEM INITIALLY POLARIZED THROUGH PARA-HYDROGEN

Os-3(CO)(10)(NCCH3)(2) has been hydrogenated with para-hydrogen to yie ld H2Os3(CO)(10) where the two hydrogen nuclei remain magnetically equ ivalent and therefore in a singlet state. Despite this equivalence, an enhanced longitudinal magnetization is observed to decrease toward th ermal equilibrium. It is postulated that this enhanced magnetization i s created through a nuclear relaxation interference mechanism (cross-c orrelation between dipolar interaction and chemical shift anisotropy); decay curves are then successfully analyzed by means of a spin relaxa tion theory adapted to this situation.