NUCLEAR-MAGNETIC-RESONANCE STUDIES OF MULTINUCLEAR CHROMIUM ASSEMBLIES

H-1 NMR and H-2 NMR resonances of a series of oxo-centred trinuclear chromium complexes of the form [Cr3O(O2CR)6(L)3]+ (R = -CH3, -CH2CH3, -Ph, -4-MePh; L = H2O, py, 2-Mepy, 3-Mepy, 4-Mepy) have been observed and assigned. The role of pi- and sigma-bonding frameworks in the delocalization of unpaired electron density onto the ligand protons is examined. The pi-delocalization mechanism dominates where ligands contain aromatic substituents or carboxylate functionalities, consistent with the presence of a metal centre where unpaired electrons reside solely in t2g orbitals. A comparison of the importance of these mechanisms with that in trinuclear manganese and iron complexes is reported. These results suggest that H-1 and H-2 NMR studies could be useful probes of proteins containing coupled multinuclear chromium assemblies.