O-17 NMR-STUDY OF METAL-CARBONYL CLUSTER COMPOUNDS .4. THE SUBSTITUENT EFFECT ON THE O-17 NMR CHEMICAL-SHIFTS FOR A SERIES OF TRI-NUCLEAR METAL-CARBONYL CLUSTER COMPOUNDS

17O NMR spectra have been measured for series of cobalt carbonyl cluster derivatives, RCCo3(CO)(9-x)- (PPh3)(x), (RC2R')Co(3-x-y)Fe(x)Mo(y)(CO)(9-y)Cp(y), and R(3-x)Sn[Co(CO)4](x+1). The small 17O-chemical shift differences due to the change of R and/or introduction of PPh3 have been interpreted in terms of the electron buffer action of the Co3 core for RCCo3(CO)(9-x)(PPh3)(x). Good linear correlations between 17O-chemical shifts and CO stretching frequencies have been observed for these derivatives. Some effect of the magnetic anisotropy resulted from the ring current along the metal-triangle on 17O-chemical shifts has been suggested for metal-triangle clusters.