STRUCTURAL AND SPECTROSCOPIC EVIDENCE OF DELOCALIZATION IN CYANIDE-BRIDGED TRINUCLEAR COMPOUNDS

MELINA B. ROSSI; PABLO ALBORES; LUIS M. BARALDO

Salt Lake City - USA

Congreso; 237th ACS National Meeting; 2009

Continuing our exploration of the properties of cyanide bridged compounds, we have prepared the trinuclear compound trans-[(DMAP)4RuII{(m-NC)OsIII(CN)5}2]4-(DMAP = 4-dimethylaminopyridine). The crystal structure of the Ph4P+ salt of this compound shows significant differences with its Fe analogue and suggest that the redox state of the metals are intermediate between +2 and +3, as a result of delocalization of the electron. For example, the average NDMAP-Ru distance (2.089 Å) has a value that is significantly shorter than the 2.104 Å value observed in trans-[(DMAP)4RuII{(m-NC)FeIII(CN)5}2]4-, but larger than the value of 2.069 Å observed for trans-[(DMAP)4RuIII{(m-NC)FeIII(CN)5}2]3-. This delocalization has its origin in the interaction between the dp orbitals of the metals promoted by the cyanide bridges. This interaction results in a considerably shortening of the Ru-NNitrile and the Os-C bonds and an elongation of the C-N distance for the cyanide bridge. Other properties of the complexes, like its electrochemistry and electronic spectroscopy, also reflects this phenomena. For example, in methanol, the reduction of the Os moieties is separated by 600 mV. The interpretation of the electronic spectroscopy is difficult, due to the presence of two Os centers. To avoid this complication we have prepared another trinuclear complex, where we have replaced an Os by a Co(III) ion. The NIR spectroscopy of this compound, in methanol, also shows evidence of delocalization.