Intramolecular energy transfer processes in binuclear Re-Os complexes.

A series of bimetallic complexes of general formula [(phen)Re(CO)(3)LOs(trpy)(bpy)](3+) (bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, trpy = 2,2':6',2' '-terpyridine, and L = 4,4'-bipyridine (4,4'-bpy), trans-1,2-bis(4-pyridyl)ethylene (t-bpe), or 1,2-bis(4-pyridyl)ethane (bpa)) and the model mononuclear species [(phen)Re(CO)(3)L](+) and [Os(trpy)(bpy)L](2+) have been synthesized and their photophysical and photochemical properties studied. In the binuclear species an efficient Re(I)-Os(II) energy transfer is observed, which is analyzed in terms of Förster theory. In the binuclear [(phen)Re(CO)(3)(t-bpe)Os(trpy)(bpy)](3+) complex, the trans to cis isomerization of the coordinated t-bpe ligand, characteristic of the [(phen)Re(CO)(3)(t-bpe)](+) subunit, is inhibited by competitive intramolecular energy transfer.