ELECTRON DELOCALIZATION IN MOLECULE-BRIDGED POLYMETALLIC SYSTEMS - UNIQUE NEUTRAL COMPLEXES OF TCNE OR TCNQ AND UP TO 4 ORGANOMETALLIC FRAGMENTS (C5R5)(CO)2MN

Electron transfer between the x-accepting TCNE or TCNQ (TCNX) ligands and x-electron-rich organometallic species (C5R5)(CO)2Mn(THF) (R = H, CH3) results in the formation of polynuclear complexes [equation omitted] until full coordinative saturation is achieved at the nitrile groups (n = 4). Infrared spectroscopy points to the net transfer of one x electron to the TCNX acceptor ligand and indicates a highly symmetrical and strongly coupled situation for the tetranuclear complexes. The polynuclear complexes have intense ([equation omitted]) absorption bands in the near-infrared region (0.8–1.5 gm), and the corresponding transitions may be formulated either as metal-to-metal ([equation omitted]) charge transfer in a localized, mixedvalencc formulation or as [equation omitted] transitions of polymetal-containing x systems in a delocalized description. The polynuclear systems may serve as models for the MLCT excited states of symmetrical dimers and tetramers. Results from Hiickel molecular orbital calculations involving [equation omitted] bonding correlate with the changes in absorption energies on successive polynucleation. The small energy differences between frontier orbitals are confirmed by results from cyclic voltammetry. As an additional complication, the complexes contain metal centers that possess an easily attainable intermediate-spin state (S = 1) despite their 18-valence-electron configuration. © 1990, American Chemical Society. All rights reserved.