Electron delocalization in molecule-bridged polymetallic systems. Unique neutral complexes of TCNE or TCNQ and up to four organometallic fragments (C5R5)(CO)2Mn
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Inorganic Chemistry 29 (25): 5046--5053 (1990)

Electron transfer between the p-accepting TCNE or TCNQ (TCNX) ligands and p-electron-rich organometallic species (C5R5)(CO)2Mn(THF) (R = H, CH3) gave polynuclear complexes (C5R5)(CO)2Mnn(nn-TCNX) until full coordinative satn. is achieved at the nitrile grops (n = 4). IR spectroscopy points to the net transfer of one p electron to the TCNX acceptor ligand and indicates a highly sym. and strongly coupled situation for the tetranuclear complexes. The polynuclear complexes have intense (log e \textgreater 4.3) absorption bands in the near-IR region (0.8-1.5 mm-1), and the corresponding transitions may be formulated either as metal-to-metal (MnI $\rightarrow$ MnII) charge transfer in a localized, mixed-valence formulation or as n $\rightarrow$ n* transitions of polymetal-contg. p systems in a delocalized description. The polynuclear systems may serve as models for the MLCT excited states of sym. dimers and tetramers. Results from HMO calcns. involving d(p)-p(p) 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 addnl. complication, the complexes contain metal centers that possess an easily attainable intermediate-spin state (S = 1) despite their 18-valence-electron configuration. on SciFinder(R)
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