Optoelectronics of Mixed-Valence Transition Metal Complexes

 

Data are discussed which provide benchmark parameters for valence trapped dicarboxylate bridge complexes of the type [(tBuCO2)3MM']2(μ-O2C-X-CO2) (M, M' = Mo, W) and for the related paddlewheel oligomers and polymers. The electronic and vibrational spectroscopic properties of MM'(O2CBut)4 (M, M' = Mo, W) pertaining to their single electron oxidized radical cations have been measured. The radical cations of these species have been prepared by in situ oxidation with Cp2FePF6 and have been spectroscopically probed. The Raman, UV/Vis, and EPR spectroscopic parameters of these neutral and oxidized species are compared with recent predictions of the molecular and electronic structure of the analogous acetates, performed using density functional theory. EPR spectroscopy corroborates theoretical predictions that the single electron of MoW(O2CBut)4+ resides in a polarized MM δ orbital having 70% Mo and 30% W character. Measurements are also reported of the third-order nonlinear optical responses of solutions of the paddlewheel complexes M2(O2CBut)4 and M2Cl4(PMe3)4 (M = Mo, W), as well as of the metal-metal triply-bonded complexes Mo2(OPri)6, W2(OPri)6, and M2(NMe2)6, using picosecond degenerate four-wave mixing at 1064 nm. These complexes display only very small instantaneous electronic polarizations when excited with cross-polarized beams. As well, the preparation and phase properties of the Mo24+ and Ru24+ complexes of the benzoate of a liquid crystalline benzoic acid are described, as is an EPR investigation of partially oxidized liquid crystalline Mo2(O2C(CH2)6CH3)4.

          EPR, electronic absorption, and resonance Raman spectroscopic data reveal that in the oxalate-bridged compounds, [[(tBuCO2)3M2]2(μ-O2CCO2)]+[PF6]-, the unpaired electron is delocalized over four metal centers (M = Mo or W) as a result of M2 δ to bridge π conjugation, but in the related cationic perfluoroterephthalate-bridged species, the tungsten complex is delocalized and the molybdenum analogue valence trapped. The molybdenum radical cations are unstable, and mass spectroscopy reveals that a variety of higher-order aggregates likely result from their disproportionation. The electronic delocalization in the dimeric analogues with the bridges 2,5-thienyldicarboxylate and 9,10-anthracenedicarboxylate, as revealed by EPR spectroscopy, is also described. Finally, preliminary evidence is presented for the formation of the complex [MoW(O2CBut)3]2(μ-O­2CCO2).

 

“Cations M2(O2CtBu)4+, where M = Mo and W, and MoW(O2CtBu)4+. Theoretical, spectroscopic, and structural investigations.”

Pate, B. D.; with Chisholm, M. H.; D'Acchioli, J. S.; Patmore, N. J.; Dalal, N. S.; Zipse, D. J.

(authors alphabetized)

Inorganic Chemistry 44 (2005) 1061-7.

 

“9,10-Anthracene dicarboxylate bridged complexes with M2 quadruply bonded dimetal units: [{M2(O2CtBu)3}2(΅-9,10-An(CO2)2)], where M = Mo or W.”

Pate, B. D.; with Byrnes, M. J.; Chisholm, M. H.; Dye, D. F.; Hadad, C. M.; Wilson, P. J.; Zaleski, J. M.

(authors alphabetized)

Dalton Transactions (2004) 523-9.

 

“Preparation and physical properties of molecular materials based on metalloporphyrazines (M = Co, Ni, Cu, Zn) and paddlewheel complexes (M = Mo, W, Ru).”

Pate, B. D.

Doctoral Thesis (2004).

 

 “On the electron delocalization in the radical cations formed by oxidation of MM quadruple bonds linked by oxalate and perfluoroterephthalate bridges.”

Pate, B. D.; with Chisholm, M. H.; Wilson, P. J.; Zaleski, J. M.

(authors alphabetized)

Chemical Communications (2002) 1084-5.

 

 “Third-order nonlinear optical properties of complexes with MM triple and quadruple bonds (M = Mo, W) at 1064 nm by degenerate four-wave mixing.”

Pate, B. D.; Thorne, J. R. G.; Click, D. R.; Chisholm, M. H.; Denning, R. G.

Inorganic Chemistry 41 (2002) 1975-8.

 

 

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