Distinguishing the Strength of Electronic Coupling for Mo-2-Containing Mixed-Valence Compounds within the Class III Regime

摘要

Two, symmetrical, mixed-valence (MV), complex cations{[Mo-2(DAniF)(3)](2)(-oxamidate)}(+) (1(+)) and {Mo-2(DAniF)(3)](2)(-dithiooxamidate)}(+) (2(+); DAniF=N,N-di(p-anisyl)formamidinate)are significantly differentiated in terms of electronic coupling between the two [Mo-2] units. For 1(+) the intervalence (IV) charge-transfer band in the near-IR spectrum is truncated in half on the low-energy side as predicted for MV compounds at the Class II-III limit (2H(ab)/=1; for which H-ab=electronic coupling matrix element and =reorganization energy). In contrast, the very strongly coupled analogue 2(+), as indicated by 2H(ab)/=3.5 (1), exhibits a higher energy and more symmetrical IV band. As rare examples, this pair of MV species shows distinct optical behaviors for MV systems crossing the ClassIII region. Optical analysis and DFT calculations are carried out to elucidate the transformation from vibronic to electronic vertical transition.