| All the time, Electron transfer is the essence in the physical, chemical and biological process. People have carried out a lot of research in the field of electron transfer and significant development was achieved both in theoretically and experimentally. Classification of mixed-valence compounds, calculation for electronic coupling constants and electron transfer kinetics are the main theoretical framework in electron transfer research. D-B-A compound, which is the model compound for studying electron transfer, contain electron donor (D), bridging ligand (B) and electron acceptor (A). Although people have designed and synthesized various D-B-A molecules, but the electron transition spectra of these model compounds are complicated. It gives rise to a difficulty in researching the intramolecular electron transfer mechanism. They cannot verify the consistency of CNS superexchange formalism and classical Hush theory. In our group, [Mo2] compound has a clear electronic configuration (σ2π4δ2). The optical, electronic, magnetic and redox properties of these compounds are concerned with δ electrons. Furthermore, energy level of δ electron in ground state and excited state can determine by electrochemistry and optical spectrum. The electronic feature of [Mo2] unit simplifies the complicated electron transition spectrum and in favors of researching electron transfer mechanism on molecular orbital level.Three new symmetrical dimolybdenum dimers bridged by 2,6-naphthalenedicarboxylic acid and the partially and fully thiolated derivatives have been synthesized. As generally denoted by [O2-(2,6-naph)-O2], [OS-(2,6-naph)-OS] and [S2-(2,6-naph)-S2]. X-ray structural analyses show that the complexes of naphthyl systems share the same molecular scaffold and small torsion angle between bridge and [M02] units. In addition, we have also analyze the nuclear magnetic resonance spectroscopy and electrochemistry. With the increase of sulfur atom on the bridge ligand, metal to ligand charge transfer (MLCT) absorption band has gradually red shifted from full oxygen-donor complexes of 499 nm to full sulfur-donor complexes of 673 nm and metal to metal charge transfer (MMCT) absorption band has gradually red shifted from full oxygen-donor complexes of 1658 nm to full sulfur-donor complexes of 3000 nm. It indicates that the electronic coupling between the dimetal units is gradually enhanced by replacing oxygen atoms to sulfur atoms step by step.To further explore the electronic coupling interaction of these compounds. The mixed-valence complexes, [O2-(2,6-naph)-O2]+, [OS-(2,6-naph)-OS]+, and [S2-(2,6-naph)-S2]+, were prepared by one-electron oxidation of the corresponding neutral compound with one equiv of ferrocenium hexafluorophosphate (Cp2FePF6). The mixed-valence compound has been characterized by UV-vis-NIR spectrophotometer. The electronic coupling matrix elements (Hab) of the naphthyl systems calculated from the Mulliken-Hush, these compounds belong to Class Ⅱ in terms of Robin-Day’s scheme.In order to further explore the influence of the electron transfer distance on the electronic coupling, we make a comparsion for the three systems with the same [Mo2] but different bridge (phenyl, naphenyl and biphenyl). It is clear that the electronci coupling effect (Hab) and electron transfer rate (ket) decay with the accepted decay laws, Hab, and ket are exponentially related to rab, by an attenuation factor(β) that reflects the intrinsic electronic characteristics of the bridge. The implication of these results is that the donor-acceptor separation is the major factor in affecting electronic coupling... |
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