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Tuning the Electronic Coupling and Electron Transfer in Mo 2 Donor–Acceptor Systems by Variation of the Bridge Conformation
Author(s) -
Kang Mei Ting,
Meng Miao,
Tan Ying Ning,
Cheng Tao,
Liu Chun Y.
Publication year - 2016
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201504033
Subject(s) - intramolecular force , chemistry , homo/lumo , superexchange , crystallography , electron transfer , acceptor , dihedral angle , ligand (biochemistry) , phenylene , bridging ligand , photochemistry , stereochemistry , hydrogen bond , molecule , crystal structure , ion , physics , receptor , biochemistry , organic chemistry , condensed matter physics , polymer
Assembling two quadruply bonded dimolybdenum units [Mo 2 (DAniF) 3 ] + (DAniF= N,N′ ‐di( p ‐anisyl)formamidinate) with 1,4‐naphthalenedicarboxylate and its thiolated derivatives produced three complexes [{Mo 2 (DAniF) 3 } 2 (μ‐1,4‐O 2 CC 10 H 6 CO 2 )], [{Mo 2 (DAniF) 3 } 2 (μ‐1,4‐OSCC 10 H 6 COS)], and [{Mo 2 (DAniF) 3 } 2 (μ‐1,4‐S 2 CC 10 H 6 CS 2 )]. In the X‐ray structures, the naphthalene bridge deviates from the plane defined by the two Mo−Mo bond vectors with the torsion angle increasing as the chelating atoms of the bridging ligand vary from O to S. The mixed‐valent species exhibit intervalence transition absorption bands with high energy and very low intensity. In comparison with the data for the phenylene analogues, the optically determined electronic coupling matrix elements ( H ab =258–345 cm −1 ) are lowered by a factor of two or more, and the electron‐transfer rate constants ( k et ≈10 11 s −1 ) are reduced by about one order of magnitude. These results show that, when the electron‐transporting ability of the bridge and electron‐donating (electron‐accepting) ability of the donor (acceptor) are both variable, the former plays a dominant role in controlling the intramolecular electron transfer. DFT calculations revealed that increasing the torsion angle enlarges the HOMO–LUMO energy gap by elevating the (bridging) ligand‐based LUMO energy. Therefore, our experimental results and theoretical analyses verify the superexchange mechanism for electronic coupling and electron transfer.