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Strong Electronic Interaction between Two Dimolybdenum Units Linked by a Tetraazatetracene

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posted on 23.01.2006, 00:00 by F. Albert Cotton, Zhong Li, Chun Y. Liu, Carlos A. Murillo, Dino Villagrán
The large rigid dianion fluoflavinate, C14H8N42-, consisting of four fused and planar six-membered rings with four nitrogen donor atoms, has been used to link two metal-to-metal bonded and redox-active Mo2n+ units which are each locally bridged by three additional groups, collectively denoted [Mo2]. In 1, the [Mo2] units are Mo2(DAniF)3 (DAniF = N,N-di-p-anisylformamidinate), and in 5, they are trans-Mo2(DAniF)2(O2CCH3) groups. These [Mo2](fluoflavinate)[Mo2] compounds show three reversible one-electron oxidation steps, one more than all other [Mo2](linker)[Mo2] species known to date. The first two redox processes are metal-based, and the third one has been assigned to a ligand oxidation by comparison to that of paddlewheel compound 4 which contains only one dimolybdenum unit with a monoanionic fluoflavinate ligand. Chemical oxidations of 1 produce the singly- and doubly-oxidized species 2 and 3, respectively. All compounds have been characterized by X-ray crystallography and, as appropriate, by various techniques such as NMR, EPR, near-IR, and UV−vis. The fluoflavinate ligand strongly mediates electronic communication between the dimetal units, and the mixed valence species 2 can be described as electronically delocalized. Calculations at the DFT level using a variety of functionals support such an assignment and indicate that a strong transition in the NIR for the singly oxidized species can be assigned to the HOMO-1 to SOMO transition.