METAL-ORGANIC ION PAIRS WITH DITHIOOXALATE D(8) METAL DONORS AND VIOLOGENS - SPECTROSCOPIC, STRUCTURAL AND ELECTRONIC CHARACTERIZATION

摘要

Ion-pair charge-transfer complexes of the type {A(2+) [M(dto)(2)](2-)} where A(2+) represents bipyridinium and phenanthrolinium compounds of different redox potential, M = Ni, Pd, Pt, and dto = 1,2-dithiooxalate, were synthesized and characterized with respect to their spectroscopic, structural and electronic properties. A weak absorption band at the red-tail of the low-energy two-band system of the complex donor component can be attributed to the ion-pair charge-transfer (IPCT) transition type. As expected from electrochemical data, the IPCT band of these systems is markedly hypsochromically shifted compared with ion pairs containing dithiolene donors. The different nature of the highest occupied MO may offer an explanation for the distinct electro-and photochemical properties. Applying the Hush model reorganization energies are estimated in the range 107-125 kJ mol(-1) for the thermal electron transfer from [Ni(dto)(2)](2-) to the acceptor site. The amount of charge that is transferred from the donor to the acceptor (alpha(2)) is calculated as 10(-5) - 10(-6), lowered by 2-3 orders of magnitude compared with the metal dithiolenes. As shown by X-ray analysis of HEM[Ni(dto)(2)] (HEM = N-2-hydroxyethyl-N'-methyl-4,4'-bipyridiniumcation), the molecular structure consists of alternating donor-acceptor stacks with a typical plane-to-plane distance of 345 pm, In addition to supramolecular interactions both components are bonded by a hydrogen bridge between the OH group of the cation and the electron-rich oxygen of the dto ligand. [References: 50]