R. Benedix et al., METAL-ORGANIC ION-PAIRS WITH DITHIOOXALATE D(8) METAL DONORS AND VIOLOGENS - SPECTROSCOPIC, STRUCTURAL AND ELECTRONIC CHARACTERIZATION, Inorganica Chimica Acta, 262(2), 1997, pp. 177-185
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-dithiooxalat
e, were synthesized and characterized with respect to their spectrosco
pic, structural and electronic properties. A weak absorption band at t
he red-tail of the low-energy two-band system of the complex donor com
ponent can be attributed to the ion-pair charge-transfer (IPCT) transi
tion type. As expected from electrochemical data, the IPCT band of the
se systems is markedly hypsochromically shifted compared with ion pair
s containing dithiolene donors. The different nature of the highest oc
cupied MO may offer an explanation for the distinct electro-and photoc
hemical properties. Applying the Hush model reorganization energies ar
e estimated in the range 107-125 kJ mol(-1) for the thermal electron t
ransfer from [Ni(dto)(2)](2-) to the acceptor site. The amount of char
ge that is transferred from the donor to the acceptor (alpha(2)) is ca
lculated as 10(-5) - 10(-6), lowered by 2-3 orders of magnitude compar
ed with the metal dithiolenes. As shown by X-ray analysis of HEM[Ni(dt
o)(2)] (HEM = 2-hydroxyethyl-N'-methyl-4,4'-bipyridiniumcation), the m
olecular structure consists of alternating donor-acceptor stacks with
a typical plane-to-plane distance of 345 pm, In addition to supramolec
ular interactions both components are bonded by a hydrogen bridge betw
een the OH group of the cation and the electron-rich oxygen of the dto
ligand.