Electronic dinuclear complexes

In the last few years McCleverty, Ward, and co-workers have reported the NIR electrochromic behavior of a series of mononuclear and dinuclear complexes containing the oxo-Mo(iv) v core unit [Mo(Tp )(0)Cl(OAr)], where Ar denotes a phenyl or naphthyl ring system [Tp = hydro-hydrotris(3,5-dimethylpyrazolyl)borate].184-189 Mononuclear complexes of this type undergo reversible MoIV/Mov and Mov/MoVI redox processes with all three oxidation states accessible at modest potentials. Whilst reduction to the MoIV state results in unremarkable changes in the electronic spectrum, oxidation to MoVI results in the appearance of a low-energy phenolate- (or naphtholate)-to-MoVI LMCT process.184,185... 

Dialkylzinc compounds have a tendency to form colored, and sometimes paramagnetic, adducts with 7r-acceptor ligands. The potentially bridging nitrogen donor pyrazine (and 4,4 -bipyridine) formed dinuclear complexes, Scheme 31, while the chelating 2,2 - bipyridine formed mononuclear adducts with diisopropylzinc.78 In the bis(diisopropylzinc)-pyrazine adduct 33, the presence of an unpaired electron was detected, but the resolution of the ESR spectra was insufficient for an unambiguous structural assignment. 

Even if one can create the SCO ligand-field around one end of a covalently-bridged dinuclear complex, the SCO might influence the ligand-field at the other end. There are many inter-dependent effects to bear in mind of a bonding, electronic and structural kind, and attempts to delineate these are given below. Inter-cluster or inter-chain effects will play difficult-to-control roles in crystalline SCO polynuclear materials, and these have already been alluded to for mononuclear complexes. 

An interesting aspect of the results is that catalysis by the IMDA complex proceeds via the one-electron instead of the four-electron path. The three empty coordination sites in this complex would allow simultaneous coordination of HA- and 02 and the formation of a dinuclear complex similar to the one formed with the Ru(III) ion. 

The dinuclear complex tru 5-[(NO)(py)4Ru(//-CN)Ru(py)4(CN)] has been prepared and spectroscopically characterized. Photoinduced extrusion of NO occurs when the complex is irradiated at the donor-acceptor CT band. Electronic coupling in the complex is discussed, as well as the results of controlled potential reduction (of NO) and oxidation (of Ru in the dicyano chromo-phore). " Bridging NO ligands are observed in [(acac)2Ru(/u-NO)2Ru(acac)2] which formally possesses a Ru2(NO)2 " " core. The complex exhibits two one-electron reductions (one reversible and the other irreversible) and an irreversible two-electron oxidation in which decomposition to cw-[Ru(NO)(MeCN)(acac)2] occurs. ... 

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