A first radical cation chelate ligand: electron paramagnetic resonance spectra of singly reduced 3,3′-diazamethylviologen, DAMV˙+and the rhenium(I) complex [(DAMV˙+)Re+(CO)3(PPh3)]2+

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Abstract
Diquaternization of 4,4′-bipyrimidine with methyl or ethyl in the 1,1′-position leads to 3,3′-diaza analogues of the well known methylviologen redox system. The radical cation intermediates of the new redox systems are formed at less negative potentials, they display higher stability constants and absorption energies in the visible. EPR measurements and hyperfine analysis based on HMO/McLachlan calculations of π spin populations reveal how the overall spin distribution is affected by the introduction of additional nitrogen centres. The increased stability of the radical cation and the availability of two metal chelating coordination centres allows one to use this system as a cationic spin label ligand for metal centres. The paramagnetic complex with Re+(CO)3(PPh3) thus displays a fairly well resolved EPR spectrum, dominated by a relatively small 185,187Re isotope coupling.

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