The isomeric title complexes were obtained in almost equimolar ratio from the reaction of Ru(trpy)Cl3 and L. Crystal structure analyses of the perchlorate hemihydrates, electrochemical and spectroscopic (NMR, UV/VIS, EPR) studies, supported by DFT calculations, reveal distinct differences between the isomeric redox series [1]n+
(tetrazine-Nttrans to Cl) and [2]n+
(pyrazolyl-Nptrans to Cl; n
= 0, 1, 2). The latter system with the π acceptors trpy and tetrazine in the equatorial plane and the pyrazolyl and chloride donors in the axial positions exhibits facilitated oxidation, lower energy MLCT transitions, more balanced chelate coordination, and a higher g anisotropy in the oxidised (RuIII) state. According to partially resolved EPR spectra of one-electron reduced neutral compounds 1 and 2 they have the unpaired electron predominantly in the tetrazine ring of L.
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