[en] The chemistry of the trinuclear clusters (Ru ₃ O (C H ₃ CO ₂) ₄ L ₃) where L = imidazole, pyridine or pyrazine type of ligands, was investigated based on spectroscopic and electrochemical techniques. These complexes are of great interest from the point of view of their electronic and redox properties, providing multi site species for electron transfer processes. They were isolated in solid state, and characterized by means of elementary analyses and infrared spectra. The electrochemical behaviour in acetonitrile solution was typically reversible; the cyclic voltamograms exhibited a series of four or five mono electronic waves ascribed to the successive Ru ^IV Ru ^III Ru ^III / Ru ^III Ru ^III Ru ^III/ ... Ru ^II Ru ^II Ru ^II redox couples. The differences between the successive redox potentials were about 1 V, indicating strong metal-metal interaction in the trinuclear Ru ₃ O centre. The E values were strongly sensitive to the nature of the N-heterocyclic ligand, increasing with the pi-acceptor properties of the pyridine and pyrazine derivatives, but in a much less pronounced way in the case of the imidazole derivatives. (author)