Ru-III complexes of the type [RuX(L)(2)(E)] (X = Cl or Br; L = novel bidentate Schi. base ligand; E = PPh3 or AsPh3) have been prepared by reacting [RuX3(E)(3)] or [RuBr3(PPh3)(2)(MeOH)] with two novel bidentate Schiff base ligands derived from 4-(1-methyl-1-mesitylcyclobutane-3-yl)-2-aminothiazole, in a 1:2 molar ratio in benzene, and characterised by analytical, spectral (i.r., electronic, H-1-, C-13-n.m.r., and e.p.r.) and electrochemical data. An octahedral structure has been tentatively proposed for all the new complexes. The thermal properties of the ligands and their complexes have been studied by t.g.a. The new Ru-III complexes are effective catalysts for the oxidation of alcohols to carbonyl compounds but are unable to oxidise alkenes in the presence of N-methylmorpholine-N-oxide (NMO) as co-oxidant. The antimicrobial activity of the ligands and complexes have also been tested against six microorganisms.