Areneruthenium(II) molecular complexes of the formula [Ru(arene)(Q)Cl], containing diverse 4-acyl-5-pyrazolonate ligands Q with arene = cymene or benzene, have been synthesized by the interaction of HQ and [Ru(arene)Cl-(mu-Cl)](2) dimers in methanol in the presence of sodium methoxide. The dinuclear compound [{ Ru(cymene)Cl}(2)Q4Q] (H(2)Q4Q = bis(4-(1-phenyl-3-methyl-5-pyrazolone)dioxohexane), existing in the RRuSRu (meso form), has been prepared similarly. [Ru(cymene)(Q)Cl] reacts with sodium azide in acetone, affording [Ru(cymene)(Q)N-3] derivatives, where Cl- has been replaced by N-3(-). The reactivity of [Ru(cymene)(Q)Cl] has also been explored toward monodentate donor ligands L (L = triphenylphosphine, 1-methylimidazole, or 1-methyl-2-mercaptoimidazole) and exo-bidentate ditopic donor ligands L-L (L-L = 4,4 '-bipyridine or bis(diphenylphosphino)propane) in the presence of silver salts AgX (X = SO3CF3 (0I)center dot ClO4), new ionic mononuclear complexes of the formula [Ru(cymene)(Q)L]X, and ionic dinuclear complexes of the formula [{Ru(cymene)(Q)}(2)L-L]X-2 being obtained. The solid-state structures of a number of complexes were confirmed by X-ray crystallographic studies, Their redox properties have been investigated by cyclic voltammetry and controlled potential electrolysis, which, on the basis of their measured Ru-II/III reversible oxidation potentials, have allowed the ordering of the bidentate acylpyrazolonate ligands according to their electron-donor character and are indicative of a small dependence of the HOMO energy upon the change of the monodentate ligand. This is accounted for by DFT calculations, which show a relevant contribution of acylpyrazolonate ligand orbitals to the HOMOs, whereas that from the monodentate ligand is minor.