Preparation and properties of a series of (μ-oxo)di(μ-acetato) diruthenium(III) complexes, [Ru2(μ-O)(μ-CH3COO)2(pyridine)4(L)2]2+ and [Ru2(μ-O)(μ-CH3COO)2(AA)2(L)2]2+, where AA is 2,2′-bipyridine or 1,10-phenanthroline, and L is a monodentate ligand