When the cations [M'(NH3)(5)H2O](3+) or [M'(NH3)(5)H2O](2+) (M' = Ru, Os) are added in excess of the co-reactants [M(CN)(6)](4-) (M = Fe, Ru, Os), inner-sphere binding ends abruptly at the 4:1 ratio. The [M(CN)(6)](4-) --> [M'(NH3)(5)](3+) charge transfer (CT) absorption shifts slightly to higher energy as the cations accumulate in the cluster, and there is a progressive decrease in intensity per additional oscillator introduced. The absorption bands and the electrochemical properties reveal the presence of isomeric forms in complexes of order 2 and above. The successive stages of reduction of [Ru(NH3)(5))](3+) take place in a narrow range of potentials, despite the close proximity of the peripheral cations in a cluster. Clusters containing Ru(II) and Ru(m) show also the [Ru(NH3)(5)](2+) --> [Ru(NH3)(5)](3+) CT transition. While [Ru(NH3)(5)](2+) has little effect on M(II)--> M'(III) CT absorption, acculation of M'(III) in a cluster containing the M'(II) --> M'(III) oscillator, despite an increase in the number of these oscillators, leads to no significant increase in the intensity. The energy of the [RU(NH3)(5)](2+) --> [Ru(NH3)(5)](3+) transition is 1500 cm(-1) greater when M = Ru than when it is Fe or Os, for which it appears at 8000 cm(-1). This difference is attributed to rapid isomerization of the (RuCNRuIII)-C-II linkage causing a shift to higher energy. This interpretation is in accord with the deep seated degradation of the clusters which occurs whenever [Ru(NH3)(5)](2+)) is present (complete loss of the M'(II) --> M'(III) and M(II) --> M'(III) oscillators), which is most rapid when M=Ru(II).