Inner-Sphere Cluster Formation by [Ru(NH(3))(5)H(2)O](3+) or [Os(NH(3))(5)H(2)O](3+) in Combination with [M(CN)(6)](4)(-) (M = Fe, Ru, or Os).

Abstract

When the cations [M'(NH(3))(5)H(2)O](3+) or [M'(NH(3))(5)H(2)O](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'(NH(3))(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(NH(3))(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(III) show also the [Ru(NH(3))(5)](2+) --> [Ru(NH(3))(5)](3+) CT transition. While [Ru(NH(3))(5)](2+) has little effect on M(II) --> M'(III) CT absorption, accumulation 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(NH(3))(5)](2+) --> [Ru(NH(3))(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 Ru(II)CNRu(III) linkage causing a shift to higher energy. This interpretation is in accord with the deep seated degradation of the clusters which occurs whenever [Ru(NH(3))(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).