The syntheses of pentaammineruthenium(I1) and pentaammineruthenium(II1) complexes of pyridine and analogous aromatic nitrogen heterocycles are reported here. The pentaammineruthenium(I1) complex of each of these heterocyclic ligands has an intense absorption band in the visible region which, on the basis of evidence presented below, is assigned to a metal-to-ligand charge-transfer transition. The pentaamminepyrazineruthenium-(11) complex ion can be protonated in a reversible fashion, presumably at the noncoordinated nitrogen of the 1,4-diazine. The pK, of this complex demonstrates that the dipositive ion is approximately two orders of magnitude more basic than the free ligand. This result and related data are interpreted in terms of ground-state ir back-bonding from the ruthenium(I1) to the aromatic ligand. e undertook the present work in the hope that com-

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The position of bond breaking is not known for the aquation of either the chloratoor nitratochromium(111) complex. (16) The reactions are balanced only with respect to chromium and chlorine.The formulation for the higher charged product is speculative. [See (a)

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