Cyanopyridine Complexes of Pentaammineruthenium(II)

The nitrile-coordinated pentaammineruthenium(II) complexes of 2-, 3-, and 4-cyanopyridine are described. In each case, coordination of the nitrile results in a negative shift in the carbon-nitrogen triple bond stretching frequency (v(CN)). Protonation of the pyridine nitrogen results in an even greater decrease in v(CN) from the free-ligand value (where the free ligand is the cyanopyridinium salt). Using spectral techniques, the protonation constants of the nitrile-coordinated pentaammine(cyanopyridine)ruthenium(II) complexes were determined. Each of these complexes is more basic than the corresponding uncoordinated cyanopyridine having p.K.'s 0.80, 1.75, and 2.72 for coordinated 2-, 3-, and 4-cyanopyridine, respectively, compared to -0.26, 1.45, and 1.90 for the respective free cyanopyridines.