A crystallographic and kinetic study of the formation of the tricyanonitrido(pyridine-2-carboxylato-κN,κO)rhenate(V) ion, [ReN(η2-pic)(CN)3]2−

The reaction between [ReN(H2O)(CN)4]2− and pic− (pyridine-2-carboxylato anion) resulted in the substitution of the aqua and a cyano ligand from the coordination sphere to produce the title complex, [ReN(η2-pic)(CN)3]2−. The carboxylato oxygen of the pic− anion is bonded trans to the nitrido ligand with a Re–O bond distance of 2.289(3) Å while the pyridine nitrogen bonds cis with respect to the nitrido ligand at a bond distance of 2.169(3) Å. Two consecutive reactions were spectrophotometrically observed and kinetically investigated. The fast reaction is attributed to the aqua substitution of [ReN(H2O)(CN)4]2− with a forward rate constant of 1.92(5) × 10−1 M−1 s−1 at 40.3 °C, while a rate of 4.1(2) M−1 s−1 was observed for the reaction between the conjugate base [ReN(OH)(CN)4]3− and pic− at the same temperature. The second, slower reaction is attributed to the cyano substitution with a rate constant of 1.84(2) × 10−2 s−1 at 80 °C. Negative entropy of activation of −133.4(3) J K−1 mol−1 for the slow reaction points to associative activation.

Graphical abstractThe substitution reaction between [ReN(H2O)(CN)4]2− and pic− (pyridine-2-carboxylato anion) resulted in the substitution of the aqua and cyano ligands to form the [ReN(η2-pic)(CN)3]2− complex. The two consecutive reactions were kinetically investigated with the fast aqua substitution resulting in a rate constant of 1.92(5) × 10−1 M−1 s−1 at 40.3 °C. A rate constant of 1.84(2) × 10−2 s−1 at 80 °C was obtained for the second, slower cyano substitution. The negative entropy of activation of −133.4(3) J K−1 mol−1 for the slow reaction points to associative activation.Figure optionsDownload full-size imageDownload as PowerPoint slide