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

Abstract

The reaction between [ReN(H 2O)(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(η 2-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(H 2O)(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.