A crystallographic and kinetic study of the formation of the tricyanonitrido(pyridine-2-carboxylato-kappa N,kappa O)rhenate(V) ion, [ReN(eta(2)-pic)(CN)(3)](2-)

摘要

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(eta(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) angstrom while the pyridine nitrogen bonds cis with respect to the nitrido ligand at a bond distance of 2.169(3) angstrom. 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) x 10(-1) M-1 s(-1) at 40.3 degrees 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) x 10(-2) s(-1) at 80 degrees C. Negative entropy of activation of -133.4(3) J K-1 mol(-1) for the slow reaction points to associative activation. (c) 2006 Elsevier Ltd. All rights reserved.