Mechanism of nucleophilic substitution in chromium(III) complexes. III. formation of Azidopentamminechromium(III) ion from aquopentamminechromium(III) ion in NaN3–HN3 buffer media

Abstract

AbstractThe kinetics of formation of [Cr(NH3)5N3]2+ in the reaction of [Cr(NH3)5(OH2)3+] in NaN3–HN3 buffer media (pH ca. 3.4–4.3) has been studied spectrophotometrically under different conditions for elucidation of reaction mechanism. The reaction occurs in two concurrent paths involving reactions of the aquo complex and its conjugate base (the hydroxo complex) with azide ion (gross rate constants k1 and k2 respectively). Results, including values of the activation parameters (ΔH≠ and ΔS≠) are in agreement with SN1 IP mechanism for both the paths. The observed relativ nucleophilicityo of N3− compared to that reported in literature for Cl− and NCS− is N > NCS− > Cl−.