Formation and kinetics of decomposition of monoaquobis(ethylenediamine)(pyridylmethyl)chromium(III) complexes

Abstract

Monoaquobis(ethylenediamine)(pyridylmethyl)chromium(III) complexes, 2-NC₅H₄CH₂Cr(en)₂(H₂O)²⁺ and 3-NC₅H₄CH₂Cr(en)₂(H₂O)²⁺, are prepared by the reduction of the corresponding picolyl chlorides by the Cr^II(en)₂²⁺ ion. The decomposition of these ions is studied in 0·01–1·0M-perchloric acid and in acetate buffers of pH 1–7. Spectral changes show that these complexes undergo aquation before carbon–chromium bond cleavage. Product studies as well as kinetic data and activation parameters obtained indicate that the 2- and 3-ions decompose via the penta-aquo-derivative, 2-NC₅H₄CH₂Cr(H₂O)₅²⁺, and the trisaquo-derivative, 3-NC₅H₄CH₂Cr(en)(H₂O)₃²⁺ respectively. Acetate-ion catalysis is also observed for the decomposition of these ions.