Kinetics of Substitution and Isomerization of Nitrite Ion on Aqua(7-Methyl-4,10-Dithia-1,7,13-Triazatridecane)Cobalt(III) and the Structure of the Product

Abstract

Abstract The influence of placing a CH3N- linkage trans to a site of nitro substitution and spontaneous nitrito-to-nitro isomerization is reported for the Co(NSNSN)H2O3+ cation where NSNSN is 7-methyl-4,10-dithia-1,7,13-triazatridecane, NH2CH2CH2-S-CH2CH2-N(CH3)-CH2CH2-S-CH2CH2NH2. Preparation and characterization is described for the aqua and nitrito complexes. Co(NSNSN)H2O3+ is 435 times more reactive than Co(NH3)5H2O3+ under identical conditions. Nitrito-to-nitro isomerization is much slower than the conversion of Co(NSNSN)H2O3+ to Co(NSNSN)ONO2+. The isomerization was studied at a number of wavelengths, temperatures and at various concentrations of acid and nitrite ion at ionic strengths of 0.11–0.60 m. Isomerization rate constants are 1.10±0.11 × 10-5sec-1 at 20.0[ddot]C, 5.24 ± 0.83 × 10-5sec-1 at 30.0[ddot]C, and 18.1 ± 1.1 × 10-5 sec-1 at 39.0[ddot]C. Thermodynamic activation parameters are ΔHΔ = 109.3 kJ mol-1, ΔSΔ = + 33 J mol-1 K-1 and ΔGΔ = 99.4 kJ mol-1. Single-crystal X-ray diffraction data ...