Equilibrium and kinetic study of nitric oxide binding to phthalocyaninatoiron(II) in dimethyl sulphoxide

The equilibrium and kinetics of the reaction between nitric oxide and phthalocyaninatoiron(II), [Fe(pc)], in dimethyl sulphoxide (dmso) has been studied at 20 ± 0.5 °C. In the presence of a large excess of NO, [Fe(pc)] binds nitric oxide in a 1:1 mol ratio via pseudo-first-order kinetics. The observed rate constant has the general form k_obs. = k_f[NO], i.e. with and intercept close to zero and a slope k_f = (2.2 ± 0.4) × 10⁴ dm³ mol^-1s^-1. From the values of the equilibrium constant [K = (1.1 ± 0.1) × 10⁶ dm³ mol^-1] and second-order rate constant (k_f) for the binding of NO, the dissociation rate constant (k_r) has been estimated to be (2.0 ± 0.4) × 10^-2s^-1. The present results are discussed in the light of related previous investigations.