Effects of First‐Coordination Sphere and Buffers on the Nitrosyl‐Nitrite Conversion Rate in Ru(II) Complexes

Abstract

Nitrogen oxide derivative ruthenium compounds can deliver nitric oxide (NO) by chemical, electrochemical, or photochemical processes. Among these compounds, nitrosyl ruthenium complexes have been one of the most studied species. The σand π-character of the co-ligand L in [RuL 5 (NO)] n + exerts a unique and determining effect on the structure of the complex and the NO delivery mode. We have found inconsistencies in this assertion. How the buffer medium influences the hydrolysis rate constant of nitrosyl ruthenium complexes such as cis-[Ru(NO)(bpy) 2 L] 3 + + (L = 4-pic; py; isn and 4-acpy) has been evaluated in biphthalate, phosphate, and imidazole buffer solutions. For the studied ruthenium complexes, hydrolysis depended on the π-acceptor character of ligand "L", with k obs increasing in the following order: 4-pic < py < isn < 4-acpy. For nitrite conversion, the relative efficiency of the buffers increased in the order: biphthalate < phosphate < imidazole for all the studied nitrosyl ruthenium complexes. On the basis of these findings, we hypothesized that the second-coordination sphere interacts with the ruthenium complexes. By conducting theoretical modeling studies, we have elucidated the potential contribution of this interaction to nitrosyl/nitrite interconversion.