INFLUENCE OF SOLVENT EFFECTS ON THE BASICITY OF PENTAAMMINE(PYRAZINE)RUTHENIUM(II) AND PENTACYANO(PYRAZINE)RUTHENATE(II) IONS - A DENSITY-FUNCTIONAL STUDY

Quantum chemical calculations using density functional theory have bee n carried out to investigate the basicity of pentaammine(pyrazine)ruth enium(II) and pentacyano(pyrazine)ruthenate(II) ions. Gas phase equili brium geometries were fully optimized at the local density approximati on (LDA) level. Single-point calculations were performed at the optimi zed gas phase geometries using a generalized gradient approximation (G GA) functional. The basicity of the uncoordinated nitrogen on pyrazine was investigated in gas phase and in aqueous solution, modeling solve nt effects using a self-consistent reaction field (SCRF) Onsager model , a discrete electrostatic representation of the water molecules in th e first solvation shell, and also a combined SCRF-discrete model withi n the DFT-GGA methodology. A reasonable level of agreement between the ory and experiment is obtained only when using the SCRF-discrete model , suggesting that both specific interactions in the first solvation sh ell and long-range dielectric effects affect the reactivity of the com plexes.