Structure, solvation, and bonding in pentacyano(L)ferrate(II) ions (L=aliphatic amine): a density functional study

Abstract.

Quantum chemical calculations using density functional theory have been carried out to investigate the influence of aqueous solvation on the structure and bonding in [Fe(CN)₅L]^3–with L an aliphatic amine (ammonia, methylamine, hydrazine, and ethylenediamine). Gas phase equilibrium geometries were fully optimized at the generalized gradient approximation (GGA) level. Solvent effects were modeled within the DFT methodology by using a discrete electrostatic representation of the water molecules in the first solvation shell. For the hydrazine and ethylenediamine complexes in vacuum we found two internal hydrogen bonds between the terminal amino group hydrogens and two equatorial cyanide ligands. However, considering the first solvation shell, an open structure in which the terminal amino group is solvated by water molecules becomes more stable in the ethylenediamine case. Metal–L dissociation energies were computed in vacuum, taking the first solvation shell into account. The results obtained were compared with experimental kinetic data in aqueous solution in order to assess the role of solvation in the reactivity of these complexes.