Theoretical investigation on the electronic structure of pentacyano(L)ferrate(II) complexes with NO+, NO, and NO- ligands. Redox interconversion, protonation, and cyanide-releasing reactions

Reaction pathways for the one- and two-electron reductions of [Fe(CN)(5)NO] (2-) have been investigated by means of a density functional theory (DFT) a pproach combined with the polarized continuum model (PCM) of solvation. In addition, UV-vis spectroscopic data were obtained using ZINDO/S calculation s including a point-charge model simulation of solvent effects. DFT methodo logies have been used to assess the thermodynamical feasibility of protonat ion and cyanide-release processes for the reduced species. We conclude that [Fe(CN)(5)NO](3-) is a stable species in aqueous solution but may release cyanide yielding [Fe(CN)(4)NO](2-), consistent with experimental results. O n the other hand, the [Fe(CN)(5)NO](4-) complex turns out to be unstable in solution, yielding the product of cyanide release, [Fe(CN)(4)NO](3-), and/ or the protonated HNO complex. All the structural and spectroscopic (IR, UV -vis) predictions for the [Fe(CN)(5)HNO](3-) ion are consistent with the sc arce but significant experimental evidence of its presence as an intermedia te in nitrogen redox interconversion chemistry. Our computed data support a n Fe-II(LS) + NO+ assignment for [Fe(CN)(5)NO](2-), an Fe-II(LS) + NO assig nment for the one-electron reduction product, but an Fel(LS) + NO+ for the one-electron product after dissociation,of an axial cianide, and an Fe-II singlet NO- for the two-electron reduction species.