On the “Brown‐Ring” Reaction Product via Density‐Functional Theory.

Abstract

On the basis of the density-functional theory, the properties of the reaction product [Fe(H2O)5(NO)]2+ of the classical “brown-ring” reaction are studied via the B3LYP hybrid method. Here we have found that the Fe−N−O bond in the optimized structure of [Fe(H2O)5(NO)]2+ is linear. In addition, the vibrational frequency, atomic net charges, and spin density are analyzed and then the solvent effects are incorporated via the polarized continuum model self-consistent reaction field. Furthermore, the excitation energies are evaluated using the CIS method. Results when compared with experimental data indicate that the spin-quartet ground state of [Fe(H2O)5(NO)]2+ is best described by the presence of FeII (S = 2) antiferromagnetically coupled to NO (S = 1/2), yielding [FeII(H2O)5(NO)]2+. This is clearly different from either [FeIII(H2O)5(NO-)]2+ or conventional textbook [FeI(H2O)5(NO+)]2+ assignment.