Quantum-chemical study of the Fe(NO)2 fragment in the cation of mononuclear nitrosyl iron complex [Fe(SC(NH2)2)2(NO)2]Сl·H2O

Abstract

Quantum-chemical study of the Fe(NO)2 fragment in the Fe(SC(NH2)2)2(NO)2+ cation of mononuclear nitrosyl iron complex has been performed using various approaches in the frame of density functional method. Both local (Bp86, PW91PW91, BLYP, TPSSTPSS), and hybrid (B3LYP, B3PW91, TPSSh) functionals were used in order to understand which of them are the most suitable for description of the electronic and molecular structures of cations of this type. Using NBO and AIM methods, main characteristics of the Fe(NO)2 fragment bonds were determined. In the Fe(NO)2 fragment of the complex π-interactions are strong, this being the reason of re-distribution of the electron density along Fe–N–O. However, the Fe–N bond in this complex differs from a common covalent bond because, according to some topological characteristics, it corresponds to the interaction with closed shells, while the ratio of contributions of kinetic and potential energy densities corresponds to covalent bonds. Local functionals overstate energy of the Fe–NO bond, this being due to the overestimation of the energy of orbital mixing of antibonding orbitals of the Fe–N and N–O bonds.