Experimental and theoretical study of the arrangement, electronic structure and properties of neutral paramagnetic binuclear nitrosyl iron complexes with azaheterocyclic thyolyls having ‘S-C-N type’ coordination of bridging ligands

Geometrical and electronic structures of neutral paramagnetic binuclear nitrosyl iron complexes with azaheterocyclic thyolyls Fe₂(μ-SR)₂)(NO)₄] with bridging ligands: aminomercaptotriazolyl, RC₂N₃H(NH₂) (1), mercaptoimidazolyl, RC₃N₂H₃ (2), methylmercaptoimidazolyl, RC₃N₂H₂CH₃ (3), and dihydromercaptoimidazolyl, RC₃N₂H₅ (4) have been calculated by the methods of density functional, B3LYP and PBE. Coordination of bridging ligands corresponds to ‘S-C-N type’, more energetically preferable than μ-S type coordination. This results in big Fe?Fe distances, with the value of intramolecular exchange interaction being inconsiderable; therefore the complexes are paramagnetic at ambient temperature, with effective magnetic moment about 2.5 Bohr magneton. The interaction of the Fe atoms spins and intermolecular exchange are antiferromagnetic, and this should be taken into account while describing the temperature dependence of magnetic susceptibility. The electronic configuration of the Fe(NO)₂ unit with one unpaired electron (similar to that in binuclear diamagnetic complexes) forms due to binding of spin 3/2 of Fe⁺d⁷ center with oppositely oriented spins 1/2 of two NO groups. Theoretical approaches describe satisfactorily not only the experimental structure of the complexes but also their IR spectra.