Modelling pyrazine and tetrazine complex ions of iron by DFT

Abstract

In coordination chemistry, mixed valency is widespread, from superconductors to minerals, magnetic molecular clusters and even enzymes. Mixed valency occurs when the same chemical element is found in two different oxidation states in the same molecule or solid. After the detailed structure and electronic analysis of the ligands tetrazine(tz) and pyrazine(pyz) the metal framework of iron with CN co-ligands, in a progressive manner, mononuclear [(L)Fe(CN)5]-2,-3 (L:tz, pyz), dinuclear [(μ-L){Fe(CN)5}2]-4,-5 complexes and trinuclear trans/cis [Fe(CN)5(L)Fe(CN)4(L)Fe(CN)5]-5,-6,-7 complexes are optimized. Some studies on the mononuclear complex (mnc) and mixed valent dinuclear complex (dnc) of Fe in the literature exist but none on tnc complexes. These complexes have been modeled making use of B3LYP (Becke-3-parameters-Lee-Yang-Parr functional) calculations. Comparison of bond lengths, Muliken charges, frontier orbitals, and spins of odd electron species at each level allows a close look at the presence of metal ligand charge transfer (MLCT) and/or intervalence charge transfer (IVCT) of pyrazine and tetrazine iron complexes.