Synthesis, characterization, crystal structure determination and computational study of the high-spin iron(II) 2-cyanopyrazine complex trans-[Fe(pzCN)4Cl2]

A new mononuclear high-spin complex, trans-[Fe(pzCN)(4)Cl-2] (1), was prepared from the reaction of FeCl2.4H(2)O and 2-cyanopyrazine (pzCN) in acetonitrile as a solvent. Suitable crystals of this complex for crystal structure determination were collected by slow evaporation of the produced pale orange solution. Complex 1 was characterized by elemental analysis (CHN), spectral methods (IR and UV-Vis), and single-crystal X-ray diffraction. The X-ray structural analysis indicated that the iron(II) is six-coordinated in an octahedral configuration by four N atoms from four 2-cyanopyrazine ligands and two chloride anions. Furthermore, the average of Fe-N bond lengths is 2.284(1)angstrom. It is well known that in the high-spin iron(II) phenanthroline and bipyridine complexes, the Fe-N bond lengths are around 2.2 angstrom. So, due to the Fe-N bond length in this complex, the iron(II) is unambiguously high-spin. The experimental evaluations on 1 have been complemented theoretically by the density functional theory (DFT) and TD-DFT calculations. The character of the Fe-N and Fe-Cl bonds was investigated using quantum theory of atoms in molecules. Additionally, electron delocalization and hyper-conjugative interactions of the synthesized complex were evaluated by natural bond orbital calculations.