Theoretical Study on Structure Prediction and Molecular Formula Determination of Polymeric Complexes Comprising Fe(II) and 1,2,4-H-Triazole Ligand

The structure and the molecular formula of Fe(II) 1,2,4-H-triazole complex has been predicted by using Hartree-Fock (HF) and Density Functional Theory (DFT) methods. The distance between the Fe(II) ions and Fe-N bond length show good agreement with experimental measurements at the low-spin state. It has been conducted by using hybrid/basis set functions of B3LYP/6-31G(d), TPSSh/TZVP, and MO6-2x/6-31G(d). The distance between the Fe(II) ions complexes with deprotonated ligands are 3.30–3.75, 3.44–3.74, and 3.46–3.79 Å, respectively, and undeprotonated ligands are 3.41–4.04, 3.49–3.90, and 3.52–4.09 Å. Meanwhile, the Fe-N bond lengths in the complex with the deprotonated ligand are 1.84–2.07, 1.85–2.04, and 1.89–2.11 Å, respectively, while in the complex with undeprotonated ligands they are 1.89–2.20, 1.84–2.12, and 1.96–2.21 Å. The molecular formula of Fe(II)-Htrz complex is ([Fe(Htrz)2(trz)]+)n which has been obtained by comparing the energy difference between the complex formation with deprotonated ligands being lower than that with undeprotonated complex. The computational results on the hybrid/basis set function of B3LYP/6-31G(d) induces the difference of energy formation of [Fe2(Htrz)4(trz)2]2+, [Fe2(Htrz)6]4+, [Fe4(Htrz)8(trz)4]4+, [Fe4(Htrz)12]8+, [Fe6(Htrz)12(trz)6]6+, and [Fe6(Htrz)18]12+ complexes to be −5613.38, −3082.67, −11013.19, −147.40, −16101.36, and −6825.09 kJ/mol, respectively.