Impact of coordination ability of the selected anions on tuning the structure of Hg(II) complexes constructed from a neutral dithione ligand: Iodine uptake and DFT theoretical studies

Abstract

In view to examine the role of coordination potential of the selected anions on architect of complexes, HgL2](ClO4)2 (C1) and [HgL2](PF6)2 (C2) were synthesized with a HgS4 core structure by a flexible sulfur donor (1,1-bis(3-methyl-4-imidazoline-2-thione)methane ligand(L). The C1 was crystalized via a branched tube method in MeOH/H2O as a solvent. They have been characterized by the FT-IR, elemental analysis, X-ray powder diffraction (PXRD), density functional theory (DFT) calculations, and considered for the iodine adsorption experiments. Although MOFs and CPS were extensively being studied, but mono and binuclear complexes were rarely used as an adsorbent for removal of the iodine. Additionally, to probe the impact of anions on the structure of complexes, and iodine uptake properties, C1 and C2 were compared with the published dimeric ones [Hg2L2Cl4](C3) and [Hg2L2Br4](C4) with a HgX2S2 core structure. All complexes showed a good performance in removal of iodine from the pollutants. This was supported by a sharp decrease in the intensity of a band at 523 nm nominated to the π*g(p) (HOMO) → σ*u(p) (LUMO) transitions in the free I2 molecule. The iodine capture performance of the monomeric complexes is substantially different with the dimeric ones. C1and C2 remove more than 99% of iodine molecules in the solution within 2 h, whereas C3 and C4 need 24 h to achieve the equilibrium point. The DFT studies and band gap calculations confirmed a charge transfer transition from each of the complexes to the σ*u(p) (LUMO) of the adsorbed iodine molecules with a lower energy relative to the free I2 band gap. Nonlinear optical responses (NLO) and charge transfer properties of the C1-C4 complexes were inspected by the DFT calculations.