Eight New Sulfur Coordination Compounds Based on Group 12 Metal Ions with Variable Structures and Extraordinary Capacity for Iodine Adsorption: Synthesis, Structural Characterizations, and Density Functional Theory Calculations

Eight new sulfur-based coordination compounds ranging from 0D to 2D have been designed and synthesized. These compounds were created using bidentate flexible ligands based on methimazole with varying spacers of 2, 3, or 5 methylene groups (termed L2, L3, and L5). These compounds include [ZnBr2(L3)2]n (1), [Zn2Cl2(μ2-L3)(μ-L3)2(PF6)2] (2), [Cd2(N3)2(μ2-N3)2(μ2-L3)2] (3), [CdCl2(μ-L3)] (4), [CdCl2(L2)2]n (5), [CdBr2(L2)2]n (6), [HgBr2(L2)2]n (7), and {[Hg(L5)4]}n[ClO4]n (8), where Ln = 1, n-bis(1-methyl imidazole-2-thione)alkane. In the case of 1D polymers 1, 5, 6, and 7 with bridging bidentate ligands, the halides have not contributed to the expansion of the structures. In the centrosymmetric dimeric compound 2, with terminal chlorine groups, one of the ligands bridging two Zn(II) ions, while the other two display a chelating coordination mode. In the dimeric species of 3, the Cd(II) ions are connected by two bridging azides, while the remaining coordination sites of five-coordinate metal ions are satisfied by a chelating mode of the ligand and a terminal azide group, preventing the expansion of the structure. In the monomeric structure of 4, neither the ligand nor the halides are in their bridging mode. The longer spacer length of the ligand in 8 and the use of uncoordinated ClO4– anions lead to the formation of a 2D sulfur-rich structure with hca topology. These compounds were examined for their ability to adsorb iodine in both the vapor and solution phases. The maximum iodine uptake capacity in the solution ranged from 196.72 to 801.33 mg/g, setting an incredible record for such nonporous adsorbents. The effects of azide and chlorine on the geometry, electronic structures, and iodine adsorption capacity of complexes 3 and 4 were studied by using density functional theory (DFT) at the B3LYP/6-31G(d,p)/LANL2DZ level in both gas and solvent. These results were then compared with experimental data.