Effect of anion variation on the iodine adsorption capacity of new silver(i)-dithione coordination polymers

Abstract

Seven novel silver–dithione coordination polymers, namely, [AgL^sSCN]_n (CP-1), {[Ag(L^s)₂][SCN]}_n (CP-2), {[Ag(L^s)₂][NO₃]}_n (CP-3), [Ag(L^s)(NO₃)]_n (CP-4), {[AgL^s][ClO₄]}_n (CP-5), {[AgL^s][BF₄]}_n (CP-6), and {[AgL^s][PF₆]}_n (CP-7), were designed and synthesized using a bidentate sulfur donor ligand containing a benzene spacer. These complexes were systematically investigated to explore the influence of anions on iodine adsorption capacity. CP-1 and CP-2 were synthesized using AgSCN and AgCN salts, respectively, with CP-2 exhibiting a unique detoxification process in which cyanide anions were converted into thiocyanate via sulfur transfer from the ligand. CP-3 and CP-4 were obtained through the self-assembly of silver nitrate and the L^s ligand in different solvents. CP-3 features a one-dimensional cationic network neutralized by nitrate counterions, while CP-4 represents the first reported two-dimensional organometallic complex based on a dithione ligand, marking a significant advancement in the field. CP-5–CP-7 are isostructural, differing only in their uncoordinated anions (ClO₄⁻, BF₄⁻, and PF₆⁻anions), making them ideal for comparative studies on anion effects. The iodine adsorption capacities of all the synthesized compounds were thoroughly evaluated, with CP-2 demonstrating the highest adsorption efficiency due to the presence of unbound thiocyanate (SCN⁻) anions. Thiocyanate's high negative charge density and strong Lewis basicity facilitate enhanced charge transfer interactions with σ*(I₂), outperforming NO₃⁻, ClO₄⁻, BF₄⁻, and PF₆⁻anions. Additionally, all the complexes exhibited exceptional stability during the adsorption process, which was attributed to the robust soft–soft acid–base interactions between the silver ions and sulfur donors. This study not only provides new insights into the design of coordination polymers for iodine capture but also highlights the potential of silver–dithione complexes in environmental remediation applications.