Preparation of one-dimensional coordination polymers of a flexible tripyridyl disulfide with diverse topologies

Abstract

A novel flexible tripyridyl disulfide ligand (L, 2,6-bis(4-pyridinesulfanylmethyl)pyridine) having a pyridyldithioether backbone was synthesized and its diverse types of one-dimensional (1D) coordination polymers (1–4) with coinage metal (copper and silver) salts were isolated. The complexation with copper(II) nitrate afforded a loop chain type product {[Cu(L)₂(NO₃)₂]·CH₂Cl₂}_n (1), in which twisted Cu₂L₂ metallacycles in an S-configuration of L share one copper(II) node. The complexations with silver(I) salts (X = NO₃⁻, PF₆⁻, and ClO₄⁻) resulted in three 1D coordination polymers; {[Ag(L)NO₃]·CH₂Cl₂}_n (2, NO₃-form), {[Ag(L)(CH₃CN)]PF₆}_n (3, PF₆-form), and {[Ag(L)ClO₄]·CH₂Cl₂}_n (4, ClO₄-form). Both products 2 (NO₃-form) and 3 (PF₆-form) show a similar Ag₂L₂ metallacycle-based ribbon structure with a C-configuration of L except for the anion coordination (NO₃⁻) in 2 and the solvent (CH₃CN) coordination in 3. Product 4 (ClO₄-form) displays a deformed ladder structure; two parallel (Ag-L)_n chains with an out-of-phase of the S-configuration of L as rails, and the crosslinking Ag–S bonds as rungs. Anion exchange studies revealed that the PF₆⁻ in 3 was replaced by NO₃⁻ to yield product 2 but the reverse process was not possible. Compared to the free ligand L with a medium photoluminescence (PL) intensity, the silver(I) products showed enhanced emissions while the copper(II) complex was silent.