Involvement of various anions in tuning the structure of silver(i) coordination polymers based on a S-donor ligand: syntheses, crystal structure and uptake properties

Abstract

An investigation of the impact of the shape, size and coordination ability of counterions was carried out on five silver(I) 1,2-bis(1-methylthioimidazolyl)ethane coordination polymers, namely, [Ag₂L(NO₃)₂]_n (1), [Ag₂L(SO₃CF₃)₂]_n (2), {[AgL][ClO₄]}_n (3), {[AgL]₂[BF₄]₂}_n (4) and {[AgL]₃[PF₆]₃}_n (5). They have been characterized by elemental analysis, IR spectroscopy, PXRD and single-crystal X-ray diffraction. [Ag₂L(NO₃)₂]_n (1) was produced in the presence of a strongly coordinating anion (NO₃⁻). In the 1D structure of 1, the ligand appears in a pentadentate form and the nitrate acts as a co-ligand in a bidentate coordination fashion. As in 1, in 2 CF₃SO₃⁻ with a moderately coordinating potential builds up a natural structure with only one kind of coordination mode for the ligand and two types of coordination geometry for the silver atoms. The difference between structures 1 and 2 can be attributed to the size and coordination ability of their anions, which changed the coordination environment of silver ions without changing the coordination fashion of the ligand. In polymer 3, by decreasing the coordination ability and increasing the size of perchlorate relative to that of the previously considered anions, the coordination mode of the ligand and hence the coordination environment of the silver centers were changed. Unlike all the title compounds in the cationic structure of 3, one of the crystallographically independent Ag^I centers adopts a distorted trigonal planar environment. Complex 4 with an extended helical chain of [Ag₂L]_n²⁺ was obtained when AgBF₄ with a small, non-coordinated anion was used to react with the L ligand. X-ray diffraction analysis reveals that the most changes were detected in polymer 5 with a rare triple chain structure and a scarce coordination mode of the ligand by using the bulky, uncoordinated PF₆⁻ anion. In fact, changing the type of the anion causes a change in the coordination mode of the ligand and in turn in the structural coordination geometry of the polymer. Additionally, the adsorption potential of the polymers was examined by using NH₃ and H₂S gases.