Diverse structural assemblies and variable conductivities of silver-hexamethylenetetramine coordination polymers with 2-, 3-, and 4-sulfobenzoate ligands

Abstract

Self-assembly reactions of sulfobenzoates and Ag(I)-hmt system resulted in the formation of one previously reported complex, {[Ag₄(hmt)₂(2-sb)₂(H₂O)]·2H₂O}_n (1), and two new silver-sulfobenzoate complexes {[Ag₄(hmt)₂(3-sb)₂(H₂O)₂]·2H₂O}_n (2), and {[Ag₃(hmt)₂(4-sb)(NO₃)(H₂O)]·3H₂O}_n (3) (sb = sulfobenzoate and hmt = hexamethylenetetramine). These coordination polymers were characterized by single-crystal X-ray analyses, elemental analyses, IR spectra, TG analyses, fluorescence studies, and electric conductivity. Complexes 2 and 3 are 3D coordination networks having novel topologies with different channels, where the Ag–Ag bonds play vital roles. In these complexes, hmt ligands act as μ₃- and μ₄- bridges in 1 and 3, and just μ₄- in 2. The configurations of the Ag-hmt units in 1–3 are different: chair types in 1 and 2, and boat type in 3. The disparately relative positions of carboxylate and sulfonate groups on benzyl rings of 2, 3, and 4-sulfobenzoate ligands and the different coordination modes of sulfobenzoates lead to the different dimensionalities and networks. The different packing environments of Ag–Ag bonds in 1–3 (no Ag–Ag interaction in 1 and the strongest Ag–Ag interactions in 2) result in the distinct fluorescence properties and electric conductivity. There is no any study of electric conductivity for Ag-hmt complexes in the references so far, and the complex 2 has the best electric conductivity in all our reported Ag-sulfobenzoate complexes.