Silver(I) coordination architectures with quinoxaline-based N,S-donor ligands: structures and luminescent properties

Abstract

Three new quinoxaline-based ligands with N,S-bidentate chelating sites, 2,3-bis(n-propylthiomethyl)quinoxaline (L¹), 2,3-bis(tert-butylthiomethyl)quinoxaline (L²) and 2,3-bis[(o-aminophenyl)thiomethyl]quinoxaline (L³) have been synthesized and their coordination behavior with Ag(I) was studied. Four Ag(I) complexes varying from 0D to 3D have been obtained by these structurally related ligands with AgX (X = ClO₄⁻, NO₃⁻). Single crystal X-ray diffraction analyses show that the structures of 1 and 2 are directed by the counter-anions used in such a system: the reaction of L¹ with AgClO₄ yielded a tetranuclear molecular cage {[AgL¹](ClO₄)}₄ (1), while using AgNO₃ instead led to the formation of a 2D layer framework with π⋯π stacking {[Ag₂L¹(NO₃)₂](H₂O)_0.5}_n (2). When L² was used instead of L¹ to react with AgNO₃, a non-centrosymmetric 3D network with (8².9)₂ (8².9.10) topology [Ag₃L²(NO₃)₃]_n (3) was obtained, and L³ instead of L¹ to react with AgClO₄, a 1D chain with Ag⋯Ag interaction {[Ag₂L³(DMF)](ClO₄)₂(H₂O)}_n (4) was formed. The structural differences between 2 and 3, 1 and 4, respectively, clearly show the important effect of the terminal groups of ligands on the structural modulation in such coordination architectures. Moreover, there are two coordination modes of S atoms in 1–4: one is µ₂-bridging (in 2 and 3), and the other is a mono-coordination (in 1 and 4). In addition, the luminescence properties of these compounds have also been studied in solid state at room temperature.