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

Three new quinoxaline-based ligands with N,S-bidentate chelating sites, 2,3-bis(n-propylthiomethyl)quinoxaline (L-1), 2,3-bis(tert-butylthiomethyl) quinoxaline (L-2) and 2,3-bis[(o-aminophenyl) thiomethyl] quinoxaline (L-3) 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 L-1 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 pi center dot center dot center dot pi stacking {[Ag2L1(NO3)(2)](H2O)(0.5)}(n) (2). When L-2 was used instead of L-1 to react with AgNO3, a non-centrosymmetric 3D network with (8(2).9)(2)(8(2).9.10) topology [Ag3L2(NO3)(3)](n) (3) was obtained, and L-3 instead of L-1 to react with AgClO4, a 1D chain with Ag center dot center dot center dot 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 mu(2)-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.