Solvent-assisted construction of diverse Mg-TDC coordination polymers†
Abstract
Upon alteration of selected solvents, the reactions of 2,5-thiophenedicarboxylic acid (H2TDC) and Mg(NO3)2·6H2O afforded four diverse coordination polymers, namely Mg2(TDC)2(EG)2.5·0.5EG (1), Mg(TDC)(DMSO) (2), (Me2NH2)[Mg2(TDC)2(Ac)]·1.5DMA·0.5H2O (3), and [Mg2(TDC)2(DMF)2(EtOH)(H2O)2]·DMF (4) (EG = ethylene glycol, DMSO = dimethyl sulfoxide, Ac = acetate anion, DMA = N,N′-dimethylacetamide, DMF = N,N′-dimethylformamide, EtOH = ethanol). Single-crystal X-ray diffraction analyses indicated that compounds 1–3 possessed a three-dimensional (3D) network while 4 adopted a two-dimensional (2D) layered structure. Noticeably, the coordinated solvent molecules adopt distinct coordination modes which play a vital role in constructing the Mg-TDC structures. In 1, the solvent EG molecules as bi-dentate bridging ligands help in interconnecting the Mg-TDC layers to a 3D framework, whereas the solvent DMSO molecules in 2 and the Ac− anions generated from decomposition of DMA in 3 are coordinated in a μ2-fashion and in a (k2-k2)-μ3 mode, respectively, leading to infinite chains as secondary building units. In the layered structure of 4, the collaboration of coordinated DMF, EtOH and H2O molecules assists in inducing the noncentrosymmetric structure. The compounds were fully characterized by PXRD, TGA, EA, and IR. The luminescence properties of 1–3 and the second-harmonic generation (SHG) properties of 4 were studied. 3 emitted bright green light upon the excitation of 365 nm UV light, while 4 displayed sound SHG response.