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.