The structural diversity, band gap energy and photoluminescence properties of thiophenedicarboxylate based coordination polymers†
Abstract
A series of 2,5-thiophenedicarboxylic acid (TDC) ligand based coordination polymers were solvothermally synthesized, namely, 1, [Mg3(OH)2(H2O)4(TDC)2]; 2, [NH2(CH3)2]2[Mg3(TDC)4]; 3, [Mg2(TDC)2(DMF)2]; 4, [Zn2(TDC)2(bpe)](solvent)X; and 5, [(CH3)2NH2][In(TDC)], where DMF = N,N′-dimethylformamide and bpe = 1,2-bis(4-pyridyl)ethane. Compound 1 was synthesized in a MeOH–H2O solvent mixture and it has a two dimensional layered structure. Compound 2 was obtained using a DMF–H2O mixture and it has a three dimensional structure. It contains Mg3O16 trimeric units which are linked by TDC anions to form the three-dimensional connectivity. Compounds 3 and 5 were synthesized using only DMF as a solvent and compound 4 was synthesized using a DMF–MeOH mixture. Compound 3 also has a three-dimensional structure where Mg4O20 clusters are linked through the TDC anions. Compounds 4 and 5 have three-dimensional structures with a 2-fold interpenetration. All the compounds are characterized well through powder X-ray diffraction, IR spectroscopy, photoluminescence spectroscopy and thermogravimetric analysis. Interestingly compound 5 crystallizes in a chiral space group which has been confirmed by solid state circular dichroism (CD) spectroscopy. We have measured the optical band gap energy for all the compounds and the results showed that the band gap energy varies from 3.44 eV to 3.86 eV. This variation in the band gap energy may be due to the difference in structural arrangement.