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.