Three Co(II) metal-organic frameworks based on a substituted thiophene carboxylic acid ligand with semiconductive properties

Three Co(II) metal-organic frameworks, namely, {[Co(L)(dpyb)_0.5(H₂O)₂]·3H₂O}_n (1), {[Co(L)(dpyb)_0.5]·CH₃CN}_n (2), and {[Co₂(L)₂(dpyp)_1.5(H₂O)]}_n (3) have been hydrothermally synthesized based on a substituted thiophene carboxylic acid 3,3′-(thiophene-2,5-diyl)dibenzoic acid (H₂L) and auxiliary N-donor co-ligands 1,4-di(pyridin-4-yl)benzene (dpyb) and 1,3-di(4-pyridyl)propane (dpyp). 1 possesses a 1D double chains structure, which is further extended into a 3D supramolecular framework via O–H···O hydrogen bonds and π···π interactions. 2 shows a novel 2D + 2D→ 2D network with unusual polyrotaxane entanglements of (4, 4)-sql subnets. The two sets of adjacent such networks are further extended via C–H···π interactions into a 3D supramolecular framework. 3 displays a non-interpenetrated 2D sheet with the point symbol {4⁴.6²} sql net topology and further extends via π···π interactions into a 3D supramolecular framework. The three MOFs were characterized by IR spectra, elemental analysis, thermal analysis and single crystal X-ray diffraction. In addition, solid-state UV–vis spectra experiments show that 1, 2, and 3 exhibit semiconductive properties with band gap of 2.23, 2.95, and 3.12 eV.