Metal–organic frameworks with a sulfur-rich heterocycle: synthesis, gas adsorption properties, and metal exchange

Abstract

Three new three-dimensional (3D) metal–organic frameworks [M₂(ttdc)₂(dabco)] (M = Zn(II), 1-Zn; Cu(II), 1-Cu; and Zn/Cu, 1-ZnCu) based on thieno[3,2-b]thiophene-2,5-dicarboxylate (ttdc²⁻) were synthesized and characterized by a combination of physicochemical methods (single crystal X-ray diffraction, powder X-ray diffraction, chemical and thermogravimetric analyses and IR spectroscopy). 1-Cu demonstrated permanent porosity (V_pore = 0.790 cm³ g⁻¹ and S_BET = 1725 m² g⁻¹) and significant CO₂, CH₄, C₂H₂, C₂H₄ and C₂H₆ gas uptakes under ambient conditions. The adsorption selectivities for gas mixtures, calculated by IAST, were 10.8 (10.7), 14.6 (9.4), 1.7 (1.6) and 1.5 (1.6) for the equimolar gas mixture compositions CO₂/N₂, C₂H₆/CH₄, C₂H₆/C₂H₄ and C₂H₆/C₂H₂ at 1 bar and 273 K (298 K), respectively. The mixed-metal compound 1-ZnCu was prepared by a crystal-to-crystal ion exchange metathesis reaction from 1-Zn with a 52% degree of ion substitution, confirmed by energy-dispersive X-ray spectroscopy, optical microscopy and single crystal X-ray diffraction analysis.