Abstract
This study reports on the synthesis, structural characterization and gas sorption studies of a homometallic 2D Cd(2+) MOF and two heterometallic 3D Cd(2+)/Ca(2+) and Cd(2+)/Sr(2+) -MOFs based on the angular tetracarboxylic ligand 3,3',4,4'-sulfonyltetracarboxylic acid (H(4)STBA). The homometallic 2D Cd(2+) MOF with the formula [NH(2)(CH(3))(2)](+)(2)[Cd(STBA)](2-)(n)·nDMF·1.5nH(2)O-(1)(n)·nDMF·1.5nH(2)O was synthesized from the reaction of CdCl(2)·H(2)O and 3,3',4,4'-diphthalic sulfonyl dianhydride (3,3',4,4'-DPSDA) with stoichiometric ratio of 1:1.3 in DMF/H(2)O (5/2 mL) at 100 °C. The two heterometallic Cd(2+)/Ca(2+) and Cd(2+)/Sr(2+) compounds were prepared from analogous reactions to this afforded (1)(n)·nDMF·1.5nH(2)O with the difference that the reaction mixture also contained AE(NO(3))(2) (AE(2+) = Ca(2+) or Sr(2+)) and, in particular, from the reaction of AE(NO(3))(2), CdCl(2)·H(2)O and 3,3',4,4'-DPSDA with stoichiometric ratio 1:1.1:1.4 in DMF/H(2)O (5/2 mL) at 100 °C. Notably, compounds [CdCa(STBA)(H(2)O)(2)](n)·0.5nDMF-(2)(n)·0.5nDMF and [CdSr(STBA)(H(2)O)(2)](n)·0.5nDMF-(3)(n)·0.5nDMF are the first heterometallic compounds M(n+)/AE(2+) (M = any metal ion) reported containing ligand H(4)STBA. The structure of (1)(n)·nDMF·1.5nH(2)O comprises a 2D network based on helical 1D chain secondary building unit (SBU) [Cd(2+)(STBA)(4-))](2-). The 2D sheets are linked through hydrogen bonding interactions, giving rise to a pseudo-3D structure. On the other hand, compounds (2)(n)·1.5nH(2)O and (3)(n)·1.5nH(2)O display 3D microporous structures consisting of a helical 1D chain SBU [Cd(2+)AE(2+)(STBA)(4-))]. All three compounds contain rhombic channels along c axes. The three MOFs exhibit an appreciable thermal stability, up to 350-400 °C. Gas sorption measurements on activated materials (2)(n) and (3)(n) revealed moderate BET surface areas of 370 m(2)/g and 343 m(2)/g, respectively, along with CO(2) uptake capacity of 2.58 mmol/g at 273 K.