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Herein, we present a new method for preparing homoligand 3D coordination polymers. First, a layered metal-organic framework Zn3(BDC)3(H2O)2·4DMF 1 (BDC is terephthalate, DMF is N,N-dimethylformamide) was fabricated from a H2BDC by liquid-liquid diffusion. Second, the layered product, 1, was used as a precursor to solvothermally react with further H2BDC at 140-180 °C, resulting in two products of BDC insertion into the layered structure. These are [Zn3(p-BDC)4]·2HPIP, 2 (HPIP is partly protonated piperazine), and [Zn3(p-BDC)3(H2BDC)]·(C6H15NO)·H2O·3DMF, 3 (C6H15NO is triethylamine N-oxide). Single-crystal X-ray diffraction shows that 2 possesses a layer- pillared structure of μ2-BDC, with 1D channels, while 3 has a layer-pillared structure of μ2-BDC, with 2D channels. N2-sorption experiments show 3 has a relatively high BET surface area of 750 m²/g. It is proposed that 2 follows the crystal growth mechanism of Ostwald ripening, whereas the crystal structure of 3 might be formed by an insertion mechanism. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks with tunable functional groups like solid-solution have received considerable interest. In this paper, a crs-type structure built of [Zn3(OH)(dmtrz)3] triazolate-trinuclear and [Zn2(COO)4] paddlewheel units, linked by 3,5-dimethyl-1,2,4-triazolate (dmtrz) and isophthalate (ipa) ligands (named as MAC-4-A), has been used as a prototype framework. Four types of functional groups (B: 5-hydroxyisophthalate, C: 5-aminoisophthalate, D: 5-ethoxyisophthalate, and E: 5-acetamidoisophthalate) have been integrated into the framework, giving isostructures of MAC-4-B to E, respectively. Then, by the solid-solution framework approach, four group samples are prepared, which are MAC-4-AB-x, MAC-4-AC-x, MAC-4-AD-x, and MAC-4-AE-x (x denoted as the ratio of functional ligands in the framework, x = 0.3, 0.5, 0.7), and their CO2 and N2 adsorptions have been studied. Our results revealed that the CO2 capacity is enhanced with the increase of functional groups and then decreases, showing a maximum uptake amount on MAC-4-AB-0.5, MAC-4-AC-0.5, MAC-4-AD-0.7, and MAC-4-AE-0.5 at 298 K and 1 bar, respectively. On the other hand, the calculated selectivity of CO2 over N2 gradually increases, giving the highest selectivity after the pore surface is completely functionalized. [ABSTRACT FROM AUTHOR]