Syntheses of Metal−2-(Pyridin-4-yl)-1<i>H</i>-imidazole-4,5-dicarboxylate Networks with Topological Diversity: Gas Adsorption, Thermal Stability and Fluorescent Emission Properties

Abstract

Six new metal−organic frameworks (MOFs), namely, {[Fe(HPIDC)(H 2 O)]·2H 2 O} n ( 1 ), [Cd(HPIDC)(H 2 O)] n ( 2 ), [Zn(HPIDC)(H 2 O)] n ( 3 ), {[Eu 3 (HPIDC) 4 (H 2 O) 8 ]·NO 3 ·4H 2 O} n ( 4 ), {[Tb 3 (HPIDC) 4 (H 2 O) 8 ]·Cl·4H 2 O} n ( 5 ), and {[Y 3 (HPIDC) 4 (H 2 O) 8 ]·Cl·4H 2 O} n ( 6 ), were hydrothermally synthesized and characterized (H 3 PIDC = 2-(pyridin-4-yl)-1 H -imidazole-4,5-dicarboxylic acid). Single crystal X-ray diffractions show ligands H 3 PIDC are doubly deprotonated in all compounds, and the doubly deprotonated HPIDC 2− coordinates in the μ 3 or μ 4 mode to generate 2D or 3D MOFs, displaying four coordination modes. Both 1 and 2 are 3D MOFs, but different in structure topologies. In 1 the ligand HPIDC 2− and metal center Fe(II) act as 3-connected nodes to fabricate a (10,3) porous metal−organic net with 1D open channels where 1D zigzag water chains are reside through hydrogen-bonding interactions. This dehydrated porous material can absorb for N 2, with a determined BET surface area of 9.07 m 2 g −1 . In 2, however, ligand HPIDC 2− and metal center Cd(II) serve as 4-connected nodes to form a 3D honeycomb framework. Complexes 3 − 6 all are 2D MOFs built up from T-shaped 3-connected HPIDC 2− and 3- or 4-connected metal nodes. With the 3-connected metal nodes Zn(II), a stairway-like MOF with (4.8 2 ) topology in 3 is created. As for 4-connected metal nodes Eu(III), Tb(III) or Y(III), isostructural MOFs with novel (4 2 .6) 2 (4.6 2 ) 2 (4 2 .6 3 .8) 2 (4 2 .6 2 .8 2 ) nets in 4 − 6 form. Notably, ligands HPIDC 2− in 1, 3 and 4 − 6 are all T-shaped 3-connectors, but belong to different coordination modes, and the coordination lability also results in structural diversity, even with similar 3-connected nodes such as Fe(II) in 1 and Zn(II) in 3 . The luminescent nature for 4 and 5 is the typical narrow emission bands of Eu(III) and Tb(III) ions, respectively. For 2, 3 and 6, the slightly blue-shifted emission bands are mainly due to intraligand emissions.