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 LiXia WuBen-Lai NiuCao-Yuan NiuYun-Yin ZhangHong-Yun 2009 Six new metal−organic frameworks (MOFs), namely, {[Fe(HPIDC)(H<sub>2</sub>O)]·2H<sub>2</sub>O}<sub><i>n</i></sub> (<b>1</b>), [Cd(HPIDC)(H<sub>2</sub>O)]<sub><i>n</i></sub> (<b>2</b>), [Zn(HPIDC)(H<sub>2</sub>O)]<sub><i>n</i></sub> (<b>3</b>), {[Eu<sub>3</sub>(HPIDC)<sub>4</sub>(H<sub>2</sub>O)<sub>8</sub>]·NO<sub>3</sub>·4H<sub>2</sub>O}<sub><i>n</i></sub> (<b>4</b>), {[Tb<sub>3</sub>(HPIDC)<sub>4</sub>(H<sub>2</sub>O)<sub>8</sub>]·Cl·4H<sub>2</sub>O}<sub><i>n</i></sub> (<b>5</b>), and {[Y<sub>3</sub>(HPIDC)<sub>4</sub>(H<sub>2</sub>O)<sub>8</sub>]·Cl·4H<sub>2</sub>O}<sub><i>n</i></sub> (<b>6</b>), were hydrothermally synthesized and characterized (H<sub>3</sub>PIDC = 2-(pyridin-4-yl)-1<i>H</i>-imidazole-4,5-dicarboxylic acid). Single crystal X-ray diffractions show ligands H<sub>3</sub>PIDC are doubly deprotonated in all compounds, and the doubly deprotonated HPIDC<sup>2−</sup> coordinates in the μ<sub>3</sub> or μ<sub>4</sub> mode to generate 2D or 3D MOFs, displaying four coordination modes. Both <b>1</b> and <b>2</b> are 3D MOFs, but different in structure topologies. In <b>1</b> the ligand HPIDC<sup>2−</sup> 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<sub>2</sub>, with a determined BET surface area of 9.07 m<sup>2</sup> g<sup>−1</sup>. In <b>2</b>, however, ligand HPIDC<sup>2−</sup> and metal center Cd(II) serve as 4-connected nodes to form a 3D honeycomb framework. Complexes <b>3</b>−<b>6</b> all are 2D MOFs built up from T-shaped 3-connected HPIDC<sup>2−</sup> and 3- or 4-connected metal nodes. With the 3-connected metal nodes Zn(II), a stairway-like MOF with (4.8<sup>2</sup>) topology in <b>3</b> is created. As for 4-connected metal nodes Eu(III), Tb(III) or Y(III), isostructural MOFs with novel (4<sup>2</sup>.6)<sub>2</sub>(4.6<sup>2</sup>)<sub>2</sub>(4<sup>2</sup>.6<sup>3</sup>.8)<sub>2</sub>(4<sup>2</sup>.6<sup>2</sup>.8<sup>2</sup>) nets in <b>4</b>−<b>6</b> form. Notably, ligands HPIDC<sup>2−</sup> in <b>1</b>, <b>3</b> and <b>4</b>−<b>6</b> 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 <b>1</b> and Zn(II) in <b>3</b>. The luminescent nature for <b>4</b> and <b>5</b> is the typical narrow emission bands of Eu(III) and Tb(III) ions, respectively. For <b>2</b>, <b>3</b> and <b>6</b>, the slightly blue-shifted emission bands are mainly due to intraligand emissions.