Exploration of Structural Topologies in Metal–Organic Frameworks Based on 3‑(4-Carboxyphenyl)propionic Acid, Their Synthesis, Sorption, and Luminescent Property Studies

Four new compounds (two coordination polymers (CPs) and two metal organic frameworks (MOFs)), namely, [Zn­(cpp)­(H₂O)]_<i>n</i> (<b>1</b>), [Cu­(cpp)­(4-bpmh)]_<i>n</i><i>­·n</i>H₂O­·<i>n</i>MeOH (<b>2</b>), [Cd₂(cpp)₂­(3-bpmh)₂]_<i>n</i>­4<i>n</i>H₂O­·2<i>n</i>MeOH (<b>3</b>), and [Cd­(cpp)­(bpy)­(H₂O)₂]_<i>n</i>­·2<i>n</i>H₂O (<b>4</b>), have been synthesized through the slow diffusion technique using cpp ligand and different neutral linkers (H₂cpp = 3-(4-carboxyphenyl)­propionic acid, 4-bpmh = <i>N</i>,<i>N</i>-bis-pyridin-4-ylmethylene-hydrazine, 3-bpmh = <i>N</i>,<i>N</i>-bis-pyridin-3-ylmethylene-hydrazine, bpy = 4,4-bipyridine). Single crystal X-ray analysis of compounds <b>1</b>–<b>4</b> reveals their structural diversities which might have been generated due to both rigidity (aryl carboxylate) and flexibility (aliphatic carboxylates) of cpp ligands as well their bridging modes and the orientation of nitrogen atoms of the neutral linkers. In addition, the dihedral angle in the aliphatic carboxylates of cpp ligand is also playing an important role in directing the final structural arrangement. Compound <b>1</b> exhibits a uninodal 6-connected three-dimensional (3D) coordination polymer with point Schälfli symbol {3³.5⁹.6³} and shows an uncommon <i>lcy; 6/3/c1</i> topological type. Compound <b>2</b> reveals a 6-connected uninodal 3D framework with point Schälfli symbol {4⁸.6⁶.8} and shows a rare <i>rob</i> topology. Compound <b>3</b> formed a 4-connected uninodal two-dimensional framework with point Schälfli symbol {4⁴.6²} and displays a <i>sql/Shubnikov tetragonal plane</i> net topology, whereas <b>4</b> forms a one-dimensional CP which subsequently extended to 3D supramolecular networks through hydrogen bonding interactions. Gas adsorption studies reveal that compounds <b>1</b> and <b>2</b> show selective adsorption of CO₂ over other gases (N₂, CH₄) at low temperature, whereas <b>3</b> and <b>4</b> show no uptake. Vapor sorption studies reveal that compounds <b>1</b>,<b> 2</b>, and <b>4</b> show high uptake capacities for H₂O over MeOH and EtOH. Solid state luminescence studies of compounds <b>1</b>,<b> 3</b>, and <b>4</b> display significant red shifts compared to free ligands