5-(3',4'-Dicarboxylphenoxy)isophthalate/5-(2',3'-Dicarboxylphenoxy)isophthalate-Based 3D Cadmium(II) Coordination Polymers: Synthesis, Structure, and Sensing of Nitrobenzene.

5-(3',4'-Dicarboxylphenoxy)isophthalic acid (H L1) and 5-(2',3'-dicarboxylphenoxy)isophthalic acid (H L2) were reacted with Cd salt with/without the assistance of N-donor ligands, creating five 3D Cd coordination polymers [Cd (L1)(H O) ]⋅H O (1), [Cd (L1)(bpe)(H O)] (bpe=1,2-bis(4-pyridyl)ethene; 2), [Cd (L1)(bpa)(H O)] (bpa=1,2-bis(4-pyridyl)ethane; 3), [Cd (L1)(bpp)] (bpp=1,3-bis(4-pyridyl)propane; 4), and [Cd (L2)(bpp) (H O) ]⋅H O (5). Crystal-structure analysis reveals 1) in 1, phthalate moieties for L1 link Cd1 centers into a 1D slightly helical chain; Cd2 centers act as bridges, linking 1D helical chains into a 3D network with a (3,5)-connected topology; 2) in 2-4, although Cd centers were further modified by the introduction of organic bases, L1 molecules still link Cd centers into 3D networks, which can all be simplified as pcu topology; 3) in 2-4, phthalate moieties first link Cd centers into an oligomer, in which carboxylate-bridged discrete or rod-shaped secondary building units (SBUs) are found (tetranuclear SBU in 2 and 3, rod-shaped SBU in 4); and 4) in 5, L2 molecules link Cd centers into a 2D (4,4) net; introduced bpp molecules serve as pillar linkers, extending Cd -L2 layers into a 3D network of 5. The sensing abilities of 2-5 for nitrobenzene (NB) were investigated. Results revealed that they could all serve as fluorescence probes to sense NB at ppm concentrations.