Cd(II) Coordination Complexes Built from Semirigid Bis(dimethylbenzimidazole) Ligand and Different Carboxylates: Fluorescent Sensor and Recognition Mechanism for p-Nitrophenol, Erythromycin and 2,6-Dichloro-4-nitroaniline

Three Cd(II) coordination complexes, formulated as [Cd(dbim)(p-phda2−)]n (1), [Cd(dbim)1.5(suc2−)]n (2), [Cd(dbim)0.5(m-bdc2−)(2H2O)]n (3) (dbim = 1-(4-((2,5-dimethyl-3aH-benzo[d]imidazol-1(7aH)-yl)methyl)benzyl)-3a,7a-dihydro-2,5-dimethyl-1H-benzo[d]imidazole, p-H2phda = p-phenylenediacetic acid, H2suc = succinic acid, m-H2bdc = 1,3-benzenedicarboxylic acid), have been obtained by hydrothermal reactions. Complex 1 features a 4-connected 2D topological net with a point symbol of 44·62. Complex 2 possesses a 3-connected 2D layer with a point symbol of 63. Complex 3 presents a chain structure ornamented with uncoordinated Lewis basic O donor. Complex 3 shows highly sensing for p-Nitrophenol, Erythromycin and 2,6-Dichloro-4-nitroaniline with fluorescence quenching/enhancement, by energy transfer process. The binding constants were calculated as 2.9 × 104 mol−1 for p-Nitrophenol, 5.3 × 103 mol−1 for Erythromycin and 7.2 × 103 mol−1 for 2,6-Dichloro-4-nitroaniline, respectively. The study indicates that Complex 3 can be as a rare sensory material for efficiently detecting p-Nitrophenol, Erythromycin and 2,6-Dichloro-4-nitroaniline.