Lanthanide coordination polymers functionalized by 5-nitroisophthalic acid: Synthesis, structure-DFT correlation and photoluminescent sensor of Cd2+ ion

Lanthanide coordination polymers (LnCPs) are influential chemosensors when designed to undergo a detectable change in optical properties upon interacting with target analytes. This work reports interaction of metal ions with LnCPs leading to elicit changes in fluorescence emission intensity, an essential step en route to developing sensitive and selective systems for metal-ion sensing. Towards this goal, solvothermal reaction of 5- Nitroisophthalic Acid (5-NIAH2) and Ln (NO3)3⋅xH2O produced seven Ln-coordination polymers {[Nd (5-NIA) (5-NIAH) (H2O)2]⋅CH3CN}n (1), {[Sm (5-NIA) (5-NIAH) (H2O)2]⋅CH3CN⋅H2O}n (2), {[Gd (5-NIA) (5-NIAH) (H2O)2]⋅(H2O)2}n (3), {[Tb (5-NIA) (5-NIAH) (H2O)2]⋅CH3CN)}n (4), [Dy (5-NIA) (5-NIAH) (H2O)2]n (5), [Ho(5-NIA) (5-NIAH) (H2O)2]n (6) and [Er2 (5-NIA)3(H2O)3(CH3CN)]n (7) with two-dimensional structures. The as-synthesized polymers are characterized by powder X-ray crystallography, infrared spectroscopy, thermogravimetric analysis, photoluminescence and DFT studies. The luminescence properties of [Tb (5-NIA) (5-NIAH) (H2O)2]⋅CH3CN)}n (4) is investigated. The CP-4 is highly sensitive for the detection of Cd2+ exhibiting most intensive fluorescence quenching with the lowest limit of detection. Other metal ions, including Co2+, Fe3+, Fe2+ and Pb2+ are also detected demonstrating the range of sensing capabilities.