A 2D zinc coordination polymer constructed from long and flexible N-containing tricarboxylate ligand for encapsulating Ln³⁺ ions and luminescent sensing

A new anionic coordination polymer (CP) has been solvothermally prepared with the long and flexible N-containing tricarboxylate ligand 5-[(3-(4-carboxyphenyl)-1H-pyrazol-1-yl)methyl]isophthalic acid (H₃L) and zinc ions. {(Me₂NH₂)[Zn(L)(H₂O)]·DMF}_n (1) (DMF = N,N-dimethylformamide) exhibits a fascinating undulant two dimensional (2D) layered structure and adjacent layers are further linked by π-π interactions to form three dimensional (3D) frameworks with the rhombic channels along the b axis, in which the (Me₂NH₂)⁺ cations are located. 1 emits blue light in solid state and possesses highly stability in different organic solvents. Moreover, it exhibits excellent luminescent sensing properties for Fe³⁺ and Cr₂O₇²⁻ with high sensitivity and selectivity, respectively. The K_sv value of Fe³⁺ ions is 2.06 × 10⁴ M⁻¹, while 1.35 × 10⁴ M⁻¹ for Cr₂O₇²⁻ ions. The luminescence quenching can be attributed to resonance energy transfer between 1 and analytes. Furthermore, the lanthanide ions doped materials Ln³⁺@1 are successfully prepared by cation-exchange, in which Eu³⁺/Tb³⁺ codoped materials show tunable luminescence and white-light emission by adjusting different molar ratios of Eu³⁺ and Tb³⁺ ions.