Four 2D Ln–Cd heterometal–organic coordination polymers based on tetranuclear Ln–Cd oxo-cluster with highly selective luminescent sensing of organic molecules and metal cations

Abstract

Two series of novel lanthanide–cadmium (Ln–Cd) heterometal–organic coordination polymers, i.e., [Ln₂Cd₂(DTPA)₂(H₂O)₄] (H₂O)₄ (I: Ln = Eu 1a; Gd 1b) and [Ln₂Cd₃(DTPA)₂Cl₂(H₂O)₆] (II: Ln = Eu 2a; Sm 2b) (H₅DTPA = diethylenetriamine pentaacetic acid), have been synthesized using a hydrothermal method. Compounds I and II both possess 2D grid-layer structure based on distinct tetranuclear Ln–Cd oxo-cluster units as secondary building units (SBUs). Two enantiomeric forms, i.e., α and β, exist in [Cd(DTPA)]³⁻ in compounds I. Interestingly, compound 1a displays not only a highly sensitive sensing of small molecular organic solvents, especially methanol, triethylamine and ethanol amine, but also the sensing of cations, especially Cr³⁺ and Fe³⁺ ions. Moreover, Cr³⁺, Fe³⁺, Co²⁺, Ni³⁺, Cu²⁺, Nd³⁺ cations quenched the emissions of the Eu³⁺ ions of compound 2a, which indicates the potential of 1a and 2a for sensing of metal cations.