Luminescent lanthanide mixed N-phthaloylglycinate and terephthalate coordination polymers: Structural and optical properties

A new class of lanthanide mixed-carboxylate ligands compounds with formula {[Ln₂ (phthgly)₄ (bdc)(H₂ O)₆ ]·(H₂ O)₄ }_∞ , labelled as Ln³⁺ : Eu (1) and Gd (2) coordination polymers (CP) were synthesized under mild reaction conditions between lanthanide nitrate salts and a solution of N-phthaloylglycine (phthgly) and terephthalic (bdc) ligands. The (1) and (2) coordination polymers were formed by symmetric binuclear units, in which phthgly and bdc carboxylate ligands are coordinated to the lanthanide ions by different coordination modes. Surprisingly, all organic ligands participate in hydrogen bonding interactions, forming an extremally rigid crystalline structure. The red narrow emission bands from the ⁵ D₀ →⁷ F_J transitions of the Eu³⁺ ion show a high colour purity. The intramolecular energy transfer process from L→Eu³⁺ ion has been discussed. The experimental intensity parameters (Ω_2,4 ) reflect lower angular distortion and polarizability of the chemical environment around the metal ion compared with other Eu³⁺ compounds reported in the literature. This novel class of coordination polymer offers a more attractive platform for developing luminescent functional materials for different applications.