Luminescence enhancement by mixing carboxylate benzoate–pentafluorobenzoate ligands in polynuclear {Eu2Zn2} and {Tb2Zn2} complexes

Abstract

This study investigates mixed-carboxylate benzoate (bz)–pentafluorobenzoate (pfb) {Eu₂Zn₂} and {Tb₂Zn₂} compounds with 1,10-phenanthroline (phen) molecules. It is demonstrated that variation of the synthesis conditions yields mixed-carboxylate compounds with different compositions: [Ln₂Zn₂(phen)₂(bz)_5.2(pfb)_4.8] (Ln = Eu (1_Eu), Tb (1_Tb)) and [Eu₂Zn₂(phen)₂(bz)₄(pfb)₆]·4MeCN (2_Eu). In these structures, bz⁻ and pfb⁻ anions occupy specific positions in various ratios. Benzoate compounds [Ln₂Zn₂(phen)₂(bz)₁₀] (Ln = Eu (3_Eu), Tb (3_Tb)) were synthesized in order to compare the structures and photoluminescence properties of complexes 1 and 2 with their homoanionic analogues, and comparison was also made with previously reported pentafluorobenzoate complexes [Ln₂Zn₂(pfb)₁₀(phen)₂] (Ln = Eu (4_Eu), Tb (4_Tb)). It was found that the introduction of a second type of anion into the studied compounds improves the photoluminescence properties and alters the geometry of the metal core, the polyhedra of rare-earth elements (REEs), and the system of non-covalent interactions compared to benzoate and pentafluorobenzoate complexes.