Effects of combining fluorinated and non-fluorinated monocarboxylate anions in lanthanide complexes on the structure and photoluminescence properties

Abstract

Mixed-carboxylate europium compounds with various combinations of fluorinated and non-fluorinated monocarboxylic acid anions have been investigated: [Eu₂(phen)₂(pfb)_2,6(4-phb)_3,4] (1_Eu; pfb⁻ – pentafluorobenzoate anion; 4-phb⁻ – 4-phenylbenzoate anion), [Eu₂(H₂O)₂(phen)₂(pfb)₄(2-nap)₂] (2; 2-nap⁻ – 2-naphthoate anion), and [Eu₂(phen)₂(fpAc)₂(napAc)₄]·4MeCN (3; fpAc⁻ – 2,3,5,6-tetrafluoro-4-(trifluoromethyl)phenylacetate anion and napAc⁻ – 1-naphthaleneacetate anion). The compound [Gd₂(phen)₂(pfb)_2,6(4-phb)_3,4] (1_Gd) containing a gadolinium ion is a structural analogue of compound 1_Eu and was also synthesized. According to X-ray diffraction (XRD) data, in compound 1_Eu, the simultaneous presence of pentafluorobenzoate and 4-phenylbenzoate anions leads to disorder at one of the coordination sites. Complexes 2 and 3 are individual stoichiometric compounds. Variation in the combination of fluorinated and non-fluorinated monocarboxylate anions in compounds 1–3 affects the molecular geometry and the system of non-covalent interactions within the crystal, significantly influencing their photoluminescence properties. The supramolecular crystalline structures of the novel compounds are stabilized by π–π, CF⋯π, CH⋯O, and CH⋯F non-covalent interactions. The obtained compounds were characterized using single-crystal and powder X-ray diffraction, luminescence spectroscopy, infrared (IR) spectroscopy, thermogravimetric analysis (TGA), differential thermal analysis (DTA), and elemental (CHN) analysis. Photoluminescence properties were studied for the solid-state samples of the synthesized compounds.