Synthesis, Structures, Thermodynamic Properties, and Fluorescence Behavior of Lanthanide(III) Coordination Compounds with Nitrogen and Oxygen Containing Ligands

The single crystals of three novel binuclear lanthanide coordination compounds, [Ln(2‑FBA)3terpy]2·2(2-FHBA)·nH2O (2-FHBA is 2-fluorobenzoic acid, 2-FBA is 2-fluorobenzoate, terpy is 2,2':6',2"-terpyridine) (Ln = Sm (1), n = 3; Ln = Eu (2), Gd (3), n = 2) have been obtained and characterized. Notably, coordination compounds 1–3 are isostructural. In each binuclear unit two Ln(III) ions are linked by two 2-FBA ligands in the bidentate-bridging mode. The remaining four 2-FBA ligands are in the bidentate chelating mode. The terpy ligands are in the tridentate chelating mode. Binuclear coordination compounds 1–3 is stitched by C–H…F bonds and π–π stacking to form one-dimensional and two-dimensional structures. Thermogravimetric analysis of coordination compounds 1–3 is investigated through TG-DSC/FTIR techniques, revealing that the coordination compounds begin to decompose at around 360 K and eventually form lanthanide oxides. The coordination compounds 1 and 2 exhibit certain fluorescence characteristics. The fluorescence lifetime and intrinsic quantum yields of coordination compound 2 is 1.27 ms and 15.96%, respectively. The fluorescence intensity and fluorescence lifetime of the coordination compounds are higher than that of Ln(III) ions. What’s more, the heat capacities of coordination compounds 2 and 3 are measured, and the thermodynamic functions are deduced from the molar heat capacity data.