Syntheses, crystal structures, luminescence properties and Hirshfeld surface analyses of two mononuclear 2,2′:6′,2′'-terpyridine lanthanide complexes with different β-diketones

Six ternary lanthanide complexes with different beta-diketones as primary "antenna" ligand and 2,2':6',2"-terpyridine as neutral ancillary ligand, namely [Ln(hfac)3(tpy)] [Ln(III) = Eu (1), Gd (2), Tb (3); hfac 1/4 hexafluoroacetylacetone; tpy = 2,2':6',2"-terpyridine] and [Ln(btfa)3(tpy)] [Ln(III) = Eu (4), Gd (5), Tb (6); btfa = 4,4,4-trifluoro-1-phenyl-1,3-butanedione], were synthesized and characterized by elemental analysis, infrared spectroscopy, thermogravimetric analysis, single crystal X-ray diffraction and powder X-ray diffraction. The three-dimensional Hirshfeld surface map and two-dimensional fingerprint analysis reveal that the substitution of hfac with btfa result in the decrease of the H...F/F...H and F...F interactions and the increase of the C...H/H...C and H...H interactions. Solid-state luminescence investigations indicate that the Eu(III) complexes (1-Eu and 4Eu) and the Tb(III) complexes (3-Tb and 6-Tb) display the characteristic lanthanide-centered luminescence upon UV excitations. 1-Eu and 4-Eu emit red light at CIE: 0.6827, 0.3172 and CIE: 0.6819, 0.3179 with the quantum yields (QY) of 78.70 % and 68.85 % and the lifetimes (z) of 0.768 and 0.808 ms, respectively. 3-Tb and 6-Tb emit green light at CIE: 0.2677, 0.7221 and CIE: 0.2680, 0.7217 with the QY values of 7.56 % and 1.38 % and the z values of 0.076 and 0.022 ms, respectively. For the Eu(III) complexes, the substitution of hfac by btfa makes the QY value lower from 78.70 % to 68.85 % and slightly prolong the z value from 0.768 to 0.808 ms, while for the Tb(III) complexes, both of the QY and z values decrease. The results suggest that the structures of the primary beta-diketone ligands could affect the luminescence performances such as QY and z values of the Eu(III) and Tb(III) complexes.