Two complexes of Eu3+ ion with pentadentate Schiff-base ligands exhibiting red photoluminescence

Two luminescent europium complexes, Eu(DAPBH)2(NO3)3·2H2O (1) and Eu(DAPBH)(CH3CH2OH)(SCN)3·H2O (2) (where DAPBH = (1,1′-(pyridine-2,6-diyl)bis(ethan-1-yl-1-ylidene))dibenzohydrazide, have be synthesized and structurally characterized. The Eu3+ ion is 10-coordinated with six N atoms and four O atoms from two pentadentate DAPBH ligands to form a distorted bicapped tetragonal antiprism geometry and the nitrate counter ions are not coordinated to Eu3+ ion in 1, while the 9-coordinate Eu3+ ion is bound to the N atoms of three monodentate thiocyanates (counter ions), three N atoms and two O atoms of a pentadentate DAPBH ligand as well as to the O atom of an ethanol molecule with a distorted monocapped tetragonal antiprism coordination environment in 2. Two complexes exhibit a red luminescence of Eu3+ ion, stemming from the intra-4f transitions, which is contributed to that (1) the coordination sphere of Eu3+ ion completed by pentadentate DAPBH ligands or counter anions effectively protect the excited state of Eu3+ ion from being quenched by water molecules in 1 and 2; (2) there should be a better match between the pentadentate DAPBH ligand triplet excited state and europium 5D0 excited state.

Graphical abstractEfficient energy transfer from conjugated pentadentate ligands to Eu3+ center leads to two mononuclear europium complexes, Eu(DAPBH)2(NO3)3·2H2O (1) and Eu(DAPBH)(C2H5OH)(SCN)3·H2O (2) (DAPBH = 2,6-diacetylpyridinebis(benzoic acid hydrazone) emitting characteristic red luminescence of Eu3+ ion.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► A pentadentate pyridyl-based Schiff-base ligand was used for constructing luminescent Eu3+ complex. ► The ligand has efficient ‘antenna effect’ for Eu3+ ion. ► Two complexes of Eu3+ ion with the ‘antenna effect’ ligand show intensely characteristic emission of Eu3+ ion.