Eu(III) complexes derived from 2-quinolinecarbohydrazide Schiff base ligand, relations between structure and luminescence properties

• Crystal structures of four coordination complexes of Eu(III) and new Schiff base ligand were reported. • Luminescence features were investigated. • New complexes were investigated by FT-IR and DTA, TGA. A series of Eu(III) complexes were obtained following the template condensation of 2-quinolinecarbohydrazide and 2,6-diacetylpyridine, namely: [Eu(H 2 pbqh)(NO 3 ) 3 ]·MeOH ( 1 ), [Eu(Hpqh)(NO 3 ) 3 ]·2MeCN ( 2 ), [Eu(H 2 pbqh)(SCN 2 )(MeOH) 2 ](SCN) ( 3 ) and [Eu 2 (pbqh) 2 (NO 3 ) 2 (H 2 O) 2 ]·2.5MeOH ( 4 ). The structures of complexes and a new H 2 pbqh ligand ( N',N'''-((1E,1′E)-pyridine-2,6-diylbis(ethan-1-yl-1-ylidene))bis(quinoline-2- carbohydrazides )) were elucidated by single-crystal X-ray diffraction. H 2 pbqh coordinate pentadentate ONNNO and forms mononuclear complexes 1 and 3 . The bis -deprotonated ligand pbqh 2- act as hexadentate/bridging mode generates the binuclear complex in 4 . The partially condensed ligand Hpqh, tetradentate ONNO, was recorded in complex 2 . The crystallographic results reveals that the coordinated H 2 pbqh/Hpqh ligands and Eu 3+ cation form a planar structure in these complexes and nitrate anions coordinate chelate, completing the coordination sphere of Eu 3+ . The solid state photoluminescent emission was investigated highlighting the nitrate complexes 1 and 2 that exhibit red intense luminescence (λ max = 618 nm). Moreover, the computational calculations reveal different pathways of energy transfer from ligand to Eu 3+ electronic states explaining the luminescent behavior.