Preparation, X-ray and spectroscopic investigations of europium(III) trinitrato complexes with the macrocycle derived from 2,6-diformyl-4-chlorophenol and diethylenetriamine

The macrocyclic europium(III) complex [Eu- (H2L)(NO3)2]NO3, where H2L is derived from the condensation of 2,6-diformyl-4-chlorophenol and diethylenetriamine, was prepared and crystallized in two forms, yellow and red. The two forms are iso- structural but display slightly different spectroscopic properties. The crystal structure of the red form was determined by X-ray crystallography. The compound is monoclinic, space group View the MathML source, with a = 23.783(3), b = 14.377)(3), c = 19.346(3) Å, ? = 91.76(4)°; Dc = 1.69 g cm-3 for Z = 8. The structure was refined to Rf = 0.053. The europium ion is nine-coordinate, being directly bonded to four oxygen atoms of two bidentate nitrate ions while the third nitrate is ionic. Two oxygen and three nitrogen atoms of the ligand complete the coordination polyhedron. The distances from the metal ion to the bonded atoms are slightly longer than those found for the analogous terbium compound owing to the larger ionic radius of europium. Average distances are: Eu?O(nitrate) 2.50(3) Å, Eu?O(ligand) 2.28(1) Å, Eu?N(ligand) 2.57(3) Å. Spectroscopic measurements suggest that the difference in colour of the two crystalline forms arises from differences in the stacking of the molecules in the unit cell.