Emission spectra of europium(III) complexes

Abstract With the purpose to obtain reliable information on the microsymmetry around the central metal ion we have undertaken, lacking specific X-ray studies, the study of the following europium(III) complexes: Eu(PU) 8 X 3 , Eu(EU) 8 X 3 (II), Eu(2-HAN) 8 (ClO 4 ) 3 (III), Eu(biquO 2 ) 4 (ClO 4 ) 3 (IV), Eu(HBPz 3 ) 3 (V), Eu(PA) 4 (ClO 4 ) 3 (VI), Eu(PA) 3 (NO 3 ) 3 (VII), Eu(PA) 3 (NCS) 3 (VIII), Eu(biquO 2 ) 2 (NO 3 ) 3 (IX), Eu(DMU) 3 (NO 3 ) 3 ·2H 2 O (X) Eu(DEU) 3 (NO 3 ) 3 ·2H 2 O (IX), Eu(PU) 3 (NO 3 ) 3 ·3H 2 O (XII), Eu(pyO) 8 X 3 (XIII), Eu(bipyO 2 ) 4 (ClO 4 ) 3 (XIV) and Eu(bipyO 2 ) 2 (NO 3 ) 3 (XV) (X = NO 3 , ClO 4 ). Spectral and conductivity data suggested eight-coordination for the complexes I, II, III, IV, VI, XIV, nine-coordination for the complex VIII and ten-coordination for the complexes IX, XV, but doubt remained about the complexes VII, X, XI, XII, V. The structural analysis of the complex Nd(pyO) 8 (ClO 4 ) 3 showed that the coordination polyhedron closely approximates to the square-antiprism (D 4d ) while the complex La(pyO) 8 (ClO 4 ) 3 has a geometry intermediate between a cube and a square-antiprism (D 4 ) [1]. The emission spectrum of the complex XIII agrees with that geometry found for the lanthanum complex; it closely approximates to the cube [2]. BipyO 2 , biquO 2 and PA are chelating ligands which may give rise to octacoordinated species. The coordination polyhedron of the complex La(bipyO 2 ) 4 (ClO 4 ) 3 has been found to be a cube [3]. The emission spectrum of the complex XIV well agrees with D 4 site symmetry [4]. Dodecahedron (D 2d ) for complex IV and bicapped trigonal prism (C 2v ) for complex VI, bicapped dodecahedron having D 2 symmetry for complex XV and C 2v symmetry for complex IX have been suggested by proper emission spectrum. In complex VIII the coordination polyhedron is made up of three oxygen and six nitrogen atoms. The emission spectrum suggests monocapped square-antiprismatic geometry and C 4v site symmetry for the europium(III) ion. On the basis of IR and conductivity data one must attribute twelve-coordination to europium(III) ion in complex VII. However, the emission spectrum agrees with bicapped dodecahedron and D 2 site symmetry. One nitrate group is thus ionic or two are monodentate. Depending on the number of coordinated water molecules, the C.N. of europium in complexes X, XI, XII may be nine or greater. Monocapped square-antiprism (C 4v ) and tricapped trigonal prism (D 3h ) for nine-coordination and bicapped square-antiprism (D 4d ) and bicapped dodecahedron (D 2 or C 2v ) for ten-coordination are polyhedra encountered for lanthanide(III) complexes. The emission spectra of these complexes exclude C 4v , C 2v , D 4d symmetries. Tricapped trigonal prism and bicapped dodecahedron can be proposed as the polyhedra of these three complexes. This requires only one or no molecule of coordinated water. Square-antiprismatic geometry but lower than D 4d symmetries have been assigned on the basis of the emission spectra to the complexes I, II and III. X-ray study of the complex Yb(HBPz 3 ) 3 showed that the coordination polyhedron is a bicapped trigonal prism [5]. This requires that two molecules of ligand are tridentate whilst the third one is bidentate. The emission spectrum of the complex V is consistent with square-antiprismatic geometry having nearly perfect D 4d symmetry. In general, no correlation exists between low symmetry and high intensity of the hypersensitive transitions or high symmetry and low intensity. This increases in the order: HBPz 2 2 . In the same order increases the intensity ratio 5 D 0 → 7 F 2 / 5 D 0 → 7 F 1 in europium(III) complexes. Abbreviations: PU = perhydropyrimidin-2-one; EU = imidazolin-2-one; DMU = N,N′-dimethylurea; DEU = N,N′-diethylurea; PA = picolinamide; pyO = pyridine-N-oxide; bipyO 2 = 2,2′-bipyridyl-N,N′-dioxide; biquO 2 = 2,2′-biquinolyl-N,N′-dioxide; 2-HAN = 2-quinolinecarboxylic acid; HBPz = hydrotrispyrazolylborate ion.