Dinuclear lanthanide(III) complexes from the use of di-2-pyridyl ketone: Preparation, structural characterization and spectroscopic studies

The use of di-2-pyridyl ketone ((py)2CO) in lanthanide(III) chemistry has yielded neutral dinuclear complexes. The 1:1:1 Ln(NO3)3 · xH2O/(py)2CO/LiOH · H2O reaction mixtures in MeOH–EtOH afford the complexes [Ln2(NO3)3{(py)2C(OMe)O}2{(py)2C(OH)O}] (Ln = Pr, 1; Ln = Eu, 2; Ln = Tb, 3; Ln = Er, 4). The monoanionic derivatives of the hemiacetal and the gem-diol forms of di-2-pyridyl ketone have been derived from the Ln(III)-mediated addition of solvent (MeOH, H2O involved in the alcohols and in the starting materials) on the carbonyl group of (py)2CO. The crystal structure of the representative complex 4 · 0.8EtOH · 0.4MeOH has been solved by single-crystal X-ray crystallography. The two ErIII atoms are doubly bridged by the deprotonated oxygen atoms of the η1:η2:η1:μ2 (py)2C(OH)O− ligand and one η1:η2:η1:μ2 (py)2C(OMe)O− ion. One ErIII atom is in a nine-coordinate tricapped trigonal prismatic ligand environment comprising the two bridging hydroxyl oxygen atoms, four oxygen atoms from two chelating nitrato ligands and three 2-pyridyl nitrogen atoms, while dodecahedral, eight-coordination at the other ErIII atom is completed by two oxygen atoms of the third chelating nitrato ligand, one nitrogen atom of the bridging (py)2C(OMe)O− ligand and the N,N,Odeprotonated triad from one tridentate chelating (py)2C(Me)O− ion. The complexes were characterized by room-temperature effective magnetic moments and spectroscopic (IR, solid-state f–f) techniques. All data are discussed in terms of the nature of bonding and known (4) or assigned (1–3) structures. The Eu(III) and Tb(III) complexes 2 and 3 display in the solid state and at room temperature an intense red and green emission, respectively; this photoluminescence is achieved by an indirect process (antenna effect).

The reactions between Ln(NO3)3 · xH2O (Ln = Pr, Eu, Tb, Er) and di-2-pyridyl ketone in a mixture of MeOH and EtOH give dinuclear nitrate complexes containing the monoanions of both the gem-diol and hemiacetal derivatives of the ketone as ligands. The ligands adopt the three shown coordination modes in every complex. The Eu(III) and Tb(III) complexes display an intense red and green emission, respectively, in the solid state, the photoluminescence being achieved by an indirect process (antenna effect).Figure optionsDownload as PowerPoint slide