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

Abstract

The use of di-2-pyridyl ketone ((py) 2CO) in lanthanide(III) chemistry has yielded neutral dinuclear complexes. The 1:1:1 Ln(NO 3) 3 · xH 2O/(py) 2CO/LiOH · H 2O reaction mixtures in MeOH–EtOH afford the complexes [Ln 2(NO 3) 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, H 2O 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 Er III atoms are doubly bridged by the deprotonated oxygen atoms of the η 1:η 2:η 1:μ 2 (py) 2C(OH)O − ligand and one η 1:η 2:η 1:μ 2 (py) 2C(OMe)O − ion. One Er III 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 Er III 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,O deprotonated 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).