Solution and solid state spectroscopy of tetrakis complexes of 2,2′-bipyridine-1,1′-dioxide with europium(III)

Previous studies on the crystal structure of a complex formed with 2,2'-bipyridine-1,1'-dioxide (bpyO(2)) and La(III) ions have shown the existence of an tetrakis eight coordinate complex in which the metal ion sits in a site of approximate D-4 symmetry. In this paper we describe high-resolution luminescence and circularly polarized luminescence results on Eu(bpyO(2))(4)(3+). The appearance of several crystal-field transitions in the emission for the Eu(III) complex are interpreted in terms of distortions from the D-4 symmetry seen for the La(III) analog. Extraordinarily large absorption and emission intensities for the hypersensitive transitions of Nd(bpyO(2))(4)(3+) and Eu(bpyO(2))(4)(3+) are observed and discussed. Large circularly polarized luminescence is observed from Eu(bpyO(2))(4)(3+) dissolved in acetonitrile following circularly polarized laser excitation. This result suggests that the complex occurs in solution as a racemic complex that does not racemize on the emission time scale. (C) 2000 Elsevier Science B.V. All rights reserved.