One dimensional energy transfer in lanthanoid picolinates. Correlation of structure and spectroscopy

Abstract

Optical and structural properties of rare earth complexes with 2-pyridine carboxylic acid (‘Hpic’) are evaluated by luminescence spectroscopy, decay measurements, X-ray crystal structure determination, FTIR, DTA and metal content analysis. Corresponding Tb3+and Eu3+ complexes of this ligand are extraordinarily efficient with respect to their luminescence. In the crystalline state the series is isostructural and composed of M[Ln(pic)4]·nH2O (M = Na, NH4; Ln = Eu, Gd, Tb, Ho) with pic-linked [Ln(pic)4]− units forming a chain-like structure, which gives rise to a one-dimensional exchange communication between the rare earth ions; this energy transfer being confined to the chains. Energy transfer of the Coulomb type between the ligands appears to be of significance only, if suitable rare earth acceptor states are not accessible, as is shown for a series of [La(pic)4]− series, in which La3+ is gradually substituted by Tb3+ or Eu3+.