Synthesis, crystal structures, and luminescence of organic-lanthanide complexes with nicotinate and isonicotinate ligands

Abstract

Six lanthanide coordination compounds with two isomeric carboxylic acids, nicotinic acid (HL 1) and isonicotinic acid (HL 2), [(L 1) 3Ln(H 2O) 2] 2 (Ln = Eu, 1; Gd, 2; Tb, 3) and [(L 2) 2Ln(H 2O) 4][NO 3] (Ln = Eu, 4; Gd, 5; Tb, 6), have been synthesized and structurally characterized by single-crystal X-ray diffraction. Complexes 1-3 are dimeric whereas 4-6 are polymeric, all with 8-coordination of Ln 3+. The distinction between these lanthanide complexes is readily accomplished from the 10 K high resolution electronic emission spectra. Spectral interpretation is given for the Eu 3+ complexes 1, 4, whereas the spectra of 3 and 6 are more complex. The relationships between spectroscopic and crystallographic site symmetries are discussed. The calculated second rank crystal field strengths of Eu 3+ in 1 and 4 are intermediate in magnitude. © 2008 American Chemical Society.