The tridentate ligand N,N'-dimethyl-N,N'-diphenylpyridine-2,6-dicarboxyamide (DMDPhPDA) and the corresponding lanthanum complex [La(NO3)(3)(DMDPhPDA)(2)] have been prepared and structurally characterised. The crystal structure of DMDPhPDA shows syn-anti conformation. In the lanthanum complex, two DMDPhPDA molecules coordinated to La(III) in a tridentate fashion and to three nitrate ions in a bidentate fashion make the lanthanum atom 12-coordinate. The crystal structure of [La(NO3)(3)(DMDPhPDA)(2)] has a C-2 symmetry. The stability constants determined by spectrophotometric titration suggest that [Ln(DMDPhPDA)(2)](3+) is the primary product in CH3CN solution and [Ln(DMDPhPDA)(3)](3+) is difficult to form. However, [Ln(QMDPhPDA)(2)](3+) could not be distinguished in H-1 NMR spectra. The H-1 NMR titration results imply that a fast ligand exchange process takes place. (c) 2007 Elsevier B.V. All rights reserved.