A series of Ln-p-chlorobenzoic acid–terpyridine complexes: lanthanide contraction effects, supramolecular interactions and luminescent behavior

Abstract

Fifteen new lanthanide p-chlorobenzoic acid complexes, [PrL₃(terpy)(H₂O)]₂ (1), [LnL₃(terpy)(H₂O)]₂ (Ln = Nd (2), Sm (3), and Eu (4)), and [LnL₃(terpy)(H₂O)] (Ln = Sm (3′), Eu (4′), Gd (5), Tb (6), Dy (7), Ho (8), Er (9), Tm (10), Yb (11), Lu (12), and Y (13); HL: p-chlorobenzoic acid; terpy: 2,2′:6′,2′′-terpyridine), have been synthesized hydrothermally at varying temperatures and structurally characterized by single crystal and powder X-ray diffraction. The series is comprised of binuclear molecular units (Pr–Eu) that give way to mononuclear molecular complexes (Sm–Y) as the lanthanide contraction takes effect. All fifteen complexes feature a tridentate terpyridine ligand, p-chlorobenzoic acid ligands exhibiting multiple binding modes, bidentate, bridging bidentate, and monodentate, and a bound water molecule. Binuclear complexes 1–4 are stitched together via intermolecular interactions: aromatic–aromatic interactions for 1, halogen⋯halogen interactions for 2–4, to form 1D chains. Mononuclear complexes 3′, 4′, and 5–13 utilize supramolecular hydrogen and halogen bonding to form 2D sheets. Visible and near-IR solid state luminescence studies were performed on complexes 2, 3, 3′, 4, 4′, 6, 7 and 11 and the characteristic visible luminescence of Sm(III), Eu(III), Tb(III), and Dy(III) was exhibited. The near-IR spectra of the Nd(III) and Yb(III) complexes exhibit weak characteristic luminescence, showing that terpy can act as a sensitizing chromophore in these systems.