A new salicylaldehyde-based azo dye and its two lanthanide(iii) complexes displaying slow magnetic relaxation

Abstract

A new salicylaldehyde-based azo dye 5-azotriazolyl-3-methoxysalicylaldehyde (H₂TMSA) and its two Ln³⁺ complexes {[Ln(HTMSA)₃(H₂O)₂][Ln(HTMSA)₃(DMF)(H₂O)]}·15H₂O (Ln = Dy(1) and Tb(2)) have been synthesized and characterized by IR, Raman, ¹H NMR and single-crystal X-ray diffraction techniques. H₂TMSA shows an azo form in acidic (pH < 5.05) and strong basic (pH > 12.41) conditions, and a pH-dependent azo-hydrazone tautomerism in the range of pH 5.05 to 12.41, which is demonstrated by the time-dependent density functional theory (TD-DFT) calculations. Single-crystal X-ray diffraction reveals that 1 and 2 are isostructural complexes in which the Ln³⁺ ions are surrounded by six oxygen atoms from three dichelate HTMSA⁻ ligands and two oxygen atoms from two solvent molecules forming a distorted square-antiprismatic geometry. Complex 1 shows distinct slow magnetic relaxation under a zero dc field, while 2 displays field-induced slow magnetic relaxation. Ab initio calculations were performed on the two complexes to understand their magnetic anisotropy and their different magnetic dynamics.