The coordination chemistry of benzhydrazide with lanthanide(iii) ions: hydrothermalin situligand formation, structures, magnetic and photoluminescence sensing properties

Abstract

The influence of synthetic conditions on the solid-state structural formation of lanthanide(iii) complexes based on a hydrazide ligand have been investigated and reported. Depending on the solvents and reaction temperatures, the reactions of hydrated Ln(NO3)3with a benzohydrazide (bzz) ligand afforded three classes of lanthanide(iii) coordination complexesviz. [Ln(bzz)(NO3)](NO3)2(1Ln; Ln = Sm (1), Eu (2), Gd (3), Tb (4), Dy (5)), [Ln(bzz)(ben)3(H2O)]·H2O (2Ln; Ln = Pr (6), Nd (7), Sm (8), Eu (9), Gd (10), Tb (11), Dy (12), Er (13)), and [Ln3(ben)3] (3Ln; Ln = Eu (14), Gd (15), Tb (16), Dy (17), Er (18), Tm (19), Yb (20), Lu (21)). Complexes1-5in series1Lnwere isolated by slow evaporation of their isopropanol solutions at ambient temperature, and the complexes display similar discrete structures bearing distinct intermolecular N-H⋯O hydrogen bonds to generate a three-dimensional (3D) supramolecular architecture. Complexes6-13in series2Lnwere obtained under hydrothermal conditions at 110 °C where thein situgenerated benzoate (ben) ligands participated in the formation of one-dimensional (1D) coordination polymers (CPs) with the bzz ligands. At a temperature of 145 °C the hydrothermal conditions result in the formation of the thermodynamically more stable products of14-21in series3Ln, in which the bzz ligand underwent completein situhydrolysis to create the ben ligand. These coordination assemblies feature 1D zigzag chains that are formed by unusual low coordination numbers of the six- and seven-fold coordinated Ln3+centers bridged by the ben ligands inμ2- andμ3-coordination modes. Notably, the chain structures of2Lncan be transformed into the zigzag tape-like structures of3Lnupon heating the crystalline samples to 400 °C in air. In the solid state at room temperature, the Eu- (2,9,14) and Tb- (4,11,16) containing complexes emit red and green light, respectively. The luminescence investigations show that the Eu- (9,14) and Tb-(11,16) based CPs could be used as fluorescent probes for acetone and Co2+ionsviaan energy competition mechanism. Meanwhile, the Gd- (10,15)and Dy- (12,17) based CPs show typical antiferromagnetic interactions.