Construction of lanthanide ternary complexes based on 2,4-difluorobenzoic acid and 5,5'-dimethyl-2,2'–bipyridine: Crystal structures, thermoanalysis and luminescence properties

Abstract

Two isostructural complexes are assembled into the 1D, 2D supramolecular structures by C-H⋯F hydrogen bonding interactions. Thermal stability as well as pathways of thermal decomposition of both complexes are investigated by means of the TG/DSC-FTIR methods. The differential scanning calorimetry method is applied to measure heat capacities in 262.15–349.15 K temperature range and the C p,m values of two complexes are found to increased steadily with temperature. Additionally, the luminescence spectrum and lifetime of complex 1 have been investigated. • Two isostructural 2D lanthanide complexes had been synthesized and structurally characterized. • Thermal behaviour of the complexes was investigated by the TG/DSC-FTIR methods. • The heat capacities of the complexes were measured and the thermodynamic parameters were calculated. • Tb 3+ complex exhibited bright green luminescence with a fluorescence lifetime of 1.054 ms. The reactions of 2,4-difluorobenzoic acid, 5,5′-dimethyl-2,2′-bipyridine with Ln(NO 3 ) 3 ·6H 2 O resulted in the formation of two isostructural binuclear complexes [Ln(2,4-DFBA) 3 (5,5′-DM-2,2′-bipy)] 2 (H 2 O) 2 (2,4-DFBA = 2,4-difluorobenzoate, 5,5′-DM-2,2′-bipy = 5,5′-dimethyl-2,2′-bipyridine, Ln = Tb (1), Dy (2)). Their structures were first detected by single crystal X-ray diffraction and further characterized by elemental analysis and TG/DSC-FTIR techniques. The X-Ray crystal structures confirmed that each metal ion resided in distorted triangular prism geometry and both of them had triclinic characteristics with P ī space group. Besides, the complexes also existed as one dimensional chain which was further assembled into two-dimensional supramolecular framework via extensive hydrogen bonds (C-H … F). Heat capacities of the complexes were measured by a DSC instrument over the temperature range from T = 262.15–349.15 K. Additionally, the luminescence spectra and lifetime of complex 1 were evaluated.