Lanthanide complexes with 2-bromo-5-methoxybenzoic acid and 5,5′-dimethyl-2,2′-bipyridine: Crystal structures, thermodynamic properties and luminescence behaviors

• Published in: The Journal of chemical thermodynamics 2018-08, Vol.123, p.99-106
• Main Authors: Wu, Xiao-Hui, Ren, Ning, Zhang, Jian-Jun, Wang, Da-Qi
• Format: Article
• Language: English
• Subjects: 2-Bromo-5-methoxybenzoic acid; Crystal structure; Heat capacity; Lanthanide complexes; Luminescence spectrum; Thermodynamic properties
• ISSN: 0021-9614; 1096-3626
• DOI: 10.1016/j.jct.2018.04.002

The complexes 1 and 2 are isostructural. The centre Ln3+ ions are nine-coordinated with a distorted monocapped square antiprismatic coordination geometry. The binuclear molecules are assembled into the 1D, 2D, 3D supramolecular structures by CH⋯Br and CH⋯O hydrogen bonding and π–π stacking interactions. The thermal decomposition mechanism of complexes 1 and 2 is studied by TG analysis and further authenticated by TG/DSC-FTIR technique. The molar heat capacity values of complexes 1 and 2 increases with the increasing of temperature. The similar heat capacity value reflect that the complexes have the same structure. The luminescence spectra indicate that the complexes 1 and 2 exhibit the characteristic emission of Sm3+ ion (4G5/2 → 6H5/2-9/2) and Eu3+ ion (5D0 → 7F0-4). The luminescence lifetime of complex 2 is 1.435 ms. [Display omitted] •The structures of two lanthanide binuclear complexes were obtained.•The 1D, 2D, 3D supramolecular structures were assembled.•The thermal decomposition mechanism was investigated.•The molar heat capacities and thermodynamic functions were calculated.•The luminescence spectrum of two complexes and lifetime of the complex 2 were studied. Two ternary lanthanide complexes [Ln(2-Br-5-MOBA)3(5,5′-DM-2,2′-DIPY)]2 (Ln = Sm(1), Eu(2); 2-Br-5-MOBA = 2-bromo-5-methoxybenzoate; 5,5′-DM-2,2′-DIPY = 5,5′-dimethyl-2,2′-bipyridine) with 2-bromo-5-methoxybenzoic acid and 5,5′-dimethyl-2,2′-bipyridine have been synthesized and characterized. The Single-crystal X-ray diffraction date show that complexes 1 and 2 are isostructural in the triclinic system, space group P1¯. Infrared spectra (IR) and X-ray powder diffraction (PXRD) further confirm that complexes 1 and 2 are isostructural. The basic structural unit forms a 1D chain through the weak CH⋯Br hydrogen bond interaction along the b-axis, and forms a 2D sheet through the π–π stacking interactions along the a-axis. The 2D sheets are further interconnected by the CH⋯O hydrogen bond interaction to assembled into a 3D supramolecular network along the c-axis. In addition, the simultaneous thermal analysis (TG, DTG and DSC) of the complexes and the FTIR spectra of the escaped gas were measured. The heat capacities of the complexes were determined by DSC in the temperature region of 258.15–393.15 K. Furthermore, the luminescence spectrum of the complexes 1 and 2 and luminescence lifetime of complex 2 were also measured.