Tl benzene multicarboxylic acid coordination polymers: Structural, thermal and fluorescence studies

[Tl₃(μ-1,2,3-btc)]_n (1,2,3-H₃btc = 1,2,3-benzenetricarboxylic acid) (1), [Tl₂(μ-1,3,5-Hbtc)(H₂O)]_n (1,3,5-H₃btc = 1,3,5-benzenetricarboxylic acid) (2) and [Tl₄(μ-1,2,4,5-btc)]_n (1,2,4,5-H₄btc = 1,2,4,5-benzenetetracarboxylic acid) (3), three new Tl^I coordination polymers have been synthesized, characterized by elemental analysis and IR spectroscopy and their structures determined by single-crystal X-ray diffraction. The thermal stability of compounds 1-3 were studied by thermal gravimetric (TG) and differential thermal analyses (DTA). The single-crystal X-ray analysis of compounds 1-3 shows that the compounds are structurally diverse showing three-dimensional coordination polymers. The carboxylic groups of the ligands 1,2,3-btc³⁻, 1,3,5-Hbtc²⁻ and 1,2,4,5-btc⁴⁻ in the new Tl^I coordination polymers are not chelated and only act as bridging groups. In compounds 1-3, the lone pair of Tl(I) atoms is ‘active’ in the solid state and the coordination spheres are hemisphere type. Solution state luminescent spectra of compound 2 indicate intense fluorescent emissions at ca. 400 nm.