Thermal, spectroscopic and luminescence investigations of lanthanide(III) coordination polymers based on V-shaped 4,4′-sulfonyldibenzoic acid

• The polycrystalline complexes have been obtained by hydrothermal method.
• They decompose in several steps with formation of stable intermediate products: Ln2sdb3 and oxysulfates.
• Water, carbon oxides, sulphur dioxide and benzene are volatile products of thermal decomposition in nitrogen.
• The Eu(III) and Tb(III) complexes exhibit luminescence.

The complexes of lanthanide ions with V-shaped 4,4′-sulfonyldibenzoic acid (Hssdb) of the formula Ln2sdb3·nH2O, where Ln = La(III), Nd(III), Eu(III), Tb(III), Dy(III), Yb(III) and n = 2–6 have been prepared by the hydrothermal method. The complexes were examined by elemental analysis, infrared spectroscopy (ATR-FTIR), X-ray diffraction pattern measurements and different methods of thermal analysis (TG-DSC and TG-FTIR). The luminescence properties of Eu(III) and Tb(III) complexes have been also investigated. The complexes crystallize in the triclinic (La, Nd and Eu) or monoclinic (Tb, Dy, Yb) crystal systems. Additionally, pentahydrate complexes of Dy(III) and Tb(III) are isostructural. 4,4′-sulfonyldibenzoate ligand coordinates lanthanide ions through both carboxylate groups. Heating of the complexes resulted in dehydration and formation of stable Ln2sdb3 compounds. Combustion of the organic ligand leads to the formation of intermediate stable lanthanide oxysulfate Ln2O2SO4 which further decompose into the suitable oxides. In nitrogen atmosphere, investigated complexes release: water, carbon oxides, disulphur oxide and benzene molecules. The Eu(III) and Tb(III) complexes exhibit characteristic red and green luminescence.