Europium and terbium pyrrole-2-carboxylates: Structures, luminescence, and energy transfer

[Display omitted] •New lanthanide pyrrole-2-carboxylates were synthesized.•A distorted single-capped square antiprism is the Ln3+ coordination polyhedron.•The low-energy LMCT state was identified in the europium compound.•LMCT state in Eu3+ pyrrole-2-carboxylate is a luminescence quencher.•The energy of activation for the crossover 5D0 – LMCT is 3900 ± 100 cm−1. Lanthanide pyrrole-2-carboxylates [{Ln(L)3(H2O)2}·H2O]n (Ln = Eu, Gd, Tb) were synthesized and investigated using single crystal X-ray diffraction and optical spectroscopy (luminescence, luminescence excitation and vibrational IR spectra). The europium pyrrole-2-carboxylate crystallizes as a 2D network structure in the P21/c space group. The Eu3+ coordination polyhedron formed by five carboxylic groups and two water molecules can be described as a distorted single-capped square antiprism. The luminescence spectra indicate a low symmetry of the charge distribution around the Ln3+ ion that corresponds to the C1 symmetry of the coordination environment of Eu3+ ion in the [{Eu(L)3(H2O)2}·H2O]n crystal lattice. The low-energy ligand–metal charge transfer (LMCT) state was identified in the europium compound. The shortening of the 5D0 (Eu3+) lifetime in the 230–295 K temperature region, when the compound is heated from 77 to 295 K, and the low luminescence intensity of the europium pyrrole-2-carboxylate are caused by the participation of the LMCT state in quenching processes. The energy of activation determined for the 5D0 – LMCT crossover is 3900 ± 100 cm−1.