Add time:08/20/2019         Source:sciencedirect.com

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.

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