Synthesis, phosphorescence and luminescence properties of novel europium and gadolinium tris-acylpyrazolonate complexes

Two new lanthanide (III) complexes, namely [Ln(QCy)3(H2O)] (Ln = Eu (1), Gd (2); HQCy = 1-phenyl-3-methyl-4-cyclohexylcarbonyl-pyrazol-5-one), have been obtained by reaction of corresponding Ln(NO3)3·xH2O with excess of HQCy and MOH, M = Li, Na, K or Cs. Unexpectedly, formation of the [Ln(QCy)4]− species was not observed, also when the reaction was carried out in ligand excess and by varying reaction conditions and molar ratios. [Eu(QCy)3(H2O)] (1) has been structurally characterized by single crystal X-ray study. The crystal structure of 1 is based on molecular [Eu(QCy)3(H2O)] moieties connected by O–H…N hydrogen bonds into 1D-chain. Phosphorescence spectra of 2 allowed to determine the very high energy of the triplet level of the ligand (QCy) 23,640 cm−1, which correlates well with the calculated value of 24,040 cm−1. Weak luminescence of the europium species 1 is observed even at room temperature.