Crystal structure and absorption spectroscopy of Ln(HF2CCOO)(3)center dot 3H(2)O (Ln = Pr, Er) single crystals

Crystal structures of Ln(HF2CCOO)(3).3H(2)O (Ln = Pr, Er) compounds were de termined by X-ray analysis. Both crystals proved to be isomorphous. They ar e triclinic, space group P (1) over bar, with a = 8.394(2) Angstrom, b = 9. 509(2) Angstrom, c = 9.623(2) Angstrom, a = 66.60(2)degrees, beta = 79.34(2 )degrees, gamma = 77.74(2)degrees and Z = 2 for the Pr compound and a = 8.2 58(2) Angstrom, b = 9.358(2) Angstrom, c = 9.458(2) Angstrom, alpha = 66.90 (2)degrees, beta = 79.34(2)degrees, gamma = 77.80(2)degrees and Z = 2 for t he Pr one. The Ln(III) ion adopts an 8-coordinate geometry with six oxygen atoms from carboxylate groups and two oxygen atoms from water molecules, wh ich is best described as the best slightly deformed square antiprism. Absor ption spectra of the Pr(HF2CCOO)(3).3H(2)O single crystal were measured at room and low temperatures. Intensities of the f-f transitions were analysed on the basis of the Judd-Ofelt theory. The results for the praseodymium di fluoroacetate single crystals are compared to those for the lanthanide trif luoroacetates monocrystals. Vibronic mechanism of 4f-4f transitions is disc ussed. (C) 2000 Elsevier Science B.V. All rights reserved.