Emission spectra of europium(III) complexes with 4-methylmorpholine- N-oxide

Abstract

Complexes of Eu(III) with 4-methylmorpholine- N-oxide (MMNO), with perchlorate, hexafluorophosphate and trifluoro-methane-sulfonate as counter ions were prepared and characterized by elemental analysis and IR spectroscopy. The room temperature fluorescence spectrum of Eu(ClO 4) 3·6MMNO suggests an Oh symmetry for the Eu(O) 6 chromophore. The spectrum is highly modified at 77 K, suggestive of a C 3v symmetry. The very unusual sharp transition in the fluorescence behavior occurs at 25 K as obtained from a ln intensity vs. 1/ T (K), plot and is interconvertible to the original room temperature spectrum. The spectra of the corresponding hexafluorophosphate and trifluoromethanesulfonate complexes, at both 298 and 77 K are consistent with a C 3v symmetry, no changes with temperature being observed.