Coordination compounds of 4-methylmorpholine-n-oxide (MMNO) with lanthanide trifluoromethanesulfonates and iodides

Full text: Interest in amine-N-oxide complexes of lanthanides has grown in recent years. Trifluoromethanesulfonate and iodide ions seem to have a low coordination ability. The adducts were prepared from the corresponding salts, in ethanol and acetone medium, by reaction with NO excess of MMNO. Analytical data indicate that compounds with compositions LnX3.Y(MMNO) (X=CF3SO3-, Y=5; X=I-, Y=6; Ln=La, Nd, Eu, Er, Yb, Y) were obtained. Conductance data show a 1:2 electrolyte behaviour for the CF3 SO3- and 1:3 for the iodide complexes in acetonitrile. Infrared absorption spectra show that the NO stretching mode is shifted to lower frequencies with relation to the free ligand, indicating coordination through the oxygen. The peaks attributed to νasSO3 and δsSO3 are split, indicating lowering of the symmetry of the CF3SO3- anion, due to coordination. From the absorption spectra of Nd(CF3SO3)3.5(MMNO) in the solid state, the nephelauxetic parameter (b=0.896), covalent factor (b1/2 =0.084) and Sinha's parameter (δ=1.42) were calculated. The oscillator strengths, calculated from absorption spectra in nitromethane, acetonitrile and ethanol, were 19.5, 16.5 and 19.2, respectively. The emission spectra of the Eu adducts are very similar. They present one 5D0 → 7F0, two and one shoulder 5D0 → 7F1 and four peaks attributed to 5D0 → 7F2 transitions. These results were interpreted, taking into account also conductance and IR data, in terms of a coordination number equal to six and a C3v symmetry for the coordination polyhedron