Complexes of lanthanide ions with the crown ether 1,4,7,10,13,16-hexaoxacyclo-octadecane

Abstract

The title crown ether forms three types of compound with lanthanide ions, [M(NO₃)₃(crown)](M = La—Nd), M₄(NO₃)₁₂(crown)₃(M = La—Gd), and [M(NO₃)₃(OH₂)₃]·crown (M =Gd—Lu). Crystal structures of the first and third types have been determined by X-ray diffraction. The complex [La(NO₃)₃(crown)] is orthorhombic, space group Pbca, with a= 12.249, b= 15.618, c= 21.852 Å, and Z= 8. Least-squares refinement using 3 607 observed [I > 1.5σ(I)] intensity data has given R= 0.039 9. The lanthanum co-ordination comprises the six crown oxygens [La–O = 2.627–2.771(3)Å] and two oxygens from each of the three bidentate nitrates [La–O = 2.644–2.675(3)Å]. The complex [Gd(NO₃)₃(OH₂)₃]·crown is also orthorhombic, space group probably Pn2₁a, with a= 15.259, b= 14.302, c= 11.094 Å, and Z= 4. The structure has been refined to R= 0.029 using 2 314 observed data. Here the crown is not co-ordinated to the metal ion but is linked to the [Gd(NO₃)₃(OH₂)₃] molecule by O ⋯ HO bonds. The Gd–O bond lengths are 2.41–2.53(1)Å for nitrato- and 2.30–2.46(1)Å for water oxygens.