Increase in coordination number of lanthanide complexes with 2,2′-bipyridine and 1,10-phenanthroline by using β-diketonates with electron-withdrawing groups

The coordination chemistry of Ln(hfpd)3 (hfpd=1,1,1,5,5,5-hexafluoropentane-2,4-dionate) with phen and bpy depends on the size of the Ln3+ ion and on the used solvent. The complexes [Er(hfpd)3(phen)] (7) and [Er(hfpd)3(bpy)] (14) were obtained from the synthesis of Er(CF3SO3)3 with Hhfpd, CsOH and either 1,10-phenanthroline or 2,2′-bipyridine in acetonitrile. The structure of 7 was determined by X-ray crystallography. Similar reactions, but performed in methanol, with various other lanthanide elements resulted in isolation of five different types of complexes, according to stoichiometry and spectral properties. With elements later in the lanthanide series eight-coordinated complexes of the types [Ln(hfpd)3(bpy)] (for Ln=Dy, Ho and Yb) and [Ln(hfpd)3(phen)] (for Ln=Tb, Ho and Yb), like 7, were obtained, whereas with the early lanthanide elements ten-coordinated complexes of the types [Ln(hfpd)3(bpy)2] (for Ln=La and Sm) and [Ln(hfpd)3(phen)2] (for Ln=La, Ce, Pr and Nd) were isolated. The X-ray crystal structure of [La(hfpd)3(bpy)2] (9) was determined, which provided proof for ten-coordination around the La ion. In addition to [Sm(hfpd)3(bpy)2], the synthesis with Sm and bpy and a trace of water yielded a second compound: the nine-coordinated complex [Sm(hfpd)3(H2O)(bpy)]·(bpy) (11), which was structurally characterised by X-ray crystallography. The LnN distances vary largely, depending on the used N-donor and the Ln3+ ion, and do not run parallel with the Ln3+ ionic radius.