Stoichiometric control: 8- and 10-coordinate Ln(hfac)3(bpy) and Ln(hfac)3(bpy)2 complexes of the early lanthanides La-Sm.

The coordination sphere of early lanthanide(iii) ions is highly versatile, exhibiting the ability to form 8-, 9-, and 10-coordinate complexes with the same ligand set. The ability to isolate 10-coordinate complexes decreases across the period, and the late lanthanides typically cannot support a coordination number higher than eight. Using two common, commercially available ligands, hfac (1,1,1,5,5,5-hexafluoroacetylacetonato-) and bpy (2,2'-bipyridine), the 8- and 10-coordinate series Ln(hfac)3(bpy) and Ln(hfac)3(bpy)2 (Ln = La-Sm) are compiled in a single investigation, demonstrating that the desired coordination number can be targeted through stoichiometry. Solvent-free syntheses of Ln(hfac)3(bpy) and Ln(hfac)3(bpy)2 complexes from Ln(hfac)3(H2O)3 precursors are investigated using a mechanochemical approach. Structural and spectroscopic properties as well as melting point trends are reported for the series.