Lanthanide(III) ion coordination by a concave reagent

A macrobicylic ligand 1 formed by the A,D-bridging of a calix[6]arene with a 2,9-disubstituted 1,10-phenanthroline unit reacts with Yb(III) under basic conditions in dimethylformamide (dmf) to give a neutral, mononuclear complex characterised by X-ray crystallography as [Yb(1-3H)(dmf)] center dot 3dmf. The structure shows that although the metal can be considered to lie within a cavity formed by the "concave reagent" ligand, this does not entirely prevent its coordination to a dmf molecule between arms of the macrobicycle. Stability constant measurements indicate that I forms complexes of similar strength across the lanthanide(III) series. (c) 2005 Elsevier Ltd. All rights reserved.