The rare earth centres are all seven-coordinate with four nitrogen and three oxygen donors (Figure ). The arrangement of the ligands results in complexes with C3-symmetry. In all cases, the coordination geometry is closest to a capped octahedron with only a small distortion from the ideal geometry; the distortions increase with increasing RE 3+ atomic radii according to continuous shape analysis performed with the SHAPE 2.1 software (Figure and Table ). The RE-O1/N bond lengths are consistent with RE 3+ and the lanthanoid contraction (Table ). Table . Interatomic distances (Å), and hydrogen-bond angles (°) for 1-RE. A search of the Cambridge Crystallographic Database suggests that this cooperative coordination motif has not been observed in a molecular complex with any transition or RE metals. However, a similar motif was observed in a Ca based tetraoxolene coordination polymer. Two enantiomers of 1-RE are present in the structures (Figure ) Å (Table ).