Metallacrowns as Templates for Diabolo-like {LnCu8 } Complexes with Nearly Perfect Square Antiprismatic Geometry.

A series of diabolo-like nonanuclear {LnIII CuII8 } (Ln=Tb, Dy, Ho, Er, Tm, Yb, and Y) clusters were prepared in which the LnIII ion is capped by two 8-MC-4 metallacrown ligands to form a nearly ideal square antiprismatic (SAP) coordination geometry with D4d symmetry. Despite the lack of crystallographic symmetry, these molecules engender the lanthanide ions with highly axial mJ states. The axial/equatorial nature of the crystal field in environments close to ideal SAP geometry is very subtle and influenced by the nature of the ligand lone pairs. Slow magnetic relaxation behaviour was observed for the DyIII , ErIII , TmIII , and YbIII analogues, and the obtained effective energy barriers are not consistent with excitations on the LnIII ion, suggesting a more nuanced situation.