Topological Self-Assembly of Highly Symmetric Lanthanide Clusters: A Magnetic Study of Exchange-Coupling Fingerprints in Giant Gadolinium(III) Cages

The creation of a perfect hollow nanoscopic sphere of metal centers is clearly an unrealizable synthetic challenge. It is, however, an inspirational challenge from the viewpoint of chemical architecture and also as finite molecular species may provide unique microscopic insight into the origin and onset of phenomena such as topological spin-frustration effects found in infinite 2D and 3D systems. Herein, we report a series of high-symmetry gadolinium(III) (S = 7/2) polyhedra, Gd-20, Gd-32, Gd-50, and Gd-60, to test an approach based on assembling polymetallic fragments that contain different polygons. Structural analysis reveals that the Gd-20 cage resembles a dodecahedron; the vertices of the Gd-32 polyhedron exactly reveal symmetry O-h; Gd-50 displays an unprecedented polyhedron in which an icosidodecahedron Gd-30 core is encapsulated by an outer Gd-20 dodecahedral shell with approximate I-h symmetry; and the Gd-60 shows a truncated octahedron geometry. Experimental and theoretical magnetic studies show that this series produces the expected antiferromagnetic interaction that can be modeled based on classical spins at the Gd sites. From the magnetization analyses, we can roughly correlate the derivative bands to the Gd-O-Gd angles. Such a magneto-structural correlation may be used as fingerprints to identify these cages.