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, Gd20, Gd32, Gd50, and Gd60, to test an approach based on assembling polymetallic fragments
that contain different polygons. Structural analysis reveals that
the Gd20 cage resembles a dodecahedron; the
vertices of the Gd32 polyhedron exactly reveal
symmetry Oh; Gd50 displays an unprecedented polyhedron in which an
icosidodecahedron Gd30 core is encapsulated
by an outer Gd20 dodecahedral shell with approximate Ih symmetry; and the Gd60 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.