each Fe center adopted an octahedral geometry [46]. More recently, when metalcarbonyl-cluster-coordinated dipyridyl donors were combined with a linear Pt-based
acceptor, the reaction products could be tuned between a pentagon/hexagon mixture
and pure pentagons, depending on the bulkiness of the building blocks used [47].
4 Supramolecular Polyhedra
The 2D SCCs described above serve to illustrate the versatility of the directional
bonding method in the preparation of supramolecular metallacycles. However, this
design strategy is in not limited to planar assemblies. Whereas the edge-directed
deconstruction of polygons demands the use of ditopic ligands of various angles,
introducing a third, fourth, or more donor or acceptor sites on a given building block
unlocks the rational design of 3D architectures. Although theoretically more
complex than their metallacyclic counterparts, in practice, the formation of
metallacages follows the same basic design principles first established for the
formation of molecular squares and extended to higher order polygons.
Whereas the building blocks of metallacycles occupy the edges of their target
polygons, dubbed “edge-directed assembly”, the formation of polyhedra via the
coordination-driven self-assembly permits “face-directed” strategies in which
precursors can be used to occupy entire faces of a target metallacage. This can be
illustrated by considering the cube; edge-directed assembly demands eight tectons
to represent the vertices in the form of tritopic species with 90
angularities between
binding sites. These vertices can then be joined by 12 linear ditopic donors to act as
the edges of the cube [48]. In contrast, the six faces of a cube can be represented by
tetratopic panels with 90
angles between each adjacent binding site [49]. These
panels will become the faces of a cube upon assembly with twelve 90
ditopic
building blocks, which lie at the center of each edge (Fig. 5).
4.1 Platonic and Archimedean Solids
The Platonic solids were popularized thousands of years ago when Plato
hypothesized that they were the building blocks of the classical elements. The
criteria of possessing congruent regular polygonal faces that meet at symmetrical
vertices limits the number of Platonic solids to five: tetrahedron, cube, octahedron,
dodecahedron, and icosahedron (Fig. 6). These requisites are relaxed slightly in the
classification of Archimedean solids, which possess two types of regular polygonal
faces but still demand identical vertices. Of the 15 polygons of this type, the
truncated tetrahedron, cuboctahedron, and rhombicuboctahedron are the most
relevant in the context of coordination-driven self-assembly, although other
geometries have been realized.
236
T.R. Cook and P.J. Stang
acceptor, the reaction products could be tuned between a pentagon/hexagon mixture
and pure pentagons, depending on the bulkiness of the building blocks used [47].
4 Supramolecular Polyhedra
The 2D SCCs described above serve to illustrate the versatility of the directional
bonding method in the preparation of supramolecular metallacycles. However, this
design strategy is in not limited to planar assemblies. Whereas the edge-directed
deconstruction of polygons demands the use of ditopic ligands of various angles,
introducing a third, fourth, or more donor or acceptor sites on a given building block
unlocks the rational design of 3D architectures. Although theoretically more
complex than their metallacyclic counterparts, in practice, the formation of
metallacages follows the same basic design principles first established for the
formation of molecular squares and extended to higher order polygons.
Whereas the building blocks of metallacycles occupy the edges of their target
polygons, dubbed “edge-directed assembly”, the formation of polyhedra via the
coordination-driven self-assembly permits “face-directed” strategies in which
precursors can be used to occupy entire faces of a target metallacage. This can be
illustrated by considering the cube; edge-directed assembly demands eight tectons
to represent the vertices in the form of tritopic species with 90
angularities between
binding sites. These vertices can then be joined by 12 linear ditopic donors to act as
the edges of the cube [48]. In contrast, the six faces of a cube can be represented by
tetratopic panels with 90
angles between each adjacent binding site [49]. These
panels will become the faces of a cube upon assembly with twelve 90
ditopic
building blocks, which lie at the center of each edge (Fig. 5).
4.1 Platonic and Archimedean Solids
The Platonic solids were popularized thousands of years ago when Plato
hypothesized that they were the building blocks of the classical elements. The
criteria of possessing congruent regular polygonal faces that meet at symmetrical
vertices limits the number of Platonic solids to five: tetrahedron, cube, octahedron,
dodecahedron, and icosahedron (Fig. 6). These requisites are relaxed slightly in the
classification of Archimedean solids, which possess two types of regular polygonal
faces but still demand identical vertices. Of the 15 polygons of this type, the
truncated tetrahedron, cuboctahedron, and rhombicuboctahedron are the most
relevant in the context of coordination-driven self-assembly, although other
geometries have been realized.
236
T.R. Cook and P.J. Stang