Otherwise Unstable Structures Self-Assemble in the Cavities of Cuboctahedral Coordination Cages

We present a method for the directed
self-assembly of interlocked
structures and coordination complexes in a set of metal–organic
hosts. New homo- and heteroleptic metal complexesspecies that
cannot be prepared outsideform within the cavities of cuboctahedral
coordination cages. When linear bidentate guests and macrocycles are
sequentially introduced to the host, a rotaxane is threaded internally;
the resulting ternary host–guest complex is a new kind of molecular
gyroscope. Tetradentate guests segregate the cavities of these cages
into distinct spaces, promoting new stoichiometries and modes of ligand
binding to metal ions. The behaviors of bound complexes were observed
to alter markedly as a result of confinement: In situ oxidations and spin transitions, neither of which occur ex situ, were both observed to proceed. By providing a tailored
space for new modes of coordination-driven self-assembly, the inner
phases of cuboctahedral coordination cages provide a new medium for
synthetic coordination chemistry.