Conspectus
Coordination polymers, commonly known as infinite
crystalline lattices,
are versatile networks and have diverse potential applications in
the fields of gas storage, molecular separation, catalysis, optics,
and drug delivery, among other areas. Secondary building blocks, mainly
incorporating rigid polydentate organic linkers and metal ions or
clusters, are commonly employed to construct coordination polymers.
Recently, novel building blocks such as coordination polyhedra have
been utilized as metal nodes to fabricate coordination polymers. Benefiting
from the rigid porous structure of the coordination polyhedron, prefabricated
designer “pores” can be incorporated in this type of
coordinate polymer. In this Account, coordination polymers built by
pyrogallol[4]arene-assembled metal–organic nanocapsules are
summarized. This class of metal–organic nanocapsule possesses
the following advantages that make them excellent candidates in the
construction of coordination polymers: (i) Various geometrical shapes
with different volumes of the inner cavities can be obtained from
these capsules. Among them, the two main categories illustrated are
dimeric and hexameric capsules, which comprise two and six pyrogallol[4]arenes
units, respectively. (ii) A wide range of possible metal ions ranging
from main group metals to transition metals and even lanthanides have
been demonstrated to seam the capsules. Therefore, these coordination
polymers can be endowed with fascinating functionalities such as magnetism,
semiconductivity, luminescence, and radioactivity. (iii) Up to 24
metal ions have been successfully embedded on the surface of the nanocapsule,
each a potential reaction site in the construction of coordination
polymers, opening up pathways for the formation of multidimensional
frameworks.
In this Account, we focus primarily on the synthesis
and the structural
information on pyrogallol[4]arene-derived coordination polymers. Coordination
polymers can be formed by introducing linkers with two coordination
sites, using pyrogallol[4]arenes with coordination sites on the tail,
or even via metal ions cross-linking with each other. Machine learning
was recently developed to help us predict and screen the structures
of the coordination polymers. With single crystal analysis in hand,
detailed structural information provides a molecular-level perspective.
Significantly, following the formation of coordination polymers, the
overall shape and structure of the discrete metal–organic nanocapsules
remains essentially unchanged, with full retention of the prefabricated
pores. If a rigid linker is used to connect capsules, more than one
lattice void with different volumes can be found within the framework.
Thus, molecules with different sizes could potentially be encapsulated
within these coordination polymers. In addition, flexible ligands
can also be employed as linkers. For example, polymers have been employed
as large linkers that transform the crystalline coordination polymers
into polymer matrices, paving the way toward the ...