Ligand-Based Phase Control in Porous Zirconium Coordination Cages

Zirconium-based coordination cages have received considerable recent
attention as a result of their structural tunability and amenability
to postsynthetic modification. Although these structures have adopted
tetrahedral (4-vertex) or cigar (2-vertex) geometries depending on
the shape and nuclearity of the ligand used in their assembly, their
structures have not previously been shown to be either tunable or
dynamic. Here, we examine the speciation of a series of zirconium-based
cages where the geometry and nuclearity of the product cage can be
tuned via judicious functionalization of dicarboxylate ligands. We
further show that many of these materials exist as both cage structures
in solution or the solid state. With appropriate solvent exchange
and activation conditions, the cigar structures can display Brunauer–Emmett–Teller
(BET) surface areas as high as 123 m2/g. As a result of
their expanded pore structures, the tetrahedra display significantly
increased BET surface areas approaching 700 m2/g. These
results show that by appropriate ligand functionalization the structures
of zirconium-based cages can be modified to tune their phase and surface
area. Finally, the isolation of phase-pure cages allows for the utilization
of anion metathesis reactions to tune their solubility.

近年来，锆基配位笼因其结构可调性及可进行后合成修饰的特性，受到了广泛关注。尽管这类结构会根据组装所用配体的形状与核数，呈现四面体（4顶点）或雪茄形（2顶点）的几何构型，但此前研究尚未证实其结构具备可调性或动态性。本文中，我们针对一系列锆基配位笼的物种分布展开研究，通过对二羧酸配体进行合理的官能化修饰，即可调控产物配位笼的几何构型与核数。我们还证实，诸多此类材料在溶液与固态下均可呈现两种配位笼结构。通过选用合适的溶剂交换与活化条件，雪茄形配位笼的布鲁诺尔-埃米特-特勒（Brunauer–Emmett–Teller, BET）比表面积最高可达123 m²/g。得益于孔径结构的拓展，四面体配位笼的BET比表面积显著提升，最高接近700 m²/g。上述结果表明，通过合理的配体官能化修饰，可调控锆基配位笼的物相与比表面积。最后，通过分离得到纯物相的配位笼，可利用阴离子复分解反应调控其溶解性。