Versatile Assembly of Metal-Coordinated Calix[4]resorcinarene Cavitands and Cages through Ancillary Linker Tuning

We
propose a design strategy for assembly of metal-coordinated
calix[4]­resorcinarene cavitands and cages by tuning of the ancillary
linkers. Assembly of newly functionalized cavitand with angular isophthalic
acid analogs affords three intriguing metal-coordinated cavitands
with deep cavities, 1a–1c. Further,
by mediating appropriate spacers between two isophthalic acids, two
bowl-shaped cavitands are successfully joined together to produce
three elegant coordination cages with tunable sizes and shapes, 2a–2c. The cavitand and cage crystals
possess considerable amount of accessible porosities, as clearly established
by gas adsorption measurements. Remarkably, 1a–1c also exhibit high structural flexibilities, reversibly
transforming between the open-pore and the narrow-pore structures,
upon removal and sorption of guest molecules, as evidenced by diffraction
and gas adsorption measurements. By combining experimental studies
with density functional theory (DFT) calculations, we thoroughly elucidated
the mechanism of the structural transformations in response to external
stimuli in this new class of flexible porous solids.