Hierarchical Assembly of Tubular Frameworks Driven by Covalent and Coordinate Bonding

Hierarchical assembly is used to construct complex materials using elementary building units, mainly depending on the non-covalent interactions involving dynamic bonds. Here we present a hierarchical assembly strategy to build highly crystalline tubular frameworks. A multi-level assembly process driven by dynamic covalent bonds and coordination bonds is shown to produce a supramolecular nanotubular framework and three tubular covalent organic frameworks (COFs). These materials consist of well-ordered triangular nanotubes assembled in an oriented manner. In tubular COFs, the spacing between adjacent nanotubes can be systematically adjusted by altering the connector lengths to create mesoporous structures with adjustable pore size. Moreover, reversible transformations between tubular COFs and layered COFs were achieved by the reversible addition and removal of Zn(NO3)2. The facile demetallation-remetallation process confers tuneable structural properties to the materials and enables the layered COFs to serve as efficient 'sponges' for metal ions. This study represents a notable advance in hierarchical assembly; incorporating covalent bonding into this process is expected to greatly accelerate the development of new materials. Driven by dynamic covalent and coordinate bonding, hierarchical components are formed in situ and assembled in an ordered manner, yielding highly crystalline supramolecular nanotubular frameworks and tubular covalent organic frameworks.