COF in the end is a single crystal, MOF crystal, crystal polymer, or both?
Polyelectrolyte single crystal is obtained by polymerization of the topology, i.e. a small molecule crystal monomer is formed first and then form a polymer in situ polymerization of a single crystal. This is not a universal method, How can the single crystal from the polymer solution obtained as the direct crystallization of small molecules to obtain a single crystal like remains a challenge. frame material (organic frameworks) in the past three decades has been a hot topic, in less than two years ago in the summer of 2018, \”Science\” 361 of 6397 total volume of two serial COF article on single crystal structure, from the United States Dichtel research group at Northwestern University and Lanzhou University Tianqiong Ma, the father of Omar Yaghi molecular framework of cooperation team, the first time the COF single crystal. 
from the MOF to the COF and then to the recent HOF, each synthesized a new molecule, if not its single crystal structure, the work will always feel incomplete. And because covalently linked not very flexible, single-crystal COF has been long recognized as the most difficult one. COF can grow a single crystal of a two-dimensional or three-dimensional structure is not easy, one-dimensional culture COF crystal even more difficult. Considering the two and three dimensions are usually centrosymmetric COF secondary frequency overlay (second-harmonic generation, SHG) (ferroelectricity) and a ferroelectric deletion limit its application, the preparation of one-dimensional crystal becomes more COF meaningful. From another perspective, a COF-dimensional crystal can be regarded as one-dimensional single-crystal polymer having a frame structure. There are many polymer is amorphous, some are semi-crystalline (including liquid crystalline), such as for the production of a variety of plastic products, high density polyethylene (HDPE) is a semi-crystalline polymer, rendering the appearance the opaque state. How to make crystal polymer chain both densely stacked without that form the frame structure? How to control the polymer structure so that it becomes crystalline to thereby obtain a single crystal structure having a periodicity? 
Recently, a metal binding ligand is not covalent chemical stability and dynamic, from NUS Kian PingLoh and from Peking University [ 123] JunliangSun , etc. Researchers cleverly design the dimensional polymer having a periodic frame structure, the one-dimensional crystal COF successfully prepared. Preparation of self-assembled binding \”V\” shaped rigid monomers and condensation polymerization. Interestingly, the single crystal structure of this one-dimensional COF silver is highly dependent on the molecular chain of the recurring – nitrogen complexation, while the silver is not directly determine the structure of the frame unit, but in a sense may be regarded as a special MOF, which is referred to herein oF metallo-COF (mCOF-Ag). The authors found that when the ratio of the polymerizable monomer I and monomer II is 1: 1 when, can form a low-crystalline random configuration (shown in Figure 1 a). But merely changing the ratio of 3: 1, with the help of AgBF4 form mCOF-Ag (as shown at FIG. 1). MCOF-Ag polymerization process can be simply understood as: 1 monomer I and monomer II according to 1: 1 AB type condensation occurs randomly polymerized to form a linear polymer; 2 two excess does not participate in the polymerization reaction monomer I, respectively, but with a silver complex directly on monomer repeat units I AB polymer and a monomer repeat unit II, to form a stable single-crystal structure. As can be seen, as a polymer chain \”Z\” shaped arrangement, the structure remains in a large number of reactive amino, the excess monomer by the introduction of active amino I will play a greater role in the later.
FIG 1.mCOF-Ag synthesized single crystal
FIG 2.mCOF-Ag structural characterization and analysis
Original link: https: //doi.org/10.1038/s41467-020-15281-1
