Covalent organic frameworks (COFs) have inherited the features of metal organic frameworks (MOFs) to create 2D or 3D highly porous crystalline architectures with surface areas easily above 1000 m2/g. In addition, COFs are composed of only light elements (C, H, N, O, B), which gives them potential to be effectively used as gas transport and storage materials. Whereas the all-covalent bonding in boronate based COFs results in high thermal stability (> 300 �C), the presence of electron-deficient boron sites make them susceptible to nucleophilic attack. Consequently, even ambient humidity is sufficient to completely decompose COF 1, 5, 10, etc. within hours. We demonstrated the ability of a trace amount of pyridine to stabilize Covalent Organic Frameworks (COF) � 5 and -10 in humid air.  At a low dose, pyridine forms a Br�nsted-type interaction with unreacted HO-C HHTP sites in both COF-5 and -10.  This interaction weakens the B-O-C bonds sufficiently to break boronate ester bonds at higher pyridine dose, resulting in a full decomposition of both products, disappearance of B[3], and formation of Py..HO and B[4]. Lacking HHTP, the boroxine based COF-1 structure precludes the presence of these destabilizing Br�nsted-type defect sites, and forms weak Lewis-type interactions that convert B[3] sites to B[4], resulting in a partially distorted structure.  COF-1 remains unstable to the presence of moisture at all pyridine doses studied.

Effects of Br�nsted sites on stabilizing B-COFs' structure

248th National Meeting (2014)

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