Urea-Linked Covalent Organic Frameworks

2D
covalent organic frameworks (COFs) with flexible urea linkages
have been synthesized by condensation of 1,3,5-triformylphloroglucinol
(TFP) with 1,4-phenylenediurea (BDU) or 1,1′-(3,3′-dimethyl-[1,1′-biphenyl]-4,4′-diyl)­diurea
(DMBDU). The resulting COF-117 and COF-118 undergo reversible structural
dynamics within their layers, in response to inclusion and removal
of guest molecules, emanating from urea CN bond rotation and
interlayer hydrogen-bonding interactions. These compounds are the
first urea-linked COFs, serving to expand the scope of reticular chemistry.