Chemical conversion of metal–organic frameworks into hemi-covalent organic frameworks

Abstract

Metal–organic frameworks (MOFs) and covalent organic frameworks (COFs) represent two dominant kinds of reticular materials. Mutual chemical conversion of these two species, however, still remains unreported. Herein, the reaction of a two-dimensional MOF, Ni₃(HITP)₂ (HITP = 2,3,6,7,10,11-hexaiminotriphenylene), with 1,1,3,3-tetramethoxypropane induces the cyclization transformation of partial bis(diimine) nickel coordination subunits to tetraaza[14]annulene (TAA) metallomacrocycle moieties. A hemi-covalent organic framework, P-Ni₃(TAA)₃, with different conversion efficiencies (P) of 34–72% for bis(diimine) nickel units depending on the reaction time has been obtained and preserves permanent porosity and crystallinity. The corresponding time-dependent conversion has been assessed by FT-IR spectroscopy, XPS, SEM, TEM, and powder X-ray diffraction analyses. In comparison with Ni₃(HITP)₂, 40%-Ni₃(TAA)₃ exhibits improved chemical stability under acidic conditions and significantly enhanced catalytic properties towards the photocatalytic CO₂ reduction. This result will be surely helpful in mutual investigations covering both MOFs and COFs.