Construction of Robust Open Metal−Organic Frameworks with Chiral Channels and Permanent Porosity

Four new metal−organic frameworks (MOFs) containing chiral channels have been synthesized using an achiral,
triazine-based trigonal-planar ligand, 4,4‘,4‘ ‘-s-triazine-2,4,6-triyltribenzoate (TATB), and an hourglass secondary
building unit (SBU):  Zn3(TATB)2(H2O)2·4DMF·6H2O (1); Cd3(TATB)2(H2O)2·7DMA·10H2O (2); [H2N(CH3)2][Zn3(TATB)2(HCOO)]·HN(CH3)2·3DMF·3H2O (3); [H2N(CH3)2][Cd3(TATB)2(CH3COO)]·HN(CH3)2·3DMA·4H2O (4). MOFs 1 and
2 are isostructural and possess (10,3)-a nets containing large chiral channels of 20.93 and 21.23 Å, respectively,
but are thermally unstable due to the easy removal of coordinated water molecules on the SBU. Replacement of
these water molecules by formate or acetate generated in situ leads to 3 and 4, respectively. Formate or acetate
links SBUs to form infinite helical chains bridged by TATB to create three-dimensional anionic networks, in which
one of the two oxygen atoms of the formate or acetate is uncoordinated and points into the void of the channels.
This novel SBU-stabilization and channel-functionalization strategy may have general implications in the preparation
of new MOFs. Thermogravimetric analysis (TGA) shows that solvent-free 3‘ is thermally stable to 410 °C, while
TGA studies on samples vapor-diffused with water, methanol, and chloroform show reversible adsorption. MOF 3
also has permanent porosity with a large Langmuir surface area of 1558 m2/g. All complexes exhibit similar strong
luminescence with a λmax of approximately 423 nm upon excitation at 268.5 nm.