posted on 2023-11-20, 13:20authored byArjun Halder, David C. Bain, Tristan A. Pitt, Zixiao Shi, Julia Oktawiec, Jung-Hoon Lee, Stavrini Tsangari, Marcus Ng, José J. Fuentes-Rivera, Alexander C. Forse, Tomče Runčevski, David A. Muller, Andrew J. Musser, Phillip J. Milner
Metal–organic frameworks (MOFs) are porous, crystalline
materials constructed from organic linkers and inorganic nodes with
potential utility in gas separation, drug delivery, sensing, and catalysis.
Small variations in the MOF synthesis conditions can lead to a range
of accessible frameworks with divergent chemical or photophysical
properties. New methods to controllably access phases with tailored
properties would broaden the scope of MOFs that can be reliably prepared
for specific applications. Herein, we demonstrate that simply increasing
the reaction concentration during the solvothermal synthesis of M2(dobdc) (M = Mg, Mn, Ni; dobdc4– = 2,5-dioxido-1,4-benzenedicarboxylate)
MOFs unexpectedly leads to trapping of a new framework termed CORN-MOF-1
(CORN = Cornell University) instead. In-depth spectroscopic, crystallographic,
and computational studies support that CORN-MOF-1 has a structure
similar to that of M2(dobdc) but with partially protonated
linkers and charge-balancing or coordinated formate groups in the
pores. The resultant variation in linker spacing causes CORN-MOF-1
(Mg) to be strongly photoluminescent in the solid state, whereas H4dobdc and Mg2(dobdc) are weakly emissive due to
excimer formation. In-depth photophysical studies suggest that CORN-MOF-1
(Mg) is the first MOF based on the H2dobdc2– linker that likely does not emit via an excited-state intramolecular
proton transfer (ESIPT) pathway. In addition, CORN-MOF-1 variants
can be converted to high-quality samples of the thermodynamic M2(dobdc) phases by heating in N,N-dimethylformamide (DMF). Overall, our findings support that high-concentration
synthesis provides a straightforward method to identify new MOFs with
properties distinct from known materials and to produce highly porous
samples of MOFs, paving the way for the discovery and gram-scale synthesis
of framework materials.