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How Does the Fluorination of the Linker Affect the Stability of Trimesate-Based Coordination Polymers and Metal–Organic Frameworks?
journal contribution
posted on 2019-06-19, 18:41 authored by John Krautwurst, Daniel Smets, Rainer Lamann, Uwe RuschewitzThe
syntheses and crystal structures of the monopotassium salts
of difluorinated and tri/perfluorinated trimesic acid (1,3,5-benzenetricarboxylic
acid ≡ H3BTC) are presented, namely, K(H2dF-BTC) (Fdd2, Z = 16) and K(H2pF-BTC) (Cc, Z = 4). For the first time, together with already
known K(H2mF-BTC), all fluorination degrees
of trimesic acid are accessible and can be used for a systematic study
of the influence of fluorination on the stability of the resulting
coordination polymers and metal–organic frameworks (MOFs).
The monopotassium salts show a decreasing (chemical) stability in
water upon heating, as well as a decreasing thermal stability, as
evidenced by differential scanning calorimetry/thermogravimetric analysis
(DSC/TGA). A similar decreasing thermal stability is found for two
series of isostructural coordination polymers (UHM-33 topology: ∞2[Cu2(L)2(DMA)2]·2DMA with L2– = HmF-BTC2– and HdF-BTC2–) and MOFs (∞3[Ba(L)(H2O)2]·1/2H2O with L2– = HBTC2‑, HmF-BTC2– and
HdF-BTC2–). Remarkably, while the
decomposition temperatures decrease with increasing fluorination of
the linker, the releasing temperatures for embedded solvent molecules
(DMA and H2O, respectively) increase. To identify possible
candidates for the synthesis of isostructural coordination polymers
and MOFs with BTC3– ligands with different degrees
of fluorination, a database-adapted approach was developed, which
utilizes the increased torsion angle between the carboxylate groups
and the phenyl rings in these materials as a structure-determining
parameter.
