Charge-Separated Metal–Organic Frameworks Derived from Boron-Centered Tetrapods

Thapa, S.; Dickie, D. A.; Qin, Y. Charge-Separated Metal–Organic Frameworks Derived from Boron-Centered Tetrapods. Crystal Growth & Design 2020, 20, 1598-1608.

Abstract

Metal–organic frameworks (MOFs) are an emerging class of microporous materials that have potential applications in a wide range of areas. As a subclass of MOFs, ionic MOFs, especially charge-separated MOFs, have been relatively less studied but possess unique features including strong host–guest interactions from the exposed charged centers. We report the synthesis and single-crystal structural characterization of five new charge-separated MOFs (UNM 1–5) based on two tetrapodal borate ligands: tetrakis(4-(4-pyridineethynyl)-2,3,5,6-tetrafluorophenyl)borate (T1) and tetrakis(4-(4-pyridyl)-2,3,5,6-tetrafluorophenyl)borate (T2) having rigid arms of different lengths and pyridine groups at the end of each arm. Coordination of these tetrapods with Cu(I), Cu(II), and Ag(I) ions under specific conditions led to a series of new charge-separated MOFs in single crystalline forms. UNM-1 and UNM-2/UNM-3, which crystallize respectively in tetragonal I4̅ space group and monoclinic C2/c space group, are derived from Cu(CH3CN)4BF4 and Cu(NO3)2 upon coordination with T1. On the other hand, coordination of T2 with Cu(CH3CN)4BF4 and AgBF4 respectively yielded UNM-4 and UNM-5 in the monoclinic I2/a space group. All these MOFs possess several degrees of interpenetration that are correlated with the arm lengths of ligands. Noticeably, UNM-1 is 4-fold interpenetrated, leading to the highest stability among all five MOFs, while still displaying an impressive Brunauer–Emmett–Teller (BET) surface area (SABET) of ca. 621 m2/g. Our findings highlight the versatility of tetrapodal borate ligands in engineering charge-separated MOFs with diverse structures and controlled functionality.

Last updated on 01/17/2021