Postsynthetic Metal and Ligand Exchange in MFU‐4l: A Screening Approach toward Functional Metal–Organic Frameworks Comprising Single‐Site Active Centers

Abstract

The isomorphous partial substitution of Zn(2+) ions in the secondary building unit (SBU) of MFU-4l leads to frameworks with the general formula [M(x)Zn(5-x)Cl4(BTDD)3], in which x≈2, M = Mn(II), Fe(II), Co(II), Ni(II), or Cu(II), and BTDD = bis(1,2,3-triazolato-[4,5-b],[4',5'-i])dibenzo-[1,4]-dioxin. Subsequent exchange of chloride ligands by nitrite, nitrate, triflate, azide, isocyanate, formate, acetate, or fluoride leads to a variety of MFU-4l derivatives, which have been characterized by using XRPD, EDX, IR, UV/Vis-NIR, TGA, and gas sorption measurements. Several MFU-4l derivatives show high catalytic activity in a liquid-phase oxidation of ethylbenzene to acetophenone with air under mild conditions, among which Co- and Cu derivatives with chloride side-ligands are the most active catalysts. Upon thermal treatment, several side-ligands can be transformed selectively into reactive intermediates without destroying the framework. Thus, at 300 °C, Co(II)-azide units in the SBU of Co-MFU-4l are converted into Co(II)-isocyanate under continuous CO gas flow, involving the formation of a nitrene intermediate. The reaction of Cu(II)-fluoride units with H2 at 240 °C leads to Cu(I) and proceeds through the heterolytic cleavage of the H2 molecule.

Mixed-metal metal–organic frameworks

“…They can involve either cluster models of the reactive sites, or fully periodic models. In 2015, Volkmer et al 84 used DFT calculations to characterize the respective activities of Cu and Co metals centers in mixedmetal Cu-Zn and Co-Zn MOFs, by calculating formation enthalpies and activation energies for the preparation of MFU-4l derivatives by side-ligand exchange reactions. Lan et al 85 in 2018 used cluster-based DFT calculations to characterize bimetallic electrocatalysis in oxygen evolution reaction in a series of trinuclear metal carboxylate clusters Fe2M(µ3-O)(CH3COO)6(H2O)3 (M = Fe, Co, Ni, Zn).…”

CFA-7: an interpenetrated metal–organic framework of the MFU-4 family

“…3c,4 Aiming to extend the range of isoreticular MFU-4-type frameworks, we here report on the synthesis and the structure of CFA-7 (Coordination Framework Augsburg University-7) containing the largest straight linker molecule when compared to the organic bistriazolate linkers previously employed in the synthesis of porous MFU-4-type frameworks. [5][6][7][8][9][10] The modular MFU-4 family is based on Kuratowski-type 11 pentanuclear secondary building units (SBUs) of the general formula [M II 5 X 4 (L 6 )] (Fig. 1).…”

A structurally flexible triazolate-based metal–organic framework featuring coordinatively unsaturated copper(i) sites

“…The so-formed PINO ( phthalimide N-oxyl) radical acts as initiator for the radical oxidation of C-H bonds. 15 The mechanism of this type of reaction has been described by Ishii et al in detail. [39][40][41][42][43] An induction period at the beginning of the reaction indicates the slow formation of PINO radicals needed as an initiator.…”