Mixed-Valence Iron(II, III) Trimesates with Open Frameworks Modulated by Solvents

Abstract

Solvothermal reactions with different solvents produced two iron trimesates [Fe2(H2O)2(BTC)4/3]Cl x 4.5(DMF) (1) and [Fe4Cl(BTC)8/3]Cl2 x H2O x 2.5(DEF) (2) (BTC = 1,3,5-benzenetricarboxylate, DMF = N,N'-dimethylformamide, DEF = N,N'-diethylformamide). The framework of 1 is a (3,4)-connected net constructed from mixed-valence paddlewheel Fe2(II, III) units and BTC linkers, while the framework of 2 is a (3,8)-connected net built from mixed-valence square-planar Fe4(III, III, III, II) units and BTC linkers. The large volume inside the framework of 1 (or 2) is occupied by disordered Cl- anions and guest DMF (or DEF) molecules. The mixed-valence character of the frameworks of 1 and 2 was confirmed by Mössbauer spectroscopy studies. The active electronic property of iron cations may be the origin of the variability of the iron-organic frameworks, which are readily affected by some synthetic factors, such as solvents. Magnetic studies reveal that there are antiferromagnetic exchange interactions among the Fe atoms in 1 and 2. Ion-exchange studies for 1 show that the Cl- anions inside the framework of 1 can be exchanged by CNS- anions.

Ethylene Epoxidation with Nitrous Oxide over Fe–BTC Metal–Organic Frameworks: A DFT Study

“…The average bond angle of Fe−Fe−O is 83.1°. These values compare well with the experimental results of 2.98 Å for the Fe−Fe bond, 2.10–2.12 Å for the Fe−O bond and 78.7° for the Fe−Fe−O angle . The adsorption complexes of our reactant and products, nitrous oxide (N 2 O) and the acetaldehyde and ethylene oxide molecules on the Fe site in Fe–BTC are shown in Figure b. N 2 O binds to the Fe active site through its lone pair with an O1⋅⋅⋅Fe intermolecular distance of 2.43 Å.…”

“…Figure illustrates the unit cell of Fe–BTC . Its paddle‐wheel unit, in which metals are bridged by the BTC linkers, is well known.…”

“…The computedF e ÀFe distance is 2.73 ,w hereas the average FeÀOb ond length is 2.15 .T he average bond angle of FeÀFeÀOi s8 3.18.T hese values compare wellw ith the experimental resultso f2 .98 for the FeÀFe bond, 2.10-2.12 for the FeÀOb ond and 78.78 for the FeÀFeÀOa ngle. [20] The adsorption complexeso fo ur reactant and products, nitrous oxide (N 2 O) and the acetaldehyde and ethylene oxide molecules on the Fe site in Fe-BTC are showni nF igure 2b.N 2 Ob inds to the Fe active site through its lone pair with an O1···Fe intermolecular distance of 2.43 .T he NÀO···Fe-BTC angle is 111.18.T he interaction induces as light lengthening of the NÀOb ond from 1.19 to 1.20 .I na ddition, the natural population analysis( NPA) reveals an electron transfer from the O1 atom to the Fe site, which leads to ar educed positive chargeo nt he Fe site from 1.155 to 0.991 j e j ,w hereas the N 2 Om olecule becomes slightly more positive by 0.068 j e j . The calculated adsorption energy is À11.9 kcal mol À1 .…”

“…Figure 1i llustrates the unit cell of Fe-BTC. [20] Its paddle-wheel unit, in which metals are bridged by the BTC linkers, is well known.T he bimetallic FeÀFe fragment connects to four organic BTC linkerst of orm ap orous network with the unit formula [Fe 3 (btc) 2 ]. Thes implest cluster model of [Fe 2 (btc) 4 ]( Figure2a) is used to represent Fe-BTC in this work to reduce the computationalc ost.…”

Synthesis, crystal structure, and physicochemical properties of the new metal-organic framework — the iron(iii) complex with benzene-1,3,5-tricarboxylate

“…There fore, the crystals are composed of paddlewheel structural units, which form the three dimensional structure of the MOF. The positive charge of the framework is compen sated by chloride ions, which are located in the cavities similar to those in the structure of complex 2, 14 and co ordinated hydroxide ions. The amount of chloride ions was fixed at the level of 1.7 Cl -ions per two Fe 3+ ions, which is consistent with the elemental analysis data (the localization of the Cl -ions was described in detail in the Experimental section).…”