Dihydroxybenzoquinone as Linker for the Synthesis of Permanently Porous Aluminum Metal–Organic Frameworks

Abstract

Two new dihydroxybenzoquinone-based metal-organic frameworks, ((CH3)2NH2)3[Al4(L1)3(L1(•))3]·3DMF (1, denoted CAU-20) and ((CH3)2NH2)3[Al4(L2)3(L2(•))3]·9DMF (2, denoted CAU-20-Cl2), were synthesized at 120 °C in DMF using 2,5-dihydroxy-p-benzoquinone ((C6H2(OH)2(O)2), H2L1) and 2,5-dichloro-3,6-dihydroxy-p-benzoquinone ((C6Cl2(OH)2(O)2), H2L2), respectively. Compared to other Al-MOFs, which contain carboxylate or phosphonate groups that connect the metal sites, in 1 and 2 the Al(3+) are coordinated by oxido groups. The metal ions are octahedrally surrounded by oxygen atoms of the deprotonated linker molecules to generate honeycomb layers with a metal to linker ratio of Al: L1/L2 = 2:3. The layers contain L1(2-) and L2(2-) ions as well as linker radical ions L1(•3-) and L2(•3-) in a molar ratio of 1 to 1. The presence of radical ions was confirmed by EPR and UV-vis-spectroscopic measurements, and the composition was determined from a combination of PXRD, (1)H NMR, TG, and elemental analyses. Charge balance is accomplished through intercalation of (CH3)2NH2(+) ions which are formed by partial hydrolysis of DMF. In the structures of 1 and 2 the eclipsed layers are AA and ABAB stacked, respectively, and one-dimensional hexagonal channels with diameters of ca. 9 and 6 Å are formed. Both compounds exhibit permanent porosity and have specific surface areas of 1440 and 1430 m(2) g(-1), respectively.

Synthesis and Characterization of [M2(OH)2(C4O4)2(H2O)4]·2H2O (M = Al or Ga)

“…Two water molecules are coordinating to each central metal atom in equatorial position, respectively, to complete the coordination sphere of the metal ions. The M –O distances for 1 (1.876(3)–1.906(2) Å) and 2 (1.973(6) and 2.044(8) Å) compare well with values reported in the literature , , . The intramolecular M ··· M distances in compounds 1 and 2 are 2.924(2) and 3.018(2) Å, respectively, which are within the range of the M ··· M distances of the isostructural compounds [Fe 2 (OH) 2 (C 4 O 4 ) 2 (H 2 O) 4 ] · 2H 2 O (3.0722(6) Å) and [Cr 2 (OH) 2 (C 4 O 4 ) 2 (H 2 O) 4 ] · 2H 2 O (2.998 Å) …”

“…Recently, we started a systematic investigation on the use of non‐carboxylic linker molecules for the synthesis of Al‐MOFs. Thus the use of dihydroxy‐ and dichloro‐dihydroxy‐benzoquinone led to permanently porous Al‐MOFs . Following these studies we subsequently focused on the use of squarate ions which are also small non‐carboxylic linker molecules containing vicinal dioxo groups .…”

Square Grid Metal–Chloranilate Networks as Robust Host Systems for Guest Sorption

“…Under certain circumstances an intermediate À3r adical form (II)c an also be identified. [6] The ability of the bridging ligand to exist in multiple oxidation states therefore offers the prospectofforming redox-active networks.…”

A Metal–Organic Framework with Tetrahedral Aluminate Sites as a Single‐Ion Li+ Solid Electrolyte

“…[10,11] Moreover,o nly two examples of MOFs,n amely CAU-4 and CAU-20, constructed from isolated AlO 6 octahedral units have been reported (Scheme 1). [12] Herein, we demonstrate asimple strategy to prepare such anionic Al-MOFs based on tetrahedral AlO 4 units allowing free Li + loading values never before achieved for MOFs.…”