Orthogonalization of Polyaryl Linkers as a Route to More Porous Phosphonate Metal‐Organic Frameworks
Martin Glavinović, Justin H. Perras, Benjamin S. Gelfand, Jian‐Bin Lin, George K. H. Shimizu
Abstract
Abstract The coordinative pliancy of the phosphonate functional group means that metal‐phosphonate materials often self‐assemble as well‐packed structures with minimal porosity, as efficient inter‐ligand packing is enabled. Here, we report a multistep synthesis of a novel aryl‐phosphonate linker with an orthogonalized ligand core, 1,3,5‐tris(4’‐phosphonophenyl)‐2,4,6‐trimethylbenzene (H 6 L2) designed to form more open structures. A series of crystalline metal‐phosphonate frameworks (CALF‐35 to ‐39) have been assembled by coordinating to divalent metals (Ba, Sr, Ca, Mg, Zn). H 6 L2 is unable to pack efficiently and, as a consequence, yields several distinct microporous structures. The resulting structures are discussed in detail, with a focus on the solid‐state packing of the sterically rigidified linker. Combined with larger cations (Sr, and Ba), H 6 L2 packs in a parallel‐offset manner, yielding isomorphous and microporous metal‐organic frameworks (CALF‐35 (Sr), and (Ba)). When coordinated to smaller metals (Ca, Mg, Zn), H 6 L2 forms four new structures. Two Ca MOFs of different stoichiometry, (CALF‐36 and 37) and a Mg MOF CALF‐38 show narrow pores and have high selectivities for CO 2 over N 2 and CH 4 . Finally, in CALF‐39 (Zn), H 6 L2 linkers pack in a herringbone fashion, resulting in a material with 10.9×10.1 Å 2 square channels. The stability of all structures was tested, and the most porous structure, CALF‐39 (Zn), was found to retain its structure and gas adsorption after immersion in water over pH 3–11.