Larger pores via shorter pillars in flexible layer coordination networks

Abstract

Metal organic frameworks are porous coordination networks that offer tunable structures via modular synthetic routes. It is well established that zinc 3-amino-1,2,4-triazolate (ATz) forms structures with cationic layers. These layers can be pillared by anions to generate pores. We present three new Zn2(ATz)2(A) structures with A = 1,4-benzenedicarboxylate (BDC) pillars, 2-amino-1,4-benzene-dicarboxylate (BDC-NH2) and 2-methyl-1,4-benzenedicarboxylate (BDC-Me) to give the CALF-24 series of metal organic frameworks. Initially, these compounds were prepared to assess their CO2 capture ability and these data are presented. More significantly, comparing these and published ZnATz relatives, primarily from the group of X.M. Chen, we propose that, for layered systems with some flexibility in their bonding, larger pores actually result by pillaring with shorter linkers. While this may seem counterintuitive, a rationale is offered as borne out by the library of existing data. This offers a general concept for making porous materials based on the rigidity of the building units.