Post-synthetic reversible incorporation of organic linkers into porous metal-organic frameworks through single-crystal-to-single-crystal transformations and modification of gas-sorption properties

The porous metal-organic framework (MOF) {[Zn(2)(TCPBDA)(H(2)O)(2)]⋅30 DMF⋅6 H(2)O}(n) (SNU-30; DMF = N,N-dimethylformamide) has been prepared by the solvothermal reaction of N,N,N',N'-tetrakis(4-carboxyphenyl)biphenyl-4,4'-diamine (H(4)TCPBDA) and Zn(NO(3))(2)⋅6 H(2)O in DMF/tBuOH. The post-synthetic modification of SNU-30 by the insertion of 3,6-di(4-pyridyl)-1,2,4,5-tetrazine (bpta) affords single-crystalline {[Zn(2)(TCPBDA)(bpta)]⋅23 DMF⋅4 H(2)O}(n) (SNU-31 SC), in which channels are divided by the bpta linkers. Interestingly, unlike its pristine form, the bridging bpta ligand in the MOF is bent due to steric constraints. SNU-31 can be also prepared through a one-pot solvothermal synthesis from Zn(II), TCPBDA(4-), and bpta. The bpta linker can be liberated from this MOF by immersion in N,N-diethylformamide (DEF) to afford the single-crystalline SNU-30 SC, which is structurally similar to SNU-30. This phenomenon of reversible insertion and removal of the bridging ligand while preserving the single crystallinity is unprecedented in MOFs. Desolvated solid SNU-30' adsorbs N(2), O(2), H(2), CO(2), and CH(4) gases, whereas desolvated SNU-31' exhibits selective adsorption of CO(2) over N(2), O(2), H(2), and CH(4), thus demonstrating that the gas adsorption properties of MOF can be modified by post-synthetic insertion/removal of a bridging ligand.