Noninvasive Substitution of K+ Sites in Cyclodextrin Metal-Organic Frameworks by Li+ Ions.

Co-crystallization of K[+] and Li[+] ions with γ-cyclodextrin (γ-CD) has been shown to substitute the K[+] ion sites partially by Li[+] ions, while retaining the structural integrity and accessible porosity of CD-MOF-1 (MOF, metal -- organic framework). A series of experiments, in which the K[+]/Li[+] ratio was varied with respect to that of γ-CD, have been conducted in order to achieve the highest possible proportion of Li[+] ions in the framework. Attempts to obtain a CD-MOF containing only Li[+] ions resulted in nonporous materials. The structural occupancy on the part of the Li[+] ions in the new CD-MOF has been confirmed by single-crystal X-ray analysis by determining the vacancies of K[+]-ion sites and accounting for the cation/γ-CD ratio in CD-MOF-1. The proportion of Li[+] ions has also been confirmed by elemental analysis, whereas powder X-ray diffraction has established the stability of the extended framework. This noninvasive synthetic approach to generating mixed-metal CD-MOFs is a promising method for obtaining porous framework unattainable de novo. Furthermore, the CO[sub 2] and H[sub 2] capture capacities of the Li[+]-ion-substituted CD-MOF have been shown to exceed the highest sorption capacities reported so far for CD-MOFs. [ABSTRACT FROM AUTHOR]