Framework-Templated Single Clathrate Hydrate Cages in Metal–Organic Frameworks

Molecular simulations identify metal–organic framework (MOF) pores that retain single methane hydrate cages and, for a nonstandard 16-water cage, support its assembly from disordered water. In smooth spherical pores, a methane molecule assembled twenty waters into the pentagonal dodecahedron of structure I hydrate and sixteen waters into a 435661 cage, a polyhedron that no known hydrate crystal contains. These idealized models were built by language-model agents and then walked back toward real materials, an approach referred to here as agentic doodling, and they guided a screening of 120,419 experimental MOF structures. Most size-matched pores pulled the cage apart, but a small set of frameworks kept it intact at 216 K, better with methane than without, and ELOZIQ kept the dodecahedron up to 270 K, near the melting temperature of the water model. In XODDED and GUQMAH, the nonstandard cage was held at least as well as in an ideal spherical pore, and it self-assembled around methane from randomly placed water, with nearly all of its edges hydrogen bonded. The pores template the cages through a moderate attraction spread over the cage corners rather than through strong binding sites placed at the corners. These results open a route to designing MOFs that hold single hydrate cages, including cages that do not occur in bulk hydrates.