Attempts to use mechanochemical ball milling to synthesize a known interpenetrated diamondoid (dia) mercury(II) imidazolate metal-organic framework (MOF) yielded instead a novel, more stable polymorph based on square-grid (sql) layers. Simultaneously, the previously reported dia-form was found to be highly elusive, observed only as a short-lived intermediate during solvent-free synthesis and not at all from solution. The destabilization of the dense dia-framework relative to a lower dimensionality one is in contrast to the behavior of other imidazolate MOFs, which have generally been constructued with lighter 1st and 2nd row metals . Periodic density functional theory (DFT) calculations indicate that the persistence of the layered form arises from weak interactions, including structure-stabilizing agostic C-H - Hg contacts. This system is the first reported example of the “disappearing polymorph” phenomenon, previously only known to occur in organic solids, in a metal organic framework. While providing a new link between MOFs and the crystal engineering of organic solids, these findings highlight a role for agostic interactions in directing the topology and stability of MOF polymorphs. Synthesis, in-situ monitoring, and computational analysis of the mercury(II) imidazolate system will be discussed.

2D's company, 3D's a crowd: Mechanochemical synthesis of a low dimensionality mercury(II) imidazolate framework

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.