Sequential Solid-State Transformations Involving Consecutive Rearrangements of Secondary Building Units in a Metal-Organic Framework

Abstract

Solid-state transformations in metal-organic framework (MOF) systems are important phenomena and have led to the creation of new MOF structures. Solid-state transformations from interpenetrated to non-interpenetrated networks involving rearrangement of secondary building units (SBUs) in a single-crystal-to-single-crystal (SCSC) fashion have not been explored to date. Herein, we report the sequential, thermally stimulated solid-state transformations in a barium-organic framework ( UPC-600 ). The two-fold interpenetrated framework of UPC-600 is converted at 373 K to UPC-601 , a non-interpenetrated framework. This proceeds in a SCSC fashion and involves the rearrangement of two proximate rod-shaped SBUs in different nets to generate a new rod-shaped SBU. At 473 K, a continuous solid-state transformation involving a second rearrangement occurred, UPC-601 converted to UPC-602 by the rearrangement of the 1D rod-shaped SBU to a 2D layer SBU. This is the first example of such a thermally-driven stepwise transformation involving simultaneous cleavage and regeneration of multiple bonds. This result will enable detailed studies of solid-state transformations, and encourages a deep understanding of the role of solid-state transformations in the synthesis of MOF materials.

Keywords: Metal-organic framework; secondary building units; single-crystal-to-single-crystal; solid-state transformations; thermally-driven.