Solid-State Reactivity of Supramolecular Isomers: A Study of the <i>s</i>‑Block Coordination Polymers
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Four coordination polymers of s-block metal ions, namely, Na(I), K(I), and Ba(II) with rctt-cyclobutanetetracarboxylate (rctt-cbtc) ligand were synthesized, and their solid-state structures were determined by X-ray crystallography. Of these, [Na2(rctt-cbtc-H2)(H2O)4] (1) and (2) are supramolecular isomers with mog and pcu topologies. While the three-dimensional structure of [K2(rctt-cbtc)(H2O)2] (3) is constructed based on a (6,8) net, [Ba2(rctt-cbtc)(H2O)6] (4) has fsh topology with (4,6) connectivity. Compounds 1–3 have been found to undergo thermal isomerization, contrary to the expected thermal cleavage of the cyclobutane ring, in the temperature range 200–250 °C cleanly to the rtct isomer in 50–85% yield, but not 4. Interestingly, recrystallization of the isomerized product of 1 yielded single crystals of [Na3(rtct-cbtc-H)(H2O)3]n (5). Although the composition has changed in this process, the stereochemistry at the cyclobutane ring was confirmed in this three-dimensional coordination polymer with a new topology.
