Solid-State Reactivity of Supramolecular Isomers: A Study of the s-Block Coordination Polymers

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, [Na-2(rctt-cbtc-H-2)(H2O)(4)] (1) and (2) are supramolecular isomers with mog and pcu topologies. While the three-dimensional structure of [K-2(rctt-cbtc)(H2O)(2)] (3) is constructed based on a (6,8) net, [Ba-2(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 degrees 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 [Na-3(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.