Guest-triggered supramolecular isomerism in a pillared-layer structure with unusual isomers of paddle-wheel secondary building units by reversible single-crystal-to-single-crystal transformation

Abstract

Solvothermal reaction of Zn(NO3)2×4 H 2O, 1,4-bis[2-(4-pyridyl)ethenyl]benzene (bpeb) and 4,4′-oxybisbenzoic acid (H2obc) in the presence of dimethylacetamide (DMA) as one of the solvents yielded a threefold interpenetrated pillared-layer porous coordination polymer with pcu topology, [Zn2(bpeb)(obc)2]×5 H2O (1), which comprised an unusual isomer of the well-known paddle-wheel building block and the trans-trans-trans isomer of the bpeb pillar ligand. When dimethylformamide (DMF) was used instead of DMA, a supramolecular isomer [Zn2(bpeb) (obc)2]×2 DMF×H2O (2), with the trans-cis-trans isomer of the bpeb ligand with a slightly different variation of the paddle-wheel repeating unit, was isolated. In MeOH, single crystals of 2 were transformed by solvent exchange in a single-crystal-to-single-crystal (SCSC) manner to yield [Zn2(bpeb)(obc)2]×2 H 2O (3), which is a polymorph of 1. SCSC conversion of 3 to 2 was achieved by soaking 3 in DMF. Compounds 1 and 2 as well as 2 and 3 are supramolecular isomers. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.