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

Solvothermal reaction of Zn(NO 3 ) 2 ⋅ 4 H 2 O, 1,4‐bis[2‐(4‐pyridyl)ethenyl]benzene (bpeb) and 4,4′‐oxybisbenzoic acid (H 2 obc) in the presence of dimethylacetamide (DMA) as one of the solvents yielded a threefold interpenetrated pillared‐layer porous coordination polymer with pcu topology, [Zn 2 (bpeb)(obc) 2 ] ⋅ 5 H 2 O ( 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 [Zn 2 (bpeb)(obc) 2 ] ⋅ 2 DMF ⋅ H 2 O ( 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 [Zn 2 (bpeb)(obc) 2 ] ⋅ 2 H 2 O ( 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.