Crystal Structures of Azoarene-Capped Analogues of 1.10-Diaza-4,7,14,17-tetraoxa-and 1.10-Diaza-4,7,14,17-tetrathiacy clooc tadecane. Comparison of C-0 and C-S Bond Conformations in Capped Crown Analogues

Macropolycyclic polyethers contain intramolecular cavities lined with molecular segments capable of binding cations in three-dimensional cagelike structures. The Azoarene-capped O and S crown ethers (e.g., 1-3) undergo photoinduced reversible inter-Conversion between the trans and cis azo linkages, resulting in substantial changes in their cation binding properties.³ The X-ray structures of the azopyridine-capped analogue of l,10-diaza-18-crown-6 (1) and the azobenzene-capped sulfur analogue (3) have been determined as a step in understanding how ion selectivity and binding are controlled by the cavity structure. The conformations of the crown rings in 1 and 3 are substantially different from those of the “free” analogues, the latter containing the first example of the C-S anti conformation in a thiacrown macrocycle.