Syntheses of photoresponsive cyclobutane-1,2-dicarbonyl-capped 2·n diazacrown ethers by intramolecular [2 + 2]photocycloaddition and the structures of their lithium and mercury(II) complexes

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Abstract
Photoresponsive cyclobutane-1,2-dicarbonyl-capped 2·n diazacrown ethers (7) have been prepared by intramolecular [2 + 2]photocycloaddition of p,p′-trimethylenedicinnamoyl-capped 2·n diazacrown ethers (5); the cyclobutane-1,2-dicarbonyl-capped 2.1 diazacrown ether (7a) showed a highly selective complexing ability for the lithium cation, although (5) did not show any complexing abilities for alkali, alkaline-earth, and other metal ions. The crystal structures of (5a), the 1 : 1 lithium and mercury(II) thiocyanate complexes (8) and (9) of (7a) have been determined by X-ray analyses. The structures of (8) and (9) revealed that the configuration of the cyclobutane ring is in the β-form and slightly distorted. Complex (8) consists of dimeric molecules in which the lithium atom is directly bonded to the two oxygen atoms of the amido groups and the two nitrogen atoms of the thiocyanate group of the counter anion and adjacent complex in a slightly distorted tetrahedral configuration. The Hg atom in (9) is also bonded directly to the two oxygen atoms of the amido groups, the two sulphur atoms of the thiocyanate groups, and the simple nitrogen atom of the counter anion of the adjacent complex in a distorted trigonal bipyramidal configuration.

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