Positional isomeric effect of acyclic hosts on supramolecular recognition of anionic guests

Abstract

Abstract Two or more supramolecular hydrogen-bonding receptor scaffolds having identical molecular formulas act as positional isomers only when the position of a substituent or a receptor arm or double/triple bond of one isomer differ from another isomer. The review summarizes the research on anion coordination chemistry of last decade affected by the positional isomeric acyclic receptors. The detailed and comprehensive account of reported examples of one or more anionic guest/hydrated-anionic guest assisted self-assemblies (neutral or charged) of artificial acyclic isomers (monopodal or linear, dipodal, triodal, hexapodal), affected by the terminal aryl substituents or the receptor arms with respect to central aryl spacer are systematically incorporated in the review. The review specifically consolidates the underexplored broad area of anion recognition chemistry affected by positional isomerism of acyclic amine, amide, urea, thiourea functionalized receptors/sensors in solid as well as in solution state. These substituent dependent isomeric systems could provide insights into the fundamental hydrogen-bonded anion-receptor chemistry and also useful for understanding the biological and environmental processes followed by the crystal engineering as well as extraction, aerial CO2 fixation, sensing or transport phenomena of anions. Discussions relating to the construction of some typical examples of anion-coordinated self-assembled supramolecular architectures such as molecular capsules, barrels, helicates, foldamer, tetrahedral cages and mechanically interlocked systems by these positional isomeric podands are also included in this review.