Crystal engineering of chiral superstructures based on (R)-(+)-1,1′-bi-2-naphthol and the alkali derivatives of racemic (R,S)-1,1′-bi-2-naphthol

Abstract

(R)-(+)-1,1′-Bi-2-naphthol [(R)-(+)-(HOC₁₀H₆C₁₀H₆OH)] has been used as a chiral building block in the construction of chiral organo-organometallic crystals. The reaction of the neutral molecule with [Co(η⁵-C₅H₅)₂] in diethyl ether yields the supramolecular salts [Co^III(η⁵-C₅H₅)₂][(R)-(+)-(HOC₁₀H₆C₁₀H₆O)]·[(R)-(+)-(HOC₁₀H₆C₁₀H₆OH)] (1) and [Co^III(η⁵-C₅H₅)₂][(R)-(+)-(HOC₁₀H₆C₁₀H₆O)]·[(R)-(+)-(HOC₁₀H₆C₁₀H₆OH)]_0.5 (2), depending on the stoichiometric ratios between the binaphthol and the organometallic sandwich compound. Molecular aggregation is achieved ia a combination of neutral and charge-assisted O–H···O bonds between the binaphthol and binaphtholate components and ia weaker interactions of the C–H···O and C–H···π types involving the [Co^III(η⁵-C₅H₅)₂]⁺ cation. The same reaction with racemic 1,1′-bi-2-naphthol in diethyl ether, followed by recrystallisation from nitromethane, yields the solvate species [Co^III(η⁵-C₅H₅)₂][(R,S)-(HOC₁₀H₆C₁₀H₆O)]·[(R,S)-(HOC₁₀H₆C₁₀H₆OH)][MeNO₂]_1.5 (3). For comparison, the alkali salts Cs[(R,S)-(HOC₁₀H₆C₁₀H₆O)]·[(R,S)-(HOC₁₀H₆C₁₀H₆OH)] (4) and Rb[(R,S)-(HOC₁₀H₆C₁₀H₆O)]· [(R,S)-(HOC₁₀H₆C₁₀H₆OH)] (5) have also been prepared by treating [(R,S)-(HOC₁₀H₆C₁₀H₆OH)] with the Cs and Rb hydroxides. Both organometallic and alkali salts show how the cations tend to be encapsulated within a niche formed by the folding of hydrogen-bonded naphthol–naphtholate chains.