Exploring the inclusion properties of new clathrate hosts derived from tartaric acid. X-ray structural characterization of the free ligands and their selective interaction modes with alkylamine guests

A new host 4,5-bis(hydroxydiphenylmethyl)-2,2-dimethyl-1,3-dioxolane (1) was found to form very selectively crystalline complexes with simple alkylamines. Crystals of the three different stereochemical species of this host, optically resolved (1a), racemic (1b), and meso (1c), as well as of the inclusion complexes formed by (1a) and (1b) with PrⁿNH₂, Prⁿ₂NH, and Prⁿ₃N have been studied by X-ray diffraction. The clathrate inclusion behaviour of (1) is related to structure, and patterns of molecular recognition between this host and the amine guests are characterized. The three different hosts (1a), (1b), and (1c) contain an intramolecular hydrogen bond and are rather rigid; they dimerize in the solid by hydrogen bonding through their hydroxy groups, forming eight-membered (OH)₄ rings. Circular motifs of 2:1 (which involve ten-membered rings of H-bonded -OH and -NH moieties) and 2:2 (involving 12-membered circles) co-ordination between host and guest have also been observed in the inclusion complexes of (1a) with Prⁿ₂NH and of (1b) with PrⁿNH₂, respectively. Crystals of the other inclusion complexes between (1a) and the primary and tertiary amines, and between (1b) and the secondary and tertiary amines are characterized by localized 1:1 co-ordination between the complexing partners. It appears that preferential co-ordination of a given host with an amine guest is associated mainly with the formation of larger clusters of H-bonded molecules. The host-guest binding patterns are discussed in detail, in relation to those found in related systems of co-ordination-assisted clathrates.