Isostructuralism in a series of methylester/methylamide derivatives of (R,R)-O,O'-dibenzoyl tartaric acid; inclusion properties and guest-dependent homeotypism of the crystals of (R,R)-O,O'-dibenzoyltartaric acid diamide.

The compounds studied are methyl ester, amide and methylamide derivatives of (R,R)-O,O'-dibenzoyl tartaric acid. The molecules adopt the planar T conformation of the four-carbon chain with the terminal C=O bonds situated antiperiplanar with respect to the nearest C*-O bond. All investigated molecules occupy a twofold symmetry site in the crystal, including the mono(N-methylamide) monomethylester which lacks the C(2) molecular symmetry. Connected with this is the static disorder in which the methylester and the N-methylamide groups replace each other and isostructuralism within the methylester/methylamide series. (R,R)-O,O'-Dibenzoyltartaric acid diamides [(R,R)-O,O'-dibenzoyl-2,3-dihydroxybutanediamides], both primary and secondary, form hydrogen-bond aggregation patterns typical for amides, despite the presence of other hydrogen-bond acceptors in the molecule. However, in primary amides such packing leads to the creation of homeotypic crystal structures in which structural voids are filled by cyclic solvent molecules (pyridine, 1,4-dioxane). The presence of polyamide ladders, consisting of 'fused' hydrogen-bond rings, seems to be responsible for the low solubility and high melting point of these substances.