Double-Diamond Inclusion Compounds of 2,6-Dimethylideneadamantane-1,3,5,7-tetracarboxylic Acid

Article abstract of DOI:10.1002/hlca.19910740417

The crystal structures of four inclusion compounds of 2,6-dimethylideneadamantane-1,3,5,7-tetracarboxylic acid (4) are descrbed, which involve the following guest species: a) a mixture of 4-methylpent-3-en-2-one, 2,6-dimethylhepta-2,5-dien-4-one, and mesitylene (condensation products of acetone); b) mesitylene; c) a mixture of 4-methylpent-3-en-2-one and mesitylene; d) (tert-butyl)benzene.In all four cases, the host architectures consist of two interpenetrating sper-diamond networks built up by the tetra-acid molecules via pairwise H-bonds between the tetrahedrally directed COOH groups.In the first three cases (tetragonal crystal symmetry), the two diamond-like host lattices interpenetrate symmetrically, in the fourth case (monoclinic) asymmetrically.This asymmetry is brought about by the increased steric bulk of the (tert-butyl)benzene guest molecules.Attempts to enforce an inclusion compound of 4 with a single, extremely hollow diamond-like host lattice by offering still bulkier guest molecules have as yet not been met with success.The generally very high propensity of 4 to form inclusion compounds was envisaged and designed beforehand by appropriate evaluation and modulation of the crystal structure of the parent adamantane-1,3,5,7-tetracarboxylic acid, which represents a fivefold diamond-like self-inclusion compound.Crystals of the free, uncomplexed 4 appear to be extremely unstable and could so far not be obtained.On the other hand, from aqueous solution a very stable monohydrate of 4 may be crystallized (4*H2O), which was also subjected to X-ray analysis.The (triclinic) crystal structure of 4*H2O involves an interesting dichotomy inasmuch its pattern of H-bonding may be rationalized either in terms of a double, cross-linked super-zincblende (sphalerite) arhitecture, or as a system of porous, puckered 4-connected sheets, which interpenetrate each other pairwise and are cross-linked by the H2O molecules.Various structure and (space group) symmetry characteristics of the supramolecular solid-state complexes reported here are highlighted by pointing out analogies with comparable structures retrieved from the literature.