SELF-ORGANIZATION OF 2,5-DI-N-ALKOXY-1,4-BENZOQUINONES IN THE SOLID-STATE - MOLECULAR RECOGNITION INVOLVING INTERMOLECULAR DIPOLE-DIPOLE, WEAK C-H-CENTER-DOT-CENTER-DOT-CENTER-DOT-O=C HYDROGEN-BOND AND VAN-DER-WAALS INTERACTIONS

In the solid state 2,5-di-n-alkoxy-1,4-benzoquinones 1(n) organize int o a two-dimensional layered structure with columnarly stacked 1,4-benz oquinone moieties along the a and b axis leading to improved intermole cular pi-overlap. An interplay between intermolecular merocyanine-type dipole-dipole interactions, directional weak C-H ... O hydrogen bond interactions and nondirectional van der Waals interactions is responsi ble for this packing motif. DSC of 1(n) shows that for n = 3-19 pronou nced solid-solid phase transitions are discernible. Concomitant with a lkoxy chain length odd-even effects are observed. Linear relationships are found between enthalpy and entropy changes, respectively, at dist inct phase transitions for 1(n) with n greater than or equal to 9 (n = odd) and n greater than or equal to 10 (n even) indicative for identi cal packing motifs in both series, respectively. Picnometry reveals th at the densities of 1(n) with n = odd are higher than those for n = ev en. As shown by single-crystal X-ray structure analyses (1(3), 1(9), a nd 1(10)) and wide-angle X-ray diffraction (WAXD, 1(n), 9 less than or equal to n less than or equal to 19), this can be attributed to impro ved end-group packing of the alkoxy chains in the odd series.