Diels−Alder Adduct of Pentacene and Maleimide: Crystal Growth and the Influence of Solvent Molecules on Structure and Hydrogen Bonding

Abstract

Crystals of the soluble Diels−Alder adduct of pentacene and maleimide, C26H17NO2, as well as of the corresponding 1:1 inclusion compounds with 1,2-dichlorobenzene and toluene and the 2:3 compound with pyridine, have been grown by either solution growth techniques (1, C26H17NO2·C6H4Cl2; 2, C26H17NO2·C6H5CH3; and 3, 2C26H17NO2·3C5H5N) or by vacuum sublimation (4, C26H17NO2). Each of the crystal structures are comprised of discrete C26H17NO2 molecules, with the maleimide moiety adding to the third (central) ring of the original pentacene molecule. The structures present several distinct hydrogen-bonding patterns, depending upon the character of the solvent used. Whereas the C26H17NO2 molecules in 4 (no solvent) are arranged in extended hydrogen-bonded (N−H···O) chains, in 1 and 2, the C26H17NO2 molecules form hydrogen-bonded (N−H···O) dimers, alternating with the included solvent molecules. In 3, the N−H···O bonds are replaced with N−H···N and weak C−H···O interactions between C26H17NO2 and pyridine molecules, leading to hydrogen-bonded C26H17NO2···C5H5N pairs. The inclusion compounds thermally decompose in the temperature range 125−160 °C, losing the solvent molecules and leaving behind C26H17NO2, which principally sublimes rather than undergoing the retro-Diels−Alder decomposition in the temperature range 275−340 °C.