Acridine form IX

Abstract

We report a new polymorph of acridine, C13H9N, denoted form IX, obtained as thin needles by slow evaporation of a toluene solution. The structure was solved and refined from powder X-ray data. The structures of five unsolvated forms were previously known, but this is only the second with one molecule in the asymmetric unit. The melting point [differential scanning calorimetry (DSC) onset] and heat of fusion are 108.8 (3) °C and 19.2 (4) kJ mol−1, respectively.

The (Current) Acridine Solid Form Landscape: Eight Polymorphs and a Hydrate

“…(a) Stick model of the structure of acridine form IX ( P 2 1 / n , Z ′ = 1) . Shadings as used in Figure .…”

“…3 Subsequent studies, prior to our work, have turned up seven anhydrous forms, of which the crystal structures were known of five, and one hydrate. [4][5][6][7][8][9][10][11][12][13][14] Over the years, inconsistent naming of the solid forms has led to confusion in characterizing, distinguishing, and identifying the various solid forms. The nomenclature in this review is consistent with forms identified in the 2019 edition of the Cambridge Crystal Structure Database.…”

“…Interestingly, the structure computed to have the lowest energy had not been experimentally observed at the outset of this work, and the experiments turned up a previously unknown phase that turned out to match the predicted structure, now designated form IX. 14…”

“…Acridine was first isolated in 1870 and was known to be crystalline well before Kofler’s hot stage microscope studies revealed five forms, including crystal habit, phase transitions, and melting points all between 106 and 110 °C . Subsequent studies, prior to our work, have turned up seven anhydrous forms, of which the crystal structures were known of five, and one hydrate. − Over the years, inconsistent naming of the solid forms has led to confusion in characterizing, distinguishing, and identifying the various solid forms. The nomenclature in this review is consistent with forms identified in the 2019 edition of the Cambridge Crystal Structure Database …”

“…This review grew from coordinated experimental and computational efforts to map the solid form landscape of acridine and to search for the lowest energy crystal structures of this simple, rigid molecule. Interestingly, the structure computed to have the lowest energy had not been experimentally observed at the outset of this work, and the experiments turned up a previously unknown phase that turned out to match the predicted structure, now designated form IX …”