Pseudodimorphism of the Trans-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboxylic Acid Clathrates with Acetic and Propionic Acids

The versatile host compound trans-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboxylic acid (1) forms under ambient conditions isostructural complexes with acetic and propionic acids being true clathrates without host-guest type H-bonds. A new modification of the clathrate between 1 and acetic acid (1a) is obtained at sub-room temperature (5 °C) while for preparation of the new crystal form of the clathrate with propionic acid (1b) crystallization temperature should be increased up to 50 °C. Crystal structures of the pseudodimorphs show that homo carboxylic acid dimers existing in the conventional phases are also observed here, demonstrating the new compounds to be of same clathrate type. Crystal data: for 1a: triclinic P-1, a = 8.626(2) Å, b = 9.073(2) Å, c = 12.042(2) Å, α = 76.34(3)°, β = 77.41(3)°, γ = 84.13(3)°, V = 892.5(4) ų, Z = 2, R = 0.0446 for 3171 reflections; for 1b: monoclinic C2/c, a = 13.268(3) Å, b = 12.636(3) Å, c = 21.786(4) Å, β = 90.56(3)°, V = 3652.3(14) ų, Z = 8, R = 0.0618 for 2365 reflections.