Whole Molecule Disorder in a Solid Solution of Two Indoloacridines

Abstract

Dehydrogenation of a 5,6-dihydro-acridine with palladium on carbon led to partial dehydrochlorination and formation of a mixture of two indolacridines C₂₆H₁₇ClN₂ and C₂₆H₁₈N₂ which are only distinguished by substitution of a chlorine by hydrogen atom. They co-crystallize from ethanol as a solid solution of the two compounds with ratios between 90:10 and 42:58 by whole molecule disorder in a triclinic $P \bar {1}$ setting. Unit cell dimensions for a crystal with a 0.615(2) to 0.305(2) ratio are a = 9.1952(16), b = 10.2589(18), and c = 10.6268(19) Å, and α = 79.688(3), β = 67.156(3), and γ = 86.897(3)°. The replacement of chlorine by the smaller hydrogen causes all atoms of both molecules to be shifted against each other within the unit cell by 0.3–0.4 Å. The structure is thus a rarely reported example of a true solid solution of two chemically distinct organic compounds. Weak packing forces (C–H···Cl, C–H···π and π···π stacking interactions) give the structure enough flexibility to accommodate the co-crystallization of the two spatially different molecules.

Graphical Abstract

Two indolacridines C₂₆H₁₇ClN₂ and C₂₆H₁₈N₂ only distinguished by substitution of a chlorine by hydrogen atom co-crystallize by whole molecule disorder to form a solid solution of the two compounds. They take up the same volume within the unit cell with occupancies between 90 and 42% for the chlorinated derivative. The replacement of chlorine by the smaller hydrogen causes all atoms of both molecules to be shifted against each other within the unit cell by 0.3–0.4 Å. The structure is thus a rarely reported example of a solid solution of two chemically distinct organic compounds.