Proposed crystal structure of dequalinium chloride Form A, C ₃₀ H ₄₀ N ₄ Cl ₂

Abstract The crystal structure of Form A of dequalinium chloride has been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional theory techniques. Dequalinium chloride Form A crystallizes in space group P4 2 2 1 2 (#94) with a = 26.2671(8), c = 9.1119(4) Å, V = 6,286.9(4) Å 3 , and Z = 8 at 298 K. Despite the conventional representation of the cation, the ring N atoms are not positively charged. The positive charges are distributed on the ring carbon atoms ortho and para to these N atoms. The central decyl chain conformation is more kinked than the all- trans that might be expected in the solid state, but contains only one unusual torsion angle. The crystal structure consists of an array of dequalinium cations, with chloride anions located in regions between the cations. There are short stacks of roughly parallel rings in multiple directions. There is only one classical hydrogen bond in the structure, N–H···Cl between one of the amino groups and one of the chloride anions. Several C–H···Cl hydrogen bonds are prominent, involving ring, chain, and methyl hydrogen atoms as donors. Particularly noteworthy are the hydrogen bonds from the first and second C atoms at each end of the decyl chain. The powder pattern has been submitted to the International Centre for Diffraction Data (ICDD) for inclusion in the Powder Diffraction File ™ (PDF ® ).