X-Ray Crystal Structures and Directional Diamagnetic Susceptibility Calculations of Decyl and Dodecylammonium Chlorides

Abstract

The crystal and molecular structures of decylammonium chloride (DACl) and dode-cylammonium chloride (DDACl) were determined. The crystal data for DACl is: a = 5.700(3), b = 7.173(1), c = 15.507(2) Å, β = 91.23(3)° monoclinic, space group P2₁ with two molecules in the unit cell and for DDACl is: a = 5.676(3), b = 7.186(2), c = 17.770(4) Å, β = 92.72(3)°; monoclinic, space group P2₁ with two molecules in the unit cell. The structures were solved by direct methods and refined anisotropic (DACl) and isotropically (DDACl) to R-values of 0.083 and 0.091 for 975 and 337 observed reflections, respectively. Each NH₃ ⁺ group in both structures is involved in hydrogen bonds and ionic bonds with three Cl⁻ions, with mean distance of 3.144 Å.

The directional diamagnetic susceptibilities of the title compounds were calculated by the Flygare method using the structural data as determined. The values of X calculated by this method are shown to be in good agreement with those given by the Pascal method.

While it is not possible to make a direct comparison of the calculated directional susceptibility of the molecule and the measured directional susceptibility of the lyo-mesophase, it is possible to compare the calculated and the measured anisotropies. When reasonable assumptions are made as to the order and structure of the nematic mesophase, our calculated anisotropy for DACl is well within the range of the available experimental values.

Key Words:

• crystal structure
• directional susceptibility
• lyotropic systems
• surfactants
• diamagnetic anisotropy