The crystal structure of lysidine · HAu(CN) 2—A model compound of a weak-base anion-exchange resin loaded with gold cyanide

Abstract

The crystal structure of lysidine · HAu(CN) 2 was determined so that the influence of steric hindrance at the active site of weak-base imidazoline resins could be established. These resins, which have alkyl groups attached to the basic nitrogen, have lower basicities, and are also eluted more slowly, than imidazoline resins that have no substituents at the active site. The crystal structure of lysidine · HAu(CN) 2 (a model compound for one of the unsubstituted resins) consists of two interpenetrating hydrogen-bonded networks that are perpendicular to each other. The structure suggests that the presence of an alkyl substituent on the basic nitrogen of an imidazoline weak-base resin could hinder the approach of a hydrogen atom and the gold cyanide anion to the basic nitrogen in the functional group, thus lowering the basicity of the amine. However, the crystal structure does not explain the steric effects that have been postulated as causing the rate of elution of disubstituted imidazoline resins to be slower than that of monosubstituted imidazoline resins.