Syntheses and Properties of the Copper(II) Complexes of the Amphoteric Surfactants, N-Alkyl-β-alanine

Abstract
Copper(II) complexes of amphoteric surfactants, N-alkyl-β-alanine (NAA) (the number of carbon atoms in the alkyl chains: n=2, 4, 6, 8, 10, 12), Were synthesized from NAA and copper(II) chloride dihydrate by mixing in aqueous solutions. The properties and structures of these bluish flaky complexes were investigated by elemental analyses, infrared and far-infrared spectroscopy, electronic diffuse reflection spectroscopy, X-ray diffractometry, and thermal analyses. As a result, all of these complexes were found to be composed of one copper(II) ion and two NAA molecules, regardless of the chain length in the alkyl group, (Cu(NAA)2·2H2O), and were also found to have a laminated structure in the crystalline state. A linear relationship was found between the long spacings (d/nm) of the laminated structure and the numbers of carbon atoms (n) in the N-alkyl substituents; d=0.135n+0.62. From these results it was concluded that copper(II) complex molecules have a trans configuration, and are extended and parallel to the normal line of the laminated planes in the crystal. A multiunilayer model for the molecular arrangement of these copper(II) complexes has been proposed, which is quite different from those so far proposed to explain the long spacings observed for metal soap crystals, lyotropic liquid crystal and so on. Also, the role of the alkyl substituents in complex formation has been indicated.

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