Cationic Copper(II)-containing Surfactants: Molecular Structures, Film Morphology, and Influence on the Alignment of Nematic Mesogens

Abstract

We discuss the synthesis and amphiphilic behavior of the cationic metallosurfactants [(L(Py14))2Cu(II)ClO4]ClO4 (1), [(L(Py16))2Cu(II)ClO4]ClO4 (2), [(L(Py18))2Cu(II)ClO4]ClO4 (3), [(L(Py18))2Cu(II)NO3]NO3 (4), [(L(Py18))2Cu(II)Cl]Cl (5), and [(L(Py18))2Cu(II)Br]Br (6) obtained by treatment of the appropriate alkylaminemethyl-2-pyridine ligand containing tetra-, hexa-, or octadecyl chains with copper salts. These metallosurfactants show excellent agreement between infrared spectroscopic bands, spectrometric masses with isotopic patterns, and elemental composition. Single-crystal X-ray data available for 1, 2, 5 and the previously published 3 reveal a trigonal bipyramidal copper(II) ion bound at the basal plane to the amine and pyridine of each alkylaminemethylpyridine ligand and an anionic coligand to the apical position. Except for the surfactant with the shortest tetradecyl (C14) chain, these species yield Langmuir films with collapse pressures of 45-55 mN·m(-1) and average areas of ca. 50 Å(2). A plateau around 15 mN·m(-1) is observed for 3, 4, and 5 and associated with the formation of dendritic domains about 50 μm in size. Species 2 and 6 lack this plateau and show domains of ca. 5 μm. Once transferred onto solid substrates, the resulting Langmuir-Blodgett film of 3 at 18 mN·m(-1) influences the alignment of the nematic liquid crystal N-(4-methoxybenzylidene)-4-butylaniline.

Aggregation and surface behavior of aqueous solutions of cis-bis(1,3-diaminopropane)bis(dodecylamine)cobalt(iii) nitrate. A double-chained metallosurfactant

“…6 Many metallosurfactants are also reported to be biologically active. [10][11][12][13][14][15][16][17][18][19] Metallosurfactants synthesized till now are grouped into three types: (i) in type 1 metallosurfactants, the central metal ion along with its primary coordination sphere acts as the hydrophilic head group and the ligand with long hydrocarbon chain coordinated to the metal ion acts as the hydrophobic tail; [4][5][6]10,[20][21][22][23][24][25][26][27][28][29][30][31][32] (ii) in type 2 metallosurfactants, a metal complex is coordinated to a conventional ionic surfactant from the tail end such that the metal forms a part of the hydrocarbon tail. [33][34][35][36] Metallosurfactants of this type are similar to bolaforms; (iii) in type 3 metallosurfactants, the metal complex forms the counterion.…”