The Synthesis and Characterization of Imidazolium Lithium Phthalocyanines

by Kelley, John J.

A series of 1,3-di-substituted-imidazolium lithium phthalocyanines, in which the substituents on the imidazolium nitrogens were combinations of methyl, ethyl, pentyl, hexyl, isopropyl, adamantyl or 2,4,6-trimethylphenyl groups, was synthesized. The cation exchange of a single lithium ion of dilithium phthalocyanine for a 1,3-disubstituted-imidazolium ion was performed by mixing their salts in common organic solvents under ambient conditions. This afforded a number of imidazolium lithium phthalocyanines in moderate yields. They exhibited poor solubility in most solvents. Their composition and purity were initially verified by 1H and 13C-NMR and elemental analysis. The 1H-NMR spectra also indicated that the imidazolium and lithium phthalocyanine ions are present in a 1:1 ratio. Infrared spectra confirmed the C-C and C-N stretching modes that are characteristic of phthalocyanine and imidazolium aromatic structures. UV-Vis spectra for each compound showed essentially no change in absorption from that of dilithium phthalocyanine, which suggests a lack of influence of the imidazolium ions. Thermal properties of the title compounds were determined through melting points and TGA, in which high melting temperatures (330-370°C) were seen for several complexes and lowered thermal stability was seen for all. The crystal structure of the bis(adamantyl)imidazolium derivative was determined through X-ray diffraction. It was found that water molecules are associated to imidazolium and lithium phthalocyanine ions through hydrogen-bonding, which is possibly the basis for crystallization in imidazolium-lithium-phthalocyanines.