Quadruple Phthalocyanines

Stacked complexes made by sandwiching metal ions between the carbon-nitrogen macrocyclic ligand phthalocyanine (Pc) exhibit a range of potentially useful electrochromic and magnetic properties. So far, chemists have been limited to making triple-decker versions containing two metal centers and three Pc groups. Takamitsu Fukuda, Tsuneaki Biyajima, and Nagao Kobayashi of Tohoku University, in Japan, have now upped those numbers by creating the first quadruple-decker Pc complex (J. Am. Chem. Soc., DOI: 10.1021/ja100125e). Because Pc is a dianion and lanthanides are trivalent cations, the researchers noted that the known triple-decker Lu₂Pc₃ can be regarded as LuPc₂ ^– coordinated by LuPc⁺, and that LuPc₂ ^– was a good candidate for stacking a second LuPc₂ ^– unit if the right metal ion could be found to hold them together. The Tohoku team found Cd²⁺ to be a match. The researchers treated LuPc₂(N[(CH₂)₃CH₃]₄) with Cd(CO₂CH₃)₂ at 400 °C to obtain the quadruple complex as a dark purple powder in low yield. They made positive identification by using ion cyclotron resonance mass spectrometry and confirmed the quadruple stacking by using NMR spectroscopy to analyze the distinct sets of hydrogen atoms on the inner and outer Pc ligands.