Magnesiumphthalocyanine (MgPc) is a near-IR-active photoconductor used for laser printers. Our recent structure analysis revealed that the MgPc molecule is not flat in the solid state, but the central Mg atom is projected upward, forming a pyramidal structure. The present arrangement is quite indicative of an appreciable interaction along the stacking axis through the formation of a five-coordinate Mg-complex. Therefore, the Mg-N interaction along the molecular stack has been investigated by energy partition analysis based on semi-empirical MO calculations. The Mg-N bond energy along the molecular stack is found to be roughly one-third of the Mg-N bond in the molecular plane and approximately one-half of the Mg-O bond of the MgPc six-coordinate complexes: MgPc/(H2O)2(NMP)2 and MgPc/(2-methoxyehtanol)2. These results indicate the chain formation of five-coordinate MgPc complexes along the stacking axis, showing considerable π-π interactions thorough the central Mg atom.
J. Mizuguchi, "π-π Interactions of Magnesiumphthalocyanine as Evaluated by Energy Partition Analysis" in Proc. IS&T Int'l Conf. on Digital Printing Technologies (NIP17), 2001, pp 561 - 563, https://doi.org/10.2352/ISSN.2169-4451.2001.17.1.art00028_2