Molecular mechanics calculations on cobalt phthalocyanine dimers

In order to obtain insight into the structure of cobalt phthalocyanine dimers, molecular mechanics calculations were performed on dimeric cobalt phthalocyanine species. Molecular mechanics calculations are first presented on monomeric cobalt(II) phthalocyanine. Using the Tripos force field for the organic part of the molecule and parameters derived from the literature and subsequently optimized to describe the CoII force field resulted in a geometry that is in very good agreement with experimental data from the literature. Optimization of the dimeric structure leads to a geometry in which both phthalocyanines are separated by 3.2 Å and one of the molecules is shifted 2.38 Å in both the X- and Y-directions with respect to the other. This geometry is in excellent agreement with literature data on ß-Co(pc) crystals and with other calculated and experimental data on similar systems. All calculations were performed with three possible charge distributions in the phthalocyanine molecule and it was shown that varying the charge distribution had no significant effect on the final dimeric structure. This method provides valuable insight into the most important energetic interactions leading to dimer formation.