The effects of φ - φ interactions on molecular structure and resonance raman spectra of crystalline copper(II) octaethylporphrin

This paper reports on single crystal resonance Raman measurements which were performed on two crystalline phases of copper(II) octaethylporphyrin (CuOEP): triclinic A and Triclinic B forms. These are compared to previously acquired resonance Raman data on the triclinic A and triclinic B phases of nickel(II) octaethylporphyrin (NiOEP). The difference in crystal packing between the triclinic A and B structures allows for more extensive π-π interactions in the B form than in the A form. Differences in the single crystal Raman spectra of the triclinic A and B forms of both Cu- and NiOEP are attributed to these π-π interactions. Specifically, the Raman core-size marker lines ν3 ν2 and ν10, and the oxidation state market line, ν4, are affected by the different packing interactions in the two crystals and the same Raman shifting patterns between the triclinic A and B phases are observed for both Cu- and NiOEPs. The metal centers exert a slight influence over the packing-induced frequency shifts in the Raman modes. Spectral results on the CuOEP crystals are also compared to solution Raman data on π-π aggregated and monomeric copper(II) uroporphyrin (CuUroP)