Knowledge Bank

Metalloporphyrins are introduced into has the gas phase by heating the porphyrins to $350\circ$ C under high vacuum. Resonance Raman measurements in conjunction with absorption spectroscopy and mass spectral studies indicate the Ni(II) octaethylporphin and Co(II) octaethylporphin are stable as four-coordinate gas phase species. The geometry of these gas phase porphyrins appear to be identical to that of the condensed phase species at similar temperature. Resonance Raman temperature dependent studies of both gas and condensed phase metalloporphyrins indicate a general lowering of the Raman frequencies as the temperature increases. These data suggest significant anharmonicities for low frequency porphyrin vibrations. The temperature dependent results will be related to the frequency shifts observed in recent photochemically generated transient Raman studies of heme proteins. In contrast to the Co and Ni porphyrins, ligated ferric porphyrins and manganese(III) etioporphyrin undergo internal oxidation-reductions as the sample are introduced into the gas phase. The metal is reduced while the ligand leaves as an atomic species. These results will be discussed in the context of porphyrin chemistry.