Open-shell porphyrin

Porphyrin complexes and the many important biological or commercial compounds that are based upon the porphyrin structure show distinct intense electronic spectra that vary in form depending on the exact structure of the ligand and the identity of the central metal ion. Simple porphyrin complexes have D4h symmetry as do many porphyrin derivatives. A large number of lower symmetry related molecules can be approximated successfully as D4h. Porphyrin complexes can be closed-shell or open-shell depending on the identity of the central metal. MCD spectroscopy, a technique that it sensitive to the space and spin symmetry of the ground... 

This section is divided into two parts. In the first part, detailed calculations of some closed-shell porphyrins (135,136) will be described. Our investigations of a pair of open-shell complexes (50,127) will be discussed briefly in the second part. 

So far, we have encountered the spin density as a variable both in the description of electronic structures of open-shell character and in the analysis of local quantities such as local spins or bond orders. For an accurate treatment of open-shell molecules, spin-spin interactions and chemical bonding, reliable spin densities are thus mandatory. However, the determination of rehable spin density distributions can be a difficult task in quantum chemistry [199, 200]. Examples of such difficult cases are iron nitrosyl complexes containing salen or porphyrin ligands for which DFT spin densities considerably depend on the approximate exchange-correlation functional [87,199]. 

The requirement for picosecond excited state lifetimes limits the choice of central metals in porphyrin type complexes suitable for LHC maquette design. Open rZ-shell transition metals provide efficient... 

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