The results of ENDOR investigations of magnetically dilute single crystals of Ag(II) and Cu(II) tetraphenylporphyrins (TPP) are presented and discussed. The complete hyperfine tensors, and quadrupole tensor for nitrogen, have been determined for the metal ions, nitrogens and pyrrole protons. The non-first order 14N ENDOR spectra resulting from multiple equivalences among the nitrogen nuclei have been completely analysed by exact diagonalization. The standard ligand-field treatment of electron-nuclear coupling parameters can largely accommodate the 14N results; among other conclusions, it is shown that the nominally d-like odd-electron is only ≤62 per cent 3d in Cu(TPP) and in fact is only ≤ 38 per cent 4d in Ag(TPP). This treatment cannot describe the observed degree of o-π mixing manifested in the significantly nonaxial 14N hyperfine tensors observed. The 14N nuclear quadrupole couplings are analysed to obtain the total electronic distribution at nitrogen; in addition, the assignment of quadrupole tensor orientation and sign is discussed. The pyrrole proton hyperfine couplings are indicative of both the M(TPP) site geometry and the extent and mode of delocalization of the unpaired electron. The predictions of recent Xα calculations on Cu (porphine) are compared to the experimental results.
ASJC Scopus subject areas
- Molecular Biology
- Condensed Matter Physics
- Physical and Theoretical Chemistry