UV-vis Absorption Spectra (Table and Figures ). The electronic absorption spectra of M-2 metalloporphyrins without an axial ligand (D 4h symmetry) are dominated by a weak Q band carrying fine structure and by a very strong Soret band. Those metalloporphyrins with an axial ligand (C 4v symmetry) are much more complex. This is attributable to an interaction of 3d orbitals of the metal dication with the pi-electron system of the porphyrin dianion and the presence of ligand-to-metal charge transfer bands in the spectrum. For six of the metalloporphyrins, the situation has been analyzed in considerable detail elsewhere. Nuclear Magnetic Resonance (NMR, Table and Figures S... -S...). 1 H, C and 15 N spectra were observed for all the M-2 metalloporphyrins, except the Cu(II), Co(II) and VO(II) salts. Only small variation was found in the chemical shifts of the meso and the â protons of the diamagnetic Mg(II), Zn(II) and Ni(II) salts. The 1 H NMR signals of the â protons of the Mn(III) and Fe(III) complexes exhibit significant paramagnetic shifts, and those of the Mn(III) salts also a substantial paramagnetic line broadening. when compared to the diamagnetic analogues (e.g., the Direct acquisition of the N NMR chemical shifts would require the preparation of isotopically labeled metalloporphyrins and we determined them from ( 1 H, 15 N) HMBC correlation spectra. They are in the range 190-207 ppm in 2, Mg-2, and Zn-2, but the value for Ni-2 is 123.1 ppm, suggesting the presence of a rapid equilibrium in which a fraction of the molecules is in the triplet state.