Unusual solvent dependent electronic absorption spectral properties of nickel(II) and copper(II) perhaloporphyrins

Electronic absorption spectra of divalent metal (Ni(II) and Cu(II)) complexes of 2,3,7,8,12,13,17,18-octa(bromo/chloro)-5,10,15,20- tetraphenylporhyrins (MOXTPP; X = Br, C1) were examined in various solvents. M(II) perhaloporphyrins exhibited dramatic shifts in their optical absorption spectral features relative to the corresponding metallotetraphenylporphyrins, MTPPs. Copper(II) perhaloporphyrins show significant red-shifts of the absorption bands in coordinating solvents relative to that observed for nickel(II) perhaloporphyrins. The large redshift of the electronic absorption bands and the gain in intensity of the longest wavelength band (Q(0,0)), of Cu(II) perhaloporphyrins in certain coordinating solvents is comparable to that found in meso-tetraphenylporphinatozinc(II), ZnTPP. The solvent dependent spectral features of M(II) perhaloporphyrins are attributed to a coordinative interaction of the solvent with the core metal ion induced by the electron deficient porphyrin macrocycle. Copyright © 2004 Society of Porphyrins & Phthalocyanines.