Porphyrins. XXXI. Chemical Properties and Electronic Spectra of do Transition-Metal Complexes
Gouterman, M., Hanson, L.K., Khalil, G.-E., Buchler, J.W., Rohbock, K., and David Dolphin
J. Am. Chem. Soc.
The octaethylporphin complexes of forms (OEP)MXnLm , (OEP)MO, and (OEP)M(O)X[M = Sc(III), Ti(IV), Zr(IV), Hf(IV), Nb(V), and Ta(V); X = univalent anion; L = neutral ligand] all show fluorescence and phosphorescence, as does the tetraphenylporphine complex (TPP)ScX. The fluorescence yields (Φ f .apprx.0.2) and phosphorescence lifetimes (apprx.400 msec) of (OEP)ScX show very low spin-orbit coupling, i.e., no heavy-atom effect. The complexes of (OEP)ZrX2L2 and (OEP)HfX2 L2 have fluorescence yields (Φf = 0.02 and 0.007), phosphorescence yields (Φp = 0.096 and 0.171), and phosphorescence lifetimes (Τ p = 65 and 8.4 msec) that exhibit regular heavy-atom effects; the values for (OEP)TiO show greater spin-orbit effect than in (OEP)ZrX2L 2, which may be due to the smaller Ti out-of-plane distance. The data for Nb(V) and Ta(V) are similar to those of Zr(IV) and Hf(IV), but show greater spin-orbit coupling; they also show an unexplained wavelength dependence of luminescence. The Sc(III) porphyrins form binuclear μ-oxo complexes, which also show fluorescence and phosphorescence.