(b) Spectroscopic and structural characterization. The diamagnetic AHP derivatives (M = Pd and Pt) yielded well-resolved 1 H NMR spectra, with the expected doubling of the number of unique b-protons relative to corroles (8 versus 4, Figure ). Conclusive proof of structure came from two single-crystal X-ray diffraction analyses, one for free base H2[Me-AHP] and one for its Pd complex Pd[Me-AHP] (Figure ). The free-base structure exhibits the same hydrogen bonding motif and tautomer as previously observed. Both the free-base and Pd structures are structures exhibit a nonplanar macrocycle, with the pyrrole ring attached to the 4aminotriazole-derived nitrogen tilted relative to the mean plane of the other three pyrrole units. Cyclic voltammetry (Figure ) and UV-vis-NIR spectroscopy (Figure ) afforded electronic structural insight into the compounds studied (Table ). The free-base, Pd, and Pt AHPs were all found to exhibit two irreversible oxidations and two reversible reductions.