Fig. 2. X-ray crystal structures of (a) 3 and (b) 10. (Left: top view; right: side view; thermal ellipsoids are set at the 50% probability; N-butyl groups are omitted for clarity in the side views). (c) Deformation angles α and β for the colored pyrrole rings in 3, 4 and 10. α is the averaged deviation angle between the mean planes of N–C(3)–C(4) and N–C(2)–C(3), and β is the averaged deviation angle between the mean plane N–C(2)–C(3) and a C(2)–C(external) bond.