NONPLANAR PORPHYRINS - X-RAY STRUCTURES OF (2,3,7,8,12,13,17,18-OCTAETHYL-5,10,15,20-TETRAPHENYLPOPHINATO)ZINC(II) AND (2,3,7,8,12,13,17,18-OCTAMETHYL-5,10,15,20-TETRAPHENYLPORPHINATO)ZINC(II)

X-ray structures of the peripherally crowded porphyrins, (2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenylporphinato) Zn(II)-3MeOH solvate (ZnOETPP·3MeOH) and (2,3,7,8,12,13,17,18-octamethyl-5,10,15,20-tetraphenylporphinato) Zn(II)-pyridine-2HCCl3 (ZnOMTPP·py·2HCCl3) are reported. Both molecules are severely nonplanar and assume saddle shapes. 1H NMR data confirm that the conformational distortions are maintained in solution. The consequences of distorting the macrocycles are significant: optical, redox, basicity, and excited-state properties are altered in agreement with previous theoretical calculations. These results form part of an expanding body of structural information that clearly demonstrates that porphinoid skeletons are flexible and that distortions of the macrocycles can be imposed by steric interactions in vitro and in vivo. Conformational variations thus provide an attractively simple mechanism for modulating a wide range of physical and chemical properties of porphyrinic chromophores and prosthetic groups in vitro and in vivo. Crystallographic data. ZnN4C60H60·3CH3OH: triclinic space group P1, a = 14.017 (10) Å, b = 16.494 (7) Å, c = 13.073 (9) Å, α = 96.12 (5)°, β = 107.48 (6)°, γ = 105.23 (6)°, V = 2724.5 Å3, Z = 2; RF and RwF = 0.062, based on 4281 reflections with Fo > 2σFo; T = 200 K. ZnN4C52H44·C5D5N·2HCCl3: monoclinic space group C2/c, a = 22.411 (23) Å, b = 12.552 (10) Å, c = 19.287 (12) Å, β = 98.66 (10)°, V = 5363.6 Å3, Z = 4; RF = 0.060 and RwF = 0.061, based on 1722 reflections with Fo > 2σFo; T= 298 K. © 1990, American Chemical Society. All rights reserved.