Electron Transfer and Geometric Conversion of Co − NO Moiety in Saddled Porphyrins: Implications for Trigger Role of Tetrapyrrole Distortion Min Tang, † Yan Yang, † Shaowei Zhang, † Jiafu Chen, ‡ Jian Zhang, § Zaichun Zhou, * , † and Qiuhua Liu * , † Abstract The electrons of NO and Co are strongly delocalized in normal {Co-NO} 8 species. In this work, {Co-NO} 8 complexes are induced to convert from (Co II ) + • − NO • to Co III − NO − by a core contraction of 0.06 Å in saddled cobalt(II) porphyrins. This intramolecular electron transfer mechanism indicates that nonplanarity of porphyrin is involved in driving conversion of the NO units from electrophilic NO • as a bent geometry to nucleophilic NO − as a linear geometry. This implies that distortion acts as a trigger in enzymes containing tetrapyrrole. The electronic behaviors of the Co II ions and Co − NO moieties were ...