Zinc Substitution of Cobalt in Vitamin B(12): Zincobyric acid and Zincobalamin as Luminescent Structural B(12)‐Mimics

Replacing the central cobalt ion of vitamin B(12) by other metals has been a long‐held aspiration within the B(12)‐field. Herein, we describe the synthesis from hydrogenobyric acid of zincobyric acid (Znby) and zincobalamin (Znbl), the Zn‐analogues of the natural cobalt‐corrins cobyric acid and vitamin B(12), respectively. The solution structures of Znby and Znbl were studied by NMR‐spectroscopy. Single crystals of Znby were produced, providing the first X‐ray crystallographic structure of a zinc corrin. The structures of Znby and of computationally generated Znbl were found to resemble the corresponding Co(II)‐corrins, making such Zn‐corrins potentially useful for investigations of B(12)‐dependent processes. The singlet excited state of Znby had a short life‐time, limited by rapid intersystem crossing to the triplet state. Znby allowed the unprecedented observation of a corrin triplet (E (T)=190 kJ mol(−1)) and was found to be an excellent photo‐sensitizer for (1)O(2) (Φ(Δ)=0.70).