Performances of simplified models of cyanocobalamin for first-principles calculations

Cyanocobalamin (CNCbl) is a key member of the family of organometallic molecular catalysts. Consequently, both experimental and theoretical investigations of CNCbl are essential for advancing the fundamental understanding of its structural and catalytic properties. However, the inherent complexity of its molecular architecture poses significant challenges for theoretical studies. To address this, several studies have employed simplified structural models of CNCbl. In the present work, we systematically investigate the structural, electronic, and magnetic properties of various reduced CNCbl models, alongside the complete CNCbl molecule, using density functional theory. Our results reveal that the electronic structure, magnetic behavior, and oxidation state undergo substantial modifications in the reduced models compared to the full CNCbl system. In particular, the complete CNCbl structure exhibits a non-magnetic semiconducting character with a +3 oxidation state of the Co center, whereas the overly simplified models display magnetic behavior with a +2 oxidation state. These pronounced changes in oxidation and magnetic character also lead to significant alterations in catalytic properties. The influence of these effects is further demonstrated through Cl adsorption studies. In the full CNCbl model, Cl binds strongly at the Co site, while in the reduced models, the interaction becomes considerably weaker. These findings underscore that, despite advances in computational resources, the use of oversimplified CNCbl models can yield misleading predictions. Therefore, the complete CNCbl structure should be preferred for reliable theoretical investigations of both its fundamental and catalytic behavior.