Abstract
The d9-Cu(II)-corrin cupribyrate (Cuby) was synthesized in 93% crystalline yield by rapid chelation of Cu2+-ions by the metal-free corrin-ligand of vitamin B12. Single crystals of the EPR-active Cuby allowed for the first X-ray structure determination of a Cu-corrin. SCF-calculations provided insights complementary to the experimental data of Cuby and indicated an out-of-plane displacement of the reduced d10-Cu(I)-ion, consistent with the observed reductive activation of Cuby towards loss of its Cu-center.