Electronic spectrum of Co-corrin calculated with the TDDFT method

The electronic spectrum of Co-corrin was calculated with the TDDFT/B3LYP method. The calculated spectrum is compared to the experimental spectrum of vitamin B-12s which is known to be four coordinate in solution. Three basis sets were used in the calculations, one with the 6-311G*++ basis and two with the LANL2DZ+d basis on the cobalt atom. The results are similar for the several longest wave transitions in all the three bases. The bands at 700 and 554 nm are assigned as d --> pi* transitions. The band at 460 nm has a prevailing d --> d character. The bands at 385 and 300 mn are mainly of pi --> pi and d --> pi* character. The average energy error of calculated excitation energies for these bands is about 0.2 eV. The higher energy bands at 286 and 280 nm can be assigned as mainly d --> pi* and pi --> pi* transitions from the calculated spectrum with the 6-311G*++ basis. In LANL2DZ + d the transitions to 4p orbitals dominate in this part of the spectrum. The problem with calculating the highest energy transitions in Co-corrin may be traced to the high-lying HOMO orbital of this molecule. (C) 2003 Elsevier B.V. All rights reserved.