Calculations and Electronic Analyses of ~(55)Mn and ~(13)C Nuclear Magnetic Shielding Constants for Mn(CO)_5X (X= H, F, Cl, Br, I, and CH_3) and M(CO)(NH_3)_3 (M = Cr ~(2+), Fe~(2+), Cu~+, and Zn~(2+))

摘要

We calculated ~(55)Mn and ~(13)C magnetic shielding constants for Mn(CO)_5X (X= H, F, Cl, Br, I, and CH_3) and M(CO)(NH_3)_3 (M = Cr~(2+), Fe~(2+), Cu ~+, and Zn~(2+)), respectively. For the first molecular group, we compared the calculated ~(55)Mn chemical shifts with the experimental values, and clarified effects of the basis sets. The calculated magnetic shielding constants using the second-order Douglas-Kroll-Hess (DKH2) method showed good agreement with the experimental results. According to the atomic orbital (AO) contribution analysis, the origin of the chemical shifts was attributed to the d-d transitions of Mn. In particular, the 3dπ orbital mainly contributed to the paramagnetic term of the Mn chemical shift. For the second molecular group, the ~(13)C chemical shifts were dependent on the metal atoms. When the metal centers were Cr~(2+) or Fe~(2+), lower field shifts were seen. When the metal centers were Cu~+ or Zn~(2+), upper field shifts were observed. These results were in good agreement with the experimental trends. The change of the paramagnetic term mainly depended on the d orbital configurations of the metal of centers, and the donation from the metal d orbital to the CO anti-bonding π~* orbitals is expected to affect the chemical shift.