IMIT   21220
INSTITUTO DE MODELADO E INNOVACION TECNOLOGICA
Unidad Ejecutora - UE
artículos
Título:
Core and environment dependent relativistic corrections to the nuclear magnetic shieldings in XH4-nYn (n =0,..,4 ; X = Si, Ge, Sn and Y = H, F, Cl, Br, I) model compounds
Autor/es:
A. F. MALDONADO; G. A. AUCAR; J. I. MELO
Revista:
JOURNAL OF MOLECULAR MODELING - (Print)
Editorial:
SPRINGER
Referencias:
Lugar: Berlin; Año: 2014 vol. 20 p. 2417 - 2431
ISSN:
1610-2940
Resumen:
NMR nuclear magnetic shieldings of Si, Ge and Sn in XH4-nYn molecular systems (X = Si, Ge, Sn; Y = F, Cl, Br, I and n = 1,...,4) are highly influenced by the substitution of one or more hydrogen by halogen heavy atoms. We applied the linear response elimination of small components (LRESC) formalism to calculate such shieldings and learn whether including only few terms is enough for getting quantitative reproduction of the full relativistic value. It is observed that the nuclear magnetic shielding value of the central atom changes when the number and weight of the substituent heavy-halogen atoms varies, and in general the pattern of sigma(X) does not exhibit the normal halogen dependence (NDH) behaviour that can be found in similar molecular systems containing C atom. We analyse also each relativistic corrections given by the LRESC method and separate them in core dependent and environment dependent trying to learn the electronic mechanisms involved in the different relativistic effects and in the total relativistic value. Based on this analysis, we were able to study the electronic mechanism involved in a recently proposed relativistic effect, the "heavy atom effect on vicinal heavy atom" (HAVHA), in more detail. We found that the main electronic mechanism is the spin-orbit or sigma T(3) correction, although other corrections such as sigma S(1) and sigma S(3) are also important. Finally, we analyzed proton magnetic shieldings and found that, for molecules containing Sn as the central atom, sigma(H) decreases as the number of heavy halogen substituents (of the same type: either F, Cl, or Br) increases, albeit at different rates for different halogens. sigma(H) only increase as the number of halogen substituents increases if the halogen is iodine.