The UKB prescription and the heavy atom effects on the nuclear magnetic shielding of vicinal heavy atoms

ALEJANDRO MALDONADO; GUSTAVO A. AUCAR

PHYSICAL CHEMISTRY CHEMICAL PHYSICS

ROYAL SOC CHEMISTRY

Lugar: Londres; Año: 2009 vol. 11 p. 5615 - 5627

1463-9076

Fully relativistic calculations of NMR magnetic shielding on XYH3 (X = C, Si, Ge and Sn;Y = Br, I), XHn (n = 1?4) molecular systems and noble gases performed with a fully relativisticpolarization propagator formalism at the RPA level of approach are presented. The rate ofconvergence (size of basis set and time involved) for calculations with both kinetic balanceprescriptions, RKB and UKB, were investigated. Calculations with UKB makes it feasible toobtain reliable results for two or more heavy-atom-containing molecules. For such XYH3systems, the influence of heavy vicinal halogen atoms on s(X) is such that heavy atom effects on heavy atoms (vicinal plus their own effects or HAVHA + HAHA effects) amount to 30.50% for X = Sn and Y = I; being the HAHA effect of the order of 25%. So the vicinal effect alone is of the order of 5.5%. The vicinal heavy atom effect on light atoms (HALA effect) is of the order of 28% for X = C and Y = I. A similar behaviour, but of opposite sign, is observed for s(Y) for which sRNR(I; X = C) (HAHA effect) is around 27% and sRNR(I; X = Sn) (HAVHA + HAHA effects) is close to 21%. Its electronic origin is paramagnetic for halogen atoms but both dia- and paramagnetic for central atoms. The effect on two bond distant hydrogen atoms is such that the largest variation of s(H) within the same family of XYH3 molecules appears for X = Si and Y = I: around 20%. In this case s(H; X = Sn, Y = I) = 33.45 ppm and s(H; X = Sn, Y = H) = 27.82 ppm.