Nuclear magnetic resonance shielding constants and chemical shifts in linear 199Hg compounds: A comparison of three relativistic computational methods

被引:52
作者
Arcisauskaite, Vaida [1 ]
Melo, Juan I. [2 ,3 ]
Hemmingsen, Lars [1 ]
Sauer, Stephan P. A. [4 ]
机构
[1] Univ Copenhagen, Fac Life Sci, Dept Basic Sci & Environm, DK-1871 Frederiksberg, Denmark
[2] Univ Buenos Aires, Fac Ciencias Exactas & Nat, Dept Fis, RA-1428 Buenos Aires, DF, Argentina
[3] Consejo Nacl Invest Cient & Tecn, RA-1428 Buenos Aires, DF, Argentina
[4] Univ Copenhagen, Dept Chem, DK-2100 Copenhagen O, Denmark
关键词
chemical shift; density functional theory; Gaussian distribution; mercury compounds; nuclear magnetic resonance; organic compounds; potential energy functions; relativistic corrections; spin-orbit interactions; GENERALIZED GRADIENT APPROXIMATION; CORRELATED MOLECULAR CALCULATIONS; ORDER REGULAR APPROXIMATION; INCLUDING ATOMIC ORBITALS; GAUSSIAN-BASIS SETS; ZETA BASIS-SETS; ELECTRON-DIFFRACTION; CONTINUOUS TRANSFORMATION; COUPLING TENSORS; KINETIC BALANCE;
D O I
10.1063/1.3608153
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
We investigate the importance of relativistic effects on NMR shielding constants and chemical shifts of linear HgL2 (L = Cl, Br, I, CH3) compounds using three different relativistic methods: the fully relativistic four-component approach and the two-component approximations, linear response elimination of small component (LR-ESC) and zeroth-order regular approximation (ZORA). LR-ESC reproduces successfully the four-component results for the C shielding constant in Hg(CH3)(2) within 6 ppm, but fails to reproduce the Hg shielding constants and chemical shifts. The latter is mainly due to an underestimation of the change in spin-orbit contribution. Even though ZORA underestimates the absolute Hg NMR shielding constants by similar to 2100 ppm, the differences between Hg chemical shift values obtained using ZORA and the four-component approach without spin-density contribution to the exchange-correlation (XC) kernel are less than 60 ppm for all compounds using three different functionals, BP86, B3LYP, and PBE0. However, larger deviations (up to 366 ppm) occur for Hg chemical shifts in HgBr2 and HgI2 when ZORA results are compared with four-component calculations with non-collinear spin-density contribution to the XC kernel. For the ZORA calculations it is necessary to use large basis sets (QZ4P) and the TZ2P basis set may give errors of similar to 500 ppm for the Hg chemical shifts, despite deceivingly good agreement with experimental data. A Gaussian nucleus model for the Coulomb potential reduces the Hg shielding constants by similar to 100-500 ppm and the Hg chemical shifts by 1-143 ppm compared to the point nucleus model depending on the atomic number Z of the coordinating atom and the level of theory. The effect on the shielding constants of the lighter nuclei (C, Cl, Br, I) is, however, negligible. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3608153]
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页数:11
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