Nuclear magnetic shielding of monoboranes : calculation and assessment of 11B NMR chemical shifts in planar BX3 and in tetrahedral [BX4]- systems
Abstract
11B NMR chemical shifts of tricoordinated BX3 and tetracoordinated BX4- compounds (X = H, CH3, F, Cl, Br, I, OH, SH, NH2, and CH=CH2) were computed and the shielding tensors were explored not only within the nonrelativistic GIAO approach but also by applying both relativistic ZORA computations including spin-orbit coupling as well as by employing scalar nonrelativistic ZORA computations (BP86 level of density functional theory). The contributions of the spin-orbit coupling to the overall shieldings are decisive for X = Br and I in both series. No relationship was found between the 2p orbital occupancies or 1/∆E (difference between LUMO and suitably occupied MO that can be coupled with LUMO) with the shielding tensors (or their principal values) in the BX3 series. However, a multidimensional statistical approach known as factor analysis (frequently used in chemometrics) revealed that three factors account for 92 % of the cumulative proportion of total variance. The main components of the first factor are occupancies in the 2px and 2py orbitals and 1/∆E, the second factor is mainly the occupancy in the 2pz orbital and the inductive substituent parameters by Taft and, finally, the third factor consists exclusively (99.3 %) of the electrostatic potentials (Vmax), which is directly related to the so-called π-hole magnitudes.
Citation
Machacek , J , Buehl , M , Fanfrlik , J & Hnyk , D 2017 , ' Nuclear magnetic shielding of monoboranes : calculation and assessment of 11 B NMR chemical shifts in planar BX 3 and in tetrahedral [BX 4 ] - systems ' , Journal of Physical Chemistry A , vol. 121 , no. 50 , pp. 9631-9637 . https://doi.org/10.1021/acs.jpca.7b09831
Publication
Journal of Physical Chemistry A
Status
Peer reviewed
ISSN
1089-5639Type
Journal article
Description
The financial support of the Czech Science Foundation (project No. 17-08045S) is gratefully acknowledged.Collections
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