Nuclear Magnetic Shielding of Monoboranes: Calculation and Assessment of 11B NMR Chemical Shifts in Planar BX3 and in Tetrahedral [BX4]− Systems

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 121; no. 50; pp. 9631 - 9637
• Main Authors: Macháček, Jan, Bühl, Michael, Fanfrlík, Jindřich, Hnyk, Drahomír
• Format: Journal Article
• Language: English
• Published: American Chemical Society 21.12.2017
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.7b09831

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 application of both relativistic ZORA computations including spin–orbit coupling as well as 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/ΔE (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 2p x and 2p y orbitals and 1/ΔE; the second factor is mainly the occupancy in the 2p z orbital and the inductive substituent parameters by Taft. Finally, the third factor consists exclusively (98.4%) of the electrostatic potential (V max), which is directly related to the so-called π-hole magnitudes.