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Effects of Halogen, Chalcogen, Pnicogen, and Tetrel Bonds on IR and NMR Spectra
oleh: Jia Lu, Steve Scheiner
Format: | Article |
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Diterbitkan: | MDPI AG 2019-08-01 |
Deskripsi
Complexes were formed pairing FX, FHY, FH<sub>2</sub>Z, and FH<sub>3</sub>T (X = Cl, Br, I; Y = S, Se, Te; Z = P, As, Sb; T = Si, Ge, Sn) with NH<sub>3</sub> in order to form an A⋯N noncovalent bond, where A refers to the central atom. Geometries, energetics, atomic charges, and spectroscopic characteristics of these complexes were evaluated via DFT calculations. In all cases, the A−F bond, which is located opposite the base and is responsible for the σ-hole on the A atom, elongates and its stretching frequency undergoes a shift to the red. This shift varies from 42 to 175 cm<sup>−1</sup> and is largest for the halogen bonds, followed by chalcogen, tetrel, and then pnicogen. The shift also decreases as the central A atom is enlarged. The NMR chemical shielding of the A atom is increased while that of the F and electron donor N atom are lowered. Unlike the IR frequency shifts, it is the third-row A atoms that undergo the largest change in NMR shielding. The change in shielding of A is highly variable, ranging from negligible for FSnH<sub>3</sub> all the way up to 1675 ppm for FBr, while those of the F atom lie in the 55−422 ppm range. Although smaller in magnitude, the changes in the N shielding are still easily detectable, between 7 and 27 ppm.