Department of Chemistry and Biochemistry, Utah State University, Logan, UT 84322-0300, USA.
Molecules. 2019 Aug 2;24(15):2822. doi: 10.3390/molecules24152822.
Complexes were formed pairing FX, FHY, FHZ, and FHT (X = Cl, Br, I; Y = S, Se, Te; Z = P, As, Sb; T = Si, Ge, Sn) with NH 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 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 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.
为了形成 A⋯N 非共价键，将 FX、FHY、FHZ 和 FHT（X=Cl、Br、I；Y=S、Se、Te；Z=P、As、Sb；T=Si、Ge、Sn）与 NH 配对形成配合物，其中 A 指的是中心原子。通过 DFT 计算评估了这些配合物的几何形状、能量、原子电荷和光谱特性。在所有情况下，位于碱基对面且负责 A 原子上 σ 空穴的 A-F 键都会延长，其伸缩频率会向红移。这种位移从 42 到 175cm 不等，对于卤素键最大，其次是硫属元素、四元素和磷属元素。随着中心 A 原子的增大，位移也会减小。A 原子的 NMR 化学位移增加，而 F 和电子给体 N 原子的化学位移降低。与 IR 频率位移不同，是第三周期 A 原子的 NMR 屏蔽发生了最大的变化。A 的屏蔽变化高度可变，从 FSnH 的可忽略不计到 FBr 的 1675ppm，而 F 原子的屏蔽范围在 55-422ppm 之间。尽管幅度较小，但 N 屏蔽的变化仍然很容易检测到，在 7 到 27ppm 之间。
