Distinct Difference in the Geometries of NCCL <sup>–</sup> Anions (L = N <sub>2</sub> , CO, CS): A Balance Between π Conjugation and Steric Repulsion
Jia Wei, Rui Ma, Jinshuai Song, Yandong Duan, Xiaoyan Li, Huaiyu Zhang, Yirong Mo
Abstract
High Resolution Image Download MS PowerPoint Slide NCCL – anions (L = N 2, CO and CS) exhibit notable geometric differences: NCCNN – favors a bent structure, whereas NCCCO – and NCCCS – prefer linear configurations. Here, we investigate the origin of their geometric differences using the conventional density functional theory (DFT) and block-localized wave function (BLW) method. Computations reveal that the bent structure is preferred for all species at the BLW state in which the in-plane π // back-donation from NCC – to ligands is disabled. For NCCNN –, enforcing linearity leads to a gain in the π // electron delocalization (conjugation) stability, but it is insufficient to offset the steric penalty. Differently, NCCCO – and NCCCS – experience reduced steric repulsion in linear geometries, thereby favoring more linear geometries as their energy minima. “ In situ ” orbital correlation diagrams reveal an orbital swap in NCC – with the approaching of the ligand L and confirm the carbone theory proposed by the Frenking group. Overall, the geometries (or the degree of bending) of NCCL – anions are governed by the balance between the π // conjugation and steric repulsion. Substituting the electron-withdrawing NC group with CH 3 or F, which provides in-plane σ-electrons or lone pairs, further bends the ∠RCL angle in RCNN – anions, while RCCO – and RCCS – retain their nearly linear forms.