Boron Tunneling in the "Weak" Bond-Stretch Isomerization of N-B Lewis Adducts

Some nitrile-boron halide adducts exhibit a double-well potential energy surface with two distinct minima: a "long bond" geometry (LB, a van der Waals interaction mostly based on electrostatics, but including a residual charge transfer component) and a "short bond" structure (SB, a covalent dative bond). This behavior can be considered as a "weak" form of bond stretch isomerism. Our computations reveal that complexes RCN-BX₃ (R=CH₃ , FCH₂ , BrCH₂ , and X=Cl, Br) exhibit a fast interconversion from LB to SB geometries even close to the absolute zero thanks to a boron atom tunneling mechanism. The computed half-lives of the meta-stable LB compounds vary between minutes to nanoseconds at cryogenic conditions. Accordingly, we predict that the long bond structures are practically impossible to isolate or characterize, which agrees with previous matrix-isolation experiments.

Radical Molecular Modulator for High-Performance Perovskite Solar Cells

The long-term stability of perovskite solar cells (PSCs) remains an issue impeding their commercialization. Generally, polycrystalline perovskite thin films have many defects on the grain boundaries, which affect the optoelectronic performance and stability of the devices under moisture, heat, illumination, and the presence of an electric field condition. The O-donor Lewis base is often employed to regulate the performance of PSCs such as carbonyl and carboxyl compounds. Herein, we have developed a concept of radical molecular modulation using the O-donor group for high-performance perovskite photovoltaic devices. The judiciously designed radical modulators 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), which located at the perovskite grain boundary through interaction with the perovskite surface sites, effectively passivated the surface defects while templating the formation of large grain crystal and high-quality perovskite thin films. Accordingly, the optimized TEMPO-modulated PSCs achieved a power conversion efficiency of 20.73% with superior stability. This work makes an important contribution for exploring the effect of radical in perovskites to improve the performance of PSCs and other optoelectronic devices.

Reply to the Comment on "Realization of Lewis Basic Sodium Anion in the NaBH3 - Cluster"

We reply to the comment by S. Pan and G. Frenking who challenged our interpretation of the Na^- :→BH₃ dative bond in the recently synthesized NaBH₃ ^- cluster. Our conclusion remains the same as that in our original paper (https://doi.org/10.1002/anie.201907089 and https://doi.org/10.1002/ange.201907089). This conclusion is additionally supported by the energetic pathways and NBO charges calculated at UCCSD and CASMP2(4,4) levels of theory. We also discussed the suitability of the Laplacian of electron density (QTAIM) and Adaptive Natural Density Partitioning (AdNDP) method for bond type assignment. It seems that AdNDP yields more sensible results. This discussion reveals that the complex realm of bonding is full of semantic inconsistencies, and we invite experimentalists and theoreticians to elaborate this topic and find solutions incorporating different views on the dative bond.

Realization of Lewis Basic Sodium Anion in the NaBH3 - Cluster

We report a Na:^- →B dative bond in the NaBH₃ ^- cluster, which was designed on the principle of minimum-energy rupture, prepared by laser vaporization, and characterized by a synergy of anion photoelectron spectroscopy and electronic structure calculations. The global minimum of NaBH₃ ^- features a Na-B bond. Its preferred heterolytic dissociation conforms with the IUPAC definition of dative bond. The lone electron pair revealed on Na and the negative Laplacian of electron density at the bond critical point further confirm the dative nature of the Na-B bond. This study represents the first example of a Lewis adduct with an alkalide as the Lewis base.