The Na⋅⋅⋅B Bond in NaBH 3 − : A Different Type of Bond

Inter-Alkali-Metal Dative Bond in the MMN3 - (M=Alkali Metal) Cluster

Alkali metals are generally Lewis acids. On the contrary, Lewis basic character of alkali metals forming donor - acceptor complexes is a very rare phenomenon. In this contribution, I have theoretically designed an anionic cluster MMN₃ ^- (M=alkali metals) on the basis of experimentally known reagent, alkali salt of azide ion MN₃ , which shows unprecedented M:^- →M donor-acceptor interaction. To the best of author's knowledge, the characterization of such donor-acceptor interaction among alkali metals is unprecedented. Formation of the 2c-2e donor-acceptor bonds have been confirmed by quantum theory of atoms in molecules and electron localization function analyses. The calculated bond dissociation energies are significant suggesting their possible spectroscopic identification.

Planar Hypercoordinate Carbons in Alkali Metal Decorated CE3 2- and CE2 2- Dianions

After exploring the potential energy surfaces of M_m CE₂ ^p (E=S-Te, M=Li-Cs, m=2, 3 and p=m-2) and M_n CE₃ ^q (E=S-Te, M=Li-Cs, n=1, 2, q=n-2) combinations, we introduce 38 new global minima containing a planar hypercoordinate carbon atom (24 with a planar tetracoordinate carbon and 14 with a planar pentacoordinate carbon). These exotic clusters result from the decoration of V-shaped CE₂ ^2- and Y-shaped CE₃ ^2- dianions, respectively, with alkali counterions. All these 38 systems fulfill the geometrical and electronic criteria to be considered as true planar hypercoordinate carbon systems. Chemical bonding analyses indicate that carbon is covalently bonded to chalcogens and ionically connected to alkali metals.

Diboron Bonds Between BX3 (X=H, F, CH3 ) and BYZ2 (Y=H, F; Z=CO, N2 , CNH)

The ability of B atoms on two different molecules to engage with one another in a noncovalent diboron bond is studied by ab initio calculations. Due to electron donation from its substituents, the trivalent B atom of BYZ₂ (Z=CO, N₂ , and CNH; Y=H and F) has the ability to in turn donate charge to the B of a BX₃ molecule (X=H, F, and CH₃ ), thus forming a B⋅⋅⋅B diboron bond. These bonds are of two different strengths and character. BH(CO)₂ and BH(CNH)₂ , and their fluorosubstituted analogues BF(CO)₂ and BF(CNH)₂ , engage in a typical noncovalent bond with B(CH₃ )₃ and BF₃ , with interaction energies in the 3-8 kcal/mol range. Certain other combinations result in a much stronger diboron bond, in the 26-44 kcal/mol range, and with a high degree of covalent character. Bonds of this type occur when BH₃ is added to BH(CO)₂ , BH(CNH)₂ , BH(N₂ )₂ , and BF(CO)₂ , or in the complexes of BH(N₂ )₂ with B(CH₃ )₃ and BF₃ . The weaker noncovalent bonds are held together by roughly equal electrostatic and dispersion components, complemented by smaller polarization energy, while polarization is primarily responsible for the stronger ones.

Na⋅⋅⋅B Bond in NaBH3 - : Solving the Conundrum

Bonding in the recently synthesized NaBH₃ ^- cluster is investigated using the high level Valence Bond BOVB method. Contrary to earlier conclusions, the Na-B bond is found to be neither a genuine dative bond, nor a standard polar-covalent bond at equilibrium. It is rather revealed as a split and polarized weakly coupled electron-pair, which allows this cluster to be more effectively stabilized by a combination of (major) dipole-dipole electrostatic interaction and (secondary) resonant one-electron bonding mechanism. Our analysis of this unprecedented bonding situation extends to similar clusters, and the VB model unifies and articulates the previously published variegated views on this exotic "bond".

Neither too Classic nor too Exotic: One-Electron Na⋅B Bond in NaBH3 - Cluster

It is here reported that the NaBH₃ ^- cluster exhibits a Na⋅B one-electron bond, a well-established type of electron-deficient bonding in the literature. The topological analysis of the electron localization function, at the correlated level, reveals that Na^- , when approaching the bonding distance, fairly distributes its valence electron pair between two lobes. One of these electrons is used to bond with BH₃ , which participates through its boron empty p-orbital. Furthermore, the bonding situation of LiBH₃ ^- , KBH₃ ^- , MgBH₃ , and CaBH₃ global minima structures are similar to that of NaBH₃ ^- , extending the family of these new one-electron bond systems with biradicaloid character.

Planar Hexacoordinate Carbons: Half Covalent, Half Ionic

Herein, the first global minima containing a planar hexacoordinate carbon (phC) atom are reported. The fifteen structures belong to the CE₃ M₃ ⁺ (E=S-Te and M=Li-Cs) series and satisfy both geometric and electronic criteria to be considered as a true phC. The design strategy consisted of replacing oxygen in the D_3h  CO₃ Li₃ ⁺ structure with heavy and less electronegative chalcogens, inducing a negative charge on the C atom and an attractive electrostatic interaction between C and the alkali-metal cations. The chemical bonding analyses indicate that carbon is covalently bonded to three chalcogens and ionically connected to the three alkali metals.