Isolated [B2(CN)6]2-: Small Yet Exceptionally Stable Nonmetal Dianion

Electronic Instability and Solvation Stabilization of Oxocarbon Dianions (CnOn)2- (n = 4-6)

Oxocarbon dianions (CnOn)2- have been recently found to be promising candidates in the design of high-capacity and fast rechargeable batteries but are intrinsically unstable in the isolated form. Fundamental understandings of their electronic structures, solvent stabilization, and interactions with solvents and counterions are crucial in comprehending their electron transfer reactions occurring in batteries. In this article, we employed microsolvated dianionic clusters as models and combined negative ion photoelectron spectroscopy (NIPES) and theoretical computations to probe the electronic instability and solvation stabilization of (CnOn)2- (n = 4-6) dianions. Through the smallest observable members in each series of microhydrated dianions and their recorded adiabatic and vertical detachment energies (ADEs and VDEs), the minimum numbers of H2O molecules required to stabilize (CnOn)2- dianions are determined to be 4, 3, and 2 for n = 4, 5, and 6, respectively, while 3 and 2 water molecules can make (C4O4)2- and (C5O5)2- metastable and detectable. Using theoretical calculations, we determined the lowest energy structures of each complex. The first few H2O molecules prefer to be directly hydrogen bonded to two adjacent O atoms around the oxocarbon ring. The water binding strengths are generally comparable when each H2O molecule is bound at a separate binding pocket, but the binding strengths decrease when all binding pockets are occupied, in parallel with the observed ADE and VDE shift trends. Moreover, hydrated (C4O4)2- dianions are found to possess distinct electronic structures compared to its (C5O5)2- and (C6O6)2- analogues due to its near-degenerate HOMO and HOMO-1, while there exists a larger gap for the latter two dianions. Upon hydration, the overall electronic structure patterns are maintained without much distortion, but fine changes are noticeable, which warrant future studies.

Exploring the properties of new super-chalcogens based on multiple electron counting rules: a combined DFT and ab initio study on [M(B2C4X6)2]2- dianion clusters

The theoretical exploration of the super-chalcogen properties of multi-charged sandwich structures whose geometry simultaneously satisfyies the octet rule and Hückel's 4n+2 rule is reported here via a case study of dianion clusters [M(B2C4X6)2]2- (M = Be, Mg or Ca; X = H, F or Cl). The properties of these dianion clusters [M(B2C4X6)2]2- are close to or even superior to those of traditional clusters based on separate electron-counting rules, i.e., the octet rule and Hückel's 4n+2 rule. At the theoretical level of combined ab initio and DFT methods, these clusters, including halogen-substituents (F, Cl) are super-chalcogens due to their high first vertical electron detachment energy (FVDE), of which the largest value is 1.64 eV. This may be attributed to the strong ability of halogen-substituents (F, Cl) to attract an extra electron, according to an analysis of the distribution of the extra electron, and the spin density and the contribution of HOMO orbitals, leading to a larger spatial extent of the extra electron on both the ring skeleton and halogen ligands, which will lower the electronic kinetic energy according to fundamental quantum mechanics.

Photoelectron Spectroscopy and Computational Study on Microsolvated [B10H10]2- Clusters and Comparisons to Their [B12H12]2- Analogues

Microhydrated closo-boranes have attracted great interest due to their superchaotropic activity related to the well-known Hofmeister effect and important applications in biomedical and battery fields. In this work, we report a combined negative ion photoelectron spectroscopy and quantum chemical investigation on hydrated closo-decaborate clusters [B10H10]2-·nH2O (n = 1-7) with a direct comparison to their analogues [B12H12]2-·nH2O and free water clusters. A single H2O molecule is found to be sufficient to stabilize the intrinsically unstable [B10H10]2- dianion. The first two water molecules strongly interact with the solute forming B-H···H-O dihydrogen bonds while additional water molecules show substantially reduced binding energies. Unlike [B12H12]2-·nH2O possessing a highly structured water network with the attached H2O molecules arranged in a unified pattern by maximizing B-H···H-O dihydrogen bonding, distinct structural arrangements of the water clusters within [B10H10]2-·nH2O are achieved with the water cluster networks from trimer to heptamer resembling free water clusters. Such a distinct difference arises from the variations in size, symmetry, and charge distributions between these two dianions. The present finding again confirms the structural diversity of hydrogen-bonding networks in microhydrated closo-boranes and enriches our understanding of aqueous borate chemistry.

Observation of the Transition from Triple Bonds to Single Bonds between Ru-Ge Bonding in RuGeO(CO)n- (n = 3-5)

This work reports the observation and characterization of heterobinuclear transition-metal main-group metal oxide carbonyl complex anions, RuGeO(CO)n- (n = 3-5), by combining mass-selected photoelectron velocity map imaging spectroscopy and quantum chemistry calculations. The experimentally determined vertical electron detachment energy of RuGeO(CO)3- surpasses those of RuGeO(CO)4- and RuGeO(CO)5-, which is attributed to distinctive bonding features. RuGeO(CO)3- manifests one covalent σ and two Ru-to-Ge dative π bonds, contrasting with the sole covalent σ bond present in RuGeO(CO)4- and RuGeO(CO)5-. Unpaired spin density distribution analysis reveals a 17-electron configuration at the Ru center in RuGeO(CO)3- and an 18-electron configuration in RuGeO(CO)4- and RuGeO(CO)5-. This work closes a gap in the quantitative physicochemical characterization of heteronuclear oxide carbonyl complexes, enhancing our insights into catalytic processes of CO/GeO on the metal surface at the molecular level.

Reactivity of a Hexaaryldiboron(6) Dianion as Boryl Radical Anions

Our study unveils a novel approach to accessing boryl radicals through the spontaneous homolytic cleavage of B-B bonds. We synthesized a hexaaryl-substituted diboron(6) dianion, 1, via the reductive B-B coupling of 9-borafluorene. Intriguingly, compound 1 exhibits the ability to undergo homolytic B-B bond cleavage, leading to the formation of boryl radical anions, as confirmed by EPR studies, in the presence of the 2.2.2-cryptand at room temperature. Moreover, it directly reacts with diphenylacetylene, producing an unprecedented 1,6-diborylated allene species, where the phenyl ring is dearomatized. Density functional theory computational studies suggest that homolytic B-B bond cleavage is favored in the reaction path, and the formation of the boryl radical anion is crucial for dearomatization. Additionally, it achieves the dearomative diborylation of anthracene and the activation of elemental sulfur/selenium under mild conditions. The borylation products have been successfully characterized by NMR spectra, HRMS, and X-ray single-crystal diffraction.

Lewis Acid Decorated Hexacyanodiborane(6) Dianion

First examples of diborane(6) dianions decorated with weakly coordination B(C6F5)3 (BCF) groups and SiEt3 + moieties have been synthesized demonstrating the synthetic potential of the [B2(CN)6]2- dianion. [B2{CNB(C6F5)3}6]2- (1) was isolated as potassium and tetrabutylammonium salt. 1 is a rare example for a weakly coordinating dianion and it was used for the stabilization of the carbocation [Ph3C]+ and the oxonium acid [H(OEt2)2]+. Reaction of [Ph3C]21 with HSiEt3 resulted in the silylated neutral diborane(6) [B2{CNB(C6F5)3}4(CNSiEt3)2] (2) in which two BCF groups have been selectively replaced by SiEt3 + substituents, underscoring the stability and chemical versatility of the [B2(CN)6]2- dianion. The chemical properties and physicochemical data of 1 and 2 provide insight into electronic, coordinating, and steric properties of theses novel diborane(6) compounds.

Dismutation of Tricyanoboryllead Compounds: The Homoleptic Tetrakis(tricyanoboryl)plumbate Tetraanion

A series of unprecedently air-stable (tricyanoboryl)plumbate anions was obtained by the reaction of the boron-centered nucleophile B(CN)3 2- with triorganyllead halides. Salts of the anions [R3 PbB(CN)3 ]- (R=Ph, Et) were isolated and found to be stable in air at room temperature. In the case of Me3 PbHal (Hal=Cl, Br), a mixture of the anions [Me4-n Pb{B(CN)3 }n ]n- (n=1, 2) was obtained. The [Et3 PbB(CN)3 ]- ion undergoes stepwise dismutation in aqueous solution to yield the plumbate anions [Et4-n Pb{B(CN)3 }n ]n- (n=1-4) and PbEt4 as by-product. The reaction rate increases with decreasing pH value of the aqueous solution or by bubbling O2 through the reaction mixture. Adjustment of the conditions allowed the selective formation and isolation of salts of all anions of the series [Et4-n Pb{B(CN)3 }n ]n- (n=2-4) including the homoleptic tetraanion [Pb{B(CN)3 }4 ]4- .