Observation of Boron Bonds in Aromatic Boron Water Complexes B13(H2O)n+ (n = 1,2) and B12H(H2O)+ Analogous to Benzene

Gas-phase B_n⁺ monocations exhibit strong hydrophilicity due to the prototypical electron-deficiency of boron. Joint chemisorption experiment and first-principles theory investigations performed herein indicate that the experimentally known planar magic-number C_2v B₁₃⁺ can react with H₂O at room temperature to form a series of quasi-planar aromatic boron water complexes C₁ B₁₃(H₂O)⁺ (1), C₂ B₁₃(H₂O)₂⁺ (2), and C₁ B₁₂H(H₂O)⁺ (3) analogous to benzene C₆H₆. Extensive theoretical calculations and analyses unveil their chemisorption pathways, bonding patterns, and more importantly, the effective in-phase LP(H₂O:)→LV(B) orbital overlaps between the more electronegative O atom in H₂O as lone-pair (LP) σ-donor and periphery electron-deficient B atoms in B₁₃⁺ (B₃@B₁₀⁺) and B₁₂H⁺ (B₃@B₉H⁺) with lone vacant (LV) orbitals as LP σ-acceptors, evidencing the existence of the newly proposed boron bonds in chemistry. A LP(H₂O:)→LV(B) boron bond in these boron water complexes possesses about 15 ~ 20% of the dissociation energy of a typical O–B covalent bond. Boron bonds are expected to exist in a wide range of boron-based complex systems with typical molecular ligands like H₂O, CO, and NH₃ as effective σ-donors.

Graphical Abstract

Joint chemisorption experiment and first-principles theory investigations indicate that B₁₃⁺ monocation can react with H₂O to form a series of quasi-planar aromatic boron water complexes C₁ B₁₃(H₂O)⁺, C₂ B₁₃(H₂O)₂⁺, and C₁ B₁₂H(H₂O)⁺ analogous to benzene, evidencing the existence of boron bonds in chemistry.