NiB₁₀, NiB₁₁⁻, NiB₁₂, and NiB₁₃⁺: Half-Sandwich Complexes with the Universal Coordination Bonding Pattern of σ Plus π Double Delocalization

Abstract

Transition-metal-doped boron clusters have received considerable attention in recent years. The experimentally observed planar or quasi-planar C_2h B₁₀(I), C_2v B₁₁⁻(II), C_3v B₁₂(III), and C_2v B₁₃⁺ (IV) are known to be boron analogs of benzene. Extensive global minimum searches and first-principles theory investigations performed herein indicate that doping these aromatic boron clusters with a nickel atom generates the closed-shell half-sandwich complexes C_2v NiB₁₀(1,¹A₁), C_s NiB₁₁⁻(2, ¹A^′), C_3v NiB₁₂(3, ¹A₁), and C_s NiB₁₃⁺ (4, ¹A^′) which are all well-defined global minima of the systems with the coordination numbers of CN = 10, 11, 12, and 13, respectively. Detailed bonding analyses indicate that these Ni-doped boron complexes are effectively stabilized by coordination interactions between the Ni center and aromatic B ^−/0/+_n ligands (n = 10–13) and follow the universal coordination bonding pattern of σ plus π double delocalization. Molecular dynamics simulations show that, among these complex clusters, NiB₁₁⁻(2) behaves like a Wankel motor at room temperature with the B₃ inner wheel rotating almost freely inside the quasi-rotating B₈ outer bearing in a concerted mechanism, revealing typical bonding fluctuations/fluxionalities in a molecular motor due to thermal vibrations. The IR, Raman and electronic spectra of the concerned species are computationally simulated to facilitate their experimental characterizations.