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

Transition-metal-doped boron clusters have received considerable attention in recent years. The experimentally observed planar or quasi-planar C-2h B-10(I), C-2v B-11(-)(II), C-3v B-12(III), and C-2v B-13(+) (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,(1)A(1)), C-s NiB11-(2, (1)A), C-3v NiB12(3, (1)A(1)), and C-s NiB13+ (4, (1)A) 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/+ ligands (n=10-13) and follow the universal coordination bonding pattern of sigma plus double delocalization. Molecular dynamics simulations show that, among these complex clusters, NiB11-(2) behaves like a Wankel motor at room temperature with the B-3 inner wheel rotating almost freely inside the quasi-rotating B-8 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.