Theoretical investigation of perfect fullerene-like borospherene Ih-B20 protected by alkaline earth metal: multi-layered spherical electride molecules as electric field manipulated second-order nonlinear optical switches

Abstract

For the challenge of stabilizing a fullerene-like borospherene, a perfect fullerene-like borospherene B₂₀ with I_h symmetry is stabilized theoretically for the first time by selected 12 η⁵ (pentahapto)-Mg atoms capped on the 12 B₅ pentagons, forming an exohedral metalloborospherene I_h Mg₁₂&B₂₀ molecule. Owing to the pull–push electron transfer relay, the molecule is converted to a spherical electride molecule (Mg²⁺)₁₂&B₂₀¹⁸⁻ + 6e⁻ with multiexcess electrons and high-valent B₂₀¹⁸⁻ polyanion with a full-shell electronic configuration, performing the stabilization of the fullerene-like B₂₀ cage. Furthermore, we embed the metal M atom in the B₂₀ cage, forming new endohedral electride molecules (Mg²⁺)₁₂&(Mⁿ⁺@B₂₀¹⁸⁻) + (6 + n)e⁻ (M = Li, n = 1 and Mg, n = 2). The embedded atom M increases the excess electron number. Notably, these electride molecules possess two different types of superatomic characteristics, exhibiting the behavior of an electron reservoir. Moreover, a compound (Mg₁₂&B₂₀)₂O is designed and obtained, so Mg₁₂&B₂₀ might serve as a nano-building block. In addition, the Mg₁₂&B₂₀ and Mg₁₂&(Mg@B₂₀) electride molecules are efficient external electric field-manipulated nonlinear optical (NLO) switches with high sensitivity and reversibility. The embedding metal atom in the B₂₀ cage can also serve as a new strategy to manipulate NLO switching.