Metalloborospherenes with the stabilized classical fullerene-like borospherene B36 as electric field manipulated second-order nonlinear optical switches

Abstract

For a new challenge of stabilizing a classical fullerene-like borospherene composed of five- and six-membered rings, we take the lead to theoretically present a novel exohedral metalloborospherene Mg₁₂Li₈&B₃₆ molecule (D_6h). It features 12 η⁵(pentahapto)-Mg atoms and 8 η⁶-Li atoms capping 12 pentagonal faces and 8 hexagonal faces of classical fullerene-like borospherene D_6h B₃₆, respectively. Due to the pull-push electron transfer relay, the molecule is converted to an electride molecule (Mg²⁺)₁₂(Li⁺)₈&B₃₆³⁰⁻ + 2e⁻ with two excess electrons and an extraordinary high-valent B₃₆³⁰⁻ polyanion with a full-shell electronic configuration, performing the stabilization of the classical fullerene-like B₃₆ cage. As further findings emerge from this study, both the (Mg₁₂Li₈&B₃₆)²⁺ cation (D_6h) and the Mg₁₂Li₆&B₃₆ salt (D_6h) have higher stability than electride Mg₁₂Li₈&B₃₆. Furthermore, embedding a metal atom pair in the boron cage of Mg₁₂Li₈&B₃₆ leads to new endohedral electride molecules (Mg²⁺)₁₂(Li⁺)₈&(Mⁿ⁺₂@B₃₆³⁰⁻) + (2 + 2n) e⁻ (M = Li, n = 1 and Be, n = 2). The embedded metal atom pair plays a prominent role in adding excess electrons. Notably, the Mg₁₂Li₈&B₃₆ electride molecule can serve as both electron donor and electron acceptor and consequently acts as an electron reservoir. Encouragingly, Mg₁₂Li₈&B₃₆ and its endohedral derivatives can be used as efficient external electric field manipulated second-order nonlinear optical (NLO) switches with high sensitivity and reversibility. In this sense, embedding a metal atom pair in the B₃₆ cage provides a new strategy to manipulate NLO switching.