Exploring the effect of external dopants on the electride characteristics of bimetallic sandwich complexes based on the B4N4H8 ligand, M2(B4N4H8)2Ca2 (M = Na and K)

Abstract

Bimetallic sandwich complexes based on the borazocine (B₄N₄H₈) ligand have been studied using density functional theory (DFT). The studied Ca–Ca covalent bond length agrees well with the experimental Ca₂ bond length. For the studied complexes, the non-nuclear attractor (NNA) is found at the Ca–Ca bond of K₂(B₄N₄H₈)₂Ca₂ and Na₂(B₄N₄H₈)₂Ca₂. The negative Laplacian at the NNA is noticed for these two complexes, indicating that these complexes are electrides. This study for the first time reports the electride complexes based on the B₄N₄H₈ ligand. Interestingly, upon asymmetric doping with Na and K, no NNA point is found for the complex NaK(B₄N₄H₈)₂Ca₂, indicating that this complex is not an electride. Our study points out one of the fascinating outcomes that asymmetric doping can affect the occurrence of the NNA in a system. The complex Na₂(B₄N₄H₈)₂Ca₂ exhibits the highest second hyperpolarizability value of 2.2 × 10⁶ au at the ωB97XD/6-311++G(3df,3pd) level among the studied sandwich complexes.