B12Fn0/− (n = 1–6) series: when do boron double chain nanoribbons become global minima?

Abstract

We present an extensive density-functional and wave function theory study of partially fluorinated B₁₂F_n^0/− (n = 1–6) series, which show that the global minima of B₁₂F_n^0/− (n = 2–6) are characterized to encompass a central boron double chain (BDC) nanoribbon and form stable BF₂ groups at the corresponding BDC corner when n ≥ 3, but the B₁₂F^0/− system maintains the structural feature of the well-known quasi-planar C_3v B₁₂. When we put the spotlight on B₁₂F₆^0/− species, our single-point CCSD(T) results unveil that albeit with the 3D icosahedral isomers not being their global minima, C₂ B₁₂F₆ (6.1, ¹A) and C₁ B₁₂F₆⁻ (12.1, ²A) as typical low-lying isomers are 0.60 and 1.95 eV more stable than their 2D planar counterparts D_3h B₁₂F₆ (6.7, ¹A′) and C_2v B₁₂F₆⁻ (12.7, ²A₂), respectively, alike to B₁₂H₆^0/− species in our previous work. Detailed bonding analyses suggest that B₁₂F_n^0/− (n = 2–5) possess ribbon aromaticity with σ plus π double conjugation along the BDC nanoribbon on account of their total number of σ and π delocalized electrons conforming the common electron configuration (π²⁽ⁿ⁺¹⁾σ²ⁿ). Furthermore, the simulated PES spectra of the global minima of B₁₂F_n⁻ (n = 1–6) monoanions may facilitate their experimental characterization in the foreseeable future. Our work provides new examples for ribbon aromaticity and powerful support for the F/H/Au/BO analogy.