Boron rings enclosing planar hypercoordinate group 14 elements

Sets of boron rings enclosing planar hypercoordinate group 14 elements (AB_n^(n-8)); A = group 14 element; n = 6-10) are designed systematically based on geometrical and electronic fit principles: the size of a boron ring must accommodate the central atom comfortably. The electronic structures of the planar minima with hypercoordinate group 14 elements are doubly aromatic with six π and six in-plane radial MO systems (radial MOs are comprised of boron p orbitals pointing toward the ring center). This is confirmed by induced magnetic field and nucleus-independent chemical shift (NICS) computations. The weakness of the "partial" A-B bonds is compensated by their unusually large number. Although a C_7v pyramidal SiB₈ structure is more stable than the D_8h isomer, Born-Oppenheimer molecular dynamics simulations show the resistance of the D_8h local minimum against deformation and isomerization. Such evidence of the viability of the boron ring minima with group 14 elements encourages experimental realization.