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 7 v pyramidal SiB8 structure is more stable than the D 8 h isomer, Born−Oppenheimer molecular dynamics simulations show the resistance of the D 8 h local minimum against deformation and isomerization. Such evidence of the viability of the boron ring minima with group 14 elements encourages experimental realization.