Planar Tetra-, Penta-, Hexa-, Hepta-, and Octacoordinate Silicons:  A Universal Structural Pattern

Abstract

A universal structural pattern has been presented at density function theory level to incorporate planar tetra-, penta-, hexa-, hepta-, and octacoordinate silicons in C2v B(n)E2Si series (E = CH, BH, or Si; n = 2-5) and D8h B8Si. The equivalence in valence electron counts and one-to-one correspondence of the delocalized pi and sigma valence orbitals with small boron clusters strongly support the optimized structures containing planar coordinate silicons. Planar B(n)E2Si series are predicted to be aromatic in nature, and the vertical detachment energies of their anions are presented to facilitate future photoelectron experiments. This structural pattern can be applied to form other planar coordinate nonmetals including Ge, P, As, Al, and Ga and needs to be confirmed in experiments to open a new branch of chemistry on planar coordinate main group elements.

Boron rings containing planar octa-and enneacoordinate cobalt, iron and nickel metal elements

“…Some species with other planar hyper-coordinate main group atoms, such as planar hyper-coordinate silicon [46,47] , have also been reported [30,35,[45][46][47][48][49][50] . Even boron rings with higher planar octa-, planar ennea-, and planar deca-coordinate atoms, such as Si, Ge, Sn, and Pb, have also been investigated computationally [27] .…”

Planar or quasi-planar octa- and ennea-coordinate aluminum and gallium in boron rings

“…We recently investigated the possibility of the sandwich-typed [η 6 -B 6 X] 2 M (X=C, N; M=Mn, Fe, Co, Ni) [7] and bowl-and tire-shaped B n M [8] at density functional theory (DFT) level. We also presented a universal structural pattern for planar hyper-coordinate Si in B n H 2 Si series [9] . Very recently, Luo proposed planar octa-and ennea-coordinate transition metals in M@B n (M=Fe, Co; n=8, 9) at DFT [10] .…”

“…We also presented a universal structural pattern for planar hyper-coordinate Si in B n H 2 Si series [9] . Very recently, Luo proposed planar octa-and ennea-coordinate transition metals in M@B n (M=Fe, Co; n=8, 9) at DFT [10] . Bigger boron rings were even employed to host multiple planar coordinate carbons [11] .…”

M@B9 and M@B10 molecular wheels containing planar nona- and deca-coordinate heavy group 11, 12, and 13 metals (M=Ag, Au, Cd, Hg, In, Tl)

“…Our group also proposed a universal structural pattern for planar hyper-coordinate Si in B n H 2 Si which contained fan-shaped B n frames as ligands [10] , and predicted the possibility of planar octa-and nona-coordinate group 13 elements centered in D nh M@B 8 − and M@B 9 wheels (M=Al, Ga) at DFT and ab initio levels [11] . However, to the best of our knowledge, there have been no investigations on planar nona-or decacoordinate heavy group 11, 12 and 13 metals reported to date.…”

“…It is well known that to host a planar hyper-coordinate metal atom (M) at the center of a B n ring stably, the less electronegative central atom M and surrounding ring B n must match both geometrically and electronically. The M@B n complexes thus formed usually possess the delocalized π molecular orbitals (MOs) lying higher in energy than their more effectively overlapped in-plane radial σ counterparts [10,[12][13][14][15] . The results obtained in this work indicate that planar wheel-shaped M@B 9 2− , M@B 9 , M@B 1 − 0 (M=Ag, Au), M@B 10 (M=Cd, Hg), and M@B 1 + 0 (M=In, Tl) clusters well follow these principles and all turn out to be true minima on the potential energy surfaces of the systems.…”