Planar tetra-coordinate Si and Ge in perfectly squared Ni4Cl4X complexes

Density functional theory investigations performed in this work indicate that planar tetra-coordinate silicon and germanium can be stabilized at the centers of the perfectly squared M4Cl4 ligands to form D4h M4Cl4X complexes (M = Ni, Pd, Pt; X = Si, Ge). M4Cl4 ligands prove to be flexible enough to host other planar or quasi-planar tetra-coordinate inorganic atoms including C, B, Al, Ga, N, P, and As. Delocalized δ, π, and σ molecular orbitals are found to play important roles in stabilizing these novel structures. The ionization potentials of the neutrals and first vertical electron detachment energies of the anions have also been calculated to facilitate future experiments. The results obtained in this work complete the series of planar coordinate silicon and germanium with the highest symmetries of D4h, D5h, and D6h in MnNnX series (M = transition metals; N = H, Cl; n = 4, 5, 6).