SiCNN - A new stable isomer with Si≡C triple bonding

To predict potentially stable molecules with Si≡C triple bonding, theoretical calculations at the B3LYP/ 6-311G(d) and CCSD(T)/6-311G(2df) (single-point) levels were employed to study the structures, energetics, and isomerization of various SiCN₂ isomers. A schematic potential energy surface (PES) of SiCN₂ was established to discuss the kinetic stability of the isomers. A new isomer SiCNN was found to possess a typical Si≡C triple bond, as confirmed by comparative calculations at the B3LYP, QCISD, QCISD(T), CCSD, and CCSD(T) levels on the bond lengths of SiCNN and other experimentally or theoretically known species of RSiCH (R = H, F, Cl, OH). Moreover, SiCNN resides in a very deep potential; the stabilization barrier is at least 53.2 kcalmol^-1. Thus, SiCNN may be considered as the most kinetically stable isomer with Si≡C triple bonding known to date, and it may represent a very promising molecule for future experimental characterization. In addition, the stability of the other isomers, such as the four linear species SiNCN, SiNNC, NSiCN and NSiNC, a three-membered NNC ring isomer with exocyclic C-Si bonding, and a four-membered SiCNN ring isomer is discussed and compared with SiCNN.