A quest for triplet silylenes XHSi3 at ab initio and DFT levels (X = H, F, Cl and Br)

Four ground state triplet silylenes are found among 30 possible silylenic XHSi3 structures (X = H, F, Cl and Br), at seven ab initio and DFT levels including: B3LYP/6-311++G∗∗, HF/6-311++G∗∗, MP3/6-311G∗, MP2/6-311+G∗∗, MP4(SDTQ)/6-311++G∗∗, QCISD(T)/6-311++G∗∗ and CCSD(T)/6-311++G∗∗. The latter six methods indicate that the triplet states of 3-flouro-1,2,3-trisilapropadienylidene, 1-chloro-1,2,3-trisilapropargylene and 3-chloro-1,2,3-trisilapropargylene are energy minima. These triplets appear more stable than their corresponding singlet states which cannot even exist for showing negative force constants. Also, triplet state of 1-flouro-1,2,3-trisilapropargylene is possibly accessible for being an energy minimum, since its corresponding singlet state is not a real isomer. Some discrepancies are observed between energetic and/or structural results of DFT vs. ab initio data.