Theoretical prediction of complexes with a sulfur-carbon triple bond: SCX(2+), SCXF(+), and SCXF2 (X = Be, Mg, Ca).

A new series of compounds with a sulfur-carbon triple bond-SCX(2+), SCXF(+), and SCXF2 (X = Be, Mg, Ca)-were investigated using quantum chemical computations. The B3LYP, M06-2X, MP2, CCSD, and G4 methods were employed to predict the structures, harmonic vibrational frequencies, Wiberg bond indices, and adiabatic bond dissociation energies (ABDEs) for these compounds. When calculated at the B3LYP/cc-pVTZ level, the S≡C bonds were found to be rather short: 1.4855-1.4984, 1.4893-1.5078, and 1.5123-1.5184 Å for the doubly charged cations, singly charged cations, and neutral molecules, respectively. Interestingly, they are much shorter than in the strong sulfur-carbon triple bond in carbon monosulfide (1.5371 Å). Moreover, NBO analysis together with the results for the structures and Wiberg bond indices indicated that the S≡C bonds in SCX(2+), SCXF(+), and SCXF2 (X = Be, Mg, Ca) should be strong triple bonds. Further, the ABDE values of S≡C in SCX(2+) (209.8-250.6 kcal/mol) and SCXF(+) (174.6-217.6 kcal/mol), but not SCXF2 (150.5-174.4 kcal/mol), are larger than that of S≡C in carbon monosulfide (170.7 kcal/mol); however, upon comparing them with previously published data on other compounds with sulfur-carbon triple bonds, the S≡C bonds in SCXF2 molecules appear to be much stronger than those S≡C triple bonds. In general, all of the results calculated in this work clearly indicate that the SCX(2+), SCXF(+), and SCXF2 (X = Be, Mg, Ca) species each contain a strong sulfur-carbon triple bond.