Investigation Of Spin-Flip Reactions Of Transition Metals And Acetonitrile By Relativistic Density Functional Theory

Recently, experimental chemists have found that transition-metal atoms M and their cations M+ have peculiar activations to the C-H, C-C and C-O bonds of small organic compounds in the gas phase. Theoretical approaches to these reactions also indicated that often the reactants and products had ground states of different spin multiplicities, and the transformations of spin multiplicities occurs frequently in thermal reactions. Usually, more than one state is involved in reaction process, which ensures the whole reaction always proceeds on the low-energy potential energy surface(PES).Such a phenomenon is called"Two-state reactivity"(TSR) or"Multi-state reactivity"(MSR).Based on recent research on reactions between M (M=V, Nb, Ta, Zr) and acetonitrile, we explore the details of the reaction mechanisms in possible different spin-state potential energy surfaces, also predict mechanism of Ti and Hf with acetonitrile. Density functional theory (DFT) with the relativistic zero-order regular approximation at the PW91/TZ2P level has been applied. The complicated minimum energy reaction path involves four transition states (TS), stationary states (1) to (5) and also, several spin inversion may occur (indicated by (?)): M + NCCH₃→Mη¹-NCCH₃ (1)→TS_1/2→Mη²-(NC)CH₃ (2)→TS_2/3→MHη³-(NCCH₂) (3)→TS_3/4→CNMCH₃ (4) (?) TS_4/5→CN(MH)CH₂ (15). The minimum energy crossing point was determined with the help of the DFT fractional-occupation-number approach. The spin inversions accelerate the reaction. All intermediate and product species were frequency and NBO analyzed. The species can be rationalized with the help of Lewis type formulas.