High-Spin Stability of Triiminiummethane Ion -A Comparative Study with Trimethylenemethane-

Abstract

High-spin stability of non-Kekulé-type molecule triiminiummethane ion (TIM³⁺) is discussed using the semiempirical molecular orbital method. The triplet ground state ³A₂' with a D_3h geometry is predicted to lie below the Jahn-Teller distorted singlet states similar to trimethylenemethane (TMM). The lowest singlet states ¹B₁, ¹B₂ and ¹A₁ with C_2v geometries are nearly degenerate. The spin-density distribution of the ³A₂' state is calculated and the origin of the spin alignment is discussed relating to the spin-polarization rule characteristic of high-spin organic molecules. The valence bond analysis on the spin states of TIM³⁺ is also carried out.