(Received: January 12, 2006; Accepted for publication: March 24, 2006; Published on Web: July 18, 2006)
High-spin stability of non-Kekule-type molecule triiminiummethane ion (TIM3+) is discussed using the semiempirical molecular orbital method. The triplet ground state 3A2' with a D3h 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 C2v 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.
Keywords: Non-Kekule-type molecules, Molecular orbital method, High-spin organic molecules, Spin density, Triiminiummethane ion
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