Ab initio CASSCF study on doublet and quartet states of 1,3,5-tris(methylene)benzene and 1,3,5-benzenetriamine trication

Ab Initio CASSCF results of 1,3,5-tris(methylene)benzene (TMB) and 1,3,5-benzenetriamine trication (BTA(3+)), which are model molecules of the actively researched triradicals with star-branched topology, are presented. This study included a geometry determination of the four low-lying states ((4)A(1)", (4)A(2), (2)A(2), B-2(1)) of TMB and BTA(3+). The doublet-quarter splitting energies (DeltaE(D-Q)) of TMB and BTA(3+) were calculated to be 12.7 and 3.1 kcal mol(-1), respectively. Furthermore, the doublet-doublet splitting energies of TMB and BTA(3+), which arise from a Jahn-Teller distortion of the doubly degenerate E-2" state, were suitably estimated to be 2.5 and 6.8 kcal mol(-1), respectively, due to obviation of the spin-contamination problem. As a result of configuration mixing, it was found that the doublet states for TMB and BTA(3+) have to be represented at least by two configurations or more. In addition, the doublet states of TMB were regarded as being a doubler triradical, while those of BTA(3+) were close to a doublet monoradical; associated with this result, the lowest doubler states of TMB and BTA(3+) were found to be (2)A(2) and B-2(1), respectively.