Title: Electronic structure 1,3,5-triaminobenxene trication and related triradicals: Doublet versus quartet ground state
Authors: Nguyen, HMT ×
Dutta, A
Morokuma, K
Nguyen, Minh Tho #
Issue Date: Apr-2005
Series Title: Journal of Chemical Physics vol:122 issue:15
Conference: date:Univ Louvain, Dept Chem, B-3001 Louvain, Belgium; Emory Univ, Cherry L Emerson Ctr Sci Computat, Atlanta, GA 30322 USA; Emory Univ, Dept Chem, Atlanta, GA 30322 USA
Article number: 154308
Abstract: Quantum chemical calculations have been carried out to determine the electronic ground state of the parent 1,3,5-triaminobenzene trication triradical (TAB(3+), C6H9N33+) containing a six-membered 3 benzene ring coupled with three exocyclic amino NH2+ groups, each containing an unpaired electron, as the simplest model for high-spin polyarylamine polycations. Related triradicals, including the 1,3,5-trimethylenebenzene (TMB, C9H9) and its nitrogen derivatives such as the monocation C8H9N+, the dication C7H9N22+, and the neutral C8H8N, C7H7N2, and C6H6N3 systems containing NH groups, have also been considered. Results obtained using the CASSCF [multiconfigurational complete active space (SCF-self-consistent field)] method, with active spaces ranging from (9e/9o) to (15e/12o), followed by second-order perturbation theory [CASPT2 and MS-CASPT2 (MS-multistate)] with polarized 6-311G(d,p) and natural orbital (ANO-L) basis sets reveal the following: (i) both TAB(3+) and TMB (D-3h) have a quartet (4)A''(1), ground state with doublet-quartet B-2(1)-(4)A''(1) energy gaps of 8.0+/-2.0 and 12.4+/-2.0 kcal/mol, respectively; (ii) in the neutral N series, the quartet state remains the electronic ground state, irrespective of the number of N atoms, but each with slightly reduced gap, 11 kcal/mol for C8H8N ((4)A''), 10 kcal/mol for C7H7N2 ((4)A(2)), and 9 kcal/mol for C6H6N3 ((4)A(2)); and (iii) the ground state of monoamino cation and diamino dication is a low-spin doublet state (B-2(1) for C8H9N+ and (2)A(2) for C7H9N22+) and lying 2 well below the corresponding quartet state by 10 and 12 kcal/mol, respectively. In the monocationic and dicationic amino systems, a slight preference is found for the low-spin state, apparently violating Hund's rule. This effect is due to the splitting of the orbital energies and the presence of the positive charge whose delocalization strongly modifies the electronic distribution and some structural features. In the latter cations, the positive charge basically pushes impaired electrons onto the ring forming a kind of distonic radical cations and thus gives a preference for a low-spin state. 2005 American Institute of Physics.
ISSN: 0021-9606
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Quantum Chemistry and Physical Chemistry Section
× corresponding author
# (joint) last author

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