Comparative analysis of the multicenter, long bond in [TCNE].- and phenalenyl radical dimers: A unified description of multicenter, long bonds

Journal of the American Chemical Society

Volumn 131, Issue 22, 2009, Pages 7699-7707

  Mota, Fernando ^a   Miller, Joel S ^b   Novoa, Juan J ^a  

^a UNIVERSITY OF BARCELONA   (Spain)

^b UNIVERSITY OF UTAH   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ANION RADICALS; ATOMIC CENTERS; BOND ENERGIES; COMPARATIVE ANALYSIS; ELECTROSTATIC COMPONENTS; INTERACTION ENERGIES; NUMBER OF ELECTRONS; PHENALENYL; RADICAL DIMERS; UNIFIED DESCRIPTION; VAN DER WAALS BONDS;

DIMERS; ELECTROSTATICS; VAN DER WAALS FORCES;

DISPERSIONS;

DIMER; RADICAL;

ARTICLE; CHEMICAL ANALYSIS; CHEMICAL BOND; CHEMICAL INTERACTION; COMPARATIVE STUDY; CONTROLLED STUDY; COVALENT BOND; DISPERSION; ELECTRICITY; ELECTRON; ENERGY;

EID: 67650555658     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja9002298     Document Type: Article

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27. In CASSCF(2,2) calculations, a pure closed-shell singlet would present an occupation of the two active orbitals of 2.0 and 0.0, while a pure open-shell singlet would have an occupation of 1.0 and 1.0. An occupation of 1.63 and 0.37 indicates that the ground state singlet is mostly closed-shell in nature, but has a non-negligible contribution of the open-shell singlet.
28. 1 singlet configurations, whose description requires at least a CASSCF(2,2) wavefunction.
29. 2- involves three electrons sitting on the two C=C atoms of each fragment. The bond is formed between the unpaired electrons, and there are two equivalent resonant forms: one where the two bonded atoms are the left ones, and one where the two bonded atoms are the right ones (in both forms, the other atoms hold two electrons each).
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35. This description is based on a molecular orbital formalism. It is also possible an equivalent valence bond description of the long bond in phenalenyl dimers, where the most evident resonant form is that where the unpaired electron is placed in the central C atom in both fragments. The two unpaired electrons from each fragment form then a C-C bond. There are more resonant forms, which delocalize the unpaired electron over all peripheral C atoms (see refs 2 and 3).
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37. Note that the computed interaction energy of a phenalenyl dimer and the experimental DH in solution necessarily differ, due to the phenalenyl-solvent interactions in solution and to the reorganization energy of the solvent when the pairs are formed.
38. 2 dimers at the minimum of their interaction energy curves are-0.16,-1.0 and-1.8 kcal/mol, being the associated equilibrium distances 3.842, 3.058 and 3.800 Å, respectively (see ref 10).
39. As justified in ref 16, an occupation of 1.72 and 0.28 in CASSCF(2,2) calculations indicates that the ground state singlet is mostly closed-shell in nature, but with a non-negligible contribution of the open-shell singlet.
40. 1 singlet configurations, whose description requires at least a CASSCF(2,2) wavefunction.
41. 2(N2) dimer was that indicated above.