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Please use this identifier to cite or link to this item: http://dspace.library.iitb.ac.in/jspui/handle/10054/3700

Title: Ab initio quantum chemical investigation of intramolecular magnetic interaction in some diradical derivatives of imino nitroxide and nitronyl nitroxide
Authors: ALI, ME
VYAS, S
DATTA, SN
Keywords: density-functional theory
electron-spin-resonance
valence-bond theory
hyperfine coupling-constants
transition-metal dimers
singlet ground-state
low-lying triplet
organic-molecules
m-phenylene
binuclear complexes
Issue Date: 2005
Publisher: AMER CHEMICAL SOC
Citation: JOURNAL OF PHYSICAL CHEMISTRY A, 109(28), 6272-6278
Abstract: The magnetic properties of the monoradicals 2-(4-phenyl acetylene)-4,4,5,5-tetramethyl-4,5-dihydro-IHimidozolyl-oxyl (1) and 2-(4-phenyl acetylene)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl-3-oxide (2) and the diradicals 2,2'-(1,2-ethynediyldi-4,1-phenylene)bis[4,4,5,5-tetramethyl-4,5-dihydro-1H-imidozolyloxyl] (3), 2,2'-(l,2-ethynediyldi-4,1 3,1-phenylene)bis[4,4,5,5-tetramethyl-4,5-dihydro-1H-imidozolyl-oxyl] (4), and 2,2'-(I,2-ethynediyldi-4,I 3,1-phenylene)bis[4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-l-oxyl3-oxide] (5) are investigated by ab initio quantum chemical methods. The rule of spin alternation in the unrestricted Hartree-Fock (UHF) method clearly shows that the radical sites are antiferromagnetically coupled in 3 and ferromagnetically coupled in 4 and 5, which is consistent with a previous experiment. The molecular geometries are optimized at Hartree-Fock levels. This is followed by single-point calculations using the density functional (UB3LYP) treatment and the multiconfigurational complete active space self-consistent field (CASSCF) methodology. Magnetic exchange coupling constants are determined from the broken-symmetry approach. The calculated J values, -3.60 cm(-1) for 3, 0.16 cm(-1) for 4, and 0.67 cm(-1) for 5, are in excellent agreement with the observed values. Because of the very large size of the diradicals 3-5, the CASSCF (10,10) calculations cannot yield realistic J values. Nevertheless, the CASSCF calculations support the antiferromagnetic nature of the magnetic coupling in 3 and the ferromagnetic nature of the coupling in 4 and 5. The existence of an intramolecular magnetic coupling in 3-5 is also confirmed through computations of the isotropic hyperfine coupling constants for monoradicals 1 and 2 as well as diradicals 3-5.
URI: http://dx.doi.org/10.1021/jp050282v
http://dspace.library.iitb.ac.in/xmlui/handle/10054/3700
http://hdl.handle.net/10054/3700
ISSN: 1089-5639
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