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Torsional Angular Dependence of 1 J (Se,Se) and Fermi Contact Control of 4 J (Se,Se): Analysis of n J (Se,Se) ( n =1–4) Based on Molecular Orbital Theory
Author(s) -
Nakanishi Waro,
Hayashi Satoko
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200701532
Subject(s) - homo/lumo , fermi contact interaction , crystallography , fermi level , atomic physics , physics , bond length , paramagnetism , chemistry , condensed matter physics , molecule , quantum mechanics , crystal structure , electron
Abstract n J (Se,Se) ( n =1–4) nuclear couplings between Se atoms were analyzed by using molecular orbital (MO) theory as the first step to investigating the nature of bonded and nonbonded n J (Se,Se) interactions between Se atoms. The values were calculated by employing Slater‐type triple ξ basis sets at the DFT level, which were applied to structures optimized with the Gaussian 03 program. The contribution from each occupied MO (ψ i ) and ψ i →ψ a (ψ a =unoccupied MO) transition was evaluated separately. 1 J (Se,Se) was calculated for the MeSeSeMe model compound, which showed a typical dependence on the torsion angle ( ϕ (C Me SeSeC Me )). This dependence explains the small values (≤64 Hz) of 1 J obsd (Se,Se) observed for RSeSeR′ and large values (330–380 Hz) of 1 J obsd (Se,Se) observed for 4‐substituted naphtho[1,8‐ c,d ]‐1,2‐diselenoles, which correspond to synperiplanar diselenides. The HOMO→LUMO and HOMO−1→LUMO transitions contribute the most to 1 J (Se,Se) at ϕ =0 and 180° to give large values of 1 J (Se,Se), whereas various transitions contribute and cancel each other out at ϕ =90° to give small values of 1 J (Se,Se). Large 4 J obsd (Se,Se) values were also observed in the nonbonded Se⋅⋅⋅Se, Se⋅⋅⋅SeO, and OSe⋅⋅⋅SeO interactions at naphthalene 1,8‐positions. The Fermi contact (FC) term contributes significantly to 4 J (Se,Se), whereas the paramagnetic spin‐orbit (PSO) term contributes significantly to 1 J (Se,Se). 2 J (Se,Se) and 3 J (Se,Se) were analyzed in a similar manner and a torsional angular dependence was confirmed for 3 J (Se,Se). Depending on the structure, the main contribution to n J (Se,Se) ( n =2, 3) is from the FC term, with a lesser contribution from the PSO term. Analysis of each transition enabled us to identify and clearly visualize the origin and mechanism of the couplings.