| Abstract
| - To investigate the nature of weak nonbonded selenium···halogen interactions (Se···X interactions;X = F, Cl, and Br), three types of model compounds [2-(CH2X)C6H4SeY (1−3), 3-(CH2X)-2-C10H6SeY (4−6), and 2-XC6H4CH2SeY (7−9); Y = CN, Cl, Br, SeAr, and Me] were synthesized, and their77Se NMR spectroscopic behaviors were analyzed in CDCl3. The gradual upfield shifts of 77Se NMRabsorptions observed for series 1−3 and 4−6 suggested that the strength of Se···X interactiondecreases in the order of Se···F > Se···Cl > Se···Br. The quantum chemical calculations at theB3LYP/631H level using the polarizable continuum model (PCM) revealed that the most stableconformer for 1−3 is the one with an intramolecular short Se···X atomic contact in CHCl3 (ε = 4.9)and also that the nX → σ*Se-Y orbital interaction (ESe···X) can reasonably explain the order of strengthfor the Se···X interactions. On the other hand, the 77Se NMR absorptions observed for series 7−9did not shift significantly from the reference compounds (C6H5CH2SeY), indicating the absence ofthe Se···X interaction for 7−9 presumably due to attenuation of basicity for the halogen atom thatis substituted directly to the aromatic ring. These observations suggested that the nX → σ*Se-Yorbital interaction is a dominant factor for formation of weak Se···X interactions. Electron correlationwas also suggested to be important for the stability.
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