Preparation and Properties of Organic Chalcogen Compounds Bearing Long-chain Bonds Constructed by more than four Chalcogen Atoms

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The structures of 1-[8-(p-YCィイD26ィエD2HィイD24ィエD2Se)CィイD210ィエD2HィイD26ィエD2]SeSe[CィイD210ィエD2HィイD26ィエD2(SeCィイD26ィエD2HィイD24ィエD2Y-p]-8']-1' (1a(Y = H)) and 1-(MeSe)-8-(p-YCィイD26ィエD2HィイD24ィエD2Se)CィイD210ィエD2HィイD26ィエD2 (2a(Y = H), 2b(Y = OMe), and 2d(Y = Cl)) are determined by the X-ray crystallographic analysis. Those of 1a, 2a, 2b, and 2d are double type A-type B pairing, type C-type C pairing, pseudo-type A-type B pairing, and pure type A-type B pairing, respectively. The structure is type A if the Se-C bond being almost perpendicular to the naphthyl plane, type B when the Se-C bond being placed on the plane, or type C for the intermediate between type A and type B. Double type A-type B pairing in 1a is characterized by the four center-six electron bond (4c-6e) and type A-type B pairing in 2b and 2d by 3c-4e. Type C-type C pairing in 2a is analyzed by the distorted nonbonded π-type 2c-4e interaction, which avoid severe exchange repulsion due to the nonbonded π-type 2c-4e interaction.The ィイD177ィエD1Se NMR chemical shifts (δ(Se)) of 1a-1g (Y = H, OMe, Me, Cl. Br, COOEt, NOィイD22ィエD2 for a-g, respectively) are measured, together with those of 2a-2g. While the plot of δ(Se) at 8-positions versus those at 1-positions gives a negative proportionality constant of -0.282 for 1 (inverse correlation), the value is positive for 2 (0.252 : regular correlation). The inverse correlation must be the results of the four center-six electron bond constructed by the four Se atoms aligned linearly in 1. The regular correlation is expected for the 2c-4e with some contribution of the through-bond mechanism via the naphthalene π-system. In order to clarify the mechanism for the correlations, ab initio MO calculations, containing δ(Se) based on the GIAO theory, are performed on the models of 1 and 2. The results exhibit the important role of the 4c-6e for the inverse correlation in 1.