Theoretical study of the substituent effects of the equatorial ligands on penta-coordinated trigonal bipyramidal compounds.(Natural Sciences)

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We have studied the substituent effect of equatorial ligands of some penta-coordinated trigonal bipyramidal compounds (MX_3Y_2: M=N, P and As; X=H, F, CH_3 and CN; Y=H and F) by using the ab initio molecular orbital method. We divided the whole molecule into two parts i.e. the equatorial part and the apical part, and discussed the stabilization of apical orbitals by drawing the orbital energy correlation diagram. The apical bond stabilization energy is considerably affected through the change of the symmetric apical orbital interaction for fluorine compounds. The substituent effect on HOMO of the equatorial part comes from the antibonding σ-donating interaction between ligand orbital and the lone-pair orbital of the central atom, while LUMO is affected through the σ-type attractive interaction between ligand and ndz^2 orbital of the central atom. The strong substituent effect on LUMO is induced by F through the σ-type interaction. On the other hand π-type effect on HOMO becomes important when CH_3 is introduced to the equatorial part. As the number of CN increases, the antibonding π-type interaction between ligands and the central atom decreases and HOMO of the equatorial part is stabilized. The energy gaps between HOMO and LUMO of nitrogenous compounds are much wider than those of phosphorous and arsenious compounds.
岐阜大学の論文
1998-03-26