Relationship betweeen X- or L-Band ESR Spectra and Coordination Structures of Copper(II) Complexes with a CuO_4 Coordination Mode

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ESR spectrometry is useful for studyin the coordination environment around lone pair electrons of paramagnetic metal ions, such as the copper(II) (Cu(II)) ion. To this purpose, X-band ESR spectrometry has generally been used. In the present study, along with the x-band ESR, we applied L-band ESR spectrometry first, which allows for the ESR measurements of Cu(II) complexes under lower dielectric loss by water molecules than that of X-band ESR. x- and L-band ESR parameters analyzed for Cu(II) complexes with CuN_4 coordination mode were found to relate to the coordination structures of the Cu(II) complexes and to other physical parameters, such as stability constants and halfwave potentials of the complexes. Several important features were observed in both the X- and L-band ESR spectra of the Cu(II) complexes as follows : Coordination to the axial positions or tetrahedral distortion of the square-planar Cu(II) complexes decreased in the hyperfine coupling constant, A-value. The g-value decreased when the stability constants increase or when the halfwave potentials shift to become more negative. Both x- and L-band ESR spectrometries are proposed to be very useful for analyzing the coordination structures of Cu(II) complexes in aqueous solutions.
公益社団法人日本薬学会の論文
1996-11-15