Department of Inorganic Chemistry, Madurai Kamaraj University, Madurai-825 021 Manuscript received 17 August 1981, accepted 28 September 1982 Cu(II), Ni(II) and Co(H) \(bis\)-shelates of the type ML2, where L=2'-hydroxy-4-­chalcone(X=CH3, CH3O, Cl, Br), have been prepared and investigated. All of them are monomeric, low-spin and square-planar. The plot of \(v\)(C=O) and \(v\)(PhC=C) of the ligands against the Hammett a-constants is a straight line. On the other band, plots of \(v\)(C=O),

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... hC=C) and w(M-O) of the complexes of a metal against the σ-parameters yield two straight lines ; the points for the electron-releasing substituents and the unsubstituted complex lie on one straight line and those for the electron-with­drawing substituents and the unsubstituted complex on the other. This indicates the presence of both σ- and π interaction between metal and ligand. The electron-releasing, substituents favour σ-interaction while the electron-withdrawing substituents π-inter­action and the unsubstituted complexes are more stable than the substituted ones. The stability of the complexes, on the basis of \(v\)(M - O), follows the order H > CH3> CH3O > Br > CI ; the M - L σ-bond being more important than the M - L π bond. For a given substituent, the order of stability of the complexes is Cu > Ni < Co as expected from crystal field.theory.