A method of calculation of bond parameters is proposed for magnetic molecular orbitals which describe the 3d9 configuration in the case of complexes with a rhombic surrounding (D2h symmetry), when the experimental spin Hamiltonian is known. This treatment contains as a particular case that of Kivelson et al. for square planar structures and allows us to evaluate both the anisotropic presence of unpaired spin at the various ligands, and the mixing of the d3z2−r2 orbital in the ground state which is essentially dx2−y2. Applications of this treatment in calculating the bond parameters in the CuCl2·2H2O and CuF2·2H2O compounds allow a comparison between the covalent characters of the Cu–Cl and Cu–F bonds in a similar surrounding. The results show that there is a relevant spin density at the halide ions in both compounds and that, in CuCl2·2H2O, the anisotropy of covalence in the principal plane of coordination is strong. The reliability of the proposed criteria is considered by a comparison between the covalence values obtained following our method and those obtained directly from the extrahyperfine structure in the case of a square planar copper complex.

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Some chlorosubstituted cupric acetates are studied by E P R (X-band) in order t o examine the effect of different environments on the exchange interactions between the cupric ions. I n hydrated and anhydrous tri-and dichlorosubstituted cupric acetates only isolated ions are present, while hydrated cupric acetate and monochloroacetate show only exchange-coupled ion pairs. However, in anhydrous cupric acetate and monochloroacetate both these situations are found to occur. Some possible interpretations of these results are given.Nous avons etudie par la r.p.e. (bande X) quelques acetates de cuivre chlorosub stitues pour examiner l'influence du different entourage sur les interactions d'echange entre les ions cuivriques. Dans les acetates de cuivre tri-et dichlorosubstitues, hydrates et anhydres, on trouve seulement des ions isolks, et dans l'acetate e t le monochloroacetate hydrates seulement des paires d'ions couples par Bchange. Dans l'acetate et le monochloroacetate anhydres nous avons observe tous les deux situations et nous donnons des possibles interprktations.

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