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Pope, Quicksall, et al. and 1.03 µ 1 which, for intensity and energy, correspond to d-d transitions of distorted tetrahedral copper(II) complexes. Also the ESR data, with the high g3 value of the hyperfine coupling constant, conform to this view, since it has been suggested that these are the features which characterize tetrahedral copper(II) complexes.28The band at 1.46 µ -1 in the electronic spectra is very intense and can be assigned to a charge transfer transition, presumably involving the metals and the system of the MeNN and chloride ligands.29 A low-energy transition was observed also in the mixed valence complexes [NÍ2X2(NN)4]+ and it was found to possess polarization properties compatible with Ni-NN charge transfer nature.2 Since no such band is observed in the corresponding monomeric nickel(II) and copper(II) complexes the lowering of the energy of the absorption can be ascribed to the reduced charge on the metal in the mixed valence compound and to the formation of the dimer.26An alternative interpretation of the spectra may be that the equivalence of the two copper atoms is not retained in the instantaneous vision provided by the electronic specta, a fact similar to that commonly observed in Jahn-Teller distorted copper(II) ions.30 In this case the 1.46 kcm-1 band might be due to an intervalence transition, making the complex, as regards the electronic spectra, a class II mixed valence compound.29 It is worth noting however that the polarization properties of the mixed valence nickel compound do not confirm this assignment.Acknowledgment. Thanks are due to Mr. G. Scapacci for technical assistance.Registry No. [Cu2Cl3(MeNN)2], 60325-89-5. Supplementary Material Available: A listing of structure factor amplitudes (5 pages). Ordering information can be found on any current masthead page.

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