The infrared spectra have been studied for cis-and trans-isomers of complexes of the type [Co(en),-(halac),]C104, where en = ethylenediamine and halac = CH3CO2-, CH2ClC0,-, CHCIZCO,-, CCl,CO,-, CHBr,C02-, and CF3C0,-. Characteristic differences between the spectra of cis-and :mlrs-isomers have been examined and correlated mith data for similar complexes. The most consistent variations are in the 500-610 cm-I region where Co-N stretching modes occur.

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symmetry to allow proposing of the scheme of Figure 10 is consistent with crystal structure results24 (which indicate that the deviation from Td in Ni [(C6H5)3P]C12, which is isomorphous to Co [(C6H5)3P]2C12, is very pronounced) and with the absence of an observed strong charge-transfer band just to the blue side of about 17,000 cm"1. This reconciliation as well as the good correspondence of our formulation with experiment as seen from Tables IV, VI, and VII lend credibility to the underlying model.Inspection of Figures 1 and 2 of ref 14 and comparison with our Tables IV, VI, and VII indicate that the present model provides an improvement over previous work. Gaussian fitting of poorly resolved spectra adds to the utility of the model. Where distortion in terms of bond angles and lengths from tetrahedral symmetry is pronounced, a choice between the constant charge-variable ligand distance ap-proach14 and our variable charge-tetrahedral geometry method might be necessary since the former model may be more physically meaningful. Crystallographic studies, whenever available, should aid this choice. To some extent, geometric distortions are also taken into account by the empirical nature of the parameter Ds in the present model. The structure of Co(apy)2Cl2 can be inferred from the data for the iso structural25 compound Zn(apy)2Cl2. The crystallographic results show that neither model has much correspondence to (25) .

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Complexes of the type [Co(en)2ha]Cl, where ha is the diacid anion of lactic or pantoic (2,4-dihydroxy-3,3-dimethylbutyric ) acid, were prepared by the reaction of optically active lactic acid with rac-[Co(en)2C03] + and optically active pantoyl lactone with trans-[Co(en)2Cl2]C104. Several optical isomers have been isolated from the reaction products by thin layer chromatography. These complexes have been characterized by nmr, electronic absorption, ORD, and CD spectra and their relative absolute configurations have been assigned. Data suggest that the hydroxy acid anions coordinate in a preferred conformation and configurational and vicinal contributions to the optical activity of these complexes are discussed.