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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) .

Absorption and magnetic circular dichroism (mcd) spectra of toluene solutions of zinc octamethyltetrabenzporphyrin, Zn(OMBP), exhibit marked concentration and temperature dependence. Monomeric Zn(OMBP), 1, characterized by a429 nm Soret band, dominates at low concentrations M, 300 K) and higher temperatures M , 320K) in toluene solution. Decreasing temperatures (320 to 235 K for a M solution) and increasing concentrations M to M , 300 K) result in 8-10 nm red shifts in this band. These spectral changes are attributed to the concurrent formation of a species 2 with a low extinction coefficient and another compound, 3, with h,,, at 439nm. At the highest concentrations M) and lowest temperatures (225-190K) used, a dramatic blue shift (439 to 422nm) due to a fourth species (4) is observed. All the spectral changes observed are completely reversible. In addition, and consistent with self-association, species 2, 3, and 4 are formed at higher temperatures as the concentration is increased. Possible aggregate structures are proposed and evidence is presented for a novel Zn-N (pyrrole) intermolecular bond. [Traduit par le journal]

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