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The compounds [Cr(RNH2)5C1](C104)2, where R = H, CH3, C2H5, n-C3H7, and n-C4H9, have been prepared and the replacement of chloride by either water or hydroxide ion subjected to kinetic examination. Below about p H 7 the reaction was acid independent, and AHA* was 22.4 kcal mole-' when ammonia was the inert ligand compared with about 26.4 kcal mole-' when the inert ligand was a primary amine. The corresponding ASA* values increased continuously with R from H to 11-C4HI) At higher pH the rate became inversely dependent upon the acidity of the solution, and AHB* decreased from 26.7 kcal mole-' for ammonia as the inert ligand to 25.4 kcal mole-' for an amine as the inert ligand. For the pH dependent reaction the values obtained for AS,* were much larger than for the p H independent reaction but the pattern of variation as the inert ligands were changed was quite similar in the two cases. The great similarity in the trends of AS* values for the acid and base hydrolysis reactions has been interpreted in terms of a rate-determining step that is primarily dissociative in both cases.

The absorption spectra of a number of cupric, cuprous, and ferrous complexes are described and discussed. The stabilities of some of the complexes are also determined. We show that description of the spectra requires a different relative emphasis on Q-and x-bonding in the complexes from that required in discussion of their stability.THE absorption spectra of transition-metal complexes are relatively well understood. In particular the treatment of d-d transitions by ligand-field theory is in excellent agreement with experimental observations in so far as the number of bands and their relative positions are often accurately predictab1e.l Two problems remain, the intensity of the bands and their absolute positions. In this paper we describe an approach to these problems through the study of some cupric complexes. The other common optical transitions of the transition-metal complexes are the intense so-called charge-transfer bands. These transitions are less well understood. In the second part of the paper we examine the charge-transfer spectra of a large number of ferrous and cuprous complexes in an attempt to clarify the nature of these intense absorption bands. We have also examined the stabilities of a number of the complexes of these cations. A comparison between the spectroscopic and the thermodynamic information illustrates the very different effects of change of the ligand substituents on the different properties of the complexes.Cztpric CompZexes.-Fig. 1 illustrates the absorption spectra of some typical cupric salts in pyridine. Table 1 lists the positions and intensities of the absorption bands of a series of such salts in the same solvent. The band shape vanes little from compound to compound within a group. We shall follow ligand-field theory in relating band positions to the field strength parameter, A, and the asymmetry of the bands to distortion from cubic symmetry (Fig. 1). A more detailed discussion follows below. The complexes can be formulated as (A) C~(py)~(carboxylate),, (B) Cu(salicylaldehyde),(py),, and (C) Cu-(salicylaldehyde imine),(py),, where py = pyridine. The orders of the wavelengths, (C) < (A) < (B) , show a decrease with increase in donor strength of the ligand, as expected,

The absorption spectra and circular dichroism spectra of some Cu(II) N,N′-diglycylethylenediamine analogues are interpreted in terms of a square-planar structure of the biuret type.

The rate of first-order hydrogen-ion independent chromium isotope exchange between benzylchromium(III) and chromium(II) ions is 1.2 × 10−2 M−1 s−1 at 0°C in a 70% methanol-water solvent, ΔS≠ = −28.5 eu, ΔH≠ = 10.3 kcal M−1. For the corresponding exchange between benzylchromium(III) and p-chlorobenzylchromium(III) ions, these figures are 1.2 × 10−3M−1 s−1, −32.2 eu, and 10.9 kcal M−1.

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