Absorption Band Intensities and Stereochemistry of Copper ll

To the writer s knowledge, it has not been pointed out that moderate deviations from the highest symmetry available to the chromophore, producing comparatively high intensities of Laporte-forbidden transitions and a variety of observable effects, are characteristic for soft central atoms. At an instantaneous picture, Cu(H20) 2 and other instances of Cu(II)06 are not cubic, i.e. having three equivalent Cartesian axes. 

The oscillator strength P (called/by many authors) is proportional to the area of an absorption band, the molar extinction coefficient e as a function of the wave-number o in cm 1 called v in many cases). When the band is a Gaussian error curve e = e0 2 (a - °° 16 with the maximum e0 at o0 and the one-sided half-width 5, the area is 2.1289 e0S and 

It is not easy to explain Irving and Williams rule that complex formation constants show a maximum for Cu(II) between Ni(II) and Zn(II) as a consequence of ligand field stabilization. It is true that multidentate ligands sterically predisposed to low ratios of tetragonality (such as 1.35 for ethylenediaminetetra-acetate) also show this effect to a less pronounced extent. Thus, log/f j can be compared6 22,23 with bidentate en and tridentate den  

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