A CELLULAR LIGAND-FIELD MODEL FOR L-L SPECTRAL INTENSITIES .4. PLANARAND NEAR-PLANAR TETRACHLOROCOPPER(II) IONS

The intensity distributions in the 'd-d' spectra of three planar CuCl4 2- chromophores are reproduced quantitatively within the theoretical m odel described in the preceding paper. Intensity for these species, na mely phenylhexyldimethylammonium)tetrachlorocopper(II), o-1-methyl-4-i midazolidinium)tetrachlorocopper(II) and methylphenyl-ethylammonium)-t etrachlorocopper(II), is deemed to arise dynamically via the bending v ibrations. Fair reproduction of experimental absorbances is achieved u sing the b2u mode alone, this being known to be the softest vibration in these systems. The roles of spin-orbit coupling and small departure s from D4h symmetry are discussed. Nearly perfect reproduction of expe riment is obtained with addition of small contributions from the e(u) bend. The intensity distribution in the 'd-d' spectrum of the pseudo-t etrahedral chromophore, bis(N-benzylpiper-azinium)tetrachlorocopper(II ), is reproduced quantitatively within the 'static' model described in part I of this series. Comparisons between the parameter values obtai ned from the 'static' analysis with those from the 'dynamic' analysis for the planar chromophores suggest that dynamic modelling with both b 2u and e(u) modes is the more physically persuasive. The efficacy of t he model in part IV is critically reviewed in this first application.