Temperature and pressure effects on the electronic transitions of nickel(II) complexes with C,C-dimethylethylenediamine and N,N-dimethylethylenediamine

Electronic spectra of NiL2X2 (L = C,C-dimethylethylenediamine and N,N-dimethylethylenediamine; X = various anions) thermochromic complexes were obtained at different temps. and pressures; increasing temp. shifts the electronic transition toward lower frequencies whereas the effects of pressure are opposite in direction with blue shifts occurring. At least with diamines involving alkyl groups of the bulk of Et or Me, steric factors are minimal, and the chief mechanism detg. thermochromism in these complexes is the Lever effect. An increase in temp. causes the equatorial interactions to decrease with a simultaneous increase in axial interactions. With an increase in pressure the reverse occurs; the equatorial interactions increase while the axial interactions decrease. There was an anion effect on the d-d transitions with increasing pressure.