Electronic spectra of tris(2,2′-bipyridyl) complexes—I

Abstract Electronic spectra of the electron-transfer complexes of [MN 6 ] type, [Cr(bipy) 3 ] z , where z = +3, +2, +1, 0 and bipy = 2,2′-bipyridyl, are reported between 5000 and 50,000 cm −1 . For z = +3, the values of the spectral parameters Δ = 23,400 cm −1 , B 55 = 738 cm −1 , and B 35 = 495 cm −1 (β 55 = 0·80, β 35 = 0·54) are determined from d → d type bands. Intensity and vibrational structure indicate that the bands have limited charge-transfer character. For z = +2, +1, and 0, the bands which have intensities corresponding to log ϵ between 3 and 4 ( f = 0·1 to 1·0) are classified as L → M, M → L ∗ , and internal ligand L → L ∗ . For z = +2, the energy of some of the bands is reasonably accounted for by ligand field theory assuming Δ = 17,370 cm −1 and B 35 = 604 cm −1 (β 35 = 0·73). For z = +1, a considerable amount of electron delocalization in the ground and excited states is suggested. The spectrum of [Cr(bipy) 3 ] 0 may be assigned largely in terms of internal transitions within the bipy − ion thus substantiating the presence of bipy − in the electronic ground state of the complex.