Chromium complexes, absorption wavelength

Metal carbonyl halides can also undergo photoredox reactions if an MLCT chromophoreofsuitableenergyispresentinthecomplex.ThecomplexCrI(CO)5, for example, has a characteristic long-wavelength absorption at 638 nm that is due to an I - Cr (LMCT) absorption. Irradiation into this chromophore for a solution of CrI(CO)5 in acetonitrile leads to the formation of iodine and the zerovalent chromium complex Cr(CO)5MeCN with a quantum yield of 0.01 (Ref. 65) ... 

Transient absorption measurements have recently been recorded from the organometallic species chromium hexacarbonyl in ethanol solution [94], Absorption of a 65-fs, 310-nm excitation pulse was followed by measurement of excited-state absorption of a 65-fs, 480-nm probe pulse. The data shown in Figure 14 indicate a rapid nonexponential decay at short times followed by a gradual exponential rise. The slower feature was observed previously [95] and is known to correspond to the solvent complexation of Cr(CO)5 to yield Cr(CO)j(MeOH). The initial feature, which is observed at other probe wavelengths as well, is believed to correspond to the initial ligand loss reaction. Note that this case is different from ICN in that the initially excited wavepacket is not on the side of the Sj potential but rather (as is clear from the molecular symmetry) on a local potential maximum. The wavepacket must then spread that is, dissociation along either direction is equally likely. The rapid nonexponential decay was analyzed in terms of classical kinematics along a dissociative potential. 

The charge transfer absorption band of the chromium to benzene ring transition in 28 and its derivatives is found at considerably longer wavelengths than in the reference complex 158a (Fig. 38) [29, 40, 123]. The corresponding bis(tricarbonylchromium) complexes show a further bathochromic shift [29,40,... 

Cotton constructed an apparatus to measure optical rotations and CD over a range of wavelengths. He established Cotton effects for potassium chromium tartrate and potassium copper tartrate solutions. These were the first ORD and CD studies of coordination compounds, but the complexes were not isolated. For a long period there was little activity in ORD or CD studies of complexes. Kuhn (13) was interested in metal complexes in connection with his ideas about the theory of optical activity (14), J. P. Mathieu (15,16) presented combined studies of ORD, CD, and absorption spectra of many complexes of Co, Cr, Pt, Rh, and Ir during the 1930s. After his work there was no activity in CD studies of complexes for many years. 

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