Photochemistry of trans-[Cr(en)₂Br₂]⁺ and trans-[Cr(en)₂Cl₂]⁺

Abstract

. Can. J. Chem. 54, 2335(1976.trans-[Cr(en)2Br2]+ has been found to photoaquate mainly with bromide loss (+578 = 0.36. 4436 = 0.27, $406 = 0.27) but accompanied by a small, also wavelength dependent, proton uptake (+578 = 0.003, 4436 = 0.075, +406 = 0.042). The main photoproduct of trans-[Cr(en)2-Br2If and tran~-[Cr(en)~Cl~]+ has been shown to be predominantly cis in configuration (95 rt 5% for the dibromo and 99.27, for the dichloro system). The results are discussed in the context of current models of chromium (II1) . On discute des resultats en terme des modeles courants pour la photochimie du chrome(II1). Le fait que les rhctions dependent de la longueur d'onde implique une participation de plus d'un Ctat excite dans la reaction. Par ailleurs la stCrCospCcificitC des changements stCrCochimiques implique une entree du solvant d'une f a~o n concertke avcc la perte de l'halogenure.[Traduit par le journal]

Photochemistry of trans-difluorobis(ethylenediamine)chromium(III)

“…It is interesting to note that in-plane labilization (ethylenediamine detachment) is always larger than axial labilization (F" release), contrary to what happens for other trans-Cr-(en)2X2+ 5,11,17 and trans-Cr(en)2XY+ 6,7,10 complexes. Considering the irradiation of the lowest quartet ligand field band (4Eg(4T2g) excited state), the quantum yield of the axial labilization decreases in the series Br > Cl > NCS > F, whereas the quantum yield of the in-plane labilization increases along the same series.…”

“…Considering the irradiation of the lowest quartet ligand field band (4Eg(4T2g) excited state), the quantum yield of the axial labilization decreases in the series Br > Cl > NCS > F, whereas the quantum yield of the in-plane labilization increases along the same series. 39 In particular, in going from trans-Cr(en)2Br2+ 17 to i/-any-Cr(en)2F2+ the / ratio varies more than three orders of magnitude. These results may be discussed in terms of -bonding effects,4•7,11,15 -bonding effects,18"20 and relative populations of the d¿ and orbitals in the lowest quartet excited state.…”

“…íra«í-Cr(en)2F2+ is an important member within the family of the mixed-ligand Cr(III) complexes because of its spectroscopic properties.24"26 Experiments carried out by Pyke and Linck4 using 520-nm excitation have in fact indicated that the photochemical behavior of this complex is different from that of the other irans-Cr(en)2X2+ complexes. 5,11,17 This paper reports a quantitative investigation of the photochemical behavior of irony-Cr(en)2F2+ at three different excitation wavelengths.…”

Photochemical and photophysical behavior of trans-diisothiocyanatobis(ethylenediamine)chromium(III)

“…However, a concerted associative mechanism is most probable in view of the high degree of stereochemical change brought about by the photosubstitution reactions. 30,31 A quantitative discussion of this mechanism can be done on the basis of the scheme shown in Figure 6. The following relations can be obtained between mechanistic and experimental quantities:55 7479 rrib = 72 + 7174 = 0.8 wp where 10 is the total photoreaction quantum yield ( ß-+ +) on direct excitation, "0 ,9 is its unquenchable part, " is the total limiting photoreaction quantum yield on sensitization conditions, and and 6 $ are the corresponding phosphorescence quantum yields.…”