Chromium (III) complexes were prepared from sulphur containing ligands; Potassium alkyl xanthate, (PAX), these complexes were: 1- Tris (methylxanthato) chromium (III) complex Cr(mex)3. 2- Tris (ethylxanthato) chromium (III) complex Cr(etx)3.. 3- Tris (isopropylxanthato) chromium (III) complex Cr(prx)3. 4- Tris (butylxanthato) chromium (III) complex Cr(bux)3. 5- Tris (hexylxanthato) chromium (III) complex Cr(hex)3.
The prepared complexes were characterized by FTIR and UV-Vis spectrophotometeric techniques; in addition some physical properties such, as melting point and magnetic susceptibility were measured. The photodecomposition reactions of the complexes under investigation in DMSO solvent were studied after irradiation by monochromatic light of =311±1nm at room temperature.The photodecomposition constants for the above complexes were found to follow the first order reaction mechanism and consequently dependent only on the concentration of the complex. The specific rate constants (Kd) were measured employing the decrease in the absorbance readings at that wavelength after irradiation of the complexes. This study has also shown that the photodecomposition rate constants depend clearly on the number of alkyl group in the complexes. A large rate constant was observed as the number of alkyl group decrease. The Kd for Cr(mex)3 has a value of (8.700 × 10-5 s-1 )compared to ( 2.170 × 10-5 s-1) for Cr(hex)3 The variation in absorbance after irradiation of the complexes was employed to study the reaction kinetics for the photodecomposition reaction. The results showed that the first excitation step of the complexes were the slowest among other photodecomposition reactions. This followed immediately by the breakage of Cr-S bond of the tris(alkylxanthato)chromium(III) complexes and other fast radical reactions. Based on the above results, the relative photodecomposition reactivity ratio were calculated for all tris(alkylxanthato)chromium(III) complexes. The quantum yield of the photodecomposition reactions of the five complexes were also calculated and it was found to be in the range (1.925 × 10-3 - 7.762 × 10-3) from tris(hexylxanthato)chromium(III) complex to tris(metylxanthato)chromium(III) complex. The quantum yield values were ranked in the following order: (C6H13OCS2)3CrIII < (C4H9OCS2)3CrIII < (C3H7OCS2)3CrIII < (C2H5OCS2)3CrIII < (CH3OCS2)3CrIII