Spectroscopy and kinetics of intermediates in photochemistry of xanthate Ni(S2COEt)2 complex in CCl4

Abstract

The laser flash photolysis made it possible to determine the mechanism of photochemical reactions of the xanthate Ni(S2COEt)2=Ni(xan)2 complex in CCl4. Upon the excitation of Ni(xan)2 complex, several fast processes occur. In the first of them, an electron is transferred from −S2COEt = −xan ligand to Ni(II) ion with the formation of ·S2COEt=·xan radical in coordination sphere of now Ni(I) ion. Then electron is transferred from Ni(I) to CCl4 molecule located in the second coordination sphere (CCl4 is a good electron acceptor). The nascent CCl4·- anion-radical rapidly dissociates into Cl- ion and CCl3· radical. In the solvent with low dielectric constant, a negatively charged Cl- ion is incorporated into the coordination sphere of positively charged Ni+2(-xan)(·xan)+ complex with the formation of neutral primary transient [Cl-Ni2+(-S2COEt)(·S2COEt)]=[Cl-Ni2+(-xan)(·xan)] radical complex during a laser pulse (5 ns). This particle disappears in a fast reaction with the initial Nixan2 complex with the formation of [ClNi(xan)(·xan)Nixan2] dimer (rate constant 2 × 109 M−1 s−1). The dimers disappear in second-order reaction (recombination) in millisecond time range with the formation of xan2 disulfide and ClNi(xan) complex. The ClNi(xan) complexes in a slow disproportionation reaction are transformed into NiCl2 and initial Ni(xan)2 complex. Thus, the final products of Ni(xan)2 photolysis are the xan2 disulfide and NiCl2 complex insoluble in CCl4.