Photooxidation of bis(ethylxanthato)nickel(II) containing aromatic nitrogen heterocyclic ligands in chloroform

摘要

The photochemistry of the complexes Ni(Etxn)2(N-N) Etxn=ethylxanthate,N-N=2,2′-bipyridine(bpy), 4,4′-dimethyl-2,2′-bipyridine (4,4′-Me-bpy), 1,10-phenanthroline (phen) or 2,2′-bipyrimidine (bpym) has been investigated. These complexes were not light sensitive in most solvents such as acetonitrile. Upon irradiation of chloroform solutions of these complexes, a photoredox reaction occurred giving the parent Ni(Etxan)2. It is suggested that the reactive excited state is of the charge-transfer-to-solvent (CTTS) type. The energy of this state depends on the redox potentials of the solvent. When CHCl3as solvent was replaced by the stronger oxidant CCl4, the photoactive wavelength region was shifted to the red. It was blue shifted when the weaker oxidant CH2Cl2was used. From quantum yield measurements it is concluded that the photostability of the studied complexes decreases in the following order:bpym>phen>bpy>4,