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Photochemistry of eight-coordinate-chelate complexes of tungsten(IV) and molybdenum(IV)
Abstract
A series of tungsten(IV) and molybdenum(IV) eight-coordinate-chelate complexes were prepared with chelating heterocyclic ligands containing nitrogen, oxygen and/or sulfur donor atoms. The complexes in solution displayed sensitivity to solvent dipole moment in the form of negative solvatochromism. The tungsten complexes exhibit reversible oxidations between +1.3 to $-$1.3 volts vs the normal hydrogen electrode window. The molybdenum(IV) complexes displayed non-reversible behavior at slow scan rates in the cyclic voltammetry experiment. Electronic absorptions associated with metal-to-ligand charge-transfer transitions in the region between 470 nm and 700 nm were monitored for their emissive behavior when excited by visible light. Excitation of the charge-transfer bands of the picolinato, methylpicolinato, and ethylpicolinato complexes of tungsten(IV) results in the appearance of rich and varied emission in poly(methyl methacrylate) and poly(vinyl chloride) films as well as in acetonitrile and dichloromethane solutions at room temperature. All of the complexes showed some emissive behavior. The emission bands for the complexes were generally asymmetric and showed little structure. An excited-state model assigning these emission to a triplet metal-to-ligand charge-transfer state is proposed. Irradiation of the charge-transfer bands of the tetrakis(2-mercaptopyrimidinato)tungsten(IV) and tetrakis(picolinato)tungsten(IV) complexes in the presence of tris(2,4-pentanedionato)cobalt(III) in acetonitrile solutions resulted in diminution of the bands with quantum yields on the order of 10$\sp{-4}.$ Excited-state electron transfer from the tungsten(IV) complexes to the cobalt(III) complex is proposed as a possible cause for the loss of band intensity in the tungsten(IV) species.
Subject Area
Inorganic chemistry|Chemistry
Recommended Citation
White, Adrian Alvin, "Photochemistry of eight-coordinate-chelate complexes of tungsten(IV) and molybdenum(IV)" (1993). Doctoral Dissertations Available from Proquest. AAI9408359.
https://scholarworks.umass.edu/dissertations/AAI9408359