Photocatalytic reactions of metal diphthalocyanine complexes

Nensala, Ngudiankama (2000) Photocatalytic reactions of metal diphthalocyanine complexes. PhD thesis, Rhodes University.

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Abstract

Photocatalytic reactions oftin diphthalocyanine, Sn f\·Pc2 and anionic form ofNd III, Oy III, Eu III, Tm III and Lu III diphthalocyanine complexes ( [Pc(-2)NdIIIpc(-2)] -, [Pc(-2)Oy!ilPc(-2)] -, [Pc(-2)EuIIIPc(-2)l, [Pc(-2)TmIIlPc(-2)r and [Pc(-2)LuIIIpc(-2)r respectively) in the presence of CH2CI2, S02, pentachlorophenol (PCP), 4-chlorophenol (4-Cp) and thionyl chloride have been studied. Photoreactions involving lanthanide diphthalocyanines, filtered and unfiltered radiations were employed, whereas for photoreactions involving tin diphthalocyanine, only unfiltered radiation was employed. For lanthanide diphthalocyanine complexes, LnPce-, the photosensitization power increases with the decrease of the lanthanide ionic radii, implying that the photocatalytic activity ofLnPc2- complexes is associated with the 11:-1t: interaction between both phthalocyanine rings. Thus, LuPc2- IS a better photocatalyst than other lanthanide diphthalocyanine complexes. Photolysis ofSnPc2 in an acetonitrile/dichloromethane solvent mixture, using unfiltered radiation from a tungsten lamp, results in the one-electron oxidation of this species to [Pc( -2 )Sn(IV)Pc(-1)] -. The relative quantum yields for the disappearance of SnPc2 are in the order of 10 --I. The photoreaction of SnPc~ is preceded by excitation to nn* excited states, before been ,quenched by CH2CI2· The one-electron oxidation speci~s, [Pc(-2)Sn(lV)pc(-1)r was also formed during the photolysis of SnPc2 in dichloromethane containing S02, and with quantum yields of order of 10-'Visible photolysis of[Pc( -2)NdIIIpc(-2)] -, [Pc( -2)Oy!ilPc( -2)] -and [Pc( -2)LuIIIpc( -2)] - in N,N. dimethylformamide (DMF)/dichloromethane solvent mixture containing SO, results in the formation of the one-electron oxidation species, Pc( -2 )Ndillpc( -1), Pc( -2) DyillPc( -1) and Pc(-2)Luillpc( -1), respectively. The relative quantum yields are in the order of 10-2. The photoreactions are preceded by population of the excited triplet state,~rr-rr* [ LnPc2] - complex, before exchanging an electron with S02. The one-electron oxidation species of Dy ill and Lu ill diphthalocyanine complexes have also been formed from visible photolysis of[Pc( -2 )D~Pc(-2)] -and [Pc( -2)Luillpc( -2)] -in acetonitrile containing PCP. The PCP is reductively dechlorinated to tetra- and trichlorophenols. The quantum yields for the photosensitization reactions are in the order of 1 0 -~. Photolysis, using visible radiation from 220 W Quartzline lamp, of an aqueous solution of 4-Cp, saturated with oxygen and containing a suspension of solid [Pc(-2)Ndillpc(-2)] -, results in the formation of benzoquinone, hydro quinone and 4-chlorocatechol. The quantum yields for the degradation of 4-Cp are in the order of 10--+. Langmuir-Hinshelwood kinetic model shows the adsorption of 4-chlorophenol onto solid [Pc( -2)Ndillpc( -2)] -. Lanthanide diphthalocyanine complexes ( (Pc -2)Ndillpc(-2)] -. [Pc(-2)Euillpc(-2)] '. (Pc(-2)Tmillpc( -2)] - and (Pc( -2)Luillpc( -2)] -) undergo one or two-electron oxidation in the presence of thionyl chloride. At low concentrations of SOCI2 « I 0 -~ mol dm -\ the visible yhotolysis of [Pc( -2 )LnPc( -2)] - complexes result in the one-electron oxidation, giving neutral lanthanide diphthalocyanine species, Pc( -2 )Lnillpc( -1). The Pc( -2 )LnPc( -I) species undergoes one-electron photooxidation to [Pc( -I )LnPc( -I)] . in dichloromethane and in the presence of SOCI2. At large concentrations of SOCl2 (> 10 -2 mol dm -3), direct two-electron oxidation of the (Pc( -2 )LnPc (- 2)] . species to (Pc( -1 )LnPc( -1)] - occurs Spectroelectrochemical behaviours of Sn l\Pc2 have been also studied. The cyclic voltammetry ofSnPc2 in CH2CI/TBAP show two reduction couples at -0.56 V and -0.89 V versus saturated calomel electrode (SCE) and one oxidation couple at 0.35 V versus SCE. In DMFITEAP system, the reduction couples are observed at -0.44 V and -0.81 V versus SCE whereas the oxidation couple occurred at 0.43 V versus SCE. The oxidation couple corresponds to [Pc( -2 )Snl\"pc(-2 )]/[Pc( -2)SnIVPc( -I)] . and the reduction couples to [Pc( -2)SnI\·pc( -2 )]/[Pc( -2 )SnI\pc( -3 )]- and [Pc( -2)Snl\pc( -3)] -/[Pc( -3 )Snl\pc( -3)] 2-, respectively. The electronic absorption spectra of these reduced and oxidized species are reported.

Item Type:Thesis (PhD)
Uncontrolled Keywords:Metal complexes, Electrochemistry, Photochemistry, Pentachlorophenol
Subjects:Q Science > QD Chemistry
Divisions:Faculty > Faculty of Science > Chemistry
ID Code:2467
Deposited By: Mrs Carol Perold
Deposited On:13 Feb 2012 09:08
Last Modified:13 Feb 2012 09:08
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