ACH - Models in Chemistry 136. (1999)
4. szám - RESEARCH ARTICLES - Šima, J.: Origin of the wavelength dependence of the photoredox quantum yield for iron(III) complexes
376 SiMA: Wavelength dependence of the photoredox quantum yield for iron(III) complexes specifically to iron(III) complexes lies in the fact that almost all of them exhibit no luminescence which prevents to obtain data enabling to formulate more definite conclusions. In this paper, the results on the photoredox behaviour of [FeL3] and [Fe(HEDTA)] are given (where L- means anion of allomaltol). Based on both the obtained and literature data some general conclusions concerning the reasons for different wavelength dependence of Fe11 formation quantum yields are offered. Experimental 1,10-Phenanthroline (Aldrich), potassium tris(oxalato)ferrate(III) (Oxford Organic Chemicals), 5,5-dimethyl-l-pyrrolidine-A,-oxide (DMPO) (Sigma) were used as received. 5-Hydroxo-2-methyl-4#-pyran-4-one (allomaltol, HL) was prepared and characterized according to published procedure [6]. Other chemicals were purchased from Lachema and used without further purification. All commercial chemicals were of analytical grade. All photolyzed solutions were prepared using twice-distilled water. The complex (Fe(HEDTA)(H20)] was synthesized and characterized according to the described procedure [5]. In the photochemical experiments, aqueous solutions of the complex with the initial c(Fein) = 2.Ox 10-4 M and natural pH were used. For irradiation at 222 nm, 313 nm, 365 nm or 436 nm, a solution of the complex [FeL3] was prepared in situ from stock aqueous solutions of Fe(N03)3, HL and NaOH so as to obtain a system with the initial c(Feni) = 4.Ox 10-4 M, c(HL) = 4.0x 10~3 M and pH = 6.40. The influence of free HL on the quantum yield of Fe11 formation was investigated by 254 nm-irradiation of the solutions prepared as above with the constant initial c(Feni) = 4.Ox 10-4 M and pH = 6.40, and with the concentration of HL being c(HL) = 3.0x 10“3 M, 4.0xl0~3 M, 6.Ox 10-3 M, 8.0 xl0~3 M and 1.0xlO-2 M. The effect of the concentration of FeL3 on the quantum yield of Fe11 formation was investigated by 254 nm-irradiation of the solutions prepared as above with the initial c([FeL3]) = 2.Ox 10-4 M, 4.0x10 4 M, 8.Ox 10~4 M and pH = 6.40. О Fig. 1. Structure of allomaltol (HL) '*г ц - modeis in Chemistry 136. 1999