Photochemistry of fac-Pt(NO2)(3)Cl-3(2-) complexes in water solutions

The photochemical transformation of fac-Pt(NO2)(3)Cl-3(2-) complex in water solutions and frozen matrices has been studied by laser Rash photolysis, o ptical, ESR, and NMR spectroscopies. Upon steady state photolysis of liquid water solutions, the fac-Pt(NO2)(3)Cl-3(2-) absorption bands disappear in the optical spectrum with both the preservation of isosbestic point at 43 6 20 cm(-1) and the appearance of a new absorption band with a maximum at 48 000 cm(-1), belonging to R(II) complexes. Applying the NMR method to nuclei Pt-195 and N-14, we have shown that the final photolysis products are main ly complexes [PtCl3(NO2)](2-), Pt(NO2)(2)(H2O)(2) and [Pt(NO2)(6)](2-). The photolysis of frozen (H2O + LiCl or H2O + MgClO4) matrices containing the fac-Pt(NO2)(3)Cl-3(2-) complex yields a new wide absorption band with a max imum in a region of 30 000 cm(-1) which belongs to the [PtCl3(NO2)(2)(ONO)] (2-) nitrito-isomer of the initial complex. A longer irradiation causes pho todissociation of nitrito-isomer into a complex of trivalent platinum [PtCl 3(NO2)(2)](2-) and free NO2. radical whose characteristic lines are manifes ted in the ESR spectrum. The laser flash photolysis shows that in solution at room temperature, the [PtCl3(NO2)(2)(ONO)](2-) nitrito-isomer thermally dissociates in about 300 ns with an activation energy of 48.6 +/- 1.7 kJmol (-1). The [PtCl3(NO2)(2)](2-) complex dissociates in about 7 mus giving the second free NO2. radical and a [PtCl3(NO2)](2-) complex. This reaction has an activation energy of 37.6 +/- 1.5 kT mol(-1). It is shown that dissocia tion of the [PtCl3(NO2)(2)](2-) complex is reversible and the NO2. radical coordinates again with the [PtCl3NO2)](2-) ion with a rate constant 4.2 x 1 0(9) M-1 s(-1). In addition to the repeated coordination, the NO2. radical also disappears in a reversible reaction of recombination (2k(rec) = 1.8 x 10(9) M-1 s(-1)) to give N2O4 molecule. (C) 2001 Elsevier Science B.V. All rights reserved.