The kinetics of a fast leuco-Methylene Blue (LMB) re-oxidation to Methylene Blue (MB) by copper()-halide (Cl Ϫ , Br Ϫ ) complexes in acidic aqueous media has been studied spectrophotometrically using a stopped-flow technique. The reaction follows a simple first order rate expression under an excess of the copper() species (and H ϩ (aq)), and the pseudo-first order rate constant (kЈ obs ) is largely independent of the atmosphere used (air, oxygen, argon). The rate law, at constant Cl Ϫ (Br Ϫ ) anion concentration, is given by the expression:where K is the protonation constant, and k a and k b are the pseudosecond order rate constants for protonated and deprotonated forms of LMB, respectively. The rate law was determined based on the observed kЈ obs vs. [Cu II ] and [H ϩ ] dependences. The rate dramatically increases with [Cl Ϫ ] over the range: 0.1-1.5 M, reflecting the following reactivity order: Cu 2ϩ (aq) Ӷ CuCl ϩ (aq) < . . . < CuCl 4 2Ϫ. The slow re-oxidation of LMB by oxygen has also been briefly examined at different [H ϩ ]. ESR results provide clear evidence for the formation of an intermediate radical. The mechanistic consequences of all these results are discussed.

Three water-soluble ruthenium(III) compounds, Y[cis-RuCl 2 (pic) 2 ]⋅nH 2 O (where pic = picolinate anion, Y = H(Hpic) 2 + (1), H 2 pic + (2) or K + (3), n = 2, 1.5 and 2.5, respectively), were synthesized and their X-ray structures determined. Compound 1 was fully characterized both as solid and in aqueous solution by elemental analysis, magnetic susceptibility measurements, EPR, IR and UV-Vis spectroscopy, cyclic voltammetry, microwave plasma atomic emission and mass spectrometry, capillary electrophoresis and chromatographic methods. It was shown that the coordination geometry around the low spin (S = ½) Ru III center is distorted octahedral with the chloride ligands in a cis configuration. Furthermore, all the measurements showed that the structures in the solid state and solution are absolutely identical with the cis-[RuCl 2 (pic) 2 ] − anion being inert in aqueous solution. Microbial studies showed that 1 exerts a strong inhibition on the growth and increased mortality level of the bacterial strains -E. coli, Pseudomonas sp., Sarcina sp., Micrococcus sp., Serratia sp., Bacillus cereus, B. subtilis and yeastSaccharomyces cerevisiae.

The crystal structure of [Pd(dbtp) 2 Cl 2 ]ؒ0.5 C 2 H 5 OH 4c was resolved by X-ray diffraction analysis, exhibiting monomeric, nearly square-planar cis geometry and N(3) co-ordination. A small tetrahedral distortion from the co-ordination plane was observed. The Pd-Cl distances are 2.276(1) and 2.283(1) Å, and Pd-N 2.042(3) and 2.040(3) Å. Spectroscopic measurements (UV-VIS, IR, NMR) suggested analogous structures for 1, 2 and 3. Compounds 4a and 4b are most likely rotational isomers in solution and distortional isomers in the solid state. 15 N-1 H heteronuclear correlation NMR was measured for 2, 4a and 4b whereas 1 and 3 were characterized with 13 C and 15 N CP MAS. Significant shielding of the co-ordinated N(3) and adjacent C(2) or C(3a) nuclei was observed.

In this contribution, we report the synthesis and full characterization of the first mixed-valence Ru(II)/Ru(III) ion-pair complex, [Ru II (bipy) 2 (pic)] + [cis-Ru III Cl 2 (pic) 2 ] − , in the solid state and in aqueous solution, where bipy = 2,2′bipyridine and pic − = picolinate. In addition, unexpected high-frequency electron paramagnetic resonance evidence for interactions between two neighboring Ru(III) ions, resulting in a triplet state, S = 1, was found.

The oxidation of methylene blue (MB + ) by cerium(IV) was studied in 0.1-5 M H 2 SO 4 . The reaction proceeds via MB radical (MB 2+• ) formed by one electron transfer to the oxidant. The radical is observed spectrophotometrically by a very intense absorbance at k max = 526 nm and by the e.p.r signal at g = 2.000. The kinetics of the fast radical formation are two orders of magnitude slower than its decomposition, which were examined using a stopped-flow method at 298 K under pseudo-first order conditions. The rate laws for the both steps were determined and a likely mechanism reported.