The kinetics of a fast leuco-Methylene Blue (LMB) re-oxidation to Methylene Blue (MB) by copper(II)–halide (Cl⁻, Br⁻) 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(II) species (and H⁺(aq)), and the pseudo-first order rate constant (k′_obs) is largely independent of the atmosphere used (air, oxygen, argon). The rate law, at constant Cl⁻ (Br⁻) anion concentration, is given by the expression: (d[MB⁺])/dt = ((k_aK[H⁺] + k_b)/(1 + K[H⁺]))·[Cu^II][LMB] = k′_obs[LMB], where K is the protonation constant, and k_a and k_b are the pseudo-second order rate constants for protonated and deprotonated forms of LMB, respectively. The rate law was determined based on the observed k′_obsvs. [Cu^II] and [H⁺] dependences. The rate dramatically increases with [Cl⁻] over the range: 0.1–1.5 M, reflecting the following reactivity order: Cu²⁺(aq) ≪ CuCl⁺(aq) < … < CuCl₄ ²⁻. The slow re-oxidation of LMB by oxygen has also been briefly examined at different [H⁺]. ESR results provide clear evidence for the formation of an intermediate radical. The mechanistic consequences of all these results are discussed.

Two bimetallic complexes [M(en)₃]_n[{M(en)₂Cr(NCS)₆}_2n] (M = Ni 1, Zn 2; en = ethylenediamine) have been prepared and structurally and magnetically characterised. They present a unique structure consisting of two distinct units: the catena-μ-NCS-M(en)₂-μ-SCN-Cr(NCS)₄ 1-D polymeric anion and the monomeric cations [M(en)₃]²⁺. Complex 1 crystallized in the monoclinic system, space group C2/c, with a = 28.330(3), b = 14.256(1), c = 16.013(1) Å, β = 117.26(1)°, V = 5748.9(8) ų and Z = 4. The crystal structure of 1 has been refined to R1 = 0.0808. The bridging NCS ligands occupy the rare cis positions in the Ni²⁺ coordination sphere and are coordinated to nickel via their sulfur atoms. The coordination sphere of Cr³⁺ is formed by six nitrogen atoms of the NCS ligands. The Ni–N distances vary from 2.052(5) to 2.131(5) Å, the Ni–S distances are 2.584(2) and 2.632(2) Å, whereas the Cr–N distances vary from 1.971(6) to 2.003(6) Å. A variable temperature magnetic susceptibility study of 1 has been performed over the temperature range of 4–300 K. The compound shows antiferromagnetic coupling (J ≈ −20 cm⁻¹). This moderate antiferromagnetic interaction could be explained by the structural features related to μ-_N,S-NCS bridged units being in cis positions at both metallic centres. The isostructural complex 2 exhibits magnetic behaviour that agrees well with that expected for isolated [Cr(NCS)₆]³⁻ units with small inter- and/or intra-chain antiferromagnetic interactions.

Palladium(II) complexes of formula [Pd(tp)₂Cl₂] 1, [Pd(dmtp)₂Cl₂]·H₂O 2, [Pd(dptp)₂Cl₂]·H₂O 3, [Pd(dbtp)₂Cl₂] 4a, 4b, where tp = 1,2,4-triazolo[1,5-a]pyrimidine, dmtp = 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine, dptp = 5,7-diphenyl-1,2,4-triazolo[1,5-a]pyrimidine, dbtp = 5,7-di-tert-butyl-1,2,4-triazolo[1,5-a]pyrimidine, were prepared. The crystal structure of [Pd(dbtp)₂Cl₂]·0.5 C₂H₅OH 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. ¹⁵N–¹H heteronuclear correlation NMR was measured for 2, 4a and 4b whereas 1 and 3 were characterized with ¹³C and ¹⁵N CP MAS. Significant shielding of the co-ordinated N(3) and adjacent C(2) or C(3a) nuclei was observed.

The kinetics of the oxidation of imipramine and desipramine using cerium(IV) complexes were studied in the presence of a large excess of azepine derivative (TCA) in acidic sulfate media using UV-Vis spectroscopy. The reaction proceeds viadibenzoazepine radical formation, identified by EPR measurements. The kinetics of the first degradation step were studied independently of the further slower degradation reactions. Linear dependences, with zero intercept, of the pseudo-first-order rate constants (k_obs) on [TCA] were established for both dibenzoazepine radical formation processes. Rates of reactions decreased with increasing concentration of the H⁺ ion indicating that cerium(IV) as well as both reductants exist in an equilibrium with their protolytic forms. The activation parameters for the degradation of dibenzoazepine derivatives in the first oxidation stage were as follows: ΔH^≠ = 39 ± 2 kJ mol⁻¹, ΔS^≠ = −28 ± 8 J K⁻¹ mol⁻¹ for imipramine and ΔH^≠ = 39 ± 2 kJ mol⁻¹, ΔS^≠ = −28 ± 6 J K⁻¹ mol⁻¹ for desipramine, respectively. Imipramine and desipramine radicals dimerized leading to an intermediate radical dimer, which decayed in a first-order consecutive decay process. These two further reactions proceed with rates which are characterized by non-linear dependences of the pseudo-first-order rate constants (k_obs) on [TCA]. The degradation reaction of the intermediate radical dimer leads to an uncharged dimer as a final product. Mechanistic consequences of all the results are discussed.