Przemysław Kita

The crystal structures of bis(oxalato)chromium(III) complexes with histamine and B6 vitamin: Na[Cr(ox)2(hm)]·3H2O and Na[Cr(ox)2(PM)]·H2O (hm, histamine; PM, pyridoxamine)

The crystal structures of two bis(oxalato)chromium(III) complexes with histamine and B 6 vitamin, Na[Cr(ox) 2 (hm)]·3H 2 O ( 1 ) and Na[Cr(ox) 2 (PM)]·H 2 O ( 2 ) (hm, histamine; PM, pyridoxamine) were determined by the single crystal X-ray diffraction technique. In the complexes, hm and PM act as bidendate ligands; hm is coordinated by N atoms of the aminoethyl group and imidazole, and PM by the N atom of the aminoethyl group and the O atom of the phenol group. Two oxalato ligands in the complexes 1 and 2 additionally coordinate to sodium cations by various coordination modes, forming one-dimensional and three-dimensional networks, respectively.

Kinetics and mechanism of aquation of [Cr(NCS)(edtrp)]-, [Cr(NCS)(R-pdtrp)]-, [Cr(edtrp)(NCSHg)]+ and [Cr(R-pdtrp) (NCSHg)]+ complexes. Unexpected rate retardation in strongly acidic media for NCS- ligand release

Three new complex ions, [Cr(NCS)(R-pdtrp)]-, [Cr(R-pdtrp)(NCSHg)]+ and [Cr(edtrp)(NCSHg)]+, that are derivatives of the trans-equatorial isomers of [Cr(R-pdtrp)(H2O)]0 and [Cr(edtrp)(H2O)]0 (edtrp= ethylenediamine-N,N,N′-tripropionate, R-pdtrp= R-propane-1,2-diamine-N,N,N′-tripropionate) have been obtained and characterized in solution. Rate constants and activation parameters, including, in two cases, volumes of activation, have been determined. Rate retardation for NCS- ligand release has been observed with increasing acidity within the pH 0–2 range. The mechanism of the reactions has been discussed.

Kinetics and mechanism of electron transfer processes in a hydrogen peroxide—trispicolinatoruthenate(II) system

Oxidation of trispicolinatoruthenate(II) complex by hydrogen peroxide leads to the formation of mer-trispicolinatoruthenium(III) in acidic or neutral solutions. Kinetics of the reaction were studied under a large excess of H2O2 at constant pH. The initial rate method gives a rate expression of the form:

Kinetic studies on spontaneous ligand substitution in [Cr(S-pdtra)(H2O)]–NCS– and [Cr(edtrp)(H2O)]–NCS– systems

- \hbox{d}[{\text{Ru}}({\text{II}})]/{\text{d}}t = k^{II} [{\text{H}}_{2} {\text{O}}_{2} ][{\text{Ru}}({\text{II}})]

Base hydrolysis of macrocyclic chromium(III) complexes. Importance of ion-pair formation for kinetics and mechanism

but the overall process examined till completion is far more complex. The rate of the reaction decreases with increasing pH to be practically completely retarded in alkaline media. The key step in the proposed reaction mechanism is the picolinato chelate ring opening followed by the substitution of the coordinated water by H2O2 and two-electron intramolecular ruthenium(II) oxidation. Formation of the final ruthenium(III) complex is assigned rather to the ruthenium(IV) reduction by H2O2 than ruthenium(II)–ruthenium(IV) comproportionation. The obtained results show the much slower rate of the trispicolinatoruthenate(II) oxidation by hydrogen peroxide or dioxygen than the mer-trispicolinatoruthenium(III) reduction by such bioreductants as cytochrome cII or some cobalt(II) reductants.

Kinetics and mechanism of the base hydrolysis of cis-eq-[Cr(NCS)(S-pdtra)]−, trans-eq-[Cr(NCS)(edtrp)]− and trans-eq-[Cr(NCS)(R-pdtrp)]− complexes. Strong rate enhancement for NCS− ligand release with an increase of [OH−] only for the trans-equatorial isomers

Two new complex anions, [Cr(N3)(S-pdtra)]− and [Cr(N3)(edtrp)]−, were obtained in solution by N3−/HN3 anation of the aqua analogues (S-pdtra = S-propane-1,2-diamine-N,N,N′-triacetate, edtrp = ethylenediamine-N,N,N′-tripropionate). Aquation of these species in acidic media leads to the same geometrical isomers as those used for the synthesis. The aquation rate is strongly dependent upon [H] and is substantially higher in D2O than in H2O. Protonation of the coordinated azide was not observed spectrophotometrically. The rate law and activation parameters have been determined and discussed.

Kinetics and mechanism of a fast leuco-Methylene Blue oxidation by copper(II)–halide species in acidic aqueous media

The kinetics of anation of [Cr(S-pdtra)(H2O)] and [Cr(edtrp)(H2O)] complexes (S-pdtra=S-propane-1,2-diamine-N,N,N′ -triacetate, edtrp=ethylenediamine-N, N,N′-tripropionate) by thiocyanates and aquation of the [Cr(NCS)(S-pdtra)]– and [Cr(NCS)(edtrp)]– ions have been studied in aqueous HClO4 solutions. The rate laws and the activation parameters have been determined and discussed. The observed decrease in reactivity for the edtrp complexes corresponds with a changeover of the reaction mechanism from Ia to Id for reactions of the CrIII-S-pdtra and CrIII-edtrp species, respectively.

Hydrogen peroxide as a reductant of hexacyanoferrate(III) in alkaline solutions: kinetic studies

The title complexes have been synthesized, chromatographically isolated and characterized by their ligands to metal ratio determinations and spectroscopic analyses. The kinetics of the first aquation stage, i.e., the amino acid chelate ring opening via the Cr–N bond cleavage, has been studied spectrophotometrically in acidic and alkaline media. Hydrogen peroxide oxidizes the complexes in alkaline media to CrO42− anion and a relatively stable Cr(V) complex. Consecutive biphasic kinetics through two first-order steps were observed for the base hydrolysis and the oxidation process, whereas the acid-catalyzed aquation obeys a simple first-order pattern. Based on the kinetic and spectroscopic data, mechanisms of the coordinated amino acid liberation and chromium(III) oxidation are discussed.