Lars Ivar Elding

Palladium(II) halide complexes. I. Stabilities and spectra of palladium(II) chloro and bromo aqua complexes

Stability constants, βn, n = 1, 2, 3, 4, for the chloro and bromo complexes of palladium(II) have been calculated, using a least squares programme, from spectrophotometric measurements at 222, 234.5 and 279 nm (chloride) and at 247, 265, and 332 nm (bromide). The following values of lg(βn/M−n) were obtained: 4.47±0.01, 7.76±0.04, 10.17±0.07, and 11.54±0.09 (chloride) and 5.17±0.02, 9.42±0.04, 12.72±0.06, and 14.94±0.08 (bromide). Spectra of the species PdXn(H2O)4−n2−n, n = 0, 1, 2, 3, 4; X = Cl, Br, have been determined in the wave length region 210 to 600 nm. The temperature was 25.0°C and the ionic medium 1.00 M perchloric acid.

Stabilities of platinum(II) chloro and bromo complexes and kinetics for anation of the tetraaquaplatinum(II) ion by halides and thiocyanate

Abstract The anations of Pt(H2O)2+4 and PtX(H2O)+3 (to trans-PtX(H2O)2) by X− = Cl−, Br−, I− and SCN− and the anation of trans-PtX(H2O)2) by X− = Cl−,Br− and I− have been studied at 25 °C and 1.00 M perchlorate medium using both stopped-flow and conventional spectrophotometry. For large excess of X−, PtX2−4 is formed according to the mechanism in Figure 1. The results indicate an entering ligand order of Cl−

Manganese-catalysed autoxidation of dissolved sulfur dioxide in the atmospheric aqueous phase

Autoxidation of SO2(aq) in the presence of manganese(II) is one of the important pathways for sulfuric acid formation in atmospheric clouds and fogs. Recent experimental results indicating that the catalyzed reaction takes place via a complex free-radical mechanism are discussed. Previous literature is reviewed in the light of this mechanism. Under atmospheric conditions of low total concentrations of manganese(II) ( < 2 × 10−5 M) and sulfur(IV) ( ≤ 10−5 M) and 2.5 < pH < 5, the rate law for conversion of SO2(aq) to SO3(aq) is reduced to d[S(IV)]/dt = k[Mn(II)][S(IV)], where [S(IV)] denotes the total concentration. A value of the overall rate constant k of 1.4 × 103 M−1s−1 is recommended for use in atmospheric model calculations.

Preparation and properties of the tetra-aquaplatinum(II) ion in perchloric acid solution

Abstract Dilute solutions of the square-planar tetra-aqua complex pt(H2O)42+ have been prepared in a 1.00 M perchloric acid medium by addition of excess silver(I) perchlorate to potassium tetrachloroplatinate(II), equilibration at 70°C, filtration of the silver chloride precipitate, and subsequent separation of the excess silver from the solution by electrolysis. The complex has also been prepared by addition of mercury(II) perchlorate to tetrachloroplatinate(II) solutions. The UV and visible absorption spectrum of the complex has been recorded and its hydrolysis qualitatively studied. The experiments indicate that Pt(H2O)42+ is a weak acid with pKa>2.5. A while, amphoteric hydroxide of platinum(II) is precipitated in the pH region 4 to 10.

Palladium(II) halide complexes, II. Acid hydrolyses and halide anations of palladium(II) chloro and bromo aqua complexes

Abstract The rate constant for the chloride and bromide anations of Pd(H2O)42+, the chloride anations of PdCl3H2O−, the bromide anation of PdBr3H2O− and the acid hydrolysis of Pd(H2O)3+, PdBr(H2O)3+, PdCl42−, and PdBr42− have been determined at 15, 25 and 35 °C using a stopped-flow technique. The ionic strength was 1.00 M and the supporting electrolyte perchloric acid. The obtained rate constants are given in Table IV and the activation enthalpies and entropies in Table V. A comparison with the corresponding reactions for platinum(II) complexes indicates that the acid hydrolyses are 1×105 to 2×105 times faster and the halide anations 4×101 to 6×104 times faster for palladium. The increased rates of reaction are due to a decrease in activation enthalpies. The reactions are typically square planar substitutions with respect to entering and leaving groups. The mechanism appears to be associative in nature.

Kinetics and mechanism for reduction of anticancer-active tetrachloroam(m)ine platinum(IV) compounds by glutathione.

Glutathione (GSH) reduction of the anticancer-active platinum(IV) compounds trans-[PtCl4(NH3)(thiazole)] (1), trans-[PtCl4(cha)(NH3)] (2), cis-[PtCl4(cha)(NH3)] (3) (cha=cyclohexylamine), and cis-[PtCl4(NH3)2] (4) has been investigated at 25 °C in a 1.0 M aqueous medium at pH 2.0–5.0 (1) and 4.5–6.8 (2–4) using stopped-flow spectrophotometry. The redox reactions follow the second-order rate law d[Pt(IV)]/dt=k[GSH] tot[Pt(IV)], where k is a pH-dependent rate constant and [GSH] tot the total concentration of glutathione. The reduction takes place via parallel reactions between the platinum(IV) complexes and the various protolytic species of glutathione. The pH dependence of the redox kinetics is ascribed to displacement of these protolytic equilibria. The thiolate species GS− is the major reductant under the reaction conditions used. The second-order rate constants for reduction of compounds 1–4 by GS− are (1.43±0.01)×107, (3.86±0.03)×106, (1.83±0.01)×106, and (1.18±0.01)×106 M−1 s−1, respectively. Rate constants for reduction of 1 by the protonated species GSH are more than five orders of magnitude smaller. The mechanism for the reductive elimination reactions of the Pt(IV) compounds is proposed to involve an attack by glutathione on one of the mutually trans coordinated chloride ligands, leading to two-electron transfer via a chloride-bridged activated complex. The kinetics results together with literature data indicate that platinum(IV) complexes with a trans Cl-Pt-Cl axis are reduced rapidly by glutathione as well as by ascorbate. In agreement with this observation, cytotoxicity profiles for such complexes are very similar to those for the corresponding platinum(II) product complexes. The rapid reduction within 1 s of the platinum(IV) compounds with a trans Cl-Pt-Cl axis to their platinum(II) analogs does not seem to support the strategy of using kinetic inertness as a parameter to increase anticancer activity, at least for this class of compounds.

Kinetics and mechanism for reduction of halo- and haloam(m)ine platinum(IV) complexes by l-ascorbate

Reduction of the model platinum(IV) complexes cis-[PtCl4(NH3)(2)] (1), trans-[PtCl4(NH3)(2)] (2). trans-[PtCl2(en)(2)](2+) (3), trans-[PtBr2(NH3)(4)](2+) (4), [PtCl6](2-) (5), and [PtBr6](2-) (6) with L-ascorbic acid (H(2)Asc) in 1.0 M aqueous medium at 25 degreesC in the region 1.75 less than or equal to pH less than or equal to 7.20 has been investigated using stopped-flow spectrophotometry. The redox reactions follow the rate law: -d[Pt(IV]/dt = k[H(2)Asc](tot)[Pt(IV)] where k is a pH-dependent second-order rate constant and [H(2)Asc](tot), the total concentration of ascorbic acid. The pH-dependence of k is attributed to parallel reduction of Pt(IV) by the protolytic species HAsc(-) and Asc(2-). Analysis of the kinetics data reveals that the ascorbate anion Asc(2-) is up to seven orders of magnitude more reactive than HAsc(-) while H(2)Asc is unreactive. Electron transfer from HAsc(-)/Asc(2-) to the Pt(IV)) compounds is suggested to take place by a mechanism involving a reductive attack on any one of the mutually trans-halide ligands by Asc(2-) and/or HAsc(-) forming a halide-bridged activated complex, The rapid reduction of these complexes supports the assumption that ascorbate Asc(2-) might be an important reductant at physiological conditions for anticancer active Pt(IV) pro-drugs capable of undergoing reductive trans elimination. The parameters DeltaH(not equal) and DeltaS(not equal) for reduction of Pt(IV) with Asc(2) hake been determined from the study of the temperature dependence of k

Trans influence of triphenylstibine. Crystal and molecular structures of cis-[PtCl2(SbPh3)2] and trans-[PtI2(SbPh3)2]

Crystals of cis-[PtCl2(SbPh3)2] (1) are monoclinic, space group . Substitution of chloride for iodide yields trans-[PtI2(SbPh3)2] (2), the crystals of which are monoclinic, space group . The average PtCl distance in 1 is 2.338(12) A, implying a trans influence of triphenyl stibine comparable with that of triphenyl phosphine, as opposed to what has been reported earlier. IR and Raman data for 1 and 2 are reported and discussed.

Mechanisms for acceleration of halide anation reactions of platinum(IV) complexes: REOA versus ligand assistance and platinum(II) catalysis without central ion exchange

Chloride anation of trans-Pt(CN)4ClOH2− has been studied with and without Pt(CN)42− present at 25.0°C by use of stopped-flow and conventional spectrophotometry and a 1.00 M perchlorate medium. The rate law in the absence of Pt(CN)42− is compatible with a chloride assistance via an intermediate of the type Cl-Cl-Pt(CN)4···OH22−, in which the reactivity of the aqua ligand is enhanced due to a partial reduction of the platinum. This mechanism of halide assistance is in principle the same as the modified reductive elimination oxidative addition (REOA) mechanism proposed by Poe, in which the intermediate is not split into free halogen, platinum(II) and water, and in which electron transfer not necessarily involves complete reduction to platinum(II). To avoid confusion with complete reductive eliminations, reactions without split of the intermediates are here termed halide-assisted reactions. The pH-dependence indicates acid catalysis via a protonated intermediate ClClPt(CN)4···OH3−.Reaction between PtCl5OH2− and chloride is accelerated by Pt(CN)42− and gives PtCl62− as the reaction product. The rate law is derived at 35.0°C and for a 1.50 M perchlorate acid medium. The reaction takes place without central ion exchange. Alternative mechanisms with two consecutive central ion exchanges can be excluded. The role of Pt(CN)42− in this reaction is very similar to that of the assisting halide in the halide assisted anations. [p ]Reaction between trans-Pt(CN)4ClOH2− and PtCl42− gives Pt(CN)42− and PtCl5OH2− as products. The formation of an aqua complex as the primary reaction product and the rate independent of [Cl−] shows that formation of a bridged intermediate of the type Pt(II)Cl4ClPt(IV)(CN)4OH23− is formed in the initial reaction step, not five-coordinated PtCl53−.

Synthesis and crystal structure of potassium tetranitrato palladate(II)

Abstract K 2 [Pd(NO 3 ) 4 ] has been prepared and its crystal structure determined by use of a CAD-4 diffractometer with monochromatic Mo Kα radiation. The space group is P 2 1 / c with Z = 4; a= 7.940(2); b = 15.469(4); c = 9.453(2) A; β = 91.10(3)°. The refinement converged to R = 0.023. The structure contains discrete complexes of [Pd(NO 3 ) 4 ] 2− with pseudosymmetry C 4. Pd coordinates four oxygens from different unidentate nitrato groups. The average Pd-O distance is 2.000(7) A. The coordination around Pd is distorted square-planar, with Pd situated 0.139 A above the plane through the four coordinated oxygens. Similar to [Pt(NO 3 ) 4 ] 2− , but in contrast with [Au(NO 3 ) 4 ] − , all four nitrato ligands are situated on the same side of the coordination plane forming a basket-like structure. This is probably due to interactions between the non-coordinated oxygens of the nitrato ligands and suitably located potassium ions. Comparison with the structure of cis -[Pd- (NO 3 ) 2 (DMSO) 2 ] indicates strong ground-state trans - influence of dimethyl sulfoxide in palladium complexes.