Thermal Behaviour of Metal Complexes of 6-(2-Pyridylazo)-3-acetamidophenol

The present work aims chiefly to study the thermal behaviour of complex compounds with general formula: [M(HL)xH₂O](A)yH₂O (where HL=C₁₃H₁₁N₄O₂=6-(2-pyridylazo)-3-acetamidophenol (PAAP), M=Cu(II), Zn(II), Cd(II) and Fe(III) x=1, 3; y=2, 5) while A=CH₃COO^– (Ac), Cl₂. The second formula is [M(H₂L)xH₂O]Cl₂yH₂O, (where H ₂ L=C₁₃H₁₂N₄O₂ (PAAP), M=Ni(II), Co(II) x=3; y=4, 6). The compounds were identified by elemental analysis, FT-IR spectra and TG/DTG,DTA methods. It was found that during the thermal decomposition of complex compounds water molecules of crystallization are released in the first step. In the next step the pyrolysis of organic ligand takes place. Metal oxide remained as a solid product of the thermal decomposition. Mass spectroscopy has been used for the determination of the thermal decomposition on the intermediate products. It was found that the thermal stability of the studied compounds increases as the ionic radii decreases. The activation energy E, the entropy change S ^*, the enthalpy H ^* change and Gibbs free energy change G ^* were calculated from TG curve.This revised version was published online in November 2005 with corrections to the Cover Date.     

Synthesis and characterization of the complexes of lanthanide(III) chlorides and nitrates with the tetradentate schiff base diethyl(ethylenebis-β-aminocrotonate)

Summary The Schiff base ligand diethyl(ethylenebis--aminocrotonate) (LH₂) reacts with lanthanide(III) chlorides and nitrates in various solvents to give solid complexes of the stoichiometriesLn(LH₂)Cl₃ (Ln=La–Yb),Ln(LH₂)₂Cl₃ (Ln=La–Sm),Ln ₂(LH₂)₃Cl₆(Ln=Eu–Yb) andLn(LH₂)(NO₃)₃ (Ln=La–Yb). Properties, conductivity measurements, X-ray powder patterns, thermal data, magnetic moments and spectroscopic (IR,¹H-NMR, electronic diffuse reflectance and solid state emission f-f spectra) are discussed in terms of the nature of the bonding and the possible structural types.

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Synthese und Charakterisierung der Komplexe von Lanthanid(III)chloriden und -nitraten mit der vierzähnigen Schiff-Base Diethyl(ethylenbis--aminocrotonat)

Zusammenfassung Der Schiffbasen-Ligand Diethyl(ethylenbis--aminocrotonat) reagiert mit Lanthanid(III)chloriden und -nitraten in verschiedenen Lösungsmitteln unter der Bildung von festen Komplexen der StöchiometrienLn(LH₂)Cl₃ (Ln = La – Yb),Ln(LH₂)₂Cl₃ (Ln = La – Sm),Ln(LH₂)₃Cl₆ (Ln = Eu – Yb) undLn(LH₂)(NO₃)₃ (Ln = La – Yb). Die allgemeinen Eigenschaften, Leitfähigkeitsmessungen, Röntgen-Pulverdiagramme, thermische Daten, magnetische Momente und spektroskopische Daten (IR,¹H-NMR, Elektronenreflexionsspektren und Festkörperemissions-f-f-Spektren) werden im Hinblick auf die Bildungsverhältnisse im Komplex und strukturelle Möglichkeiten diskutiert.

     

Synthesis of uniform-sized bimetallic iron–nickel phosphide nanorods

We synthesized uniform-sized nanorods of iron–nickel phosphides from the thermal decomposition of metal–phosphine complexes. Uniform-sized (Fe_xNi_1−x)₂P nanorods (0x1) of various compositions were synthesized by thermal decomposition of Ni–trioctylphosphine (TOP) complex and Fe–TOP complex. By measuring magnetic properties, we found that blocking temperature and coercive field depend on Ni content in the nanorods. Both parameters were more sensitive to doping compared with bulk samples.     

Coupling of o and/or m-substituted arylamines with the ortho-C–H function of the pendant aryl ring in coordinated arylazopyrimidinepalladium(II) complexes. Spectral and electrochemical characterisation of the products

2-(Arylazo)pyrimidines (aapm) are N,N-chelators which form palladium(II) complexes, Pd(aapm)Cl₂ (1). The reaction of Pd(aapm)Cl₂ (1) with arylamines (ArNH₂) yields Pd(aapm-N-Ar)Cl, (2)–(7), complexes of the tridentate N,N,N-donor system in which arylamines are fused to the ortho C–H function of the pendant aryl ring in the coordinated 2-(arylazo)pyrimidine, leading to the C–N coupled product. Pd(aapm-N-Ar)Cl, complexes (2)–(7), exhibit a broad intense absorption band in n.i.r. region (870–920 nm), while the parent complex, Pd(aapm)Cl₂, shows an intense absorption at 425 nm. Cyclic voltammograms of (2)–(7) exhibit an oxidation couple at positive potential to s.c.e. together with three reductions at negative side. The oxidation may involve conversion of the chelated azoarylamine to semibenzoquinone azoarylamine fragment. The reduction is due to the accommodation of electrons in the azoimine function. The absorption spectra in the n.i.r. region may be regarded as HOMO LUMO intravalence charge transfer (i.v.c.t.) transitions.     

Synthesis and characterization of some methyl complexes of palladium(II). Part 2(1)

Summary Dichloro complexes of Pd^II, [Pd(L–L)Cl₂], where L–L=1-(thiomethyl)-2-(diphenylarsino)ethane (S–As) or 1-(thiomethyl)-2-(diphenylphosphino)ethane (S–P) andtrans-[PdL₂Cl₂], where L=diphenyl(2-phenylethyl)-phosphine (PE), diphenyl(1-naphthyl)phosphine (PN) orN-methyl-2-thiophenealdimine (SN), have been prepared and characterized. The reactions of these complexes with MeLi were investigated. The dimethyl complexes [Pd(L–L)Me₂] (L–L=S–As, S–P) and [Pd(PE)Me₂] were isolated and characterized. Reaction of [Pd(L–L)Me₂] (L–L=S–As, S–P) with HCl affords the monomethyl derivatives [Pd(L–L)Me(Cl)]. In contrast to the Pt analogues, [Pd(L–L)Me₂] and [Pd(L–L)Me(Cl)] are relatively less stable than [Pt(L–L)Me₂] and [Pt(L–L)Me(Cl)].     

Two-Dimensional Supramolecular from the Self-Assembly of Dissymmetrical Oxamidato-Bridged Heterometallic Trinuclear Building Blocks: Synthesis, Crystal Structure, and Magnetic Properties

Two heterometallic trinuclear complexes {[Cu(oxbp)]₂Co(H₂O)₂}1.5DMF0.5H₂O (complex 1) and {[Cu(oxbm)]₂Co(H₂O)₂}2DMF (complex 2) were obtained from the self-organization of two new dissymmetrical oxamidato-bridged copper(II) building blocks [Cu(oxbp)]^– and [Cu(oxbm)]^–[H₃oxbp=N-benzoato-N'-(3-aminopropyl)oxamido, H₃oxbm=N-benzoato-N'-(2-amino-2-methylethyl)oxamido, DMF=dimethylformamide]. The crystal structure of complex 1 has been determined. Complex 1 crystallize in triclinic system, space group P-1, a=8.0609(16) Å, b=10.661(2) Å, c=22.279(5) Å, =85.32(3), =86.64(3), =70.90(3), and Z=1. The crystal structure of complex 1 consists of neutral trinuclear complex units, and hydrogen bond involved DMF and water molecules. Through the hydrogen bonds, weak coordination and CuCu weak interactions, complex 1 features a 2-D supramolecular structure. Magnetic susceptibility measurements (5–100 K) indicate that the central Co(II) and terminal copper metal ions are antiferromagnetically coupled with J=–28.09 and J=–29.70 cm^–1 for complex 1 and 2, respectively.     

Cesium dimethyltetrachloroplatinate,a complex of dimethylplatinum(IV). Synthesis and some reductive elimination reactions involving the monomethylplatinum(II) complex as an intermediate

The reduction of Pt(IV) complexes followed by the oxidative addition of dimethyl sulfate to Pt(II) affords Cs₂PtMe₂Cl₄, a complex of dimethylplatinum(IV). On treatment with such nucleophiles as Cl^–, Br^–, I^–, and PtCl₄ ^2– in aqueous solutions at 368 K this complex undergoes reductive elimination to give MeX and Pt^IIMe as a transient species. The latter is further converted to methane upon protolysis, whereas in the presence of an oxidant (Na₂PtCl₆) it gives rise to the Pt^IVMe species. The kinetics of decomposition of Cs₂PtMe₂Cl₄ in aqueous HCl-KCl systems (2M or 3M in Cl^–; [Pt^IVMe₂][Cl^–]) were studied. The reaction takes place as anS _N 2 attack of X^– on the carbon atom of a methyl group located with thetrans position with respect to the aqua-ligand of the [PtMe₂Cl₃(H₂O)]^– complex.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 389–395, February, 1993.     

Thermochemical investigation

The stoichiometry of the thermal decomposition and the stereochemistry of the following compounds was studied: NiR₄Cl₂ (I), NiR₄Br₂ (II), NiR₄I₂·2H₂O (III) and NiR₄(NCS)₂ (IV) (R=3-pyridylcarbinol, ronicol). In complexes I and II the loss of the volatile ligands (on the TG curves) occurs in three steps (–2R, –R, –R), in complex III in four steps (–2H₂O, –2R, –R, –R) and in complex (IV) in one step (–4R). According to the quasi-equilibrium decomposition temperatures, the thermodynamic stability of NiR₄X₄ complexes can be ordered in the sequence (according to X):Cl相似文献   

Studies of thermal decomposition of palladium(II) complexes with olefin ligands

Thermal decomposition kinetics of ML₂ (M = Ni(II) and Co(II); L = 5-(2-(1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)hydrazono)-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione) complexes were investigated by thermogravimetric analysis (TGA). The first decomposition process of the NiL₂ and CoL₂ complexes occurs in the temperature range of 320–350 °C. Kinetics parameters corresponding to this step, such as activation energy, E_α, and apparent pre-exponential factor, ln A_aap, were calculated from the thermogravimetric data at the heating rates of 5, 10, 15 and 20 K min⁻¹ by differential (Friedman's equation) and integral (Flynn–Wall–Ozawa's equation) methods. The results show that the activation energy evidently depends on the extent of conversion. As far as their activation energy is concerned, NiL₂ complex shows a higher thermal stability than the CoL₂ complex.     

Thermal Decomposition Kinetics of the Zn(II) Complex with Norfloxacin in Static Air Atmosphere

The thermal decomposition of Zn[NFA]₂5H₂O (NFA=C₁₆H₁₈FN₃O₃, norfloxacin) and its kinetics were studied under non-isothermal conditions in air by TG-DTG and DTA methods. The intermediate and residue for each decomposition were identified from the TG curve. The non-isothermal kinetic data were analyzed by means of the Achar method and the Madhusudanan-Krishnan-Ninan (MKN) method. The possible reaction mechanisms were investigated by comparing the kinetic parameters. The kinetic equation for the second stage can be expressed as d/dt=Aexp(–E/RT)(1–).This revised version was published online in November 2005 with corrections to the Cover Date.     

Preparation,NMR studies and crystal structure of mononuclear and dinuclear Pd(II) and Pt(II) complexes that contain 1,2-bis[3-(3,5-dimethyl-1-pyrazolyl)-2-thiapropyl]benzene

The reaction between 1,2-bis[3-(3,5-dimethyl-1-pyrazolyl)-2-thiapropyl]benzene (bddf) and [MCl₂(CH₃CN)₂] (M = Pd(II), Pt(II)) in a 1:1 M/L ratio in CH₂Cl₂ or acetonitrile solution, respectively, gave the complexes trans-[MCl₂(bddf)] (M = Pd(II) (1), Pt(II) (4)), and in a 2:1 M/L ratio led to [M₂Cl₄(bddf)] (M = Pd(II) (2), Pt(II) (5)). Treatment of 1 and 4 with AgBF₄ and NaBPh₄, respectively, gave the compounds [Pd(bddf)](BF₄)₂ (3) and [Pt(bddf)](BPh₄)₂ (6). When complexes 3 and 6 were heated under reflux in a solution of Et₄NBr in CH₂Cl₂/CH₃OH (1:1) for 24 h, analogous complexes to 1 and 4 with bromides instead of chlorides bonded to the metallic centre were obtained. These complexes were characterised by elemental analyses, conductivity measurements, infrared, ¹H, ¹H{¹⁹⁵Pt}, ¹³C{¹H}, ¹⁹⁵Pt{¹H} NMR, HSQC and NOESY spectroscopies. The X-ray crystal structure of the complex [Pd(bddf)](BF₄)₂ · H₂O has been determined. The metal atom is tetracoordinated by the two azine nitrogen atoms of the pyrazole rings and two thioether groups.     

On the Thermal Decompositions of the Trivalent Trioxalato Complexes of Al, Cr, Mn, Fe and Co

The thermal decompositions of the complexes K₃[M(ox)₃]3H₂O(M=Al, Cr, Mn, Fe, Co; ox=C₂O₄^2–) were studied. Dehydration of the complexes occurs up to 200°C, this being a three-step process for M=Al, Cr, Mn and Co, and a two-step process for M=Fe. Decomposition of the dehydrated complexes proceeds in several steps. For M=Al, Cr and Fe, the decomposition takes place with the evolution of CO, whereas for M=Mn and Co the decomposition of the oxalate ligand yields solid C besides CO. The temperature of CO liberation decreases in the series Cr<Al<Co<Mn<Fe. For M=transition metal, this trend can be explained by the fact that the strength of the C—C bond in the oxalate ligand decreases in the series Cr<Co<Mn<Fe.This revised version was published online in November 2005 with corrections to the Cover Date.     

Mössbauer spectroscopic studies of thermal decomposition of substituted pentacyanoferrate(II) complexes

The thermal behaviour of substituted pentacyanoferrates(II) of the type Na₃[Fe(CN₅)L]·xH₂O, whereL=n-, sec-, tert- oriso-butylamine,di-iso-butylamine ortri-n-butylamine, was investigated with the aid of Mössbauer spectroscopy, XRD and TG-DTG-DTA. The Mössbauer spectra of these complexes exhibit a quadrupole doublet with E _Q=0.70–0.83 mm s^–1 at room temperature. The isomer shift, =0.00±0.03 mm s^–1 suggests that the iron atom is in the +2 low-spin state. The complexes start to decompose at 50°C, yielding a residual mass of 5.8 –21.3% in the temperature range 900–950°C. The Mössbauer spectra recorded after heating at 150 and 300°C exhibit an asymmetric doublet, suggesting partial decomposition. The Mössbauer spectra at higher temperature are complex. At different stages of the thermal process, the presence of -Fe₂O₃, -Fe₂O₃, -Fe, Fe₃C and Fe₃O₄ was demonstrated.On leave from A. N. College, Anandwan-442 914, IndiaWe are grateful to the Monbusho (Ministry of Education, Science, Sports and Culture) for the award of a fellowship to RBL and for financial assistance for the research work. Thanks are also due to Dr. T. Nakamoto for valuable cooperation.     

Interaction Between Pd(RaaiR′)Cl<Subscript>2</Subscript> and Adenine: Reaction Dynamics and Mechanism [RaaiR′ = 1-alkyl-2-(arylazo)imidazole]

Nucleophilic substitution of Pd(RaaiR′)Cl₂ [RaaiR′=1-alkyl-2-(arylazo)imidazole, p-R—C₆H₄— N=N—C₃H₂NN-1-R′; where R= H(a)/Me(b)/Cl(c) and R′ = Et(1)/Bz(2)] with adenine (A) in MeCN–water (1:1) at 298 K, to form [Pd(A)₂]Cl₂, has been studied spectrophotometrically under pseudo-first-order conditions and the analyses support a nucleophilic association path. The reaction follows the rate law, rate = {a+k [A] ₀²[Pd(RaaiR′)Cl₂]: first-order in Pd(RaaiR′)Cl₂ and second-order in A. The rate increases as follows: Pd(RaaiEt)Cl₂(1) < Pd(RaaiBz)Cl₂(2) and Pd(MeaaiR′)Cl₂(b) < Pd(HaaiR′)Cl₂(a) < Pd(ClaaiR′)Cl₂(c). External addition of Cl⁻ (LiCl) suppresses the rate (rate 1/[Cl⁻]). The activation parameters, H⁰ and S⁰ of the reactions were calculated from the Eyring plot and support the proposed mechanism.     

Synthesis and spectroscopic investigations of Rh(III) and Pd(II) complex compounds with N-(pyridine-2-yl)morpholine-4-carbothioamide

The present paper describes the synthesis and spectral properties of Rh(III) and Pd(II) coordination compounds with N-(pyridine-2-yl)morpholine-4-carbothioamide (PMCTA). The compounds have the general composition [RhL₂Cl₂]Cl · C₂H₅OH (1), [PdL₂]Cl₂ (2), [PdL₂](ClO₄)₂ · 2C₃H₆O (2a), [PdLCl₂] · 2H₂O (3). All complexes were characterized by elemental analysis, IR, ¹H NMR, ¹³C NMR, XPS and UV–Vis spectra. It has been shown that PMCTA behaves as a bidentate (N,S)-ligand, forming six membered metallocycles and coordinating to the metal ion through the carbothioamide sulfur atom and the pyridine nitrogen atom. The UV–Vis spectra suggest that the Pd(II) complexes are square planar, while the Rh(III) complex has an octahedral geometry. The molecular structure of the Pd(II) complex with PMCTA (M:L = 1:2) was determined by single-crystal X-ray diffraction.     

Structural studies on 3-acetyl-1,5-diaryl and 3-cyano-1,5-diaryl formazan chelates with cerium(III), thorium(IV) and uranium(VI)

Summary Solid complexes of 3-acetyl-1,5-diaryl and 3-cyano-1,5-diaryl formazans were prepared and characterized by elemental analysis, IR, NMR, TGA and DTA analyses. Based on these studies, the suggested general formula for the complexes is [M(HL) _m (OH^–) _n or (NO ₃ ^– or Cl^–) _x ·(H₂O) _y or (C₂H₅OH orDMSO) _z , where HL=formazanM=Ce³⁺, Th⁴⁺, and UO ₂ ²⁺ ,m=1–2,n=0–3,x=0–3,y=0–4 andz=0–3. The metal ions are expected to have coordination numbers 6–8.

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Strukturuntersuchungen an 3-Acetyl-1,5-diaryl- und 3-Cyan-1,5-diaryl-formazan-Chelaten mit Cer(III), Thorium(IV) und Uran(VI)

Zusammenfassung Die hergestellten Chelate wurden mittels Elementaranalyse, IR, NMR, TGA und DTA charakterisiert. Darauf basierend wird die generelle Formel [M(HL) _m (OH^–) _n bzw. (NO ₃ ^– oder Cl^–) _x ·(H₂O) _y oder (C₂H₅OH bzw.DMSO) _z ] vorgeschlagen, wobei HL=Formazan,M=Ce³⁺, Th⁴⁺ oder UO ₂ ²⁺ ,m=1–2,n=0–3,x=0–3,y=0–4 undz=0–3. Die Metallionen haben Koordinationszahlen von 6–8.

     

Solution equilibria and stability of the complexes of pyridinecarboxylic acids: Complexation reaction of mercury(II) with 2-hydroxynicotinic acid

Summary The solution equilibria of 2-hydroxynicotinic acid (hyna) complexes with mercury(II) have been studied spectrophotometrically in 50% (v/v) ethanol at 20°C and an ionic strength of 0.1mol dm^–3 (NaClO₄). Three mercuric complexes are formed in solution in dependence on the acidity of the medium. The basic characteristics of the different complexes are determined and the analytical aspects of the complexation reaction are demonstrated. A critical investigation has also been presented of the solution equilibria and stability of the mixed complex of mercury(II) withhyna and thiosalicylic acid (tsa). The various complex transitions leading to the formation of the 1 : 1 : 1 Hg(tsa)(hyna) ternary complex in solution are investigated. The non-charged mono-ligand complex Hg(hyna) is used for UV-spectrophotometric determination of mercury atpH 4.5–5 (_max=325nm, =0.8·10⁴lmol^–1cm^–1). The system obeyed Beer's law up to 36.1 µg ml^–1 of Hg(II). The optimum concentration range (Ringbom) is between 6 and 28.5µg ml^–1. Interference caused by a number of ions was masked by the addition of fluoride ions.

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Lösungsgleichgewichte und Stabilitätskonstanten von Komplexen der Pyridincarbonsäuren: Die Komplexierungsreaktion von Quecksilber(II) mit 2-Hydroxynikotinsäure

Zusammenfassung Die Lösungsgleichgewichte von 2-Hydroxynikotinsäure (hyna) mit Hg(II) wurde spektrophotometrisch in 50% (v/v) Ethanol bei 20°C und einer Ionenstärke von 0.1 mol dm^–3 (NaClO₄) untersucht. In Abhängigkeit von der Acidität des Mediums werden drei Quecksilberkomplexe gebildet. Die grundlegenden Charakteristika der Komplexe wurden bestimmt und die analytischen Aspekte aufgezeigt. Die gemischten Komplexe von Hg(II) mithyna und Thiosalicylsäure (tsa), insbesondere die verschiedenen Komplexübergänge zum ternären 1 : 1 : 1 Hg(tsa)(hyna)-Komplex, wurden ebenfalls untersucht. Der ungeladene Monoligandenkomplex Hg(hyna) kann beipH 4.5–5 zur UV-spektroskopischen Quecksilberbestimmung eingesetzt werden (_max=325nm, =0.8·10⁴lmol^–1cm^–1). Das System gehorcht bis zu einer Hg(II)-Konzentration von 36.1µgml^–1 dem Beerschen Gesetz. Der optimale Konzentrationsbereich (Ringbom) liegt zwischen 6 und 28.5µgml^–1. Interferenzen mit einer Reihe anderer Ionen konnten durch Maskierung mit Fluoridionen umgangen werden.

     

Complex formation followed by internal electron transfer: The reaction between cysteine and iron(III)

Summary A kinetic study of the anaerobic oxidation of cysteine (H₂ L) by iron(III) has been performed over thepH-range 2.5 to 12 by use of a stopped-flow high speed spectrophotometric method. Reaction is always preceded by complex formation. Three such reactive complex species have been characterized spectrophotometrically: FeL ⁺ (_max=614 nm, =2 820 M^–1cm^–1); Fe(OH)L (_max=503 nm; shoulder at 575 nm, =1 640 M^–1cm^–1); Fe(OH)L ₂ ^2– (_max=545 nm; shoulder at 445 nm, =3 175 M^–1 cm^–1). Formation constants have been evaluated from the kinetic data: Fe³⁺+L ^2– FeL ⁺: logK ₁ ^M =13.70±0.05; Fe(OH)²⁺+L ^2– Fe(OH)L: logK ₁ ^MOH =10.75±0.02; Fe(OH)L+L ^2– Fe(OH)L ₂ ^2– ; logK ₂ ^MOH =4.76±0.02. Furthermore the hydrolysis constant for iron(III) was also obtained: Fe(OH)²⁺+H⁺ Fe _aq ³⁺ : logK ^FeOH=2.82±0.02). Formation of the mono-cysteine complexes, FeL ⁺ and Fe(OH)L, is via initial reaction of Fe(OH)²⁺ with H₂ L (k=1.14·10⁴M^–1s^–1), the final product depending on thepH. FeL ⁺ (blue) formed at lowpH decomposes following protonation with a second-order rate constant of 1.08·10⁵M^–1s^–1. Fe(OH)L (purple) decomposes with an apparent third order rate constant ofk=3.52·10⁹M^–2s^–1 via 2 Fe(OH)L+H⁺ products, which implies that the actual (bimolecular) reaction involves initial dimer formation. Finally, Fe(OH)L ₂ ^2– (purple) is remarkably stable and requires the presence of Fe(OH)L for electron transfer. A rate constant of 8.36·10³M^–1s^–1 for the reaction between Fe(OH)L and Fe(OH)L ₂ ^2– is evaluated.Dedicated to Prof. Dr. mult. Viktor Gutmann on the occasion of his 70th birthday     

Kinetics and mechanism of electroreduction of Pd(II) complexes

The kinetics and mechanism of processes of reduction of Pd(II) complexes with a number of inorganic (NH₃ , Cl^– , etc.) and organic (ethylenediamine, glycine, -alanine, etc.) ligands on a dropping-mercury electrode and a Pd electrode in solutions with various concentrations of ligands, hydrogen ions, and supporting electrolytes are reviewed. The nature of electrochemical and chemical steps of processes of reduction of various complexes of Pd(II) is discussed.Translated from Elektrokhimiya, Vol. 40, No. 12, 2004, pp. 1494–1502.Original Russian Text Copyright © 2004 by Kravtsov.     

Hydrolysis of cis- and trans-Diammineplatinum(II) Complexes: Hydration, Equilibrium, and Kinetics Properties

We have used a combination of ultrasound and density techniques to measure the hydration parameters, apparent molar volume, and apparent molar adiabatic compressibility, of the antitumor drug cis-dichlorodiammineplatinum(II), cis-[Pt(NH₃)₂Cl₂], and its inactive isomer trans-dichlorodiammineplatinum(II), trans-[Pt(NH₃)₂Cl₂], in 10 mM NaNO₃, pH 5.6 at 37°C. The data have been interpreted in terms of the overall hydration of each isomer, the actual hydration contribution to the adiabatic compressibility, K _h, ranges from –56.4 × 10^–4 to –20.3 × 10^–4 cm³-mol^–1-bar^–1, and the volume contribution, V _h, ranges from –16.3 to –6.4 cm³-mol^–1. The negative signs of these hydration contributions indicate that the volume and compressibility of the water immobilized by the platinum complexes is smaller than the volume and compressibility of bulk water. The V _h and K _h parameters for all platinum complexes investigated are linearly dependent on the relative amount of hydrolyzed chlorides. The values of each parameter become more negative with increasing hydrolysis, and show that the degree of hydration increases. The similar dependence of the amount of hydrolyzed chloride ligands reveals similar hydration properties for these two complexes. Thus, the symmetry of the complexes, which is of crucial importance for anticancer activity, has no influence on their hydration properties. Under our experimental conditions, the equilibrium constants for the hydrolysis of cis-[Pt(NH₃)₂Cl₂] are K ₁ = 2.52 mM and K ₂ = 0.04 mM. The equilibrium constant for the first step of hydrolysis of trans-[Pt(NH₃)₂Cl₂] is 0.03 mM, while the second chloride ligand cannot be substituted by water, even in the irreversible reaction with AgNO₃. Furthermore, continuous measurements of the ultrasonic velocity during hydrolysis permits the accurate evaluation of the pseudo-first-order rate constant k ₁ for the hydrolysis of the first chloride ligand of cis-[Pt(NH₃)₂Cl₂], which is 16±1×10^–5 s^–1.