Thermodynamics of complexation of zinc(II) with chloride,bromide and iodide ions in hexamethylphosphoric triamide

The complexation of zinc(II) with chloride, bromide and iodide ions has been studied by calorimetry in hexamethylphosphoric triamide (HMPA) containing 0.1 mol-dm^–3 (n-C₄H₉)₄NClO₄ as a constant ionic medium at 25°C. The formation of [ZnX_n]^(2–n)+ (n=1,2,3,4 for X=Cl; n=1,2 for X=Br, I) is revealed, and their formation constants, enthalpies and entropies were determined. It is proposed that the zinc(II) ion is fourcoordinated in HMPA and the coordinating HMPA molecules are stepwise replaced with halide ions to form [ZnX_n(hmpa)_4–n]^(2–n)+ (n=1–4), as is the case for the cobalt(II) ion. Furthermore, the formation of [ZnClI], [ZnBrI], [ZnBrCl] and [ZnBrCl₂]^– is revealed in the relevant ternary systems. It is found that the affinity of a given halide ion X^– to [ZnCl]⁺, [ZnBr]⁺ and [Znl]⁺ is practically the same.     

Transition metal chemistry of oxime-containing ligands,part XI. Copper(II) complexes of syn-phenyl-2-pyridylketoxime and syn-methyl-2-pyridylketoxime

Summary Some copper(II) complexes of the types: Cu(HPPK)-(PPK)X, Cu(HMPK)(MPK)X (where HPPK = syn-phenyl-2-pyridylketoxime, HMPK = syn-methyl-2-pyridylketoxime and X = Cl^–, Br^–, I^–, NO₃ ^–, SCN^– or SeCN^–) Cu(HPPK)₂SO₄ 3 H₂O and Cu(HMPK)₂SO₄ · 3 H₂O were synthesized and characterized by analysis, magnetic susceptibility, e.s.r., reflectance and i.r. spectral measurements. The spectral data suggest that Cu(HPPK)(PPK)X and Cu(HMPK)(MPK)X containcis square-coplanar [Cu(HPPK)(PPK)]⁺ and [Cu(HMPK)(MPK)]⁺ units respectively, linked by weakly coordinated anions, giving infinite polymeric highly distorted octahedral chain structures, whereas Cu(HPPK)₂SO₄ · 3H₂O and Cu(HMPK)₂SO₄ · 3 H₂O have acis distorted octahedral structure containing two ligand molecules of ketoxime and a bidentate sulphate group. The polycrystalline e.s.r. spectra suggest a distorted octahedral stereochemistry for the Cu^II ion involving a ground-state. By using e.s.r. and reflectance spectral data, the orbital reduction parameters, k₁₁ and k₁ were calculated and interpreted in terms of molecular orbital coefficients.     

Osmotic coefficients of dilute aqueous solutions of unsymmetrical cobalt-amine type salts at 0°C

The osmotic coefficients of dilute aqueous solutions of [Co(pn)₃]X₃ [pn=1,2-diaminopropane and X=Cl^–, Br^– and (NO₃)^–] and [Co(tn)₃]X₃ (tn=1,3-diaminopropane and X=Cl^– and Br^–) have been measured from 0.00 to 0.02 mol-kg^–1 at 0°C by the freezing point method. The results have been compared with those obtained from the numerical integration of the Poisson-Boltzmann equation.     

Synthesis of Silver Complexes in DMSO–HX and DMSO–HX–Ketone Systems

Comparative analysis of the oxidizing and complexing properties of the DMSO–HX (X = Cl, Br, I) and DMSO–HX–ketone (X = Br, I; the ketone is acetone, acetylacetone, or acetophenone) systems toward silver was performed. The reaction products are AgX (X = Cl, Br, I), [Me₃S⁺]Ag _n X^– _m (n= 1, 2; m= 2, 3; X = Br, I) and [Me₂S⁺CH₂COR]AgX^– ₂(R = Me, Ph; X = Br, I). The composition of the obtained complexes depends on both the DMSO : HX ratio and the nature of HX, as well as on the methods used to isolate solid products from the solution. It was noted that the formation of the [Me₂S⁺CH₂COMe]AgBr^– ₂complex in the Ag⁰–DMSO–HBr–acetylacetone system occurs with cleavage of the acetylacetone C–C bond and follows a specific reaction course. The optimum conditions for production of the silver compounds in the title systems are determined.     

Structural studies of diamine complexes of cobalt(II) and nickel(II) thiocyanates and selenocyanates

Summary Complexes of the types ML₂X₂ [M = cobalt(II) or nickel(II); L = hydrazine, ethylenediamine (en) or o-phenylenediamine (opd) and X = SCN^– or SeCN^–] and NiL₂(NCS)₂MCl₂ [M = cadmium(II) or mercury(II)] have been prepared and characterised by elemental analysis, molar conductance, molecular weight determination, magnetic susceptibility, electronic and i.r. spectral measurements.     

Kinetics of reactions of N1-phenylbiguanidine with CeIV and [MnO4]− in aqueous sulphuric acid media

Summary In the title reaction each mole of N¹-phenylbiguanidine, R–HNC(=X)NHC(=NH)NH₂ (R=Ph, X=NH), consumes 4 moles of Ce^IV and produces guanylurea (R=H, X=O), 1,4-benzoquinone and ammonia. On the other hand, the reaction of N¹-phenylbiguanidine (pbg) with [MnO₄]^– proceeds with variable stoicheiometry which depends on reaction conditions. In the case of [MnO₄]^– no benzoquinone is detected among the reaction products; instead, carbon dioxide, guanylurea, and ammonia were identified. Pbg itself in acid solution slowly hydrolyses to aniline which rapidly reacts with Ce^IV and [MnO₄]^–. The kinetics for the reactions of pbg with the oxidants is consistent with the rate law –d[oxidant]/dt=k[pbg].The k values and the corresponding activation enthalpies and entropies for the reaction of bpg with Ce^IV, [MnO₄]^–, and Cr^VI lie within a narrow range. These results are interpreted in terms of rate-determining hydrolysis of pbg in all the three cases.     

Coordination chemistry of poly(1-pyrazolyl)alkanes,part IV. Copper(II) complexes of bis- and tris-(1-pyrazolyl)methane

Summary The reactions of some copper(II) salts with bis(1-pyrazolyl)methane, H₂Cbpz, bis(3,5-dimethylpyrazolyl)methane, H₂Cbdmpz, and tris(1-pyrazolyl)methane, HCtpz give the following solid complexes: CuLX₂ · nH₂O (L=H₂Cbpz, H₂Cbdmpz or HCtpz; X=Cl^–, Br^–, NO ₃ ^– , OAc^–, or 1/2 SO ₄ ^2– and n=0, 1, 3 or 5) and CuL₂X₂ · nH₂O (L=HCtpz, X= C^–, Br^–, NO ₃ ^– or ClO ₄ ^– and n=0 or 2). The complexes have been characterised by elemental analysis, visible and i.r. spectral measurements.The reactions of Cu(HCtpz)X₂ · nH₂O (X=Cl^– or Br^–) with acetylacetonate (acac^–), dialkyldithiocarbamate (S₂CNMe ₂ ^– , S₂CNEt ₂ ^– ) or poly(1-pyrazolyl)borate (H₂Bbpz^–, HBtpz^–) in aqueous solutions lead to the displacement of HCtpz and the subsequent formation of neutral [Cu(acac)₂], [Cu(S₂CNR₂)₂], [Cu(H₂Bbpz)₂] and Cu(HBtpz)₂ while the reaction with oxalate ion, C₂O ₄ ^2– yields a stable neutral solid compound, [Cu(HCtpz)(C₂O₄)].     

Pyrolysis of eicosane in supercritical water

Pyrolysis of eicosane and redox reactions of the pyrolysis products in supercritical water (SCW) were studied in a batch reactor at 30 MPa, in the temperature range from 450 to 750 °C and with reaction times ranging from 75 to 600 s. The rate constants for eicosane pyrolysis (k" = 10^16.5±0.5exp[–(32000±2000)/T] s^–1) and for the formation of H₂ (k = 10^25±0.8exp[–(64000±4000)/T] s^–1) were determined. The time and temperature dependences of the heat of reaction were elucidated. Water accelerates pyrolysis and participates in the subsequent transformations of the pyrolysis products. The yield of H₂ sharply increases for T > 700 °C.     

Preparation and characterisation of copper(II) complexes with bis(1-pyrazolyl)propane

Summary The synthesis and characterisation of the coordination compounds of some copper(II) salts with bis (1-pyrazolyl)propane, Me₂Cpz₂, are reported. Coloured stable solid complexes of the type Cu(Me₂Cpz₂) X₂(X = Cl^–, Br^– or AcO^–), Cu(Me₂Cpz₂)(ClO₄)₂ · H₂O, [Cu(Me₂Cpz₂)SO₄ · 2 H₂O] · H₂O and [Cu(Me₂Cpz₂)₂X]X (X = NO ₃ ^– or ClO ₄ ^– ) have been isolated and characterised by elemental analysis, electronic, i.r. and magnetic measurements. Probable structures of the complexes are discussed on the basis of their spectral data.     

Thermally induced solid-state isomerisation and decomposition of 2,2-dimethyl-1,3-propanediamine nikel(II) complexes

Summary Complexes [NiL₃]Br₂·H₂O (L=2,2-dimethyl-1,3-propanediamine), [NiL₂X₂] (X=Cl, Br, NCS, CF₃CO₂, HCCl₂CO₂ or CCl₃CO₂ and X₂=SO₄ or SeO₄) and [NiL(HCCl₂CO₂)₂]·H₂O have been synthesised and their thermal studies have been investigated in the solid state. The complexes, [NiL₂X₂] (X=Cl or Br) and NiLX₂ (X=Cl or HCCl₂CO₂) have been isolated thermally in the solid state. All the complexes possess octahedral geometry. [NiL₂Br₂] and [NiL₂(CF₃CO₂)₂] exist in two interconvertible isomeric forms. H for the conversions were determined. [NiL₂(HCCl₂CO₂)₂] (5) undergoes an irreversible phase transition (178–188°C; H=4.4kJ mol^–1]. NiL(HCCl₂CO₂)₂·H₂O shows an exothermic irreversible phase transition (104–128°C; H=–5.8 kJ mol^–1) after losing water. The phase transitions are assumed to be due to the conformational changes in the chelate ring of diamine.     

Mechanistic aspects of the reduction of ruthenium(III) catalyzed

The kinetics of Ru_III catalyzed reduction of hexacyanoferrate(III) [Fe(CN)₆]^3–, by atenolol in alkaline medium at constant ionic strength (0.80 mol dm^–3) has been studied spectrophotometrically, using a rapid kinetic accessory. The reaction between atenolol and [Fe(CN)₆]^3– in alkaline medium exhibits 1:2 stoichiometry [atenolol:Fe(CN)₆ ^3–]. The reaction showed first order kinetics in [Fe(CN)₆]^3– concentration and apparent less than unit order dependence, each in atenolol and alkali concentrations. Effect of added products, ionic strength and dielectric constant of the reaction medium have been investigated. A retarding effect was observed by one of the products i.e., hexacyanoferrate(II). The main products were identified by i.r., n.m.r., fluorimetric and mass spectral studies. A mechanism involving the formation of a complex between the atenolol and the hydroxylated species of ruthenium(III) has been proposed. The active species of oxidant and catalyst were [Fe(CN)₆]^3–and [Ru (H₂O)₅OH]²⁺, respectively. The reaction constants involved in the mechanism were evaluated. The activation parameters were computed with respect to the slow step of the mechanism, and discussed.     

Structural and energetic aspects of hydrogen bonding and proton transfer to ReH2(CO)(NO)(PR3)2 and ReHCl(CO)(NO)(PMe3)2 by IR and X-ray studies

The interaction of rhenium hydrides ReHX(CO)(NO)(PR₃)₂ 1 (X=H, R=Me (a), Et (b), iPr (c); X=Cl, R=Me (d)) with a series of proton donors (indole, phenols, fluorinated alcohols, trifluoroacetic acid) was studied by variable temperature IR spectroscopy. The conditions governing the hydrogen bonding ReHHX in solution and in the solid state (IR, X-ray) were elucidated. Spectroscopic and thermodynamic characteristics (−ΔH=2.3–6.1 kcal mol⁻¹) of these hydrogen bonded complexes were obtained. IR spectral evidence that hydrogen bonding with hydride atom precedes proton transfer and the dihydrogen complex formation was found. Hydrogen bonded complex of ReH₂(CO)(NO)(PMe₃)₂ with indole (2a–indole) and organyloxy-complex ReH(OC₆H₄NO₂)(CO)(NO)(PMe₃)₂ (5a) were characterized by single-crystal X-ray diffraction. A short NHHRe (1.79(5) Å) distance was found in the 2a–indole complex, where the indole molecule lies in the plane of the Re(NO)(CO) fragment (with dihedral angle between the planes 0.01°).     

Cobalt(II), nickel(II) and copper(II) complexes of syn-2-picolyl phenyl and syn-2-quinaldyl phenyl ketoximes

Summary The syn-2-picolyl phenyl ketoxime (HL₁) and the syn-2-quinaldyl phenyl ketoxime (HL₂) give [M(HL)LX], [M(HL)₂X₂] and [ML] solid complexes (M=Co, Ni and Cu; X=Cl^–, Br^– and NO ₃ ^– which have been characterized by elemental analysis, room temperature magnetic moments and electronic and i.r. spectral measurements.     

Copper(I) and copper(II) complexes of diamino-dithioether ligands

Summary Copper(II) salts were reacted with two diamino-dithioether ligands, i.e. 1,3-di(o-aminophenylthio)propane (abbreviated H₂L¹) and 1,2-di(o-aminophenylthio)xylene (abbreviated H₂L²). Mixtures of copper(I) and copper(II) complexes were obtained with Cl^– and ClO ₄ ^– counterions. The major products were the copper(I) complexes, which were obtained pure after recrystallisation from MeCN-MeOH. The ligands lose two protons from the amine functions to form copper(I) complexes of general formula [CuL]X, where X = ClO ₄ ^– or Cl^–. The complexes were oxidised to [CuL]X₂ with H₂O₂ in DMF. Cu(NO₃)₂ on the other hand gave [CuH₂LNO₃]NO₃.     

Salt effects on the protonation of imidazole in aqueous solution at different ionic strengths: A tentative explanation by a complex formation model

Imidazole protonation constants were determined potentiometrically, using a (H⁺)-glass electrode, in LiCl, NaCl, KCl, CaCl₂, MgCl₂, tetramethylammonium (Me₄N-) iodide and chloride, Et₄N-, Pr₄N- and Bu₄N-iodides. Salt effects were tentatively explained by assuming that complexes [H(Im)X]^o (Im = imidazole, X^–=Cl^– or I^–), [M(Im)]²⁺ (M²⁺=Mg²⁺ or Ca²⁺) and [A(Im)]⁺ (A⁺ = tetraalkylammonium cation) were formed in solution. Calcium(II)-selective electrode measurements confirmed our hypothesis about the formation of the Ca²⁺-imidazole complex. The reliability of the complex formation model is discussed on the basis of its self consistency and in light of previous results.     

Kinetics and mechanisms of oxidation by metalions. Part XI(1). Kinetics of the osmium(VIII)-catalysed oxidation of glycols by alkaline hexacyanoferrate(III)

Summary The kinetics of the Os^VIII-catalysed oxidation of glycols by alkaline hexacyanoferrate(III) ion exhibits zerothorder dependence in [Fe(CN) ₆ ^3– ] and first-order dependence in [OsO₄]. The order with respect to glycols is less than unity, whereas the rate dependence on [OH^–] is a combination of two rate constants; one independent of and the other first-order in [OH^–]. These observations are commensurate with a mechanism in which two complexes, [OsO₄(H₂O)G]^– and [OsO₄(OH)G]^2–, are formed either from [OsO₄(H₂O)(OH)]^– or [OsO₄(OH)₂]^2– and the glycol GH, or by [OsO₄(H₂O)₂] and [OsO₄(H₂O)(OH)]^– and the glycolate ion, G^–, which is in equilibrium with the glycol GH through the reaction between GH and OH^–. Hence there is an ambiguity about the true path for the formation of the two Os^VIII-glycol complexes. A reversal in the reactivity order of glycols in the two rate-determining steps, despite the common attack of OH^– ion on the two species of Os^VIII-complexes, indicates that the two complexes are structurally different because S changes from the negative (corresponding to k₁₁) to positive (related to k₂).     

The base hydrolysis ofmer-[Co(1,5-diamino-3-azapentane)(amino acidate)X]+ (X = Cl or NO2) complexes and base hydrolysis of complexed peptides in the coordination sphere of the [Co(dien)]3+ moiety

Summary A variety ofmer-[Co(dien)(AA)X]⁺ (AA = amino acidate, dien = 1,5-diamino-3-azapentane) andmer-[Co(dien)(dipeptideOR)X]²⁺ complexes (X = Cl or NO₂) have been prepared and characterised. Base hydrolysis of the peptide bond in the carbonyl bonded glycyl peptides has been studied at 25°C and I = 0.1 mol dm^–3. The rate constants k_OH for peptide bond hydrolysis fall within the 0.67–0.88 mol dm^–3s^–1 range. Base hydrolysis of the complexed peptide isca. 2×10⁴ times faster than for the uncomplexed peptide ligand at 25 °C. The base hydrolysis of the chloro- and nitro-ligands in these complexes has also been studied. Very rapid hydrolysis occurs if the dien ligand adopts amer-configuration and the reactions are 10²–10⁴ times faster than for analogous complexes where the dien ligand adopts afac-configuration. These results are in agreement with Tobe's criteria for rapid base hydrolysis in cobalt(III) complexes.The following abbreviations are used thoughout this paper; dien 1,5-diamino-3-azapentane - dpt 1,7-diamino-4-azaheptane - glyO glycinate - glyOH glycine - glyOR glycine ester - glyNH₂ glycine amide - glyglyO glycylglycinate - glyglyOR glycylglycine ester - glyglyglyOH triglycine - -alaO -alaninate     

Synthesis,characterisation and solid state thermal behaviour of nickel(II) diamine complexes

Summary [NiL₂X₂] (L =N,N-dimethyl-1,2-ethanediamine; X = Cl^–, CF₃CO ₂ ^– , CC1₃CO ₂ ^– and CBr₃CO ₂ ^– ), [NiL₂C₂O₄] · H₂O and [NiL₂X₂] · 2 H₂O (X = Br^–, 0.5 SO ₄ ^2– and 0.5 SeO ₄ ^– ) have been synthesised and their thermal studies carried out. Thermally induced phase transition phenomena are noticed in [NiL₂X₂] (X = CF₃CO ₂ ^– and CCl₃CO ₂ ^– ) and their probable mechanisms are described. [NiL₂X₂] (X = Br^–, 0.5 SO ₄ ^2– and 0.5 SeO ₄ ^2– ) and [NiLX₂] (X = Cl^–, 0.5 C₂O ₄ ^2– and 0.5 SO ₄ ^2– ) have been prepared by solid state pyrolysis from the respective parent diamine complexes. [NiL₂X₂] have been made in solid state by temperature arrest technique from [NiL₂(CX₃CO₂)₂] (X = Cl^– and Br^–).     

Kinetics of tetraamminecopper(II)-catalysed oxidation of sulphur(IV) by peroxodisulphate in ammonia buffer

The kinetics of tetraamminecopper(II)-catalysed oxidation of SO^2– ₃ to SO^2– ₄ in ammonia buffers and in a nitrogen atmosphere obeys the rate law: –d[S^IV]/dt = k ₂[Cu^II][SO₃ ^2–][NH₃]^–1. There is spectrophotometric evidence for the formation of the intermediate complex [Cu(NH₃)₃(SO₃)] in a pre-equilibrium.     

Kinetics and mechanism of ligand substitution of mono(polyamine)-nickel(II) complexes with 4-(2-pyridylazo)resorcinol

Summary The kinetics and mechanism of ligand substitution reactions of tetraethylenepentamine nickel(II), Ni (Teren), and triethylenetetraamine nickel(II), Ni(Trien), with 4-(2-pyridylazo)resorcinol (parH₂) have been studied spectrophotometrically at I=0.1 M (NaClO₄) at 25°C. In both systems two distinct reaction steps are observed. The rapid first step follows the rate law d[Ni(Polyamine)(ParH₂)]/dt=k₁ [Ni(Polyamine)] [ParH₂]. The formation of ternary complexes of Ni (Polyamine) with ParH₂ has been investigated under second order equal concentration conditions. The values of second order rate constants for the Trien and Teren reactions are (2.1±0.2)×10⁴ M^–1s^–1 and (7.8±0.6)×10³ M^–1s^–1 respectively at pH=9.0, I=0.1 M and 25°C.The rate law for the second step may be written as d[Ni(Par)₂]/dt=k₂[Ni(Polyamine)(ParH₂)]. Values of k₂ for the Trien and Teren systems are (2.5±0.1)×10^–4 s^–1 and (4.76±0.3)×10^–5 s^–1 respectively.