Cyclic and open-chain tautomerism and complex formation behaviour of the condensation product of 2-amino-3-aminomethyl-4- methoxymethyl-6-methylpyridine with salicylaldehyde

The crystalline product obtained by the condensation of 2-amino-3-aminomethyl-4-methoxymethyl-6-methylpyridine and salicylaldehyde was characterized by spectrometric methods (UV, IR, ¹H NMR and MS). It was shown that the dissolution of the crystalline cyclic diamine afforded its tautomeric conversion to the enolimine form of the Schiff base [2-amino-4-methoxymethyl-6-methyl-3(salicylideneaminomethyl) pyridine] with a rate of the process and a ratio of both forms attained at equilibrium dependent upon the solvent. The presence of the ketoamine form was not evidenced. The behaviour of the condensation product as the ligand in formation of complexes with Cu(II), Ni(II), Co(II) and Cd(II) was investigated in methanolic solution. Coordination with Cu(II) and Ni(II) caused partial hydrolysis of the ligand and the formation of complexes of the bis Schiff base [4-methoxymethyl-6-methyl-2-(salicylideneamino)-3-(salicylideneaminomethyl)pyridine] characterized after their isolation by elemental analyses and spectrometric data.     

A potentiometric study on the complex equilibria between nickel(II) and 2-mercapto-2-phenylacetic acid

Complex formation between nickel(II) and 2-mercapto-2-phenylacetic acid (H₂MPA) has been studied at 25°C and 1 mol dm^?3 ClO₄^? in     

Adduct formation of copper(II) chelates of 1-hydroxypyrazole 2-oxides with substituted pyridines

Equilibrium constants have been determined for the adduct formation of 10 copper(II) chelates of the derivatives of 1-hydroxypyrazole 2-oxide with nine substituted pyridines at room temperature in chloroform solution. These adducts were shown to have 1:1 stoichiometry. All the stabilities of the adducts were governed by: (1) σ-donating ability of the nitrogen atom in the substituted pyridines to the copper(II) chelates, (2) electron-attracting forces of substituents at the 3- and 4-positions of the phenyl ring in the chelate ligands, and (3) the magnitude of the polar substituent constant of the substituents in the pyrazole ring of the chelate ligands.     

A potentiometric study on complex formation of cadmium(II) ion with 2-mercaptoacetic and 2-mercaptopropionic acids

Complex equilibria between cadmium ions and 2-mercaptoacetic acid (H₂maa) or 2-mercaptopropionic acid (H₂mpa) have been studied in aqueous solutions containing 3 mol dm^?3 LiClO₄ as a constant ionic medium at 25°C by potentiometric titration. Formation constants of mono-η and bis-2-mercaptoalkanoato)cadmium complexes were found to ge log K₁₁ = 4.34 and log K₁₂ = 2.15 for the cadmium-H₂maa complexes, and log K₁₁ = 5.66 and log K₁₂ = 2.85 for the cadmium-H₂mpa complexes, respectively. The protonated complexes, CdHmaa⁺ and CdHmpa⁺, and a mixed ligand complex, Cd(maa)(mpa)²- were also detected.     

Palladium(II) halide complexes with 2,5-dimethyl-, 2-amino-, 2-amino-5-methyl-, 2-ethylamino- and 2-mercapto-5-methyl-1,3,4-thiadiazole

Some palladium(II) halide complexes with 2,5-dimethyl- (DTZ), 2-amino- (ATZ), 2-amino-5-methyl- (MATZ), 2-ethylamino- (EATZ) and 2-mercapto-5-methyl-1,3,4-thiadiazole (MTTZ) have been prepared and studied: PdX₂ · 2L (L = DTZ, ATZ, MATZ : X = Cl, Br, I; L = EATZ: X = Br, I; L = MTTZ: X = I), PdCl₂ · 2.5EATZ, PdCl₂ · 3MTTZ, PdBr₂ · 1.5MTTZ and PdX₂ · L (L = DTZ, ATZ, MATZ, EATZ: X = Cl, Br; L = MTTZ: X = Cl(H₂O), Br). In the PdX₂ · 2L, PdCl₂ · 2.5EATZ and PdCl₂ · 3MTTZ complexes the palladium ions are cis-(2X, 2L)-coordinated, the coordination sites being N_ring for DTZ, NR₂ for ATZ, MATZ, EATZ and C = S for MTTZ. PdBr₂ · 1.5MTTZ may be formulated as cis[PdBr₂-2L] · [PdBr₂ · L]. In the PdX₂ · L complexes the ligand very likely acts as bidentate by using a ring-nitrogen atom as the second coordination site.     

A spectrophotometric investigation into the complex formation between bismuth(III) and 2-mercaptoethanol in aqueous solution

Complex formation between bismuth(III) and 2-mercaptoethanol was studied at 25°C and I = 1.0 mol dm^?3 HClO₄. The results were used to test the validity of an empirical equation for the calculation of formation constants.     

Metal complexes of 2-(2′-carboxymethylthio-phenylazo)-5-nitrotoluene—II. Complex formation equilibria with copper(II) ion in several dioxane—water solvent mixtures

Stability constants of copper(II) complexes formed by 2-(2′-carboxymethyl-thiophenylazo)-5-nitrotoluene in dioxane—water solvent mixtures of several different compositions [50, 60 and 75% dioxane (v/v)] were determined from EMF measurements, at 25°C and 0.1 mol dm^?3 NAClO₄ ionic medium. Graphical treatment of experimental data gives for the equilibria nA^?+Cu²⁺ = CuA_n^(2-n)+ (n = 1 or 2), in a solvent with X% (v/v) dioxane, the following values of log β₁, and log β₂ (given here successively). X = 50:2.41, 6.77; X = 60:3.36, 7.45; X = 75:4.33, 7.64. The relation between solvent composition and the values found for the stability constants is discussed. From EMF measurements made with the copper(II) ion-selective electrode, at constant pH, the nature of the effective donor groups in this potentially terdentate ligand is inferred.     

Copper(I) and silver(I) complexes of 2-amino-1,3,4-thiadiazole and 2-ethylamino-1,3,4-thiadiazole

The following copper(I) and silver(I) complexes of 2-amino-1,3,4-thiadiazole (atz) and 2-ethylamino-1,3,4-thiadiazole (eatz) have been prepared and studied by conductometric, IR and Raman methods: CuXL(X = Cl, Br, I; L = atz, eatz), CuXL₃(X = ClO₄, NO₃; L = atz, eatz), AgClO₄·1.5atz·1/3 EtOH, AgNO₃·2.5atz, AgClO₄·3eatz, AgNO₃·eatz. The ligands are bonded through the amine nitrogen atoms with ν(MN) bands in the 520–410 cm^?1 region. The CuXL complexes have a trigonal (N, 2X_b) coordination with a probable weaker axial interaction. The CuXL₃ and AgCIO₄·3eatz complexes probably have a trigonal pyramidal (3N,O) coordination. In the atz complexes of silver perchlorate and nitrate some ligand molecules are bridging. The AgNO₃·2.5atz complex is likely to have a dimeric structure with tetrahedral coordination of the silver ion.     

Metal complexes of pyrimidine-derived ligands—IV. synthesis,characterisation and coordinating properties of two guanidino pyrimidines: Ni(II) complexes with 2-guanidino-4,6-dimethyl pyrimidine and 2-phenyl guanidino-4,6-dimethyl pyrimidine—potential ligands or biological interest

Synthesis and spectroscopic characterisation (IR, mass, PMR) of 2-guanidino 4,6-dimethyl pyrimidine (GPym) and 2-phenyl guanidino 4,6-dimethyl pyrimidine (PG-Pym) are reported. Complexation of the title ligands with nickel(II) salts in moisture-free condition furnish complex species of the type: Ni(GPym)₂X₂[X = Cl, Br, SCN and NO₃] and Ni(PGPym)₂X₂ [X = Cl, Br, I and SCN]. Physico-chemical characterisation of the complex species have been made from molar conductance data, magnetic susceptibility measurements, electronic and vibrational spectra. Magnetic and electronic spectral features suggest a pseudo-octahedral environment of the central Ni(II) ion in all these complexes. IR spectra have furnished positive information regarding the bonding sites of the ligand molecules (namely, the pyrimidyl nitrogen and the imino nitrogen of the guanidine residue) and the mode of the attachment of the counterion(X) to the metal ion.     

Equilibrium and kinetic studies of the Fe(III) complex formation with glycinehydroxamic acid

Spectrophotometric methods were utilized for stability constant determinations of the Fe(III) interaction with glycinehydroxamic acid (GX) at I = 0.15 M NACl and T = 25°C. Program SQUAD II was used to assess the absorbance data in the wavelength range 300–520 nm. Four constants were determined for 1:1:1, 1:1:0, 2:1:1 or 3:1:3 and 2:1:0 complex species in the pH range 1.0–7.5. The kinetics of the interactions of Fe(III) with GX were also studied in the pH range 1.0–3.0 by the stopped flow method. The observed rate constant at a given pH was k_obs = _A + BT_GX. The parameters A and B are functions of pH in the range 1.7–3.0 and only A is a function of pH in the range 1.0–1.7. The mechanism of complex formation was discussed in the light of the experimental results and the equilibrium study. It has been concluded that FeOH²⁺ is the reactive species in the complex formation of FeGXH³⁺ species while Fe(OH)₂⁺ is the reactive species in the complex formation of FeGX²⁺ species.     

Zinc(II), cadmium(II) and mercury(II) complexes of 4,6-dimethyl-pyrimidine-2(1H)-one

The following zinc(II), cadmium(II) and mercury(II) complexes of 4,6-dimethylpyrimidine-2(1H)-one (L) have been prepared and investigated by conductometric,IR and Raman methods: MX₂L₂ (M = Zn, X = Cl, Br(CHCl₃, I(CHCl₃, CF₃COO; M = Cd, X = Cl, Br CF₃COO; M = Hg, X = Cl, CF₃COO), Cd₂I₄L₃, Hg₃X₆L₂ (X = Cl, Br), Hg₃X₆L₄(X = Br, I), MX₂L₄·6H₂O (M = Zn, Cd, X = CIO₄, BF₄; M = Hg, X = CIO₄. The ligand is principally bonded through the unprotonated nitrogen atom and in some complexes also through the carbonylic oxygen atom. The zinc halide complexes are tetrahedrally coordinated, the trifluoroacetate ion is coordinated as a monodentate ligand.     

Preparation and characterization of tetrahalodimolybdenum(II) complexes with alkyl-substituted pyridines

The preparation and characterization of new tetrahalodimolybdenum(II) complexes with alkyl-substituted pyridines is described. IR and visible data are used to infer structural information with respect to previously prepared complexes of this type.     

Quaternary liquid-liquid equilibria: Experimental determination and correlation of equilibrium data. Part III. New methods of representation and correlation of liquid-liquid equilibria in quaternary systems

Part III of this work describes two new methods of representation and correlation of liquid-liquid equilibria in quaternary systems. These methods are appropiate for the interpolation of new nonexperimental equilibrium data. The methods suggested are applied to the quaternary systems presented in Parts I and II of this series (Ruiz and Prats, 1982a,b).     

Rhodium(I) complexes with pyridazine, 4,6-dimethyl-pyrimidine, 4,6-bis(3,5-dimethylpyrazol-1-yl)pyrimidine, 3,6-bis(3,5-dimethylpyrazol-1-yl)pyridazine and 3-(3,5-dimethylpyrazol-1-yl)-6-chloropyridazine

The synthesis and properties of rhodium(I) complexes of formulae [“RhCl(diolefin)”₂(L)] (or [Rh(Cl(diolefin)(L)]), and [Rh(diolefin)(L)]_n(ClO₄)_n are reported. These complexes react with carbon monoxide to yield the related carbonyl derivatives. Ligands used were pyridazine, 4,6-dimethyl-pyrimidine, 4,6-bis(3,5-dimethylpyrazol-1-yl)pyrimidine, 3,6-bis(3,5-dimethylpyrazol-1-yl)pyridazine and 3-(3,5-dimethyl-pyrazol-1-yl)-6-chloropyridazine. Related iridium(I) and gold(I) compounds are also reported.     

Kinetic and competition studies of substitution reactions of the trans-aquosulphitotetracyanocobalt complex,Co(CN)4(SO)3(OH2)3−

The relative nucleophile efficiencies predicted for NH₃, CH₃NH₂ and CN^? from their rates of reaction with trans-Co(CN)₄(SO)₃(OH₂)^3? are confirmed by competition experiments with similar nucleophiles (NH₃-CH₃NH₂) but not by experiments with contrasting nucleophiles (NH₃-CN^?). This system, though substantially dissociative in mechanism, (D), possesses some interchange properties, (I_d).     

Solubility equilibria of solid solutions of hydroxyl- and chlor-apatite of arsenic

The solubility equilibria of arsenic hydroxylapatite, Ca₁₀(AsO₄)₆(OH)₂, chlorapatite, Ca₁₀(AsO₄)₆(Cl)₂, and their nine solid solutions were investigated at 37°C in the pH range, 4.6 to 7.8, in buffered systems through microanalytical determination of calcium, arsenic and chloride in their saturated solution. Stoichiometric dissolution of the samples was proved by the constancy of the ionic products of the apatite phase in the saturated solution.     

Thermal decomposition of oxovanadium(IV) complexes with substituted pyridines

The kinetics of decomposition of solid complexes of bis(dibenzoylmethanato) oxovanadium(IV) with pyridine and several methyl, dimethyl and aminopyridines has been studied using differential scanning calorimetry. Activation energies have been determined and, in general show an increase with increasing basicity of the ligands. A linear relationship exists between pK_b values of the bases and the temperatures for the decomposition, except for the complexes obtained with 4 aminopyridine and 4 methylpyridine. These complexes are less stable than expected from the basicity of the ligands. These observations are discussed in terms of the nature of the metalligand bond.     

Ionic equilibria in ferric sulfate-sulfuric acid solutions

The ionic equilibria of ferric sulfate-sulfuric acid aqueous solution are modeled mathematically, taking into account the effect of ionic strength. Results of this analysis indicate that ion interactions can significantly change the ionic concentration of the solutions which could lead to errors in the evaluation of data on iron(III) extraction kinetics or equilibrium.     

Stereochemical nonrigidity of the square complex (PPh3)2Pt(HgGePh3)(GePh3)

³¹P, ¹⁹⁵Pt and ¹⁹⁹Hg NMR spectra of complex (PPh₃)₂Pt(HgGePh₃)(GePh₃) (I) have been studied. The spectra at temperatures below ?40°C prove that (I) is a cis-isomer with the square-planar coordination of the Pt atom. The reversibility of temperature dependences of spectra, insensitivity of line shape to the solvent, concentration and presence of free phosphine establish the fluxional behaviour of (I). The activation parameters of the intramolecular rearrangement which is realized, most probably, through a digonal twist, are: Δ^≠₂₉₈ = 51.5 ± 2.9 kJ/mol, ΔH^≠ = 59.3 ± 2.9 kJ/mol, ΔS^≠ = 26.2 ± 9.7 J/mol. K.     

Synthesis and characterisation of ReOCl3(DTO)2 and ReOCl3(MBT)2 complexes

New complexes of Re(V) with dithiooxamide and 2-mercaptobenzothiazole with the general formula ReOCl₃L₂, were prepared starting from potassium perrhenate. The compounds were characterised by chemical analysis, optical spectra and magnetic susceptibilities.