Pier Giuseppe Daniele

Spectrum–structure correlation for visible absorption spectra of copper(II) complexes in aqueous solution

Abstract In this study an analysis of visible spectrophotometric data was carried out using more than 100 copper(II) complexes formed by ligands with different coordination environments, and whose aim is the λmax value estimation for equatorially-coordinated copper(II) complexes in solution. Calculations were performed with a least-squares procedure and a bootstrap-based method for accuracy assessment. The results obtained are in good agreement to previous reports describing the coordination of amino, peptide (negatively-charged), pyridine-imidazole nitrogen and carboxylate oxygen, while it was possible to calculate an individual contribution for hydroxide, alcoholate and water oxygen donors. The spectrum–structure correlation for copper(II) complexes in solution is widely discussed in this paper, and an estimation of the uncertainty in relation to the prediction of λmax of copper(II) complexes has also been made.

Ionic strength dependence of formation constants—I: Protonation constants of organic and inorganic acids

The protonation constants of formic, acetic, benzoic, oxalic, phthalic, maleic, malonic, succinic, dl-malic, dl-tartaric, aminoacetic, citric, nitrilotriacetic, ethylenediaminetetra-acetic, sulphuric and orthophosphoric acids have been determined from pH measurements, in tetraethylammonium iodide solution, at various ionic strengths in the range 0.01-1.0M (for phosphoric and sulphuric acids 0.01-0.5M). For each acid the dependence of the protonation constants on ionic strength was determined and an equation, valid for all the acids studied, to describe this was derived. The use of tetraethyl-ammonium salts as background to avoid ion-pair formation is discussed.

On the possibility of determining the thermodynamic parameters for the formation of weak complexes using a simple model for the dependence on ionic strength of activity coefficients: Na+, K+, and Ca2+ complexes of low molecular weight ligands in aqueous solution

Alkali-metal and calcium(II) complexes of monocarboxylate A–(acetate and salicylate), dicarboxylate A2–(malonate, maleate, succinate, malate, tartrate, phthalate, and oxydiacetate), or amino acid HA (glycine or L-histidine) ligands have been studied potentiometrically, using a glasssaturated calomel electrode, at different temperatures and ionic strengths. The monocarboxylate ligands form [MA] and the dicarboxylates [MA] and [M(HA)] species (charges omitted) with both alkali metals and calcium. Glycine and L-histidine form [MA]+ and [M(HA)]2+{and [M(H2A)]3+ for L-histidine} complexes with Ca2+, whilst alkali metals form only [M(HA)]+ with glycine. Some interesting regularities in the formation constants are pointed out. From the dependence on temperature of formation constants, values of ΔH⊖ and ΔS⊖ have been determined. The function log β=f(I) has been carefully studied in the range 0.02 ⩽I⩽ 1 mol dm–3. The reliability of a new model for the dependence on ionic strength of formation constants (when dealing with weak complexes it is in practice impossible to use the constant ionic medium method) is widely discussed. Two methods of calculation are described and the more general method has been checked by simulated curves.

Ultraviolet–circular dichroism spectra for structural analysis of copper(II) complexes with aliphatic and aromatic ligands in aqueous solution

An attempt has been made to identify the characteristic positions, and their eventual displacements with changing co-ordination, of the charge-transfer bands involving donor groups located on molecules of biological interest [L-malic acid, N-acetyl-L-aspartic acid, (1R,2R)-cyclohexane-1,2-diamine, L-alanyl-L-alanine, L-γ-glutamyl-L-Iµ-lysine, N-acetyl-L-histidine, β-alanyl-L-histidine and N-benzoylglycyl-L-histidyl-L-leucine] such as carboxylate, alcoholate, amine, deprotonated peptide and imidazole. Information about the species formed in solution was obtained by means of pH-metric readings while ultraviolet–circular dichroism spectra were recorded, at fixed pH values, 298 K and I= 0.1 mol dm–3, for the proton–ligand and proton–copper(II)–ligand systems, in order to evaluate a spectrum for each complex formed in solution. Intraligand and charge-transfer bands were assigned for each spectrum with the aim of relating spectral features to the structure of the species formed in solution.

Ionic strength dependence of formation constants—XVIII. The hydrolysis of iron(III) in aqueous KNO3 solutions☆

The hydrolysis of iron(III) was studied potentiometrically at different ionic strengths in KNO(3) aqueous solutions, at 25 degrees C, to determine the dependence of hydrolysis constants on ionic strength (nitrate media), to check the existence of nitrate-ferric ion interactions, and to confirm the formation of high polymeric species. Under the experimental conditions 0.03 I (KNO(3)) 1M, 0.3 C 12 mM, the species Fe(OH)(2+), Fe(2)(OH)(4+)(2), Fe(OH)(+)(2) and Fe(12)(OH)(2+)(34) were found, and the hydrolysis constants log beta(11) = 2.20, log beta(12) = -2.91, log beta(22) = -5.7, log beta(12,34) = -48.9 (I = 0M) were calculated. The ionic strength dependence of hydrolysis constants is quite close to that found for several protonation and metal complex formation constants reported elsewhere.

Copper(II) complexes of N-(phosphonomethyl)glycine in aqueous solution: a thermodynamic and spectrophotometric study

Copper(II) complexes with the herbicide N-(phosphonomethyl)glycine (glyphosate) have been investigated in aqueous solution by means of pH-metric measurements at different temperatures, 5 </= T </= 45 degrees C, calorimetry and visible spectrophotometry. Potentiometric data, at all the considered temperatures in the range 2.5 </= pH </= 10.5, can be explained assuming the formation of the species CuLH(0), CuL(-), CuLH(2 -)(- 1), CuL(4 -)(2) and Cu(2)L(+). By using thermodynamic data and calculated electronic spectra for each complex a structural definition is proposed for the different species. Copper(II)-glyphosate complexes are quite stable and must be taken into account in the speciation of natural fluids.

Salt effects on the protonation of ortho-phosphate between 10 and 50°C in aqueous solution. A complex formation model

Protonation constants of o-phosphate were studied potentiometrically, using the (H+)-glass electrode in aqueous NaCl, KCl and tetraethylammonium iodide solutions, at 0≤I≤IM and 10≤T≤50°C. The differences found in the protonation constants for different salt solutions are explained by a complex formation model. The formation of the species MPO42−, MHPO4−, MH2PO40, M2PO4− and M2HPO40 (M=Na+, K+) is hypothesized. In mixed NaCl-KCl solutions, it is possible to find the mixed metal species NaKPO4− and NaKHPO40. Ionic strength and temperature dependence parameters are reported for all species. The relevance of Na+ and K+ complexes is discussed in connection with speciation problems of natural fluids, such as marine water and urine.

Ionic-strength dependence of formation constants. XII: A model for the effect of background on the protonation constants of amines and amino-acids

From analysis of literature data on the protonation of N-donor and N,O-donor ligands at 25 degrees , a simple model has been derived for the dependence of amine and amino-acid protonation constants on the background electrolytes, which takes into account the formation of weak complexes between the protonated forms of the amines (or amino-acids) and the background anions and between the amino-acid carboxylate group and alkali-metal cations.

Ionic strength dependence of formation constants. Part 4. Potentiometric study of the system Cu2+-Ni2+-citrate

SummaryThe ternary Cu2+-Ni2+-citrate (cit3−) system was investigated potentiometrically in aqueous solution, at different temperatures, 10≤t≤45°C, and ionic strengths, 0.03≤I≤0.8 mol dm−3, using potassium nitrate or tetraethylammonium bromide as background salt. Since the citrate anion forms weak complexes with potassium, the stability constants here reported differ according to whether the potassium association is considered or not. In the presence of both Cu2+ and Ni2+, the mixed metal species, [CuNi(cit)2H−2]4− is formed with citrate in solution, in addition to the various binary complexes. We have obtained the dependence for all the formation constants on ionic strength and temperature. The previous suggestions concerning a general equation for describing the dependence, log β=f(I), are confirmed; from the study of log β=f(T) we have obtained the values of thermodynamic parameters. The dependence of ΔH on ionic strength is discussed.

Mixed metal complexes in solution. Thermodynamic and spectrophotometric study of copper(II)-citrate heterobinuclear complexes with nickel(II), zinc(II) or cadmium(II) in aqueous solution

SummaryA thermodynamic study of CuII−MII-citrate (MII=NiII, ZnII or CdII) ternary systems has been performed by means of potentiometric measurements of hydrogen ion concentration at different temperatures (10, 25, 35 and 45°C) and at I=0.1 mol dm−3 (KNO3).The different binary and ternary systems involved have been further characterized by visible spectra and by calculating the spectra (ε versus λ) of all the CuII complexes.The thermodynamic data suggest strong entropic stabilization for the species under discussion. As regards the visible spectral characteristics of CuII(d-d transitions), the substitution of one CuII ion in the dimer [Cu2(cit)2H−2]4− by NiII or ZnII to form heterobinuclear [CuM(cit)2H−2]4− complexes, gives rise to a change in the visible spectrum.