Metal Stability Constants Research Articles

STUDIES ON NOVEL METAL COMPLEXES OF COUMARIN SCHIFF BASE: SYNTHESIS, STABILITY CONSTANT, ANTIMICROBIAL AND ANTICANCER ACTIVITY

A facile synthetic protocol was employed to synthesize new coumarin Schiff base (E)-3-(1-((2-hydroxy-5- methylphenyl)imino)ethyl)-2H-chromen-2-one] and their Co and Cu metal complexes. Synthesized molecules were characterized by various spectroscopic methods. The results of antibacterial studies demonstrated that the maximum level of growth inhibition for S. aureus and B. subtilis was shown by compound 5, with inhibition zones of 16±1 mm and 18.5±1.3 mm, respectively, while, Compound 4 exhibited 12.5±0.5 mm and 14±0.25 mm, respectively. Invitro Cytotoxicity of Cu-complex 5 towards human hepatocellular adenocarcinoma cancer cells, at concentrations of 12.5, 25, 50, and 100 g/mL, displayed a reduction in the percentage of cell viability in a dose-dependent manner, with values of 72.45%, 60.12%, 48.69%, and 23.25%, respectively. The results revealed that Compound 5 has the potential to interact with the bacterial membrane surface, leading to the disruption of the same. Additionally, potentiometric analysis was used to estimate the proton-ligand dissociation constant of HL as well as its metal stability constants with Co2+ and Cu2+ .

Machine learning-based analysis of overall stability constants of metal–ligand complexes

The stability constants of metal(M)-ligand(L) complexes are industrially important because they affect the quality of the plating film and the efficiency of metal separation. Thus, it is desirable to develop an effective screening method for promising ligands. Although there have been several machine-learning approaches for predicting stability constants, most of them focus only on the first overall stability constant of M-L complexes, and the variety of cations is also limited to less than 20. In this study, two Gaussian process regression models are developed to predict the first overall stability constant and the n-th (n > 1) overall stability constants. Furthermore, the feature relevance is quantitatively evaluated via sensitivity analysis. As a result, the electronegativities of both metal and ligand are found to be the most important factor for predicting the first overall stability constant. Interestingly, the predicted value of the first overall stability constant shows the highest correlation with the n-th overall stability constant of the corresponding M-L pair. Finally, the number of features is optimized using validation data where the ligands are not included in the training data, which indicates high generalizability. This study provides valuable insights and may help accelerate molecular screening and design for various applications.

Reactivity and a Charge-Transfer Model Analysis in Aminopolycarboxylic-Metal Complexes.

In the present work, we have calculated several density functional theory (DFT) reactivity descriptors for the aminopolycarboxylate (APC) acids at the B3LYP/6311++G (d,p) levels of theory, aiming to analyze their reactivity. Reactivity descriptors such as ionization energy, molecular hardness, electrophilicity, and condensed Fukui function local indices have been determined to predict the reactivity of APCs. The influence of the solvent was taken into account by employing the CPCM model. The results indicate that the solvation slightly modifies the tendency of the reactivity of the APCs studied. On the other hand, we applied a global and local charge-transfer partitioning model, which introduces two charge-transfer channels [one for accepting electrons (electrophilic) and another for donating one (nucleophilic)] to the complexation reaction of a set of APC acids with transition metals (Mn, Co, and Ni targets enlarged by Fe, Cu, and Zn). The correlation between the charges obtained for the interaction between APC acids and transition metal stability constants provides support for their interpretation as measures of the electrophilicity and nucleophilicity of a chemical species and, at the same time, allows one to describe the donation and back-donation processes in terms of the DFT of chemical reactivity. Also, the application of dual descriptors for these acids provides valuable information concerning the atoms in the reactants playing the most important roles in the reaction, thus helping to improve our understanding of the reaction under study.

Computational predictions of metal-macrocycle stability constants require accurate treatments of local solvent and pH effects.

Rational design of molecular chelating agents requires a detailed understanding of physicochemical ligand-metal interactions in solvent phase. Computational quantum chemistry methods should be able to provide this, but computational reports have shown poor accuracy when determining absolute binding constants for many chelating molecules. To understand why, we compare and benchmark static- and dynamics-based computational procedures for a range of monovalent and divalent cations binding to a conventional cryptand molecule: 2.2.2-cryptand ([2.2.2]). The benchmarking comparison shows that dynamics simulations using standard OPLS-AA classical potentials can reasonably predict binding constants for monovalent cations, but these procedures fail for divalent cations. We also consider computationally efficient static procedure using Kohn-Sham density functional theory (DFT) and cluster-continuum modeling that accounts for local microsolvation and pH effects. This approach accurately predicts binding energies for monovalent and divalent cations with an average error of 3.2 kcal mol-1 compared to experiment. This static procedure thus should be useful for future molecular screening efforts, and high absolute errors in the literature may be due to inadequate modeling of local solvent and pH effects.

Predicting stability constants of transition metals; Y3+, La3+, and UO2 2+ with organic ligands using the 3D-QSPR methodology

Stability constants prediction plays a critical role in the identification and optimization of ligand design for selective complexation of metal ions in solution. Thus, it is important to assess the potential of metal-binding ligand organic in the complex formation process. However, quantitative structure-activity/property relationships (QSAR/QSPR) provide a time-and cost-efficient approach to predict the stability constants of compounds. To this end, we applied a free alignment three-dimensional QSPR technique by generating GRid-INdependent Descriptors (GRINDs) to rationalize the underlying factors effecting on stability constants of transition metals; 105 (Y3+), 186 (La3+), and 66 (UO2 2+) with diverse organic ligands in aqueous solutions at 298 K and an ionic strength of 0.1 M. Kennard– Stone algorithm was employed to split data set to a training set of 75% molecules and a test set of 25% molecules. Fractional factorial design (FFD) and genetic algorithm (GA) applied to derive the most relevant and optimal 3 D molecular descriptors. The selected descriptors using various feature selection were correlated with stability constants by partial least squares (PLS). GA-PLS models were statistically validated ( = 0.96, q2 = 0.82 and R2 pred=0.81 for Y3+; = 0.90, q2 = 0.73 and R2 pred=0.82 for La3+ and = 0.95, q2 = 0.81 and R2 pred=0.88 for UO2 2+), and from the information derived from the graphical results confirmed that hydrogen bonding properties, shape, size, and steric effects are the main parameters influencing stability constant of metal complexation. The provided information in this research can predict the stability constant of the new organic ligand with the transition metals without experimental processes.

Determination of stoichiometry and stability constants of iron complexes of phenanthroline, Tris(2-pyridyl)-s-triazine, and salicylate using a digital camera

The determination of stoichiometric ratios and stability constants of metal–ligand complexes is of great importance for physical, chemical, biochemical, and environmental studies and often require relatively expensive and sophisticated instruments. Herein, we introduce a simple, accurate, and low-cost method for determining these parameters by a conventional digital camera. The stoichiometric ratios and stability constants of iron complexes of 1,10-phenanthroline, 2,4,6-Tris(2-pyridyl)-s-triazine, and salicylate were determined, as model examples, using the molar ratio and the continuous variation methods. Digital images of solutions with various metal–ligand ratios were captured and analyzed, and the Yxy color absorbance and the ΔELUV color difference parameters were used as convenient analytical signals that favorably compete with conventional spectrophotometric signals. For the three studied iron complexes, the results of stoichiometric ratios and stability constants obtained from digital images were in excellent agreement with the spectrophotometric and the previously reported literature’s data.

Comparative Activation Process of Pb, Cd and Tl Using Chelating Agents from Contaminated Red Soils.

Adding chelating agents is a critical technique of heavy metal activation for enhancing phytoextraction through the formation of soluble metal complexes which will be more readily available for extraction. The preliminary, dynamic, equilibrium activation experiments and speciation analysis of Pb, Cd and Tl in contaminated red soils were used to select six chelates with relatively good activation performance from nine chelates, and the effects of dosage and pH on the heavy metals activation were studied systematically. Results showed that the activation of Pb, Cd and Tl by chelates reached equilibrium within 2 h, and the activation process showed three stages. Under neutral conditions, chelates had better activation performance on Pb- and Cd-contaminated soils. Except for S,S-ethylenediamine disuccinic acid (S,S-EDDS) and citric acid (CA), the maximum equilibrium activation effect (MEAE) of ethylenediaminetetraacetic acid (EDTA), N,N-bis (carboxymethyl) glutamic acid (GLDA), diethylenetriaminepentaacetic acid (DTPA) and aminotriacetic acid (NTA) was over 81%. The MEAE of Tl-contaminated soil was less than 15%. The decreasing order of the dosage of chelating agents corresponding to MEAE for three types of contaminated soils was Pb-, Cd- and Tl-contaminated soil, relating to the forms of heavy metals, the stability constants of metal–chelates and the activation of non-target elements Fe in red soil. Under acidic conditions, the activation efficiencies of chelates decreased to differing degrees in Pb- and Cd-contaminated soils, whereas the activation efficiencies of chelating agents in Tl-contaminated soils were slightly enhanced.

New version of calculation of stability constant of metal–fulvate complexes on the example of zinc fulvate

Natural macromolecular organic substances—fulvic acids—take an active part in complex formation processes and stipulate migration forms of heavy metals in natural waters. In spite of researches, experimental data on stability constants of complex compounds of fulvic acids with heavy metals (among them zinc) are heterogenous and they differ in several lines from each other. One of the reasons of such condition is ignoring an average molecular weight of the associates of fulvic acids, which finally causes the wrong results. Complex formation process between zinc (II) and fulvic acids was studied by the solubility method at pH = 8.0. ZnO suspension was used as a solid phase. Fulvic acids were isolated from Paravani lake by the adsorption chromatographic method. This article shows that during the complex formation process, every 1/5 part of an associate of fulvic acids inculcates into zinc’s (II) inner coordination sphere, as an integral ligand. So it may assume that the average molecular weight of the associate of fulvic acids which takes part in complex formation process equals to 1252. This part of the associate of fulvic acids was conventionally called an “active associate.” The average molecular weight of the “active associate” was used for determining the composition of zinc fulvate complex, the concentration of free ligand and stability constant, which equals to $$1.6 \times 10^{4}$$ .

Polymer complexes. LXV. Potentiometry, theoretical and molecular docking studies of azo allylrhodanine derivatives and their metal complexes in monomeric and polymeric forms

Azo dyes of 3-allyl-5-((4-derivative phenyl)diazenyl)-2-thioxothiazolidin-4-one ligands (HLn) are synthesized and characterized using different spectroscopic techniques. The X-ray diffraction, XRD, pattern of the ligand (HL2) is polycrystalline nature. The geometrical structures of the ligand are carried out by HF method with 3-21G basis set. Molecular docking was used to predict the binding between azo dye ligand and the receptor of prostate cancer mutant 2q7k-hormone and the receptor of breast cancer mutant 3hb5-oxidoreductase. The predicted pKa obtained by docking measurements for the ligands are in agreement with experimental values. The predicted and expermently calculated pKH values of the ligands increases in the order HL3, HL2 and HL1 as expected from Hammett's constant (σR). The proton-ligand dissociation constants of HLn and their metal stability constants with Mn2+, Co2+, Ni2+ and Cu2+ have been determined potentiometrically in monomeric and polymeric forms using 2,2′-azobisisobutyronitrile as initiator. The potentiometric studies were carried out in 0.1M (KCl) and 50% (by volume) DMSO-water mixture. The effect of temperature was studied at 298, 308 and 318K and the corresponding thermodynamic parameters (ΔG, ΔH and ΔS) were derived and discussed. The dissociation process is non-spontaneous, endothermic and entropically unfavorable. The formation of the metal complexes has been found to be spontaneous, endothermic and entropically favorable.

Geometrical structure, potentiometric, molecular docking and thermodynamic studies of azo dye ligand and its metal complexes

The ligand of 6-(4-benzenesulfonic acid azo)-3-aminophenol (HL) is prepared and characterized by elemental analyses, IR, 1H NMR spectra, mass spectra and X-ray diffraction analysis. The proton–ligand dissociation constants of HL ligand and its metal stability constants with Mn(II), Co(II), Ni(II) and Cu(II) ions have been determined using potentiometric studies as described by Irving and Rossotti. The optimized structure and the calculated quantum chemical parameters of HL ligand were studied. The potentiometric studies were carried out in 0.1M KCl and 20% (by volume) DMF–water mixture. The effect of different temperatures was studied and the thermodynamic functions (ΔG, ΔH and ΔS) were calculated. The dissociation process is non-spontaneous, endothermic and entropically unfavorable. The formation of the metal complexes has been found to be spontaneous, endothermic and entropically favorable. Molecular docking was used to predict the binding between azo dye ligand and the receptor of prostate cancer mutant 2q7k-hormone and the receptor of breast cancer mutant 3hb5-oxidoreductase.

Geometrical structure, molecular docking and potentiometric studies of Schiff base ligand

Schiff base ligand of 4-(((2-hydroxynaphthalen-1-yl)methylene)amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (HL) was synthesized and characterized by IR spectroscopy. The molecular structure of the ligand is optimized theoretically and the quantum chemical parameters are calculated. Molecular docking was used to predict the binding of the ligand with the receptor of prostate cancer 2q7k-hormone and 3hb5-oxidoreductase receptor of breast cancer. The proton–ligand dissociation constant of HL and its metal stability constants with Mn2+, Co2+, Ni2+ and Cu2+ have been determined potentiometrically. The potentiometric studies were carried out in 0.1M KCl and 20% (by volume) DMF–water mixture. At constant temperature the stability constants of the formed complexes increase in the order of Cu2+>Ni2+>Co2+>Mn2+. The effect of temperature was studied at 298, 308 and 318K and the corresponding thermodynamic parameters (ΔG, ΔH and ΔS) were derived and discussed. The dissociation process is non-spontaneous, endothermic and entropically unfavorable. The formation of the metal complexes has been found to be spontaneous, endothermic and entropically favorable.

Geometrical structure, molecular docking, potentiometric and thermodynamic studies of 3-aminophenol azodye and its metal complexes

The proton–ligand dissociation constants of 4-(2,3-dimethyl-1-phenylpyrazol-5-one azo)-3-aminophenol (HL) and its metal stability constants with Mn(II), Co(II), Ni(II) and Cu(II) ions have been determined using potentiometric studies. The molecular structure of the ligand is optimized theoretically and the quantum chemical parameters are calculated. The proton–ligand dissociation constants of HL and its metal stability constants with Mn(II), Co(II), Ni(II) and Cu(II) have been determined potentiometrically. The potentiometric studies were carried out in 0.1M KCl and 20% (by volume) DMF–water mixture. At constant temperature the stability constants of the formed complexes decrease in the order of Cu(II)>Ni(II)>Co(II)>Mn(II). The effect of temperature was studied at 298, 308 and 318K and the corresponding thermodynamic parameters (ΔG, ΔH and ΔS) were derived and discussed. The dissociation process is non-spontaneous, endothermic and entropically unfavorable. The formation of the metal complexes has been found to be spontaneous, endothermic and entropically favorable. Molecular docking was used to predict the binding between azodye ligand and the receptor of prostate cancer mutant 2q2k-Hormon and receptor of breast cancer mutant 3hb5-Oxidoreductase.

Geometrical structure, potentiometric and thermodynamic studies of rhodanine azodye and its metal complexes

5-(2,3-Dimethyl-1-phenylpyrazol-5-one azo)-2-thioxo-4-thiazolidinone (HL) was synthesized and characterized using different spectroscopic techniques. The molecular structures of the ligand are optimized theoretically and the quantum chemical parameters are calculated. The proton–ligand dissociation constants of HL and its metal stability constants with Mn2+, Co2+, Ni2+ and Cu2+ have been determined potentiometrically. The potentiometric studies were carried out in 0.1M KCl and 10% (by volume) DMF–water mixture. At constant temperature the stability constants of the formed complexes decreases in the order Cu2+, Ni2+, Co2+ and Mn2+. The effect of temperature was studied at (298, 308 and 318K) and the corresponding thermodynamic parameters (ΔG, ΔH and ΔS) were derived and discussed. The dissociation process is non-spontaneous, endothermic and entropically unfavorable. The formation of the metal complexes has been found to be spontaneous, endothermic and entropically favorable

Journal of Thermodynamics & Catalysis

N-Acryloyl-4-aminosalicylic acid (AAS) was synthesized and characterized using different spectroscopic techniques. The geometrical structures of the ligand are carried out by HF method with 3-21G basis set. The proton-ligand dissociation constants of AAS and its metal stability constants with (Mn2+, Co2+, Ni2+ and Cu2+) have been determined potentiometrically in monomeric and polymeric forms using 2,2’-azobisisobutyronitrile as initiator. The potentiometric studies were carried out in 0.1 M (KCl) and 20% (by volume) ethanol-water mixture. The effect of temperature was studied at (298, 308 and 318 K) and the corresponding thermodynamic parameters (ΔG, ΔH and ΔS) were derived and discussed. The dissociation process is non-spontaneous, endothermic and entropically unfavorable. The formation of the metal complexes has been found to be spontaneous, endothermic and entropically favorable.

Evaluation of 1,2-dimethyl-3-hydroxy-4-pyridinecarboxylic acid and of other 3-hydroxy-4-pyridinecarboxylic acid derivatives for possible application in iron and aluminium chelation therapy

Four new possible chelating agents for iron and aluminium, 1,2-dimethyl-3-hydroxy-4-pyridinecarboxylic acid (DT712), 3-hydroxy-1,2,6-trimethyl-4-pyridinecarboxylic acid, 2,6-dimethyl-3-hydroxy-4-pyridinecarboxylic acid, and 2-ethyl-3-hydroxy-1-methyl-4-pyridinecarboxylic acid, were synthesized, and their complex formation with Fe(III) and Al(III) was studied by potentiometry, UV–Vis, 1H NMR, and electrospray mass spectrometry (ESI-MS). Number, stoichiometry, and stability constants of metal–ligand complexes were obtained at 25°C in aqueous (Na)Cl 0.6m. DT712 is the most promising hydroxypyridinecarboxylic acid considered so far for iron chelation therapy, as it forms the strongest Fe(III) complexes. This compound was further investigated to better clarify its possible behaviour in vivo with particular respect to iron chelation therapy. UV–Vis measurements were performed to determine the kinetics by which DT712 extracts Fe(III) from transferrin. DT712 resulted to have better kinetic properties than existing iron chelators. Ternary metal/DT712/citric acid complexes were studied by ESI-MS to check the competition with a typical low molecular weight ligand in the blood. The formation of only binary Fe(III)/DT712 and Al(III)/DT712 complexes (and ternary complexes in aged solutions), suggests that DT712 effectively compete with citric acid in the metal complexation. Standard reduction potentials of Fe(III)/DT712 complexes, and the kinetic constants of complex formation, were obtained by cyclic voltammetry. Accordingly, no redox cycling is expected to occur at in vivo conditions, and Fe(III)/DT712 complex formation should not be kinetically limited. On the basis of the present results, DT712 is proposed as candidate for iron chelation therapy.

Estimation of stability constants for metal–ligand complexes containing neutral nitrogen donor atoms with applications to natural organic matter

Linear free energy relationships (LFERs) were developed for estimating 1:1 metal–ligand stability constants (logKML) for small organic molecules containing neutral nitrogen donor atoms. A data set of 44 monodentate and 112 bidentate ligands for six metal ions: Mn2+, Co2+, Ni2+, Cu2+, Zn2+ and Cd2+ was employed to parameterize the LFER equations. Monodentate and bidentate logKML values were adequately described using Irving–Rossotti LFERs previously developed for ligands containing negatively-charged oxygen functional groups. Modifications to the LFER equations were necessary to account for steric hindrances to metal complexation by primary, secondary, and tertiary amines. The resulting LFER equations can be used to estimate logKML values for monodentate and bidentate ligands with neutral nitrogen donor groups where such values do not currently exist in the literature. Comparison of these results to our previous work with negatively-charged oxygen donor atoms reveals that neutral nitrogen functional groups are weaker than their oxygen counterparts for metal ions classified as “hard” on the basis of Hard–Soft Acid–Base (HSAB) theory. For “soft” metals, the opposite is true. These LFERs can be used to incorporate nitrogen functional groups in models for metal ion binding to natural organic matter (NOM).

Application of the Surface Complexation Model to the Biosorption of Cu(II) and Pb(II) Ions onto Pseudomonas Pseudoalcaligenes Biomass

In this study, a potentiometric titration was performed to investigate the surface acid-base properties of Pseudomonas pseudoalcaligenes isolated from activated sludge. Batch sorption as a function of pH was performed to explain the sorption behaviour of Cu(II) and Pb(II) ions onto the bacterial surface. The surface complexation approach in the frame of constant capacitance model was applied to determine the deprotonation constants, site concentrations and metal stability constants for the important surface-functional groups on the biomass. The optimized results showed that the three discrete sites-three pK(a)s model, involving three distinct types of functional groups, namely, carboxyl, phosphate and hydroxyl, could actually fit the protonation of the bacterial functional groups, with average pK(a) values of 4.18, 6.31 and 9.18, and site concentrations of 0.526, 0.525 and 0.478 mmol/g, respectively. The two sites model provided the best fit for the biosorption of Cu(II) and Pb(II) ions onto the biomass by forming complexes with carboxyl and phosphate surface sites, with average log stability constants of 5.95 and 6.94 for Cu(II), and 6.64 and 8.08 for Pb(II), respectively. These results suggested that the surface complexation model yielded the accurate prediction for the biosorption behaviour of Cu(II) and Pb(II) ions on the bacterial biomass and the affinity of P. pseudoalcaligenes biomass for the adsorption of Cu(II) and Pb(II) ions was high enough to remove the metal ions from water.

Metal speciation in natural waters and metal complexing with humic matter

The stability constants of metal and humic matter complexes extracted from different soils were calcu� lated. Speciation of metals in natural waters was deter� mined taking into account their chemical composition and content and properties of organic matter. We established metal speciation in water objects with account for competitive reactions resulting in forma� tion of hydroxide, hydrocarbonate, sulfate, and chlo� ride metal complexes and obtained a competitive series of metal activity in natural waters of the zones considered. An important specific feature of metals as contam� ination elements is the fact that when they occur in the environment, their potential toxicity and bioavailabil� ity depend significantly on their speciation. In recent years, lakes have been continuously enriched in haz� ardous elements such as Pb, Cd, Al, and Cr on a global (regional) basis [1]. Metals occur in natural waters as free ions, simple complexes with inorganic and organic ligands, and mineral and organic particles of molecules and ions sorbed on the surface. The occur� rence of soluble metal forms in natural waters depends on the presence of organic and inorganic anions. The most important organic ligands are humic matter (HM) washed out from soils; inorganic complexes formed include hydroxide groups, hydrocarbonates, sulfates, and chlorides. HM of natural waters com� posed of fulvic (FA) and humic (FA) acids contributes most significantly to metal inactivation. The concen� trations of these acids in surface waters attain 1– 100 mg/l [2, 3]. The concentrations of water biota exometabolites are much lower. Due to specific water formation in the whole humid territory of Russia, the colored waters are quite widespread. They are characterized by high concen� trations of humic matter, which is able to inactivate metals and to decrease their toxicity in natural waters. A characteristic feature of the water chemical compo� sition in these regions is elevated Fe, Al, and Mn con� centrations. Russian water quality standards concern� ing metals do not take into account regional and local specific features of the water chemical composition, which predefine speciation of metals and their ecotoxic properties. However, direct determinations are rather difficult. Our current task is to develop methods that would make it possible to forecast ele� ment speciation predefining toxic properties of water by the chemical composition of the water. The objective of this work was to investigate metal and humic matter complexing and to determine metal occurrence forms on the basis of experimentally obtained constants of metal and humic matter com� plexes extracted from typical soils of different natural climatic zones.

Electrophoretic Studies of Biologically Important Mixed Metal – Ascorbic Acid –Nitrilotriacetate Complexes

Quantitative indication of a complex formation comes from the estimation of the stability or formation constants characterizing the equilibria corresponding to the successive addition of ligands. The binary equilibria of metal (II) / (III) - ascorbic acid and also mixed equilibria metal (II) / (III) - ascorbic acid - NTA have been studied using ionophoretic technique. The stability constants of metal - ascorbic acid binary complexes are found to be 10 3.77 , 10 2.47 ,10 2.27 and that of metal - ascorbic acid - NTA mixed complexes have been found to be 10 6.05 , 10 5.93 , 10 5.75 , for Fe(III), Cu(II) and Co(II) complexes, respectively at 25 °C and ionic strength Ic = 0.1 mol dm -3 (HClO4). (doi: 10.5562/cca1778)

Stability Constants of Metal(II) Complexes with Amines and Aminocarboxylates with Special Reference to Chelation

Abstract Equations derived on the basis of mechanistic considerations have been utilized to calculate the stability constants of binary and ternary copper(II) complexes of amine(s) or aminocarboxylates. Calculated values of 185 copper(II) amine complexes have been compared with the observed. For 89 complexes including ammonia, ethylenediamine, cyclohexane-1,2-diamine, imidazole, pyridine, and some substituted analogs, the calculated values agree with the observed within 0.3 log unit. These complexes may be regarded as regular. Among the remaining non-regular complexes we find some complexes with lower stability constants due to steric hindrance, and some others with higher constants resulting from aromatic π–π interactions and/or hydrophobic interactions between coordinated ligands. Mechanistic considerations have also been successfully utilized to predict stability constants of polyamine and aminocarboxylate chelates of nickel(II), cobalt(II), and copper(II) according to Adamson’s approach.