CoII Complexes Research Articles

How Ligand Geometry Affects the Reactivity of Co(II) Cyclam Complexes

AbstractCobalt complexes are extensively studied as bioinspired models for non‐heme oxygenases as they facilitate both the stabilization and characterization of metal‐oxygen intermediates. As an analog to the well‐known Co(cyclam) complex Co{N4} (cyclam=1,4,8,11‐tetraazacyclotetradecane), the CoII complex Co{i‐N4} with the isomeric isocyclam ligand (isocyclam=1,4,7,11‐tetraazacyclotetradecane) was synthesized and characterized. Despite the identical N4 donor set of both complexes, Co{i‐N4} enables the 2e−/2H+ reduction of O2 with a lower overpotential (ηeff of 385 mV vs. 540 mV for Co{N4}), albeit with a diminished turnover frequency. Characterization of the intermediates formed upon O2 activation of Co{i‐N4} reveals a structurally identified stable μ‐peroxo CoIII dimer as the main product. A superoxo CoIII species is also formed as a minor product, as indicated by EPR spectroscopy. In further reactivity studies, the electrophilicity of these in situ generated Co−O2 species was demonstrated by the oxidation of the O−H bond of TEMPO−H (2,2,6,6‐tetramethylpiperidin‐1‐ol) via a H atom abstraction process. Unlike the known Co(cyclam), Co{i‐N4} can be employed in oxygen atom transfer reactions oxidizing triphenylphosphine to the corresponding phosphine oxide highlighting the impact of geometrical modifications of the ligand while preserving the ring size and donor atom set on the reactivity of biomimetic oxygen activating complexes.

Spin Crossover and Fluorine-Specific Interactions in Metal Complexes of Terpyridines with Polyfluorocarbon Tails.

In coordination chemistry and materials science, terpyridine ligands are of great interest, due to their ability to form stable complexes with a broad range of transition metal ions. We report three terpyridine ligands containing different perfluorocarbon (PFC) tails on the backbone and the corresponding FeII and CoII complexes. The CoII complexes display spin crossover close to ambient temperature, and the nature of this spin transition is influenced by the length of the PFC tail on the ligand backbone. The electrochemical properties of the metal complexes were investigated with cyclic voltammetry revealing one oxidation and several reduction processes. The fluorine-specific interactions were investigated by EPR measurements. Analysis of the EPR spectra of the complexes as microcrystalline powders and in solution reveals exchange-narrowed spectra without resolved hyperfine splittings arising from the 59 Co nucleus; this suggests complex aggregation in solution mediated by interactions of the PFC tails. Interestingly, addition of perfluoro-octanol in different ratios to the acetonitrile solution of the sample resulted in the disruption of the F F interactions of the tails. To the best of our knowledge, this is the first investigation of fluorine-specific interactions in metal complexes through EPR spectroscopy, as exemplified by exchange narrowing.

Structural Characterization of Zinc(II)/Cobalt(II) Complexes of Chiral N-(Anthracen-9-yl)methyl-N,N-bis(2-picolyl)amine and Evaluation of DNA Photocleavage Activity.

We designed and synthesized a chiral ligand N-(anthracen-9-ylmethyl)-1-(pyridin-2-yl)-N-(pyridin-2-ylmethyl)ethanamine (APPE) DNA photocleavage agent to investigate the effects of chirality of bis(2-picolyl)amine on the DNA photocleavage activity of metal complexes. The structures of ZnII and CoII complexes in APPE were analyzed via X-ray crystallography and fluorometric titration. APPE formed metal complexes with a 1 : 1 stoichiometry in both the crystalline and solution states. Fluorometric titration was used to show that the ZnII and CoII association constants of these complexes (log Kas) were 4.95 and 5.39, respectively. The synthesized complexes were found to cleave pUC19 plasmid DNA when irradiated at 370 nm. The DNA photocleavage activity of the ZnII complex was higher than that of the CoII complex. The absolute configuration of the methyl-attached carbon did not affect DNA cleavage activity and, unfortunately, an achiral APPE derivative without the methyl group (ABPM) was found to perform DNA photocleavage more effectively than APPE. One reason for this may be that the methyl group suppressed the structural flexibility of the photosensitizer. These results will be useful for the design of new photoreactive reagents.

Intramolecular charge transfer in bulky “diazabutadiene-M(II)-catecholate” chromophores (M = Ni, Co): A role of a molecular geometry

Two monomeric heteroleptic charge transfer (CT) complexes NiII(3,6-Cat)(DADdipp) (1) and CoII(3,6-Cat)(DADdipp) (2) of “α-diimine-MII-catecholate” general type were prepared in the course of two-step synthetic procedures, based on 3,6-di-tert-butyl-o-benzoquinone (3,6-DTBQ) and 1,4-bis(2,6-di-isopropylphenyl)-1,4-diaza-1,3-butadiene (DADdipp). Square-planar coordination environment in complex 1 enables an implementation of a low energy ligand-to-ligand charge transfer (LL’CT), thus making NIR NiII chromophore (λmax = 1107 nm, in toluene) with high absorptivity of light and a fine sensitivity of CT energy towards solvent polarity (red solvatochromic shift from CH3CN to toluene at 192 nm). Energy of frontiers orbitals and HOMO-LUMO gap of 1 is evaluated in synergy of UV-vis-NIR spectroscopy, cyclic voltammetry, and DFT calculations, with a good accordance of data sets. A significant ligands’ bulkiness provided a tetrahedral distortion of square-planar N2O2 polyhedron of 2 in solutions (CH3CN, CH2Cl2, THF, toluene), that changed CT nature drastically with a concomitant decrease of absorptivity and an elimination of solvatochromism. Electrochemical behavior of studied complexes is defined by the differences in geometry of a coordination environment and corresponding mutual arrangement of metal and ligand orbitals (in solution): one-electron redox processes of square-planar NiII derivative 1 are predominantly ligand-centered, while redox transitions in tetrahedral CoII complex 2 proceed with the substantial participation of cobalt center.

Electrochemistry and Spin‐Crossover Behavior of Fluorinated Terpyridine‐Based Co(II) and Fe(II) Complexes

AbstractDue to their ability to form stable molecular complexes that have tailor‐made properties, terpyridine ligands are of great interest in chemistry and material science. In this regard, we prepared two terpyridine ligands with two different fluorinated phenyl rings on the backbone. The corresponding CoII and FeII complexes were synthesized and characterized by single‐crystal X‐ray structural analysis, electrochemistry and temperature‐dependent SQUID magnetometry. Single crystal X‐ray diffraction analyses at 100 K of these complexes revealed Co−N and Fe−N bond lengths that are typical of low spin CoII and FeII centers. The metal centers are coordinated in an octahedral fashion and the fluorinated phenyl rings on the backbone are twisted out of the plane of the terpyridine unit. The complexes were investigated with cyclic voltammetry and UV/Vis‐NIR spectroelectrochemistry. All complexes show a reversible oxidation and several reduction processes. Temperature dependent SQUID magnetometry revealed a gradual thermal SCO behavior in two of the complexes, while EPR spectroscopy provided further insights on the electronic structure of the metal complexes, as well as site of reduction.

The Nephelauxetic Effect Becomes an Important Design Factor for Photoactive First‐Row Transition Metal Complexes

AbstractThe expansion of d‐orbitals as a result of metal‐ligand bond covalence, the so‐called nephelauxetic effect, is a well‐established concept of coordination chemistry, yet its importance for the design of new photoactive complexes based on first‐row transition metals is only beginning to be recognized. Until recently, much focus has been on optimizing the ligand field strength, coordination geometries, and molecular rigidity, but now it becomes evident that the nephelauxetic effect can be a game changer regarding the photophysical properties of 3d metal complexes in solution at room temperature. In CrIII and MnIV complexes with the d3 valence electron configuration, the nephelauxetic effect was exploited to shift the well‐known ruby‐like red luminescence to the near‐infrared spectral region. In FeII and CoIII complexes with the low‐spin d6 electron configuration, charge‐transfer excited states were stabilized with respect to detrimental metal‐centered excited states, to improve their properties and to enhance their application potential. In isoelectronic (3d6) isocyanide complexes of Cr0 and MnI, the nephelauxetic effect is likely at play as well, enabling luminescence and other favorable photoreactivity. This minireview illustrates the broad applicability of the nephelauxetic effect in tailoring the photophysical and photochemical properties of new coordination compounds made from abundant first‐row transition metals.

The Nephelauxetic Effect Becomes an Important Design Factor for Photoactive First-Row Transition Metal Complexes.

The expansion of d-orbitals as a result of metal-ligand bond covalence, the so-called nephelauxetic effect, is a well-established concept of coordination chemistry, yet its importance for the design of new photoactive complexes based on first-row transition metals is only beginning to be recognized. Until recently, much focus has been on optimizing the ligand field strength, coordination geometries, and molecular rigidity, but now it becomes evident that the nephelauxetic effect can be a game changer regarding the photophysical properties of 3d metal complexes in solution at room temperature. In CrIII and MnIV complexes with the d3 valence electron configuration, the nephelauxetic effect was exploited to shift the well-known ruby-like red luminescence to the near-infrared spectral region. In FeII and CoIII complexes with the low-spin d6 electron configuration, charge-transfer excited states were stabilized with respect to detrimental metal-centered excited states, to improve their properties and to enhance their application potential. In isoelectronic (3d6 ) isocyanide complexes of Cr0 and MnI , the nephelauxetic effect is likely at play as well, enabling luminescence and other favorable photoreactivity. This minireview illustrates the broad applicability of the nephelauxetic effect in tailoring the photophysical and photochemical properties of new coordination compounds made from abundant first-row transition metals.

Complexes of NiII, CoII, ZnII, and CuII with Promising Anti-Tuberculosis Drug: Solid-State Structures and DFT Calculations

Four new NiII, CoII, ZnII, and CuII complexes with the promising anti-tuberculosis drug (E/Z)-N′-((5-Hydroxy-3,4-bis(hydroxymethyl)-6-methylpyridin-2-yl)methylene)-isonicotino-hydrazide (LH) were synthesized and characterized by structural methods: single-crystal X-ray diffraction, vibrational spectroscopy, and mass spectrometry. The NiII, CoII, and ZnII metal ions form only amorphous phases with various morphologies according to mass spectrometry and IR spectroscopy. The CuII forms a crystalline 1D coordination polymer with the relative formula {[CuLCl]·0.5H2O}∞1. Even though the LH ligand in the crystalline state includes a mixture of E-/Z-isomers, only the tautomeric iminol E-/Z-form is coordinated by CuII in the crystal. The copper(II) complex crystallizes in the monoclinic P21/n space group with the corresponding cell parameters a = 16.3539(11) Å, b = 12.2647(6) Å, and c = 17.4916(10) Å; α = 90°, β = 108.431(7)°, and γ = 90°. DFT calculations showed that the Z-isomer of the LH ligand in solution has the lowest formation energy due to intramolecular hydrogen bonds. According to the quantum chemical calculations, the coordination environment of the CuII atom during the transfer of the molecule into the solution remains the same as in the crystal, except for the polymeric bond, namely, distorted trigonal bipyramidal. Some of the complexes investigated can be used as effective sensors in biosystems.

Polypyridyl CoII -Curcumin Complexes as Photoactivated Anticancer and Antibacterial Agents.

Four new CoII complexes, [Co(bpy)2 (acac)]Cl (1), [Co(phen)2 (acac)]Cl (2), [Co(bpy)2 (cur)]Cl (3), [Co(phen)2 (cur)]Cl (4), where bpy=2,2'-bipyridine (1 and 3), phen=1,10-phenanthroline (2 and 4), acac=acetylacetonate (1 and 2), cur=curcumin monoanion (3 and 4) have been designed, synthesized and fully characterized. The X-ray crystal structures of 1 and 2 indicated that the CoN4 O2 core has a distorted octahedral geometry. The photoactivity of these complexes was tuned by varying the π conjugation in the ligands. Curcumin complexes 3 and 4 had an intense absorption band near 435 nm, which made them useful as visible-light photodynamic therapy agents; they also showed fluorescence with λem ≈565 nm. This fluorescence was useful for studying their intracellular uptake and localization in MCF-7 breast cancer cells. The acetylacetonate complexes (1 and 2) were used as control complexes to understand the role of curcumin. The white-light-triggered anticancer profiles of the cytosol targeting complexes 3 and 4 were investigated in detail. These non-dark toxic complexes displayed significant apoptotic photo-cytotoxicity (under visible light) against MCF-7 cells through ROS generation. The control complexes 1 and 2 did not induce significant cell death in the light or dark. Interestingly, 1-4 produced a remarkable antibacterial response upon light exposure. Overall, the reported results here can increase the boundary of the CoII -based anticancer and antibacterial drug development.

DNA interactions, docking and in vitro cytotoxicity studies of [M(Hvalmea)2] complexes (M = CuII, CoIII)

Two new Schiff base mononuclear CuII and CoIII complexes were synthesized by the condensation of monoethanolamine and o-vanillin precursors. The X-ray crystallography of the complexes were reported. Both complexes had same ligands in their structures with different environment around transition metal ions. Different experimental such as absorption studies, cyclic voltammetry, ethidium bromide displacement studies and viscosity measurement besides of docking method were used to study the binding of the complexes to DNA. Based on these studies, intercalation was proposed to be the main mode of binding for both complexes and CuII complex was a better intercalator in interaction with DNA than CoIII complex. Also, CuII complex triggered double strand break in presence of oxidized agent, H2O2. The MTT and Apoptosis/necrosis analysis were revealed that CuII complex induced apoptosis as compared with anticancer agent, Cisplatin.

Metal complexes of 1,4-bis(2-hydroxyethyl) piperazine: Thermodynamic and theoretical approach.

In the present study, the acid-base equilibria of 1,4-bis(2-hydroxyethyl)piperazine (BHEB) and the formation equilibria of complexes with the metal ions Cu(II), Ni(II), Co(II) and Zn(II) are investigated using the potentiometric technique. The acid-dissociation constants of BHEP in the protonated form and the formation constants of the complexes are determined using the Miniquad-75 program in the temperature range (15oC - 35oC). The thermodynamic parameters were determined and discussed. The concentration distribution diagrams of the complexes are evaluated. The effect of metal ion properties such as atomic number, ionic radius, electronegativity, and ionization potential are investigated. The complexes were synthesized and characterized by elemental analysis and mass spectra. Density Functional Theory (DFT) calculations have been performed to study the equilibrium geometry of 1,4-bis(2-hydroxyethyl)piperazine and its complexes. The optimization of the structure of the complexes reveals that CuII and CoII complexes have distorted octahedral geometry. NiII complex has a distorted square planar geometry. ZnII complex has a distorted tetrahedral geometry. The calculated total energies, energies of highest occupied molecular orbital (HOMO), energies of lowest unoccupied molecular orbital (LUMO) and dipole moments are reported. The N---N distance for uncoordinated 1,4-bis(2-hydroxyethyl)piperazine is calculated to be 2.870 Å and decreased to 2.588 Å, 2.491 Å, 2.502 Å, 2.479 Å, and 2.552 Å for Cu(II), Co(II), Ni(II) and Zn(II) complexes respectively. Also, bonds connected to N atoms are elongated upon complex formation. The interactions with the receptors as breast cancer oxidoreductase were feasible as evidenced by Docking analysis.

Catalytic Reductive Amination of Aromatic Aldehydes on Co-Containing Composites

The performance of a series of cobalt-based composites in catalytic amination of aromatic aldehydes by amines in the presence of hydrogen as well as hydrogenation of quinoline was studied. The composites were prepared by pyrolysis of CoII acetate, organic precursor (imidazole, 1,10-phenantroline, 1,2-diaminobenzene or melamine) deposited on aerosil (SiO2). These composites contained nanoparticles of metallic Co together with N-doped carboneous particles. Quantitative yields of the target amine in a reaction of p-methoxybenzaldehyde with n-butylamine were obtained at p(H2) = 150 bar, T = 150 °C for all composites. It was found that amination of p-methoxybenzaldehyde with n-butylamine and benzylamine at p(H2) = 100 bar, T = 100 °C led to the formation of the corresponding amines with the yields of 72–96%. In the case of diisopropylamine, amination did not occur, and p-methoxybenzyl alcohol was the sole or the major reaction product. Reaction of p-chlorobenzaldehyde with n-butylamine on the Co-containing composites at p(H2) = 100 bar, T = 100 °C resulted in the formation of N-butyl-N-p-chlorobenzylamine in 60–89% yields. Among the considered materials, the composite prepared by decomposition of CoII complex with 1,2-diaminobenzene on aerosil showed the highest yields of the target products and the best selectivity in all studied reactions.

Derivatives of cyclam-1,8-diacetic acid: Synthesis and complexes with divalent transition metal ions

1,4,8,11-tetraazacyclotetradecane-1,8-diacetatic acid, H2te2a, and series of its derivative bearing two substituted N-benzyl groups were synthesized and their complexes were studied. Series of CoII and ZnII complexes was prepared in the solid-state and X-ray diffraction analysis showed that the metal ions are hexacoordinated by four nitrogen atoms of the macrocycle and two oxygen atoms of the carboxylate pendants. The two oxygen atoms were in cis and trans mutual position in the CoII and ZnII complexes, respectively. Potentiometric study of CoII, ZnII, CuII and NiII-H2te2a systems showed that the complexes are highly thermodynamically stable and the ligand is selective for CuII ions (logK = 27.5) over the other ions (logK = 21–22). UV-VIS and electrochemical data for the CoII-H2te2a system showed that complexation was rather slow (several hours at pH 4.5, 25 °C) and the complex undergoes slow oxidation with air oxygen.

Synthesis and Spectroscopic methods on the complexation ofCoII, NiII and CuII

The Ligand was synthesized by condensation of Indol 3-hydroxy aldehyde, Glycine and Hydrazine hydrate. The reaction of the ligand with ions (CoII, NiII and CuII ions) yielded complexes, these compounds were characterized by physical and spectroscopic techniques. The conductivity showed a non-electrolytic nature for these compounds. The elemental analysis indicated the ligand to metal ratio as 1:1 with general molecular formula M(L)(H2O)nCl2 (L=ligand; M=metal ions. IR data showed the ligand coordinated to the metal ion via azomethine nitrogen and amine of hydrazide in addition to the amine of indol ring with CuΙΙ. The spectral and magnetic studies of the complexes showed that octahedral geometry for CoΙΙ and NiΙΙ while for CuΙΙ distorted octahedral geometry. The particle size and strain of these compounds have been discussed using X-ray diffraction. The antioxidant study for ligand proved to be a good antioxidant. The compounds have been evaluated for their antimicrobial activity against various organisms.

Incorporation of Switchable Inorganic Building Blocks into Heterometallic Coordination Polymers

A new terpyridine-based ligand with a pyridyl-1,2,4-triazoyl bidentate pocket “out the back” has been used to synthesize monometallic CoII, FeII, and RuII complexes where the octahedral metal is bound in a N6 bis-terpyridine coordination sphere. All four complexes ([MII(Lpyrtz-tpy)2](X)2 where MII = FeII, RuII, CoII with X = BF4–, or MII = CoII with X = PF6–) were structurally characterized confirming the expected bis-terpyridine coordination sphere. The monometallic complexes all show reversible MII/III redox processes, while the CoII complexes also undergo a slow spin crossover over the temperature range 50 K – 350 K. Utilizing the free triazole-pyridine bidentate pocket we show the ability of these complexes to act as supramolecular building blocks able to form 1D and 2D coordination polymers, {[MIIMI(Lpyrtz-tpy)2(MeCN)m]X3}n, with MI being CuI or AgI metal ions, MII = CoII, FeII, or RuII, X = BF4 or PF6, and m = 0 or 1, all five of which were structurally characterized.

Phosphinoquinoline supported CoII, NiII, and FeII complexes: divergent behaviour upon reduction.

The reduction of [CoLBr2], a CoII complex supported by a diisopropylphosphinoquinoline (L) ligand, induced a ligand coupling giving access to a (PNNP) supported CoII complex which was isolated in 70% yield. This complex was formed using a minimum of 2 equivalents of a reductant (either Mn or KC8). The fate of [CoLBr2] in the presence of 1 equivalent of a reductant was more difficult to study; nevertheless, a CoI complex was characterised in the solid state. In order to determine whether this ligand coupling could occur with other 3d metals, L supported FeII and NiII complexes were synthesised. While no compound could be identified upon reduction of [FeLBr2], both [NiLBr2] and [NiL2Br](Br) led to the reduction at the metal center allowing the isolation of an original Ni0 trimer in a satisfactory yield. This study shows the different behaviours of these 3d metal complexes in the presence of a reductant.

Field induced single ion magnet behavior in CoII complexes in a distorted square pyramidal geometry.

We report three CoII-based complexes with the general formula [CoII(L)(X)2] by changing the halide/pseudo-halide ions [X = NCSe (1SeCN); Cl (2Cl) and Br (3Br)]. The obtained τ5 and CShM values confirm a distorted square pyramidal geometry around the CoII ion in all these complexes. In these three complexes, the central CoII ion is situated above the basal plane of the square pyramidal geometry. The extent of distortion from the ideal SPY-5 geometry differs upon changing the coordinating halide/pseudo-halide ion in these complexes. This essentially results in the alteration of the anisotropic parameter D and hence impacts the magnetic properties in these complexes. This phenomenon has been corroborated with the aid of theoretical investigations. All these complexes display field-induced SIM behaviour with magnetic relaxation occurring through a combination of processes depending on the applied dc magnetic field values and dilution.

Cobalt complexes with multi-dentate N-donor ligands: Redox, X-ray photoelectron spectroscopic and theoretical study

Five CoII complexes were prepared with different multi-dentate N-donor ligands (5-Nitro-1,10-phenanthroline, 1,10-phenanthroline, 2,2′:6′,2″-terpyridine, 2,2′-dipyridyl or 4,4′-dimethoxy-2,2′-bipyridine). Complexation was confirmed with the blue-shift of stretching frequency of the CN moiety of the ligands as measured by ATR FTIR and by XPS spectra. The average XPS binding energies (BE) of the main and satellite structures of Co 2p3/2 photoelectron lines for CoII were ca. 780.3 eV and 785.0 eV respectively. The diffusion controlled formal reduction potential E0′ of the CoII/III redox couple measured in aqueous medium ranged between 0.08 and 0.58 V versus NHE. Ihe CoII/I redox couple measured in DMF ranged between between −1.1 and −1.7 V vs HFc/HFc+. Directly proportional relationships were established between the E0′ of both the CoII/III and CoII/I redox couples and the BE of the main CoII 2p3/2 photoelectron lines and DFT calculated energies and charges. These relationships all illustrate the electronic influence of the different N-donor ligands on the effective charge of the central cobalt(II) ion the ligands are coordinated to, can be quantised by the different experimental redox and XPS BE values and DFT calculated electronic descriptors.

Homoleptic octahedral CoII complexes as precatalysts for regioselective hydroboration of alkenes with high turnover frequencies.

Homoleptic complexes adopting octahedral coordination modes are usually less active in catalysis due to the saturated coordination around metal centers that prevents substrate activation in a catalytic event. In this work, we demonstrated that a homoleptic octahedral cobalt complex (1) of 4'-pyridyl-2,2';6',2''-terpyridine that experienced monoprotonation at the non-coordinating pyridyl moiety upon crystallization could serve as a highly efficient precatalyst for the hydroboration of styrene derivatives with Markovnikov selectivity. The solid-state structure of this precatalyst along with relevant homoleptic CoII and FeII complexes has been characterized by X-ray crystallography. In the solid state, 1 features one-dimensional hydrogen-bonded chains that are further stacked by interchain π⋯π interactions. The newly synthesized complexes (1-3) along with several known analogues (4-6) were examined as precatalysts for the hydroboration of alkenes. The best-performing system, 1/KOtBu was found to promote Markovnikov hydroboration of substituted styrenes with high turnover frequencies (TOFs) up to ∼47 000 h-1, comparable to the most efficient polymeric catalyst [Co(pytpy)Cl2]n reported to date. Although some limitations in substrate scope as well as functional group tolerance exist, the catalyst shows good promise for several relevant hydrofunctionaliation reactions.

Cationic surfactant influence on ternary complexes of CoII, NiII, CuII and ZnII ions with aspartic and citric acids

A potentiometric titration study has been undertaken to determine the cationic surfactant influence on mixed ligand complexes in ternary systems consisting of cobalt (II), nickel (II), copper (II), and zinc (II) with aspartic and citric acids at various concentrations (0.0–2.5% w/v) of the CTAB (Cetyltrimethyl ammonium bromide)-surfactant solution while maintaining an ionic strength of 0.16 mol L-1 (NaCl) at 30 °C. Titrations were performed in the presence of different ratios (M:L:X = 1:2:2, 1:4:2, and 1:2:4) of metal (M) and aspartic acid (L) to citric acid (X) using sodium hydroxide. Model systems were developed based on statistical parameters and residual analysis. For Co(II), Ni(II), Cu(II), and Zn(II), the species detected were MLXH2, MLX2H5, and MLX3. The electrostatic relationship of the ligands' side chains, charge neutralization, chelate effect, stacking interactions, and hydrogen bonding are used to explain the trend in the variation of logarithm of stability constants (log β) values with changing dielectric constant and mole fraction of the surfactant. The variation in species distribution as a function of pH and surfactant composition is also presented and discussed, as are plausible equilibria for the formation of the species and structures of the ternary complexes are also presented and discussed.