Cadmium Complexes Research Articles

Microwave assisted synthesized graphene oxide nanocomposites for remediation of toxic metal ions

Here we report the eco-friendly synthesis of graphene magnetic and non-nonmagnetic nanocomposites, namely GO/Fe3O4 and GO-Ni(OH)2, by employing microwave energy. The nanocomposites were explored for the adsorption of toxic Pb2+ and Cd2+ ions. The characterization techniques of XRD, Raman, FESEM and HRTEM confirmed the structure quality and morphology of both nanocomposites. The adsorption studies were conducted using ICP-OES characterization data. The adsorption of Pb2+ and Cd2+ ions on the surface of the nanocomposites were described well by the Freundlich model. The results of the adsorption studies show that the GO/Fe3O4 nanocomposite shows a high adsorption of Cd2+ ions relative to Pb2+ ions due to the formation of a cadmium complex (CdOH +) in the solution which has a higher stability constant value as compared to the lead complex PbOH +. However, the nonmagnetic GO-Ni(OH)2 nanocomposite shows a higher adsorption of Pb2+ ions due to its high electronegativity relative to Cd2+ ions. It was found that the adsorption varies with the concentration of the metal ions.

Synthesis of a new Cd (II) complex as ionophores and its application in construction of a highly selective and sensitive cadmium (II) sensor in petroleum water samples

The measurement of Cd (II) ions in various matrices requires the development of sensors that are selective, sensitive, and simple to produce. The cadmium complex of a ligand prepared by the reaction of 2‐pyridinecarbohydrazide with sodium 3‐formyl‐4‐hydroxybenzenesulfonate, [Cd (NaPH)(H2O)].H2O, was synthesized, analyzed by elemental analysis, and structurally elucidated using various spectroscopic techniques. The infrared spectrum of Cd (II) complex suggests a bi‐negative tri‐dentate ONO behavior for the ligand via deprotonated form of both the enolic oxygen atom (C‐O−) and the hydroxyl group of phenolic ring in addition to the azomethine group. The thermal behavior of this complex was revealed using TGA analysis. Applying Coast–Redfern and Horowitz–Metzger equations, we were able to calculate the kinetic and thermodynamic parameters to support the proposed fragmentation experiment for the Cd (II) complex. Cyclic voltammetry measurement was measured to estimate the electrochemical behavior of the Cd (II) ions as well as the impact of adding various NaH2PH ligand concentrations. The biological applications of [Cd (NaPH)(H2O)].H2O complex were assessed as antioxidant, anticancer, and antimicrobial. Based on the Cd (II) complex, we were able to modify Cd (II) ions carbon paste electrode (modified carbon paste electrode, MCPE) as a Cd (II) selective modifier. The created electrode displays a Nernstian slope in the linear range of 0.0001 to 10 mmol/L of 29.16 ± 0.03 mV decade−1, a quick reaction time of 6 s, and pH independence from 3–7. The suggested MCPE demonstrated strong selectivity to Cd (II) ions relative to many other cations and displayed negligible change in the slope or operating range if the experiment was achieved in a partially non‐aqueous solution. This fabricated MCPE was used to determine Cd (II) ions in diverse water samples.

Pyridine‐derived Schiff base copper (II), zinc (II), and cadmium (II) complexes: Synthesis, structural properties, biological evaluation, and docking studies

Herein, Cu (II), Zn (II), and Cd (II) complexes, [DEP(M)X2], encompassing the pyridine‐derived Schiff‐base ligand DEP, where DEP is (E)‐N,N‐diethyl‐2‐([pyridine‐2‐ylmethylene]amino)ethane‐1‐amine, are synthesized. X‐ray diffraction studies reveal distorted square pyramidal geometries for the Cd (II) and Cu (II) complexes, whereas the geometry of [DEP (Zn)Cl2] can best be described as trigonal bipyramidal. The antibacterial potential of DEP and its [DEP(M)X2] complexes were evaluated against four bacterial strains: Salmonella typhi, Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa; five fungal strains: Candida glabrata, Candida albicans, Microsporum canis, Fusarium solani, and Aspergillus flavus; and Leishmania major protozoan. Complexes exhibited superior bactericidal, fungicidal, and leishmanicidal inhibition potential against all tested microbes compared with the free ligand. The preliminary cytotoxic activity of [DEP(M)X2] complexes on breast and colon carcinoma cells, that is, MCF‐7cell line and HCT‐116 cell line, respectively, revealed that studied complexes showed high cytotoxicity compared with ligand (DEP). Among the studied complexes, [DEP (Cd)Br2] exhibited an excellent inhibitory profile, as confirmed by the docking study. The molecular docking studies showed a good correlation between the biological activities of synthesized metal complexes and docking studies. We have confidence in the contribution of these complexes toward the design of new metal‐derived candidates that can treat infectious diseases.

Monomeric and dimeric cadmium(II) complexes of N4-phenyl semicarbazones: Spectral features, thermogravimetric analysis, DFT study and crystal structure of a bromido bridged complex

Seven cadmium(II) complexes ([Cd(HPySc)Br2] (1), [Cd(HPySc)(OAc)2]·3H2O (2), [Cd(HPySc)Cl2] (3), [Cd(PySc)N3] (4), [Cd(BpSc)(OAc)] (5), [Cd(HBpSc)Cl2] (6), and [Cd2(BpSc)2Br4]) (7) were synthesized using two semicarbazone ligands (HPySc and HBpSc) and characterized by elemental analyses, IR, UV–Vis, thermogravimetric analyses, conductance and single crystal XRD studies. It is found that all the complexes are non-electrolytes in nature and one of the compounds has three molecules of lattice water in the complex. Single crystal study of the complex 7 exhibits a binuclear centrosymmetric structure with a distorted octahedron arrangement around the cadmium(II) centre with Cd⋯Cd non-bonding distance of 4.0809(14) Å. A two-dimensional supramolecular hydrogen bonding network with a zig-zag arrangement is found in the crystal system supported by means of a non-classical hydrogen bonding. DFT calculations reveal that the dimeric complex is the softest and having high chemical reactivity, low stability and high polarizability compared to the other complexes. The NPA and charge distribution analysis indicate that the complexes have significant coordinating sites and potential preferred electron donor sites to metal centers.

Designing of two new cadmium(II) complexes as bio-active materials: Synthesis, X-ray crystal structures, spectroscopic, DFT, and molecular docking studies

The reaction of cadmium(II) chloride hydrate or cadmium(II) nitrate tetrahydrate with 4-fluorobisaroylhydazone ligand (L) in an organic solvent under ambient conditions, produced two different mononuclear cadmium(II) complexes: [CdII(L)2Cl2] (1) and [CdII(L)2(NO3)2] (2) respectively, with different coordination modes and geometrical shapes. A neutral six-coordinate complex with octahedral geometry was obtained for 1, while, a neutral eight-coordinate complex with distorted dodecahedral geometry was confirmed for 2. The geometry optimization and other function analyses were performed using the density functional theory (DFT). In addition, molecular electrostatic potential (MEP) and Hirshfeld surface analyzes were carried out to examine the reactive regions of the crystals. The most suitable conformation bond between our compounds (L, 1, and 2) and the urease or α-glucosidase enzymes has been examined by molecular modeling software, in order to calculate the structure-activity relationship and their binding energies. However, in vitro enzyme inhibition, pharmacokinetics, enzyme kinetic mechanism, and antimicrobial activity studies have been investigated. These studies revealed that the synthesized compounds have a high affinity for binding to both enzymes. Also indicate that compounds 1 and 2 are good candidates as inhibitors for some bacterial strains and enzymes (urease and α-glucosidase) with respect to their MIC and IC50 values.

Structure regulation, fluorescence and explosive identification of cadmium(II) complexes based on 4,5-imidazoledicarboxylic acid ligand

Three new Cd(II) complexes containing 4,5-imidazoledicarboxylic acid (H3IDC) ligand, [Cd(H2IDC)2(H2O)3]·H2O (1), Li2[Cd8(H2IDC)6(HIDC)6]@H2O (2), {[Cd(HIDC)(BBM)]·H2O}n (3) (BBM = 2,2-(1,4-butanediyl)bis-1,3-benzimidazole) have been hydrothermally synthesized under the same conditions and structurally characterized. The compounds show unprecedentedly high structural diversity. Compound 1 is a mononuclear, whereas complex 2 forms a body-centered cubic ion cluster when introducing LiOH·H2O into the reaction system. Complex 3 shows a three-dimensional structure while the bridging ligand BBM was added to the reaction system of complex 1. The degree of H3IDC deprotonating is significant in determining structural diversity. Solid-state fluorescence studies show that the order of solid fluorescence intensity of the three complex is 2 >3 >1. In addition, complex 3 can highly sensitive sense 2,4-dinitrotoluen (2,4-DNT) and 2,4,6-trinitrophenol (TNP) through luminescence quenching effect, the quenching constants are up to 3.6 × 104 M−1 and 1.9 × 105 M−1.

The Anion Impact on Dimensionality of Cadmium(II) Complexes with Nicotinamide

Three novel cadmium(II) coordination compounds, the dimeric [Cd(CH3COO)2(nia)2]2 (1), the polymeric {[Cd(nia)4](ClO4)2}n (2), and the monomeric [Cd(H2O)3(nia)3](ClO4)2·nia (3), were prepared in the reactions of the nicotinamide (pyridine-3-carboxamide, nia) with the corresponding cadmium(II) salts. All prepared compounds were characterized by elemental analyses, FT-IR spectroscopy, TGA/DTA, and single crystal X-ray analysis. The impact of anions (acetate, perchlorate) and solvent used on the dimensionality of cadmium(II) complexes and the cadmium(II) coordination environment was investigated. The bridging capabilities of acetate ions enabled the formation of dimers in the crystal structure of 1. It was shown that the dimensionality of perchlorate complexes depends on the solvent used. The coordination polymer 2 is isolated from an ethanol solution, while monomeric compound 3 was obtained by using a water/ethanol mixture as a solvent. The pentagonal-bipyramidal coordination of cadmium(II) was found in the presence of chelating and bridging acetate ions in 1. In the presence of non-coordinating perchlorate anions in 2 and 3, the coordination geometry of cadmium(II) is found to be octahedral. The supramolecular amide-amide homosynthon R22(8) was preserved in the hydrogen-bonded frameworks of all three compounds.

Distribution of Cd (II) Between Buffered Aqueous Solutions and Chloroform Solution of 4,4´-(1e,1e´)-1,1´-(ethane-1,2-diylbis(azan-1-yl-1ylidene)bis(5-methyl-2-phenyl-2,3-dihydro-1h-pyrazol-3-ol) (H2BuEtP)

The distribution of Cd(ll) between buffered aqueous solutions and chloroform solution of 4,4´-(1e,1e´)-1,1´-(ethane-1,2-diylbis(azan-1-yl-1ylidene)bis(5-methyl-2-phenyl-2,3-dihydro-1h-pyrazol-3-ol) (H2BuEtP) and the effect of 1-(3-hydroxy-5-methyl-2-phenyl-2,3-dihydro-1h-pyrazol-4-yl) butan-1-one (HBuP) as a synergist in the distribution was studied. The concentration of Cd (ll) in aqueous phase after shaking was determined with an Atomic Absorption Spectrophotometer at wavelength of 228nm and the distribution determined by difference. pH 4. 75 - 7.5 was the range in which > 90% distribution of cadmium into organic phases occurred. Slope analysis was used to predict the probable extraction reactions and also the distributing cadmium complexes as Cd(HBuEtP)X and Cd(HBuEtP.BuP) respectively. HBuP slightly increased the pH1/2 from 3.87 ± 0.18 to 4.88 ± 0.12 and partition coefficient KD from 2.19 ± 0.35 to 3.15 ± 0.42. However, the extraction constant Kex2Cd ((-10.09 ± 0.09) in the presence of HBuP was < Kex1Cd (-3.01± 0.9) for H2BuEtP alone. It was recommended that kinetics studies and effect of acids, anions and auxiliary complexing agents on the distribution of cadmium be investigated to fully evaluate the potentials of H2BuEtP in the extraction of cadmium from aqueous media.

A 2D open-framework cadmium(II) complex templated by 1,4-bis(3-aminopropyl)piperazine: crystal structure, optical properties, theoretical and biological study

A 2D open-framework cadmium(II) complex templated by 1,4-bis(3-aminopropyl)piperazine: crystal structure, optical properties, theoretical and biological study

Complex formation of halogen substituted tetraphenylporphyrins and Cd(II)-tetraphenylporphyrins with MnCl2 in DMF

Reactions of complex formation of 5,10,15,20-tetra-(2,6-dichlorophenyl)porphyrin, 5,10,15,20-tetra-(2,6-difluorophenyl)porphyrin and metal exchange of their cadmium complexes with manganese chloride(II) in dimethylformamide were investigated. ortho -Substituted manganese complexes were synthesized by prolonged refluxing of the corresponding porphyrins with an excess of MnCl2 in dimethylformamide. Using the metal exchange reaction of Cd(II)-5,10,15,20-tetra-(2,6-dichlorophenyl)porphyrin and Cd(II)-5,10,15,20-tetra-(2,6-difluorophenyl) porphyrin, the corresponding Mn(III)-tetraphenylporphyrins were obtained. On the contrary, the coordination reactions of porphyrins substituted at the pyrrole and phenyl rings with manganese chloride in dimethylformamide proceed under mild conditions with the formation of complexes Mn(II)-2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetra-(2,6-dichlorophenyl)porphyrin [the compound oxidizes in air to a mixture of Mn(II) and Mn(III)-porphyrins] and Mn(II)-2,3,7,8,12,13,17,18-octachloro-5,10,15,20-tetra-(2,6-difluorophenyl)porphyrin. The synthesized compounds were identified using UV-Vis, 1H NMR spectroscopy and mass-spectrometry. Metal exchange reaction of ortho -substituted Cd(II)-porphyrins and complex formation of 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetra-(2,6-dichlorophenyl)porphyrin with manganese chloride in dimethylformamide were studied by the spectrophotometric method. The kinetic parameters of the reactions were calculated. A strong effect of β- and ortho -substitution on the reactions of complex formation and metal exchange of the studied compounds was found.

Complexation of Halogen-Substituted Tetraphenylporphyrins and Cadmium(II) Tetraphenylporphyrins with MnCl2 in DMF

Complexation of Halogen-Substituted Tetraphenylporphyrins and Cadmium(II) Tetraphenylporphyrins with MnCl2 in DMF

Cd(II) complexes derived from thiazoline, hydrazide and carbodithioate ligands: synthesis, crystal structures and electrochemical sensing of uric acid

Three novel Cd(II) metal complexes 1–3 have been synthesized with different derivatives of thiazoline, hydrazide and carbodithioate. These metal complexes are abbreviated as [Cd (tht)2]n, [Cd (Hpph)2]n and [Cd (mpps)2]n along with their respective ligands Htht, H2pph and mpps. The developed metal complexes are characterized using X‐ray diffraction (XRD) data and other spectroscopic techniques (Infrared [IR], nuclear magnetic resonance [NMR], ultraviolet–visible [UV–vis] and fluorescence). The polymeric nature of these cadmium complexes have been ascertained by single XRD data. Several significant interactions were also revealed, which aid in the stabilization of these complexes' supramolecular architecture. Comparing complex 2 with complexes 1 and 3, the absorption spectra of complex 2 exhibits a greater λmax. On comparing the fluorescence study of these complexes, complex 2 has a higher fluorescence than complexes 1 and 3. The cyclic voltammetry (CV) approach was employed to detect the electrochemical behaviour of these complexes, as well as the sensing of uric acid (UA) by these complexes via modified glassy carbon electrodes (GCEs). According to the conclusions received by CV study, the modified electrode containing complex 3 has admirable UA electro catalytic activity. This UA electrochemical sensing device offers a low detection limit (0.3 μM), fine linear ranges (30–1500 μM), reasonable sensitivity, and a fast reaction time.

The selective and sustainable separation of Cd(II) using C6MImT/[C6MIm]PF6 extractant

Cadmium has been classified as a kind of human carcinogens, and has a strong mobility in the water environment and this can result in serious harm to human health and environmental safety. Here, a new selective and efficient extraction-recovery strategy for Cd purification is provided by using C6MimT/[C6Mim]PF6 as the green extractant. Due to the high compatibility between C6MimT and [C6Mim]PF6, C6MimT-Cd was efficiently separated from the aqueous phase. When the concentration of Cd(II) was 1000 mg/L, the extraction rate could reached 99.9 %. By comparing [C6MIm]BF4 with [C6MIm]PF6, the hydrophobicity restrained the ion exchange between cation and Cd and significantly reduced the loss of extractant. The extracted Cd(II) was separated in the form of precipitation after stripping. The extraction system of C6MimT/[C6Mim]PF6 was stable after several extraction-stripping cycles. The extraction of Cd(II) by C6MimT/[C6Mim]PF6 system mainly realized by forming a neutral and extractable cadmium complexes between Cd(II) and thione. Based on the natural complexation mechanism between metal and C6MImT, Cd exists as obvious competitive advantage in coordination with C6MimT compare to Pb, Zn, Mg, Cr, Fe. This work overcomes the problems of extractant loss and organic pollution caused by volatile or ion exchange, which can only reduce environmental hazards, but also promote the recovery of cadmium and other valuable resources.

Synthesis, spectral characterization, DFT studies, and computational screening of 4‐amino‐3‐mercapto‐5‐methyl‐1,2,4‐triazole and its cadmium(II) mixed ligands complexes as potential antimalaria drug

AbstractIn this research paper we report the detailed synthesis, spectral (1H‐NMR, FT‐IR, and UV‐Vis), crystal structure determination, DFT studies, and molecular modeling of 4‐amino‐3‐mercapto‐5‐methyl‐1,2,4‐triazole (L2) Schiff base ligand and its complexes of cadmium as suitable bioactive agents for the treatment of malaria. From the spectroscopic results, the synthesized Schiff base has potentialtridentate coordination with themetal ion via hydroxy naphthalinic‐O, azomethine‐N and sulphur atom of the thione group. First principle theoretical calculations within the framework of density functional theory (DFT) were conducted to scrutinize the stability, reactivity, energetics, and the nature of bonding interactions in the studied Schiff base and its complexes. In‐silico molecular simulation was also executed to comprehend the conformation of interaction of the studied compounds against malaria (1LS5) protein for possible treatment of the disease. The observed binding affinity for the ligand (L2), its mono‐ligand complex [CdL2Cl], mixed ligands complex [CdL2TH]Cl and the standard drug are ‐7.23, ‐7.63, ‐7.3, and ‐7.60 kcal/mol, respectively, indicating that the Schiff base and is Cd2+ complexes have the potential to be developed into therapeutic drug for the treatment of malaria.

Homodinuclear tetradentate Schiff base complexes of nickel(II), cadmium(II) and mercury(II): synthesis, photophysical and mesophase investigation

ABSTRACT Dinuclear Ni(II), Cd(II) and Hg(II) complexes have been prepared from photoluminescent salicylaldimine tetra-coordinated [N4O4] donor compartmental Schiff base ligand. The photophysical and mesogenic properties of the compounds are investigated. The compounds are characterized by elemental analyses, mass, 1HNMR, FT-IR and UV–visible spectroscopy. The complexes adopted distorted square planar geometry. The ligand and Ni complex exhibit monotropic thermal transition in DSC thermogram whereas Cd or Hg complexes are non-mesogenic. All the complexes displayed blue emission at ∼450 nm.

Study on Fluorescence Recognition of Fe3+, Cr2O72- and p-Nitrophenol by a Cadmium Complex and Related Mechanism.

The effective detection of environmental pollutants is very important to the sustainable development of human health and the environment. A luminescent Cd(II) coordination complex, {[Cd(dbtdb)(1,2,4-H3btc)]·0.5H2O}n (1) (dbtdb = 1-(2,3,5,6-tetramethyl-4-((2-(thiazol-4-yl)-2H-benzo[d]imidazol-3(3aH)-yl)methyl)benzyl)-2,7a-dihydro-2-(thiazol-4-yl)-1H-benzo[d]imidazole, 1,2,4-H3btc = 1,2,4-benzenetricarboxylic acid), was obtained by hydrothermal reactions. Complex 1 has a chain structure decorated with uncoordinated Lewis basic O and S donors and provides good sensing of Fe3+, Cr2O72-, and p-nitrophenol with fluorescence quenching through an energy transfer process. The calculated binding constants were 3.3 × 103 mol-1 for Fe3+, 2.36 × 104 mol-1 for Cr2O72-, and 9.3 × 103 mol-1 for p-nitrophenol, respectively. These results show that 1 is a rare multiresponsive sensory material for efficient detection of Fe3+, Cr2O72-, and p-nitrophenol.

Varying growth behavior of redox-sensitive nanoparticles on 1:1 and 2:1 clay surfaces: Mechanistic insights on preferential toxic ions removal in mono, co, and multi-metal contaminated waters

In the current study, contrasting growth behaviour of redox sensitive Fe0 nanoparticles (nZVI) was observed on different clay surfaces i.e., 1:1 non-swelling kaolinite (K-nZVI) and 2:1 swelling bentonite (B-nZVI). Osmotic swelling of bentonite led to Fe0 nucleation and growth of 5–7 nm size particles in the broadened interlayer spaces. B-nZVI had negative zeta potential due to the domination of the surface charge of bentonite clay. In contrast, kaolinite has shown dominant surface growth of nZVI particles (>24.8 ± 7.4 nm) and positive zeta potential, suggesting domination of Fe0 nanoparticles (nZVI) characteristics. This surface-dependent variation led to higher and faster removal of oxy-anions with K-nZVI, i.e., chromium and arsenic (87.5 and 157.35 mg/g) than B-nZVI (18.4 and 86.9 mg/g). In comparison, B-nZVI has shown higher sorption of cations i.e., nickel and cadmium (36 mg/g and 46 mg/g) than K-nZVI (25 and 27 mg/g). XPS and pXRD analysis of reaction precipitates confirmed reductive sorption of chromium, co-precipitation/ complexation of arsenic, electrostatic attraction and complexation of nickel and cadmium as major removal mechanisms. Drastically higher total contaminant sorption capacities of B-nZVI (327 mg/g) and K-nZVI (372 mg/g) in multi-contaminant (Cr + As + Ni + Cd) solutions than individual capacities in mono-ionic solutions was due to co-operative effects and newer sites induced via sorption and redox-transformation of other ionic species. K-nZVI removed chromium and arsenic to below drinking water permissible limits whereas B-nZVI succeeded in separating nickel and cadmium to drinkable levels in groundwater, freshwater, river water, and wastewater samples, emphasizing their applicability in high cationic—low anionic and low cationic-higher anionic species contaminated waters, respectively.

Two Schiff-base complexes of cadmium and manganese on modified MCM-41 as practical, recyclable and selective nanocatalysts for the synthesis of sulfoxides

Two Schiff-base complexes of cadmium and manganese on modified MCM-41 as practical, recyclable and selective nanocatalysts for the synthesis of sulfoxides

Synthesis and Characterization of Mixed Ligands Cadmium (II) Complexes with N-Hydroxymethylsaccharinate and diphosphines

Reaction of cadimium(II) chloride CdCl2.6H2O with two equivalents of N-hydroxymethylsaccharin (Sac-CH2OH) (1) in the presence of NEt3 afforded the presumably tetrahedral complex [Cd(K2-Sac-CH2O)2] (2). The Sac-CH2O- ligand behaves as a bidentate chelate. Reaction of (2) with one equivalent of the bidentate ligands (dipos); Ph2P(CH2)nPPh2, (n = 1 dppm; 2 dppe; 3 dppp; 4 dppb), Ph2P(S)(CH2)P(S)Ph2 (dppmS2) afforded tetrahedral complexes of the type [Cd(K1-Sac-CH2O)2(diphos)] (3-7). The reaction with two equivalents of the monodentate ligands (phos); Ph3P or Ph3PS gave [Cd(K1-Sac-CH2O)2(phos)2] (8,9). The N-hydroxymethylsaccharinate anion acts as a monodentate ligand to the cadmium center through the hydroxymethyl oxygen atom. The complexes were characterized by physico-chemical and spectroscopic methods.

Synthesis and Characterization of Zinc(II), Cadmium(II), and Palladium(II) Complexes with the Thiophene-Derived Schiff Base Ligand.

Zn(II), Pd(II), and Cd(II) complexes, [L TH MCl 2 ] (M = Zn, Pd; X = Br, Cl) and [L TH Cd(μ-X)X] n (X = Cl, Br; n = n, 2), supported by the (E)-N 1,N 1-dimethyl-N 2-(thiophen-2-ylmethylene)ethane-1,2-diamine (L TH ) ligand are synthesized and structurally characterized. Density functional theory (DFT) electronic structure calculations and variable-temperature NMR support the presence of two conformers and a dynamic interconversion process of the minor conformer to the major one in solution. It is found that the existence of two relevant complex conformers and their respective ratios in solution depend on the central metal ions and counter ions, either Cl- or Br-. Among the two relevant conformers, a single conformer is crystallized and X-ray diffraction analysis revealed a distorted tetrahedral geometry for Zn(II) complexes, and a distorted square planar and square pyramidal geometry for Pd(II) and Cd(II) complexes, respectively. It is shown that [L TH MCl 2 ]/LiO i Pr (M = Zn, Pd) and [L TH Cd(μ-Cl)Cl] n /LiO i Pr can effectively catalyze the ring-opening polymerization (ROP) reaction of rac-lactide (rac-LA) with 94% conversion within 30 s with [L TH ZnCl 2 ]/LiO i Pr at 0 °C. Overall, hetero-enriched poly(lactic acid)s (PLAs) were provided by these catalytic systems with [L TH ZnCl 2 ]/LiO i Pr producing PLA with higher heterotactic bias (P r up to 0.74 at 0 °C).