Interactions of N-acetyl-l-cysteine with metals (Ni2+, Cu2+ and Zn2+): an experimental and theoretical study

In recent years, interactions of metal ions with amino acid derivatives have been studied extensively due to their immense importance in the life-supporting processes. Here, we report the synthesis of three metal (Ni²⁺, Cu²⁺, and Zn²⁺) complexes of N-acetyl-l-cysteine (NAC) using a solvent-free solid-state method. Characterization of the complexes by elemental analyses, molar conductance, SEM, infrared and electronic absorption spectra reveals that the metal ions bind to the NAC molecules in 1:2 molar ratio (metal:ligand) via the S-atoms. Theoretical calculations are carried out using the B3LYP hybrid functional in combination with 6-31++G(d,p) and LANL2DZ basis sets to investigate the effects of metal coordination on the backbone structural features of NAC and geometry about the α-carbon atom. The molecular geometries of NAC as well as its metal complexes are fully optimized in gas phase without applying any geometrical constraint, and a second derivative analysis confirms that all the optimized geometries are true minima. TD-DFT single-point calculations are performed in aqueous phase to obtain the theoretical λ _max values. The gas-phase interaction enthalpies (metal ion binding affinities), Gibbs energies, HOMO/LUMO energies as well as their energy gaps, rotational constants, dipole moments, and theoretically predicted vibrational spectra of all the reaction species are also calculated and thoroughly analyzed. Most of the experimental results are well reproduced by the B3LYP level of calculations. Metal ion coordination to NAC modifies its backbone structural features as well as the geometry about the α-carbon atom.     

Complexation of Cd2+, Ni2+, and Ag+ metal ions with 4,13-didecyl-l,7,10,16-tetraoxa-4,13-diazacyclooctadecane in acetonitrile-ethylacetate binary mixtures

Conductometric titrations have been performed in acetonitrile-ethylacetate (AN-EtOAc) binary solutions at 288, 298, 308, and 318 K to obtain the stoichiometry, the complex stability constants and the standard thermodynamic parameters for the complexation of Cd²⁺, Ni²⁺, and Ag⁺ cations with 4,13-didecyl-1,7,10,16-tetraoxa-4,13-diazacyclooctadecane (cryptand 22DD). The stability constants of the resulting 1: 1 complexes formed between the metal cations and the ligand were determined by computer fitting of the conductance-mole ratio data. There is a non-linear relationship between the logK _f values of complexes and the mole fraction of ethylacetate in the mixed solvent system. In addition, the conductometric data show that the stoichiometry of the complexes formed between the Cd²⁺, Ni²⁺, and Ag⁺ cations with the ligand changes with the nature of the solvent. The standard enthalpy and entropy values for the 1: 1 [ML] complexation reactions were evaluated from the temperature dependence of the formation constants. Thermodynamically, the complexation processes of the metal cations with the C22DD, is mainly entropy governed and the values of thermodynamic parameters are influenced by the nature and composition of the binary mixed solvent solutions.     

Synthesis,characterization, molecular modelling and biological activity of 2‐(pyridin‐1‐ium‐1‐yl) acetate and its Cu2+, Pt4+, Pd2+, Au3+ and Nd3+ complexes

A new series of Cu²⁺, Pt⁴⁺, Pd²⁺, Au³⁺ and Nd³⁺ complexes derived from 2‐(pyridin‐1‐ium‐1‐yl) acetate have been synthesized and characterized using elemental analyses, spectral (infrared (IR), UV–visible, mass, ¹³C NMR and ¹H NMR), magnetic and thermal measurements. IR results suggest that the ligand acts in a neutral monodentate fashion in all complexes. Octahedral geometry is proposed for Cu²⁺ and Pt⁴⁺ complexes and square‐planar for Pd²⁺ and Au³⁺ complexes. The bond lengths, bond angles, and HOMO and LUMO were calculated. Superoxide dismutase‐like radical scavenger activity and cytotoxic activity of the isolated complexes on HepG2 liver cancer cells have been screened. Ligand and complexes (Pt⁴⁺ and Nd³⁺) exhibit potent antioxidant activity upon coordination while Cu²⁺ and Au³⁺ complexes do not show superoxide dismutase‐like radical scavenger activity. The cytotoxic activity assay against HepG2 cell line proves that the ligand and its Pt⁴⁺ complex have a high cytotoxic activity, while the other complexes showed no cytotoxic activity. Copyright © 2014 John Wiley & Sons, Ltd.     

Metal complexes of macrocyclic ligands. Part XXXIII. Effect of the side-chain length on the on/off equilibrium in the Ni2+ and Cu2+ complexes of 11-(2-aminoethyl)- and 11-(3-aminopropyl)-1,4,7,11-tetraazacyclotetradecane

Alkylation of 1,4,7-tritosyl-1,4,7,11-tetraazacyclotetradecane with CH₂O/KCN or acrylonitrile gave the corresponding cyanomethyl or 2-cyanoethyl derivatives, which, by treatment with Na in BuOH, were detosylated and reduced to the macrocyclic pentaamines 1 and 2 . The Ni²⁺ and Cu²⁺ complexes with 1 and 2 show a reversible pH-dependent change in geometry, in which the side-chain amino group is either coordinated to the metal ion (basic form) or protonated and, thus, non-coordinated (acidic form). The length of the side chain determines the log K_a values of these protonation/deprotonation equilibria: 1.89 and ～ 2.0 for the Cu²⁺ and Ni²⁺ complexes of ligand 1 with the 2-aminoethyl side chain, and 6.17 and 7.43 for the Cu²⁺ and Ni²⁺ complexes of ligand 2 with the 3-aminopropyl side chain.     

Synthesis,spectroscopic characterization and study the effect of gamma irradiation on VO2+, Mn2+, Zn2+, Ru3+, Pd2+, Ag+ and Hg2+ complexes and antibacterial activities

Novel complexes of VO²⁺, Mn²⁺, Zn²⁺, Ru³⁺, Pd²⁺, Ag⁺ and Hg²⁺ have been prepared by reacting their metal salts with ligand, named (4-(4-chlorophenyl)-1-(2-(phenylamino) acetyl) thiosemicarbazone). Study of synthesized metal complexes was confirmed by different analytical and spectral techniques (¹H NMR, MS, FT-IR, UV–Vis, EPR and Powder X-ray diffraction), thermogravimetric studies as well as molecular modeling. FT-IR spectra showed that the compound behave as neutral or monobasic tetradentate. In case of complexes of Mn²⁺, Zn²⁺, Ag⁺ and VO²⁺, through (N2H), (CO) or (CO) groups. While, the ligand behave as neutral bidentate in case of complexes with Pd²⁺ and Hg²⁺. X-ray diffraction pattern of Mn²⁺, Pd²⁺ and Ag⁺ complexes before and after irradiation are recorded. XRD studies exhibited that decrease in the crystalline size of sample Mn²⁺ as compared of samples Ag⁺ and Pd²⁺ upon irradiation and irradiation influenced the crystallinity of the complexes. The possible structures of the ligand, Mn²⁺, Pd²⁺ and Hg²⁺complexes have been computed by means of the molecular mechanic calculations using the hyper chem. 8.03 molecular modeling program. The bond length, bond angle, HOMO, LUMO and dipole moment have been studied to verify the geometry of Mn²⁺, Pd²⁺ and Hg²⁺ complexes. The effect of gamma irradiation was investigated by recording the new results of pervious spectroscopic techniques and other measurements. Thermal studies of these chelates before and after γ-irradiation showed that the complexes after γ-irradiation were more thermally stable than before γ-irradiation. The compound and its metal complexes have been experienced for their inhibitory outcome on the growth of microorganisms against gram positive and gram negative. The results proved that the complexes B₁–B₇ have potent antibacterial activity as compared to that of ligand.     

Metal complexes with macrocyclic ligands. Part XXII. Synthesis two of bis-tetraaza-macrocycles and study of the structures,electrochemistry, VIS and EPR spectra of their binuclear Cu2+ and Ni2+ complexes

The two bis-macrocycles 4 and 5 in which the tetraaza units are separated by a chain of different length, have been synthesized using 1,4,7-tritosyl-1,4,7,11-tetraazacyclotetradecane as starting compound and bifunctional alkylating agents. The bis-macrocycles give binuclear complexes with Ni²⁺ and Cu²⁺, the properties of which have been studied to obtain information about the interaction of the two subunits as a function of the distance. The VIS spectra of the Ni²⁺ and Cu²⁺ complexes indicate that both metal ions are in a square-planar geometry as expected from the results of the analogous complexes with 1,4,7,11-tetraazacyclotetradecane 7 . Cyclic voltammetry and differential pulse polarography of the binuclear Ni²⁺complexes in CH₃CN show a single two-electron step for ligand 5 , whereas two distinct one-electron redox processes can be observed for ligand 4 , indicating that the two metal ions interact with each other when the chain length is shorter. Similarly, the EPR studies of frozen solutions of the binuclear Cu²⁺ complexes clearly show that a magnetic dipolar interaction between the two paramagnetic centers exists, and that the strength of it depends upon the length of the bridge. Finally, from the X-ray structures of the binuclear Ni²⁺ complexes with 4 and 5 , it is seen that the two rings are kept apart as far as possible, the distances between the two metal ions determined in the solid correlate well with the observations in solution.     

Syntheses,Characterization, and DNA Binding Studies of a Series of Copper(II), Nickel(II), Platinum(II) and Zinc(II) Complexes Derived from Schiff Base Ligands

Three series of metal salophen complexes derived from Zn²⁺, Cu²⁺, Pt²⁺ and Ni²⁺ have been synthesized and their interaction with quadruplex DNA has been evaluated. The compounds differ on the number of ethyl piperidine substituents. They have been characterized by ¹H NMR, IR and UV-visible spectroscopies and by HR-mass spectrometry. Their luminescent properties have been also evaluated and we can observe that, as expected, Zn²⁺ and Pt²⁺ complexes are those displaying more interesting luminescence with an emission band red-shifted with respect to the corresponding uncoordinated ligand. DNA interactions with G4 and duplex DNA were evaluated by FRET melting assays (for the Zn²⁺, Cu²⁺ and Ni²⁺ complexes) and by emission titrations (for one Pt²⁺ complex) which indicated that the disubstituted compounds 2-Ni and 2-Pt are the only ones that display good affinity for G4 DNA structures.     

New Mononuclear and Binuclear Cu(II), Co(II), Ni(II), and Zn(II) Thiosemicarbazone Complexes with Potential Biological Activity: Antimicrobial and Molecular Docking Study

Herein, we report the synthesis of eight new mononuclear and binuclear Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ methoxy thiosemicarbazone (MTSC) complexes aiming at obtaining thiosemicarbazone complex with potent biological activity. The structure of the MTSC ligand and its metal complexes was fully characterized by elemental analysis, spectroscopic techniques (NMR, FTIR, UV-Vis), molar conductivity, thermogravimetric analysis (TG), and thermal differential analysis (DrTGA). The spectral and analytical data revealed that the obtained thiosemicarbazone-metal complexes have octahedral geometry around the metal center, except for the Zn²⁺-thiosemicarbazone complexes, which showed a tetrahedral geometry. The antibacterial and antifungal activities of the MTSC ligand and its (Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺) metal complexes were also investigated. Interestingly, the antibacterial activity of MTSC- metal complexes against examined bacteria was higher than that of the MTSC alone, which indicates that metal complexation improved the antibacterial activity of the parent ligand. Among different metal complexes, the MTSC- mono- and binuclear Cu²⁺ complexes showed significant antibacterial activity against Bacillus subtilis and Proteus vulgaris, better than that of the standard gentamycin drug. The in silico molecular docking study has revealed that the MTSC ligand could be a potential inhibitor for the oxidoreductase protein.     

Frontispiece: Square-Planar Anionic Pt0 Complexes

A T-shaped Pt⁰ complex with a diphosphine-borane (DPB) ligand was prepared. The Pt→B interaction enhances the electrophilicity of the metal and triggers the addition of Lewis bases to give the corresponding tetracoordinate complexes. For the first time, anionic Pt⁰ complexes are isolated and structurally authenticated. X-ray diffraction analyses show the anionic complexes [(DPB)PtX]⁻ (X=CN, Cl, Br, I) to be square-planar. The d¹⁰ configuration and Pt⁰ oxidation state of the metal were unambiguously established by X-ray photoelectron spectroscopy and DFT calculations. The coordination of Lewis acids as Z-type ligands is a powerful mean to stabilize elusive electron-rich metal complexes and achieve uncommon geometry.     

Nickel(II), palladium(II) and platinum(II) complexes of <Emphasis Type="Italic">N</Emphasis>-allyl-<Emphasis Type="Italic">N</Emphasis>′-pyrimidin-2-ylthiourea

Platinum(II), palladium(II) and nickel(II) complexes with N-allyl-N′-pyrimidin-2-ylthiourea were synthesized in 1:1 and 1:2 [metal:ligand] stoichiometric ratios and characterized by elemental analyses, molar conductivities, magnetic susceptibilities and by i.r., u.v.-vis., ¹H- and ¹³C-n.m.r. and mass spectra. The ¹H- and ¹³C- n.m.r. chemical shifts reveal coordination of one pyrimidine-N and sulphur atoms to Pt^II and Pd^II. The i.r. spectra indicate that the ligand behaves as a neutral monodentate towards Ni^II; coordinates via a pyrimidine-N and as a bidendate towards Pd^II and Pt^II coordinates via thione-S and a pyrimidine-N. The magnetic moments and electronic spectral data suggest a square-planar geometry for Pt^II and Pd^II complexes, a mixture of square-planar and tetrahedral geometries for the tetracoordinate Ni^II complex and octahedral for the six-coordinate one. The E.I. mass spectra of the complexes showed some isotope ion peaks of [M]⁺ and fragments containing metals; assignments of fragments containing metal ions were supported by the appearance of their peaks among isotope clusters.     

Analysis of vibrational spectra (FT-IR and VCD) and nonlinear optical properties of [Ru(L)3]2+ complexes

Density functional theory calculations were performed on [Ru(L)₃]²⁺ (L = 1,10-phenanthroline, 2,2′-bipyridine, 2,2′-bipyrimidine, 2,2′-bipyrazine) complexes by employing B3PW91 functional and LAN2DZ basis set to predict their spectra and nonlinear optical response. The geometrical and coordination energy studies explained that the stability of [Ru(L)₃]²⁺ metal complexes depends on the extent of interaction of the dπ orbitals of Ru²⁺ with the π* ligand orbitals, which is maximum for 1,10-phenanthroline. The two enantiomers of the [Ru(L)₃]²⁺ show IR absorption peaks in the region of 1100–1800 cm^?1, and a slight shift occurs to lower frequency by solvent. The vibrational circular dichroism peaks of [Ru(phen)₃]²⁺ had major contribution from out-of-phase stretching of 1,10-phenanthroline rings and a minor contribution from H–C=C–H wagging and C=C stretching of rings. Maximum hyperpolarizability was observed for [Ru(phen)₃]²⁺ due to stronger anharmonicity in the π-electron system. Among the [Ru(L)₃]²⁺ (L = bpy, bpm, and bpz) complexes, [Ru(bpm)₃]²⁺ shows enhanced hyperpolarizability due to increase in the dipole along the X-direction. In derivative Ru²⁺ complexes, we found that hyperpolarizability depends on electron-donating capability of the substituent. As per FMOs study, the HOMO is predominantly metal fragment based, the LUMO is primarily ligand based, and the larger value of hyperpolarizability corresponds to the lower E_LUMO–E_HOMO gap, reflecting that nonlinear optical response is a consequence of additive dipolar responses of charge transfer and hyperpolarizability.     

Study of Complex Formation Between Dicyclohexano-18-Crown-6 (DCH18C6) with Mg 2+, Ca2+, Sr 2+, and Ba2+ Cations in Methanol–Water Binary Mixtures Using Conductometric Method

The complexation reactions between Mg²⁺,Ca²⁺,Sr²⁺ and Ba²⁺ metal cations with macrocyclic ligand, dicyclohexano-18-crown-6 (DCH18C6) were studied in methanol (MeOH)–water (H₂O) binary mixtures at different temperatures using conductometric method . In all cases, DCH18C6 forms 1:1 complexes with these metal cations. The values of stability constants of complexes which were obtained from conductometric data show that the stability of complexes is affected by the nature and composition of the mixed solvents. While the variation of stability constants of DCH18C6-Sr ²⁺ and DCH18C6-Ba²⁺versus the composition of MeOH–H₂O mixed solvents is monotonic, an anomalous behavior was observed for variations of stability constants of DCH18C6-Mg²⁺ and DCH18C6-Ca²⁺ versus the composition of the mixed solvents. The values of thermodynamic parameters (ΔH_c°, ΔS_c°) for complexation reactions were obtained from temperature dependence of formation constants of complexes using the van’t Hoff plots. The results show that in most cases, the complexation reactions are enthalpy stabilized but entropy destabilized and the values of thermodynamic parameters are influenced by the nature and composition of the mixed solvents. The obtained results show that the order of selectivity of DCH18C6 ligand for metal cations in different concentrations of methanol in MeOH–H₂O binary system is: Ba²⁺>Sr²⁺>Ca²⁺> Mg²⁺.     

Formation of MSeO4(aq) complexes (M2+ = Mg2+, Co2+, Ni2+, Cu2+, Cd2+) studied as a function of temperature by affinity capillary electrophoresis

Complexation of divalent cations (Mg²⁺, Co²⁺, Ni²⁺, Cu²⁺, Cd²⁺) by selenate ligand was studied by ACE (UV indirect detection) in 0.1 mol/L NaNO₃ ionic strength solutions at various temperatures (15, 25, 35, 45 and 55°C). For each solution, a unique peak was observed as a result of a fast equilibrium between the free ion and the complex (labile systems). The migration time corresponding to this peak changed as a function of the solution composition, namely the free and complexed metal concentrations, according to the complexation reactions. The results confirmed the formation of a unique 1:1 complex for each cation. The thermodynamic parameters were fitted to the experimental data at 0.1 mol/L ionic strength: (25°C) = ?(6.5 ± 0.3), ?(7.5 ± 0.3), ?(7.7 ± 0.3), ?(7.7 ± 0.3), and –(8.1 ± 0.3) kJ/mol and = 2.5 ± 0.2, 4.7 ± 0.4, 4.5 ± 0.6, 8.4 ± 1.1, and 7.2 ± 0.6 kJ/mol for M²⁺ = Mg²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Cd²⁺, respectively. Complexes with alkaline earth and transition metal cations could be distinguished by their relative stabilities. The effect of the ionic medium was treated using the specific ion interaction theory and the thermodynamic parameters at infinite dilution were compared to previously published data on metal–selenate, metal–sulfate, and metal–chromate complexes.     

Spectrophotometric and conductometric studies of the thermodynamics complexation of Zn2+, Ni2+, Co2+, Pb2+ and Cu2+ ions with 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane ligand in acetonitrile solution

The complexation reaction between 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane ligand (Kryptofix5) and Zn²⁺, Ni²⁺, Co²⁺, Pb²⁺ and Cu²⁺ ions were studied conductometrically in acetonitrile solution. The formation constants of the resulting 1:1 complexes were calculated from the computer fitting of the molar conductance and absorbance measurements in various mole ratios. The enthalpy and entropy changes of the complexation reactions were derived from titration conductometry in acetonitrile at various temperatures. At 25 °C, the stability of the resulting complexes varied in the order Pb²⁺ > Zn²⁺ > Cu²⁺> Co²⁺> Ni²⁺.     

Synthesis,characterization and interaction with DNA of mononuclear metal complexes with oxolinic acid

Seven new neutral mononuclear metal complexes of VO²⁺, Mn²⁺, Fe³⁺, Co²⁺, Ni²⁺, Zn²⁺ and Cd²⁺ with the quinolone antibacterial agent oxolinic acid (=Hoxo) have been prepared and characterized with physicochemical and spectroscopic techniques. In all the complexes, oxolinic acid acts as a bidentate deprotonated ligand bound to the metal through the pyridone oxygen and one carboxylate oxygen. The metals in all the complexes are six-coordinate with slightly distorted octahedral geometry. The lowest energy model structures of the complexes Fe(oxo)₃, VO(oxo)₂(H₂O) and Mn(oxo)₂(H₂O)₂ have been determined with molecular modeling calculations. The ability of all the complexes to bind to calf-thymus DNA has been investigated with diverse spectroscopic techniques.     

Untersuchung der Komplexierung von Na+, K+, Ca2+ und Ba2+ mit einigen elektrisch neutralen Liganden durch Messung von 13C-chemischen Verschiebungen und Spin-Gitter-Relaxationszeiten

Investigation of the complexing of Na⁺, K⁺, Ca²⁺ and Ba²⁺ with some uncharged ligands by ¹³C-chemical shift and spin-lattice relaxation time measurements The influence of Na⁺, K⁺, Ca²⁺ and Ba²⁺ ions on ¹³C chemical shifts and on spin-lattice relaxation times of some electrically neutral ion carriers was investigated. In the solvents CD₃CN and CD₃OD and in presence of an excess of metal ions ligand 4 (see the Scheme) forms complexes of 1:1 stoichiometry. All four oxygen atoms of the ligand as well as solvent molecules take part in the coordination. In CDCl₃ as solvent, for all ions investigated except sodium, only 1:2 complexes (metal/ligand) were observed with 4 . Sodium ions form both 1:1 and 1:2 complexes in this solvent. In the 1:2 complexes of the investigated monovalent ions only one, in those of the divalent ions both amide carbonyl groups of ligand 4 take part in the coordination.     

Novel nanostructured dendrimer based on 1,3-bis(4,6-dichloro-1,3,5-triazine-2-yl)urea as an excellent adsorbent for Pb2+, Ni2+, Co2+ and Zn2+ metal ions

Human health is seriously harmed by the consumption of poor-quality water. Due to high toxicity and water solubility, heavy metals are present in wastewater discharged from numerous industries. In the environmental realm, metal-containing water must be treated before being released. A dendrimer is a superior adsorbent for the removal of heavy metal ions due to its nanostructure and hydrophilic end group. In this work, a novel triazine-based hydroxy-terminated dendrimer up to generation three is designed employing a carbamide core. The dendrimer's structure was explored using FT-IR and ¹H NMR studies. Full generation dendrimers UG1.0, UG2.0, and UG3.0 were utilized as an adsorbent for Pb²⁺, Ni²⁺, Co²⁺ and Zn²⁺ metal ion removal from water in a series of tests. The ability of dendrimers to uptake Pb²⁺, Ni²⁺, Co²⁺ and Zn²⁺ metal ions was investigated under various pH, time interval and dendrimer generation parameters. The presence of metal in the dendrimer was confirmed by FT-IR studies of dendrimer-metal complexes. The overall results show that Pb²⁺, Ni²⁺, Co²⁺ and Zn²⁺ metal ions uptake increases with the generation, time, and pH.     

Spectral and electro-chemical characterization of transition metal complexes of a modified [N<Subscript>6</Subscript>] macrocycle. A mimic to cyclic hexapeptide

The 16-membered modified [N₆] macrocylic ligand (L), a mimic to cyclic, hexapeptide is reacted with MCl₂ and MCl₃ resulting in complexes with stoichiometrices [MLCl₂] (M = Cr, Mn, Co, Ni, Cu), [MLCl₃] (M = Pt, Pd) and [MLCl₂]Cl (M = Fe, Ru). Its reactions with the precursors [M(Ph₃P)₂Cl₂] (M = Co, Ni, Pt, Pd) follow a ligand displacement path affording the final products which do not contain coordinated Ph₃P. Complexes have been characterized from results of elemental analyses, conductometric, magnetic susceptibility, i.r. and u.v.–vis (ligand field) spectral studies. Magnetic susceptibility and ligand field spectral data are consistent with a hexacoordinate geometry for Cr²⁺, Mn²⁺, Fe³⁺, Co²⁺, Ni²⁺ and Cu²⁺ and four coordinate square-planar geometry for Pt²⁺ and Pd²⁺. Molecular orbital computations using CSChem ultra MOPAC software for an optimized minimum energy plot of the structure shows that the ligand binds metal ions as a tetradentate (N,N,N,N) chelating agent. Cyclic voltammetric studies indicate formation of stable reversible or quasi-reversible redox couples in solutions, which corroborates a kinetic stability of these complexes in their variable oxidation states.     

Influence of the central metal on the crystal structures and electronic structures of biferrocene trinuclear complexes

Five metal-bridged biferrocene complexes of the Schiff-base ligand (HL = S-benzyl-N-(ferrocenyl-1-methyl-methylidene)dithiocarbazate) have been studied by single crystal X-ray diffraction and ⁵⁷Fe Mössbauer spectroscopy. The crystal structures of the complexes show that the central metal ions are tetra-coordinated by two ligands in two modes: the central d⁸ transition metal ions (Ni²⁺, Pd²⁺, and Pt²⁺) are nearly square-planar coordinated and the d¹⁰ transition metal ions (Zn²⁺ and Cd²⁺) are tetrahedrally coordinated. Interestingly, the isomer shifts in ⁵⁷Fe Mössbauer spectroscopy are also of two kinds: d⁸ transition metal ions (0.097-0.247 mm/s) and d¹⁰ transition metal ions (0.416-0.435 mm/s).