Phosphonate Oxygen Research Articles

A Homochiral Hexagadolinium Phosphonate Cluster: Structure, Chiral Electrochemical Recognition and a Large Magnetocaloric Effect

AbstractChiral lanthanide clusters have promising applications in chiral recognition, magneto‐optical memories, and spintronic devices. Nonetheless, the precise prediction and controlled development of homochiral polynuclear Ln‐complexes is still a challenge. Herein, through multidentate chelate synthetic strategy, a new homochiral hexagadolinium phosphonate cluster designated as R/S‐[Gd6(pmhpH)8(NO3)2(H2O)8]⋅19H2O (R/S‐1) was successfully obtained by reacting chiral phosphonomethylhomoproline(pmhpH3) with Gd(III) salt. The cluster, shaped like a lantern, is constructed from {GdO8} polyhedra and {PO3C} tetrahedra surrounded by eight pmhpH2− ligands. Within the structure, two types of gadolinium ions with different coordination modes are observed. Each Gd(III) ion is bound to two carboxylate oxygens and six phosphonate oxygens from the coordinated pmhpH2− ligands. Circular dichroism spectra comfirmed that R/S‐1 exists as a pair of enantiomers. Moreover, the cluster exhibits high thermal stability, decomposing at temperatures exceeding 335 °C. Notably, the chiral cluster materials can be used for enantiomeric recognition for tryptophan (Trp) with the differential pulse voltammetry (DPV) peak current ratio (ID/IL) 2.74. Besides, the magnetic measurements revealed that compound R‐1 exhibits a good magnetocaloric effect (MCE) with a maximum entropy change of −ΔSmmax=36.84 Jkg−1 K−1 at T=2 K and ΔH=7 T.

Syntheses, crystal structures, and fluorescence properties of two new copper phosphonates from hydroxy-functionalized bisphosphonic acid ligand

Exploring metal phosphonates with new crystal structures is of significance for the development of metal-organic frameworks (MOFs). In this work, two new copper phosphonates, [tetraauqa-1,4-phenylenebis(hydroxymethylene))bisphosphonate biscopper(II)] bishydrate [Cu2(H2L)(H2O)4]·2H2O (1) and 1,4-phenylenebis(hydroxymethylene))bisphosphonate-(4,4’-bipy) copper(II) [Cu(H4L)(4,4’-bipy)] (2) (4,4’-bipy = 4,4’-bipyridine), have been synthesized from a hydroxy functionalized bisphosphonate ligand, H6L = (1,4-phenylenebis(hydroxymethylene))bis(phosphonic acid). The introduction of a hydroxy group can regulate the crystal structures. The bisphosphonate ligand in 1 is hexadentate, binding six copper ions with its six phosphonate oxygen atoms and two hydroxy oxygen atoms, forming a three-dimensional framework structure with rectangle channels running along the b-direction. For 2, the bisphosphonate ligands are double deprotonated and chelate or bridge two copper ions, showing a two-dimensional layered crystal structure. These compounds have interesting fluorescence properties with emission maxima (307 and 410 nm) lying in the blue region.

Tailoring hole-selective contacts via self-assembled monolayers for advancing indoor organic photovoltaic and capacitor devices

Amidst the growing demand for transparent devices, the current research is centered on the advancement of technologies involving self-assembled monolayer (SAM)-treated transparent conductive electrodes. However, the detailed mechanisms governing surface energy reactions in these devices at the molecular scale remain unclear, underscoring the need for additional investigations. This study explored the effect of [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) derivatives (MeO-2PACz, 2PACz, Br-2PACz) with a carbazole core on the properties of indium tin oxide (ITO) electrodes. On adsorbing 2PACz molecules onto the ITO surfaces, interfacial dipoles formed through chemisorption between the phosphonic acid oxygen and indium atoms, elevating the work function (WF). 2PACz treatment enhanced the electronic properties of the electrodes for indoor organic photovoltaics (OPV) and metal–insulator-metal (MIM)-capacitors.. The optimized Br-2PACz-based indoor OPVs achieved a remarkable 31.0 % power conversion efficiency and an excellent fill factor of 78.0 % under LED 1000 lx conditions. Furthermore, Br-2PACz-based MIM-capacitors exhibited a reduction in leakage current greater than 19,000 times compared to that of the TiN-electrode-based MIM-capacitors. These outstanding electronic device achievements were attributed to the elevated WFs of the electrodes achieved through the 2PACz treatment. This research underscores the manifold enhancements in device performance achieved through refined energy-level alignment stemming from the increased WFs facilitated by SAM integration.

Synthesis and In Situ Monitoring of Mechanochemical Preparation of Highly Proton Conductive Hydrogen-Bonded Metal Phosphonates.

Crystalline porous materials are recognized as promising proton conductors for the proton exchange membrane (PEM) in fuel cell technology owing to their tunable framework structure. However, it is still a challenging bulk synthesis for real-world applications of these materials. Herein, we report the mechanochemical gram-scale synthesis of two isostructural metal hydrogen-bonded organic frameworks (MHOFs) of Co(II) and Ni(II) based on 1-hydroxyethylidenediphosphonic acid (HEDPH4) with 2,2'-bipyridine (2,2'-bipy): Co(HEDPH3)2(2,2'-bipy)·H2O (1) and Ni(HEDPH3)2(2,2'-bipy)·H2O (2). In situ monitoring of the mechanochemical synthesis using different synchrotron-based techniques revealed a one-step mechanism - the starting materials are directly converted to the product. With the existence of extensive hydrogen bonds with amphiprotic uncoordinated phosphonate hydroxyl and oxygen atoms, both frameworks exhibited proton conduction in the range of 10-4 S cm-1 at room temperature under humid conditions. This study demonstrates the potential of green mechanosynthesis for bulk material preparation of framework-based solid-state proton conductors.

Extreme flexibility and unusual piezomechanical properties of zinc-alkyl-based metal-organic frameworks: A first principles study

The behavior of three Zn-alkyl-based MOFs, ZnGA (Zn-Glutarate), ZnAA (Zn-Adipate), and ZAG-4 (Zinc Alky Gate), under hydrostatic compression has been investigated using first-principles DFT simulation, which has proven its reliability in previous studies. Due to the lack of the high pressure experimental data for ZnGA and ZnAA, the reliability of the simulation parameters was tested by taking ZAG-4, whose structural flexibility has been previously reported experimentally and computationally, as a benchmark. All three structures were found to exhibit elastic deformation under pressure up to 15 GPa, due to the flexibility of the alkyl chains that allow the structures to move without disrupting the metal-ligand coordination. Interestingly, the structures exhibit different mechanical properties, with ZAG-4 showing negative linear compressibility (NLC), ZnGA showing positive linear compressibility (PLC), and ZnAA showing zero linear compressibility (ZLC). The NLC in ZAG-4 is attributed to the proton transfer between phosphonate oxygen and water in the structure as previously reported, while the ZLC in ZnAA is due to a dumbbell-like structural motif formed by substructures displaying both NLC and PLC.

Bio-Inspired Synthetic Hydrogen-Bonded Organic Frameworks for Efficient Proton Conduction.

Hydrogen-bonded organic frameworks (HOFs) are a rising class of promising proton-conducting materials. However, they always suffer from the inherent contradiction between chemical stability and proton conduction. Herein, inspired by the self-assembly of lipid bilayer membranes, a series of aminomethylphosphonic acid-derived single-component HOFs are successfully developed with different substituents attached to the phosphonate oxygen group. They remain highly stable in strong acid or alkaline water solutions for one month owing to the presence of charge-assisted hydrogen bonds. Interestingly, in the absence of external proton carriers, the methyl-substituted phosphonate-based HOF exhibits a very high proton conductivity of up to 4.2×10-3 Scm-1 under 80°C and 98% relative humidity. This value is not only comparable to that of HOFs consisting of mixed ligands but also is the highest reported in single-component HOFs. A combination of single-crystal structure analysis and density functional theory calculations reveals that the high conductivity is attributed to the strengthened H-bonding interactions between positively charged amines and negatively charged phosphonate groups in the channel of bio-inspired HOFs. This finding demonstrates that the well-defined molecular structure of proton conductors is of great importance in the precise understanding of the relationship between structure and property.

Deprotonation of the amine group of Glyphosate studied by XPS and DFT

Glyphosate (N-(phosphonomethyl)glycine, C3H8NO5P) in aqueous solutions undergoes three deprotonation reactions generally assigned to the carboxylate oxygen (pKa1 ~ 2.2), the phosphonate oxygen (pKa2 ~ 5.5), and the amine group (pKa3 ~ 10.2). A couple of recent studies (J. Phys. Chem. A 2015, 119, 5241–5249 and J. Phys. Chem. B 2016, 120, 2132–2137), however, have put forward a new sequence in which the amine group deprotonates before the phosphonate oxygen. In this study we present experimental and theoretical data with the aim of resolving the controversy over the order of the last two deprotonations. On the experimental side, we analysed the evolution of the N1s photoemission spectrum with the pH of the aqueous solution, finding conclusive evidence that the last deprotonation occurs at the amine group. On the theoretical side, we compared the stabilities of several configurations for each glyphosate moiety, finding again that the last group that undergoes deprotonation is the amine group.

A turn-on fluorescence sensor based on Cu2+ modulated DNA-templated silver nanoclusters for glyphosate detection and mechanism investigation

The abuse application of glyphosate can result in a potential hazard for environment and human, however its ultrasensitive detection remains challenging. Herein, a Cu2+ modulated DNA-templated silver nanoclusters (DNA-AgNCs) sensor was constructed to sensitively determine glyphosate based on the turn-on fluorescence strategy. The fluorescence quenching of DNA-AgNCs occurred with the existence of Cu2+. Upon the presence of glyphosate, the functional groups on the surface of glyphosate could chelate with Cu2+, following the fluorescence recovery of DNA-AgNCs. Through the stoichiometric methods, we unveil that Cu2+-trigged fluorescence quenching mode is a combination of static and dynamic quenching with the static mode being predominant. In DNA-AgNCs/Cu2+ system, the carboxylate, amine, and phosphonate groups of glyphosate interact with Cu2+ through chelation, in which the carboxylate oxygen, the phosphonate oxygen atoms, and the monoprotonated secondary amine nitrogen atom and Cu2+ form chelate rings. This fluorescence sensor showed a desired linearity of glyphosate analysis under the optimum conditions, ranging from 15 to 100 μg/L with a low detection down to 5 μg/L. Moreover, the proposed sensor was successfully utilized to measure glyphosate in real samples, indicating a promising application in pesticide residues detection.

Dysprosium Coordination Polymer Incorporating Dianthracene: Thermo‐induced Phase Transition Accompanied with Magnetic and Optical Changes

AbstractDianthracene ligands obtained through photocycloaddition reaction can undergo de‐dimerization upon heating. Here we report the first examples of lanthanide‐dianthracene coordination polymers with chain structures, namely, [LnL(depma2)]Br ⋅ xH2O [1‐Ln, Ln=Dy (x=5), Gd (x=4); H2L=N1,N3‐bis(salicylideneimino)diethylenetriamine, depma2=photodimerized 9‐diethylphosphonomethylanthracene]. The lanthanide ions possess pseudo‐D5h geometries with five equatorial positions occupied by three N and two O atoms from L2− and two axial positions by the phosphonate oxygen atoms from bridging depma2 ligands. Thermo‐induced structural transformation is observed for both compounds between 120 and 140 °C, which involves de‐dimerization of depma2 and elimination of bromoethane. The structural transformation is accompanied with the switch‐on of photoluminescence and, in the case of 1‐Dy, also changes of magnetic dynamics.

A series of C-Shaped heterometallic Diruthenium(II,III) phosphates: NH4[{M(H2O)5}2Ru2(HPO4)2(PO4)2(H2O)2]·4H2O (M = Mg, Co, Ni and Zn)

A series of heterometallic diruthenium(II,III) phosphates, namely NH4[{M(H2O)5}2Ru2(HPO4)2(PO4)2(H2O)2]·4H2O [M = Mg(1), Co(2), Ni(3) and Zn(4)], were synthesized from reaction of Ru2(PO4)47- and M2+ in aqueous solution. They are composed of ionic crystals with the [{M(H2O)5}2Ru2(HPO4)2(PO4)2(H2O)2]- : NH4+ ratio of 1:1, in which each Ru2 unit is connected in a cis manner to two octahedral environment M(H2O)52+ through phosphonate oxygen (Op) atoms forming a C-shaped ionic structure [{M(H2O)5}2Ru2(HPO4)2(PO4)2(H2O)2]-. The magnetism data fitting with the temperature dependent susceptibility χ(T,D,θ,) and extensional Brillouin function M(H,D,θ) equations convinces that the protonated HPO4 bridges between Ru2(II,III) dimer and M(II) ions mediate ferromagnetic coupling.

Three-Component Reaction of Diamines with Triethyl Orthoformate and Diethyl Phosphite and Anti-Proliferative and Antiosteoporotic Activities of the Products.

A three-component reaction between diamines (diaminobenzenes, diaminocyclohexanes, and piperazines), triethyl orthoformate, and diethyl phosphite was studied in some detail. In the case of 1,3- and 1,4-diamines and piperazines, products of the substitution of two amino moieties—the corresponding tetraphosphonic acids—were obtained. In the cases of 1,2-diaminobenzene, 1,2-diaminocyclohexanes and 1,2-diaminocyclohexenes, only one amino group reacted. This is most likely the result of the formation of hydrogen bonding between the phosphonate oxygen and a hydrogen of the adjacent amino group, which caused a decrease in the reactivity of the amino group. Most of the obtained compounds inhibited the proliferation of RAW 264.7 macrophages, PC-3 human prostate cancer cells, and MCF-7 human breast cancer cells, with 1, trans-7, and 16 showing broad nonspecific activity, which makes these compounds especially interesting in the context of anti-osteolytic treatment and the blocking of interactions and mutual activation of osteoclasts and tumor metastatic cells. These compounds exhibit similar activity to zoledronic acid and higher activity than incadronic acid, which were used as controls. However, studies of sheep with induced osteoporosis carried out with compound trans-7 did not support this assumption.

Octahedral erbium and ytterbium ion encapsulated in phosphorescent iridium complexes showing field-induced magnetization relaxation

Abstract Four isostructural heptanuclear clusters [LnIr6(ppy)12(bpp)2(bppH)4](CF3SO3)·xH2O (Ir6Ln, Ln = Eu, Tb, Er, Yb) are reported, where the lanthanide ions are six-coordinated by the phosphonate oxygen donors from six [Ir(ppy)2(bpp)] (ppy− = 2-phenylpyridine, bpp2− = 2-pyridylphosphonate) chromophores. All show phosphorescence originating from the IrIII moieties. For compounds Ir6Er and Ir6Yb, field-induced slow magnetization relaxation is also observed, thus providing the first examples of Ir-Er or Ir-Yb complexes showing bifunctional phosphorescence and field-induced single ion magnet behaviors.

Fac-99mTc/Re-tricarbonyl complexes with tridentate aminocarboxyphosphonate ligands: Suitability of the phosphonate group in chelate ligand design of new imaging agents

Ligands that coordinate via dianionic phosphonate groups have not been widely utilized in radiopharmaceuticals. N-(phosphonomethyl)iminodiacetic acid (1, PMIDA) and N-(phosphonomethyl)glycine (2, PMG) were investigated as new chelators for the 99mTc/Re-tricarbonyl “core” (fac-M(CO)3, M = 99mTc, Re) present in a major class of radiopharmaceuticals.fac-M(CO)3(PMIDA) and fac-M(CO)3(PMG) complexes were studied by HPLC and 1H/13C/31P NMR methods for M = Re (Re-1 and Re-2) and by HPLC for M = 99mTc (99mTc-1 and 99mTc-2). Re-1 and 99mTc-1 complexes exhibit a similar pH-dependent equilibrium between geometric linkage isomers (M-1a and M-1b). However, only one isomer exists for M-2 under all conditions. Structural characterization by X-ray crystallography reveals the presence of a bond between a phosphonate oxygen and the Re(I) center in fac-Re(CO)3(PMG) (Re-2). Detailed comparisons of NMR data for Re-2 conclusively demonstrate that the phosphonate group is coordinated in Re-1b (isomer favored at high pH) but not in Re-1a, which has a dangling N-(phosphonomethyl) group. To our knowledge, Re-1b and Re-2 and their 99mTc analogs are the first well-documented examples of complexes with these metal-tricarbonyl cores having a dianionic phosphonate group directly coordinated in a fac-M(CO)3-O-P grouping. Pharmacokinetic studies using Sprague-Dawley rats reveal that 99mTc-2 is a robust tracer. Hence, phosphonate groups should be considered in designing 99mTc and 186/188Re radiopharmaceuticals, including agents with bioactive moieties attached to dangling carboxylate or phosphonate groups.

Coordination polymers of transition metal diphosphonates: Synthesis, crystal structure and magnetic behaviour

Five new transition metal coordination polymers: [Cu2L(4,4′-bipy)(H2O)0.5] (1), [Cu(H2L)H2O] (2), [Cd2(H2L)2H2O] (3), [Co2L(H2O)2]·0.184H2O (4), [Fe3L2(OH)(H2O)3]·2H2O (5) (H4L = 4-CH3-C6H4CH2N(CH2PO3H2)2), were obtained through hydrothermal reactions. The complexes have been characterized by IR, elemental analysis, TGA and XRD. Crystal structure analysis reveals that all of 2–5 contain 2D inorganic layer structures, constructed by the coordination interactions between metal ions and phosphonate oxygen atoms. 4,4′-bipy molecules in 1 act as a bridging ligand to connect the adjacent 2D layers into a 3D framework. Moreover, magnetic properties of the complexes have been quantificationally investigated by the classical spin approximation and PHI software program, revealing that 2, 4 and 5 exhibit antiferromagnetism, while 1 shows ferromagnetism.

Molecular Insights into Glyphosate Adsorption to Goethite Gained from ATR-FTIR, Two-Dimensional Correlation Spectroscopy, and DFT Study.

Glyphosate (PMG) complexation on iron (hydr)oxides impacts its fate and transport in the environment. To decipher the molecular-level interfacial configuration and reaction mechanism of PMG on iron (hydr)oxides, the PMG protonation process, which influences the chemical and physical properties of PMG, was first determined using ATR-FTIR spectroscopy. The FTIR results reveal that the deprotonation occurs at carboxylate oxygen when pKa1< pH < pKa2, at phosphonate oxygen when pKa2< pH < pKa3, and at amino nitrogen when pH > pKa3. PMG complexation on goethite was investigated using in situ flow-cell ATR-FTIR, two-dimensional correlation spectroscopy (2D-COS), and density functional theory (DFT) calculations. The results indicate that the phosphonate group on PMG interacts with goethite to form inner-sphere complexes with multiple configurations depending on pH: binuclear bidentate (BB) and mononuclear bidentate (MB) without proton under acidic conditions (pH 5), mononuclear monodentate (MM) with proton and BB without proton at pH 6-8, and MM without proton under alkaline conditions (pH 9). Phosphate competition significantly impacted the PMG adsorption capacity and its interfacial configurations. As a result, the stability of the adsorbed PMG was impaired, as evidenced by its elevated leachability. These results improve our understanding of PMG-mineral interactions at the molecular level and have significant implications for risk assessment for PMG and structural analog pollutants.

Structural basis of the broad substrate tolerance of the antibody 7B9-catalyzed hydrolysis of p-nitrobenzyl esters

Catalytic antibody 7B9, which was elicited against p-nitrobenzyl phosphonate transition-state analogue (TSA) 1, hydrolyzes a wide range of p-nitrobenzyl monoesters and thus shows broad substrate tolerance. To reveal the molecular basis of this substrate tolerance, the 7B9 Fab fragment complexed with p-nitrobenzyl ethylphosphonate 2 was crystallized and the three-dimensional structure was determined. The crystal structure showed that the strongly antigenic p-nitrobenzyl moiety occupied a relatively shallow antigen-combining site and therefore the alkyl moiety was located outside the pocket. These results support the observed broad substrate tolerance of 7B9 and help rationalize how 7B9 can catalyze various p-nitrobenzyl ester derivatives. The crystal structure also showed that three amino acid residues (AsnH33, SerH95, and ArgL96) were placed in key positions to form hydrogen bonds with the phosphonate oxygens of the transitions-state analogue. In addition, the role of these amino acid residues was examined by site-directed mutagenesis to alanine: all mutants (AsnH33Ala, SerH95Ala, and ArgL96Ala) showed no detectable catalytic activity. Coupling the findings from our structural studies with these mutagenesis results clarified the structural basis of the observed broad substrate tolerance of antibody 7B9-catalyzed hydrolyses. Our findings provide new strategies for the generation of catalytic antibodies that accept a broad range of substrates, aiding their practical application in synthetic organic chemistry.

Synthesis, structures, and properties of a series of similar structural coordination polymers with triphosphonate anions as ligands

The hydrothermal reactions of metal precursors with aminotri(methylenephosphonic acid) yielded a series of similar structural coordination polymers of general formula {M[HN(CH2PO3H)3](H2O)3}n [M = Mg(II) (1), Mn(II) (2), Co(II) (3), Zn(II) (4) and Cd(II) (5)]. Compounds 1–5 were characterized by X-ray single crystal diffraction, elemental analyses, and thermogravimetric analyses. Compounds 1–5 all reveal the wave-like 1D chain structures and the structures are constructed by two types of eight-membered, square-like rings linked alternatively via the phosphonate oxygen atoms, generating double-channel systems. The magnetic studies of 2 and 3 reveal that antiferromagnetic interactions are mediated between the metal ions.

Thermodynamics of the Protonation of an Analogue of Glyphosate, N-(phosphonomethyl)-l-proline, in Aqueous Solutions

N-(phosphonomethyl)-l-proline is an analogue of glyphosate. The protonation for N-(phosphonomethyl)-l-proline was studied by potentiometry, calorimetry, 31P NMR spectroscopy and quantum chemical calculations to further understand the protonation process of glyphosate. The results confirmed that the order of successive protonation sites of totally deprotonated N-(phosphonomethyl)-l-proline are a phosphonate oxygen, amino nitrogen, and finally the carboxylate oxygen. The results can improve the understanding of the biological activity of these types of molecules in solution.

3D Framework and Supramolecular Structures Assembly from a Carboxyphosphonic Acid and Transition Metals: Sensing of Nitro Compounds and Surface Photovoltage Properties

AbstractThree new metal carboxyphosphonates with 3D framework and supramolecular structures, namely, [Zn(H4L)2] (1), [Cu2(HL)(H2O)2] (2) and [NH(CH2)4NH]0.5[Cu(H3L)] (3) (H5L=4‐HOOC‐C6H4‐CH2N‐(CH2PO3H2)2), have been synthesized under hydrothermal conditions. For compound 1, {ZnO6} and {CPO3} polyhedra are interconnected into a 2D layer via corner‐sharing, which is further assembled into a 3D supramolecular structure through π‐π stacking interactions. Compound 2 exhibits a 3D framework structure. The interconnection of {CuO4N}, {CuO5} polyhedra and {CPO3} tetrahedra via corner‐sharing forms a 2D inorganic layer. These inorganic layers are further linked via the organic backbone {−C6H4CH2N(CH2)2−} of the carboxyphosphonate ligands, generating a 3D framework structure. In compound 3, two {CuO4N} polyhedra and four {CPO3} tetrahedra are interconnected into a unit, and then these units are further connected into a 1D infinite chain via corner‐sharing. Neighboring chains are assembled into a 2D layered structure through hydrogen bond interactions between the nitrogen atoms from piperazine and uncoordinated phosphonate oxygen atoms. Then, such layers are further assembled into a 3D supramolecular network via interlayer hydrogen bonds. Compound 1 has been realized for the sensitive sensing of 4‐nitrophenol (4‐NP) by luminescence quenching method in the liquid phase. Surface photovoltage properties of compounds 2 and 3 have been investigated.

Two new supramolecular metal diphosphonates: Synthesis, characterization, crystal structure and inhibiting effects on metallic corrosion

Two new divalent metal(II) aminodiphosphonates with layered structure, namely, Cu(H3L1)2·2H2O (1), [H4L1=methyl-N(CH2PO3H2)2] and Cd2(H2L2)4(2), [H4L2=n-propyl-N(CH2PO3H2)2] were synthesized and characterized. The Cu(II) ions in complex 1 are octahedrally coordinated by four oxygen atoms from two chelating ligands and two phosphonate oxygen atoms from two neighboring Cu(H3L1)2 units. The Cu(H3L1)2 units are interconnected by bridging phosphonate groups, forming a 2-D metal phosphonate layer. The structure of complex 2 contains two unique Cd(II) ions octahedrally-coordinated by six phosphonate oxygen atoms from four H2L2 diphosphonate anions. Corrosion inhibition performances of 1 and 2 were also compared with each other in order to study the effect of combinations of externally added Cd/H4L2 and Cu/H4L1 (1:1 ratio) on corrosion rates of carbon steel. It was found that at pH 3.0, Cd/H4L2 or Cu/H4L1 combinations do not have noticeable corrosion inhibition efficiency for carbon steel. In contrast, at pH 7.0, higher corrosion inhibition efficiency was achieved for Cd/H4L2. Physical characterizations such as scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) were applied to study the corrosion specimens and film material.