Zirconium Complexes Research Articles

The structure of tetranuclear zirconium pivalate ZR<sub>4</sub>O<sub>2</sub> [(CH<sub>3</sub>)<sub>3</sub>CCO<sub>2</sub>]<sub>12</sub> according to X-ray diffraction analysis and quantum chemical calculations

The crystal and molecular structure of a polynuclear pivalate complex obtained by the interaction of ZrCl4 with pivalic acid was determined by X-ray diffraction analysis. The compound C71H124O28Zr4 (compound 1) crystallizes in the monoclinic crystal system. The crystal structure was refined in the nonstandard space group I2. The asymmetric part of the structure includes three Zr atoms, six pivalate ligands, a bridging µ3-O oxygen atom, as well as disordered crystallization molecules of pivalic acid with an occupancy of 50% and benzene with an occupancy of 50%. The zirconium complex molecule is a tetranuclear cluster that contains three types of Zr atoms that differ in ligand environment. Comparison of the results of quantum chemical calculations of the model reaction ZrCl4 with acetic acid with the literature data on reactions of ZrCl4 with aliphatic acids have shown the possibility of the formation of both mononuclear Zr(RCO2)4 and polynuclear clusters in this reaction, which is a new route for obtaining polynuclear zirconium clusters. The structure of the clusters formed depends on the steric properties of carboxylate ligands.

Zirconium and Hafnium Complexes Bearing Tridentate ONN-Ligands: Extremely High Activity toward Ethylene (Co)Polymerization.

The pursuit of high-performance catalysts in the realm of polyolefins is a constant goal. In this study, a range of zirconium (1-ZrCl3, 2-ZrCl3, 3-ZrCl4, 12-Zr) and hafnium (1-HfCl3, 12-Hf) complexes featuring phenoxy-imine-amine ONN-ligands (2,6-R2-C6H3-NH-C6H4-N═CH-C6H2-3,5-tBu2-OH; 1-L: R = H; 2-L: R = F; 3-L: R = iPr) were synthesized and characterized using NMR spectroscopy, as well as single-crystal X-ray diffraction for 2-ZrCl3, 3-ZrCl4, and 12-Zr. These Zr and Hf complexes exhibited remarkable efficiency for ethylene homopolymerization and copolymerization with 1-octene when paired with MAO as the cocatalyst. Notably, the Zr complexes outperformed the Hf complexes with the same ligand, underscoring the substantial impact of the metal center on catalytic performance. The substituents and coordination modes of the ligands also exerted significant influence on the catalytic behavior, affecting both the activity and properties of the resulting polymers. Particularly noteworthy was the exceptional activity of 1-ZrCl3, achieving activity as high as 6.30 × 108 g(PE)·mol-1(Zr)·h-1 for ethylene homopolymerization and generating bi- or multimodal distribution polyethylene. The activation of 1-ZrCl3 by 5 or 20 equiv of d-MAO afforded a dinuclear Zr complex bridged by two chlorides (μ-Cl2-(1-ZrCl2)2), which was analyzed and confirmed by in situ 1H NMR spectroscopy and single-crystal X-ray diffraction.

Zirconium Complexes Bearing Methyl/tButyl Salicylate and Their Catalytic Activity on ε-Caprolactone

In this study, methyl/tbutyl salicylate-bearing zirconium complexes (C1–C8) were prepared by the reaction of zirconium (IV) propoxide/butoxide with salicylic acid, 3-methylsalicylic acid, 4-methylsalicylic acid, and 3,5-di-tert-butylsalicylic acid in alcohols, respectively. All these complexes (C1–C8) were characterized by 1H NMR, 13C NMR, FTIR, mass spectroscopy (MS), elemental, and thermogravimetric analyses (TGA). These complexes were utilized as catalysts in the ring-opening polymerization (ROP) of Ɛ-caprolactone and were very effective. Polycaprolactone (PCL) was characterized by 1H-NMR, 13C NMR, and gel permeation chromatography (GPC). In this study, perhaps for the first time, the effects of electron-donating substituents (Me and tBu) on Ɛ-caprolactone polymerization reactions on salicylate ligands linked to zirconium atoms were investigated.

Synthesis, Structural Analysis, and Polymerization Activity of Noncyclopentadienyl Constrained Geometry Complex [Me2Si(Ph2C)(tBuN)]ZrCl2(thf)

ABSTRACTConstrained geometry complexes (CGCs) are homogeneous olefin polymerization catalysts that have been improved because of their considerably high activity and their copolymerization abilities for ethylene with α‐olefins. The ancillary ligands in CGCs comprise bridged 6π‐electron moieties (e.g., cyclopentadienyl (Cp) and fluorenyl) and amide donors. In this study, we investigated the effect of changing the 6π‐electron moieties to a diphenylmethyl moiety (Ph2C) on the polymerization activity of [Me2Si(Ph2C)(tBuN)]ZrCl2(thf) (thf = tetrahydrofuran). We synthesized [Me2Si(Ph2C)(tBuN)]ZrCl2(thf) and characterized it via 1H nuclear magnetic resonance analysis and single‐crystal X‐ray crystallography. Ethylene polymerization at 2 MPa using a catalyst of the [Me2Si(Ph2C)(tBuN)]ZrCl2(thf) and modified methylaluminoxane (MMAO) as a cocatalyst yielded a linear polyethylene (PE) with a high melting point (124°C–134°C); moreover, the polymerization activity of the catalyst was found to be up to 445 g (PE) mmol (Zr)−1 h−1. The polymerization of styrene using the zirconium complex and MAOs did not proceed, but the polymerization of 1,3‐butadiene produced a small amount of polybutadiene with ~60% cis‐1,4‐structure. These results indicate that non‐Cp‐type CGCs, which can be defined as metal complexes bearing an ancillary ligand in which non‐Cp moieties (benzyl moiety in this study) and an amido group are bridged by an organic linker, can become a new family of homogeneous olefin polymerization catalysts.

Synthesis, spectral analysis, XRD, molecular docking simulation of dithranol and glycine mixed ligand complexes and their potential role in suppressing breast cancer cells via down‐regulating the expression of protein metalloproteinase‐9

Five novel complexes of nickel (II)(1), zinc (II)(2), zirconium (IV)(3), lanthanum (III)(4), thorium (IV)(5), with the dithranol (Dithr) ligand and glycine (Gly) were synthesized and characterized. Their structures were investigated using elemental analysis, molar conductance (Λ), magnetic studies (μeff), spectroscopic methods (FT‐IR, UV–Vis., 1H NMR, XRD), mass spectrometry, TG/DTG and DTA. Findings revealed that Dithr was chelated via two hydroxyl oxygen atoms and carbonyl group while, Gly chelated through carboxylic oxygen and nitrogen atom. All complexes appeared with molar ratio 1:1:1 (M:Dithr:Gly) and were electrolytes with 1:1 for (1), (2) and (3) complexes, 1:2 for (4) complex, and 1:3 for (5) complex according to elemental analysis and molar conductivity data. All metal‐chelates, except Th (IV)‐complex, were confirmed to have lattice water molecules based on their thermal behavior. Average crystalline size of all compounds was calculated using XRD analysis and found in the range 35.50–55.57 nm, indicating the compounds existed as nanocrystalline structure, except zirconium (IV) complex. Then, we studied cytotoxic effects of our synthetic drugs on the survival of an aggressive‐breast‐cancer‐histotype“66cl‐4.” Given its involvement in cancer‐metastasis, matrix‐metalloproteinase‐(MMP)‐9 protein expression was evaluated using western‐blotting‐assays. Th(IV)‐complex emerged as the most effective option in inhibiting cancer‐cells‐proliferation (IC50: 9.39 μM), and suppressed expression MMP‐9 levels by 86%, at 25 μM dose, and drug‐binding‐affinity was interpreted via molecular modeling.

Mixed Liquid and Solid Phase Synthesis of Isopeptidic Desferrioxamine Analogues for Complexation of Zirconium

Abstract89Zr has a number of advantageous properties for PET‐imaging, but optimal chelators for its widespread clinical application still need to be found. Tetrahydroxamates derived from the natural siderophore DFOB are promising candidates in this context. This study describes a solid‐phase approach to isopeptide analogs of DFOB (termed ipDFO*) with four hydroxamate groups for stable Zr(IV)‐chelation. The route uses either commercial or easily available Fmoc‐protected precursors and allows the synthesis of ipDFO* and clickable AZA−ipDFO* derivatives in only a few hours. The solid‐phase synthesis reduces the workload for the synthesis of ipDFO* and AZA−ipDFO* derivatives thus significantly compared to a previous multistep solution synthesis. The route is also modular and allows the synthesis of various ipDFO* derivatives with variation in the spacer length between the hydroxamate groups. This spacing is a critical parameter for finding the optimal chelator for hard metal cations like Zr(IV). It might thus help to speed up the search for an ideal Zr‐chelator for PET‐imaging and might also allow the extension to other metal cations of different size.

Synthesis, Characterization and Evaluation of the Antimicrobial and Herbicidal Activities of Some Transition Metal Ions Complexes with the Tranexamic Acid.

New tranexamic acid (TXA) complexes of ferric(III), cobalt(II), nickel(II), copper(II) and zirconium(IV) were synthesized and characterized by elemental analysis (CHN), conductimetric (Λ), magnetic susceptibility investigations (μeff), Fourier transform infrared (FT-IR), proton nuclear magnetic resonance (1H-NMR), ultraviolet visible (UV-vis.), optical band gap energy (Eg) and thermal studies (TG/DTG and DTA). TXA complexes were established in 1 : 2 (metal: ligand) stoichiometric ratio according to CHN data. Based on FT-IR and 1H-NMR data the disappeared of the carboxylic proton supported the deprotonating of TXA and linked to metal ions via the carboxylate group's oxygen atom as a bidentate ligand. UV-visible spectra and magnetic moment demonstrated that all chelates have geometric octahedral structures. Eg values indicated that our complexes are more electro conductive. DTA revealed presence of water molecules in inner and outer spheres of the complexes. DTA results showed that endothermic and exothermic peaks were identified in the degradation mechanisms. The ligand and metal complexes were investigated for their antimicrobial and herbicidal efficacy. The Co(II) and Ni(II) complexes showed antimicrobial activity against some tested species. The obtained results showed a promising herbicidal effect of TXA ligand and its metal complexes particularly copper and zirconium against the three tested plants.

Bifunctional octadentate pseudopeptides as Zirconium-89 chelators for immuno-PET applications

BackgroundPositron emission tomography (PET) is a highly sensitive method that provides fine resolution images, useful in the field of clinical diagnostics. In this context, Zirconium-89 (89Zr)-based imaging agents have represented a great challenge in molecular imaging with immuno-PET, which employs antibodies (mAbs) as biological vectors. Indeed, immuno-PET requires radionuclides that can be attached to the mAb to provide stable in vivo conjugates, and for this purpose, the radioactive element should have a decay half-life compatible with the time needed for the biodistribution of the immunoglobulin. In this regard, 89Zr is an ideal radioisotope for immuno-PET because its half-life perfectly matches the in vivo pharmacokinetics of mAbs.ResultsThe main objective of this work was the design and synthesis of a series of bifunctional octadentate pseudopeptides able to generate stable 89Zr complexes. To achieve this, here we investigated hydroxamate, N-methylhydroxamate and catecholate chelating moieties in complexing radioactive zirconium. N-methylhydroxamate proved to be the most effective 89Zr-chelating group. Furthermore, the increased flexibility and hydrophilicity obtained by using polyoxyethylene groups spacing the hydroxamate units led to chelators capable of rapidly forming (15 min) stable and water-soluble complexes with 89Zr under mild reaction conditions (aqueous environment, room temperature, and physiological pH) that are mandatory for complexation reactions involving biomolecules. Additionally, we report challenge experiments with the competitor ligand EDTA and metal ions such as Fe3+, Zn2+ and Cu2+. In all examined conditions, the chelators demonstrated stability against transmetallation. Finally, a maleimide moiety was introduced to apply one of the most promising ligands in bioconjugation reactions through Thiol-Michael chemistry.ConclusionCombining solid phase and solution synthesis techniques, we identified novel 89Zr-chelating molecules with a peptide scaffold. The adopted chemical design allowed modulation of molecular flexibility, hydrophilicity, as well as the decoration with different zirconium chelating groups. Best results in terms of 89Zr-chelating properties were achieved with the N-methyl hydroxamate moiety. The Zirconium complexes obtained with the most effective compounds were water-soluble, stable to transmetallation, and resistant to peptidases for at least 6 days. Further studies are needed to assess the potential of this novel class of molecules as Zirconium-chelating agents for in vivo applications.

Biomass-derived polycarboxylate–aluminum–zirconium complex tanning system: A sustainable and practical approach for chrome-free eco-leather manufacturing

Biomass-derived polycarboxylate–aluminum–zirconium complex tanning system: A sustainable and practical approach for chrome-free eco-leather manufacturing

Moving Beyond Isothiocyanates: A Look at the Stability of Conjugation Links Toward Radiolysis in 89Zr-Labeled Immunoconjugates.

Zirconium-89 is the most widely used radioisotope for immunoPET because its physical half-life (78.2 h) suits the one of antibodies. Desferrioxamine B (DFO) is the standard chelator for the complexation of zirconium(IV), and its bifunctional version, containing a phenylisothiocyanate function, is the most commonly used for the conjugation of DFO to proteins. However, preliminary results have shown that the thiourea link obtained from the conjugation of isothiocyanate and lysines is sensitive to the ionizing radiation generated by the radioisotope, leading to the rupture of the link and the release of the chelator/radiometal complex. This radiolysis phenomenon could produce nonspecific signal and prevent the detection of bone metastasis, as free zirconium accumulates into the bones. The aim of this work was to study the stability of a selection of conjugation linkers in 89Zr-labeled immunoconjugates. We have synthesized several DFO-based bifunctional chelators appended with an isothiocyanate moiety, a bicyclononyne, or a squaramate ester. Two antibodies (trastuzumab and rituximab) were conjugated and radiolabeled with zirconium-89. The effect of increasing activities of zirconium-89 on the integrity of the bioconjugate bearing thiourea links was evaluated as well as the impact of the presence of a radioprotectant. The stability of the radiolabeled antibodies was studied over 7 days in PBS and human plasma. Radioconjugates' integrity was evaluated using iTLC and size-exclusion chromatography. This study shows that the nature of the linker between the chelator and biomolecule can have a strong impact on the stability of the 89Zr-labeled conjugates, as well as on the aggregation of the conjugates.

Combining Desferriferrioxamine B and 1-Hydroxy-2-Piperidone ((PIPO)H) to Chelate Zirconium. Solution Structure of a Model Complex of the [89Zr]Zr-DFOcyclo*-mAb Radioimmunoconjugate.

89Zr-immunoPET is a hot topic as 89Zr cumulates the advantages of 64Cu and 124I without their drawbacks. We report the synthesis of a model ligand of a chiral bioconjugable tetrahydroxamic chelator combining the desferriferrioxamine B siderophore and 1-hydroxy-2-piperidone ((PIPO)H), a chiral cyclic hydroxamic acid derivative, and the study by NMR spectroscopy of its zirconium complex. Nuclear Overhauser effect measurements (ROESY) indicated that the complex exists in the form of two diastereomers, in 77 : 23 ratio, resulting from the combination of the central chiralities at the 3-C of the (PIPO)H component and at the Zr4+ cation. The 44 lowest energy structures out of more than 1000 configurations/conformations returned by calculations based on density functional theory were examined. Comparison of the ROESY data and the calculated interatomic H⋅⋅⋅H distances allowed us to select the most probable configuration and conformations of the major complex.

Half-Sandwich Zirconium and Hafnium Amidoborane Complexes: Precursors of Hydride Derivatives.

Half-sandwich zirconium(IV) and hafnium(IV) complexes with amidoborane and hydride ligands have been isolated in the stoichiometric reactions of mono(pentamethylcyclopentadienyl)metal alkyl and amido derivatives with the amine-boranes NHR2BH3 (R2 = H2, Me2, HtBu). Treatment of the tris(trimethylsilylmethyl) complexes [M(η5-C5Me5)(CH2SiMe3)3] with NH3BH3 (3 equiv) gives the seven-coordinate species [M(η5-C5Me5)(NH2BH3)3] (M = Zr (1), Hf (2)) with three κ2N,H-NH2BH3 ligands. The tris(neophyl) [M(η5-C5Me5)(CH2CMe2Ph)3] or tris(dimethylamido) [M(η5-C5Me5)(NMe2)3] derivatives react with NHMe2BH3 (≥3 equiv) to afford bis(dimethylamidoborane) hydride complexes [M(η5-C5Me5)H(NMe2BH3)2] (M = Zr (3), Hf (4)) via thermally unstable [M(η5-C5Me5)(NMe2BH3)3] species. The reaction of [M(η5-C5Me5)(NMe2)3] and NH2tBuBH3 (≥4 equiv) affords analogous mixed amidoborane hydride derivatives [M(η5-C5Me5)H(NHtBuBH3)(NMe2BH3)] (M = Zr (5), Hf (6)) with κ2N,H-NHtBuBH3 and κ3N,H,H-NMe2BH3 ligands. The addition of NHR2BH3 (≥1 equiv) on the mono(dimethylamido) complexes [M(η5-C5Me5)Cl2(NMe2)] in hexane leads to the precipitation of the ionic compounds [(NHR2)2BH2][{M(η5-C5Me5)Cl2}2(μ-H)3] (R2 = Me2, M = Zr (7), Hf (8); R2 = HtBu, M = Zr (9), Hf (10)). Molecular hydride species [Cl2(η5-C5Me5)M(μ-Cl)(μ-H)2M(η5-C5Me5)Cl(NH2tBu)] (M = Zr (11), Hf (12)) could be isolated from mixtures of complexes [M(η5-C5Me5)Cl2(NMe2)] and lower ratios of NH2tBuBH3. The zirconium complex 11 decomposes in solution to give the mononuclear tert-butylamido derivative [Zr(η5-C5Me5)Cl2(NHtBu)] (13) along with other byproducts.

Synthesis of Amido-quinoline Hafnium and Zirconium Complexes with Improved Performances toward Ethylene/1-Octene Copolymerization

Synthesis of Amido-quinoline Hafnium and Zirconium Complexes with Improved Performances toward Ethylene/1-Octene Copolymerization

Selective fluoride detection based on modulation of red emissive carbon dots fluorescence by zirconium-alizarin complex: Application to Nile River water and human saliva samples

Fluoride is an essential ion for dental health that is optimally supplemented through drinking water, toothpastes, and other oral hygiene products. This work reports a selective, simple, and inexpensive fluorescent sesnor for fluoride quantification. The sensor exploits the red fluorescence of carbon dots coupled with the colorimetric response of a zirconium-alizarin complex. The zirconium-alizarin exhibits an absorption band at 530 nm that overlaps the carbon dot excitation peak, resulting in inner filter effect-based quenching of the 612 nm red emission. However, in the presence of fluoride, binding disrupts the zirconium complex, releasing free alizarin with an absorption blue shifted to 420 nm. This reduces spectral overlap and restores carbon dot fluorescence. The carbon dots were synthesized by a hydrothermal method and exhibited excellent fluorescence quantum yield (16.3 %). Structural and optical characterizations were performed using TEM, XRD, XPS, FTIR, UV–vis, and fluorescence techniques. Under optimized conditions, the probe provided selective turn-on fluorescence detection of fluoride with a linear response from 1.0 to 130.0 μM and limit of detection (S/N = 3) of 0.32 μM. Practical utility was demonstrated by accurate quantification of fluoride in Nile River water and human saliva samples. This dual nanoprobe strategy offers a rapid and cost-effective platform for fluoride analysis in support of healthcare and environmental monitoring applications.

Study of Heterogeneity of Ethylene/1-Octene Copolymers Synthesized with Zirconium and Titanium Complexes Bearing Diamine-bis(phenolate) Ligands.

A series of ethylene/1-octene copolymers synthesized with diamine-bis(phenolate) complexes activated with Al(iBu)3/[Ph3C][B(C6F5)4] were subjected to preparative temperature rising elution fractionation (TREF). The complexes used differed in the type of metallic center (Zr or Ti) or the amine donor in the pendant arm of the ligand (NMe2 or NiPr2). The obtained fractions were then characterized via FTIR, DSC and GPC methods. It was found that all the copolymers had very broad chemical composition distributions, and the most heterogeneous was the copolymer produced by the titanium complex bearing a ligand with the NiPr2 donor group. The difference in the comonomer incorporation into the macromolecules of the fractions was as high as 8.3 mol%. The melting temperature and molecular weight of the fractions changed nearly linearly with the increased elution temperature. Copolymers produced by zirconium catalysts were also fractionated by molecular weight using the solvent/non-solvent technique with subsequent analysis of the fractions. It was shown that the fractions have a similar composition, low molecular weight distribution and very broad comonomer distribution. Therefore, the comonomer content in the fractions was not a function of the molecular weight as was observed for the copolymers synthesized with the Ziegler-Natta catalysts.

Synthesis of dinuclear pyridyl-amido hafnium and zirconium complexes toward olefin polymerization with unexpected stereospecificity and ultra-high molecular weight capability

Dinuclear syn-Hf2 exerts an unexpected stereospecificity toward propylene polymerization and affords ultra-high molecular weight atactic polypropylene as a thermoplastic elastomer.

Zirconium complexes of an aminophenolate-etherphenolate ONO'O ligand: Synthesis, characterization and catalytic properties

A synthetic protocol to access new aminophenolate-etherphenolate ONO'O ligands is presented. Zirconium iso-propoxide and benzyl complexes of a prototypical tert-butyl substituted ONO'O ligand can be synthesized in high yields as single conformational isomers. Combined NMR spectroscopy and single-crystal X-ray diffraction studies on (ONO'O)Zr(OiPr)2 show that the ligand binds to the metal center in a fac-fac coordination mode, like the well-known bis(aminophenolate) ONNO analogue. The iso-propoxide complex (ONO'O)Zr(OiPr)2 proved to be a competent catalyst for L- and rac-lactide polymerization, exhibiting a productivity similar to that of the benchmark (ONNO)Zr(OiPr)2 in solution and in neat monomer. The benzyl complex (ONO'O)ZrBn2 is inactive in ethylene polymerization under the reaction conditions explored, unlike the benchmark (ONNO)ZrBn2. DFT studies suggest that a larger range of geometries is accessible for cationic active species with ONO'O ligands compared to ONNO or OO'O'O ligands.

Stereoselectivity in Butadiene Polymerization Promoted by Using Ziegler–Natta Catalysts Based on (Anilidomethyl)pyridine Group (IV) Complexes

The stereoselective polymerization of conjugated dienes promoted by using transition metal complexes has attracted much interest in both industrial and academic environments for the relevance of polydienes as synthetic rubbers and for the challenging reaction mechanisms. Among the different transition metal complexes, those based on group IV have been demonstrated to be versatile and efficient catalysts. Titanium complexes are generally more active than zirconium complexes. A rare exception to this trend is represented by a series of Zr(IV) complexes supported by (anilidomethyl)pyridine ligands that, after activation by using Al(iBu2H)/MAO, were found to be highly active affording exclusively cis-1,4-polybutadiene. To rationalize this unexpected trend and to obtain more insights into the parameters that control the reactivity of group IV complexes, a theoretical investigation of the entire polymerization mechanism, employing density functional methods, was undertaken. In the framework of the widely accepted polymerization scheme, the different intermediates featuring h4 (both cis and trans) coordination of the monomer and h1 or h3 (syn or anti)allyl coordination of the growing chain were scrutinized. Subsequently, the effects of the metal center on the free-energy profiles of the elementary steps involved in the reaction were examined. The results presented herein aim to achieve a better knowledge of the influence of the metal on the polymerization rates and on the stereoselectivity of the reaction.

Determination of Membrane Degradation in Polymer Electrolyte Fuel Cells with in-Situ and Ex-Situ Measurements

Fuel cells convert chemical energy directly into electrical energy with high efficiency and without pollutants. The decomposition products in the clean exhaust gas caused by the chemical degradation of the membrane of polymer electrolyte fuel cells (PEFCs) can be used to monitor the service life of the cell. For perfluorinated sulfonic acid (PFSA)-based membranes, chemical degradation is investigated via ex situ monitoring of the effluent water. The decomposition of the PFSA backbone, which is part of the polymer electrolyte membrane (PEM), can be detected by the degradation products such as fluoride or fluorinated compounds [1]. There are multiple methods for measuring fluoride in water. We have developed a new method for the simple and precise measurement of fluoride based on the optical change caused by the quenching of a zirconium complex. This method requires only 900 µL of the sample and 100 µL of the complex [2].We have extended the two fluoride measurement methods, namely fluoride sensitive electrode (FSE) and photometry (PM), to include ion chromatography (IC). This serves as an additional point of comparison with high accuracy and expands the measuring scope to include other ions like sulfate and their potential influence on photometric measurements.The electrochemical characterization of the materials has been improved by adapted electrochemical impedance spectroscopy (EIS) equivalent circuits, which include a more detailed analysis of the contribution of degradation processes. Linear sweep voltammetry (LSV) was used to measure the gas crossover through the membrane. Cyclic voltammetry provides information about the change in electrochemical surface area. Electrochemical characterizations and fluoride measurements are supplemented by ex situ imaging methods to determine membrane thinning.[1] M. A. Yandrasits, A. Komlev, K. Kalstabakken, M. J. Kurkowski, and M. J. Lindell, “Liquid Chromatography/Mass Spectrometry Analysis of Effluent Water from PFSA Membrane Fuel Cells Operated at OCV,” J. Electrochem. Soc., vol. 168, no. 2, p. 024517, Feb. 2021, doi: 10.1149/1945-7111/abe56a.[2] M. Heidinger, E. Kuhnert, K. Mayer, D. Sandu, V. Hacker, and M. Bodner, “Photometric Method to Determine Membrane Degradation in Polymer Electrolyte Fuel Cells,” Energies 2023, Vol. 16, Page 1957, vol. 16, no. 4, p. 1957, Feb. 2023, doi: 10.3390/EN16041957.

Amidoxime-Containing Zr and Hf Atomic Layer Deposition Precursors for Metal Oxide Thin Films.

In this article, we discuss the synthesis of eight novel zirconium and hafnium complexes containing amidoxime ligands as potential precursors for atomic layer deposition (ALD). Two amidoximes, viz., (E)-N'-hydroxy-N,N-dimethylacetimidamide (mdaoH) and (Z)-N'-hydroxy-N,N-dimethylpivalimidamide (tdaoH), along with their Zr and Hf homoleptic complexes, Zr(mdao)4 (1), Hf(mdao)4 (2), Zr(tdao)4 (3), and Hf(tdao)4 (4) were prepared. We further synthesized heteroleptic compounds with different physical properties by introducing cyclopentadienyl (Cp) ligand, namely, CpZr(mdao)3 (5), CpHf(mdao)3 (6), CpZr(tdao)3 (7), and CpHf(tdao)3 (8). Thermogravimetric analysis was used for the assessment of the evaporation characteristics of complexes 1, 2, 5, and 6, and it revealed multistep weight losses with high residues. On the other hand, the thermogravimetric analysis curves of complexes 3, 4, 7, and 8 comprising tdao ligands revealed single-step weight losses with moderate residues. Single-crystal X-ray diffraction studies of complexes 1, 3, and 7 showed that all of the complexes have monomeric molecular structures. Complex 7 exhibited a low melting point (75 °C), good volatility, and high thermal stability compared with other complexes. Therefore, an atomic layer deposition process for the growth of ZrO2 was developed by using ZrCp(tdao)3 (7) as a novel precursor.