Zirconium Complexes Research Articles

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.

Low-dimensional compounds containing bioactive ligands. Part XXIII: A comprehensive study of the preparation and cytotoxic activities of zirconium(IV) complexes with 8-hydroxyquinoline and its derivatives

Nine zirconium(IV) complexes, [Zr(8-HQ)4]·DMF·H2O (1), [Zr(dClQ)4]·EtOH (2), [Zr(ClNQ)4]·EtOH (3a), [Zr(ClNQ)4]·DMF (3b), [Zr(BrQ)4] (4), [Zr(dBrQ)4]·DME (5), [Zr(2-MedBrQ)4]·2DMF (6), [Zr2Cl2(CQ)4µ2-O(DMF)2]·0.33DMF (7), and [Zr2Cl2(ClBrQ)4µ2-O(DMF)2]·DMF (8) (DME = 1,2-dimethoxyethane, H8-HQ = 8-hydroxyquinoline, HdClQ = 5,7-dichloro-8-hydroxyquinoline, HClNQ = 5-chloro-7-nitro-8-hydroxyquinoline, HBrQ = 7-bromo-8-hydroxyquinoline, HdBrQ = 5,7-dibromo-8-hydroxyquinoline, H2-MedBrQ = 2-methyl-5,7-dibromo-8-hydroxyquinoline, HCQ = 5-chloro-7-iodo-8-hydroxyquinoline, HClBrQ = 5-chloro-7-bromo-8-hydroxyquinoline), have been prepared and characterized by elemental, single crystal X-ray structure analysis and IR spectroscopy. Complexes 1 – 6 are mononuclear complexes with Zr(IV) atoms octacoordinated by four bidentate quinoline ligands. Complexes 7 and 8 are binuclear complexes in which two Zr(IV) atoms are coordinated by two bidentate quinoline, one DMF and one chloro ligands, and the seventh coordination place occupies an oxygen atom bridging both complex species. The stability of complexes soluble in a DMSO was verified by NMR spectroscopy. In vitro cytotoxic properties of complexes 1, 2, 4, 5, and 6, and corresponding ligands were studied against 8 cancer cell lines, and their selectivity was verified on BJ-5ta non-cancerous cell line. The most potent complexes are 1 and 4 with the smallest quinoline ligands.

Hafnium and Zirconium Complexes Bearing ONN-Tridentate Ligands and Their Catalytic Properties toward Olefin Polymerization

Hafnium and Zirconium Complexes Bearing ONN-Tridentate Ligands and Their Catalytic Properties toward Olefin Polymerization

Exploration of Thermally Activated Delayed Fluorescence (TADF)-Based Photoredox Catalyst To Establish the Mechanisms of Action for Photodynamic Therapy.

The mechanisms of action (MoA) have been proposed to further reduce the O2 dependence of photodynamic therapy (PDT) significantly. However, the triplet states of traditional photosensitizers are relatively short and also are easily deactivated by the quenching of H2O or O2. This is not conducive for the electron transfer in the photocatalytic process and poses a great obstacle to establish the MoA. Therefore, we selected and synthesized a zirconium(IV) complex (Zr(MesPDPPh)2) reported by Milsmann to address this issue. The specific symmetric and intact geometry endowed Zr(MesPDPPh)2 NPs with long-lived triplet excited state (τ = 350 μs), desired sensitized ability, and improved anti-interfering performance on O2, which was matched with the requirements of photoredox catalyst significantly. The results showed that while PDT (I) and PDT (II) could be achieved simultaneously by leveraging Zr(MesPDPPh)2 NPs, it also could be served as a rare example of thermally activated delayed fluorescence (TADF)-based photoredox catalyst to implement the MoA of PDT. It involved the oxidation of NADH and the establishment of catalytic cycle collaborating by O2 and cytochrome c (cyt c) in normoxia and hypoxia, respectively. As a result, the oxygen-free PDT and tumor-growth inhibition was realized.

Catalytic Behavior of Half‐Metallocene Non‐Cp‐Type Group 4 Metal Complexes (M=Zr, Hf) with a Cyclooctatetraenyl Dianion during Olefin Polymerization

AbstractSignificant advancements have been made in metallocene catalysis due to the development of cyclopentadienyl (Cp) ligands by numerous researchers. Furthermore, various ligand combinations have been realized in the last 20 years for the development of post‐metallocene catalysts. Although ligands containing a Cp have been widely reported, only a few reports exist ligands based on other carbon‐only π‐electron moieties. Herein, we focused on the zirconium and hafnium with the 10π‐electron cyclooctatetraenyl (Cot) dianion as an ancillary ligand and investigated the olefin‐polymerization ability of these complexes. Thus, we performed ethylene and ethylene‐1‐octene (co)polymerization using dMAO, MMAO, and Ph3C[B(C6F5)4]/iBu3Al as cocatalysts and confirmed that completion of the polymerization reaction; the catalytic system except dMAO exhibited activities for olefin polymerization to give linear polyethylene or ethylene‐1‐octene copolymer. Furthermore, the zirconium complexes bearing trimethylsilyl‐substituted Cot ligand exhibited enhanced activities for ethylene polymerization compared with an unsubstituted CotZr catalyst.

Design of Highly Conductive Leather Based on Zirconium Ion Coordination for Health Protection in Severe Harsh Conditions

AbstractFlexible electric heaters with softness, comfort and heating performance have application prospects in the fields of life and health, medical security and so on. In this study, by taking advantage of the soft and comfortable properties of leather itself, collagen fibers and carbon nanotubes (CNTs) are composited through zirconium ion (Zr4+) coordination and complexation. The composition, microstructure and Joule heating performance of the prepared flexible conductive leather (CNTs@Zr@OTL) are investigated in detail. The characterisation results prove the (Zr4+) coordination effect and the successful preparation of CNTs@Zr@OTL. At the same time, it has a resistance of about 250 Ω, a shrinkage temperature (Ts) of about 75°C, mechanical property of about 8 MPa, 60 h strong biodegradability and Joule heating of about 65°C under 15 V DC voltage. The obtained product can be further designed as a flexible Joule heating heater (Jhh) with softness, comfort as well as conductivity, and excellent Joule heating performance, and its practical application effect in heating wrists, fingers, joints and car seats is explored, as well as the heating effect under the actual movement of human body such as squatting, sitting and walking. This work provides an idea and method for the intelligent interaction of flexible heaters.

Determination of HOMO and LUMO of bis(β-diketonate)zirconium(IV) compound used as a catalyst in the ring opening polymerization of ε-Caprolactone and δ-Valerolactone

Poly(ε-caprolactone) (PCL) and poly(δ-valerolactone) (PVL) are aliphatic polyesters that can generally be used for basic medical materials such as bone and dental implant materials, drug delivery systems, and scaffolds in tissue engineering. PCL and PVL belong to the polylactone group which have superior properties such as good biocompatibility, nontoxicity, flexibility, thermoplastic and can be biodegraded in a controlled manner. These superior properties make it the main choice in producing medical materials. This study aims to determine the degree of polymerization of PCL and PVL catalyzed using a bis(β-diketonate)zirconium(IV) complex. In addition, analysis of the Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) was also carried out on the catalyst complex. The ring-opening polymerization reaction (ROP) of ε-caprolactone (ε-CL) and δ-valerolactone (δ-VL) lasted for 4 h at 100 °C. The resulting PCL and PVL were then characterized for their chemical and thermal properties using FTIR, 1HNMR, XRD, DTA and TGA. Both PCL and PVL are semicrystalline. On the other hand, the resulting PCL has a melting point of 65.5 °C, with a degree of polymerization (DP) of 17. Meanwhile, the resulting PVL has a melting point of 63.4 °C with a DP of 8.

Isospecific polymerization of sterically bulky α‐olefins catalyzed by zirconium(IV) complex possessing an [OSSO]‐type bis(phenolate) ligand

AbstractDibenzyl zirconium(IV) complex (1), featuring an [OSSO]‐type bis(phenolate) ligand, served as a highly efficient pre‐catalyst for the polymerization of sterically bulky α‐olefins, such as vinyl cyclohexane (VCH) and 3‐methyl‐1‐butene (3‐MB). Upon activation with dried modified‐methylaluminoxane (dMMAO), the polymerization of VCH proceeded smoothly at 25°C to yield exclusively isotactic poly(VCH)s ([mm] >95%, Mw = 6500–19,400 g mol−1, PDI = 1.4), exhibiting good activity up to 924 g mmol(1)−1 h−1. The 1/dMMAO catalyst system also facilitated the polymerization of 3‐MB, producing colorless insoluble poly(3‐MB)s. DSC, TGA, and 13C CP‐MAS analyses showed the presence of highly isotactic microstructures in the resulting poly(3‐MB)s. Remarkably, the corresponding activity reached an impressive value of 898 g mmol(1)−1 h−1, surpassing that of previously reported homogeneous catalysts.

A blue emission of zirconium (IV) complex based on 2, 6-pyridinedicarboxylic acid ligand: Syntheses, crystal structure, and luminescence sensing

A novel blue emission of zirconium complex, formulated as [Zr(pydc)3]·[(CH3)2NH2]2 (1), has been synthesized by using a mixture of zirconium nitrate and 2, 6-pyridinedicarboxylic acid (H2pydc). The complex 1 presents a three-dimensional supramolecular network structure due to the intermolecular NH···O, OH···O hydrogen bonds. Additionally, the crystals of 1 exhibit blue luminescence and demonstrate a highly selective and sensitive sensing capability for detection of Co2+ ions with a Ksv value of 1.22 × 104 M−1 and limit of detection (LOD) of 1.20 × 10−5 M. Furthermore, the fluorescence lifetime and quantum yield of the complex 1 is τ = 6.22 μs and Φ = 25.9 %.

Zirconium Complex as an Efficient Catalyst in the Hydroboration of Nitriles, Alkynes, and Carboxylic Esters: A Combined Experimental and Computational Study

Zirconium Complex as an Efficient Catalyst in the Hydroboration of Nitriles, Alkynes, and Carboxylic Esters: A Combined Experimental and Computational Study

Synthesis and physicochemical properties of tin(IV), zirconium(IV), and hafnium(IV) 2(3),9(10),16(17),23(24)-tetrakis-(4-tritylphenoxy)phthhalocyaninates

The reaction of 4-tritylphenoxyphthalonitrile with SnCl2, ZrCl4 and HfCl4 in the presence of urea under ammonium molybdate catalysis was used to synthesize tetrakis-(4-tritylphenoxy)phthalocyaninates of tin(IV), zirconium(IV), and hafnium(IV). The complexes were characterized by spectral methods of analysis, including mass spectrometry, 1Н NMR, vibrational and electron spectroscopy. All of them form J -type dimer associates in chloroform at concentrations up to ~1.5×10-6 mol/L and lower, are not associated in a mixture of toluene and pyridine up to concentrations of ~3×10-5 mol/L and higher, have catalytic activity in electroreduction reactions of molecular oxygen. The complexes of zirconium and hafnium showed the highest activity. Tin and zirconium complexes are thermally stable in an inert atmosphere up to a temperature of 200°C.

Low-dimensional compounds containing bioactive ligands. XXII. First crystal structure, cytotoxic activity and DNA and HSA binding of a zirconium(IV) complex with 8-hydroxyquinoline-2-carboxylic acid.

A new zirconium(IV) complex, diaquabis(8-hydroxyquinoline-2-carboxylato-κ3N,O2,O8)zirconium(IV) dimethylformamide disolvate, [Zr(C10H5NO3)2(H2O)2]·2C3H7NO or [Zr(QCa)2(H2O)2]·2DMF (1) (HQCaH is 8-hydroxyquinoline-2-carboxylic acid and DMF is dimethylformamide), was prepared and characterized by elemental analysis, IR spectroscopy and single-crystal X-ray structure analysis. Complex 1 is a mononuclear complex in which the ZrIV atoms sit on the twofold axis and they are octacoordinated by two N and six O atoms of two tridentate anionic QCa2- ligands, and two aqua ligands. Outside the coordination sphere are two DMF molecules bound to the complex unit by hydrogen bonds. The structure and stability of complex 1 in dimethyl sulfoxide were verified by NMR spectroscopy. The cytotoxic properties of 1 and HQCaH were studied in vitro against eight cancer cell lines, and their selectivity was tested on the BJ-5ta noncancerous cell line. Both the complex and HQCaH exhibited low activity, with IC50 > 200 µM. DNA and human serum albumin (HSA) binding studies showed that 1 binds to calf thymus (CT) DNA via intercalation and is able to bind to the tryptophan binding site of HSA (Trp-214).

Total Synthesis of Azulene Derivative, a Blue Pigment Isolated from Lactarius indigo, and Colorant Application of Its Aqueous Dispersion.

Safety concerns in the food industry have increased the demand for natural food colorants. However, the application ranges of natural blue colorants are insufficient because they are scarce in nature, and the currently available natural blue dyes are limited to water-soluble products. In this study, we investigated a fat-soluble azulene derivative isolated from the mushroom Lactarius indigo as a potential candidate for a natural blue colorant. We developed its first total synthesis, where the azulene skeleton was constructed from a pyridine derivative and an ethynyl group was converted into an isopropenyl group using zirconium complexes. Moreover, nanoparticles of the azulene derivative were prepared via reprecipitation method, and their colorant ability was investigated in aqueous solutions. The new candidate food colorant exhibited a deep-blue color in an organic solvent and aqueous dispersion.

Anti-tumoral Titanium(IV) Complexes Stabilized with Phenolato Ligands and Structure-Activity Relationship.

Titanocene dichloride and budotitane have opened a new chapter in medicinal chemistry of titanium(IV) complexes being novel non-platinum antitumor metallic agents. Numerous efforts have led to the discovery of the diamino bis-phenolato titanium(IV) complexes. Among which, the [ONNO] and [ONON] type ligands namely Salan, Salen and Salalen coordinated titanium(IV) alkoxyl complexes have demonstrated significantly enhanced aqueous stability, their in vitro and in vivo antitumor efficacy, mechanism of action, structure-activity relationships and combined tumor therapy have been intensively investigated. Replacement of the labile alkoxyls with a second chelator resulted in structural rigid titanium(IV) complexes, which showed exceedingly good aqueous stability and potent antitumor activity both in vitro and in vivo. The unique ligand system successfully allowed the access of isotopic [45Ti]Titanium(IV) complexes, post-synthetic modification, facile synthetic protocols and antitumor congeneric zirconium(IV) and hafnium(IV) complexes. This review presents recent research progress in the field of antitumor group 4 metal complexes stabilized with phenolato ligands; especially their structure-activity relationships are summarized.

Synthesis and cytotoxicity study of water soluble 8-hydroxyquinoline stabilized zirconium(Ⅳ) complexes

Three octacoordinated zirconium(IV) tetrakis-(8-hydroxyquinolinate) complexes [(L1-3)4Zr(IV)] were synthesized smoothly in THF at room temperature using ZrCl4 as a starting material with yields ranging from 74% to 83%. Their structures were characterized by 1H, 13C NMR and X-ray diffraction spectroscopy. [(L1-3)4Zr(IV)] exhibited excellent solubility and stability in H2O and DMSO, and they have demonstrated enhanced cytotoxicity against human Hep G2, Hela S3 and PC9 cells than cisplatin. Among them, [(L1)4Zr(IV)] bearing non-substituted 8-hydroxyquinoline showed about 2 orders of magnitude higher inhibition activity against Hep G2 cells than cisplatin (IC50: 0.14 ± 0.1 μM, cisplatin: 13.82 ± 1.3 μM). The selectivity towards tumor cells was preliminary evidenced by their partial or completely vanished inhibition activity against AML12 cells. Additionally, [(L1)4Zr(IV)] could almost exclusively induce the apoptosis of Hep G2 cells.

Lewis Acid Catalyzed Amide Bond Formation in Covalent Graphene-MOF Hybrids.

Covalent hybrids of graphene and metal-organic frameworks (MOFs) hold immense potential in various technologies, particularly catalysis and energy applications, due to the advantageous combination of conductivity and porosity. The formation of an amide bond between carboxylate-functionalized graphene acid (GA) and amine-functionalized UiO-66-NH2 MOF (Zr6O4(OH)4(NH2-bdc)6, with NH2-bdc2- = 2-amino-1,4-benzenedicarboxylate and UiO = Universitetet i Oslo) is a highly efficient strategy for creating such covalent hybrids. Previous experimental studies have demonstrated exceptional properties of these conductive networks, including significant surface area and functionalized hierarchical pores, showing promise as a chemiresistive CO2 sensor and electrode materials for asymmetric supercapacitors. However, the molecular-level origin of the covalent linkages between pristine MOF and GA layers remains unclear. In this study, density functional theory (DFT) calculations were conducted to elucidate the mechanism of amide bond formation between GA and UiO-66-NH2. The theoretical calculations emphasize the crucial role of zirconium within UiO-66, which acts as a catalyst in the reaction cycle. Both commonly observed hexa-coordinated and less common hepta-coordinated zirconium complexes are considered as intermediates. By gaining detailed insights into the binding interactions between graphene derivatives and MOFs, strategies for tailored syntheses of such nanocomposite materials can be developed.

Understanding the Mechanism and Selectivity of 1,1-Diborylalkanes from Alkenes Catalyzed by a Zirconium Complex.

The synthesis of 1,1-diborylalkanes from readily available alkenes is an appealing method. The density functional theory (DFT) method was employed to investigate the reaction mechanism of 1,1-diborylalkanes, which was synthesized from alkenes and a borane, and the reaction was catalyzed by a zirconium complex Cp2ZrCl2. The entire reaction is divided into two cycles: dehydrogenative boration to form vinyl boronate esters (VBEs) and hydroboration of VBEs. This article focuses on the hydroboration cycle and elaborates on the role of the reducing reagents in the equilibrium of self-contradictory reactivity (dehydrogenative boration and hydroboration). The H2 and HBpin pathways were investigated as the reducing reagents in the hydroboration process. The calculated results showed that it is more advantageous to use H2 as a reducing agent (path A). Furthermore, the σ-bond metathesis is the rate-determining step (RDS) with an energetic span of 21.4 kcal/mol. This is consistent with the self-contradictory reactivity balance proposed in the experiment. The reaction modes of the hydroboration process were also discussed. These analyses revealed the origin of selectivity in this boration reaction, in which the σ-bond metathesis of HBpin needs to overcome the strong interaction between HBpin and the Zr metal. Meanwhile, the origin of the selectivity of different positions of H2 is the interaction between the σ(H1-H2) → σ*(Zr1-C1) overlap and these findings have implications for catalyst design and application.

Efficient Access to Sequence-Controlled Poly(α-hydroxy acids) with Ax(BC)yDz-Type and Ax(BC)yAz-Type Triblock Structures via Self-Switchable Ring-Opening Polymerization of Monomer Mixtures.

Synthesizing block-sequence-controlled poly(α-hydroxy acids) of three or four α-hydroxy acids remains challenging in one step. In this study, a strategy was employed using three monomers of O-carboxyanhydrides (OCAs) consisting of one α-hydroxy acid (A), asymmetric cyclic diester (B and C, two different α-hydroxy acids of B and C), and symmetric cyclic diester (one α-hydroxy acid of D) with remarkably different activities toward a stereoselective, regioselective, and chemoselective initiator of a zirconium complex. Then, via a self-switchable approach, these monomers can be copolymerized in a well-controlled block sequence of Ax(BC)yDz and Ax(BC)yAz without an external stimulus. Moreover, upon addition of more monomer mixtures during the copolymerization process, more complicated sequence-controlled poly(α-hydroxy acids) can be achieved with up to 15 blocks.

Synthesis of Modular Desferrioxamine Analogues and Evaluation of Zwitterionic Derivatives for Zirconium Complexation.

The natural siderophore desferrioxamine B (DFOB) has been used for targeted PET imaging with 89 Zr before. However, Zr-DFOB has a limited stability and a number of derivatives have been developed with improved chelation properties for zirconium. We describe the synthesis of pseudopeptidic analogues of DFOB with azido side chains. These are termed AZA-DFO (hexadentate) and AZA-DFO* (octadentate) and are assembled via a modular synthesis from Orn-β-Ala and Lys-β-Ala. Nine different chelators have been conjugated to zwitterionic moieties by copper-catalyzed azide-alkyne cycloaddition (CuAAC). The resulting water-soluble chelators form Zr complexes under mild conditions (room temperature for 90 min). Transchelation assays with 1000-fold excess of EDTA and 300-fold excess of DFOB revealed that a short spacing of hydroxamates in (Orn-β-Ala)3-4 leads to improved complex stability compared to a longer spacing in (Lys-β-Ala)3-4 . We found that the alignment of amide groups in the pseudopeptide backbone and the presence of zwitterionic sidechains did not compromise the stability of the Zr-complexes with our chelators. We believe that the octadentate derivative AZA-DFO* is particularly valuable for the preparation of new Zr-chelators for targeted imaging which combine tunable pharmacokinetic properties with high complex stability and fast Zr-complexation kinetics.