Phosphonate Ligands Research Articles

Catena-Poly[oxidanium [tris{μ-[amino(iminio)methyl]phosphonato}zincate(II)]

The crystal structure of the anionic zinc-[amino-(iminio)meth-yl]phospho-nate one-dimensional coordination polymer, Zn-AIMP, is reported; the negative charge is balanced by an oxidanium cation (H3O+) to give the composition {(H3O)[Zn(CH4N2PO3)3]} n . The building unit of the coordination polymer comprises a divalent Zn2+ cation (site symmetry ..) and three [amino(iminio)meth-yl]phospho-nate mono-anionic ligands (point group symmetry m). The AIMP ligand exists in a zwitterionic form with a total charge -1 as the phospho-nate is fully deprotonated (-PO3 2-), while the amino-(iminio)methyl moiety is protonated (H2N-C-NH2 +).

Mapping out the Aqueous Surface Chemistry of Metal Oxide Nanocrystals: Carboxylate, Phosphonate, and Catecholate Ligands.

Iron oxide and hafnium oxide nanocrystals are two of the few successful examples of inorganic nanocrystals used in a clinical setting. Although crucial to their application, their aqueous surface chemistry is not fully understood. The literature contains conflicting reports regarding the optimum binding group. To alleviate these inconsistencies, we set out to systematically investigate the interaction of carboxylic acids, phosphonic acids, and catechols to metal oxide nanocrystals in polar media. Using nuclear magnetic resonance spectroscopy and dynamic light scattering, we map out the pH-dependent binding affinity of the ligands toward hafnium oxide nanocrystals (an NMR-compatible model system). Carboxylic acids easily desorb in water from the surface and only provide limited colloidal stability from pH 2 to pH 6. Phosphonic acids, on the other hand, provide colloidal stability over a broader pH range but also feature a pH-dependent desorption from the surface. They are most suited for acidic to neutral environments (pH <8). Finally, nitrocatechol derivatives provide a tightly bound ligand shell and colloidal stability at physiological and basic pH (6–10). Whereas dynamically bound ligands (carboxylates and phosphonates) do not provide colloidal stability in phosphate-buffered saline, the tightly bound nitrocatechols provide long-term stability. We thus shed light on the complex ligand binding dynamics on metal oxide nanocrystals in aqueous environments. Finally, we provide a practical colloidal stability map, guiding researchers to rationally design ligands for their desired application.

The effects of amidophosphonate ligand immobilization method on the uranium extraction efficiency of functionalized silica

The effects on the uranium extraction efficiency of the functionalization method of three kinds of functionalized silica materials were evaluated in low sulfate (pH = 2) and high sulfate (pH = 1) solutions, with compositions representative of typical effluents from uranium mines and leaching solutions from uranium ore treatment, respectively. Silica supports were functionalized with amidophosphonate moieties either by peptide grafting or by non-covalent impregnation. Prior to impregnation, the surface of the silica supports was modified with either alkyl chains or ionic liquid groups. The selectivity of the modified silica supports for uranium was determined in the presence of iron and molybdenum as competing cations. Our results show that both incorporation methods yield materials with good extraction efficiency and selectivity in low sulfate solutions. EXAFS data indicate that uranyl species have to first be desulfurized to be extracted by the phosphonate ligand. This process appears more energetically favorable for the impregnated ligands than for the grafted ones under high sulfate conditions; likely because the grafted ligands compete less efficiently with the bidentate sulfates coordination in uranyl coordination sphere.

The Role of Subsurface Valence Band Localization in the Passivation of Perovskite Nanocrystals

AbstractTraditional colloidal quantum dots rely on larger‐bandgap semiconductor shells for the localization of excitons in their emissive core. Unshelled quantum dots are typically weakly luminescent due to severe quenching by deep electronic traps. Lead halide perovskite nanocrystals deviate from this convention and require only common monofunctional aliphatic ligands on their surfaces to attain near‐unity luminescence quantum yields. Here, a combination of density functional theory calculations and experimental studies is employed to elucidate the mechanistic role of the ligands. The attachment of a surface ligand leads to a distortion of the surface, which results in the localization of the valence band deeper into the subsurface layers. This creates an energetic profile that is similar to a conventional core–shell quantum dot and renders the valence electrons unavailable for interaction with adventitious chemical species. It is further shown that a phosphonate moiety offers significantly stronger binding and leads to the long‐term preservation of this beneficial subsurface localized band structure. As experimental proof, a red‐emitting mixed‐halide perovskite nanocrystal, which is usually susceptible to degradation and spectral shifts, exhibits remarkable stability under a phosphonate ligand shell. These findings and mechanistic insights may guide the future engineering of robust perovskite nanocrystals for color displays and light‐emitting applications.

A Phosphonate Substituent in a 1,10‐Phenanthroline Ligand Boosts Light‐Driven Catalytic Water Oxidation Performance Sensitized by Ruthenium Chromophores

AbstractA series of new Ruthenium(II) complexes based on the (1,10‐phenanthrolin‐5‐yl)diethyl phosphonate ligand L2 and their corresponding phosphonic acid along with reference compounds are synthesized in order to evaluate the influence of the phosphonate substitution on the catalytic performance of such molecules. UV‐vis absorption and emission spectroscopy show, that introduction of a phosphonate moiety into the periphery of the phenanthroline ligand does not alter the photophysical properties of the complex. In contrast, the electrochemical features of all compounds are affected upon respective functionalization compared to the reference molecule [Ru(bpy)3](PF6)2 in aqueous medium. Photostability tests in water or in water/persulfate show a dependency of the stability towards photodecomposition on quenching efficiency with persulfate anion. The lower quenching efficiency thus leads to increased stability based on the negative charge of the phosphonate moiety in 2 and P1 in aqueous medium following a quenching efficiency trend of [Ru(bpy)3](PF6)2&gt;1&gt;2&gt;P1. Photocatalytic water oxidation using [Ru(dpp)(pic)2](PF6)2 reveals that compound 1 and [Ru(bpy)3](PF6)2 doe not exhibit any activity under the utilized conditions, P1 shows a negligible TON of 7, whereas compound 2 reaches a TON of 140 after 1 h. This fact highlights that the redox potential is not the sole driver in the catalytic cycle and accentuates the importance of different criteria determining the suitability of photosensitizers in light‐driven water oxidation, such as light absorption, redox potential of the RuIII/RuII event, photostability towards and quenching efficiency with the sacrificial agent.

Assembly of cobalt-p-sulfonatothiacalix[4]arene frameworks with phosphate, phosphite and phenylphosphonate ligands

Abstract Three cobalt-calixarene coordination frameworks, namely, {[Co4Cl(H4TC4AS)]4(HPO3)8}4− (CIAC-253), {[Co4Cl(H4TC4AS)]4(PO4)8}12− (CIAC-254) and {[Co4Cl(H4TC4AS)]3(Ph-PO3)6}3− (CIAC-255) were obtained by solvothermal reaction of a cobalt salt, sodium p-sulfonatothiacalix[4]arene (Na4H4TC4AS) and phosphate, phosphite and phosphonate ligands. In CIAC-253 and CIAC-254, the shuttlecock-like Co4Cl-(TC4AS) secondary building units (SBUs) are bridged by HPO3 2− or PO4 3− anions into two quadrilateral frameworks while in CIAC-255, the Co4Cl-(TC4AS) SBUs are linked into a triangular framework by phenylphosphonate anions. The supramolecular interactions between the phenyl groups of phosphonate and TC4AS play a crucial role in the formation of the triangle. Magnetic measurements revealed that all the cobalt(II) centers exhibit antiferromagnetic interactions.

Dual-Functional Metal-Organic Framework for Luminescent Detection of Carcinoid Biomarkers and High Proton Conduction.

It remains a challenge to exploit dual-functional metal-organic frameworks (MOFs) for applications, including luminescence detection and proton conduction. With the deliberate selection of the bifunctional organic ligand 5-sulfoisophthalic acid monosodium salt (NaH2bts), and the phosphonic acid ligand N,N'-piperazine (bismethylenephosphonic acid; H4L), a robust three-dimensional (3D) noninterpenetrating dual-functional MOF, [Tb(H2L)(H2bts)(H2O)]·H2O (1), has been synthesized hydrothermally. On the basis of the excellent thermal and chemical as well as superior luminescence stabilities in water and solutions with different pHs, 1 can serve as the simple, rapid, and highly selective and sensitive luminescence detection of the carcinoid biomarkers 5-hydroxytryptamine (HT) and its metabolite 5-hydroxyindole-3-acetic acid (HIAA) with detection limits of nanomolar magnitude in water and in simulated blood plasma and urine systems. Due to the change in the signals that could be readily differentiated by the naked eye under a UV lamp, a portable test paper has been developed. The probable quenching mechanisms are discussed in detail. In addition, a great number of hydrogen-bonding networks are formed among the uncoordinated carboxylic oxygen atoms, sulfonate oxygen atoms, protonated nitrogen atoms, and water molecules, which provide potential proton-hopping sites for proton conduction, leading to a maximum proton conductivity of 2.3 × 10-4 S cm-1 at 368 K and 95% relative humidity. The above results suggest that rationally designed dual-functional MOFs can open an avenue for the development of occupational diagnostic tools and alternative energy technology.

Does the length of the alkyl chain affect the complexation and selectivity of phenanthroline-derived phosphonate ligands? – Answers from DFT calculations

The soft–hard-donor-combined phosphonate-based ligands are one of the popular extractants for the separation of actinide from lanthanide in nuclear waste management. Among them, tetradentate phenanthroline-derived phosphonate (POPhen) ligands attract much attention. A recent report suggests that n-butyl substituted POPhen shows better portioning behaviour compared to its ethyl derivative. However, the effect of the alkyl chain on the extraction and complexation behaviour is yet to be explored. We addressed this issue by designing POPhen ligands with alkyl chains of different lengths (methyl to n-hexyl) using DFT calculations. Results show that the n-butyl substituted ligand has an excellent extraction capability with high selectivity towards Am(III) over Eu(III) ion. Electronic structure studies demonstrate that MN and MO bond lengths are greater in the Eu complexes than the corresponding Am complexes. Atoms in Molecules analysis was done on the optimized geometries to ascertain the nature of interactions present in these ML(NO3)3 complexes. In addition, bond order analysis reiterates that the n-butyl substituted ligand is having a better extraction ability towards Am(III) ions through higher MO and MN bond orders. The calculated separation factor of the ligand with n-butyl substitution is greater than that of other ligands. Increasing the length of the alkyl chain until the n-butyl increases the selectivity and binding, beyond which, the chain length is not of much use in improving the selectivity as well as the binding ability of these POPhen ligands. This work brings out an ideal alkyl chain length (n-butyl) required for better binding and extraction capability of POPhen ligands. Overall this computational study sheds light on the need for tailoring ligands with optimum alkyl chain for effective lanthanide/actinide separation.

Photocatalytic application of a phosphonate-based metal-organic framework for the removal of bisphenol A under natural sunlight

Photocatalytic removal of bisphenol A, one of the most widely and emerging pollutants in the aquatic environment, was investigated by advanced oxidation process under natural sunlight. The removal process by a metal-organic framework, synthesized with phosphonic acid ligand, namely STA-12 (Fe) and hydrogen peroxide revealed excellent results. Therefore, the optimal conditions for the degradation of bisphenol A by the photo-Fenton mechanism were studied. The removal process follows the first-order kinetics with respect to the contaminant and a significant synergy was observed in the catalytic system of hydrogen peroxide/sunlight/STA-12 (Fe). The Optimal values for pH, irradiation time, catalyst amount and H2O2 dosage for oxidation of bisphenol A in 30 mg / l aqueous solution were determined to be 5, 90 minutes, 10 mg and 12 μl, respectively. Under these conditions, the best removal efficiency was 79.8%. Also, the mineralization value of organic pollutant was determined to equal 51% by measuring TOC. To determine the most important species that affected the photocatalytic reduction, trapping experiments were carried out, using various kinds of scavengers and the results showed that the hydroxyl radicals (•OH) are the main oxidizing agent in the photocatalytic system and superoxide radical and the holes in the photocatalyst surface are less involved in the process of contaminant degradation. Finally, a probable reaction mechanism has been investigated in detail. In addition, the catalyst has recyclability and stability in the photocatalytic reaction. This study is the first report for application of a phosphonate-based MOF for the removal of an emerging pollutant with a photo-Fenton mechanism and presents a new example of solar-driven advanced oxidation process for the treatment of aquatic sources and environmental protection.

Alkyl-Substituted Aminobis(phosphonates)-Efficient Precipitating Agents for Rare Earth Elements, Thorium, and Uranium in Aqueous Solutions.

The efficient and environmentally sustainable separation process for rare earth elements (REE), especially for adjacent lanthanoids, remains a challenge due to the chemical similarity of REEs. Tetravalent actinoids, thorium, and traces of uranium are also present in concentrates of REEs, making their separation relevant. This study reports six simple water-soluble aminobis(phosphonate) ligands, RN[CH2P(O)(OH)2]2 (1 R = CH2CH3, 2 R = (CH2)2CH3, 3 R = (CH2)3CH3, 4 R = (CH2)4CH3, 5 R = (CH2)5CH3, 6 R = CH2CH(C2H5)(CH2)3CH3) as precipitating agents for REEs, Th, and U, as well as gives insight into the coordination modes of the utilized ligands with REEs at the molecular level. Aminobis(phosphonates) 4–6 with longer carbon chains were found to separate selectively thorium, uranium, and scandium from REEs with short precipitation time (15 min) and excellent separation factors that generally range from 100 to 2000 in acidic aqueous solution. Ligands 1–6 also improved separation factors for adjacent lanthanoids in comparison to traditional oxalate precipitation agents. Importantly, precipitated metals can be recovered from the ligands with 3 molar HNO3 with no observed ligand decomposition enabling the possibility of recycling the ligands in the separation process. NMR-monitored pH titrations for 1 showed deprotonation steps at pKa 1.3, 5.55, and >10.5, which indicate that the ligands remain in a deprotonated [L]−1 form in the pH range of 0–4 used in the precipitation studies. 31P NMR titration studies between 1 and M(NO3)3 (M = Y, La, Lu) gave satisfactory fits for 1:3, 1:2, and 1:1 metal–ligand stoichiometries for Y, La, and Lu, respectively, according to an F-test. Therefore, aminobis(phosphonate) precipitation agents 1–6 are likely to form metal complexes with fewer ligands than traditional separation agents like DEHPA, which coordinates to REEs in 1:6 metal–ligand ratio.

Metal-organic framework based on Co and 4,4′-dimethylenebiphenyl diphosphonic acid as an efficient methylene blue adsorbent

Dyestuff in industrial wastewater continues to entail environmental pollution and thus developing an adsorbent with superior adsorption performance is urgently required for the survival of future generations. In this work, a novel Co– and H4dbp based metal-organic framework (MOF, denoted as Co-MOF) adsorbent was developed for the removal of methylene blue (MB) from aqueous solution. Hydrothermal synthesis was employed for the fabrication of the Co-MOF with phosphonic acid organic ligand. X-ray diffraction, Fourier-transform infrared spectroscopy, field emission-scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and N2 adsorption-desorption isothermal analysis were utilized for Co-MOF characterization. MB adsorption by as-prepared adsorbent obeys pseudo-second-order adsorption kinetics and follows Langmuir isotherm model with the maximum adsorption capacity of 147.99 mg g−1, which is superior to other analogies. Furthermore, the recoverability of this adsorbent material was astonishing with an excellent MB removal capacity of 89.34 % of initial dye concentration after the fifth cycle. The thermodynamic parameters affirm that this adsorption process exhibits a spontaneous endothermic process with sufficient molecular randomness due to the adsorbent-adsorbate interaction suggesting a great potentiality as an adsorbent to be used for industrial wastewater treatment to mitigate the environment.

Homochiral Dysprosium Phosphonate Nanowires: Morphology Control and Magnetic Dynamics.

Controllable synthesis of uniformly distributed nanowires of coordination polymers with inherent physical functions is highly desirable but challenging. In particular, the combination of chirality and magnetism into nanowires has potential applications in multifunctional materials and spintronic devices. Herein, we report four pairs of enantiopure coordination polymers with formulae S-, R-Dy(cyampH)3 ⋅ CH3 COOH ⋅ 2H2 O (S-1, R-1), S-, R-Dy(cyampH)3 ⋅ 3H2 O (S-2, R-2), S-, R-Dy(cyampH)2 (C2 H5 COO) ⋅ 3H2 O (S-3, R-3) and S-, R-Dy(cyampH)3 ⋅ 0.5C2 H5 COOH ⋅ 2H2 O (S-4, R-4) [cyampH2 =S-, R-(1-cyclohexylethyl)aminomethylphosphonic acids], which were obtained depending on the pH of the reaction mixtures and the specific carboxylic acid used as pH regulator. Interestingly, compounds 3 were obtained as superlong nanowires, showing 1D neutral chain structure which contains both phosphonate and propionate anion ligands. While compounds 1, 2 and 4 appeared as block-like crystals, superhelices and nanorods, respectively, and exhibited similar neutral chain structures containing only phosphonate ligand. Slow magnetization relaxation characteristic of single-molecule magnet (SMM) behavior was observed for compounds S-1 and S-3. Theoretical calculations were performed to rationalize the magneto-structural relationships.

Water-Dispersible Fe3O4 Nanoparticles Modified with Controlled Numbers of Carboxyl Moieties for Magnetic Induction Heating

Monodisperse Fe3O4 nanoparticles (NPs) with excellent water dispersibility and stability were prepared by the introduction of the carboxyl group (−COOH) on the surface of the as-prepared oleyl-capped Fe3O4 NPs. Controlled introduction of the COOH moieties on the NP surface was carried out by a simple ligand exchange reaction using two types of phosphonic acid ligands with dodecyl moiety and the terminal COOH group. The degree of modification of the COOH group on the particle surface was controlled by tuning the molar ratios of the two phosphonic acids. During the ligand exchange reaction, no change was observed in the crystal structure and morphology of the Fe3O4 NPs. The results of Fourier transform infrared (FT-IR) spectroscopy confirmed that the two ligands were bound to the Fe3O4 NP surface through their phosphoric acid functional groups. The surface coverage and molar ratios of the two ligands were evaluated by thermal gravimetric analysis (TGA) and via proton nuclear magnetic resonance (1H NMR) measurements, respectively. Results obtained from the thermal analyses were consistent with the initial molar ratios of the ligands used in the reaction, which reflect on the efficiency of the developed ligand exchange process. Our COOH-modified Fe3O4 NPs could be dispersed in water by deprotonation for over 6 months and exhibit a typical ferrofluid behavior without the addition of other surfactants and dispersants, showing high dispersion stability. Furthermore, the magnetic induction heating performance of the Fe3O4 NPs in aqueous dispersions was evaluated and the specific absorption rate (SAR) value was estimated to be 38.3 W/g Fe. These results suggest that our COOH-modified Fe3O4 NPs with the desired number of COOH surface moieties can be advantageous for applications such as precise surface design, water-based ferrofluid, and hyperthermia treatment.

Modulating Structural and Electronic Properties of Rare Archimedean and Johnson-Type Mn Cages.

High-nuclearity Mn complexes have attracted significant scientific attention due to their fascinating magnetic properties and their relevance to bioinorganic systems and catalysis. In this work, we demonstrate how the strong binding characteristics of phosphonate ligands can be coupled with sterically hindered carboxylate groups to influence the symmetry of Mn coordination clusters. We describe the structure of two high-nuclearity Mn coordination cages, {Mn12} and {Mn15}, synthesized using this approach. These cages are structurally related to the truncated tetrahedral geometry and adopt rare topological features of Archimedean and Johnson-type solids. Their structural attributes distinctively influence their magnetic properties and electrocatalytic H2O oxidation characteristics.

A Tetradentate Phosphonate Ligand-based Ni-MOF as a Support for Designing High-performance Proton-conducting Materials.

Developing a robust metal-organic framework (MOF) which facilitates proton hopping along the pore channels is very demanding in the context of fabricating an efficient proton-conducting membrane for fuel cells. Herein, we report the synthesis of a novel tetradentate aromatic phosphonate ligand H8 L (L=tetraphenylethylene tetraphosphonic acid) based Ni-MOF, whose crystal structure has been solved from single-crystal X-ray diffraction. Ni-MOF [Ni2 (H4 L)(H2 O)9 (C2 H7 SO)(C2 H7 NCO)] displays a monoclinic crystal structure with a space group of P 21 /c, a=11.887 Å, b=34.148 Å, c=11.131 Å, α=γ=90°, β=103.374°, where a nickel-hexahydrate moiety located inside the void space of the framework through several H-bonding interactions. Upon treatment of the Ni-MOF in different pH media as well as solvents, the framework remained unaltered, suggesting the presence of strong H-bonding interactions in the framework. High framework stability of Ni-MOF bearing H-bonding interactions motivated us to explore this metal-organic framework material as proton-conducting medium after external proton doping. Due to the presence of a large number of H-bonding interactions and the presence of water molecules in the framework we have carried out the doping of organic p-toluenesulfonic acid (PTSA) and inorganic sulphuric acid (SA) in this Ni-MOF and observed high proton conductivity of 5.28×10-2 S cm-1 at 90 °C and 98% relative humidity for the SA-doped material. Enhancement of proton conductivity by proton doping under humid conditions suggested a very promising feature of this Ni-MOF.

Novel Tetradentate Phosphonate Ligand Based Bioinspired Co-Metal–Organic Frameworks: Robust Electrocatalyst for the Hydrogen Evolution Reaction in Different Mediums

The limited stock of classical nonrenewable energy sources has motivated researchers to explore efficient strategies for sustainable and renewable energy production. Hydrogen production via electrochemical water splitting is one of the key solutions that can meet this demand. Today 3d transition metal based nanomaterials offer a huge opportunity in the hydrogen evolution reaction (HER) via electrochemical water splitting. Herein, we report an easy and convenient synthesis route for designing the novel tetradentate phosphonate ligand based metal–organic framework (MOF, H8L-Co-crystal). The material has been characterized by single crystal X-ray diffraction (SXRD), powder XRD, thermogravimetric analysis, scanning electron microscopy, and Fourier transform infrared spectroscopy, and explored in the HER from various mediums including seawater. This single crystal belongs to the monoclinic phase having C2/c space group, with unit cell parameters a = 29.364(8) (Å), b = 12.204(4) (Å), c = 9.925(3) (Å), α = 90° = γ, β = 97.405° (CCDC no. 1922964) and the unit cell volume = 3527.04 Å3. The material H8L-Co-crystal shows very good catalytic activity towards H2 evolution with a low overpotential of 243 mV at a current density 10 mA/cm2 as well as a low Tafel slope of 102 mV/dec in acidic medium, which is comparable to commercial HER catalysts, and one of the best among non-postsynthetically modified MOFs. The electrochemical active surface area (ECSA) data have been measured to explain the high hydrogen evolution rate in different mediums. Density functional theory (DFT) study based on first-principle calculations provides a very useful understanding about the structure–catalytic property relationship and reveals the role of surface active sites toward electrochemical HER.

Ligand Exchange Reactions between Phosphonic Acids at TiO2 Nanoparticle Surfaces

AbstractUnderstanding the surface chemistry of organic‐inorganic interfaces is a prerequisite for the design of novel nanohybrid materials. Herein, we disclose that phosphonate ligands tightly bind to TiO2 nanoparticle surfaces and cannot be displaced even through repetitive decantation by methanol. However, 1D 1H solution NMR analyses unambiguously show that they can be effectively exchanged by other phosphonic acids. A key enabler for successful measurements is the design and synthesis of a novel phosphonic acid ligand that stabilizes TiO2 nanoparticles in toluene to form homogeneous colloidal conditions.

Unfolding the Extraction and Complexation Behaviors of Trivalent f-Block Elements by a Tetradentate N,O-Hybrid Phenanthroline Derived Phosphine Oxide Ligand.

In this work, a tetradentate N,O-hybrid 2,9-bis(diphenylphosphine oxide)-1,10-phenanthroline (Ph2-BPPhen) ligand was studied for the coextraction of trivalent f-block elements from nitric acid media. The extraction as well as the complexation behaviors of Ph2-BPPhen with f-block elements were thoroughly investigated using 31P and 1H NMR spectrometry, UV-vis spectrophotometry, single crystal X-ray diffraction, and density functional theoretical (DFT) calculation. Ph2-BPPhen exhibits remarkably extraction ability for both Am(III) and Eu(III) and more than 99.5% of Am(III) and Eu(III) were extracted from 1.0 M HNO3 solution. Slope analysis suggests that both 2:1 and 1:1 ligand/metal complexes were probably formed during the extraction. The 1:1 and 2:1 Ln(III) complexes with Ph2-BPPhen were also identified in CH3OH solution by NMR spectrometry, and the stability constants were determined via UV-vis spectrophotometry. Structures of the 1:1 Eu(Ph2-BPPhen)(NO3)3 and Am(Ph2-BPPhen)(NO3)3 complexes were further elucidated by single X-ray crystallography and DFT calculations. The higher extractability of Ph2-BPPhen toward trivalent Am(III) and Eu(III) compared with the previously reported phenanthroline-derived amide and phosphonate ligands was attributed to the stronger affinity of the -P═O(R)2 group to metal ions. The results from this work indicate that the N,O-hybrid 1,10-phenanthroline derived phosphine oxide ligand can serve as a new and promising candidate for coextraction of trivalent f-block elements in the treatment of nuclear waste.

Insight into the Active Contribution of N-Coordinated Cobalt Phosphate Nanocrystals Coupled with Carbon Nanotubes for Oxygen Electrochemistry

The exploration of efficient nonprecious bifunctional electrocatalysts toward both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is highly desirable for the development of the rechargeable metal–air battery. Herein, “diamond necklace”-like N-coordinated cobalt phosphate nanocrystals coupled with carbon nanotubes (CoPiC-DP/CNTs) are synthesized through the facile hydrothermal-carbonization approach and employed as the bifunctional electrocatalyst for ORR and OER. The CNTs act like the “chain” as support, the “diamond”-like N-coordinated cobalt phosphate nanocrystals serve as catalytic active sites, and the N-doped carbon derived from the phosphonate ligand-like “linker” can not only protect the “diamond” from leaching but also promote the mass transfer. Such advanced structure and composition features endow CoPiC-DP/CNTs with impressive ORR and OER electrochemical activities. To probe the active contribution of CoPiC-DP/CNTs toward ORR, a series of cobalt phosphate–carbon hybrids are prepared by adjusting the types of phosphonate ligands of the cobalt phosphonate precursor to rationally control their active components. The comprehensive investigation from structural characterizations and electrochemical measurements of these cobalt phosphate–carbon hybrids verifies that both N-coordinated cobalt sites and the suitable carbon substrate are essential for the enhanced electrocatalytic performance. Furthermore, the liquid- and solid-state zinc–air batteries with these fabricated CoPiC-DP/CNTs employed as the air cathode exhibit decreased charge–discharge potential gaps, high power density, and considerable cycling durability, which are beneficial for the potential development of flexible/portable electronic devices.

Thermodynamics of Composition Dependent Ligand Exchange on the Surfaces of Colloidal Indium Phosphide Quantum Dots

Quantum dot surfaces can have a substantial effect on their physical, chemical, and optoelectronic properties. When the chemistry that occurs at the surface of nanocrystals is studied, critical insights can be gained into the fundamental structural, thermodynamic, and optical properties of quantum dot materials providing a valuable guide for how to best adapt them for desired applications. Colloidal quantum dots are often terminated with organic ligands that consist of a long aliphatic chain and a head group that binds tightly to the nanocrystal surface. While extensive work has been done to understand how ligand head groups influence quantum dot properties, studies to unravel the influence of the organic ligand tail on ligands and surface reaction equilibria are incomplete. To further investigate the driving forces of quantum dot surface modification, a series of ligand exchange reactions with oleic acid were performed on indium phosphide quantum dots, initially terminated with straight-chain carboxylates of variable lengths. The reaction was monitored using isothermal titration calorimetry and 1H NMR to determine the extent of each reaction and its associated thermodynamics. From these measurements, interligand interactions were observed to be dependent on the length of the straight-chain ligand. A modified Ising model was used to investigate the enthalpic and entropic effects contributing to these ligand exchanges and reveal that interligand interactions play a much larger role than previously thought. Additional experimentation with phosphonic acid ligand exchange reveals complexity in the reaction mechanism but further illustrates the significant impact of ligand tail group length on thermodynamics, even in cases where there is a large difference in head group binding energy.