Oxide Ligands Research Articles

Accurate Evaluation of Dispersion Energies at Coupled Cluster Level to Understand the Substituent Effects in Am(III) and Eu(III) Complexes.

The effect of cyclic and aromatic substituents on the complexation behavior of phosphine oxide ligands with Am(III) and Eu(III) was investigated at density functional theory (DFT) and domain-based local pair natural orbital coupled-cluster (DLPNO-CC) levels. Combining DFT with accurate coupled cluster methods, we have evaluated the dispersion energy contributions to the complexation energies for trivalent Am and Eu complexes for the first time. Irrespective of the nature of substituents on the P atom, the electronic structure of the P═O group remains identical in all of the ligands. The study reveals the importance of dispersion interactions during complexation and is estimated to be more significant for Am(III) than for Eu(III) complexes.

Stabilized Perovskite Quantum Dot Solids via Nonpolar Solvent Dispersible Covalent Ligands.

The ligand exchange procedure of CsPbI3 perovskite quantum dots (PQDs) enables the fabrication of thick and conductive PQD solids that act as a photovoltaic absorber for solution-processed thin-film solar cells. However, the ligand-exchanged CsPbI3 PQD solids suffer from deterioration in photovoltaic performance and ambient stability due to the surface traps, such as uncoordinated Pb2+ sites on the PQD surface, which are generated after the conventional ligand exchange process using ionic short-chain ligands dissolved in polar solvents. Herein, a facile surface stabilization is demonstrated that can simultaneously improve the photovoltaic performance and ambient stability of CsPbI3 PQD photovoltaic absorber using covalent short-chain triphenylphosphine oxide (TPPO) ligands dissolved in a nonpolar solvent. It is found that the TPPO ligand can be covalently bound to uncoordinated Pb2+ sites and the nonpolar solvent octane can completely preserve the PQD surface components. Owing to their synergetic effects, the CsPbI3 PQD photovoltaic absorber stabilized using the TPPO ligand solution dissolved in octane exhibit higher optoelectrical properties and ambient stability than the control absorber. Consequently, CsPbI3 PQD solar cells composed of PQD photovoltaic absorbers fabricated via surface stabilization strategy provide an improved power conversion efficiency of 15.4% and an enhanced device stability.

Effect of bis(methylimidazolium) ionic liquid on the extraction of actinides and lanthanides with bis(carbamoylmethylphosphine oxide) extractant from nitric acid solutions

Abstract A novel bis(methylimidazolium) ionic liquid 3,3′-(pentane-1,5-diyl) bis(1-methylimidazolium) bis(trifluoromethanesulfonul)imide [C5(mim)2][Tf2N]2 has been synthesized. Its effect on the extraction of U(VI), Th(IV), Am(III), and lanthanides(III) from nitric acid solutions with a polydentate neutral bis(carbamoylmethylphosphine oxide) ligand L containing two bidentate fragments Ph2P(O)CH2C(O)NH–, interconnected by 4,7,10-trioxatridecane spacer through amide nitrogen atoms has been investigated. The efficiency of the extraction of metal ions with solutions of L in 1,2-dichloroethane (DCE) significantly increases in the presence of [C5(mim)2][Tf2N]2. A synergistic effect in the extraction of metal ions in this system has been explained with the high hydrophobicity of the Tf2N− anions, which are involved in the formation of extracted complexes as counterions. The value of the synergistic effect decreases with increasing acidity of the aqueous phase. The influence of the composition of the aqueous and organic phases on the efficiency of the extraction of metal ions into the organic phase is considered, and the stoichiometry of the extracted complexes is determined. The effect of the HTf2N coextraction with L on the extraction of metal ions in the L – [C5(mim)2][Tf2N]2 system is discussed. The synergistic effect in the extraction of Ln(III) from 3 M HNO3 solutions with the mixture of L and [C5(mim)2][Tf2N]2 in DCE is higher than that in the L – [C4mim][Tf2N] – DCE system.

Palladium-Catalyzed Cyanation of Aryl Sulfonium Salts.

A palladium-catalyzed cyanation of aryl dimethylsulfonium salts using cheap, nontoxic, and bench-stable K4[Fe(CN)6]·3H2O as the cyanating reagent has been developed. The reactions proceeded well under base-free conditions with various sulfonium salts and provided aryl nitrile with yields of up to 92%. Aryl sulfides can be transformed to aryl nitriles directly via a one-pot process, and the protocol is scalable. Density functional theory calculations were performed to investigate the reaction mechanism that involved a catalytic cycle involving oxidative addition, ligand exchange, reductive elimination, and regeneration to yield the product.

Bioinspired Active Site with a Coordination-Adaptive Organosulfonate Ligand for Catalytic Water Oxidation at Neutral pH

Many enzymes use adaptive frameworks to preorganize substrates, accommodate various structural and electronic demands of intermediates, and accelerate related catalysis. Inspired by biological systems, a Ru-based molecular water oxidation catalyst containing a configurationally labile ligand [2,2':6',2″-terpyridine]-6,6″-disulfonate was designed to mimic enzymatic framework, in which the sulfonate coordination is highly flexible and functions as both an electron donor to stabilize high-valent Ru and a proton acceptor to accelerate water dissociation, thus boosting the catalytic water oxidation performance thermodynamically and kinetically. The combination of single-crystal X-ray analysis, various temperature NMR, electrochemical techniques, and DFT calculations was utilized to investigate the fundamental role of the self-adaptive ligand, demonstrating that the on-demand configurational changes give rise to fast catalytic kinetics with a turnover frequency (TOF) over 2000 s-1, which is compared to oxygen-evolving complex (OEC) in natural photosynthesis.

Role of sulphur and oxygen in phosphine ligands in the extraction process of Am3+ over Eu3+ ions in water medium – A theoretical study

Spent nuclear fuel management, particularly the separation of minor actinides, is critical to the continued growth of the nuclear industry and to address the global energy crisis. However, due to the identical chemical properties of trivalent An3+ and Ln3+, it is difficult to distinguish them. Therefore, theoretical research on the mechanism of selective extraction of An3+ is needed. Two phosphine oxide ligands and two phosphine sulphide ligands with similar structures but different bridging frameworks namely phenanthroline and biphenyl, were theoretically explored and compared using relativistic density functional theory in the solvent phase. Here, the M-O bonds are stronger than the M-S bonds. QTAIM shows that the M-O/N bonds of the phosphine oxide ligands have a small amount of covalent character. Gibbs free energy shows that the formation of the complexes is spontaneous while energy decomposition analysis deciphers the binding of M(NO3)3 to these ligands. All the ligands studied had greater affinity for Am3+ than for Eu3+, which contributes to the selectivity of Am3+ over Eu3+ in the water medium. This study provides some important information for the An/Ln separation of phosphine oxide and phosphine sulphide ligands, which may help in the development of more effective phosphine based ligands for the separation of An3+/Ln3+ ions.

How to get deeper insights into the optical properties of lanthanide systems: a computational protocol from ligand to complexes

Abstract Theoretical calculations are proving as an essential tool to understand luminescence processes even for systems including lanthanide (Ln3+) ions. As such, the aim of this study is that of presenting a general and comprehensive theoretical protocol based on DFT calculations to rationalize and possibly drive the design of new luminescent Ln3+ complexes through the ab initio determination of the electronic properties of a ligand and two Eu3+ complexes. Different theoretical methodologies have been combined to look into the excited state energies, the luminescence quantum yield, and the energy transfer processes. The protocol has been validated for a β-diketone ligand and two Eu3+ complexes, which contain, in addition to the main ligand, ethanol or triphenylphosphine oxide. Moreover, by starting from the geometry optimization up to the estimation of the ligands’ singlet and triplet lowest energy states, theoretical results quantitatively agree with luminescence experimental parameters, providing at the same time insights into the different energy transfer processes. The different quantum yields of the two complexes have been correctly reproduced.

Tuning the Thermometric Features in 1D Luminescent EuIII and TbIII Coordination Polymers through Different Bridge Phosphine Oxide Ligands.

TbIII and EuIII systems have been investigated as ratiometric luminescent temperature probes in luminescent coordination polymers due to TbIII → EuIII energy transfer (ET). To help understand how ion-ion separation, chain conformation as well as excitation channel impact their thermometric properties, herein, [Eu(tfaa)3(μ-L)Tb(tfaa)3]n one-dimensional (1D) coordination polymers (tfaa- = trifluoroacetylacetonate, and L = [(diphenylphosphoryl)R](diphenyl)phosphine oxide, R = ethyl - dppeo - or butyl - dppbo) were synthesized. The short μ-dppeo bridge ligand leads to a more linear 1D polymeric chain, while the longer μ-dppbo bridge leads to tighter packed chains. As the temperature rises from 80 K, upon direct TbIII excitation at 488 nm, the TbIII emission intensity decreases, while the EuIII emission intensity increases after 160 and 200 K when L = dppeo or dppbo, respectively. The temperature-dependent emission intensities, due to TbIII → EuIII ET, enable the development of ratiometric luminescent temperature probes featuring maximum relative thermal sensitivity up to 3.8% K-1 (250 K, L = dppbo, excitation at 488 nm). On the other hand, the same system displays maximum thermal sensitivity up to 3.5% K-1 (323 K) upon ligand excitation at 300 nm. Thus, by changing the excitation channel and bridge ligand that leads to modification of the polymer conformations, the maximum relative thermal sensitivity can be tuned.

An Electron‐Deficient CpE Iridium(III) Catalyst: Synthesis, Characterization, and Application to Ether‐Directed C−H Amidation

AbstractThe synthesis, characterization, and catalytic performance of an iridium(III) catalyst with an electron‐deficient cyclopentadienyl ligand ([CpEIrI2]2) are reported. The [CpEIrI2]2 catalyst was synthesized by complexation of a precursor of the CpE ligand with [Ir(cod)OAc]2, followed by oxidation, desilylation, and removal of the COD ligand. The electron‐deficient [CpEIrI2]2 catalyst enabled C−H amidation reactions assisted by a weakly coordinating ether directing group. Experimental mechanistic studies and DFT calculations suggested that the high catalytic performance of [CpEIrI2]2 is due to its electron‐deficient nature, which accelerates both C−H activation and IrV‐nitrenoid formation.

An Electron-Deficient CpE Iridium(III) Catalyst: Synthesis, Characterization, and Application to Ether-Directed C-H Amidation.

The synthesis, characterization, and catalytic performance of an iridium(III) catalyst with an electron-deficient cyclopentadienyl ligand ([CpE IrI2 ]2 ) are reported. The [CpE IrI2 ]2 catalyst was synthesized by complexation of a precursor of the CpE ligand with [Ir(cod)OAc]2 , followed by oxidation, desilylation, and removal of the COD ligand. The electron-deficient [CpE IrI2 ]2 catalyst enabled C-H amidation reactions assisted by a weakly coordinating ether directing group. Experimental mechanistic studies and DFT calculations suggested that the high catalytic performance of [CpE IrI2 ]2 is due to its electron-deficient nature, which accelerates both C-H activation and IrV -nitrenoid formation.

Characteristic stacked structures and luminescent properties of dinuclear lanthanide complexes with pyrene units.

A novel design strategy of stacked organic fluorophores using dinuclear lanthanide (Ln(III)) complexes is demonstrated for the formation of excimer. The dinuclear Ln(III) complexes are composed of two Ln(III) (Eu(III) or Gd(III)) ions, six hexafluoroacetylacetonate (hfa), and two pyrene-based phosphine oxide ligands. Single-crystal analysis revealed a rigid pyrene-stacked structure via CH-F (pyrene/hfa) intramolecular interactions. The rigid aggregation structures of the two-typed organic ligands around Ln(III) resulted in high thermal stability (decomposition temperature: 340°C). The aggregated ligands exhibited excimer-type green emission from the stacked pyrene-center. The change in the Ln(III) ion promotes effective shifts of excimer emissions (Gd(III):500nm, Eu(III):490nm). The organic aggregation system using red-luminescent Eu(III) also provides temperature-sensitive ratiometric emission composed of π-π* and 4f-4f transitions by energy migration between aggregated ligands and Eu(III).

Small Molecule Activation on a Base-stabilized Phosphinidene.

Reduction of (NP)PCl2 (NP=phosphinoamidinate [PhC(NAr)(=NPPri 2 )]- ) with KC8 affords the phosphinoamidinato-supported phosphinidene (NP)P (9). Reaction of 9 with a N-heterocyclic carbene (MeC(NMe))2 C: results in the NHC-adduct NHC→P-P(Pri 2 )=NC(Ph)=NAr featuring an iminophosphinyl group. Reactions of 9 with HBpin and H3 SiPh led to the metathesis products (NP)Bpin and (NP)SiH2 Ph, respectively, whereas with HPPh2 a base-stabilized phosphido-phosphinidene, the product of N-P and H-P bond metathesis, was obtained. Reaction of 9 with tetrachlorobenzaquinone results in oxidation of P(I) to P(III), accompanied by oxidation of the amidophosphine ligand into P(V). Addition of benzaldehyde to 9 results in a phospha-Wittig reaction affording a product of P=P and C=O bond metathesis. Related reaction with phenylisocyanate results in a product of N-P(=O)Pri 2 addition to the C=N bond of an intermediate iminophosphaalkene to produce a phosphinidene intramolecularly stabilized by a diaminocarbene.

Computational Study on Ni−Al Bimetal‐Catalyzed Twofold C−H Annulation Reaction: Mechanism, Origin of Selectivity, and Role of SPO Ligand

AbstractDensity functional theory calculations have been performed to probe the reaction mechanism of the recently reported twofold C−H annulation of arylformamides with alkynes by Ni−Al bimetallic catalysis. The main pathway consisted of the formyl C−H activation, phenyl C−H activation, migratory insertion, and reductive elimination steps in succession. The desired annulation product was found to be the equilibrium‐controlled product, while the minor hydrocarbamoylation product was the kinetics‐controlled product. Calculated free‐energy profiles indicated that the annulation and hydrocarbamoylation pathways could intersect with each other and merge into a mechanism unity, in which the reaction system entered the hydrocarbamoylation pathway in early stage and switched to the annulation pathway afterwards via suitable transition states. The modified mechanism picture demonstrated the phenyl C−H activation step to be the rate‐determining step with a free‐energy barrier of 27.7 kcal/mol. However, this barrier was only 19.4 kcal/mol on the basis of a single annulation pathway, which could not satisfactorily agree with the experimental conditions and kinetic isotope effects. In addition, the crucial role of the bifunctional secondary phosphine oxide ligand in promoting the reactivity and selectivity was elucidated in detail.

Synthesis and Structural Studies of Complexes of Bis(pentafluorophenyl)mercury with Di(phosphane oxide) Ligands

The reaction of bis(pentafluorophenyl)mercury with the ligands bis(diphenylphosphano) methane P,P’-dioxide ({Ph2P(O)}2CH2) (1), bis{2-(N,N,N’N’-tetraethyldiaminophosphano) imidazol-1-yl} methane P,P’-dioxide ({2-PO(NEt2)2C3N2H2}2CH2) (2) and bis (2-diphenylphosphanophenyl) ether P,P’-dioxide ({2-PPh2(O)C6H4}2O) (3) afforded crystalline σ-donor complexes [{Hg(C6F5)2}2{Ph2P(O)}2CH2] (1Hg), [Hg(C6F5)2{2-PO(NEt2)2C3N2H2}2CH2]n (2Hg) and [Hg(C6F5)2{2-PPh2(O)C6H4}2O] (3Hg), respectively. The molecular structures of 1Hg, 2Hg and 3Hg show considerable differences. In complex 1Hg, a single bridging bidentate ligand connects two three-coordinate T-shape mercury atoms with a near linear C-Hg-C atom array. Complex 2Hg is a one-dimensional coordination polymer in which adjacent four-coordinate mercury atoms with a linear C-Hg-C atom array are linked by bridging bidentate O,O’- ligands, whilst in complex 3Hg a T-shape three-coordinate mercury atom is ligated by (3) in a monodentate fashion. The Hg-O bond lengths of complexes 1Hg, 2Hg and 3Hg differ substantially (range 2.5373(14)-2.966(3) Å) owing to structural and bonding differences.

A label-free multicolor colorimetric and fluorescence dual mode biosensing of HIV-1 DNA based on the bifunctional NiFe2O4@UiO-66 nanozyme

Finding the DNA of the human immune deficiency virus (HIV) with simple and sensitive detection is the main challenge in early diagnosis of AIDS. Herein, two-point separation strategies based on the colorimetric and fluorescence are introduced. The naked-eye qualitative and semiquantitative colorimetric, and also accuracy fluorescence quantification of HIV-1 DNA were applied using label-free NiFe2O4@UiO-66 nanozyme with both functions of peroxidase-mimetic like and emitting fluorescence. The DNA probe-conjugated nanozyme is employed to hybridize a sequence of HIV-1. NiFe2O4@UiO-66 nanozymes catalyze the decomposition of H2O2 to •OH which can produce a remarkable fluorescent product 2-hydroxyterephthalic acid (TAOH) by the oxidation of the bridging ligand of weakly fluorescent terephthalic acid (TA). The accessibility of H2O2 toward confined-NiFe2O4 MNPs was reduced by increasing the HIV-1 target DNA concentration, resulting in the fluorescence intensity of TAOH being decreased. Meanwhile, remaining the unreacted H2O2 was transferred an acidic colorimetric solution containing FeSO4 and gold nanorods (AuNRs). Increasing the amount of H2O2 available for longitudinal etching of AuNRs due to •OH-generating Fe+2-catalyzed H2O2 is reponsible for different colors from brownish to colorless depending on the HIV-1 target DNA concentration. The fluorescence intensity and obtained colors have offered the sensitive biosensing methods with a linear range from 0.05 to 300 and 1–200 pM, respectively with a detection limit as low as 1 fM. Our study revealed that the applied sensing assay provides a cost-effective and straightforward qualitative, semiquantitative, and sensitive quantitation visible monitoring without the necessity of high-end instruments for HIV-1 detection in a human blood plasma/serum samples.

Siderophore-Mediated Mobilization of Manganese Limits Iron Solubility in Mixed Mineral Systems.

Recent laboratory and field studies show the need to consider the formation of aqueous Mn(III)-siderophore complexes in manganese (Mn) and iron (Fe) geochemical cycling, a shift from the historical view that aqueous Mn(III) species are unstable and thus unimportant. In this study, we quantified Mn and Fe mobilization by desferrioxamine B (DFOB), a terrestrial bacterial siderophore, in single (Mn or Fe) and mixed (Mn and Fe) mineral systems. We selected manganite (γ-MnOOH), δ-MnO2, lepidocrocite (γ-FeOOH), and 2-line ferrihydrite (Fe2O3·0.5H2O) as relevant mineral phases. We found that DFOB mobilized Mn(III) as Mn(III)-DFOB complexes to varying extents from both Mn(III,IV) oxyhydroxides but reduction of Mn(IV) to Mn(III) was required for the mobilization of Mn(III) from δ-MnO2. The initial rates of Mn(III)-DFOB mobilization from manganite and δ-MnO2 were not affected by the presence of lepidocrocite but decreased by a factor of 5 and 10 for manganite and δ-MnO2, respectively, in the presence of 2-line ferrihydrite. Additionally, the decomposition of Mn(III)-DFOB complexes through Mn-for-Fe ligand exchange and/or ligand oxidation led to Mn(II) mobilization and Mn(III) precipitation in the mixed-mineral systems (∼10% (mol Mn/mol Fe)). As a result, the concentration of Fe(III) mobilized as Fe(III)-DFOB decreased by up to 50% and 80% in the presence of manganite and δ-MnO2, respectively, compared to the single mineral systems. Our results demonstrate that siderophores, through their complexation of Mn(III), reduction of Mn(III,IV), and mobilization of Mn(II), can redistribute Mn to other soil minerals and limit the bioavailability of Fe in natural systems.

Investigation of the Photocatalytic Hydrogen Production of Semiconductor Nanocrystal-Based Hydrogels.

Destabilization of a ligand-stabilized semiconductor nanocrystal solution with an oxidizing agent can lead to a macroscopic highly porous self-supporting nanocrystal network entitled hydrogel, with good accessibility to the surface. The previously reported charge carrier delocalization beyond a single nanocrystal building block in such gels can extend the charge carrier mobility and make a photocatalytic reaction more probable. The synthesis of ligand-stabilized nanocrystals with specific physicochemical properties is possible, thanks to the advances in colloid chemistry made in the last decades. Combining the properties of these nanocrystals with the advantages of nanocrystal-based hydrogels will lead to novel materials with optimized photocatalytic properties. Thisworkdemonstrates that CdSe quantum dots, CdS nanorods, and CdSe/CdS dot-in-rod-shaped nanorods as nanocrystal-based hydrogels can exhibit a much higher hydrogen production rate compared to their ligand-stabilized nanocrystal solutions. The gel synthesis through controlled destabilization by ligand oxidation preserves the high surface-to-volume ratio, ensures the accessible surface area even in hole-trapping solutions and facilitates photocatalytic hydrogen production without a co-catalyst. Especially with such self-supporting networks of nanocrystals, the problem of colloidal (in)stability in photocatalysis is circumvented. X-ray photoelectron spectroscopy and photoelectrochemical measurements reveal the advantageous properties of the 3D networks for application in photocatalytic hydrogen production.

Ligand-Promoted Bifunctional Cobalt-Catalyzed Carbonylation-Polymerization of Epoxides: One Step to Polyhydroxyalkanoates

Poly(3-hydroxyalkanoates) (PHAs) are an important category of biodegradable plastics with properties similar to those of conventional ones. The development of a simple and efficient catalytic system for PHAs from the most abundant chemicals is economically important. Now we report an in situ generated bifunctional cobalt-catalyzed direct carbonylation-polymerization of epoxides in high efficiency in the presence of a diphosphine oxide ligand WenPhos oxide, which can be easily made from diphenyl sulfone in three steps with regular reagents. In addition, this ligand can promote the disproportionation of Co2(CO)8 to [Co(CO)4]− and Co(II) which is coordinated with phosphine oxide and sulfone oxide. Mechanistic studies indicate that this reaction is not from the ring-opening polymerization of in situ generated β-lactone. Instead, the phosphine oxide coordinated cobalt cation and [Co(CO)4]− anion pair catalyzed direct carbonylation-polymerization of epoxide was proposed based on previous studies, some control experiments, and X-ray structures of the cobalt complexes.

Boron-Centered Lewis Superacid through Redox-Active Ligands: Application in C-F and S-F Bond Activation.

A series of redox-responsive ferrocenyl-substituted boranes and boronic esters were synthesized. Oxidation of the ferrocenyl ligand to the ferrocenium resulted in a drastic increase in the Lewis acidity beyond the strength of SbF5 , which was investigated experimentally and computationally. The resulting highly Lewis acidic boron compounds were used for catalytic C-F and S-F bond activation.

High-Gain of NdIII Complex Doped Optical Waveguide Amplifiers at 1.06 and 1.31µm Wavelengths Based on Intramolecular Energy Transfer Mechanism.

Chelate phosphine oxide ligand (9,9-dimethyl-9H-xanthene-4,5-diyl) bis (diphenylphosphineoxide) (XPO) is prepared as a neutral ligand to synthesize complex Nd (TTA)3 (XPO) (TTA = 2-thenoyltrifluoroacetone). An appropriate energy gap between the XPO and TTA ligands, which can support two additional energy transfer routines from the first excited triplet state (T1 ) energy level of the XPO to that of the TTA, improves energy transfer in the Nd complex. Based on intramolecular energy transfer mechanism, optical gains at 1.06 and 1.31µm are demonstrated in Nd (TTA)3 (XPO)-doped polymer waveguides with the excitation of low-power light-emitting diodes (LEDs) instead of semiconductor lasers as pump sources. Using the vertical top-pumping mode of a 365nm LED, relative gains of 22.5 and 8.4dBcm-1 are obtained at 1.06 and 1.31µm, respectively, in a 0.2 cm long embedded waveguide with a cross-section of 8×5µm2 . The active core layer is Nd (TTA)3 (XPO)-doped SU-8 polymer. Moreover, relative gains are achieved in evanescent-field waveguide with a cross-section of 6×4µm2 . The 21.0 and 5.6dBcm-1 relative gains are achieved at 1.06 and 1.31µm, respectively, with a net gain of 13.8±0.3dBcm-1 obtained at 1.06µm in a 0.9 cm long SU-8 waveguide with Nd (TTA)3 (XPO)-doped polymethylmethacrylate as upper cladding.