Oxide Ligands Research Articles

Amide-bridged Eu(III) coordination polymer for stable luminescent glass material

A novel lanthanide coordination polymer composed of Eu(III) ion, low-vibrational frequency hfa (hfa: hexafluoroacetylacetonato), and phosphine oxide ligand with amide groups (dpba: N,N'-(ethane-1,2-diyl)bis(4-(diphenylphosphoryl)benzamide)), Eu-dpba is reported. A lanthanide coordination polymer with alkyl groups (dph: 1,6-bis(diphenylphosphoryl)hexane), Eu-dph is also prepared, as a reference sample. Eu-dpba showed phase transition behavior at 128 °C, although alkyl-bridged Eu-dph showed no phase transition behavior by differential scanning calorimeter measurements. The smooth surface on the Eu-dpba after heat treatment was observed using scanning electron microscope. The photophysical properties were estimated using the emission spectra and the emission lifetimes. We found that the emission quantum yield of Eu-dpba with heat treatment is the same as that of Eu-dpba without heat treatment.

Removal of heavy metals from wastewaters using an effective and natural bionanopolymer based on Schiff base chitosan/graphene oxide

The nanochitosan was extracted from shrimp wastes and modified by Schiff base ligand and graphene oxide. Nanochitosan characterization was carried out by Fourier-transform infrared spectroscopy, scanning electron microscope, transmission electron microscopy, energy-dispersive X-ray spectroscopy, atomic force microscopy, and elemental analysis. This study was done to apply nanopolymer based on shrimp wastes as a biodegradable and recoverable biosorbent for removal of heavy of metals including copper and lead from contaminated water. The effects of initial solution pH, biosorbent dose, initial concentrations of lead(II) and copper(II) and contact time on the uptake capacity of the related metals were investigated using batch experiments. This nanopolymer biomass exhibited the highest uptake capacity for the metal ions (466 and 698.8 mg/g for lead and copper ions, respectively) at the pH value of 6.0, the biomass dose of 0.01 g/L, the metal concentration of 200 mg/L and the contact time of 420 min. These remarkable uptake capacity values indicate the high efficiency of the absorbent in wastewater treatment for heavy metals. Its structural stability and efficient absorbent ability were proved after four times absorption–desorption cycles. After these times, the uptake capacity decreased from 698.8 to 343.8 for copper and from 466 to 226.9 for lead, which are still high values for uptake capacity, and therefore this nanopolymer can be used in repeated absorption–desorption cycles. This nanochitosan is able to treat and absorb lead and copper from dense aqueous solutions with low amount of biosorbent.

Stimulation of Redox-Induced Electron Transfer by Interligand Hydrogen Bonding in a Cobalt Complex with Redox-Active Guanidine Ligand.

Octahedrally coordinated cobalt(II) complexes with a redox‐active bisguanidine ligand and acac co‐ligands were synthesized and their redox chemistry analysed in detail. The N−H functions in a bisguanidine ligand with partially alkylated guanidino groups form N−H⋅⋅⋅O hydrogen bonds with the acac co‐ligands, thereby massively influencing the redox chemistry. For all complexes, the first one‐electron oxidation is metal‐centred, leading to CoIII complexes with neutral bisguanidine ligand units. Further one‐electron oxidation is ligand‐centred in the case of Co–bisguanidine complexes with fully alkylated guanidino groups, giving CoIII complexes with radical monocationic bisguanidine ligands. On the other hand, the hydrogen‐bond strengthening upon oxidation of the Co–bisguanidine complex with partially alkylated guanidino groups initiates metal reduction (CoIII→CoII) and two‐electron oxidation of the guanidine ligand, providing the first example for the stimulation of redox‐induced electron transfer by interligand hydrogen bonding.

Amphiphilicity in Oxygen Atom Transfer Reactions of Oxobis(iminoxolene)osmium Complexes.

Oxobis(iminoxolene)osmium(VI) compounds (Rap)2OsO (Rap = 2-(4-RC6H4N)-4,6-tBu2C6H2O) are readily deoxygenated by phosphines and phosphites to give five-coordinate (Rap)2Os(PR'3) or six-coordinate (Rap)2Os(PR'3)2. Structural data indicate that this net two-electron reduction is accompanied by apparent oxidation of the iminoxolene ligands due to their greater ability to engage in π donation to the reduced deoxy form of the osmium complex. In (Rap)2Os(PR'3)2, the HOMO is a ligand-based combination of the iminoxolene redox-active orbitals, while the LUMO is a highly covalent metal-iminoxolene π* orbital. In the trans isomer, the HOMO is required to be ligand-localized by symmetry, while in the cis isomer, the ligands adopt a conformation that minimizes metal-ligand π* interactions in the HOMO. Kinetic studies indicate that the deoxygenations involve the rate-determining attack of the phosphorus(III) reagent on the five-coordinate oxo complexes. Varying the substituents of the aryl groups on the iminoxolene ligands or on the triarylphosphines has little effect on the rate of oxygen atom transfer, with the best correlation shown between oxygen atom transfer rates and the HOMO-LUMO gap of the oxo complexes. This suggests that the osmium oxo group shows a balance between electrophilic and nucleophilic character in its oxygen atom transfer reactions with phosphorus(III) reagents.

Formation and Destruction of Platinum Carbonyl [Pt(CO)2

X-ray diffraction, IR spectroscopy, and thermogravimetry and analyses of the composition of platinum carbonyl destruction products showed that oligomeric platinum carbonyl [Pt(CO)2]n is unstable in the air at room temperature and quickly decomposes with the loss of CO ligands due to their removal from the complex as a result of CO dissociation and CO ligand oxidation by atmospheric oxygen. The destruction processes of platinum carbonyl [Pt(CO)2]n and the composition of destruction products were described.

Unexpected Coordination Modes of Bisphosphoramides with Lanthanum(III) and Thorium(IV) Salts: Synthesis, Structural Characterization, Stability, and Extraction Studies

AbstractA series of bisphosphoramides of the type R2P(O)NHCH2CH2NHP(O)R2 (L) (where R=n‐butyl, n‐hexyl, n‐octyl, ethoxy, phenyl) is synthesized in two‐steps by Atherton‐Todd reaction of ethylenediamine and H‐phosphonate derived from the reaction of diethylphosphite and the Grignard reagent. These ligands were employed in the preparation of La(III) and Th(IV)complexes of the general type [LaCl3(L)2]n and [Th(NO3)4Th(IV)2]. Notably, La(III) complexes of bisphosphoramides are found as infinite coordination polymers with bridging phosphine oxide ligands in an intermolecular fashion. In contrast, Th(IV) complexes are formed with two chelating bisphosphoramide ligands around the metal center intramolecularly. All these ligands and the corresponding metal complexes are characterized by spectroscopic and analytical data. The single‐crystal X‐ray analyses of lanthanum and thorium complexes each confirm the coordination modes. Further, these ligands were evaluated to check the extraction behavior with Am(III), U(VI), Th(IV), and Pu(IV) as a function of nitric acid concentration.

Cover Feature: The Impact of Ligand Oxidation State and Fold Angle on the Charge Transfer Processes of MoIVO‐Dithione Complexes (Eur. J. Inorg. Chem. 10/2021)

The Cover Feature shows the impact of ligand fold angle on LL'CT charge transfer between thiophenol and dithione ligands. Reducing the fold angle along the S⋅⋅⋅S vector, shown with gray planes, decreases charge transfer energy, as electron accepting orbitals (green) are better aligned with electron donating orbitals (red). The Mo dxy orbital (blue) plays an active role in facilitating charge transfer between donor and acceptor ligands. The relationship between fold angle and charge transfer energy is supported by crystallographic data, absorption spectra, and theoretical calculations. More information can be found in the Full Paper by P. Basu and co-workers.

Synthesis and Characterization of Tellurium Catecholates and Their N-Oxide Adducts.

Tellurium catecholate complexes were investigated to probe the redox chemistry of tellurium, whose oxidation state can span from -2 to +6. Treating TeO2 with catechols resulted in tellurium coordination complexes in high yields within minutes to hours at room temperature or with extended heating, depending on the ligand substituents, giving Te(IV) complexes of the form Te(C)2, where C = 3,5-di-tert-butylcatecholate, o-catecholate, or tetrachlorocatecholate. The redox behavior of these complexes was investigated through addition of organic oxidants, giving nearly quantitative adducts of pyridine N-oxide or N-methylmorpholine N-oxide with each tellurium complex, the latter set leading to ligand oxidation upon heating. Each compound was characterized crystallographically and computationally, providing data consistent with a mostly electrostatic interaction and very little covalent character between the N-oxide and Te complex. The Te N-oxide bond orders are consistently lower than those with the catechol derivatives, as characterized with the Mayer, Gopinathan-Jug (G-J), and first Nalewajski-Mrozek (N-M1) bond indices. The tellurium lone pair is energetically buried by 1.93-2.81 eV, correlating with the observation that the ligands are more reactive than the tellurium center toward oxidation. This combined experimental and theoretical study finds structure-property relationships between ligand design and reactivity that will aid in future efforts for the recovery of tellurium.

Diverse and unexpected outcomes from oxidation of the platinum(II) anticancer agent [Pt{(p-BrC6F4)NCH2CH2NEt2}Cl(py)] by hydrogen peroxide

Oxidation of the anti-tumour agent [Pt{(p-BrC6F4)NCH2CH2NEt2}Cl(py)], 1 (py = pyridine) with hydrogen peroxide under a variety of conditions yields a range of organoenamineamidoplatinum(II) compounds [Pt{(p-BrC6F4)NCH=C(X)NEt2}Cl(py)] (X = H, Cl, Br) as well as species with shared occupancy involving H, Cl and Br. Thus, oxidation of the –CH2–CH2– backbone (dehydrogenation) occurs, often accompanied by substitution. Oxidation of 1 with H2O2 in acetone yielded 1:1 co-crystallized [Pt{(p-BrC6F4)NCH=CHNEt2}Cl(py)], 1H and [Pt{(p-BrC6F4)NCH=C(Cl)NEt2}Cl(py)], 1Cl. The former was obtained pure in low yield from the oxidation of 1 with (NH4)2[Ce(NO3)6] in acetone, and the latter was obtained from 1 and H2O2 in CH2Cl2 at near reflux. From the latter reaction under vigorous refluxing [Pt{(p-BrC6F4)NCH=C(Br)NEt2}Cl(py)], 1Br was isolated. In refluxing acetonitrile, oxidation of 1 with H2O2 yielded [Pt{(p-BrC6F4)NCH=C(H0.25Br0.75)NEt2}Cl(py)], 1H0.25Br0.75, in which the alkene is mainly substituted by Br in a dual occupancy. Treatment of 1 with H2O2 and tetrabutylammonium hydroxide in acetone at room temperature formed [Pt{(p-HC6F4)NCH2CH2NEt2}Cl(py)], 2. Oxidation of [Pt{(p-HC6F4)NCH2CH2NEt2}Br(py)], 3 with H2O2 in boiling acetonitrile gave the ligand oxidation product [Pt{(p-HC6F4)NCH=C(Br)NEt2}Br(py)], 3Br. All major products were identified by X-ray crystallography as well as by 1H and 19F NMR spectra. In cases of mixed crystals or dual occupancy compounds, the 19F and 1H NMR spectra showed dissociation into the components in the solution in the same proportions as in isolated crystalline material.

Investigation of Structural Changes of Cu(I) and Ag(I) Complexes Utilizing a Flexible, Yet Sterically Demanding Multidentate Phosphine Oxide Ligand.

The syntheses of a sterically demanding, multidentate bis(quinaldinyl)phenylphosphine oxide ligand and some Cu(I) and Ag(I) complexes thereof are described. By introducing a methylene group between the quinoline unit and phosphorus, the phosphine oxide ligand gains additional flexibility. This specific ligand design induces not only a versatile coordination chemistry but also a rarely observed and investigated behavior in solution. The flexibility of the birdlike ligand offers the unexpected opportunity of open-wing and closed-wing coordination to the metal. In fact, the determined crystal structures of these complexes show both orientations. Investigations of the ligand in solution show a strong dependency of the chemical shift of the CH2 protons on the solvent used. Variable-temperature, multinuclear NMR spectroscopy was carried out, and an interesting dynamic behavior of the complexes is observed. Due to the introduced flexibility, the quinaldinyl substituents change their arrangements from open-wing to closed-wing upon cooling, while still staying coordinated to the metal. This change in conformation is completely reversible when warming up the sample. Based on 2D NMR spectra measured at -80 °C, an assignment of the signals corresponding to the different arrangements was possible. Additionally, the copper(I) complex shows reversible redox activity in solution. The combination of structural flexibility of a multidentate ligand and the positive redox properties of the resulting complexes comprises key factors for a possible application of such compounds in transition-metal catalysis. Via a reorganization of the ligand, occurring transition states could be stabilized, and selectivity might be enhanced.

The Impact of Ligand Oxidation State and Fold Angle on the Charge Transfer Processes of MoIVO‐Dithione Complexes

AbstractWe report a series of mononuclear monooxo Mo(IV) complexes possessing either one or two fully oxidized dithiolene ligands; [MoOCl(R2Dt0)2][X], (1 and 2), and MoO(p‐SC6H4Y)2(R2Dt0), (3 and 4), (R=Me, iPr; X=PF6, SbF6, BF4; Y=H, Cl, F, CF3, Me, tBu, OMe). Either four or two quasi‐reversible ligand‐based redox couples are detected depending upon the number of fully oxidized dithiolene ligands present. The molecular structure of 3 and 4 exhibit a large (47° to 70°) fold angle along the S⋅⋅⋅S vector of the dithione ligand. The UV‐Vis spectra of 3 and 4 exhibit a low energy charge transfer band at ∼540 nm that are red‐shifted ∼200 nm compared to the spectra of 1 and 2. Density Functional Theory (DFT) calculations show that the low energy charge transfer band of 3 and 4 is heavily influenced by ligand fold angle. Reducing the fold angle decreases the charge transfer energy, and the transition becomes more ligand‐based.

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.

Photochemical degradation of iron(III) citrate/citric acid aerosol quantified with the combination of three complementary experimental techniques and a kinetic process model

Abstract. Iron(III) carboxylate photochemistry plays an important role in aerosol aging, especially in the lower troposphere. These complexes can absorb light over a broad wavelength range, inducing the reduction of iron(III) and the oxidation of carboxylate ligands. In the presence of O2, the ensuing radical chemistry leads to further decarboxylation, and the production of .OH, HO2., peroxides, and oxygenated volatile organic compounds, contributing to particle mass loss. The .OH, HO2., and peroxides in turn reoxidize iron(II) back to iron(III), closing a photocatalytic cycle. This cycle is repeated, resulting in continual mass loss due to the release of CO2 and other volatile compounds. In a cold and/or dry atmosphere, organic aerosol particles tend to attain highly viscous states. While the impact of reduced mobility of aerosol constituents on dark chemical reactions has received substantial attention, studies on the effect of high viscosity on photochemical processes are scarce. Here, we choose iron(III) citrate (FeIII(Cit)) as a model light-absorbing iron carboxylate complex that induces citric acid (CA) degradation to investigate how transport limitations influence photochemical processes. Three complementary experimental approaches were used to investigate kinetic transport limitations. The mass loss of single, levitated particles was measured with an electrodynamic balance, the oxidation state of deposited particles was measured with X-ray spectromicroscopy, and HO2. radical production and release into the gas phase was observed in coated-wall flow-tube experiments. We observed significant photochemical degradation with up to 80 % mass loss within 24 h of light exposure. Interestingly, we also observed that mass loss always accelerated during irradiation, resulting in an increase of the mass loss rate by about a factor of 10. When we increased relative humidity (RH), the observed particle mass loss rate also increased. This is consistent with strong kinetic transport limitations for highly viscous particles. To quantitatively compare these experiments and determine important physical and chemical parameters, a numerical multilayered photochemical reaction and diffusion (PRAD) model was developed that treats chemical reactions and the transport of various species. The PRAD model was tuned to simultaneously reproduce all experimental results as closely as possible and captured the essential chemistry and transport during irradiation. In particular, the photolysis rate of FeIII, the reoxidation rate of FeII, HO2. production, and the diffusivity of O2 in aqueous FeIII(Cit) ∕ CA system as function of RH and FeIII(Cit) ∕ CA molar ratio could be constrained. This led to satisfactory agreement within model uncertainty for most but not all experiments performed. Photochemical degradation under atmospheric conditions predicted by the PRAD model shows that release of CO2 and repartitioning of organic compounds to the gas phase may be very important when attempting to accurately predict organic aerosol aging processes.

A highly effective green catalyst Ni/Cu bimetallic nanoparticles supported by dendritic ligand for chemoselective oxidation and reduction reaction

The highly active Ni/Cu bimetallic nanoparticles (NPs) of the different molar ratios of Ni and Cu (1:1, 1:3, 3:1) assisted by dendritic ligand 2,4,6-Tris (di-4-chlorobenzamido)-1,3-diazine were synthesized successfully confirmed by Scanning Electron Microscopy (SEM), Electron Diffraction X-ray (EDX), X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), and Transmission Electron Microscopy (TEM) analysis. These NPs were studied as a heterogeneous catalyst for the chemoselective oxidation of alcohol to the corresponding aldehyde at 30 min and chemoselective reduction of aromatic nitro substituents to the corresponding amino substituents at 20 min, while the Ni/Cu (3:1) NPs were found to be the most effective among other Ni/Cu (1:1) and Ni/Cu (1:3) NPs at room temperature under mild conditions. The Ni/Cu (3:1) NPs can be recycled for at least five successive runs with no perceptible decrease in catalytic activity.

Small angle X-ray scattering analysis of ligand-bound forms of tetrameric apolipoprotein-D.

Human apolipoprotein-D (apoD) is a glycosylated lipocalin that plays a protective role in Alzheimer’s disease due to its antioxidant function. Native apoD from human body fluids forms oligomers, predominantly a stable tetramer. As a lipocalin, apoD binds and transports small hydrophobic molecules such as progesterone, palmitic acid and sphingomyelin. Oligomerisation is a common trait in the lipocalin family and is affected by ligand binding in other lipocalins. The crystal structure of monomeric apoD shows no major changes upon progesterone binding. Here, we used small-angle X-ray scattering (SAXS) to investigate the influence of ligand binding and oxidation on apoD oligomerisation and conformation. As a solution-based technique, SAXS is well suited to detect changes in oligomeric state and conformation in response to ligand binding. Our results show no change in oligomeric state of apoD and no major conformational changes or subunit rearrangements in response to binding of ligands or protein oxidation. This highlights the highly stable structure of the native apoD tetramer under various physiologically relevant experimental conditions.

Immobilization of (l)-valine and (l)-valinol on SBA-15 nanoporous silica and their application as chiral heterogeneous ligands in the Cu-catalyzed asymmetric allylic oxidation of alkenes

Chiral heterogeneous ligands AL*-i-Pr-SBA-15 and AA*-i-Pr-SBA-15 were synthesized and then used in Cu-catalyzed asymmetric allylic oxidation of alkenes. Allylic esters with moderate enantiomeric excess and good yields were obtained.

Synthesis and Characterization of Eu3+ + 2-thenoyltrifluoroacetone + triphenylphosphine Oxide Ternary Complex

Rare earth europium ion (Eu3+) can emit red characteristic fluorescence under UV excitation and is preferred for the preparation of red phosphors for near-UV white LEDs. In this paper, the effects of solvent, reflux time and preparation method on the preparation of europium ternary complexes were studied with europium ion as the central coordination ion, 2-thenoyltrifluoroacetone as the first ligand and triphenylphosphine oxide as the second ligand. The results showed that the better reaction solvent was anhydrous ethanol and the better reflux time was 8 hours. Both the common synthesis method and the solvothermal method could successfully synthesize the europium ternary complex, and the solvothermal method has a higher yield. The europium ternary complex was characterized by inductively coupled plasma emission spectroscopy, element analysis and infrared spectroscopy, and it was proved that the europium complex could emit a strong characteristic red fluorescence of europium with the structure of Eu(TTA)3(TPPO)2 in 1:3:2 coordination ratio.

Constructing adjacent phosphine oxide ligands confined in mesoporous Zr-MOFs for uranium capture from acidic medium

Adjacent phosphine oxide ligands confined in the mesoporous Zr-MOFs could coordinate with one uranyl ion collaboratively in strong acidic solutions.

Physicochemical implications of surface alkylation of high-valent, Lindqvist-type polyoxovanadate-alkoxide clusters.

We report a rare example of the direct alkylation of the surface of a plenary polyoxometalate cluster by leveraging the increased nucleophilicity of vanadium oxide assemblies. Addition of methyl trifluoromethylsulfonate (MeOTf) to the parent polyoxovanadate cluster, [V6O13(TRIOLR)2]2- (TRIOL = tris(hydroxymethyl)methane; R = Me, NO2) results in functionalisation of one or two bridging oxide ligands of the cluster core to generate [V6O12(OMe)(TRIOLR)2]1- and [V6O11(OMe)2(TRIOLR)2]2-, respectively. Comparison of the electronic absorption spectra of the functionalised and unfunctionalised derivatives indicates the decreased overall charge of the complex results in a decrease in the energy required for ligand to metal charge transfer events to occur, while simultaneously mitigating the inductive effects imposed by the capping TRIOL ligand. Electrochemical analysis of the family of organofunctionalised polyoxovanadate clusters reveals the relationship of ligand environment and the redox properties of the cluster core: increased organofunctionalisation of the surface of the vanadium oxide assembly translates to anodic shifts in the reduction events of the Lindqvist ion. Overall, this work provides insight into the electronic effects induced upon atomically precise modifications to the surface structure of nanoscopic, redox-active metal oxide assemblies.

Structural, magnetic and theoretical analyses of anionic and cationic phthalocyaninato-terbium(III) double-decker complexes: magnetic relaxation via higher ligand-field sublevels enhanced by oxidation.

Crystal structural and magnetic analyses were performed for the anionic (1-) and cationic (1+) forms of phthalocyaninato-Tb3+ double-decker single-molecule magnets (SMMs). Both charged species showed slow magnetic relaxations and magnetic hysteresis characteristics for SMMs. 1+ showed longer magnetic relaxation times (τ) and higher activation energy for spin reversal (ΔE) than 1- did. Ligand field (LF) splitting calculated using ab initio methods revealed that the experimental ΔE values in 1- and 1+ were considerably larger than the first excited LF levels but rather close to the higher excited ones, indicating the magnetic relaxation via higher excited states.