Oxide Ligands Research Articles

Adjustable coordination of a hybrid phosphine-phosphine oxide ligand in luminescent Cu, Ag and Au complexes.

A potentially tridentate hemilabile ligand, PPh2-C6H4-PPh(O)-C6H4-PPh2 (P(3)O), has been used for the construction of a family of bimetallic complexes [MM'(P(3)O)2](2+) (M = M' = Cu (1), Ag (2), Au (3); M = Au, M' = Cu (4)) and their mononuclear halide congeners M(P(3)O)Hal (M = Cu (5-7), Ag (8-10)). Compounds 1-10 have been characterized in the solid state by single-crystal X-ray diffraction analysis to reveal a variable coordination mode of the phosphine-oxide group of the P(3)O ligand depending on the preferable number of coordination vacancies on the metal center. According to the theoretical studies, the interaction of the hard donor P[double bond, length as m-dash]O moiety with d(10) ions becomes less effective in the order Cu > Ag > Au. 1-10 exhibit room temperature luminescence in the solid state, and the intensity and energy of emission are mostly determined by the nature of metal atoms. The photophysical characteristics of the monometallic species were compared with those of the related compounds M(P(3))Hal (11-16) with the non-oxidized ligand P(3). It was found that in the case of the copper complexes 5-7 the P(3)O hybrid ligand introduces effective non-radiative pathways of the excited state relaxation leading to poor emission, while for the silver luminophores the P[double bond, length as m-dash]O group leads mainly to the modulation of luminescence wavelength.

Markovnikov hydroformylation catalyzed by ROPAC in the presence of phosphine and phosphine oxide ligands

Rhodium-catalyzed hydroformylation of 1-octene in the presence of different phosphine and phosphine oxide ligands has been investigated. The molecular structure of new phosphine ligand, fluorenylidine methyl phenyl diphenylphosphine, was determined by single-crystal X-ray crystallography. Parameters such as different ligands, molar ratio of ligand to rhodium complex, ratio of olefin to rhodium complex, pressure of CO : H2 mixture, and time of the reaction were studied. The linear aldehyde was the main product when the phosphine ligands were used as auxiliary ligands while the selectivity was changed to the branched products when the related phosphine oxide ligands were used. Under optimized reaction conditions, in the presence of [Rh(acac)(CO)(Ph3P)]-di(1-naphthyl)phenyl phosphine oxide, conversion of 1-octene reached 97% with 87% selectivity of branched aldehyde.

Synthesis and photophysical studies of tetrazolate-based Eu(III) photoluminescent ternary complexes containing N-heterocyclic phosphine oxides auxiliary co-ligands.

Two new ternary tetrazolate Eu(III) complexes with phosphine oxide co-ligands Eu(PTO)3 ·(P1/P2) [PTO = 5-(2-pyridyl-1-oxide)tetrazole, P1 = diphenylphosphorylamino-phenylphosphoryl-benzene, P2 = diphenylphosphorylpyridine)-bis-isobutyricphosphoryl] were synthesized and characterized using UV, fluorescence, IR and (1) H NMR spectroscopic techniques. The analytical data prove that the complexes are mononuclear in nature and the central Eu(III) ion is coordinated by three N and three O atoms of tetrazolate, and two O atoms of the corresponding bidentate phosphine oxide ligands. The ancillary ligand increased the photoluminescence efficiency of Eu(PTO)3 ·P1 (complex 3) by twofold compared with our previously reported Eu(PTO)3 complex (complex 1). Copyright © 2015 John Wiley & Sons, Ltd.

Bis(Diphenylcarbamoylmethylphosphine Oxide) Ligand Containing 4, 7, 10 – Trioxatridecane Spacer: Novel Effective Extractant for Actinides and Lanthanides

ABSTRACTA novel polydentate neutral organophosphorus ligand 1 containing two Ph2P(O)CH2C(O)NH- bidentate moieties connected by a 4, 7, 10 - trioxatridecane spacer through amide nitrogen atoms was synthesized and studied as an extractant for U(VI), Th(IV), and lanthanides(III) ions from HNO3 solutions. The influence of aqueous and organic phases on the extraction efficiency was elucidated and stoichiometry of the complexes extracted was determined. Bis-CMPO ligand 1 was found to possess a higher extraction efficiency towards U(VI), Th(IV), and lanthanides(III) ions than its mono analog diphenylphosphorylacetic acid N-nonylamide 5 and bis-CMPO ligands containing a di- and a triethylene glycol spacers. The values of DU, DTh, and DLn for compound 1 are more than two orders of magnitude higher than those for its mono-CMPO analog 5.

Halide copper(II) complexes of aromatic N-donor containing ligands: Structural, magnetic and reactivity studies

The preparation of four new copper(II) complexes with different N-donor ligands [CuBr2(2-benzylpyridine)2] (1), [CuBr2(2-benzylpyridine)(2,2′-bipyridine)]·H2O (2), [CuBr2(3-methyl-2-phenylpiridine)2] (3), [Cu(picolinate)2]·KI (4) from copper(I) halides as starting material is described. During the preparation of compound 4 a ligand oxidation reaction took place to give the picolinate ligand starting from 2-(2-methylaminoethyl)pyridine. The complexes were characterized by elemental analyses, IR spectroscopy and crystallographic studies. Single crystal X-ray diffraction analysis of the complexes reveals their monomeric penta- and tetracoordinated nature. For all compounds, the copper(II) present a common square planar coordination except for compound 2 which is five coordinated in a quasi-square pyramidal configuration with τ of 0.29. The Cu–N distances for these compounds are in the range of 1.959(4)-2.041(3) A, Cu–O distance was 1.961(3) A and Cu–Br distances were in the range of 2.4052(4)-2.4381(6) A for the square base configuration while for apical distance it was 2.6745(7) A. Magnetic properties have been investigated for all compounds in the temperature range 2-300 K. Compound 1 shows weak antiferromagnetic intermolecular interaction.

Effect of concomitant oxidation and deprotonation of hydrated Mn centres in rationalising the FTIR difference silence of D1-Asp170 in Photosystem II

The observation of negligible FTIR differences in carboxylate vibrational modes for the D1-Asp170 residue of Photosystem II (PSII) on successive one-electron oxidations of the Mn4CaO5 oxygen-evolving complex (OEC) is counterintuitive in light of the apparent ligation of D1-Asp170 to an oxidisable Mn ion in the X-ray crystallographic structures of PSII. Here, we show computational support for the hypothesis that suppression of the FTIR difference spectrum in the 1100cm−1 to 1700cm−1 region of D1-Asp170 occurs by concomitant Mn oxidation and deprotonation of water ligands bound to the ligated metal centre. Density functional theory calculations on the model species [MnIICa(COOH)(OH)2(H2O)2]+ over two successive oxidations of the Mn ion are performed, where those oxidations are accompanied by deprotonation of water and μ-hydroxo ligands coordinated to the Mn ion. In contrast, dramatically increased FTIR difference activity is observed where these oxidations are unaccompanied by proton loss.

Near-infrared Light Responsive Upconversion Nanoparticles for Imaging, Drug Delivery and Therapy of Cancers

Cancers have become serious threat to human health and life, and they are critical to develop safe and effective theranostic methods for diagnosis and therapy of tumors. In recent years, real time cancer theranostic visualization systems (RT-CTVS) based on light-responsive nanoparticles have been developed. Especially, upconversion nanoparticles (UCNPs) have excellent optical properties and unique near-infrared (NIR) responsive. The minimized photodamage, low autofluorescence and high penetration depth can be achieved with UCNPs. Therefore, UCNPs are widely used in real time NIR mediated visualization systems of cancer diagnosis and therapy. In this review, we focus on the latest developments of rare earth ions doped upconversion fluorescence nanoparticles. First, the synthesis methods of UCNPs were briefly introduced. Second, the strategies of UCNPs surface modifications, including the ligand exchange, ligand oxidation, ligand interaction, ligand free synthesis, layer by layer growth and surface silanization were summarized. Third, the recent research progress in applying UCNPs to construct NIR light stimuli-responsive RT-CTVS, including imaging, drug delivery and photodynamic therapy (PDT) were highlighted. Finally, some of the current problems and future effort directions in these fields were also proposed.

Catalytic behavior of an iron(III) complex containing an N,O-type bidentate oxazoline ligand for selective oxidation of sulfides

The reaction of Fe(acac)3 and 2-(2′-hydroxyphenyl)oxazoline (Hphox) as a bidentate O,N donor ligand afforded a six-coordinated iron(III) complex [Fe(phox)2(acac)] with distorted octahedral configuration. The complex was isolated as an air-stable crystalline solid and characterized by elemental analysis, FTIR, solution electrical conductivity, and by single-crystal X-ray structure analysis. The structure, electronic properties, and vibrational normal modes of the complex were investigated by DFT. The use of this complex as a catalyst for the oxidation of sulfides to their corresponding sulfoxides using urea hydrogen peroxide as the primary oxidant was investigated. The catalyst shows very efficient reactivity, giving high yields and selectivities at room temperature under air.

Analysis of Homogeneous Water Oxidation Catalysis with Collector-Generator Cells.

A collector-generator (C-G) technique has been applied to determine the Faradaic efficiencies for electrocatalytic O2 production by the homogeneous water oxidation catalysts Ru(bda)(isoq)2 (1; bda = 2,2'-bipyridine and isoq = isoquinoline) and [Ru(tpy)(bpz)(OH2)](2+) (2; tpy = 2,2':6',2″-terpyridine and bpz = 2,2'-bipyrazine). This technique uses a custom-fabricated cell consisting of two fluorine-doped tin oxide (FTO) working electrodes separated by 1 mm with the conductive sides facing each other. With a catalyst in solution, water oxidation occurs at one FTO electrode under a sufficient bias to drive O2 formation by the catalyst; the O2 formed then diffuses to the second FTO electrode poised at a potential sufficiently negative to drive O2 reduction. A comparison of the current versus time response at each electrode enables determination of the Faradaic efficiency for O2 production with high concentrations of supporting electrolyte important for avoiding capacitance effects between the electrodes. The C-G technique was applied to electrocatalytic water oxidation by 1 in the presence of the electron-transfer mediator Ru(bpy)3(2+) in both unbuffered aqueous solutions and with the added buffer bases HCO3(-), HPO4(2-), imidazole, 1-methylimidazole, and 4-methoxypyridine. HCO3(-) and HPO4(2-) facilitate water oxidation by atom-proton transfer (APT), which gave Faradaic yields of 100%. With imidazole as the buffer base, coordination to the catalyst inhibited water oxidation. 1-Methylimidazole and 4-methoxypyridine gave O2 yields of 55% and 76%, respectively, with the lower Faradaic efficiencies possibly due to competitive C-H oxidation of the bases. O2 evolution by catalyst 2 was evaluated at pH 12 with 0.1 M PO4(3-) and at pH 7 in a 0.1 M H2PO4(-)/HPO4(2-) buffer. At pH 12, at an applied potential of 0.8 V vs SCE, water oxidation by the Ru(IV)(O)(2+) form of the catalyst gave O2 in 73% yield. In a pH 7 solution, water oxidation at 1.4 V vs SCE, which is dominated by Ru(V)(O)(3+), gave O2 with an efficiency of 100%. The lower efficiency for Ru(IV)(O)(2+) at pH 12 may be due to competitive oxidation of a polypyridyl ligand.

Complexation of amidocarbamoyl phosphine oxides with Ln+3 (Ln = La, Nd, Pm, Sm and Eu) cation series: structural and thermodynamical features

Abstract In the present study, we have mainly investigated the nature of interactions in Ln3+ (Ln = La, Nd, Pm, Sm, Eu) complexes with amidocarbamoyl methyl phosphine oxide (CMPO) and amidocarbamoyl propyl phosphine oxide (CPPO) ligands based on density functional theory (DFT) approaches. In the first step, thermodynamical properties for complexation of CMPO and CPPO ligands with Ln3+ cation series have been determined in the gas phase and with the presence of three solvents: n-hexane, chloroform and toluene, via polarized continuum model (PCM) computations. The trend of metal-ligand interaction strength has been analyzed and compared with the trend of ionic hardness within the series of lanthanide cations and different size of alkyl chain of amidocarbamoyl phosphine oxide ligand. The calculated thermochemical results in the gas and solution phases reveals that there is a consistency between increasing trend in the hardness of Ln3+ cation series and also electron-donating property of alkyl chain with increasing in thermodynamical stability of [Ln–CMPO]3+ and [Ln–CPPO]3+ complex series. We have also demonstrated that in the complexation reaction of all complex series, using n-hexane as solvent is more favorable thermodynamically than chloroform and toluene. It should be stated that this issue has been observed in many experiments. Finally, analysis of calculated deformation energies and also the variation in bond order of some selected key bonds in CMPO and CPPO ligands and their corresponded Ln+3 complexes series show a similar trend with increasing in the hardness of Ln3+ cation series and electron-donating of alkyl chain of amidocarbamoyl phosphine oxide ligand.

Luminescent Thin Films Composed of Nanosized Europium Coordination Polymers on Glass Electrodes.

Luminescent thin films composed of thermostable lanthanide coordination polymers on glass electrodes were prepared using a novel combination of micelle reactions and electrochemical deposition techniques. The micelle-encapsulated luminescent polymers were obtained by the polymerization of [Eu(hfa)3 ] (hfa=hexafluoroacetylacetonate) with bridging phosphine oxide ligands in micelles using a redox-active ferrocenyl-containing surfactant in water. Films were electrochemically deposited on indium tin oxide coated glass electrodes by potentiostatic polarization of micelle-encapsulated EuIII coordination polymers. The luminescence properties of the electrochemically deposited films were characterized by measuring their emission spectra, emission lifetimes and emission quantum yields.

Degradation of β-O-4 model lignin species by vanadium Schiff-base catalysts: Influence of catalyst structure and reaction conditions on activity and selectivity

In the pursuit of value-added products from the degradation of the abundant aromatic biopolymer lignin, homogeneous catalysis has the potential to provide a mild, selective route to monomeric phenols. Homogeneous vanadium catalysts have previously been shown to effectively cleave dimeric β-O-4 model lignin compounds, with selectivity for CC or CO cleavage, or benzylic oxidation, depending on the ligand structure and oxidation state of the metal. In this study, a systematic kinetic investigation was undertaken in order to gain further understanding of the role of ligand structure and reaction conditions on the activity of vanadium Schiff-base catalysts towards a non-phenolic β-O-4 model lignin dimer, and the selectivity of these species towards CO bond cleavage. Catalytic activity was found to be increased by the addition of bulky, alkyl substituents at the 3′-position of the phenolate ring, whereas electron-withdrawing substituents were found to dramatically reduce activity irrespective of their size. Selective depolymerization of a phenolic β-O-4 dimer was also achieved.

Oxidation of a binuclear ruthenium carbonyl complex

The aerobic oxidation of the binuclear ruthenium(0) carbonyl complexes [Ru2(CO)5(μ-dppm)2], dppm = Ph2PCH2PPh2, 1, and [Ru2(μ-H) (CO)5(μ-dppm)2]+X−, 2, has been studied. In acidic solution a 4-electron oxidation of 2 occurs to give [Ru2(μ-OH)2CO)4(μ-dppm)2]X2, X = ReO4 or BF4. However, in neutral solution aerobic oxidation occurs in 2-electron steps, with parallel 2-electron oxidation of a carbonyl ligand. The reaction of complex 1 in acetone solution gave a diruthenium(I) formate derivative [Ru2(μ-OH) (O2CH) (CO)3(μ-dppm)2], while reaction in dichloromethane solution gave a diruthenium(II) carbonate derivative [Ru2(CO3) (CO) (Cl) (μ-OH) (μ-CO) (μ-dppm)2]. The aerobic oxidation of 1 in the presence of methyl isocyanide and NH4[PF6] gave [Ru2(CO)2(CNMe)4(μ-dppm)2][PF6]2. The structural characterization of the products is described, and likely mechanisms of reaction are discussed.

Seven‐Coordinate Luminophores: Brilliant Luminescence of Lanthanide Complexes with C3v Geometrical Structures

AbstractEnhanced luminescence properties of mononuclear lanthanide complexes with asymmetric seven‐coordination structures are reported for the first time. The lanthanide complexes are composed of a lanthanide ion (EuIII or TbIII), three tetramethyl heptanedionato ligands, and one triphenylphosphine oxide ligand. The coordination geometries of the lanthanide complexes have been evaluated by using single‐crystal X‐ray analyses and shape‐measurement calculations. The complexes are categorized to be seven‐coordinate monocapped octahedral structures (point group C3v). The seven‐coordinate lanthanide complexes show high intrinsic emission quantum yields, extra‐large radiative rate constants, and unexpected small nonradiative rate constants. The brilliant luminescence properties have been elucidated in terms of the asymmetric coordination geometry and small vibrational quanta related to thermal relaxation.

Enhanced Performance of Light-Emitting Diodes by Surface Ligand Modification on Quantum Dots.

The electrical characteristics of quantum dots (QDs) can vary depending on the surface modulation, which can change the luminance and efficiency of electroluminescent devices. Thus, understanding surface ligand is essential in improving the performance of QDs-based light-emitting diodes (LEDs). We analyzed the performance of QDs-based LEDs with respect to the QD surface volume. On the QD surfaces, the 1.1 nm-long tryoctylphosphine oxide (TOPO) ligand with three neck-type structure was replaced with a 1.7 nm-long oleic acid (OA) ligand with a one neck-type structure to evaluate the dependence of the LED properties on the ligand length. With all other conditions being identical, the luminance and efficiency of the QDs-based LEDs with an OA ligand were approximately 1,000 cd/m2 greater and 1.5 times higher, respectively, than those of the QDs-based LEDs with a TOPO ligand. These results show that if the physical length of the surface ligand is relatively long, decreasing the surface area would result in increased injection of electrons and holes into the QDs, increasing the luminance and efficiency.

A Pyrazolate‐Bridged Bis(pentadentate) Ligand and Its Dinuclear Ruthenium Complex

AbstractA new bis(pentadentate) pyrazole‐bridged proligand HLbis5 providing two {N5} binding pockets and its diruthenium complex [Lbis5Ru2(MeCN)2](PF6)3 (1) have been synthesized, and the structure of 1 has been elucidated by X‐ray diffraction. The two exogenous MeCN ligands in 1 are both directed into the central pocket created by the two metal ion compartments and interfere with each other, which leads to some distortion of the dimetallic framework. According to an Eyring analysis of variable‐temperature NMR spectroscopic data, interconversion of the resulting enantiomeric forms is rapid with a free activation energy of ΔG≠ = 43.7 kJ mol–1 at 298 K (ΔH≠ = 30.8 kJ mol–1, ΔS≠ = –43.2 J mol–1 K–1). Cyclic voltammetry of 1 shows two sequential reversible oxidations at ca. 0.85 and 1.25 V (vs. SCE), and the mixed‐valent RuIIIRuII species has been characterized by spectroelectrochemistry, UV/Vis/NIR and EPR spectroscopy. Complex 1 was found to be a poor catalyst for water oxidation: under standard conditions [triflic acid, pH 1, using cerium(IV) ammonium nitrate as oxidant] rapid degradation by oxidative ligand fragmentation at its benzylic‐type CH2 groups was observed.

Evidence for Bidirectional Noninnocent Behavior of a Formazanate Ligand in Ruthenium Complexes.

Redox series of the complexes [Ru(L)(L')2](n), L = 1,5-diphenyl-3-(4-tolyl)-formazanate and L' = 2,4-pentanedionate (acac(-)), 2,2'-bipyridine (bpy), or 2-phenylazopyridine (pap), were studied by cyclic and differential pulse voltammetry and by TD-DFT-supported spectroelectrochemistry (UV-vis-NIR, EPR). The precursors [Ru(III)(L(-))(acac(-))2], [Ru(II)(L(-))(bpy)2]ClO4, and [Ru(II)(L(-))(pap)2]ClO4 were identified in their indicated oxidation states by X-ray crystal structure determination. The six-membered formazanato-ruthenium chelate rings have an envelope conformation with puckering of the metal. DFT calculations indicate a pronounced sensitivity of the N-N bond lengths toward the ligand oxidation state. Several electrochemically accessible charge states were analyzed, and the derived oxidation numbers Ru(II), Ru(III), or Ru(IV), L' or (L')(•-), and L(-), L(•2-), or the new formazanyl ligand L(•) for the two-way noninnocent formazanate reflect the increasing acceptor effect of the ancillary ligands L' in the series acac(-) < bpy < pap.

S–S Bond Activation in Multi‐Copper ­Aggregates Containing Perthiocarboxylato Ligands

AbstractThe direct reaction between [Cu(OAc)2·(H2O)]2 and n‐butyldithiocarboxylic acid affords two copper(I) aggregates with dithiocarboxylato, [Cu(S2C‐n‐butyl)]4 (1), and perthiocarboxylato ligands, [Cu(S3C‐n‐butyl)]4 (2), in which the oxidation of dithiocarboxylato ligand is triggered by the CuII centers. The activation of the S–S bond in 2 by two reducing agents, PPh3 and NaBH4, has been investigated both experimentally and by DFT calculations. The successive S–S activation in 2 by reaction with 4 equiv. of PPh3 is a cooperative process, which implies that the intermediate species remain elusive. Such intermediates have been analyzed by DFT calculations, which established that the reactivity of the multi‐copper structures depends on the balance between the interactions in the different coordination spheres imposed on the copper centers and the Cu···Cu distances. Furthermore, weak cuprophilic interactions are conditioned by the orbital orientation imposed by the structure. This implies that these metal–metal interactions are not always found between the pairs of Cu atoms with the shortest distances. Although different products have been isolated depending on the reducing agent, the overall theoretical data indicate that the reagent always attacks the terminal sulfur atom of the perthio group.

Synthesis and lanthanide coordination chemistry of CMPO-decorated dibenzothiophene and dibenzothiophene sulfone platforms

Syntheses and spectroscopic characterization data for two new hybrid chelating ligands, 4,6-bis[(diphenyl-N,N-diethylcarbamoylmethylphosphine oxide)methyl]dibenzothiophene (2) and 4,6-bis[(diphenyl-N,N-diethylcarbamoylmethylphosphine oxide)methyl]dibenzothiophene 5,5-dioxide (3), that contain two CMPO fragments grafted onto dibenzothiophene and dibenzothiophene sulfone platforms, respectively, are presented. Coordination chemistry with selected lanthanide nitrates is described along with a X-ray crystal structure determination for an unexpected Eu(III) complex, Eu(4)(NO3)3 that contains the intermediate ligand oxidation species 4,6-bis[(diphenyl-N,N-diethylcarbamoylmethylphosphine oxide)methyl]dibenzothiophene 5-oxide (4).

Organo-lanthanide luminophores bridged by phosphine oxide ligands

Organo-lanthanide luminophores composed of lanthanide ions and specific phosphine oxide ligands exhibit characteristic photo- and thermo-properties for future photonic applications. In this review, lanthanide coordination polymers with strong luminescence, thermostability, and thermo-responsive emission properties are introduced. We also present a strategy for luminescent lanthanide compounds with amorphous formability. Photofunctional organo-lanthanide luminophores are expected to contribute to the development of new and better performing materials and devices.