Mixed Ligand System Research Articles

C–H···π(metal–ligand ring) interaction in a mesaconate bridged Cd(II) 1-D coordination polymer: structural elucidation, theoretical study, and photophysical properties

A Cd(II)-based one-dimensional coordination polymer (1-D CP), [Cd2(mes)2(4-phpy)4] (1), was prepared using mesaconic acid (H2mes) and 4-phenyl pyridine (4-phpy) mixed ligand system. Compound 1 has been characterized by elemental analysis, infrared spectroscopy, thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD) pattern and single crystal X-ray diffraction (SCXRD) techniques. Structural elucidation reveals a 1-D chain which contains a 14-membered metal-ligand ring composed of two mes ligands and two Cd(II) centers. Further, the 1-D chains are assembled into a two-dimensional (2-D) supramolecular network by C–H···π(metal-ligand ring) interactions. The fluorescence lifetime of 1 shows a good range of average lifetime. The theoretical band gap has also been calculated by density functional theory (DFT) computations, which shows that 1 may possess semiconducting properties.

Metformin-based copper(II) complexes: synthesis, structural characterization and mimicking activity of catechol oxidase and phenoxazinone synthase

Synthesis and characterization of the ternary copper(II) complexes containing metformin-based mixed ligand system (LL′) in which L is metformin and L′ is glycine or iminodiacetic acid (IDAH2) is the initial goal of the present study. Analytical investigations, mass spectra, electrochemical, thermal, magnetic and spectroscopic measurements assigned the suggested molecular formulae of the current copper(II) chelates. Magnetic and spectral studies suggested square-pyramidal stereochemistry for the three complexes. Furthermore, X-ray structural analysis results demonstrated the square-pyramidal geometry around copper(II) center of complexes 1, 2 and 3. Catechol oxidase and phenoxazinone synthase mimetic activity examinations displayed that the current copper(II) oxidase models efficiently catalyze the oxidative coupling of o-aminophenol (o-APH3) to the corresponding oxidation product aminophenoxazin-3-one core (APX). As well, the current metformin copper(II)-based chelates showed excellent catalytic performance toward the air conversion of the model substrate 3,5-di-tertbutylcatechol (3,5-DTBCH2) to the biologically significant 3,5-di-tertbutylquinone. The catalytic reaction rate dependence on the substrate concentration is consistent with two orders profiles: first order at low substrate concentration and saturation kinetic at the high concentration of substrate. The catalytic efficiency was described by the ratio kcat/KM which follows the order 2 > 1 > 3, and the same order holds for the geometry irregularity of the studied copper(II) complexes. Electrochemical data were employed to describe parameters that determine the rate of intramolecular reactions including the driving force of the reaction (i.e., the free energy change, − ΔGo), the reorganization energy, λ of the reacting redox centers during the aerobic catalytic oxidation of the studied substrates. Based on the kinetic measurements by using stopped-follow spectrophotometer, the probable mechanistic implications of the studied catalytic reactions are discussed.

Synthesis and spectroscopic characterization of ternary copper(ii) complexes containing nitrogen and oxygen donors as functional mimics of catechol oxidase and phenoxazinone synthase

Two ternary copper(ii) complexes1[(Cu2Me4en)4(EDTA)] and2[(CuMe4en)2(MIDA)] containing the mixed ligand system of 1,1′,4,4′-tetramethylethylenediamine (Me4en) (L) andN-methyliminodiacetic (MIDAH2) (L′) or ethylenediaminetetraacetic acid (EDTAH4) (L′) were synthesized.

Two new entangled Zn and Cd coordination polymers based on a rich «mix» feature of the O- and N-donor ligand system: Synthesis, structure, and fluorescent properties

A prominent mixed-ligand system with rich «mix» features, which are rigid multicarboxylate O-donor ligands cooperating with flexible bisazole N-donor linkers, is explored to coordinate with Zn2+/Cd2+ centers. Two new entangled coordination polymers ([Cd(Hbtc)(bbi)] (1) and [Zn(btec)0.5(dtp)]×5H2O (2)) are gained. Complex 1 exhibits a fascinating 3D (3,5)-connected net with a Schläfli symbol of the (63.610) topology, and 3D nets penetrate into each other to give rise to twofold interpenetrations. Complex 2 displays a 2D layer with similar 9.9·12.0 Å2 hexagonal channels, the adjacent layers stacking with each other to form a 3D supramolecular structure. The effects and functions of the ligands in the complexes are discussed. Moreover, the thermal stabilities and fluorescence properties of complexes 1 and 2 are investigated.

Designing of Pb(II)-Based Novel Coordination Polymers (CPs): Structural Elucidation and Optoelectronic Application.

[Pb2(bdc)1.5(aiz)]n (1) and [Pb2(bdc)1.5(aiz)(MeOH)2]n (2) (H2bdc = 1,4-benzene dicarboxylic acid, aiz = (E)-N′-(thiophen-2-ylmethylene)isonicotinohydrazide) have been synthesized, and structural characterization has been established by X-ray analysis and thermogravimetric analysis (TGA). Here, bdc2– links two Pb(II) centers and the aiz ligand binds the metal centers in two different manners: chelating and monodonating. Thus, polymerizations have taken place from the combination of mixed ligand system. Optical band gaps have been studied via UV measurements. Again, the experimental and calculated (from density functional theory (DFT)) band gaps agree well and the semiconducting properties of synthesized polymeric materials have been approved. Thus, optoelectronic and photonic devices can be made by this type of coordination polymers (CPs). The I–V representative curves of 1 (device-A) and 2 (device-B) in both dark and illuminated conditions show that device-A has a higher magnitude of current than device-B. Dark- and photo-conductivity values of device-A are calculated as 2.94 × 10–6 and 6.12 × 10–6 S m–1, respectively, whereas for device-B, the values of dark- and photo-conductivity are 2.92 × 10–7 and 3.66 × 10–7 S m–1, respectively, at room temperature.

Engineering Green-to-Blue Emitting CsPbBr3 Quantum-Dot Films with Efficient Ligand Passivation

A series of challenging issues such as field-driven spectral drift for the CsPbClxBr3–x system and mixed phases in quasi-two-dimensional structures still exist when devising blue-emitting perovskites. In this Letter, the CsPbBr3 quantum-dot (QD) system is proposed to overcome these challenges. However, to date, the CsPbBr3 QD films with tunable colors from green to blue still cannot be achieved using existing methods. Herein, a simple one-step spin-coating route incorporated with efficient ligand passivation is developed to realize this goal. The size restriction of CsPbBr3 QDs is enabled by a diammonium ligand, propane-1,3-diammonium bromide (PDAB). A mixed-ligand system of phenethylammonium bromide (PEAB) with PDAB is further explored to enhance their optical performance. The CsPbBr3 QDs experience a second growth process upon controlled air exposure, which is utilized to realize their size control and emission wavelength tunability. The CsPbBr3 QD-based devices exhibit no spectral drift in electrolumin...

Replacing Cu(II)Br2 with Me6-TREN in Biphasic Cu(0)/TREN Catalyzed SET-LRP Reveals the Mixed-Ligand Effect.

The mixed-ligand system consisting of tris(2-aminoethyl)amine (TREN) and tris(2-dimethylaminoethyl)amine (Me6-TREN) during the Cu(0) wire-catalyzed single electron transfer-living radical polymerization (SET-LRP) of methyl acrylate (MA) in "programmed" biphasic mixtures of the dipolar aprotic solvents NMP, DMF, and DMAc with H2O is reported. Kinetic and chain end analysis studies by NMR and MALDI-TOF before and after thio-bromo "click" reaction demonstrated that Me6-TREN complements and makes the less expensive TREN a very efficient ligand in the absence of externally added Cu(II)Br2. Statistical analysis of the kinetic data together with control experiments demonstrated that this mixed-ligand effect enhanced the apparent rate constant of propagation, monomer conversion, and molecular weight control. The most efficient effect was observed at a 1/1 molar ratio between these two ligands, suggesting that in addition to a fast exchange between the two ligands, a new single dynamic ligand generated by hydrogen bonding may be responsible for the mixed ligand observed.

Determination of complex forming ability of mixed-ligand organic systems relative to the metal ions

It is shown that classical and specific methods for determining the complex forming ability of mixed-ligand organic systems relative to the metal ions is not perfect. Determination of complex-forming ability of mixed-ligand organic systems relative to the metal ions using the method of turbidimetry for media containing biometal chlorides, mixed-ligand systems and sodium carbonate is proposed. As mixed-ligand systems used the culture fluid Bifidobacterium bifidum AC-1670 (mixed-ligand system I), the culture fluid of the composition of probiotic bacteria (mixed-ligand system II), the culture fluid of the composition of probiotic bacteria with the introduction of exogenous chelating agents (mixed-ligand system III), culture fluid of probiotic bacteria composition and products of their cell walls processing (mixed-ligand system IV). A solution of metal chloride (magnesium or calcium, or cuprum, or manganese, or ferrum or zinc) was added discretely to the aliquots of the solution of the organic mixed-ligand system. The mixture was stirred and kept for 30 minutes at 40 °C, then a solution of sodium carbonate was added to the aliquots and discretely measured turbidity of the solution by turbidimetric method at a wavelength of 450 nm. When the increasing of the turbidity magnitude system by 0.02 opt. un, a conclusion about the maximum value of the mixed-ligand organic systems complex forming capacity relative to the metal ion was made. Further increase in the turbidity of the system indicates an increase in the metal content in inorganic form, respectively the complex formation potential of the mixed-ligand system is exhausted. It is determined that the highest complex forming ability in relation to ions of biometals has mixed-ligand system III. The proposed method allows precisely to determine the complex formation capacity of mixed-ligand organic systems in relation to metal ions without the use of aggressive reagents capable of destroying chelate bonds and without involving high-cost rare equipment.

Two isostructural Co/Ni fluorine-containing metal-organic frameworks for dye adsorption and supercapacitor

Based on the mixed ligand system of tetrafluoroterephthalic acid (H2tfbdc) and 1,4-bis((1H-imidazol-1-yl)methyl)benzene (1,4-bimb), two isostructural metal-organic frameworks viz. [Co(tfbdc)(1,4-bimb)(H2O)2]n (1) and [Ni(tfbdc)(1,4-bimb)(H2O)2]n (2) have been synthesized by solvothermal method and characterized. Complexes 1–2 revealed three-dimensional (3D) 3-fold interpenetrating diamond frameworks. Due to the existence of fluorine-donor sites in the network, complexes 1–2 exhibited selective adsorption towards Congo red (CR) than methyl orange (MO), methyl blue (MB), rhodamine B (RhB) and methylene blue (MLB). Moreover, complexes 1–2 can be used as the electrode material for supercapacitor, and a high rate performance was observed for 1 (it retains 71.21% of its initial capacitance up to a high current density of 10 A g−1).

Mixed organic ligand-based colorimetric and ratiometric chemosensors for Co2+: structure-activity relationships.

In this work, chemosensors based on mixed ligands were proposed for the cooperative detection of Co2+. The relationship between the specifically selected mixed organic ligands and the detection activities is discussed. Diverse responses to metal ions can be tuned by controlling the structural features of organic ligands, such as different sizes, geometries, substituents, and connectivity. Among the nine investigated systems, DHAB-Tpy, DHAB-Phen, and DHAB-Dpa displayed high selectivity and sensitivity for Co2+, with detection limits of 4.5 × 10-7M, 1.1 × 10-7M, and 8.0 × 10-8M, respectively. The detection of Co2+ was not affected by other metal ions, anions, amino acids, proteins, nucleic acids, lipids and pH conditions. Furthermore, the proposed method was validated in the analysis of Co2+ in real water samples with satisfactory recovery and relative standard deviation values. TAC-Phen and TAC-Dpa could recognize Co2+ qualitatively, but could not detect Co2+ quantitatively. While TAC-Tpy, PAN-Tpy, PAN-Phen, and PAN-Dpa showed no metal ion selectivity. The experimental results were also rationalized by theoretical studies. A mixed ligand system can be used to produce a ratiometric absorption signal to avoid most ambiguities, such as the chemosensor environment and concentration, via self-calibration of two absorption bands. Structural insights derived from detection activities can provide valuable information for the design of new metal ion chemosensors by varying the type of organic ligands. Graphical abstracts The work represents a simple strategy for obtaining synthesis-free, inexpensive, and sensitivity-tunable chemosensors through mixing organic ligands of different sizes, substitutions, geometries, and connectivity to modulate the sensing behaviors.

Obtaining and characteristic of the magnesium organic forms on the basis of products of bifidobacteria processing and their metabolites

The possibility of obtaining bioavailable mixed ligand chelate complexes of Magnesium has been considered. As bioligands, it is proposed to use the metabolites and products of enzymatic hydrolysis of the peptidoglycans of the cell walls of Bifidobacterium bifidum AC-1670. As ligands, fragments of peptidoglycans of cell walls of bifidobacteria, which have their own immunotropic effects, were used. Destruction of bacterial cells was done by ultrasound treatment with subsequent enzymatic hydrolysis with papain. It was found that the highest content of potential ligands for chelation was obtained by ultrasound treatment at a frequency of 35 kg for 600 seconds with subsequent enzymatic hydrolisys, which lasted for 180 minutes at a ratio of the enzyme: substrate 1:1. In this case, the accumulation of amino acids in the hydrolyzate was 11.35 mg/cm3, low molecular weight peptides - 7.54 mg/cm3. The liquid phase of the product of the disintegration of the bacterial mass is investigated for the presence of metabolites that can participate in the formation of chelating magnesium complexes. Qualitative composition and quantitative content of organic acids are determined. It is established that in the product of disinfection of bifidobacteria the following acids are present: acetic (445.5 mg/dm3), lactic (284.6 mg/dm3), benzoic (1.3 mg/dm3). It has been established that the obtained mixed ligand systems are effective chelating agents and bind magnesium in an amount of 14 mg/cm3. The method of IR spectroscopy has proved that this system is formed with the participation of polydentant ligands. Determination of the pH stability of the complex showed that in the range of pH values 4–7, the chelate system is stable, at pH 2 only 10% of the complex is stored, at a pH of 9 – 60%. The thermostability of the complex was investigated by the method of differential scanning calorimetry. It was established that the complex is stable in the temperature range of 20-122 ° С, and therefore can be used as a physiologically functional ingredient in the health foods, the technology of which involves high-temperature processing.

New Silver Complexes with Mixed Thiazolidine and Phosphine Ligands as Highly Potent Antimalarial and Anticancer Agents

Five silver(I) complexes containing a mixed ligand system of phosphine and thiazolidine were successfully synthesized. The structural information of the complexes was assembled using various spectroscopic techniques such as CHN elemental analysis, Fourier transformed infrared (FTIR), 1H, 13C, and 31P{1H} NMR spectroscopy, and thermogravimetric analysis (TGA). A bidentate phosphine ligand acted as a chelating agent which bond to the silver in 1 : 2 molar ratios. Meanwhile, thiazolidine was attached to the silver in a 1 : 1 molar ratio. The antiplasmodial properties of all synthesized complexes were investigated on chloroquine-resistant P. falciparum parasite via HRP2 assays and cytotoxicity tests on Vero cells. Of all the synthesized complexes, complex 2 showed the highest SI value (more than 12.4) followed by complex 5 (6.6). The potent properties of compounds 2 and 5 were also noted in the in vitro antiproliferative assays involving MDA-MB-231 and MCF-7 breast cancer cell lines as well as HT-29 colon cancer cell line. Complex 2 was selective for MDA-MB-231 cells (GI50 = 1.9 ± 0.3 µM), while complex 5 acted predominantly on breast carcinoma cells (GI50 MDA-MB-231 = 4.7 ± 1.1 µM; MCF-7 = 2.9 ± 0.9 µM) instead of colon carcinoma (HT-29) cells (GI50 = 15.1 ± 1.9 µM).

OBTAINING AND CHARACTERISTICS OF CALCIUM ORGANIC FORMS ON THE BASIS OF METABOLITES AND PROCESSING PRODUCTS OF PROBIOTIC BACTERIA

The possibility of obtaining bioavailable mixed ligand chelate complexes of calcium has been considered. As bioligands, it is proposed to use the metabolic products of probiotic bacteria combination and products of enzymatic hydrolysis of peptidoglycans of their cell walls. The culture fluid of probiotic bacteria composition has been investigated for the determination of metabolites in its composition that can participate in the formation of calcium chelate complexes. The qualitative composition and quantitative content of organic acids of a culture fluid have been determined. It has been established that it contains the following acids: oxalic (1.6 mg/dm3), citric (22.1 mg/dm3), acetic (575.8 mg/dm3), lactic (236.3 mg/dm3), benzoic (1.5 mg/dm3). In addition, it has been found that in the composition of the culture liquid, free amino acids and soluble protein are also present in the amount of 1.2 mg/cm3 and 5 mg/cm3, respectively.In order to obtain fragments of peptidoglycans of cell walls of probiotic bacteria as potential bioligands for complex formation, their enzymatic hydrolysis with pancreatin has been performed. It has been established that the highest content of biologically active muropeptides is 5.1 mg/cm3 and it is accumulated during hydrolysis of the substrate for 180 minutes, the ratio of enzyme: substrate 1: 100 and 5.1 mg/cm3.By methods of nephelometry and spectrophotometry, it has been established that the obtained mixed ligand systems are effective chelating agents and, depending on the composition, bind calcium in amounts of 9, 14 and 16 mg/cm3. Identification of the pH stability of the complex has been shown that in the range of pH values 4–7, the chelate system is stable, at pH 2 only 10% of the complex is stored, at pH 9 60% is preserved. By method of differential scanning calorimetry the thermostability of the complex has been investigated. It has been established that the complex is stable in the temperature range of 20–122°С, and therefore can be used in the composition of health foods, the technology of which involves high-temperature processing.

Dy2 and Dy4 hydroxo clusters assembled using o-vanillin based Schiff bases as ligands and β-diketone co-ligands: Dy4 cluster exhibits slow magnetic relaxation

The reaction of DyCl3.6H2O with the mixed ligand system consisting of o-vanillin based Schiff base ligand H2L [2-(2-hydroxy-3-methoxybenzylideneamino) phenol], dibenzoylmethane (Ph2acac) and acetylacetone (Acac) in the presence of triethylamine as the base afforded, di and tetranuclear dysprosium hydroxo clusters having formulae [Dy2(L)2(Ph2acac)2(H2O)2]3(1) and [Dy4(L)4(acac)2(OH)2(H2O)2(C6H5N)4] (2) respectively. The solid state structures of these products were established by Single Crystal X-ray diffraction technique. Magnetism studies reveal Dy4 exhibits slow magnetic relaxation behavior.

Self-assembled energetic coordination polymers based on multidentate pentazole cyclo-N5−

Coordination to form polymer is emerging as a new technology for modifying or enhancing the properties of the existed energetic substances in energetic materials area. In this work, guanidine cation CN3H6+ (Gu) and 3-amino-1,2,4-triazole C2H4N4 (ATz) were crystallized into NaN5 and two novel energetic coordination polymers (CPs), (NaN5)5[(CH6-N3)N5](N5)3– ( 1 ) and (NaN5)2(C2H4N4) ( 2 ) were prepared respectively via a self-assembly process. The crystal structure reveals the co-existence of the chelating pentazole anion and organic component in the solid state. In polymer 1 , Na+ and N5– were coordinated to form a cage structure in which guanidine cation [C(NH2)3]+ was trapped; for polymer 2 , a mixed-ligand system was observed; N5– and ATz coordinate separately with Na+ and form two independent but interweaved nets. In this way, coordination polymer has been successfully utilized to modify specific properties of energetic materials through crystallization. Benefiting from the coordination and weak interactions, the decomposition temperatures of both polymers increase from 111°C (1D structure [Na(H2O)(N5)]∙2H2O) to 118.4 and 126.5°C respectively. Moreover, no crystallized H2O was generated in products to afford the anhydrous compounds of pentazole salts with high heats of formation (> 800 kJ mol–1). Compared to traditional energetic materials, the advantage in heats of formation is still obvious for the cyclo -N5– based CPs, which highlights cyclo -N5– as a promising energetic precursor for high energy density materials (HEDMs).

Enhancement of the Fluorescence Quantum Yield of Thiol-Stabilized CdTe Quantum Dots Through Surface Passivation with Sodium Chloride and Bicarbonate

Abstract Colloidal quantum dots (QDs) have potential for several applications, e.g. as novel light sources; as photoluminescent probes; and for solar energy conversion devices, but their sensitivity towards their environmental surroundings, and the presence of surface defects may still degrade their emission properties. Herein, we present a post-synthetic treatment of CdTe QDs stabilized by mixed thiol ligands using chloride and bicarbonate ions to achieve near-complete surface passivation, resulting in a two-fold increase of the photoluminescence quantum yield (PL QY) and significant suppression of non-radiative recombination. Time-resolved PL measurements reveal fluorescence lifetime and PL QY trends did not both track identically; in the most favorable cases a suppression of non-radiative recombination and a slight increase in the radiative recombination rates after the salt treatment took place. The optimized conditions demonstrated here are proven to work for different sizes of CdTe QDs, and also show a dependence on the composition of the mixed ligand systems used.

One ligand capable of in situ reaction in a mixed-ligand system with two new different frameworks

The in situ ligand 2,3-pyrazinedicarboxylic acid (2,3-H2pzdc) mixed with 1,1′-(1,4-butanediyl)bis(benzimidazole) (bbbi) is used to form two coordination polymers ([Cd(2,3-pzdc)(bbbi)] (1) and [Cd2Cl3(2-pzc)(bbbi)2] (2)) under hydrothermal conditions. Complex 1 was obtained in the absence of in situ reaction and 2 was synthesized with 2,3-H2pzdc in situ generating 2-pyrazinecarboxylate (2-pzc−). The structural details reveal that 1 has a 3D framework with dia topology, and 2 is a 2D layer structure and develops a 3D supramolecular structure via strong π⋯π stacking interactions. The ligand effects were compared for the two frameworks. In addition, fluorescence properties and thermal stabilities of 1 and 2 in the solid were studied.

Study on mixed ligand complexes of Pb(II) with EDTA and dietary ligands to investigate the applicability on chelation therapy

Lead is the most distributed toxic metal in the world and chelation therapy is a remedy for removing it from the body, if a person is intoxicated. Stability constants of both binary and mixed ligand complexes of Pb(II) with salicylic acid, ascorbic acid, vitamin B 1 (thiamine), vitamin B 3 (niacin) and Na 2 EDTA were potentiometrically studied, in aqueous media at the temperature of 37.0 ± 0.2 ⁰ C and the ionic strength of 0.15 mol dm -3 in order to identify better mixed ligand systems suitable for chelation therapy of lead. Both metal-ligand and proton-ligand formation constants were calculated using Irving-Rossotti equations. The Formation of ternary complexes was further confirmed theoretically by plotting composite curves. Δ log K values calculated revealed that all mixed complexes were more stable than the complexes of corresponding binary systems. EDTA-Vitamin B 1 and EDTA-Ascorbic mixed complexes with Pb(II) disclosed very high stability constants, which were two times greater than that of EDTA binary complex. Vitamin B 1 revealed a remarkably high ability in forming mixed ligand complexes with all other four ligands. Results of this work clearly indicate that (EDTA-Vitamin B 1 ), (EDTA-Ascorbic), (Vitamin B 1 -Ascorbic), (Vitamin B 1 -Salicylic) and (Vitamin B 1 -Vitamin B 3 ) combinations can be used for detoxification of lead more effectively using dietary ligands.

Copper(I)–N-Heterocyclic Carbene Complexes as Efficient Catalysts for the Synthesis of 1,4-Disubstituted 1,2,3-Sulfonyltriazoles in Air

Bis-NHC and mixed NHC/PR3 copper(I) complexes (NHC = N-heterocyclic carbene) were found to be efficient catalysts enabling the azide–alkyne cycloaddition reaction leading to the formation of 1,2,3-sulfonyltriazoles under Click conditions. The mechanism of this transformation was probed and decoordination of the NHC ligand (even in the NHC/PR3 mixed ligand systems) during the catalytic transformation was observed.

Selective Decarbonylation of Fatty Acid Esters to Linear α-Olefins

Selective decarbonylation of p-nitrophenol esters of fatty acids to the corresponding linear α-olefins (LAOs) was achieved using palladium catalysis. After extensive ligand screening, a mixed-ligand system exploiting the trans-spanning diphosphine XantPhos and an N-heterocyclic carbene (IPr) was identified as the most effective in yielding high α-selectivity and high conversions of the ester (>98% selectivity, >90% conversion using 2.5 mol % of PdCl2 and 5 mol % of the ligands, 190 °C, 2–2.5 h). On the basis of insights from modeling at the density functional level of theory, we propose that the mixed-ligand set achieves high α-selectivity by promoting olefin dissociation from the palladium center following β-hydride elimination, which is especially facilitated both by the combined steric bias of the mixed-ligand set and by the ability of the XantPhos ligand to coordinate in both mono- and bidentate fashions.