Yb Metal Research Articles

Imidobis(tetraphenylphosphinato)lanthanoid(III) complexes: Synthesis by oxidative protolysis, and redox transmetallation/protolysis, structural studies and Hirshfeld surface analysis

Redox protolysis of [YbCp2(dme)] (dme = 1,2-dimethoxyethane) by imidotetraphenyldiphosphinate, ({Ph2PO}2NH) LH yields [YbCp{(Ph2PO)2N}2}(MeCN)] 1 and [Yb{(Ph2PO)2N}3] 2 with the last also obtained by oxidative protolysis of Yb(C6F5)2. The complexes [Ln{(Ph2PO)2N}3] ((Ln = Yb 2, Er 3, Gd 4), [Sm{(Ph2PO)2N}3(MeCN)3] 5 and [Nd{(Ph2 PO)2N}3] 6 have all been prepared by redox transmetallation/protolysis reactions between Yb, Er, Gd, Sm or Nd metals, bispentafluorophenylmercury and proligand LH. Complex 1 is formally eight coordinate with an acetonitrile, cyclopentadienyl (Cp) and two chelating O,O′-(Ph2PO)2N ligands, with the MeCN trans to the Cp ring. Complexes 2 and 4·C7H8 are six coordinate monomers with three chelating O,O′ diphosphinate ligands. By contrast 5 is a highly symmetrical nine-coordinate monomer with three acetonitrile and three chelating O,O′-L ligands. The three-dimensional Hirshfeld surface (3D-HS) analysis and the two-dimensional fingerprint plots (2D-FP) were quantified for different intermolecular interactions in complexes 2 and 4.

Electrochemical behavior and separation of ytterbium from NaCl-CaCl2 molten salt by reactive electrodes

To electro-extract Yb from NaCl–CaCl2 molten salt, the electrochemical behavior of Yb(III) was studied by cyclic voltammetry (CV), square wave voltammetry (SWV), chronopotentiometry (CP) and open circuit chronopotentiometry (OCP) on inert Mo and reactive Ni and Cu electrodes in NaCl–CaCl2 molten salt at 923 K. It was found that Yb(III) was reduced to Yb(II) on the Mo electrode and no Yb metal was formed prior to the reduction of Na+/Ca2+ ions, suggesting that the electroreduction of Yb(II) to Yb on inert Mo electrode is impossible. The diffusion coefficient of Yb(III) was determined by CV and CP and the results by the two methods showed good consistency. However, the reduction peaks of four Ni-Yb and five Cu-Yb intermetallic compounds were formed on reactive electrodes Ni and Cu, respectively. Thus, the reduction of Yb(II)/Yb became possible by this cathodic alloying method. To investigate the feasibility of the separation of ytterbium from this molten salt, potentiostatic electrolysis were carried out at −1.83 V, −2.0 V, −2.2 V, and −2.4 V (vs. Ag/AgCl) respectively on the Ni electrode and at −2.1 V (vs. Ag/AgCl) on the Cu electrode. The results showed that the yield of Yb atoms in the electrolytic alloy layer becomes higher when the applied potential shifts negatively, and Ni electrode is confirmed more suitable than Cu material for Yb separation in NaCl–CaCl2 molten salt.

Synthesis of cationic lanthanoid tetraphenylborate crown ether complexes

The efficacy of Me3NHBPh4 as a protolytic agent in the generation of reactive lanthanoid cations has been further explored. Reaction of [Nd(BH4)3(thf)4] with Me3NHBPh4 in a 1:3 mole ratio, and dibenzo-18-crown-6 (DB18C6) in thf did not yield [Nd(thf)n][BPh4]3, but [Nd(BH4)2(DB18C6)][BPh4]⋅2THF (1), a complex primed for further functionalisation, was isolated. The structure has an eight coordinate Nd atom with two trans tridentate BH4− ligands. Redox transmetallation/protolysis (RTP) reactions between Yb metal, PhHgC6F5, and Me3NHBPh4 in the presence of 18-crown-6 (18C6) or DB18C6 in MeCN or in thf followed by work up with MeCN yields [Yb(CE)(MeCN)3][BPh4]2⋅nMeCN (CE = 18C6, n = 0 (2), and DB18C6 n = 3 (3)), the structures of which have nine coordinate Yb atoms. Two pairs of MeCN ligands are transoid, whereas the third pair have a small cis NYbN angle. In the absence of a crown ether ligand, the RTP reaction in MeCN yields the known [Yb(MeCN)8] [BPh4]2.

Mapping the redox state of the young Solar System using ytterbium valence state

We have determined the valence state of Ytterbium (Yb) in a collection of meteorites covering 4–5 orders of magnitude in oxygen fugacity (fO2) by X-ray absorption near-edge structure (XANES) spectroscopy at the Yb L2 edge. In the studied meteorite minerals, Yb abundance was between 1 and 30 ppm. The data were obtained from merrillite grains (theoretical formula Ca18Na2Mg2(PO4)14) from two equilibrated ordinary chondrites (one H6 and one LL6), on oldhamite grains (theoretical formula CaS) from three EH enstatite chondrites (from EH3 to EH5) and four EL enstatite chondrites (from EL3 to EL6), on one merrilite grain and one stanfieldite grain (theoretical formula Ca4(Mg,Fe,Mn)5(PO4)6) from a pallasite, on merrillite grains from a eucrite, and in a phosphorous-bearing phase from an ungrouped primitive achondrite (NWA 11119). The obtained Yb XANES spectra were compared to those measured in terrestrial apatites (containing 17–79 ppm Yb) and in synthetic materials (metallic Yb, YbS, Yb2S3, Yb2O3). In terrestrial apatites, as well as in ordinary chondrites, in the eucrite, in the pallasite, and in the ungrouped achondrite NWA 11119, Yb is present as Yb3+ only. In enstatite chondrites, about half of the Yb in CaS is in the Yb2+ form and the fraction of Yb2+ may be slightly higher in EH compared to EL. It appears that Yb redox state can be used to build a redox scale for the most reduced objects of the Solar System as shown by this slight difference between EH and EL. However, the absence of a strong difference in Yb redox state between EH and EL chondrites suggests that the observed difference in Yb abundance anomalies in oldhamites found between EH and EL is not due to oxygen fugacity prevailing during parent-body equilibration but rather to fractionation related to volatility.

Molecular traps based nitrobenzofurazan-appended pillar[5]arene having fluorescent sensing for biologically accumulable lanthanide ions

The effective detection of lanthanide ions is very important due to the penetration of these ions to the living cells. In this paper, novel Pillar[5]arenes, as a new fascinating class supramolecular chemistry, including ten and five nitrobenzofurazan (NBD) fragments were prepared to examine their optical behavior towards trivalent lanthanide ions. The Pillar[5]arene derivatives including ten or five NBD units were named as d-NBD-P5 and p-NBD-P5, respectively. The target macrocyclic compounds were characterized by some techniques such as NMR, melting point, FT-IR, elemental analysis and mass spectroscopy. The response of the synthesized probes towards trivalent lanthanide ions was fluorometrically examined with fluorescence spectroscopy in a half aqueous medium that the probes have especially sensitivity for two metal ions, Eu (III) and Yb (III). The confocal microscope was also used to support visually the sensitivity of d-NBD-P5 and p-NBD-P5 towards target lanthanide ions on living cells. Thus, the results obtained from the solution medium were also supported in the cell medium and both macrocyclic compounds have low toxicity.

Largely improving the lifetime by inserting a Yb metal layer into the charge generation layer in tandem organic light-emitting diodes

Largely improving the lifetime by inserting a Yb metal layer into the charge generation layer in tandem organic light-emitting diodes

Passivation phenomenon and variable properties of ytterbium in different Lewis acid AlCl3-NaCl melts

To further explore the application of the low-temperature molten salt in processing heavy rare earths, the properties of ytterbium in AlCl3-NaCl melts have been investigated. In this melt, YbCl2 powder products are prepared by electrolysis based on the dissolution reaction of Yb metal. The properties of Yb(II) in AlCl3-NaCl melts have also been studied in detail. In-situ UV–VIS absorption spectroscopy demonstrates that the coordination of Yb(II) changes in AlCl3-NaCl melts with different Lewis acidity, leading to variations in its diffusion ability. In addition, the conversion of Yb(II)/Yb(III) shows typical soluble-soluble reversible electrochemical behavior in strongly acidic AlCl3-NaCl. However, the electrochemical behavior of Yb(II) on inert electrodes becomes complicated when the amount of AlCl3 in AlCl3-NaCl melts less than 52 mol%. This change is attributed to the formation of a YbCl3 passivation film on the inert electrode during the electro-oxidation of Yb(II). Soaking the passivated electrode in the melt can alleviate the passivation. Understanding the electrochemical and spectroscopic properties of ytterbium in AlCl3-NaCl melts paves the way for its subsequent applications.

Tailoring abundant active-oxygen sites of Prussian blue analogues-derived adsorbents for highly efficient Yb(III) capture.

The removal of rare earth elements in mineral processing wastewater is highly desirable but still challenging. In this study, three bimetallic Prussian blue analogues (PBA) and six corresponding oxides are prepared by co-precipitation and calcination methods, and then utilized to adsorb aqueous Yb(III) solution. The results of XRD, SEM, BET, and XPS indicate the successful synthesis of all the adsorbents. Among them, three PBA-oxide samples (PBO-800) exhibit the superior adsorption capacities (˃250mg/g). The adsorption processes of Yb(III) are in accordance with the pseudo-second-order kinetic model and Langmuir model, simultaneously showing the spontaneous and endothermic thermodynamics. Moreover, PBO-800 can be reused after alkaline solution regeneration with less than 10% degradation after five consecutive adsorption-desorption cycles. More importantly, PBO-800 exhibits the impressive separation selectivity of Yb(III) and most light rare earth ions (e.g., 5.51 of Yb/La, 4.03 of Yb/Pr), as well as the selectivity of Yb(III) and alkali metal ions (e.g., 300.5 of Yb/Na, 256.2 of Yb/Ca). According to the characterization analysis and DFT calculation, the adsorption mechanism of Yb(III) by PBO-800 is mainly attributed to the strong interaction between the abundant active-oxygen sites and Yb(III), and the significant electrostatic attraction.

Количественный анализ пленочных структур с диффузной границей раздела, исследованных методом электронной Оже-спектроскопии

A model is proposed for interpreting the results of Auger electron spectroscopy in the case of film systems with reactive interfaces. A quantitative relationship has been established between the parameters of the transition layer and the shape of dependences of the Auger signal of the substrate on the film thickness in such systems. The model was tested for three rare-earth metal (Yb, Sm, Gd) – Si(111) interfaces. Quantitative data have been obtained concerning their structure and stoichiometric composition, as well as the dependence of these characteristics on the thermodynamic properties of the studied rare earth metals.

Synthesis, modification, and adsorption properties of Yb‐MOF: Kinetic and thermodynamic studies

In this paper, a novel Yb metal–organic frameworks {[Yb(L)(DMA)(H2O)]·(3H2O)}n(Yb‐MOF, H3Lis 4‐(N,N′‐bis(4‐carboxylbenzyl)amino)benzenesulfonic acid) was synthesized by solvothermal reaction. ModifiedYb‐MOFwas prepared by the potassium permanganate method for removing the Cu(II) and As(V) from simulated wastewater. The optimal pH value of modifiedYb‐MOFfor Cu(II) and As(V) adsorption was 5, and the optimal dosage of adsorbent was 0.04 mg/10 ml by static adsorption test. Four isothermal adsorption models (Freundlich, Langmuir, Temkin, and Dubinin–Radushkevich models) were fitted and analyzed. The adsorption processes of Cu(II) and As(V) were consistent with Freundlich, Langmuir, and Temkin models. The highest Cu(II) and As(V) adsorption capacity are 59.418 and 81.169 mg/g, respectively. The adsorption kinetic model and thermodynamic analysis of the modifiedYb‐MOFfor Cu(II) and As(V) were studied. The results showed revealed that the pseudo‐second‐order kinetic had a higher correlation association with the Cu(II) and As(V) adsorption process, indicating that chemisorption was dominant in both processes. At 298 and 308 K, the Cu(II) and As(V) adsorption by modifiedYb‐MOFis spontaneous.

Trends in Siting of Metals in Heterometallic Nd-Yb Metal-Organic Frameworks and Molecular Crystals.

Several studies suggest that metal ordering within metal-organic frameworks (MOFs) is important for understanding how MOFs behave in relevant applications; however, these siting trends can be difficult to determine experimentally. To garner insight into the energetic driving forces that may lead to nonrandom ordering within heterometallic MOFs, we employ density functional theory (DFT) calculations on several bimetallic metal-organic crystals composed of Nd and Yb metal atoms. We also investigate the metal siting trends for a newly synthesized MOF. Our DFT-based energy of mixing results suggest that Nd will likely occupy sites with greater access to electronegative atoms and that local homometallic domains within a mixed-metal Nd-Yb system are favored. We also explore the use of less computationally extensive methods such as classical force fields and cluster expansion models to understand their feasibility for large system sizes. This study highlights the impact of metal ordering on the energetic stability of heterometallic MOFs and crystal structures.

Reinvestigation of Reactions of HgPh2 with Eu and Yb Metal and the Synthesis of a Europium(II) Bis(tetraphenylborate).

Europium bis(tetraphenylborate) [Eu(thf)7][BPh4]2⋅thf containing a fully solvated [Eu(thf)7]2+ cation, was synthesized by protolysis of "EuPh2" (from Eu and HgPh2) with Et3NHBPh4, and the structure was determined by single-crystal X-ray diffraction. Efforts to characterize the putative "Ph2Ln" (Ln = Eu, Yb) reagents led to the synthesis of a mixed-valence complex, [(thf)3YbII(μ-Ph)3YbIII(Ph)2(thf)]⋅2thf, resulting from the reaction of Yb metal with HgPh2 at a low temperature. This mixed-valence YbII/YbIII compound was studied by 171Yb-NMR spectroscopy and single-crystal X-ray diffraction, and the oxidation states of the Yb atoms were assigned.

Electroextraction of Ytterbium on the Liquid Lead Cathode in LiCl-KCl Eutectic

The reduction mechanisms of Yb(III) on W electrodes in molten LiCl-KCl-YbCl3 were explored at 773 K, and the diffusion coefficient of Yb(III) was determined. Then, various electrochemical techniques were employed to investigate the electroreduction of Yb(III) in molten LiCl-KCl on a liquid Pb film and Pb electrode. Electrochemical signals were associated with forming Pb3Yb, PbYb, Pb3Yb5, and PbYb2. The deposition potentials and equilibrium potentials of four Pb-Yb intermetallics were obtained through open-circuit chronopotentiometry. Metallic Yb was extracted by potentiostatic electrolysis (PE) on a liquid Pb electrode, and XRD analyzed the Pb-Yb alloy obtained at different extraction times. The recovered Yb was found in the form of Pb3Yb and PbYb intermetallics. The extraction efficiency of Yb was calculated according to ICP analysis results, and extraction effectivity could attain 94.5% via PE at −1.86 V for 14 h.

Newly synthesized lanthanides complexes of ferrocene-based Schiff base with high biological activities and improved molecular docking data

Amino acids are the fundamental building blocks of proteins and are involved in all major biological activities. Schiff bases being active biological moieties and possessing diverse pharmacological activities. Herein, the previously synthesized Schiff base ligand (HL) underwent metal complex formation, to get their La(III), Er(III) and Yb(III) metal complexes. These metal complexes were characterized using different spectroscopic tools as elemental analysis, FT-IR, mass, UV-Vis spectra, thermal analysis (TG) and scanning electron microscope (SEM). According to the elemental analysis data, the complexes were found to have octahedral geometry with the formula [M(L)(H2O)2Cl]Cl.nH2O (M = La(III), n = 2; Er(III), n = 4 and Yb(III), n = 1). The ligand binds to the metal ions with mononegative tridentate mode through the carboxylic oxygen, imidazole nitrogen and azomethine nitrogen as deduced from the IR spectra. The complexes decomposed within two or three steps from room temperature to 1000 °C as elucidated from TG. Also, biological and anticancer activities were tested and promising activities. Molecular docking was studied on two different proteins, the receptor of breast cancer mutant oxidoreductase (3HB5) and the receptor of colon cancer isomerase (2HQ6). The results recommended that Yb(III) complex can be used as breast and colon cancer drugs.

Structural phase transition and superconductivity of ytterbium under high pressure

Recent advances in theory and experiment declare the rare-earth (RE) hydrogen-rich compound $\mathrm{La}{\mathrm{H}}_{10}$ is a near room-temperature superconductor under high pressure. To understand the underlying mechanism of superconductivity and explore the crucial role of lanthanides in forming the RE-based polyhydrides, we here perform a theoretical study on the structural phase transition and superconductivity of late lanthanide ytterbium (Yb) metal under high pressure up to 240 GPa. Two alternative structures, $R\overline{3}m$ and $I4/mmm$ phases, of Yb are presented. Most interestingly, the $P{6}_{3}/mmc$ phase of Yb is serendipitously discovered to be a superior superconductor with a critical temperature value of 19.5 K at 160 GPa, which is higher than other known RE elemental superconductors. The present findings establish an alternative structural phase transition sequence of Yb, which offers insights for further understanding the vital physics mechanisms of a lanthanide-based superconductor.

Synthesis, Structure, and Electric Conductivity of Higher Hydrides of Ytterbium at High Pressure.

While most of the rare-earth metals readily form trihydrides, due to increased stability of the filled 4f electronic shell for Yb(II), only YbH2.67, formally corresponding to YbII(YbIIIH4)2 (or Yb3H8), remains the highest hydride of ytterbium. Utilizing the diamond anvil cell methodology and synchrotron powder X-ray diffraction, we have attempted to push this limit further via hydrogenation of metallic Yb and Yb3H8. Compression of the latter has also been investigated in a neutral pressure-transmitting medium (PTM). While the in situ heating of Yb facilitates the formation of YbH2+x hydrides, we have not observed clear qualitative differences between the systems compressed in H2 and He or Ne PTM. In all of these cases, a sequence of phase transitions occurred within ca. 13–18 GPa (P3̅1m–I4/m phase) and around 27 GPa (to the I4/mmm phase). The molecular volume of the systems compressed in H2 PTM is ca. 1.5% larger than of those compressed in inert gases, suggesting a small hydrogen uptake. Nevertheless, hydrogenation toward YbH3 is incomplete, and polyhydrides do not form up to the highest pressure studied here (ca. 75 GPa). As pointed out by electronic transport measurements, the mixed-valence Yb3H8 retains its semiconducting character up to >50 GPa, although the very low remnant activation energy of conduction (<5 meV) suggests that metallization under further compression should be achievable. Finally, we provide a theoretical description of a hypothetical stoichiometric YbH3.

Electronic and Magnetic Properties of The Graphene/RE/Ni(111) (RE: La, Yb) Intercalation‐Like Interfaces: A DFT Analysis

AbstractThe effect of the rare‐earth (RE) metals (La and Yb) intercalation on the electronic and magnetic properties of the graphene/Ni(111) interface is studied using state‐of‐the‐art density functional theory calculations. In both systems, the intercalation of RE leads to the dramatic decrease of the magnetic moments of the Ni‐interface atoms and to the negligible moments of C‐atoms in a graphene layer, compared to the parent graphene/Ni(111) system. At the same time, the significant ‐doping of graphene together with a band‐gap opening is observed in both cases of the RE intercalation with a position of the graphene Dirac point reaching eV. Also the large density of states is found in the vicinity of the Fermi level () along the direction for the graphene‐derived states which can be attributed to the joint effect of the intercalated RE and interface Ni atoms. These factors – increased density of states at and absence of magnetism of C‐atoms in a graphene layer – indicate the possibility of the observation of the superconductive state in graphene in the considered RE‐based systems, which is important for the understanding of these and other electronics effects in the graphene‐based systems.

Facile synthesis of rare earth metal dual-doped Pr2O3 nanostructures: Enhanced electrochemical water-splitting and antimicrobial properties

Dual metal doping is a state-of-the-art technique for improving the electrocatalytic characteristics for oxygen evolution reaction (OER) and enhancement of the antibacterial activity of the material. Series of rare earth dual metal-doped Pr2O3 electrocatalysts (Pr2CeMO3, M = Sm, Yb, Er) were successfully fabricated by employing sol-gel treatment. The antimicrobial and electrochemical applications of grown products were studied along with physical properties using advanced techniques such as FESEM, EDX, XRD, FTIR, IV, CV, LSV, EIS, and ECSA. The prepared products retain the monoclinic Pr2O3 structure with the successful doping of rare-earth elements. From the FESEM analysis, grown products have the grainy conglomerate shape, icy monoclinic boxes, irregular lamellar shaped, and well-crystallized grains with the plate-like morphology. EDX has confirmed the presence of metal elements Pr, Ce, Sm, Yb, and Er in grown samples. The electrochemical measurements exhibited the enhancement by dual-doping, and Pr2CeSmO3 has an extraordinarily low overpotential of 189 mV to reach 10 mAcm−2 density and lower Tafel slope (75 mV/dec) for oxygen evolution reaction (OER) in 1.0 M KOH electrolyte. Furthermore, the electrocatalytic efficiency of Pr2CeSmO3 electrocatalyst for OER is extremely long-lasting for (>16 h). The antibacterial test showed that all grown single and dual-doped nanostructures have good antibacterial performance, but Pr2CeSmO3 exhibits strong inhibition activity towards E. coli, K. pneumoniae, S. aureus, and P. vulgaris bacterial strains with maximum inhibition zone diameter 30, 32, 35, and 31 mm, respectively. This low-cost method for the production of rare earth dual metal-doped materials holds a lot of potential for making efficient catalysts, electrochemical energy-conversion devices, and economical antibacterial agents.

Influence of Anomalous Changes in the Crystal Structure on the Transport Properties of YbNi1-xCuxAl Series of Alloys.

Results of the transport properties of the YbNi1−xCuxAl (x = 0, 0.2, 0.5, 0.8 and 1.0) series of alloys are reported. The previous analysis of X-ray diffraction patterns indicates that all compounds crystallize in the hexagonal ZrNiAl structure with a linear behavior of the unit cell volume as a function of the Cu concentration (x). This is not found in the unit cell parameters, showing a discontinuity between x = 0.5 and 0.8. Such discontinuities affect the behavior of the electrical resistivity, in which the position of the minimum temperature changes from 95 K to 175 K, and a rise in the low temperature slope in the magnetic contribution (with -lnT dependence) from 21 μΩcm to 212 μΩcm is observed. In addition, the electronic coefficient of the specific heat increases almost twofold from 125 mJ/mol·K2 (x = 0.5) to 246 mJ/mol·K2 (x = 0.8). These changes are attributed to the variation of the distance between Yb and transition metals (Ni and Cu) along the series and the different electronic properties of the transition metals (Ni and Cu).

Preparation, spectroscopic characterization and antitumor-antimicrobial studies of some Schiff base transition and inner transition mixed ligand complexes

Mixed ligand complexes of Mn(II), Ni(II), Zn(II), La(III), Er(III) and Yb(III) metal ions were prepared from bidentate Schiff base ligand (L) as a primary ligand, derived from condensation of benzophenone and 1,8-naphthylenediamine, and 1,10-phenanthroline (Phen) as a secondary ligand. The new Schiff base ligand (N1-(diphenylmethylene)naphthalene-1,8-diamine) and its mixed ligand complexes were characterized by using elemental microanalysis, conductometric measurements, magnetic susceptibility and spectroscopic studies (UV–Vis, mass spectral analysis, IR, 1H NMR and SEM). In addition, their thermal analytical (TG and DTG) behavior has been reported. Measurements of the molar conductivity of the complexes in DMF solvent pointed out the electrolytic nature of all complexes except Mn(II) and Zn(II) complexes were non electrolytes. According to the elemental analyses data, it was observed that the mixed ligand chelates had the general formulae [M(L)(Phen)Cl2]Cl.2H2O (M = La(III), Er(III) and Yb(III)), [M(L)(Phen)Cl2].H2O (M = Mn(II) and Zn(II)) and [Ni(L)(Phen)Cl(H2O)]Cl.H2O. Based on these findings, all mixed ligand complexes had octahedral geometry. The SEM image of the Schiff base ligand illustrated its rods like morphology with and average particle size of 77 nm while, the image of Ni(II) complex showed non-uniform platelets structure with some scattered rods with an average particle size of 54 nm. Considerable applications were done to ensure the biological significance of Schiff base ligand and its new mixed ligand complexes with Phen against Gram-negative bacteria (Escherichia coli), Gram-positive bacteria (Bacillus subtilis) and fungal (Aspergillus flavus and Candida albicans) strains and anti-cancer activities against (MCF7 breast cancer cell line). The results obtained revealed that the complexes exhibited promising biological and anticancer activity. Moreover, molecular docking studies were applied to determine the probable binding mode among the Schiff base ligand and the active site of the crystal structure of E. coli YcbB acylated with meropenem (PDB ID: 6NTW) and breast cancer estrogen mutant L536S (PDB ID: 6SBO) receptors.