Excess Of Ligand Research Articles

Bidentate NHC‐Containing Ligands for Copper Catalysed Synthesis of Functionalised Diaryl Ethers

Diaryl and heteroaryl ethers are important and common motifs in drug discovery and agrochemicals. Here we present a catalytic system for the copper catalysed arylation of phenols with aryl halides. Bidentate N‐heterocyclic carbene ligands provide a well‐defined catalytic system that enable low loading of copper in effective coupling reactions (0.5 mol% Cu or lower). The reaction scope of aryl iodides and aryl bromides is developed, that is tolerant of functional groups and a library of biaryl ethers with lead‐like properties is prepared. The presence of excess ligand (in a 1:3 ratio) is shown to be optimal to prevent catalyst degradation, presumably by avoiding decomplexation of the ligand. This is also supported by the catalytic results obtained with pre‐formed copper complexes. The kinetics of the reaction are examined and shown to be first order in copper, supportive of a well‐defined catalyst species, first order in phenol and aryl iodide, and zero order in base under the developed conditions. Computational studies performed using Minnesota MN15‐L parametrisation method support an oxidative addition–reductive elimination pathway. Reductive elimination would be turnover limiting and occurr through an intimate ion pair intermediate.

Impact of the P‐Ligand Concentration on the Formation of Hydroformylation Catalysts: An in situ FTIR Spectroscopic Study

AbstractThe formation of hydrido rhodium(I) complexes of the type [HRh(CO)3L] and [HRh(CO)2L2] from [Rh(acac)(CO)2]/L (L: bulky monophosphite ligand) requires a ligand‐to‐rhodium ratio [L]/[Rh] > 10 to prevent the possible partial generation of [Rh6(CO)16] under typical hydroformylation conditions. Significant fractions of formed [Rh6(CO)16] at lower ratios of [L]/[Rh] can be reactivated towards the hydrido complexes after the addition of the monophosphite ligand in the presence of synthesis gas. It was also found that [Rh6(CO)16] can be transformed by treatment with an excess of monophosphite ligand under inert gas to form a mononuclear complex of the type [L`Rh(CO)L] with an ortho‐metallated ligand.

Synthesis, Jahn-Teller labeled via crystal structure in trans-(ClO4)2CuII(Me2N-Py)4 complex: S9/S6/C-H…O synthons, thermal, physicochemical and 1BNA-docking

The synthesis of the trans-(ClO4)2CuII(Me2N-Py)4 complex (where Me2N-Py = N,N-dimethylpyridin-4-amine ligand) in significant yield involved the reaction of excess Me2N-Py ligand with Cu(ClO4)2·6H2O in MeOH solvent. The progression of the complex synthesis was monitored by UV–Vis, FT-IR, EDX, XRD, MS, SEM, CHN-EA, and TG/DTG. The resulting complex crystallized in the Triclinic space P1¯. In the solid state, the desired complex structure discrete a neutral trans-(ClO4)2CuII(Me2N-Py)4 formula, with copper(II) adopting a distorted octahedral environment formed by four Me2N-Py ligands occupying the square planar position Cu(Py)4, meanwhile, the two ClO4 are in linear trans-position. The XRD measurements proved the existence of elongation Jahn-Teller distortion in the synthesized complex. Furthermore, a comprehensive analysis of the desired complex, including. XRD/HSA interactions revealed the presence of two S9 and S6 main 2D-synthons primarily formed through Cph-H….OClO3 and CMe-H…OClO3 non-classical H-bonding interactions. Thermal stability assessments through TG/DTG indicated that the complexes with the most stable behavior underwent two degradation steps. The molecular docking of the desired complex against 1BNA-DNA was also evaluated.

Study of Mixed Re(I)/99mTc(I) Thiosemicarbazonate Complexes. Estrogen Receptor Affinity and Stability in Biological Media

Nine potentially bidentate thiosemicarbazone (HLn) ligands and their tricarbonylrhenium(I) complexes, [ReY(HLn)(CO)3] (Y = Cl, Br), were synthesized and their binding affinity towards estrogen beta receptors were determined using a competitive radiometric assay with [3H]‐estradiol. Even in the absence of a base, coordinated thiosemicarbazones can undergo deprotonation causing the release of the coordinated halide forming dimeric species, [Re2(Ln)2(CO)6]. The formation of the dinuclear complex with the thiosemicarbazone ligand zwitterionic form, [Re2(HL9)2(CO)6]Br2, motivated the theoretical study of the relative stability of these species. Despite the ease of formation of the dimer complexes, it was possible to optimize a synthetic route to obtain the complexes [2+1] [Re(Ln)(pym)(CO)3] where pym is a monodentate ligand 4‐dimethylamino‐pyridine or 4‐hydroxy ‐pyridine. The inclusion of this additional ligand substantially improves the affinity against the receptors. Complexes [99mTc(Ln)(pym)(CO)3] were also prepared using [99mTc(H2O)(CO)3]+, an excess of HLn ligand and in the presence of pym. The radiochromatograms show the formation of the first complex but also the presence of species resulting from the substitution of pym by chloride and water. However, the ratio of intensities between the three signals remains constant with the variation of the relative concentration suggesting an equilibrium between the three complexes.

Hydrophobic CHA-ZIFs with a junctional trap between cha and d6r cages for adsorption of 2,3-butanediol in aqueous solution

Hydrophobic CHA-ZIFs with a junctional trap between cha and d6r cages for adsorption of 2,3-butanediol in aqueous solution

Superalkalis with Hydrogen as Central Electronegative Atom and their Possible Applications: Ab Initio and DFT Study.

Superalkalis are unusual species having ionization energies lower than that of the alkali metals. These species with various applications are of great importance in chemistry due to their low ionization energies and strong reducing property. A typical superalkali contains a central electronegative core decorated with excess metal ligands. In the quest for novel superalkalis, we have designed the superalkalis HLi2, HLiNa and HNa2 using hydrogen as central electronegative atom for the first time employing high level ab initio (CCSD(T), MP2) and density functional theory (ωB97X-D) methods. The superalkalis exhibit very low ionization energies, even lower than that of cesium. Stability of these species is verified from binding energy and dissociation energy values. The superalkalis are capable of reducing SO2, NO, CO2, CO and N2 molecules by forming stable ionic complexes and therefore can be used as catalysts for the reduction or activation of systems possessing very low electron affinities. The superalkalis form stable supersalts with tailored properties when interact with a superhalogen. They also show remarkably high non-linear optical responses, hence could have industrial applications. It is hoped that this work will enrich the superalkali family and spur further theoretical and experimental research in this direction.

Continuous Nanomanufacturing of Inorganic Lead Halide Perovskite Nanocrystals with High-Concentration Precursors.

The microscale flow preparation scheme has been widely used in the preparation of inorganic perovskite nanocrystals (NCs). It is considered to be the most promising method for large-scale production. Recently, it has been suggested that increasing the precursor concentration can further improve efficiency, but there is still a lack of understanding of high-concentration synthesis. Here, we develop a microscale flow synthesis scheme using high-concentration precursors, and the typical concentration value in the reaction phase reaches 0.035 mol/L using cesium acetate. The CsPbBr3 NCs with sharp photoluminescence (PL) at 515.7 nm can be obtained, and their PL quantum yield after post-treatment exceeds 90%. The effect of the molar ratio of Pb/Cs (Rm), reaction time, reaction temperature, and excess ligands on this flow reaction is studied. Several new phenomena are observed in our experiment. At 120 °C, some Cs4PbBr6 NCs exist in addition to the usual CsPbBr3 nanoplatelets. Excess ligands lead to the formation of numerous Cs4PbBr6 NCs with a bright green PL, and these NCs will spontaneously transform into a nonemission form in the film. Moreover, mixed-halide CsPbBrxI3-x NCs and CsPbI3 NCs are also prepared in this scheme, and then they are used to obtain LEDs in a range of colors.

Abstract IA21: Mechanisms of Resistance to HER2-Targeted Therapies in HER2-positive Breast Cancer

Abstract Recent advancements in HER2-targeted therapies for HER2+ BC have revolutionized patient outcome. Yet, intrinsic and acquired resistance, especially in the advanced setting remains a clinical challenge. In the era of precision oncology, better understanding of these mechanisms of resistance is key to identifying new strategies to overcome resistance and for developing personalized treatment approaches. Our recent studies suggest that a subset of HER2+ BCs, associated with high and homogeneous levels of HER2 gene amplification, protein, and activity, are addicted to HER2 and may therefore benefit from chemotherapy-sparing HER2-targeted regimens. However, even in such tumors, constitutive activation of the PI3K/AKT pathway due to deregulations in the downstream PI3K pathway can lead to resistance. In all HER2+ BCs, failure to achieve a comprehensive blockade of the HER receptor layer is one of the major mechanisms of resistance due to the functional redundancy of the HER receptors and compensatory signaling within the pathway. But, in some cases, effective inhibition of HER receptors might be challenged by molecular masking of the receptors (e.g., MUC4) or by epi/genetic or post-translational alterations in the receptors itself (e.g., HER2 L755S, p95HER2). Indeed, we recently reported that acquisition of HER2 L755S, either alone or together with PIK3CA mutation, and hyperactive EGFR signaling due to acquired EGFR amplification or excess HER ligands are associated with resistance to HER2-targeted therapy, especially tyrosine kinase inhibitors. Likewise, clinically, HER mutations have been reported to be further enriched in the metastatic vs. primary HER2+ tumors. When HER2 does remain sustainably inhibited by HER2-targeted agents, resistance may arise due to the emergence of alternative signaling pathways transmitting compensatory proliferative and survival signals, such as ER, receptor tyrosine kinases, or downstream/intracellular signaling. Further, the emergence of metabolic pathways as alternative pathways of resistance have also been documented. We recently reported the activation of the cholesterol biosynthetic mevalonate (MVA) pathway as an escape mechanism that provides alternative signals through the YAP/TAZ-mTORC1-survivin axis to evade HER2 blockade. This resistance could be overcome using MVA pathway inhibitors (e.g., statins). Additionally, activation of the cell cycle regulatory complex cyclin D1/CDK4 has been shown to be associated with HER2-targeted therapy resistance, which could be exploited as a potential therapeutic vulnerability by using CDK4/6 inhibitors. Finally, response to HER2-targeted therapy could potentially be also modulated by the tumor microenvironment itself, including components of the host immune system and extracellular matrix. Together, a better understanding of the underlying mechanisms of resistance in the context of tumor and host biology, and treatment setup is fundamental to develop new treatment strategies and to guide patient stratification for personalized treatments and improved patient outcomes. Citation Format: Jamunarani Veeraraghavan, Fu-Tien Liao, Lanfang Qin, Tia Gordon, Alekya Raghavan, Caroline Sabotta, Rachel Kaplan, Carolina Gutierrez, C. Kent Osborne, Mothaffar F. Rimawi, Rachel Schiff. Mechanisms of Resistance to HER2-Targeted Therapies in HER2-positive Breast Cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr IA21.

Effect of ion to ligand ratio on the aqueous to organic relative solubility of a lanthanide-ligand complex.

In the solvent extraction of rare earth elements, mechanistic aspects remain unclear regarding where and how extractant molecules coordinate metal ions and transport them from the aqueous phase into the organic phase. Molecular dynamics simulations were used to examine how unprotonated di(2-ethylhexyl)phosphoric acid (DEHP-) ligands that coordinate the Gd3+ ion can transfer the ion across the water-organic interface. Using the umbrella sampling technique, potential of mean force profiles were constructed to quantify the relative solubility of the Gd3+ ion coordinated to 0-3 DEHP- ligands in either water, 1-octanol, or hexane solvents and at the water-organic interfaces. The simulations show the Gd-DEHP- complexes, at varying Ln-ligand ratios, preferentially solvate on water-organic interfaces. While the Gd(DEHP-)3 complex will diffuse past the aqueous-organic interface into the octanol solvent, it is thermodynamically preferred for the Gd(DEHP-)3 complex to remain in the water-hexane interface when there is no amphiphilic layer of excess ligand.

The Molecular Aspects of Functional Activity of Macrophage-Activating Factor GcMAF.

Group-specific component macrophage-activating factor (GcMAF) is the vitamin D3-binding protein (DBP) deglycosylated at Thr420. The protein is believed to exhibit a wide range of therapeutic properties associated with the activation of macrophagal immunity. An original method for GcMAF production, DBP conversion to GcMAF, and the analysis of the activating potency of GcMAF was developed in this study. Data unveiling the molecular causes of macrophage activation were obtained. GcMAF was found to interact with three CLEC10A derivatives having molecular weights of 29 kDa, 63 kDa, and 65 kDa. GcMAF interacts with high-molecular-weight derivatives via Ca2+-dependent receptor engagement. Binding to the 65 kDa or 63 kDa derivative determines the pro- and anti-inflammatory direction of cytokine mRNA expression: 65 kDa-pro-inflammatory (TNF-α, IL-1β) and 63 kDa-anti-inflammatory (TGF-β, IL-10). No Ca2+ ions are required for the interaction with the canonical 29 kDa CLEC10A. Both forms, DBP protein and GcMAF, bind to the 29 kDa CLEC10A. This interaction is characterized by the stochastic mRNA synthesis of the analyzed cytokines. Ex vivo experiments have demonstrated that when there is an excess of GcMAF ligand, CLEC10A forms aggregate, and the mRNA synthesis of analyzed cytokines is inhibited. A schematic diagram of the presumable mechanism of interaction between the CLEC10A derivatives and GcMAF is provided. The principles and elements of standardizing the GcMAF preparation are elaborated.

Transient Measurements and Simulations Correlate Exchange Ligand Concentration and Trap States in Colloidal Quantum Dot Photodetectors.

Colloidal quantum dot (CQD) photodetectors (PDs) can detect wavelengths longer than the 1100 nm limit of silicon because of their highly tunable bandgaps. CQD PDs are acutely affected by the ligands that separate adjacent dots in a CQD-solid. Optimizing the exchange solution ligand concentration in the processing steps is crucial to achieving high photodetector performance. However, the complex mix of chemistry and optoelectronics involved in CQD PDs means that the effects of the exchange solution ligand concentration on device physics are poorly understood. Here we report direct correspondence between simulated and experimental transient photocurrent responses in CQD PDs. For both deficient and excess conditions, our model demonstrated the experimental changes to the transient photocurrent aligned with changes in trap state density. Combining transient photoluminescence, absorption, and photocurrent with this simulation model, we revealed that different mechanisms are responsible for the increased trap density induced by excess and deficient active layer ligand concentrations.

Unexpected Single-Ligand Occupancy and Negative Cooperativity in the SARS-CoV-2 Main Protease.

Many homodimeric enzymes tune their functions by exploiting either negative or positive cooperativity between subunits. In the SARS-CoV-2 Main protease (Mpro) homodimer, the latter has been suggested by symmetry in most of the 500 reported protease/ligand complex structures solved by macromolecular crystallography (MX). Here we apply the latter to both covalent and noncovalent ligands in complex with Mpro. Strikingly, our experiments show that the occupation of both active sites of the dimer originates from an excess of ligands. Indeed, cocrystals obtained using a 1:1 ligand/protomer stoichiometry lead to single occupation only. The empty binding site exhibits a catalytically inactive geometry in solution, as suggested by molecular dynamics simulations. Thus, Mpro operates through negative cooperativity with the asymmetric activity of the catalytic sites. This allows it to function with a wide range of substrate concentrations, making it resistant to saturation and potentially difficult to shut down, all properties advantageous for the virus' adaptability and resistance.

Chiral, air stable, and reliable Pd(0) precatalysts applicable to asymmetric allylic alkylation chemistry

Stereoselective carbon-carbon bond formation via palladium-catalyzed asymmetric allylic alkylation is a crucial strategy to access chiral natural products and active pharmaceutical ingredients. However, catalysts based on the privileged Trost and Pfaltz-Helmchen-Williams PHOX ligands often require high loadings, specific preactivation protocols, and excess chiral ligand. This makes these reactions uneconomical, often unreproducible, and thus unsustainable. Here we report several chiral single-component Pd(0) precatalysts that are active and practically-applicable in a variety of asymmetric allylic alkylation reactions. Despite the decades-long history and widespread use of Trost-type ligands, the precatalysts in this work are the only reported examples of stable, isolable Pd(0) complexes with these ligands. Evaluating these precatalysts across nine asymmetric allylic alkylation reactions reveals high reactivity and selectivity at low Pd loading. Importantly, we also report an unprecedented Pd-catalyzed enantioselective allylation of a hydantoin, achieved on gram scale in high yield and enantioselectivity with only 0.2 mol% catalyst.

Dormancy and double-activation strategy for construction of high-performance mixed-matrix membranes.

Mixed-matrix membranes (MMMs) have the potential for energy-efficient gas separation by matching the superior mass transfer and anti-plasticization properties of the fillers with processability and scaling up features of the polymers. However, construction of high-performance MMMs has been prohibited due to low filler-loading and the existence of interfacial defects. Here, high MOF-loaded, i.e., 55 wt %, MMMs are developed by a 'dormancy and double-activation' (DDA) strategy. High MOF precursor concentration suppresses crystallization in the membrane casting solution, realizing molecular level mixing of all components. Then, the polymeric matrix was formed with uniform encapsulation of MOF nutrients. Subsequently, double-activation was employed to induce MOF crystallization: the alkali promotes MOFs nucleation to harvest small porous nanocrystals while excessive ligands activate the metal ions to enhance the MOFs conversion. As such, quasi-semi-continuous mass transfer channels can be formed in the MMMs by the connected MOFs nanocrystals to boost the gas permeability. The optimized MMM shows significantly ameliorated CO2 permeability, i.e., 2841 Barrer, five-fold enhancement compared with pristine polymer membrane, with a good CO2 /N2 selectivity of 36. Besides, the nanosized MOFs intensify their interaction with polymer chains, endowing the MMMs with good anti-plasticization behaviour and stability, which advances practical application of MMMs in carbon capture.

Dormancy and double‐activation strategy for construction of high‐performance mixed‐matrix membranes

AbstractMixed‐matrix membranes (MMMs) have the potential for energy‐efficient gas separation by matching the superior mass transfer and anti‐plasticization properties of the fillers with processability and scaling up features of the polymers. However, construction of high‐performance MMMs has been prohibited due to low filler‐loading and the existence of interfacial defects. Here, high MOF‐loaded, i.e., 55 wt %, MMMs are developed by a ‘dormancy and double‐activation’ (DDA) strategy. High MOF precursor concentration suppresses crystallization in the membrane casting solution, realizing molecular level mixing of all components. Then, the polymeric matrix was formed with uniform encapsulation of MOF nutrients. Subsequently, double‐activation was employed to induce MOF crystallization: the alkali promotes MOFs nucleation to harvest small porous nanocrystals while excessive ligands activate the metal ions to enhance the MOFs conversion. As such, quasi‐semi‐continuous mass transfer channels can be formed in the MMMs by the connected MOFs nanocrystals to boost the gas permeability. The optimized MMM shows significantly ameliorated CO2 permeability, i.e., 2841 Barrer, five‐fold enhancement compared with pristine polymer membrane, with a good CO2/N2 selectivity of 36. Besides, the nanosized MOFs intensify their interaction with polymer chains, endowing the MMMs with good anti‐plasticization behaviour and stability, which advances practical application of MMMs in carbon capture.

Decay-Associated Fluorescence for Boron Determination in Uranium-Based Nuclear Fuels.

Herein is reported a novel as well as simple, sensitive, and cost-effective method for determination of boron by time-resolved fluorescence spectrometry in uranium-based nuclear fuels. Boron is complexed with fluorescent ligand chromotropic acid, and the complex formed is a measure of boron. Since the steady-state fluorescence spectra of excess ligand and complex are overlapping, the developed method emphasizes the power of time resolution. The signatory fluorescence decay times of ligand and complex are employed to derive their decay-associated spectra (DAS) and, thereby, spectroscopically eliminate the high background of ligand fluorescence. The calibration plot has a wide linear dynamic range of 5-100 ppb with r2 better than 0.998. Precision is better than 5% at the 10 ppb level and 4% at the 50 ppb level (n = 9). The detection limit is 1.5 ppb, and recovery of spiked boron (25 ppb) from the uranium samples was better than 94%. The developed method was validated by analyzing U3O8-based ILCE Standards and applied to enriched uranium fuel samples. The main advantage of the developed method is a reduction in sample size requirement due to better sensitivity and selectivity. This in turn reduces the load of uranium recovery from analytical waste, especially in the case of enriched uranium samples. Additionally, it eliminates the need of organic solvents/medium.

Dynamically Tunable Assemblies of Superparamagnetic Nanoparticles Stabilized with Liquid Crystal-like Ligands in Organic Thin Films.

The process of arranging magnetic nanoparticles (MNPs) into long-range structures that can be dynamically and reversibly controlled is challenging, although interesting for emerging spintronic applications. Here, we report composites of MNPs in excess of LC-like ligands as promising materials for MNP-based technologies. The organic part ensures the assembly of MNP into long-range ordered phases as well as precise and temperature-reversible control over the arrangement. The dynamic changes are fully reversible, which we confirm using X-ray diffraction (XRD). This methodology allows for the precise control of the nanomaterial's structure in a thin film at different temperatures, translating to variable unit cell parameters. The composition of the materials (XPS, TGA), their structure (XRD), and magnetic properties (SQUID) were performed. Overall, this study confirms that LC-like materials provide the ability to dynamically control the magnetic nanoparticles in thin films, particularly the reversible control of their self-organization.

Cerium(IV) Pyrasal Complexes: A pH-Dependent 8- to 10-Coordinate Cerium Chelate Switch.

In this work, five cerium(IV) complexes were synthesized, three of which were structural isomorphs from the same pyrasal ligand with the solid-state result identified by structural analysis dependent on the initial pH of the reaction solution and the temperature at which the reaction is performed. The ligands explored here are pyrasal ligands, which are Schiff-base ligands formed by the condensation of 2,3-diaminopyrazine and a salicylaldehyde derivative. Pyrasal ligands have weaker binding than other salophen-type ligands due to the electron-withdrawing effect of the nitrogen atoms contained within the pyrazine ring. The weaker binding leaves the ligand more susceptible to the changes in pH and temperature that alternate the chelating environment from 8- to 10-coordinate. This electron-withdrawing effect of the pyrazine backbone also deactivates the second amine after the first condensation addition of salicylaldehyde. Without a metal to template the complex formation reaction, even with extended reaction times and the addition of a large excess of ligand, the result is the addition of only one salicylaldehyde.

PbS Colloidal Quantum Dots Infrared Solar Cells: Defect Information and Passivation Strategies

Large‐sized lead sulfide quantum dots (PbS QDs) offer strong absorption in the infrared, making them suitable for bottom cells in tandem devices. However, current QD‐based tandem devices underperform compared to single junction devices. This review focuses on defect information and passivation strategies in large‐sized QD solar cells. Defects from oxidation, polydispersity, and nonbonding sites on the (001) facet during QD synthesis are examined. Ligand‐exchange‐related defects such as tangled atoms, incomplete passivation, and excess ligands are analyzed. Surface and interface defects resulting from solar cell fabrication are also discussed. Strategies including cation exchange, thermodynamic growth, kinetic growth, and mixed halide ligands are summarized. Post‐treatment approaches could also help to address surface and interface defects. Large‐sized PbS‐QDs show promise as infrared radiation absorbers. Overcoming defects and implementing effective passivation strategies are crucial for single junction and tandem solar cells.

Factors Controlling Complex Morphologies of Isomorphous Metal-Organic Frameworks.

We demonstrate here how nitrate salts of bivalent copper, nickel, cobalt, and manganese, along with an achiral organic ligand, assemble into various structures such as symmetrical double-decker flowers, smooth elongated hexagonal bipyramids, and hexagonal prisms. Large morphological changes occur in these structures because of different metal cations, although they maintain isomorphous hexagonal crystallographic structures. Metal cations with stronger coordination to ligands (Cu and Ni) tend to form uniform crystals with unusual shapes, whereas weaker coordinating metal cations (Mn and Co) produce crystals with more regular hexagonal morphologies. The unusual flower-like crystals formed with copper nitrate have two pairs of six symmetrical petals with hexagonal convex centers. The texture of the petals indicates dendritic growth. Two different types of morphologies were formed by using different copper nitrate-to-ligand ratios. An excess of the metal salt results in uniform and hexagonal crystals having a narrow size distribution, whereas the use of an excess of ligand results in double-decker morphologies. Mechanistically, an intermediate structure was observed with slightly concave facets and a domed center. Such structures most likely play a key role in the formation of double-decker crystals that can be formed by fusion processes. The coordination chemistry results in isostructural chiral frameworks consisting of two types of continuous helical channels. Four pyridine units from four separate ligands are coordinated to the metal center in a plane having a chiral (propeller-type) arrangement. The individual double-decker flower crystals are homochiral and a batch consists of crystals having both handedness.