Anionic Ligands Research Articles

Evaluation of anticancer activities, apoptosis, molecular docking, and antioxidant studies of new Ni(II), VO(IV), Cu(II) and Co(III) Schiff base complexes

New Schiff base complexes have been synthesized via appropriate conventional methods using 2-ethoxy-6-(E)-[(prop-2-em-1-yl)imino]methylphenol (HL) as a Schiff base ligand. The compounds obtained were characterized by spectral analysis and X-ray diffraction. Recrystallization from methanol provided single crystals with rod-shaped (1) and rhombus-shaped (2) shapes. The complexes were found to be composed of NiL2 and (VO)L2, with the anionic ligand L- acting as a bidentate ligand, coordinating to metal centers via imino N and hydroxyl oxygen atoms in all cases. Compound (1) crystallizes in the orthorhombic system with the Pccn space group, while compound (2) crystallizes in the monoclinic system with the P21/n space group. Cyclic voltammetry experiments in DMF show a metal-centered reduction peak at (−1.23), (−1.32), (−0.82, 1.36), and (−0.61, −1.55) V, corresponding to the Ni II/NiI, VO2+/VO+, CuII/CuI, and CoIII/II-CoII/I, respectively. The complexes were evaluated for anticancer activity in a human tumor cell line (HT-29). 5-fluorouracil was used as a standard drug. All tested compounds of Schiff base ligand and complexes (1–4) showed anticancer activity with inhibitory concentration (IC50) values of 85.28(HL), 15.13(1), 10.83(2), 28.53(3) and 30.21(4) (μM), respectively. The in vitro cytotoxicity screening results revealed that all compounds showed promising activity against colorectal cancer. In particular, compounds (1) and (2) showed excellent activity against tumor cell lines. The antioxidant activity of the synthesized Schiff base was determined using the DPPH method (1, 1-diphenyl-2- picryl hydrazyl). The effective concentration (EC50) indicates that all compounds have good antioxidant activity (EC50 = 143.02(HL), 168.03(1), 27.31(2), 160.3(3) and 173.41(4). The biological activity spectra of synthesized compounds are predicted by the Pass Online Web Resource. In addition to the PASS program's prediction, molecular docking studies were also performed to find bind affinity to protein cyclooxygenase inhibitor (the structure PDB code 1CX2).

Solvothermal synthesis and crystal structures of two new cadmium coordination polymers containing polynitrile ligands

Two new coordination polymers of cadmium-containing polynitrile ligands have been synthesized using sovothermal methods. In both poly[trans,trans,trans-bis(μ-dicyanamido-κ2 N 1:N 3)bis(2-methylbenzimidazole-κN)cadmium(II)], [Cd(C2N3)2(C8H8N2)2] n , (I), and poly[trans,trans,trans-bis(2-methylbenzimidazole-κN)bis(μ-tricyanomethanido-κ2 N:N′)cadmium(II)], [Cd(C4N3)2(C8H8N2)2] n , (II), the Cd atom lies on a centre of inversion, in space groups P21/n and P21/c, respectively. In each polymer, each anionic ligand acts as a bridge between two metal centres, forming sheets of 24-membered rings, and in each structure a single N—H...N hydrogen bond links the polymer sheets to form a three-dimensional framework structure. Comparisons are made with the structures of some related complexes.

Crystal structure of bis{3-(3,5-dichlorophenyl)-5-[6-(1H-pyrazol-1-yl)pyridin-2-yl]-4H-1,2,4-triazol-4-ido}iron(II) methanol disolvate

The asymmetric unit of the title compound, [FeII(C16H9Cl2N6)2]·2CH3OH, consists of half of a charge-neutral complex molecule and a discrete methanol molecule. The planar anionic tridentate ligand 2-[5-(3,5-dichlorophenyl)-4H-1,2,4-triazol-3-ato]-6-(1H-pyrazol-1-yl)pyridine coordinates to the FeII ion through the N atoms of the pyrazole, pyridine and triazole groups, forming a coordination sphere of the central ion that deviates moderately from an octahedral geometry. The average Fe—N bond distance is 1.953 Å, indicating the low-spin state of the FeII ion. The cone-like-shaped molecules, nested into each other, are linked through double weak C—H(pz)...π(ph) interactions into mono-periodic columns, which are further linked through weak C—H...N′/C′ interactions into di-periodic layers. The layers interact through double weak C–H(ph)...Cl bonds with neighbouring molecules. Energy framework analysis at the B3LYP/6–31 G(d,p) theory level reproduces the strong interaction within the layers and the weaker interlayer interactions. Intermolecular contacts were quantified using Hirshfeld surface analysis and two-dimensional fingerprint plots, the relative contributions of the contacts to the crystal packing being H...H 26.1%, H...C/C...H 24.4%, H...Cl/Cl...H 18.9% and H...N/N...H 12.1%.

Catalytic desymmetrization of the mechanical bond

In the October issue of Chem , Chong Tian, Ye Zhu, and co-workers describe a post-synthetic catalyst-controlled desymmetrization strategy for synthesizing mechanically planar chiral rotaxanes by relying on distal ionic interactions between a prochiral rotaxane and a novel anionic chiral phosphine ligand to trigger a desymmetrizing Pd-catalyzed Suzuki-Miyaura coupling. In the October issue of Chem , Chong Tian, Ye Zhu, and co-workers describe a post-synthetic catalyst-controlled desymmetrization strategy for synthesizing mechanically planar chiral rotaxanes by relying on distal ionic interactions between a prochiral rotaxane and a novel anionic chiral phosphine ligand to trigger a desymmetrizing Pd-catalyzed Suzuki-Miyaura coupling.

Coordination polymers derived from magnesium and barium complexes of redox-active ligands

The reactions of monomeric complexes [(dpp-bian)M(THF)n](M = Mg, n = 3; M = Ba, n = 5; dpp-bian = 1,2-bis[(2,6-di-isopropylphenyl)imino]acenaphthene) with 4,4'-bipyridine (4,4'-bipy) in THF proceed with electron transfer from dpp- bian2– to 4,4'-bipy0 to afford 1D coordination polymers [(dpp-bian)M(4,4'-bipy)(THF)n]m (M = Mg, n = 1; M = Ba, n = 2) that contain simultaneously radical anion ligands dpp-bian– and 4,4'-bipy . Addition of DME to coordination polymer [(dpp-bian)Mg(4,4'-bipy)(THF)n]m results in fragmentation of polymeric chains to give dinuclear magnesium species [{(dpp-bian)Mg(DME)}2(4,4'-bipy)]. Barium analogue [{(dpp-bian)Ba(DME)2}2(4,4'-bipy)] has been prepared by reacting of complex [(dpp-bian)Ba(DME)2.5] with 4,4'-bipy in DME.

Deciphering competing radiative relaxation pathways observed in Pr3+-Activated yttrium-based compounds: UV emission versus visible emission

Pr3+-activated yttrium-based compounds have garnered significant research interest as the electronic transition of Pr3+ dopant incorporated in host lattices are quite versatile, giving rise to the production of either UV or visible electromagnetic radiation. The tunable 5d orbital energy level of Pr3+ with an electronic configuration [Xe]4f15d1 depending on the external crystal fields, coordinating anion ligands (mainly determined by covalency of anion ligands), and symmetry of crystal structures can indeed control the radiative decay processes whether to generate UV or self-trapped exciton-mediated visible emission. We have investigated three different Pr3+-activated crystals of YPO4, YBO3, and Y2SiO5 using two different excitation processes including direct host lattice excitation (cathodoluminescence: CL) and f-d excitation of Pr3+ dopants (photoluminescence: PL). Such radiative decay mechanism observed in Pr3+-doped yttrium-based compounds has been deciphered that photoexcitation of Pr3+ ions results in 4f15d1→4f2 electronic transition with UV emission (PL) whereas above-bandgap excitation of host lattices brings about the efficient production of visible emission mediated through self-trapped excitons (CL). When changing the anion sublattices, the emission peak corresponding to 4f15d1→4f2 transition shifted to longer wavelength as a result of modulated covalency and crystal field strength. As the host lattices changes as a function of anion sublattices, the bandgap reduced from 8.6 eV (for YPO4) to 7.6 eV (for YBO3) and to 6.1 eV (for Y2SiO5), directly influencing rate of trapping of exciton and their formation of self-trapped exciton, which further give rise to production of the self-trapped exciton mediated visible emission. The fundamental understanding of the multiple, radiative relaxation pathways provides a designing principle for achieving more efficient UV emitting phosphors (at the same time by suppressing visible emission or vice versa) for germicidal and medical applications.

Chelate Coordination Strengthens Surface Termination to Attain High-Efficiency Perovskite Solar Cells.

Solar cell efficiency and stability are two key metrics to determine whether a photovoltaic device is viable for commercial applications. The surface termination of the perovskite layer plays a pivotal role in not only the photoelectric conversion efficiency (PCE) but also the stability of assembled perovskite solar cells (PSCs). Herein, a strong chelate coordination bond is designed to terminate the surface of the perovskite absorber layer. On the one hand, the ligand anions bind with Pb cations via a bidentate chelating bond to restrict the ion migration, and the chelate surface termination changes the surface from hydrophilic to hydrophobic. Both are beneficial to improving the long-term stability. On the other hand, the formation of the chelating bonding effectively eliminates the deep-level defects including PbI and Pb clusters on the Pb-I and FA-I terminations, respectively, as confirmed by theoretical simulation and experimental results. Consequently, the PCE is increased to 24.52%, open circuit voltage to 1.19V, and fill factor to 81.53%; all three are among the highest for hybrid perovskite cells. The present strategy provides a straightforward means to enhance both the PCE and long-term stability of PSCs.

Front Cover: H‐Bonded Counterion‐Directed Catalysis: Enantioselective Gold(I)‐Catalyzed Addition to 2‐Alkynyl Enones as a Case Study (Eur. J. Org. Chem. 42/2022)

The Front Cover illustrates the ability of the squaramide group to remove a chiral anionic ligand from Au(I) by H-bonding interactions, by analogy with a magnet that attracts a metallic sphere. H-bonded counterion-directed catalysis was used to perform an enantioselective tandem cycloisomerization-nucleophile addition to 2-alkynyl enones. More information can be found in the Research Article by A. M. Echavarren, A. Franchino et al.

The Elusive Mononitrosylated [Fe4S4] Cluster in Three Redox States

AbstractIron‐sulfur clusters are well‐established targets in biological nitric oxide (NO) chemistry, but the key intermediate in these processes—a mononitrosylated [Fe4S4] cluster—has not been fully characterized in a protein or a synthetic model thereof. Here, we report the synthesis of a three‐member redox series of isostructural mononitrosylated [Fe4S4] clusters. Mononitrosylation was achieved by binding NO to a 3 : 1 site‐differentiated [Fe4S4]+ cluster; subsequent oxidation and reduction afforded the other members of the series. All three clusters feature a local high‐spin Fe3+ center antiferromagnetically coupled to 3[NO]−. The observation of an anionic NO ligand suggests that NO binding is accompanied by formal electron transfer from the cluster to NO. Preliminary reactivity studies with the monocationic cluster demonstrate that exposure to excess NO degrades the cluster, supporting the intermediacy of mononitrosylated intermediates in NO sensing/signaling.

The Elusive Mononitrosylated [Fe4 S4 ] Cluster in Three Redox States.

Iron-sulfur clusters are well-established targets in biological nitric oxide (NO) chemistry, but the key intermediate in these processes-a mononitrosylated [Fe4 S4 ] cluster-has not been fully characterized in a protein or a synthetic model thereof. Here, we report the synthesis of a three-member redox series of isostructural mononitrosylated [Fe4 S4 ] clusters. Mononitrosylation was achieved by binding NO to a 3 : 1 site-differentiated [Fe4 S4 ]+ cluster; subsequent oxidation and reduction afforded the other members of the series. All three clusters feature a local high-spin Fe3+ center antiferromagnetically coupled to 3 [NO]- . The observation of an anionic NO ligand suggests that NO binding is accompanied by formal electron transfer from the cluster to NO. Preliminary reactivity studies with the monocationic cluster demonstrate that exposure to excess NO degrades the cluster, supporting the intermediacy of mononitrosylated intermediates in NO sensing/signaling.

Crystal structure of bis-{3-(3,4-di-methyl-phen-yl)-5-[6-(1H-pyrazol-1-yl)pyridin-2-yl]-4H-1,2,4-triazol-4-ido}iron(II) methanol disolvate.

As a result of the high symmetry of the Aea2 structure, the asymmetric unit of the title compound, [FeII(C18H15N6)2]·2MeOH, consists of half of a charge-neutral complex mol-ecule and a discrete methanol mol-ecule. The planar anionic tridentate ligand 2-[5-(3,4-di-methyl-phen-yl)-4H-1,2,4-triazol-3-ato]-6-(1H-pyrazol-1-yl)pyridine coordinates the FeII ion meridionally through the N atoms of the pyrazole, pyridine and triazole groups, forming a pseudo-octa-hedral coordination sphere of the central ion. The average Fe-N bond distance is 1.955 Å, indicating a low-spin state of the FeII ion. Neighbouring cone-shaped mol-ecules, nested into each other, are linked through double weak C-H(pz)⋯π(ph') inter-actions into mono-periodic columns, which are further linked through weak C-H⋯N'/C' inter-actions into di-periodic layers. No inter-actions shorter than the sum of the van der Waals radii of the neighbouring layers are observed. Energy framework analysis at the B3LYP/6-31 G(d,p) theory level, performed to qu-antify the inter-molecular inter-action energies, reproduces the weak inter-layer inter-actions in contrast to the strong inter-action within the layers. Inter-molecular contacts were qu-anti-fied using Hirshfeld surface analysis and two-dimensional fingerprint plots, showing the relative contributions of the contacts to the crystal packing to be H⋯H 48.5%, H⋯C/C⋯H 28.9%, H⋯N/N⋯H 16.2% and C⋯C 2.4%.

Study on Fundamental Properties of Solvate Electrolytes and Their Application in Batteries

Li salts and polar solvents form solvates, and certain solvates have low melting temperatures and remain in a liquid state at room temperature. Liquid-state solvates exhibit ionic conductivity and can be used as electrolytes in lithium batteries. The author and co-workers have systematically studied the interactions of Li+ ions with solvents and anions, Li+-coordination structures, thermal properties, transport properties, and electrochemical properties in molten-solvate electrolytes. In molten solvates, almost all solvent molecules are coordinated to Li+ ions, and uncoordinated (free) solvents are rare. Additionally, anions are involved in the coordination of the Li+ ions. The molten solvate electrolytes show non-flammability and negligible vapor pressure at room temperature because of the extremely low concentration (activity) of the free solvent, which can improve the thermal stability of Li batteries. The low activity of the free solvent results in a wide electrochemical window of the molten-solvate electrolytes, thereby suppressing undesired side reactions in Li batteries. The activity of the free solvent in the electrolytes significantly affects the electrochemical reaction processes, such as the reduction reaction of sulfur (S8) in a Li–S battery and the oxygen reduction reaction (ORR) in a Li–air battery. The solubility of the reaction intermediates of the S8 cathode and the ORR decreases with the decrease in solvent activity, which enables the highly efficient charge–discharge of Li–S and Li–air batteries. In molten solvates, Li+ ions diffuse and migrate by exchanging ligands (solvents and anions). Certain molten-solvate electrolytes show high Li+ ion transference numbers over 0.5, and these high transference numbers are useful in mitigating the concentration overpotential during the charging and discharging of Li batteries at high current densities.

Origin of the Second-Order Proton Catalysis of Ferriin Reduction in Belousov-Zhabotinsky Reactions: Density Functional Studies of Ferroin and Ferriin Aggregates with Outer Sphere Ligands Sulfate, Bisulfate, and Sulfuric Acid.

The detailed mechanisms of Belousov-Zhabotinsky oscillating reactions continue to present grand challenges, even after half a century of study. The origin of the pH dependence of the oscillation pattern had never been rigorously identified. In our recent kinetic study of one of the key Belousov-Zhabotinsky reactions, the iron-catalyzed bromate oxidation of malonic acid, compelling agreement between experiments and kinetic simulations was achieved only with the inclusion of second-order proton catalysis of the reduction of the [Fe(phen)3]3+ species. After exhausting all other avenues in search of an explanation of this proton catalysis, we considered the possibility that the parent iron-phenanthroline complexes could aggregate with neutral and anionic outer sphere ligands (OSLs) in the highly concentrated sulfuric acid solution, and we hypothesized that OSL protonation would increase the capacity of the aggregated complex to oxidize the organic fuel. We performed potential energy surface analyses at the SMD(APFD/6-311G*) level of complexes of the types [Fe(phen)3(SO42-)m(HSO4-)n(H2SO4)o](c-2m-n)+ for ferriin (c = 3) and ferroin (c = 2) aggregated with m sulfate, n bisulfate, and o sulfuric acid OSLs. We present structures of the OSL aggregates, develop a nomenclature for their description, and characterize their electronic structure. The structural chemistry provides the foundation to discuss the ferroin/ferriin redox couple with emphasis on the relationship between the vertical electron affinities of ferriin aggregates and their OSL protonation states. For proton catalysis to manifest itself, double-protonation paths that are slightly endergonic should be present, and proton affinities of aggregated OSLs allow the identification of such double-protonation chains. As a first test of our mechanistic proposal for the second-order proton catalysis of the Belousov-Zhabotinsky reaction, the results presented here provide compelling evidence in support of the importance of outer sphere ligation of the iron catalyst.

Three-Dimensional Metal-Organic Network Glasses from Bridging MF62- Anions and Their Dynamic Insights by Solid-State NMR.

Glassy-state coordination polymers (CPs) are a new class of network-forming glasses. In this work, we constructed glass-forming CPs composed of both anionic and neutral ligands as network formers. With the use of hexafluoro anions (MF62-) and 1,3-bis(4-pyridyl)propane (bpp), two isostructural CP crystals, [Zn(SiF6)(bpp)2] (ZnSi) and [Zn(TiF6)(bpp)2] (ZnTi), were synthesized. Solid-state 19F NMR revealed rotational motion of MF62- with dissociation and re-formation of the Zn-F coordination bonds in both CP crystals, which reflects the thermodynamic parameters related to the glass formability. The mobility of SiF62- is larger than that of TiF62-, suggesting a higher glass formability of ZnSi. When mechanical ball milling was conducted, ZnSi completely changed into a glassy state, whereas ZnTi showed incomplete glass formation. Examination of the amorphous structures elucidated retention and partial destruction of the Zn-F coordination bonds in ball-milled ZnSi and ZnTi, respectively. These results provide the relationship between the ligand dynamics and glass formability of CPs.

Effects of a triangular nanocage structure on the binding of neutral and anionic ligands to CoII and ZnII porphyrins

Interactions of neutral pyridine ligands and anionic benzoate ligands with the metalloporphyrin walls of M6L3 nanocages (M = [(tmeda)Pt]2+, L = tetra(3-pyridyl)porphyrin-M′, M′ = CoII, Co3-1; ZnII, Zn3-1) were evaluated in CD3CN. The binding of ligands to simple tetra(N-methyl-3-pyridinium)porphyrin-M′ complexes Co-2 and Zn-2 was also evaluated. It was found that pyridine ligands bind with generally similar strength to the monomeric porphyrins as to the outer faces of the corresponding cage. Coordination is enhanced inside the cages for the binding of one equivalent of pyridine, 3-methylpyridine, or 3,5-dimethylpyridine. In contrast, 4-(4′-methoxyphenyl)pyridine cannot bind inside the cages, and 4-methylpyridine shows weaker binding inside than outside. Steric effects play a complex role in influencing ligand binding since 4-tert-butylpyridine binds more strongly in the cages than 4-methylpyridine. These latter two ligands also reveal a subtle allosteric effect in which binding of ligands inside Zn3-1 becomes increasingly favored over external binding once some of the external sites are occupied. It was confirmed that benzoate and 3,5-di-tert-butylbenzoate can also coordinate to the walls of M3-1, but quantitative analysis of these interactions was complicated by competing affinity of the anions for other sites of the cages, limiting detailed insight.

Enantiodivergent epoxidation of alkenes with a photoswitchable phosphate manganese-salen complex.

The development of enantiodivergent catalysts capable of preparing both enantiomeric products from one substrate in a controlled fashion is challenging. Introducing a switching function into the catalyst can address this challenge, allowing the chiral reaction environment to reversibly change during catalysis. Here we report a photoswitchable phosphate ligand, derived from 2,2'-biphenol, which axially coordinates as the counter ion to an achiral manganese(III) salen catalyst, providing the latter with the ability to switch stereoselectivity in the epoxidation of alkenes. The enantiomers of the chiral ligand exist as a pair of pseudo-enantiomers, which can be interconverted by irradiation with light of different wavelengths. The opposite axial chirality of these pseudo-enantiomers is efficiently transferred to the manganese(III) salen catalyst. With this switchable supramolecular catalyst, the enantioselectivity of the epoxidation of a variety of alkenes can be controlled, resulting in opposite enantiomeric excesses of the epoxide products. This transfer of chirality from a photoswitchable anionic ligand to a metal complex broadens the scope of supramolecular catalysts.

Trivalent Cobalt Complexes with NNS Tridentate Thiosemicarbazones: Preparation, Structural Study and Investigation of Antibacterial Activity and Cytotoxicity against Human Breast Cancer Cells

New complexes of trivalent cobalt with substituted thiosemicarbazone ligands having an NNS donor system {HL1 = 4-(4-nitrophenyl)-1-((pyridin-2-yl)methylene)thiosemicarbazide and HL2 = 4-(2,5-dimethoxyphenyl)-1-((pyridin-2-yl)methylene)thiosemicarbazide} were synthesized via the in situ oxidation of divalent cobalt chloride accompanying its addition to the ligands. The complexes C1 and C2 were characterized via elemental (CHNS) analysis and 1H NMR, FT-IR and UV-Vis. spectroscopic data. Further, conductometric studies on the DMF solutions of the complexes indicated their 1:1 nature, and their diamagnetism revealed the low-spin trivalent oxidation state of the cobalt in the complexes. The X-ray diffraction analysis of complex C1 indicated that it crystallizes in the triclinic space group P-1. The metal exhibits an octahedral environment built by two anionic ligands bound via pyridine nitrogen, imine nitrogen and thiol sulfur atoms. The complex is counterbalanced by a chloride ion. In addition, two lattice water molecules were detected in the asymmetric unit of the unit cell. The ligand HL2 (20 mg/mL in DMSO) displayed inhibition zones of 10 mm against both S. aureus and E. coli, and the same concentration of the respective complex raised this activity to 15 and 12 mm against these bacterial strains, respectively. As a comparison, ampicillin inhibited these bacterial strains by 21 and 25 mm, respectively. Screening assay by HL1 on four human cancer cells revealed the most enhanced activity against the breast MCF-7 cells. The induced growth inhibitions in the MCF-7 cells by all compounds (0–100 μg/mL) have been detected. The ligands {HL1 and HL2} and complex C2 gave inhibitions with IC50 values of 52.4, 145.4 and 49.9 μM, respectively. These results are more meaningful in comparison with similar cobalt complexes, but less efficient compared with the inhibition with IC50 of 9.66 μM afforded by doxorubicin. In addition, doxorubicin, HL1 and HL2 induced cytotoxicity towards healthy BHK cells with IC50 values of 36.42, 54.8 and 110.6 μM, but surviving fractions of 66.1% and 62.7% of these cells were detected corresponding to a concentration of 100 μg/mL of the complexes (136.8 μM of C1 and 131.4 μM of C2).

Triggering of Valence Tautomeric Transitions in Dioxolene-Based Cobalt Complexes Influenced by Ligand Substituents, Co-ligands, and Anions

We report the multistep synthesis of the 1,1′-(piperazine-1,4-diyl)bis(N,N-bis(pyridin-2-ylmethyl)methanamine)(Ltpbap) octadentate ligand, which, in combination with the known 3,5-di-tert-butylcatechol (3,5-dbcat), allowed the preparation of two di-nuclear cobalt complexes [Co2(Ltpbap)(3,5-dbcat)2](SO4)·5.5MeOH·2H2O (3a) and [Co2(Ltpbap)(3,5-dbcat)2 ](ClO4)2·1.5H2O (3b). We also report the synthesis of two mono-nuclear cobalt complexes [Co(3,5-dbsq)(3,5-dbcat)(4-Mepip)2] (1) with 4-Mepip being 4-methylpiperidine and (Hpip)[Co(tbcat)2(pip)2]·CH3CN (2) where Hpip denotes a piperidinium cation and tbcat is the tetra-bromocatechol ligand. The obtained complexes were characterized by single-crystal X-ray crystallography, SQUID magnetometry, and IR spectroscopy. The structure of the crystalline material in all the cases was determined at 173 K. The magnetic properties of all complexes were measured between 2 and 380 K. The magnetic data clearly show that mono-nuclear complex 1 and di-nuclear complex 3a exhibit valence tautomerism with onset around 300 K and 370 K, respectively, whereas the other two complexes 2 and 3b remain unchanged over the measured temperature range.

Mechanically planar chiral rotaxanes through catalytic desymmetrization

<h2>Summary</h2> Establishing mechanical chirality has remained a substantial synthetic hurdle despite the fast-growing applications of interlocked architectures in supramolecular chemistry. Here, we report the development of a catalyst-controlled desymmetrization strategy that decouples the creation of mechanically planar chirality and assembly of interlocked bonds. Employing a novel class of anionic chiral phosphine ligands, the Pd-catalyzed Suzuki-Miyaura reactions enable enantioselective access to various mechanically planar chiral rotaxanes. This study demonstrates that precise catalytic stereocontrol over mechanical chirality is achievable by engaging distal ionic substrate-catalyst interactions, despite the noncovalent nature of the interlocking stereogenic elements.

Ligand Effect in 1-Octanethiol Passivation of InP/ZnSe/ZnS Quantum Dots-Evidence of Incomplete Surface Passivation during Synthesis.

The lack of anionic carboxylate ligands on the surface of InP/ZnSe/ZnS quantum dots (QDs), where zinc carboxylate ligands can be converted to carboxylic acid or carboxylate ligands via proton transfer by 1-octanethiol, is demonstrated. The as-synthesized QDs initially have an under-coordinated vacancy surface, which is passivated by solvent ligands such as ethanol and acetone. Upon exposure of 1-octanethiol to the QD surface, 1-octanethiol effectively induces the surface binding of anionic carboxylate ligands (derived from zinc carboxylate ligands) by proton transfer, which consequently exchanges ethanol and acetone ligands that bind on the incomplete QD surface. These systematic chemical analyses, such as thermogravimetric analysis-mass spectrometry and proton nuclear magnetic resonance spectroscopy, directly show the interplay of surface ligands, and it associates with QD light-emitting diodes (QD-LEDs). It is believed that this better understanding can lead to industrially feasible QD-LEDs.