Simultaneously resolving BINOL and proline using a stoichiometric cocrystal switch.

We here highlight the importance of stoichiometry for simultaneous cocrystal resolution. Focusing on combining the racemates of binol and proline, we show that a 1 : 2 ratio leads to formation of a full racemic compound, whereas a 2 : 1 ratio, leads to conglomerate formation, with simultaneous resolution of both binol and proline. Playing on stoichiometry, one achieves a reversible switch between the racemic compound and conglomerate. This is the first investigation of such behavior combining two racemates.

Synthesis, Crystal Structures, Genotoxicity, and Antifungal and Antibacterial Studies of Ni(II) and Cd(II) Pyrazole Amide Coordination Complexes.

In this study, we synthesized two coordination complexes based on pyrazole-based ligands, namely 1,5-dimethyl-N-phenyl-1H-pyrazole-3-carboxamide (L1) and 1,5-dimethyl-N-propyl-1H-pyrazole-3-carboxamide (L2), with the aim to investigate bio-inorganic properties. Their crystal structures revealed a mononuclear complex [Ni(L1)2](ClO4)2 (C1) and a dinuclear complex [Cd2(L2)2]Cl4 (C2). Very competitive antifungal and anti-Fusarium activities were found compared to the reference standard cycloheximide. Additionally, L1 and L2 present very weak genotoxicity in contrast to the observed increase in genotoxicity for the coordination complexes C1 and C2.

Spin-state versatility in FeII4L6 supramolecular cages with a pyridyl-hydrazone ligand scaffold modulated by solvents and counter anions.

Discrete spin crossover (SCO) tetranuclear cages are a unique class of materials that have potential use in next-generation molecular recognition and sensing. In this work, two new edge-bridged SCO FeII4L6 (L = 2,7-bis(((E)-pyridin-2-ylmethylene)amino)benzo[lmn] [3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone) supramolecular cages with different counter anions: ClO4- (2) and CF3SO3- (3) were constructed via subcomponent self-assembly to investigate both solvent and anion influences on their magnetic properties and compare them to cage 1 with a BF4- anion. Pyridyl-hydrazone bidentate ligand scaffolds were employed to replace the 'classical' imidazole/thiazolyl-imine coordination units to induce SCO behaviour in these cages. 2 and 3 were structurally characterized by single-crystal X-ray diffraction analysis and electrospray ionization time-of-flight mass spectrometry. Magnetic susceptibilities of 1-3 and 1-3·desolvated indicate that the solvents' presence is in favor of the low-spin (LS) state. While different counter anions in 1-3·desolvated affect the spin-state configurations of the four FeII metal centers. According to the 57Fe Mössbauer spectral analysis, the spin-state distributions in 1-3 at 80 K are [2 high-spin (HS)-2LS], [1HS-3LS] and [2HS-2LS], respectively and density functional theory calculations were employed to investigate the reasons. These findings provide insights to regulate the spin-state versatility of SCO FeII cage systems in the solid state.

Coordination Complexes Built from a Ditopic Triazole-Pyrazole Ligand with Antibacterial and Antifungal Performances.

Four mononuclear complexes (H3O){[NiL3](ClO4)3} (1), [CoL3](ClO4)2·2H2O (2), [CdL2Cl2] (3) and [CuL3](NO3)2 (4) have been prepared employing a newly synthesized 1,2,4-triazole ligand: 3-(3,5-dimethyl-1H-pyrazol-1-yl)-1H-1,2,4-triazole (L). The structures of the complexes, which crystallized in P63/m (1), P-1 (2), P1 (3), and P21/c (4), are reviewed within the context of the cooperative effect of the hydrogen bonding network and counter anions on the supramolecular formations. Moreover, within the framework of biological activity examination, these compounds showed favorable antibacterial performances compared to those of various species of bacteria, including both Gram-positive and Gram-negative strains. Significant antifungal inhibitory activity towards Fusarium oxysporum f. sp. albedinis fungi was recorded for 3 and 4 over the ligand L.

Modular metallotecton for engineering permanently porous frameworks: supernumerary role of ancillary ion.

The formation of robust supramolecular frameworks built from hetero-polytopic metal complexes and interacting with different ancillary ions remains a long-standing and underexplored desire. Herein, the secondary sphere interaction chemistry of [Ru(5-oxido-6-hydroxy-1,10-phenanthroline)a(5,6-dihydroxy-1,10-phenanthroline)(3-a)]-(a-2) (1) (a = 1, 3) coordination ion is reported, where the π-conjugated phenanthroline ligands are functionalized with catecholate groups used as H-bond donors and ligands. The deprotonation of the catechols is found to control the overall charge stoichiometry in 1, acting as a metallotecton to interact with anions of different basicity (Cl- in 1.Cl and Br- in 1.Br) as well as with Li+ cations (in 1.Li+). These interactions lead to the formation of 2D porous honeycomb networks without any significant alteration in the molecular packing. This implies that the self-assembly process is controlled by complementary intermolecular non-covalent interactions making the choice of the ancillary ion insignificant. The robust porous structure of the frameworks is established by uptake of D2O and I2 molecules within the microporous channels. This work demonstrates that supramolecular frameworks appear as flexible candidates for applications in gas sorption, separation and chemical sensing.

Formation, Reactivity, and Catalytic Behavior of a Keggin Polyoxometalate/Bipyridine Hybrid in the Epoxidation of Cyclooctene with H2O2.

The present study further explores the behavior of polyoxometalate-based hybrid compounds as catalysts for liquid-phase cyclooctene epoxidation with H2O2. Precisely, it unveils the nature of the relevant active species derived from the hybrid based on Keggin polyoxometalate (POM) and bipyridines (bpy) of formula (2,2'-Hbpy)3[PW12O40] (1). Whereas (i) it is generally accepted that the catalytic oxidation of organic substrates by H2O2 involving Keggin HPAs proceeds via an oxygen transfer route from a peroxo intermediate and (ii) the catalytically active peroxo species is commonly postulated to be the polyperoxotungstate {PO4[W(O)(O2)2]4}3- complex (PW4), we show that the studied epoxidation reaction seems to be more sophisticated than commonly reported. During the catalytic epoxidation, 1 underwent a partial transformation into two oxidized species, 2 and 3. Compound 3 corresponding to 2,2'-bipyridinium oxodiperoxotungstate of formula [WO(O2)2(2,2'-bpy)] was shown to be the main species responsible for the selective epoxidation of cyclooctene since 2 (in which the POM is associated with a protonated mono-N-oxide derivative of 2,2'-bpy of formula (2,2'-HbpyO)3[PW12O40]) exhibited no activity. The structures of 1, 2, and 3 were solved by single-crystal X-ray diffraction and were independently synthesized. The speciation of 1 was monitored under catalytic conditions by 1H and 1H DOSY NMR spectroscopies, where the formation in situ of 2 and 3 was revealed. A reaction mechanism is proposed that highlights the pivotal, yet often underestimated, role of H2O2 in the reached catalytic performances. The active species responsible for the oxygen transfer to cyclooctene is a hydroperoxide intermediate species that is formed by the interaction between the anionic structure of the catalyst and H2O2. The latter operates as a "conservative agent" whose presence in the catalytic system is required to prevent the catalysts from deactivating irreversibly.

Revealing the reversible solid-state electrochemistry of lithium-containing conjugated oximates for organic batteries.

In the rising advent of organic Li-ion positive electrode materials with increased energy content, chemistries with high redox potential and intrinsic oxidation stability remain a challenge. Here, we report the solid-phase reversible electrochemistry of the oximate organic redox functionality. The disclosed oximate chemistries, including cyclic, acyclic, aliphatic, and tetra-functional stereotypes, uncover the complex interplay between the molecular structure and the electroactivity. Among the exotic features, the most appealing one is the reversible electrochemical polymerization accompanying the charge storage process in solid phase, through intermolecular azodioxy bond coupling. The best-performing oximate delivers a high reversible capacity of 350 mAh g-1 at an average potential of 3.0 versus Li+/Li0, attaining 1 kWh kg-1 specific energy content at the material level metric. This work ascertains a strong link between electrochemistry, organic chemistry, and battery science by emphasizing on how different phases, mechanisms, and performances can be accessed using a single chemical functionality.

Structural insight into the magnesium borohydride - ethylenediamine solid-state Mg-ion electrolyte system.

A highly complex crystal structure of stoichiometric Mg5(en)6(BH4)10 was solved from single crystal synchrotron X-ray diffraction and confirmed by neutron powder diffraction (NPD) on isotopically substituted Mg(en)1.2(11BD4)2. We highlight the role of the amorphous Mg(BH4)2 in the reactivity of the Mg(BH4)2-en system and characterized a previously overlooked phase, Mg(en)2(BH4)2.

High performance Li-, Na-, and K-ion storage in electrically conducting coordination polymers.

Coordination polymers (CPs) made of redox-active organic moieties and metal ions emerge as an important class of electroactive materials for battery applications. However, the design and synthesis of high voltage alkali-cation reservoir anionic CPs remains challenging, hindering their practical applications. Herein, we report a family of electrically conducting alkali-cation reservoir CPs with the general formula of A2-TM-PTtSA (wherein A = Li+, Na+, or K+; TM = Fe2+, Co2+, or Mn2+; and PTtSA = benzene-1,2,4,5-tetra-methylsulfonamide). The incorporation of transition metal centers not only enables intrinsic high electrical conductivity, but also shows an impressive redox potential increase of as high as 1 V as compared to A4-PTtSA analogues, resulting in a class of organometallic cathode materials with a high average redox potential of 2.95-3.25 V for Li-, Na- and K-ion batteries. A detailed structure - composition - physicochemical properties - performance correlation study is provided relying on experimental and computational analysis. The best performing candidate shows excellent rate capability (86% of the nominal capacity retained at 10C rate), remarkable cycling stability (96.5% after 1000 cycles), outstanding tolerance to low carbon content (5 wt%), high mass loading (50 mg cm-2), and extreme utilisation conditions of low earth orbit space environment tests. The significance of the disclosed alkali-ion reservoir cathodes is further emphasized by utilizing conventional Li-host graphite anode for full cell assembly, attaining a record voltage of 3 V in an organic cathode Li-ion proof-of-concept cell.

A spin crossover FeII4L6 cage based on pyridyl-hydrazone sites.

Reported here is the first FeII based supramolecular cage with pyridyl-hydrazone ligand scaffolds that exhibits temperature induced spin crossover behaviour. Density functional theory calculations were employed to investigate the cause of the occurrence of this phenomenon based on the ligand structure. These results indicate that the reported low-spin cages with pyridyl-imine sites could be reconsidered for spin crossover by carefully manipulating the functional groups in the ligand system.

Complexation: An Interesting Pathway for Combining Two APIs at the Solid State.

Combining different drugs into a single crystal form is one of the current challenges in crystal engineering, with the number of reported multi-drug solid forms remaining limited. This paper builds upon an efficient approach to combining Active Pharmaceutical Ingredients (APIs) containing carboxylic groups in their structure with APIs containing pyridine moieties. By transforming the former into their zinc salts, they can be successfully combined with the pyridine-containing APIs. This work highlights the successfulness of this approach, as well as the improvement in the physical properties of the obtained solid forms.

L-Proline, a resolution agent able to target both enantiomers of mandelic acid: an exciting case of stoichiometry controlled chiral resolution.

We present a thought-provoking development in chiral resolution. Using a resolving agent of a given handedness, L-proline, we show that both R- and S-enantiomers of mandelic acid can be resolved from a racemic mixture simply by varying the stoichiometry. We are the first to report this specific feature, achieved by the existence of stoichiometrically diverse cocrystal systems between R- and S-mandelic acid and L-proline.

Synthesis, Structure, and Thermal Stability of a Mesoporous Titanium(III) Amine-Containing MOF.

The first mesoporous bimetallic TiIII/Al metal-organic framework (MOF) containing amine functionalities on its linkers has been selectively obtained by converting the cheap commercially available (TiCl3)3AlCl3 into Ti3-xAlxCl3(THF)3 and reacting this complex with 2-aminoterephthalic acid in dimethylformamide (DMF) under soft solvothermal conditions. This compound is structurally related to the previously described NH2-MIL-101(M) (M = Cr, Al, and Fe) MOFs. Thermal gravimetric analyses and in situ powder X-ray diffraction (PXRD) measurements demonstrated that this highly air-sensitive TiIII-containing MOF is structurally stable up to 200 °C. Nuclear magnetic resonance (NMR) spectroscopy, elemental analysis, and inductively coupled plasma (ICP) revealed that NH2-MIL-101(TiIII) contains trinuclear Ti3(µ3-O)Cl(DMF)2(RCOO)6 clusters with strongly bound DMF molecules and a small amount of aluminum. Sorption experiments revealed a higher affinity of this MOF for hydrogen compared to the previously described monometallic unfunctionalized MIL-101(TiIII) MOF.

New Cathode Materials in the Fe-PO4 -F Chemical Space for High-Performance Sodium-Ion Storage.

Sodium and iron make up the perfect combination for the growing demand for sustainable energy storage systems, given the natural abundance and sustainability of the two building block elements. However, most sodium-iron electrode chemistries are plagued by intrinsic low energy densities with continuous ongoing efforts to solve this. Herein, the chemical space of a series of (meta)stable, off-stoichiometric Fe-PO4 -F phases is analyzed. Some are found to display markedly improved electrochemical activity for sodium storage, as compared to the amorphous or thermodynamically stable phases of equivalent composition. The metastable crystalline Na1.2 Fe1.2 PO4 F0.6 delivers a reversible capacity of more than 140 mAh g-1 with an average discharge potential of 2.9 V (vs Na+ /Na0 ) resulting in a practical specific energy density of 400 Wh kg-1 (estimated at the material level), outperforming many developed Fe-PO4 analogs thus far, with further multiple possibilities to be explored toward improved energy storage metrics. Overall, this study unlocks the possibilities of off-stoichiometric Fe-PO4 -F cathode materials and reveals the importance to explore the oft-overlooked metastable or transient state materials for energy storage.

Functionalization of Mono- and Bimetallic MIL-100(Al,Fe) MOFs by Ethylenediamine: Postfunctionalization, Brønsted Acido-Basicity, and Unusual CO2 Sorption Behavior.

The metal sites of MIL-100(Fe), MIL-100(Fe,Al), and MIL-100(Al) metal-organic frameworks (MOFs) were decorated with ethylenediamine (EN). Interestingly, the Al-containing MOFs presented hierarchized porosity, and their structural integrity was maintained upon functionalization. Solution and solid-state NMR confirmed the grafting efficiency in the case of MIL-100(Al) and the presence of a free amine group. It was shown that MIL-100(Al) can be functionalized by only one EN molecule in each trimeric Al3O cluster unit, whereas the other two aluminum sites are occupied by a hydroxyl and a water molecule. The -NH2 sites of the grafted ethylenediamine can be used for further postfunctionalization through amine chemistry and are responsible for the basicity of the functionalized material as well as increased affinity for CO2. Furthermore, the presence of coordinated water molecules on the Al-MOF is responsible for simultaneous Brønsted acidity. Finally, the Al-containing MOFs show an unusual carbon dioxide sorption mechanism at high pressures that distinguishes those materials from their iron and chromium counterparts and is suspected to be due to the presence of polarized Al-OH bonds.

Functionalized 1,8-Diazaiptycenes as Monomers for Aromatic Oligoamide Foldamers.

Diversification of the structures and the applications possible for foldamers rely on expansion of the building block library available for their synthesis. In this work, we describe the synthesis of a range of three dimensional heteroaromatic monomers, based on iptycene scaffolds, that are suitable for the synthesis of aromatic oligoamide foldamers. These units can be obtained in gram quantities in up to 80 % yield through [4+2] cycloaddition between diester, diamine, and amino acid derivatives of 1,8-diazaanthracenes and a variety of dienophiles. X-ray structural studies of the monomers and an oligomer show that the new motif orients the two heterocyclic rings and attached groups at an angle of approximately 120° to each other, opening new geometric considerations for the design of this class of foldamer.

An Electrically Conducting Li-Ion Metal-Organic Framework.

Metal-organic frameworks (MOFs) have emerged as an important, yet highly challenging class of electrochemical energy storage materials. The chemical principles for electroactive MOFs remain, however, poorly explored because precise chemical and structural control is mandatory. For instance, no anionic MOF with a lithium cation reservoir and reversible redox (like a conventional Li-ion cathode) has been synthesized to date. Herein, we report on electrically conducting Li-ion MOF cathodes with the generic formula Li2-M-DOBDC (wherein M = Mg2+ or Mn2+; DOBDC4- = 2,5-dioxido-1,4-benzenedicarboxylate), by rational control of the ligand to transition metal stoichiometry and secondary building unit (SBU) topology in the archetypal CPO-27. The accurate chemical and structural changes not only enable reversible redox but also induce a million-fold electrical conductivity increase by virtue of efficient electronic self-exchange facilitated by mix-in redox: 10-7 S/cm for Li2-Mn-DOBDC vs 10-13 S/cm for the isoreticular H2-Mn-DOBDC and Li2-Mg-DOBDC, or the Mn-CPO-27 compositional analogues. This particular SBU topology also considerably augments the redox potential of the DOBDC4- linker (from 2.4 V up to 3.2 V, vs Li+/Li0), a highly practical feature for Li-ion battery assembly and energy evaluation. As a particular cathode material, Li2-Mn-DOBDC displays an average discharge potential of 3.2 V vs Li+/Li0, demonstrates excellent capacity retention over 100 cycles, while also handling fast cycling rates, inherent to the intrinsic electronic conductivity. The Li2-M-DOBDC material validates the concept of reversible redox activity and electronic conductivity in MOFs by accommodating the ligand's noncoordinating redox center through composition and SBU design.

Correction: Water binding stabilizes stacked conformations of ferrocene containing sheet-like aromatic oligoamides.

Correction for 'Water binding stabilizes stacked conformations of ferrocene containing sheet-like aromatic oligoamides' by Ya-Zhou Liu et al., Org. Biomol. Chem., 2021, DOI: 10.1039/d1ob00580d.

Urea as a Cocrystal Former-Study of 3 Urea Based Pharmaceutical Cocrystals.

Cocrystallization is commonly used for its ability to improve the physical properties of APIs, such as solubility, bioavailability, compressibility, etc. The pharmaceutical industry is particularly interested in those cocrystals comprising a GRAS former in connection with the target API. In this work, we focus on the potential of urea as a cocrystal former, identifying three novel pharmaceutical cocrystal systems with catechin, 3-hydroxyl-2-naphthoic and ellagic acid. Interestingly, the stability of catechin under high humidity or high temperature environment is improved upon cocrystallization with urea. Moreover, the solubility of ellagic acid is improved about 17 times. This work displays the latent possibility of urea in improving the physical property of drug molecules using a cocrystallization approach.

Water binding stabilizes stacked conformations of ferrocene containing sheet-like aromatic oligoamides.

While water clusters play an essential role in the stability of biological structures, their ability to stabilize synthetic oligomers is less understood. We have synthesized a heptameric sheet-like aromatic oligoamide foldamer with ferrocene as turn unit. It shows strong interactions with water in the solid state and in solution. The water binding limits the fluxional processes resulting from the flexible ferrocene unit, highlighting the importance of such interactions for conformational studies on this class of molecule.