Bridging Motif Research Articles

Tackling activity-stability paradox of reconstructed NiIrOx electrocatalysts by bridged W-O moiety

One challenge remaining in the development of Ir-based electrocatalyst is the activity-stability paradox during acidic oxygen evolution reaction (OER), especially for the surface reconstructed IrOx catalyst with high efficiency. To address this, a phase selective Ir-based electrocatalyst is constructed by forming bridged W-O moiety in NiIrOx electrocatalyst. Through an electrochemical dealloying process, an nano-porous structure with surface-hydroxylated rutile NiWIrOx electrocatalyst is engineered via Ni as a sacrificial element. Despite low Ir content, NiWIrOx demonstrates a minimal overpotential of 180 mV for the OER at 10 mA·cm−2. It maintains a stable 300 mA·cm−2 current density during an approximately 300 h OER at 1.8 VRHE and shows a stability number of 3.9 × 105 noxygen · nIr−1. The resulting W – O–Ir bridging motif proves pivotal for enhancing the efficacy of OER catalysis by facilitating deprotonation of OER intermediates and promoting a thermodynamically favorable dual-site adsorbent evolution mechanism. Besides, the phase selective insertion of W-O in NiIrOx enabling charge balance through the W-O-Ir bridging motif, effectively counteracting lattice oxygen loss by regulating Ir-O co-valency.

From Mono- to Polynuclear 2-(Diphenylphosphino)pyridine-Based Cu(I) and Ag(I) Complexes: Synthesis, Structural Characterization, and DFT Calculations.

A series of monometallic Ag(I) and Cu(I) halide complexes bearing 2-(diphenylphosphino)pyridine (PyrPhos, L) as a ligand were synthesized and spectroscopically characterized. The structure of most of the derivatives was unambiguously established by X-ray diffraction analysis, revealing the formation of mono-, di-, and tetranuclear complexes having general formulas MXL3 (M = Cu, X = Cl, Br; M = Ag, X = Cl, Br, I), Ag2X2L3 (X = Cl, Br), and Ag4X4L4 (X = Cl, Br, I). The Ag(I) species were compared to the corresponding Cu(I) analogues from a structural point of view. The formation of Cu(I)/Ag(I) heterobimetallic complexes MM'X2L3 (M/M' = Cu, Ag; X = Cl, Br, I) was also investigated. The X-ray structure of the bromo-derivatives revealed the formation of two possible MM'Br2L3 complexes with Cu/Ag ratios, respectively, of 7:1 and 1:7. The ratio between Cu and Ag was studied by scanning electron microscopy-energy-dispersive X-ray analysis (SEM-EDX) measurements. The structure of the binuclear homo- and heterometallic derivatives was investigated using density functional theory (DFT) calculations, revealing the tendency of the PyrPhos ligands not to maintain the bridging motif in the presence of Ag(I) as the metal center.

Metal-ring interactions in group 2 ansa-metallocenes: assessed with the local vibrational mode theory.

Ansa-metallocenes, a vital class of organometallic compounds, have attracted significant attention due to their diverse structural motifs and their pivotal roles in catalysis and materials science. We investigated 37 distinct group 2 ansa-metallocenes at the B3LYP-D3/def2-TZVP level of theory. Utilizing local mode force constants derived from our local vibrational mode theory, including a special force constant directly targeting the metal-ring interaction, we could unveil latent structural differences between solvated and non-solvated metallocenophanes and the influence of the solvent on complex stability and structure. We could quantify the intrinsic strength of the metal-cyclopentadienyl (M-Cp) bonds and the influence of the bridging motifs on the stiffness of the Cp-M-Cp angles, another determinant of complex stability. LMA was complemented by the analysis of electronic density, utilizing the quantum theory of atoms in molecules (QTAIM), which confirmed both the impact of solvent coordination on the strength of the M-Cp bond(s) and the influence of the bridging motif on the Cp-M-Cp angles. The specific effect of the ansa-motif on the M-Cp interaction was further elucidated by a comparison with linear/bent metallocene structures. In summary, our results identify the local mode analysis as an efficient tool for unraveling the intricate molecular properties of ansa-metallocenes and their unique structural features.

Phosphine and Selenoether peri-Substituted Acenaphthenes and Their Transition-Metal Complexes: Structural and NMR Investigations.

A series of peri-substituted acenaphthene-based phosphine selenoether bidentate ligands Acenap(iPr2P)(SeAr) (L1-L4, Acenap = acenaphthene-5,6-diyl, Ar = Ph, mesityl, 2,4,6-trisopropylphenyl and supermesityl) were prepared. The rigid acenaphthene framework induces a forced overlap of the phosphine and selenoether lone pairs, resulting in a large magnitude of through-space 4JPSe coupling, ranging from 452 to 545 Hz. These rigid ligands L1-L4 were used to prepare a series of selected late d-block metals, mercury, and borane complexes, which were characterized, including by multinuclear NMR and single-crystal X-ray diffraction. The Lewis acidic motifs (BH3, Mo(CO)4, Ag+, PdCl2, PtCl2, and HgCl2) bridge the two donor atoms (P and Se) in all but one case in the solid-state structures. Where the bridging motif contained NMR-active nuclei (11B, 107Ag, 109Ag, 195Pt, and 199Hg), JPM and JSeM couplings are observed directly, in addition to the altered JPSe in the respective NMR spectra. The solution NMR data are correlated with single-crystal diffraction data, and in the case of mercury(II) complexes, they are also correlated with the solid-state NMR data and coupling deformation density calculations. The latter indicate that the through-space interaction dominates in free L1, while in the L1HgCl2 complex, the main coupling pathway is via the metal atom and not through the carbon framework of the acenaphthene ring system.

Ferrocenyl-based di- and trinuclear lanthanide complexes: solid state structures, (spectro)electrochemical and DFT studies.

Dinuclear and trinuclear ferrocenylcarboxylato-bridged lanthanide complexes of type [Ln(μO:κ2OO'-O2CFc)(O2CFc)2(H2O)(dmf)]2·(dmf)2 (Ln = Sm (2), Eu (3), Gd (4), Tb (5); Fc = Fe(η5-C5H4)(η5-C5H5)), and novel [Bu4N][Ln3(μ-O2CFc)3(μO:κ2OO'-O2CFc)3(O2CFc)3(μ3-OH)]·[Bu4N]Cl (Ln = Gd (6), Tb (7)) were prepared by the reaction of [LnCl3·6H2O] (synthesis of 2-5) or LnCl3 (synthesis of 6, 7) with FcCO2H (1) in the ratio of 1 : 3. As evidenced by single crystal X-ray structure determination, in 2-5 the lanthanide ions are connected by symmetric FcCO2 units. In addition, two ferrocenylcarboxylato groups are μ-bridged to LnIII. Each LnIII ion is coordinated by nine oxygen donor atoms derived from one H2O, one dmf and three carboxylates. The latter are found in chelating κ2 and bridging μ,κ3 coordination modes. Complexes 6 and 7 assemble three LnIII cores around a central μ3-netting hydroxide and nine FcCO2 entities. A combination of κ2, μ,κ2 and μ,κ3 coordination modes results in an eight-fold coordination sphere for each metal, which is best described as bicapped trigonal prismatic. IR spectroscopy confirms the chelating and bridging motifs. Electrochemical studies of complexes 2-7via cyclic voltammetry (CV) and square-wave voltammetry (SWV) showed one redox event between E°' = 250 and 260 mV vs. FcH/FcH+ for 2-5 with all six FcCO2 redox events superimposed. Complexes 6 and 7 show a total of three events in the CV with the oxidations of the nine FcCO2 units occurring in close proximity. Deconvolution of individual redox events correlates well with the mononuclear complex [Bu4N][Gd(O2CFc)4]. UV-Vis/NIR spectroelectrochemical measurements of 7 did not reveal electron transfer between either Fc units, nor the coordinated lanthanides and resembled the absorption behavior of [Bu4N][Tb(O2CFc)4]. DFT (Density Functional Theory) calculations on the B3LYP def2-TZVP level of theory were carried out to assign the order of redox events in 6 showing that the spatial distance towards the most recent redox center, instead of the binding mode, is decisive.

Spectrophotometric Determination of Trace Amount of Total FeII/FeIII and Live Cell Imaging of a Carboxylato Zn(II) Coordination Polymer.

The coordination polymer, (Zn(II)-CP, 1), {[Zn(2,6-NDC)(4-Cltpy)](H2O)4} (1) (2,6-H2NDC = 2,6-naphthalene dicarboxylic acid and 4-Cltpy = 4'-chloro-[2,2';6',2″]terpyridine) is structurally characterized by single crystal X-ray diffraction measurement and other physicochemical studies (PXRD, FTIR, thermal analysis, microanalytical data). 4-Cltpy acts as end-capping ligand, and NDC2- is a carboxylato bridging motif to constitute ZnN3O2 distorted trigonal bipyramid core that propagates to construct 1D chain. The coordination polymer, 1, detects total iron (Fe3+ and Fe2+) in aqueous solution by visual color change, colorless to pink. Absorption spectrophotometric technique in aqueous medium measures the limit of detection (LOD) 0.11 μM (Fe2+) and 0.15 μM (Fe3+), and binding constants (Kd) are 6.7 × 104 M-1 (Fe3+) and 3.33 × 104 M-1 (Fe2+). Biocompatibility of 1 is examined in live cells, and intracellular Fe2+ and Fe3+ are detected in MDA-MB 231 cells. Zn(II) substitution is assumed upon addition of FeIII/FeII solution to the suspension of the coordination polymer, 1, in water-acetonitrile (41:1) (LZnII + FeIII/II → LFeIII + ZnII, where L is defined as coordinated ligands), which is accompanied by changing from colorless to pink at room temperature. The color of the mixture may be assumed to the charge transfer transition from carboxylate-O to Cltpy via Fe(II/III) bridging center (carboxylate-O-Fe-CltPy). The product isolated from the reaction is finally characterized as Fe(III)@1-CP. It is presumed that product Fe(II)@1-CP may undergo fast aerial oxidation to transform Fe(III)@1-CP. The FeIII exchanged framework (Fe(III)@1-CP) has been characterized by PXRD, IR, TGA and energy dispersive X-ray analysis (EDX)-SEM. The MTT assay calculates the cell viability (%), and the tolerance limit is 100 μM to total Fe2+ and Fe3+.

Targeting Diverse Bridging Motifs within Actinide Borosulfates and Establishing an Unconventional Structural Hierarchy.

The first actinide borosulfates, (UO2)[B(SO4)2(SO3OH)] (TSUBOS-1) and (UO2)2[B2O(SO4)3(SO3OH)2] (TSUBOB-1), were synthesized solvothermally in oleum using UO3. The classical borosulfate crystal structure of TSUBOS-1 is partially consistent with an established conventional hierarchy. Uranyl pentagonal bipyramids limit the anionic network linkages and isolate sulfate tetrahedra within the anionic network. Therefore, the classical one-dimensional chain established in the hierarchy does not fully describe the structure. The structure of TSUBOB-1 is the first actinide borosulfate that contains an unconventional borate-to-borate bridging mode (denoted B-O-B) and a zero-dimensional oxoanionic unit consisting of one sulfate tetrahedron that shares vertices with two B-O-B bridged borate tetrahedra that each share a vertex with two sulfate tetrahedra. As this structure departs from the existing structural hierarchy, a modified approach for understanding the unconventional borosulfate substructure and dimensionality is proposed, together with a new graphical notation. In the course of our synthesis experiments, a novel uranyl disulfate compound (UO2)2[(S2O7)(SO3OH)2] (TSUDS) was isolated and characterized. The structure of TSUDS is a framework consisting of uranyl pentagonal bipyramids and sulfate tetrahedra. Each uranyl pentagonal bipyramid is surrounded by five sulfate tetrahedra, two of which share a vertex creating a disulfate with a S-O-S bridging mode. The uranyl bipyramids are linked to one another via the singular sulfate or disulfate groups.

Carboranethiol-Protected Propeller-Shaped Photoresponsive Silver Nanomolecule

We report the synthesis, structural characterization, and photophysical properties of a propeller-shaped Ag21 nanomolecule with six rotary arms, protected with m-carborane-9-thiol (MCT) and triphenylphosphine (TPP) ligands. Structural analysis reveals that the nanomolecule has an Ag13 central icosahedral core with six directly connected silver atoms and two more silver atoms connected through three Ag-S-Ag bridging motifs. While 12 MCT ligands protect the core through metal-thiolate bonds in a 3-6-3-layered fashion, two TPP ligands solely protect the two bridging silver atoms. Interestingly, the rotational orientation of a silver sulfide staple motif is opposite to the orientation of carborane ligands, resembling the existence of a bidirectional rotational orientation in the nanomolecule. Careful analysis reveals that the orientation of carborane ligands on the cluster's surface resembles an assembly of double rotors. The zero circular dichroism signal indicates its achiral nature in solution. There are multiple absorption peaks in its UV-vis absorption spectrum, characteristic of a quantized electronic structure. The spectrum appears as a fingerprint for the cluster. High-resolution electrospray ionization mass spectrometry proves the structure and composition of the nanocluster in solution, and systematic fragmentation of the molecular ion starts with the loss of surface-bound ligands with increasing collision energy. Its multiple optical absorption features are in good agreement with the theoretically calculated spectrum. The cluster shows a narrow near-IR emission at 814 nm. The Ag21 nanomolecule is thermally stable at ambient conditions up to 100 °C. However, white-light illumination (lamp power = 120-160 W) shows photosensitivity, and this induces structural distortion, as confirmed by changes in the Raman and electronic absorption spectra. Femtosecond and nanosecond transient absorption studies reveal an exceptionally stable excited state having a lifetime of 3.26 ± 0.02 μs for the carriers, spread over a broad wavelength region of 520-650 nm. The formation of core-centered long-lived carriers in the excited state is responsible for the observed light-activated structural distortion.

A cuboidal [Cu4(SO4)4] structure supported by β-picoline ligands.

The solid-state structure of the cobalt-β-picoline-sulfate complex tetra-μ3-sulfato-tetra-kis-[bis-(3-methyl-pyridine)-cobalt(II)], [Co4(SO4)4(C6H7N)8], is reported. The tetra-meric cobalt cluster contains a cuboidal core comprised of four cobalt(II) cations and four sulfate anions at alternate cube vertices. The cobalt corners are each capped with two β-picoline ligands. The sulfate anions adopt a rare [3.2110] bridging motif, and the cuboidal cluster is unprecedented in coordination chemistry.

Dinitrogen complexation and reduction at low-valent calcium.

Here we report that attempted preparation of low-valent CaI complexes in the form of LCa-CaL (where L is a bulky β-diketiminate ligand) under dinitrogen (N2) atmosphere led to isolation of LCa(N2)CaL, which was characterized crystallographically. The N2 2- anion in this complex reacted in most cases as a very potent two-electron donor. Therefore, LCa(N2)CaL acts as a synthon for the low-valent CaI complex LCa-CaL, which was the target of our studies. The N2 2- anion could also be protonated to diazene (N2H2) that disproportionated to hydrazine and N2 The role of Ca d orbitals for N2 activation is discussed.

Calcium catches dinitrogen

Inorganic Chemistry Although lithium reduces dinitrogen, the other alkali and alkaline Earth metals have proven largely inert to the gas under ambient conditions. Rosch et al. report that with just the right β-diketiminate ligand and an assist from potassium as terminal reductant, calcium can mediate dinitrogen reduction. Crystallography and spectroscopic characterization revealed a product in which doubly reduced dinitrogen adopted a side-on bridging motif between two calcium centers. A subsequent reaction with coordinated tetrahydrofuran appeared to release diazene. Science , this issue p. [1125][1] [1]: /lookup/doi/10.1126/science.abf2374

Tuneable structures and magnetic properties of pseudohalo-bridged dinuclear Ni(ii) complexes derived from {N4} and {N3O} donor ligands

Six new dinickel(ii) complexes with different bridges and bridging motifs showing overall diverse magnetic interactions (AF to F interactions) have been discussed and rationalized.

Phase Trapping in Multistep Spin Crossover Compound.

The dimeric motif is the smallest unit for two interacting spin centers allowing for systematic investigations of cooperative interactions. As spin transition compounds, dinuclear complexes are of particular interest, since they potentially reveal a two-step spin crossover (SCO), switching between the high spin-high spin [HS-HS], the high spin-low spin [HS-LS], and the low spin-low spin [LS-LS] states. Herein, we report the synthesis and characterization of six dinuclear iron(II) complexes [FeII2(μ2-L1)2](BF4)4 (C1), [FeII2(μ2-L1)2](ClO4)4 (C2), [FeII2(μ2-L1)2](F3CSO3)4 (C3), [FeII2(μ2-L2)2](BF4)4 (C4), [FeII2(μ2-L2)2](BF4)4 (C5), and [FeII2(μ2-L2)2](BF4)4 (C6), based on the 1,3,4-thiadiazole bridging motif. The two novel bis-tridentate ligands (L1 = 2,5-bis{[(1H-imidazol-2-ylmethyl)-amino]-methyl}-1,3,4-thiadiazole and L2 = 2,5-bis{[(thiazol-2-ylmethyl)-amino]-methyl}-1,3,4-thiadiazole) were employed in the presence of iron(II) salts with the different counterions. Upon varying ligands and counterions, we were able to change the magnetic properties of the complexes from a temperature-independent [HS-HS] spin state over a one-step spin transition toward a two-step SCO. When cooled slowly from room temperature, the two-step SCO goes along with two distinct phase transitions, and in the intermediate mixed [HS-LS] state distinct HS/LS pairs can be identified unambiguously. In contrast, rapid cooling precludes a crystallographically observable phase transition. For the mixed [HS-LS] state Mössbauer spectroscopy confirms a statistical (random) orientation of adjacent [HS-LS]·[HS-LS]·[HS-LS] chains.

Long and short isoforms of c-FLIP act as control checkpoints of DED filament assembly.

The assembly of the death-inducing signaling complex (DISC) and death effector domain (DED) filaments at CD95/Fas initiates extrinsic apoptosis. Procaspase-8 activation at the DED filaments is controlled by short and long c-FLIP isoforms. Despite apparent progress in understanding the assembly of CD95-activated platforms and DED filaments, the detailed molecular mechanism of c-FLIP action remains elusive. Here, we further addressed the mechanisms of c-FLIP action at the DISC using biochemical assays, quantitative mass spectrometry, and structural modeling. Our data strongly indicate that c-FLIP can bind to both FADD and procaspase-8 at the DED filament. Moreover, the constructed in silico model shows that c-FLIP proteins can lead to the formation of the DISCs comprising short DED filaments as well as serve as bridging motifs for building a cooperative DISC network, in which adjacent CD95 DISCs are connected by DED filaments. This network is based on selective interactions of FADD with both c-FLIP and procaspase-8. Hence, c-FLIP proteins at the DISC control initiation, elongation, and composition of DED filaments, playing the role of control checkpoints. These findings provide new insights into DISC and DED filament regulation and open innovative possibilities for targeting the extrinsic apoptosis pathway.

{MnIII2LnIII2} (Ln = Gd, La or Y) butterfly complexes: Ferromagnetic exchange observed between bis-μ-alkoxo bridged manganese(III) ions

Three tetranuclear {MnIII2LnIII2} ‘butterfly’ complexes with common MnIII2 µ3-alkoxo bridging motifs surrounded by two LnIII ions (Ln = Gd, La or Y) have been studied by structural, magnetic and density functional theoretical calculations. The exchange coupling constant between the body–body Mn(III) ions is ferromagnetic in all cases, the La and Y examples being diamagnetic at the wing-wing positions. The wing-body Jwb (Mn–Gd) interaction is small and negative. Reasons are given for these JMnMn values, including the effects of the terminal LnIII ions, comparison to analogous Mn2 dinuclears, and the effects of spin polarisation.

Insights into Interfaces, Stability, Electronic Properties, and Catalytic Activities of Atomically Precise Metal Nanoclusters from First Principles.

Atomically precise, ligand-protected metal nanoclusters are of great interest for their well-defined structures, intriguing physicochemical properties, and potential applications in catalysis, biology, and nanotechnology. Their structure precision provides many opportunities to correlate their geometries, stability, electronic properties, and catalytic activities by closely integrating theory and experiment. In this Account, we highlight recent theoretical advances from our efforts to understand the metal-ligand interfaces, the energy landscape, the electronic structure and optical absorption, and the catalytic applications of atomically precise metal nanoclusters. We mainly focus on gold nanoclusters. The bonding motifs and energetics at the gold-ligand interfaces are two main interests from a computational perspective. For the gold-thiolate interface, the -RS-Au-SR- staple motif is not always preferred; in fact, the bridging motif (-SR-) is preferred at the more open facets such as Au(100) and Au(110). This finding helps understand the diversity of the gold-thiolate motifs for different core geometries and sizes. A great similarity is demonstrated between gold-thiolate and gold-alkynyl interfaces, regarding formation of the staple-type motifs with PhC≡C- as an example. In addition, N-heterocyclic carbenes (NHCs) without bulky groups also form the staple-type motif. Alkynyls and bulky NHCs have the strongest binding with the gold surface from comparing 27 ligands of six types, suggesting a potential to synthesize NHC-protected gold clusters. The energy landscape of nanosystems is usually complex, but experimental progress in synthesizing clusters of the same Au-S composition with different R groups and isomers of the same Au n(SR) m formula have made detailed theoretical analyses of energetic contributions possible. Ligand-ligand interactions turn out to play an important role in the cluster stability, while metastable isomers can be obtained via kinetic control. Although the superatom-complex theory is the starting point to understand the electronic structure of atomically precise gold clusters, other factors also greatly affect the orbital levels that manifest themselves in the experimental optical absorption spectra. For example, spin-orbit coupling needs to be included to reproduce the splitting of the HOMO-LUMO transition observed experimentally for Au25(SR)18-, the poster child of the family. In addition, doping can lead to structural changes and charge states that do not follow the superatomic electron count. Atomically precise metal nanoclusters are an ideal system for understanding nanocatalysis due to their well-defined structures. Active sites and catalytic mechanisms are explored for selective hydrogenation and hydrogen evolution on thiolate-protected gold nanoclusters with and without dopants. The behavior of H in nanogold is analyzed in detail, and the most promising site to attract H is found to be coordinately unsaturated Au atoms. Many insights have been gained from first-principles studies of atomically precise, ligand-protected gold nanoclusters. Interesting and important questions remaining to be addressed are pointed out in the end.

Two Unsupported Terminal Hydroxido Ligands in a μ-Oxo-Bridged Ferric Dimer: Protonation and Kinetic Lability Studies.

The dinuclear complex [(susan){FeIII(OH)(μ-O)FeIII(OH)}](ClO4)2 (Fe2(OH)2(ClO4)2; susan = 4,7-dimethyl-1,1,10,10-tetra(2-pyridylmethyl)-1,4,7,10-tetraazadecane) with two unsupported terminal hydroxido ligands and for comparison the fluorido-substituted complex [(susan){FeIIIF(μ-O)FeIIIF}](ClO4)2 (Fe2F2(ClO4)2) have been synthesized and characterized in the solid state as well in acetonitrile (CH3CN) and water (H2O) solutions. The Fe-OH bonds are strongly modulated by intermolecular hydrogen bonds (1.85 and 1.90 Å). UV-vis-near-IR (NIR) and Mössbauer spectroscopies prove that Fe2F22+ and Fe2(OH)22+ retain their structural integrity in a CH3CN solution. The OH- ligand induces a weaker ligand field than the F- ligand because of stronger π donation. This increased electron donation shifts the potential for the irreversible oxidation by 610 mV cathodically from 1.40 V in Fe2F22+ to 0.79 V versus Fc+/Fc in Fe2(OH)22+. Protonation/deprotonation studies in CH3CN and aqueous solutions of Fe2(OH)22+ provide two reversible acid-base equilibria. UV-vis-NIR, Mössbauer, and cryo electrospray ionization mass spectrometry experiments show conservation of the mono(μ-oxo) bridging motif, while the terminal OH- ligands are protonated to H2O. Titration experiments in aqueous solution at room temperature provide the p Ka values as p K1 = 4.9 and p K2 = 6.8. Kinetic studies by temperature- and pressure-dependent 17O NMR spectrometry revealed for the first time the water-exchange parameters [ kex298 = (3.9 ± 0.2) × 105 s-1, Δ H⧧ = 39.6 ± 0.2 kJ mol-1, Δ S⧧ = -5.1 ± 1 J mol-1 K-1, and Δ V⧧ = +3.0 ± 0.2 cm3 mol-1] and the underlying Id mechanism for a {FeIII(OH2)(μ-O)FeIII(OH2)} core. The same studies suggest that in solution the monoprotonated {FeIII(OH)(μ-O)FeIII(OH2)} complex has μ-O and μ-O2H3 bridges between the two Fe centers.

Initial Oxygen Incorporation in the Prismatic Surfaces of Troilite FeS

We present a theoretical investigation of the prismatic (0110) surface of troilite in an oxidizing environment, which aims to elucidate the presence of oxygen detected experimentally in the pyrrhotite Fe1–xS nanoparticles. We find that atomic oxygen adsorbs in Fe–O–Fe bridging motifs, which are thermodynamically stable under ambient conditions. During the first oxidation steps, the formation of the S–O bond is less favored than Fe–O, suggesting that the sulfur oxides detected experimentally form only subsequently. We predict, moreover, that substitution of sulfur for oxygen can occur. The appearance of Fe–O–Fe–O–Fe bridging motifs due to successive adsorptions points toward a clustering growth of the oxidic units. In agreement with the experimental observations, the oxidation of troilite is exothermic, where the equilibrium between adsorption and substitution is influenced by the presence of Fe vacancies.

Design of Metal-Halide Inverse-Hybrid Perovskites

We recently introduced a new class of perovskites, with inorganic anions on the A- and B-sites and an organic cation on the X-site, the so-called inverse-hybrid perovskites (IHPs). We found compounds that are predicted to be stable, possess large polarization, and span a wide range of electronic properties. Here, we present the materials search strategy that enabled these results. We demonstrate the design principles in terms of ion and site composition. Overall, we consider elements from most main groups of the periodic table, investigating their ability to form mono- or divalent anions in the framework of IHPs. We observe structural changes based on tolerance factor. Compounds are found in the perovskite or the related CaIrO3 structure, and different orientations of the employed organic cation (methylammonium) lead to different B···X···B bridging motifs. Furthermore, we demonstrate how the perovskite structure can be favored by interchanging B- and A-site anions and adjusting the ions within groups of t...

Drug-Clinical Agent Molecular Hybrid: Synthesis of Diaryl(trifluoromethyl)pyrazoles as Tubulin Targeting Anticancer Agents.

Twenty-three combretastatin A-4 (CA-4) analogues were synthesized by judiciously incorporating a functional N-heterocyclic motif present in Celecoxib (a marketed drug) while retaining essential pharmacophoric features of CA-4. Combretastatin-(trifluoromethyl)pyrazole hybrid analogues, i.e., 5-trimethoxyphenyl-3-(trifluoromethyl)pyrazoles with a variety of relevantly substituted aryls and heteroaryls at 1-position were considered as potential tubulin polymerization inhibitors. The cytotoxicity of the compounds was evaluated using MCF-7 cells. Analog 23 (C-23) was found to be the most active among the tested compounds. It showed pronounced cytotoxicity against HeLa, B16F10, and multidrug-resistant mammary tumor cells EMT6/AR1. Interestingly, C-23 displayed significantly lower toxicity toward noncancerous cells, MCF10A and L929, than their cancerous counterparts, MCF-7 and B16F10, respectively. C-23 depolymerized interphase microtubules, disrupted mitotic spindle formation, and arrested MCF-7 cells at mitosis, leading to cell death. C-23 inhibited the assembly of tubulin in vitro. C-23 bound to tubulin at the colchicine binding site and altered the secondary structures of tubulin. The data revealed the importance of (trimethoxyphenyl)(trifluoromethyl)pyrazole as a cis-restricted double bond-alternative bridging motif, and carboxymethyl-substituted phenyl as ring B for activities and interaction with tubulin. The results indicated that the combretastatin-(trifluoromethyl)pyrazole hybrid class of analogues has the potential for further development as anticancer agents.