Metal Center Research Articles

α,β‐C—C—C Agostic Bonding Interactions in Ruthenacyclobutane and π‐Complex Assisted Olefin Metathesis Catalyzed by Ruthenium‐Alkylidene Complexes

ABSTRACTComputational aspects of concerted [2+2] oxidative‐retrocycloaddition‐cycloreversion reaction through ruthenium alkylidene π‐complexes and ruthenacyclobutane with α,β‐(C—C—C) agostic bonding interactions in olefin metathesis are presented. d6‐Ruthenium carbene complexes, with ruthenium in the oxidation state +2, undergo successive [2+2] cycloaddition and cycloreversion steps, through associative, dissociative, or interchange mechanisms. This process involves coordination of the olefin to 16‐electron Ru complex followed by phosphine dissociation, or first phosphine dissociation then coordination of the olefin to the 14‐electron Ru complex with rearrangement to a ruthenacyclobutane intermediate, followed by symmetrical reverse steps. Donation of σ‐electron density from the two C—C σ‐bonds to the metal center leads to α,β‐(C—C—C) agostic bonds, which stabilized metallacyclobutane as a formally 16‐electron complex, with lower energy than the corresponding π‐complex. In the transformation from π‐complex to ruthenacyclobutane the ruthenium atom is formally oxidized to Ru(IV). The most efficient ligands are those that stabilize the high‐oxidation state metallacyclobutane (IV) intermediate relative to the ruthenium carbene.

Synthesis, Characterisation, and Coordination Behaviour of Novel Pyridyl‐formamidine Based Mn(I), Cu(II), Zn(II), and Pd(II) Complexes

We report a new synthetic approach for the synthesis of less‐explored unsymmetrical pyridyl‐formamidine ligands and their coordination behaviour to form Mn(I), Cu(II), Zn(II), and Pd(II) complexes. The one‐step process for synthesising the unsymmetrical pyridyl‐formamidine compounds offers the advantage of being functional‐group tolerant and less cumbersome. Generally, the pyridyl‐formamidine ligands coordinate to the metal centres in a bidentate fashion to form a six‐membered chelate as established by spectroscopic and crystallographic analysis. It was observed that the formamidine functionality is prone to hydrolysis in the presence of methoxy substituent on the phenyl ring and/or acetate‐containing metal precursors.

Silver(I) and gold(III) complexes with miconazole: The influence of the metal ion on the antimicrobial activity of the coordinated azole

To develop a new antimicrobial agent, we used the clinically approved antifungal azole, miconazole (mcz), as a ligand for the synthesis of silver(I) and gold(III) complexes. The new complexes [Ag(NO3-O)(mcz-N)2] (1) and [AuCl3(mcz-N)] (2) were synthesized and characterized by 1H NMR, IR and UV–Vis spectroscopy and mass spectrometry, while the crystal structure of 1 was determined by single-crystal X-ray diffraction analysis. From the results obtained, it can be concluded that in both complexes, mcz is monodentately coordinated to the silver(I) and gold(III) ions through the imidazole nitrogen atom N3. In the solid state, complex 1 contains two mcz ligands and monodentately coordinated nitrate in the third position, while in the case of 2 gold(III) ion is coordinated by one mcz and three chlorido ligands, resulting in the expected square-planar arrangement around the metal center. DFT and TDDFT calculations were employed to elucidate the electronic structures and thermodynamic stability of the synthesized complexes in solution to complement the experimental findings. The coordination of mcz to silver(I) and gold(III) ions leads to an enhancement of its activity against Gram-negative Escherichia coli and Pseudomonas aeruginosa strains, while against the panel of Staphylococcus aureus and Candida species, only 2 shows improved activity compared to mcz. Both complexes 1 and 2 were tested in vitro for their antimycobacterial activity against the strain Mycobacterium tuberculosis H37Rv and showed good growth inhibition with minimum inhibitory concentration (MIC) values of 3.12 and 8.69 μM, respectively, with complex 1 being twice effective as mcz (MIC = 7.50 μM). Complex 2 significantly reduced the production of pyocyanin, a virulence factor in P. aeruginosa controlled by quorum sensing, while this effect was not observed for 1.

The suprachelate effect: a pathway to supramolecules with Cu(II) and ethylenediamine

ABSTRACT This paper portrays the solution-phase dynamics as copper(II) and ethylenediamine explore a multitude of different complexes. The data from five spectrophotometric titrations were globally analysed, evidencing four predominant species ([Cu]2+, [Cu(en-N,N’)]2+, [Cu(en-N,N’)2]2+, [Cu(en-N)4]2+) along with their molar absorptivity curves and associative binding constants. The data also seem to support a fifth species, [Cu2(µ-en-N,N’)]4+, in which ethylenediamine bridges two Cu(II) centres. The thermodynamic stability of all five species is corroborated by ab initio computational calculations. The potential existence of [Cu(en-N)4]2+ highlights the suprachelate effect – going beyond the chelate effect – where multidenticity is overtaken by monodenticity. Such dangling multidentate ligands are available to bind to additional metal centres and thus build towards self-assembling supramolecules.

Hydrogenation Reactions with Heterobimetallic Complexes.

Hydrogenations are fundamentally and industrially important reactions that are atom economical paths to synthesize value-added products from feedstock chemicals. The cooperative effects of two or more metal centers in multimetallic active sites is a successful strategy to activate small molecules and facilitate catalytic reactions, and this strategy has been recently applied to catalytic hydrogenation reactions. Furthermore, heterobimetallic complexes have been well-documented to provide novel reaction pathways and improved selectivity, compared to their homo-bimetallic and monometallic analogues. This minireview provides a historical perspective on the development of heterobimetallic catalysts for the hydrogenation of unsaturated substrates and describes recent developments in this burgeoning research area.

Development of Group IV Metal Complexes Bearing Thioether-Amido Ligands with Enhanced High-Temperature Catalytic Performance toward Olefin Copolymerization.

The development of homogeneous metal catalysts with both high activity and exceptional thermal stability is crucial for the efficient synthesis of polyolefin elastomers (POEs) through solution-phase olefin polymerization. In this study, a series of Hf (Hf1-Hf5), Zr (Zr1), and Ti (Ti1) complexes featuring thioether-amido ligands were synthesized and carefully characterized using advanced techniques such as 1H and 13C NMR spectroscopy as well as single-crystal X-ray diffraction analysis for Hf4 and Hf5. The results revealed that the catalytic activity and 1-octene incorporation efficiency of these metal complexes followed the trend Hf > Zr > Ti, underscoring the significant impact of the metal center on catalytic performance. Furthermore, the choice of ligands was found to play a critical role in dictating the catalytic properties, with ligands bearing less steric hindrance on the sulfur atom proving to be more favorable for copolymerization reactions. Notably, the Hf complex Hf1, featuring a methyl group on the sulfur atom, displayed exceptional catalytic activity as high as 21,060 kg(polymer)·mol-1(Hf)·h-1 toward ethylene/1-octene copolymerization at 120 °C and produced POE with a high molecular weight (Mw = 6.3 × 104 g·mol-1), relatively narrow distribution (Đ = 2.4), and high incorporation of 1-octene (34.1 mol %). This study demonstrates the potential of tailored ligand design in developing efficient metal catalysts for the production of high-value-added POEs.

A Highly Conjugated Nickel(II)-Acetylide Framework for Efficient Photocatalytic Carbon Dioxide Reduction.

The incorporation of transition-metal single atoms as molecular functional entities into the skeleton of graphdiyne (GDY) to construct novel two-dimensional (2D) metal-acetylide frameworks, known as metalated graphynes (MGYs), is a promising strategy for developing efficient catalysts, which can combine the tunable charge transfer of GDY frameworks, the catalytic activity of metal and the precise distribution of single metallic centers. Herein, four highly conjugated MGY photocatalysts based on NiII, PdII, PtII, and HgII were synthesized for the first time using the 'bottom-up' strategy through the use of M-C bonds (-C≡C-M-C≡C-). Remarkably, the NiII-based graphyne (TEPY-Ni-GY) exhibited the highest CO generation rate of 18.3 mmol g-1 h-1 and a selectivity of 98.8%. This superior performance is attributed to the synergistic effects of pyrenyl and -C≡C-Ni(PBu3)2-C≡C- moieties. The pyrenyl block functions as an intramolecular π-conjugation channel, facilitating kinetically favorable electron transfer, while the -C≡C-Ni(PBu3)2-C≡C- moiety serves as the catalytic site that enhances CO2 adsorption and activation, thereby suppressing competitive hydrogen evolution. This study provides a new perspective on MGY-based photocatalysts for developing highly active and low-cost catalysts for CO2 reduction.

Ammonia Storage in Metal-Organic Framework Materials: Recent Developments in Design and Characterization.

Since the advent of the Haber-Bosch process in 1910, the global demand for ammonia (NH3) has surged, driven by its applications in agriculture, pharmaceuticals, and energy. Current methods of NH3 storage, including high-pressure storage and transportation, present significant challenges due to their corrosive and toxic nature. Consequently, research has turned towards metal-organic framework (MOF) materials as potential candidates for NH3 storage due to their potential high adsorption capacities and structural tunability. MOFs are coordination networks composed of metal nodes and organic linkers, offering unprecedented porosity and surface area, and allowing incorporation of various functional groups and metal sites that can enhance NH3 adsorption. However, the stability of MOFs in the presence of NH3 is a significant concern since many degrade upon exposure to NH3, primarily due to ligand displacement and framework collapse. To address this, recent studies have focused on the synthesis and postsynthetic modification of MOFs to enhance both NH3 uptake and stability. In this Account, we summarize recent developments in the design and characterization of MOFs for NH3 storage. The choice of metal centers in MOFs is crucial for stability and performance. High-valence metals such as AlIII and TiIV form strong metal-linker bonds, enhancing the stability of the framework to NH3. The MFM-300 series of materials composed of high-valence 3+ and 4+ metal ions and carboxylic linkers demonstrates high stability and high NH3 uptake capacities. Ligand functionalization is another effective strategy for improving the NH3 adsorption. Polar functional groups such as -NH2, -OH, and -COOH enhance the interaction between the framework and NH3, particularly at low partial pressures, while postsynthetic modification allows fine-tuning of these functionalities to optimize the framework for higher adsorption capacities and stability. For example, MFM-303(Al), incorporating free carboxylic acid groups, exhibits a high NH3 packing density comparable to that of solid NH3. Creating defect sites by removing linkers or adding metal ions increases the number of active sites available for NH3 adsorption and shows promise for enhancing uptake. UiO-66, a stable MOF framework, can be modified to include defect sites, significantly enhancing the level of NH3 uptake. The full characterization of MOFs and especially their interactions with NH3 are vital for understanding and improving their performance. Techniques such as neutron powder diffraction (NPD), inelastic neutron scattering (INS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), electron paramagnetic resonance (EPR) spectroscopy, and solid-state nuclear magnetic resonance (ssNMR) spectroscopy can elucidate host-guest interactions and binding dynamics between NH3 and the framework structure and afford crucial information for the future design and rational development of new sorbents. This Account highlights our current strategies for the synthesis and characterization of MOFs for NH3 capture, providing an overview of this rapidly evolving field.

Dinuclear zinc(II) acetate complexes derived from N,N',S-tridentate Schiff bases: synthesis, structural study and Hirshfeld surface analysis.

Three dinuclear zinc(II) acetate complexes of the general formula [Zn{Ln}(AcO)]2, namely, di-μ-acetato-κ4O:O'-bis[({2-[(pyridin-2-ylmethylidene)amino]phenyl}sulfanido-κ3N,N',S)zinc(II)], [Zn2(C12H9N2S)2(C2H3O2)2] (n= 1), 4, μ-acetato-1:2κ2O:O'-acetato-2κO-[μ-(2-{[1-(pyridin-2-yl)ethylidene]amino}phenyl)sulfanido-1κS:2κ3N,N',S][(2-{[1-(pyridin-2-yl)ethylidene]amino}phenyl)sulfanido-1κ3N,N',S]dizinc(II), [Zn2(C13H11N2S)2(C2H3O2)2] (n= 2), 5, and μ-acetato-1:2κ2O:O'-acetato-2κO-[μ-(2-{[phenyl(pyridin-2-yl)methylidene]amino}phenyl)sulfanido-1κS:2κ3N,N',S][(2-{[phenyl(pyridin-2-yl)methylidene]amino}phenyl)sulfanido-1κ3N,N',S]dizinc(II)-bis(2-aminophenyl) disulfide (2/1), [Zn2(C18H13N2S)2(C2H3O2)2]·0.5C12H12N2S2 (n= 3), 6·0.5(2-APS)2, were obtained from the reaction of 2-R-(pyridin-2-yl)benzothiazoline precursors (R= H, 1; R= Me, 2; R= Ph, 3) with zinc acetate dihydrate in a 1:1 ratio. All the complexes crystallized as dinuclear species and complex 6 cocrystallized with one molecule of bis(2-aminophenyl) disulfide (2-APS)2. The anionic Schiff base ligands {Ln}- displayed a κ2N,κS-tridentate coordination mode with the formation of two five-membered chelate rings. In 4, 5 and 6·0.5(2-APS)2, both ZnII ions are pentacoordinated and the coordination sphere of 4 was different with respect to those in 5 and 6·0.5(2-APS)2. For 4, the X-ray diffraction study showed a dinuclear complex containing two bridging acetate ligands linked to both ZnII ions. For 5 and 6·0.5(2-APS)2, the dinuclear complexes displayed one bridging acetate ligand linked to both ZnII ions, where the first ZnII ion includes a dative bond with one S atom from an adjacent anionic Schiff base {Ln}-, while the second ZnII ion is coordinated to one terminal acetate ligand. In each dinuclear complex, the geometry is the same for both ZnII metal centres. The local geometry of the ZnII cation in 4 is halfway between trigonal bipyramidal and square pyramidal local geometries; in 5 and 6, the local geometries are described as distorted square pyramidal. Hirshfeld surface analysis of 5 and 6 showed the predominance of H...H interactions, as well as the contribution of C-H...C, C-H...O and C-H...S noncovalent interactions to the cohesion of the crystalline network of the ZnII complexes.

Dinuclear Cobalt(II) Bis-Dipyrromethane Complexes: Synthesis via Divergent Transmetalation Reactions.

A bis-dipyrromethane ligand, 4,4'-bis(1,1-bis(3,5-dimethyl-1H-pyrrol-2-yl)ethyl)-1,1'-biphenyl, [H4-MeBDPM-BPh] (1), is synthesized via acid-catalyzed electrophilic aromatic substitution of 2,4-dimethylpyrrole with 4,4'-diacetylbiphenyl. Subsequent deprotonation of 1 with n-BuLi yields the corresponding Li-salt [Li4-MeBDPM-BPh] (2). Transmetalation involving 2 and either CoCl2 or [Co(HMDS)2] (HMDS = -N(Si(CH3)3)2) results in dinuclear Co(II) complexes. In the case of CoCl2, the formation of the ate-complex 2[Li(THF)4][(MeBDPM-BPh){Co(μ-Cl)2Li(THF)2}2] (3) is observed where each metal center occupies a tetrahedral geometry with noninteracting metal centers. However, when utilizing [Co(HMDS)2], the dinuclear complex 2[Li(THF)4][(MeBDPM-BPh){Co(HMDS)}2] (4) is obtained with the formation of LiHMDS as the product of elimination. The Co metal centers of complex 4 are both three-coordinate and trigonal planar. Displacement of LiHMDS from 4 readily occurs upon treatment with the ylide base, H2CPPh3, yielding the neutral complex [(MeBDPM-BPh){Co(H2CPPh3)2}2] (5). At room temperature, complexes 3-5 have magnetically noninteracting metal centers with S = 3/2 spin states.

Crystal structure and optical properties of a new 0D Sb-based hybrid metal halide: (3,5-DMP)3Sb2Br9

Zero-dimensional (0D) lead-free hybrid organic-inorganic metal halides (OIMHs) have recently garnered tremendous attention due to their diversified structures and unique structure-dependent photoluminescent (PL) properties. Herein, we report a novel Sb-based 0D hybrid organic-inorganic metal halide (OIMH), with the chemical formula (3,5-DMP)3Sb2Br9 [3,5-DMP+ = 3,5-dimethyl piperidinium cation, C7H16N+]. The (3,5-DMP)3Sb2Br9 compound crystallizes in the triclinic crystal system (P1‾ space group), possessing a typical zero-dimensional (0D) structure with isolated face-sharing (Sb2Br9)3− bi-octahedral units encased by (3,5-DMP)+ organic cations. The isolated bi-octahedral units are distorted due to the strong stereochemical expression of the 5s2 lone pair on Sb3+ and intermolecular H-bonding between the organic moieties and inorganic clusters. The compound exhibited good thermal and environmental stability and possessed an indirect band gap of 2.92 eV. Upon 390 nm UV light excitation, the compound displayed a broad emission band centred at 555 nm, which was attributed to the self-trapped excitons (STEs) formed due to strong electron-phonon coupling in this compound. This study suggests the possibility of new types of 0D OIMHs by introducing different metal centers and bulky organic cations and provides a reference for the structure-property relationship in these compounds, thus, offering guidance for examining the structural evolution and improving their luminescent properties.

Insight into the Structural Optimization and Electrical Conductivity of NiII/MnII Bipyridine–Dicyanamide Complexes

AbstractTwo monomeric octahedral complexes {[Ni(N(CN)2)2(bpy)2]2·H2O (1) and [Mn(N(CN)2)2(bpy)2] (2) where bpy = 2,2′‐bipyridine} were synthesized and characterized by single crystal X‐ray diffraction, elemental analysis, UV–visible, and IR spectra. The geometry optimization through DFT measurements predicts that both the complexes have similar monomeric structures with hexa‐coordinated metal centers having a couple of bpy and mononegative dca anions and thus satisfying the octahedral geometry. Moreover, it is found that the HOMO–LUMO energy gaps are ΔE = 4.981 and 5.563 eV for complexes 1 and 2, respectively, which are responsible for the stabilization of the complex formation. The calculated absorption bands are located at 304 and 235 nm, which are in excellent agreement with the experimental result. Moreover, the DFT study of the electronic spectra of both complexes shows that the calculated absorption bands are in well agreement with the experimental results. In the electrical studies, direct current (dc) measurements on the copper/complex (1 or 2)/copper structure confirm a definite development in the device current with applied bias. Complex 1 has shown better electrical conductance compared to complex 2 based on the reduction of device resistance.

Dynamic Adaptation of Active Site Driven by Dual‐side Adsorption in Single‐Atomic Catalysts During CO2 Electroreduction

Single‐atom iron embedded in N‐doped carbon (Fe‐N‐C) is among the most representative single‐atomic catalysts (SACs) for electrochemical CO2 reduction reaction (CO2RR). Despite the simplicity of the active site, the CO2‐to‐CO mechanism on Fe‐N‐C remains controversial. Firstly, there is a long debate regarding the rate‐determining step (RDS) of the reactions. Secondly, recent computational and experimental studies are puzzled by the fact that the CO‐poisoned Fe centers still remain highly active at high potentials. Thirdly, there are ongoing challenges in elucidating the high selectivity of hydrogen evolution reaction (HER) over CO2RR at high potentials. In this work, we introduce a novel CO2RR mechanism on Fe‐N‐C, which was inspired by the dynamic of active sites in biological systems. By employing grand‐canonical density functional theory and kinetic Monte‐Carlo, we found that the RDS is not fixed but changes with the applied potential. We demonstrated that our proposed dual‐side mechanisms could clarify the reason behind the high catalytic activity of CO‐poisoned metal centers, as well as the high selectivity of HER over CO2RR at high potential. This study provides a fundamental explanation for long‐standing puzzles of an important catalyst and calls for the importance of considering the dynamic of active sites in reaction mechanisms.

Mononuclear phenoxy-imine Mg(II) compounds as catalysts for the ring-opening copolymerization of epoxides with CO2

The ring-opening copolymerization (ROCOP) of epoxides with CO2 is an efficient gateway for synthesizing sustainable aliphatic polycarbonates. The demand for the use of biocompatible metals for the copolymerization is an appealing research goal. The oxophilic Mg(II) has been employed as a metal center in homodinuclear and heterodinuclear catalyst frameworks. However, there is scarce literature involving mononuclear Mg(II) compounds. This work investigates the catalytic activity of two series of phenoxy-imine containing mononuclear Mg(II) compounds for the copolymerization studies of epoxides with CO2 in conjugation with cocatalyst tetraphenylphosphonium chloride (TPPCl). The two series of Mg(II) compounds differed from each other in the number of ancillary ligands attached to the Mg(II) center. The two epoxides employed for the study include cyclohexene oxide (CHO) and propylene oxide (PO). The catalytic activity of the disubstituted Mg(II) compounds was higher compared to monosubstituted compounds. In addition, the dependence of catalytic activity and percentage of carbonate linkage with the variation in the substituent of the phenolate core and imine side arm were studied. At 40 bar CO2 pressure and 80 °C, the catalyst exhibited carbonate linkage up to 97 % for ROCOP with cyclohexene oxide (CHO) with the percentage of the highest m-centered tetrad reaching up to 94 %. The mechanism for the ROCOP of CHO with CO2 is proposed based on kinetics studies and experimental data, which is further supported by density functional theory-based calculations.

Band Structure Engineering in 2D Metal-Organic Frameworks.

The design of 2D metal-organic frameworks (2D MOFs) takes advantage of the combination of the diverse electronic properties of simple organic ligands with different transition metal (TM) centers. The strong directional nature of the coordinative bonds is the basis for the structural stability and the periodic arrangement of the TM cores in these architectures. Here, direct and clear evidence that 2D MOFs exhibit intriguing energy-dispersive electronic bands with a hybrid character and distinct magnetic properties in the metal cores, resulting from the interactions between the TM electronic levels and the organic ligand π-molecular orbitals, is reported. Importantly, a method to effectively tune both the electronic structure of 2D MOFs and the magnetic properties of the metal cores by exploiting the electronic structure of distinct TMs is presented. Consequently, the ionization potential characteristic of selected TMs, particularly the relative energy position and symmetry of the 3d states, can be used to strategically engineer bands within specific metal-organic frameworks. These findings not only provide a rationale for band structure engineering in 2D MOFs but also offer promising opportunities for advanced material design.

Efficient screening of single-atom Porphyrazine-coordinated transition metal catalysts for electrochemical nitric oxide reduction: Insights from first-principles calculations

The electrochemical conversion of NO to NH3 is gaining attention in green energy for its dual benefits of producing ammonia and eliminating toxic NO. However, the lack of efficient and durable electrocatalysts limits its application, highlighting the need for improved catalysts to advance this promising strategy. The emerging transition metal porphyrazine frameworks (TM − Pz), which combine the advantages of single-atom metal (SAC) centers with the coordination of surrounding 4 N ligands, present promising opportunities in the field of electrochemical catalysis. We have designed a series of 3d transition metal single-atom catalysts (SACs) and conducted high-throughput screening, based on first-principles computations, to identify effective catalysts for the electrocatalytic conversion of NO to NH3. Our findings reveal that the Ti − Pz, Fe − Pz, and V − Pz nanosheets exhibit significantly lower UL values of −0.11, −0.24, and −0.31 V, respectively, when compared to the experimentally and theoretically determined criterion of −0.32 V. The correlation between limiting potentials (UL) and a specific descriptor (φ) is particularly significant for constructing a volcano plot, which illustrates the intrinsic properties of metal atoms in various TM − Pz series and their associated remarkable nitric oxide reduction reaction (NORR) performance. Among the range of nanosheets evaluated, the Ti − Pz and Fe − Pz models emerge as particularly noteworthy, demonstrating significantly higher selectivity and NORR activity than their counterparts. This research deepens our comprehension of the distinctive and advantageous properties of SACs, presenting progressive perspectives that can directly facilitate the discovery and optimization of SACs for NORR applications.

Development of a novel ternary MOF nanozyme-based smartphone-integrated colorimetric and microfluidic paper-based analytical device for trace glyphosate detection

Given the significant and potential fatal implications of glyphosate (GLY) residues on human health and the integrity of ecosystems, their presence has garnered substantial global concern and scrutiny. Herein, we introduced a pioneering colorimetric sensing platform, the first of its kind, based on ternary metal-organic frameworks (ZnCo-ZIFs@MIL-101(Fe)). This innovative platform enabled ultra-sensitive, affordable, portable and rapid on-site detection of GLY. This platform achieved a wider linear range for GLY of 0.02–40 μg/ml with an exhibiting remarkable detection limit of 1 ng/ml, which was attributed to the electronic hybridization of the Fe3+, Co2+, and Zn2+ metal centers of ZnCo-ZIFs@MIL-101(Fe), significantly enhancing the composite's catalytic performance. The assay was successfully employed to detect GLY in food and herb samples. Moreover, to meet the demand of in-field detection for GLY, a smartphone detection method based on ZnCo-ZIFs@MIL-101(Fe) with visual, intelligent, and portable features was fabricated. This detection concentration range of GLY was 0–1 μg/ml, and the limit of smartphone detection was 23 ng/ml. Furthermore, this sensor seamlessly integrated with smartphones and paper-based microfluidic chips (μPADs), which constructed a portable test strips-smartphone sensing platform for facilitating real-time and on-site visual quantitative detection of GLY. The detection concentration range was 0–1 μg/ml, and the limit was calculated as low as 75 ng/ml. The assay was highly adaptable in practical applications. In summary, our study paved a novel pathway for the design and utilization of multi-metal MOF nanozymes in on-site pesticide monitoring.

Increasing catalytic efficiency of cobalt centers in oxygen reduction reaction - Evidence from cobalt with salen ligands polymer complex

Substantial research is performed for cobalt-based catalysts for various applications in catalysis, including oxygen reduction reaction (ORR) catalysis in nonaqueous electrolytes. Cobalt exhibits high catalytic activity due to partially filled d-orbitals, which promote the formation of chemisorption bonds with various molecules. The catalytic activity of metal centers can be influenced both by changing their immediate environment and by varying the reaction conditions. This paper investigates the influence of solvent type, electrolyte concentration, and organic framework conductivity on the efficiency of ORR catalysis in non-aqueous electrolytes as illustrated by poly-CoSal polymer complex. The findings show that the increase in the solvent donor number of and conductivity of the organic backbone leads to highly efficient cobalt catalysts, which can be potentially be applied in oxygen cathodes of Li-O2 batteries. CoSal-based catalysts increase the discharge voltage of Li-O2 cells and can operate in dry atmospheric air.

Natural Abundance 195Pt-13C Correlation NMR Spectroscopy on Surfaces Enabled by Fast MAS Dynamic Nuclear Polarization

Surface organometallic chemistry has developed as an effective strategy for the rational design and synthesis of well-defined, single-site Pt-based heterogeneous catalysts. Given its high sensitivity to changes in electronic structure, 195Pt solid-state NMR spectroscopy offers a unique approach to investigate the chemical structure and local environment of Pt surface sites, providing invaluable insights for establishing structure-activity relationships. However, this approach is typically hindered by severe sensitivity issues, due to the low loading of Pt sites and the often-encountered large 195Pt chemical shift anisotropies. To overcome this limitation, 195Pt NMR signature of surface metal centers can be indirectly detected through protons. Indirect detection on 13C spins, has also been demonstrated to be feasible by combining isotopic labeling with dynamic nuclear polarization (DNP). Here, we extend this methodology to a supported Pt complex at natural abundance. The material was prepared by grafting (COD)PtMeOSi(OtBu)3 (COD = 1,5-cyclooctadiene, Me = methyl and tBu = tert-butyl) onto partially dehydroxylated silica. DNP enhanced two-dimensional through-bond 13C{195Pt} heteronuclear correlation experiments were successfully implemented at fast magic angle spinning. They enabled the detection of the 0.37% NMR-responsive surface species, thereby showcasing the remarkable sensitivity of this approach and its broad applicability. Key bonding information was obtained by measuring the correlated 13C and 195Pt isotopic chemical shifts as well as 1J(13C-195Pt) coupling constants, confirming directly the coordination structure of the surface Pt sites.

Structural studies and physicochemical properties of indium(III) complexes with 2-formyl-8-hydroxyquinoline-derived hydrazones

The reaction of InCl3 with 2-formyl-8-hydroxyquinoline-4-nitroimidazole hydrazone (H2L1) in ethanol gave [In(H2L1)(HL1)Cl2], complex (1), as the product. Experimental data and theoretical DFT calculations suggested that complex (1) presents coordination number (CN) 8, with one neutral and one anionic ligand coordinated to the metal center through the O-Npy-N tridentate chelating system together with two chloride ions. The reaction with 2-formyl-8-hydroxyquinoline-4-nitrobenzene hydrazone (H2L2) in methanol gave [In(HL2)Cl2(CH3OH)], complex (2), as the product while [In(HL2)Cl2]·CH3CH2OH, complex (3), was formed as the product using ethanol as solvent. Experimental data indicated that in complexes [In(HL2)Cl2(CH3OH)] (2) and [In(HL2)Cl2]·CH3CH2OH (3) one anionic ligand is attached to the indium(III) center through the O-Npy-N-O tetradentate chelating system along with two chlorides. The crystal structure of the complex [In(HL2)Cl2(CH3OH)] (2) revealed that the indium(III) center presents CN 7. Calculated bond lengths in complex (2) were in accordance with the experimental values. The experimental and calculated electronic spectra of complexes (1) and (2) presented the same pattern and allowed the attribution of the absorption peaks to π - π* transitions.