Metal Center Research Articles

Hofmann-type MOF-derived CuNiOx photocathode for effective PEC H2 production

A novel mixed metal oxide of CuNiOx has been successfully obtained via electrosynthesis and thermal conversion of a Hofmann-type MOF Cu(pz)2[Ni(CN)4] (pz = pyrazine). CuNiOx has demonstrated a significant enhancement in light absorption within a visible light range, leading to an impressive increase in photocurrent density and photocatalytic activity during light irradiation compared to CuO. The exceptional photoelectrochemical properties of the photocathodes of CuNiOx have been studied using multiple photoelectrochemical instrumental techniques, which proved the electrodes were stable over the whole water photolysis. The coupling of two metal centers has explained their outstanding performance.

Controlled formation of CoOOH/Co(III)-MOF active phase for boosting electrocatalytic alkaline water oxidation

Surface reconstituted metal-organic frameworks (MOFs) offer appealing properties for electrocatalysis due to their unique structural and compositional advantages. In this work, a controlled potential-induced reconstruction of a two-dimensional cobalt metal-organic framework for boosting oxygen evolution reaction in alkaline media is reported. The current MOF is shown to undergo a partial structural transformation that generates a heterogeneous system, where the original MOF coexists with an oxyhydroxide phase. In fact, the potential-induced stabilization of Co(III) metal centers in the MOF is crucial for delaying its full degradation in alkaline media. This partial retention of the Co(III)MOF phase in the so-derived heterogeneous catalyst has been demonstrated to be decisive for boosting the alkaline electrocatalytic oxygen evolution reaction (OER), displaying superior OER activity in terms of both thermodynamic and kinetic merits compared to the benchmark IrO2 and RuO2 electrocatalysts and the prototypical cobalt (oxy)hydroxides, with a Tafel slope of 52 mV dec−1 and a turnover frequency (TOF) of 6.8 s−1 at 450 mV. Remarkably, the generated final product is stable, exhibiting high robustness and long durability for long-term OER electrolysis. This work provides new insight into the impact of the reconstruction of a MOF for alkaline OER under typical electrochemical conditions, which ultimately benefits the rational design of MOF-based catalysts with high electrocatalytic activity for oxidation reactions.

Influence of Metal Ions on the Structural Complexity of Mixed-Ligand Divalent Coordination Polymers

The reactions of the angular ligand 4,4′-oxybis(N-(pyridin-3-yl)benzamide) (L1) and 1,4-naphthalenedicarboxylic acid (1,4-H2NDC) with divalent metal salts yielded three distinct coordination polymers (CPs): {[Zn2(L1)(1,4-NDC)2]·MeOH}n, 1, {[Cu(L1)(1,4-NDC)(H2O)]·3H2O}n, 2, and {[Cd(L1)(1,4-NDC)]·2H2O}n, 3. Complex 1 features a 2-fold interpenetrated 3D framework with the (412·63)-pcu topology, while complex 2 reveals a 1D triple-strained helical chain and complex 3 displays a 3-fold interpenetrated 3D framework with (66)-dia topology. Additionally, the reactions of the flexible ligand N,N′-bis(3-methylpyridyl) adipoamide (L2) afforded {[Co4(L2)0.5(1,4-NDC)3(H2O)3(µ3-OH)2]·EtOH·2H2O}n, 4, {[Zn2(L2)(1,4-NDC)2]·2CH3OH}n, 5, and [Cd(L2)(adipic)(H2O)]n (H2adipic = adipic acid), 6, exhibiting a self-catenated 3D framework with the (420·68)-8T32 topology, a 2D layer with the (413·62) − (4,4)IIb topology, and a 2D layer with the (44·62)-sql topology, respectively. The structural diversity observed in complexes 1–6 highlights the pivotal influence of the metal center on the degree of entanglement in CPs within mixed-ligand systems. The thermal stability and luminescent properties of complexes 1–3, 4, and 6 are also discussed.

Improving the electrochemical performance of nickel-cobalt organic framework by hybridizing with carbon quantum dots

To improve the electrochemical properties of nickel-cobalt metal-organic skeleton materials, two carbon quantum dots (CQDs), namely, CQD-CA and N-doped CQD-CAn, were prepared by using citric acid as carbon source and then introduced into NiCo-MOF to prepare CQDs/NiCo-MOF composites. Through the application of physical characterization and electrochemical analysis methods, such as SEM, TEM, XRD, XPS and BET, it was found that NiCo-MOF@CA and NiCo-MOF@CAn exhibited a nano thinner lamellar structure, higher specific surface area, larger pore structure, and excellent electron transport ability. Especially, by introducing CQDs, the charge could transfer from oxygen to Ni and Co, and there was some higher electron cloud density around active metals Ni and Co in NiCo-MOF@CAn than in NiCo-MOF, effectively activating the metal center Ni and Co. As the result, the specific capacitance of NiCo-MOF@CAn reached 1917.7 F·g−1 at the potential scan rate 5 mV·s−1, significantly higher than that of NiCo-MOF (1173.4 F·g−1) and NiCo-MOF@CA (1489.3 F·g−1). The method might provide an alternative strategy for modulating the morphology, porous structure and the partial electron structure of the target materials by introducing various CQDs.

Isolation of Elusive Fluoflavine Radicals in Two Differing Oxidation States.

Facile access and switchability between multiple oxidation states are key properties of many catalytic applications and spintronic devices yet poorly understood due to inherent complications arising from isolating a redox system in multiple oxidation states without drastic structural changes. Here, we present the first isolable, free fluoflavine (flv) radical flv(1-•) as a bottleable potassium compound, [K(crypt-222)](flv•), 1, and a new series of organometallic rare earth complexes [(Cp*2Y)2(μ-flvz)]X, (where Cp* = pentamethylcyclopentadienyl, X = [Al(OC{CF3}3)4]- (z = -1), 2; X = 0 (z = -2), 3; [K(crypt-222)]+ (z = -3), 4) comprising the flv ligand in three different oxidation states, two of which are paramagnetic flv1-• and flv3-•. Excitingly, 1, 2, and 4 constitute the first isolable flv1-• and flv3-• radical complexes and, to date, the only isolated flv radicals of any oxidation state. All compounds are accessible in good crystalline yields and were unambiguously characterized via single-crystal X-ray diffraction analysis, cyclic voltammetry, IR-, UV-vis, and variable-temperature EPR spectroscopy. Remarkably, the EPR spectra for 1, 2, and 4 are distinct and a testament to stronger spin delocalization onto the metal centers as a function of higher charge on the flv radical. In-depth analysis of the electron- and spin density via density functional theory (DFT) calculations utilizing NLMO, QTAIM, and spin density topology analysis confirmed the fundamental interplay of metal coordination, ligand oxidation state, aromaticity, covalency, and spin density transfer, which may serve as blueprints for the development of future spintronic devices, single-molecule magnets, and quantum information science at large.

Schiff base substituted non-peripheral symmetrical cupper, cobalt, and manganese phthalocyanines: Synthesis, design, electrochemistry, and spectroelectrochemistry

Novel CoII (nANTHCoPc), CuII (nANTHCuPc), and MnIIICl (nANTH-MnClPc) phthalocyanines were obtained by substituting the 3-(4-((1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-ylimino)methyl)phenoxy) Schiff base compound (nANTHOH) obtained by the acid-catalyzed condensation reaction of 4-aminoantipyrine and 4-hydroxybenzaldehyde at non-peripheral positions. By using various spectroscopic techniques, (NMR, MALDI-TOF, FT-IR, and UV–Vis), the structures of green-colored phthalocyanine compounds and precursor phthalonitrile compounds were identified. The electrochemical responses of cobalt (II) (nANTHCoPc), cupper (II) (nANTHCuPc), and manganese (III) (nANTH-MnClPc) phthalocyanines were determined, and their redox responses were analyzed based on the different metal centers. The results indicated that using redox-active Co2+ and Mn3+ cations instead of Cu2+enhanced the redox richness of the complexes due to the observation of extra metal-based electron transfer reactions in addition to the Pc-based ones. In-situ spectroelectrochemical analyses of the complexes were used to support the peak assignments of the redox processes and the spectrum and color of the electrogenerated species during the redox reactions. Supported these redox mechanisms. Multi-electron transfer processes and distinct color changes during these processes indicate the possible usage of these complexes in various electrochemical and opto-electrochemical processes. Metal-based electron transfer reactions illustrated different spectral changes than those of the Pc-based ones, and these spectral changes significantly differed the color of the anionic and cationic species.

Spin Crossover Quenching by "Racemization" in a Family of trans-1,2-Di(tetrazol-1-yl)cyclopentane-Based Fe(II) 1D Coordination Polymers.

Optically pure (RR)- and racemic (RR/SS)-trans-1,2-di(tetrazol-1-yl)cyclopentane were synthesized and used to prepare homo- and heterochiral Fe(II) coordination compounds. [Fe((RR/SS)-C7H10N8)2(CH3CN)2](BF4)2 (1A), [Fe((RR/SS)-C7H10N8)2(C2H5CN)2](BF4)2 (2A), [Fe((RR)-C7H10N8)2(CH3CN)2](BF4)2·2CH3CN (1B·solv), and [Fe((RR)-C7H10N8)2(C2H5CN)2](BF4)2 (2B) form a family of one-dimensional coordination polymers. Fe(II) cations in these complexes are characterized by a heteroleptic coordination environment: the neighboring metal centers are bridged by two 1,2-di(tetrazol-1-yl)cyclopentane molecules, while the nitrile molecules (acetonitrile or propionitrile, respectively) occupy the axial positions. Independently of the kind of nitrile coligands, an ability to thermally induce spin crossover (SCO) is governed by chirality. 1B·solv and 2B exhibit abrupt and complete SCO occurring at T1/2 = 144 K and T1/2 = 228 K, respectively. Desolvated form, 1B (of the same stoichiometry as 2B), also exhibits SCO (T1/2 = 215 K). In contrast, an exchange within the polymeric chain of half of the RR molecules with the SS enantiomeric form results in formation of 1A and 2A, which remain in stable high-spin (HS) form down to 10 K. It has been shown that moving from a homochiral to a heterochiral system changes the structure of the polymeric unit (while maintaining the same polymer dimensionality and bridging fashion) that leads to the deep reorganization of the further coordination spheres, including the anion network.

Investigating the catalytic influence of MIL-101(Cr) and MIL-101(Cr)-NH2 on glucose dehydration into 5-hydroxymethylfurfural and modelled through response surface methodology

Dehydration of glucose into 5-hydroxymethylfurfural (5-HMF) is an effective approach for generating bio-based chemicals. Metal-organic frameworks (MOFs) are notable catalysts for this process due to their unsaturated metal centers. Functionalized MOFs further enhance these catalytic properties. This study investigates the catalytic abilities of MIL-101(Cr) and MIL-101(Cr)-NH2 for glucose dehydration into 5-HMF using an H2O + DMSO solvent system. Using Response Surface Methodology (RSM), the reaction parameters (temperature, time, and catalyst amount) were optimized to maximize 5-HMF yield. Results showed that at 180 °C, MIL-101(Cr) achieved a 5-HMF yield of 21 % with a selectivity of 22 %, while MIL-101(Cr)-NH2 achieved a 5-HMF yield of 55 % with a selectivity of 56 %. MIL-101(Cr) demonstrated a glucose conversion rate of 92 %, and MIL-101(Cr)-NH2 achieved a conversion rate of 99 % after 3 h at 180 °C. The optimized 5-HMF yield predicted by RSM for MIL-101(Cr) was 53.8 %, whereas the experimentally obtained value was 24.23 %. For MIL-101(Cr)-NH2, the predicted 5-HMF yield was 35.46 %, with an experimental value of 47.51 %. The Lewis acidic nature of MIL-101(Cr) arises from the Cr sites, while MIL-101(Cr)-NH2 exhibits both Lewis acidic characteristics from the Cr sites and Brønsted basic characteristics from the non-coordinated primary amine groups. The experimental results highlight the potential of MIL-101(Cr)-NH2, which produced a higher 5-HMF yield compared to MIL-101(Cr). The dual nature of MIL-101(Cr)-NH2 enhances glucose dehydration to 5-HMF, resulting in significantly higher yields. This study underscores the effectiveness of MIL-101(Cr)-NH2 in converting glucose to 5-HMF, advancing biomass utilization efficiency.

Strategies and Mechanisms of First-Row Transition Metal-Regulated Radical C-H Functionalization.

Radical C-H functionalization represents a useful means of streamlining synthetic routes by avoiding substrate preactivation and allowing access to target molecules in fewer steps. The first-row transition metals (Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) are Earth-abundant and can be employed to regulate radical C-H functionalization. The use of such metals is desirable because of the diverse interaction modes between first-row transition metal complexes and radical species including radical addition to the metal center, radical addition to the ligand of metal complexes, radical substitution of the metal complexes, single-electron transfer between radicals and metal complexes, hydrogen atom transfer between radicals and metal complexes, and noncovalent interaction between the radicals and metal complexes. Such interactions could improve the reactivity, diversity, and selectivity of radical transformations to allow for more challenging radical C-H functionalization reactions. This review examines the achievements in this promising area over the past decade, with a focus on the state-of-the-art while also discussing existing limitations and the enormous potential of high-value radical C-H functionalization regulated by these metals. The aim is to provide the reader with a detailed account of the strategies and mechanisms associated with such functionalization.

Novel copper-drugs bearing dipodal bis-mercaptobenzimidazoles: Synthesis, crystal structures, in vitro biological activities, DNA binding, DFT calculations and molecular docking

Three novel copper(II) complexes, 1–3, bearing dipodal bis-mercaptobenzimidazole derivatives based on ortho-, meta- or para-xylene (L1, L2, and L3) were successfully prepared and characterized by using various spectral techniques, including elemental analysis, FT-IR, 1H NMR, and UV–Vis spectroscopy, LC-MS spectrometry and TGA. The analysis revealed that the ligand/metal molar ratio in all copper(II) complexes is 1:1 and the ligand coordinates as a neutral N-donor onto metal center. Additionally, the crystal structures of L1, L2, L3, and copper(II) complex 2 were determined using single crystal X-ray diffraction (SC-XRD) analysis. Copper(II) complexes 1–3 displayed significant stability at pH range of 4–10. The antibacterial effect of ligands and complexes was tested against both gram-negative (Escherichia coli, E. coli ATCC 25922 PTCC 1399) and gram-positive (Staphylococcus aureus, S. aureus ATCC 6538 PTCC 1112) bacterial strains. It should be noted that the complexes showed enhanced antibacterial activity (up to 99 %) when compared to their free ligands. The in vitro studies of all synthesized compounds consisted of testing them against the human colorectal carcinoma cancer cell line (HCT-116) using the MTT assay. The findings revealed that the copper(II) complexes exhibited lower CC50 values (CC50 ranging from 0.045 mM to 0.135 mM) compared to their corresponding ligands (CC50 ranging from 0.150 mM to 0.240 mM) and carboplatin (CC50 = 0.165 mM), indicating higher anticancer activity of the complexes. Additionally, DAPI staining and fluorescence spectroscopy (at three different temperatures) were performed to further examine the impact of complexes 1–3 on inducing apoptosis and to explore their interaction with DNA, respectively. The results revealed a dynamic quenching mechanism, with hydrophobic forces playing a dominant role in the binding process. The viscosity measurements indicated that all complexes could interact in a groove binding manner with DNA. Density functional theory (DFT) calculations were employed to support the structural and vibrational studies and to predict the chemical reactivity. Docking simulations were conducted to evaluate their behavior of the synthesized compounds towards DNA (PDB: 1BNA). These results suggested that various elements, including NH groups, imidazole rings, thioetheric sulfur atom and sulfate moieties of ligands and complexes, are involved in groove binding with DNA.

Metal-organic frameworks with dinuclear metal centers for synergistically boosting CO2 photoreduction

Metal-organic frameworks with dinuclear metal centers for synergistically boosting CO2 photoreduction

Experimental and computational investigations of supramolecular interactions in Cd(II)‐organic hydrate: catalytic applications in the Knoevenagel condensation reaction under solvent‐free conditions

A dinuclear cadmium(II) complex, [Cd2(Hhqc)2(H2O)4] (H3hqc= 4,8‐dihydroxyquinoline‐2‐carboxylic acid) was synthesized and characterized by single crystal X‐ray diffraction studies, elemental analyses and thermo‐gravimetric studies. The metal centers are found to be six coordinated with distorted pentagonal pyramidal geometry around them. The complex shows few significant intermolecular hydrogen bonding interactions to produce a three dimensional supramolecular network comprising of T8(2) water tapes. Besides these non‐covalent interactions few other supramolecular interactionsare also involved within the molecular dimer like π···π stacking, Cd···π etc. They have been analyzed using DFT calculations, MEP surface analyses and NCI plot index analyses. The detailed study‐highlights the complex interplay of π‐stacking, H‐bonding, and spodium interactions in stabilizing the dimers of complex, which providing precious insights into their energetic and structural characteristics. Furthermore, the catalytic efficiency of the synthesized complex has been investigated as an effective heterogeneous catalyst in the Knoevenagel condensation reaction under solvent‐free conditions.

Copper Single-Atom Nanozyme Mimicking Galactose Oxidase with Superior Catalytic Activity and Selectivity.

Due to the low stability and high cost of some natural enzymes, nanozymes have been developed as enzyme-imitating nanomaterials. Single-atom nanozymes are a class of nanozymes with metal centers that mimic the structure of metal-based natural enzymes. Herein, Cu-N-C single-atom nanozyme (SAN) is synthesized with excellent peroxidase- and enhanced oxidase-like activities to mimic the action of natural galactose oxidase. Cu-SAN demonstrates stereospecific activity akin to that of natural galactose oxidase by oxidizing D-galactose and primary alcohol but not L-Galactose or other carbohydrates. The SAN can catalyze the oxidation of galactose in the presence of oxygen, producing hydrogen peroxide as a sub-product. The produced hydrogen peroxide then oxidizes 3,3',5,5'-tetramethylbenzidine catalyzed by the SAN, yielding the typical blue product. The relationship between absorbance and galactose concentration is linear in the 1-60µm range with a detection limit as low as 0.23µm. This strategy can be utilized in the diagnosis of galactosemia disorder and detection of galactose in some dairy and other commercial products. DFT calculations clarify the high activity of the Cu sites in the POD-like reaction and explain the selectivity of the Cu-SAN oxidase-like reaction toward D-galactose.

Synthetic and theoretical study on novel N-ylidic complexes of mercury as new antibacterial agents

The novel structure of Hg(II) complexes including the pyridinium ylide C5H5NCHC(O)C6H4-m-Br (Y) were synthesized and reported in this study. In the first step, the pyridinium salt C5H5NCH2C(O)C6H4-m-Br (S) was produced by reacting 2,3′-dibromoactophenone and pyridine. then, treatment of S with K2CO3 gave the related pyridinium ylide Y. Finally, the reaction of Y with HgX2 and Hg(NO3)2·H2O leads to the formation of novel binuclear [HgY2][HgX4] (X=Cl (1); X=Br (2); X=I (3)) and polymeric [HgY(NO3)2]n (4) complexes. The structure of complex 2 was also determined by X-ray diffraction analysis. The obtained analyses proved the coordination through the ylidic carbon to metallic center. Additionally, Natural Bond Orbital (NBO), Energy Decomposition Analysis (EDA), and EDA-NOCV studies are also used to investigate the nature of metal–ligand bonding in the complexes. Finally, the antibacterial activity of 1–4 was also examined against Gram positive and negative represented significant levels of inhibitory potency respected to used standards.

A [2.2]Isoindolinophanyl-Based Carbene (iPC) Ligand: Synthesis, Electronic and Photophysical Properties, and Application in Photocatalysis.

Cyclic amino(alkyl) and cyclic amino(aryl) carbenes (cAACs/cAArCs) have been established as very useful ligands for catalytic and photonic applications of transition metal complexes. Herein, we describe the synthesis of a structurally related sterically demanding, electrophilic [2.2]isoindolinophanyl-based carbene (iPC) that bears a [2.2]paracyclophane moiety. The latter leads to more delocalized frontier orbitals and intense green fluorescence of (HiPC)OTf (2) from an intra-ligand charge transfer (1ILCT) state in the solid state. Base-promoted synthesis of the free carbene led to an unusual ring expansion and subsequent dimerization reaction, but the beneficial ligand properties can be exploited by trapping in situ at a metal center. The iPC ligand is a very potent π-chromophore, which participates in low energy metal-to-ligand (ML)CT transitions in [RhCl(CO)2(iPC)] (4) and IL-"through-space"-CT transitions in [Au(iPC)2]OTf (5). The steric demand of the iPC leads to high stability of 5 against air, moisture, or solvent attack, and ultralong-lived green phosphorescence with a lifetime of 185 μs is observed in solution. The beneficial photophysical and electronic properties of the iPC ligand, including a large accessible π surface area, were exploited by employing highly efficient energy transfer (EnT) photocatalysis in a [2+2] styrene cycloaddition reaction using 5, which outperformed other established photocatalysts in comparison.

Spirobipyridine Ligand Enabled Iridium‐Catalyzed Site‐Selective C−H Activation via Non‐Covalent Interactions

AbstractThe selective borylation of specific C−H bonds in organic synthesis remains a formidable challenge. In this study, we present a novel spirobipyridine ligand that features a binaphthyl backbone. This ligand facilitates the iridium‐catalyzed selective C−H borylation of benzene derivatives. The ligand is designed with “side‐arm‐wall” substituents that allow vicinal di‐ or multi‐substituted benzene derivatives to approach metal center and effectively block other reactive sites by non‐covalent interactions with substrates. The effectiveness of this strategy is demonstrated by the successful selective distal C−H activation of various alkaloids and its broad compatibility with functional groups.

Redox-active sp2-c connected metal covalent organic frameworks for selective detection and reductive separation of uranium

It is economically desirable to develop a material that can simultaneously detect and recover uranium. Herein, a CC-bridged two-dimensional metal-covalent organic framework (Cu-BTAN-AO MCOF) was constructed by condensation of metal single crystals with a rigid structure (Cu3(PyCA)3) and cyano monomers (BTAN) via Knoevenagel reaction for simultaneous detection and adsorption of uranium. The amidoxime group within the pore and the presence of unsaturated Cu(I) in the framework facilitate the adsorption of uranyl ions onto the amidoxime group, leading to fluorescence quenching via the photoinduced electron transfer (PET) mechanism, achieving a detection limit of as low as 167 nM uranyl ions. Furthermore, Cu-BTAN-AO demonstrates exceptional efficiency in capturing uranium from wastewater characterized by rapid kinetics and superior selectivity. It is noteworthy that Cu-BTAN-AO is the first example of simultaneous detection, adsorption and chemical reduction of uranium using metal centers and functional groups in MCOF, indicating that Cu-BTAN-AO has great potential for the detection and recovery of uranium-containing wastewater. This design strategy may also be applicable to advancing sensing and energy materials for other important metal ions.

Glycyrrhizic acid and glycyrrhetinic acid loaded cyclodextrin MOFs with enhanced antibacterial and anti-inflammatory effects for accelerating diabetic wound healing

A water stable cyclodextrin MOF (Cu-SD) was synthesized with γ-cyclodextrin derivative as organic ligand and Cu2+ as metal center to co-crystallizely load glycyrrhizic acid (GL) and glycyrrhetinic acid (GA). Cu-SD has a high drug loading capacity for GL (499.91 μg/mg) and GA (112.37 μg/mg), and the drug-loaded materials had a controlled release in different meadiums. In addition, Cu-SD and its drug loaded materials demonstrated better inhibiting α-glucosidase activity than the control drug acarbose. Furthermore, Cu-SD presented excellent antibacterial activity, and the antibacterial activity was significantly enhanced after GA and GL being encapsulated by Cu-SD. Moreover, both free and drug-loaded materials had good anti-inflammatory activities, and the anti-inflammatory effects of GL@Cu-SD and GA@Cu-SD were superior to those of their corresponding free drugs. Cu-SD, GL@Cu-SD and GA@Cu-SD demonstrated good biocompatibility and were applied to treat the wounds of diabetic rats. The experimental results showed that GL@Cu-SD and GA@Cu-SD had good promoting effects on the recovery of chronic diabetic wounds by suppressing wound inflammation.

Synthesis of Rare Earth Metal Complexes Stabilized by Amine Bridged Bis(phenolato) Ligands and Their Performance in the Polymerization of rac-β-Butyrolactone.

A series of rare earth alkoxides bearing amine-bridged bis(phenolato) ligands were synthesized through sequential reactions of RE(C5H5)3(THF) (RE = Y, Lu) or Nd[N(SiMe3)2]3 with bis(phenols) LH2 and CF3CH2OH. Complexes REL(OCH2CF3)(THF)n (1-6) bearing different aryl-substituents were obtained in good yields of 59-70%. They were applied in the ring-opening polymerization (ROP) of rac-β-butyrolactone (rac-BBL), which showed good activity (TOF up to 27,300 h-1), resulting in syndiotactically enriched poly(3-hydroxybutyrate) (PHB) (Pr up to 0.86) with narrow polydispersities (PDI ≤ 1.27). The yttrium complex 3 bearing bulky o-1,1-diphenylethyl substituents outperformed other complexes, suggesting that the smaller ionic radii of metal centers and bulky ortho substituents of ancillary ligands play crucial roles in controlling the activity and stereoselectivity in ROP of rac-BBL. Kinetics of the polymerization of rac-BBL initiated by complex 3 was investigated, which revealed first order dependences on the monomer and initiator concentrations, respectively.

Microstructure and corrosion properties of Al1-xWxN coatings for potential use in gas turbine blades

Herein, a numerical approach of Al1-xWxN thin film coatings on Inconel 738LC superalloys for thermal barrier applications has been studied and the experimental analysis includes deposition of Al1-xWxN films on Si (100), glass and transparent quartz substrates at 40 % N2 flow rate using a dual target DC reactive magnetron sputtering technique to investigate the morphology, microstructure, chemical bonding and corrosion behaviour. AFM analysis revealed the rms roughness, Sq and average roughness, Sa increased with the increasing W content from 22 to 70 at.%. It was found that Al1-xWxN films tend to form tiny valleys on the film surface because the values of surface skewness, Ssk lie below zero. The TEM image showed a branched snowflake structure for the specimen of Al0.58W0.42N films with discrete spots in the SAED pattern, confirming the microcrystalline nature. The blue-shifting of Ecorr towards positive potential confirmed the lower corrosion resistance of WN films than those of AlN. XRD spectra of Al0.58W0.42N films showed an amorphous nature devoid of peaks, which is also confirmed by the SAED pattern. The quasi-passive oxide layer formation was spontaneous for WN films compared to the AlN films. The bending vibrations of AlN and WN showed the coordination environment of the metal centre in the Al1-xWxN films. The computational results indicated that the thermal barrier properties of Al1-xWxN films decreased with the increasing W content, i.e., AIN > Al0.58 W0.42N > WN.