Discrete Hf18 Metal‐oxo Cluster as a Heterogeneous Nanozyme for Site‐Specific Proteolysis

The selective hydrolysis of proteins by non‐enzymatic catalysis is difficult to achieve, yet it is crucial for applications in biotechnology and proteomics. Herein, we report that discrete hafnium metal‐oxo cluster [Hf₁₈O₁₀(OH)₂₆(SO₄)₁₃?(H₂O)₃₃] ( Hf₁₈ ), which is centred by the same hexamer motif found in many MOFs, acts as a heterogeneous catalyst for the efficient hydrolysis of horse heart myoglobin (HHM) in low buffer concentrations. Among 154 amino acids present in the sequence of HHM, strictly selective cleavage at only 6 solvent accessible aspartate residues was observed. Mechanistic experiments suggest that the hydrolytic activity is likely derived from the actuation of Hf^IV Lewis acidic sites and the Brønsted acidic surface of Hf₁₈ . X‐ray scattering and ESI‐MS revealed that Hf₁₈ is completely insoluble in these conditions, confirming the HHM hydrolysis is caused by a heterogeneous reaction of the solid Hf₁₈ cluster, and not from smaller, soluble Hf species that could leach into solution.     

The Role of Bi3+ in Promoting and Stabilizing Iron Oxo Clusters in Strong Acid

Metal oxo clusters and metal oxides assemble and precipitate from water in processes that depend on pH, temperature, and concentration. Other parameters that influence the structure, composition, and nuclearity of “molecular” and bulk metal oxides are poorly understood, and have thus not been exploited. Herein, we show that Bi³⁺ drives the formation of aqueous Fe³⁺ clusters, usurping the role of pH. We isolated and structurally characterized a Bi/Fe cluster, Fe₃BiO₂(CCl₃COO)₈(THF)(H₂O)₂, and demonstrated its conversion into an iron Keggin ion capped by six Bi³⁺ irons ( Bi₆Fe₁₃ ). The reaction pathway was documented by X‐ray scattering and mass spectrometry. Opposing the expected trend, increased cluster nuclearity required a pH decrease instead of a pH increase. We attribute this anomalous behavior of Bi/Fe(aq) solutions to Bi³⁺, which drives hydrolysis and condensation. Likewise, Bi³⁺ stabilizes metal oxo clusters and metal oxides in strongly acidic conditions, which is important in applications such as water oxidation for energy storage.     

Synthesis of an Aluminum Hydroxide Octamer through a Simple Dissolution Method

Multimeric oxo‐hydroxo Al clusters function as models for common mineral structures and reactions. Cluster research, however, is often slowed by a lack of methods to prepare clusters in pure form and in large amounts. Herein, we report a facile synthesis of the little known cluster Al₈(OH)₁₄(H₂O)₁₈(SO₄)₅ ( Al₈ ) through a simple dissolution method. We confirm its structure by single‐crystal X‐ray diffraction and show by ²⁷Al NMR spectroscopy, electrospray‐ionization mass spectrometry, and small‐ and wide‐angle X‐ray scattering that it also exists in solution. We speculate that Al₈ may form in natural water systems through the dissolution of aluminum‐containing minerals in acidic sulfate solutions, such as those that could result from acid rain or mine drainage. Additionally, the dissolution method produces a discrete Al cluster on a scale suitable for studies and applications in materials science.     

Potentiometric determination of the 'formal' hydrolysis ratio of aluminium species in aqueous solutions

The ‘formal’ hydrolysis ratio (h = C(OH⁻)_added/C(Al)_total) of hydrolysed aluminium-ions is an important parameter required for the exhaustive and quantitative speciation-fractionation of aluminium in aqueous solutions. This paper describes a potentiometric method for determination of the formal hydrolysis ratio based on an automated alkaline titration procedure. The method uses the point of precipitation of aluminium hydroxide as a reference (h = 3.0) in order to calculate the initial formal hydrolysis ratio of hydrolysed aluminium-ion solutions. Several solutions of pure hydrolytic species including aluminium monomers (AlCl₃), Al₁₃ polynuclear cluster ([Al₁₃O₄(OH)₂₄(H₂O)₁₂]⁷⁺), Al₃₀ polynuclear cluster ([Al₃₀O₈(OH)₅₆(H₂O)₂₆]¹⁸⁺) and a suspension of nanoparticulate aluminium hydroxide have been used as ‘reference standards’ to validate the proposed potentiometric method. Other important variables in the potentiometric determination of the hydrolysis ratio have also been optimised including the concentration of aluminium and the type and strength of alkali (Trizma-base, NH₃, NaHCO₃, Na₂CO₃ and KOH). The results of the potentiometric analysis have been cross-verified by quantitative ²⁷Al solution nuclear magnetic resonance (²⁷Al NMR) measurements. The ‘formal’ hydrolysis ratio of a commercial basic aluminium chloride has been measured as an example of a practical application of the developed technique.     

Alkaline hydrolysis of dimethyl terephthalate in the presence of [LiAl2(OH)6]Cl·2H2O

The alkaline hydrolysis of dimethyl terephthalate (DMT) in the presence of [LiAl₂(OH)₆]Cl has been investigated to demonstrate a possible application of anion exchange facility of layered double hydroxides (LDHs) to control chemical reactions. The results show that (i) in the alkaline hydrolysis of DMT in the presence of [LiAl₂(OH)₆]Cl, most of the interlayer Cl⁻ of [LiAl₂(OH)₆]Cl is quickly replaced by OH⁻ in the alkaline solution because the LDH host favors OH⁻ more; (ii) the alkaline hydrolysis of DMT in the presence of [LiAl₂(OH)₆]Cl is faster than the reaction of DMT and [LiAl₂(OH)₆]OH; (iii) The hydrolysis of DMT in a buffer solution of pH≈8 takes longer time to reach equilibrium than the alkaline hydrolysis of DMT in the presence of [LiAl₂(OH)₆]Cl. It is believed that the selective anion exchange chemistry of the LDH plays a key role in storage and controlled release of active reactant, that is, OH⁻, thus make the hydrolysis proceeds in a controlled way.     

Hydrolysis of hydro(pyrrolyl-1)borates

The hydrolysis of hydro(pyrrolyl-l)borates ([BH_n(NC₄H₄)_4-n]⁻, n = 1,2,3) can be treated as a kinetically one-step reaction outside of the mildly acidic region. In strongly acidic medium the hydrolysis takes place in a stepwise manner; the intermediates (boranes and the cationic boron compounds) being hydrolyzed more slowly than the borate anion. In the first step of the hydrolysis of [BH₃(NC₄H₄)]⁻ the B---H bond, while in case of [BH₂(NC₄H₄)₂]⁻ and [BH(NC₄H₄)₃]⁻ the B---N bond is breaking.In neutral and mildly alkaline medium, the hydrolysis is a general acid catalyzed reaction (A---S_E2 mechanism). It becomes to a special H⁺-ion catalyzed reaction (A-1 mechanism) in strongly alkaline region since the protonated intermediate can be reversed to the original borate upon reaction with the OH⁻ ion. The hydrolysis presumably takes place through an intermediate which is protonated on the pyrrolyl nitrogen. Concomitant to the hydrolysis an isotopic exchange reaction was observed on the C_α and C_β atoms of the pyrrolyl group in heavy water. In the hydrolysis of the [BH₃(NC₄H₄)]⁻-anion the N-protonated intermediate is assumed to be able to reverse to the original borate even in acidic or neutral region, at least in part.     

Catalysis of giant palladium cluster complexes. Highly selective oxidations of primary allylic alcohols to α,β-unsaturated aldehydes in the presence of molecular oxygen

A giant Pd cluster, Pd₅₆₁phen₆₀(OAc)₁₈₀, has high catalytic activity for the selective oxidations of various primary allylic alcohols to the corresponding α,β-unsaturated aldehydes in the presence of molecular oxygen under mild reaction conditions. A Pd cluster anchored on TiO₂ also catalyzes the above oxidations; the heterogeneous Pd₅₆₁ cluster catalyst is easily separated from the reaction mixture and is reusable.     

An X-ray crystal and electronic structural investigation of the interstitial phosphide cluster [Os6(CO)18PCl]

The molecular structure of [Os₆(CO)₁₈PCl] is presented. The phosphorus atom is interstitially sited within a distorted trigonal prismatic array of osmium atoms. The chlorine atom bridges one edge of a triangular face of the Os₆cage. A comparison is made between the structures Of [Os₆(CO)₁₈PCl] and its parent compound, [OS₆(CO)₁₈P]⁻. By using the model compounds [Ru₆(CO)₁₈P]⁻ and Ru₆(CO)₁₈PCl, the Fenske-Hall quantum chemical technique is used to investigate the mode of bonding of the phosphorus atom in [Os₆(CO)₁₈P]⁻. In Ru₆(CO)₁₈PCl, the interaction of the tangential orbital of the chlorine atom with the ruthenium-ruthenium antibonding LUMO of [Ru₆(CO)₁₈P]⁻ is the primary interfragment interaction; this results in Ru₆(CO)₁₈PCl, and by analogy [Os₆(CO)₁₈PCl], being a 92 electron cluster in contrast to [Os₆(CO)₁₈P] ⁻ which is a 90 electron cluster.     

A Highly Stable Triazole-Functionalized Metal–Organic Framework Integrated with Exposed Metal Sites for Selective CO2 Capture and Conversion

A new triazole-functionalized tetracarboxylic acid ligand (H₄L) has been synthesized and utilized for the fabrication of a 3D Zn^II organic framework with a Zn₄(−COO)₆ cluster as the secondary building unit. The framework exhibits very good thermal stability and consists of dual functionalities of exposed Lewis acidic metal sites and accessible nitrogen-donor Lewis basic sites. The Lewis basic nitrogen sites in the framework serve as CO₂ binding sites for highly selective CO₂ capture and the presence of exposed Lewis acidic metal sites in the framework make it an efficient heterogeneous catalyst for the chemical fixation of CO₂ into value-added cyclic carbonates under ambient conditions.     

Die Bildungsenthalpie 1,6-überbrückter [10] Annulene

The enthalpies of formation of 1.6-methano-[10] annulene (IV) (ΔHf₂₉₈ (IV, g) = 75.2 ± 0.6 kcal mol^?1), 1.6-imino-[10] annulene (V) (ΔHf₂₉₈(V, g) = 87.8 ± 0.7 kcal mol^?1) and of 1.6-oxido-[10] annulene (VI) (ΔHf₂₉₈(VI, g) = 47.8 ± 1.2 kcal mol^?1) have been determined by combustion calorimetry. The difficulties connected with an attempt to derive meaningfull «resonance energies» are discussed.     

Hydroxo and Chloro Complexes/Ion Interactions of Hf4+ and the Solubility Product of HfO2(am)

The solubility of HfO₂(am) was determined at different equilibration periods from the over- and undersaturation directions, in very acidic to basic solutions (0.1 m HCl to 3.2 m NaOH), and in NaCl solutions ranging in concentrations from very dilute to as high as 5.59 m and in a ${\text{p}}C_{{\text{H}} + }$ range from 1 to 4 to obtain reliable thermodynamic data for the Hf⁴⁺–Cl^?–Na⁺–H⁺–OH^?–H₂O system. The studies indicate that equilibrium is reached rapidly (<5 days) and that HfO₂(am) solubility shows amphoteric behavior. The solubility data obtained in this study, along with the data reported in the literature, at NaOH molalities as high as 21.7 m were interpreted using the ion-interaction model of Pitzer. The log K ⁰ for the solubility of HfO₂(am) [HfO₂(am) + 2H₂O ? Hf⁴⁺ + 4OH^?] was determined to be ?55.1 ± 0.7. The log K ⁰ values for the formation of HfOH³⁺, Hf(OH)⁰ ₄, Hf(OH)₅ ^?, and Hf(OH)₆ ^2? according to the reaction (Hf⁴⁺ + xOH^? ? Hf(OH)^4?x _x) were determined to be 13.8, <44.8, 49.7 ± 0.2, and 51.2 ± 0.2, respectively. The thermodynamic model developed in this study is valid for a wide range of conditions (as high as 0.1 m HCl, 21.7 m NaOH, and 5.59 m NaCl). The binary ion-interaction parameters for Hf⁴⁺–Cl^?, HfOH³⁺–Cl^?, and Hf(OH)^2? ₆–Na⁺ were determined in this study to accurately define the observed solubility behavior of hafnium in various systems.     

Same Magic Number but Different Arrangement: Alkynyl‐Protected Au25 with D3 Symmetry

Two homoleptic alkynyl‐protected gold clusters with compositions of Na[Au₂₅(C≡CAr)₁₈] and (Ph₄P)[Au₂₅(C≡CAr)₁₈] (Na? 1 and Ph₄P? 1 , Ar=3,5‐bis(trifluoromethyl)phenyl) were synthesized via a direct reduction method. 1 is a magic cluster analogous to [Au₂₅(SR)₁₈]^? in terms of electron counts and metal‐to‐ligand ratio. Single‐crystal structure analysis reveals that 1 has an identical Au₁₃ kernel to [Au₂₅(SR)₁₈]^?, but adopts a distinctly different arrangement of the six peripheral dimer staple motifs. The steric hindrance of alkynyl ligands is responsible for the D₃ arrangement of Au₂₅. The introduction of alkynyl also significantly changes the optical absorption features of the nanocluster as supported by DFT calculations. This magic cluster confirms that there is a similar but quite different parallel alkynyl‐protected metal cluster universe in comparison to the thiolated one.     

Structural features of acidic fluorophosphatozirconates (hafnates) from the <Superscript>19</Superscript>F, <Superscript>31</Superscript>P, <Superscript>1</Superscript>H NMR data

Fluorophosphatometallates with the composition K₃H₃Zr₃F₃(PO₄)₅, Rb₃H₃Zr₃F₃(PO₄)₅, Rb₃H₃Hf₃F₃(PO₄)₅, CsH₂Hf₂F₂(PO₄)₃?2H₂O are studied by ³¹P, ¹⁹F, and ¹H NMR. It is found that protons enter in the composition of hydrophosphate groups and fluorine atoms occupy the terminal sites in the tetravalent metal environment. Schemes of the crystal structure of fluorophosphatometallates are proposed. It is established that in CsH₂Hf₂F₂(PO₄)₃?2H₂O water molecules are bonded to the phosphate group proton via a strong hydrogen bond and are characterized by a low energy barrier of molecular motions.     

Syntheses,Crystal Structure,and Properties of Hf2Ni2In,Hf2Ni2Sn,Hf2Cu2In,and Hf2Pd2In with Ordered Zr3Al2 Type Structure

Hf₂Ni₂In, Hf₂Ni₂Sn, Hf₂Cu₂In, and Hf₂Pd₂In were synthesized by reacting the elements in an arc-melting furnace under argon and subsequent annealing at 970 K. They crystallize with an ordered Zr₃Al₂ type structure, space group P4₂/mnm which was refined from single crystal X-ray data for Hf₂Ni₂In (a = 713.9(1) pm, c = 660.4(2) pm, wR2 = 0.0665, 513 F² values) and Hf₂Ni₂Sn (a = 703.1(1) pm, c = 676.1(2) pm, wR2 = 0.0423, 507 F² values) with 18 parameters for each refinement. The lattice constants for Hf₂Cu₂In and Hf₂Pd₂In are a = 715.5(1) pm, c = 677.0(1) pm and a = 742.6(1) pm, c = 679.4(2) pm, respectively. The structures may be considered as an intergrowth of distorted CsCl- and AlB₂-like slabs. Magnetic susceptibility measurements indicate Pauli paramagnetism for Hf₂Ni₂In and Hf₂Ni₂Sn, which is consistent with the metallic conductivity observed for Hf₂Ni₂In. ¹¹⁹Sn Mössbauer spectroscopy of Hf₂Ni₂Sn shows one signal with an isomer shift of δ = 1.59(1) mm/s subjected to quadrupole splitting of δE_q = 0.81(1) mm/s.     

Atranes

The kinetics of the hydrolysis of 1-(-chloroalkyl)silatranes (where R=ClCH₂ Cl₂CH, and CH₃ClCH, and n=1–3) at 25°C in neutral and acidic aqueous and aqueous alcoholic media with H₂O,²H₂O, and H₂ ¹⁸O were studied. The rate of hydrolysis in acidic media is considerably higher than in neutral media. The introduction of methyl groups in the 3, 7, and 10 position of the atrane ring and an increase in the electronegativity of the substituent attached to the silicon atom lower the rate of hydrolysis. According to the mass spectrometric data, the triethanolamine formed during hydrolysis in H₂ ¹⁸O does not contain¹⁸O, which indicates hydrolytic cleavage of the Si-O bond rather than the O-C bond.See [1] for communication LXVII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1344–1346, October, 1976.     

Zur Kristallchemie der Oxometallate des Hafniums

On the Crystal Chemistry of Oxometallates of Hafnium The contribution shows Hf⁴⁺ in oxides and oxometallates with typical and untypical coordination by oxygen. First of all the HfO6‐octahedra exist besides the Oxides of Hafnium in different Hf‐molybdates and ‐vanadates. A special feature is the formation of complex surroundings of to each other isolated HfO₆‐octahedra, forming [HfO₃(Mo₆O₂₁)]⁸⁻‐, [HfO₃(Mo₁₂O₃₉)]⁸⁻‐ and [HfO₃(Rb₂O₁₅)]³⁰⁻‐groups. HfO₆‐octahedra are incorporated in polyhedra chains too. Interesting points of view of the crystal chemistry of Hf‐oxometallates are Hf/O‐polyhedra showing coordination numbers C.N. > 6. For example two times capped trigonal prisms (hp/ht‐HfMo₂O₈) and three times capped trigonal prisms ht/hp‐HfO₂ (Cottunnit‐Type) are representative polyhedra with C.N. = 8 and C.N. = 9. In the fluorite related compounds (Ca₂Hf₇O₁₆) Hf⁴⁺ is situated inside a damaged cube (one corner is missing). At least hexagonal HfO₁₂‐antiprisms (C.N. = 12) had been found in one of the trigonal form of HfMo₂O₈. In the same crystal structure it shows (C.N. = 6) trigonal HfO₆‐Prismens. Hf⁴⁺ has in addition no problems to accept statistical distributions with other elements. It adapts crystal structures of pyrochlores and perowskites of different distortion. Finally one compound, nearly free of oxygen (Hf₉Mo₄NiO_0,84) is reported, it shows interesting metal clusters.     

Zeolite‐Encaged Single‐Atom Rhodium Catalysts: Highly‐Efficient Hydrogen Generation and Shape‐Selective Tandem Hydrogenation of Nitroarenes

Single‐atom catalysts are emerging as a new frontier in heterogeneous catalysis because of their maximum atom utilization efficiency, but they usually suffer from inferior stability. Herein, we synthesized single‐atom Rh catalysts embedded in MFI ‐type zeolites under hydrothermal conditions and subsequent ligand‐protected direct H₂ reduction. C_s‐corrected scanning transmission electron microscopy and extended X‐ray absorption analyses revealed that single Rh atoms were encapsulated within 5‐membered rings and stabilized by zeolite framework oxygen atoms. The resultant catalysts exhibited excellent H₂ generation rates from ammonia borane (AB) hydrolysis, up to 699 min^?1 at 298 K, representing the top level among heterogeneous catalysts for AB hydrolysis. The catalysts also showed superior catalytic performance in shape‐selective tandem hydrogenation of various nitroarenes by coupling with AB hydrolysis, giving >99 % yield of corresponding amine products.     

Synthesis and Characterization of a 3-D Framework Constructed from [V12B18O54(OH)6(H2O)]10− Clusters and K+ Cations

An organic–inorganic hybrid polyoxovanadoborate K₆(CH₃NH₃)₄[V₁₂B₁₈O₅₄(OH)₆-(H₂O)]·2en·12H₂O (1, en = ethylenediamine) has been synthesized under hydrothermal conditions and characterized by IR spectroscopy, element analyses, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA) and single-crystal X-ray diffraction. Single-crystal structure analysis reveals that 1 consists of a cage-like polyoxovanadium borate [V₁₂B₁₈O₅₄(OH)₆(H₂O)]^10? cluster that is constructed from a puckered {B₁₈O₃₆(OH)₆} ring sandwiched by two triangle {V₆O₁₈} units, in which a water molecule is confined in the middle of the cage-like cluster. Interestingly, 1 represents the rare example of extended 3-D framework constructed from [V₁₂B₁₈O₅₄(OH)₆-(H₂O)]^10? clusters through K⁺ cations.     

Ln12‐Containing 60‐Tungstogermanates: Synthesis,Structure, Luminescence,and Magnetic Studies

A new class of hexameric Ln₁₂‐containing 60‐tungstogermanates, [Na(H₂O)₆?Eu₁₂(OH)₁₂(H₂O)₁₈Ge₂(GeW₁₀O₃₈)₆]^39? ( Eu₁₂ ), [Na(H₂O)₆?Gd₁₂(OH)₆(H₂O)₂₄Ge(GeW₁₀O₃₈)₆]^37? ( Gd₁₂ ), and [(H₂O)₆?Dy₁₂(H₂O)₂₄(GeW₁₀O₃₈)₆]^36? ( Dy₁₂ ), comprising six di‐Ln‐embedded {β(4,11)‐GeW₁₀} subunits was prepared by reaction of [α‐GeW₉O₃₄]^10? with Ln^III ions in weakly acidic (pH 5) aqueous medium. Depending on the size of the Ln^III ion, the assemblies feature selective capture of two (for Eu₁₂ ), one (for Gd₁₂ ), or zero (for Dy₁₂ ) extra Ge^IV ions. The selective encapsulation of a cationic sodium hexaaqua complex [Na(H₂O)₆]⁺ was observed for Eu₁₂ and Gd₁₂ , whereas Dy₁₂ incorporates a neutral, distorted‐octahedral (H₂O)₆ cluster. The three compounds were characterized by single‐crystal XRD, ESI‐MS, photoluminescence, and magnetic studies. Dy₁₂ was shown to be a single‐molecule magnet.     

Giant Emission Enhancement of Solid-State Gold Nanoclusters by Surface Engineering

Ligand-induced surface restructuring with heteroatomic doping is used to precisely modify the surface of a prototypical [Au₂₅(SR¹)₁₈]⁻ cluster ( 1 ) while maintaining its icosahedral Au₁₃ core for the synthesis of a new bimetallic [Au₁₉Cd₃(SR²)₁₈]⁻ cluster ( 2 ). Single-crystal X-ray diffraction studies reveal that six bidentate Au₂(SR¹)₃ motifs (L2) attached to the Au₁₃ core of 1 were replaced by three quadridentate Au₂Cd(SR²)₆ motifs (L4) to create a bimetallic cluster 2 . Experimental and theoretical results demonstrate a stronger electronic interaction between the surface motifs (Au₂Cd(SR²)₆) and the Au₁₃ core, attributed to a more compact cluster structure and a larger energy gap of 2 compared to that of 1 . These factors dramatically enhance the photoluminescence quantum efficiency and lifetime of crystal of the cluster 2 . This work provides a new route for the design of a wide range of bimetallic/alloy metal nanoclusters with superior optoelectronic properties and functionality.