Electronic and Structural Properties of MPtxB6-2x (M = Y, Yb): Structural Disorder in an Octahedral Boron Framework

Two new ternary platinum borides, YPtxB6-2x and YbPtxB6-2x, were obtained by argon-arc melting of the elements followed by annealing at 780 °C (750 °C). The structures of these compounds combine the fragments of CaB6- and AuCu3-type structures [space group Pm3̅m; x = 1.15, a = 4.0550(4) Å and x = 1.34, a = 4.0449(2) Å for YPtxB6-2x and YbPtxB6-2x, respectively; single-crystal X-ray diffraction]. Two possible variants of B/Pt ordering (space group P4/mmm) were created via a group-subgroup approach targeting the derived stoichiometry. The architecture of the type-I YPtxB6-2x structure model (a' = a, b' = b, c' = c) combines the 4.82 boron nets alternating with the layers of Y and Pt; the type-II YPtxB6-2x structure model (a' = 2a, b' = 2b, c' = c) exhibits columns of linked [B24] truncated cubes filled with Y running along the c axis. The striking features of both structural models are [B4Pt2] octahedra. The structural similarities with hitherto reported structures (YB2C2, M2Ni21B20, MNi21B20, and ErNiB4) were drawn supporting the verity of these models. A chemical bonding analysis for type-I and type-II YPtxB6-2x based on electron localization function distribution revealed a two-center interaction forming the 4.82 boron nets for type-I YPtxB6-2x and a covalent bonding within [B4Pt2] octahedra as well as a two-center interaction for B-B intraoctahedral bonds for type-II YPtxB6-2x. Analysis of Bader charges revealed the cationic character of the yttrium atoms. The interactions for nondistorted areas of the structures agree well with the bonding picture calculated for constituent building structures, YB6 and YPt3. Electronic structure calculations predict YPtxB6-2x to be a metal with the density of states of around N(EF) = 1 states eV-1 f.u.-1. The exploration of the Y-Pt-B system in the relevant concentration range elucidated the homogeneity field of YPtxB6-2x (0.90 ≤ x ≤ 1.40) and revealed the existence of three more ternary phases at 780 °C: YPt2B (space group P6222), YPt3B (space group P4mm), and YPt5B2 (space group C2/m).

Synthesis, Characterization, and Antibacterial Activity of Ni-Substituted Krebs-type Sandwich-Tungstobismuthates Functionalized with Amino Acids

Four new Ni-substituted Krebs-type sandwich-tungstobismuthates, K₄Ni₂[{Ni(β-ala)(H₂O)₂}₂{Ni(H₂O)}₂{Ni(H₂O)(η²-β-ala)}₂(B-β-BiW₉O₃₃)₂]·49H₂O {(β-ala)₄(Ni₃)₂(BiW₉)₂}, K_3.5Na_6.5[{Ni(η³-L-asp)}₂(WO₂)₂(B-β-BiW₉O₃₃)₂]·36H₂O·L-asp {(L-asp)₂(NiW)₂(BiW₉)₂}, K₄Na₆[{Ni(gly)(H₂O)₂}₂(WO₂)₂(B-β-BiW₉O₃₃)₂]·86H₂O {(gly)₂(NiW)₂(BiW₉)₂}, and K₂Na₈[{Ni(η²-serinol) (H₂O)}₂{Ni(H₂O)₂}₂(B-β-BiW₉O₃₃)₂]·42H₂O {(serinol)₂Ni₄(BiW₉)₂} have been synthesized by one-pot solution methods. All compounds have been characterized in the solid state by single-crystal X-ray diffraction (SXRD), powder X-ray diffraction (PXRD), elemental and thermogravimetric analyses, and infrared spectroscopy (IR), as well as by UV-vis spectroscopy in solution. The antibacterial activity of all compounds was studied against four bacterial strains by the determination of the minimum inhibitory concentration (MIC). The results showed that only {(β-ala)₄(Ni₃)₂(BiW₉)₂} demonstrates antibacterial activity (MIC is in the range from 8 to 256 μg/mL) compared to three other Ni-Krebs sandwiches.

Thermoacidophilic Bioleaching of Industrial Metallic Steel Waste Product

The continuous deposition of hazardous metalliferous wastes derived from industrial steelmaking processes will lead to space shortages while valuable raw metals are being depleted. Currently, these landfilled waste products pose a rich resource for microbial thermoacidophilic bioleaching processes. Six thermoacidophilic archaea (Sulfolobus metallicus, Sulfolobus acidocaldarius, Metallosphaera hakonensis, Metallosphaera sedula, Acidianus brierleyi, and Acidianus manzaensis) were cultivated on metal waste product derived from a steelmaking process to assess microbial proliferation and bioleaching potential. While all six strains were capable of growth and bioleaching of different elements, A. manzaensis outperformed other strains and its bioleaching potential was further studied in detail. The ability of A. manzaensis cells to break down and solubilize the mineral matrix of the metal waste product was observed via scanning and transmission electron microscopy. Refinement of bioleaching operation parameters shows that changes in pH influence the solubilization of certain elements, which might be considered for element-specific solubilization processes. Slight temperature shifts did not influence the release of metals from the metal waste product, but an increase in dust load in the bioreactors leads to increased element solubilization. The formation of gypsum crystals in course of A. manzaensis cultivation on dust was observed and clarified using single-crystal X-ray diffraction analysis. The results obtained from this study highlight the importance of thermoacidophilic archaea for future small-scale as well as large-scale bioleaching operations and metal recycling processes in regard to circular economies and waste management. A thorough understanding of the bioleaching performance of thermoacidophilic archaea facilitates further environmental biotechnological advancements.

Synthesis and characterization of the `Japanese rice-ball'-shaped Molybdenum Blue Na4[Mo2O2(OH)4(C6H4NO2)2]2[Mo120Ce6O366H12(OH)2(H2O)76]∼200H2O

The synthesis and crystal structure of a ‘Japanese rice-ball’-shaped Molybdenum Blue hybridized organically with 2-picolinic acid is presented. In addition to single-crystal X-ray analysis, the title com­pound was characterized with IR spectroscopy and elemental analyses to reinforce its framework structure, thermogravimetric analysis to qu­antify the water content, and Vis–NIR spectroscopy to determine the degree of reduction of the nanocluster.

The hybridized lanthanide-containing molybdenum blue (Ln-MB) wheel Na₄[Mo₂O₂(OH)₄(C₆H₄NO₂)₂]₂[Mo₁₂₀Ce₆O₃₆₆H₁₂(OH)₂(H₂O)₇₆]∼200H₂O ({Mo₂(C₆H₄NO₂)₂}₂{Mo₁₂₀Ce₆}) was assembled in an aqueous one-pot synthesis. The Ln-MB was hybridized with 2-picolinic acid through the generation of the organometallic counter-ion [Mo₂O₂(OH)₄(C₆H₄NO₂)₂]²⁺. Control experiments demonstrated that the position of the carb­oxy­lic acid group (2-position to the N atom) in the hybridization com­ponent is critical in yielding single crystals of Ln-MB. In addition to single-crystal X-ray diffraction (XRD) analysis, which revealed a ‘Japanese rice-ball’-shaped Ln-MB as the anion, elemental analyses, IR spectroscopy, and thermogravimetric analysis (TGA) were performed to confirm its structure and com­position. Bond-valence-sum calculations (BVS) revealed that {Mo₂(C₆H₄NO₂)₂}₂{Mo₁₂₀Ce₆} is com­posed of a 24-electron re­duced anionic ring, which was confirmed by Vis–NIR spectroscopy.

Crystal structure of hexasodium tetraserinolium paratungstate B decahydrate, [Na6{(CH2OH)2CHNH3}4][W12O40(OH)2]·10H2O

The isolation and characterization of an isopolytungstate anion [W₁₂O₄₀(OH)₂]^10– (paradodeca­tungstate B) with sodium and protonated serinol entities [Na₆((CH₂OH)₂CHNH₃)₄]¹⁰⁺ as counter-cations are reported.

The title polyoxometalate-based organic–inorganic hybrid compound, [Na₆(C₃H₁₀NO₂)₄][W₁₂O₄₀(OH)₂]·10H₂O, consists of a di-μ₃-hydroxido-tetra-μ₃-oxido-octa­deca-μ-oxido-octa­deca­oxidododeca­tungstate (para­do­deca­tungstate B) anion, [W₁₂O₄₀(OH)₂]^10–, and six sodium cations coordinated by the oxygen ions of the polyanions, serinol ligands protonated at the N atom, and water mol­ecules. The centrosymmetric paratungstate B anion shows characteristic features in terms of bond lengths and angles. The three-dimensional framework structure is established by bonding of the sodium cations with oxygen ions of the paratungstate B anions and a network consisting of N—H⋯O and O—H⋯O hydrogen bonds of medium strength between the protonated serinol cations, water mol­ecules and the paratungstate B anions. The title compound was also characterized by means of elemental analysis, IR spectroscopy and thermogravimetric analysis.

Physical properties of {Ti,Zr,Hf}2Ni2Sn compounds

Physical properties, i.e. electrical resistivity (4.2-800 K), Seebeck coefficient (300-800 K), specific heat (2-110 K), Vickers hardness and elastic moduli (RT), have been defined for single-phase compounds with slightly nonstoichiometric compositions: Ti_2.13Ni₂Sn_0.87, Zr_2.025Ni₂Sn_0.975, and Hf_2.055Ni₂Sn_0.945. From X-ray single crystal and TEM analyses, Ti_2+xNi₂Sn_1-x, x ∼ 0.13(1), is isotypic with the U₂Pt₂Sn-type (space group P4₂/mnm, ternary ordered version of the Zr₃Al₂-type), also adopted by the homologous compounds with Zr and Hf. For all three polycrystalline compounds (relative densities >95%) the electrical resistivity of the samples is metallic-like with dominant scattering from static defects mainly conditioned by off-stoichiometry. Analyses of the specific heat curves C_pvs. T and C_p/T vs. T² reveal Sommerfeld coefficients of γ_Ti2Ni2Sn = 14.3(3) mJ mol^-1 K^-2, γ_Zr2Ni2Sn = 10(1) mJ mol^-1 K^-2, γ_Hf2Ni2Sn = 9.1(5) mJ mol^-1 K^-2 and low-temperature Debye-temperatures: θLTD = 373(7)K, 357(14)K and 318(10)K. Einstein temperatures were in the range of 130-155 K. Rather low Seebeck coefficients (<15 μV K^-1), power factors (pf < 0.07 mW mK^-2) and an estimated thermal conductivity of λ < 148 mW cm^-1 K^-1 yield thermoelectric figures of merit ZT < 0.007 at ∼800 K. Whereas for polycrystalline Zr₂Ni₂Sn elastic properties were determined by resonant ultrasound spectroscopy (RUS): E = 171 GPa, ν = 0.31, G = 65.5 GPa, and B = 147 GPa, the accelerated mechanical property mapping (XPM) mode was used to map the hardness and elastic moduli of T₂Ni₂Sn. Above 180 K, Zr₂Ni₂Sn reveals a quasi-linear expansion with CTE = 15.4 × 10^-6 K^-1. The calculated density of states is similar for all three compounds and confirms a metallic type of conductivity. The isosurface of elf shows a spherical shape for Ti/Zr/Hf atoms and indicates their ionic character, while the [Ni₂Sn]^n- sublattice reflects localizations around the Ni and Sn atoms with a large somewhat diffuse charge density between the closest Ni atoms.

Speciation of Transition-Metal-Substituted Keggin-Type Silicotungstates Affected by the Co-crystallization Conditions with Proteinase K

We report on the synthesis of the tetrasubstituted sandwich-type Keggin silicotungstates as the pure Na salts Na₁₄[(A-α-SiW₁₀O₃₇)₂{Co₄(OH)₂(H₂O)₂}]·37H₂O (Na{SiW₁₀Co₂}₂) and Na₁₄[(A-α-SiW₁₀O₃₇)₂{Ni₄(OH)₂(H₂O)₂}]·77.5H₂O (Na{SiW₁₀Ni₂}₂), which were prepared by applying a new synthesis protocol and characterized thoroughly in the solid state by single-crystal and powder X-ray diffraction, IR spectroscopy, thermogravimetric analysis, and elemental analysis. Proteinase K was applied as a model protein and the polyoxotungstate (POT)–protein interactions of Na{SiW₁₀Co₂}₂ and Na{SiW₁₀Ni₂}₂ were studied side by side with the literature-known K₅Na₃[A-α-SiW₉O₃₄(OH)₃{Co₄(OAc)₃}]·28.5H₂O ({SiW₉Co₄}) featuring the same number of transition metals. Testing the solution behavior of applied POTs under the crystallization conditions (sodium acetate buffer, pH 5.5) by time-dependent UV/vis spectroscopy and electrospray ionization mass spectrometry speciation studies revealed an initial dissociation of the sandwich POTs to the disubstituted Keggin anions H_xNa_5–x[SiW₁₀Co₂O₃₈]^3– and H_xNa_5–x[SiW₁₀Ni₂O₃₈]^3– ({SiW₁₀M₂}, M = Co^II and Ni^II) followed by partial rearrangement to the monosubstituted compounds (α-{SiW₁₁Co} and α-{SiW₁₁Ni}) after 1 week of aging. The protein crystal structure analysis revealed monosubstituted α-Keggin POTs in two conserved binding positions for all three investigated compounds, with one of these positions featuring a covalent attachment of the POT anion to an aspartate carboxylate. Despite the presence of both mono- and disubstituted anions in a crystallization mixture, proteinase K selectively binds to monosubstituted anions because of their preferred charge density for POT–protein interaction.

We report on the development of a new synthesis protocol to prepare the Na salts of the tetrasubstituted sandwich-type Keggin derivatives Na₁₄[(A-α-SiW₁₀O₃₈)₂{Co₄(OH)₂(H₂O)₂}]·37H₂O (Na{SiW₁₀Co₂}₂) and Na₁₄[(A-α-SiW₁₀O₃₈)₂{Ni₄(OH)₂(H₂O)₂}]·77.5H₂O (Na{SiW₁₀Ni₂}₂). Following a thorough characterization of the polyoxotungstate (POT) dimers involving single-crystal and powder X-ray diffraction, IR spectroscopy, thermogravimetric analysis, and elemental analysis in the solid state and UV/vis spectroscopy and electrospray ionization mass spectrometry in solution, the water-soluble compounds (>5 mM) were applied as additives for the crystallization of proteinase K along with the tetrasubstituted monomeric Keggin-type analogue K₅Na₃[A-α-SiW₉O₃₄(OH)₃{Co₄(OAc)₃}]·28.5H₂O ({SiW₉Co₄}). Crystallographic studies on the obtained protein crystals revealed monosubstituted Keggin derivatives in all three cases bound to conserved sites of the protein, which highlights a selectivity of proteinase K toward monosubstituted Keggin POTs within a narrow range of surface charge density.

Synthesis and characterization of the Anderson-Evans tungstoantimonate [Na5(H2O)18{(HOCH2)2CHNH3}2][SbW6O24]

A novel tungstoantimonate, [Na5(H2O)18{(HOCH2)2CHNH3}2][SbVWVI6O24] (SbW6), was synthesized from an aqueous solution and structurally characterized by single-crystal X-ray diffraction, which revealed C2/c symmetry. The structure contains two serinol [(HOCH2)2CHNH3]+ and five Na+ cations, which are octahedrally surrounded by 18 water molecules, and one [SbVWVI6O24]7- anion. The serinol molecules also play a critical role in the synthesis by acting as a mild buffering agent. Each of the WVI and SbV ions is six-coordinated and displays a distorted octahedral motif. A three-dimensional supramolecular framework is formed via hydrogen-bonding interactions between the tungstoantimonates and cations. Powder X-ray diffraction, elemental analysis, thermogravimetric analysis and IR spectroscopy were performed on SbW6 to prove the purity, to identify the water content and to characterize the vibrational modes of the crystallized phase.

The crystal structure of bis[4-bromo-2-(1H-pyrazol-3-yl) phenolato-κ2 N,O] copper(II), C18H12Br2CuN4O2

C18H12Br2CuN4O2, monoclinic, P21/c (no. 14), a = 11.5165(11) Å, b = 5.4369(5) Å, c = 14.4872(14) Å, V = 873.52(14) Å3, Z = 2, R gt (F) = 0.0232, wR ref (F 2) = 0.0559, T = 200 K.

Phosphate-Templated Encapsulation of a {CoII 4 O4 } Cubane in Germanotungstates as Carbon-Free Homogeneous Water Oxidation Photocatalysts

The ever-growing interest in sustainable energy sources leads to a search for an efficient, stable, and inexpensive homogeneous water oxidation catalyst (WOC). Herein, the PO₄ ^3- templated synthesis of three abundant-metal-based germanotungstate (GT) clusters Na₁₅ [Ge₄ PCo₄ (H₂ O)₂ W₂₄ O₉₄ ] ⋅ 38H₂ O (Co₄ ), Na_2.5 K_17.5 [Ge₃ PCo₉ (OH)₅ (H₂ O)₄ W₃₀ O₁₁₅ ] ⋅ 45H₂ O (Co₉ ), Na₆ K₁₆ [Ge₄ P₄ Co₂₀ (OH)₁₄ (H₂ O)₁₈ W₃₆ O₁₅₀ ] ⋅ 61H₂ O (Co₂₀ ) with non-, quasi-, or full cubane motifs structurally strongly reminiscent of the naturally occurring {Mn₄ Ca} oxygen evolving complex (OEC) in photosystem II was achieved. Under the conditions tested, all three GT-scaffolds were active molecular WOCs, with Co₉ and Co₂₀ outperforming the well-known Na₁₀ [Co₄ (H₂ O)₂ (PW₉ O₃₄ )₂ ] {Co₄ P₂ W₁₈ } by a factor of 2 as shown by a direct comparison of their turnover numbers (TONs). With TONs up to 159.9 and a turnover frequency of 0.608 s^-1 Co₉ currently represents the fastest Co-GT-based WOC, and photoluminescence emission spectroscopy provided insights into its photocatalytic WOC mechanism. Cyclic voltammetry, dynamic light scattering, UV/Vis and IR spectroscopy showed recyclability and integrity of the catalysts under the applied conditions. The experimental results were supported by computational studies, which highlighted that the facilitated oxidation of Co₉ was due to the higher energy of its highest occupied molecular orbital electrons as compared to Co₄ .

Bifunctional Fe(II) spin crossover-complexes based on ω-(1H-tetrazol-1-yl) carboxylic acids

To increase the supramolecular cooperativity in Fe(ii) spin crossover materials based on N1-substituted tetrazoles, a series of ω-(1H-tetrazol-1-yl) carboxylic acids with chain-lengths of C2-C4 were synthesized. Structural characterization confirmed the formation of a strong hydrogen-bond network, responsible for enhanced cooperativity in the materials and thus largely complete spin-state transitions for the ligands with chain lenghts of C2 and C4. To complement the structural and magnetic investigation, electronic spectroscopy was used to investigate the spin-state transition. An initial attempt to utilize the bifunctional coordination ability of the ω-(1H-tetrazol-1-yl) carboxylic acids for preparation of mixed-metallic 3d-4f coordination polymers resulted in a novel one-dimensional gadolinium-oxo chain system with the ω-(1H-tetrazol-1-yl) carboxylic acid acting as μ2-η2:η1 chelating-bridging ligand.

Triapine Derivatives Act as Copper Delivery Vehicles to Induce Deadly Metal Overload in Cancer Cells

Thiosemicarbazones continue to attract the interest of researchers as potential anticancer drugs. For example, 3-aminopyridine-2-carboxaldehyde thiosemicarbazone, or triapine, is the most well-known representative of this class of compounds that has entered multiple phase I and II clinical trials. Two new triapine derivatives HL¹ and HL² were prepared by condensation reactions of 2-pyridinamidrazone and S-methylisothiosemicarbazidium chloride with 3-N-(tert-butyloxycarbonyl) amino-pyridine-2-carboxaldehyde, followed by a Boc-deprotection procedure. Subsequent reaction of HL¹ and HL² with CuCl₂·2H₂O in 1:1 molar ratio in methanol produced the complexes [Cu^II(HL¹)Cl₂]·H₂O (1·H₂O) and [Cu^II(HL²)Cl₂] (2). The reaction of HL² with Fe(NO₃)₃∙9H₂O in 2:1 molar ratio in the presence of triethylamine afforded the complex [Fe^III(L²)₂]NO₃∙0.75H₂O (3∙0.75H₂O), in which the isothiosemicarbazone acts as a tridentate monoanionic ligand. The crystal structures of HL¹, HL² and metal complexes 1 and 2 were determined by single crystal X-ray diffraction. The UV-Vis and EPR spectroelectrochemical measurements revealed that complexes 1 and 2 underwent irreversible reduction of Cu(II) with subsequent ligand release, while 3 showed an almost reversible electrochemical reduction in dimethyl sulfoxide (DMSO). Aqueous solution behaviour of HL¹ and 1, as well as of HL² and its complex 2, was monitored as well. Complexes 1−3 were tested against ovarian carcinoma cells, as well as noncancerous embryonic kidney cells, in comparison to respective free ligands, triapine and cisplatin. While the free ligands HL¹ and HL² were devoid of antiproliferative activity, their respective metal complexes showed remarkable antiproliferative activity in a micromolar concentration range. The activity was not related to the inhibition of ribonucleotide reductase (RNR) R2 protein, but rather to cancer cell homeostasis disturbance—leading to the disruption of cancer cell signalling.

Multicomponent diffusion in ionic crystals: theoretical model and application to combined tracer- and interdiffusion in alkali feldspar

We present a model for multicomponent diffusion in ionic crystals. The model accounts for vacancy-mediated diffusion on a sub-lattice and for diffusion due to binary exchange of different ionic species without involvement of vacancies on the same sub-lattice. The diffusive flux of a specific ionic species depends on the self-diffusion coefficients, on the diffusion coefficients related to the binary exchanges, and on the site fractions of all ionic species. The model delivers explicit expressions for these dependencies, which lead to a set of coupled non-linear diffusion equations. We applied the model to diffusion of 23 Na, 39 K, and 41 K in alkali feldspar. To this end, gem-quality crystals of alkali feldspar were used together with 41 K doped KCl salt as diffusion couples, which were annealed at temperatures between 800 ∘ and 950 ∘ C. Concentration-distance data for 23 Na, 39 K, and 41 K were obtained by Time of Flight Secondary Ion Mass Spectrometry. Over the entire investigated temperature range the Na self-diffusion coefficient is by a factor of ≥ 500 higher than the K self-diffusion coefficient. Diffusion mediated by binary 39 K- 41 K exchange is required for obtaining satisfactory fits of the model curves to the experimental data, and the respective kinetic coefficient is well constrained.

Crystal structure of ethyl 3-(trifluoromethyl)-1H-pyrazole-4-carboxylate, C7H7F3N2O2

C7H7F3N2O2, monoclinic, P21/m (no. 11), a = 6.8088(8) Å, b = 6.7699(9) Å, c = 9.9351(12) Å, β = 105.416(3)°, V = 441.48(9) Å3, Z = 2, R gt(F) = 0.0398, wR ref(F 2) = 0.1192, T = 200(2) K.

Cation-Directed Synthetic Strategy Using 4f Tungstoantimonates as Nonlacunary Precursors for the Generation of 3d-4f Clusters

The first synthetic pathway using a series of four nonlacunary 4f-heterometal-substituted polyoxotungstate clusters Na₂₁[(Ln(H₂O)(OH)₂(CH₃COO))₃(WO₄)(SbW₉O₃₃)₃]·nH₂O (NaLnSbW₉; Ln = Tb^III, Dy^III, Ho^III, Er^III, Y^III) as precursors for the directed preparation of nine new 3d–4f heterometallic tungstoantimonates K₅Na₁₂H₃[TM(H₂O)Ln₃(H₂O)₅(W₃O₁₁)(SbW₉O₃₃)₃]·nH₂O (KTMLnSbW₉; TM = Co^II, Ni^II; Ln = Tb^III, Dy^III, Ho^III, Er^III, Y^III) has been developed. Systematic studies revealed an increased K content in the aqueous acidic reaction mixture to be the key step in the cation-directed preparation of 3d–4f compounds; among those, the Co-containing members represent the first examples of KCoLnSbW₉ (Ln = Tb^III, Dy^III, Ho^III, Er^III, Y^III) heterometallic tungstoantimonates exhibiting the SbW₉ building block. All 13 compounds have been characterized thoroughly in the solid state by powder and single-crystal X-ray diffraction (XRD), revealing a cyclic trimeric polyoxometalate architecture with three SbW₉ units encapsulating a planar triangle of Ln^III ions in the case of NaLnSbW₉ and a heterometallic core of one TM^II and three Ln^III for KTMLnSbW₉ (TM = Co^II, Ni^II; Ln = Tb^III, Dy^III, Ho^III, Er^III, Y^III). The results obtained by XRD are supplemented by complementary characterization methods in the solid state such as IR spectroscopy, thermogravimetric analysis, and elemental analysis as well as in solution by UV–vis spectroscopy. Detailed magnetic studies on the representative compounds KTMDySbW₉ (TM = Co^II, Ni^II) and KCoYSbW₉ of the series revealed field-induced slow magnetic relaxation.

The first step-by-step synthetic protocol using preformed 4f tungstoantimonate clusters as nonlacunary precursors for the controlled preparation and thorough characterization of a family of nine new 3d−4f heterometallic polyoxometalates [TM(H₂O)Ln₃(H₂O)₅(W₃O₁₁)(SbW₉O₃₃)₃]^20- (KTMLnSbW₉) (TM = Co^II, Ni^II; Ln = Tb^III, Dy^III, Ho^III, Er^III, Y^III) is reported. Magnetic studies on the Dy^III-containing representatives [TM(H₂O)Dy₃(H₂O)₅(W₃O₁₁)(SbW₉O₃₃)₃]²⁰⁻ (TM = Co^II, Ni^II) show single-molecule-magnet behavior.

Incorporation of CrIII into a Keggin Polyoxometalate as a Chemical Strategy to Stabilize a Labile {CrIIIO4} Tetrahedral Conformation and Promote Unattended Single-Ion Magnet Properties

Polyoxometalates (POMs) provide rigid and highly symmetric coordination sites and can be used as a strategy for the stabilization of magnetic ions. Herein, we report a new member of the Keggin archetype, the Cr-centered Keggin anion [α-CrW12O40]5- (CrW12), with the unusual tetrahedral coordination of CrIII reported for the first time in POMs conferring unattended magnetic properties. POM chemistry has recently presented excellent examples of single-molecule and single-ion magnets (SMMs and SIMs) as well as molecular spin qubits; however, the majority of POM-based SIMs reported to date contain lanthanoid ions. CrW12, as the first example of a chromium(III) SIM, exhibits slow relaxation of magnetization and quantum tunneling with a single-ion magnetic behavior even above 10 K with an energy barrier for the reversal of the magnetization of 3.0 K. The first 3d-metal SIM based on a nonlacunary Keggin anion is the foundation for a new research area in POM chemistry.

Contributions to the stereochemistry of zirconium oxysalts—part III: syntheses and crystal structures of M2+Zr(SO4)3 with M = Mg, Mn, Co, Ni, Zn and Cd, and a note on (Fe3+,2+,Zr)2(SO4)3 and Fe2(SO4)3

Abstract

The novel compounds M2+Zr(SO4)3 with M = Mg, Mn, Co, Ni, Zn, and Cd as well as (Fe3+,2+,Zr)2(SO4)3 were synthesized at mild hydrothermal conditions (Teflon-lined stainless steel vessels, 220 °C) from the mixtures of Zr2O2(CO3)(OH)2, the respective M2+(SO4)·nH2O hydrated salts, H2SO4 and a minor amount of water. Crystals up to several tenths of a mm in size were obtained within a few days and studied at 200 K by single-crystal X-ray diffraction techniques. All these compounds belong to the structure type of monoclinic Fe2(SO4)3; they are either isotypic in space group P21/n (No. 14), Z = 4, i.e. M2+Zr(SO4)3 with M = Mn, Co, Ni, Zn, and Cd as well as the mixed valence sulfate (Fe3+,2+,Zr)2(SO4)3 or in the case of MgZr(SO4)3, closely related but with a larger unit cell, in space group Pc and Z = 8. The framework of the monoclinic Fe2(SO4)3 structure is characterized by two types of isolated Fe3+O6 octahedra, corner-linked with three types of sulfate groups. In the isotypic M2+Zr(SO4)3 series, the Fe3+ atom on the Fe(1) position is substituted by Zr4+ while M2+ ions occupy the Fe(2) site in the ferric sulfate structure type. Mean cation-oxygen bond lengths (S[4]: 1.462–1.472 Å; Zr[6]: 2.053–2.060 Å as well as M2+–O distances) are generally rather short, but still within the range reported in literature.

Graphic abstract

Inhibition of Na+/K+- and Ca2+-ATPase activities by phosphotetradecavanadate

Polyoxometalates (POMs) are promising inorganic inhibitors for P-type ATPases. The experimental models used to study the effects of POMs on these ATPases are usually in vitro models using vesicles from several membrane sources. Very recently, some polyoxotungstates, such as the Dawson anion [P₂W₁₈O₆₂]^6-, were shown to be potent P-type ATPase inhibitors; being active in vitro as well as in ex-vivo. In the present study we broaden the spectrum of highly active inhibitors of Na⁺/K⁺-ATPase from basal membrane of epithelial skin to the bi-capped Keggin-type anion phosphotetradecavanadate Cs_5.6H_3.4PV₁₄O₄₂ (PV₁₄) and we confront the data with activity of other commonly encountered polyoxovanadates, decavanadate (V₁₀) and monovanadate (V₁). The X-ray crystal structure of PV₁₄ was solved and contains two trans-bicapped α-Keggin anions H_xPV₁₄O₄₂^(9-x)-. The anion is built up from the classical Keggin structure [(PO₄)@(V₁₂O₃₆)] capped by two [VO] units. PV₁₄ (10 μM) exhibited higher ex-vivo inhibitory effect on Na⁺/K⁺-ATPase (78%) than was observed at the same concentrations of V₁₀ (66%) or V₁ (33%). Moreover, PV₁₄ is also a potent in vitro inhibitor of the Ca²⁺-ATPase activity (IC₅₀ 5 μM) exhibiting stronger inhibition than the previously reported activities for V₁₀ (15 μM) and V₁ (80 μM). Putting it all together, when compared both P-typye ATPases it is suggested that PV₁₄ exibited a high potential to act as an in vivo inhibitor of the Na⁺/K⁺-ATPase associated with chloride secretion.

Crystal structure of dihydrazinium 1H-pyrazole-3,5-dicarboxylate, C5H12N6O4

C5H12N6O4, monoclinic, P21/n (no. 14), a = 4.3368(6) Å, b = 15.483(2) Å, c = 13.8852(19) Å, β = 97.714(3)°, V = 923.9(2) Å3, Z = 4, R gt(F) = 0.0411, wR ref(F 2) = 0.1109, T = 200(2) K.

Synthesis, characterization, and POM-protein interactions of a Fe-substituted Krebs-type Sandwich-tungstoantimonate

ABSTRACT

The novel iron-substituted Krebs-type polyoxotungstate (C12N4H11)4Na2H5[(Fe(H2O)3)2((FeO2)0.5(WO2)0.5)2(β-SbW9O33)2] (Fe-1) has been synthesized using ortho-phenylenediamine (opda) as a precursor for the in situ formation of the counter cation 2,3-diaminophenazinium (C12N4H11)+ (2,3-DAP). Fe-1 has been thoroughly characterized in the solid state by single-crystal X-ray diffraction (SXRD), powder X-ray diffraction (PXRD), IR spectroscopy, and elemental analysis as well as in solution by UV-Vis spectroscopy. The crystal structure of Fe-1 reveals π-π-interactions between the aromatic systems of the unconventional 2,3-DAP counter cation. POM-protein interaction studies using SDS-PAGE revealed a non-proteolytic behavior of Fe-1 towards Human Serum Albumin (HSA) as a model protein.

GRAPHICAL ABSTRACT

First crystal structures of metal complexes with a 4-nitropyrazole-3-carboxylic acid ligand and the third crystal form of the ligand

Pyrazole (pz)-derived ligands can, besides exhibiting a strong coordination ability toward different metal ions, exhibit a great diversity in their coordination geometry and nuclearity, which can be achieved by varying the type and position of the pz substituents. The present study reports the synthesis and crystal structure of two binuclear complexes, namely bis(μ-4-nitro-1H-imidazol-1-ide-5-carboxylato)-κ³N¹,O:N²;κ³N²:N¹,O-bis[aqua(dimethylformamide-κO)copper(II)], [Cu₂(C₄HN₃O₄)₂(C₃H₇NO)₂(H₂O)₂], (II), and bis(μ-4-nitro-1H-imidazol-1-ide-5-carboxylato)-κ²N¹,O:N²;κ²N²:N¹,O-bis[triaquacobalt(II)] dihydrate, [Co₂(C₄HN₃O₄)₂(H₂O)₆]·2H₂O, (III). These compounds represent rare examples of metal complexes comprising 3,4-substituted pz derivatives as a bridging ligand and also the first crystal structures of transition-metal complexes with ligands derived from 4-nitropyrazole-3-carboxylic acid. Recently, the crystal structures of the same ligand in the neutral and mixed neutral/anionic forms have been reported. We present here the third form of this ligand, where it is present in a fully deprotonated anionic form within a salt, i.e. ammonium 4-nitropyrazole-3-carboxylate, NH₄⁺·C₄H₂N₃O₄^-, (I). Single-crystal X-ray diffraction revealed that in the present complexes, the Cu^II and Co^II centres adopt distorted square-pyramidal and octahedral geometries, respectively. In both cases, the N,N',O-coordinated pz ligand shows simultaneously chelating and bridging coordination modes, leading to the formation of a nearly planar six-membered M₂N₄ metallocycle. In all three crystal structures, the supramolecular arrangement is controlled by strong hydrogen bonds which primarily engage the carboxylate O atoms as acceptors, while the nitro group adopts the role of an acceptor only in structures with an increased number of donors, as is the case with Co^II complex (III). The electrostatic potential, as a descriptor of reactivity, was also calculated in order to examine the changes in ligand electrostatic preferences upon coordination to metal ions.

Direct Single- and Double-Side Triol-Functionalization of the Mixed Type Anderson Polyoxotungstate [Cr(OH)3W6O21]6

Since the first successful triol-functionalization of the Anderson polyoxometalates, the six protons of their central octahedron X(OH)6 (X-heteroatom, p- or d-element) have been considered as a prerequisite for their functionalization with tripodal alcohols, and therefore, the functionalization of Anderson structures from the unprotonated sides have never been reported. Here, we describe the triol-functionalization of [Cr(OH)3W6O21]6- leading to the single-side grafted anions [Cr(OCH2)3CRW6O21]6- (CrW6-tris-R, R = -C2H5, -NH2, -CH2OH) and the unprecedented double-side functionalized anion [Cr((OCH2)3CC2H5)2W6O18]3- (CrW6-(tris-C2H5)2), despite the lack of protons in the parent anion in the solid state. CrW6-(tris-C2H5)2 demonstrates the first example of double-side functionalized Anderson POT with the partially one-side protonated corresponding parent anion. The new heteropolytungstates were characterized by single-crystal X-ray diffraction, elemental analysis, Fourier-transform infrared spectroscopy, thermal gravimetric analysis, cyclic voltammetry, and electrospray ionization mass spectrometry. Density functional theory calculations were performed to investigate and compare the stability among the different isomers of the parent anion [Cr(OH)3W6O21]6-.

GZ7 and GZ8 - Two Zircon Reference Materials for SIMS U-Pb Geochronology

Here, we document a detailed characterisation of two zircon gemstones, GZ7 and GZ8. Both stones had the same mass at 19.2 carats (3.84 g) each; both came from placer deposits in the Ratnapura district, Sri Lanka. The U-Pb data are in both cases concordant within the uncertainties of decay constants and yield weighted mean ²⁰⁶Pb/²³⁸U ages (95% confidence uncertainty) of 530.26 Ma ± 0.05 Ma (GZ7) and 543.92 Ma ± 0.06 Ma (GZ8). Neither GZ7 nor GZ8 have been subjected to any gem enhancement by heating. Structure-related parameters correspond well with the calculated alpha doses of 1.48 × 10¹⁸ g^-1 (GZ7) and 2.53 × 10¹⁸ g^-1 (GZ8), respectively, and the (U-Th)/He ages of 438 Ma ± 3 Ma (2s) for GZ7 and 426 Ma ± 9 Ma (2s) for GZ8 are typical of unheated zircon from Sri Lanka. The mean U mass fractions are 680 μg g^-1 (GZ7) and 1305 μg g^-1 (GZ8). The two zircon samples are proposed as reference materials for SIMS (secondary ion mass spectrometry) U-Pb geochronology. In addition, GZ7 (Ti mass fractions 25.08 μg g^-1 ± 0.18 μg g^-1; 95% confidence uncertainty) may prove useful as reference material for Ti-in-zircon temperature estimates.

Synthesis of the first Zn6-hexagon sandwich-tungstoantimonate via rearrangement of a non-lacunary Krebs-type polyoxotungstate

For the first time, the Krebs-POM archetype was used as a non-lacunary precursor expanding the rarely reported hexagon sandwich-POM family.

A novel synthetic pathway to obtain the first Zn₆ hexagon tungstoantimonate [(Zn(H₂O))₆(B-α-SbW₉O₃₃)₂]^6– ([Zn₆-α-SbW₉] (1)) via rearrangement of a non-lacunary Krebs-POM precursor (C₁₂N₄H₁₁)₄K₄[(Mn(H₂O)₃)₂((Mn_0.5W_0.5)O₂)₂(B-β-SbW₉O₃₃)₂] ([Mn-β-SbW₉]) has been developed. Addition of ortho-phenylenediamine (opda) in order to optimize the synthesis of [Mn-β-SbW₉] led to the crystallization of a novel Krebs-type Zn-POM (C₁₂N₄H₁₁)₄Na₅[((Zn₀.₈W_0.2)(H₂O)₃)₂((Zn_0.2W_0.8)O₂)₂(B-β-SbW₉O₃₃)₂] ([(Zn/W)₂-β-SbW₉] (2)) comprising four disordered Zn-centers after replacement of MnCl₂ with ZnCl₂. The compounds were characterized in the solid state by single-crystal and powder X-ray diffraction (XRD), IR spectroscopy, thermogravimetric analysis (TGA) and elemental analysis and in solution by UV-vis spectroscopy and ESI-mass spectrometry. The Krebs-POM archetype and the Zn₆ hexagon tungstoantimonate have been investigated towards their interactions with Human Serum Albumin (HSA) as a model protein using SDS-PAGE and trypthophan fluorescence quenching.

Synthesis and characterization of hybrid Anderson hexamolybdoaluminates(III) functionalized with indometacin or cinnamic acid

The single-side Al-centred tris-functionalized hybrid organic-inorganic Anderson polyoxomolybdates (C16H36N)3[Al(OH)3Mo6O18(OCH2)3CNH(C10H8O)]·C9H7N·4CH3OH·5H2O (AlMo6-NH-Cin; Cin is cinnamic acid, C10H9O2) and (C16H36N)3[Al(OH)3Mo6O18(OCH2)3CNH(C19H15ClNO3)]·9H2O (AlMo6-NH-Indo; Indo is indometacin, C19H16ClNO4) have been prepared in a mild three-step synthesis and structurally characterized by single-crystal X-ray diffraction, 1H NMR and IR spectroscopies and elemental analysis. Both AlMo6-NH-Cin and AlMo6-NH-Indo crystallize in the orthorhombic space group Pbca. The antibacterial activities of AlMo6-NH-Cin and AlMo6-NH-Indo against the Gram-negative human mucosal pathogen Moraxella catarrhalis were investigated by determination of the minimum inhibitory concentration, which is 32 µg ml-1 for AlMo6-NH-Cin and 256 µg ml-1 for AlMo6-NH-Indo.

Total Synthesis, Stereochemical Assignment, and Divergent Enantioselective Enzymatic Recognition of Larreatricin

A concise and efficient total synthesis of the lignan natural product larreatricin as well as an unambiguous assignment of configuration of its enantiomers are reported, resolving a long-held controversy. Enzyme kinetic studies revealed that different polyphenol oxidases show high and remarkably divergent enantioselective recognition of this secondary metabolite.

Diffusion-controlled crack propagation in alkali feldspar

The chemically driven propagation of interacting parallel cracks in monoclinic alkali feldspar was studied experimentally. Single crystals of potassium-rich gem-quality sanidine were shifted towards more sodium-rich compositions by cation exchange with a NaCl-KCl salt melt at a temperature of 850 ∘ C and close to ambient pressure. Initially, a zone with elevated sodium content formed at the crystal surfaces due to the simultaneous in-diffusion of sodium and out-diffusion of potassium, where the rate of cation exchange was controlled by sodium-potassium interdiffusion within the feldspar. A chemical shift of potassium-rich alkali feldspar towards more sodium-rich compositions produces highly anisotropic contraction of the crystal lattice. This induced a tensile stress state in the sodium-rich surface layer of the crystals, which triggered the formation of a system of nearly equi-spaced parallel cracks oriented approximately perpendicular to the direction of maximum shortening. Crack propagation following their nucleation was driven by cation exchange occurring along the crack flanks and was controlled by the intimate coupling of the diffusion-mediated build-up of a tensile stress state around the crack tips and stress release by successive crack propagation. The critical energy release rate of fracturing was determined as 1.8-2.2 J m - 2 from evaluation of the near-tip J-integral. The mechanism of diffusion-controlled crack propagation is discussed in the context of high-temperature feldspar alteration.

Halogenated Alkyltetrazoles for the Rational Design of FeII Spin-Crossover Materials: Fine-Tuning of the Ligand Size

1-(3-Halopropyl)-1H-tetrazoles and their corresponding Fe^II spin-crossover complexes have been investigated in a combined experimental and theoretical study. Halogen substitution was found to positively influence the spin transition, shifting the transition temperature about 70 K towards room temperature. Halogens located at the ω position were found to be too far away from the coordinating tetrazole moiety to have an electronic impact on the spin transition. The subtle variation of the steric demand of the ligand in a highly comparable series was found to have a comparatively large impact on the spin-transition behavior, which highlights the sensitivity of the effect to subtle structural changes.

Boron-phil and boron-phob structure units in novel borides Ni3Zn2B and Ni2ZnB: experiment and first principles calculations

The crystal structures of two novel borides in the Ni-Zn-B system, τ₅-Ni₃Zn₂B and τ₆-Ni₂ZnB, were determined by single crystal X-ray diffraction (XRSC) in combination with selected area electron diffraction in a transmission electron microscope (SAED-TEM) and electron probe microanalysis (EPMA). Both compounds crystallize in unique structure types (space group C2/m, a = 1.68942(8) nm, b = 0.26332(1) nm, c = 0.61904(3) nm, β = 111.164(2)°, R_F = 0.0219 for Ni₃Zn₂B, and space group C2/m, a = 0.95296(7) nm, b = 0.28371(2) nm, c = 0.59989(1) nm, β = 93.009(4)°, R_F = 0.0163 for Ni₂ZnB). Both compounds have similar building blocks: two triangular prisms centered by boron atoms are arranged along the c-axis separated by Zn layers, which form empty octahedra connecting the boron centered polyhedra. Consistent with the (Ni+Zn)/B ratio, isolated boron atoms are found in τ₅-Ni₃Zn₂B, while B-B pairs exist in τ₆-Ni₂ZnB. The crystal structure of Ni₂ZnB is closely related to that of τ₄-Ni₃ZnB₂, i.e. Ni₂ZnB can be formed by removing the nearly planar nickel layer in Ni₃ZnB₂ and shifting the origin of the unit cell to the center of the B-B pair. The electrical resistivity and specific heat of τ₅-Ni₃Zn₂B reveal the metallic behavior of this compound with an anomaly at low temperature, possibly arising from a Kondo-type interaction. Further analysis on the lattice contribution of the specific heat reveals similarity with τ₄-Ni₃ZnB₂ with some indications of lattice softening in τ₅-Ni₃Zn₂B, which could be related to the increasing metal content and the absence of B-B bonding in τ₅-Ni₃Zn₂B. For the newly found phases, τ₅-Ni₃Zn₂B and τ₆-Ni₂ZnB as well as for τ₃-Ni₂₁Zn₂B₂₀ and τ₄-Ni₃ZnB₂ density functional theory (DFT) calculations were performed by means of the Vienna Ab initio Simulation Package (VASP). Total energies and forces were minimized in order to determine the fully relaxed structural parameters, which agree very well with experiment. Energies of formations in the range of -25.2 to -26.9 kJ mol^-1 were calculated and bulk moduli in the range of 179.7 to 248.9 GPa were derived showing hardening by increasing the B concentration. Charge transfer is discussed in terms of Bader charges resulting in electronic transfer from Zn to the system and electronic charge gain by B. Ni charge contributions vary significantly with crystallographic position depending on B located in the neighbourhood. The electronic structure is presented in terms of densities of states, band structures and contour plots revealing Ni-B and Ni-Zn bonding features.