Water-Soluble Polyoxometal Clusters of Molybdenum (V) with Pyrazole and Triazole: Synthesis and Study of Cytotoxicity and Antiviral Activity.

Among well-studied and actively developing compounds are polyoxometalates (POMs), which show application in many fields. Extending this class of compounds, we introduce a new subclass of polyoxometal clusters (POMCs) [Mo12O28(µ-L)8]4- (L = pyrazolate (pz) or triazolate (1,2,3-trz or 1,2,4-trz)), structurally similar to POM, but containing binuclear Mo2O4 clusters linked by bridging oxo- and organic ligands. The complexes obtained by ampoule synthesis from the binuclear cluster [Mo2O4(C2O4)2(H2O)2]2- in a melt of an organic ligand are soluble and stable in aqueous solutions. In addition to the detailed characterization in solid state and in aqueous solution, the biological properties of the compounds on normal and cancer cells were investigated, and antiviral activity against influenza A virus (subtype H5N1) was demonstrated.

Correction: Optical property trends in a family of {Mo6I8} aquahydroxo complexes.

Correction for 'Optical property trends in a family of {Mo6I8} aquahydroxo complexes' by Margarita V. Marchuk et al., Dalton Trans., 2021, 50, 8794-8802, https://doi.org/10.1039/D1DT01293B.

Chemical Diversity of Mo5S5 Clusters with Pyrazole: Synthesis, Redox and UV-vis-NIR Absorption Properties.

The chemistry of transition metal clusters has been intensively developed in the last decades, leading to the preparation of a number of compounds with promising and practically useful properties. In this context, the present work demonstrates the preparation and study of the reactivity, i.e., the possibility of varying the ligand environment, of new square pyramidal molybdenum chalcogenide clusters [{Mo5(µ3-S)i4(µ4-S)i(µ-pz)i4}(pzH)t5]1+/2+ (pzH = pyrazole, i = inner, t = terminal). The one-step synthesis starting from the octahedral Mo6Br12 cluster as well as the substitution of the apical pyrazole ligand or the selective bromination of the inner pyrazolate ligands were demonstrated. All the obtained compounds were characterized in detail using a series of physicochemical methods both in solid state (X-ray diffraction analysis, etc.) and in solution (nuclear magnetic resonance spectroscopy, mass spectrometry, etc.). In this work, redox properties and absorption in the ultraviolet-visible and near-infrared region of the obtained compounds were studied.

Crystal Structure and Thermal Properties of Double-Complex Salts [M1(NH3)6][M2(C2O4)3] (M1, M2 = Co, Rh) and K3[Rh(NH3)6][Rh(C2O4)3]2∙6H2O.

Here, seven new double-complex salts, [M1(NH3)6][M2(C2O4)3] (M1, M2 = Co, Rh) and K3[Rh(NH3)6][Rh(C2O4)3]2∙6H2O types, are synthesised. The crystal structure and composition of DCS (double-complex salts) are studied by SCXRD, XRD, CHN and IR methods. The complex salts of the [M1(NH3)6][M2(C2O4)3] (M1, M2 = Co, Rh) type can be crystallised both as a crystalline hydrate [M1(NH3)6][M2(C2O4)3]·3H2O (sp. gr. P-3) and as an anhydrous complex (sp. gr. P-1) depending on the synthesis conditions. The process of [Rh(NH3)6][Rh(C2O4)3] formation is significantly dependent on the synthesis temperature. At room temperature, a mixture is formed comprising [Rh(NH3)6][Rh(C2O4)3] and K3[Rh(NH3)6][Rh(C2O4)3]2∙6H2O, while the [Rh(NH3)6][Rh(C2O4)3] target product crystallises at elevated temperatures. The thermal behaviour of double-complex salts is studied by the STA, EGA-MS, IR and XRD methods. The complete decomposition of complex salts in helium and hydrogen atmospheres resulting in metals or CoxRh1-x solid solutions is achieved at temperatures of 320-450 °C.

Potassium and Cesium Fluorinated ß-Diketonates: Effect of a Cation and Terminal Substituent on Structural and Thermal Properties.

As potential precursors for the synthesis of fluoroperovskites, a family of heavy alkali metal (MI = K, Cs) fluorinated ß-diketonates were prepared and characterized by elemental analysis, IR, and powder-XRD. The crystal structures of the new six complexes, MI(ß-dikF)(H2O)X, X = 0 or 1, were also determined. The structural diversity of this poorly explored class of complexes was discussed, including the preferred types of cation polyhedra and the ligand coordination modes, and the thermal properties of the metal ß-diketonates were studied by TG-DTA in an inert (He) atmosphere. The data obtained allowed us to reveal the effect of the metal cation and the terminal substituent on the structural and thermal features of this family of complexes.

Chromium-Lanthanide Complexes Containing the Cr═P═Cr Fragment: Synthesis, Characterization, and Computational Study.

Heterometallic complexes [Cp*2Ln(µ-isoCO)2{Cr2(µ-P)Cp2(CO)2}] [Ln = Yb (1), Sm (2)] were obtained in reactions of [Cp*2Ln(thf)2] (Ln = Sm, Yb) with [{CpCr(CO)2}2(µ,η2:2-P2)] (4). An analogous yttrium compound [Cp*2Y(µ-isoCO)2{Cr2(µ-P)Cp2(CO)2}] (3) was synthesized using a three-component reaction between [Cp*2Y(BPh4)], 4, and KC8. Compounds 1-3 were isolated as solvent-free crystalline phases; in the case of 2, the 2·0.5C7H8 solvate was also obtained. The structures of all crystalline phases were determined by single-crystal X-ray diffraction analysis. All compounds contain a unique {((CO)2CpCr═P═CrCp(CO)2)}- unit, which is linked to Ln3+ ions through CO ligands in the isocarbonyl mode. Compounds 1 and 3 have a molecular structure, while compound 2 contains polymeric chains of triangular [Cp*2Sm(µ-isoCO)2{Cr2(µ-P)Cp2(CO)2}] units linked by µ-isoCO-ligands. 31P NMR studies demonstrated similar dramatic downfield shifts for complexes 1-3. To realize the electronic structure of 1-3 and to elucidate the nature of the high downfield chemical 31P shift, quantum chemical calculations were performed both for 1-3 and for related Cr- and Fe-phosphido complexes. Calculations show that the anomalously high downfield chemical shifts for 1-3 are due to the anisotropic effect of the Cr═P double bonds.

Spin Crossover and Thermochromism in Iron(II) Complexes with 2,6-Bis(1H-imidazol-2-yl)-4-methoxypyridine.

New iron(II) complexes with 2,6-bis(1H-imidazol-2-yl)-4-methoxypyridine (L) of the composition [FeL2]An∙mH2O (A = SO42-, n = 1, m = 2 (I); A = ReO4-, n = 2, m = 1 (II); A = Br-, n = 2, m = 2 (III)) have been synthesized and investigated. To determine the coordination ability of the ligand, a single crystal of a copper(II) complex of the composition [CuLCl2] (IV) was obtained and studied by X-ray technique. Compounds I-III were studied using methods of X-ray phase analysis, electron (diffuse reflection spectra), infrared and Mössbauer spectroscopy, static magnetic susceptibility. The study of the µeff(T) dependence showed that the 1A1 ↔ 5T2 spin crossover manifests itself in the compounds. The spin crossover is accompanied by thermochromism: there is a distinct color change orange ↔ red-violet.

Cs2Ln3CuS8 (Ln = La-Nd, Sm-Tb): Synthesis, Crystal Structure, and Magnetic and Optical Properties.

This work reports the preparation of new quaternary sulfides Cs2Ln3CuS8 (Ln = La-Nd, Sm-Tb), their original crystal and electronic structures, and their magnetic properties. The sulfides were prepared using a reactive flux method from mixtures of Ln2S3 (EuS), Cs2S6, Cu2S, and S. They crystallize in a new type of structure (C2/m space group) and exhibit a layer-like crystal structure, which is a hybrid of those of the ACe2CuS6 series (A = Cs, K) and that of K2CeCu2S4. The values of the optical band gap calculated by the Kubelka-Munk equation are in the range of 1.2-2.62 eV depending on the nature of the Ln ion. The Cs2Gd3CuS8 compound displays relatively great magnetic refrigerating properties at cryogenic temperature with the mass entropy change (-ΔSM) reaching 19.5 J kg-1 K-1 at 3.5 K for ΔH = 5 T.

Structural, Spectroscopic, Electric and Magnetic Properties of New Trigonal K5FeHf(MoO4)6 Orthomolybdate.

A new multicationic structurally disordered K5FeHf(MoO4)6 crystal belonging to the molybdate family is synthesized by the two-stage solid state reaction method. The characterization of the electronic and vibrational properties of the K5FeHf(MoO4)6 was performed using density functional theory calculations, group theory, Raman and infrared spectroscopy. The vibrational spectra are dominated by vibrations of the MoO4 tetrahedra, while the lattice modes are observed in a low-wavenumber part of the spectra. The experimental gap in the phonon spectra between 450 and 700 cm-1 is in a good agreement with the simulated phonon density of the states. K5FeHf(MoO4)6 is a paramagnetic down to 4.2 K. The negative Curie-Weiss temperature of -6.7 K indicates dominant antiferromagnetic interactions in the compound. The direct and indirect optical bandgaps of K5FeHf(MoO4)6 are 2.97 and 3.21 eV, respectively. The K5FeHf(MoO4)6 bandgap narrowing, with respect to the variety of known molybdates and the ab initio calculations, is explained by the presence of Mott-Hubbard optical excitation in the system of Fe3+ ions.

Unusual Square Pyramidal Chalcogenide Mo5 Cluster with Bridging Pyrazolate-Ligands.

The family of chalcogenide molybdenum clusters is well presented in the literature by a series of compounds of nuclearity ranging from binuclear to multinuclear articulating octahedral fragments. Clusters actively studied in the last decades were shown to be promising as components of superconducting, magnetic, and catalytic systems. Here, we report the synthesis and detailed characterization of new and unusual representatives of chalcogenide clusters: square pyramidal complexes [{Mo5(µ3-Se)i4(µ4-Se)i(µ-pz)i4}(pzH)t5]1+/2+ (pzH = pyrazole, i = inner, t = terminal). Individually obtained oxidized (2+) and reduced (1+) forms have very close geometry (proven by single-crystal X-ray diffraction analysis) and are able to reversibly transform into each other, which was confirmed by cyclic voltammetry. Comprehensive characterization of the complexes, both in solid and in solution, confirms the different charge state of molybdenum in clusters (XPS), magnetic properties (EPR), and so on. DFT calculations complement the diverse study of new complexes, expanding the chemistry of molybdenum chalcogenide clusters.

Water-Soluble Chalcogenide W6-Clusters: On the Way to Biomedical Applications.

Despite the great potential of octahedral tungsten cluster complexes in fields of biomedical applications such as X-ray computed tomography or angiography, there is only one example of a water-soluble W6Q8-cluster that has been reported in the literature. Herein we present the synthesis and a detailed characterization including X-ray structural analysis, NMR, IR, UV-Vis spectroscopies, HR-MS spectrometry, and the electrochemical behavior of two new cluster complexes of the general formula W6Q8L6 with phosphine ligands containing a hydrophilic carboxylic group, which makes the complexes soluble in an aqueous medium. The hydrolytic stability of the clusters' aqueous solutions allows us to investigate for the first time the influence of W6-clusters on cell viability. The results obtained clearly demonstrate their very low cytotoxicity, comparable to the least-toxic clusters presented in the literature.

Synthesis and investigation of the thermal properties of [Co(NH3)6][Co(C2O4)3]·3H2O and [Ir(NH3)6][Ir(C2O4)3].

The complexes [Co(NH3)6][Ir(C2O4)3] and [Ir(NH3)6][Co(C2O4)3]·H2O have previously been synthesized and their thermal properties studied. The [Ir(NH3)6][Ir(C2O4)3] and [Co(NH3)6][Co(C2O4)3]·3H2O complexes considered here are the end members in a series of possible isostructural solid solutions based on the complex salts in the Co-Ir system. Their crystal structures and thermal properties are described in detail, including temperature-dependent in situ X-ray diffraction. During the thermolysis of these compounds, layered metal nanoparticles are formed. Close attention is paid to the details of the [Co(NH3)6][Ir(C2O4)3] synthesis. It has been shown that the formation of this complex salt is temperature dependent; upon heating, a new phase of the K3[Co(NH3)6][Ir(C2O4)3]2·6H2O salt is formed, which incorporates the initial iridium compound into the crystal structure of the double complex salt. The target [Co(NH3)6][Ir(C2O4)3] product is obtained if the synthesis is carried out at room temperature.

Revisiting Sodium Hexafluoroiridates: Perspective Precursors for Electronic, Quantum, and Related Materials.

The following salts have been synthesized and structurally characterized: Na2[IrF6]·2H2O (C2/m, a = 6.6327(4), b = 10.0740(6), c = 5.9283(5) Å, ß = 122.3880(10)°) and Na3[IrF6]·2H2O (R-3, a = 7.5963(3), b = 7.5963(3), c = 9.8056(4) Å) (for the first time) by single-crystal X-ray diffraction; the unit cell parameters of a tetragonal phase (P4 2/mnm, a = 5.005(2), c = 10.074(4) Å) of the stable α-Na2[IrF6] were determined for the first time; and the unit cell parameters of ß-Na2[IrF6] (P321, a = 9.332(4), c = 5.136(2) Å) and Na3[IrF6] (P21/n, a = 5.567(4), b = 5.778(4), c = 8.017(2) Å, ß = 90.41(2)°) were determined using powder X-ray diffraction (PXRD). The data of the thermal stability was obtained by differential thermal analysis (DTA) for all substances. The presence of Na3[IrF6]·H2O monohydrate is predicted. H2[IrF6] was prepared in a solution and was demonstrated to behave as a strong dibasic acid.

Self-Assembled Microporous M-HOFs Based on an Octahedral Rhenium Cluster with Benzimidazole.

Substitution of apical halide ligands in [{Re6Sei8}Xa6]3- (X = Cl, Br) by benzimidazole (bimzH) accompanied by a self-assembly process leads to the formation of microporous Re6-based hydrogen-bonded organic frameworks (Re6-HOFs) constructed on N-H···X hydrogen bonds and π-π-stacking interactions between bimzH ligands. Re6-HOFs demonstrate sorption properties with a Brunauer-Emmett-Teller surface area of up to 443 m2 g-1 and luminescence with a quantum yield and an emission lifetime of up to 0.16 and 16 µs, respectively. The compounds obtained complement small groups of transition-metal cluster-based HOFs, which are a perspective for the development of multifunctional frameworks.

Optical property trends in a family of {Mo6I8} aquahydroxo complexes.

Luminescence is one of the key properties of octahedral molybdenum cluster complexes and the basis for most areas of their possible practical applications. Nevertheless, the factors affecting the optical properties of the clusters are insufficiently studied and establishing them will allow us to tune both absorption and emission more precisely. In this work, we obtained two new cationic [{Mo6I8}(H2O)4(OH)2](An)2·nH2O (An = NO3-, n = 3; An = OTs-, n = 2, OTs- - p-toluenesulfonate), and two neutral [{Mo6I8}(H2O)2(OH)4]·nH2O (n = 2, 12) aquahydroxo complexes. Due to the similar compositions of the clusters obtained, we determined the influence of crystal packing and ligand environment on the absorption and photo- and radioluminescence properties. Thus, the four-component nature of the cluster emission was established using Gaussian deconvolution of the photoluminescence spectra. It was shown that the influence of both ligand type and crystal density decreases when moving to the red (lower-energy) part of the spectra, with only the first two components located in the blue (higher-energy) part of the spectra being strongly affected. Also, it was found that protonation of two hydroxo ligands leads to a significant decrease in absorption in the visible spectral region.

Remarkable thermal stability of light-induced Ru-ON linkage isomers in mixed salts of a ruthenium amine complex with a trans-ON-Ru-F coordinate.

Two new complexes trans-(H3O)[RuNO(NH3)4F](NO3)1.5F1.5·0.5H2O (I) and trans-[RuNO(NH3)4F](ClO4)Cl (II) are synthesized and characterized by single crystal X-ray diffraction. The complexes crystallized in the centrosymmetric space groups I4/m and P21/n due to specific intermolecular interactions; the strongest ones are represented by N-HO contacts. The irradiation of the complexes in the blue-light range induces the formation of Ru-ON isomers (MS1), determined by IR spectroscopy and differential scanning calorimetry (DSC). The subsequent excitation of MS1 by infrared light induces the formation of Ru-(η2-(NO)) (MS2) isomers, confirmed by the same techniques. Using combined IR and DSC analysis, the activation barriers (Ea) and frequency factors (lg k0) of the MS1 → GS and MS2 → GS reactions are determined. According to the kinetic parameters, the calculated lifetimes (k-1) of MS1 at 300 K are 33 and 178 min for I and II, respectively. To the best of our knowledge, the thermal stability of MS1 in II is the highest among known related complexes. The thermal stability of MS2 was found to be lower (the lifetimes are 0.12 and 0.02 s at 300 K for I and II, respectively), which is characteristic of these states. The high thermal stability of MS1 can be applied for the design of photochromic materials and to generally facilitate the investigation of the states.

Exploration of the Structural and Vibrational Properties of the Ternary Molybdate Tl5BiHf(MoO4)6 with Isolated MoO4 Units and Tl+ Conductivity.

The phase relations in the subsolidus region of the Tl2MoO4-Bi2(MoO4)3-Hf(MoO4)2 system were studied with the "intersecting cuts" method. The formation of the novel ternary molybdate Tl5BiHf(MoO4)6 is found in this ternary system. The compound has a phase transition at Tpt = 731 K (ΔH = -3.15 J/g) and melts at Tm = 871 K (ΔH = -41.71 J/g), as determined by a thermal analysis. Tl5BiHf(MoO4)6 single crystals were obtained by the spontaneous nucleation method. The crystal structure of Tl5BiHf(MoO4)6 was revealed by structure analysis methods. This molybdate crystallizes in the trigonal space group R3̅c with the unit cell parameters a = 10.6801(4) Å, c = 38.5518(14) Å, V = 3808.3(2) Å3, and Z = 6. The vibrational characteristics of Tl5BiHf(MoO4)6 were determined by Raman spectroscopy. The Tl5BiHf(MoO4)6 conductivity was measured at frequencies of 0.1, 1.0, and 10 kHz in the temperature range of 293-773 K; in this temperature range, the conductivity level was 10-12-10-7 S/cm.

Water-Soluble Rhenium Clusters with Triazoles: The Effect of Chemical Structure on Cellular Internalization and the DNA Binding of the Complexes.

Here we explore the effect of the nature of organic ligands in rhenium cluster complexes [Re6 Q8 L6 ]4- (where Q=S or Se, and L=benzotriazole, 1,2,3-triazole or 1,2,4-triazole) on the biological properties of the complexes, in particular on the cellular toxicity, cellular internalization and localization. Specifically, the study describes the synthesis and detailed characterization of the structure, luminescence and electrochemical properties of the four new Re6 clusters with 1,2,3- and 1,2,4-triazoles. Biological assays of these complexes are also discussed in addition to those with benzotriazole using cervical cancer (HeLa) and immortalized human fibroblasts (CRL-4025) as model cell lines. Our study demonstrates that the presence of hydrophobic and π-bonding rich units such as the benzene ring in benzotriazole significantly enhances cellular internalization of rhenium clusters. These ligands facilitate binding of the clusters to DNA, which results in increased cytotoxicity of the complexes.

Tetraammineplatinum(II) and Tetraamminepalladium(II) Chromates as Precursors of Metal Oxide Catalysts.

[M(NH3 )4 ]A (M=Pt, Pd; A=CrO4 , Cr2 O7 ) and [Pt(NH3 )4 (NO2 )(Cr2 O7 )]NO3 complex salts were synthesized and characterized by a number of physicochemical methods of analysis (IR, single-crystal and powder XRD, and simultaneous thermogravimetry and differential scanning calorimetry with evolved gas analysis mass spectrometry). Thermolysis of the salts obtained in a hydrogen atmosphere proceeds with the partial reduction of chromium to a metallic state and the formation of Mx Cr1-x (M=Pt, Pd) metal solid solution with a chromium content of up to 22 at % and chromium(III) oxide. The thermal decomposition of salts in an inert and oxidizing atmosphere passes through the formation stage of the MCrO2 phase with the delafossite structure followed by its subsequent decomposition into chromium(III) oxide and noble metal. Nanosized Pt-Cr2 O3 and Pd-Cr2 O3 composites obtained by the thermolysis of precursor salts in air at 500 °C and being held at this temperature for 1 h showed a high catalytic activity in the CO total oxidation (TOX) and preferential oxidation in the excess of hydrogen (PROX) processes compared with that of monometallic Pt and Pd powders.

Synthesis, Crystal Structure, and Liquid Exfoliation of Layered Lanthanide Sulfides KLn2CuS6 (Ln = La, Ce, Pr, Nd, Sm).

Among the great amount of known lanthanide nanoparticles, reports devoted to chalcogenide ones are deficient. The properties of such nanoparticles remain almost unknown due to the lack of simple and proper synthetic methods avoiding hydrolysis and allowing preparation of oxygen-free lanthanide nanoparticles. A liquid exfoliation method was used to select the optimum strategy for the preparation of quaternary lanthanide sulfide nanoparticles. Bulk KLn2CuS6 (Ln = La-Sm) materials were obtained via a reactive flux method. The crystal structures of three new members of the KLn2CuS6 series were determined for Pr, Nd, and Sm as well as for known KLa2CuS6. KLn2CuS6 (Ln = La, Pr, Nd) compounds crystallize in the monoclinic C2 /c space group, whereas KSm2CuS6 crystallizes in the orthorhombic Fddd space group. The analysis of their electronic structures confirms that the main bonding interactions occur within the anionic {Ln2CuS6}- layers. Due to their layered structure, exfoliation of these compounds is possible using ultrasonic treatment in appropriate solvents with the formation of colloidal solutions. Colloidal particles show a plate-like morphology with a lateral size of 100-200 nm and a thickness of 2-10 nm. Highly negative or positive charges found in isopropanol and acetonitrile dispersions, respectively, are associated with high stability and concentration of the dispersions.