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.

Potassium and Cesium Fluorinated β-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 β-diketonates were prepared and characterized by elemental analysis, IR, and powder-XRD. The crystal structures of the new six complexes, MI(β-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 β-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,η^2:2-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]A_n∙mH₂O (A = SO₄^2-, 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 µ_eff(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 (-ΔS_M) reaching 19.5 J kg^-1 K^-1 at 3.5 K for ΔH = 5 T.

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, β = 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 β-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, β = 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}X^a₆]^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

The novel complexes with trans-ON–Ru–F coordinate exhibit the highest thermal stability of Ru–ON photoinduced isomers.

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.

Melting of nucleobases. Getting the cutting edge of "Walden's Rule"

Walden's Rule is an empirical observation of an invariant fusion entropy during fusion of non-associated organic compounds. For the five nucleobases, adenine, thymine, cytosine, guanine, and uracil, surprisingly high fusion temperatures and enthalpies have been measured using a specially developed fast scanning calorimetry method that prevents decomposition. Even when nucleobases admittedly possess very high fusion temperatures, e.g. the value of 862 K measured for guanine really exceeds all expectations of the feasible dimension of the fusion temperature for such a relatively small and simple organic molecule. Hirshfeld surface analysis has been applied in order to find out an explanation for such extremely unusual thermal behavior of nucleobases. We rationalized the observed trends in terms of fusion entropy (Walden's constant = 56.5 J K^-1 mol^-1) as the entropic penalty of fusion not only for "non-associated", as proposed by Walden in 1908, but also for "ideal associated" systems like nucleobases.

A fresh look at the structural diversity of dibenzoylmethanide complexes of lanthanides

Synthetic methods for dibenzoylmethanide lanthanide complexes as well as heterolanthanide ones were systematized revealing several species.

Water-soluble Re6-clusters with aromatic phosphine ligands – from synthesis to potential biomedical applications

New hexarhenium clusters exhibit radio- and photoluminescence, have low cytotoxicity, are capable of penetrating into cells and exhibit photodynamic toxicity.

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.

High thermal stability of the Ru–ON (MS1) linkage isomer of the ruthenium nitrosyl complex [RuNO(Py)4F](ClO4)2 with the trans NO–Ru–F coordinate

The [RuNO(Py)₄F](ClO₄)₂ complex with the highest thermal stability of the Ru–ON linkage isomer.

A comparative study of optical properties and X-ray induced luminescence of octahedral molybdenum and tungsten cluster complexes

Octahedral W cluster complexes have more intensive X-ray excited optical luminescence than Mo ones.

Structure-property relationships in halogenbenzoic acids: Thermodynamics of sublimation, fusion, vaporization and solubility

Temperature dependences of vapor pressures for 2-, 3-, and 4-bromobenzoic acid, as well as for five isomeric bromo-methylbenzoic acids were studied by the transpiration method. Melting temperatures and enthalpies of fusion for all isomeric bromo-methylbenzoic acids and 4-bromobenzoic acid were measured with a DSC. The molar enthalpies of sublimation and vaporization were derived. These data together with results available in the literature were collected and checked for internal consistency using a group-additivity procedure and results from X-ray structural diffraction studies. Specific (hydrogen bonding) interactions in the liquid and in the crystal phase of halogenbenzoic acids were quantified based on experimental values of vaporization and sublimation enthalpies. Structure-property correlations of solubilities of halogenobenzoic acids with sublimation pressures and sublimation enthalpies were developed and solubilities of bromo-benzoic acids were estimated. These new results resolve much of the ambiguity in the available thermochemical and solubility data on bromobenzoic acids. The approach based on structure property correlations can be applied for the assessment of water solubility of sparingly soluble drugs.

Octahedral molybdenum cluster complexes with aromatic sulfonate ligands

Synthesis, structure and systematic study of the redox and spectroscopic properties of [{Mo₆X₈}(aromatic sulfonate)₆]²⁻.

New NIR-emissive tetranuclear Er(iii) complexes with 4-hydroxo-2,1,3-benzothiadiazolate and dibenzoylmethanide ligands: synthesis and characterization

Two new Er complexes were prepared and studied.

The first water-soluble hexarhenium cluster complexes with a heterocyclic ligand environment: synthesis, luminescence, and biological properties

The hexarhenium cluster complexes with benzotriazolate apical ligands [{Re6(μ3-Q)8}(BTA)6](4-) (Q = S, Se; BTA = benzotriazolate ion) were obtained by the reaction of [{Re6(μ3-Q)8}(OH)6](4-) with molten 1H-BTA (1H-benzotriazole). The clusters were crystallized as potassium salts and characterized by X-ray single-crystal diffraction, elemental analyses, and UV-vis and luminescence spectroscopy. In addition, their cellular uptake and toxicity were evaluated. It was found that both clusters exhibited luminescence with high lifetimes and quantum yield values; they were taken up by the cells illuminating them under UV irradiation and, at the same time, did not exhibit acute cytotoxic effects.

X-(Diiodoarsanyl)benzoic acid (X = 3 and 4)

The title compounds, 4-(diiodoarsanyl)benzoic acid, (I), and 3-(diiodoarsanyl)benzoic acid, (II), both [As(C(7)H(5)O(2))I(2)], which possess a -COOH coordinating group, form molecular crystal structures composed of hydrogen-bonded dimers, the packing differences of which are caused by the relative position of the diiodoarsanyl groups. The para isomer, with Z' = 1, crystallizes in a layered structure with shortened contacts of the As atoms to only the arene rings of adjacent molecules. In contrast, the meta isomer, with Z' = 3, forms separate rectangular blocks of three ribbons, each composed of dimeric molecular units positioned almost directly above each other and with the As atoms possessing only two As···I contacts to the I atoms of neighbouring molecules.