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Seven tetraammineoxalatocobalt(III) salts with oxomolybdate anions of different nuclearities, such as [Co(C2O4)(NH3)4]2[MoO4]·H2O (1), [Co(C2O4)(NH3)4]2[Mo2O4(μ-O)(C2O4)2(H2O)2]·4H2O (3), Na2[Co(C2O4)(NH3)4]2[Mo2O4(μ-O)2(C2O4)2]·4H2O (4), [Co(C2O4)(NH3)4]4[Mo3O6(μ-O)2(C2O4)3(H2O)2]·5H2O (5), [Co(C2O4)(NH3)4]4[Mo8O26]·12H2O (8), [Co(C2O4)(NH3)4]4[SiMo12O40]·6H2O (9) and [Co(C2O4)(NH3)4]4[Mo8O26]·10H2O (10), along with [Mo5Co2O17(HCO3)(H2C3O4H)(NH3)7]·5H2O (6) and [Mo5Co2O18(NH3)7]·5H2O (7), were isolated using a one-pot reaction of sodium molybdate with [Co(C2O4)(NH3)4]NO3·H2O or [Co(CO3)(NH3)4]NO3· H2O and mono- or dicarboxylic acids in an aqueous medium. Polyoxomolybdate anions are built up from {MoO4}, {Mo2O4(μ-O)}, {Mo2O4(μ-O)2}, {Mo3O6(μ-O)2}, {Mo5O17}, {Mo5O18}, {Mo8O26} and {SiMo12O40} units, respectively, depending on the nature of the carboxylic acid additive used in the synthesis. The isolation of these salts confirmed that the carboxylic acids act not only as ligands, primarly, but also as structure-directing agents in the polyoxoanion self-assembly processes. All products were characterized in the solid state via single-crystal and powder X-ray diffraction, infrared spectroscopy as well as thermogravimetric and elemental analyses. [ABSTRACT FROM AUTHOR]

Five hexamolybdate and five octamolybdate-based organic–inorganic hybrid assemblies, with dioxomolybdenum(VI) hydrazonato complex cations, were synthesized from the [MoO2(acac)2] and isonicotinoyl hydrazone ligands bearing OH (H2L1,2) and OMe (H2L3,4) electron-donating groups. They can be classified into four categories including one known (i) [MoO2(HL1–4)(D)]2[Mo6O19]·xMeCN·yH2O, where D = H2O or MeCN, and three novel (ii) [Mo2O2(μ-O)2(HL3)2][Mo6O19], (iii) [MoO2(HL1,2)(H2O)]4[Mo8O26]·xMeCN·yH2O, and (iv) [MoO2(H2L2,4)(H2O)]2[Mo8O26]·xMeCN·yH2O, thus extending the structural landscape of Mo-complex–POM hybrids. Characterization of the hybrids, employing X-ray crystallography, IR-ATR, and TG analysis, was carried out. The effects of the reaction conditions and coordination nature of the Mo(VI) complex cations on the structure of the hybrid compounds were investigated. Relative differences in the standard Gibbs energies of formation () of the structures were calculated to determine the possibility of developing the covalently anchored POM–Mo-complex hybrids. The impact of the metal–organic components and various solvents on the particular type of hybrid formation was evaluated. [ABSTRACT FROM AUTHOR]

Unsymmetrically substituted carbohydrazides, containing chelating o-hydroxyaryl and non-chelating pyridyl subunits were synthesized via two-step functionalization of carbohydrazide. Anion binding and coordinative propensities of the compounds were tested in reactions with appropriate Mo(VI) species. Such procedures yielded four types of products: monomeric dioxomolybdenum(VI) complexes, dimeric and oligomeric/polymeric dioxomolybdenum(VI)-containing ensembles, hybrid hexamolybdate systems where the protonated ligand acts as cation and the hybrid hexamolybdate salts where the cation is the protonated form of the monomeric dioxomolybdenum(VI) complex. The solid-state structures of the compounds were elucidated by X-ray diffraction and infrared spectroscopy, while their thermal stability was inspected via thermogravimetric analysis and differential scanning calorimetry experiments. The behaviour of the ligands, monomeric, dimeric, and oligomeric/polymeric ensembles in DMSO solution was investigated by nuclear magnetic resonance. In the isolated materials, carbohydrazide ligands adopt altogether four distinctive protonation forms: neutral, monoprotonated in the corresponding hexamolybdate salt, doubly deprotonated while forming {MoO2}2+ complexes, and neutral zwitterionic when shaping the hybrid salt. In all these structures the unsymmetrical carbohydrazide framework retains robust conformation and geometry. [ABSTRACT FROM AUTHOR]

Symmetrical disubstituted carbohydrazides (H4L1–6) when reacted with [MoO2(acac)2] (in 1 : 2 molar ratio) afford the corresponding discrete complexes, [(MoO2)2L1,5,6(MeOH)2], [(MoO2)2L1,5,6(Im)2] (Im = imidazole), and/or polymeric ensembles, [(MoO2)2L1–6]n, depending on the reaction solvent, the ligand framework and the presence of ancillary coordinating species. In these assemblies, asymmetrical dimolybdenum(VI) entities, [(MoO2)2L1–6], wherein the corresponding carbohydrazide acts as an adaptable two-compartment ligand offering ONO and ONN coordination environments, serve as the main building blocks. The solid-state structures of the obtained materials were elucidated via X-ray diffraction and infrared spectroscopy, whereas the behaviour of polymeric ensembles in DMSO-d6 solution was investigated by nuclear magnetic resonance. Thermal studies revealed that the discrete species transform to the corresponding polymeric ensembles upon heating, whereas upon grinding they either remain intact or afford their reactive and coordinatively unsaturated (pentacoordinated) counterparts. While the discrete methanol-based complexes have a comparable spatial arrangement of ancillary ligands, imidazole-based ones offer substantially different scenario which was addressed in detail via density functional theory calculations. Finally, the polymeric ensembles were shown to be efficient catalysts for cyclooctene epoxidation under eco-friendly conditions while employing aqueous tert-butyl hydroperoxide as an oxidant. [ABSTRACT FROM AUTHOR]

The synthesis and structures of the Mo(VI) coordination polymer [MoO2(L)]n (1), mononuclear complexes [MoO2(L)(MeOH)] (2α, 2β, and 2γ), and salts [MoO2(HL)(MeOH)]X, where X = Cl (3), Br (4), NO3 (5), and MeOSO3 (6), and L = 4-methoxysalicylaldehyde isonicotinoylhydrazonato ligand, are described. Polymer 1 can be quantitatively self-assembled from the neutral mononuclear complex upon vapour-mediated desolvation. The efficiency of the solid-state transformation is driven by the proximity of reaction centres due to O–H⋯N interactions. Additionally, the conversion seems to be sensitive to solvent polarity and can be achieved only in the presence of polar non-coordinating solvents. In the case of salts 3–6, an examination of the crystal structures shows that two architecturally different supramolecular assemblies are obtained. When anion X is Cl or Br, hydrogen bonded dimers are constructed while in the case of NO3 or MeOSO3 infinite hydrogen-bonded 1D chains are achieved. In the deprotonation reactions with Et3N, crystals of 3 or 4 and 5 or 6 serve as heteronuclear templates, affording polymorphic forms 2α and 2γ, respectively. A common feature of 2α and 2β forms is the association of the molecules into discrete dimers, whereas in the case of 2γ, 1D chains are formed as a consequence of O–H⋯N hydrogen bonding interactions. The non-porous complex 2α is shown to undergo a single-crystal-to-single-crystal transformation when crystals are exposed to moisture, thus yielding chains of hydrogen bonded dimers of [MoO2(L)(H2O)] (2w-α). The potent and broad-spectrum activity of 2–6 was established against selected Gram-positive and Gram-negative bacteria. The cytotoxicity of the compounds was evaluated on HepG2 and THP-1 cell lines. [ABSTRACT FROM AUTHOR]

Ageing a mixture of sodium molybdate, malonic acid, and tris(ethylenediamine)cobalt(iii) chloride using different synthetic routes, namely, solution-based methods at room temperature or 110 °C, and a mechanochemically accelerated vapour-assisted method, yielded the polyoxomolybdate [Co(en)3]5Na[Mo7O24(μ-Mo8O26)Mo7O24]·nH2O (1). The new polyoxomolybdate anion 1 comprised three fragments, namely, two {Mo7O24} units bridged by a {Mo8O26} unit, which were interconnected by the terminal oxygen atoms of MoO6 octahedra and represent a unique structural motif not yet described in the structurally versatile chemistry of polyoxomolybdates (POMos). The ageing reaction was found to occur via a series of intermediates, two of which were isolated and identified as the heptamolybdate coordination polymer [Co(en)3]2[NaMo7O24]Cl·nH2O (2), comprising {Mo7O24} units bridged by a sodium atom, and the heptamolybdate (H3O)[Co(en)3]2[Mo7O24]Cl·9H2O (3). An identical reaction procedure with [Co(C2O4)(en)2]+ instead of [Co(en)3]3+ yielded the orthomolybdate [Co(C2O4)(en)2]2[MoO4]·9H2O (4) and the hydrogen malonate [Co(C2O4)(en)2]C3O4H3 (5). The new polyoxomolybdate [Co(en)3]5Na[Mo7O24(μ-Mo8O26)Mo7O24]·nH2O was also examined as a catalyst for the epoxidation of cyclooctene, and was superior to both heptamolybdate and octamolybdate catalysts over 24 h. The heptamolybdate [Co(NH3)6]2[Mo7O24]·8H2O (6) was isolated as the only reaction product of sodium molybdate and hexaamminecobalt(iii) nitrate in the presence of malonic acid using solution-based methods. [ABSTRACT FROM AUTHOR]

The focus of this work was on the synthesis, characterization and catalytic activity of Mo(vi) complexes with hemilabile polydentate ligands that show a high tendency to form discrete small-sized self-assembled structures. A series of mononuclear, [MoO2(L1 or 3)(MeOH)] (1a and 3a) and [MoO2(L1)(EtOH)] (1b), and dinuclear, [MoO2(L1–3)]2 (1–3), complexes was synthesised by using 2-aminobenzoylhydrazone ligands derived from salicylaldehyde (H2L1), 3-methoxy-2-hydroxybenzaldehyde (H2L2) and 4-methoxy-2-hydroxybenzaldehyde (H2L3). Different reaction conditions led to the formation of several crystalline forms of the dinuclear cyclic species [MoO2(L1 or 3)]2 (1-α, 1-β, 1-γ, 1·CH3CN, 3-α, 3-β and 3·2CH3CN), a feature which is observed for the first time in the case of the metallosupramolecular compounds incorporating cis-MoO22+ subunits. These complexes were tested as catalysts for cyclooctene epoxidation under eco-friendly reaction conditions by using aqueous tert-butyl hydroperoxide as an oxidant without the addition of an organic solvent. The use of the hemilabile ligands provided the opportunity to employ relatively stable coordinatively saturated dinuclear Mo(vi) complexes, which in turn offered access to highly reactive pentacoordinated species in the presence of olefins. Lastly, the hemilabile ligand induced catalytic enhancement was addressed by using density functional theory calculations. [ABSTRACT FROM AUTHOR]

Cyclic dinuclear molybdenum(vi) complexes [MoO2(L1–3)]2 (1, 2-α, 2-β and 3) were synthesized through the use of coordination-driven self-assembly of a MoO22+ core and 4-aminobenzoylhydrazone ligands (salicylaldehyde (H2L1), 3-methoxysalicylaldehyde (H2L2) or 4-methoxysalicylaldehyde 4-aminobenzoylhydrazone (H2L3)). Their X-ray diffraction (XRD) analysis revealed that these types of ligands could serve as organic linkers for cis-octahedral complexes containing a MoO22+ core. Mononuclear complexes [MoO2(L1–3)(MeOH)] (1a–3a) and [MoO2(L1–3)(EtOH)] (1b, 2b-α, 2b-β and 3b) were also obtained. In the presence of strong donors, such as dmf, ligand substitution occurred and the structures of 1–3 changed into [MoO2(L1)(dmf)] (1c), [MoO2(L2)(dmf)] (2c) and [MoO2(L3)(H2O)]·dmf (3c·dmf), respectively. The dioxidomolybdenum(vi) complexes were tested for catalytic epoxidation of cyclooctene under eco-friendly reaction conditions by using aqueous tert-butyl hydroperoxide (TBHP) as an oxidant without the addition of an organic solvent. The present study showed much better activity of the dinuclear catalysts than the mononuclear ones due to the weak donor properties of the amino group and high geometric constraints occurring in such small sized self-assembled systems as confirmed by density functional theory calculations. [ABSTRACT FROM AUTHOR]

The reaction of two methoxy substituted salinazid-based hydrazones, 4-methoxysalicylaldehyde isonicotinoyl hydrazone (L1) and 3-methoxysalicylaldehyde isonicotinoyl hydrazone (L2), with HCl, HBr, HNO3 and H2SO4 in methanol yielded salts of different stoichiometries (1 : 1 or 2 : 1) and/or polymorphic forms. In such a way, (HL1)+X− and (HL2)+X− salts, where X = Cl, Br, NO3, HSO4, as well as [H(L1)2]+Br− and (HL1)2+SO42− were obtained. The solid state properties and the propensity for transformation between different forms in solution were also investigated. The crystal structures of compounds (HL1)+Cl−, (HL1)+Br− (α and β), [H(L1)2]+Br−, (HL1)2+SO42−, (HL2)+Br−·MeOH and (HL2)+NO3− were solved by the single-crystal X-ray diffraction method while the structures of (HL1)+NO3− and (HL1)+HSO4− (α and β) were solved by the powder diffraction method. The details of anion binding with the isoniazid functionality are discussed. The aroylhydrazone salts were evaluated for cytotoxic activity in vitro. All compounds exhibited weak cytotoxicity against THP-1 and no cytotoxicity against HepG2 cells. In a preliminary antimicrobial screening assay, these compounds were not only active against antibiotic susceptible Gram-positive bacteria, but also exhibited antibacterial effects on a wide range of multidrug-resistant Gram-positive as well as multidrug resistant Gram-negative bacterial pathogens. [ABSTRACT FROM AUTHOR]

A systematic study of the possibility of controlling the formation of oxalatomolybdate anions by the choice of a counterion and adjustment of pH was presented. Using four CoIII(ammine) macrocations ([Co(NH3)6]3+, [Co(NO2)(NH3)5]2+, [Co(en)3]3+ and [Co(ox)(en)2]+) in acidic aqueous solutions, ten crystalline solids were obtained. They were found to contain a total of six different oxalatomolybdate species, three of which, a cyclic tetramer, [Mo2O4(μ-O)2(ox)2]28−, a linear tetramer [Mo4O8(μ-O)3(ox)4(H2O)2]6− and a polymer, [Mo4O11(ox)4(H2O)]n6n– have not been reported to date. The oxalatomolybdate species found in solids mostly do correspond with the predominant species in solution at the pH of the solution from which they were obtained. Condensation of those species can be correlated with the hydrogen bonding ability of the used macrocation, a complex cation of Co(iii). [ABSTRACT FROM AUTHOR]

Synthesis of hydrazones was performed via both conventional and solvent-free routes using the corresponding hydrazide (isonicotinic hydrazide, nicotinic hydrazide, 2-aminobenzhydrazide or 4-aminobenzhydrazide) and appropriate aldehyde (salicylaldehyde, 3-methoxysalicylaldehyde or 4-methoxysalicylaldehyde). A systematic study dedicated to solvatomorphism or polymorphism screening resulted in the formation of twelve novel crystalline forms, and eight of these were characterized via the single crystal X-ray diffraction method. In all studied structures, the molecules were assembled into endless supramolecular chains, discrete rings, chains of rings or nets. The mechanochemical synthesis employing liquid-assisted grinding was also applied and the nicotinic- and isonicotinic-based hydrazones were found to form readily from their corresponding precursors. The chemometric study using principal component analysis for mechanochemical synthesis monitoring was implemented for the first time to provide an insight into the reaction profiles. A thoughtful combination of ex situ powder X-ray diffraction and chemometric analysis was essential to identify a stepwise mechanism for the hydrazone formation via an intermediate phase. In five investigated reactions the first principal component accounted for at least 75% of the total variance, whereas in the case of two reactions this component accounted for 69.72 and 46.23% of the total variance. The hydrazones were also evaluated for cytotoxic activity in vitro. All compounds exhibited weak to moderate cytotoxicity against THP-1 and no cytotoxicity against HepG2 cells. Substantial antibacterial activity was obtained against Moraxella catarrhalis while no growth inhibition of Staphylococcus aureus, Enterococcus faecalis and Escherichia coli was observed. [ABSTRACT FROM AUTHOR]

The dinuclear copper(ii) complexes [Cu2(LH)2] (1), [Cu2(L3OMe)2] (2), [Cu2(L4OMe)2] (3) as well as the tetranuclear complex [Cu4(L3OMe)4]·4MeOH·2H2O (2a·4MeOH·2H2O), (where LH = 2-oxybenzaldehyde benzhydrazonato, L3OMe = 3-methoxy-2-oxybenzaldehyde benzhydrazonato or L4OMe = 4-methoxy-2-oxybenzaldehyde benzhydrazonato) were synthesized by reacting copper(ii) acetate with the corresponding aroylhydrazone. Reactions in the presence of N-donor ligands D (pyridine, 4,4′-bipyridine or 1,10-phenanthroline) afforded complexes with different nuclearities and Cu : L : D ratios. They can be classified as dinuclear, [Cu2(LH)2(py)2] (1py), [Cu2(L3OMe)2(py)2]·3H2O (2py·3H2O), [Cu2(L4OMe)2(py)2] (3py), [{Cu(LH)}2(bpy)] (1bpy), [{Cu(L3OMe)}2(bpy)] (2bpy), and [{Cu(L4OMe)}2(bpy)] (3bpy), mononuclear [Cu(LH)(phen)] (1phen), [Cu(L3OMe)(phen)] (2phen) and [Cu(L4OMe)(phen)] (3phen), and polynuclear [{Cu(LH)}2(bpy)]n·2nMeOH (1bpy*·2MeOH) complexes. Conversion of complexes 1py–3py to complexes 1–3 proceeded via solid state reactions. The crystal and molecular structures of 2a·4MeOH·2H2O, 2py·3H2O, 3py, 1bpy*·2MeOH, 2bpy, 1phen and 3phen were determined by the single crystal X-ray diffraction method. All complexes were characterized by means of elemental and thermogravimetric analysis, FT-IR spectroscopy and the powder X-ray diffraction method. In vitro cytotoxicity of benzhydrazone-related ligands and their copper(ii) complexes against THP-1 and HepG2 cells demonstrated that the complexes are significantly more cytotoxic than the corresponding ligands. [ABSTRACT FROM AUTHOR]

A series of copper(ii) complexes with 4-hydroxybenzhydrazone-related ligands was synthesized by using various methods, including the conventional solution-based method, solvothermal route and electrochemical synthesis. The complexes can be classified as mononuclear [Cu(L3OMe)(py)] (2py), dinuclear [Cu2(LH)2(py)2] (1py), [Cu2(LH)2] (1α and 1β), [Cu2(LH)2(py)2] (1py), [Cu2(L4OMe)2(py)2] (3py), [Cu2(L4OMe)2] (3), [Cu2(L4OMe)2(MeOH)2] (3MeOH), [Cu2(L4OMe)2(EtOH)2] (3EtOH), cubane tetranuclear [Cu4(L3OMe)4]·xsolv (xsolv = 10H2O·CH3OH and 2.8EtOH·0.2H2O for 2MeOH and 2EtOH, respectively), or polynuclear [Cu(LH)(py)]n (1py*), where LH = 2-oxybenzaldehyde 4-hydroxybenzhydrazonato, L3OMe = 3-methoxy-2-oxybenzaldehyde 4-hydroxybenzhydrazonato, and L4OMe = 4-methoxy-2-oxybenzaldehyde 4-hydroxybenzhydrazonato ligands. The presented study indicates that complexes having different nuclearities and geometries can be achieved by changing the synthetic conditions and methods. Thermally induced structural transformations of the dinuclear complexes under solvent-free conditions were also investigated. Crystal and molecular structures of 1β, 1py*, 2MeOH, 2EtOH, 2py, 3 and 3MeOH were determined using the single crystal X-ray diffraction method. All complexes were characterized using microanalysis, FT-IR and CW-EPR spectroscopy, thermogravimetric analysis and a powder X-ray diffraction method. [ABSTRACT FROM AUTHOR]

Synthesis of the dioxidomolybdenum(vi) complexes [MoO2(HLR)(MeOH)]Cl (1–3) was carried out by using MoO2Cl2 and the corresponding ONO aroylhydrazone ligand H2LR (ligand H2LR is salicylaldehyde isonicotinoylhydrazone (H2LSIH), 2-hydroxy-naphthaldehyde isonicotinoylhydrazone (H2LNIH), or p-(N,N′-diethylamino)salicylaldehyde isonicotinoylhydrazone (H2LEt2NSIH) in methanol. Compounds [MoO2(HLR)(H2O)]Cl (1a–3a) were obtained upon exposure of the corresponding mononuclear complexes 1–3 to moisture. Deprotonation of the mononuclear complexes 1–3 was performed by using Et3N as a base (by the conventional solution based-method and by the mechanochemical approach) as well as by UV-light assisted reactions yielding [MoO2(LSIH)(MeOH)] (4), [MoO2(LNIH)(MeOH)] (5) and [MoO2(LEt2NSIH)]n (6), respectively. Crystal and molecular structures of all complexes were determined by the single crystal X-ray diffraction method. The complexes were further characterized by elemental analysis, IR spectroscopy, TG analysis, one- and two-dimensional NMR spectroscopy and powder X-ray diffraction. [ABSTRACT FROM AUTHOR]

Synthesis of the dioxomolybdenum(vi) complexes [MoO2(L3OMe)(EtOH)] (1), [MoO2(L4OMe)(EtOH)] (2) and [MoO2(LH)(EtOH)] (3) and dioxotungsten(vi) complexes [WO2(L3OMe)(EtOH)] (4), [WO2(L4OMe)(EtOH)] (5) and [WO2(LH)]n (6a) was carried out using [MO2(C5H7O2)2] (M = Mo or W) and the corresponding aroylhydrazone ligand H2LR (3-methoxysalicylaldehyde 4-hydroxybenzhydrazone (H2L3OMe), 4-methoxysalicylaldehyde 4-hydroxybenzhydrazone (H2L4OMe), or salicylaldehyde 4-hydroxybenzhydrazone (H2LH) in ethanol. Compounds obtained upon heating of the mononuclear complexes in acetonitrile or dichloromethane, [MO2(LR)]n (1a–6a) or [MoO2(L3OMe)]2 (1b), respectively, were also investigated. Crystal and molecular structures of the mononuclear 1, 2 and 3, polynuclear 1a·MeCN and dinuclear 1b complexes were determined by the single crystal X-ray diffraction method. Powder X-ray diffraction showed isostructurality of 1 and 4, and 2 and 5. The complexes were further characterized by elemental analysis, IR spectroscopy, TG and DSC analyses, and one- and two-dimensional NMR spectroscopy. The catalytic performances of 1–5 and 6a were investigated for epoxidation of cyclooctene using aqueous tert-butyl hydroperoxide (TBHP) as the oxidant. [ABSTRACT FROM AUTHOR]

Organic–inorganic hybrids, based on the Lindqvist-type polyoxometalate (POM) and dioxomolybdenum(vi) complexes, have been synthesized by hydrolysis of [MoO2(acac)2] (acac = acetylacetonate) in the presence of aroylhydrazone ligands in weak donor solvents. This provides an efficient route to materials that contain open coordination sites or sites occupied by labile ligands. Removal upon grinding or heating of the labile acetonitrile and acetone molecules on the dioxomolybdenum centres and the reaction in the solid-state represent a way for designing structures with the Lindqvist Mo6O192−anion coordinated to the metal centres of two complex cations. The compounds were characterised by the single crystal and powder X-ray diffraction methods, elemental analysis, IR spectroscopy, TG and DSC analyses. [ABSTRACT FROM AUTHOR]