Binuclear Molybdenum Research Articles

A molybdenum-ciprofloxacin complex with an isopolyoxometalate having DNA binding and antibacterial activity

In this study, an antibacterial complex based on the quinolone antibacterial drug ciprofloxacin (CF) and a polyoxometalate was synthesized, Mo2O5(CF)2(CFd)2(β-Mo8O26)·5H2O (1). Complex 1 was characterized by elemental analysis and X-ray single-crystal diffraction. Single-crystal structural analysis revealed that 1 was made of β-Mo8 clusters, binuclear molybdenum clusters Mo2O5(CF)2(CFd)2, and water molecules. The antibacterial activity of 1 has been tested against three microorganisms (Staphylococcus aureus, Escherichia coli, and Bacillus subtilis strains); the antibacterial activities of 1 were higher than those of free CF at the same mass amounts. The interaction between 1 and calf thymus DNA (CT-DNA) was investigated using Uv-vis spectroscopy to determine the binding constants. The results indicated that intercalation is the probable mode of action, with 1 demonstrating higher binding constants (K b) to CT-DNA (1.8 × 105 M−1) compared to pure CF (4.9 × 104 M−1). These findings show that the implementation of molybdate for ciprofloxacin modification resulted in the formation of a metal complex with enhanced antibacterial activity over CF and significantly improving its binding affinity to DNA.

A comparative investigation: evaluating the epoxidation of styrene with binuclear molybdenum(VI) complexes under conventional heating and microwave-assisted conditions

Two bis-[cis-MoO2]2+ core bearing complexes, designated as [{MoVIO2}2(L1)(H2O)2] (1) and [{MoVIO2}2(L2)(H2O)2] (2), were created by reacting MoO2(acac)2 with dihydrazone ligands, namely H4L1(i) and H4L2(ii) (generated from a 2:1 ratio of hydrazide of terephthalate and salicylaldehyde or o-vanillin) in a 2:1 ratio in a methanolic solution. These complexes were extensively characterized using several spectroscopic techniques. The shape of the complex [{MoVIO2}2(L1)(H2O)2] (1) was confirmed by SC-XRD, revealing an octahedral geometry. Moreover, the crystallographic analysis of complex (1) elucidates the substitution of a single facet of the water molecule with DMF, accompanied by the inclusion of an additional DMF molecule within the crystal lattice. These synthesized compounds were evaluated as potential catalysts for the epoxidation of styrene in the existence of oxidant (H2O2). The oxidation reactions were conducted using both conventional and microwave-assisted methods, and the obtained data were compared in terms of activity and selectivity.

In Vitro Characterization of a Threonine-Ligated Molybdenyl-Sulfide Cluster as a Putative Cyanide Poisoning Antidote; Intracellular Distribution, Effects on Organic Osmolyte Homeostasis, and Induction of Cell Death.

Binuclear molybdenum sulfur complexes are effective for the catalytic conversion of cyanide into thiocyanate. The complexes themselves exhibit low toxicity and high aqueous solubility, which render them suitable as antidotes for cyanide poisoning. The binuclear molybdenum sulfur complex [(thr)Mo2O2(μ-S)2(S2)]- (thr - threonine) was subjected to biological studies to evaluate its cellular accumulation and mechanism of action. The cellular uptake and intracellular distribution in human alveolar (A549) cells, quantified by inductively coupled plasma mass spectrometry (ICP-MS) and cell fractionation methods, revealed the presence of the compound in cytosol, nucleus, and mitochondria. The complex exhibited limited binding to DNA, and using the expression of specific protein markers for cell fate indicated no effect on the expression of stress-sensitive channel components involved in cell volume regulation, weak inhibition of cell proliferation, no increase in apoptosis, and even a reduction in autophagy. The complex is anionic, and the sodium complex had higher solubility compared to the potassium. As the molybdenum complex possibly enters the mitochondria, it is considered as a promising remedy to limit mitochondrial cyanide poisoning following, e.g., smoke inhalation injuries.

Naphthophosphacyclophanes based on 1,6-dihydroxynaphthalene as bidentate ligands in the synthesis of molybdenum(0) carbonyl complexes

Binuclear molybdenum(0) carbonyl complexes were synthesized based on naphthophosphacyclophanes containing a 1,6-dihydroxynaphthalene fragment and diethylamide linkers. The physicochemical and spectral characteristics of the synthesized coordination systems were studied.

Binuclear molybdenum alkoxide as the versatile catalyst for the conversion of carbon dioxide

CO2was transformed into different products in mild conditions with high yield and excellent selectivity using a single catalyst.

Molybdenum complexes with a μ-O{MoO2}2 core: their synthesis, crystal structure and application as catalysts for the oxidation of bicyclic alcohols using N-based additives

Binuclear molybdenum(vi) complexes with a μ-O{MoO2}2 core as catalysts for the oxidation of bicyclic alcohols (fenchyl alcohol and isoborneol), using 30% H2O2 as the oxidant in the presence of NEt3 as the additive, are reported.

State of molybdenum clusters in solutions: III. Formation enthalpies of intermediate products of stepwise K2[Мо2(SO4)4] oxidation in 1 M H2SO4 solution

The enthalpies of stepwise oxidation reactions of the ions [Mo2(SO4)4]4– → [Mo2(SO4)4]3– → [Mo2(SO4)4]2– → [Мо2(μ-О)2O2(Н2О)6]2– → 2(MoO4)2–, and also the enthalpies of formation of the binuclear molybdenum complexes K3[Mo2(SO4)4], K2[Mo2(SO4)4], and [Мо2(μ-О)2O2(Н2О)6]SO4 in a 1 М sulfuric acid solution at 298.15 K were determined by the calorimetric titration with continuous titrant input.

Oxidation of alkenes and sulfides catalyzed by a new binuclear molybdenum bis-oxazoline complex

A novel bis(oxazoline) ligand derived from 1,3-dicyanobenzene was prepared and applied as a ligand for the preparation of a new binuclear molybdenyl complex. This ligand was characterized by UV–Vis, mass, 1H NMR, and FT-IR spectroscopic methods, thermal and elemental analysis and X-ray diffraction. The molybdenum complex was prepared by the reaction of this ligand with MoO2(acac)2. The catalyst was also characterized by FT-IR, UV–Vis, and ICP spectroscopy, elemental and thermal analysis. This catalytic system was efficiently used for the oxidation of alkenes and sulfides in the presence of TBHP. The effect of different solvents and kind of oxygen donor was also studied in the oxidation reactions.

Intriguing Chemistry of Molybdenum Corroles

The development of new methodologies for gaining access to low-valent molybdenum complexes led to spectroscopic identification of mononuclear (oxo)molybdenum(IV) corroles, as well as the full characterization of a binuclear molybdenum(IV) corrole that is bridged through axial O atoms by a Mg(THF)4 moiety.

Molybdenum-catalysed oxidation of cyclohexene with hydrogen peroxide in the presence of alcohols and X-ray structures of octamolybdate [C4mim]4[Mo8O26] and tetraperoxodimolybdate [Htmpy]2[{MoO(O2)2}2(μ-O)] complexes

The direct formation of a β-alcoxyalcohol from the corresponding olefin was investigated through the study of the oxidation of cyclohexene with hydrogen peroxide, as test reaction, catalysed by commercially available MoO3 in the presence of alcohols. The formation of the corresponding β-alcoxycyclohexanol was favourable in the order Me>Et>iPr>tBu, reaching approximately no yield for tBuOH. In this reaction, the lack of selectivity was due to the simultaneous formation of cyclohexane-1,2-diol by epoxide hydrolysis, a reaction that it is competitive with respect to the epoxide ring-opening reaction by the alcohol. In order to decrease the cyclohexane-1,2-diol yield, by preventing the hydrolysis reaction, several strategies were analysed and discussed. In particular, 2-methoxycyclohexanol was obtained with high yields and 99% selectivity by using as catalyst the [C4mim]4[Mo8O26] complex (C4mim=1-butyl-3-methylimidazolium). The structure of the latter octamolybdate and also that of the tetraperoxodimolybdate [Htmpy]2[{MoO(O2)2}2(μ-O)] (tmpy=2,4,6-trimethylpyridine) complex were determined by X-ray crystallography. The latter complex shows a μ2-oxygen bridging atom and two μ2-κ2–κ1-peroxo bridging ligands. This overall coordination assembly is unprecedented for binuclear molybdenum complexes.

Molecular properties and electronic structure of phenazine ligand in binuclear molybdenum and manganese metal complexes: A density functional theory study

DFT calculations with full geometry optimization have been performed on the series of hypothetical and characterized binuclear compounds of general formula (L3M)2(C12N2H8) (M=Mo and Mn, L3=(CO)3, (PH3)3 and Cp− and C12N2H8=phenazine ligand). The various structures with syn and anti configurations have been investigated. The phenazine ligand can bind to the metals involving its C6 and C4N2 rings through η6–η4 and η6–η6 coordination modes giving rise to syn and anti structures, respectively, in agreement with the favored 34 electron count with closed-shell and open-shell configurations. This study has shown that the electronic communication between the metal centers depends on their oxidation state and the attached ligands. A more crowded attached ligand imposes an anti configuration despite its electron deficiency.

QTAIM Analysis of the Bonding in Mo–Mo Bonded Dimolybdenum Complexes

A number of local and integral topological parameters of the electron density of relevant bonding interactions in the binuclear molybdenum complexes [Mo(2)Cl(8)](4-), [Mo(2)(μ-CH(3)CO(2))(4)], [Mo(2)(μ-CF(3)CO(2))(4)], [Mo(2)(μ-CH(3)CO(2))(4)Br(2)](2-), [Mo(2)(μ-CF(3)CO(2))(4)Br(2)](2-), [Mo(2)(μ-CH(3)CO(2))(2)Cl(4)](2-), [Mo(2)(μ-CH(3)CO(2))(2)(μ-Cl)(2)Cl(4)](2-), and [Mo(2)(μ-Cl)(3)Cl(6)](3-) have been calculated and interpreted under the perspective of the quantum theory of atoms in molecules (QTAIM). These data have allowed a comparison between related but different atom-atom interactions, such as different Mo-Mo formal bond orders, ligand-unbridged versus Cl-bridged, CH(3)CO(2)-bridged, and CF(3)CO(2)-bridged Mo-Mo interactions, and Mo-Cl(terminal) and Mo-Cl(bridge) versus Mo-Br and Mo-O interactions. Calculations carried out using nonrelativistic and relativistic approaches afforded similar results.

Molybdenum–Molybdenum Multiple Bonding in Homoleptic Molybdenum Carbonyls: Comparison with Their Chromium Analogues

The binuclear molybdenum carbonyls Mo(2)(CO)(n) (n = 11, 10, 9, 8) have been studied by density functional theory using the BP86 and MPW1PW91 functionals. The lowest energy Mo(2)(CO)(11) structure is a singly bridged singlet structure with a Mo-Mo single bond. This structure is essentially thermoneutral toward dissociation into Mo(CO)(6) + Mo(CO)(5), suggesting limited viability similar to the analogous Cr(2)(CO)(11). The lowest energy Mo(2)(CO)(10) structure is a doubly semibridged singlet structure with a Mo═Mo double bond. This structure is essentially thermoneutral toward disproportionation into Mo(2)(CO)(11) + Mo(2)(CO)(9), suggesting limited viability. The lowest energy Mo(2)(CO)(9) structure has three semibridging CO groups and a Mo≡Mo triple bond analogous to the lowest energy Cr(2)(CO)(9) structure. This structure appears to be viable toward CO dissociation, disproportionation into Mo(2)(CO)(10) + Mo(2)(CO)(8), and fragmentation into Mo(CO)(5) + Mo(CO)(4) and thus appears to be a possible synthetic objective. The lowest energy Mo(2)(CO)(8) structure has one semibridging CO group and a Mo≡Mo triple bond similar to that in the lowest energy Mo(2)(CO)(9) structure. This differs from the lowest energy Cr(2)(CO)(8) structure, which is a triply bridged structure. A higher energy unbridged D(2d) Mo(2)(CO)(8) structure was found with a very short Mo-Mo distance of 2.6 Å. This interesting structure has two degenerate imaginary vibrational frequencies. Following the corresponding normal modes leads to a Mo(2)(CO)(8) structure, lying ~5 kcal/mol above the global minimum, with two four-electron donor bridging CO groups and a Mo═Mo distance suggesting a formal double bond. All of the triplet Mo(2)(CO)(n) (n = 10, 9, 8) structures were found to be relatively high energy structures, lying at least 22 kcal/mol above the corresponding global minimum. The singlet-triplet splittings for the Mo(2)(CO)(n) (n = 10, 9, 8) structures are significantly higher than those of the Cr(2)(CO)(n) analogues. The Mo-Mo Wiberg bond indices confirm our assigned bond orders based on predicted bond distances.

Substitution of Silver for Copper in the Binuclear Mo/Cu Center of Carbon Monoxide Dehydrogenase from Oligotropha carboxidovorans

Carbon monoxide dehydrogenase from Oligotropha carboxidovorans catalyzes the aerobic oxidation of carbon monoxide to carbon dioxide, providing the organism both a carbon source and energy for growth. The active site of the native enzyme is a unique binuclear molybdenum- and copper-containing center. Here we show that silver can be substituted for copper in the active site to yield a functional enzyme. The characteristic hyperfine coupling of the I = ½ nucleus of Ag is evident in the EPR signal of the binuclear active site observed upon reduction with CO, indicating both the incorporation of silver into the active site and, remarkably, retention of the catalytic activity. The silver-substituted enzyme is reduced by CO with an observed limiting rate constant of 8.1 s(-1), which can be compared with the value of 51 s(-1) for the wild-type enzyme. Steady-state kinetics for the Ag-substituted enzyme yielded k(cat) = 8.2 s(-1) and K(m) = 2.95 μM at pH 7.2.

Synthesis, chemical, electrochemical, and structural characterization of binuclear dioxo-bridged molybdenum(VI) complexes of tridentate ONS donors

A number of dioxo-bridged binuclear molybdenum(VI) complexes with diprotic tridentate ONS donor Schiff bases (H2L1, H2L2, H2L3, and H2L4) obtained by the condensation of salicylaldehyde/2-hydroxyacetophenone with S-benzyl and S-methyl dithiocarbazates have been synthesized using the Mo(V) complex (NH4)2[MoVOCl5] as starting material. All these reactions are carried out in air and the MoVO center of the precursor complex undergoes spontaneous aerial oxidation leading to the formation and isolation of molybdenum(VI) complexes Mo2O4L2. The complexes were characterized by elemental analyses, various spectroscopic techniques (UV-Vis, infrared etc.), magnetic susceptibility at room temperature, molar conductivity, and cyclic voltammetry. One of the complexes, Mo2O4L2 1 (1), was structurally characterized by single-crystal X-ray crystallography.

A binuclear molybdenum oxyfluoride: μ-oxido-bis[(2,2′-bipyridyl)fluoridodioxidomolybdenum(VI)

The title compound, [Mo2F2O5(C10H8N2)2], is a centrosymmetric binuclear molybdenum(VI) species with the metal atoms in a distorted octa­hedral environment. The coordination geometries of the symmetry-equivalent molybdenum sites are defined by the cis-terminal oxide groups and the N-atom donors of the bipyridyl ligand in the equatorial plane with axial F and bridging O atoms. The bridging O atom occupies a center of symmetry. The mol­ecules stack in the a-axis direction, and the crystal packing is stabilized by weak intra- and inter­molecular C—H⋯O and C—H⋯F hydrogen bonds.

Heptahapticity in Binuclear (Cycloheptatrienyl)molybdenum Carbonyl Derivatives: The Interplay between Ring Hapticity/Planarity and Metal–Metal Multiple Bonding

Theoretical studies on the binuclear (cycloheptatrienyl)molybdenum carbonyl complexes [(C(7)H(7))(2)Mo(2)(CO)(n)] (n=6, 5, 4, 3, 2, 1, 0) indicate structures with fully bonded heptahapto eta(7)-C(7)H(7) rings and four or fewer carbonyl groups to be energetically competitive. This is in striking contrast to the corresponding chromium derivatives. The lowest energy of such a structure for [(eta(7)-C(7)H(7))(2)Mo(2)(CO)(4)] is a singlet unbridged structure with a formal Mo--Mo single bond with a length of approximately 3.2 A. A higher-energy pentahapto structure [(eta(5)-C(7)H(7))(2)Mo(2)(CO)(4)] is also predicted with a formal Mo [triple bond]Mo triple bond with a length of approximately 2.56 A. Low-energy structures are predicted for [(C(7)H(7))(2)Mo(2)(CO)(3)] with two heptahapto eta(7)-C(7)H(7) rings, either one or two bridging carbonyl groups, and formal Mo=Mo double bonds with a length of approximately 2.8 A. However, the global minimum for [(C(7)H(7))(2)Mo(2)(CO)(3)] is a [(eta(7)-C(7)H(7))(eta(5)-C(7)H(7))Mo(2)(CO)(3)] structure with a formal Mo[triple bond]Mo triple bond with a length of approximately 2.53 A. The lowest-energy structures for [(C(7)H(7))(2)Mo(2)(CO)(2)] and [(C(7)H(7))(2)Mo(2)(CO)] have heptahapto eta(7)-C(7)H(7) rings and predicted metal-metal bond lengths of approximately 2.54 and 2.31 A, respectively, consistent with the formal triple and quadruple bonds, respectively, needed to give both metal atoms the favored 18-electron configuration. The lowest-energy structures for the carbonyl-richer systems [(C(7)H(7))(2)Mo(2)(CO)(n)] (n=6, 5) contain one trihapto eta(3)-C(7)H(7) ring and one pentahapto eta(5)-C(7)H(7) ring.

10.1007/s11176-008-2004-z

Effect of ortho-methyl groups in the benzene rings of the macrocyclic matrix on the chemistry of cavitands with phosphorous amide bridges in the upper rim is studied. The presence of ortho-methyl groups is shown to prevent formation of phosphacavitands of C 4v symmetry and favor formation of macrocyclic systems of C 2v symmetry, enhance solubility of phosphacavitands in organic solvents, hinder oxidation of phospha(III)cavitands and decrease the yield of phospha(V)cavitands, prevent formation of binuclear molybdenum complexes of phosphorous amide cavitands, and favor formation of their tetranuclear analogs.

The Investigation of Improvement Effects on Friction Properties of Mononuclear MoDTCs having Azaheterocycles by Episulfidation

The effects of episulfidation on the frictional properties of mononuclear molybdenum dithiocarbamates having azaheterocycles were investigated. It was shown that the friction coefficients of the lubricants with the episulfided mononuclear molybdenum dithiocarbamates, as measured by the SRV friction test, were lower than those with non-episulfided ones. The friction coefficients of episulfided compounds are also similar to that of binuclear molybdenum dithiocarbamate, which is frequently used as friction modifier in lubricants in actual practice. The extent of decrease in friction in the SRV test differed with the number of carbon atoms in the azaheterocycles of the molybdenum compounds, suggesting that the thermal stability of the compounds affected the friction characteristics of the tested oils. The results from EPMA surface analyses of the disks from the SRV tests suggest that episulfidation of the molybdenum compounds led to effective formation of molybdenum disulfide film by the corresponding oils during the friction tests.

Effect of ortho-methyl groups in the benzene rings of the macrocyclic frame on the chemistry of phosphacavitands

Effect of ortho-methyl groups in the benzene rings of the macrocyclic matrix on the chemistry of cavitands with phosphorous amide bridges in the upper rim is studied. The presence of ortho-methyl groups is shown to prevent formation of phosphacavitands of C4v symmetry and favor formation of macrocyclic systems of C2v symmetry, enhance solubility of phosphacavitands in organic solvents, hinder oxidation of phospha(III)cavitands and decrease the yield of phospha(V)cavitands, prevent formation of binuclear molybdenum complexes of phosphorous amide cavitands, and favor formation of their tetranuclear analogs.