Synthesis,Characterization, and Crystal Structure of Mononuclear and Dinuclear Dioxomolybdenum(VI) Complexes with Tridentate Schiff‐base Ligands. Part 2

Mononuclear [MoO₂LD], and dinuclear [MoO₂L]₂ or [MoO₂L]₂ · D dixomolybdenum(VI) complexes have been prepared by the reaction of tridentate Schiff‐base ligands L with [MoO₂(acac)₂]. The Schiff‐base ligands have been synthesized from salicylaldehyde ( 1 , 1a , 1c , 1d ), 2‐hydroxy‐1‐naphthaldehyde ( 2 , 2c ) and 2‐hydroxy‐3‐methoxybenzaldehyde ( 3a , 3b , 3c , 3d , 3e ) with 2‐amino‐p‐cresol. All prepared complexes consist of cis‐MoO₂²⁺core coordinated by Schiff‐base ligand through two deprotonated hydroxyl groups and one imino nitrogen atom. The usual octahedral coordination around the molybdenum atoms is completed by the neutral ligand D (methanol, ethanol, dimethyl sulfoxide, imidazole or 4, 4′‐bipyridine). All compounds were characterized by elemental analyses, IR spectroscopy and some of them by X‐ray crystallography ( 1a , 2c , 3a , 3b , 3c and 3e ).     

Synthesis,characterization, density functional theory studies and antibacterial activity of a new Schiff base dioxomolybdenum(VI) complex with tryptophan as epoxidation catalyst

A cis ‐dioxomolybdenum(VI) complex was prepared with MoO₂(acac)₂ and a Schiff base ligand (2‐((2‐hydroxybenzylidene)amino)‐3‐(1H ‐indol‐3‐yl)propanoic acid) derived from salicylaldehyde and l ‐tryptophan in ethanol and designated as [MoO₂(Sal‐Tryp)(EtOH)]. It was characterized using several techniques including thermogravimetric and elemental analyses and mass, Fourier transform infrared and UV–visible spectroscopies. Theoretical calculations were performed using density functional theory for studying the molecular structure. An in vitro antibacterial activity evaluation showed that [MoO₂(Sal‐Tryp)EtOH] complex exhibits good inhibitory effects against Gram‐positive (Bacillus subtilis , Staphylococcus aureus ) and Gram‐negative (Escherichia coli , Pseudomonas aeruginosa ) bacteria in comparison to standard antibacterial drugs. It was also found that [MoO₂(Sal‐Tryp)EtOH] complex successfully catalyses the epoxidation of cyclooctene, norbornene, cyclohexene, styrene, α‐methylstyrene and trans ‐stilbene, with 45–100% conversions and 64–100% selectivities. Based on the obtained results, the heterogeneity and reusability of the catalyst seem promising.     

Cis di-oxomolybdenum(VI) complexes with a tridentate ONO donor ligand; synthesis,X-ray crystal structure,spectroscopic properties and oxotransfer chemistry

The molybdenum complexes of Schiff base ligands viz. [MoO₂LH₂O] where L¹ = tris(hydroxymethyl)(salicylide-neamino)methane, L² = tris(hydroxymethyl)(2,3-dihydroxybenzylideneamino)methane and L³ = tris(hydroxymethyl)(2,3,4-trihydroxybenzylideneamino)methane have been synthesized and characterized by spectroscopic and electrochemical techniques. The X-ray crystal structure of the complex [MoO₂L¹H₂O] reveals a distorted octahedral geometry with one ligand and a water molecule coordinated to the MoO₂ center. No previous complex of this type contains a coordinated water molecule. The complex undergoes an oxotransfer in the presence of Bu₃P to form a -oxobridged molybdenum(V,V) dimer. This rules out Mo—S coordination as a prerequisite for oxotransfer in such molybdenum(VI) complexes.     

Dioxomolybdenum(VI) complexes of 2-hydroxybenzaldehyde 4-phenyl-S-methylthiosemicarbazone

Mixed ligand complexes of dioxomolybdenum(VI) with 2-hydroxybenzaldehyde 4-phenyl-S-methylthiosemicarbazone (H₂L) were prepared with the formula [MoO₂(L)D] (D = H₂O, methyl, n-butyl, and n-undecyl alcohol, DMF, DMSO, pyridine, 4-picoline, and 3,5-lutidine). The compounds were characterized by elemental analysis, IR and ¹H NMR spectroscopy. The thermal decomposition of the compounds were investigated by using TGA, DTG, and DTA methods in air, and the thermal behavior depending on the second ligand molecule was discussed. A single crystal of the DMF coordinated complex was studied by X-ray diffractometry. The text was submitted by the authors in English.     

Synthesis,spectral characterization and crystal structure studies of a new hydrazone Schiff base and its dioxomolybdenum(VI) complex

A new hydrazone Schiff base, (E)-N′-(3-ethoxy-2-hydroxybenzylidene)isonicotinohydrazide (H₂L), has been prepared and characterized by elemental analyses, spectroscopic methods, and single-crystal X-ray diffraction. The corresponding dioxomolybdenum(VI) complex [Mo(O)₂(L)(CH₃OH)] was synthesized and characterized by spectroscopic methods and by single-crystal X-ray diffraction. The hydrazone ligand coordinates to Mo through the phenolate O, imine N, and enolic O. The Mo center displays a distorted octahedral geometry with the three donors of the ligands and an oxo defining the equatorial plane, and one methanol and another oxo occupying the axial positions.     

Dioxidomolybdenum(VI) complexes of allyl N'-2-hydroxy-3-methoxybenzylidenecarbamohydrazonothioate: synthesis,spectral, and theoretical investigations

The new dibasic NNO ligand H₂L (H₂L = allyl N′-2-hydroxy-3-methoxybenzylidenecarbamohydrazonothioate) was synthesized by condensation of 2-hydroxy-3-methoxybenzaldehyde with the product resulting from the reaction of thiosemicarbazide with allyl bromide. Four dioxidomolybdenum(VI) complexes with the general formula [MoO₂L(S)] (S=MeOH, EtOH, DMSO, and 1-methylimidazole) were synthesized and characterized by elemental analysis, FT-IR, EI-MS and UV-Vis spectroscopy, and by X-ray crystallography. Spectroscopic evidence indicates that the cis-MoO₂ chelates have octahedral geometry in which H₂L coordinates via the phenolate oxygen, azomethine nitrogen and deprotonated thioamide nitrogen. The other sites are occupied by two oxido and an additional ligand (S). Density functional theory calculations of spectral parameters were also carried out for these systems.     

Homo‐ and Heteronuclear Compounds with a Symmetrical Bis‐hydrazone Ligand: Synthesis,Structural Studies,and Luminescent Properties

Nine new coordination compounds have been synthesized by the reaction of salts of bivalent metal ions (a=Zn^II, b=Cu^II, c=Ni^II, d=Co^II) with the bis(benzoylhydrazone) derivative of 4,6‐diacetylresorcinol (H₄L). Three kinds of complexes have been obtained: homodinuclear compounds [M₂(H₂L)₂]?nH₂O ( 1 a , 1 b , 1 c , and 1 d ), homotetranuclear compounds [M₄(L)₂]?n(solv) ( 2 a and 2 c ), and heterotetranuclear compounds [Zn₂M₂(L)₂]?n(solv) ( 2 ab , 2 ac , and 2 ad ). The structures of the free ligand H₄L?2 DMSO and its complexes [Zn₂(H₂L)₂(DMSO)₂] ( 1 a* ), [Zn₄(L)₂(DMSO)₆] ( 2 a* ), and [Zn_0.45Cu_3.55(L)₂(DMSO)₆]?2 DMSO ( 2 ab* ) were elucidated by single‐crystal X‐ray diffraction. The ligand shows luminescence properties and its fluorimetric behavior towards M^II metals (M=Zn, Cu, Ni and Co) has been studied. Furthermore, the solid‐state luminescence properties of the ligand and compounds have been determined at room temperature. ¹H NMR spectroscopic monitoring of the reaction of H₄L with Zn^II showed the deprotonation sequence of the OH/NH groups upon metal coordination. Heteronuclear reactions have also been monitored by using ESI‐MS and spectrofluorimetric techniques.     

New magnetic supported hydrazone Schiff base dioxomolybdenum (VI) complex: An efficient nanocatalyst for epoxidation of cyclooctene and norbornene

A new dioxomolybdenum (VI) complex with tridentate hydrazone Schiff base ligand (H₂L) derived from 2‐hydroxy‐5‐nitrobenzaldehyde and benzhydrazide was synthesized and designated as [MoO₂L (DMF)]·2H₂O. The Fe₃O₄@SiO₂‐CPS‐L‐MoO₂ (EtOH) nanocatalyst was successfully prepared by grafting H₂L ligand on modified Fe₃O₄ nanoparticles followed by reacting with MoO₂ (acac)₂. The complex and nanocatalyst were characterized by various techniques such as elemental analysis, mass, FT‐IR, UV–Vis, ¹H NMR, ¹³C{¹H}‐NMR, TGA, XRD, XPS, TEM, SEM and VSM. The catalytic activity of [MoO₂L (DMF)]2H₂O and Fe₃O₄@SiO₂‐CPS‐L‐MoO₂ (EtOH) were evaluated for the oxidation of various alkenes (cyclooctene, norbornene, cyclohexene, styrene and α‐methyl styrene) in the presence of tert‐butylhydroperoxide as oxidant. The results revealed that the catalysts were especially efficient for oxidation of cyclooctene and norbornene with 100% selectivity towards corresponding epoxide product. Fe₃O₄@SiO₂‐CPS‐L‐MoO₂ (EtOH) showed higher catalytic activity, shorter reaction time and higher turnover number (TON) compared with homogeneous complex [MoO₂L (DMF)]·2H₂O. Moreover, simple magnetic recovery from the reaction mixture and reuse for several times with no significant loss in activity were other advantages of the nanocatalyst.     

Transition-metal complexes with hydrazides and hydrazones

Several new complexes of dioxomolybdenum(VI) of the general formula [MoO₂(L)S], whereL is the dianion of salicylaldehydep-hydroxybenzoylhydrazone andS denotes H₂O, MeOH, py, PPh₃, DMSO or DMF, were synthesized and characterized by elemental analysis, electronic UV-VIS and IR spectra, thermal analysis, molar conductivity and magnetic susceptibility measurements. Salicylaldehydep-hydroxybenzoylhydrazone participates in the coordination as a tridentate ligand with the ONO set of donor atoms. The complexes contain acis-MoO₂ group and are of octahedral geometry. Complexes of the MoO₂L type were also prepared by synthesis in CHCl₃ solution and by isothermal heating of [MoO₂(L)S] complexes. The MoO₂L complex synthesized in CHCl₃ solution has most probably a pentacoordinated structure while the complex obtained by isothermal heating of [MoO₂(L)S] has a polymeric hexacoordinated structure.The authors are grateful to the Serbian Republic Research Fund for financial support and to academician Prof. M. ui for his interest in this work.     

Synthesis,X-ray studies,and catalytic activity of tridentate Schiff base dioxo-molybdenum(VI)

The reaction of a solution of MoO₂(acac)₂ in CH₃OH and salicylidene 2-picoloyl hydrazone as a tridentate ONO donor Schiff base (ONO) afford a six-coordinated Mo(VI) complex [MoO₂(ONO)(CH₃OH)], with a distorted octahedral configuration. [MoO₂(ONO)(CH₃OH)] was isolated as an air-stable crystalline solid and fully characterized by single-crystal X-ray structure analysis. [MoO₂(ONO)(CH₃OH)] shows reactivity in the oxidation of sulfides to their corresponding sulfoxides using urea hydrogen peroxide as the oxidant at room temperature under air.     

Synthesis,structure and properties of eight novel molybdenum(VI) complexes of the types: [MoO2LD] and [{MoO2L}2D] (L = thiosemicarbazonato ligand,D = N-donor molecule)

Eight new molybdenum(VI) complexes with 4-(diethylamino)salicylaldehyde and 2-hydroxy-3-methoxybenzaldehyde thiosemicarbazones have been prepared. They were characterized as mononuclear [MoO₂LD] or dinuclear [{MoO₂L}₂D] complexes. In all the compounds the MoO₂²⁺ core is coordinated by a tridentate ONS thiosemicarbazonato ligand and by the N-donor molecule (imidazole, pyridine or γ-picoline). All the complexes were characterized by chemical analysis, IR spectroscopy and thermogravimetry. Three of the mononuclear complexes, dioxo[(2-hydroxy-3-methoxybenzaldehyde thiosemicarbazonato)(pyridine)]molybdenum(VI), dioxo[(2-hydroxy-3-methoxybenzaldehyde thiosemicarbazonato)(γ-picoline)]molybdenum(VI) and dioxo[(2-hydroxy-3-methoxybenzaldehyde thiosemicarbazonato)(imidazole)]molybdenum(VI) were also characterized by single-crystal X-ray structural analysis. A spectrophotometric method for the determination of molybdenum based on extraction of ion-pairs formed by the cationic surfactant and the [MoO(SCN)₄]⁻ anion is described.     

Syntheses,crystal structures,and catalytic properties of dioxomolybdenum(VI) complexes with hydrazone ligands

Two new dioxomolybdenum(VI) complexes, [MoO₂L¹(CH₃OH)] (1) and [MoO₂L²(H₂O)] (2), where L¹ and L² are dianionic form of N′-(2-hydroxy-3-methoxybenzylidene)-4methoxybenzohydrazide and N′-(2-hydroxy-3methoxybenzylidene)-2-hydroxybenzohydrazide, respectively, have been synthesized and structurally characterized by spectroscopic methods and single-crystal X-ray determination. The complexes are mononuclear molybdenum(VI) compounds. Mo in each complex is octahedral. The difference in the substituent groups in the benzohydrazides leads to coordination of different solvent molecules. Crystals of the complexes are stabilized by hydrogen bonds. The complexes are effective catalysts for sulfoxidation.     

A novel tridentate Schiff base dioxo-molybdenum(VI) complex: Synthesis,crystal structure and catalytic performance in green oxidation of sulfides by urea hydrogen peroxide

A new dioxo-molybdenum(VI) complex [MoO₂(L)(CH₃OH)] has been synthesized, using 2-[(2-hydroxypropylimino)methyl]phenol as tridentate ONO donor Schiff base ligand (H₂L) and MoO₂(acac)₂. A monoclinic space group P2₁/c was determined by X-ray crystallography from single-crystal data of this complex. The high catalytic activity of this new Schiff base complex has been observed in the oxidation of various sulfides by urea hydrogen peroxide in ethanol affording sulfoxides and sulfones using different molar ratio of oxidant/sulfide in high/excellent yields and selectivity under mild and eco-friendly conditions. The relative high stability and desired turnover numbers have been observed for this Mo-catalyst in the oxidation reactions.     

Synthesis,Characterization, and Fluorescence Chemosensor Properties of a cis‐Dioxomolybdenum(VI) Complex Containing Multidentate Hydrazone Ligands

The homobimetallic molybdenum(VI) complex, [(MoO₂)₂(slsch)(DMF)₂], derived from multidentate hydrazone ligand (H₄slsch = disalicylaldehyde succinoyldihydrazone) was synthesized. The complex was obtained by reaction of the ligand with Mo₂(acac)₂ in 1:2 molar ratio in methanol. It was characterized by using various spectroscopic techniques. The structure of the complex was established by single crystal X‐ray diffraction. The complex shows fluorescence emission, responds toward Al^III ions, and hence it can be used as fluorescence chemosensor for sensing Al^III ions. The sensing properties show that the complex is more efficient and sensitive towards Al^III ions than the rest of the ions used in the presented study.     

Mononuclear Co(III), Ni(II) and Cu(II) complexes of tridentate di‐tert‐butylphenylhydrazone: Synthesis,characterization, X‐ray crystal structures,Hirshfeld surface analysis,molecular docking and in vivo anti‐inflammatory activity

A new hydrazone (LH₂) derived from the condensation of 2‐(4‐fluorobenzamido)benzohydrazide with 3,5‐di‐tert‐butyl‐2‐hydroxybenzaldehyde was used to synthesize Co(III), Ni(II) and Cu(II) complexes. These were characterized using various physicochemical, thermal, spectroscopic and single‐crystal X‐ray diffraction techniques. All the complexes crystallize in a monoclinic crystal system with P2₁/n space group and Z = 4. Structural studies of [Co(L)(LH)]?H₂O indicate the presence of both amido and imidol tautomeric forms of the ligand, resulting in a distorted octahedral geometry around the Co(III) ion. On the other hand, in the [Ni(L)(DMF)] and [Cu(L)(H₂O)] complexes, the ligand coordinates to the metal through imidol form resulting in distorted square planar geometry, in which the fourth position is occupied by the oxygen of coordinated DMF in [Ni(L)(DMF)] and by a water molecule in [Cu(L)(H₂O)]. Hirshfeld surface calculations were performed to explore hydrogen bonding and C―H???π interactions. Molecular docking studies were carried out to study the interaction between the synthesized compounds and proteins (cyclooxygenase‐2 and 5‐lipoxygenase). The complexes along with the parent ligand were screened for their in vivo anti‐inflammatory activity, using the carrageenan‐induced rat paw oedema method. The complexes show significant anti‐inflammatory potencies.     

Synthesis, crystal, and molecular structure of the solvated complex [MoO2(L)] · DMF (L2− = 2-[N-(2-hydroxynaphthylidene)amino]propane-1,2,3-triol anion)

A new dioxomolybdenum(VI) complex, [MoO₂(L)] · DMF, where L^2? = 2-[N-(2-hydroxynaphthylidene)amino]propane-1,2,3-triol, has been synthesized. Its structure has been determined by X-ray diffraction analysis. The Mo atom is octahedrally coordinated by two oxo ligands that are in cis-positions with respect to each other, two oxygen atoms, the nitrogen atom of the tridentate bis(chelate) ligand L, and the DMF oxygen atom.     

Oxomolybdenum(VI) complexes with glycine bisphenol [O,N,O,O′] ligand: synthesis and catalytic studies

The oxomolybdenum(VI) complex [MoOCl(L)] with a tetradentate glycine bisphenol ligand (H₃L) was prepared by reaction of [MoO₂Cl₂(DMSO)₂] with a ligand precursor in hot toluene. The product was isolated in moderate yield as separable cis and trans isomers along with the third minor component, [MoO₂(HL)]. The solid-state structure of trans-[MoOCl(L)] was determined by X-ray diffraction. The ligand has tetradentate coordination through three oxygens and one nitrogen, which is located trans to the terminal oxo whereas the sixth coordination site is occupied by a chloride. Both cis and trans isomers of [MoOCl(L)] are active catalysts for epoxidation of cis-cyclooctene and sulfoxidation of tolyl methyl sulfide. The cis isomer gave higher activity in epoxidation and sulfoxidation reactions at room temperature than the trans isomer but they performed identically at 50?°C.     

Solvent‐assisted formation of ruthenium(II)/copper(I) complexes containing thiourea derivatives: Synthesis,crystal structure,density functional theory,enzyme mimetics and in vitro biological perspectives

N ,N ‐[(diethylamino)(thiocarbonyl)]‐substituted benzamidine ligands have been synthesized from the reaction of N ,N ‐[(diethylamino)(thiocarbonyl)]benzimidoyl chloride with functionalized amines such as 2‐aminophenol and 2‐picolylamine. The reaction of N ,N ‐[(diethylamino)(thiocarbonyl)]‐2‐hydroxyphenylbenzamidine ( H ₂ L ₁ ) with ruthenium(II) precursor [RuHCl(CO)(PPh₃)₃] afforded complex 1 of the type [Ru(L₁)(CO)(PPh₃)₂] in which the ligand coordinated in tridentate ONS mode. The reaction of H ₂ L ₁ with copper precursor [Cu(CH₃COO)(PPh₃)₂] induced C═N bond cleavage of the ligand and afforded complex 3 of the type [Cu(1,1‐DT)(Cl)(PPh₃)₂] (1,1‐DT = 1,1‐diethylthiourea) in which the ligand coordinated in a monodentate fashion. The ligand N ,N ‐[(diethylamino)(thiocarbonyl)]‐2‐picolylbenzamidine ( HL ₂ ) reacted with ruthenium(II) and copper(I) precursors to form complex 2 of the type [Ru(1,1‐DT)(Cl₂)(CO)(PPh₃)₂] and complex 3 , respectively, in which the ligand underwent C═N cleavage and coordinated in a monodentate fashion via C═S group. In complexes 1 and 2 , the two triphenylphosphine co‐ligands coordinated in trans position whereas, in complex 3 , the two triphenylphosphine co‐ligands coordinated in cis position. All the compounds were characterized using infrared, UV–visible, (¹H, ¹³C, ³¹P) NMR, ESI‐MS and elemental analyses. The molecular structures of ligand H ₂ L ₁ and complexes 1 – 3 were determined using X‐ray crystallography, which confirmed the coordination mode of the ligands with metals. The crystal structure of complexes 1 and 2 revealed a distorted octahedral geometry around the ruthenium ion and the structure of complex 3 indicated a tetrahedral geometry around the copper ion. With the X‐ray structures, density functional theory computations were carried out to determine the electronic structure of the compounds. The interactions of complexes 1 – 3 with calf thymus DNA and bovine serum albumin protein were investigated using UV–visible and fluorescence spectroscopic and viscometric methods. Catecholase‐ and phosphatase‐like activities promoted by complexes 1 – 3 under physiological conditions have been studied. In vitro anticancer activities have been demonstrated by MTT assay, acridine orange/ethidium bromide and diamidino‐2‐phenylindole staining against various cancerous cell lines.     

Synthesis,characterization and antioxidant activities of dioxomolybdenum(VI) complexes of new Schiff bases derived from substituted benzophenones

Abstract

Five novel ONS donor Schiff base ligands were synthesized by the reaction of 2-hydroxybenzophenone (L1), 2-hydroxy-4-methoxybenzophenone (L2), 2-hydroxy-4-octyloxybenzophenone (L3), 2-hydroxy-4-methoxy-4′-methylbenzophenone (L4), and 2-hydroxy-4-allyloxybenzophenone (L5) with thiocarbohydrazide. Neutral solvate dioxomolybdenum(VI) complexes with the general formula [MoO₂L(ROH)], [C1–C5] (L?=?L1, L2, L3, L4, L5 and R?=?CH₃, C₂H₅, or C₄H₉), were prepared from these Schiff bases. Characterization of all compounds was carried out by means of elemental analysis, conductivity measurements, ¹H-NMR, FT-IR, UV-Vis spectroscopy and mass spectrometry (for L1, C2, and C4) techniques. The crystal structures of ligand (L5) and complex (C1) were determined by single-crystal X-ray crystallography. Spectroscopic data and X-ray diffraction studies confirmed that the ligand is coordinated to the cis-MoO₂²⁺ core through ONS, while the sixth coordination site is occupied by solvent (ROH). The ligands and complexes were tested for in vitro antioxidant capacities. The TEAC coefficients of the ligands and complexes were found higher than reference compound. DPPH radical scavenging activities of these compounds were also investigated.     

Syntheses and Structures of Three New Copper(II) Coordination Polymers Involving 2, 2‐(4, 6‐Dinitro‐1, 3‐phenylenedioxy)­diacetic Acid

Three copper(II) coordination polymers, namely, {[CuL(H₂O)₂] · 4H₂O}_n( 1 ), [CuL(H₂O)(DMF)]_n( 2 ), and [CuL(2, 2′‐bipy)(DMSO)] · DMSO ( 3 ) [H₂L = 2, 2′‐(4, 6‐dinitro‐1, 3‐phenyl‐enedioxy)diacetic acid] were synthesized in different solvents (H₂O, DMF, and DMSO). X‐ray single crystal diffraction studies show that both complexes 1 and 3 belong to triclinic crystal system and P$\bar{1}$ space group and complex 2 belongs to the monoclinic crystal system and P2₁/c space group. In three complexes, all the central Cu^II ions coordinate with the ligand, forming a square pyramidal configuration. Both complexes 1 and 2 show similar 1D chain‐like structure and the chains are further connected by hydrogen bonds, forming 3D frameworks. Complex 3 exhibits a 0D structure due to the introduction of the ligand 2, 2′‐bipy. In addition, the luminescence properties of these complexes were investigated.