Oxomolybdenum(VI) and oxomolybdenum(V) thiocarbohydrazone complexes

Summary Dioxomolybdenum(VI) complexes [MoO₂L]H₂O and oxomolybdenum(V) complexes [Mo₂O₃L₂]H₂O and [Mo₂O₃(LH)₂(OH)₂(H₂O)₂] (where LH₂=thiocarbohydrazones derived from thiocarbohydrazide with salicylaldehyde, 5-methyl-, 5-chloro-, 5-bromo-, 3-methoxysalicylaldehyde and 2-hydroxy-1-naphthaldehyde) have been prepared and characterised by elemental analysis, conductivity, magnetic moment, i.r., u.v-vis, e.p.r. and thermal studies. The data suggests that molybdenum(VI) complexes are non electrolytes, diamagnetic, monomeric and have distorted octahedral geometry, whereas the molybdenum(V) complexes are non electrolytes, paramagnetic and have distorted octahedral structures with possible metal intereaction via oxo bridging.     

Binuclear molybdenum(V) complexes with morpholin carbamate

Summary Novel oxo-and sulphido-bridged molybdenum(V) complexes with morpholin carbamate as ligand, have been prepared, identified by i.r., electronic spectra, magnetic susceptibility and analytical data and assigned the formulae [Mo₂O₃(LL)₄], [Mo₂O₄(LL)₂], [Mo₂O₂S₂(LL)₂] and [Mo₂O₃S(LL)₂]. The spectra are modified by introduction of sulphur atoms into the bridge system. The low magnetic moments are thought be due, at least in part, to intramolecular metal-metal interactions. A comparison of the spectra of these complexes with those of analogous morpholin dithiocarbamate compounds has been made.     

Oxomolybdenum(V) complexes of 2-benzothiazolyl hydrazones

Summary Oxomolybdenum(V) complexes of general formulae [Mo₂O₃L₂Cl₂]H₂O and [Mo₂O₃L₂(OH)₂(H₂O)₂] (LH = hydrazones derived from 2-hydrazinobenzothiazole with salicyladehyde, 5-methyl-, 5-chloro-, 5-bromo-, 3-methoxysalicyldehyde and 2-hydroxy-1-naphthaldehyde) have been prepared and characterized by elemental analysis, conductivities, magnetic moments, thermal studies, and i.r., u.v.-vis. and e.p.r. spectra. The data suggest that the complexes are non-electrolytes, paramagnetic and have distorted octahedral structures with possible metal-metal interactions via oxo bridging.     

Molybdenum(VI) and molybdenum(V) mononuclear and dinuclear complexes with 1,3-diphenyl-1,3-propanedione

Summary The synthesis and the dinuclear or mononuclear nature of several molybdenum(VI) and molybdenum(V) oxocomplexes derived from 1,3-diphenyl-1,3-propanedione (HLL) are described. These complexes were identified by i.r. and electronic spectra, magnetic susceptibility and analytical data, and are assigned the following formulae: [MoO₂(LL)₂], [Mo₂O₅(LL)₂], [Mo₂O₄(LL)₂], [MoOCl(LL)₂], [MoCl₂(LL)] and [MoO(OH)(LL)₂)]. The low magnetic moments of the dinuclear complexes are due, in part, to intramolecular interactions. The i.r. data show that the dionate is bound by two oxygen atoms forming a chelate six-membered ring.     

Molybdenum(V) dimeric complexes with dialkyl carbamates

Syntheses are reported for a number of novel oxo and sulphido bridged molybdenum(V) complexes with N-methyl-N-cyclohexyl carbamate and N,N-dicyclohexyl carbamate as ligands, and we have compared these complexes with the molybdenum(V) complexes with dialkyldithiocarbamates as ligands. These complexes were identified by IR and electronic spectra, magnetic susceptibility and analytical data, and were assigned the formulae [Mo₂O₃(LL)₄], [Mo₂O₄(LL)₂], [Mo₂O₂S₂(LL)₂] and [Mo₂O₃S(LL)₂]. IR and electronic spectra of these compounds are sensitive to substitution of sulphur atoms into the bridge system. It is suggested that the low magnetic moments observed are due, at least in part, to intramolecular metal-metal interactions.     

Synthesis of homobimetallic molybdenum(VI) complex of bis(2-hydroxy-1-naphthaldehyde)malonoyldihydrazone and its reaction with electron and proton bases

The diamagnetic dioxomolybdenum(VI) complex [(MoO₂)₂(CH₂L)(H₂O)₂]H₂O (1) has been isolated in solid state from reaction of MoO₂(acac)₂ with bis(2-hydroxy-1-naphthaldehyde)malonoyldihydrazone (CH₂LH₄) in 3:1 molar ratio in ethanol at higher temperature. The reaction of the complex (1) with electron donor bases gives diamagnetic molybdenum(VI) complexes having composition [Mo₂O₅(CH₂LH₂)]·2A·2H₂O (where A = pyridine (py, 2), 2-picoline (2-pic, 3), 3-picoline (3-pic, 4), 4-picoline (4-pic, 5)). Further, when the complex (1) is allowed to react with protonic bases such as isonicotinoylhydrazine (inhH₃) and salicyloylhydrazine (slhH₃), reduction of molybdenum(VI) centre occurs leading to isolation of homobimetallic molybdenum(V) complexes [Mo₂(CH₂L)(inh)₂(H₂O)₂] (6) and [Mo₂(CH₂L)(slh)₂] (7), respectively. The composition of the complexes has been established by analytical, thermo-analytical and molecular weight data. The structure of the molybdenum(VI) complexes (1)–(5) has been established by electronic, IR, ¹H NMR and ¹³C NMR spectral studies while those of the complexes (6) and (7) by magnetic moment, electronic, IR and EPR spectral studies. The dihydrazone is coordinated to the metal centres in staggered configuration in complex (1) while in anti-cis configuration in complexes (2)–(7). The complexes (6) and (7) possess magnetic moment of 2.95 and 3.06 BM, respectively, indicating presence of two magnetic centre in the complexes per molecule each with one unpaired electron on each metal centre without any metal–metal interaction. The electronic spectra of the complexes are dominated by strong charge transfer bands. All of the complexes involve six coordinated molybdenum centre with octahedral arrangement of donor atoms except in the complex (6), in which the molybdenum centre has rhombic arrangement of ligand donor atoms. The probable mechanism for generation of oxo-group in the complexes (2)–(5) involving coordinated water molecule has been proposed.     

Spectral and thermogravimetric studies of oxohalobis(4-morpholinyldithiocarbamato)molybdenum(V) complexes

Summary Molybdenum(V) complexes [MoOX(4-Morphdtc)₂] (X=F, Cl, Br or I; 4-Morphdtc = 4-morpholinyldithiocarbamate) have been prepared from molybdenum trioxide using hydrazine hydrohalides as reducing agents. The magnetic moment values atca. 1.65 B.M. and e.p.r. studies indicated that the complexes are mononuclear and that molybdenum is in + 5 oxidation state. The i.r. spectral bands at 1500 and 960 cm^–1 suggest that the dithiocarbamate acts as a univalent bidentate ligand and the bands at 930 cm^–1 confirms the presence of a MoO³⁺ moiety in the complex. The low conductivity values for the complexes inN, N-dimethylformamide indicate that the complexes are non-ionic. The [MoOX(4-Morphdtc)₂] complexes (X=F, Cl or Br) decompose in the first step by the loss of one dithiocarbamate group, whereas in [MoOI(4-Morphdtc)₂] the iodine atom is lost in the first step. The second and third steps lead to the formation of MoS₃ and MoO₃, respectively. A six coordinate structure around Mo with an oxo, halo and two dithiocarbamate groups is proposed.     

Electrochemical and chemical reduction studies of molybdenum(VI)-and molybdenum (V)-ethylenediaminetetraacetic acid complexes

Summary The electrochemical reduction characteristics of the molyb-denum(VI)-and molybdenum(V)-ethylenediaminetetraacetate complexes, [(MoO₃)₂Y]^4– and [Mo₂O₄Y]^2– respectively have been investigated as a function of pH and free ligand concentration. The nature of chemical reduction of these two complexes with sodium borohydride and sodium dithionite have also been studied in acetate and borate buffers. The electroactive species undergoing electrode reductions have been ascertained by analysing polarograms of the complexes. A mechanism has been proposed to account for the differences observed in the reactivities of these two complexes.     

A novel chain-like molybdenum phosphate: hydrothermal synthesis,crystal structure and characterization of [NH3(CH2CH2)2NH3]3[NH3(CH2CH2)2NH2]-Na5[Mo6O12(OH)3(PO4)(HPO4)3]2·4H2O

A novel organic/inorganic hybrid molybdenum phosphate, [NH₃(CH₂CH₂)₂NH₃]₃[NH₃(CH₂CH₂)₂NH₂]Na₅-[Mo₆O₁₂(OH)₃(PO₄)(HPO₄)₃]₂·4H₂O (1), involving molybdenum presented in V oxidation, has been hydrothermally prepared and characterized by elemental analysis, i.r., u.v.–vis., x.p.s., t.g. and single crystal X-ray diffraction. The structure of the title compound (1) may be considered to consist of two [Mo₆O₁₂(OH)₃(PO₄)(HPO₄)₃] units bonded together with NaO₆ octahedra, forming dimers. Further, these dimers connect with each other through four Na⁺ cations as bridges, giving rise to novel one-dimensional chain-like skeleton. Piperazines exist among inorganic chains acting as charge balancing cations.     

Synthesis,Structure and Characterization of Dinuclear Pentacoordinate Molybdenum(V) Complexes with Thiosemicarbazone Ligands

New dinuclear pentacoordinate molybdenum(V) complexes, [Mo₂^VO₃L₂] [L = thiosemicarbazonato ligand: C₆H₄(O)CH:NN:C(S)NHR′ and C₁₀H₆(O)CH:NN:C(S)NHR′; R′ = H, CH₃, C₆H₅) were obtained either by oxygen atom abstraction from Mo^VIO₂L with triphenylphosphine or by using [Mo₂O₃(acac)₄] in the reaction with the corresponding ligands H₂L. Crystal and molecular structure of [Mo₂O₃{C₆H₄(O)CH:NN:C(S)NHC₆H₅}₂] · CH₃CN has been determined by the single‐crystal X‐ray diffraction method.     

Synthesis and Spectroscopic Studies of Chosen Heteropolytungstates and Their Ln(III) Complexes

The heteropolytungstates [(Na)P₅W₃₀O₁₁₀]^4– (I), [(Na)Sb₉W₂₁O₈₆]^18– (II) and [(Na)As₄W₄₀O₁₄₀]^27– (III) and the monovacant Keggin structure of the general formula [XW_11–xMo_xO₃₉]^n– (X-Si, P; n = 7 for P and 8 for Si) (IV) as well as their europium(III) complexes were studied. The structures of I–IV as well as the europium(III) encrypted [(Eu)P₅W₃₀O₁₁₀]^12– (VI), [(Eu)Sb₉W₂₁O₈₆]^16– (VII), [(Eu)As₄W₄₀O₁₄₀]^25– (VIII) and sandwiched [Eu(XW_11–xMo_xO₃₉)₂]^n– (n =11 for P and n = 13 for Si) (V) complexes were synthesized and spectroscopically characterized. The complexes were studied using UV-Vis absorption and luminescence, as well as the laser-induced europium ion luminescence spectroscopy. Absorption spectra of Nd(III) were used to characterize the complexes formed. Excitation and emission spectra of Eu(III) were obtained for solid complexes and their solutions. The relative luminescence intensities of the Eu(III) ion, expressed as the ratio of the two strongest lines at 594 nm and 615 nm, = I₆₁₅/I₅₉₄, which is sensitive to the environment of the primary coordination sphere about the Eu(III) ion, was calculated. In the case of the sandwiched [Eu(XW_11–xMo_xO₃₉)₂]^n– complexes a linear dependence of the luminescence quantum yield of Eu(III) ion, , (calculated using [Ru(bpy)₃]Cl₂ as a standard) on the content of Mo (number of atoms, x) in the [Eu(XW_11–xMo_xO₃₉)₂]^n– structure was observed.     

Dinuclear peroxo complexes of molybdenum(VI) containing Mannich base ligands

Dinuclear molybdenum(VI) peroxo complexes containing Mannich base ligands having formulae [Mo₂O₄(O₂)₂L-L(H₂O)₂] · H₂O [where L-L = N-[1-morpholinobenzyl] acetamide (MBA), N-[1-piperidinobenzyl] acetamide (PBA), N-[1-morpholino(-4-nitrobenzyl)] benzamide (MPNBB), N-[1-piperidino(-3-nitrobenzyl)] benzamide (PMNBB), N-[1-morpholino(-2-nitrobenzyl)] acetamide (MONBA), and N-[1-morpholino(-3-nitrobenzyl)] acetamide (MMNBA)] have been synthesized by stirring ammonium heptamolybdate with excess 30% aqueous hydrogen peroxide followed by treatment with ethanolic solution of corresponding ligands. The complexes have been characterized by elemental analysis, molar conductance, magnetic measurements, infrared (IR), electronic, TGA/DTA, mass spectral, and ¹H NMR studies. The complexes are non-electrolytes and diamagnetic. The IR spectral studies suggest that the ligands are bidentate to metal through carbonyl oxygen and ring nitrogen. Thermal analyses provide conclusive evidence for the presence of coordinated, as well as lattice water in the complexes. Dinuclear complexes preserve the individuality of the molybdenum oxo peroxo core. The complexes exhibit higher antibacterial activity against bacterium Ralastonia solanacearum (Pseudomonas solanacearum) than the free ligands.     

Synthesis and characterization of oligomeric molybdenum complexes of N-alkylphenothiazines

Summary Polynuclear molybdenum(IV/V) oxide - phenothiazine complexes which are oligomeric in nature have been prepared. The complexes were characterized by elemental analyses and spectroscopic data. The molecular formulae of the new complexes are [Mo₄O₉(OH₂)₂(PTZ)₂], PTZ = chlorpromazine or promethazine, [Mo_{4 8}(OH₂)₂(TR)₂], TR = thioridazine, [Mo₅O₁₀(OH_O2)₂(EP)₂], EP = ethopropazine, and [Mo₆O₁₂(OH₂)₂(TF)₂], TF = trifluoperazine. Tentative structures are proposed.     

Synthesis,structure, and properties of polynuclear molybdenum(v,vi) oxomethoxides with magnesium

General conditions for the formation of heterometallic clusters by the simultaneous methanolysis of MoCl₅ and MgCl₂ were determined. The resultant alkalinity of the reaction solution, the Mg/Mo molar ratio, and the presence of traces of water are key factors responsible for the composition and structure of the mixed magnesium molybdenum methoxides that formed. The new decanuclear mixed-valence Mo^V,VI Mg oxomethoxide [Mo^V ₄O₄(μ₃-O)₂(μ₂-O)₂Mo^VI ₂-O₄(OMe)₂Mg₄(MeOH)₆(μ₃-OMe)₆(μ₂-OMe)₈] (1) was synthesized by the reaction of lowernuclearity magnesium molybdenum oxoalkoxide complexes: NaMo^V of the complex Na(MeOH)Mo^V ₂O₂(μ₂-OMe)₃(OMe)₄ (2) and MgMo^VI of the complex [Mo^VIO₂Mg(MeOH)₂-(OMe)₄]₂ (3). The molecular structure of 1 was determined by X-ray diffraction.     

New Molybdenum(V) Complexes Prepared by the Oxidation of Dinuclear Quadruply-Bonded Molybdenum(II) Monothiocarboxylates

Oxidation of molybdenum(II) thiopivalate and thiobenzoate in the presence of -picoline or pyridine results in the formation of dinuclear molybdenum(V) complexes of the general formulae [Mo₂O₂(-O)₂(-SO₄)L₄] with L = -picoline or pyridine and [Mo₂O₂(-O)(-S)(-SO₄)L₄] with L = -picoline. As determined by X-ray structure analysis, two complexes with -picoline differ in their bridging cores: In one complex, two Mo atoms are doubly bridged through two oxygen atoms; in the other, one Mo atom is doubly bridged through oxygen and sulfur atoms. However, they both crystallize together. The product is solvated with -picoline and water molecules. Molybdenum atoms exhibit distorted octahedral coordinations. The same complexes were prepared also through direct reactions of [Mo₂O₃(O₂CCH₃)₄] with thiopivalic and thiobenzoic acid in the presence of -picoline or pyridine. The appearance of the oxo-oxygens and sulfido-sulfur as well as sulfato ligand is explained by the molybdenum-catalyzed oxidation of thiocarboxylates.     

Two mononuclear molybdenum(VI) oxo complexes with tridentate hydrazone ligands: Synthesis and crystal structures

Reaction of [MoO₂(Acac)₂] (Acac = acetylacetonate) with two similar hydrazone ligands in methanol yielded two mononuclear molybdenum(VI) oxocomplexes with general formula [MoO₂(L)(CH₃OH)], where L = L¹ = (4-nitrophenoxy)acetic acid [1-(3-ethoxy-2-hydroxyphenyl)methylidene]hydrazide (H₂L¹) and L = L² = (4-nitrophenoxy)acetic acid [1-(5-bromo-2-hydroxyphenyl)methylidene]hydrazide (H₂L²). Crystal and molecular structures of the complexes were determined by single crystal X-ray diffraction method. All investigated compounds were further characterized by elemental analysis and FT-IR spectra. Single crystal X-ray structural studies indicate that the hydrazone ligands coordinate to the MoO₂ cores through enolate oxygen, phenolate oxygen, and azomethine nitrogen. The Mo atoms in both complexes are in octahedral coordination.     

Reactions of molybdenum and ruthenium carbonyls with some pyridylamine ligands

The interaction of Mo(CO)₆ and Ru₃(CO)₁₂ with 2-aminoethylpyridine (aepy), 2-hydrazinopyridine (hzpy) and dipicolylamine (dpa) have been investigated. Molybdenum complexes were found to have either mono- or binuclear derivatives, [MoO₂(CO)₂(aepy)] (1), [MoO₂(CO)₂(hzpy)] (2), [Mo₂O₆(aepy)₂] (3), [Mo₂O₆(hzpy)₂] (4), and [Mo₂O₄(dpa)₂] (5), depending on the reactions conditions. Ruthenium complexes are shown to have a molecular formulae of a mononuclear species; [Ru(CO)₃(aepy)] (6), [Ru(CO)₃(hzpy)] (7) and [Ru(CO)₂(dpa)] (8). The proposed structures of the complexes were elucidated using elemental analyses, i.r., u.v.–vis. and n.m.r. spectroscopy. The thermal stabilities of the reported complexes were also investigated using the t.g. technique.     

Structural Study and Solution Integrity of Dioxomolybdenum(VI) Complexes with Tridentate Schiff Base and Azole Ligands

Four new molybdenum complexes [Mo^VIO₂(L¹)(Him)] ( 1 ), [Mo^VIO₂(L¹)(3‐MepzH] ( 2 ), [Mo^VIO₂(L²)(3‐MepzH)] ( 3 ), and [(Mo^VIO₂)₂(μ‐L³)(MeOH)₂] ( 4 ) were synthesized and characterized by IR, NMR, ESI‐MS, and single‐crystal structure analysis [H₂L¹ = 2‐(salicylideneamino)‐2‐methyl‐1‐propanol, H₂L² = 2‐(3‐methoxysalicylideneamino)‐2‐methyl‐1‐propanol, H₄L³ = 1, 7‐bis(salicylidene)dihydrazide malonic acid, Him = imidazole and 3‐MepzH = 3‐methylpyrazole]. In all four structures the molybdenum atom has a distorted octahedral coordination with the three meridional donor atoms from the Schiff base di‐ or tetraanion (L^{1, 2})^2—/(L³)^4— and one oxo group occupying the sites of the equatorial plane. The other oxo group and the azole or methanol molecule occupy the apical sites. In 1—3 two centrosymmetrically related molecules form a hydrogen‐bonded pair through the (azole)N‐H···O(alkoxo) interaction. Additional crystal packing appears to be controlled mostly by π stacking between the aromatic rings of the salicyl moiety. ESI‐MS investigations reveal that the integrity of complexes 1—4 is largely retained in methanol solution. At the same time evidence is provided that di‐ to tetranuclear oligomers of formula [{Mo^VIO₂(L)}_x] and [{Mo^VIO₂(L)}_x(3‐MepzH)] with L = L¹, L², x = 2, 3, 4 are present simultaneously with 2 and 3 in methanol solution, respectively the tetranuclear species [{(Mo^VIO₂)₂(L³)}₂] with 4 .     

High potential isomeric dihalobis[2-(arylazo)pyridine] osmium(III) perchlorate monohydrate

Summary The preparation of isomeric complexes [Os^IIIX₂L₂]ClO₄· H₂O [{(4)} and (5): X = Cl or Br, L(1) = 2-(phenylazo)-pyridine (L¹) or 2-(m-tolylazo)pyridine(L²)] via stereo-retentive oxidation of the corresponding osmium(II) precursors [(2) and (3), respectively] is described. The complexes were characterized using spectroscopic and electrochemical methods. The low-spin (idealized t _2g ⁵ ; S = 1/2) paramagnetic complex ions display characteristic osmium(III) e.p.r. spectra in frozen (-196° C) MeCNPhMe. In dry MeCN solution, the OsX₂N₄ unit exhibits irreversible [OsX₂L₂]²⁺/[OsX₂L₂]⁺ and reversible [OsX₂L₂]⁺/[OsX₂L₂] couples at ca. 1.8 and 1.0 V versus saturated calomel electrode (s.c.e.), respectively. The use of (4)/(5) as an oxidant is noted.     

Reactivity of the tetrathiomolybdate(VI) anion towards hard and soft base chelating agents

Summary The interaction of hard base chelating agents (LH) such as 8-quinolinol (oxH), salicylaldehyde (salH) andN-nitrosophenylhydroxylamine (NphaH) with ammonium tetrathiomolybdate(VI), (1), in aqueous solution yields disulphidomolybdenum(VI) complexes, [MoS₂L₂]. The i.r. absorptions at 540 and 510 cm^–1 are assigned tov(Mo-S), which indicate that the two sulphido-groups arecis to each other, The interaction of (1) with soft base chelating agents (SS), such as dithiocarbamates (dtc), dithiophosphate (dtp) and xanthates (xan) yields dimeric sulphido-bridged sulphidomolybdenum(V) complexes, [Mo₂S₄(SS)₂] and with potassium ethylthioxanthate (KEttxan) yields a molybdenum(IV) complex, [Mo(Ettxan)₄]. The [Mo₂S₄(R₂dtc)₂] complexes were also obtained by the interaction of [MoO₂(R₂dtc)₂] with phosphorus pentasulphide in xylene. It was concluded that tetrathiomolybdate(VI) undergoes facile reduction when compared with tetraoxomolybdate(VI).