Synthesis and characterization of molybdenum(V,VI) complexes derived from bis(2-hydroxy-1-naphthaldehyde)malonoyldihydrazone

Monometallic molybdenum(VI) complexes [MoO₂(CH₂LH₂)]?·?H₂O (1), [Mo₂O₄(CH₂LH₂)₂(A)₂] (A?=?py (2), 2-pic (3), 3-pic (4) and 4-pic (5)) and molybdenum(V) complexes [Mo(CH₂LH₂)(inh)]?·?H₂O (6) and [Mo(CH₂LH₂)(slh)] (7) of bis(2-hydroxy-1-naphthaldehyde)malonoyldihydrazone (CH₂LH₄) have been synthesized and characterized by various physico-chemical and spectroscopic studies. The compositions of the complexes have been established by elemental analyses and molecular weight determination. The structural assessment of the complexes has been done on the basis of data obtained from molar conductances, magnetic moment studies, electronic, infrared, electron paramagnetic resonance (EPR), proton nuclear magnetic resonance, and ¹³C proton nuclear magnetic resonance spectroscopic studies. The molar conductance values for the complexes in DMSO suggest that they are non-electrolytes. The magnetic moment values for 6 and 7 correspond to one unpaired electron while the remaining complexes are diamagnetic. Complexes 1, 6, and 7 have six-coordinate octahedral stereochemistry around molybdenum, while 2–5 are eight-coordinate dodecahedral around the metal centers. EPR spectral features suggest that 7 is less symmetrical than 6.     

Synthesis and spectral studies on heterobimetallic complexes of manganese and ruthenium derived from bis[N-(2-hydroxynaphthalen-1-yl)methylene]oxaloyldihydrazide

The complex [Mn(L)(H₂O)₂] [H₄L = bis[N-(2-hydroxynaphthalen-1-yl)methylene]-oxaloyldihydrazide] reacts with activated ruthenium(III) chloride in methanol in 1:1.2 M ratio under reflux resulting in heterobimetallic complex of the composition [Mn(L)(H₂O)₄RuCl₂]Cl. The complexes of the composition [Mn(L)(A)₄RuCl₂]Cl were obtained when the above reaction was carried out in presence of heterocyclic nitrogen bases(A) such as pyridine(py), 3-picoline(3-pic) and 4-picoline(4-pic). The molar conductance values for these complexes in DMF(N,N-dimethyl formamide) solution indicate their 1:1 electrolytic nature. Magnetic moment values suggest that these heterobimetallic complexes contain Mn(IV) and Ru(III) in the same structural unit. Electronic spectral studies suggest six coordinated metal ions in these complexes. IR spectra reveal that the H₄L ligand coordinates in its keto-form to Mn(IV) and Ru(III).     

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.     

Synthesis and properties of mononuclear and binuclear molybdenum complexes derived from bis(2-hydroxy-1-naphthaldehyde)oxaloyldihydrazone

The monomer molybdenum(VI) complex [MoO(2)(napoxlhH(2))].2H(2)O (1) has been synthesized from the reaction of MoO(2)(acac)(2) with bis(2-hydroxy-1-naphthaldehyde)oxaloyldihydrazone (napoxlhH(4)) in 1:1 molar ratio in ethanol under reflux. This complex on reaction with pyridine/3-picoline/4-picoline yielded the dimer molybdenum(VI) complexes [Mo(2)O(4)(napoxlhH(2))(2)(A)(2)].2H(2)O (A=py (2), 3-pic (3), 4-pic (4)), whereas reaction with isonicotinoylhydrazine (inhH(3)) and salicyloylhydrazine (sylshH(3)) lead to the reduction of the metal centre yielding monomeric molybdenum(V) complexes [Mo(napoxlhH(2))(hzid)].2H(2)O (where hzidH(3)=inhH(3) (5) and sylshH(3) (6)). The complexes have been characterized by elemental analyses, molecular weight determinations, molar conductance data, magnetic moment data, electronic, IR, ESR and (1)H NMR spectroscopic studies. The complexes (5) and (6) are paramagnetic to the extent of one unpaired electron. The electronic spectra of the complexes are dominated by strong charge transfer bands. In all of the complexes, the principal dihydrazone ligand has been suggested to coordinate to the metal centres in the anti-cis-configuration. The complexes (1), (5) and (6) are suggested to have six-coordinate octahedral stereochemistry around molybdenum(VI) and molybdenum(V) metal centres, respectively, while the complexes (2)-(4) are suggested to have eight coordinate dodecahedral stereochemistry around molybdenum(VI) metal centre.     

Molybdenum(VI), (V) and (IV) complexes with chiral benzoin thiosemicarbazone

The chiral (ONS) dianionic Schiff base ligand benzoin thiosemicarbazone (H₂L) reacts with MoO₂(acac)₂ to give the polymeric complex [(MoO₂L) _n ] (1) (Type 1). The reaction of MoO₂L with pyridine (py), 3-picoline (3-pic) or 4-picoline (4-pic) gives [Mo^VIO₂LD] (D = py, 3-pic or 4-pic) (Type 1). Further, the reaction of [MoO₂L] or [MoO₂LD] with PPh₃ or reaction of [MoO₂L] with PPh₃ (plus bpy or phen, D) in the presence of donor reagents D gives [Mo^IVOL] or [Mo^IVOLD] (Type 2). On the other hand, the reaction of [MoO₂L] with hydrazides (zdhH₃) such as benzoylhydrazine (bhH₃), isonicotinoylhydrazine (inhH₃), nicotinoylhydrazine (nhH₃), salicyloylhydrazine (slhH₃) and thiosemicarbazide (tscH₃) produced non-oxo–diazenido complexes [MoL(zdh)] (Type 3). The complexes have been characterized by elemental analyses, molar conductance, magnetic moment, electronic, i.r. and e.s.r. spectroscopic measurements.     

Synthesis,crystal structure,spectroscopy, thermal properties and carbonic anhydrase activities of new metal(II) complexes with mefenamic acid and picoline derivatives

The mononuclear six metal(II) complexes ([Co(mef)₂(3-pic)₂(CH₃OH)₂] (1), [Ni(mef)₂(3-pic)₂(CH₃OH)₂] (2), [Cu(mef)₂(3-pic)₂] (3), [Co(mef)₂(4-pic)₂] (4), [Ni(mef)₂(4-pic)₂] (5), and [Cu(mef)₂(4-pic)₂] (6) with mefenamic acid and picoline ligands were synthesized, characterized, and their carbonic anhydrase inhibitory activities were evaluated. The six complexes were characterized by elemental analysis, FT-IR spectroscopy, and thermal analyses. The crystal structures of 1, 3, and 6 were determined by X-ray crystallography. The complexes have octahedral geometry. In 1, the mefenamato ligand behaved as monodentate whereas in 3 and 6, the mefenamato ligand acted as a bidentate ligand. Complexes 3 and 6 consist of the mefenamate and 4-picoline ligands. In 1, unlike the other complexes, methanol acted as a ligand and was involved in the coordination. Carbonic anhydrase I and II isoenzymes were purified from human erythrocytes. The in vitro effects of mefenamic acid, 3-picoline, 4-picoline, and the six metal(II) complexes on these isoenzymes were evaluated.     

Synthesis and characterization of manganese(IV) and ruthenium(III) complexes derived from bis (2-hydroxy-1-naphthaldehyde)oxaloyldihydrazone

Bis(2-hydroxy-1-naphthaldehyde)oxaloyldihydrazone(naohH₄) interacts with manganese(II) acetate in methanol followed by addition of KOH giving [Mn^IV(naoh)(H₂O)₂]. Activated ruthenium(III) chloride reacts with naohH₄ in methanol yielding [Ru^III(naohH₄)Cl(H₂O)Cl₂]. The replacement of aquo by heterocyclic nitrogen donor in these complexes has been observed when the reaction is carried out in presence of heterocyclic nitrogen donors such as pyridine(py), 3-picoline(3-pic) or 4-picoline(4-pic). The molar conductance values in DMF for these complexes suggest non-electrolytic nature. Magnetic moment values suggest +4 oxidation state for manganese in its complexes, however, ruthenium(III) complexes are paramagnetic with one unpaired electron. Electronic spectral studies suggest six coordinate metal ions. IR spectra reveal that naohH₄ coordinates in enol-form and keto-form to manganese and ruthenium, respectively. ESR and cyclic voltammetric studies of the complexes have also been reported.     

Synthesis,crystal, molecular and electronic structures of thiocyanate ruthenium complexes with pyridine and its derivatives as ligands

The complexes [Ru(SCN)₂(PPh₃)₂(L)₂], where L = py and γ-pic, and [Ru(SCN)₂(PPh₃)₂(L)], where L = py-2-CH₂NH₂ and py-2-CH₂O, have been prepared and studied by IR, NMR, EPR, UV–Vis spectroscopy and X-ray crystallography. The complexes were prepared in the reactions of [RuCl₂(PPh₃)₃] with pyridine, γ-picoline, 2-(aminomethyl)pyridine and 2-(hydroxymethyl)pyridine in methanol solutions. The electronic structures of the obtained compounds have been calculated using the DFT/TD-DFT method.     

Synthesis and structural characterization of manganese(III,IV) and ruthenium(III) complexes derived from 2-hydroxy-1-naphthaldehydebenzoylhydrazone

Reaction of 2-hydroxy-1-naphthaldehydebenzoylhydrazone(napbhH₂) with manganese(II) acetate tetrahydrate and manganese(III) acetate dihydrate in methanol followed by addition of methanolic KOH in molar ratio (2 : 1 : 10) results in [Mn(IV)(napbh)₂] and [Mn(III)(napbh)(OH)(H₂O)], respectively. Activated ruthenium(III) chloride reacts with napbhH₂ in methanolic medium yielding [Ru(III)(napbhH)Cl(H₂O)]Cl. Replacement of aquo ligand by heterocyclic nitrogen donor in this complex has been observed when the reaction is carried out in presence of pyridine(py), 3-picoline(3-pic) or 4-picoline(4-pic). The molar conductance values in DMF (N,N-dimethyl formamide) of these complexes suggest non-electrolytic and 1 : 1 electrolytic nature for manganese and ruthenium complexes, respectively. Magnetic moment values of manganese complexes suggest Mn(III) and Mn(IV), however, ruthenium complexes are paramagnetic with one unpaired electron suggesting Ru(III). Electronic spectral studies suggest six coordinate metal ions in these complexes. IR spectra reveal that napbhH₂ coordinates in enol-form and keto-form to manganese and ruthenium metal ions in its complexes, respectively. ESR studies of the complexes are also reported.     

Oxomolybdenum(V) complexes of bis-(2-benzimidazolyl) alkanes

Summary Oxomolybdenum(V) complexes of the type (LH₄) [MoOCl₅] (where LH₂ = dimethylene bis-2-benzimidazole or tetramethylene bis-2-benzimidazole), [MoOCl₃(LH₂)] (where LH₂ = tetramethylene bis-2-benzimidazole), [(Mo₂O₄Cl₂-(H₂O)₃)₂(LH₂)] (where LH₂ = dimethylene bis-2-benzimidazole, tetramethylene bis-2-benzimidazole or hexamethylene bis-2-benzimidazole) and [Mo₂O₃Cl₄(LH₂)₂] (where LH₂ = tetramethylene bis-5-nitro-2-benzimidazole) were prepared and characterised. The mononuclear complexes show u.v.-vis. absorptions characteristic of octahedral molybdenum(V). The dinuclear complexes do not absorb in the visible region, possibly due to the presence of an Mo₂O ₄ ^{2 +}} core, which is also indicated by their diamagnetic behaviour. The biological activities of the free ligands and their complexes have been studied.     

Synthesis,characterization and fluorescence properties of hexanuclear zinc(II) complexes

Two hexanuclear zinc(II) complexes, [Zn₆(L¹)₂(μ₂-OH)₂(μ₂-CH₃COO)₈] · CH₃CN (1 · CH₃CN) and [Zn₆(L²)₂(μ₂-OH)₂(μ₂-CH₃COO)₈] · 4CH₃CN (2 · 4CH₃CN), where HL¹ = 4-methyl-2,6-bis(cyclohexylmethyliminomethyl)-phenol and HL² = 4-methyl-2,6-bis(1-naphthalylmethyliminomethyl)-phenol, have been synthesized and characterized by elemental analysis, FT-IR and fluorescence spectroscopic methods, and by X-ray diffraction analysis. In the asymmetric unit of complex 1, two of the three zinc atoms have pentacoordinate geometries and the other is tetrahedrally coordinated, whereas the three distinct Zn atoms in complex 2 adopt three different coordination environments, namely distorted octahedral, trigonal bipyramidal and tetrahedral. The fluorescence properties of the ligands and complexes have been investigated.     

Synthesis and spectral studies on heterobimetallic complexes of manganese and ruthenium derived from N-(2-hydroxynaphthalen-1-yl)methylenebenzoylhydrazide

The complex [Mn^IV(napbh)₂] (napbhH₂ = N-(2-hydroxynaphthalen-1-yl)methylenebenzoylhydrazide) reacts with activated ruthenium(III) chloride in methanol in 1 : 1.2 molar ratio under reflux, giving heterobimetallic complexes, [Mn^IV(napbh)₂Ru^IIICl₃(H₂O)] · [Ru^III(napbhH)Cl₂(H₂O)] reacts with Mn(OAc)₂·4H₂O in methanol in 1 : 1.2 molar ratio under reflux to give [Ru^III(napbhH)Cl₂(H₂O)Mn^II(OAc)₂]. Replacement of aquo in these heterobimetallic complexes has been observed when the reactions are carried out in the presence of pyridine (py), 3-picoline (3-pic), or 4-picoline (4-pic). The molar conductances for these complexes in DMF indicates 1 : 1 electrolytes. Magnetic moment values suggest that these heterobimetallic complexes contain Mn^IV and Ru^III or Ru^III and Mn^II in the same structural unit. Electronic spectral studies suggest six coordinate metal ions. IR spectra reveal that the napbhH₂ ligand coordinates in its enol form to Mn^IV and bridges to Ru^III and in the keto form to Ru^III and bridging to Mn^II.     

Coordination chemistry of gold(II) with amidinate,thiolate and ylide ligands

Various reagents such as Cl₂, Br₂, I₂, benzoyl peroxide and CH₃I add to the dinuclear gold(I) amidinate complex [Au₂(2,6-Me₂Ph-form)₂] to form oxidative-addition gold(II) metal–metal bonded complexes. The gold–gold distance in the dinuclear complex decreases upon oxidative-addition with halogens from 2.7 to 2.5 Å, similar to observations made with dithiolate and ylide ligands. The sodium salt of the guanidinate Hhpp ligand, Hhpp = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine reacts with (THT)AuCl in THF or CH₂Cl₂ to form a Au(II) complex, [Au₂(hpp)₂Cl₂], either by solvent oxidation or disproportionation of the Au(I) to Au(II) and the metal. Density functional theory (DFT) and MP2 calculations on [Au₂(hpp)₂Cl₂] find that the highest occupied molecular orbital (HOMO) is predominately hpp and chlorine-based with some Au–Au δ* character. The lowest unoccupied molecular orbital (LUMO) has metal-to-ligand (M–L) and metal-to-metal (M–M) σ* character (approximately 50% hpp/chlorine, and 50% gold). The charge-transfer character of the deeply colored solutions is observed in all the oxidative-addition products of the dinuclear gold(II) nitrogen ligands. This contrasts with the colors of the gold(II) ylide oxidative-addition products which are pale yellow. The colors of the crystalline gold(II) nitrogen complexes are dark orange to brown. This review will focus on the chemistry of gold(II) with nitrogen ligands and compare this with the well reviewed chemistry of gold(II) thiolate and ylide complexes.     

Mono(amidinate) rare earth metal bis(alkyl) complexes: Synthesis,structure and their activity for l-lactide polymerization

Alkane elimination reaction between Ln(CH₂SiMe₃)₃(THF)₂ (Ln = Y, Lu) with one equivalent of the amidines with different steric demanding HL ([CyC(N-2,6-ⁱPr₂C₆H₃)₂]H (HL₁), [CyC(N-2,6-Me₂C₆H₃)₂]H (HL₂), [PhC(N-2,6-Me₂C₆H₃)₂]H (HL₃)) in THF afforded a series of mono(amidinate) rare earth metal bis(alkyl) complexes [CyC(N-2,6-ⁱPr₂C₆H₃)₂]Ln(CH₂SiMe₃)₂(THF) (Ln = Y (1), Lu (3)), [CyC(N-2,6-Me₂C₆H₃)₂]Ln(CH₂SiMe₃)₂(THF)₂ (Ln = Y (4), Lu (6)), and [PhC(N-2,6-Me₂C₆H₃)₂]Y(CH₂SiMe₃)₂(THF)₂ (7) in 75–89% isolated yields. For the early lanthanide metal Nd, THF slurry of NdCl₃ was stirred with three equiv of LiCH₂SiMe₃ in THF, followed by addition of one equiv of the amidines HL₁ or HL₂ gave an “ate” complex [CyC(N-2,6-ⁱPr₂C₆H₃)₂]Nd(CH₂SiMe₃)₂(μ-Cl)Li(THF)₃ (2) in 48% yield and a neutral [CyC(N-2,6-Me₂C₆H₃)₂]Nd(CH₂SiMe₃)₂(THF)₂ (5) in 52% yield, respectively. They were characterized by elemental analysis, FT-IR, NMR spectroscopy (except for 2 and 5 for their strong paramagnetic property). Complexes 2, 3, 4 and 5 were subjected to X-ray single crystal structure determination. These neutral mono(amidinate) rare earth metal bis(alkyl) complexes showed activity towards l-lactide polymerization to give high molecular weight and narrow molecular weight distribution polymers.     

Synthesis and magnetic properties of heptadecametallic Fe(III) clusters

Heptadecametallic, all-ferric pieces of molecular magnetite of general formula HL_x[Fe₁₇O₁₆(OH)₁₂(L)₁₂Br₄]Br_3+x (L = β-picoline, isoquinoline, 3,5-lutidine; x = 0, 1) are made by the simple dissolution of FeBr₃ in L. The β-picoline (or equivalent) molecules act simultaneously as solvent, base and capping ligand. The resultant structure consists of a metal–oxygen core containing both octahedral and tetrahedral Fe(III) ions that is the exact analogue of the metal–oxygen positions seen in the magnetite lattice. Antiferromagnetic exchange between the tetrahedral and octahedral Fe(III) ions lead to the stabilization of an S = 35/2 spin ground state.     

Silver alkoxide and amino N-heterocyclic carbenes; syntheses and crystal structures

Silver(I) complexes of heterobidentate ligands that incorporate one or two N-heterocyclic carbene moieties coupled with an alcohol or amine group have been made by direct deprotonation of ligands of the form [HOCR¹R²CH₂(1-HC{NCHCHNR})][X], H₂L¹X (X = Br, I), [H₂NR¹CHR²CHR²(1-HC{NCHCHNR})][Br]₂ H₃L²X₂ (X = Cl, Br), and [H₂N{CH₂CH₂(1-HC[NCHCHNMes])}₂][X]₃ H₄L³X₃ (X = Cl, Br). Silver(I) oxide is sufficiently basic to deprotonate both the imidazolium and the alcohol functional groups of all but one of the L¹ ligand precursors, to afford rare examples of silver alkoxide complexes [Ag(L¹)], stabilised by the soft donor carbene. Another complex of L¹ is characterised as the carbene alcohol adduct [Ag(HL¹)₂I]. The analogous reactions of silver(I) oxide with the amino imidazolium precursors afford silver amino-carbenes [Ag(HL²)Br] with the potentially bidentate L² ligand, and [Ag(HL³)X] (X = Cl, Br) with the potentially tridentate L³ ligand. A single crystal X-ray diffraction study of the latter complex confirms that the neutral amine of the potentially tridentate L³ ligand is unco-ordinated; instead the structure contains discrete chains of T-shaped silver bis(carbene) halide moieties that bridge to form a zig-zag 2-connected polymer. Protonolysis of two of the silver alkoxide and amino adducts, [Ag(L^1a)] and [Ag(HL^2a)Br], affords imidazolium complexes salts [H₂L^1a][AgCl₂] and [Ag(H₂L^2a)Br][AgBr₂] that retain the Ag(I) centre as complex counterions. The single crystal X-ray structures of these salts have been determined and show the silver(I) cations are now incorporated into ladders or chains as silver(I) halo-anions, and a silver amine dative bond is present in the latter complex.     

Dinuclear triple helical Mn(III), Fe(III) and Co(III) complexes

Synthesis, characterization and physical properties of the dinuclear triple helical complexes [Mn₂(μ-L)₃] (1), [Fe₂(μ-L)₃] (2) and [Co₂(μ-L)₃] (3) with the tetradentate Schiff base (H₂L) derived from 1 mol equiv. of hydrazine and 2 mole equiv. of 2-hydroxy-1-naphthaldehyde are described. Triple helical molecular structures of 2 and 3 have been confirmed by X-ray crystallography. Magnetic susceptibility measurements reveal complex 3 is diamagnetic while a weak antiferromagnetic interaction is operative between the metal centres in both 1 and 2.     

Synthesis,structure and magnetic properties of {Mn5(OC(O)CH3)6(OC(O)C6H5)4}∞

The ligand exchange reaction between Mn(OC(O)CH₃)₂ and benzoic acid under solvothermal conditions in toluene at 110 °C yields colorless crystals of {Mn₅(OC(O)CH₃)₆(OC(O)C₆H₅)₄}_∞ (1). The asymmetric unit of this complex is Mn_2.5(OC(O)CH₃)₃(OC(O)C₆H₅)₂ with each of the three different Mn(II) atoms in 6-fold coordination and one of the benzoate ligands exhibiting the rare μ₃-symmetric bridging mode (O–Mn–O angle = 57°). The structure consists of edge-shared Mn₁₂ loops arranged in a honeycomb-like 2D sheet with the acetate ligands displaced slightly out of the plane. The sheets are spaced at 12 Å and linked into a 3D network via weak intersheet interactions. Magnetic susceptibility characterization of 1 indicates antiferromagnetic exchange with a Weiss constant of −165 K and a transition toward ferromagnetic exchange below 10 K corroborated with a finite imaginary component in the variable temperature susceptibility data.     

Palladium and platinum complexes with planar chiral 1,2-disubstituted ferrocenes containing phosphine and thioether donor groups

Three palladium(II) complexes and four platinum(II) complexes having general formula CpFe{1,2-C₅H₃(PPh₂)(CH₂SR)}MCl₂ (M = Pd, R = Ph, Et and tBu; M = Pt, R = Ph, Et, tBu and Cy) have been synthesized by reaction of the corresponding CpFe{1,2-C₅H₃(PPh₂)(CH₂SR)} ligands with PdCl₂(CH₃CN)₂ or PtCl₂(CH₃CN)₂. These complexes have been fully characterized in solution and in solid state. In all cases, monomeric square planar complexes were obtained as pure diastereoisomers.     

Macrocyclic Pd(II) dithiolate complexes as catalysts in Heck reactions

The supramolecular palladium dithiolate complexes, [Pd₂(dppe)₂{S(C₆H₄)_nS}]₂(OTf)₄ and [Pd₂(dppe)₂(SCH₂C₆H₄CH₂S)]₄(OTf)₈ (dppe = 1,2-bis(diphenylphosphino)ethane) has been investigated as highly stable and robust catalysts in Heck C-C coupling reactions. The arylation of butyl acrylate and styrene with various aryl bromides under optimized catalytic systems, showed excellent yield and turnover number (410,000) of the products. The tetranuclear complexes showed slightly higher catalytic activity than the octanuclear complex.