Synthesis,characterization, electrochemical behaviour and catalytic activity of manganese(II) complexes with linear and tripodal tetradentate ligands derived from Schiff bases

New manganese(II) complexes, [Mn(H₂L)(H₂O)₂]Cl₂· xH₂O, with linear and tripodal tetradentate ligands have been synthesized and characterized by elemental analysis, molar conductance, i.r. spectra, magnetic measurements and electronic and e.s.r. spectra. The data show that the ligands are neutral and coordinate to manganese in a tetradentate manner; the other axial sites are occupied by the water molecules. Magnetic and e.s.r. data show that manganese(II) adopts a high-spin configuration in the complexes. The electrochemical behaviour of the complexes, determined by cyclic voltammetry, shows that the chelate structure, ligand geometry and electron donating effect of the ligand substituents are among the factors influencing the redox potentials of the complexes. In addition, we note that linear ligands stabilize the manganese(III) state to a greater extent than tripodal ligands and their complexes vigorously catalyse the disproportionation of hydrogen peroxide in the presence of added imidazole.     

Dimeric tetrahedral complexes of manganese(II) and iron(II) with benzoyl hydrazones

Summary Dimeric manganese(II)and iron(II)complexes, (ML)₂, derived from benzoyl hydrazones ofo-hydroxyaryl aldehydes and ketones arc described and characterised by elemental analyses and by conductance, molecular weight, magnetic, electronic and i.r. spectral measurements. The dimeric nature of the complexes is revealed by i.r. spectra which show bands atca. 885 Mn²⁺ and 820 cm^–1 Fe²⁺, characteristic of ring vibrations. The i.r. spectra reveal the terdentate nature of the ligands. The electronic spectra in dimethylformamide are consistent with the tetrahedral nature of the complexes. The appreciable lowering in _eff is attributed to the presence of exchange interactions between two paramagnetic atomsvia oxygen bridges.Reprints of this article are not available.     

Investigations of chromium(III), manganese(III), tin(II) and lead(II) dithiocarbamate complexes

Piperidine-, morpholine-4-, N-methylpiperazine-4- and thiornorpholine-4-carbodithioate complexes of chromium(III), manganese(III), tin(II) and lead(II) are prepared and characterized by chemical analyses, spectroscopic methods (I.R. and electronic spectra), magnetic susceptibilities, conductivity measurements and mass spectra. The complexes are of the type M(R₂dtc)n, where n is the oxidation number of the metal ion. Where possible a tentative stereochemistry of the complexes is discussed on the basis of the results obtained. In all the complexes the dithiocarbamate ligands show bidentate behaviour.     

Thermodynamics of formation of urea complexes with manganese(II), nickel(II) and zinc(II) ions in N,N-dimethylformamide

The complexation of urea (ur) with manganese(II), nickel(II) and zinc(II) ions has been studied by titration calorimetry in N,N-dimethylformamide (DMF) containing 0.4M (C(2)H(5))(4) NBF(4) as a constant ionic medium at 25 degrees C. The calorimetric data were well explained in terms of the formation of [Mn(ur)](2+), [Mn(ur)(2)](2+) and [Mn(ur)(4)](2+) for manganese(II), [Ni(ur)](2+) for nickel(II) and [Zn(ur)](2+) and [Zn(ur)(2)](2+) for zinc(II), and their formation constants, reaction enthalpies and entropies were determined. The complexation of the nickel(II)-urea system in DMF has also been studied by means of spectrophotometric titration and electronic spectra of individual nickel(II) complexes were determined. On the basis of the stepwise thermodynamic quantities and the individual electronic spectra of the complexes, it is revealed that the [Mn(ur)](2+), [Mn(ur)(2)](2+), [Ni(ur)](2+), [Zn(ur)](2+) and [Zn(ur)(2)](2+) complexes have a six-coordinate octahedral structure, while the [Mn(ur)(4)](2+) complex has a four-coordinate tetrahedral structure.     

Formation constants for the complexes of levulinate and acetate with manganese(II), cobalt(II), nickel(II), copper(II), zinc(II) and hydrogen ions

Formation constants are reported for the levulinate complexes of manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) at 25 degrees in 0.1M chloride medium. In addition, results are presented for the corresponding acetate complexes for comparison. Protonation constants for the two ligands are also reported.     

Manganese(II) complexes of substituted thio-and selenosemicarbazones of 2-acetylpyridine: E.s.r., magnetic and electronic spectral studies

Summary Manganese(II) bis(ligand) complexes of substituted thiosemicarbazones and selenosemicarbazones derived from 2-acetylpyridine of general formula [MnL₂] (where L=deprotonated ligand) have been synthesized and characterised by elemental analyses, electronic spectra in solution, i.r. spectra, magnetic measurements and e.s.r. spectra recorded in polycrystalline state and in solution at room temperature and 77K. The terdentate character of the ligands in all the complexes is inferred from i.r. spectra. The electronic spectra along with e.s.r. spectra suggest an octahedral environment around the manganese(II). The metal-ligand bonds are moderately covalent. Thus all the complexes reported here are six-coordinated and high-spin octahedral.     

Synthesis and characterization of iron(III), manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) complexes of salicylidene-N-anilinoacetohydrazone (H2L1) and 2-hydroxy-1-naphthylidene-N-anilinoacetohydrazone (H2L2)

Salicylidene-N-anilinoacetohydrazone (H(2)L(1)) and 2-hydroxy-1-naphthylidene-N-anilinoacetohydrazone (H(2)L(2)) and their iron(III), manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) complexes have been synthesized and characterized by IR, electronic spectra, molar conductivities, magnetic susceptibilities and ESR. Mononuclear complexes are formed with molar ratios of 1:1, 1:2 and 1:3 (M:L). The IR studies reveal various modes of chelation. The electronic absorption spectra and magnetic susceptibility measurements show that the iron(III), nickel(II) and cobalt(II) complexes of H(2)L(1) have octahedral geometry. While the cobalt(II) complexes of H(2)L(2) were separated as tetrahedral structure. The copper(II) complexes have square planar stereochemistry. The ESR parameters of the copper(II) complexes at room temperature were calculated. The g values for copper(II) complexes proved that the Cu-O and Cu-N bonds are of high covalency.     

Mononuclear and binuclear manganese(II) complexes with tridentate bis-benzimidazolyl ligands

Summary Manganese(II) complexes of bis(2-benzimidazolylmethyl) ether (DGB), bis(2-benzimidazolylmethyl) sulphide (TGB) and the n-butyl derivative of DGB (BDGB) were prepared and characterised. The solution e.p.r. spectrum of [Mn(TGB)Cl₂] in DMF at 143 K is commensurate with an axially distorted monomeric manganese(II) complex, room temperature magnetic moment (6.04 B.M.) per manganese(II) atom being in the range found for other d⁵ monomeric manganese(II) complexes. The solution e.p.r. spectrum of [Mn(BDGB)Cl₂]-2H₂O in DMF at 143 K indicates the presence of two equivalent manganese(II) ions coupled by an exchange interaction, fostered by bridging chlorides. Evidence for this is provided by a nearly isotropic 11 line hyperfine structure of ⁵⁵Mn, with a coupling constant 45 ± 5G. Contact-shifted ¹H n.m.r. data also supports an exchange coupled dimeric manganese complex. The room temperature magnetic moment, 5.64 B.M., per manganese(II) indicates quenching of the magnetic moment below that of monomeric manganese(II) ion. The [Mn(DGB)Cl₂]·H₂O complex exhibits a magnetic moment of 6.02 B.M. per manganese, indicating a monomeric manganese complex. E.p.r. data of the complex diluted in an analogous Zn-DGB complex (1∶20) correlates well for D = 0.22cm⁻¹ and λ ∼- 0.267. The [Mn(DGB)-(C1O₄)₂] and [Mn(BDGB)(ClO₄)₂] complexes, diluted in analogous Zn-DGB and Zn-BDGB complexes (1∶20), show a strong single e.p.r. line at g _eff ∼- 2. The complexes have low magnetic moments; 4.44 B.M./Mn and 4.39 B.M./Mn, at room temperature.     

Methods for analysis of the mononuclear and binuclear manganese(III) cyano-complexes

Simple titrimetric methods are described for the analysis of potassium hexacyanomanganate(III) and of heptapotassium mu-oxo-bis[pentacyanomanganate(III)] cyanide. Mn(2)O(CN)(6-)(10) is determined by potentiometric titration with hexacyanoferrate(III). Cyanide is determined in both complexes by back-titration with Hg(II) and SCN(-), and manganese(III) is determined by back-titration with Fe(II) and MnO(-)(4). The absorption spectra of both cyano-complexes in cyanide and in acidic solutions are also described, and their molar absorptivities are reported.     

Synthesis and characterization of nickel(II), cobalt(II), copper(II), manganese(II), zinc(II), zirconium(IV), dioxouranium(VI) and dioxomolybdenum(VI) complexes of a new Schiff base derived from salicylaldehyde and 5-methylpyrazole-3-carbohydrazide

Summary Synthesis of a new Schiff base derived from salicylaldehyde and 5-methylpyrazole-3-carbohydrazide, and its coordination compounds with nickel(II), cobalt(II), copper(II), manganese(II), zinc(II), zirconium(IV), dioxouranium(VI) and dioxomolybdenum(VI) are described. The ligand and the complexes have been characterized on the basis of analytical, conductance, molecular weight, i.r., electronic and n.m.r. spectra and magnetic susceptibility measurements. The stoichiometries of the complexes are represented as NiL · 3H₂O, CoL · 2H₂O, CuL, MnL · 2H₂O, ZnL · H₂O, Zr(OH)₂(LH)₂, Zr(OH)₂L · 2MeOH, UO₂L · MeOH and MoO₂L · MeOH (where LH₂ = Schiff base). The copper(II) complex shows a subnormal magnetic moment due to antiferromagnetic exchange interaction while the nickel(II), cobalt(II) and manganese (II) complexes show normal magnetic moments at room temperature. The i.r. and n.m.r. spectral studies show that the Schiff base behaves as a dibasic and tridentate ligand coordinating through the deprotonated phenolic.oxygen, enolic oxygen and azomethine nitrogen.     

Synthesis and characterization of seven-coordinate tripodal imidazole complexes of iron(II) and manganese(II)

The iron(II) and manganese(II) complexes of the N(7) Schiff-base condensate of tris(3-aminopropyl)amine with 1-methyl-2-imidazolecarbaldehyde and the manganese(II) complex of the N(7) Schiff-base condensate of tris(3-aminopropyl)amine with 4-imidazolecarbaldehyde are high-spin mono capped octahedral seven-coordinate complexes with a short, approximately 2.44 è, metal to apical nitrogen bond.     

Polymetallic complexes: Part XI,cobalt(II), nickel(II), copper(II), manganese(II), zinc(II), cadmium(II) and mercury(II) complexes with ON−NO tetradentate Schiff base,N,N'-bis(benzoin) benzidine

Summary The ON–NO donor Schiff base,N,N'-bis(benzoin)benzidine forms mono-, di- and tetra-nuclear complexes with metal cations. The cobalt(II) complex is a blue monomei of tetrahedral configuration. The nickel(II) and manganese(II) complexes are dimers and octahedral. A tetranuclear square planar chloro-bridged structure is proposed for the copper(II) complex. A dimeric pentacoordinated square pyramidal configuration is assigned to zinc(II) and a dinuclear tetrahedral stereochemistry is suggested for the cadmium(II) and mercury(II) complexes on the basis of analytical, conductance, magnetic susceptibility, molecular weight, i.r., electronic, d.t.g. and d.t.a. data.     

Synthesis and characterisation of nickel(II), cobalt(II), manganese(II), copper(II), zinc(II), dioxouranium(VI) and dioxomolybdenum(VI) complexes of tridentate dibasic ONO donor Schiff bases derived from 2-benzothiazolecarbohydrazide and salicylaldehyde/2-hydroxy-1-naphthaldehyde

Summary The syntheses of several new coordination complexes of nickel(II), cobalt(II), manganese(II), copper(II), zinc(II), dioxouranium(VI) and dioxomolybdenum(VI) with new Schiff bases derived from 2-benzothiazolecarbohydrazide and salicylaldehyde or 2-hydroxy-1-naphthaldehyde are described. These complexes have been characterised by elemental analyses, electrical conductance, magnetic susceptibility, molecular weight, i.r. and electronic spectra. The Schiff bases behave as dibasic and tridentate ligands coordinating through the ONO donor system and form complexes of the types NiL · 3H₂O, MnL · 2H₂O, CoL · 2H₂O, CuL, ZnL · H₂O, UO₂L · MeOH and MoO₂L · MeOH (where LH₂ = Schiff base). The copper(II) complexes exhibit subnormal magnetic moments indicating the presence of an antiferromagnetic exchange interaction, whereas the nickel(II), cobalt(II) and manganese(II) complexes behave normally at room temperature. Zinc(II), dioxouranium(VI) and dioxomolybdenum(VI) complexes are diamagnetic; the zinc (II) complexes are tetrahedral, the copper(II) complexes are square planar, all the other complexes are octahedral. Thev(C=N),v(C-O),v(N-N) andv(C-S) shifts have been measured in order to locate the Schiff base coordination sites.     

Copper(II) and nickel(II) complexes of 2-formylpyridine 3-piperidinyl-, 3-hexamethyleneiminyl- and 3-azabicyclo[3.2.2]nonylthiosemicarbazones

Summary Copper(II) and nickel(II) complexes of 2-formylpyridine 3-piperidinyl-, 3-hexamethyleneiminyl- and 3-azabicyclo-[3.2.2]nonylthiosemicarbazones were prepared and characterized spectroscopically. ¹H and ¹³C n.m.r. spectra of the thiosemicarbazones and a diamagnetic nickel(II) complex are reported, together with i.r., electronic and e.s.r. spectra of the metal complexes. The thiosemicarbazones and their copper(II) and nickel(II) complexes exhibit considerable growth inhibitory activity against Paecilomyces variotii, but show minimal activity against Aspergillus niger.     

Synthesis,magnetic and spectral studies of nickel(II) and zinc(II) complexes of 4-formylantipyrine N(4)-substituted thiosemicarbazones

The synthesis and characterization of nickel(II) and zinc-(II) complexes with 4-formylantipyrine N(4)-methyl-, N(4)-dimethyl- and 3-piperidylthiosemicarbazones are reported. Elemental analyses, molar conductivities, magnetic measurements and spectral (i.r., electronic and n.m.r.) studies have been used to characterize the complexes. The i.r. spectra show that the thiosemicarbazones behave as bidentate or tridentate ligands, either in the thione or thiolato form. Stereochemistries are proposed for the complexes on the basis of spectral and magnetic studies.     

Tuning the redox properties of manganese(II) and its implications to the electrochemistry of manganese and iron superoxide dismutases

Superoxide dismutases (SODs) catalyze the disproportionation of superoxide to dioxygen and hydrogen peroxide. The active metal sites of iron and manganese superoxide dismutases are structurally indistinguishable from each other. Despite the structural homology, these enzymes exhibit a high degree of metal selective activity suggesting subtle redox tuning of the active site. The redox tuning model, however, up to now has been challenged by the existence of so-called cambialistic SODs that function with either metal ion. We have prepared and investigated two sets of manganese complexes in which groups of varying electron-withdrawing character, as measured by their Hammett constants sigma Para, have been introduced into the ligands. We observed that the Mn(III)/Mn(II) reduction potential for the series based on 4'-X-terpyridine ligands together with the corresponding values for the iron-substituted 4'-X-terpyridine complexes changed linearly with sigma Para. The redox potential of the iron and manganese complexes could be varied by as much as 600 mV by the 4'-substitution with the manganese complexes being slightly more sensitive to the substitution than iron. The difference was such that in the case where the 4'-substituent was a pyrrolidine group both the manganese and the iron complex were thermodynamically competent to catalytically disproportionate superoxide, making this particular ligand "cambialistic". Taking our data and those available from the literature together, it was found that in addition to the electron-withdrawing capacity of the 4'-substituents the overall charge of the Mn(II) complexes plays a major role in tuning the redox potential, about 600 mV per charge unit. The ion selectivity in Mn and FeSODs and the occurrence of cambialistic SODs are discussed in view of these results. We conclude that the more distant electrostatic contributions may be the source of metal specific enzymatic activity.     

Tetranuclear manganese(II) complexes of thiacalixarene macrocycles with trigonal prismatic six-coordinate geometries: synthesis, structure, and magnetic properties

Two tetranuclear manganese(II) complexes [Mn(II)4(thiaS)2] (1) and [Mn(II)4(thiaSO)2] (2) have been synthesized under solvothermal conditions in methanol with p-tert-butylthiacalix[4]arene (thiaS) and p-tert-butylsulfinylthiacalix[4]arene (thiaSO). For both complexes, the structure has been established from single-crystal X-ray diffraction. [Mn4(thiaS)2].H2O (1) crystallizes in the orthorhombic Immm (No. 71) space group with the following parameters: a = 18.213 (5) angstroms, b = 19.037 (5) angstroms, c = 29.159 (5) angstroms, V = 10110 (4) angstroms3, and Z = 4. [Mn4(thiaSO)2].H2O (2) crystallizes in the monoclinic C2/m (No. 12) space group with the following parameters: a = 33.046(1) angstroms, b = 19.5363 (8) angstroms, c = 15.7773 (9) angstroms, beta = 115.176 (2) degrees, V = 9218.3 (8) angstroms3, and Z = 4. The two complexes are neutral and are best described as manganese squares sandwiched between two thiacalixarene macrocycles. In both complexes, each manganese center is six-coordinated in a trigonal prismatic geometry with four phenoxo oxygen atoms plus two sulfur atoms for 1 or two oxygen atoms from SO groups for 2. The two tetranuclear complexes exhibit identical magnetic behaviors resulting from antiferromagnetic interactions between the four manganese centers. The simulation of the magnetic susceptibility was done considering a single exchange-coupling constant between the manganese(II) ions, J (H = -J(S1S2 + S2S3 + S3S4 + S1S4)). The best fits give the same result for the two complexes: g = 1.94 and J = -5.57 cm(-1).     

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.     

Biochemical aspects and structural characterization of sulphur bonded oxovanadium(V) and manganese(II) complexes

Summary The preparation, characterisation and biological activities of some oxovanadium(V) and manganese(II) complexes of ligands having nitrogen-sulphur donor sets are described. Reaction of VOCl₃ and MnCl₂ with HTSCZ (HTSCZ = thiosemicarbazone) resulted in the formation of complexes of the type [VOCl₂(TSCZ)], [MnCl(TSCZ)H₂O], [VOCl(TSCZ)₂] and [Mn(TSCZ)₂]. These have been characterized by elemental analyses, molecular weight determinations and conductivity measurements and found to be monomeric and nonelectrolytes. Distorted trigonal bipyramidal (11) and octahedral (12) geometries for the vanadium(V) complexes and a tetrahedral geometry for the manganese(II) complexes are proposed. All the free ligands and their complexes have been tested in vitro against a number of pathogenic fungi and bacteria and were found to possess good fungicidal and bactericidal properties.     

A new binucleating ligand incorporating four oxime groups and its copper(II), manganese(II) and cobalt(III) complexes

A new binucleating ligand incorporating four oxime groups, butane-2,3-dione O-[4-aminooxy-2,3-bis-(2-hydroxyimino-1-methyl-propylideneaminooxymethyl)-but-2-enyl]-dioxime, (H₄mto), has been synthesized and its dinuclear cobalt(III), copper(II), and homo- and hetero-tetranuclear copper(II)–manganese(II) complexes have been prepared and characterized by ¹H- and ¹³C-n.m.r., i.r., magnetic moments and mass spectral studies. Elemental analyses, stoichiometric and spectroscopic data indicate that the metal ions in the complexes are coordinated to the oxime nitrogen atoms (C=N) and the data support the proposed structure for H₄mto and its complexes. Moreover, dinuclear cobalt(III) and copper(II) complexes of H₄mto have a 2:1 metal:ligand ratio.