Redox chemistry of mononuclear manganese(II), binuclear manganese(III) and binuclear mixed manganese(II)-manganese(III) complexes with 3-aminopyrazine-2-carboxylate in dimethylsulphoxide

Summary Mn^II forms a yellow mononuclear species with the title ligand having a 12 stoichiometry and whose conditional stability constant is 8.9 × 10¹⁰ m ^–2. The c.v. of this complex shows an oxidation at +0.78V versus s.c.e. Controlled-potential electrolysis at +0.80V versus s.c.e. yields a binuclear species of Mn^III with a 12 metal:ligand stoichiometry.The addition of Mn^III(urea)₆(ClO₄)₃ to a solution of the ligand produces a mononuclear complex of Mn^III if the concentration of the metal ion is less than 1 mM. At higher concentrations a binuclear species is obtained. The latter is reduced in two steps, at +0.24 and –0.58 V versus s.c.e. Controlled-potential electrolysis at 0.0 V produces a dark green complex after the transfer of 0.5 equivalents of charge per mole of Mn. This binuclear L₂Mn^II-Mn^IIIL₂ mixed-valence complex can be obtained only by electrolysis of the binuclear L₂Mn^IIIMn^IIIL₂ species. Attempts to prepare the complex chemically were unsuccessful - the binuclear Mn^III species was obtained in every case.Author to whom all correspondence should be directed.     

Synthesis,crystal structure,and properties of a seven-coordinate manganese(II) complex formed with the tripodal tetradentate ligand tris (N -methylbenzimidazol-2-ylmethyl)amine and salicylate

A seven-coordinate manganese(II) complex with the tripod tetradentate ligand tris(N-methylbenzimidazol-2-ylmethyl)amine (Mentb), [Mn(Mentb)(salicylate)(DMF)](ClO₄) ? (DMF), was synthesized and characterized by elemental, electrical conductivity, infrared, and UV-Vis spectral measurements. The crystal structure of the complex has been determined by single-crystal X-ray diffraction. Mn^II is bonded to a Mentb, a salicylate and dimethylformamide through four nitrogens and three oxygens, resulting in seven-coordination. Cyclic voltammograms of the complex indicate a quasi-reversible Mn³⁺/Mn²⁺ couple. The X-band electron paramagnetic resonance spectrum exhibits a six-line manganese hyperfine pattern with g = 2, A = 93, confirming that the material is high-spin Mn(II).     

Chromium(III), manganese(II), iron(III), cobalt(II), nickel(II) and copper(II) complexes with a pentadentate, 15-membered new macrocyclic ligand

Complexes of Cr^III, Mn^II, Fe^III, Co^II, Ni^II and Cu^II containing a macrocyclic pentadentate nitrogen–sulphur donor ligand have been prepared via reaction of a pentadentate ligand (N₃S₂) with transition metal ions. The N₃S₂ ligand was prepared by [1 + 1] condensation of 2,6-diacetylpyridine with 1,2-di(o-aminophenylthio(ethane. The structures of the complexes have been elucidated by elemental analyses, molar conductance, magnetic susceptibility measurements, i.r., electronic and e.p.r. spectral studies. The complexes are of the high spin type and are six-coordinate.     

Structural studies on cadmium(II), cobalt(II), copper(II), nickel(II) and zinc(II) complexes of 1-malonyl-bis(4-phenylthiosemicarbazide)

Summary Several new complexes of the title ligand (H₂MPTS) with Co^II, Ni^II, Cu^II, and Cd^II have been prepared. Structural assignments of the complexes have been made based on elemental analysis, molar conductivity, magnetic moment and spectral (i.r.,¹H n.m.r., reflectance) studies. The compounds are non-conductors in dimethylsulphoxide. The neutral molecule is coordinated to the metal(II) sulphate as a bidentate ligandvia the two carbonyl groups. The ligand reacts with the metal(II) chlorides with the liberation of two hydrogen ions, behaving as a bianionic quadridentate (NONO) donor. Enolization is confirmed by the pH-titration of H₂ MPTS and its metal(II) complexes against NaOH. A distorted octahedral structure is proposed for the Cu^II complex, while a square planar structure is suggested for both Co^II and Ni^II complexes. The stoichiometry of the complexes formed in EtOH and buffer solutions, their apparent formation constants and the ranges for obedience to Beer's law are reported for Co^II, Ni^II and Cu^II ions. The ligand pK values are calculated. The antimicrobial activity of H₂ MPTS and its Co^II, Ni^II, Cu^II and Mn^II complexes is demonstrated.     

Coordinating behaviour of a new pyridylhydrazone; tris-complexes of manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) with 2-pyridylcarbaldehyde-N,N-dimethylhydrazone

Summary The preparation and characterization oftris-complexes of Mn^II, Co^II, Ni^II, Cu^II and Zn^II with a new pyridylhydrazone, 2-pyridylcarbaldehyde-N,N-dimethylhydrazone (pch), are described. In all the complexes pch behaves as a bidentate ligand binding through the pyridine and azomethyne nitrogen atoms. The complexes appear to be monomeric, high spin six-coordinate, and a distorted octahedral stereochemistry around the metal is suggested. The e.p.r. results for both Cu^II compounds indicate a mainly d_x ²–y² ground state with a static Jahn-Teller distortion, whilst for the Mn^II complex the e.p.r. data indicates a very low symmetry for the MnN₆ polyhedron.     

A water-soluble multisite ionophore ligand bearing pyridine and aminothiophenol functionality. Synthesis, spectroscopy and electrochemistry of its complexes, and peripheral reactivity of the (E,E)M (M = Ni) complex with Pd2+ and Ag+

The design, synthesis and coordination of a novel multisite vic-dioxime compound, LH₂, containing flexible pyridine substituents and aminophenylsulfanyl moieties on the periphery, facilitating solubility in water as pyridinium hydrochloride salt are described. LH₂ was prepared by the reaction between 2-(2-pyridylethylamino)-benzenethiol and (E,E)-dichloroglydioxime. Mononuclear [(E,E)M] (M=Ni^II, Cu^II, Co^II, Fe^II and Mn^II) and dinuclear uranyl (UO₂ ^II) complexes of LH₂ were isolated and characterized with metal:ligand ratios of 1:2 and 2:2, respectively. The reaction of Na₂PdCl₄·3H₂O and AgNO₃ in DMF with the mononuclear complex, (LH)₂Ni, resulted in the formation of the heterotrinuclear complexes [Pd₂Ni(LH)₂]Cl₄ and [Ag₂Ni(LH)₂](NO₃)₂. The complexes were characterized by elemental analysis, ¹H-n.m.r., u.v.--vis. spectroscopy, i.r., and MS (LSIMS). The redox properties of the complexes were studied by cyclic voltammetry.     

The molecular structure of high‐spin (S = ) manganese(II) phthalocyanine in tetrabutylammonium bromido(phthalocyaninato)manganese(II)

The title complex salt, (C₁₆H₃₆N)[MnBr(C₃₂H₁₆N₈)] or (TBA)[Mn^IIBr(Pc)] (TBA is tetrabutylammonium and Pc is phthalocyaninate), has been obtained as single crystals by the diffusion technique and its crystal structure was determined using X‐ray diffraction. The high‐spin (S = ) [Mn^IIBr(Pc)]⁻ macrocycle has a concave conformation, with an average equatorial Mn—N(Pc) bond length of 2.1187 (19) Å, an axial Mn—Br bond length of 2.5493 (7) Å and with the Mn^II cation displaced out of the 24‐atom Pc plane by 0.894 (2) Å. The geometry of the Mn^IIN₄ fragment in [Mn^IIBr(Pc)]⁻ is similar to that of the high‐spin (S = ) manganese(II) tetraphenylporphyrin (TPP) in [Mn^II(1‐MeIm)(TPP)] (1‐MeIm is 1‐methylimidazole).     

Ferrimagnetic Ordering and Anomalous Stoichiometry Observed for the Cubic,Extended 3D Prussian Blue Analogues (NEt3Me)2MnII5(CN)12 and (NEt2Me2)2MnII5(CN)12: A Cation-Adaptive Structure

The reactions of Mn^II(O₂CCH₃)₂ with NEt₃Me⁺CN⁻ and NEt₂Me₂⁺CN⁻ form (NEt₃Me)₂Mn^II₅(CN)₁₂ ( 1 ) and (NEt₂Me₂)₂Mn^II₅(CN)₁₂ ( 2 ), respectively. Structure model-building and Rietveld refinement of high-resolution synchrotron powder diffraction data revealed a cubic [a=24.0093 Å ( 1 ), 23.8804 Å ( 2 )] 3D extended structural motif with adjacent tetrahedral and octahedral Mn^II sites in a 3:2 ratio. Each tetrahedral Mn^II site is surrounded by four low-spin octahedral Mn^II sites, and each octahedral Mn^II site is surrounded by six high-spin tetrahedral Mn^II sites; adjacent sites are antiferromagnetically coupled in 3D. Compensation does not occur, and magnetic ordering as a ferrimagnet is observed at T_c=13 K for 2 based on the temperature at which remnant magnetization, M_r(T)→0. The hysteresis has an unusual constricted shape with inflection points around 50 and 1.2 kOe with a 5 K coercivity of 16 Oe and remnant magnetization, M_r, of 2050 emuOe mol⁻¹. The unusual structure and stoichiometry are attributed to the very ionic nature of the high-spin N-bonded Mn^II ion, which enables the maximization of the attractive van der Waals interactions through minimization of void space via a reduced ∠ MnNC. This results in an additional example of the A_xMn^II_y(CN)_x+2y (x=0, y=1; x=1, y=3; x=2, y=1; x=2, y=2; x=2, y=3; x=3, y=5; and x=4, y=1) family of compounds possessing an unprecedented stoichiometry and lattice motif that are cation adaptive structured materials.     

Chelated complexes of cadmium(II), cobalt(II), copper(II), mercury(II), nickel(II), uranyl(II) and zinc(II) with benzil bis(4-phenylthiosemicarbazone)

Summary Complexes of Co^II, Ni^II, Cu^II, Zn^II, Cd^II, Hg^II and UO ₂ ^II with benzil bis(4-phenylthiosemicarbazone), H₂BPT, have been synthesized and their structures assigned based on elemental analysis, molar conductivity, magnetic susceptibility and spectroscopic measurements. The i.r. spectra suggest that the ligand behaves as a binegative quadridentate (NSSN) (Co^II, Cu^II, Hg^II and UO ₂ ^II complexes) or as a binegative quadridentate-neutral bidentate chelating agent (Ni^II, Zn^II and Cd^II complexes). Octahedral structures for the Co^II and Ni^II complexes and square-planar structure for the Cu^II complex are suggested on the basis of magnetic and spectral evidence. The crystal field parameters (Dq, B and _B) for the Co^II complex are calculated and agree fairly well with the values reported for known octahedral complexes. The ligand can be used for the microdetermination of Ni^II ions of concentration in the 0.4–6×10^–4 mol l^–1 range and the apparent formation constant for the species generated in solution has also been calculated.     

N-benzamidosalicylaldimine complexes of copper(II), nickel(II), cobalt(II), iron(II), manganese(II), oxyvanadium(IV) and oxytitanium(IV)

Summary N-benzamidosalicylaldimine (H₂L) complexes of Cu^II, Ni^II, Co^II, Fe^II, Mn^II. VO_IV and TiO_IV have been prepared. The ligand probably coordinates to the metal from the hydroxyl, carbonyl and imino groups.     

Synthesis and characterization of novel (<Emphasis Type="Italic">E</Emphasis>,<Emphasis Type="Italic">E</Emphasis>)-dioxime and its mono- and polynuclear metal complexes containing azacrown moieties

The novel (E,E)-dioxime,7,8-bis(hydroxyimino)-1,14-bis(monoaza[8]crown-6)-benzo[f]-4,11-dioxa-1,14-diazadecane[7,8-g]quinoxaline (H₂L), has been synthesized by the reaction of 6,7-diamino-1,12-bis(monoaza[18]crown-6)benzo[f]-4,9-dioxa-1,12-diazadecane (4) which has been prepared by the reduction of 6,7-dinitro-1,12-bis(mono-aza[18]crown-6)benzo[f]-4,9-dioxa-1,12-diazdecane (3) and cyanogendi-N-oxide. Mononuclear Ni^II and Cu^II complexes of H₂L have a metal:ligand ratio of 1:2 and the ligand coordinates through two hydroxyimino nitrogen atoms, as do most of the (E,E)-dioximes. The hydrogen-bridged Ni^II complex was converted into its BF ₂ ⁺ capped anologue by the reaction with BF₃ · Et₂O. The reaction of the Cu^II complex with 2,2′-dipyridyl as an end-cap ligand gave the homotrinuclear complex. Structures for the ligand and its complexes are proposed in accordance with elemental analysis, magnetic susceptibility measurements, ¹H, ¹³C-n.m.r, IR and MS spectral data.     

Thermal decomposition of dinuclear complexes LM(μ-OOCR)<Subscript>4</Subscript>ML (L is α-substituted pyridine)

The solid-state thermal decomposition of the tetrabridged dinuclear Mn^II, Fe^II, Co^II, Ni^II, and Cu^II pivalate complexes with apical α-substituted pyridine ligands containing different substituents (2,3-dimethylpyridine or quinoline) was studied by differential scanning calorimetry and thermogravimetry. The decomposition of the Co^II complexes is accompanied by the aggregation to form the volatile octanuclear complex Co₈(μ₄-O)₂(μ_n-OOCCMe₃)₁₂, where n = 2 or 3, whereas the thermolysis of the Mn^II, Fe^II, Ni^II, and Cu^II complexes is accompanied by the degradation of the starting compounds, the phase composition of the decomposition products being substantially dependent on the nature of metal and the apical organic ligand. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1650–1659, September, 2007.     

A novel bridged asymmetric binuclear manganese(II) complex with DTPB [DTPB is 1,1,4,7,7‐pentakis(1H‐benz­imidazol‐2‐yl­methyl)‐1,4,7‐tri­aza­heptane]

The crystal structure of the title compound, tetra­chloro­[μ‐1,1,4,7,7‐pentakis(1H‐benzimidazol‐2‐yl­methyl)‐1,4,7‐tri­azaheptane]­dimanganese(II) methanol pentasolvate tetrahydrate, [Mn₂Cl₄(C₄₄H₄₃N₁₃)]·5CH₄O·4H₂O, contains an ­asymmetric dinuclear Mn^II–DTPB [DTPB is 1,1,4,7,7‐pentakis(1H‐benzimidazol‐2‐yl­methyl)‐1,4,7‐tri­aza­heptane] complex with an intra‐ligand bridging group (–NCH₂CH₂N–), as well as several solvate mol­ecules (methanol and water). Both Mn^II cations have similar distorted octahedral coordination geometries. One Mn^II cation is coordinated by a Cl⁻ anion and five N atoms from the ligand, and the other is coordinated by three Cl⁻ anions and three N atoms of the same ligand. The Mn⋯Mn distance is 7.94 Å. A Cl⋯H—O⋯H—O⋯H—N hydrogen‐bond chain is also observed, connecting the two parts of the complex.     

catena‐Poly[[aqua­bis(1H‐benzimidazole‐κN3)manganese(II)]‐μ‐adipato]

In the title polymeric complex, [Mn(C₆H₈O₄)(C₇H₆N₂)₂(H₂O)]_n, the Mn^II atom is surrounded by two adipate dianions, two benzimidazole mol­ecules and one coordinated water mol­ecule. The Mn atoms and coordinated water mol­ecule are located on a twofold axis, and the bridging adipate ligand is located on an inversion center. The adipate dianions bridge neighboring Mn^II atoms to form polymeric chains. Each Mn^II atom is seven‐coordinate, the longest Mn—O bond length being 2.5356 (16) Å.     

Isomorphous Catena Transition Metal Squarates [MII(C4O4)(dmso)2(OH2)2] (M = Co,Mn) and Magnetic Investigation into their Solid Solution M = CoxMn1–x

The crystal structures of two new isomorphous transition metal squarato complexes [M^II(C₄O₄)(dmso)₂(OH₂)₂] [M^II = Co^II (3d⁷), Mn^II (3d⁵); dmso = dimethylsulfoxide] and their magnetic properties are reported. The compounds feature two symmetrically independent chains, in which 1,3‐bridging squarato ligands connect cations in distorted octahedral surroundings of pseudo‐symmetry D_4h. From an equimolar solution of CoCl₂ · 6H₂O and MnCl₂ · 2H₂O a mixed‐metal coordination polymer crystallizes; it represents a solid solution and adopts the same structure as the corresponding monometallic compounds. The results of the diffraction experiment unambiguously proof the presence of both Co^II and Mn^II cations in either independent site albeit no precise ratio between the metal cations involved may be deduced from these findings. The difference in the magnetic properties between Co^II and Mn^II cations in the given ligand field has allowed us to establish their ratio in the solid solution more reliably than by X‐ray diffraction: Accounting for ligand field potential and spin‐orbit coupling of Co^II and regarding Mn^II as a pure spin system, the calculations yielded a fraction of 73 % Co^II in the mixed‐metal polymer. With respect to superexchange effects only weak antiferromagnetic interactions have been detected for the three coordination polymers.     

Synthesis,characterization, electrochemistry and kinetics of CTDNA binding of a bis ciprofloxacin borate copper(II) complex

A new boroderivative of ciprofloxacin and its Cu^II complex has been synthesized and characterized by elemental analysis, i.r., e.p.r., u.v.–vis., n.m.r. spectroscopy. Molar conductance measurements show that the complex is ionic. E.p.r. values and electronic spectral data suggest that it possesses square planar geometry. The reaction kinetics of the ligand K[C₃₄H₃₆N₆O₆F₂B] and its Cu^II complex with calf thymus DNA (CTDNA) has been monitored spectrophotometrically in aqueous media. The K _obs value has been calculated under pseudo-first order conditions and it has been observed that the Cu^II complex is a more efficient DNA inhibitor than the free borate of ciprofloxacin. The redox behavior of the Cu^II complex in the presence and in the absence of CTDNA in aqueous solution has been investigated by cyclic voltammetry. The cyclic voltammogram of the Cu^II complex exhibits one quasireversible redox wave for a one-electron transfer corresponding to Cu^II/Cu^I redox couple with E _1/2 values –0.613 and –0.649 V respectively. On interaction with CTDNA, the Cu^II complex exhibits a shift in E _1/2 values corresponding to 0.013 and 0.035 V respectively.     

Electron transfer reaction in the chromium(VI)-manganese(II) system in the presence of ethylenediaminetetraacetic acid (EDTA)

Upon addition of Cr ^VI to a solution of ethylenediaminetetraacetic acid (EDTA) and Mn ^II, a transient species appears which has an absorption maximum at 500 nm. Kinetic studies of the outer-sphere oxidation of the Mn ^II-EDTA complex with the Cr ^VI-EDTA complex have been investigated by visible spectrophotometry at 25 °C. The formation of a transient species has been characterized spectrophotometrically and the encounter complex formation constants have been determined (K_OS = 1.75 × 10² and 1.66 × 10³ mol^-2 dm⁶ for [EDTA] and [Mn^II] variations, respectively). The effect of total [EDTA], [Mn^II], [Cr ^VI] and [HClO₄] on the rate of the reaction was determined. On addition of HClO₄, there is a decrease in the rate constants. The reaction product is the Cr^III-EDTA complex with λ_max = 400 and 550 nm. On the basis of the various observations and product characterization a most plausible outer-sphere mechanism has been envisaged.     

Mononuclear Manganese–Peroxo and Bis(μ‐oxo)dimanganese Complexes Bearing a Common N‐Methylated Macrocyclic Ligand

Mononuclear Mn^III–peroxo and dinuclear bis(μ‐oxo)Mn^III₂ complexes that bear a common macrocyclic ligand were synthesized by controlling the concentration of the starting Mn^II complex in the reaction of H₂O₂ (i.e., a Mn^III–peroxo complex at a low concentration (≤1 mM ) and a bis(μ‐oxo)Mn^III₂ complex at a high concentration (≥30 mM )). These intermediates were successfully characterized by various physicochemical methods such as UV–visible spectroscopy, ESI‐MS, resonance Raman, and X‐ray analysis. The structural and spectroscopic characterization combined with density functional theory (DFT) calculations demonstrated unambiguously that the peroxo ligand is bound in a side‐on fashion in the Mn^III–peroxo complex and the Mn₂O₂ diamond core is in the bis(μ‐oxo)Mn^III₂ complex. The reactivity of these intermediates was investigated in electrophilic and nucleophilic reactions, in which only the Mn^III–peroxo complex showed a nucleophilic reactivity in the deformylation of aldehydes.     

Structural and Magnetic Insights into the Trinuclear Ferrocenophane and Unexpected Hydrido Inverse Crown Products of Alkali‐Metal‐Mediated Manganation(II) of Ferrocene

With the aim of introducing the diisopropylamide [NiPr₂] ^? ligand to alkali‐metal‐mediated manganation (AMMMn) chemistry, the temperature‐dependent reactions of a 1:1:3 mixture of butylsodium, bis(trimethylsilylmethyl)manganese(II), and diisopropylamine with ferrocene in hexane/toluene have been investigated. Performed at reflux temperature, the reaction affords the surprising, ferrocene‐free, hydrido product [Na₂Mn₂ (μ‐H)₂{N(iPr)₂}₄]?2 toluene ( 1 ), the first Mn hydrido inverse crown complex. Repeating the reaction rationally, excluding ferrocene, produces 1 in an isolated crystalline yield of 62 %. At lower temperatures, the same bimetallic amide mixture leads to the manganation of ferrocene to generate the first trimanganese, trinuclear ferrocenophane, [{Fe(C₅H₄)₂}₃{Mn₃Na₂(NiPr₂)₂ (HNiPr₂)₂}] ( 2 ) in an isolated crystalline yield of 81 %. Both 1 and 2 have been characterised by X‐ray crystallographic studies. The magnetic properties of paramagnetic 1 and 2 have also been examined by variable‐temperature magnetisation measurements on powdered samples. For 1 , the room‐temperature value for χT is 3.45 cm³ K mol^?1, and on lowering the temperature a strong antiferromagnetic coupling between the two Mn ions is observed. For 2 , the room‐temperature value for χT is 4.06 cm³ K mol^?1, which is significantly lower than the expected value for three isolated paramagnetic Mn^II ions.