The preparation and electrochemistry of manganese(II) complexes of an unsaturated pentadentate macrocyclic ligand

The preparation of a series of six and seven coordinate manganese(II) complexes [Mn^(II)(L)X]⁺, and [Mn^(II)(L)X₂]^2? (X = halide, water, triphenylphosphine oxide, imidazole, 1-methyl imidazole and pyridine) incorporating the pentadentate planar macrocylic ligand L is described. Cyclic voltammetry of these complexes in acetonitrile each shows a reversible one-electron reduction wave near - 1.4 V vs a Ag/AgNO₃ reference electrode. Quantitative reduction of these complexes by controlled potential electrolysis at a platinum gauze at - 1.4 V yields the corresponding one-electron reduction products which have been shown by ESR spectroscopy to be manganese(II)-ligand radical species, the electron being thought to reside on the di-imino pyridine moiety of the macrocyclic ligand. No metal reduced species could be isolated even in the presence of π-acceptor ligands such as CO or phosphines.     

Pentanuclear Ba(II) complex of a macrocyclic ligand

We report here the first pentanuclear Ba(II) complex of a new tri-aza, tri-oxa macrocycle with two carboxymethyl "arms" pending from two N atoms, H2L2. The crystal structure corresponds to the formula [Ba5(H0.375L2)4(ClO4)(CH3CH2OH)(H2O)2](ClO4)2.5 x 9.5H2O and reveals the presence of four molecules of the ligand surrounding five Ba(II) ions, giving rise to an unusual structure with the metal ions inside a spherical organic cavity.     

Synthesis and catalase-like activity of a dimanganese(II) complex with a pentadentate L-prolin-based ligand

The preparation, spectroscopic properties, and catalase-like activity of the dimanganese(II) complex [Mn₂L(OAc)(H₂O)₂](H₂O)₂ (H₃L: 2,6-bis[(prolin-1-yl)methyl]4-t-butylphenol) are reported. The title compound was a suitable catalyst for the disproportionation of H₂O₂ into water and dioxygen under ambient conditions. Kinetic measurements resulted in the bimolecular rate law of d[O₂]/dt = k[H₂O₂][Mn₂L(OAc)(H₂O)₂](H₂O)₂].     

Synthesis and properties of iron(II) and manganese(II) complexes derived from a topologically constrained pentadentate ligand

The novel bicyclic pentadentate ligand 5-methyl-1,5,9,24,25-pentaazapentacyclo[7.7.7.5.5]pentacosane11,13,15,18(25),20,22-hexene (L1) has been synthesized. Because of its cross-bridged topology it exhibits a relatively rigid preorganized conformation especially appropriate to complex formation, as shown by the crystal structure of the monoprotonated ligand salt, HL1ClH2O [orthorhombic, P212121, a = 9.4405(5) A, b = 13.3617(5) A, c = 16.710(1) A]. The complexes of L1 with both iron(II) and manganese(II) have been characterized, including the crystal structures of [FeL1CH3CN][FeCL4] and [MnL1Cl][PF6] [monoclinic, P21/n, a = 10.0460(5) A, b = 19.237(9) A, c = 15.6254(8) A, beta = 95.97(2)degrees and a = 7.745(2) A, b = 22.786(4) A, c = 14.639(4) A, beta = 105.074(10)degrees respectively]. The manganese complex is high spin with mueff = 5.96 and theta = 2.5 +/- 0.8 cm(-1), indicating weak ferromagnetic interactions. The reactions of the complexes with tert-butyl hydroperoxide and hydrogen peroxide have been shown by ESR spectroscopy to produce the tert-butyl peroxyl and hydroperoxyl radicals, as evidenced by their spin adducts with the spin traps N,N-dimethyl-1-pyrroline-N-oxide and N-tert-butyl-phenyl-nitrone.     

Magnetic ordering in a mononuclear cobalt(II) complex containing a Schiff-base pentadentate ligand

A mononuclear cobalt(II) complex CoL5, containing the pentadentate O2N3 salen-type Schiff-base ligand H2L5=N,N[prime or minute]-bis(3-tert-butyl-2-hydroxy-5-methylbenzylidenyl)-1,7-diamino-4-methyl-4-azaheptane, exhibits magnetic ordering at 4 K as proven by ac magnetic susceptibility (both in- and out-of-phase), magnetization, field-cooled magnetization and zero-field cooled magnetization measurements.     

NMR studies on a palladium(II) complex containing an incompletely coordinated facultative pentadentate Schiff base ligand

Palladium(II) dichloride reacts with 1,10‐bis(2‐pyrrolyl)‐2,5,9‐triaza‐1,9‐decadiene to give a [Pd(C₁₅H₂₀N₅)]Cl complex in which the ligand is four‐coordinated, leaving one pyrrole group dangling. By using COSY, gHSQC, gHMBC connectivities and NOE experiments it has been concluded that one linkage isomer exists in DMSO solution, in spite of the fact that different sets of N atoms of potentially pentadentate ligand might be involved in coordination, and that the three chelate rings in the complex cation are arranged in a sequence: five‐membered, six‐membered, five‐membered which is different from that (5–5–6) found by x‐ray studies on the related [Ni(C₁₅H₂₀N₅)]Cl compound. NMR studies allowed an unambiguous assignment of all ¹H and ¹³C NMR resonances for the complex. Results of x‐ray structural analysis of [Pd(C₁₅H₂₀N₅)](CH₃COO)H₂O supported the five‐membered, six‐membered, five‐membered ring sequence in the [Pd(C₁₅H₂₀N₅)]⁺ complex cation and show an E (trans) orientation of the dangling pyrrole group with respect to the metal center. Copyright © 2002 John Wiley & Sons, Ltd.     

A copper(II) complex of a pentadentate ligand featuring large ferro- and antiferromagnetic interactions

A novel pentadentate ligand based on a 2,2'-bipyridine template and functionalized with two methylene bridged nitroxide arms provides mononuclear Cu(II) and Zn(II) complexes displaying a facial and meridional conformation, respectively; for Cu large intramolecular ferromagnetic (J/kB = +173 K) and antiferromagnetic (J'/kB = -170 K) exchange interactions are evidenced from magnetic measurements.     

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.     

Preparation and electrochemical behavior of a macrocyclic heterodinuclear FeIIICoIII complex

A new macrocyclic heterodinuclear Fe^IIICo^III complex, prepared by the condensation of 2,6-diformylpyridine N-oxide with 1,3-diaminopropane in the presence of FeCl₂.4H₂O and CoCl₂.6H₂O, and formulated as FeCoLCl₆.C₂H₅OH.8H₂O, was characterized by elemental analyses, IR and Mössbauer spectra and investigated electrochemically on an ultramicrodisk platinum electrode. The results show that the electrode reaction can be thought as a nearly reversible transfer process. The diffusion coefficient is 1.93×10^-6 m² s^-1 and E^o ̄ is −0.229V (versus s.c.e) and α=0.877. The average electron transfer rate constant k^o′ is 3.21×10^-3 cm s^-1.     

Synthesis of a novel macrocyclic dinuclear iron(III) complex and its electrochemical behaviour on an ultramicrodisc platinum electrode

A new macrocyclic dinuclear iron(III) complex, prepared by condensing 2,6-diformylpyridine N-oxide with 1,3-diaminopropane in the presence of FeCl2·4H2O, and formulated as Fe2LCl6C2H5OH·6H2O, was characterized by its elemental analyses, by i.r., Mo¨ssbauer and e.p.r. spectra, and was investigated electrochemically. The results show that two iron ions are situated in the same chemical environment in the compound and that the electrode reaction can be considered as a double electron-transfer process. The diffusion coefficient is 2.16×10–6 cm2 s–1 and E° –0.169 V (versus s.c.e.) and = 0.37. The average electron transfer rate constant ko is 2.8×10–3 cm s–1.     

Catecholase activity of a copper(II) complex with a macrocyclic ligand: unraveling catalytic mechanisms

We report the structure, properties and a mechanism for the catecholase activity of a tetranuclear carbonato-bridged copper(II) cluster with the macrocyclic ligand [22]pr4pz (9,22-dipropyl-1,4,9,14,17,22,27,28,29, 30-decaazapentacyclo[22.2.1.1(4,7).1(11,14). 1(17,20)]triacontane-5,7(28),11(29),12,18, 20(30),24(27),25-octaene). In this complex, two copper ions within a macrocyclic unit are bridged by a carbonate anion, which further connects two macrocyclic units together. Magnetic susceptibility studies have shown the existence of a ferromagnetic interaction between the two copper ions within one macrocyclic ring, and a weak antiferromagnetic interaction between the two neighboring copper ions of two different macrocyclic units. The tetranuclear complex was found to be the major compound present in solution at high concentration levels, but its dissociation into two dinuclear units occurs upon dilution. The dinuclear complex catalyzes the oxidation of 3,5-di-tert-butylcatechol to the respective quinone in methanol by two different pathways, one proceeding via the formation of semiquinone species with the subsequent production of dihydrogen peroxide as a byproduct, and another proceeding via the two-electron reduction of the dicopper(II) center by the substrate, with two molecules of quinone and one molecule of water generated per one catalytic cycle. The occurrence of the first pathway was, however, found to cease shortly after the beginning of the catalytic reaction. The influence of hydrogen peroxide and di-tert-butyl-o-benzoquinone on the catalytic mechanism has been investigated. The crystal structures of the free ligand and the reduced dicopper(I) complex, as well as the electrochemical properties of both the Cu(II) and the Cu(I) complexes are also reported.     

A new high-spin iron(III) complex with a pentadentate macrocyclic amidopyridine ligand: a change from slow single-ion paramagnetic relaxation to long-range antiferromagnetic order in a hydrogen-bonded network

A new, stable iron(III) complex with a pentadentate amide-containing macrocyclic ligand was prepared and fully characterized. The complex adopted a pentagonal-bipyramidal geometry, where an equatorial plane is occupied by the pyridine nitrogen, two deprotonated amide nitrogens, and two secondary amines from the macrocycle, and two axial positions are available for monodentate ligand (chloride anion or solvent molecule) coordination. The rigid, planar iron-amide building blocks are linked in a three-dimensional network via a system of hydrogen bonds, with the shortest Fe-Fe separation of 8.02 A. The coordination of strongly electron-donating, negatively charged deprotonated amide groups resulted in expected stabilization of a high oxidation state of iron (the redox potential of the Fe(III)L/Fe(II)L couple, -0.57 V vs SCE). In contrast to the majority of the iron complexes with polydentate amide ligands, the pentagonal-bipyramidal geometry of the macrocyclic complex described in this work affords a high-spin configuration of the central metal ion (room-temperature magnetic moment is 5.84 micro(beta)). Variable-temperature iron-57 M?ssbauer spectroscopy and ac and dc magnetization studies indicate slow paramagnetic relaxation and a crossover to long-range antiferromagnetic order at T < approximately 3.2 K.     

Minimal structural reorganisation in the electrochemical oxidation of a dinuclear, double helical Cu(I) complex of a triazine-based pentadentate ligand

A dicopper(I) double helicate oxidizes and rapidly reorganises to form a stable pentadentate dicopper(II) double helicate due to the proximity of pendant pyridyl rings as studied by electrochemical and structural analyses.     

A novel manganese(III)-peroxo complex bearing a proline-derived pentadentate aminobenzimidazole ligand

A novel nonheme manganese(III)-peroxo complex bearing a proline-derived pentadentate aminobenzimidazole ligand was synthesized and spectroscopically characterized, and its reactivity in aldehyde deformylation was investigated.     

双大环配体与铜双核配合物的合成、晶体结构和磁偶合性质

由新型双功能配体2,6-双(1,5,9-三氮杂环十二烷)-2,6-二甲基苯甲酸(L)与溴化铜在甲醇中反应得到新型铜双核配合物[Cu~2LBr~2]Br.3H~2O单晶。晶体结构分析表明:2个Cu(II)中心离子由配体L中的羧酸基团桥联;2个等价的Cu(II)中心离子均由双功能配体L的1,5,9-三氮杂环十二烷([12aneN~3)的3个氮原子和羧酸的1个氧原子及1个Br^-离子配位,并都处在三角双锥的配位环境中;分子内Cu...Cu双核间的距离为0.5884(6)nm。变温磁化率数据表明:在同一分子中的2个铜核之间存在反铁磁偶合作用(J=-22.49cm^-^1)。     

A spectroscopic and electrochemical study of some copper(II) tetraaza macrocyclic complexes

Infrared, electronic, electron spin resonance and d.c. polarographic data for some copper(II) tetraaza macrocyclic complexes, involving a novel cyclam type ligand, are reported and are interpreted in terms of the structure of the complexes and the influence ofJahn-Teller distortion effects and cation-anion interactions.

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Eine spektroskopische und elektrochemische Untersuchung einiger makrocyclischer Kupfer (II)-Komplexe

Zusammenfassung Es wird über Infrarot-, Elektronenanregungs-, Elektronenspinresonanz- und D.C. Polarographie-Daten einiger tetraaza-makrocyclischer Kupfer(II)-Komplexe einschließlich eines neuen Cyclam-Typs als Ligand berichtet. Die Befunde werden hinsichtlich der Strukturen der Komplexe, dem Einfluß vonJahn-Teller-Verdrillungseffekten und Kation-Anion-Wechselwirkungen interpretiert.

     

Crystal structure of a nickel(II) complex with the macrocyclic ligand 4-methyl-1,3,5,8,11,14-hexaazatricyclooctadecane

The crystal structure of the macrocyclic complex [Ni(PCHA)](ClO₄)₂ (II) (PCHA = 4-methyl-1,3,5,8,11,14-hexaazatricyclooctadecane) is described. In the presence of succinate acid, [Ni(PCHA)](ClO₄)₂ (II) is obtained by recrystallization of orange crystals of [Ni(PCHA)](ClO₄)₂ (I), whose structure has previously been identified. The [Ni(PCHA)](ClO₄)₂ (II)crystal belongs to the monoclinic P2(1)/c space group with a = 15.8561(3) ?, b = 9.4409(2) ?, c = 13.9297(2) ?, α = 90°, β = 94.8840(10)°, γ = 90°, M _r = 526.02, Z = 4, V = 2077.65(7) ?³. The structure is ionic with [Ni(L)]²⁺ and two perchlorate anions with a supermolecular interaction.     

Magnetic studied of a binuclear Cu(II) complex constructed from Cu(II) macrocyclic complex

A new binuclear copper(II) compound [(CuL)₂(Tpha)](ClO₄)₂ · 4H₂O (I), where L = 1,3,6,9,11,14-hexaazatricyclo[12.2.1.1^6,9]octadecane, Tpha = terephthalate dianion, has been constructed and structurally characterized by X-ray crystallography. Crystal analysis denotes that complex I crystallizes in the monoclinic system, space group P2₁/c with a = 11.115(2), b = 13.185(3), c = 16.184(3) Å and β = 105.68(3)°. Magnetic measurements confirm that I present an antiferromagnetic interaction between the paramagnetic ions.     

Spectroscopic, redox and magnetic properties of a tetraiminediphenolate iron(II) macrocyclic complex: a model compound for iron proteins

The title complex [Fe(II)(tidf-H2)(H2O)2](ClO4)2*H(2)O (tidf-H2 = tetraiminediphenolate ligand) has been prepared from a transmetallation reaction between [Mg2(tidf)](NO3)2*4H2O and an iron(II) salt in methanolic solutions under inert atmosphere conditions. It was characterized by analytical, magnetic and spectroscopic methods (Mossbauer, FTIR, UV-vis), by cyclic voltammetry as well as spectroelectrochemistry.