Zur Koordinationschemie von cis-Trioxowolfram(VI)-Komplexen. Die Kristallstrukturen von LWO3 · 3 H2O, [L′WO2(OH)]Br, [LWO2Br]Br, [L2W2O5](S2O6) · 4 H2O und [LWO2(μ-O)WO(O2)2(OH2)] (L = 1,4,7-Triazacyclononan; L′ = 1,4,7-Trimethyl-1,4,7-triazacyclononan)

Coordination-chemistry of cis-Trioxotungsten(VI) Complexes. Crystal Structures of LWO₃ · 3 H₂O, [L′WO₂(OH)]Br, [LWO₂Br]Br, [L₂W₂O₅](S₂O₆) · 4 H₂O and [LWO₂(μ-O)WO(O₂)₂(OH₂)] (L = 1,4,7-Triazacyclonane; L′ = 1,4,7-Trimethyl-1,4,7-triazacyclononane) The cyclic triamines 1,4,7-triazacyclononane (L; C₆H₁₅N₃) and 1,4,7-trimethyl-1,4,7-triazacyclononane (L′; C₉H₂₁N₃) react in aqueous solution with WO₃ affording LWO₃ · 3 H₂O, 1 , and L′WO₃ · 3 H₂O, respectively, which yield [L′WO₂(OH)]Br, 2 , and [LWO₂Br]Br, 3 , in concentrated HBr solutions. In aqueous CH₃SO₃H solution 1 dimerizes. The iodide and dithionate 4 salts of [L₂W₂O₅]²⁺ have been isolated. In 35% H₂O₂ complex 1 yields the neutral species [LWO₂(μ-O)WO(O₂)₂(H₂O)] 5 . The crystal structures of 1 – 5 have been determined by X-ray analysis. Crystal data: 1 : P2₁/c; a = 7.729(2), b = 14.887(3), c = 10.774(2) Å, β = 90.77(2)°, Z = 4; 2 : Cc; 8.910(3), b = 12.220(6), c = 13.279(6) Å, β = 101.31(3)°, Z = 4; 3 : Cmc2₁, a = 8.857(5), b = 12.062(7), c = 11.218(7) Å, Z = 4; 4 : Cc, a = 17.601(7), b = 12.906(7), c = 14.107(8) Å, β = 124.08(4)°, Z = 4; 5 : P2₁2₁2₁; a = 8.452(4), b = 11.301(6), c = 13.750(6) Å, Z = 4.     

Tetranuclear Zn(II) complexes with compartmental and dicyanamido ligands: synthesis,structure, and luminescent properties

New tetranuclear compounds have been obtained by reacting binuclear complexes, [Zn₂L ⁿ (μ-OH)(H₂O)₂](ClO₄)₂, with sodium dicyanamide (HL ⁿ are end-off bicompartmental ligands resulting from condensation between 2,6-diformyl-p-cresol with N,N-dimethyl-ethylenediamine or 2-aminomethyl-pyridine). The complexes, [{L¹(μ-OH)Zn₂}(μ _1,5-dca)₂{Zn₂(μ-OH)L¹}](ClO₄)₂ (1) and [{Zn₂L²(μ ₃-OH)(dca)}₂](ClO₄)₂?·?2H₂O (2), have been characterized by single-crystal X-ray diffraction. The angular nature of the bridging dicyanamido induces the “M” shape of the tetranuclear cationic unit in 1. The tetranuclear cation, because of its particular shape, acts as a receptor toward one perchlorate ion, which is hydrogen bonded to the hydroxo groups. This tetranuclear unit in 2 has a defective heterocubane structure. The luminescence properties of the new tetranuclear complexes have been investigated.     

Coordination compounds of cobalt(II), nickel(II), and copper(II) with 4-(3-hydroxyphenyl)-1,2,4-triazole: Synthesis and study

New Co(II), Ni(II), and Cu(II) complexes with 4-(3-hydroxyphenyl)-1,2,4-triazole (L) with the compositions [Co₃L₆(H₂O)₅(C₂H₅OH)](NO₃)₆ · 2H₂O · C₂H₅OH (I), [Ni₃L₆(H₂O)₆](NO₃)₆ · 2H₂O (II), and [M₃L₆(H₂O)₆](ClO₄)₆ · nH₂O (M = Co2⁺, n = 2 (III); Ni²⁺, n = 2 (IV); Cu²⁺, n = 0 (V)) are synthesized. The complexes are studied by X-ray structure analysis, X-ray diffraction analysis, UV and IR spectroscopy, and the statistical magnetic susceptibility method. All compounds have the linear trinuclear structure. Ligand L is coordinated to the metal ions by the N(1) and N(2) atoms of the heterocycle according to the bidentate bridging mode. In all compounds the coordination polyhedron of the metal atom is a distorted octahedron. The molecular and crystal structures of compound I, [Co₃L₆(H₂O)₆](ClO₄)₆ · 8C₂H₅OH (IIIa), and [Ni₃L₆(H₂O)₆](ClO₄)₆ · 8C₂H₅OH (IVa) are determined.     

μ-Nitro-μ-hydroxo-bis(tetramminkobalt(III))-Komplexe

The preparation and the properties of 7 salts containing the complex cation [Co₂{NO₂, OH}(NH₃)₈]⁴⁺ are described. Furthermore, a di-μ-hydroxo complex of the composition [Co₂{OH}₂NO₂(NH₃)₇](ClO₄)₃ · H₂O has been prepared.     

Copper(II), Cobalt(II), and Nickel(II) Complexes of two Novel Pyridine‐derived Macrocyclic Ligands bearing o‐ and pNitrobenzyl Pendant Groups

The pendant‐armed ligands L¹ and L² were synthesized by N‐alkylation of the four secondary amine groups of the macrocyclic precursor L using o‐nitrobenzylbromide (L¹) and p‐nitrobenzylbromide (L²). Nitrates and perchlorates of Cu^II, Ni^II and Co^II were used to synthesize the metal complexes of both ligands and the complexes were characterized by microanalysis, MS‐FAB, conductivity measurements, IR and UV‐Vis spectroscopy and magnetic studies. The crystal structures of L¹, [CuL¹](ClO₄)₂·CH₃CN·H₂O, [CuL²](ClO₄)₂·6CH₃CN, [CuL²][Cu(NO₃)₄]·5CH₃CN·0.5CH₃OH and [NiL²](ClO₄)₂·3CH₃CN·H₂O were determined by single crystal X‐ray crystallography. These structural analysis reveal the free ligand L¹, three mononuclear endomacrocyclic complexes {[CuL¹](ClO₄)₂·CH₃CN·H₂O, [CuL²](ClO₄)₂·6CH₃CN and [NiL²](ClO₄)₂·3CH₃CN·H₂O} and one binuclear complex {[CuL²][Cu(NO₃)₄]·5CH₃CN·0.5CH₃OH} in which one of the metals is in the macrocyclic framework and the other metal is outside the ligand cavity and coordinated to four nitrate ions.     

Mehrkernige Kobaltkomplexe. V. Präparative Herstellung von Tetrakis (äthylendiamin)-μ-peroxo-μ-amido- und μ-peroxo-μ-thiocyanatodikobalt (III)-Komplexen ausgehend von Tetrakis (äthylendiamin)bis-(ammin)-μ-peroxo-dikobalt (III)-tetraperchlorat

Polynuclear Cobalt Complexes. V. Preparation of tetrakis (ethylenediamine)-μ-peroxo-μ-amido and μ-peroxo-μ-thiocyanato-dicobalt (III) complexes starting from tetrakis (ethylenediamine)bis-(ammine)-μ-peroxo-dicobalt (III)-tetraperchlorate Racemic tetrakis (ethylenediamine)-μ-peroxo-μ-amido-dicobalt (III) thiocyanate and its corresponding hydroperoxo- and superoxo-complexes have been isolated from [(en)₂(NH₃)Co(O₂)(NH₃)(en)₂](ClO₄)₄. A new binuclear peroxo complex containing thiocyanate as bridging ligand was prepared by the same method. The stretching frequencies of the CN- and CS-group as well as the NCS-bending frequence in the IR. spectrum of [(en)₂Co(O₂, SCN)Co(en)₂](NO₃)₃ suggest that the μ-thiocyanato group is N-bonded (2050, 750, 475 cm^?1). A comparison of IR. spectra of known singly and doubly bridged μ-peroxo complexes is made. Characteristic absorption bands, assignable to ν(O? O) and ν(Co? O) are given.     

Triaquatris(μ‐oxydiacetato)dipraseodymium(III) pentahydrate and hexaaquatris(μ‐oxydiacetato)dineodymium(III) oxydiacetic acid solvate dihydrate

Two new complexes of the Ln₂(oda)₃·nH₂O (oda =–O₂CCH₂OCH₂CO₂–) series are reported, i.e. {[Pr₂(C₄H₄O₅)₃(H₂O)₃]·5H₂O}_n and {[Nd₂(C₄H₄O₅)₃(H₂O)₆]·C₄H₆O₅·‐2H₂O}_n. The former is isostructural with the reported La analogue, while the latter is a new structural variety within the series. Each compound exhibits two independent nine‐coordinated Ln centres showing a variety of coordination geometries.     

Komplexe des Chroms mit 1,5,9-Triazacyclododecan: Darstellung,Magnetismus und Kristallstruktur von Tri-μ-hydroxo-bis[(1,5,9-triazacyclododecan)chrom(III)] tribromid Dihydrat; Kinetik und Mechanismus der Brückenspaltung mit Hydroxidionen

Complexes of Chromium Containing 1,5,9-Triazacyclododecane: Synthesis, Magnetism, and Crystal Structure of Tri-μ-hydroxo-bis[(1,5,9-triazacyclododecane) chromium (III)] tribromide · Dihydrate; Kinetic and Mechanism of its Bridge-cleavage with Hydroxide The oxidative decarbonylation of LCr(CO)₃ (L = 1,5,9-triazacyclododecane) with bromine yields green LCrBr₃. Base hydrolysis affords red [LCr(μ-OH)₃CrL]³⁺, whereas in the presence of acetate ions [L₂Cr₂(μ-OH)₂(CH₃CO₂)]³⁺ is formed. [LCr(μ-OH)₃CrL]Br₃· 2 H₂O crystallizes in the orthorhombic space group P2₁2₁2₁ with 8 formula units per unit cell. Two Cr^III centers are connected via three OH^? bridges; the spins of d³-electronic configuration are coupled intramolecularly, antiferromagnetically (2J = ?96 cm^?1). With excess OH^? but not with protons the tri-μ-hydroxo species is cleaved to give [L₂Cr₂(OH)₂(μ-OH)₂]²⁺. The kinetics of this reaction have been measured using the stopped flow technique. The mechanism is discussed.     

Three polynuclear complexes with bridging triazole ligand: crystal structures

Three polynuclear clusters, [Cu₄L₈](ClO₄)₄·4H₂O (1), [Zn₃L₆(H₂O)₆](ClO₄)₆·6H₂O (2), and [Mn₃L₆(CH₃OH)₆](ClO₄)₆·4.5H₂O (3) (L?=?4-(4-hydroxyphenyl)-1,2,4-triazole), obtained by the reactions of M(ClO₄)₂·6H₂O with L have been isolated and structurally characterized. Complex 1 featured a tetranuclear Cu(I) structure. Both 2 and 3 are linear hexapositive trimers linked by three N1,N2–1,2,4-triazole ligands to the divalent central and terminal metal ions. Furthermore, the luminescence properties of 2 were investigated at room temperature in the solid state.     

Die Kristall- und Molekülstruktur von μ-5-Pyrimidincarboxylato (O,O′)-di-μ-hydroxo-bis[triamminkobalt(III)]perchlorat

Crystal and Molecular Structure of μ-5-Pyrimidinecarboxylato(O,O′)-di-μ-hydroxo-bis-[triamminecobalt(III)]perchlorate μ-5-Pyrimidinecarboxylato(O,O′)-di-[μ-hydroxo-bis(triamminecobalt)(III)]perchlorate, [(NH₃)₃Co-μ(OH, OH, C₅H₄N₂O₂)Co(NH₃)₃](ClO₄)₄, crystallizes in the orthorhombic space group Ibca with a = 12.686, b = 13.079, c = 31.785 Å and Z = 8 formula units. The complex cation adopts C₂ symmetry, but no mirror plane is present. The Co? Co separation in the binuclear complex is 2.794 Å. The four-membered ring defined by the two Co atoms and the bridging oxygens is folded along the O? O axis, the interplanar angle being 154°. One of the ClO₄ tetrahedra is disordered over two sites in the crystal.     

Synthesis and Crystal Structures of Bis(1‐{(E)‐2‐pyridinylmethylidene}‐semicarbazone)iron(II) and ‐copper(II) Diperchlorate Monohydrates

The pyridine‐2‐carbaldehyde semicarbazone ligand (HL) reacts with iron(II) and copper(II) perchlorates in boiling ethanol to yield red‐violet [Fe^II(HL)₂](ClO₄)₂·H₂O ( 1 ) and light‐green crystals [Cu^II(HL)₂](ClO₄)₂·H₂O ( 2 ). The crystals are triclinic with the metal ions in an octahedral environment, coordinated to two nitrogen and one oxygen‐donor atom from HL. Electronic, magnetic and electrochemical properties are presented as well.     

Complexes of Co(II), Ni(II), and Cu(II) with 4-(3,4-dichlorophenyl)-1,2,4-triazole

Novel oligonuclear complexes of Co(II), Ni(II), and Cu(II) with 4-(3,4-dichlorophenyl)-1,2,4-triazole (L) of the composition [M₃L₁₀(H₂O)₂](NO₃)₆ (M = Co(II), Ni(II)), [Ni₃L₆(H₂O)₆]Hal₆ (Hal = Cl^?, Br^?), and [Cu₅L₁₆(H₂O)₂](NO₃)₁₀ · 2H₂O were synthesized and studied by magnetic susceptibility, electronic and IR spectroscopy, and powder X-ray diffraction methods. All the above complexes are X-ray amorphous. Antifer-romagnetic exchange interactions between the M²⁺ ions were discovered in the [Co₃L₁₀(H₂O)₂](NO₃)₆ and [Ni₃L₁₀(H₂O)₂](NO₃)₆ complexes, whereas ferromagnetic exchange interactions were observed in the complexes [Ni₃L₆(H₂O)₆]Cl₆, [Ni₃L₆(H₂O)₆]Br₆, and [Cu₅L₁₆(H₂O)₂](NO₃)₁₀ · 2H₂O.     

A cyclic tetramer of [Ag(1,4,7‐trithiacyclononane)]+, cyclo‐tetrakis(μ‐1,4,7‐trithiacyclononane‐κ3S1,S4,S7:κS1)tetrasilver(I) tetrakis(trifluoromethanesulfonate) nitromethane disolvate

(1,4,7‐Tri­thia­cyclo­nonane)silver tri­fluoro­methane­sulfonate crystallizes in a tetrameric form from nitro­methane, to give the title compound, [Ag₄(C₆H₁₂S₃)₄](CF₃SO₃)₄·2CH₃NO₂. The complex cation consists of four [AgL]⁺ units (L is 1,4,7‐tri­thia­cyclo­nonane), with four Ag—S—Ag bridges forming a cyclic tetramer. The almost planar Ag₄S₄ ring takes an octagonal form.     

Kronenthioetherkomplexe des Blei(II), Zink(II) und Cadmium (II) und Cadmium(II). Die Kristallstrukturen von [PbL2(ClO4)2] und [ZnL2](ClO4)2 · CH3CN (L = 1,4,7 - Trithiacyclononan)

Crown Thioether Complexes of Lead (II), Zinc(II), and Cadmium (II). Crystal Structures of [PbL₂(ClO₄)₂] and [ZnL₂](ClO₄)₂ · CH₃CN (L = 1,4,7 - Trithiacyclononane) The reaction of 1,4,7-trithiacyclononane (L) with the perchlorate salts of lead(II) and zinc(II) in CH₃CN (2:1) affords colorless crystals of [PbL₂(ClO₄)₂] and [ZnL₂](ClO₄)₂ · CH₃CN, respectively, The crystal structures have been determined. The Pb^II centre is coordinated to six sulfur atoms (the average distance Pb? S is 3.076 Å) and two oxygen atoms, one of each ClO₄^? anion (monodentate ClO₄^?). A distorted square antiprismatic polyhedron is thus generated. In [ZnL₂](ClO₄)₂ · CH₃CN the zinc(II) centre is octahedrally surrounded by six sulphur atoms (average distance Zn? S = 2.494 Å); the ClO₄^? anions are not coordinated. For[CdL₂](ClO₄)₂ · H₂O an analogous structure is proposed.     

Syntheses and characterization of nickel(II), zinc(II) and palladium(II) complexes derived from three pyrazole-based polydentate ligands

Two pyrazole-based polydentate ligands, 1,3-bis(5-methyl-3-phenylpyrazol-1-yl)-propan-2-ol (Hmppzpo) and 1,3-bis(5-methyl-3-p-isopropylphenylpyrazol-1-yl)-propan-2-ol (Hmcpzpo), have been synthesized. A third ligand, 1,3-bis(3,5-dimethylpyrazol-1-yl)-propan-2-ol (Hdmpzpo), has been synthetically modified. Seven new M(II) coordination compounds of general formula M₂L₂X₂ (M?=?Zn, Ni; X?=?NO₃ or ClO₄; L?=?dmpzpo, mppzpo or mcpzpo) or MLX (M?=?Pd; L?=?dmpzpo; X?=?Cl) were synthesized and structurally characterized by elemental analysis and FT-IR analysis. The crystal structures of [Zn₂(μ-dmpzpo-O,N,N′)₂(NO₃)₂]?·?2H₂O (1?·?2H₂O), [Ni₂(μ-dmpzpo-O,N,N′)₂(CH₃CN)₂](ClO₄)₂ (2) and Pd(μ-dmpzpo-N,N′)Cl₂ (4) were determined by single-crystal X-ray crystallography. The crystal structures show that complexes 1?·?2H₂O and 2 are center-symmetric dinuclear compounds, with two metal ions bridged by two alkoxo groups and each metal ion with a distorted square-pyramidal environment. The palladium complex, 4, displayed square-planar coordination geometry around the Pd(II) ion with trans arrangement.     

Synthesis and study of cobalt(II), nickel(II), and copper(II) complexes with 4-(4-hydroxyphenyl)-1,2,4-triazole

New complexes of Co(II), Ni(II), and Cu(II) nitrates, chlorides, and perchlorates with 4-(4-hydroxyphenyl)-1,2,4-triazole (L) were obtained and examined by single-crystal X-ray diffraction, X-ray powder diffraction, and electronic absorption and IR spectroscopy. The cations of all the complexes have linear trinuclear structures. Ligand L is coordinated to the metal ions in a bidentate bridging fashion through the N(1) and N(2) atoms of the heterocycle. The coordination polyhedron of the metal atoms is a distorted octahedron. The molecular and crystal structures of the complexes [Co₃L₆(H₂O)₆](ClO₄)₆ · 3C₂H₅OH · 3.75H₂O and [M₃L₆(H₂O)₆](ClO₄)₆ · 6H₂O (M = Cu²⁺ and Ni²⁺) were determined.     

Trigonal (-3) symmetry octahedral lanthanide(III) complexes of zwitterionic tripodal ligands: luminescence and magnetism

Sandwich coordination complexes, [Ln^III(H₃L)₂]X₃?solvents, of Tb(III), Eu(III), Dy(III), Ho(III) and Er(III) were prepared with two new zwitterionic ester-substituted tripodal amine ligands, tris((2-hydroxy-5-n-butyl benzoate)aminoethyl)-amine (H₃L¹) and tris((2-hydroxy-5-methyl benzoate)aminoethyl)-amine (H₃L²). These ligands were synthesised by condensation of the appropriately substituted salicylaldehyde with tris(2-aminoethyl)amine (tren) followed by in situ reduction of the tris-imine to tris-amine. Subsequent 2:1 reaction with lanthanide(III) ions yields [Ln^III(H₃L)₂]X₃?solvents (L = L¹, L²; X = Cl^?, NO₃^?; solvents = MeOH or H₂O). All complexes were characterised by microanalysis, infrared spectroscopy, high resolution mass spectrometry and solid-state photoluminescence measurements. The crystal structures of [Tb^III(H₃L¹)₂]Cl₃·6MeOH, [Dy(H₃L¹)₂]Cl₃·6MeOH, [Eu^III(H₃L¹)₂]Cl₃·6MeOH and [Tb^III(H₃L¹)₂](NO₃)₃ reveal high-crystallographic ?3 symmetry at the O₆-coordinated octahedral lanthanide(III) ions and that the tripodal ligands are bound in zwitterionic form: the protons from the phenolic oxygens have migrated to the amino nitrogens. Photoluminescence measurements indicate various degrees of energy transfer of the ligand chromophore to the lanthanide ions, as both ligand and lanthanide emission features are observed. Despite the high-crystallographic symmetry and the likely small transverse magnetic anisotropy of the complexes, no evidence of slow relaxation of the magnetisation, characteristic of a single-molecule magnet, was observed for [Tb^III(H₃L¹)₂]Cl₃·MeOH·3H₂O, [Dy^III(H₃L¹)₂]Cl₃·6H₂O, [Ho^III(H₃L¹)₂](NO₃)₃·2H₂O, [Er^III(H₃L¹)₂]·H₂O and [Tb^III(H₃L¹)₂](NO₃)₃ down to 2.0 K.     

Studies on solid state synthesis and the oxygenation property of cobalt (II) Schiff base (vanilline polyamine) complexes

Three new cobalt complexes were synthesized by solid-state reaction at room temperature and the resultant Co complexes reacted with two equivalent oxygen molecules at room temperature to produce the oxygenated complexes [Co·(L₁)₂·(O₂)₂](NO₃)₂·2H₂O (L₁ = N, N’-bis(4-hydroxyl-3-methoxy-benzyl)-diethylenetriamine), [Co·(L₂)₂·(O₂)₂](NO₃)₂·2H₂O (L₂ = N, N’-bis(4-hydroxyl-3-methoxy-benzyl)-triethylenetetramine), and [Co·(L₃)₂·(O₂)₂](NO₃)₂·2H₂O (L₃ = N, N’-bis(4-hydroxyl-3-methoxy-benzyl-tetraethylenepentamine). The oxygenated complexes were characterized by elemental analysis, IR (Infrared), ¹H-NMR (Nuclear Magnetic Resonance), and UV-Vis (Ultraviolet Visual) spectrometry, and TG/DTA (Thermogravimetry/Differential Thermal Analysis) analysis, and molar conductance. The coordinated oxygen contents in the oxygenated complexes were also determined by weight method. It was supposed that only one O₂ molecule coordinated to the Co ion forming a superoxo type oxygenated complex. Translated from Acta Chimica Sinica, 2006, 64(15): 1517–1522 (in Chinese)     

Phosphodiester hydrolysis promoted by dinuclear iron(III) complexes

We report the reactivity of three binuclear non-heme Fe(III) compounds, namely [Fe₂(bbppnol)(μ-AcO)(H₂O)₂](ClO₄)₂ (1), [Fe₂(bbppnol)(μ-AcO)₂](PF₆) (2), and [Fe₂(bbppnol)(μ-OH)(Cl)₂]·6H₂O (3), where H₃bbppnol = N,N′-bis(2-hydroxybenzyl)-N,N′-bis(2-methylpyridyl)–1,3-propanediamine-2-ol, toward the hydrolysis of bis-(2,4-dinitrophenyl)phosphate as models for phosphoesterase activity. The synthesis and characterization of the new complexes 1 and 3 was also described. The reactivity differences observed for these complexes show that the accessibility of the substrate to the reaction site is one of the key steps that determinate the hydrolysis efficiency.     

Synthesis and structural characterization of centrosymmetric multinuclear nickel(II) complexes with neutral tetradentate N6-ligand

A neutral tetradentate ligand L1 [L1?=?3,6-bis(pyrazol-1-yl)-pyridazine] reacts with Ni(ClO₄)₂·6H₂O and undergoes counterion exchange with PF ^?₆ to give di- and tetranuclear complexes [Ni₂(L1)₂(CH₃CN)₄](PF₆)₄·4H₂O (1) and [Ni₄(L1)₄(µ-OH)₄](ClO₄)₄·2H₂O (2), respectively. The presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as base controls the nuclearity of the complex formation. Both complexes were structurally characterized by physicochemical and spectroscopic techniques. Their crystal structures revealed that both complexes are centrosymmetric and adopt slightly distorted octahedral geometry. Complex 1 crystallizes in monoclinic space group C2/c as the Ni(II) center is octahedrally bound to L1 in a trans-isomer arrangement. Complex 2 crystallizes in tetragonal space group I4₁/amd with four L1 and four hydroxy bridging ligands linked to Ni(II) center in cis-isomer arrangement. Cyclic voltammograms of complexes 1 and 2 were measured under Ar and CO₂. Under CO₂, the quasireversible peaks of both complexes become irreversible and a current enhancement occurs under reduction.