Irène Morgenstern-Badarau

Crystal structure and magnetic and EPR properties of the heterobinuclear complex CuNi(fsa)2en(H2O)2.H2O (H4(fsa)2en = N,N'-bis(2-hydroxy-3-carboxybenzylidene)-1,2,-diaminoethane)

The goal of this paper is to investigate the exchange interaction in CuNi(fsa)2en(H2O)2·H2O, denoted [CuNi], where (fsa)2en4− is the bichelating ligand derived from the Schiff base N,N′-(1-hydroxy-2-carboxybenzylidene)-1,2-diaminoethane. For a comparison of the structure of the pair states in [CuNi] with those of Cu(II) and Ni(II) single-ion ground states, CuMg(fsa)2en(H2O)2·H2O and Ni2(fsa)2en(H2O)2·H2O, denoted [CuMg] and [NiNi], have also been investigated. The crystal structure of [CuNi] has been solved at −120 °C from 8428 reflections. [CuNi] crystallizes in the trigonal system, space group P31. The lattice constants are a = 12.8071 (4) A and c = 9.8157 (8) A with Z = 3. The structure is made of [CuNi] binuclear units, in which the copper atom is in a strictly planar −N2O2 environment and the nickel atom in a pseudooctahedral −O2O2(H2O)2 environment. The crystal structure of [NiNi] has been solved at room temperature from 3262 reflections. The space group is P32, and the structure of the binuclear units [NiNi] is very close to that of the units [CuNi]. The temperature dependence of the magnetic susceptibility of [CuNi], studied in the temperature range 4–300 K, has revealed an energy gap of −3J/2 = 213 cm−1 between the 2A1 ground state and the 4A1 excited state. The average values of the g factors for the two pair states have been compared to those of the single ions, as deduced from the magnetic behavior of [CuMg] and [NiNi]. The EPR powder spectrum of [CuNi] is typical of an axial symmetry. The single-crystal spectra at 4 K exhibit only one signal for any orientation, assigned to the ground-pair doublet state. The g tensor is axial with the unique axis perpendicular to the N2CuO2NiO2 pseudo molecular plane. The principal values are g∥ = 2.22 (5) and g⊥ = 2.30 (0). The signal broadens out against the temperature in an inhomogeneous manner, the broadening being more pronounced on the high-field side. The magnetic and the EPR data are compared. The status of the spin Hamiltonian utilized to interpret these data is discussed. Finally, the mechanism of the exchange interaction is specified. The existence of two exchange pathways, namely, [formula omitted] and [formula omitted], the former being antiferromagnetic and the latter ferromagnetic, is emphasized.

Formation in solution, synthesis, and electrochemical study of oxalato complexes of N,N′-ethylenebis(salicylideneiminato)-chromium(III) and -iron(III): crystal structures of piperidinium [N,N′-ethylenebis(salicylideneiminato)](oxalato-O1O2)-chromate(III) and ferrate(III)

Two new mononuclear complexes of formula [Hpip][M(salen)(ox)][M = CrIII(1) or FeIII(2)] and the binuclear [Fe2(salen)2(ox)]·H2O, (3) where Hpip = piperidinium, salen =N,N′-ethylenebis(saIicylideneiminate), and ox = oxalate, have been synthesized. Compounds (1) and (2) are isostructural, monoclinic, space group P21/n, Z= 4, with a= 24.425(3), b= 6.847(1), c= 14.271(2)A, and β= 100.95(2)° for (1) and a= 24.363(4), b= 6.991(2), c= 14.105(3)A, and β= 98.76(2)°for (2). The structure of (1) was solved by direct methods whereas that of (2) was solved by isomorphous replacement from the co-ordinates of (1). Both structures consist of [M (salen)(ox)]– mononuclear anions and piperidinium cations. The presence of the bidentate oxalate ligand in both complexes forces the salen ligand to adopt the non-planar cis-β configuration. The metal ions exhibit distorted octahedral geometry with the two co-ordinated oxygen atoms of the oxalate ligand and an oxygen and a nitrogen atom from the salen defining the best equatorial plane. The remaining two co-ordinating atoms of the quadridentate Schiff base are bent away from the oxalate ligand. The stability constant of the complex [Cr(salen)(ox)]– as well as [Cr(salen)(H2O)2]++ ox2– [graphic omitted] [Cr(salen)(ox)]–(i), [Cr(salen)(H2O)2]+ [graphic omitted] [Cr(salen)(OH)(H2O)]+ H+(ii), [Cr(salen)(OH)(H2O)] [graphic omitted] [Cr(salen)(OH)2]–+ H+(iii) the acidity constants of the complex [Cr(salen)(H2O)2]+ have been determined by potentiometry in aqueous solution: log β1= 4.80 ± 0.03, pKa1= 7.54 ± 0.01, and pKa2= 10.47 ± 0.01 (25 °C, 0.1 mol dm3 NaNO3). Complexes (1) and (2) undergo one-electron reduction at a platinum electrode in dimethyl sulphoxide solution. The reduction process is totally irreversible due to an inner-sphere redox reaction in the case of CrIII and to the dissociation of the anionic oxalate ligand in the case of FeIII A reactivity scheme is proposed to explain their different electrochemical behaviour.

Electrochemical and spectroscopic characterization of new cobalt(II) complexes. Catalytic activity in oxidation reactions by molecular oxygen

Abstract The synthesis and characterization of some new complexes with tetradentate Schiff bases derived from bis(salicylaldehyde)etylenediimine, H2Salen are reported in this paper. The Co(II) Schiff bases complexes investigated are: (bis(5-nitro-salicylaldehyde) ethylenediiminato)cobalt(II), (CoNSalen); (bis(α-ethyl-salicylaldehyde) ethylenediiminato)cobalt(II) (CoEtSalen); (bis(α-ethyl-3,5-diiode-salicylaldehyde) ethylenediiminato) cobalt(II),(CoDIEtSalen); (bis(α,5-dimethyl-3-iode-salicylaldehyde)ethylenediiminato)cobalt(II) (CoDMISalen) and (bis(salicylaldehyde)methylene-p,p′-diphenylene)cobalt(II), (CoSalmbfn). The characterization of the complexes was performed by elemental analysis, UV–Vis, FTIR spectroscopy, powder X-ray diffraction and cyclic voltammetry. Pyridine (py), present in the solution of complexes in DMF, coordinates to the metal ion in axial position, inducing a significant decrease of the redox potentials. Significant influences have the substituents grafted on ligands’ molecules. The separated complexes evince catalytic activity in the oxidation reaction of 2,6-di-t-butylphenol with molecular oxygen. These complexes seem capable of forming reversible adducts with molecular oxygen.

New MnII Complexes with an N/O Coordination Sphere from TripodalN-Centered Ligands − Characterization from Solid State to Solution and Reaction with Superoxide in Non-Aqueous and Aqueous Media

The crystal structure of a dimeric bis(µ‐carboxylato)MnIIMnII complex (2) with a tetradentate N‐centered tripodal ligand, N,N‐bis[(1‐methylimidazol‐2‐yl)methyl]glycinate, is presented. The carboxylates are bridging monodentate. This complex shows some striking differences to the previously published parent compound 1 obtained with the closely related ligand N‐[(1‐methylimidazol‐2‐yl)methyl]‐N‐(2‐pyridylmethyl)glycinate. The carboxylato bridges in both structures are shown to be disrupted in solution. The reactivities in solution of compounds 1 and 2 toward superoxide were studied. In anhydrous DMSO solutions, a pathway involving a bis(µ‐oxo)MnIIIMnIV complex was identified. In water solutions, IC50 values were measured by the Fridovich test (1.7 ± 0.2 µM for 2 and 2.0 ± 0.2 µM for 1), which showed these complexes to be good superoxide scavengers. Association constants for the complexes were estimated by means of a method based on IC50 measurements of the complexes under several conditions (alone and in the presence of excess ligand). They were found to be consistent with literature data.

Sterically hindered iron(II) complex of a new tripodal polyimidazole ligand: structure and reactivity toward superoxide

Abstract The new tripodal potentially heptadentate ligand N(CH2CH2NCHR)3 (L) with R = 1-triphenylmethyl-4-imidazolyl containing three 4-substitutes imidazole functions, where Nτ nitrogen atoms are protected with highly aromatic triphenylmethyl (trityl) groups, was synthesized. The corresponding iron(II) complex [Fe(L)](PF6)2 was prepared and characterized. Its molecular structure was determined by X-ray crystallography (monoclinic space group P2 1 n with a = 21.148(9), b = 23.484(9), c = 14.668(6) A , β = 97.44(4)°, Z = 4), and R = 0.0787). The Fe(II) ions is hexa-coordinated from three imine and three imidazole nitrogens. The tripodal bridging N atom is not bonded to the iron (3.1 A). The complex is high spin as shown by NMR and electron paramagnetic resonance studies. UV-Vis and electrochemical properties are also reported. The reactivity of the complex with superoxide was investigated. A new species was discovered as ultimate product of the reaction with potassium superoxide in DMSO solution, which confirms effective superoxide scavenging by the complex despite the steric hindrance of the ligand.

Effet Jahn-Teller et structure cristalline de l'hydroxyde CuSn(OH)6

Tin IV-copper II hydroxide, CuSn(OH) 6 , belongs to the isostructural family of M II Sn(OH) 6 hydroxides; these hydroxides are described as ReO 3 oxide-type superstructures. When Cu II replaces the divalent M II ion, the symmetry reduces to tetragonal. This distortion is attributed to a Cu II cooperative Jahn-Teller effect. Results of a structural analysis based on powder data are presented. It is shown that the symmetry is lowered just enough for the Cu II ground term to be nondegenerate, and, at the same time, for the typical macroscopic symmetry to be preserved.

X-Ray crystal structures and electronic aspects of two mononuclear iron(III) complexes of the class FeIIILL′ with the quadridentate ligand L = salen or nta and the bidendate ligand L′= oxalate [salen = bis(salicylidene)ethylenediamine anion, H3nta =N,N-bis(carboxymethylglycine)]

The X-ray crystal structures of two mixed-ligand six-co-ordinate iron(III) complexes, [FeIII(salen)(ox)]pipH (1) and [FeIII(nta)(ox)](dabcoH)2(2)(ox = oxalate, pipH = piperidinium cation, dabcoH = 1,4-diazabicyclo [2.2.2]octane cation) are characterized by a distorted octahedral co-ordination; the resulting ligand field rhombicity and spin–orbit coupling provide significant quantum mixing of the S= 5/2 ground state as revealed by magnetic properties studies.

A polymeric, layered bimetallic Mn(II)Fe(III) imidazolate network; crystal structure and magnetic properties

The use of a C3 complex bearing three imidazolate groups as a ‘building block’ allowed us to synthesize an infinite corrugated two-dimensional (2D) low-spin Fe(III)–high-spin Mn(II) polymer exhibiting weak ferromagnetic intralayer interaction through imidazolate bridge.

Paramagnetic NMR spectroscopy of native and cobalt substituted manganese Superoxide dismutase from Escherichia coli

Manganese containing superoxide dismutase from E. coli has been investigated through paramagnetic NMR spectroscopy. The spectrum of the native form was rationalized using a τs=3×10−11 s for the Mn(III) ion, consistent with previous estimates from NMRD measurements. Mn(III) has been replaced by a Co(II) ion and a tentative assignment of the NMR spectrum of the Co(II)‐substituted derivative has been proposed, based on T1, chemical shifts and 1D‐NOE data. The metal coordination geometry is provided by three histidines and a carboxylate group. The presence of a solvent molecule as a loosely bound fifth ligand is also proposed. The NMR data of the Co(II)‐substituted derivative of E. coli MnSOD differs from those of Co(II)SOD from other bacterial sources. This suggests that Co(II) substitution is an efficient method to address the problem of metal ion selectivity in superoxide dismutase.

{Tris[4-(2-pyridyl)-3-aza-3-butenyl]-amine}iron(II) bis(hexafluorophosphate), [Fe(py3tren)](PF6)2

The coordination polyhedron of the Fe II ion in the title compound, [Fe(C 24 H 27 N 7 )](PF 6 ) 2 , is best described as a trigonal antiprism twisted 6° towards a trigonal prism. The tris[4-(2-pyridyl)-3-aza-3-butenyl]amine ligand coordinates to the metal centre through the three pyridine and three imino N atoms, each set of atoms forming two parallel ideal equilateral triangles ; the metal ion is located between these two planes. The average values for the Fe-N pyridine and the Fe-N imino bond lengths are 1.981 and 1.950 A, respectively. The tripodal bridging amine N atom lies on the pseudo ternary axis of the molecule and is situated 3.427 (7) A from the Fe centre.