Spectroscopic properties of [M(CN)5py]n− complexes [M  Fe(II), Co(III); py = pyridine]

The IR, electronic and NMR spectra of K₂[Co(CN)₅py]·H₂O and Na₃[fe(CN)₅py]·3H₂O, as well as the Mössbauer spectrum of the latter complex, are reported and discussed. In particular it is argued that the wavenumbers and intensities of the i.r.-active CN stretching vibrations and the NMR chemical shifts of the m- and p-but not o-protons suggest greater metal to ligand back π-bonding in the Fe(II) complex than in the Co(III) complex.     

Electrophilic Substitution Co(II)→M(II) (M = Mn,Ni, Cu,Zn, Cd) in Co2[Fe(CN)6] Gelatin-Immobilized Matrices

Electrophilic substitutions Co(II) M(II) (M = Mn, Ni, Cu, Zn, Cd) in cobalt(II) hexacyanoferrate(II) gelatin-immobilized matrices in contact with aqueous solutions of corresponding chlorides MCl₂ were studied. As a result of this contact, Co(II) was shown to be replaced to some extent by Ni(II), Cu(II), Zn(II), or Cd(II) and to give heteronuclear cobalt(II) hexacyanoferrates(II) and two-charge ions. A complete substitution of Co(II) or the formation the respective mononuclear hexacyanoferrate(II) M₂[Fe(CN)₂] was observed in neither of the studied systems Co(II) M(II). No Co(II) Mn(II) substitution was observed, even though the immobilized matrix was in contact with a solution for a long time.     

Thermal behaviors of N-pyrrolidine-N′-(2-chlorobenzoyl)thiourea and its Ni(II), Cu(II), and Co(III) complexes

The N-pyrrolidine-N??-(2-chlorobenzoyl)thiourea, HL, and their Ni(II), Cu(II), and Co(III) complexes (NiL₂, CuL₂, and CoL₃) have been synthesized and characterized. The thermal decomposition reactions of all the compounds have been investigated by DTA/TG combined systems. The mass spectroscopy technique has been used to identify the products during pyrolytic decomposition. The pyrolytic final products have been analyzed by X-ray powder diffraction method. After comparison of thermogravimetric and mass results of HL, NiL₂, CuL₂, and CoL₃, the decomposition mechanism of these compounds have been suggested. The thermal stability of the Ni(II) and Cu(II) complexes according to the thermogravimetric curves follows the sequence: NiL₂?<?CuL₂. The values of the activation energy, E _a, have been obtained using model-free (Kissenger?CAkahira?CSunose, KAS, Flyn?CWall?COzawa, FWO, and Isoconversional) methods for all decomposition stages. The E _a versus the extent of conversion, ??, plots show that the values of E _a varies as ??. Thirteen kinetic model equations have been tested for selecting correct reaction models. The optimized value of E _a and Arrhenius factor, A, have been obtained using the best model equation. The thermodynamic functions (??H*, ??S*, and ??G*) have been calculated using these values.     

Ion-Exchange Processes M(II) → Fe(III) and Fe(III) → M(II) in Metal Hexacyanoferrate(II) Gelatin-Immobilized Matrices (M = Mn,Co, Ni,Cu, Zn,Cd)

Ion-exchange reactions M²⁺ Fe³⁺ and Fe³⁺ M²⁺ (M = Mn, Co, Ni, Cu, Zn, Cd) were studied in metal(II) hexacyanoferrate(II) gelatin-immobilized matrices M₂[Fe(CN)₆] in contact with aqueous FeCl₃ solutions and Fe₄[Fe(CN)₆]₃ in contact with aqueous MCl₂ solutions. It was shown that in both cases, M²⁺ was replaced by Fe³⁺ and Fe³⁺ was replaced by M²⁺ to some extent, but no complete replacement was observed in the M₂[Fe(CN)₆]–FeCl₃ or Fe₄[Fe(CN)₆]₃–MCl₂ systems under study. No electrophilic substitution Fe³⁺ Mn²⁺ was found to occur in any noticeable degree during the contact of Fe₄[Fe(CN)₆]₃ with aqueous MnCl₂ solutions even when this contact occurred for 1 h and longer.     

Self-assembled supramolecular M9 (Mn(II), Fe(III), Zn(II)), M5 (Fe(III)), and [M3]2 (Pb(II)) complexes: structural,magnetic, and Mössbauer properties

The tritopic ligand 2poap self-assembles in the presence of Zn(NO(3))(2) and Fe(NO(3))(3) to form homoleptic [3 x 3] nonanuclear M(9) (M = Zn(II), Fe(III)) square grid structures and with Pb(ClO(4))(2) to form a dimerized linear trinuclear [Pb(3)](2) structure. Cl2poap and Cl2poapz form self-assembled homoleptic [3 x 3] Mn(II)(9) square grids with Mn(ClO(4))(2) and Mn(NO(3))(2), respectively, but an unusual incompletely metalated Fe(III)(5) square grid is formed on reaction of Cl2poap with Fe(ClO(4))(3). X-ray structures are reported for [Mn(9)(Cl2poap-2H)(6)](ClO(4))(6).10H(2)O (3), [Mn(9)(Cl2poapz-2H)(6)] (NO(3))(6).22H(2)O (4), [Zn(9)(2poap-2H)(3)(2poap-H)(3)](NO(3))(9).24H(2)O (5), [Pb(3)(2poap-2H) (ClO(4))(4)](2).8H(2)O (6), and [Fe(5)(Cl2poap-H)(6)](ClO(4))(9).34.5H(2)O (7). Compound 3 crystallized in the monoclinic system, space group P(-)1, with a = 18.179(1) A, b = 18.857(1) A, c = 25.871(2) A, alpha = 70.506(2) degrees, beta = 86.440(1) degrees, gamma = 75.175(2) degrees, and z = 2. Compound 4 crystallized in the monoclinic system, space group P(-)1, with a = 16.900(2) A, b = 20.02393) A, c = 25.663() A, alpha = 84.743(3) degrees, beta = 84.885(2) degrees, gamma = 67.081(2) degrees, and z = 2. Compound 5 crystallized in the monoclinic system, space group P(-)1, with a = 18.482(1) A, b = 18.774(1) A, c = 28.112(2) A, alpha = 104.020(1) degrees, beta = 97.791(1) degrees, gamma = 117.036(1) degrees, and z = 2. Compound 6 crystallized in the monoclinic system, space group P(-)1, with a = 10.0513(6) A, b = 11.0958(6) A, c = 17.334(1) A, alpha = 100.932(1) degrees, beta = 100.387(1) degrees, gamma = 94.565(1) degrees, and z = 2. Compound 7 crystallized in the monoclinic system, space group P(-)1, with a = 19.164(1) A, b = 19.587(2) A, c = 26.673(2) A, alpha = 76.430(2) degrees, beta = 78.834(2) degrees, gamma = 64.973(1) degrees, and z = 2. Compound 3 exhibits intramolecular antiferromagnetic exchange within the nonanuclear [Mn(9)(mu-O)(12)] grid structure (J = -4.6 cm(-1)), while the analogous nonanuclear complex [Fe(9)(2poap-2H)(6)](NO(3))(15).18H(2)O (8) is dominated by intramolecular antiferromagnetic coupling at high temperatures but exhibits a low-temperature feature indicative of additional ferromagnetic interactions. The isolated pentanuclear Fe(5) [4 + 1] square grid in 7, with distant Fe-Fe bridging, exhibits very weak antiferromagnetic coupling (J = -0.2 cm(-1)). M?ssbauer spectroscopy data are consistent with high-spin Fe(III)(9) and Fe(III)(5) structures.     

Electrophilic Substitution Mn(II) → M(II) (M = Co,Ni, Cu,Zn, Cd) in Gelatin-Immobilized Mn2[Fe(CN)6]

Reactions of electrophilic substitution Mn(II) M(II) (M = Co, Ni, Cu, Zn, Cd) are studied in gelatin-immobilized Mn(II) hexacyanoferrate(II) systems brought in contact with aqueous solutions of metal chlorides MCl₂. As the result of this contact, Mn(II) is replaced by Co(II), Ni(II), Cu(II), Zn(II), or Cd(II) to give heteronuclear metal hexacyanoferrates(II) (MHCF) of Mn(II) and two-charged ions. Neither of the systems under study showed a complete substitution of Mn(II) or the formation of the respective mononuclear hexacyanoferrate(II) M₂[Fe(CN)₆]. When any of the above gelatin-immobilized MHCF was brought in contact with an aqueous solution of MnCl₂, no electrophilic substitution M(II) Mn(II) was observed even for a long contact time.     

Syntheses,crystal structures and magnetic properties of heteronuclear bimetallic compounds of [Cu(pdc)2][M(H2O)5]·2H2O [M=Ni(II), Co(II), Mn(II); pdc=2,6-pyridinedicarboxylato]

The complexes [M(H₂O)₅][Cu(pdc)₂]·2H₂O [M=Ni(II) 1, Co(II) 2, Mn(II) 3; pcd=2,6-pyridinedicarboxylato] are prepared and their crystal structures, magnetic susceptibilities and UV-Visible properties reported. In all cases, the Cu(II) ion occupies the chelating site in the pdc ligand, while the M(II) occurs as a pentaaqua ion bridged to the [Cu(pdc)₂] moiety through a carboxylate as demonstrated by both UV-Visible spectroscopy and X-ray diffraction. Single crystal X-ray diffraction shows the three complexes to be isostructural. Weak antiferromagnetic interactions between the metal ions are observed in 1 and 3, while the magnetic behavior of 2 is dominated by single ion anisotropy.     

Magnetic and spectral properties of Fe(II), Fe(III), Co(II), Ni(II), Cu(II) and Pd(II) chelates of 2′-hydroxy-3′-bromo-4-methoxy-5′-methylchalkone oxime (HBMMCO)

A number of chelates of the transition metal ions Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺ and Pd²⁺ with 2′-hydroxy - 3′ - bromo - 4 - methoxy - 5′ - methylchalkone oxime (HBMMCO) have been synthesised. Attempts have been made to assign their probable structures on the basis of elemental analysis, molar conductance, thermal analysis, absorption and reflectance spectra, IR spectra and magnetic data. The magnetic susceptibility of the Co(II) chelate follows the Curie-Weiss law and the observed temperature dependance is in favour of an octahedral configuration. The Ni(II) chelate exhibits a 6-coordinate octahedral structure, whilst distorted octahedral geometry is suggested for the Cu(II) chelate. The Fe(II) and Fe(III) chelates have high spin octahedral configurations and the dimagnetic behaviour of the Pd(II) complex indicates a square planer configuration.     

Tunability of the M(II)M(III)/M(II)(2) and M(III)(2)/M(II)M(III) (M=Mn, Co) couples in bis-μ-O,O'-carboxylato-μ-OR bridged complexes

A comparison of the electrochemical properties of a series of dinuclear complexes [M(2)(L)(RCO(2))(2)](+) with M = Mn or Co, L = 2,6-bis(N,N-bis-(2-pyridylmethyl)-sulfonamido)-4-methylphenolato (bpsmp(-)) or 2,6-bis(N,N-bis(2-pyridylmethyl)aminomethyl)-4-tert-butylphenolato (bpbp(-)) and R = H, CH(3), CF(3) or 3,4-dimethoxybenzoate demonstrates: (i) The electron-withdrawing sulfonyl groups in the backbone of bpsmp(-) stabilize the [M(2)(bpsmp)(RCO(2))(2)](+) complexes in their M(II)(2) oxidation state compared to their [M(2)(bpbp)(RCO(2))(2)](+) analogues. Manganese complexes are stabilised by approximately 550 mV and cobalt complexes by 650 mV. (ii) The auxiliary bridging carboxylato ligands further attenuate the metal-based redox chemistry. Substitution of two acetato for two trifluoroacetato ligands shifts redox couples by 300-400 mV. Within the working potential window, reversible or quasi-reversible M(II)M(III)? M(II)(2) processes range from 0.31 to 1.41 V for the [Co(2)(L)(RCO(2))(2)](+/2+) complexes and from 0.54 to 1.41 V for the [Mn(2)(L)(RCO(2))(2)](+/2+) complexes versus Ag/AgCl for E(M(II)M(III)/M(II)(2)). The extreme limits are defined by the complexes [M(2)(bpbp)(CH(3)CO(2))(2)](+) and [M(2)(bpsmp)(CF(3)CO(2))(2)](+) for both metal ions. Thus, tuning the ligand field in these dinuclear complexes makes possible a range of around 0.9 V and 1.49 V for the one-electron E(M(II)M(III)/M(II)(2)) couple of the Mn and Co complexes, respectively. The second one-electron process, M(II)M(III)? M(III)(2) was also observed in some cases. The lowest potential recorded for the E°(M(III)(2)/M(II)M(III)) couple was 0.63 V for [Co(2)(bpbp)(CH(3)CO(2))(2)](2+) and the highest measurable potential was 2.23 V versus Ag/AgCl for [Co(2)(bpsmp)(CF(3)CO(2))(2)](2+).     

[M{κ2S,S-S2C-piperazine-C2H4N=C(R)}n] {Co(III), Ni(II), Cu(II) or Zn(II)} complexes bearing pendant Schiff base moieties: spectral characterization,fluorescence, cyclic voltammetric and TGA/DTA study

A series of neutral mononuclear complexes [M{κ²S,S-S₂C-piperazine-C₂H₄N=C(R)}_n] {R?=?Ph; M?=?Co(III) 1, Ni(II) 2, Cu(II) 3, Zn(II) 4; R?=?Naph; M?=?Co(III) 5, Ni(II) 6, Cu(II) 7, Zn(II) 8; n = 2 for 2–4, 6–8 and n = 3 for 1, 5} bearing pendant Schiff base moieties were synthesized through self-assembly involving N-[phenylmethylidene]-2-piperazin-1-ylethanamine (L¹) or N-[naphthylmethylidene]-2-piperazin-1-ylethanamine (L²) with two equivalents each of CS₂ and corresponding metal acetates. The complexes 1–8 were characterized by microanalysis, ESI-MS, IR, ¹H, ¹³C NMR, DEPT 135, UV–visible absorption, and emission spectroscopy. Complexes 1, 3, and 8 exhibit fluorescence emissions at 342, 344, and 348 nm upon excitation at 273 (for 1 and 3) and 263 (for 8) with concomitant Stokes shifts of 69, 71, and 85 nm. The spectral and magnetic moment data support octahedral geometry around Co(III) and square planar/tetrahedral geometry around other metal centers. Thermal stabilities of 1–8 have been investigated by thermogravimteric analysis. The cyclic voltammograms clearly suggest that the complexes exhibit electroreduction principally associated with pendant imine moieties except Cu(II) complex 7 which displays quasi-reversible reduction corresponds to the Cu(II)/Cu(I) redox couples, in addition to reversible electroreduction of pendant imine groups associated with the coordinated ligands.     

Preparation, spectral and thermal properties of Co(II), Ni(II), Cu(II), Zn(II), and Cd(II) complexes with iodosubstituted 2,2′-dipyrrolylmethene

Complexes [ML₂] of cobalt(II), nickel(II), copper(II), zinc(II), and cadmium(II) with asymmetrically substituted (E)-3-ethyl-5-[(4-iodo-3,5-dimethyl-2H-pyrrol-2-ylidene)methyl]-2,4-dimethyl-1H-pyrrole (HL) have been prepared and characterized for the first time. The spectral properties, stability in solutions and in the solid phase at elevated temperature of the complexes have been studied. The effects of complexing metal ion and the reaction medium on the spectral luminescent properties (absorptivity, quantum yield, fluorescence lifetime, and the radiation constant) and on thermal destruction of the [ML₂] complexes have been discussed.     

Mössbauer spectroscopic studies of molecule-based magnets: NBu4[Fe(II) x Mn(II)1-x Cr(III)(ox)3] and NBu4[Fe(II) x Ni(II)1-x Fe(III)(ox)3]

The internal magnetic field (H _n ) at⁵⁷Fe nucleus was investigated for the mixed crystals, NBu₄[Fe(II) _x Mn(II)_1-x Cr(III) (ox)₃] (x=0.03?1) and NBu₄[Fe(II) _x Ni(II)_1-x Fe(III)(ox)₃]) (x=0?1) using Mössbauer spectroscopy, where NBu₄/⁺=tetra(n-butyl)ammonium ion and ox^2?=oxalate ion. With the decrease ofx, the direction ofH _n at Fe(II) in NBu₄[Fe(II) _x Mn(II)_1-x Cr(III)(ox)₃] changed gradually from parallel to perpendicular, to the honeycomb layers consisting of an alternate array of the bivalent and tervalent ions through ox^2? ligands. A variation of ca. 50° in direction was observed for theH _n at Fe(III) in NBu₄[Fe(II) _x Ni(II)_1-x Fe(III)(ox)₃].     

Synthesis,crystal structures,and magnetic properties of three K[M(bpb)(CN)2]-based trinuclear sandwich-like heterobimetallic M(III)–Ni(II) (M = Fe,Cr, Co) complexes

Three trinuclear sandwich-type cyanide-bridged M^III–Ni^II complexes, {[Ni(cyclm)[Fe(bpb)(CN)₂]₂}·8H₂O (1), {[Ni(cyclm)[Cr(bpb)(CN)₂]₂}·2H₂O (2), and {[Ni(cyclm)[Co(bpb)(CN)₂]₂}·CH₃OH·2H₂O (3) (cyclm?=?1,4,8,11-tetraazacyclotetradecane), have been synthesized using K[M(bpb)(CN)₂] (M?=?Fe, Cr, Co; bpb?=?1,2-bis(pyridine-2-carboxamido)benzenate) as building block and one Ni(II) compound containing a 14-membered macrocycle ring as assembling segment. All the complexes have been characterized by elemental analysis, IR spectroscopy, and X-ray structure determination. Single X-ray diffraction analysis shows similar sandwich-like structures, in which the two cyanide-containing building blocks are monodentate through one of their two cyanides, coordinated face to face to the central Ni(II). Investigation of the magnetic properties of 1 and 2 reveals ferromagnetic magnetic coupling between the neighboring Fe(III)/Cr(III) and Ni(II) through the bridging cyanide. A best-fit to the magnetic susceptibilities of 1 and 2 based on the trinuclear M₂Ni model leads to magnetic coupling constants J?=?5.47(1)?cm^?1 for 1 and J?=?6.37(2)?cm^?1 for 2.     

Cu(II), Co(II), Ni(II), Mn(II), and Fe(II) metal complexes containing N,N′-(3,4-diaminobenzophenon)-3,5-But2-salicylaldimine ligand: Synthesis,structural characterization,thermal properties,electrochemistry, and spectroelectrochemistry

The synthesis, structure, spectroscopic and electro-spectrochemical properties of steric hindered Schiff-base ligand [N,N′-(3,4-benzophenon)-3,5-Bu^t₂-salicylaldimine (LH₂)] and its mononuclear Cu(II), Co(II), Ni(II), Mn(II) and Fe(II) complexes are described in this work. The new dissymmetric steric hindered Schiff-base ligand containing a donor set of NONO was prepared through reaction of 3,4-diaminobenzophenon with 3,5-Bu^t₂-salicylaldehyde. Certain metal complexes of this ligand were synthesized by treating an ethanolic solution of the ligand with an equimolar amount of metal salts. The ligand and its complexes were characterized by FT-IR, UV–vis, ¹H NMR, elemental analysis, molar conductivity and thermal analysis methods in addition to magnetic susceptibility, electrochemistry and spectroelectrochemistry techniques. The tetradentate and mononuclear metal complexes were obtained by reacting N,N′-(3,4-benzophenon)-3,5-Bu^t₂-salicylaldimine (LH₂) with some metal acetate in a 1:1 mole ratio. The molar conductance data suggest metal complexes to be non-electrolytes.     

Novel heterometallic Schiff base complexes featuring unusual tetranuclear {Co(III)2Fe(III)2(μ-O)6} and octanuclear {Co(III)4Fe(III)4(μ-O)14} cores: direct synthesis, crystal structures, and magnetic properties

A one-pot reactions of cobalt powder with iron(II) chloride in dimethylformamide (DMF; 1) or dimethyl sulfoxide (DMSO; 2) solutions of polydentate salicylaldimine Schiff base ligands (H(2)L(1), 1; H(4)L(2), 2) based on 2-aminobenzyl alcohol (1) or tris(hydroxymethyl)aminomethane (2), formed in situ, yielded two novel heterometallic complexes, [Co(III)(2)Fe(III)(2)(L(1))(6)]·4DMF (1) and [Co(III)(4)Fe(III)(4)(HL(2))(8)(DMSO)(2)]·18DMSO (2). Crystallographic investigations revealed that the molecular structure of 1 is based on a tetranuclear core, {Co(III)(2)Fe(III)(2)(μ-O)(6)}, with a chainlike metal arrangement, while the structure of 2 represents the first example of a heterometallic octanuclear core, {Co(III)(4)Fe(III)(4)(μ-O)(14)}, with a quite rare manner of metal organization, formed by two pairs of {CoFe(HL(2))(2)} and {CoFe(HL(2))(2)(DMSO)} moieties, which are joined by O bridges of the Schiff base ligands. Variable-temperature (1.8-300 K) magnetic susceptibility measurements showed a decrease of the μ(B) value at low temperature, indicative of antiferromagnetic coupling (J/hc = -32 cm(-1) in 1; J/hc = -20 cm(-1) in 2) between the Fe(III) magnetic centers in both compounds. For 2, three J constants between Fe(III) centers were assumed to be identical. High-frequency electron paramagnetic resonance spectra allowed one to find spin Hamiltonian parameters in the coupled-spin triplet and quintet states of 1 and estimate them in 2. The "outer" and "inner" Fe atoms in 2 appeared separately in the M?ssbauer spectra.     

Microwave assisted synthesis and characterization of N,N′-bis(salicylaldehydo)ethylenediimine complexes of Mn(II), Co(II), Ni(II), and Zn(II)

Microwave chemistry is a green chemical method that improves reaction conditions and product yields while reducing solvent amounts and reaction times. The main aim of this article is to synthesize the tetradentate N₂O₂ ligand [HO(Ar)CH=N–(CH₂)₂–N=CH(Ar)OH] and manganese(II), cobalt(II), nickel(II), and zinc(II) complexes of the type ML by classical and microwave techniques. The resulting Schiff base and its complexes are characterized by ¹H NMR, infrared, elemental analysis, and electronic spectral data. The ligand and its Co(II) and Mn(II) complexes were further identified by X-ray diffraction and mass spectra to confirm the structure. The results suggest that the metal is bonded to the ligand through the phenolic oxygen and the imino nitrogen.     

Synthesis,characterization, spectral studies and antifungal activity of Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes with 3,3′-bis[N,N,di(carboxymethyl)-aminomethyl]- o -cresol sulphonphthalein

Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes of the type Na₄[ML(H₂O)₂] of the ligand, 3,3′-bis[N,N-di(carboxymethyl)-aminomethyl]-o-cresol sulphonphthalein (Xylenol Orange, Na₄H₂L), have been synthesized and characterized by different physico-chemical (elemental analyses, solubility, electrolytic conductances, magnetic susceptibility measurements) and spectral (u.v.-vis, i.r., e.s.r., and powder X-ray diffraction) techniques for their structure determination. The data suggest 1?:?1 (M?:?L) compositions and octahedral geometries around M(II) except for Cu(II). Antifungal activity of the complexes measured against ten fungi show significant activity against Alternaria brassicicola, Alternaria solanai, Cercospora species and Helminthosporium oryzae and moderate antifungal activity against Curvularia species, Curvularia lunata, Curvularia penniseti, Colletotrichum capsici, Aspergillus niger, Aspergillus flavus Erysiphae pisi and Fusarium udum fungi.     

Multireversible redox processes in pentanuclear bis(triple-helical) manganese complexes featuring an oxo-centered triangular {Mn(II)2Mn(III)(μ3-O)}5+ or {Mn(II)Mn(III)2(μ3-O)}6+ core wrapped by two {Mn(II)2(bpp)3}-

A new pentanuclear bis(triple-helical) manganese complex has been isolated and characterized by X-ray diffraction in two oxidation states: [{Mn(II)(μ-bpp)(3)}(2)Mn(II)(2)Mn(III)(μ-O)](3+) (1(3+)) and [{Mn(II)(μ-bpp)(3)}(2)Mn(II)Mn(III)(2)(μ-O)](4+) (1(4+)). The structure consists of a central {Mn(3)(μ(3)-O)} core of Mn(II)(2)Mn(III) (1(3+)) or Mn(II)Mn(III)(2) ions (1(4+)) which is connected to two apical Mn(II) ions through six bpp(-) ligands. Both cations have a triple-stranded helicate configuration, and a pair of enantiomers is present in each crystal. The redox properties of 1(3+) have been investigated in CH(3)CN. A series of five distinct and reversible one-electron waves is observed in the -1.0 and +1.50 V potential range, assigned to the Mn(II)(4)Mn(III)/Mn(II)(5), Mn(II)(3)Mn(III)(2)/Mn(II)(4)Mn(III), Mn(II)(2)Mn(III)(3)/Mn(II)(3)Mn(III)(2), Mn(II)Mn(III)(4)/Mn(II)(2)Mn(III)(3), and Mn(III)(5)/Mn(II)Mn(III)(4) redox couples. The two first oxidation processes leading to Mn(II)(3)Mn(III)(2) (1(4+)) and Mn(II)(2)Mn(III)(3) (1(5+)) are related to the oxidation of the Mn(II) ions of the central core and the two higher oxidation waves, close in potential, are thus assigned to the oxidation of the two apical Mn(II) ions. The 1(4+) and 1(5+) oxidized species and the reduced Mn(4)(II) (1(2+)) species are quantitatively generated by bulk electrolyses demonstrating the high stability of the pentanuclear structure in four oxidation states (1(2+) to 1(5+)). The spectroscopic characteristics (X-band electron paramagnetic resonance, EPR, and UV-visible) of these species are also described as well as the magnetic properties of 1(3+) and 1(4+) in solid state. The powder X- and Q-band EPR signature of 1(3+) corresponds to an S = 5/2 spin state characterized by a small zero-field splitting parameter (|D| = 0.071 cm(-1)) attributed to the two apical Mn(II) ions. At 40 K, the magnetic behavior is consistent for 1(3+) with two apical S = 5/2 {Mn(II)(bpp)(3)}(-) and one S = 2 noninteracting spins (11.75 cm(3) K mol(-1)), and for 1(4+) with three S = 5/2 noninteracting spins (13.125 cm(3) K mol(-1)) suggesting that the {Mn(II)(2)Mn(III)(μ(3)-O)}(5+) and {Mn(II)Mn(III)(2)(μ(3)-O)}(6+) cores behave at low temperature like S = 2 and S = 5/2 spin centers, respectively. The thermal behavior below 40 K highlights the presence of intracomplex magnetic interactions between the two apical spins and the central core, which is antiferromagnetic for 1(3+) leading to an S(T) = 3 and ferromagnetic for 1(4+) giving thus an S(T) = 15/2 ground state.     

Analytical relationships between the ionization of 1,3-dicarbonylic ligands and stability of their Cr(III), Ni(II), Co(II) and Cu(II) 1∶1 chelates

It has been demonstrated that the logarithm of the stability constant of some monochelated chromium(III) compounds, with structurally similar 1,3-dicarbonylic species, is linearly related to the negative logarithm of the acid ionization constant of the ligand. Graphical and analytical correlations which could be useful in predicting equilibrium constants of chromium(III)--diketonates, as well as other first-row transition metal derivatives, have been developed. A quantitative evaluation of the complexes stability has been carried out, providing information about the effects of ligand substituents on the equilibrium constants.     

Hexanuclear Fe(III)2Co(III)2M(II)2 (M = Cu, Ni, Mn) clusters based on Kläui's tripodal ligand and tricyanometalates: syntheses, structures and magnetic properties

With the use of Kl?ui's tripodal ligand, [(Cp)Co(P(O)(OEt)(2))(3)](-) (L(CoEt), Cp = cyclopentadiene) as the auxiliary ligand to react with different metal salts and tricyanometalate building blocks, five neutral trimetallic hexanuclear complexes: [(Tp)(2)Fe(2)(CN)(6)Cu(2)(L(CoEt))(2)]·6H(2)O (1, Tp = hydridotris(pyrazolyl)borate), [(Tp*)(2)Fe(2)(CN)(6)Cu(2)(L(CoEt))(2)]·2H(2)O (2, Tp* = hydridotris(3,5-dimethyl-pyrazolyl)borate), [(pzTp)(2)Fe(2)(CN)(6)Cu(2)(L(CoEt))(2)]·H(2)O·3MeOH (3, pzTp = tetra(pyrazolyl)borate), [(Tp)(2)Fe(2)(CN)(6)Ni(2)(L(CoEt))(2)(MeCN)(2)]·2MeCN·2H(2)O (4) and [(Tp)(2)Fe(2)(CN)(6)Mn(2)(L(CoEt))(2)(MeCN)(2)]·2MeCN (5), have been obtained and structurally characterized. Magnetic measurements confirm that there are ferromagnetic couplings between the cyano-bridged Fe and Cu/or Ni ions and antiferromagnetic interaction between the cyano-bridged Fe and Mn ions. Slow relaxation of the magnetization is observed in complexes 1 and 4, while complex 3 exhibits metamagnetic behavior with a critical field of 17.5 kOe.