Metal complexes with two tri-aza,tri-oxa pendant-armed macrocyclic ligands: Synthesis,characterization, crystal structures and fluorescence studies

Metal complexes of two new tri-aza, tri-oxa macrocycles containing ethyl acetate (L¹) or carboxymethyl (H₂L²) pendant arms with hydrated nitrate or perchlorate salts of alkaline earth, post-transition and lanthanide metal ions have been synthesized and characterized by microanalysis FAB MS, conductivity measurements, IR, UV–Vis spectroscopy and fluorescence emission studies. The synthesis and characterization of the Pb(II) complexes with the armless macrocyclic precursors L (Schiff base macrocycle) and L′ (diaminic reduced macrocycle) are also reported. The crystal structures of complexes [PbL(ClO₄)(H₂O)](ClO₄), [PbL′(ClO₄)](ClO₄) and ([Zn₂L²(Cl)(H₂O)](ClO₄))_∞ have been determined. In both lead(II) complexes, the metal ion is located inside the macrocyclic cavity and is coordinated by all N₃O₃ donor atoms in the complex with L′ but only by the nitrogen atoms present in the ligand in the complex with L. In both cases, the coordination sphere of the metal atom is completed with a perchlorate anion or a water molecule in the iminic complex of L. X-ray studies on the Zn(II) complex show the presence of a supramolecular structure that is consistent with a linear polymer formed alternately by an endomacrocyclic metal atom coordinated to a macrocyclic ligand and an exomacrocyclic metal ion in distorted octahedral and tetrahedral environments, respectively. UV–Vis and fluorescent emission studies were carried out on the ligands L¹ and H₂L² and their metal complexes, but only the luminescence spectra of the Eu(III) and Tb(III) complexes with L¹ in aqueous solution at ca. pH 7 show the characteristic visible emission of the metal. The value of the quantum yield determined for the Eu(III) complex is similar to that reported in the literature for other Eu(III) complexes.     

Template synthesis,spectroscopic, antibacterial,and antifungal studies of trivalent transition metal ion macrocyclic complexes

A novel series of complexes of the type [M(C₃₆H₂₂N₆)X]X₂, where M = Cr(III), Mn(III), Fe(III); X = Cl^?, NO₃^?, CH₃COO^?; and (C₃₆H₂₂N₆) corresponds to the tetradentate macrocyclic ligand, have been synthesized by condensation of 1,8-diaminonaphthalene and isatin in the presence of trivalent metal salts in methanolic medium. The complexes have been characterized by elemental analysis, conductance and magnetic measurements, and UV/Vis, IR, and mass spectroscopy. On the basis of these studies, a five coordinate square pyramidal geometry for all of these complexes is proposed. All synthesized macrocyclic complexes have been tested for in vitro antimicrobial activities against some pathogenic bacterial strains, viz. Staphylococcus aureus, Bacillus subtilis (Gram-positive), Escherichia coli, Pseudomonas aeruginosa (Gram-negative), and two fungal strains, viz. Aspergillus niger, Aspergillus flavus. The MICs shown by the complexes against these microbial strains have been compared with MICs shown by standard antibiotic ciprofloxacin and the antifungal drug amphotericin-B.     

Intramolecular oxidation of the ligand 4-methyl-2-N-(2-pyridylmethyl)aminophenol (Hpyramol) upon coordination with iron(II) chloride and manganese(II) perchlorate

The ligand Hpyramol (Hpyramol=4-methyl-2-N-(2-pyridylmethyl)aminophenol) is found to undergo an oxidative dehydrogenation of its amine function to an imine group upon coordination with iron(II) chloride and manganese(II) perchlorate. X-ray diffraction analyses for both complexes shows differences in the coordination geometry of the complexes most likely because of the two different counter-ions namely the strong coordinating chloride anions and the weak coordinating perchlorate anions. The coordination sphere of the iron(III) complex in [FeCl₂(pyrimol)(MeOH)](MeOH) is best described as a distorted octahedral FeN₂O₂Cl₂ chromophore, while the manganese(II) ions in [Mn(ClO₄)(pyrimol)(Hpyrimol)]₂ are in a distorted octahedral MnN₄O₂ environment with a 2:1 ligand to metal ratio instead of 1:1.     

Highly flexible O,O′,N ligands and their Fe, Ni, Cu and Zn complexes

Three new chiral ligands bearing an O,O′,N donor set (O_methoxyO_hydroxyN_pyridine) were synthesised and coordinated to Fe^III, Fe^II, Ni^II, Cu^II and Zn^II to yield complexes with the general formula [M(OON)Cl_x]_y. While the pyridine N and the hydroxy O atoms coordinate strongly to all applied metal ions, the methoxy donor seems not to be involved in coordination, although some evidence for a weak interaction between O_Me and the Zn^II were found in NMR spectra. In the bidentate O′,N coordination mode the new ligands exhibit several coordination geometries as analysed in the solid compounds by XRD, EXAFS and EPR and in solution by UV-Vis absorption, cyclic voltammetry, EXAFS, EPR or NMR spectroscopy.     

Interactions between metal ions and carbohydrates. Syntheses and spectroscopic studies of several lanthanide nitrate–d-galactitol complexes

Two complexes of neutral d-galactitol (C₆H₁₄O₆, G) with terbium nitrate, TbGN(I) and TbGN(II), and one complex with samarium nitrate SmGN were synthesized and characterized. From IR, FIR, THz and luminescence spectra the possible coordinations were suggested, and the single-crystal X-ray diffraction results confirm the spectroscopic conclusions. In TbGN(I) (Tb(NO₃)₃·C₆H₁₄O₆·3H₂O), the Tb³⁺ is 9-coordinated with three water molecules and six OH groups from two d-galactitol molecules. Nitrate ions do not coordinate to metal ions, which is different from other reported lanthanide nitrate–d-galactitol complexes. In TbGN(II) and SmGN (Ln(NO₃)₃·C₆H₁₄O₆), Ln³⁺ is 10-coordinated with six OH groups from two d-galactitol molecules and four oxygen from two bidentate nitrate ions, and one nitrate ion is hydrogen bonded. No water exists in the structures. d-Galactitol molecules provide their 1-, 2- and 3-hydroxyl groups to coordinate with one metal ion and their 4-, 5- and 6-hydroxyl groups to coordinate with another metal ion in the three structures. There is still a new topological structure that can be observed for lanthanide–d-galactitol complexes, which indicates that the coordinations between hydroxyl groups and metal ions are complicated.     

Superoxide dismutase activity of macrocyclic polyamine complexes

Copper(II) and nickel(II) complexes of macrocyclic polyamine derivatives possessing partial oligopeptide-like structures are found to suppress the xanthine-xanthine oxidase-mediated reduction of nitroblue tetrazolium and also to suppress formazan formation by potassium superoxide. The activity in the superoxide dismutase assay is dependent on ring size, type and number of donor atoms, metal ion, and substituents on the macrocycles. Some of those are more active than the known O₂^? scavengers such as copper(II)-salicylate and copper(II)-amino acid (or peptide) complexes. Nickel (II)-naphthylmethyl-dioxo-[16]ane N₅, 13, 1 : 1 complex (NiH_?2L) is the most active among the 30 chelates examined.     

Cyclic and acyclic compartmental Schiff bases, their reduced analogues and related mononuclear and heterodinuclear complexes

[1+1] macrocyclic and [1+2] macroacyclic compartmental ligands (H₂L), containing one N₂O₂, N₃O₂, N₂O₃, N₄O₂ or O₂N₂O₂ Schiff base site and one O₂O_n (n=3, 4) crown-ether like site, have been prepared by self-condensation of the appropriate formyl- and amine precursors. The template procedure in the presence of sodium ion afforded Na₂(L) or Na(HL) · nH₂O. When reacted with the appropriate transition metal acetate hydrate, H₂L form M(L) · nH₂O, M(HL)(CH₃COO) · nH₂O, M(H₂L)(X)₂ · nH₂O (M=Cu²⁺, Co²⁺, Ni²⁺; X=CH₃COO⁻, Cl⁻) or Mn(L)(CH₃COO) · nH₂O according to the experimental conditions used. The same complexes have been prepared by condensation of the appropriate precursors in the presence of the desired metal ion. The Schiff bases H₂L have been reduced by NaBH₄ to the related polyamine derivatives H₂R, which form, when reacted with the appropriate metal ions, M(H₂R)(X)₂ (M= Co²⁺, Ni²⁺; X=CH₃COO⁻, Cl⁻), Cu(R) · nH₂O and Mn(R)(CH₃COO) · nH₂O. The prepared ligands and related complexes have been characterized by IR, NMR and mass spectrometry. The [1+1] cyclic nature of the macrocyclic polyamine systems and the site occupancy of sodium ion have been ascertained, at least for the sodium (I) complex with the macrocyclic ligand containing one N₃O₂ Schiff base and one O₂O₃ crown-ether like coordination chamber, by an X-ray structural determination. In this complex the asymmetric unit consists of one cyclic molecule of the ligand coordinated to a sodium ion by the five oxygen atoms of the ligand. The coordination geometry of the sodium ion can be described as a pentagonal pyramid with the metal ion occupying the vertex. In the mononuclear complexes with H₂L or H₂R the transition metal ion invariantly occupies the Schiff base site; the sodium ion, on the contrary, prefers the crown-ether like site. Accordingly, the heterodinuclear complexes [MNa(L)(CH₃COO)_x] (M=Cu²⁺, Co²⁺, Ni², x=1; M=Mn³⁺, x=2) have been synthesised by reacting the appropriate formyl and amine precursors in the presence of M(CH₃COO)_n · nH₂O and NaOH in a 1:1:1:2 molar ratio. The reaction of the mononuclear transition metal complexes with Na(CH₃COO) · nH₂O gives rise to the same heterodinuclear complexes. Similarly [MNa(R)(CH₃COO)_x] have been prepared by reaction of the appropriate polyamine ligand H₂R with the desired metal acetate hydrate and NaOH in 1:1:2 molar ratio.     

Molecular movements inside [1+1] asymmetric compartmental macrocycles: Formation of positional mononuclear and hetero-dinuclear lanthanide(III) isomers and related homo-dinuclear complexes

The mononuclear macrocyclic lanthanide(III) complexes, [Ln(H₂L)(H₂O)₄]Cl₃ (Ln = Y, La, Ce, Cu, Tb, Yb, Lu; H₂L = H₂L_A, H₂L_B, H₂L_C) were prepared by condensation 3,3′-(3,6-dioxaoctane-1,8-diyldioxy)bis(2-hydroxybenzaldehyde) or 3,3′-(3-oxapentane-1,5-diyldioxy)bis(2-hydroxybenzaldehyde) with 1,5-diamino-3-azamethylpentane or 1,7-diamino-3-azamethylheptane in the presence of LnCl₃ · nH₂O as templating agent. The asymmetric [1+1] ligands H₂L_A, H₂L_B and H₂L_C contain one smaller or larger N₃O₂ Schiff base site and one crown-ether like O₂O₄ or O₂O₃ site. The preference of the lanthanide ion to reside into the Schiff base or the crown-ether like chamber was investigated in the solid state and in methanol or dimethylsulfoxide solution. It was found that in the solid state or in methanol the lanthanide(III) ion coordinates into the O₂O_n site while in dimethylsulfoxide demetalation and partial metal ion migration from the O₂O_n into the N₃O₂ chamber occur. The mononuclear lanthanide(III) complexes [Ln(H₂L)(H₂O)₄]Cl₃ with the Ln³⁺ ion in the O₂O_n site have been used as ligands in the synthesis of the heterodinuclear complexes LnLn′(L)(Cl)₄ · 4H₂O by reaction with the appropriate Ln′(III) chloride in methanol and in the presence of base. The related homodinuclear complexes Ln₂(L)(Cl)₄ · 4H₂O have been prepared by the one-pot condensation of the appropriate precursors in the presence of base and of the lanthanide(III) ion as templating agent.The single-crystal X-ray structure of [Eu(H₂L_A)(H₂O)₄]Cl₃ · 5H₂O has been determined. The europium ion is nine-coordinated in the O₂O₃ ligand site and bonded to four water molecules and the coordination polyhedron can be described as a square monocapped antiprism.The site occupancy of the different lanthanide(III) ions and the physico-chemical properties arising from the different dinuclear aggregation and/or from the variation of the crown-ether shape have been investigated by IR and NMR spectroscopy, MS spectrometry and SEM-EDS microscopy. In particular, site migration and/or transmetalation reactions, together with demetalation reactions, have been monitored by NMR studies in methanol and dimethylsulfoxide. It was found that these processes strongly depend on the shape of the two coordination chambers, the solvent used and the radius of the lanthanide(III) ions. Thus, these molecular movements can be tuned by changing appropriately these parameters.     

Tridentate N(2)S ligand from 2,2'-dithiodibenzaldehyde and N,N-dimethylethylenediamine: Synthesis, structure, and characterization of a Ni(II) complex with relevance to Ni Superoxide Dismutase

Nickel Superoxide Dismutase (NiSOD) and the A-cluster of Carbon Monoxide Dehydrogenase/Acetyl Coenzyme A Synthase (CODH/ACS) both feature active sites with Ni coordinated by thiolate and amide donors. It is likely that the particular set of donors is important in tuning the redox potential of the Ni center(s). We report herein an expansion of our efforts involving the use of 2,2′-dithiodibenzaldehyde (DTDB) as a synthon for metal-thiolate complexes to reactions with Ni complexes of N,N-dimethylethylenediamine (dmen). In the presence of coordinating counterions, these reactions result in monomeric square-planar complexes of the tridentate N₂S donor ligand derived from the Schiff-base condensation of dmen and DTDB. In the absence of a coordinating counterion, we have isolated a Ni(II) complex with an asymmetric N₂S₂ donor set involving one amine and one imine N donor in addition to two thiolate donors. This latter complex is discussed with respect to its relevance to the active site of NiSOD.     

Mono- and dinuclear Fe(III) complexes with the N2O2 donor 5-chlorosalicylideneimine ligands; synthesis, X-ray structural characterization and magnetic properties

Two novel monomeric [C₁₈H₁₇Cl₃N₂O₂Fe] (1) and dimeric [C₃₈H₃₆N₄O₄Cl₆Fe₂] (2) Fe(III) tetradentate Schiff base complexes have been synthesized and their crystal structures have been determined by single crystal X-ray diffraction analysis. In complex (1) the Schiff base ligand coordinates toward one iron atom in a tetradentate mode and each iron atom is five coordinated with the coordination geometry around iron atom which can be described as a distorted square pyramid. The presence of a short (2.89 Å) non-bonding interatomic Fe···O distances between adjacent monomeric Fe(III) complexes results in the formation of a dimer. Structural analysis of compound (2) shows that the structure is a centrosymmetric dimer in which the six coordinated Fe(III) atoms are linked by μ-phenoxo bridges from one of the phenolic oxygen atoms of each Schiff base ligand to the opposite metal center. The variable-temperature (2-300 K) magnetic susceptibility (χ) data of these two compounds have been investigated. The results show that for both complexes Fe(III) centers are in the high spin configuration (S = 5/2) and indicate antiferromagnetic spin-exchange interaction between Fe(III) ions. The obtained results are briefly discussed using magnetostructural correlations developed for other class of iron(III) complexes.     

Mononuclear Ni(II) and Zn(II) complexes of some potentially binucleating Schiff base ligands

Mononuclear Zn(II) and Ni(II) complexes have been prepared from two new Schiff base ligands in which two alternative co-ordination sites (N₂O₂ or O₂O₂) occur. The first ligands is the Schiff base derived from 1,2-diaminobenzene and 2-hydroxy-3-carboxyl-1-napthaldehyde (bopaH₄). The complexes of this ligand contain the metal ions in the N₂O₂ coordination site as a result of the steric requirements of the co-ordinated ligand. The second ligand series are derivatives of X-substituted 1,2-diaminobenzenes, 2-hydroxy-3-carboxy-1-naphthaldehyde and 2-hydroxy-5-methyl isophthaldehyde (X-bolaH₃). In this case Ni(II) occupies the N₂O₂ site in its complexes with the X-bolaH₃ ligands, whereas the Zn(II) complexes are co-ordinate through the O₂O₂ site since the steric restrictions are less severe.     

Mononuclear and dinuclear complexes derived from new potentially heptadentate acyclic Schiff bases

New potentially heptadentate compartmental ligands have been prepared by reaction of o-acetoacetylphenol or 3-formylsalycilic acid with diethylenetriamine or bis-3-aminopropyl-phenylphosphine.These Schiff bases contain an inner O₂N₂X (X = N, P) and an outer O₂O₂ coordination site which can bond, in close proximity, two similar or dissimilar metal ions.With some metal salts (nickel(II), copper(II) and uranyl(VI) acetates) mononuclear, homo- and heterodinuclear complexes have been synthesized. The spectroscopic, magnetic and electrochemical properties of these complexes have been studied. The catalytic activity of a binuclear copper(II) complex towards the oxidation of 3,5-di-t-butylcatechol to the corresponding quinone was also investigated.     

Synthesis,spectroscopic, and antibacterial activity of tetraazamacrocyclic complexes of trivalent chromium,manganese, and iron

A new series of macrocyclic complexes of type [M(TML)X]X₂, where M = Cr(III), Mn(III), or Fe(III), TML is tetradentate macrocyclic ligand, and X = Cl^?, NO₃^?, CH₃COO^? for Cr(III), Fe(III) and X = CH₃COO^? for Mn (III), has been synthesized by condensation of benzil and succinyldihydrazide in the presence of metal salt. The complexes have been so formulated due to the 1:2 electrolytic nature of these complexes as shown by conductivity measurements. The complexes have been characterized with the help of various physicochemical techniques such as elemental analysis, molar conductance, electronic and infrared spectral studies, and magnetic susceptibility. On the basis of these studies, a five-coordinate distorted square pyramidal geometry, in which two nitrogens and two carbonyl oxygen atoms are suitably placed for coordination toward the metal ion, has been proposed for all the complexes. The complexes have been tested for their in vitro antibacterial activity. Some of the complexes show remarkable antibacterial activities against some selected bacterial strains. The minimum inhibitory concentrations shown by these complexes have been compared with those shown by some standard antibiotics such as linezolid and cefaclor.     

Synthesis, spectroscopic, structural and complexation studies of a new tetra-naphthylmethylene pendant-armed macrocyclic ligand

A novel emissive tetra-naphthylmethylene pendant-armed macrocyclic ligand and a series of complexes with monovalent and divalent metal ions have been synthesized. Solid compounds have been isolated as mononuclear (Co(II), Cu(II) and Zn(II)) or dinuclear (Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Ag(I)), complexes, depending on the counterions used. The chemical and photophysical properties of the free ligand, the protonation behavior and its metal complexes have been investigated in solution. UV-Vis spectroscopy has revealed a 1:1 binding stoichiometry for Cu(II), Zn(II), Cd(II), Ni(II) and Co(II), and 2:1 molar ratio for Ag(I). In chloroform, the free ligand presents two emission bands related to the monomer naphthalene emission and a red-shifted band attibutable to an exciplex due to a charge transfer from the nitrogen lone electron pair to the excited chromophore. Upon protonation of the free amines or due to metal complexation, the exciplex band disappears. The crystal structure of [Ag₂L(NO₃)₂] is also reported. The structure reveals that both metal ions are into the macrocyclic cavity in a distorted square plane {AgN₃O} environment. Each Ag(I) atom interacts with two neighbouring amine nitrogen atoms, one pyridine nitrogen and one oxygen atom from a monodentate nitrate ion.     

Synthesis of a novel pyridine-diamino bridged diphosphine ligand and its macrocyclic metal complexes

A novel long chain diphosphine ligand with a pyridine-diamino bridge, 2,6-bis(N-benzyl-N-diphenylphosphinomethylamino)pyridine (PNP1), was prepared conveniently using the Mannich reaction of HPPh₂ with paraformaldehyde and 2,6-bis(N-benzylamino)pyridine in high yield. Reactions of the ligand with metal complexes, M(COD)Cl₂ (M = Pd, Pt), M(CH₃CN)₄ClO₄ (M = Cu, Ag) and M(CO)₆ (M = Mo, W) afforded the corresponding 10-numbered monometallic macrocyclic complexes with an uncoordinated pyridyl bridge. The monometallic chelate PdCl₂(PNP1) continued to react with Ag⁺ or Cu⁺ giving the μ-Cl bridged bicyclic metallic complex (μ-Cl)₂[PdCl(PNP1)]₂. The diphenylphosphine group coordinated with metal ion in cis-form in all the 10-numbered macrocyclic metal complexes. Ligand PNP1 and another known analogous 2,6-bis(N-diphenylphosphinoamino)pyridine (PNP2) reacted with Au(SMe₂)Cl giving the corresponding bimetallic Au₂Cl₂(PNP1) and Au₂Cl₂(PNP2), respectively. The latter bimetallic complexes continued to react with Ag⁺ and diphosphine ligand to give the corresponding bimetallic macrocyclic complexes Au₂(ligand)₂(ClO₄)₂. All the complexes were characterized and the structures of some complexes were confirmed by X-ray single crystallography determination.     

Correlation of proton release and ultraviolet difference spectra associated with metal binding by transferrin

A variety of metal ions can bind to the iron-transport protein, transferrin, at two specific sites. For each metal ion, a carboxylate anion is concomitantly bound. Six metal ions which were examined fall into two classes based on proton release and ultraviolet spectral changes which accompany binding to the protein. Class II ions, which include Cu²⁺ and Zn²⁺, release approximately 2 H⁺/metal bond. Class III ions, which include Fe³⁺, Ga³⁺, Al³⁺, and VO²⁺, release approximately 3 H⁺/metal bound. The increase in absorbance near 242 nm, characteristic of tyrosine ionization, has the ratio 0.55–0.75 for class II:class III ions. Both Fe³⁺ and Cu²⁺ form metal-transferrin-oxalate complexes in the presence of excess C₂O₄^2?. Fe³⁺ releases close to 3 H⁺/metal whether forming oxalate or bicarbonate complexes with transferrin. Binding of Cu²⁺ to transferrin releases 2 H⁺/metal in the presence of C₂O^2?₄ or HCO₃^?. Since equal numbers of H⁺/metal are released for both anions, it is likely that the bicarbonate ion does not lose its proton, and remains as HCO₃^? in transferrin. These results are interpreted in terms of possible combinations of ligands at the metal binding sites.     

Antibacterial activity and spectral studies of trivalent chromium,manganese, iron macrocyclic complexes derived from oxalyldihydrazide and glyoxal

A new series of complexes is synthesized by template condensation of oxalyldihydrazide and glyoxal in methanolic medium in the presence of trivalent chromium, manganese and iron salts forming complexes of the type: [M(C₈H₈N₈O₄)X]X₂ where M = Cr(III), Mn(III), Fe(III) and X = Cl^{? 1}, , CH₃COO^{? 1}. The complexes have been characterized with the help of elemental analyses, conductance measurements, magnetic susceptibility measurements, electronic, NMR, infrared and far infrared spectral studies. On the basis of these studies, a five coordinate square pyramidal geometry for these complexes has been proposed. The biological activities of the metal complexes were tested in vitro against a number of pathogenic bacteria and some of the complexes exhibited remarkable antibacterial activities.     

Functional model for intradiol-cleaving catechol 1,2-dioxygenase: Synthesis, structure, spectra, and catalytic activity of iron(III) complexes with substituted salicylaldimine ligands

A series of mononuclear iron(III) complexes with containing phenolate donor of substituted-salicylaldimine based ligands [Fe(L¹)(TCC)] · CH₃OH (1), [Fe(L²)(TCC)] · CH₃OH (2), [Fe(L³)(TCC)] (3), and [Fe(L⁴)(TCC)] (4) have been prepared and studied as functional models for catechol dioxygenases (H₂TCC = tetrachlorocatechol, or HL¹ = N′-(salicylaldimine)-N,N-diethyldiethylenetriamine, HL² = N′-(5-Br-salicylaldimine)-N,N-diethyldiethylenetriamine, HL³ = N′-(4,6-dimethoxy-salycyl-aldimine)-N,N-diethyl-diethylenetriamine, HL⁴ = N′-(4-methoxy-salicylaldimine)-N,N-diethyl-diethylenetriamine). They are structural models for inhibitors of enzyme-substrate adducts from the reactions of catechol 1,2-dioxygenases. Complexes 1-4 were characterized by spectroscopic methods and X-ray crystal structural analysis. The coordination sphere of Fe(III) atom of 1-4 is distorted octahedral with N₃O₃ donor set from the ligand and the substrate TCC occupying cis position, and Fe(III) is in high-spin (S = 5/2) electronic ground state. The in situ prepared iron(III) complexes without TCC, [Fe(L¹)Cl₂], [Fe(L²)Cl₂], [Fe(L³)Cl₂], and [Fe(L⁴)Cl₂] are reactive towards intradiol cleavage of the 3,5-di-tert-butylcatechol (H₂DBC) in the presence of O₂ or air. The reaction rate of catechol 1,2-dioxygenase depends on the redox potential and acidity of iron(III) ions in complexes as well as the substituent effect of the ligands. We have identified the reaction products and proposed the mechanism of the reactions of these iron(III) complexes with H₂DBC with O₂.     

Preparation and properties of mono, homo- and heterobinuclear complexes with a new heptadentate Schiff base ligand

A new heptadentate Schiff base, containing an inner N₃O₂ and an outer O₂O₂ site, has been obtained by the reaction of 3-formylsalicylic acid and diethylenetriamine. By reaction of this ligand with copper(II), nickel(II) or uranyl(VI) salts, mononuclear and dinuclear complexes have been synthesized. The mononuclear complexes can act as ligands towards a second metal ion giving rise to homodinuclear or heterodinuclear complexes. The enlargement of the inner coordination chamber allows the synthesis of dinuclear uranyl(VI) species, impossible to obtain with the inner N₂O₂ site of the ligands previously employed. The equatorial pentacoordination of the UO₂²⁺ group in the outer O₂O₂ chamber is reached with the coordination of a solvent molecule to the central metal ion. The electrochemical behaviour of some complexes prepared is also reported.     

Chiroptical Spectra of Tetrakis (+)‐3‐Heptafluorobutylrylcamphorate Ln(III) Complexes with an Encapsulated Alkali Metal Ion: Solution Structures as Revealed by Chiroptical Spectra

The preparation of tetrakis((+)‐hfbc) lanthanide(III) complexes with an encapsulated alkali metal and ammonium ions M[Ln((+)‐hfbc)₄] (hereafter abbreviated as M‐Ln : (+)‐hfbc, (+)‐heptafluorobutyrylcamphorate; M, ammonium or benzyl ammonium ions as well as alkali metal ions) was reported and discussed. The electronic circular dichroism (CD) spectra in the intraligand π?π* transition of M–Ln were examined in view of the solvent effect. Here, the concentration, alkali metal, and ammonium ion dependences are compared with the solid CD, ⁵D₀ ← ⁷F₀(Eu(III)) excitation spectra, circularly polarized luminescence, and vibrational circular dichroism. It has been revealed that the dodecahedral eight coordinate DD‐8‐M‐Ln complexes in crystals are equilibrated between the diastereoselectively formed square antiprism eight coordinate SAPR‐8‐M‐Ln and [Ln((+)‐hfbc)₃] in EtOH and CH₃CN solutions or between the SAPR‐8‐M‐Ln and DD‐D_2d(mmmm)‐8‐M‐Ln complexes in CHCl₃ solution. The observed CD couplets are found to reflect the exciton CD couplets which are useful to determine the four‐bladed SAPR‐(llll) absolute configuration around the lanthanide(III) ion. Chirality 24:1055–1062, 2012. © 2012 Wiley Periodicals, Inc.