Co(II)-substituted Octopus vulgaris hemocyanin

Co(II)-substituted hemocyanin (Co(II)Hc) of the octopus, Octopus vulgaris, has been prepared by dialysis of apohemocyanin against Co(II·) ion and subsequent Chelex-treatment. The blue 50%-Co(II)Hc (half-apo Co(II)Hc), in which binuclear coppers are replaced in the hemocyanin by a single Co(II), exhibits two absorption maxima at 560 (?_Co=250) and 594 nm (?_Co=320 M^?1 cm^?1) and a shoulder near 610 nm, all of which are attributed to a dd transition of high spin Co(II) (S=3/2) with a tetrahedral geometry. The magnetic circular dichroism (MCD) spectrum in this region also suggests the existence of a tetrahedral Co(II) species in the protein. The visible absorption and MCD spectra of octopus 50%-Co(II)Hc are quite similar to those of squid 50%-Co(II)Hc described in the previous paper (S. Suzuki, J. Kino, M. Kimura, W. Mori and A. Nakahara, Inorg. Chim. Acta, 66, 41 (1982)). The formation of half-apo Co(II)Hc demonstrates that the binuclear copper sites in native octopus hemocyanin may differ from each other in coordination geometry, as in other molluscan hemocyanins, squid and snail hemocyanins. The coordination environment of the active-site Co(II) substituted for Cu in the octopus hemocyanin is the same as that of the corresponding active site of the squid hemocyanin.     

A spectral investigation of the copper(II) complex of the antitumor compound bleomycin

A thorough spectral investigation of the copper(II) complex of the antitumor compound, bleomycin, has been carried out in solution employing optical, difference optical, electron spin resonance, and circular dichroism techniques. The optical spectrum of a pH = 7 solution of the 1:1 complex between copper(II) and bleomycin is characterized by a broad weak band in the visible region (λ_max = 610 nm) that cannot be resolved and intense ultraviolet bands at 317 (? = 2800), 327 (shoulder), 250 (? = 4700), and 257 nm (shoulder). The circular dichroism spectrum in the visible region shows the broad and weak visible absorption band contains at least three components (558, 675, and 880 nm) that are likely to be “d-d” in origin. The electron spin resonance spectrum is characteristic of a tetragonal d⁹ copper(II) system showing no rhombic distoritions at X-band frequencies (g_x = g_y ± 0.002). The spin Hamiltonian parameters for the pH = 7.0 solution corrected for second order effects are A_∥ = 177 × 10^?4 cm^?1, A_⊥ ? 15 × 10^?4 cm^?1, g_∥ = 2.214, g_⊥ = 2.039. Most interesting was the observation of extra hyperfine splitting due to endogenous nitrogen coordination in a 30% glycerol glass (A^N = 12.0 × 10^?4 cm^?1). That pattern is best interpreted as a seven-line sequence associated with three liganded nitrogens. A dramatic change in all spectral properties occurs when the pH of the copper(II)-bleomycin complex is lowered to 2.5. All these data taken together suggest a CuN₃O coordination complex in solution. Details and justifications as well as a discussion of the limitations of the interpretations are presented.     

Synthesis, structure, and magnetic properties of dinuclear nickel(II) complexes with a phenol-based dinucleating ligand with four methoxyethyl chelating arms

Dinuclear nickel(II) complexes [Ni₂(bomp)(MeCO₂)₂]BPh₄ (1) and [Ni₂(bomp)(PhCO₂)₂]BPh₄ (2) were synthesized with the dinucleating ligand 2,6-bis[bis(2-methoxyethyl)aminomethyl]-4-methylphenol [H(bomp)]. X-Ray analysis revealed that the complex 1 · 0.5CHCl₃ contains two nickel(II) ions bridged by phenolic oxygen and two acetate groups, forming a μ-phenoxo-bis(μ-acetato)dinickel(II) core. Electronic spectra were investigated for 1 and 2 in the range of 400-1800 nm, and the data were typical for the octahedral high-spin nickel(II) complexes. Obtained spectral components were well simulated based on the angular overlap model assuming the trigonally distorted octahedral geometry. Magnetic susceptibility was measured for 1 and 2 over a temperature range of 4.5-300 K. The optimized magnetic data were J = 1.75 cm⁻¹, zJ′ = −0.234 cm⁻¹, g = 2.21, D = 15.1 cm⁻¹, and TIP = 370 × 10⁻⁶ cm⁻¹ for complex 1 and J = 3.55 cm⁻¹, zJ′ = −0.238 cm⁻¹, g = 2.23, D = 21.8 cm⁻¹, and TIP = 470 × 10⁻⁶ cm⁻¹ for complex 2. The data revealed ferromagnetic interactions between the two nickel(II) ions.     

Nickel(II) and copper(II) complexes of Schiff base ligands containing N4O2 and N4S2 donors with pyrrole terminal binding groups: Synthesis, characterization, X-ray structures, DFT and electrochemical studies

A series of hexadentate ligands, H₂L^m (m = 1−4), [1H-pyrrol-2-ylmethylene]{2-[2-(2-{[1H-pyrrol-2-ylmethylene]amino}phenoxy)ethoxy]phenyl}amine (H₂L¹), [1H-pyrrol-2-ylmethylene]{2-[4-(2-{[1H-pyrrol-2-ylmethylene]amino}phenoxy)butoxy]phenyl}amine (H₂L²), [1H-pyrrol-2-ylmethylene][2-({2-[(2-{[1H-pyrrol-2-ylmethylene]amino}phenyl)thio]ethyl}thio)phenyl]amine (H₂L³) and [1H-pyrrol-2-ylmethylene][2-({4-[(2-{[1H-pyrrol-2-lmethylene]amino}phenyl)thio]butyl}thio) phenyl]amine (H₂L⁴) were prepared by condensation reaction of pyrrol-2-carboxaldehyde with {2-[2-(2-aminophenoxy)ethoxy]phenyl}amine, {2-[4-(2-aminophenoxy)butoxy]phenyl}amine, [2-({2-[(2-aminophenyl)thio]ethyl}thio)phenyl]amine and [2-({4-[(2-aminophenyl)thio]butyl}thio)phenyl]amine respectively. Reaction of these ligands with nickel(II) and copper(II) acetate gave complexes of the form ML^m (m = 1−4), and the synthesized ligands and their complexes have been characterized by a variety of physico-chemical techniques. The solid and solution states investigations show that the complexes are neutral. The molecular structures of NiL³ and CuL², which have been determined by single crystal X-ray diffraction, indicate that the NiL³ complex has a distorted octahedral coordination environment around the metal while the CuL² complex has a seesaw coordination geometry. DFT calculations were used to analyse the electronic structure and simulation of the electronic absorption spectrum of the CuL² complex using TDDFT gives results that are consistent with the measured spectroscopic behavior of the complex. Cyclic voltammetry indicates that all copper complexes are electrochemically inactive but the nickel complexes with softer thioethers are more easily oxidized than their oxygen analogs.     

One-dimensional helical coordination polymers of cobalt(II) and iron(II) ions with 2,2′-bipyridyl-3,3′-dicarboxylate (BPDC)

One-dimensional (1-D) helical coordination polymers, [M^II(H₂O)₃(BPDC)]_n · nH₂O (M = Co (1), Fe (2)), have been prepared by the self-assembly of cobalt(II) and iron(II) ions, respectively, with 2,2′-bipyridyl-3,3′-dicarboxylic acid (H₂BPDC) in an aqueous solution. X-ray crystal structures of compounds 1 and 2 show that each metal ion displays a distorted octahedral coordination geometry including three water oxygen atoms, one oxygen atom of the carboxylate of a BPDC²⁻ belonging to the adjacent metal ion and two nitrogen atoms from the BPDC²⁻ acting as a chelating ligand. In 1 and 2, one carboxylate oxygen atom of coordinated BPDC²⁻ binds to the neighboring metal ion, which give rise to 1-D helical coordination polymers. The helical chains of 1 and 2 are linked by the hydrogen bonding interactions between the carboxylate oxygen atom of the BPDC²⁻ ion belonging to a chain and the water molecule of the adjacent helical chain, which lead to 2-D networks extending along the ab plane. The supramolecules 1 and 2 show isomorphous structures regardless of the metal ions.     

The ternary complex of Pseudomonas aeruginosa alcohol dehydrogenase with NADH and ethylene glycol

Pseudomonas aeruginosa alcohol dehydrogenase (PaADH; ADH, EC 1.1.1.1) catalyzes the reversible oxidation of primary and secondary alcohols to the corresponding aldehydes and ketones, using NAD as coenzyme. We crystallized the ternary complex of PaADH with its coenzyme and a substrate molecule and determined its structure at a resolution of 2.3 A, using the molecular replacement method. The PaADH tetramer comprises four identical chains of 342 amino acid residues each and obeys ~222-point symmetry. The PaADH monomer is structurally similar to alcohol dehydrogenase monomers from vertebrates, archaea, and bacteria. The stabilization of the ternary complex of PaADH, the coenzyme, and the poor substrate ethylene glycol (k(cat) = 4.5 sec(-1); Km > 200 mM) was due to the blocked exit of the coenzyme in the crystalline state, combined with a high (2.5 M) concentration of the substrate. The structure of the ternary complex presents the precise geometry of the Zn coordination complex, the proton-shuttling system, and the hydride transfer path. The ternary complex structure also suggests that the low efficiency of ethylene glycol as a substrate results from the presence of a second hydroxyl group in this molecule.     

Synthesis and characterization of new adjacent-bridged tetraaza macrocyclic compounds with C-alkyl groups: crystal structure and spectral properties of a copper(II) complex

New structurally constrained tetraaza macrocycles 2,3-dimethyl-1,5,12,16-tetraazapentacyclo[14.6.3.3^5.12.0^6.11.0^17.22]octacosane (L⁶) and 2,2,4,10,12,18,20-octamethyl-1,5,9,13-tetraazatricyclo[11.3.2. 2^5.9]eicosane (L⁷) have been prepared in high yield by direct reaction of 1,3-dibromopropane with 3,14-dimethyl-2,6,13,17-tetraazatricyclo[16.4.0.0^7.12]docosane (L³) or 2,5,5,7,9,12,12,14-octamethyl-1,4,8,11-tetraazacyclodecane (L⁵). The macrocycle L⁶ readily reacts with anhydrous copper(II) ion to yield [CuL⁶]²⁺ in dry methanol but does not react with nickel(II) ion, showing a high copper(II) ion selectivity. On the other hand, neither of the metal ions is inserted into the cavity of L⁷ in similar conditions. The copper(II) complex [CuL⁶](ClO₄)₂ has a severely distorted square-planar coordination polyhedron with a rarely observed trans-IV type N-conformation. The visible absorption spectrum of [CuL⁶]²⁺ shows the d-d transition band at 490 nm (ε=690 M⁻¹ cm⁻¹); the wavelength is quite similar to that of [CuL³]²⁺, but the molar absorption coefficient is extraordinarily larger than those of [CuL³]²⁺ and other related tetraaza macrocyclic copper(II) complexes.     

Synthesis and characterization of a high spin d Fe(II) complex with the tridentate ligand dipyrido(2,3-a:3,2-j)phenazine (dpop)

A new bis-(N-tridentate) Fe(II) complex [Fe(dpop^′)₂](PF₆)₂ (dpop^′=dipyrido(2,3-a:3^′,2^′-j)phenazine) was prepared and studied. The magnetic moment of the solid was determined as μ=5.2-4.9 BM and in CH₃CN solution as μ=4.9 BM and indicate the high spin Fe(II) state. The electronic absorption spectrum displays a broad weak absorption MLCT transition at 602 nm (ε=3.8×10³ M⁻¹ cm⁻¹), consistent with CT absorptions of other Fe(II) HS complexes. The cyclic voltammogram of the complex shows an irreversible Fe^2+/3+ oxidation at +1.55 V and two dpop^′0/−1 centered reductions at −0.20 and −0.59 V versus Ag/AgCl.     

Synthesis, structure, and properties of monomeric Fe(II), Co(II), and Ni(II) complexes of neutral N-(aryl)-2-pyridinecarboxamides

We have prepared and structurally characterized six-coordinate Fe(II), Co(II), and Ni(II) complexes of types [M^II(HL¹)₂(H₂O)₂][ClO₄]₂ (M = Fe, 1; Co, 3; and Ni, 5) and [M^II(HL²)₃][ClO₄]₂ · MeCN (M = Fe, 2 and Co, 4) of bidentate pyridine amide ligands, N-(phenyl)-2-pyridinecarboxamide (HL¹) and N-(4-methylphenyl)-2-pyridinecarboxamide (HL²). The metal centers in bis(ligand)-diaqua complexes 1, 3 and 5 are coordinated by two pyridyl N and two amide O atoms from two HL¹ ligands and six-coordination is completed by coordination of two water molecules. The complexes are isomorphous and possess trans-octahedral geometry. The metal centers in isomorphous tris(ligand) complexes 2 and 4 are coordinated by three pyridyl N and three amide O atoms from three HL² ligands. The relative dispositions of the pyridine N and amide O atoms reveal that the pseudo-octahedral geometry have the meridional stereochemistry. To the best of our knowledge, this work provides the first examples of structurally characterized six-coordinate iron(II) complexes in which the coordination is solely by neutral pyridine amide ligands providing pyridine N and amide O donor atoms, with or without water coordination. Careful analyses of structural parameters of 1-5 along with that reported in the literature [M^II(HL¹)₂(H₂O)₂][ClO₄]₂ (M = Cu and Zn) and [Co^III(L²)₃] have allowed us to arrive at a number of structural correlations/generalizations. The complexes are uniformly high-spin. Spectroscopic (IR and UV/Vis) and redox properties of the complexes have also been investigated.     

Preparation and spectroscopic properties of cobalt(III), nickel(II), copper(II) and zinc(II) complexes with a novel saturated macrocyclic ligand: 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22-docosahydrodibenzo-[b,i][1,4,8,11]tetraazacyclotetradecine

1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19, 20,21,22-Docosahydrodibenzo[b,i] [1,4,8,11] tetraazacyclotetradecine was prepared by hydrogenation of the benzo-analogue. Five isomers are feasible as a result of this hydrogenation but only two have been isolated: isomer A (melting point 158.5– 161.0 °C) and isomer B (melting point 194.5– 196.0 °C). The ¹³C NMR study was initiated to clear up the conformational differences between isomers. The cobalt(III), nickel(II), copper(II) and zinc(II) complexes of isomers A and B were prepared and investigated by near-ultraviolet, visible, infrared, NMR and ESR measurements. The ligand-field band in the 15 000-30 000 cm⁻¹ region for the cobalt(III), nickel(II) and copper(II) complexes provided information on their geometry around the central metal atom. That is to say, the cobalt(III) complexes are subjected to the octahedral ligand-field with axial elongation. The copper(II) complexes and the nickel- (II) complex of isomer A are subjected to the square- planar ligand-field in these complexes. The ligand- field bands for the nickel(II)complex of isomer B display the square-planar-distorted octahedral equilibrium in the coordinating solvent. ESR measurements for the copper(II) complexes also presented the spin Hamiltonian parameters in accord with the square- planar coordination. A strong band appearing at ca. 3200 cm⁻¹ was assigned to the N-H stretching mode and this band was slightly shifted to lower frequency upon metal coordination. The vibrational spectra and the conductance data provided evidences for the formation of the complexes with perchlorate ion as the counter ion. ¹³C NMR suggest that the complexes of isomer A are the cis-syn-cis form and the complexes of isomer B are the cis-anti-cis form.     

Thiolysis of O-2,4-dinitrophenyltyrosines. Spectrophotometric monitoring of the reaction and its use in peptide synthesis.

The thiolytic cleavage of O-2,4-dinitrophenyl (Dnp) derivatives of phenols was applied to the synthesis of tyrosine-containing peptides. This paper describes the preparation and properties of starting materials for such syntheses and illustrates their use in the synthesis of some peptides containing tyrosine at either the C- or N-terminus. A spectrophotometric method for following the thiolytic removal of Dnp groups from O-Dnp-tyrosines was developed and used to establish optimal conditions for quantitative deblockage in aqueous and nonaqueous solvents. The method is based on the fact that upon thiolysis, the colorless solution of O-Dnp-tyrosine (λ_max at 298 nm, pH 8.5) becomes yellow due to the formation of a dinitrophenylated thiol (for S-Dnp-2-mercaptoethanol, λmax at 340 nm, pH 8.5). This gives rise to a difference spectrum with a maximum at 354 nm (Δ?_M = + 8680 M^?1 cm^?1), a minimum at 298 nm (Δ?_M = ?5900 M^?1 cm^?1) and a crossover point at 318 nm, which is different (in the 290–320 nm range) from the difference spectrum obtained upon thiolysis of N^Im-Dnp-histidine. This method provides a useful analytical tool in peptide and polypeptide synthesis as well as in protein chemistry.     

Preparation of new tetraaza macrocyclic nickel(II) and copper(II) complexes bearing N-propionic methyl ester groups

A 14-membered tetraaza macrocycle, 2,13-bis(2-carbomethoxyethyl)-5,16-dimethyl-2,6,13,17-tetraazatricyclo[16.4.0.^1.180^7.12]docosane (L²) bearing two N-CH₂CH₂COOMe groups, and its nickel(II) and copper(II) complexes have been prepared and characterized. The nickel(II) and copper(II) complexes of 2-(2-carbomethoxyethyl)-5,16-dimethyl-2,6,13,17-tetraazatricyclo[16.4.0.^1.180^7.12]docosane (L³) containing one N-CH₂CH₂COOMe group have also been prepared. The crystal structure of [NiL²](ClO₄)₂ shows that the complex has a slightly distorted trans-octahedral coordination geometry with two relatively short axial Ni-O (N-CH₂CH₂COOMe group) bonds (2.136(3) Å). In various solvents, however, a considerable proportion of [NiL²]²⁺ exists as a square-planar form, in which the functional pendant arms are not involved in coordination. The proportion of the square-planar isomer varies with solvents in the order of nitromethane ? acetonitrile < H₂O < DMF ? DMSO. In the case of [CuL²](ClO₄)₂, only one N-CH₂CH₂COOMe group is involved in coordination. The N-CH₂CH₂COOMe group of [NiL³](ClO₄)₂ is not directly involved in coordination even in the solid state, though the functional group of [CuL³](ClO₄)₂ is coordinated to the metal ion.     

Active site specific cadmium(II)-substituted horse liver alcohol dehydrogenase: crystal structures of the free enzyme, its binary complex with NADH, and the ternary complex with NADH and bound p-bromobenzyl alcohol

Three crystal structures have been determined of active site specific substituted Cd(II) horse liver alcohol dehydrogenase and its complexes. Intensities were collected for the free, orthorhombic enzyme to 2.4-A resolution and for a triclinic binary complex with NADH to 2.7-A resolution. A ternary complex was crystallized from an equilibrium mixture of NAD+ and p-bromobenzyl alcohol. The microspectrophotometric analysis of these single crystals showed the protein-bound coenzyme to be largely NADH, which proves the complex to consist of CdII-LADH, NADH, and p-bromobenzyl alcohol. Intensity data for this abortive ternary complex were collected to 2.9-A resolution. The coordination geometry in the free Cd(II)-substituted enzyme is highly similar to that of the native enzyme. Cd(II) is bound to Cys-46, Cys-174, His-67, and a water molecule in a distorted tetrahedral geometry. Binding of coenzymes induces a conformational change similar to that in the native enzyme. The interactions between the coenzyme and the protein in the binary and ternary complexes are highly similar to those in the native ternary complexes. The substrate binds directly to the cadmium ion in a distorted tetrahedral geometry. No large, significant structural changes compared to the native ternary complex with coenzyme and p-bromobenzyl alcohol were found. The implications of these results for the use of active site specific Cd(II)-substituted horse liver alcohol dehydrogenase as a model system for the native enzyme are discussed.     

Metal-based new sulfonamides: Design,synthesis, antibacterial,antifungal, and cytotoxic properties

Cobalt(II), copper(II), nickel(II) and zinc(II) metal complexes with 5-chlorosalicyladehyde derived Schiff base sulfonamides have been synthesized and characterized. Structure and bonding nature of all the synthesized compounds have been deduced from physical, analytical, and spectral (IR, ¹H NMR, ¹³C NMR, Mass, electronic) data. An octahedral geometry has been proposed for all the metal complexes. The ligands and their metal complexes have been screened for their in vitro antibacterial, antifungal, and cytotoxic properties and results are reported.     

Mechanistic flexibility in the reduction of copper(II) complexes of aliphatic polyamines by mercapto amino acids

The reactions of copper(II)-ahphatic polyamine complexes with cysteine, cysteine methyl ester, penicillamine. and glutathione have been investigated, with the goal of understanding the relationship between RS^?-Cu(II) adduct structure and preferred redox decay pathway. Considerable mechanistic flexibility exists within this class of mercapto ammo acid oxidations, as changes in the rate law could be induced by modest variations in reductant concentration (at fixed [Cu(II)]_o), pH, and the structure of the redox partners. With excess cysteine present at 25°C, pH 5 0, I = 0 2 M (NaOAc), decay of 1:1 cys-S^?-Cu(II) transient adducts was found to be first order in both cys-SH and transient. Second-order rate constants characteristic of Cu(dien)²⁺ (6 1 × 10³M^?1sec^?1), Cu(Me₅dien)²⁺ (2.7 × 10³M^?1 sec^?1), Cu(en)₂²⁺ (2.1 × 10³M^?1 sec^?1), and Cu(dien)₂²⁺ (4.7 × 10³ M^?1 sec ^?1) are remarkably similar, considering substantial differences in the composition and geometry of the oxidant first coordination sphere. A mechanism involving attack of cysteine on the coordinated sulfur atom of the transient, giving a disulfide anion radical intermediate, is proposed to account for these results Moderate reactivity decreases in the cysteine-Cu(dien)²⁺, Cu(Me₅dien)²⁺ reactions with increasing [H⁺] (pH 4–6) reflect partial protonation of the polyamine ligands. A very different rate law, second order in the RS^?-Cu(II) transient and approximately zeroth order in mercaptan, applies in the pH 5.0 oxidations of cysteine methyl ester, penicillamine, and glutathione by Cu(dien)²⁺ and Cu(Me₅dien)²⁺. This behavior suggests the mtermediacy of di-μ-mercapto-bridged binuclear Cu(II) species, in which a concerted two-electron change yields the disulfide and Cu(I) products. Similar hydroxo-bridged intermediates are proposed to account for the transition from first- to second-order transient dependence in cysteine oxidations by Cu(dien)²⁺ and Cu(Me₅dien)²⁺ as the pH is increased from 5 to 7. Yet another rate law, second order in transient and first order in cysteine, applies in the pH 5.0 oxidation of cysteine by Cu(Me₆tren)²⁺ (k(25°C) 7.5 × 10⁷ M^?2 sec^?1, I = 0.2 M). Steric rigidity of this trigonal bipyramidal oxidant evidently protects the coordinated sulfur atom from attack in a RSSR^?-forming pathway. Formation of a coordinated disulfide in the rate-determining step is purposed, coupled with attack of a noncoordinated cysteine molecule on a vacated coordination position to stabilize the (Me₆(tren)Cu(I) product.     

Chromophoric peptide substrates for activity determination of animal aspartic proteinases in the presence of their zymogens: A novel assay

Solid-phase synthesis was used for the preparation of pyroglutamyl-histidyl-p-nitrophenylalanyl-phenylalanyl-alanyl-leucine amide (I) and glycyl-glycyl-histidyl-p-nitrophenylalanyl-phenylalanyl-alanyl-leucine amide (II), two water-soluble and sensitive chromophoric substrates of chicken pepsin, hog pepsin A, and bovine spleen cathepsin D. The kinetic constants of hydrolysis of the p-nitrophenylalanyl-phenylalanyl bond of the substrates were measured by difference spectrophotometry at 308 nm (Δ? = 860 m^?1 cm^?1) and by ninhydrin colorimetry (substrate I, ?₅₇₀ = 2.31 × 10⁴m^?1 cm^?1). The pH optimum of cleavage is 5 for the pepsins and 3.7 for cathepsin D. Since all three proteinases still have a significant activity at pH 5.5–6 a new, simple assay was designed for submicrogram quantities of pepsins in the presence of pepsinogens without interference of the latter. The method is particularly suitable for the analyses of the zymogen activation mixtures.     

Spectroscopic, magnetic, and electrochemical studies of a dimeric N-substituted-sulfanilamide copper(II) complex. X-ray and molecular structure of the Cu2(N-(pyridin-2-yl)biphenyl-4-sulfonamidate)4 complex

A dinuclear copper(II) complex with a N-substituted sulfonamide as ligand has been investigated. The new N-(pyridin-2-yl)biphenyl-4-sulfonamide ligand has been prepared and structurally characterized. The copper(II) complex has been synthesized and its crystal structure, magnetic properties and EPR spectra were studied in detail. The metal centers are bridged by four nonlinear triatomic NCN groups. The coordination geometry of the copper(II) ions in the dinuclear entity is distorted square planar with two N-pyridyl and two N-sulfonamido atoms. Magnetic susceptibility data show a moderate antiferromagnetic coupling, with −2 J = 284 cm⁻¹. The EPR spectrum of the polycrystalline sample of the title compound has been measured at the X-band frequency at different temperatures.     

Synthesis and chemical characterization of Cu, Ni and Zn complexes of 3,5-bis(2′-pyridyl)-1,2,4-oxadiazole and 3-(2′-pyridyl)5-(phenyl)-1,2,4-oxadiazole ligands

The synthesis and structural characterization of Ni^II, Cu^II and Zn^II complexes of two chelating 1,2,4-oxadiazole ligands, namely 3,5-bis(2′-pyridyl)-1,2,4-oxadiazole (bipyOXA) and 3-(2′-pyridyl)5-(phenyl)-1,2,4-oxadiazole (pyOXA), is here reported. The formed hexacoordinated metal complexes are [M(bipyOXA)₂(H₂O)₂](ClO₄)₂ and [M(pyOXA)₂(ClO₄)₂], respectively (M = Ni, Cu, Zn). X-ray crystallography, ¹H and ¹³C NMR spectroscopy and C, N, H elemental analysis data concord in attributing them an octahedral coordination geometry. The two coordinated pyOXA ligands assume a trans coplanar disposition, while the two bipyOXA ligands are not. The latter result is a possible consequence of the formation of H-bonds between the coordinated water molecules and the nitrogen atom of the pyridine in position 5 of the oxadiazole ring. The expected splitting of the d metal orbitals in an octahedral ligand field explains the observed paramagnetism of the d⁸ and d⁹ electron configuration of the nickel(II) and copper(II) complexes, respectively, as determined by the broadening of their NMR spectra.     

Synthesis, structures, and magnetic properties of dicopper(II) and dinickel(II) complexes with a new bis(macrocycle), 7,7-(2-hydoxypropane-1,3-diyl)bis{3,7,11,17-tetraazabicyclo[11.3.1]- heptadeca-1(17),13,15-triene}

A new bis(macrocycle) ligand, 7,7^′-(2-hydoxypropane-1,3-diyl)-bis{3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene} (HL), and its dicopper(II) ([Cu₂(HL)Cl₂](NO₃)₂ · 4H₂O (4a), [Cu₂(HL)I₂]I₂ · H₂O (4b)) and dinickel(II) ([Ni₂(L)(OH₂)](ClO₄)₃ (5a), [Ni₂(L)(OH₂)]I₃ · 2H₂O (5b), [Ni₂(L)N₃](N₃)₂ · 7H₂O (5c)) complexes have been synthesized. The alkoxide bridged face-to-face structure of the dinickel(II) complex 5c has been revealed by X-ray crystallography, as well as the “half-opened clamshell” form of the bis(macrocyclic) dicopper(II) complex 4b. Variable temperature magnetic susceptibility studies have indicated that there exists intramolecular antiferromagnetic coupling (J=−33.8 cm⁻¹ (5a), −32.5 cm⁻¹ (5b), and −29.7 cm⁻¹ (5c)) between the two nickel(II) ions in the nickel(II) complexes.