Equivalent Nitrogen Atoms Research Articles

Исследование тройной системы иодид кальция-ГМТА-вода

Research relevance: synthesis, physicochemical studies of complexes bioactivity with salts of biometals and organic ligands are of great interest for bio-coordination chemistry. Materials and research methods: isothermal method was used to study heterogeneous equilibria at 25 °C. The concentration limits of compounds existence and the types of their solubility have been established. Research objectives: to investigate compounds of hexamethylenetetramine with salts of biometals with organic ligands in order to reduce toxicity, increase the bioactivity and bioavailability of coordination compounds. Research results: concentration limits of compounds existence and types of their solubility have been established. Conclusions: in obtained complexes, HMTA ligand contains four equivalent electron donor nitrogen atoms.

Degradation of Organophosphates Promoted by 1,2,4-Triazole Anion: Exploring Scaffolds for Efficient Catalytic Systems.

Organophosphate (OP) pesticides are responsible for numerous human deaths every year. Nucleophilic substitution is an important method to mitigate the toxicity of obsolete stocks of OPs. Herein, the degradation of O,O-diethyl-2,4-dinitrophenyl phosphate (DEDNPP) and pesticide diethyl-4-nitrophenyl phosphate (Paraoxon) promoted by 1,2,4-triazole (TAZ) was investigated by means of kinetic studies, nuclear magnetic resonance (NMR) analyses, and theoretical calculations. Results showed fast degradation of OPs is promoted by the anionic form of the nucleophile (TAZ(-)) in pH > 8.5 (optimal at pH = 11). Rate enhancements of 106 and 105-fold in relation to neutral hydrolysis of DEDNPP and Paraoxon were observed, respectively, consistent with alpha-nucleophiles reactivity. TAZ(-) regioselectively promotes the degradation of DEDNPP via P-O bond break, forming a quickly hydrolyzable phosphorylated intermediate, regenerating the nucleophile. Calculations using M06-2X/6-311++G(d,p) level of theory revealed that the equivalent nitrogen atoms of TAZ(-) are the main nucleophilic center of the molecule. This study expands the knowledge on the reactivity of iminic compounds as detoxificant agents of OPs, indicating the efficiency and selectivity of TAZ(-) in aqueous medium, encouraging the design of novel TAZ-based catalysts.

X-ray Absorption Near-Edge Structure Spectroscopy of a Stable 6-Oxoverdazyl Radical and Its Diamagnetic Precursor.

The electronic structure of 1,3,5-triphenyl-6-oxoverdazyl, a heteroatom-rich stable organic radical, and its diamagnetic 1,3,5-triphenyl-6-oxotetrazane precursor are probed using X-ray absorption near-edge structure (XANES) spectroscopy. The N K-edge XANES spectra of the 6-oxoverdazyl radical contain strong N 1s → π* resonances for each set of equivalent nitrogen atoms. The fact that these resonances are absent from the analogous spectra of the 6-oxotetrazane, whereas the O K-edge and C K-edge XANES spectra of both species are very similar, demonstrates that the unpaired electron of the radical is localized primarily on the N atoms of the 6-oxoverdazyl heterocycle. The O K-edge XANES spectra of both species contain strong O 1s → π* (C═O) peaks, but the peak of the radical is red-shifted by 0.5 eV relative to that of the 6-oxotetrazane, which indicates that the C═O bond in the radical is part of a larger π-conjugated system. The proposed interpretations of the XANES spectra are aided by density-functional calculations.

Iron(II) Bis-α-Benzyldioximate Complexes with 3- and 4-Pyridine Hemiacetals as Axial Ligands: Synthesis, Structure, and Physicochemical Properties

The coordination compounds [Fe(DfgH)2(HL1)2] and [Fe(DfgH)2(HL2)2], where DfgH = is the α-benzyldioxime monoanion, HL1 = 3-pyridine hemiacetals: methoxy(pyridin-3-yl)methanol (I), ethoxy(pyridin-3-yl)methanol (II); HL2 = 4-pyridine hemiacetal: methoxy(pyridin-4-yl)methanol (III), ethoxy(pyridin-4-yl)methanol (IV), and propoxy(pyridin-4-yl)methanol (V), were synthesized and studied by X-ray diffraction and IR and Mossbayer spectrosopy. According to X-ray diffration data (CIF files CCDC 1578217–1578221 for I–V, respectively), all of these Fe(II) complexes are molecular. The metal coordination polyhedron is an octahedron formed by four equatorial nitrogen atoms of two monodeprotonated α-benzyldioxime residues coordinated in the bidentate chelating fashion and by two axial nitrogen atoms of two neutral 3- or 4-pyridine hemiacetal molecules coordinated in the monodentate fashion. The DfgH– ligands in complexes I–V are joined by intramolecular O–H···O hydrogen bonds to form a pseudomacrocyclic system. The ligands HL1 and HL2 are generated in the reaction of the corresponding alcohols with 3- or 4-pyridinecarboxaldehyde. The IR and Mossbauer spectra of the products were studied. The Mossbauer spectral parameters of compounds I–V correspond to low-spin iron(II) ions.

Crystal structure of nitrido[5,10,15,20-tetra-kis(4-methylphenyl)-porphyrinato]-manganese(V).

The title compound, [Mn(C48H36N4)(N)], is a manganese(V) complex with the transition metal in a square-pyramidal coordination geometry and a nitride as the axial ligand. The complex resides on a crystallographic inversion center and only one half of it is symmetry independent. The Mn(V) atom and the nitride N atom are equally disordered across the inversion center. The MnN distance is 1.516 (4) Å. The Mn(V) atom is displaced from the plane defined by the four equatorial nitro-gen atoms toward the nitride ligand by 0.3162 (6) Å.

Crystal Structure and DFT Studies of the Hydridophosphorane HP(OC6H4NMe)2

The crystal structure of the spirobicyclic phosphorane 3,3′-dimethyl-2λ5-2,2′(3H,3′H)-spirobi[1,3,2-benzoxazaphosphole], [HP(OC6H4NCH3)2] (1) has been determined. Crystals of C14H15N2O2P are monoclinic, a = 8.483(2), b = 7.616(2), c = 19.805(6) A, Z = 4, space group P2(1)/c. Compound 1 was also characterized by 13C{1H} and 1H NMR. The crystal structure along with DFT B3LYP (6-311++G(2df,2p)) calculations, both suggest significant π-overlap between the equatorial nitrogen atoms and the phosphorus center. The crystal structure and DFT B3LYP (6-311++G(2df,2p)) calculations of the spirobicyclic phosphorane 3,3′-dimethyl-2λ5-2,2′(3H,3′H)-spirobi[1,3,2-benzoxazaphosphole], [HP(OC6H4NCH3)2] is reported.

Radical Localization in a Series of Symmetric NiIIComplexes with Oxidized Salen Ligands

Square-planar nickel(II) complexes of salen ligands, N,N'-bis(3-tert-butyl-(5R)-salicylidene)-1,2-cyclohexanediamine), in which R=tert-butyl (1), OMe (2), and NMe(2) (3), were prepared and the electronic structure of the one-electron-oxidized species [1-3](+·) was investigated in solution. Cyclic voltammograms of [1-3] showed two quasi-reversible redox waves that were assigned to the oxidation of the phenolate moieties to phenoxyl radicals. From the difference between the first and second redox potentials, the trend of electronic delocalization 1(+·) >2(+·) >3(+·) was obtained. The cations [1-3](+·) exhibited isotropic g tensors of 2.045, 2.023, and 2.005, respectively, reflecting a lower metal character of the singly occupied molecular orbital (SOMO) for systems that involve strongly electron-donating substituents. Pulsed-EPR spectroscopy showed a single population of equivalent imino nitrogen atoms for 1(+·), whereas two distinct populations were observed for 2(+·). The resonance Raman spectra of 2(+·) and 3(+·) displayed the ν(8a) band of the phenoxyl radicals at 1612 cm(-1), as well as the ν(8a) bands of the phenolates. In contrast, the Raman spectrum of 1(+·) exhibited the ν(8a) band at 1602 cm(-1), without any evidence of the phenolate peak. Previous work showed an intense near-infrared (NIR) electronic transition for 1(+·) (Δν(1/2) =660 cm(-1), ε=21,700 M(-1) cm(-1)), indicating that the electron hole is fully delocalized over the ligand. The broader and moderately intense NIR transition of 2(+·) (Δν(1/2) =1250 cm(-1) , ε=12,800 M(-1) cm(-1)) suggests a certain degree of ligand-radical localization, whereas the very broad NIR transition of 3(+·) (Δν(1/2) =8630 cm(-1), ε=2550 M(-1) cm(-1)) indicates significant localization of the ligand radical on a single ring. Therefore, 1(+·) is a Class III mixed-valence complex, 2(+·) is Class II/III borderline complex, and 3(+·) is a Class II complex according to the Robin-Day classification method. By employing the Coulomb-attenuated method (CAM-B3LYP) we were able to predict the electron-hole localization and NIR transitions in the series, and show that the energy match between the redox-active ligand and the metal d orbitals is crucial for delocalization of the radical SOMO.

Formation of an Unusual Four-Membered Nitrogen Ring (Tetrazetidine) Radical Cation

Treatment of triphenylphosphine (Ph(3)P) with an excess of diisopropyl azodicarboxylate at 0-25 °C resulted in the formation of a symmetrical tetraalkyl tetrazetidinetetracarboxylate radical cation, containing the elusive cyclic N(4) ring system. Electron paramagnetic resonance (EPR) spectroscopy revealed a 9-line spectrum, with hyperfine coupling constants indicative of four almost magnetically equivalent nitrogen atoms. The radical species was surprisingly long-lived, and could still be observed several hours after generation and standing at 25 °C. Expansion of the central resonance revealed further splitting into a pentet (hyperfine coupling to the four methine protons). Three mechanistically plausible structures containing the tetrazetidine substructure were proposed based on the 9-line EPR spectrum. Following DFT calculations, the predicted hyperfine coupling constants were used to simulate the EPR spectra for the three candidate structures. The combined calculations and simulations were consistent with a radical cation species, but not a radical anion or radical-carbenoid structure. The lowest energy conformation of the N(4) ring was slightly puckered, with the alkyl carboxylate groups all trans and the four carbonyl groups aligned in a pinwheel arrangement around the ring. Analogous results were obtained with the original Mitsunobu reagents, Ph(3)P and diethyl azodicarboxylate, but not with Ph(3)P and di-tert-butyl azodicarboxylate. A mechanism is proposed based on a radical version of the Rauhut-Currier or Morita-Baylis-Hillman reactions.

The X-ray absorption spectroscopic model of the copper(II) imidazole complex ion in liquid aqueous solution: a strongly solvated square pyramid.

Cu K-edge extended X-ray absorption fine structure (EXAFS) and Minuit X-ray absorption near-edge structure (MXAN) analyses were combined to evaluate the structure of the copper(II) imidazole complex ion in liquid aqueous solution. Both methods converged to the same square-pyramidal inner coordination sphere [Cu(Im)(4)L(ax)](2+) (L(ax) indeterminate) with four equatorial nitrogen atoms at EXAFS, 2.02 ± 0.01 Å, and MXAN, 1.99 ± 0.03 Å. A short-axial N/O scatterer (L(ax)) was found at 2.12 ± 0.02 Å (EXAFS) or 2.14 ± 0.06 Å (MXAN). A second but very weak axial Cu-N/O interaction was found at 2.9 ± 0.1 Å (EXAFS) or 3.0 ± 0.1 Å (MXAN). In the MXAN fits, only a square-pyramidal structural model successfully reproduced the doubled maximum of the rising K-edge X-ray absorption spectrum, specifically excluding an octahedral model. Both EXAFS and MXAN also found eight outlying oxygen scatterers at 4.2 ± 0.3 Å that contributed significant intensity over the entire spectral energy range. Two prominent rising K-edge shoulders at 8987.1 and 8990.5 eV were found to reflect multiple scattering from the 3.0 Å axial scatterer and the imidazole rings, respectively. In the MXAN fits, the imidazole rings took in-plane rotationally staggered positions about copper. The combined (EXAFS and MXAN) model for the unconstrained cupric imidazole complex ion in liquid aqueous solution is an axially elongated square-pyramidal core, with a weak nonbonded interaction at the second axial coordination position and a solvation shell of eight nearest-neighbor water molecules. This core square-pyramidal motif has persisted through [Cu(H(2)O)(5)](2+), [Cu(NH(3))(4)(NH(3),H(2)O)](2+), (1, 2) and now [Cu(Im)(4)L(ax))](2+) and appears to be the geometry preferred by unconstrained aqueous-phase copper(II) complex ions.

Counterion and Solvent Effects on the Primary Coordination Sphere of Copper(II) Bis(3,5‐dimethylpyrazol‐1‐yl)acetic Acid Coordination Compounds

AbstractFour copper(II) coordination compounds with the neutral ligand bis(3,5‐dimethylpyrazol‐1‐yl)acetic acid (Hbdmpza, C12H16N4O2) and its anionic form (bdmpza–), namely [Cu(Hbdmpza)2](HSO4)2 (1), [Cu(Hbdmpza)2]Cl2 (2), [Cu(bdmpza)2](CH3COOH)(H2O) (3), and [Cu(bdmpza)2][Cu2(O2CCH3)4] (4) have been synthesized starting from different metal salts. All the compounds have been fully characterized by physical and analytical methods. In addition, a single‐crystal XRD analysis revealed the 3D structure of 1, which exhibits tridentate, vicinal N,N,O‐coordination of two symmetry‐related Hbdmpza ligands in an elongated octahedral arrangement with four equatorial nitrogen atoms and two axial oxygen atoms. The neutral carboxylic moiety acts as a hydrogen‐bond donor to a HSO4– counterion. The two hydrogensulfates form a unique hydrogen‐bonded pair (HSO4–)2 with very short O···O distances (2.59 Å) bridged between adjacent [Cu(HL)2]2+ coordination units. Also a short O···O contact (2.54 Å) is present between the C–OH and an O of a hydrogensulfate. A characteristic IR C=O vibration is observed at 1700 cm–1 for 1 and 2, whereas the νas(O2C) vibration is present at 1650 cm–1 for 3 and 4. These IR data strongly suggest the presence of Hbdmpza ligands in 1 and 2 and the deprotonated form bdmpza– in 3 and 4. A mononuclear coordination unit [CuL2], as proven for 1 by X‐ray diffraction, is also proposed for the other compounds 2–4. In compound 4, an additional dinuclear [Cu2(O2CCH3)4] neutral coordination unit is present, as deduced from the vibration bands νas(O2C) at 1600 cm–1 and νs(O2C) at 1420 cm–1, which are typical of a carboxylate function, and from the two‐species analysis of the χMT(T) curve of the magnetic susceptibility data (2J = –322 cm–1). Also, the EPR spectra recorded at different temperatures agree with this structure.

Mononuclear FeII Single-Molecule Magnets: A Theoretical Approach

The single-molecule magnet behavior found in mononuclear tetracoordinate Fe(II) complexes with trigonal monopyramidal coordination due to large magnetic anisotropy has been analyzed using theoretical methods based on CASSCF-RASSI calculations. We focus our study on the dependence of such magnetic properties on the geometrical parameters of the complexes (asymmetry of the ligands and the out-of-plane shift of the Fe(II) cation with respect to the three equatorial nitrogen atoms) and the influence of the basicity of the N ligands. Low basicity, larger shifts, and larger distortions of the FeN(4) central framework decrease the D value and increase the E value. Also, we predict similar magnetic properties for similar pentacoordinate complexes adding an axial ligand that will increase the chemical stability of such systems.

EPR Study of 5-Chlorosalicylate-Cu(II)-3-Pyridylmethanol Ternary Complex Systems in Frozen Water–Methanol Solutions

Two copper(II) ternary complex systems containing 5-chlorosalicylic acid (5-ClsalH) and different copper(II) salts with varying 3-pyridylmethanol (ron = ronicol) concentration, system I [CuSO4 (aq) +2(5-ClsalH(solv)) + xron(l)] and system II [Cu(ac)2(aq) + 2(5-ClsalH(solv)) + xron(l)], where x = 0, 2, 4, 6 and 8, were prepared and studied by electron paramagnetic resonance (EPR) spectroscopy in frozen water–methanol solutions to observe the effects of different copper(II) salts and varying neutral ligand concentration on the formation of resulting complexes in solution. The trend in g-values (g|| > g⊥ > 2.0023) indicates that the unpaired electron on the copper ion is localized in the \( d_{{x}^{\rm{2}} - {y}^{\rm{2}}} \) orbital. The detailed analysis of the second-derivative Cu(II) EPR spectra has shown well-resolved 14N superhyperfine splitting in the perpendicular part of the axially symmetric spectra. The resolution of nitrogen superhyperfine multiplet patterns increased with increase in the ronicol concentration (ligand-to-metal ratio x). The number of superhyperfine lines was found to be constant (nonet) when x > 4 for system I and x ≥ 4 for system II. This fact indicates that for these x-values four equivalent nitrogen atoms could be coordinated to the central copper atom in the equatorial plane of both systems.

Unusual Magnetism of an Unsymmetrical Trinickel Chain

AbstractAn extended metal atom chain (EMAC) compound with an unsymmetrical trinickel core and the formula [Ni3(dpa)4(CH3CN)](PF6)2·2CH2Cl2 (1·2CH2Cl2, dpa is the anion of 2,2′‐dipyridylamine) has the central Ni atom in an essentially square‐planar configuration. Besides having four equatorial nitrogen atoms, the two terminal metal centers have axial interactions that are notably different with one having a strongly bound acetonitrile molecule with a Ni(3)–N(3) distance of 2.108(5) Å while the other unit has a very weak interaction with an axial PF6 anion [Ni(1)···F(1) separation of 2.690 Å]. In these outer units, the Ni(3) atom is pulled out of the idealized plane of the four equatorial nitrogen atoms by 0.239 Å, while in the one with an axial PF6 anion the metal atom is pulled from the plane of the equatorial nitrogen atoms by only 0.097 Å. In 1 there are two unpaired electrons and an S = 1 state prevails from ca. 25 to 300 K. This magnetic behavior differs considerably from that of symmetrical trinickel EMACs with two strongly pyramidal terminal nickel atoms. A discussion of the effect of various axial ligands on the geometry of the terminal nickel atoms is provided. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Isolation and Crystal Structure of [Cu(L1)(O2CH)](ClO4) · H2O: Hydrolysis of DMF (N,N-Dimethylformamide) by a Copper(II) Tetraazamacrocycle

The tetraazamacrocyclic copper(II) complex, [Cu(L)](ClO4)2 (L = 3,14-dimethyl-2,6,13,17-tetraazatricyclo[14.4.01.18.07.12]docosane), hydrolyzes DMF at room temperature. The formate anion which is one of the hydrolyzed species of DMF coordinates to the copper(II) ion to form [Cu(L1)(O2CH)](ClO4) · H2O (1). The crystals of the complex 1 were isolated and structurally characterized by a combination of analytical, spectroscopic, and crystallographic methods. In 1, the macrocyclic ligand contains two trans fused cyclohexane rings, and the coordination geometry about the copper(II) ion adopts a square pyramid with four equatorial nitrogen atoms from the macrocycle and an oxygen atom from the formato ligand with an uncoordinated perchlorate ion.

One‐Dimensional, Cofacial Porphyrin Polymers Formed by Self‐Assembly of meso‐Tetrakis(ERE Donor) Zinc(II) Porphyrins

A series of meso-tetrakis-(ERE donor) zinc(II) porphyrins nZn (ERE donor = 4-R-3,5-bis[(E)-methyl]phenyl; 1Zn: E = NMe2, R = Br; 2Zn: E = NMe2, R = H; 3Zn: E = OMe, R = Br; 4Zn: E = OMe, R = H) have been synthesized in excellent yields. As a result of the combination of a Lewis acidic site and eight Lewis basic sites within one molecule, monomeric molecules of nZn self-assemble to form one-dimensional porphyrin polymers [nZn](infinity) in the solid state, as confirmed for 1Zn and 3Zn by X-ray crystallography. The coordination environment around the zinc(II) ions in these polymers is octahedral. They are ligated by four equatorial nitrogen atoms of the porphyrin and two apical E atoms (E = N, O) provided by the EBrE donor groups of adjacent nZn molecules. Complexes 2Zn and 4Zn did not form single crystals, but solid-state UV/Vis analysis points to the formation of similar structures. Solution UV/Vis and 1H NMR spectroscopy indicated that interactions between 1Zn and 2Zn monomers in the polymers are stronger than between 3Zn and 4Zn monomers. Interestingly, they also revealed that the presence of a neighboring bromine atom in the EBrE donor groups has a considerable influence on the coordination properties of the benzylic N or O atoms. The zinc(II) ions of the porphyrins most likely adopt only hexacoordination in the solid state, owing to the unique predisposition of Lewis acidic and basic sites in the nZn molecules. Several parameters of the aggregates, for example, the interplanar separation between porphyrins and the zinc-zinc distances, change as a function of the coordinating E groups. The high degree of modularity in their synthesis makes these zinc(II) porphyrins an interesting new entry in noncovalent multiporphyrin assemblies.

Vinamidinium salts of N-substituted aminoacetic acids

Formylation of N-phthaloylglycine with the POCl3-DMF system afforded N,N,N′, N′-tetramethyl-2-(N-phthaloyl)vinamidinium perchlorate (2). X-ray diffraction study showed that molecule 2 is planar and contains two equivalent nitrogen atoms in the three-carbon vinamidinium fragment. Salt 2 undergoes transamination with primary aromatic amines to give the corresponding bis-azomethines. The reactions with hydrazines produce substituted 4-aminopyrazoles.

Synthesis and structure of a hexaazamacrocyclic copper(II) complex with maleato ligand

A hexaazamacrocyclic copper(II) complex Cu(L)(H2O) (O2CCH = CHCO2)⋅H2O (1) (L = 3,10-bis(2-hydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane) was prepared and structurally characterized by a combination of analytical, spectroscopic, and crystallographic methods. In complex 1, the coordination geometry about the copper(II) ion is six-coordinate with four equatorial nitrogen atoms from the macrocycle and two oxygen atoms from the axial maleato and aqua ligands. In 1, the one end of the maleato ligand coordinates to the central copper atom, while the other end is not bonded. The macrocycle and the axial ligands are highly involved in multiple types of hydrogen bonding interactions, resulting in the stabilization of the maleato ligand as a “coordinated ligand counter anion.”

Spectroscopic investigation of hard and soft metal binding sites in synthetic melanin

Understanding the interaction of metal ions with melanin structures is essential to know some intricate functions of this kind of compounds in the living systems. The coordination chemistry of vanadyl oxycation, VO(II), and copper, Cu(II), in a synthetic l-dopa melanin (SM) was investigated using electron paramagnetic resonance (EPR), Fourier transform infrared (FT IR) and ultraviolet–visible (UV–Vis) spectroscopy. The EPR and FT IR spectra indicated axially coordinated VO(II) ions bound to catecholate functional groups, and a fraction of the Cu(II) ions in a square planar structure partially coordinated to carboxylate functional groups. The resolved EPR perpendicular super hyperfine splitting constant, A N⊥, and the Cu(II) complex EPR parallel parameters g ‖ and A ‖ values indicated two magnetically equivalent nitrogen atoms in a plane with the coordination sphere, CuN 2O 2. The ultraviolet–visible (UV–Vis) spectra of solid samples indicate supramolecular structure constitution for the synthesized VO(II)SM and Cu(II)SM complexes.

Histidinyl Radical Formation in the Self-peroxidation Reaction of Bovine Copper-Zinc Superoxide Dismutase

In the absence of suitable oxidizable substrates, the peroxidase reaction of copper-zinc superoxide dismutase (SOD) oxidizes SOD itself, ultimately resulting in its inactivation. A SOD-centered free radical adduct of 2-methyl-2-nitrosopropane (MNP) was detected upon incubation of SOD with the spin trap and a hydroperoxide (either H(2)O(2) or peracetic acid). Proteolysis by Pronase converted the anisotropic electron paramagnetic resonance (EPR) spectrum of MNP/(center dot)SOD to a nearly isotropic spectrum with resolved hyperfine couplings to several atoms with non-zero nuclear spin. Authentic histidinyl radical (from histidine + HO(center dot)) formed a MNP adduct with a very similar EPR spectrum to that of the Pronase-treated MNP/(center dot)SOD, suggesting that the latter was centered on a histidine residue. An additional hyperfine coupling was detected when histidine specifically (13)C-labeled at C-2 of the imidazole ring was used, providing evidence for trapping at that atom. All of the experimental spectra were convincingly simulated assuming hyperfine couplings to 2 nearly equivalent nitrogen atoms and 2 different protons, also consistent with trapping at C-2 of the imidazole ring. Free histidinyl radical consumed oxygen, implying peroxyl radical formation. MNP-inhibitable oxygen consumption was also observed when cuprous SOD but not cupric SOD was added to a H(2)O(2) solution. Formation of 2-oxohistidine, the stable product of the SOD-hydroperoxide reaction, required oxygen and was inhibited by MNP. These results support formation of a transient SOD-peroxyl radical.

Trans-bis(dicyanamido)nickel(II) complexes with polyaza macrocyclic ligands

Two new trans-bis(dicyanamido)nickel(II) macrocyclic complexes, [Ni(II)(L1){N(CN)2}2] · H2O (1) and [Ni(II)-(L3){N(CN)2}2] (2), where L1 is 3,10-bis(2-hydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane and L3 is 3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,01.18,07.12]docosane, have been synthesized and structurally characterized by spectroscopic and X-ray crystallographic methods. In (1) and (2), each central nickel(II) ion possesses a distorted octahedral geometry with four equatorial nitrogen atoms from the macrocycle and two axial nitrogen atoms from dicyanamide anions, which are terminally bonded to the central nickel atom. The solid state electronic spectra of (1) and (2) using the diffuse reflectance method show a characteristic high-spin d8 nickel(II) ion in a distorted octahedral environment.