Solution <Superscript>1</Superscript>H n.m.r. of paramagnetic Co<Superscript>2+</Superscript>complexes with dioxobis(carboxymethyl)tetraazamacrocycles

Paramagnetic shifts in the ¹H n.m.r. spectra were observed for high-spin Co²⁺ complexes with 12--14-membered tetraazamacrocycles incorporating two amide groups and two pendant carboxymethyl groups. The pseudocontact term due to the dipolar interaction between the metal ion and the resonant protons was calculated on the basis of X-ray structures, and the Fermi contact term due to spin delocalization was determined. The ethylenediamine moiety of the ligand molecule is coordinated in an unsymmetric manner, even in solution, and internal motion (involving conformational change of the macrocyclic frame and exchange of coordinate bonds) is much slower than the n.m.r. observation frequency. In the 12-membered macrocyclic complex Co(L12), three of the eight CH₂ groups fix their orientation in the n.m.r. time scale; in Co(L13) only one CH₂ group fixes its orientation; in Co(L14) all CH₂ groups undergo a rapid reorientation. The facility in internal motion increases with the ring size, and shows a correlation with the chemical stabilities of these Co²⁺ complexes against oxidation; to atmospheric oxygen, Co²⁺(L12) is the most resistant and Co²⁺(L14) is the most susceptible.     

13C n.m.r. studies of the interaction of HgII with methionine and selenamethionine in the acidic aqueous solution

Summary The interactions of L-methionine (Met) and DL-selenamethionine (SeMet) with Hg²⁺ were studied using¹³C n.m.r. spectroscopy in aqueous acid. Hg²⁺ binds to the selenoether group of SeMet and the thioether group of Met exclusively. The selenoether group binds more strongly than thioether.     

Temperature effects on 13C n.m.r. chemical shifts of normal alkanes and some line r and branched 1-alkenes

¹³C n.m.r. chemical shifts of a number of 1,1-disubstituted ethylenes are presented. Moreover, effects of changing temperatures on the ¹³C n.m.r. chemical shifts of some of these compounds as well as of three normal alkanes are given. These variations in chemical shifts are attributed to varying amounts of sterically induced shifts in the different conformational equilibria. In addition to the well-known 1,4 interaction between two alkyl groups shielding effects on the carbon atoms of the connecting bonds are also proposed. No definite explanation of this effect is presented at this time. It is further shown that no simple correlations exist between ¹³C n.m.r. chemical shifts and calculated total charge densities at this level. Instead, the experimental results in 1-alkenes are rationalized by assuming a linear dependence of the ¹³C n.m.r. chemical shifts of C-1 and C-2 via rehybridizations on changes in bond angles for small skeletal deformations caused by steric interactions. These changes in geometries, as well as conformational energies in three 1-alkenes, were calculated by means of VFF calculations. Finally. upfield shifts for both C-2 and C-4 are proposed for those conformations of 1-alkenes in which the C-3? C-4 group interacts with the p_z-orbital of C-2.     

Platinum(II) and palladium(II) complexes with substituted pyrimidines

Summary Platinum(II) and Palladium(II) complexes with 2-mercaptopyrimidine, 2-thiocytosine (4-aminopyrimidine 2-thione), and isocytosine (2-amino-4-hydroxy pyrimidine) were prepared and characterised by elemental analysis, conductivity data, i.r.,¹H n.m.r. and¹³C n.M.r. spectral studies. 2-Mercaptopyrimidine and 2-thiocytosine are coordinated to the metal ion through N(3) and C₂S, thus forming a four-membered chelate ring. Isocytosine acts as a monodentate ligand and coordinates to the metal ion through N(1). All the complexes are non-electrolytes.     

2-Aminoacetophenone-2-thenoylhydrazone complexes of bivalent 3d metal ions

Summary 2-Aminoacetophenone-2-thenoylhydrazone, Haath, C₄H₃SC(O)NHN=C(Me)C₆H₄NH₂-o, forms complexes with metal(II) salts of empirical compositions [VO(Haath)₂SO₄], [M(Haath)₂Cl₂] [M=Co^II, Ni^II, Cu^II or Zn^II] and [M(aath)₂] [M=V^IVO, Co^II, Ni^II, Cu^II or Zn^II] which have been characterized by elemental analyses, molar conductance, magnetic susceptibility, electronic, e.s.r., i.r. and n.m.r. (¹H and¹³C) spectral studies. X-ray and electron diffraction patterns have been obtained in order to elucidate the structure of the Cu^II complexes. Photoacoustic spectra of powder Ni^II complexes have been recorded and interpreted in the light of u.v./vis. spectra.     

Isoamyl­cobalamin–acetone–water (1/0.385/12.650)

The title compound, [Co(C₅H₁₁)(C₆₂H₈₈N₁₃O₁₄P)]·0.385C₃H₆O·12.650H₂O, contains the isoamyl (3‐methyl­butyl) anion bonded to the Co^III ion through a C atom. The compound is thus a structural analog of the two biologically important vitamin B₁₂ coenzymes adenosyl­cobalamin and methyl­cobalamin. The lower axial Co—N bond length [2.277 (2) Å] is one of the longest ever reported for a cobalamin and reflects the strong σ‐donor ability of the isoamyl group.     

N.m.r. spectra of prostaglandin metabolites and precursors and of related pyrazoline adducts

The ¹³C n.m.r. spectra of the major human urinary metabolite of prostaglandin PGE₂ and PGE₁ are discussed together with some unsaturated precursors. Δ-2-Pyrazolines, formed by addition of diazomethane to the 11-oxo dienediones in this series, were identified by ¹³C and ¹H n.m.r. and by other physical methods.     

A Mini‐Twister Variant and Impact of Residues/Cations on the Phosphodiester Cleavage of this Ribozyme Class

Nucleolytic ribozymes catalyze site‐specific cleavage of their phosphodiester backbones. A minimal version of the twister ribozyme is reported that lacks the phylogenetically conserved stem P1 while retaining wild‐type activity. Atomic mutagenesis revealed that nitrogen atoms N1 and N3 of the adenine‐6 at the cleavage site are indispensable for cleavage. By NMR spectroscopy, a pK_a value of 5.1 was determined for a ¹³C2‐labeled adenine at this position in the twister ribozyme, which is significantly shifted compared to the pK_a of the same adenine in the substrate alone. This finding pinpoints at a potential role for adenine‐6 in the catalytic mechanism besides the previously identified invariant guanine‐48 and a Mg²⁺ ion, both of which are directly coordinated to the non‐bridging oxygen atoms of the scissile phosphate; for the latter, additional evidence stems from the observation that Mn²⁺ or Cd²⁺ accelerated cleavage of phosphorothioate substrates. The relevance of this metal ion binding site is further emphasized by a new 2.6 Å X‐ray structure of a 2′‐OCH₃‐U5 modified twister ribozyme.     

Synthesis of LiNi1/3Co1/3Mn1/3O2 cathode material by a modified sol–gel method for lithium-ion battery

LiNi_1/3Co_1/3Mn_1/3O₂ was prepared by a modified sol–gel method, selecting ethylene diamine tetraacetic acid and citric acid as the co-chelating agent. The mole ratios of ethylene diamine tetraacetic acid (EDTA) to metal ion (Mⁿ⁺) were 0:1, 1:1 and 2:1. The obtained samples were characterized by XRD, BET and SEM. The XRD showed that LiNi_1/3Co_1/3Mn_1/3O₂ had good crystallinity and well-ordered layered structure. After calcined at 850 °C, the LiNi_1/3Co_1/3Mn_1/3O₂ particles exhibited a three-dimensional space network structure, which was greatly correlated with the ratio of EDTA to metal ion. The LiNi_1/3Co_1/3Mn_1/3O₂ obtained from a mole ratio of 1:1 (EDTA:Mⁿ⁺) had the best electrochemical performance. The reversible capacities were reached 168 and 100 mAh/g at 1C and 10C discharge rate, respectively. The result of the cycling performance showed a high capacity maintenance ratio of 89.3 % at 1C and 25 °C after 50 cycles. The further electrochemical performance was evaluated by electrochemical impedance spectroscopy and cyclic voltammetry.     

N-acetyl-DL-leucinate cobalt(II), nickel(II) and zinc(II) complexes

Summary Complexes of the type M(AcLeu)₂ · B₂ (M = Co^II, Ni^II or Zn^II; B = H₂O, py, 3-pic, 4-pic; AcLeu =N-acetyl-DL-leucinate ion) and M(AcLeu)₂ B (M = Co^II or Zn^II and B = o-phen) were prepared and investigated by means of magnetic and spectroscopic measurements. The i.r. spectra of all the complexes are consistent with bidentate coordination of the amino acid to the metal ion. The room temperature solid state electronic spectra indicate that the symmetry of this species is closer toD _4h and that MO₆ and MO₄N₂ chromophores are present in the M(AcLeu)₂ · 2 H₂O and M(AcLeu)₂B_n · x H₂O (B = py, 3-pic, 4-pic, n=2 and x=0 for M = Ni^II; B = o-phen, n=1 and x=0 for M = Co^II; B = py, 3-pic, 4-pic, n=1 and x=1 for M = Co^II) complexes, respectively. By comparing the Dq values of the amino acid and those of other N-substituted amino acids previously studied, a spectrochemical series of the the cobalt(II) and nickel(II) complexes is proposed. The¹ H n.m.r. spectra of the zinc(II) complexes confirm the proposed stereochemistry.     

Synthesis and spectral studies ofo-hydroxyacetophenone (N-benzoyl)glycyl hydrazone and some of its lanthanide(III) complexes

Summary o-Hydroxyacetophenone (N-benzoyl)glycyl hydrazone (o-HABzGH) has been characterized by i.r.,¹H n.m.r.,¹³C n.m.r. and mass spectral studies, and its complexes of the types [Ln(o-HABzGH)Cl₂(H₂O)₂]Cl and [Ln(o-HABzGH–2H)OH(H₂O)₃], where Ln=La, Pr, Nd, Sm and Eu, have been synthesized. The structures of the complexes have been studied by conductance, magnetic, electronic, i.r.,¹H n.m.r. and¹³C n.m.r. spectral techniques. The hypersensitive bands of the electronic spectra suggest coordination numbers six and seven around Nd^III in its adduct and neutral complexes respectively. I.r. and n.m.r. spectral data suggest a neutral bidentate behaviour for the ligand in the adducts and a dinegative tridentate nature in the neutral complexes.     

Magnetic interactions in ternary cobalt oxides with cubic perovskite structure

Magnetic properties were measured on the cubic perovskite systems SrCoO_3?δ, (La_1?xSr_x)CoO₃ (0.5 ≦ x ≦ 1.0), and Sr(Co_1?xMn_x)O₃ (0 ≦ x ≦ 1.0). It is found that S²⁺ and La³⁺ ions strongly affect the spin state of the Co²⁺ ion and that the Mn⁴⁺ ion located at the octahedral site affects the spin state of Co⁴⁺ ion. The magnetic properties (T_c, T_θ, and σ) are explained by the magnetic interaction Co³⁺OCo³⁺, Co³⁺OCo⁴⁺, Co⁴⁺OCo⁴⁺, Mn⁴⁺OMn⁴⁺, and Mn⁴⁺OCo⁴⁺ in these systems.     

Synthesis,spectroscopy and cyclic voltammetry of cobalt(III) complexes with 5-methyl-3-formylpyrazole N(4)-cyclohexylthiosemicarbazone (HMPz4Cy): X-ray crystal structure of [Co(MPz4Cy)2]Cl · 2.75H2O

The coordination behaviour of the novel ligand, HMPz4Cy, is reported, together with solid state isolation of its diamagnetic cobalt(III) complexes, [Co(MPz4Cy)₂]X · nH₂O (X = Cl, Br, NO₃, ClO₄ and BF₄). I.r. and ¹H-n.m.r. data for the free ligand and its Co^III complexes confirm that the ligand, HMPz4Cy, acts as a uninegative anion with NNS tridentate function via the pyrazolyl nitrogen (tertiary), azomethine nitrogen and thiol sulphur. Electronic spectra (both solid and solution) are commensurate with a distorted octahedral environment for the reported Co^III species. Cyclic voltammograms of Co^III complexes indicate a quasireversible Co⁺³/Co⁺² couple. X-ray crystallography of a representative species, [Co(MPz4Cy)₂]Cl · 2.75H₂O (C2, monoclinic), has shown unambiguously that the two ligands are orthogonally coordinated to the central Co^III ion with both the thiolato sulphurs and both pyrazolyl nitrogen atoms in cis positions.     

Complexation of palladium cyanide with imidazolidine-2-thione and its derivatives

Summary Pd(CN)₂ reacts with imidazolidine-2-thione (Imt), 1,3-diazinane-2-thione(Diaz), 1,3-diazipnane-2-thione (Diap) and their derivatives to yield complexes of stoichiometry [PdL₂(CN)₂] or [PdL(CN)₂] (L = Imt, Diaz or Diap and L = Imt having N-Me, Et or Pr substituents), which were characterized by elemental analysis, i.r., ¹H and ¹³C n.m.r. spectroscopy. Both mono- and bis ligand complexes are thought to be square planar with the monoligand binding to metal via sulphur (bridging) and the bis ligand via the monodentate thione group. The ¹³C enriched Pd(¹³CN)₂ complex was prepared and the ¹³C n.m.r. recorded. The C-2 resonance of ¹³C n.m.r. of Imt, Diaz or Diap complexes of the copper(I), silver(I), gold(I) and palladium(II) were compared.     

Transition metal complexes derived from 2-hydroxyimino-3-(2′-hydrazonopyridyl)-butane

Summary The complexes of Mn^II, Co^II, Ni^II, Cu^II, Zn^II, Cd^II, Hg^II, Co^III and UO ₂ ²⁺ ions with 2-hydroxyimino-3-(2-hydrazonopyridyl)-butane (HL) have been synthesised and characterized by elemental analyses, molar conductivities, magnetic measurements and spectral (i.r., visible, n.m.r.) studies. I.r. spectra show that HL behaves as a neutral or mononegative ligand and binds in a bidentate and/or tridentate manner. Also, HL behaves as oxidizing agent towards Co^II forming diamagnetic Co^III complexes depending on the preparative conditions. Different stereochemistries are proposed for Mn^II, Co^III, Co^II, Ni^II and Cu^II on the basis of spectral and magnetic studies.     

Novel asymmetric heterobimetallic complexes of transition metals and the kinetics of oxygen binding to a cobalt(II) complex

A series of asymmetric heterobimetallic complexes of the type [LMLSn]Cl and [LMLSn]Cl₂, where L = ethylene diamine, M = Mn^II, Co^II, Ni^II and Cu^II, M = Cr^III and Fe^III and L = 1-tryptophan and 1-valine, have been synthesized and characterized by elemental analyses, u.v.–vis., i.r., e.p.r., n.m.r., cyclic voltammetry and conductivity measurements. The Co^III analogue of these complexes was characterized by two dimensional n.m.r. COSY data. The kinetics of oxygen binding with the complex [C₁₅H₂₃N₄O₂SnCo]Cl has also been studied. The kinetic data proves that Co^II of a coordinated molecule participates in the rate-determining step of the dioxygen binding process. The plots of the pseudo-first-order rate k _obs versus [O₂] are linear passing through an intercept. The electrochemical behaviour of [C₁₅H₂₃N₄O₂SnCo]²⁺ and [C₁₅H₂₃N₄O₂SnCu]⁺ was monitored by cyclic voltammetry. Comparison of the electrochemical properties of [Co^IIISn^IV]²⁺ and [Cu^IISn^IV]⁺ reveal that, in both the species, one electron transfer reaction takes place. For the [Co^IIISn^IV]²⁺ species E ⁰ = 0.272 and –1.1 V and for the [Cu^IISn^IV]⁺ species E ⁰ = 0.078 and –0.300 V values were obtained, respectively.     

Five ingol esters and a 17-hydroxyingenol ester from the latex of Euphorbia Kamerunica. Assignment of esters using 13C.N.M.R. methods.

The structures of five ingol esters and a 17-hydroxyingenol ester from the latex of $\text{Euphorbia kamerunica}$ have been determined. The ¹³C n.m.r. spectra of these compounds have been assigned using 2D δ_C/δ_H correlations. The specific positions of attachment of esters have been assigned unambiguously using ¹³C n.m.r. methods including 2D long range δ_C/δ_H correlation.     

Sol–gel preparation and electrochemical performances of LiFe1/3Mn1/3Co1/3PO4/C composites with core–shell nanostructure

LiFe_1/3Mn_1/3Co_1/3PO₄/C solid solution was prepared via a poly(ethylene glycol) assisted sol–gel method and exploited as cathode materials for lithium ion batteries. X-ray diffraction patterns indicate that LiFe_1/3Mn_1/3Co_1/3PO₄/C is crystallized in an orthorhombic structure. The scanning electron microscopy and transmission electron microscopy show that the particles are about 200 nm with a uniform carbon coating of about 8 nm in thickness to form a core–shell nanostructure. During charge–discharge cycles, LiFe_1/3Mn_1/3Co_1/3PO₄/C presented three plateaus corresponding to Fe³⁺/Fe²⁺, Mn³⁺/Mn²⁺ and Co³⁺/Co²⁺ redox couples, and a discharge capacity of 150.8 mAh g^?1 in the first cycle, remaining 121.2 mAh g^?1 after 30 cycles. Core–shell structure can optimize the performances of polyoxoanionic materials for lithium ion batteries.     

New antimony-capped iron(II) and cobalt(III) clathrochelate precursors of the polytopic hybrid cage complexes: Synthesis,X-ray structures and electrochemistry

Direct template macrocyclization of the three dimethylglyoxime molecules on the iron(II) ion and the capping of nonmacrocyclic K₃CoDm₃ tris-dimethylglyoximate with triethylantimony(V) derivatives led to the formation of triethylantimony-capped iron(II) and cobalt(III) clathrochelates. The complexes obtained have been characterized using elemental analysis, MALDI-TOF mass, IR, UV–Vis, ⁵⁷Fe Mössbauer and ¹H and ¹³C NMR spectroscopies, and X-ray crystallography. The influence of the nature of an encapsulated metal ion, the capping groups and the chelate fragments on a clathrochelate framework geometry is discussed. The cyclic voltammograms show oxidation and reduction waves assignable to Fe^2+/3+ and Co^2+/3+ couples of the encapsulated metal ion.     

Ring‐Size‐Modulated Reactivity of Putative Dicobalt‐Bridging Nitrides: C−H Activation versus Phosphinimide Formation

Dicobalt complexes supported by flexible macrocyclic ligands were used to target the generation of the bridging nitrido species [(ⁿ PDI₂)Co₂(μ‐N)(PMe₃)₂]³⁺ (PDI=2,6‐pyridyldiimine; n =2, 3, corresponding to the number of catenated methylene units between imino nitrogen atoms). Depending on the size of the macrocycle and the reaction conditions (solution versus solid‐state), the thermolysis of azide precursors yielded bridging phosphinimido [(²PDI₂)Co₂(μ‐NPMe₃)(PMe₃)₂]³⁺, amido [(ⁿ PDI₂)Co₂(μ‐NH₂)(PMe₃)₂]³⁺ (n =2, 3), and C−H amination [(³PDI₂*‐μ‐NH)Co₂(PMe₃)₂]³⁺ products. All results are consistent with the initial formation of [(ⁿ PDI₂)Co₂(μ‐N)(PMe₃)₂]³⁺, followed by 1) PMe₃ attack on the nitride, 2) net hydrogen‐atom transfer to form N−H bonds, or 3) C−H amination of the alkyl linker of the ⁿ PDI₂ ligand.