Raman, IR, UV-vis and EPR characterization of two copper dioxolene complexes derived from L-dopa and dopamine

The anionic complexes [Cu(L(1-))3](1-), L(-)=dopasemiquinone or L-dopasemiquinone, were prepared and characterized. The complexes are stable in aqueous solution showing intense absorption bands at ca. 605 nm for Cu(II)-L-dopasemiquinone and at ca. 595 nm for Cu(II)-dopasemiquinone in the UV-vis spectra, that can be assigned to intraligand transitions. Noradrenaline and adrenaline, under the same reaction conditions, did not yield Cu-complexes, despite the bands in the UV region showing that noradrenaline and adrenaline were oxidized during the process. The complexes display a resonance Raman effect, and the most enhanced bands involve ring modes and particularly the nuCC+nuCO stretching mode at ca. 1384 cm(-1). The free radical nature of the ligands and the oxidation state of the Cu(II) were confirmed by the EPR spectra that display absorptions assigned to organic radicals with g=2.0005 and g=2.0923, and for Cu(II) with g=2.008 and g=2.0897 for L-dopasemiquinone and dopasemiquinone, respectively. The possibility that dopamine and L-dopa can form stable and aqueous-soluble copper complexes at neutral pH, whereas noradrenaline and adrenaline cannot, may be important in understanding how Cu(II)-dopamine crosses the cellular membrane as proposed in the literature to explain the role of copper in Wilson disease.     

A resonance Raman,surface-enhanced resonance Raman,IR, and ab initio vibrational spectroscopic study of nickel(II) tetraazaannulene complexes

The IR and resonance Raman spectra of the nickel(II) complexes of dibenzo[b,i][1,4,8,11]tetraaza[14]annulene (TAA) and 5,7,12,14-tetramethyldibenzo[b,i][1,4,8,11]tetraaza[14]annulene (TMTAA) have been measured and compared with ab initio calculations of the vibrational wavenumbers at the B3-LYP level using the LanL2DZ basis set. An excellent fit is found between the experimental and calculated data, enabling precise vibrational assignments to be made. Surface-enhanced resonance Raman spectra were obtained following adsorption on Ag electrodes, with potentials in the range -0.1 to -1.1 V vs Ag/AgCl. There is evidence for contributions from both the electromagnetic and charge transfer (CT) surface enhancement mechanisms. The data indicate that variations in band intensities with electrode potential can be interpreted in terms of the CT mechanism.     

Preparation and characterization of mononuclear Co, Ni, and Zn complexes of dinucleating macrocyclic hexaaza-dithiophenolate ligands and their open-chain derivatives

The preparation and characterization of mononuclear complexes of the dinucleating 24-membered hexazadithiophenolate macrocycles H2L2 and H2L3 and their open-chain N3S2 analogues H2L4 and H2L5 are reported. The highly crystalline compounds [Ni(L4)] (4), [Ni(L5)] (5), [Co(L5)] (6), [NiH2(L2)]2+ (7), [ZnH2(L2)]2+ (8), and [NiH2(L3)]2+ (9) could be readily prepared by stoichiometric complexation reactions of the hydrochlorides of the free ligands with the corresponding metal(II) dichlorides and NEt3 in methanolic solution. All complexes were characterized by X-ray crystallography. Monometallic complexes 4-6 of the pentadentate ligands H2L4 and H2L5 feature distorted square pyramidal MN3S2 structures (tau = 0.01 to 0.44). Similar coordination geometries are observed for the macrocyclic complexes 7-9 of the octadentate ligands H2L2 and H2L3. The two hydrogen atoms in 7-9 are attached to the noncoordinating benzylic amine functions and are hydrogen bonded to the metal-bound thiophenolate functions. A comparison of the structures of 4-9 reveals that the macrocycles L2 and L3 have a rather flexible ligand backbone that do not confer unusual coordination geometries on the metal ions. We also report on the ability of the monometallic complexes 7 and 8 to serve as starting materials for the preparation of dinuclear complexes.     

An EPR and IR spectral study of paramagnetic cobalt dinitrosyl-o-semiquinone complexes

Conclusions Mixed paramagnetic cobalt dinitrosyl o-semiquinone complexes were obtained for the first time in solution. IR and EPR spectroscopy showed that these complexes have distorted tetrahedral structure, while their ground electronic state is [Co(NO)₂]¹⁰ with the unpaired electron on the o-semiquinone ligand.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 674–677, March, 1988.     

Synthesis,characterization and thermal decomposition of uranyl propionate complexes with Zn,Mn, Ni and Co

Journal of Thermal Analysis and Calorimetry - Uranyl propionate complexes of Zn(II), Mn(II), Ni(II) and Co(II), of the general formula M[(C2H5COO)3UO2]2 · nH2O, have been synthesized and...     

Conformational polymorphism of solid tetramesityldisilene Mes2Si=SiMes2 (Raman,UV-vis,IR and fluorescence study)

Conformational polymorphism of solid tetramesityldisilene (1) has been studied by the methods of optical spectroscopy. The three known modifications of 1: orange unsolvated 1a and two 1:1 solvates with toluene (1b) and THF (1c) have been found to transform under specific conditions to a new, most thermodynamically stable polymorph, yellow unsolvated powder 1d. The latter has been characterized by the Raman, IR, UV-vis and fluorescence data. All forms of 1 exhibit Raman spectra differing in details, which reflect their different crystal and molecular structures. Unsolvated 1a and 1d differ significantly in electronic absorption and fluorescence emission. The yellow form 1d can be converted to the orange form 1a upon illumination with laser light in the region 514-457 nm. Similarity of the Raman and UV-vis spectra of 1d to those of the solutions of 1 provides some evidence for a quasi-trans conformation of 1d.     

四元Mg0.9Ti0.1Ni0.9X0.1(X=Mn,Zn,Co,Fe)系列合金的制备及性能研究

用机械合金化法合成了Mg0·9Ti0·1Ni0·9X0·1(X=Mn,Zn,Co,Fe)系列合金.X射线衍射(XRD)结构分析表明,用X部分替代Ni后,促进了Mg0·9Ti0·1Ni合金的非晶化过程.用Co和Fe部分替代Ni提高了合金的放电容量,但却降低了合金的循环稳定性.用Zn和Mn部分替代Ni提高了合金电极的循环寿命,尤其是Mg0·9Ti0·1Ni0·9Zn0·1合金电极经10个充放电循环后,其放电容量仍可达到313·8mA·h/g.对添加Co后的合金进行p-c-T测试发现,Mg0·9Ti0·1Ni0·9Co0·1合金的吸放氢容量明显比Mg0·9Ti0·1Ni合金高,这与电化学所测到的结果一致.     

Synthesis,structure and properties of supramolecular Mn,Co, Ni and Zn complexes containing Salen-type bisoxime ligands

Four supramolecular complexes [MnL¹(H₂O)₂] (1), {[CoL²(OAc)(H₂O)]₂Co}·5CH₃CH₂OH (2), {[NiL³(OAc)(CH₃OH)]₂Ni}·2CH₃COCH₃·2CH₃OH (3) and {[ZnL²(OAc)]₂Zn}·CHCl₃ (4), have been synthesized and characterized by elemental analyses, IR, UV–Vis spectra and X-ray diffraction techniques. All the complexes have the trinuclear configuration except for Mn^II complex being mononuclear configuration. Every trinuclear complex contains two acetate ions coordinate to the three metal ions via a familiar M–O–C–O–M (M = Co, Ni, Zn) coordinated mode. Although complexes 1 and 3 display 1D supramolecular chains, the different coordination environments (mononuclear in 1, trinuclear in 3) provoke divergence in the structures and aggregations of the chain subunits. Complex 2 forms a 3D hydrogen-bonding supramolecular networks possessing a channel composing of six O–H···O hydrogen bonds, while complex 4 exhibits a 2D hydrogen-bonding supramolecular networks with the formation of “grottos” occupied by chloroform molecules through intermolecular hydrogen-bond interactions. The spectral properties of the title complexes have been further discussed in detail.     

微柱高效液相色谱法测定烟草样品中铁钴镍铜锌锰

研究了用2(2喹啉偶氮)5二甲氨基酚(QADMAP)为柱前衍生试剂,以Waters XterraTMRP18(1.0mm×50mm,2.5μm)微柱为固定相,72%的甲醇(内含0.5%的乙酸)为流动相,高效液相色谱法分离,二极管矩阵检测器检测测定铁、钴、镍、铜、锌和锰的方法。根据信噪比(S/N=3)得各金属离子的检出限分别为:铁3μg·L-1、钴和铜4μg·L-1、镍2μg·L-1、锌5μg·L-1、锰8μg·L-1,方法用于烟草中痕量铁、钴、镍、铜、锌和锰的测定,相对标准偏差在1.6%～3.8%之间,回收率在93%～107%之间,结果满意。     

Emerging Earth-abundant (Fe,Co, Ni,Cu) molecular complexes for solar fuel catalysis

Current micro review focuses on Earth-abundant molecular transition metal photosensitizers and catalysts for dye sensitized photoelectrochemical cells for direct solar energy storage. The possibility of direct conversion of solar energy into fluids (ethanol or methanol) or gases (hydrogen or methane) in a cost efficient way is considered a disruptive and innovative breakthrough for large-scale implementation of solar fuel technologies. At present, it is a fast-growing research area and the most outstanding results are highlighted.     

Microwave Synthesis of Co,Ni, Cu,Zn Ferrites

Solid-phase synthesis of cobalt, nickel, copper, and zinc ferrites with spinel structure was performed from oxides of these metals and natural magnetite under the action of microwave radiation. The optimal conditions in which the corresponding ferrites can be formed were determined by varying the irradiation parameters affecting the reaction (magnetron power and reaction duration). It was found that the solid-phase interaction of oxides of Ni, Zn, Cu, Co(II) metals gives in practically acceptable yields metal-substituted ferrospinels (NiFe₂O₄, CoFe₂O₄, ZnFe₂O₄, CuFe₂O₄) constituting the main phase of the samples. A high capacity of the precursors and target synthesis products for absorption of the microwave radiation energy at a frequency of 2.45 GHz and its transformation into heat was demonstrated. This gives reason to use these compounds when preparing catalysts for microwave-stimulated reactions.     

Metal (Fe, Co, Ni) Nanoparticles in Silica Gels: Preparation and Magnetic Properties

Metal containing silica gels with a Me/Si molar ratio between 0.01 and 0.2 are submitted to thermal treatment under hydrogen within the temperature range 600 to 1000°C. The changes occurring during these treatments are followed by X-ray diffraction, transmission electron microscopy, Mössbauer spectrometry and static magnetization measurements.During these treatments, nickel is nearly totally reduced to metal particles, the mean size of which increases from 3 to 10 nm with increasing temperature, but does not vary appreciably with nickel content. These particles exhibit a classical superparamagnetic behavior and are stable towards reoxidation when reexposed to air at room temperature.Iron and cobalt behave in a notably different manner. First, in both cases, silicates may be formed during the thermal treatment and consequently the reduction to the metallic state is not complete unless it occurs at high temperature (1000°C and above). Secondly, the particles formed are much less stable toward reoxidation, especially in the case of iron. Accordingly, the evolution of the magnetic behavior is much more complex than in the case of nickel.     

Potentiometric and thermal conductimetric studies on salicylidene Girard-P hydrazone complexes of divalent Co,Ni, Cu and Zn salts

Salicylidene Girard-P hydrazone [H₂L]Cl reacts with divalent cobalt, nickel, copper and zinc ions to form mono-ligand complexes of the type [ML·H₂O]Cl·nH₂O and [(CuL)₂]Cl₂. The formation constants of the complexesML were determined in 50% (v/v) aqueous ethanol solution at an ionic strengthl=0.1M KCl and at 25±0.1°C. The solid complexes and the ligand were subjected to differential thermal analysis and the DC electrical conductivities were measured at varying temperatures. The results obtained were explained and discussed in terms of the proposed semiconductive behaviour of the complexes and the probable occurrence of a phase transition. The activation energies (ΔE) were calculated for the ligand and the complexes; that of the ligand was higher than those of the complexes.     

Oxalate-2-ethanolamine complexes of some bivalent cations (Mn,Co, Ni,Cu, Zn and Cd)

On the refluxing ofM(II) oxalate (M=Mn, Co, Ni, Cu, Zn or Cd) and 2-ethanolamine in chloroform, the following complexes were obtained: MnC₂O₄·HOCH₂CH₂NH₂·H₂O, CoC₂O₄·2HOCH₂CH₂NH₂, Ni₂(C₂O₄)₂·5HOCH₂CH₂NH₂·3H₂O, Cu₂(C₂O₄)₂·5HOCH₂CH₂NH₂, Zn₂(C₂O₄)₂·5HOCH₂CH₂NH₂·2H₂O and Cd₂(C₂O₄)₂·HOCH₂CH₂NH₂·2H₂O. Following the reaction ofM(II) oxalate with 2-ethanolamine in the presence of ethanolammonium oxalate, a compound with the empirical formula ZnC₂O₄·HOCH₂CH₂NH₂·2H₂O¹ was isolated. The complexes were identified by using elemental analysis, X-ray powder diffraction patterns, IR spectra, and thermogravimetric and differential thermal analysis. The IR spectra and X-ray powder diffraction patterns showed that the complexes obtained were not isostructural. Their thermal decompositions, in the temperature interval between 20 and about 900°C, also take place in different ways, mainly through the formation of different amine complexes. The DTA curves exhibit a number of thermal effects.     

Vibrational analysis of hydroxyflavylium derivatives by IR,Fourier transform Raman and resonance Raman spectroscopies

In order to give a better insight into the vibrational properties of anthocyanins, the synthesis and the vibrational studies of some hydroxyflavylium derivatives with a controlled substitution pattern have been performed. The IR, Raman and resonance Raman spectra of the investigated hydroxyflavylium compounds have been recorded in the solid and solution states. A number of lines have been assigned on the basis of deuterium isotopic shifts, resonance enhancement and previous studies on parent compounds. An attempt has been made to analyze the influence of hydroxy substituents on vibrational properties of the investigated flavylium cations.     

Synthesis, molecular and electronic structures of six-coordinate transition metal (Mn, Fe, Co, Ni, Cu, and Zn) complexes with redox-active 9-hydroxyphenoxazin-1-one ligands

A series of pseudo-octahedral metal (M = Mn, Fe, Co, Ni, Cu, Zn) complexes 4 of a new redox-active ligand, 2,4,6,8-tetra(tert-butyl)-9-hydroxyphenoxazin-1-one 3, have been synthesized, and their molecular structures determined with help of X-ray crystallography. The effective magnetic moments of complexes 4 (M = Mn, Fe, Co, and Ni) measured in the solid state and toluene solution point to the stabilization of their high-spin electronic ground states. Detailed information on the electronic structure of the complexes and their redox-isomeric forms has been obtained using density functional theory (DFT) B3LYP*/6-311++G(d,p) calculations. The energy disfavored low-spin structures of manganese, iron, and cobalt complexes have been located, and based on the computed geometries and distribution of spin densities identified as Mn(IV)[(Cat-N-SQ)](2), Fe(II)[Cat-N-BQ)](2), and Co(II)[Cat-N-BQ)](2) compounds, respectively. It has been shown that stabilization of the high-spin structures of complexes 4 (M = Mn, Fe, Co) is caused by the rigidity of the molecular framework of ligands 3 that sterically inhibits interconversions between the redox-isomeric forms of the complexes. The calculations performed on complex 4 (M = Co) predict that a suitable structural modification that might provide for stabilization of the low-spin electromeric forms and create conditions for the valence tautomeric rearrangement via stabilization of the low-spin electromer and narrowing energy gap between the low-spin ground state tautomer and the minimal energy crossing point on the intersection of the potential energy surfaces of the interconverting structures consists in the replacement of an oxygen in the oxazine ring by a bulkier sulfur atom.