Molecular and electronic structures of one-electron oxidized Ni(II)-(dithiosalicylidenediamine) complexes: Ni(III)-thiolate versus Ni(II)-thiyl radical states

The dithiosalicylidenediamine Ni II complexes [Ni(L)] (R=tBu, R'=CH2C(CH3)2CH2 1, R'=C6H4 2; R=H, R'=CH2C(CH3)2CH2 3, R'=C6H4 4) have been prepared by transmetallation of the tetrahedral complexes [Zn(L)] (R=tBu, R'=CH2C(CH3)2CH2 7, R'=C6H4 8; R=H, R'=CH2C(CH3)2CH2 9, R'=C6H4 10) formed by condensation of 2,4-di-R-thiosalicylaldehyde with diamines H2N-R'-NH2 in the presence of Zn II salts. The diamagnetic mononuclear complexes [Ni(L)] show a distorted square-planar N2S2 coordination environment and have been characterized by 1H- and 13C NMR and UV/Vis spectroscopies and by single-crystal X-ray crystallography. Cyclic voltammetry and coulombic measurements have established that complexes 1 and 2, incorporating tBu functionalities on the thiophenolate ligands, undergo reversible one-electron oxidation processes, whereas the analogous redox processes for complexes 3 and 4 are not reversible. The one-electron oxidized species, 1+ and 2+, can be generated quantitatively either electrochemically or chemically with 70 % HClO4. EPR and UV/Vis spectroscopic studies and supporting DFT calculations suggest that the SOMOs of 1+ and 2+ possess thiyl radical character, whereas those of 1(py)2 + and 2(py)2 + possess formal Ni III centers. Species 2+ dimerizes at low temperature, and an X-ray crystallographic determination of the dimer [(2)2](ClO4)2.2 CH2Cl2 confirms that this dimerization involves the formation of a S-S bond (S...S=2.202(5) A).     

Interaction of Al(III) and Mg(II) aqua-ions during their copreciptitation at variable pH

The concept on ┐fractional precipitation of hydroxides has been refined. In the preparation of coprecipitated Al(III)–Mg(II) hydroxides at variable pH values, mixed aluminium-mangesium compounds are formed not only in alkaline but also in acidic media.

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. , Al(III)–Mg(II) pH , .

     

Synthesis and crystal structure of Fe(III) and Al(III) complexes with 2-diphenylacetyl-1,3-indandione

Iron(III) and aluminum(III) complexes with 2-diphenylacetyl-1,3-indandione (HL) have been synthesized. The structures of the obtained compounds FeL₃(I) and AlL₃(II) were studied. The isostructural crystals are monoclinic, I: Z = 8, space group P2_1/c, a = 16.061(3) Å, b = 16.658(3) Å, c = 22.015(4) Å, β = 111.41(3)°; II: Z = 8, space group P2_1/c, a = 16.115(14) Å, b = 16.476(8) Å, c = 21.949(20) Å, β = 111.04(11)°. The structural units of crystals I and II are neutral molecules in which each ligand is bidentately coordinated to a central metal atom through the oxygen atom of the acyl keto group and an oxygen atom of the indandione fragment to form a six-membered chelate ring. In the crystals, neutral molecules I and II form pseudodimers due to stacking of indandione moieties of two adjacent coordination spheres and additional C-H…O contacts. Each pseudodimer is in contact with six neighboring dimers also through hydrogen bonds C-H…O to form an infinite framework.     

Spectral properties and photophysical behaviour of water soluble cationic Mg(II) and Al(III) phthalocyanines

Peripherally and non-peripherally tetrasubstituted-[(N-methyl-2-pyridylthio)]phthalocyaninato magnesium (II) (5 and 6) and chloro aluminium (III) (7 and 8) tetraiodide have been synthesized and characterized. The photophysical properties of the complexes in dimethyl sulfoxide (DMSO) and aqueous medium in the presence and absence of cremophore EL have been studied. These complexes show high solubility in aqueous medium though they were aggregated. The triplet state quantum yields (F_T) and the triplet lifetimes (t_T) were found to be higher in DMSO with Φ_T ranging from 0.32 to 0.51, while t_T ranged from 282 to 622 ms in DMSO, compared to aqueous medium (pH 7.4 buffer) where Φ_T ranged from 0.15 to 0.19 and t_T from 26 to 35 ms. Addition of cremophore EL in aqueous solution resulted in partial disaggregation and increased photoactivity. The fluorescence lifetimes of the complexes showed strong dependence on their immediate environment. The ionic magnesium(II) and aluminium(III) phthalocyanines strongly bind to bovine serum albumin (BSA).      

邻羟基苄基氨乙酸及其配合物的研究 VI: Cu(II)、Co(II)、Ni(II)配合物的合成、性质和结构

合成了邻羟基苄基氨乙酸与Cu(II)的双核配合物, 并得以了单晶; 同时合成了Cu(II)、Co(II)、Ni(II)与该配体的质子化配合物, 测定了它们的组成、溶解度和摩尔电导, 研究了它们的磁性、热谱、红外光谱及电子光谱. 用四圆衍射仪测定了单晶的结构. 讨论了这些配合物的配位情况以及结构与性能的关系.     

Activation and cleavage of dinitrogen by three-coordinate metal complexes involving Mo(III) and Nb(II/III)

Density functional calculations have been employed to rationalize why the heteronuclear N(2)-bridged Mo(III)Nb(III) dimer, [Ar((t)Bu)N](3)Mo(mu-N(2))Nb[N((i)Pr)Ar](3)(Ar = 3,5-C(6)H(3)Me(2)), does not undergo cleavage of the dinitrogen bridge in contrast to the analogous Mo(III)Mo(III) complex which, although having a less activated N-N bond, undergoes spontaneous dinitrogen cleavage at room temperature. The calculations reveal that although the overall reaction is exothermic for both systems, the actual cleavage step is endothermic by 144 kJ mol(-1) for the Mo(III)Nb(III) complex whereas the Mo(III)Mo(III) system is exothermic by 94 kJ mol(-1). The reluctance of the Mo(III)Nb(III) system to undergo N(2) cleavage is attributed to its d(3)d(2) metal configuration which is one electron short of the d(3)d(3) configuration necessary to reductively cleave the dinitrogen bridge. This is confirmed by additional calculations on the related d(3)d(3) Mo(III)Nb(II) and Nb(II)Nb(II) systems for which the cleavage step is calculated to be substantially exothermic, accounting for why in the presence of the reductant KC(8), the [Ar((t)Bu)N](3)Mo(mu-N(2))Nb[N((i)Pr)Ar](3) complex was observed to undergo spontaneous cleavage of the dinitrogen bridge. On the basis of these results, it can be concluded that the level of activation of the N-N bond does not necessarily correlate with the ease of cleavage of the dinitrogen bridge.     

Molecular and electronic structure of five-coordinate complexes of iron(II/III) containing o-diiminobenzosemiquinonate(1-) pi radical ligands

The reaction of the ligand N-phenyl-1,2-benzenediamine (N-phenyl-o-phenylenediamine), H2[L(PDI)], in dry acetonitrile with [FeIII(dmf)6](ClO4)3 (dmf = N,N-dimethylformamide) affords the dimer (mu-NH,NH)[FeIII(L(ISQ))(L(PDI))]2 (1), where (L(ISQ))*- represents the pi radical monoanion N-phenyl-o-diiminobenzosemiquinonate and (L(PDI))2- is its one-electron-reduced, closed-shell form. Complex 1 possesses a diamagnetic ground-state St = 0. Addition reactions of tri-n-butylphosphane, tert-butyl isocyanide, cyclohexyl isocyanide, 4,5-diphenylimidazole, and 4-(1-phenylpentyl)pyridine with 1 in acetonitrile or toluene yields [FeII(L(ISQ))2(PBu3)] (2), [Fe(II)(L(ISQ))2(CN-tBu)] (4), [FeII(L(ISQ))2(CNCy)] (5), [FeIII(L(ISQ))2(Ph2Im)] (6), and [FeIII(L(ISQ))(L(PDI))(BuPhCH-py)].BuPhCH-py (7). Oxidation of 1 with iodine affords [FeIII(L(ISQ))2I] (3), and oxidation of 2 with ferrocenium hexafluorophosphate yields [FeIII(L(ISQ))2(PBu3)](PF6) (2ox). The structures of complexes 2, 2ox, 3, 5, 6, and 7 have been determined by X-ray crystallography at 100(2) K. Magnetic susceptibility measurements and EPR, UV-vis, and M?ssbauer spectroscopy have established that mononuclear complexes containing the [FeII(L(ISQ))2X] chromophore (2, 4, 5) are diamagnetic (St = 0) whereas those with an [FeIII(L(ISQ))2X]n chromophore (3, 2(ox), 6) are paramagnetic (St = 1/2) and those with an [FeIII(L(ISQ))(L(PDI))X] chromophore (7) possess an St = 1 ground state. It is established that all ferric species have an intrinsic intermediate spin (SFe = 3/2) which is intramolecularly antiferromagnetically coupled to one or two (L(ISQ))*- ligand radicals yielding an St = 1 (7) or St = 1/2 (2ox, 3, 6) ground state, respectively. In the ferrous complexes 2, 4, and 5 the intrinsic spin at the iron ion is either low spin (SFe = 0) or intermediate spin (SFe = 1). Antiferromagnetic coupling between two radicals (L(ISQ))*- or, alternatively, between the intermediate spin ferrous ion and two radicals yields then the observed diamagnetic ground state. In 1 two [FeIII(L(ISQ))(L(PDI))] halves with S = 1 couple antiferromagnetically affording an St = 0 ground state.     

Interactions of pyridinecarboxylic acid chelators with brain metal ions: Cu(II), Zn(II), and Al(III)

Abstract  

The interactions of Cu(II), Zn(II), and Al(III) with 1,6-dimethyl-4-hydroxy-3-pyridinecarboxylic acid (DQ716) and 2,6-dimethyl-3-hydroxy-4-pyridinecarboxylic acid (DT726), possible chelating agents in Alzheimer’s disease, were investigated in aqueous solution. The proton dissociation constants of the ligands, the stability constants, and the coordination modes of the metal complexes formed were determined by pH-potentiometric, UV–vis spectrophotometric, and ¹H NMR methods. The nitrogen of the pyridine ring changes the proton affinity of the carboxylate and phenolate moieties and these pyridine derivatives form stronger complexes with Cu(II), Zn(II), and Al(III) than salicylic acid. Interactions of the ligands with human serum albumin as their potential transporter in blood were investigated at physiological pH through ultrafiltration by UV–vis and fluorescence spectroscopy.     

Reactivity of Al(III) complexes with substituted phthalocyanines

The results of a study of reactivity of Al(III) complexes with acido ligands (Cl^?, OH^?) and substituted phthalocyanine, containing 4 and 8 substituents (Cl, Br, NO₂ or COOH) in different positions of annelated benzene residues, are reviewed. Reactivity of coordinated phthalocyanines is studied by quantum-chemical and spectrophotometric methods for acid-base reactions and reactivity of coordination core is estimated by chemical kinetics methods using reactions of dissociation at the Al-N bonds. The Hammett-Taft correlation equations are derived for mono-and diprotonated tetrasubstituted phthalocyanines of Al(III) with positive ρ values of 10.2 and 59.8, respectively     

Palladium(II)–rare-earth metal(III) paddlewheel carboxylate complexes: Easy total acetate to pivalate metathesis

Bis-paddlewheel heterobimetallic complexes in which palladium(II) is connected to the rare-earth metals(III) [Pd(μ-OOCMe)₄Ln(OH₂)(μ,η²-OOCMe)]₂ × 2HOOCMe (Ln = Nd, Sm, Eu, Yb and Tm) by four acetate bridges were synthesised by the reaction of Pd₃(μ-OOCMe)₆ with the Ln^III acetates. The tetraacetate-bridged complexes were unexpectedly found to be readily transformed by the stoichiometric amount of pivalic acid into the mono-paddlewheel tetrapivalate-bridged analogues in which the paddlewheel structure [Pd(μ-OOCR)₄Ln] maintains as established by X-ray crystallography. The role of the intra- and intermolecular H-bonding in these complexes is discussed.     

Hydrazinium metal(II) and metal(III) ethylenediamine tetraacetate hydrates

Hydrazinium metal ethylenediaminetetraacetate complexes of molecular formula (N₂H₅)₂[Mg(edta)·H₂O], (N₂H₅)₃[Mn(edta)··H₂O](NO₃)·H₂O, N₂H₅[Fe(edta)·H₂O], N₂H₅[Cu(Hedta)·H₂O] and N₂H₅[Cd(Hedta)·H₂O]·H₂O have been synthesized and characterized by elemental and chemical analysis, conductivity and magnetic measurements and spectroscopic techniques. The thermal behaviour of these complexes has been studied by thermogravimetry and differential thermal analysis. The data set provided by the simultaneous TG-DTA curves of the complexes shows the occurrence of three or four consecutive steps such as dehydration, ligand pyrolysis and formation of metal oxides. X-ray powder diffraction patterns of copper and cadmium complexes show that they are not isomorphous. These studies suggest seven coordination for Mg,Mn, Fe complexes and six coordination for Cu and Cd derivatives.     

Synthesis, spectral and electrochemical properties of Al(III) and Zn(II) complexes with flavonoids

The synthesis, electrochemical and spectral (UV-vis, 1H NMR, IR, fluorescence) properties as well as thermal behaviors of Al(III) and Zn(II) complexes with the flavonoids quercetin (H2L(1)), rutin (H2L(2)) and galangin (HL(3)) are presented. The complexes may be formulated as [Al2(L(1))(H2O)8]Cl4, [Al3(L(2))2(H2O)12]Cl5, [Al(L(3))(H2O)4]Cl2, [Zn2(L(1))(H2O)4]Cl2, [Zn3(L(2))2(H2O)6]Cl2 and [Zn(L(3))(H2O)2]Cl. The higher fluorescence intensities of the complexes related to the free flavonoids, are attributed to the coordination of the ligands to the small, highly charged Al(III) and Zn(II) ions. The coordination effectively increases the rigidity of the ligand structure and increases the fluorescence quantum yield by reducing the probability of non-radiative energy dissipation process. Antioxidant activities of the compounds were also investigated under an electrochemical point of view. The cyclic voltammetric data show a considerable decrease of the oxidation potentials of the complexes related to that of the free flavonoids. Thus, the flavonoid-metal complexes are more effective antioxidants than the free flavonoids.     

Mixed metal hydroxycarboxylic acid complexes. Spectrophotometric study of complexes of U(VI) with In(III), Cu(II), Zn(II) and Cd(II)

The formation of mixed metal complexes between uranium (VI), as the central metal ion, and aluminium (III), indium (III), copper (II), zinc (II) and cadmium (II), as the additional metal ions, with a hydroxycarboxylic acid chosen between citric, tartaric or malic, has been studied using spectrophotometric methods.The effect of pH has been examined, and the results show that at pH=4 stable complexes are formed for most of the systems. At this pH the method of mole ratio and Job's method of continuous variations, were employed to determine the stoichiometry of the mixed metal complexes. Al(III), In(III) and Cu(II) showed a high tendency to form mixed metal complexes with U(VI), while the formation of complexes is uncertain for Cd(II) and Zn(II). The ratio of the ligand to the total metal ion has been found to be 21 and metal:metal ratios of 11 and 12 have been observed.Represents part of the Ph.D. thesis submitted by Emanuel Manzurola to Ben Gurion University of the Negev.     

Asymmetric hydrogenation ofN-acetyldehydrodipeptide complexes with Mg(II) and Ca(II) ions

N-Ac--Phe-AA form labile complexes with Mg(II) ions. Potentiometric titration data show that the carboxyl group of the dehydrodipeptide in them scarcely participates in complexation, unlike the complexes with Ca(II) ions. The hydrogenation of these complexes over Pd/C occurs asymmetrically, the diastereomeric excess being as high as 58%.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 601–602, March, 1993.     

Formation and dissociation kinetics of triaza-crown-alkanoic acid complexes of transition metal(II) and lanthanide (III)

The formation and dissociation rates of some transition metal(II) and lanthanide(III) complexes of the 1,7,13-triaza-4,10,16-trioxacyclooctadecane N',N',N'-triacetic acid (1) and 1,7,13-triaza-4,10,16-trioxacyclooctadecane-N',N',N'- trimethylacetic acid (2) have been measured by the use of stopped-flow and conventional spectrophotometry. Experimental observations were made at 25.0 +/- 0.1 degrees C and at an ionic strength of 0.10 M KCl. The complexation of Zn(2+) and Cu(2+) ions with 1 and 2 proceeds through the formation of an intermediate complex (MH(3)L(+) *) in which the metal ion is incompletely coordinated. This may then lead to a final product in the rate-determining step. Between pH 4.68 and 5.55, the diprotonated (H(2)L(-)) form is revealed to be a kinetically active species despite its low concentration. The stability constants (log K (MH (3)L (+) *)) and specific base-catalyzed rate constants (k(OH)) of intermediate complexes have been determined from the kinetic data. The dissociation reactions of 1 and 2 complexes of Co(2+), Ni(2+), Zn(2+), Ce(3+), Eu(3+) and Yb(3+) were investigated with Cu(2+) ions as a scavenger in acetate buffer. All complexes exhibit acid-independent and acid-catalyzed contributions. The buffer and Cu(2+) concentration dependence on the dissociation rate has also been investigated. The metal and ligand effects on the dissociation rate of some transition metal(II) and lanthanide(III) complexes are discussed in terms of the ionic radius of the metal ions, the side-pendant arms and the rigidity of the ligands.     

The mass spectra of 1,1,1-trichloro-2,4-pentanedione and its Al(III), Cr(III), Fe(III), Mn(II), Co(II) and Cu(II) complexes

The compounds 1,1,1-trichloro-2,4-pentanedione, Cu(II)tca₂, Co(II)tca₂, Mn(II)tca₂, Al(III)tca₃, Cr(III)tca₃ and Fe(III)tca₃ (tca?1,1,1-trichloro-2,4-pentanedionato, [CCl₃COCHCOCH₃]^?) have been prepared and their mass spectra have been obtained. The mass spectral results have been compared with findings for comparable fluorinated and nonhalogenated compounds. Comparisons are made in terms of internal redox reactions and hard and soft acid base theory. Rearrangement of chloride from ligand to metal accompanied by the elimination of CO or other neutral even electron fragments emerges as an important reaction for the ions of these compounds. While the internal redox reactions characteristic of all previous β-diketonate complex mass spectra still occur, their importance appears reduced to some degree by the facility of the chlorine rearrangement.     

Influence of alkali metal and ammonium cations on the structure of iron(II) and cobalt(III) hexacyanide complexes encapsulated in faujasite

Changing the cation composition (Na⁺ to K⁺, NH₄ ⁺ Cs⁺) of faujasite with hexacyanoferrate(II) encapsulated in the large pores causes distortion of the octahedral symmetry of the complex.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 30, No. 5, pp. 293–297, September–October, 1994.