Low-valent chemistry of cobalt amide. Synthesis and structural characterization of cobalt(II) amido, aryloxide, and thiolate compounds

The binuclear cobalt(II) amide complex [(CoL2)2-(TMEDA)] (1) [L = N(Si(t)BuMe2)(2-C5H3N-6-Me); TMEDA = Me2NCH2CH2NMe2] has been synthesized by the reaction of anhydrous CoCl2 with 2 equiv of [Li(L)(TMEDA)]. X-ray crystallography revealed that complex 1 consists of two [CoL2] units linked by one TMEDA ligand molecule, which binds in an unusual N,N'-bridging mode. Protolysis of 1 with the bulky phenol Ar(Me)OH (Ar(Me) = 2,6-(t)Bu2-4-MeC6H2) and thiophenol ArSH (Ar = 2,4,6-(t)Bu3C6H2) gives the neutral monomeric cobalt(II) bis(aryloxide) [Co(OAr(Me))2(TMEDA)] (2) and dithiolate [Co(SAr)2(TMEDA)] (3), respectively. Complexes 1-3 have been characterized by mass spectrometry, microanalysis, magnetic moment, and melting-point measurements, in addition to X-ray crystallography.     

Multifunctional magnetic materials obtained by insertion of spin-crossover Fe(III) complexes into chiral 3D bimetallic oxalate-based ferromagnets

The syntheses, structures, and magnetic properties of compounds of formula [Fe(III)(5-Clsal(2)-trien)][Mn(II)Cr(III)(ox)(3)]·0.5(CH(3)NO(2)) (1), [Fe(III)(5-Brsal(2)-trien)][Mn(II)Cr(III)(ox)(3)] (2), and [In(III)(5-Clsal(2)-trien)][Mn(II)Cr(III)(ox)(3)] (3) are reported. The structure of the three compounds, which crystallize in the orthorhombic P2(1)2(1)2(1) chiral space group, presents a 3D chiral anionic network formed by Mn(II) and Cr(III) ions linked through oxalate ligands with inserted [Fe(III)(5-Clsal(2)-trien)](+), [Fe(III)(5-Brsal(2)-trien)](+), and [In(III)(5-Clsal(2)-trien)](+) cations. The magnetic properties indicate that the three compounds undergo long-range ferromagnetic ordering at ca. 5 K. On the other hand, the inserted Fe(III) cations undergo a partial spin crossover in the case of 1 and 2.     

Conformationally rigid chelate rings in metal complexes of pyridyloxy-substituted 2,2'-dioxybiphenyl-cyclotetra- and cyclotriphosphazene platforms

Divalent metal halides react with pyridyloxy-substituted 2,2'-dioxybiphenyl-cyclotri- and cyclotetraphosphazene ligands to form the complexes, [MLX2] [M=Co or Cu; L=(2,2'-dioxybiphenyl)tetrakis(2-pyridyloxy)cyclotriphosphazene (L1) or (2,2'-dioxybiphenyl)tetrakis(4-methyl-2-pyridyloxy)cyclotriphosphazene (L2); X=Cl or Br], [ZnLCl2] [L=bis(2,2'-dioxybiphenyl)bis(2-pyridyloxy)cyclotriphosphazene (L3) or bis(2,2'-dioxybiphenyl)bis(4-methyl-2-pyridyloxy)cyclotriphosphazene (L4)], [MLCl2] [M=Cu or Hg; L=tris(2,2'-dioxybiphenyl)bis(2-pyridyloxy)cyclotetraphosphazene (L5)] and [Cu2LCl4] (L=trans-bis(2,2'-dioxybiphenyl)tetrakis(2-pyridyloxy)cyclotetraphosphazene (L6)]. Single-crystal X-ray structures show the L2 ligand complexes to have a N3Cl2 five-coordinate, trigonal-bipyramidal donor set with the phosphazene ring and pendant pyridyloxy nitrogens binding to the metal ions. The coordinated L2 ligand in the complex, [CoL2Cl2], slowly hydrolyses in acetonitrile with the loss of a pyridine pendant arm to form a dimetallic species, which has been characterized by crystallography as [{CoL2aCl}]2.4MeCN (L2a=[N3P3(biph)(OPy)3(O)]-, biph=2,2'-dioxybiphenyl, OPy=2-oxopyridine). The ligands, L3, L4, L5, and L6, bind to the metal halides via gem-substituted pyridyloxy nitrogens only. The resulting rigid eight-membered chelate rings all have distorted boat conformations, which force distorted-tetrahedral N2Cl2 coordination environments onto the metal ions. The spectroscopic (ESR and electronic) and magnetic properties of the complexes are reported.     

Synthesis and characterization of homo- and heterodinuclear M(II)-M'(III) (M(II) = Mn or Fe, M'(III) = Fe or Co) mixed-valence supramolecular pseudo-dimers. The effect of hydrogen bonding on spin state selection of M(II)

Reaction of H(3)L(1), the Schiff base condensate of tris(2-aminoethyl)amine with three equivalents of 5-methyl-1H-pyrazole-3-carboxaldehyde, with manganese(II)perchlorate or iron(II)tetrafluoroborate results in the isolation of [MH(3)L(1)]X(2) (M = Mn and X = ClO(4) and M = Fe and X = BF(4)). These complexes are high spin d(5) and d(6), respectively, as inferred from the long M-N bond distances obtained by single crystal X-ray diffraction for both and variable temperature magnetic susceptibility and M?ssbauer spectroscopy for the iron complex. Aerobic treatment of a solution of [CoH(3)L(1)](2+) with three equivalents of potassium hydroxide produced [CoL(1)]. Homonuclear pseudo-dimers were prepared by the aerobic reaction of [FeH(3)L(1)](BF(4))(2) with 1.5 equivalents of potassium hydroxide to give {[FeH(1.5)L(1)](BF(4))}(2) or by the metathesis reaction of [FeH(2)L(1)][FeHL(1)](ClO(4))(2) with sodium hexafluorophosphate to give [FeH(3)L(1)][FeL(1)](PF(6))(2). The complexes were characterized by EA, IR, ESI-MS, variable temperature single crystal x-ray diffraction and M?ssbauer spectroscopy. The iron(III) atom is low spin while the iron(II) atom is spin crossover. Heteronuclear pseudo-dimers were prepared by the 1:1 reaction of [FeH(3)L(1)](BF(4))(2) or [MnH(3)L(1)](ClO(4))(2) with [CoL(1)]. [MH(3)L(1)][CoL(1)](X)(2) (M = Fe and X = BF(4) or M = Mn and X = ClO(4)), were characterized by IR, EA, variable temperature single crystal X-ray diffraction and M?ssbauer spectroscopy in the iron case. The data support a spin crossover and high spin assignment for the iron(II) and manganese(II), respectively. DFT calculations demonstrate that the spin state of the iron(II) atom in {[FeH(3)L(1)][FeL(1)]}(2+) changes from high spin to low spin as the iron(II)-iron(III) distance decreases. This is supported by experimental results and is a result of hydrogen bonding interactions which cause a significant compression of the M(II)-N(pyrazole) bond distances.     

Phenylthiyl radical complexes of gallium(III), iron(III), and cobalt(III) and comparison with their phenoxyl analogues.

Three hexadentate, asymmetric pendent arm macrocycles containing a 1,4,7-triazacyclononane-1,4-diacetate backbone and a third, N-bound phenolate or thiophenolate arm have been synthesized. In [L(1)](3)(-) the third arm is 3,5-di-tert-butyl-2-hydroxybenzyl, in [L(2)](3)(-) it is 2-mercaptobenzyl, and in [L(3)](3)(-) it is 3,5-di-tert-butyl-2-mercaptobenzyl. With trivalent metal ions these ligands form very stable neutral mononuclear complexes [M(III)L(1)] (M = Ga, Fe, Co), [M(III)L(2)] (M = Ga, Fe, Co), and [M(III)L(3)] (M = Ga, Co) where the gallium and cobalt complexes possess an S = 0 and the iron complexes an S = (5)/(2) ground state. Complexes [CoL(1)].CH(3)OH.1.5H(2)O, [CoL(3)].1.17H(2)O, [FeL(1)].H(2)O, and [FeL(2)] have been characterized by X-ray crystallography. Cyclic voltammetry shows that all three [M(III)L(1)] complexes undergo a reversible, ligand-based, one-electron oxidation generating the monocations [M(III)L(1)(*)](+) which contain a coordinated phenoxyl radical as was unambiguously established by their electronic absorption, EPR, and M?ssbauer spectra. In contrast, [M(III)L(2)] complexes in CH(3)CN solution undergo an irreversible one-electron oxidation where the putative thiyl radical monocationic intermediates dimerize with S-S bond formation yielding dinuclear disulfide species [M(III)L(2)-L(2)M(III)](2+). [GaL(3)] behaves similarly despite the steric bulk of two tertiary butyl groups at the 3,5-positions of the thiophenolate, but [Co(III)L(3)] in CH(2)Cl(2) at -20 to -61 degrees C displays a reversible one-electron oxidation yielding a relatively stable monocation [Co(III)L(3)(*)](+). Its electronic spectrum displays intense transitions in the visible at 509 nm (epsilon = 2.6 x 10(3) M(-)(1) cm(-)(1)) and 670sh, 784 (1.03 x 10(3)) typical of a phenylthiyl radical. The EPR spectrum of this species at 90 K proves the thiyl radical to be coordinated to a diamagnetic cobalt(III) ion (g(iso) = 2.0226; A(iso)((59)Co) = 10.7 G).     

Synthesis,crystal structure and infrared spectra of Cu(II) and Co(II) complexes with 4,4′‐dichloro‐2,2′‐[ethylene dioxybis(nitrilomethylidyne)]diphenol

Novel 4,4′‐dichloro‐2,2′‐[ethylenedioxybis(nitrilomethylidyne)]diphenol (H₂L) and its complexes [CuL] and {[CoL(THF)]₂(OAc)₂Co} have been synthesized and characterized by elemental analyses, IR, ¹H‐NMR and X‐ray crystallography. [CuL] forms a mononuclear structure which may be stabilized by the intermolecular contacts between copper atom (Cu) and oxygen atom (O3) to form a head‐to‐tail dimer. In {[CoL(THF)]₂(OAc)₂Co}, two acetates coordinate to three cobalt ions through Co? O? C? O? Co bridges and four µ‐phenoxo oxygen atoms from two [CoL(THF)] units also coordinate to cobalt ions. Copyright © 2008 John Wiley & Sons, Ltd.     

Molecular and electronic structures of bis(pyridine-2,6-diimine)metal complexes [ML2](PF6)n (n = 0, 1, 2, 3; M = Mn, Fe, Co, Ni, Cu, Zn)

A series of mononuclear, octahedral first-row transition metal ion complexes mer-[M(II)L0(2)](PF6)2 containing the tridentate neutral ligand 2,6-bis[1-(4-methoxyphenylimino)ethyl]pyridine (L0) and a Mn(II), Fe(II), Co(II), Ni(II), Cu(II), or Zn(II) ion have been synthesized and characterized by X-ray crystallography. Cyclic voltammetry and controlled potential coulometry show that each dication (except those of Cu(II) and Zn(II)) can be reversibly one-electron-oxidized, yielding the respective trications [M(III)L0(2)]3+, and in addition, they can be reversibly reduced to the corresponding monocations [ML2]+ and the neutral species [ML2]0 by two successive one-electron processes. [MnL2]PF6 and [CoL2]PF6 have been isolated and characterized by X-ray crystallography; their electronic structures are described as [Mn(III)L1(2)]PF6 and [Co(I)L0(2)]PF6 where (L1)1- represents the one-electron-reduced radical form of L0. The electronic structures of the tri-, di-, and monocations and of the neutral species have been elucidated in detail by a combination of spectroscopies: UV-vis, NMR, X-band EPR, Mossbauer, temperature-dependent magnetochemistry. It is shown that pyridine-2,6-diimine ligands are noninnocent ligands that can be coordinated to transition metal ions as neutral L0 or, alternatively, as monoanionic radical (L1)1-. All trications are of the type [M(III)L0(2)]3+, and the dications are [M(II)L0(2)]2+. The monocations are described as [Mn(III)L1(2)]+ (S = 0), [Fe(II)L0L1]+ (S = 1/2), [Co(I)L0(2)]+ (S = 1), [Ni(I)L0(2)]+ (S = 1/2), [Cu(I)L0(2)]+ (S = 0), [Zn(II)L1L0]+ (S = 1/2) where the Mn(II) and Fe(II) ions are low-spin-configurated. The neutral species are described as [Mn(II)L1(2)]0, [Fe(II)L1(2)]0, [Co(I)L0L1]0, [Ni(I)L0L1]0, and [Zn(II)L1(2)]0; their electronic ground states have not been determined.     

Mono‐ and Dinuclear Heteroleptic Cobalt Complexes with α‐Diimine and Polyarene Ligands

Reactions of the dimeric cobalt complex [(L^?Co)₂] ( 1 , L=[(2,6‐iPr₂C₆H₃)NC(Me)]₂) with polyarenes afforded a series of mononuclear and dinuclear complexes: [LCo(η⁴‐anthracene)] ( 2 ), [LCo(μ‐η⁴:η⁴‐naphthalene)CoL] ( 3 ), and [LCo(μ‐η⁴:η⁴‐phenanthrene)CoL] ( 4 ). The pyrene complexes [{Na₂(Et₂O)₂}{LCo(μ‐η³:η³‐pyrene)CoL}] ( 5 ) and [{Na₂(Et₂O)₃}{LCo(η³‐pyrene)}] ( 6 ) were obtained by treating precursor 1 with pyrene followed by reduction with Na metal. These complexes contain three potential redox active centers: the cobalt metal and both α‐diimine and polyarene ligands. Through a combination of X‐ray crystallography, EPR spectroscopy, magnetic susceptibility measurement, and DFT computations, the electronic configurations of these complexes were studied. It was determined that complexes 2 – 4 have a high‐spin Co^I center coupled with a radical α‐diimine ligand and a neutral polyarene ligand. Whereas, the ligand L in complexes 5 and 6 has been further reduced to the dianion, the cobalt remains in a formal (I) oxidation state, and the pyrene molecule is either neutral or monoanionic.     

Bis- and tris-(3-aminopropyl) derivatives of 14-membered tetraazamacrocycles containing pyridine: synthesis, protonation and complexation studies

New N-(3-aminopropyl) (L1, L2) and (2-cyanoethyl) (L3, L4) derivatives of a 14-membered tetraazamacrocycle containing pyridine have been synthesized. The protonation constants of L1 and L2 and the stability constants of their complexes with Ni2+, Cu2+, Zn2+ and Cd2+ metal ions were determined in aqueous solutions by potentiometry, at 298.2 K and ionic strength 0.10 mol dm(-3) in KNO3. Both compounds have high overall basicity due to the presence of the aminopropyl arms. Their copper(II) complexes exhibit very high stability constants, which sharply decrease for the complexes of the other studied metal ions, as usually happens with polyamine ligands. Mono- and dinuclear complexes are formed with L2 as well as with L1, but the latter exhibits mononuclear complexes with slightly higher K(ML) values while the dinuclear complexes of L2 are thermodynamically more stable. The presence of these species in solution was supported by UV-VIS-NIR and EPR spectroscopic data. The single crystal structures of [Cu(H2L2)(ClO4)]3+ and [CoL3Cl]+ revealed that the metal centres are surrounded by the four nitrogen atoms of the macrocycle and one monodentate ligand, adopting distorted square pyramidal geometries. In the [CoL3Cl]+ complex, the macrocycle adopts a folded arrangement with the nitrogen atom opposite to the pyridine at the axial position while in the [Cu(H2L2)(ClO4)]3+ complex, the macrocycle adopts a planar conformation with the three aminopropyl arms located at the same side of the macrocyclic plane.     

Synthesis, structure and spectroscopic behaviors of a five- and six-coordinated tri-cobalt(II) cluster: [(CoL)2(OAc)2Co].2C2H5OH

A tri-nuclear cobalt(II) cluster, [(CoL)2(OAc)2Co].2C2H5OH, has been synthesized by the reaction of cobalt(II) acetate tetrahydrate with a novel Salen-type bisoxime chelating ligand, 3,3'-dimethoxy-2,2'-[ethylenedioxybis(nitrilomethylidyne)]diphenol (H2L), and characterized by elemental analyses, IR spectra, TG-DTA and molar conductances. UV-vis spectroscopic titration in methanol solution clearly indicated the exclusive formation of the 3:2 [Co3L2]2+ cluster. The single-crystal X-ray diffraction determination of the Co(II) cluster shows that there are two acetate ions coordinate to three cobalt(II) ions through Co-O-C-O-Co bridges, and quadruple mu-phenoxo oxygen atoms from two [CoL] chelates also coordinate to cobalt(II) ions. Interestingly, different conformational central ions: five- and six-coordinated geometries were found in the cluster.     

两个含草酸根及硫氰酸根的新型三脚架钴(Ⅱ)配合物的合成、晶体结构及光谱性质(英)

本文合成了两个新型Co(Ⅱ)配合物，[LCo(μ-C₂O₄)CoL]·(ClO₄)₂·2CH₃CN (1)和[CoL(SCN)]·ClO₄ (2)，其中，L即三(3，5-二甲基吡唑甲基)胺。在配合物1中，Co与来自三脚架配体的4个氮和草酸根桥联配体的2个氧原子配位，处于扭曲八面体配位环境。由草酸根桥联两套LCo，构成了一个双核结构。在单核配合物2中，Co(Ⅱ)处于三角双锥配位构型，SCN-通过N配位与中心离子Co(Ⅱ)键联。在同一晶胞中有两个构型略微不同的分子，两个分子之间通过SCN的S原子有弱相互作用。对化合物1和2在溶液中的光谱性质做了进一步的研究和讨论。     

超分子钴(Ⅱ)配合物[CoL(H2O)2]n的合成与结构表征

A mononuclear Cobalt(Ⅱ) complex [CoL(H₂O)₂]_n (H₂L: 4,4′,6,6′-Tetrabromo-2,2′-[ethylenedioxybis(nitrilomethylidyne)]diphenol), has been synthesized and structurally characterized by elemental analysis, IR and X-ray diffraction single crystal structure analysis. The crystal of the complex belongs to monoclinic space group P2₁/c with a=2.516 8(3) nm, b=1.023 43(18) nm, c=0.789 17(14) nm, β=91.375(2)°, V=2.032 1(5) nm³, Z=4, D_c=2.317 Mg·m^-3, μ(Mo Kα)=8.747 mm^-1, F(000)=1 356, R₁=0.049 7, wR₂=0.110 4. The crystal structure of [CoL(H₂O)₂]_n indicates that the complex consists of one cobalt(Ⅱ) atom, one L^2- unit and two coordinated water molecules, and the coordination number of the cobalt(Ⅱ) atom is six. One-dimensional chain supramolecular structure is formed by intermolecular hydrogen bonds and π-π stacking of neighboring benzene rings. CCDC: 652649.     

基于柔性1，4-苯二硫乙酸和刚性的2，2′-联吡啶配体构筑的钴配合物的合成、晶体结构及电化学性质

水热法合成了2个基于柔性的1,4-苯二硫乙酸(H2L)和刚性的2,2′-联吡啶(2,2′-bipy)配体的Co(Ⅱ)配合物:{[CoL(2,2′-bipy)(H2O)].0.40H2O}n(1)和[CoL(2,2′-bipy)(H2O)2]n(2),并通过元素分析,红外光谱,热重和X-射线单晶衍射实验对其结构进行了表征。分析表明,两个配合物都是通过氢键连接一维链形成的二维层面结构。对配合物的电化学性质进行了研究,表明两个配合物有相似的电化学行为。     

Supramolecular cobalt(II) complexes: syntheses,crystal structures and solvent effects

Two Co^II complexes, namely {[CoL(MeOH)(μ-OAc)]₂Co}·2MeCN·2MeOH (1) and {[CoL(EtOH)(μ-OAc)]₂Co}·3EtOH (2) (H₂L=3,3′-dimethoxy-2,2′-[(1,3-propylene)dioxybis(nitrilomethylidyne)]diphenol), have been synthesized and characterized by X-ray crystallography. Both complexes contain octahedral coordination geometries, comprising three Co^II atoms, two deprotonated bisoxime L²⁻ units in which four μ-phenoxo oxygen atoms form two [CoL(X)] (X = MeOH or EtOH) units, two acetate ligands coordinated to three Co^II centers through Co–O–C–O–Co bridges, and coordinated and non-coordinated solvent. Both complexes exhibit 2D supramolecular networks through different intermolecular hydrogen-bonding interactions.     

Cobalt(II) dioxygen carriers based on simple diamino ligands: kinetic and ab initio studies

The kinetics of the oxygenation reaction of CoL2(2+) complexes (L=ethylenediamine (en), N,N'-dimethylethylenediamnine (dmen)) have been investigated in dimethyl sulfoxide (dmso) at 298 K and in a medium adjusted to 0.1 mol dm(-3) with Et4NClO4 by means of a UV-vis spectrophotometric technique. The reaction mechanisms are consistent with the fast formation of superoxo 1:1 initial CoL2-O2 species (L=en, dmen), whereas the dimeric mu-peroxo (CoL2)2O2 adduct is formed only when L=en, in the rate determining step. The kinetic results are discussed taking into account the effects of ligand/solvent substitution. EPR results give information on the electronic structure and the coordination geometry of the Co(II) complexes and further confirm the stoichiometry of the species formed. Ab initio calculations provide insights on the geometrical parameters of all the complexes investigated and allow us to draw some hypotheses about the influence of H.H nonbonded interactions in the eventual formation of the dimeric mu-peroxo (CoL2)2O2 complexes. Solvational effects are also considered. The formation of the (CoL3)2O2 adduct is also proved when L=en by means of O2 volumetric absorption.     

Ag(I) and Cu(II) discrete and polymeric complexes based on single- and double-armed oxadiazole-bridging organic clips

Four new oxadiazole-bridging ligands (L1-L4) were designed and synthesized by the reaction of 2,5-bis(2-hydroxyphenyl)-1,3,4-oxadiazole with isonicotinoyl chloride and nicotinoyl chloride, respectively. L1 and L3 are unsymmetric single-armed ligands (4- or 3-pyridinecarboxylate arm), and L2 and L4 are symmetric double-armed ligands (4- or 3-pyridinecarboxylate arms). Nine new complexes, [Ag(L1)]PF6.CH3OH (1), [Ag(L1)]ClO4.CH3OH (2), Cu(L2)(NO3)2.2(CH2Cl2) (3), [Cu(L2)2](ClO4)2.2(CH2CCl2) (4), Cu(L2)Cl2 (5), [Cu4(L3)2(H2O)2](L3)4(ClO4)4 (6), [Ag(L4)(C2H5OH)]ClO4 (7), [Ag(L4)(C2H5OH)]BF4 (8), and [Ag(L4)(CH3OH)]SO3CF3 (9), were isolated from the solution reactions based on these four new ligands, respectively. L1, L2, and L3 act as convergent ligands and bind metal ions into discrete molecular complexes. In contrast, L4 exhibits a divergent spacer to link metal ions into one-dimensional coordination polymers. New coordination compounds were fully characterized by infrared spectroscopy, elemental analysis, and single-crystal X-ray diffraction. In addition, the luminescent and electrical conductive properties of these new compounds were investigated.     

Synthesis and thermal studies of tetraaza macrocylic ligand and its transition metal complexes. DNA binding affinity of copper complex

A Tetraaza Macrocylic Ligand (H2L) and its complexes, [Cd(H2L)(OH2)2](NO3)(2)·1/2OH2 (I), [Co(H2L)(OH2)](NO3)(2)·1/2OH2 (II), [Cu(H2L)(NO3)2]·3/2OH2 (III) and [Ni(H2L)(NO3)(OH2)]NO3·OH2 (IV), have been synthesized and characterized on the basis of elemental analysis, molar conductivity, 1H NMR, UV-vis, FT-IR and mass spectroscopy. All results confirm that the prepared compounds have 1:1 metal-to-ligand stoichiometry, octahedral configuration and the ligand behaves as a neutral tetradendate towards the metal ions. [CdL(OH2)2] (V), [CoL(OH2)2] (VI), [CuL(OH2)2] (VII) and [Ni(H2L)(NO3)2] (VIII) were synthesized pyrolytically in solid state from corresponding compounds (I-IV). Analytical results of complexes (V-VIII) show that the ligand behaves either as a neutral tetradendate or dianionic tetradentate ligand towards the metal ions. The binding of H2L and its copper complex (III) to DNA has been investigated by ultraviolet absorption spectroscopy. The experiments indicate that H2L and its copper complex (III) can bind to DNA through an intercalative mode. The H2L and its copper complex (III) exhibited anti-tumor activity against Ehrlich Acites Carcinoma (E.A.C) at the concentration of 100 μg/ml.     

Substrate binding to vanadate-dependent bromoperoxidase from Ascophyllum nodosum: a vanadium K-edge XAS approach

The EXAFS region of vanadium K-edge XAS spectra of native vanadate-dependent bromoperoxidase (isoenzyme I) from Ascophyllum nodosum in the presence of the substrate bromide can be fitted to three shells (at 1.62, 1.73-1.78 and 1.99-2.07 A) in the first coordination sphere of vanadium plus two more distant shells at 4.1A, possibly corresponding to bromide, and 4.7 A due to light scatterers stemming from the protein pocket. Bromide does not directly bind to the vanadium centre. The XANES and the EXAFS features for the enzyme are essentially reproduced by model complexes of the general composition [VO(H(2)O)(n)(ONO)] (n= 1 or 2) where ONO is the dianion of a Schiff base from bromosalicylaldehydes (Brsal; with the Br substituent in the position 3, 4, 5 or 6) and amino acids. The 3-Brsal derivatives exhibit an outer sphere shell at 3.8 A, which is traced back to intermolecular contacts. The data obtained from EXAFS are compared to those obtained from single crystal X-ray diffraction of [VO(H(2)O)(2)(4-Brsal-gly)] and [VO(H(2)O)(2)(6-Brsal-gly)] (gly = glycinate). In the complex [VOBr(2)(ONO)']] ((ONO)' is the Schiff base from o-anisole and o-hydroxyaniline), the V-Br distance is 2.44 A.     

A series of chiral coordination polymers containing helicals assembled from a new chiral (R)-2-(4'-(4'-carboxybenzyloxy)phenoxy)propanoic acid: syntheses, structures and photoluminescent properties

Ten new chiral coordination polymers, namely, [Ni(L)(H(2)O)(2)] (1), [Co(L)(H(2)O)(2)] (2), [Cd(L)(H(2)O)] (3), [Cd(L)(phen)] (4), [Mn(2)(L)(2) (phen)(2)]·H(2)O (5), [Cd(2)(L)(2)(biim-4)(2)] (6), [Zn(2)(L)(2)(biim-4)(2)] (7), [Cd(L)(pbib)] (8), [Cd(L)(bbtz)] (9) and [Cd(L)(biim-6)] (10), where phen = 1,10-phenathroline, biim-4 = 1,1'-(1,4-butanediyl)bis(imidazole), pbib = 1,4-bis(imidazole-1-ylmethyl)benzene, bbtz = 1,4-bis(1,2,4-triazol-1-ylmethyl)benzene, biim-6 = 1,1'-(1,6-hexanedidyl)bis(imidazole), and H(2)L = (R)-2-(4'-(4'-carboxybenzyloxy)phenoxy)propanoic acid, have been synthesized under hydrothermal conditions. Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by infrared spectra (IR), powder X-ray diffraction (PXRD), elemental analyses and thermogravimetric (TG) analyses. Compounds 1 and 2 exhibit similar 1D left-handed helical chains, which are further extended into 3D supramolecular structures through O-H···O hydrogen-bonding interactions, respectively. Compound 3 shows a 2D double-layer architecture containing helical chains. Compound 4 features two types of 2D undulated sheets with helical chains, which are stacked in an ABAB fashion along the c direction. Compound 5 possesses a 1D double chain ribbon structure containing unusual meso-helical chains, which is linked by π-π interactions into a 2D supramolecular layer. These layers are further extended by hydrogen-bonding interactions to form a 3D supramolecular assembly. Compounds 6 and 7 are isostructural and exhibit 2D (4(4))-sql networks with helical chains. Neighboring sheets are further linked by C-H···O hydrogen-bonding interactions to generate 3D supramolecular architectures. Compounds 8-10 are isostructural and display 3D 3-fold interpenetrating diamond frameworks with helical chains. The effects of coordination modes of L anions, metal ions and N-donor ligands on the structures of the coordination polymers have been discussed. The luminescent properties of 3, 4 and 6-10 have also been investigated in detail.     

New 1H-pyrazole-containing polyamine receptors able to complex L-glutamate in water at physiological pH values

The interaction of the pyrazole-containing macrocyclic receptors 3,6,9,12,13,16,19,22,25,26-decaazatricyclo-[22.2.1.1(11,14)]-octacosa-1(27),11,14(28),24-tetraene 1[L1], 13,26-dibenzyl-3,6,9,12,13,16,19,22,25,26-decaazatricyclo-[22.2.1.1(1)(1,14)]-octacosa-1(27),11,14(28),24-tetraene 2[L2], 3,9,12,13,16,22,25,26-octaazatricyclo-[22.2.1.1(11,14)]-octacosa-1(27),11,14(28),24-tetraene 3[L3], 6,19-dibenzyl-3,6,9,12,13,16,19,22,25,26-decaazatricyclo-[22.2.1.1(11,)(14)]-octacosa-1(27),11,14(28),24-tetraene 4[L4], 6,19-diphenethyl-3,6,9,12,13,16,19,22,25,26-decaazatricyclo-[22.2.1.1(11,14)]-octacosa-1(27),11,14(28),24-tetraene 5[L5], and 6,19-dioctyl-3,6,9,12,13,16,19,22,25,26-decaazatricyclo-[22.2.1.1(11,14)]-octacosa-1(27),11,14(28),24-tetraene 6[L6] with l-glutamate in aqueous solution has been studied by potentiometric techniques. The synthesis of receptors 3-6[L3-L6] is described for the first time. The potentiometric results show that 4[L4] containing benzyl groups in the central nitrogens of the polyamine side chains is the receptor displaying the larger interaction at pH 7.4 (Keff = 2.04 x 10(4)). The presence of phenethyl 5[L5] or octyl groups 6[L6] instead of benzyl groups 4[L4] in the central nitrogens of the chains produces a drastic decrease in the stability [Keff = 3.51 x 10(2) (5), Keff = 3.64 x 10(2) (6)]. The studies show the relevance of the central polyaminic nitrogen in the interaction with glutamate. 1[L1] and 2[L2] with secondary nitrogens in this position present significantly larger interactions than 3[L3], which lacks an amino group in the center of the chains. The NMR and modeling studies suggest the important contribution of hydrogen bonding and pi-cation interaction to adduct formation.