Syntheses, solid-state structures, and solution studies by VT 31P NMR of [Zn[Se2P(OEt)2]2] infinity and [Zn2[Se2P(OiPr)2]4

Complexes [Zn[Se(2)P(OEt)(2)](2)]( infinity ) (1) and [Zn(2)[Se(2)P(O(i)Pr)(2)](4)] (2) are prepared from the reaction of Zn(ClO(4))(2).6H(2)O and (NH(4))[Se(2)P(OR)(2)] (R = Et and (i)Pr) in a molar ratio of 1:2 in deoxygenated water at room temperature. Positive FAB mass spectra show m/z peaks at 968.8 (Zn(2)L(3)(+)) and 344.8 (ZnL(+)) for 1 and m/z at 1052.8 (Zn(2)L(3)(+)) for 2. (1)H NMR spectra exhibit chemical shifts at delta 1.43 and 4.23 ppm for 1 and 1.41 and 4.87 ppm for 2 due to Et and (i)Pr group of dsep ligands. While the solid-state structure of compound 1 is a one-dimensional polymer via symmetrically bridging dsep ligands, complex 2 in the crystalline state exists as a dimer. In both 1 and 2, zinc atoms are connected by two bridging dsep ligands with an additional chelating ligand at each zinc atom. The dsep ligands exhibit bimetallic biconnective (micro(2), eta(2)) and monometallic biconnective (eta(2)) coordination patterns. Thus, each zinc atom is coordinated by four selenium atoms from two bridging and one chelating dsep ligands and the geometry around zinc is distorted tetrahedral. The Zn-Se distances range between 2.422 and 2.524 A. From variable-temperature (31)P NMR studies it has been found that monomer and dimer of the complex are in equilibrium in solution via exchange of bridging and chelating ligands. However, at temperature above 40 degrees C the complex exists as a monomer and shows a very sharp peak while with lowering of the temperature the percentage of dimer increases gradually at the expense of monomer. Below -90 degrees C the complex exists as a dimer and two peaks are observed with equal intensities which are due to bridging and chelating ligands. (77)Se NMR spectra of both complexes at -30 degrees C exhibit three doublets due to the presence of monomer and dimer in solution.     

Comparisons of zinc with cadmium in N2S2 coordination and as S-bonded adducts to tungsten carbonyls

The synthesis and characterization of bis-mercaptoethanediazaheptane cadmium(II) is reported and compared to the analogous zinc complex. Of significance is the dimeric form of the [Zn(N(2)S(2))](2) complex achieves penta-coordination about zinc through a bridging thiolate whereas cadmium engages two thiolate as S-bridges resulting in hexa-coordination about cadmium within a coordination polymer whose X-ray crystal structure is reported here. In the presence of W(CO)(5), this polymer breaks up, generating dimeric [Cd(N(2)S(2))](2) with two W(CO)(5) units appended to the terminal thiolates, a feat that is not observed for the zinc dimer analogue. The greater thiophilicity of cadmium over zinc is noted in several features of these complexes.     

Photochemical H2 with noble-metal-free molecular devices comprising a porphyrin photosensitizer and a cobaloxime catalyst

Among three noble-metal-free molecular devices (1-3) containing a porphyrin photosensitizer and a cobaloxime catalyst, the one with a zinc porphyrin unit displayed apparently higher efficiency for photoinduced H(2) production than complex 2 with a magnesium porphyrin and 3 with a free-base porphyrin, possibly due to the formation of a TEAZnPor-Co triad in solution.     

Mesomorphism of a tetrahedral zinc complex

Thermotropic smectic phases have been observed for the first time in a zinc coordination complex with tetrahedral geometry; this complex, which contains the pyrazole dimer bis[3,5-bis(p-decyloxyphenyl)pyrazolyl]ethane as the ligand, exhibits fluorescence.     

[Et_4N]_2[Zn_2(OPh)_2Cl_4]的合成和晶体结构

ZnCl2, PhONa和Et4NCl稨2O在乙腈溶剂中反应合成了一种二核锌配合物[Et4N]2[Zn2(OPh)2Cl4]。X射线衍射结果表明,晶体属单斜晶系,C2/m空间群,晶胞参数 a = 14.1366(2), b=13.6985(5), c=9.3308(3)牛?107.851(2)o, V=1719.92(9)?,C28H50O2N2Zn2Cl4,Mr=721.24,Z=2,Dx=1.393g/cm3,μ(MoKα)=1.732mm—1,F(000)=756, R=0.0552, wR=0.1534, S=1.027。 配合物是由2个阳离子Et4N+和1个阴离子[Zn2(OPh)2Cl4]2—组成。阴离子[Zn2(OPh)2Cl4]2—包含着1个中心Zn2O2菱形平面。配合物中的2个锌原子通过2个苯酚中的氧原子桥连,每个锌原子还与2个氯原子配位形成变形四面体结构。     

An N-heterocyclic carbene adduct of diatomic tin, :Sn[double bond, length as m-dash]Sn:

Reduction of an N-heterocyclic carbene (NHC) adduct of SnCl(2), viz. [(IPr)SnCl(2)] (IPr = :C{N(Dip)C(H)}(2); Dip = 2,6-diisopropylphenyl), with a magnesium(i) dimer, has afforded the first NHC complex of a row 5 element in its diatomic form, [(IPr)Sn[double bond, length as m-dash]Sn(IPr)]; a computational analysis of the complex indicates that it comprises a singlet state, doubly bonded tin(0) fragment, :Sn[double bond, length as m-dash]Sn:, datively bonded by two NHC ligands.     

Synthesis,Structure, and Reactivity of a Dimeric Zinc(I) Compound Stabilized by a Sterically Demanding Diiminophosphinate Ligand

The new sterically demanding aminoiminophosphorane Ph₂P(?NDip)(NHDip) (Dip=C₆H₃‐2,6‐iPr₂; LH, 1 ) has been prepared as a precursor to the potassium complex [LK] ( 2 ) and a series of heteroleptic zinc(II) complexes, namely [(LZnBr)₂] ( 3 ), [LZnMe] ( 4 ), [LZnEt] ( 5 ), and [(LZnI)₂] ( 6 ). The products have been obtained either through a salt metathesis route by using complex 2 and ZnBr₂ to give compound 3 , through a direct reaction of ligand precursor 1 and ZnR₂ (R=Me or Et) yielding complexes 4 or 5 , respectively, or through iodination of complexes 4 or 5 by using I₂ to afford compound 6 . Reduction of the heteroleptic zinc(II) halide complexes 3 or 6 by using a dimeric magnesium(I) compound as a selective, stoichiometric, and soluble reducing agent afforded the new zinc(I) dimer [(LZn)₂] ( 7 ) in good yield. Compounds 1 – 7 were crystallographically and spectroscopically characterized and the coordination behavior of the diiminophosphinate ligand has been investigated and compared with related CN‐based ligands. An initial reactivity study has been carried out on [(LZn)₂] ( 7 ) by using small‐scale reactions and the oxidative addition of small alkyl halides across the Zn? Zn bond has been found to generate equimolar amounts of the alkyl complexes 4 or 5 and the halide complexes 3 or 6 , respectively.     

Isomerization of Cyclooctadiene to Cyclooctyne with a Zinc/Zirconium Heterobimetallic Complex

Reaction of a zinc/zirconium heterobimetallic complex with 1,5‐cyclooctadiene (1,5‐COD) results in slow isomerization to 1,3‐cyclooctadiene (1,3‐COD), along with the formation of a new complex that includes a cyclooctyne ligand bridging two metal centers. While analogous magnesium/zirconium and aluminum/zirconium heterobimetallic complexes are competent for the catalytic isomerization of 1,5‐COD to 1,3‐COD, only in the case of the zinc species is the cyclooctyne adduct observed.     

A Novel Sulfur‐bridged Dimeric Zinc(II) Complex with 2, 6‐Diacetylpyridine Bis(thiosemicarbazone)

The reaction of zinc bromide with the pentadentate chelating ligand 2, 6‐diacetylpyridine bis(thiosemicarbazone) (H₂L¹) yields the formation of a novel complex. Recrystallization in a acetone/water solution leads us to isolate the mixed ligand complex of [Zn(H₂L¹)Br_0.49(OH)_0.51]₂·(HSO₄)₂·6H₂O, structurally characterized. The complex is a dimer in which each zinc atom is seven‐co‐ordinated with the SNNNS‐chelating ligand occupying the five equatorial positions, a bromine atom or hydroxo group in one of the two axial positions and a sulfur atom of the centrosymmetrical molecule occupies the other axial site making a bridge between the two zinc atoms. To the best of our knowledge is the first S‐bridged dimeric Zinc(II) complex derived from 2, 6‐diacetylpyridine bis(thiosemicarbazone) ligand. The MALDI‐TOF mass, solid state IR and ¹H NMR (in DMSO solution) spectra are also discussed.     

PROTON, Mg2+ AND PROTEIN AS COMPETING LIGANDS FOR THE FLUORESCENT PROBE, MAG-INDO-1: A FIRST STEP TO THE QUANTIFICATION OF INTRACELLULAR Mg2+ CONCENTRATION

Abstract Increasing evidence of the role of magnesium in various cellular mechanisms has led to the need to develop an accurate method for the evaluation of magnesium concentration in cells. 1H-indole-6-carboxylic acid, 2–(4- bis- [carboxymethyl]amino-3–[carboxy]ethoxy) (mag-indo-1) is used as a fluorescent indicator for ionized magnesium concentration. A physicochemical study of this probe has pointed out (1) that at concentrations higher than 10 μ M , the presence of dimers can alter the different equilibria and (2) at concentrations, avoiding the dimer (≤ 10 μ M ), three fluorescent forms are in equilibrium with the deprotonated form of mag-indo-1 (L), which are the protonated form LH, the magnesium-bound form LM and the protein-bound form LP. A model is proposed that takes into account the equilibria between the four species. In a solution containing magnesium and protein, a complex fluorescence spectrum can be resolved by a combination of the three fluorescence spectra (L, LM, LP). However, under these conditions, the LH fluorescence spectrum is not taken into account for the spectral resolution. Finally, from the contribution of characteristic fluorescence spectra in the experimental fluorescence spectrum, the magnesium concentration can be estimated with accuracy. Such a method should be further applied to magnesium determination in different cell lines.     

Supramolecular complexes of carboxy-substituted zinc porphyrinates with triethylenediamine

α,α-and α,β-Atropoisomers of zinc 5,15-bis(2-carboxyphenyl)octaalkylporphyrinate were obtained, and their complex formation with triethylenediamine in toluene was studied. The α,α-atropoisomer is present in the solution as a supramolecular dimer and forms a 1:1 complex with the two-centered nitrogen-containing base. The complex formation of the undimerized α,β-atropoisomer with triethylenediamine can give 2:1 or 1:1 complexes, depending on the reagent ratio. The stability constants of the complexes and the concentration ranges of their formation were determined by means of spectrophotometric titration and ¹H NMR spectroscopy.     

Ligand and solvent effects on cobalt(I)-catalysed reactions: Alkyne dimerisation versus [2+2+2]-cyclotrimerisation versus Diels-Alder reaction versus [4+2+2]-cycloaddition

The cobalt catalysed conversion of phenyl acetylene led to linear enyne dimerisation products when CoBr₂(dppe) was activated with magnesium in the absence of a Lewis acid. In contrast, in the presence of a Lewis acid the cyclotrimerisation process is favoured. Among several ligand systems and solvents tested the best results were obtained using a catalyst system consisting of a diimine cobalt bromide complex, zinc and zinc iodide in acetonitrile. With 2-5 mol% of the cobalt catalyst at ambient temperatures 1,2,4-triphenylbenzene could be obtained in 99% yield and in excellent regioselectivity (95:5) in 10 min reaction time. Competition experiments of phenylacetylene and isoprene were performed. A preference for the cyclotrimerisation reaction was found for the diimine cobalt complex in acetonitrile, while the Diels-Alder reaction is favoured with the cobalt(dppe) complex in dichloromethane. Also a regioselectively substituted cyclooctatriene product was formed in a [4+2+2]-cycloaddition process and isolated which allows assumptions on the reaction mechanism.     

Synthesis and electrochemical behavior of inclusion complexes based on β-cyclodextrin and alkylaromatic compounds: Electrochemical carboxylation of the β-cyclodextrin-1-(4-isobutylphenyl)ethylchloride inclusion complex on a glassy-carbon cathode in anhydrous dimethylformamide

Inclusion complexes of β-cyclodextrin with alkylaromatic compounds β-cyclodextrin-1-(4-isobutylphenyl)ethylchloride in the “guest-host” molar ratio of 1 : 2 and β-cyclodextrin-methyl-(4-isobutylphenyl)ketone in the “guest-host” molar ratio of 1 : 1, are synthesized, isolated, and characterized. It is shown that preparative electrocarboxylation of the inclusion complex β-cyclodextrin-1-(4-isobutylphenyl)ethylchloride on a glassy-carbon cathode with a dissolving magnesium anode in dimethylformamide affords S-forms of 2-(4-isobutylphenyl)propionic acid (S-Ibuprofen) in a high enantiomeric excess (97%). In addition to the acid, a dimer and a hydride form from the corresponding intermediates.     

双卟啉化合物的构象平衡及π-π作用研究

制备并表征了一系列以柔韧烷氧化相连的自由双卟啉及其锌配合物,以＾１Ｈ－ＮＭＲ考察了烷氧链长度及锌离子对双卟啉构象平衡的影响。结果表明,双卟啉存在开放式及闭合式构象平衡,随烷氧链的增长,构象平衡由开放式向闭合式移动,当链上碳原子数为４时最有利于双卟啉形成闭合式构象。     

Solid-state structures of zinc(II) benzoate complexes. Catalyst precursors for the coupling of carbon dioxide and epoxides

Zinc complexes derived from benzoic acids containing electron-withdrawing substituents have been synthesized from Zn(II)(bis-trimethylsilyl amide)(2) and the corresponding carboxylic acid (2,6-X(2)C(6)H(3)COOH, where X = F, Cl, or OMe) in THF and structurally characterized via X-ray crystallography. The 2,6-difluorobenzoate complex crystallizes from THF or CH(3)CN as a seven membered zinc aggregate, where the metal atoms are interconnected by a combination of 10 mu-benzoates and mu(4)-oxo ligands, that is, [(2,6-difluorobenzoate)(10)O(2)Zn(7)](solvent)(2), solvent = THF (1) and CH(3)CN (1a). On the other hand, the 2,6-dichlorobenzoate zinc derivative crystallizes from THF as a dimer, [(2,6-dichlorobenzoate)(4)Zn(2)](THF)(3) (2), where the two zinc centers are bridged by three benzoate ligand. One of the zinc centers possesses a tetrahedral ligand environment where the fourth ligand is a unidentate benzoate, and the other zinc center has an octahedral arrangement of ligands which is accomplished by the additional binding of three THF molecules. Upon dissolution of complex 1 or 2 in the strongly binding pyridine solvent, disruption of these zinc carboxylates occurs with concomitant formation of mononuclear zinc bis-benzoates with three pyridine ligands in the metal coordination sphere. Complexes 1 and 2 were found to be effective catalysts for the copolymerization of cyclohexene oxide and carbon dioxide to afford polycarbonates devoid of polyether linkages, that is, completely alternating copolymers. Although these catalysts or catalyst precursors in the presence of CO(2)/propylene oxide afforded mostly propylene carbonate, they did serve as efficient catalysts for the terpolymerization of carbon dioxide/cyclohexene oxide/propylene oxide. The reactivities of these zinc carboxylates were very similar to those previously reported analogous complexes which have not been structurally characterized. Hence, it is suggested here that all of these zinc carboxylates provide similar catalytic sites for CO(2)/epoxide coupling processes.     

Über die Oxydation des O-Methylbulbocapnins mit Jod

The oxidation product obtained by treatment of bulbocapnine methyl ether ( 2a ) with iodine in ethanol/water is not the tetradehydroaporphinium salt 4 as assigned by Gadamer & Kuntze, but a dimer of structure 3 . Reduction of 3 with zinc in dilute sulfuric acid gives rac-bulbocapnine methyl ether, whereas reduction with complex hydrides affords the diastereomeric dimers 7a and 7b .     

Binding of the Zn2+ ion to ferric uptake regulation protein from E. coli and the competition with Fe2+ binding: a molecular modeling study of the effect on DNA binding and conformational changes of Fur

The three dimensional structure of Ferric uptake regulation protein dimer from E. coli, determined by molecular modeling, was docked on a DNA fragment (iron box) and Zn²⁺ ions were added in two steps. The first step involved the binding of one Zn²⁺ ion to what is known as the zinc site which consists of the residues Cys 92, Cys 95, Asp 137, Asp141, Arg139, Glu 140, His 145 and His 143 with an average metal-Nitrogen distance of 2.5 Å and metal-oxygen distance of 3.1–3.2 Å. The second Zn²⁺ ion is bound to the iron activating site formed from the residues Ile 50, His 71, Asn 72, Gly 97, Asp 105 and Ala 109. The binding of the second Zn²⁺ ion strengthened the binding of the first ion as indicated by the shortening of the zinc-residue distances. Fe²⁺, when added to the complex consisting of 2Zn²⁺/Fur dimer/DNA, replaced the Zn²⁺ ion in the zinc site and when a second Fe²⁺ was added, it replaced the second zinc ion in the iron activating site. The binding of both zinc and iron ions induced a similar change in Fur conformations, but shifted residues closer to DNA in a different manner. This is discussed along with a possible role for the Zn²⁺ ion in the Fur dimer binding of DNA in its repressor activity. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Cyclic dimer of a fused porphyrin zinc complex as a novel host with two pi-electronically coupled binding sites

Upon complexation with 4,4[prime or minute]-bipyridine, a cyclic dimer of a fused porphyrin zinc complex, having two pi-electronically coupled binding sites, shows a strong negative cooperativity in the second guest binding, to allow stepwise formation of 1 : 1 and 1 : 2 inclusion complexes.     

A Mixed‐Valence Tri‐Zinc Complex, [LZnZnZnL] (L=Bulky Amide), Bearing a Linear Chain of Two‐Coordinate Zinc Atoms

Reduction of a variety of extremely bulky amido Group 12 metal halide complexes, [LMX(THF)_0,1] (L=amide; M=Zn, Cd, or Hg; X=halide) with a magnesium(I) dimer gave a homologous series of two‐coordinate metal(I) dimers, [L′MML′] (L′=N(Ar^?)(SiMe₃), Ar^?=C₆H₂{C(H)Ph₂}₂Prⁱ‐2,6,4); and the formally zinc(0) complex, [L*ZnMg(^MesNacnac)] (L*=N(Ar*)(SiPrⁱ₃); Ar*=C₆H₂{C(H)Ph₂}₂Me‐2,6,4; ^MesNacnac=[(MesNCMe)₂CH]^?, Mes=mesityl), which contains the first unsupported Zn? Mg bond. Two equivalents of [L*ZnMg(^MesNacnac)] react with ZnBr₂ or ZnBr₂(tmeda) to give the mixed valence, two‐coordinate, linear tri‐zinc complex, [L*Zn^IZn⁰Zn^IL*], and the first zinc(I) halide complex, [L*ZnZnBr(tmeda)], respectively. The analogues [L*ZnMZnL*] (M=Cd or Hg), were also prepared, the Cd species contains the first Zn? Cd bond in a molecular compound. Metal–metal bonding was studied by DFT calculations.     

Determination of the precise composition of the triple sodium uranyl acetates of magnesium, zinc and nickel, and some observations on the use of the first two compounds for the determination of sodium

Three triple sodium uranyl acetates NaM(UO(2))(3)(CH(3) COO)(9) . nH(2)O in which the bivalent metals M were magnesium, zinc and nickel, have been precipitated and the air-dried compounds analysed for uranium by a highly precise method. Despite contrary claims it has been established that the compounds are precise hexahydrates the maximum deviation of n from 6 in any one analysis being 0.1. The precipitation of sodium as the magnesium or zinc compound gives results which depend on the excess of the reagents, and positive errors can be obtained. It is also concluded that, contrary to the usual belief, the magnesium compound is rather less soluble than the zinc one and is therefore somewhat more sensitive for sodium determination.