Bis(mu-oxo)dimetal "diamond" cores in copper and iron complexes relevant to biocatalysis

Although quite a familiar feature in high-valent manganese chemistry, the M(2)(mu-O)(2) diamond core motif has only recently been found in synthetic complexes for M=Cu or Fe. Structural and spectroscopic characterization of these more reactive Cu(2)(mu-O)(2) and Fe(2)(mu-O)(2) compounds has been possible through use of appropriately designed supporting ligands, low-temperature handling methods, and techniques such as electrospray ionization mass spectrometry and X-ray crystallography with area detector instrumentation for rapid data collection. Despite differences in electronic structures that have been revealed through experimental and theoretical studies, Cu(2)(mu-O)(2) and Fe(2)(mu-O)(2) cores exhibit analogously covalent metal-oxo bonding, remarkably congruent Raman and extended X-ray absorption fine structure (EXAFS) signatures, and similar tendencies to abstract hydrogen atoms from substrates. Core isomerization is another common reaction attribute, although different pathways are traversed; for Fe, bridge-to-terminal oxo migration has been discovered, while for Cu, reversible formation of an O-O bond to yield a peroxo isomer has been identified. Our understanding of biocatalysis has been enhanced significantly through the isolation and comprehensive characterization of the Cu(2)(mu-O)(2) and Fe(2)(mu-O)(2) complexes. In particular, it has led to the development of new mechanistic notions about how non-heme multimetal enzymes, such as methane monooxygenases, fatty acid desaturase, and tyrosinase, may function in the activation of dioxygen to catalyze a diverse array of organic transformations.     

Synthesis and characterization of carboxylate-rich complexes having the [Fe2(mu-OH)2(mu-O2CR)]3+ and [Fe2(mu-O)(mu-O2CR)]3+ cores of O2-dependent diiron enzymes

The {Fe2(mu-OH)2(mu-O2CR)}3+ and {Fe2(mu-O)(mu-O2CR)}3+ cores of the carboxylate-bridged diiron(III) centers in the enzyme active sites were reproduced by small molecule model complexes that were prepared through direct oxygenation of the mononuclear iron(II) complexes. Upon oxygenation of [Fe(O2CArTol)2(Hdmpz)2], where -O2CArTol is 2,6-di(p-tolyl)benzoate and Hdmpz is 3,5-dimethylpyrazole, [Fe2(mu-OH)2(mu-O2CArTol)(O2CArTol)3(OH2)(Hdmpz)2] was generated and characterized to share close physical properties with sMMOHox, including delta = 0.45 (2) mm/s, DeltaEQ = 1.21 (2) mm/s, and J = -7.2 (2) cm-1. The compound [Fe2(mu-O)(mu-O2CAr4-FPh)(O2CAr4-FPh)3(Hdmpz)3], where -O2CAr4-FPh is 2,6-di(4-fluorophenyl)benzoate, with delta = 0.51 (2) mm/s, DeltaEQ = 1.26 (2) mm/s, and J = -117.4 (1) cm-1, was isolated as the oxygenation product of [Fe(O2CAr4-FPh)2(Hdmpz)2].     

Modular approach to tridentate N,O,N' ligands using pyrazolylborate chemistry

Two anionic tridentate N,O,N' chelators, [pz(Ph)B(mu-pz)(mu-O)B(Ph)pz](-) (3(-)) and [pz(Ph)(Ph)B(mu-pz)(mu-O)B(Ph)pz(Ph)](-) (4(-)), as well as the corresponding complexes [Fe(3)(py)Cl], [Fe(3)Cl(2)] and [Cu(3)Cl], have been synthesised and structurally characterised by X-ray crystallography (pz: pyrazolyl, pz(Ph): 3-phenylpyrazolyl, py: pyridine). Since our synthesis approach takes advantage of the highly modular pyrazolylborate chemistry, inexpensive and relatively resistant N,O,N' ligands of varying steric demand are readily accessible. The complexes [Fe(3)(py)Cl] and [Fe(3)Cl(2)] possess a distorted trigonal-bipyramidal configuration with the pyrazolyl rings occupying equatorial positions and the oxygen donor being located at an apical position. The complex [Cu(3)Cl] crystallises as chloro-bridged dimers featuring Cu(II) ions with ligand environments that are intermediate between a square-planar and a trigonal-bipyramidal geometry.     

On, off and intermediate coordination of a bridgehead triarylamine donor in tripodal complexes: towards the tuning of coordinative bond distance

A series of first row transition metal complexes of the tripodal ligand 2,2',2"-nitrilotribenzoic acid H3L has been prepared and characterised by X-ray crystallography: Mononuclear [M(L)]- species [Cu(H2O)4]3[Cu(L)(H2O)]6.25H2O (2), [Co(H2O)6][Co(L)(H2O)].8H2O (4), [Zn(H2O)6][Zn(L)(H2O)].8H2O (5) and a neutral [M(L)] complex [Fe(III)2(L)(H2O)3].5H2O (8) are formed as well as dimeric [M(L)]2 2- species (HNEt3)2[Cu(L)]2.2CH3CN (1), (HNEt3)3[Ni(L)]2(ClO4).H2O (3), (HNEt3)2[Fe(II)(L)]2.2CH3CN (6) and (HNEt3)2[Fe(III)2(L)2(mu-O)](7). The complexes display a unique variation in the M-N distance (2.09 A for Cu(II) to 3.29 A for Fe(III)) to the bridgehead triphenylamine donor and are classified into compounds with "On","Off" and "Intermediate" N-coordination. The trigonal-bipyramidal coordination polyhedron changes towards tetrahedral in the intermediate and octahedral in the Off-state. The M-N distance of individual complexes is reversibly tuned by external chemical input such as changes of metal ion oxidation state (Fe(II)/Fe(III)) or variation of the axial coligand as a consequence of solvent or pH variation. Possible reasons for the exceptional tolerance of the M-N bond to distance variations are discussed under consideration of gas phase DFT calculations of [Zn(L)]-.     

Effect of Metallic Additives on Structure and Catalytic Properties of Supported NiPB/SiO_2 Catalyst

Supportedamorphousalloycatalystshavereceivedmuchattentioninrecentyearsbecausetheyshowlargersurfacearea,higherthermalstabilityandsuperiorcatalyticproperties'-'ascomparedwithultra-fineorrapidlyquenchedmetalmetalloidamorphousalloys.Preparation,characterizationandcatalyticperformanceofsupportedNiBcatalysthavebeenreportedbyseveralresearchgroups,however,onlyonepreparationmethodofsupportedamorphousalloycatalystcontainingNiPwasproposed"'whichwasfoundbyustobeunabletodepositNiPsufficientlyontosupport.…     

Synthesis and characterization of several dicopper(I) complexes and a spin-delocalized dicopper(I,II) mixed-valence complex using a 1,8-naphthyridine-based dinucleating ligand

The synthesis of dicopper(I) complexes [Cu2(BBAN)(MeCN)2](OTf)2 (1), [Cu2(BBAN)(py)2](OTf)2 (2), [Cu2(BBAN)(1-Me-BzIm)2](OTf)2 (3), [Cu2(BBAN)(1-Me-Im)2](OTf)2 (4), and [Cu2(BBAN)(mu-O2CCPh3)](OTf) (5), where BBAN = 2,7-bis((dibenzylamino)methyl)-1,8-naphthyridine, py = pyridine, 1-Me-Im = 1-methylimidazole, and 1-Me-BzIm = 1-methylbenzimidazole, are described. Short copper-copper distances ranging from 2.6151(6) to 2.7325(5) A were observed in the solid-state structures of these complexes depending on the terminal ligands used. The cyclic voltammogram of compound 5 dissolved in THF exhibited a reversible redox wave at E1/2 = -25 mV vs Cp2Fe+/Cp2Fe. When complex 5 was treated with 1 equiv of silver(I) triflate, a mixed-valence dicopper(I,II) complex [Cu2(BBAN)(mu-O2CCPh3)(OTf)](OTf) (6) was prepared. A short copper-copper distance of 2.4493(14) A observed from the solid-state structure indicates the presence of a copper-copper interaction. Variable-temperature EPR studies showed that complex 6 has a fully delocalized electronic structure in frozen 2-methyltetrahydrofuran solution down to liquid helium temperature. The presence of anionic ligands seems to be an important factor to stabilize the mixed-valence dicopper(I,II) state. Compounds 1-4 with neutral nitrogen-donor terminal ligands cannot be oxidized to the mixed-valence analogues either chemically or electrochemically.     

Cu/Mn/ZrO2 catalyst for alcohol synthesis by Fischer-Tropsch modified elements

A Cu/Mn/ZrO₂ methanol synthesis catalyst modified by Fischer-Tropsch (F-T) element (Ni,Co,Fe) was prepared by an coprecipatation method. The addition of F-T elements had a great effect on the catalyst performance. The higher alcohol selectivity increased greatly compared with that of the Cu/Mn/ZrO₂ catalyst when nickel and cobalt were added, while the addition of iron improved the selectivity tohydrocarbon due to the interaction of the F-T element and the Cu/Mn/ZrO₂ catalyst.     

Nitric oxide reactivity of fluorophore coordinated carboxylate-bridged diiron(II) and dicobalt(II) complexes

The synthesis, structural characterization, and NO reactivity of carboxylate-bridged dimetallic complexes were investigated. The diiron(II) complex [Fe(2)(mu-O(2)CAr(Tol))(4)(Ds-pip)(2)] (1), where O(2)CAr(Tol) = 2,6-di(p-tolyl)benzoate and Ds-pip = dansyl-piperazine, was prepared and determined by X-ray crystallography to have a paddlewheel geometry. This complex reacts with NO within 1 min with a concomitant 4-fold increase in fluorescence emission intensity ascribed to displacement of Ds-pip. Although the diiron complex reacts with NO, as revealed by infrared spectroscopic studies, its sensitivity to dioxygen renders it unsuitable as an atmospheric NO sensor. The air-stable dicobalt(II) analogue was also synthesized and its reactivity investigated. In solution, the dicobalt(II) complex exists as an equilibrium between paddlewheel [Co(2)(mu-O(2)CAr(Tol))(4)(Ds-pip)(2)] (2) and windmill [Co(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(Ds-pip)(2)] (3) geometric isomers. Conditions for crystallizing pure samples of each of these isomers are described. Reaction of 2 with excess NO proceeds by reductive nitrosylation giving [Co(mu-O(2)CAr(Tol))(2)(NO)(4)] (5), which is accompanied by release of the Ds-pip fluorophore that is N-nitrosated in the process. This reaction affords an overall 9.6-fold increase in fluorescence emission intensity, further demonstrating the potential utility of ligand dissociation as a strategy for designing fluorescence-based sensors to detect nitric oxide in a variety of contexts.     

Field-induced magnetic transitions in metal phosphonates with ladderlike chain structures: (NH3C6H4NH3)M2(hedpH)2.H2O [M = Fe, Co, Mn, Zn; hedp = C(CH3)(OH)(PO3)2

This paper reports the syntheses and characterization of four isomorphous compounds (NH(3)C(6)H(4)NH(3))M(2)(hedpH)(2).H(2)O [M = Fe (1), Co (2), Mn (3), Zn (4); hedp = C(CH(3))(OH)(PO(3))(2)]. Each contains two crystallographically different kinds of {M(2)(hedpH)(2)}(n) double chains, where the {M(2)(mu-O)(2)} dimer units are connected by O-P-O bridges. The double chains are connected through extensive hydrogen bonds, hence generating a three-dimensional supramolecular network. The temperature-dependent magnetic susceptibility measurements show dominant antiferromagnetic interactions in compounds 1-3, mediated through the mu-O and/or O-P-O bridges between the metal(II) centers. The magnetization measurements reveal that compounds 1-3 experience field-induced magnetic transitions at low temperatures.     

CO氧化反应中H2O对MOx和Au/MOx催化性能的影响

过渡金属氧化物［1,2］及负载型贵金属催化剂［3～13］是催化氧化消除CO的有效催化剂,一直是研究的热点. 虽然对MOx和Au/MOx上CO的氧化性能研究得较多,但大多是在无水条件下进行的;涉及催化剂抗水性能的报道较少［3,9,10］,且仅限于对催化剂活性的研究. Haruta等［3］对Au/Fe2O3,Au/Co3O4和Au/TiO 2等体系开展了一些工作, 认为水对CO氧化活性有促进作用. 本文重点考察了水对MOx(M=Al,Ca,Co,Cr,Cu,Fe,La,Mn,Ni和Zn)催化剂上CO氧化活性的影响,以及水对Au/MOx 催化剂活性及稳定性的影响.     

[NiFe/Cu/Co/Cu]n纳米多层线的电化学制备及表征

采用电沉积法,在阳极氧化铝(AAO)模板中制备了[NiFe/Cu/Co/Cu]_n多层纳米线.利用扫描电子显微镜(SEM)及透射电子显微镜(TEM)对纳米多层线的表面形貌及结构进行了表征,纳米线阵列高度有序、直径均一、层状结构清晰,NiFe层厚度约40 nm,Cu层厚度约60 nm,Co层厚度约15 nm,各子层厚度可控.利用X射线能谱分析仪(EDS)对纳米多层线NiFe层的成分进行了测试,Ni,Fe的原子比为4:1.利用X射线衍射仪(XRD)对[NiFe/Cu/Co/Cu]_n纳米多层膜和多层线结构进行了测试,多层膜为面心立方(fcc)结构,多层线NiFe层为面心立方(fcc)结构,Cu层为六方密排hcp(100),Co层为面心立方(fcc)结构.与组成、结构完全相同的多层膜相比,[NiFe/Cu/Co/Cu]_n多层纳米线具有更优越的巨磁电阻性能.     

Synthesis, characterization, and preliminary oxygenation studies of benzyl- and ethyl-substituted pyridine ligands of carboxylate-rich diiron(II) complexes

In this study benzyl and ethyl groups were appended to pyridine and aniline ancillary ligands in diiron(II) complexes of the type [Fe(2)(mu-O(2)CAr(R))(2)(O(2)CAr(R))(2)(L)(2)], where (-)O(2)CAr(R) is a sterically hindered terphenyl carboxylate, 2,6-di(p-tolyl)- or 2,6-di(p-fluorophenyl)benzoate (R = Tol or 4-FPh, respectively). These crystallographically characterized compounds were prepared as analogues of the diiron(II) center in the hydroxylase component of soluble methane monooxygenase (MMOH). The use of 2-benzylpyridine (2-Bnpy) yielded doubly bridged [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(2-Bnpy)(2)] (1) and [Fe(2)(mu-O(2)CAr(4)(-)(FPh))(2)(O(2)CAr(4)(-)(FPh))(2)(2-Bnpy)(2)] (4), whereas tetra-bridged [Fe(2)(mu-O(2)CAr(Tol))(4)(4-Bnpy)(2)] (3) resulted when 4-benzylpyridine (4-Bnpy) was employed. Similarly, 2-(4-chlorobenzyl)pyridine (2-(4-ClBn)py) and 2-benzylaniline (2-Bnan) were employed as N-donor ligands to prepare [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(2-(4-ClBn)py)(2)] (2) and [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(2-Bnan)(2)] (5). The placement of the substituent on the pyridine ring had no effect on the geometry of the diiron(II) compounds isolated when 2-, 3-, or 4-ethylpyridine (2-, 3-, or 4-Etpy) was introduced as the ancillary nitrogen ligand. The isolated [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(2-Etpy)] (6), [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(3-Etpy)] (7), [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(4-Etpy)] (8), and [Fe(2)(mu-O(2)CAr(4)(-FPh))(2)(O(2)CAr(4)(-)(FPh))(2)(2-Etpy)(2)] (9) complexes all contain doubly bridged metal centers. The oxygenation of compounds 1-9 was studied by GC-MS and NMR analysis of the organic fragments following decomposition of the product complexes. Hydrocarbon fragment oxidation occurred for compounds in which the substrate moiety was in close proximity to the diiron center. The extent of oxidation depended upon the exact makeup of the ligand set.     

Synthesis and electrochemical studies of diiron complexes of 1,8-naphthyridine-based dinucleating ligands to model features of the active sites of non-heme diiron enzymes

A bis(mu-carboxylato)(mu-1,8-naphthyridine)diiron(II) complex, [Fe2(BPMAN)(mu-O2CPhCy)2](OTf)2 (1), was prepared by using the 1,8-naphthyridine-based dinucleating ligand BPMAN, where BPMAN = 2,7-bis[bis(2-pyridylmethyl)aminomethyl]-1,8-naphthyridine. The cyclic voltammogram (CV) of this complex in CH2Cl2 exhibited two reversible one-electron redox waves at +296 mV (DeltaE(p) = 80 mV) and +781 mV (DeltaE(p) = 74 mV) vs Cp2Fe+/Cp2Fe, corresponding to the FeIIIFeII/FeIIFeII and FeIIIFeIII/FeIIIFeII couples, respectively. This result is unprecedented for diiron complexes having no single atom bridge. Dinuclear complexes [Fe2(BPMAN)(mu-OH)(mu-O2CPhCy)](OTf)2 (2) and [Mn2(BPMAN)(mu-O2CPhCy)2](OTf)2 (3) were also synthesized and structurally characterized. The cyclic voltammogram of 2 in CH2Cl2 exhibited one reversible redox wave at -22 mV only when the potential was kept below +400 mV. The CV of 3 showed irreversible oxidation at potentials above +900 mV. Diiron(II) complexes [Fe2(BEAN)(mu-O2CPhCy)3](OTf) (4) and [Fe2(BBBAN)(mu-OAc)2(OTf)](OTf) (6) were also prepared and characterized, where BEAN = 2,7-bis(N,N-diethylaminomethyl)-1,8-naphthyridine and BBBAN = 2,7-bis[2-[2-(1-methyl)benzimidazolylethyl]-N-benzylaminomethyl]-1,8-naphthyridine. The cyclic voltammograms of these complexes were recorded. The M?ssbauer properties of the diiron compounds were studied.     

Nine non-symmetric pyrazine-pyridine imide-based complexes: reversible redox and isolation of [M(II/III)(pypzca)2](0/+) when M = Co, Fe

The non-symmetric imide ligand Hpypzca (N-(2-pyrazylcarbonyl)-2-pyridinecarboxamide) has been deliberately synthesised and used to produce nine first row transition metal complexes: [M(II)(pypzca)(2)], M = Zn, Cu, Ni, Co, Fe; [M(III)(pypzca)(2)]Y, M = Co and Y = BF(4), M = Fe and Y = ClO(4); [Cu(II)(pypzca)(H(2)O)(2)]BF(4), [Mn(II)(pypzca)(Cl)(2)]HNEt(3). These are the first deliberately prepared complexes of a non-symmetric imide ligand. X-ray crystal structures of [Cu(II)(pypzca)(2)]·H(2)O, [Co(II)(pypzca)(2)], [Co(III)(pypzca)(2)]BF(4), [Cu(II)(pypzca)(H(2)O)(2)]BF(4)·H(2)O and [Mn(II)(pypzca)Cl(2)]HNEt(3) show that each of the (pypzca)(-) ligands binds in a meridional fashion via the N(3) donors. In the first three complexes, two such ligands are bound such that the 'spare' pyrazine nitrogen atoms are positioned approximately orthogonally to one another and also to the imide oxygen atoms. In MeCN the [M(II/III)(pypzca)(2)](0/+) complexes, where M = Ni, Co or Fe, exhibit one reversible metal based M(II/III) process and two distinct, quasi-reversible ligand based reduction processes, the latter also observed for M(II) = Zn. [Mn(II)(pypzca)Cl(2)]HNEt(3) displays a quasi-reversible oxidation process in MeCN, along with several irreversible processes. Both copper(II) complexes show only irreversible processes. Variable temperature magnetic measurements show that [Fe(III)(pypzca)(2)]ClO(4) undergoes a gradual spin crossover from partially high spin at 298 K (3.00 BM) to fully low spin at 2 K (1.96 BM), and that [Co(II)(pypzca)(2)] remains high spin from 298 to 4 K. All of the complexes are weakly coloured, other than [Fe(II)(pypzca)(2)] which is dark purple and absorbs strongly in the visible region.     

Modeling features of the non-heme diiron cores in O2-activating enzymes through the synthesis, characterization, and oxidation of 1,8-naphthyridine-based complexes

Multidentate naphthyridine-based ligands were used to prepare a series of diiron(II) complexes. The compound [Fe(2)(BPMAN)(mu-O(2)CPh)(2)](OTf)(2) (1), where BPMAN = 2,7-bis[bis(2-pyridylmethyl)aminomethyl]-1,8-naphthyridine, exhibits two reversible oxidation waves with E(1/2) values at +310 and +733 mV vs Cp(2)Fe(+)/Cp(2)Fe, as revealed by cyclic voltammetry. Reaction with O(2) or H(2)O(2) affords a product with optical and M?ssbauer properties that are characteristic of a (mu-oxo)diiron(III) species. The complexes [Fe(2)(BPMAN)(mu-OH)(mu-O(2)CAr(Tol))](OTf)(2) (2) and [Fe(2)(BPMAN)(mu-OMe)(mu-O(2)CAr(Tol))](OTf)(2) (3) were synthesized, where Ar(Tol)CO(2)(-) is the sterically hindered ligand 2,6-di(p-tolyl)benzoate. Compound 2 has a reversible redox wave at +11 mV, and both 2 and 3 react with O(2), via a mixed-valent Fe(II)Fe(III) intermediate, to give final products that are also consistent with (mu-oxo)diiron(III) species. The paddle-wheel compound [Fe(2)(BBAN)(mu-O(2)CAr(Tol))(3)](OTf) (4), where BBAN = 2,7-bis(N,N-dibenzylaminomethyl)-1,8-naphthyridine, reacts with dioxygen to yield benzaldehyde via oxidative N-dealkylation of a benzyl group on BBAN, an internal substrate. In the presence of bis(4-methylbenzyl)amine, the reaction also produces p-tolualdehyde, revealing oxidation of an external substrate. A structurally related compound, [Fe(2)(BEAN)(mu-O(2)CAr(Tol))(3)](OTf) (5), where BEAN = 2,7-bis(N,N-diethylaminomethyl)-1,8-naphthyridine, does not undergo N-dealkylation, nor does it facilitate the oxidation of bis(4-methylbenzyl)amine. The contrast in reactivity of 4 and 5 is attributed to a difference in accessibility of the substrate to the diiron centers of the two compounds. The M?ssbauer spectroscopic properties of the diiron(II) complexes were also investigated.     

Carboxylate and alkyl carbonate coordination at the hydrophobic binding site of redox-active dicobalt amine thiophenolate complexes

A series of new dicobalt complexes of the permethylated macrocyclic hexaamine dithiophenolate ligand H(2)L(Me) have been prepared and investigated in the context of ligand binding and oxidation state changes. The octadentate ligand is an effective dinucleating ligand that supports the formation of bioctahedral complexes with a central N(3)Co(mu-SR)(2)(mu-X)CoN(3) core structure, leaving a free bridging position X for the coordination of the substrates. The acetato- and cinnamato-bridged complexes [(L(Me))Co(II)(2)(mu-O(2)CMe)](+) (2) and [(L(Me))Co(II)(2)(mu-O(2)CCH=CHPh)](+) (5) were prepared by reaction of the mu-Cl complex [(L(Me))Co(II)(2)(mu-Cl)](+) (1) with the corresponding sodium carboxylates in methanol. The electrochemical properties of these and of the methyl carbonate complex [(L(Me))Co(II)(2)(mu-O(2)COMe)](+) (8) were also investigated. All complexes undergo two stepwise oxidations at ca. E(1)(1/2) = +0.22 and at E(2)(1/2) = ca. +0.60 V vs SCE, affording the mixed-valent complexes [(L(Me))Co(II)Co(III)(mu-O(2)CR)](2+) (3, 6, 9) and the fully oxidized Co(III)Co(III) forms [(L(Me))Co(III)(2)(mu-O(2)CR)](3+) (4, 7, 10), respectively. Compounds 3, 6, 9 and 4, 7, 10 refer to acetato-, cinnamato-, and methylcarbonato species, respectively. The Co(II)Co(III) compounds were prepared by comproportionation of the respective Co(II)(2) and Co(III)(2) compounds. The Co(III)Co(III) species were prepared by bromine oxidation of the Co(II)Co(II) forms. The crystal structures of complexes 2.BPh(4).MeCN, 3.(I(3))(2), 5.BPh(4).2MeCN, 6.(ClO(4))(2).EtOH, 7.(ClO(4))(3).MeCN.(H(2)O)(3), and 9.(ClO(4))(2).(MeOH)(2).H(2)O were determined by single-crystal X-ray crystallography at 210 K. The oxidations occur without gross structural changes of the parent complexes. The Co(II)Co(III) complexes are composed of high-spin Co(II) (d(7)) and low-spin Co(III) (d(6)) ions. The Co(III)Co(III) complexes are diamagnetic. The oxidation reactions affect the binding mode of the substrates. In the Co(II)(2) and Co(II)Co(III) forms the carboxylates bridge the two Co(2+) ions in a symmetric mu-1,3 fashion with uniform C-O bond distances, whereas asymmetric bridging modes, with one short C=O and one long C-O distance, are adopted in the fully oxidized species. This is consistent with the observed shifts in vibrational frequencies for nu(as)(C-O) and nu(s)(C-O) across the series.     

聚苯胺/Co_(0.5)Zn_(0.5)Fe_2O_4纳米复合材料的制备及电磁性能

采用高分子凝胶法制备尖晶石型Co0.5Zn0.5Fe2O4,原位聚合法制备纯聚苯胺和聚苯胺/Co0.5Zn0.5-Fe2O4纳米复合材料.使用傅立叶红外光谱(FTIR)、紫外可见吸收光谱(UV-Vis)、X射线衍射仪(XRD)和透射电子显微镜(TEM)对复合材料进行了表征.FTIR和XRD的结果表明样品为纯聚苯胺和聚苯胺/Co0.5Zn0.5-Fe2O4.UV-Vis光谱表明聚苯胺/Co0.5Zn0.5Fe2O4苯环上的π-π*和n-π*分别红移了23nm和5nm.TEM照片可知,聚苯胺和聚苯胺/Co0.5Zn0.5Fe2O4粒子的平均粒径分别约为50nm和70nm.在8.2～12.4GHz测试频率范围内,聚苯胺/Co0.5Zn0.5Fe2O4的ε″数值在9.2～12.3之间,u″数值在0.15～0.16之间;聚苯胺/Co0.5-Zn0.5Fe2O4介电损耗低于纯聚苯胺,而磁损耗高于纯聚苯胺.     

Dioxygen-initiated oxidation of heteroatomic substrates incorporated into ancillary pyridine ligands of carboxylate-rich diiron(II) complexes

Progress toward the development of functional models of the carboxylate-bridged diiron active site in soluble methane monooxygenase is described in which potential substrates are introduced as substituents on bound pyridine ligands. Pyridine ligands incorporating a thiol, sulfide, sulfoxide, or phosphine moiety were allowed to react with the preassembled diiron(II) complex [Fe(2)(mu-O(2)CAr(R))(2)(O(2)CAr(R))(2)(THF)(2)], where (-)O(2)CAr(R) is a sterically hindered 2,6-di(p-tolyl)- or 2,6-di(p-fluorophenyl)benzoate (R = Tol or 4-FPh). The resulting diiron(II) complexes were characterized crystallographically. Triply and doubly bridged compounds [Fe(2)(mu-O(2)CAr(Tol))(3)(O(2)CAr(Tol))(2-MeSpy)] (4) and [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(2-MeS(O)py)(2)] (5) resulted when 2-methylthiopyridine (2-MeSpy) and 2-pyridylmethylsulfoxide (2-MeS(O)py), respectively, were employed. Another triply bridged diiron(II) complex, [Fe(2)(mu-O(2)CAr(4)(-)(FPh))(3)-(O(2)CAr(4)(-)(FPh))(2-Ph(2)Ppy)] (3), was obtained containing 2-diphenylphosphinopyridine (2-Ph(2)Ppy). The use of 2-mercaptopyridine (2-HSpy) produced the mononuclear complex [Fe(O(2)CAr(Tol))(2)(2-HSpy)(2)] (6a). Together with that of previously reported [Fe(2)(mu-O(2)CAr(Tol))(3)(O(2)CAr(Tol))(2-PhSpy)] (2) and [Fe(2)(mu-O(2)CAr(Tol))(3)(O(2)CAr(Tol))(2-Ph(2)Ppy)] (1), the dioxygen reactivity of these iron(II) complexes was investigated. A dioxygen-dependent intermediate (6b) formed upon exposure of 6a to O(2), the electronic structure of which was probed by various spectroscopic methods. Exposure of 4 and 5 to dioxygen revealed both sulfide and sulfoxide oxidation. Oxidation of 3 in CH(2)Cl(2) yields [Fe(2)(mu-OH)(2)(mu-O(2)CAr(4)(-)(FPh))(O(2)CAr(4)(-FPh))(3)(OH(2))(2-Ph(2)P(O)py)] (8), which contains the biologically relevant {Fe(2)(mu-OH)(2)(mu-O(2)CR)}(3+) core. This reaction is sensitive to the choice of carboxylate ligands, however, since the p-tolyl analogue 1 yielded a hexanuclear species, 7, upon oxidation.     

Multielement trace determinations in A12O3 ceramic powders by inductively coupled plasma mass spectrometry with special reference to on-line trace preconcentration

The use of inductively coupled plasma mass spectrometry (ICP-MS) for the determination of trace elements in Al₂O₃ powders is reported. Special interest is given to a preconcentration of the trace elements by on-line coupling of chromatography to ICP-MS. This is based on the complexation of Co, Cu, Cr, Fe, Ga, Mn, Ni, V and Zn with hexamethylene-dithiocarbamate (HMDC), their preconcentration on a C18 RP column by reversed phase liquid chromatography and their elution with CH₃OH-H₂O mixtures. A direct coupling of the HPLC system to the ICP-MS has been realized by high pressure pneumatic nebulization using desolvation. With the Chromatographie method developed, removal of the AI by at least 99% was achieved. For the trace elements V, Fe, Ni, Co, Cu and Ga, high and reproducible recoveries (ranging from 96–99%) were reached. The method developed has been shown to considerably enhance the power of detection as compared with direct procedures, namely down to 0.02–0.16 ( for V and Fe, respectively. The possibilities of the method are shown by the determinations of V, Mn, Fe, Ni, Co, Cu, Zn and Ga at the μg/g level in A1₂O₃ powders. The accuracy of the method at the 0.06 to 9.0 level for Co and Fe, respectively, is demonstrated by a comparison with results of independent methods from the literature.     

Hydrogen storage in the dehydrated prussian blue analogues M3[Co(CN)6]2 (M = Mn, Fe, Co, Ni, Cu, Zn)

The porosity and hydrogen storage properties for the dehydrated Prussian blue analogues M3[Co(CN)6]2 (M = Mn, Fe, Co, Ni, Cu, Zn) are reported. Argon sorption isotherms measured at 87 K afford BET surface areas ranging from 560 m2/g for Ni3[Co(CN)6]2 to 870 m2/g for Mn3[Co(CN)6]2; the latter value is comparable to the highest surface area reported for any known zeolite. All six compounds show significant hydrogen sorption at 77 K and 890 Torr, varying from 1.4 wt % and 0.018 kg H2/L for Zn3[Co(CN)6]2 to 1.8 wt % and 0.025 kg H2/L for Cu3[Co(CN)6]2. Fits to the sorption data employing the Langmuir-Freundlich equation give maximum uptake quantities, resulting in a predicted storage capacity of 2.1 wt % and 0.029 kg H2/L for Cu3[Co(CN)6]2 at saturation. Enthalpies of adsorption for the frameworks were calculated from hydrogen isotherms measured at 77 and 87 K and found to increase with M varying in the order Mn < Zn < Fe < Co < Cu < Ni. In all cases, the binding enthalpies, which lie in the range of 5.3-7.4 kJ/mol, are higher than the 4.7-5.2 kJ/mol measured for Zn4O(1,4-benzenedicarboxylate)3.