Synthesis and structure of a terminal uranium nitride complex

The terminal uranium nitride linkage is a fundamental target in the study of f-orbital participation in metal-ligand multiple bonding but has previously eluded characterization in an isolable molecule. Here, we report the preparation of the terminal uranium(V) nitride complex [UN(Tren(TIPS))][Na(12-crown-4)(2)] {in which Tren(TIPS) = [N(CH(2)CH(2)NSiPr(i)(3))(3)](3-) and Pr(i) = CH(CH(3))(2)} by reaction of the uranium(III) complex [U(Tren(TIPS))] with sodium azide followed by abstraction and encapsulation of the sodium cation by the polydentate crown ether 12-crown-4. Single-crystal x-ray diffraction reveals a uranium-terminal nitride bond length of 1.825(15) angstroms (where 15 is the standard uncertainty). The structural assignment is supported by means of (15)N-isotopic labeling, electronic absorption spectroscopy, magnetometry, electronic structure calculations, elemental analyses, and liberation of ammonia after treatment with water.     

Reductive cyclotrimerization of carbon monoxide to the deltate dianion by an organometallic uranium complex

Despite the long history of the Fischer-Tropsch reaction, carbon monoxide has proven remarkably resistant to selective homologation under mild conditions. Here, we find that an organouranium(III) complex induces efficient reductive trimerization of carbon monoxide at room temperature and pressure. The result is a triangular, cyclic C3O(2-)3, or deltate, dianion held between two uranium(IV) units. The bonding within the C3O(2-)3 unit and its coordination to the two U centers have been analyzed by x-ray diffraction and density functional theory computational studies, which show a stabilizing C-C agostic interaction between the C3 core and one U center. Solution nuclear magnetic resonance studies reveal a rapid equilibration of the deltate unit between the U centers.     

Molecular octa-uranium rings with alternating nitride and azide bridges

Uranium nitrides offer potential as future nuclear fuels and as probes of metal ligand multiple bonding involving the f-block actinide metals. However, few molecular examples are available for study owing to the difficulties in synthesis. Recent advances in organoactinide chemistry have provided a route to uranium nitride complexes that expands the options for developing UN chemistry. Several 24-membered uranium nitrogen rings, (UNUN3)4, have been synthesized by reduction of sodium azide with organometallic metallocene derivatives, [(C5Me4R)2U][(mu-Ph)2BPh2] (R = Me, H; Me = methyl, Ph = phenyl). The nanometer-sized rings contain unusual UNU nitride linkages that have short U-N distances within the double-bond range.     

A late-transition metal oxo complex: K7Na9[O=PtIV(H2O)L2], L = [PW9O34]9-

Terminal mono-oxo complexes of the late transition metal elements have long been considered too unstable to synthesize because of repulsion between the oxygen electrons and the mostly filled metal d orbitals. A platinum(IV)-oxo compound flanked by two polytungstate ligands, K7Na9[O=Pt(H2O)L2], L = [PW9O34(9-)], has now been prepared and isolated at room temperature as air-stable brown crystals. X-ray and neutron diffraction at 30 kelvin revealed a very short [1.720(18) angstrom] Pt-O bond and no evidence of a hydrogen atom at the terminal oxygen, ruling out a better precedented Pt-OH complex. Density functional theory and spectroscopic data account for the stability of the Pt(IV)-oxo unit by electron withdrawal into delocalized orbitals of the polytungstates.     

Oxygen-carrying iridium complexes: kinetics, mechanism, and thermodynamics

The rates of oxygenation and deoxygenation of a series of iridium complexes increase and decrease, respectively, with increasing electron-releasing tendency of the anionic ligands (A) attached to the metal atom in the oxygencarrying compounds, [IrA(CO)(Ph(3)P)(2)]. Calculated heats of oxygenation (-DeltaH(2)(0)), related to Ir-O(2) bond energies, are proportional to the previously reported O-O bond lengths in the oxygen adducts, [O(2)IrA(CO)(Ph(3)P)(2)].     

一种新型二茂铁丁酸混配合物的合成及晶体结构

以二茂铁基丁酸(Fb)、4,4′-联吡啶(bpy)以及Zn(AC)2.2H2O为原料合成了一个新的混配合物Zn(Fb)2(bpy)2。X-射线单晶衍射分析表明,该化合物是一个四配体六配位单核配合物,并以氢键另连接两个二茂铁分子。     

Synthesis, structure, and reactivity of an iron(V) nitride

Despite being implicated as important intermediates, iron(V) compounds have proven very challenging to isolate and characterize. Here, we report the preparation of the iron(V) nitrido complex, [PhB((t)BuIm)(3)Fe(V)≡N]BAr(F24) (PhB((t)BuIm)(3)(-) = phenyltris(3-tert-butylimidazol-2-ylidene)borato, BAr(F24) = B(3,5-(CF(3))(2)C(6)H(3))(4)(-)), by one electron oxidation of the iron(IV) nitrido precursor. Single-crystal x-ray diffraction of the iron(V) complex reveals a four-coordinate metal ion with a terminal nitrido ligand. M??bauer and electron paramagnetic resonance spectroscopic characterization, supported by electronic structure calculations, provide evidence for a d(3) iron(V) metal center in a low spin (S = 1/2) electron configuration. Low-temperature reaction of the iron(V) nitrido complex with water under reducing conditions leads to high yields of ammonia with concomitant formation of an iron(II) species.     

A stable silicon(0) compound with a Si=Si double bond

Dative, or nonoxidative, ligand coordination is common in transition metal complexes; however, this bonding motif is rare in compounds of main group elements in the formal oxidation state of zero. Here, we report that the potassium graphite reduction of the neutral hypervalent silicon-carbene complex L:SiCl4 {where L: is:C[N(2,6-Pri2-C6H3)CH]2 and Pri is isopropyl} produces L:(Cl)Si-Si(Cl):L, a carbene-stabilized bis-silylene, and L:Si=Si:L, a carbene-stabilized diatomic silicon molecule with the Si atoms in the formal oxidation state of zero. The Si-Si bond distance of 2.2294 +/- 0.0011 (standard deviation) angstroms in L:Si=Si:L is consistent with a Si=Si double bond. Complementary computational studies confirm the nature of the bonding in L:(Cl)Si-Si(Cl):L and L:Si=Si:L.     

Crystallographic and spectroscopic characterization of a nonheme Fe(IV)-O complex

Following the heme paradigm, it is often proposed that dioxygen activation by nonheme monoiron enzymes involves an iron(IV)=oxo intermediate that is responsible for the substrate oxidation step. Such a transient species has now been obtained from a synthetic complex with a nonheme macrocyclic ligand and characterized spectroscopically. Its high-resolution crystal structure reveals an iron-oxygen bond length of 1.646(3) angstroms, demonstrating that a terminal iron(IV)=oxo unit can exist in a nonporphyrin ligand environment and lending credence to proposed mechanisms of nonheme iron catalysis.     

由乙二胺、α-萘乙酸构筑的镍(Ⅱ)配合物的合成、结构和抑菌性质研究

[目的]α-萘乙酸是一种植物生长调节剂,乙二胺是一类很好的有机配体,二者与金属离子共同反应合成金属配合物,并研究配合物的抑菌活性。[方法]通过水热合成法合成新的配合物,利用牛津杯法研究配合物的抑菌活性。[结果]成功合成了配合物[Ni(C12H9O2)2(C2H8N2)3]2,采用单晶X-射线、元素分析和FT-IR对合成配合物[Ni(C12H9O2)2(C2H8N2)3]2进行结构表征。同时,研究了该配合物的抑菌活性。[结论]该晶体属于三斜晶系,P-1空间群:a=9.145(6),b=13.146(8),c=14.385(9);α=70.120(7)°,β=74.272(7)°,γ=69.819(7)°,Z=2。Ni(II)与来自3个乙二胺分子的六个氮原子配位,形成扭曲的八面体配位构型。配合物有一定的抑菌活性。     

一维链状镍配合物[Ni（C_（14）H_（10）N_2O_2）（Mf）]_n的合成和晶体结构

合成了含水杨醛缩苯甲酰腙的一维链状镍配合物[Ni（C14H10N2O2）（Mf）]n（Mf=C4H9NO,即吗啡啉）,通过元素分析,红外、电子光谱和X-射线单晶衍射进行了表征.晶体属单斜晶系,空间群为P21/c,a=0.9708（4）nm,b=1.4783（7）nm,c=1.2275（4）nm,β=95.728（14）°,V=1.7528（12）nm3,Z=4,Mr=384.07,Dc=1.455 g.cm-3,μ=1.129 mm-1,F（000）=800,R=0.0759,wR=0.2155.中心镍离子与水杨醛缩苯甲酰腙配体提供的2个氧原子与1个氮原子以及1个配位吗啡啉的氮原子配位,形成了N2O2的平面四边形的配位构型.晶体内每个配合物分子通过分子间氢键与相邻另一个配合物分子缔合成一个沿c轴方向的一维链状结构,N…N氢键键长为0.3239（10）nm,N-H…N氢键键角为173.56°.     

Spectroscopic observation of dual catalytic sites during oxidation of CO on a Au/TiO₂ catalyst

The prevailing view of CO oxidation on gold-titanium oxide (Au/TiO(2)) catalysts is that the reaction occurs on metal sites at the Au/TiO(2) interface. We observed dual catalytic sites at the perimeter of 3-nanometer Au particles supported on TiO(2) during CO oxidation. Infrared-kinetic measurements indicate that O-O bond scission is activated by the formation of a CO-O(2) complex at dual Ti-Au sites at the Au/TiO(2) interface. Density functional theory calculations, which provide the activation barriers for the formation and bond scission of the CO-O(2) complex, confirm this model as well as the measured apparent activation energy of 0.16 electron volt. The observation of sequential delivery and reaction of CO first from TiO(2) sites and then from Au sites indicates that catalytic activity occurs at the perimeter of Au nanoparticles.     

A manganese(IV)/iron(III) cofactor in Chlamydia trachomatis ribonucleotide reductase

In a conventional class I ribonucleotide reductase (RNR), a diiron(II/II) cofactor in the R2 subunit reacts with oxygen to produce a diiron(III/IV) intermediate, which generates a stable tyrosyl radical (Y*). The Y* reversibly oxidizes a cysteine residue in the R1 subunit to a cysteinyl radical (C*), which abstracts the 3'-hydrogen of the substrate to initiate its reduction. The RNR from Chlamydia trachomatis lacks the Y*, and it had been proposed that the diiron(III/IV) complex in R2 directly generates the C* in R1. By enzyme activity measurements and spectroscopic methods, we show that this RNR actually uses a previously unknown stable manganese(IV)/iron(III) cofactor for radical initiation.     

Structural aspects of reversible molecular oxygen uptake

The system IrX(CO)[P(C(6)H(5))(3)](2) in benzene solution adds mo lecular oxygen reversibly if X is chlorine and irreversibly if X is iodine. The crystal structure of the complex IrIO(2)(CO)[P(C(6)H(5))(3)](2) * CH(2)Cl(2) is reported here and compared with a previous study of the structure of IrClO(2)(CO)[P(C(6)H(5))(3)](2). The O-O bond length is 1.47 +/- 0.02 angstroms in the irreversibly oxygenated iodo-compound and 1.30 +/- 0.03 angstroms in the reversibly oxygenated chloro compound.     

三维超分子配合物Cu(2-mpac)Cl(H_2O)·H_2O的合成与结构

以2-甲基-5-羧基吡嗪为配体合成了1个三维超分子配合物Cu(2-mpac)Cl(H2O).H2O(1)(2-mpac:2-甲基-5-羧基吡嗪),并利用元素分析、IR、X-射线单晶衍射及热重分析等手段对配合物(1)进行了结构表征.结果表明:配合物(1)属于三斜晶系,P-1空间群,P-1,a=3.8306(6),b=11.395 7(18),c=11.5596(18),α=111.321(2)°,β=96.282(2)°,γ=98.667(2)°,V=457.25(12)°3,Z=2,S=1.019,,最终残差因子(I>2σ(I))R1=0.0375,wR2=0.0945,对于全部数据R1=0.0423,wR2=0.0991.     

Dinitrogen Cleavage by a Three-Coordinate Molybdenum(III) Complex

Cleavage of the relatively inert dinitrogen (N(2)) molecule, with its extremely strong N identical withN triple bond, has represented a major challenge to the development of N(2) chemistry. This report describes the reductive cleavage of N(2) to two nitrido (N(3-)) ligands in its reaction with Mo(NRAr)(3), where R is C(CD(3))(2)CH(3) and Ar is 3,5-C(6)H(3)(CH(3))(2'), a synthetic three-coordinate molybdenum(III) complex of known structure. The formation of an intermediate complex was observed spectroscopically, and its conversion (with N identical withN bond cleavage) to the nitrido molybdenum(VI) product N identical withMo(NRAr)(3) followed first-order kinetics at 30 degrees C. It is proposed that the cleavage reaction proceeds by way of an intermediate complex in which N(2) bridges two molybdenum centers.     

4-氨基-3,5二-（4-吡啶基）-1,2,4三-氮唑-Cu（Ⅰ）配合物的溶剂热合成及结构表征

采用CuBr与4-氨基-3,5-二（4-吡啶基）-1,2,4-三氮唑配体（4-abpt）在溶剂热条件下合成了配合物[CuBr（4-abpt）],并用红外光谱、元素分析及X-射线单晶衍射对其进行了结构表征.结果表明,该配合物中Cu（Ⅰ）呈现四面体配位几何,4-abpt采取μ3-桥连模式与μ3-Cu（Ⅰ）在ab平面形成了具有（4.82）拓扑结构的[Cu-（4-abpt）]层,相邻层间通过N-H…Br氢键作用和π-π堆积构筑成三维超分子网络.配合物结晶于单斜晶系,P2（1）/n空间群,a=0.768 97（6）nm,b=1.332 70（10）nm,c=1.263 38（9）nm,β=91.388（2）,V=1.294 34（17）nm3,Z=4,S=1.050,R1=0.023 1,wR2=0.056 7[I〉2σ（I）].     

Toward separation and purification of olefins using dithiolene complexes: an electrochemical approach

The complex Ni[S2C2(CF3)2]2 reacts with light olefins, including ethylene and propylene, selectively and reversibly. The reaction is not poisoned by hydrogen gas, carbon monoxide, acetylene, or hydrogen sulfide, which are commonly present in olefin streams, presumably because olefin binding occurs through the sulfur ligand rather than the metal center. The reversible reaction of olefins with Ni[S2C2(CN)2]2n (n = 0, -1, -2) can be controlled electrochemically, where the oxidation state-dependent binding and release of olefins are fast on the electrochemical time scale. The observed tolerance to poisons and controllable electrochemical reactivity present an alternative approach to the separation of olefins from complex streams.     

羟丙基-β-环糊精与三氟氯氰菊酯的包合作用研究

［目的］研究羟丙基-β-环糊精与三氟氯氰菊酯的包合作用,进而为更好地利用拟除虫菊酯类农药奠定基础。［方法］用液相法制备羟丙基-β-环糊精·三氟氯氰菊酯包合物,用红外光谱法、显微镜观察法对该包合物进行表征。［结果］三氟氯氰菊酯的红外光谱图显示：苯环C-H的伸缩振动吸收峰在3 070.08 cm^-1处;酯键C=O和苯环C=C的伸缩振动吸收峰分别在1 723.95、1 585.80、1 585.80、1 492.84和1 447.38 cm^-1处;取代苯的吸收峰在1 009.24、960.30、813.56、756.84和697.04 cm^-1处。羟丙基-β-环糊精·三氟氯氰菊酯包合物的红外光谱图显示：CD羟基的吸收峰在3 400.06 cm^-1处;三氟氯氰菊酯苯环C-H的吸收峰在2 930.33 cm^-1处;酯键C=O的吸收峰在1 724.18 cm^-1处。显微镜观察发现：包合物溶液的亚甲蓝玻片背景为蓝色,中间分散的均匀细微的透明圆点为包合物的聚集体。［结论］三氟氯氰菊酯与羟丙基-β-环糊精可形成包合物,其包合物可制成以水为基质的农药剂型。     

2,2,2-胺三乙酰-苄胺及其稀土配合物的合成·表征与荧光性质研究

[目的]研究三脚架型稀土配合物的组成、配位状态及荧光性质。[方法]通过摩尔电导率、红外光谱、核磁共振波谱、元素分析、差热-热重分析,研究三脚架型配体2,2,2-胺三乙酰-苄胺(L)及其稀土配合物的组成、荧光性质。[结果]2,2,2-胺三乙酰-苄胺的稀土配合物的组成为:Re(NO3)3.L.4H2O(Re=La3+,Sm3+,Y3+,Tb3+,Ce3+,Eu3+),在DMF中为2∶1型电解质,其中的NO3-与金属离子以单齿形式配位。各稀土配合物在248~635℃出现2~3个放热峰,相应于配合物的各级氧化分解过程。Tb(NO3)3.L.4H2O配合物具有Tb3+的特征尖锐线状荧光;在浓度为1×10-4mol/L的甲醇溶液中,配合物的荧光强度最强。[结论]溶剂的极性越大,2,2,2-胺三乙酰-苄胺对Tb3+的敏化作用越强,配合物的荧光强度越强。