含二茂铁双Schiff碱配体及其Ni(Ⅱ)配合物电子光谱和二阶非线性光学性质的密度泛函理论研究

采用密度泛函理论(DFT)B3LYP方法,对含二茂铁双Schiff碱配体及其Ni(Ⅱ)配合物的几何构型进行优化.在得到稳定构型的基础上,采用含时密度泛函理论(TD-DFT)的B3LYP方法计算了配合物的电子光谱,并结合有限场(FF)方法研究了配体和配合物的极化率和二阶非线性光学(NLO)性质.结果表明,配体中引入Ni(...     

密度泛函理论在分子磁学中的应用2.混合桥联三核镍配合物自旋交换作用

用密度泛函理论结合对称性破损方法(DFF-BS)研究了混合桥联三核镍配合物的磁交换耦合作用．这类化合物是由三唑和异硫氰酸根桥联形成的混合桥配合物．计算表明,在标题化合物中,三唑桥传递反铁磁耦合作用,而异硫氰酸根桥传递铁磁耦合作用;并且,随着异硫氰酸根取代三唑桥的数目增加,配合物的铁磁作用增强,在一定意义上说明了混合桥磁耦合作用的加合性．Mulliken自旋布居分析表明,无论是三唑桥还是异硫氰酸根桥,它们的磁交换作用机理都是磁中心的自旋离域．分子磁轨道分析显示,对于三唑桥,在局域磁轨道之间存在着强的轨道作用,导致了反铁磁耦合;对于异硫氰酸根桥,局域磁轨道之间弱的相互作用,表现了铁磁耦合作用．对标题化合物的研究说明了DFF-BS方法可用于三核体系磁交换作用的研究．     

24元大环双核铜配合物的合成及对超氧化歧化酶的模拟

合成了三个24元大环双铜(II)配合物作为SOD模拟物, 配体由2, 6-二乙酰基吡啶与3-氧杂戊烷1, 5-二胺缩合而成, 以SCN^-, N~3^-, im^-桥联, 其中前面两个桥联双铜(II)配合物是新配合物。用多种物理方法进行了表征, 并用EPR和电子光谱研究了桥基为im^-的配合物与N~3^-, SCN^-, F^-和Br^-的键合。其中N~3^-发生轴向配位, SCN^-使im^-断裂, 与SOD的键合作用类似, F^-, Br^对模拟物无明显作用。     

Noncovalent secondary interactions in Co(II)Salen complexes: O2 binding and catalytic activity in cyclohexene oxygenation

The O2 affinity of Co(II)Salen complexes 1-4 and their reactivity in cyclohexene oxygenation reactions of Co(II)Salen complexes 1-4 are modulated by noncovalent interactions such as hydrogen bonding and steric hindrance using a functionalized diamino bridge. Higher O2 affinity is observed in the case of efficient hydrogen-bonding interactions (complex 1), while increased steric hindrance (cis vs trans diamino bridge) around the Co-coordinated O2 is influencing the reactivity of the complexes.     

Core size sensitive resonance Raman bands of metallooctaethyl and protoporphyrin complexes

The high frequency resonance Raman skeletal mode frequencies ν₂, ν₃, ν₁₀, ν₁₁ and ν₁₉ of iron complexes of metallooctaethyl porphyrins (MOEP) and metalloprotoporphyrins (MPP) are examined for their dependence on core size and methine bridge stretching force constants. The force constants of these complexes are estimated from a plot between the center-to-pyrrole nitrogen distances and the methine bridge stretching force constants of Ni, Co, Cu and Zn(OEP). Another plot between these constants and the skeletal mode frequencies of MOEP and MPP complexes confirm that as the porphyrin core size increases, the methine bridge stretching force constants are reduced and the skeletal mode frequencies are lowered. These structural correlations are used to determine the possible expansion, doming or ruffling of the porphyrin core of the complexes under study. Ferrous low spin complexes of OEP and PP and Ru^II(OEP) (Py)₂ show large deviations from these correlations, indicating strong metal—porphyrin π back-bonding.     

Multiple-Edge XAS Studies of Synthetic Iron-Copper Bridged Molecular Assemblies Relevant to Cytochrome c Oxidase. Structure Determination Using Multiple-Scattering Analysis with Statistical Evaluation of Errors

An X-ray absorption spectroscopy study has been carried out at the Fe and Cu K-edges for two bridged molecular assemblies, both of which contain an Fe-X-Cu (X = O(2)(-), OH(-)) bridge unit, some of whose features are relevant to the binuclear site of cytochrome c oxidase. The two complexes [(OEP)Fe-O-Cu(Me(6)tren)](1+) and [(OEP)Fe-(OH)-Cu(Me(5)tren)(OClO(3))](1+) have similar structural fragments around the metal centers except that they differ significantly in the bridge structure (the former contains a linear oxo bridge while the latter has a bent hydroxo bridge). We report a comparative study of these complexes using multiple-scattering (MS) EXAFS analysis and the program package GNXAS. It is found that there is a dramatic increase in the amplitude of the Fe-X-Cu MS pathway as the bridge unit approaches linearity. Full EXAFS MS analysis enables accurate quantitation of bridge metrical details and geometry for both complexes. These studies were done with an expanded version of GNXAS, which allows for simultaneous multiple-edge fitting. Such multiple-edge analysis (using both Fe and Cu edge data) allows common pathways (in this case involving the Fe-X-Cu bridge) to be constrained to be the same, thus improving the observation/variable ratio and enhancing sensitivity for determination of the bridge structure. The accuracy of the structural determination for the bridge units is evaluated by a statistical analysis methodology in which correlations among fitting parameters are identified and contour plots are used to determine random error. The overall error in the EXAFS structural determination is found by establishing the variance with the crystallographically determined values: for the EXAFS-determined parameters at distances below 4 ?, distances and angles deviated on average from crystallographic values by 0.014 ? and 1.5 degrees, respectively. It is also established that structural features in the Fe absorption preedge are diagnostic of oxo vs hydroxo ligation. The relevance of this study to the structural definition of binuclear bridged sites in cytochrome c oxidase and other metalloenzymes is considered.     

Does the Sign of the Cu–Gd Magnetic Interaction Depend on the Number of Atoms in the Bridge?

Several theoretical investigations with CASSCF methods confirm that the magnetic behavior of Cu–Gd complexes can only be reproduced if the 5d Gd orbitals are included in the active space. These orbitals, expected to be unoccupied, do present a low spin density, which is mainly due to a spin polarization effect. This theory is strengthened by the experimental results reported herein. We demonstrate that Cu–Gd complexes characterized by Cu–Gd interactions through single‐oxygen and three‐atom bridges consisting of oxygen, carbon, and nitrogen atoms, present weak ferromagnetic exchange interactions, whereas complexes with bridges made of two atoms, such as the nitrogen–oxygen oximato bridge, are subject to weak antiferromagnetic exchange interactions. Therefore, a bridge with an odd number of atoms induces a weak ferromagnetic exchange interaction, whereas a bridge with an even number of atoms supports a weak antiferromagnetic exchange interaction, as observed in pure organic compounds and also, as in this case, in metal–organic compounds with an active spin polarization effect.     

Copper(II) and nickel(II) complexes with bis(azomethine)—a condensation product of 1-phenyl-3-methyl-4-formyl-5-mercaptopyrazole with 1,3-diaminopropan-2-ol

The copper(II) and nickel(II) complexes based on bis(azomethine), which is the condensation product of 1-phenyl-3-methyl-4-formyl-5-mercaptopyrazole with 1,3-diaminopropan-2-ol, are synthesized. Bis-azomethines can form both binuclear and mononuclear complexes in which the hydroxy group is not involved in coordination. The binuclear copper(II) complexes with the acetate and pyrazolate bridges exhibit an antiferromagnetic exchange, which strength is determined by the nature of the bridge (2J = ?154 and ?424 cm^?1, respectively). The structure parameters of the coordination spheres of the complexes are determined by X-ray absorption spectroscopy. The structure of the CHCl₃ solvate of the binuclear copper(II) complex with the pyrazolate bridge is solved by X-ray diffraction analysis (CIF file CCDC 964655).     

Synthesis and characterization of propylene and butylene bridged fac-tricarbonylrhenium(I) biscarbene complexes

Nine new complexes of the type fac-[(CO)(3)ReBr(L)], where L represents a chelating bis-NHC ligand consisting of two alkylene (propylene and butylene) bridged (R') N-substituted (R) imidazoline moieties (1,1'-di-R-3,3'-R'-diimidazolin-2,2'-diylidene), were synthesized. Spectroscopic methods, elemental analysis, mass spectrometry and X-ray crystallography were employed to characterize the complexes both in solution and in solid state. The complexes were compared to the analogous complexes with smaller bridge lengths in order to reveal differences and similarities. Depending on the bridge length and the ligand size in some cases dinuclear complexes were obtained as small scale side products.     

1,3,5-均苯三羧酸根金属-有机多重框架结构配合物

综述了近年来1,3,5-均苯三羧酸(H3BTC)与金属配位形成金属配合物的研究进展。对1,3,5-均苯三羧酸根(BTC)作为桥基时的配位特点及其桥联多核配合物的合成方法和结构特点进行了简要介绍,并对今后BTC类超分子网络配合物应用与结构研究的发展方向进行了展望。     

Electronic properties of Ru(II) complexes bound to a bisphenolate bridge with low lying pi* orbitals

The synthesis and a detailed investigation into the electronic properties of mononuclear and dinuclear Ru(II) complexes of the ligand bis(2-hydroxyphenyl)-2,5-dihydropyrazine (H(2)BHD) is described. In these complexes the Ru(II) moieties are bound through O,N coordination to an anionic phenolate and the pyrazine bridge. Relatively few reports are available on the dinuclear complexes bridged across a phenolate and this study provides an opportunity to examine the impact of reduced oxygen donor ligands on metal-metal communication. The results presented here reveal some very unusual behavior whereby the apparent location of the LUMO changes between the mononuclear and dinuclear complexes. The lowest energy optical transition appears to involve the peripheral bipyridine ligand as acceptor in the mononuclear complex, whereas this ligand is not involved in the lowest energy optical transition in the dinuclear complex. The origin of this difference is not clear, however, significant changes in the electronic properties of the mononuclear complex are observed on coordination of the second metal, reflected in significant alterations in the electrochemistry of the bridge and metals as well as changes in the optical spectroscopy. The BHD(2-) bridge is shown to support weakly coupled class II behavior according to the Robin and Day classification, reflected in a K(c) of 335.     

Effect of Diamine Bridge on Reactivity of Tetradentate ONNO Nickel(II) Complexes

Two new square planar ONNO nickel(II) complexes C2_core and C3_core have been synthesized and characterized by single crystal X-ray diffraction, NMR spectroscopy, thermogravimetry, and DFT calculations. The experimental results revealed the effect of the length of diamine bridge in the ligand on the behavior of the studied complexes in the reaction with N-heterocyclic aromatic amines, while DFT calculations provided a basis for the rationalization of this observation. The complex with propylenediamine bridge ( C3_core ) readily reacts with pyridine and its derivatives to form high-spin (paramagnetic) complexes with octahedral geometry as characterized by X-ray diffraction; electron-donating substituents on the pyridine ring facilitate the coordination of axial ligands. In contrast, the complex with ethylenediamine bridge ( C2_core) does not undergo such a reaction because of the high deformation energy of the core required for the formation of C2_Py complex.     

Conformational Tuning of the Intramolecular Electronic Coupling in Molecular‐Wire Biruthenium Complexes Bridged by Biphenyl Derivatives

The synthesis and characterization of a series of biphenyl‐derived binuclear ruthenium complexes with terminal {RuCl(CO)(PMe₃)₃} moieties and different structural arrangements of the phenyl rings are reported. Electrochemical studies revealed that the two metal centers of the binuclear ruthenium complexes interact with each other through the biphenyl bridge, and the redox splittings ΔE_1/2 show a strong linear correlation with cos² ?, where ? is the torsion angle between the two phenyl rings. A combination of electrochemical, UV/Vis/NIR, and in situ IR differential spectroelectrochemical analysis clearly showed that: 1) the intramolecular electronic couplings in the binuclear ruthenium complexes could be modulated by changing ?; 2) the electronic ground state of the mixed‐valent cations changes from delocalized to localized through the biphenyl bridge with increasing torsion angle ?, that is, the redox processes of these complexes change from significant involvement of the bridging ligand to an oxidation behavior with less participation of the bridge.     

双桥连二环戊二烯基金属有机化合物的研究进展

综述了双桥连二戊二烯基金属有机化合物的研究进展，根据桥链以及金属原子 的不同，分别讨论了它们的合成、结构及在催化烯烃聚合上的应用。     

Binuclear tungsten(V) oxo-complexes with 1,1-dithiolate ligands

In this paper we report the synthesis of some new oxo and sulphido bridged tungsten(V) complexes with N-ethylanilindithiocarbamate and N,N-methylcyclohexyldithiocarbamate as ligands. These complexes have been characterised by analytical, magnetochemical and spectral methods. The results permit us to assign the formulate: W₂O₃(LL)₄, W₂O₄(LL)₂, W₂O₂S₂(LL)₂ and W₂O₃S(LL)₂. The low magnetic moments observed in these complexes, are due either to an interaction through the bridging atoms or to a direct spin-spin interaction. IR and electronic absorption spectra of these complexes are sensitive to substitution of sulphur atoms into the bridge system. The systematic changes upon bridge modification are useful in characterizing the compounds and in clarifying assignments of W-O and W-S bridge stretching frequencies. The results are discussed on the basis of structural information available for tungsten complexes.     

Ansa bis(fluorenyl) complexes as homogeneous catalysts for propylene polymerization

Preparation and characterization of new ansa-metallocene complexes containing two substituted fluorenyl ligands connected by an R₂E bridge (R = Me, Ph; E = Si, Sn) are reported. The complexes, activated with methylaluminoxane (MAO), polymerize propylene. The degree of stereospecifity of the propylene polymerization depends on the size of the hetero atom in the bridge and the position of the substituents.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2334–2339, September, 1996.     

Chromotropism studies on copper(II) compounds. Part II. Dinuclear copper(II) complexes with triply-bridged hydroxo,acetate, and halo ligands

Abstract

Two triply-bridged dinuclear copper(II) complexes of formula [LCu(μ-OH)(μ-OAc)(μ-X)CuL]X?0.5H₂O where L is a bidentate ligand of N-(pyridine-2-ylmethyl)propane-2-amine and X=Cl, 1 and Br, 2 were synthesized and characterized by elemental analyses, spectroscopic techniques (IR, UV–Vis, EPR), thermal analysis, conductance measurements, and single-crystal X-ray structure determination. The structures of both complexes are similar. The complexes show a distorted square-pyramidal arrangement around each copper(II) ion with a CuN₂O₂X chromophore in which both copper(II) ions are connected by a hydroxo bridge and a triatomic syn-syn carboxylato bridge in equatorial positions and a halide ion bridge at the axial site. The chromotropism behavior of the complexes, including solvato-, thermo-, and halochromism, were investigated in detail. Their halochromism was investigated in the pH range of 2.0–11.0 by visible absorption spectroscopy. The reversible color variations from blue to colorless are attributable to deprotonation and protonation of the ligands. The complexes show reversible thermochromism in solution due to dissociation and recombination of ligands to copper ions.     

Ureases: quantum chemical calculations on cluster models

Herein, we present results from a computational study of dinickel complexes that are relevant to the catalytic hydrolysis of urea exerted by the urease enzymes. The B3LYP density functional is used to characterize the equilibrium geometry, electronic and magnetic properties, and energies for a series of realistic complexes modeling the active site of ureases. The analysis of the theoretical results gives new insight into the structure, substrate binding, and catalytic mechanism. The water bridge between the two Ni(II) ions observed in the crystallographic structures of the ureases was assigned to a hydroxide bridge in agreement with the observed small antiferromagnetic coupling. Both monodentate and bidentate urea-bound complexes, in which urea had favorable orientations for catalysis, were characterized. Finally, two reaction mechanisms were investigated starting from the monodentate and bidentate urea-bound complexes, respectively. Both a Ni1...Ni2 bridging hydroxide and a Ni2-bound water molecule play crucial roles in the two mechanisms.     

Molecular structure of Schiff bases and their transition metal ion complexes,Part XIX. [N,N′-1,2-propanebis(pyrrol-2-yl-methyleneaminato)]-copper(II) and [N,N′-1,2-propanebis(pyrrol-2-acetyl-methyleneaminato)]-copper(II)

Summary The structures of dimeric Schiff bases and copper(II) complexes derived from (R)-(-)_D-1,2-propanediamine together with pyrrole-2-aldehyde and 2-acetylpyrrole are elucidated by use of circular dichroism spectroscopy, and it is concluded that the complexes are non-planar and of opposite chirality due to 1,3-interactions between substituents on the propylene bridge and the chromophoric units.     

Exchange interactions in some binuclear iron(III)complexes studied by EPR

The binuclear iron(III) complexes have been the subject of widespread study^1–8, mainly by use of magnetic susceptibility measurements, because of their unusual magnetic properties. Among dimeric iron compounds, especially interesting features are exhibited by complexes containing an Fe-O-Fe bridge.The oxygen bridge is not confined only to dimeric iron compounds^8–10, and thus EPR has been applied to the problem of recognizing such structures and the role of iron in bridge systems. One example of this is the attempt¹¹ to recognize complexes of Fe^III with HEDTA¹, and the quintet state spectrum was obtained. The spin Hamiltonian parameter values D and E were not calculated precisely, because of the lack of data relating to resonance field angular dependence.