以N-N基团为单桥的双核Cu(II)体系磁-结构关联的理论研究

在密度泛函数理论的框架下，应用对称性破损方法，研究了以N-N基团为单桥 的二嗪类双核Cu(II)体系的磁耦合强度及磁-结构关联。计算结果表明，随着旋转 角θ的减小，反铁磁性耦合作用逐渐减小，直至出现铁磁性耦合，与实验得到的趋 势一致。破损态能量随着θ的增大发生逆转，先降低后增大。磁耦合常数J与（ε _1-ε_2)~2的关系受到破损态能量逆转的影响。当θ由65°逐渐增大到140°时， 破损态能量依次降低，J与（ε_1 - ε_2)~2呈线性关系；当θ = 150°时，破损 态能量发生逆转，由降低变为升高，二者不再保持原有线性关系。另外，（ε_1 - ε_2)~2与θ的关系也受到破损态能量逆转的影响。在θ = 65°～140°范围内， J与θ以及（ε_1 - ε_2）~2与θ的图形相似，因此可用（ε_1-ε_2)~2代替J讨 论磁性与结构的关系；θ = 150°时，二者图形不同。破损态能量的逆转对磁耦合 常数J的影响不大，而旋转角θ是影响磁耦合常数的关键因素。     

以N-N基团为单桥的双核Cu(II)体系磁-结构关联的理论研究

在密度泛函数理论的框架下,应用对称性破损方法,研究了以N-N基团为单桥 的二嗪类双核Cu(II)体系的磁耦合强度及磁-结构关联。计算结果表明,随着旋转 角θ的减小,反铁磁性耦合作用逐渐减小,直至出现铁磁性耦合,与实验得到的趋 势一致。破损态能量随着θ的增大发生逆转,先降低后增大。磁耦合常数J与（ε _1-ε_2)~2的关系受到破损态能量逆转的影响。当θ由65°逐渐增大到140°时, 破损态能量依次降低,J与（ε_1 - ε_2)~2呈线性关系;当θ = 150°时,破损 态能量发生逆转,由降低变为升高,二者不再保持原有线性关系。另外,（ε_1 - ε_2)~2与θ的关系也受到破损态能量逆转的影响。在θ = 65°～140°范围内, J与θ以及（ε_1 - ε_2）~2与θ的图形相似,因此可用（ε_1-ε_2)~2代替J讨 论磁性与结构的关系;θ = 150°时,二者图形不同。破损态能量的逆转对磁耦合 常数J的影响不大,而旋转角θ是影响磁耦合常数的关键因素。     

小分子配位对血红素活性影响的原子-键电负性均衡方法研究

应用原子-键电负性均衡方法, 计算了血红素与小分子的配位络合物的电荷分布和Fukui函数. 血红素与氧、水、一氧化碳和一氧化氮结合时, 铁离子电荷转移到配体原子上. 活性中心铁离子的Fukui函数均大于氧和水配体中的配位氧原子, 而小于一氧化碳和一氧化氮配体中的配位碳和配位氮原子的Fukui函数. 从Fukui函数可以得出, 一氧化碳和一氧化氮很难从它们与活性中心血红素结合的配位络合物中解离出来, 而氧和水易于从它们与血红素结合的配位络合物中解离出来, 进而, 血红素可以再与其它配体结合. 血红素与KCN和NaN3抑制剂作用时, 铁离子的Fukui函数均小于与其配位的碳和氮原子, 表明在过氧化氢酶中血红素的活性作用减弱或被抑制.     

烯醇式异桥双铜配合物的合成及磁交换作用的研究

合成了２个异桥双铜配合物：［Ｃｕ２（ｐｆｈｍｐ）Ｂｒ］·２Ｈ２Ｏ（１）和［Ｃｕ２（ｐｆｈｍｐ）Ｃ３Ｈ３Ｎ２］·２Ｈ２Ｏ（２），经元素分析、红外及摩尔电导等手段推知两配合物均为烯醇式构型。变温磁化率测定结果表明，由于外源桥的影响，铜离子间的反铁磁相互作用有明显差别。     

草酸根桥联双核铜(Ⅱ)体系的磁耦合机理

应用密度泛函理论,采用对称性破损方法分析了草酸根桥联双核铜(Ⅱ)体系的磁耦合机理。在该双核体系中,两铜(Ⅱ)原子的自旋布居大小相等,符号相反,磁中心间的作用为反铁磁耦合。草酸根桥配体向磁中心的电子转移使得铜(Ⅱ)原子的自旋显著离域,这种离域有利于反铁磁耦合,草酸根桥配体中的碳原子上出现自旋极化。当铜(Ⅱ)原子的配位环境由平面四方形向四面体或四方锥变化时,反铁磁耦合的强度减弱。体系的沿前轨道主要由铜(Ⅱ)原子d轨道和配体原子p轨道构成,这种构成利于草酸根桥配体与磁中心之间的电子转移。     

基式原子诱导电负性指数的简易计算

有关基团电负性的研究,曾进行了大量的工作. 运用电负性指数对物质性能进行定量化研究可避免复杂的计算工作,笔者在前人工作的基础上导出一种简易的计算方法.     

高分辨电感耦合等离子体磁质谱法测定含铜不锈钢中痕量磷

作者通过试验,用电感耦合等离子体磁质谱(HR-ICP-MS)测定含铜不锈钢中磷含量时,采用高分辨率模式,选择分辨率为4000,在此条件下磷峰可与干扰双原子分子或离子的峰分开。又通过以含铁基的磷标准溶液优化了气体流量和离子透镜的参数,使磷的信号值提高至3×105cps。而加入45Sc作为内标元素又可显著提高测定的稳定性。分别用不锈钢样品和纯铁粉作基体,加入标准溶液制作标准曲线。结果表明:两种方法的线性均较好,分别测得实际样品的结果及其相对标准偏差也基本一致。但两种方法的检出限(3s)不同,前者为1.0μg·g^-1,后者为0.18μg·g^-1。所提出方法的样品处理过程如下:称取样品0.10g置于消解罐中,加入盐酸溶液2mL及硝酸溶液1mL,待剧烈反应缓解时,将消解罐加盖并置于微波消解仪中,于100℃消解10min,升温至200℃继续消解20min。冷却后将溶液转移至100 mL石英容量瓶中,加入0.2mg·L^-1钪内标溶液1mL,加水至刻度,摇匀。此溶液在仪器工作条件下进行HR-ICP-MS测定。对含磷51μg·g^-1的含铜不锈钢,按本方法测定所得结果的相对标准偏差(n=10)小于4%。应用本方法分析了7种标准物质或已知样品(包括低合金钢、含铜不锈钢、高温合金),并同时用ICP-AES进行校对分析。结果表明,本方法与ICP-AES的测定结果基本一致。但本方法的结果与标准物质的认定值更接近,而且对低含量磷(9μg·g^-1)也可很好测定。     

密度泛函理论下的分子电负性——Ⅵ.原子键电负性均衡模型

以密度泛函理论和电负性均衡原理为基础 ,将体系的单电子密度分割为原子的单电子密度和键的单电子密度 ,得到了分子总能量、分子中原子以及键的有效电负性的表达式 .基于这些表达式 ,提出了直接计算体系的总能量和体系中电荷分布的新方法 .此模型比其他电负性均衡方法更合理 .对大量分子的总能量和电荷分布所进行的计算结果表明所提出的原子 键电负性均衡模型是可行的 ,可以应用于确定各类生物和有机大分子的总能量和电荷分布 ,给出较EEM和MEEM模型更近于从头计算的结果     

链型四核配合物中的磁交换作用

本文用不可约张量法导出了链型BAAB四核体系的自旋Hamilton算符^H的矩阵元的一般表达式。用此式系统处理了M·Cu·Cu·M(其中M是氧化数为2的Zn, Cu, Ni,Co, Fe, Mn)即S2=S3/2,S1=S4=0,1/2,1,3/2,2,5/2的六个体系, 分别得出它们的能级和磁化率公式。我们又合成了七个链型BAAB四核配合物(CuLMX4)2, 其中L为双(N-氧化吡啶-2-甲醛)缩乙二胺(L＇)或双(N-氧化吡啶-2-甲醛)缩-1,2-丙二胺(L〃)。用CF-1型提拉样品磁强计测定了它们在4.2-300K范围内的变温磁化率, 然后用理论得出的公式对实验数据进行最小二乘法拟合, 得出磁交换常数J值和J＇值以及分裂因子g值, 所得J值说明了本文中的七个(CuLMX4)2型分子中, 中间两个Cu原子之间有弱的铁磁性交换作用, 而所得的J＇值则表明链端的M与相邻的Cu之间有弱的反铁磁性相互作用。最后用AGK理论对交换途径作了说明。     

Effect of the orbitals of the bridging group on magnetic coupling

With an AXB centrosymmetrical model system, the qualitative relationship was demonstrated among the coupling constant and the fourth power of S₁₃, which is the overlap integral between the orbitals of the bridging group and the symmetrical combination of the singly occupied orbitals of magnetic centers in the local ligand field. By using density functional theory and the broken symmetry approach HHeH, [HFH]^? and OTi₂Cl₄ systems were calculated to inspect the above conclusion. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem 88: 275–279, 2002     

Useful parameter describing magnetic interactions in extended bis‐bidentate bridged dimers

A useful parameter describing magnetic coupling interactions has been inspected in transition metal dimers, in which two transition metal ions are bridged by extended bis‐bidentate ligands. This parameter is the square of overlap integral between the spatial parts of magnetic orbitals in the broken symmetry state. The oxalato‐bridged Cu (II) dimers, in which the Cu (II) atom is either in tetrahedral or square pyramid coordination environment, have been calculated with the density functional theory coupling the broken symmetry approach. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

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．     

具有光控功能的两种氮氧自由基体系磁偶合作用的理论研究

采用密度泛函结合对称性破损态(DFT-BS)方法, 通过计算具有光控磁性分子开关功能的二氮氧自由基二芳基乙烯化合物的磁偶合常数, 合理解释了其分子结构发生开环和闭环变化时, 分子磁性发生的改变．同时设计了二氮氧自由基二甲基二氢化芘分子光控开环和闭环模型, 并用同样的方法计算了模型分子的磁偶合常数, 发现这些模型分子的磁行为类似于二氮氧自由基二芳基乙烯化合物, 有可能也具有光控磁性分子开关功能．     

About the calculation of exchange coupling constants in polynuclear transition metal complexes

The application of theoretical methods based on the density functional theory with hybrid functionals provides good estimates of the exchange coupling constants for polynuclear transition metal complexes. The accuracy is similar to that previously obtained for dinuclear compounds. We present test calculations on simple model systems based on H. He and CH(2). He units to compare with Hartree-Fock and multiconfigurational results. Calculations for complete, nonmodeled polynuclear transition metal complexes yield coupling constants in very good agreement with available experimental data.     

Structural modeling and magnetostructural correlations for heterobinuclear Cu(II)–Ni(II) complex

The magnetostructural correlation of model Cu(II)–Ni(II) heterobinuclear complexes was studied by using the broken symmetry approach within the framework of density functional theory. The antiferromagnetic coupling interaction is weakened with the decrease of the dihedral angle between the plane O1CuO2 and the plane O1NiO2 in the core moiety CuO1O2Ni of the model from 180 to 125°, in agreement with the experimental results. The ferromagnetic behavior was also predicted theoretically with dihedral angle less than 125°. The magnetic coupling interaction is reinforced with the increase of the bond angle Cu? O? Ni. The relationship between the magnetic coupling interaction and the spin density localized on the magnetic centers or on the bridging O atoms was investigated. The bond angle Cu? O? Ni for the model with lowest energy was determined and the theoretical value (104°) is a little more than the experimental value (99°). © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

密度泛函理论在分子磁学中的应用1.单氧桥联双核铁(III)[Cl_3FeOFeCl_3]~(2-)磁耦合作用

通过对桥联双核铁 (III) [Cl3FeOFeCl3] 2 - 的磁耦合常数的计算 ,探讨了密度泛函理论计算条件对计算结果的影响 .基于密度泛函理论下的破损态方法 ,着重讨论了双核Fe(III) 2 的d5 d5 电子通过氧桥的超交换作用 .研究发现分子的反铁磁通道主要是Fe(III)的dyz和dz2 与 μ O的p轨道形成的 ,具有π /π 和σ /σ 特征的超交换通道     

Broken symmetry approach to calculation of exchange coupling constants for homobinuclear and heterobinuclear transition metal complexes

The application of broken symmetry density functional calculations to homobinuclear and heterobinuclear transition metal complexes produces good estimates of the exchange coupling constants as compared to experimental data. The accuracy of different hybrid density functional theory methods was tested. A discussion is presented of the different methodological approaches that apply when a broken symmetry wave function is used with either Hartree–Fock or density functional calculations. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1391–1400, 1999     

High-spin versus broken symmetry-Effect of DFT spin density representation on the geometries of three diiron (III) model compounds

Unrestricted density functional theory calculations have been conducted on three diiron(III) synthetic model compounds containing antiferromagnetically coupled high-spin (HS) irons for which crystallographic structures and Raman spectral data are available. Three density functionals have been employed: BPW91, PWC, and BOP. The study compares the effects on optimized geometries and harmonic vibrational frequencies of spin-paired (SP) low-spin, HS, and broken symmetry antiferromagnetically coupled singlet representations of the spin density distribution. The geometries around the diiron centers in the HS and broken symmetry (BS) representations are found to be similar, both markedly different from those arising from the SP representation. Small differences between the HS and BS results are seen in bond lengths, angles, Raman frequencies, and spin densities associated with oxo and peroxo bridges between the irons.     

Terminal Alkyne Coupling Reactions Through a Ring: Effect of Ring Size on Rate and Regioselectivity

Terminal alkyne coupling reactions promoted by rhodium(I) complexes of macrocyclic NHC-based pincer ligands—which feature dodecamethylene, tetradecamethylene or hexadecamethylene wingtip linkers viz. [Rh(CNC-n)(C₂H₄)][BAr^F₄] (n=12, 14, 16; Ar^F=3,5-(CF₃)₂C₆H₃)—have been investigated, using the bulky alkynes HC≡CtBu and HC≡CAr’ (Ar’=3,5-tBu₂C₆H₃) as substrates. These stoichiometric reactions proceed with formation of rhodium(III) alkynyl alkenyl derivatives and produce rhodium(I) complexes of conjugated 1,3-enynes by C−C bond reductive elimination through the annulus of the ancillary ligand. The intermediates are formed with orthogonal regioselectivity, with E-alkenyl complexes derived from HC≡CtBu and gem-alkenyl complexes derived from HC≡CAr’, and the reductive elimination step is appreciably affected by the ring size of the macrocycle. For the homocoupling of HC≡CtBu, E-tBuC≡CCH=CHtBu is produced via direct reductive elimination from the corresponding rhodium(III) alkynyl E-alkenyl derivatives with increasing efficacy as the ring is expanded. In contrast, direct reductive elimination of Ar'C≡CC(=CH₂)Ar’ is encumbered relative to head-to-head coupling of HC≡CAr’ and it is only with the largest macrocyclic ligand studied that the two processes are competitive. These results showcase how macrocyclic ligands can be used to interrogate the mechanism and tune the outcome of terminal alkyne coupling reactions, and are discussed with reference to catalytic reactions mediated by the acyclic homologue [Rh(CNC-Me)(C₂H₄)][BAr^F₄] and solvent effects.