配位化学中新型金属配合物的电子结构与成键特点

研究配合物的几何电子构型、阐明配位键的本质是配位化学中重要的理论组成部分。本文在回顾配位化学基本的成键理论基础上,介绍几例近年来具有教科书级别的国内高水平原创工作,重点阐述具有独特芳香性、低氧化态、高配位数以及锕系金属的新型金属配合物的电子结构和成键特点,对丰富和拓展配位化学的基本理论具有重要意义。     

锕系化合物荧光光谱理论研究进展

本文对锕系化合物荧光光谱的实验研究进行了系统总结,并在此基础上重点介绍了锕酰(actinyl)化合物的电子结构以及荧光光谱模拟的原理。结合我们关于铀酰-甘氨酸水合物结构、稳定性和荧光光谱模拟的研究工作,本文对锕系化合物荧光光谱理论研究的现状、理论方法和计算结果进行了综述。铀酰配合物中O-U-O单元的对称伸缩振动决定了其荧光特征,通过理论研究,结合计算化学模拟,可以解释铀酰-甘氨酸水溶液中振动分辨的实验光谱图,并阐明热带(hot band)峰强度异常高的成因。上述研究结果表明,现代计算化学和实验技术相结合,能够用于深入地分析锕系化合物的结构、光谱和性质,包括溶剂配位层、生物配体的配位结构、热力学和能量和荧光光谱等。     

基于三脚架配体构筑的锕系-配体多重键的研究进展

非水溶液体系的锕系元素化学是一个极具挑战性的前沿研究领域, 近年来在分子磁性、多重键以及小分子活化等方面获得了迅速发展. 化学键是化学科学中最重要的基本概念之一, 而金属-配体多重键是该领域重要的研究内容. 多重键的形成与锕系元素的电子结构密切相关, 相对论效应使得锕系元素的s轨道和p轨道收缩, 轨道能量降低, 收缩的s和p轨道增加了对核电荷的屏蔽效应, 从而使d和f轨道具有一定的延展性和不稳定性. 这种不稳定性降低了5f电子的结合能, 电子更容易离去, 可使锕系元素具有丰富的氧化态. 由于较高的主量子数和相对论效应, 锕系元素的5f轨道具有更大的径向延展, 在锕系元素中5f轨道的电子行为影响较大. 目前, 锕系金属-配体多重键因其独特的成键方式和电子结构特征而受到科学家的广泛关注, 在合成和分离方面存在极大的挑战, 研究锕系-配体多重键将有助于我们了解它们的电子结构和反应性. 基于口袋型拓扑结构的三脚架配体被广泛地应用于锕系-配体多重键的研究, 这为探索锕系元素的5f电子结构和锕系多重键丰富的化学行为提供了重要支撑. 本综述总结了近年来基于三脚架配体构筑的锕系-配体多重键的研究进展, 并对未来进行了展望.     

六聚吡咯大环与铀/超铀酰基离子相互作用:成键、热力学和光谱性质

采用全电子相对论密度泛函理论探索多种六聚吡咯大环锕酰基配合物(nAn;n=1~3;An=U,Np and Pu)的电子结构本质、成键规律和化学反应特性。结构优化发现大环配体空穴大小与锕酰离子尺寸相当时,配合物锕酰基采用性对规则的六角双锥结构,而当空穴尺寸相对大时,配合物则采取扭曲结构以降低体系能量。当配体相同时,随着铀、镎、钚变化,An=O伸缩振动频率逐渐变小,这与优化的键长和键级变化规律相一致。QTAIM(quantum theory of atoms in molecule)拓扑分析显示An-N为弱共价单键特征,具有较大离子性成分。依据不同铀源,得到与大环配体的反应自由能均小于146 kJ·mol~(-1),与实验合成配合物的反应能计算数值相当。对含铀配合物电子吸收光谱计算显示,低能(近红外和可见光区)的吸收带具有全部或较大的配体→金属电荷转移性质贡献。     

铀酰配合物的电子结构与化学键

本文采用群分解EHMO计算程序研究了铀酰配合物的电子结构与化学键。计算结果表明,铀酰配合物具有与UO_2~(2+)离子类似的电子结构特征,铀酰基元是典型的共价成键,而第二配体在赤面上密堆积形成离子键。这种电子结构与化学键特点被用来阐明铀酰配合物的立体化学性质以及光谱化学序列。     

希土冠醚配合物的电子结构

本文用INDO方法计算了希土冠醚配合物的分子构型、电子结构、电荷分布和键级,讨论了配位前后电荷分布特征,以及由于配位引起L→L_n电荷转移跟配合物电子结合能化学位移和配位活化的关系,解释了因冠醚内腔不同希土冠醚配合物呈现不同构型的内在原因。希土冠醚配合物的占据分子轨道以配位体轨道成分为主体(4f轨道除外),低空轨道以希土原子轨道成分为主体。其占据分子轨道可分为六组。冠醚环上引入苯环后配合物前线轨道呈现π键性质。其价键的主要贡献部份是5d轨道,其次是6p和6s。4f轨道基本上不参与成键。讨论了配合物的化学键性质及高配位数时稳定的因素。     

锕系异核双金属化合物

锕系金属有机化合物的研究已成为金属有机化学研究领域的热点之一,其化合物的合成和分离极具挑战性,其中锕系异核双金属化合物在催化和小分子活化方面有潜在的应用前景。随着人们对锕系独特电子结构及其性质的深入认识,锕系异核双金属化合物的研究也取得了一些进展。本文总结了锕系异核双金属化合物近30年的研究成果,主要包括锕系-过渡金属体系和锕系-主族金属体系的实验和理论研究。     

2-乙酰吡嗪苯甲酰腙钴、锌和铜配合物的晶体结构及荧光性质

合成了配合物[Co(L)_2](1),[Zn(L)_2](2)和[Cu_2(L)_2Cl_2](3)(HL为2-乙酰吡嗪苯甲酰腙),并通过单晶衍射、元素分析及红外光谱表征了它们的结构。单晶衍射结果表明,配合物1和2同构,配体和金属的比例为2∶1。每个配合物中,中心金属离子与来自2个阴离子配体L-的N_2O电子供体配位,形成扭曲的八面体配位构型。在双核配合物3中,Cu(Ⅱ)离子与1个阴离子三齿酰腙配体、2个μ2桥联的氯离子配位,拥有扭曲的四方锥配位构型。此外还研究了配合物的荧光性质。     

腐殖酸与锕系金属离子相互作用的研究进展

本文从腐殖酸的结构和存在形式、与锕系金属离子相互作用等两方面简要总结了近年来相关实验和理论研究进展。研究显示,腐殖酸主要通过羧基与锕系离子形成配位复合物,进而影响锕系离子在环境中的迁移。地质环境中的pH、离子强度、矿物表面等都会对腐殖酸与锕系离子的相互作用产生影响,尤以pH的影响最为显著。在较低的pH条件下,腐殖酸的出现一般会促进锕系离子在一些矿物表面的吸附;而在中性或者碱性条件下,则会减弱锕系离子在矿物表面的驻留。腐殖酸对具有氧化活性的锕系离子表现出来的还原性主要来自于还原态的醌式结构单元以及酚羟基。在还原态硫含量较高的腐殖酸中,硫也会参与氧化还原反应。论文还从实验和理论两方面展望了未来腐殖酸与锕系相互作用的研究前景。     

二苯并-18-冠-6-铵与硫氰酸钴配合物的晶体和分子结构

冠醚化合物因具有环状空腔结构的特点而有独特的配位性能.随着冠醚环上杂原子的数目、种类不同(如氧、氮、硫、磷)而有不同的配合能力及其配位本质.除此之外,冠醚环上电子密度分布对配位能力具有重要作用;金属离子的电子结构对配位性质也有很大影响.对于不是很大的冠醚环来说,通常只配位碱金属、碱土金属、镧系、锕系元素,而较难配位过渡金属离子.近年来,有人通过在冠醚环上引进吸电子基团,减低环上氧原子的电子给予体性质,以求改变配位性能.我们感兴趣的是在以普通冠醚为配体时,配合物同时包含有碱金属与过渡金属离子的配位情况与结构.作者曾对18-冠-6在有钾离子与钴离子体系中的配位情况与晶体结构作了报道,本文研究了硫氰酸铵及氯化钴与二苯并-18-冠-6反应生成的配合物结构及其特点.     

典型锕系超分子组装体的构筑原理及研究进展

锕系超分子化学是锕系元素化学的重要研究领域,可以为乏燃料后处理的配位化学基础研究提供重要信息,并为探索锕系功能材料在发光、传感、催化和分离等方面的功能应用提供关键材料体系。本文介绍了基于锕系金属离子的金属-有机超分子组装体这一新兴领域的最新研究进展。从锕系超分子组装体的构筑原理出发并结合笔者自身研究情况,对基于主客体准轮烷配体的锕系-轮烷配位聚合物、具有闭合结构的锕系配位组装体和基于超分子相互作用的锕系超分子聚合物这三类典型的锕系超分子组装体的研究进展进行了梳理和总结阐述。期望为未来新型锕系超分子组装体的设计合成提供参考,促进相关领域的进步和发展。     

EXAFS and time-resolved laser fluorescence spectroscopy (TRLFS) investigations of the structure of Cm(III)/Eu(III) complexed with di(chlorophenyl)dithiophosphinic acid and different synergistic agents

The complexes of trivalent actinide curium (Cm(III)) with di(chlorophenyl)dithiophosphinic acid ((ClPh)2PSSH) and three different neutral complexing agents as synergists in tert-butylbenzene are studied by EXAFS and time-resolved laser fluorescence spectroscopy (TRLFS). The results are compared with those from the corresponding europium (Eu(III)) complexes. The aim of these investigations is to understand the chemical interactions responsible for the high selectivity of the synergistic systems of (ClPh)2PSSH and neutral complexing agents tri-n-octylphosphine oxide, tributylphosphate and tris(2-ethylhexyl)phosphate for trivalent actinide cations in liquid-liquid extraction. In our structural chemistry study, we find that the inner coordination sphere of extracted Cm(III) and Eu(III) complexes are different. In all complexes the (ClPh)2PSSH is bound to the metal cation in a bidentate fashion and the oxygen donor of the neutral complexing agent used as synergist is directly coordinated to the metal cation. Comparison of the Cm(III) and Eu(III) complexes shows that Cm(III) preferentially binds to the sulfur of (ClPh)2PSSH, whereas Eu(III) is preferentially bound to oxygen. A good selectivity in liquid-liquid extraction is correlated with a high ratio of the sulfur coordination number to oxygen coordination number. This leads to the conclusion that the observed differences in the coordination structure between Cm(III) and Eu(III) complexes play an important role in the selectivity of these extraction systems.     

稀土-氨基多羧酸配合物的配位结构及变化规律的研究 II.二乙三胺五乙酸(dtpa)和三乙四胺六乙酸(ttha)系列

在前文的基础上,本文继续综述了氨基多羧酸类-dtpa和ttha配体与一系列稀土金属离子形成配合物的分子结构和配位结构。发现了dtpa和ttha配体与稀土金属离子的配位规律和结构变化规律。研究结果表明,稀土金属离子与dtpa和ttha配体形成配合物的配位数和配位结构明显地取决于稀土金属离子的离子半径,电子结构和氧化态以及配体的形状。     

Si?H and C?H Activation by Transition Metal Complexes: A Step Towards Isolable Alkane Complexes?

The recognition of the fundamental contributions by G. A. Olah on the elucidation of the structure of nonclassical carbocations, in the form of the award of the Nobel prize for chemistry, has recently emphasized the importance of electron-deficient bonds in the understanding of chemical bonding in organic chemistry. In the field of coordination chemistry, the formulation of electron-deficient bonds has been used for some time to describe nonclassical interactions between atoms. Traditional ligands in coordination chemistry such as amines and phosphanes bond to metal centers through their lone pair of electrons. Synergistic bonding effects dominate in the coordination of π-bonded ligands such as alkenes. In the mid-1980s the discovery of dihydrogen complexes having side-on coordination of H₂ gave fresh impetus to transition metal chemistry as well as to the understanding of the interaction of σ-coordinating ligands with transition metals. In the meantime, transiton metal complexes can be obtained with a variety of σ-coordinated X-H fragments, and their mode of bonding can be understood by a common and quite general model. The chemistry of σ-bound silane ligands is particularly varied and well-investigated. These silane ligands enable the investigation of a large range of σ-coordinated metal complex fragments up to complete oxidative addition with cleavage of the Si? H bond and formation of silyl(hydrido) complexes, which has thus also widened our general understanding of the bonding of other σ-bound ligands. Whilst there is a large range of isolable and stable H₂ and SiR₄ complexes available, there are no such alkane analogues known at present. Only when the C? H bond is part of a ligand that is already directly bonded to the transition metal center will the resulting chelate effect stabilize this agostic C-H-M interaction. The complexation of SiH₄, the simplest heavier homologue of CH₄, was achieved recently. This is a further step towards the understanding of the factors which govern σ-complexation of ligands at transition metal centers.     

Actinide Organometallic Complexes with π-Ligands

Recent developments and results from the organometallic chemistry of the actinides are reviewed. In the last one and a half years the structural data of about 15 organometallic complexes of transuranium actinides (Np or Pu) have been published, all involving π-ligands in the coordination sphere of the metal ion. On the basis of these data, a comparison of these molecules is presented. Depending on the steric demands of the ligands, effects like the actinide contraction seem to be stronger or weaker in the structural features. This indicates that the interplay between the actinide ion and the π-ligand is rather flexible, enabling the formation of stable bonds over a broad range of actinide ion oxidation states.     

Steric, electronic, and secondary effects on the coordination chemistry of ionic phosphine ligands and the catalytic behavior of their metal complexes

The effects of introducing ionic functionalities in phosphine ligands on the coordination chemistry of these ligands and the catalytic behavior of the corresponding metal complexes are reviewed. The steric and electronic consequences of such functionalizations are discussed. Apart from these steric and electronic effects, the presence of charged groups often leads to additional, supramolecular interactions that occur in the second coordination sphere of the metal complex, such as intramolecular, interligand hydrogen bonding and Coulombic repulsion. These interactions can significantly alter the behavior of the phosphine ligand in question. Such effects have been observed in phosphine-metal association/dissociation equilibria, ligand substitution reactions, and stereoisomerism in phosphine-metal complexes. By drawing general conclusions, this review offers an insight into the coordination and catalytic behavior of phosphine ligands containing ionic functionalities and their corresponding metal complexes.     

Anhydrous scandium, yttrium, lanthanide and actinide halide complexes with neutral oxygen and nitrogen donor ligands

Studies on lanthanide and actinide halide complexes with neutral O- and/or N-donor ligands have intensified in recent years due to their implications in homogeneous catalysis, magnetic and optical materials, as synthons for the synthesis of novel coordination and organometallic compounds and, for Ln(II) halide complexes, as reducing agents in organic synthesis. Synthetic strategies, structural diversity as well as some important properties and reactivities of these anhydrous metal (including scandium and yttrium) halide complexes are reviewed here. These complexes also hold potential as starting materials for constructing more sophisticated heterometallic assemblies by crystal engineering; the compounds of this class, either discrete ion-pairs or coordination polymers, being discussed separately under the heading heterometallic lanthanide and actinide halide complexes. The aim of this article is to provide a reference text for the researchers working in the lanthanide and actinide coordination chemistry field and to identify and signify the area of future research.     

Recent developments in computational actinide chemistry

This review describes recent computational investigations into the electronic and geometric structures of molecular actinide compounds. Following brief introductions to (i) the effects of relativity in chemistry and (ii) ab initio and density functional quantum chemical methods, four areas of contemporary research are discussed. These are pi backbonding in uranium complexes, the geometric structures of bis benzene actinide compounds, the valence electronic structure of the uranyl ion, and the inverse trans influence in pseudo-octahedral [AnOX5]n-. Comparisons are made with experimental studies, and similarities and differences between d- and f-block chemistry are highlighted.     

Recent Advances in the Field of Main‐Group Mono‐ and Diatomic “Allotropes” Stabilised by Neutral Ligands

The study of ligand stabilised mono‐ and diatomic zero oxidation state complexes is a young and fascinating topic. This area merges the fields of low‐oxidation‐state main‐group chemistry, homoatomic multiple bonding and fundamental coordination chemistry. As with a great deal of recent coordination chemistry within the d‐block, carbene ligands are clearly the star of the show, highlighting their importance within the p‐block as well. This Minireview focuses on the significant developments of the past two years.