Quantum-Chemical Study of Interactions between the Hydroxonium Cation and the Monomethyl Mercury Cation in Aqueous Media

The potential surface of the reaction between the polyhydrated monomethyl mercury cation and the hydroxonium cation is considered. An type reaction, resulting in solvate-separated products (mercury dication and methane molecule), was found to be thermodynamically probable. The thermal balance of the reaction is 132.3 kJ/mole. The activation energy of the limiting stage of the process is 56.7 kJ/mole.     

Modulation of Metal Carbonyl Stretching Frequencies in the Second Coordination Sphere through the Internal Stark Effect

Spectroscopic and computational examination of a homologous series of rhodium(I) pybox carbonyl complexes has revealed a correlation between the conformation of the flanking aryl-substituted oxazoline donors and the carbonyl stretching frequency. This relationship is also observed experimentally for octahedral rhodium(III) and ruthenium(II) variants and cannot be explained through the classical, Dewar–Chatt–Duncanson, interpretation of metal-carbonyl bonding. Instead, these findings are reconciled by local changes in the magnitude of the electric field that is projected along the metal-carbonyl vector: the internal Stark effect.     

Quantum-Chemical Investigation of Intermediates in the Addition of Phenylsulfenium Cation to Substituted Acetylenes

The reaction paths for the transformations of substituted acetylenes (X—CC—Y; X, Y = H, Me, Ph, CN) in reaction with phenylsulfenium cation were studied by quantum-chemical methods. It was shown that the reactions take place with the formation of acyclic and cyclic cationic intermediates. The factor that determines the structure and characteristics of these cations is the induction and polarizing action of the substituents in the acetylenes and to a lesser degree their electron-donor characteristics. The resonance effect of the phenyl substituent has a predominantly levelling action on the distribution of charges.     

Mutual Separation of Rare Earths in Monazite with Cation Exchange Elution Chromatography

Mutual separation of the individual rare earth elements (exception of cerium) in monazite from different districts was investigated by cation exchange elution method. Strong acid type cation exchange resin, Bio-Rad AG 50 Wx8 and eluting solution of a α-hydroxyisobutyric acid (α-HIBA) were used. Radioactivity tagged Eu-152, 154 or Tb-160 were used as radio active indicator for determination of the distribution coefficients by batch method or for the study of column elution conditions. By gradiently increase of the pH values from 3 to 5 in 0.3 M α-HIBA eluting solution, complete mutual separation of individual rare earth elements, exception of Dy and Y, were obtained. Dy and Y could not be separated by this scheme of separation and their elution zones were overlapped. Rare earth mixture samples of monazite from different districts were separated with this scheme and these results were compared. From this comparison followings were noticed; 1. Compositions of rare earth elements in monazite from different districts are evidently not alike. 2. Samples from Brazil and Southwestern Coast of Taiwan are much more alike in their compositions but not for those from Australia and Outskirt Island. 3. Sample from Outskirt Island has higher in contents of heavier rare earths and also Nd was higher than La.     

How Outer Coordination Sphere Modifications Can Impact Metal Structures in Proteins: A Crystallographic Evaluation

A challenging objective of de novo metalloprotein design is to control of the outer coordination spheres of an active site to fine tune metal properties. The well-defined three stranded coiled coils, TRI and CoilSer peptides, are used to address this question. Substitution of Cys for Leu yields a thiophilic site within the core. Metals such as Hg^II, Pb^II, and As^III result in trigonal planar or trigonal pyramidal geometries; however, spectroscopic studies have shown that Cd^II forms three-, four- or five-coordinate Cd^IIS₃(OH₂)_x (in which x=0–2) when the outer coordination spheres are perturbed. Unfortunately, there has been little crystallographic examination of these proteins to explain the observations. Here, the high-resolution X-ray structures of apo- and mercurated proteins are compared to explain the modifications that lead to metal coordination number and geometry variation. It reveals that Ala substitution for Leu opens a cavity above the Cys site allowing for water excess, facilitating Cd^IIS₃(OH₂). Replacement of Cys by Pen restricts thiol rotation, causing a shift in the metal-binding plane, which displaces water, forming Cd^IIS₃. Residue d -Leu, above the Cys site, reorients the side chain towards the Cys layer, diminishing the space for water accommodation yielding Cd^IIS₃, whereas d -Leu below opens more space, allowing for equal Cd^IIS₃(OH₂) and Cd^IIS₃(OH₂)₂. These studies provide insights into how to control desired metal geometries in metalloproteins by using coded and non-coded amino acids.     

Alkali Metal Cation (K+, Cs+) Induced Dissolution/Reorganization of Porous Metal Carboxylate Coordination Networks in Water

Reversible structural transformations of porous metal–organic coordination networks based on Co or Ni and the benzene‐1,2,4,5‐tetracarboxylate tetraanion among 3D (4,8)‐connected nets and a 1D zigzag chain structure occur by an unexpected dissolution/reorganization process induced by alkali metal cations (K⁺, Cs⁺) in aqueous solution (see scheme).

     

A Stable Neutral Radical in the Coordination Sphere of Aluminum

The neutral radical (Me₂‐cAAC)₂AlCl₂ ( 2 ) is stabilized by cyclic (alkyl)(amino)carbenes (cAACs). Complex 2 was synthesized by reduction of the Me₂‐cAAC:→AlCl₃ ( 1 ) adduct with KC₈ in the presence of another equivalent of Me₂‐cAAC. The crystal structure of 2 shows that the Al−C bond lengths of the two carbenes bound to the Al center are considerably different, which is likely the result of intermolecular interactions. Quantum‐chemical calculations from the gas phase give an equilibrium structure with identical Al−C bond lengths. Compound 2 exhibits monoradical character, which was confirmed by EPR measurements. A bonding analysis indicates that the unpaired electron resides mainly at the carbene carbon atoms. Compound 2 is an example for an unusual neutral Al radical.     

Multi‐Cation Coordination in Porphyrinoids

Porphyrinoid macrocycles are unbreakably linked with the coordination of central cations that drastically influence the observed behavior. A specific place has been recorded for structures where more than one cation is entrapped in a single macrocycle. It has been a characteristic feature of expanded porphyrinoids where the increased coordination space allows a multiple coordination. Because of specific steric confinements, an incorporation of more than one cation within regular or contracted porphyrinoids is more demanding but it can be realized on several ways significantly modifying the observed behavior. We will discuss synthetic strategies leading to structures with increased number of cations and the influence on the observed behavior of such modification.     

A Promising Approach for Controlling the Second Coordination Sphere of Biomimetic Metal Complexes: Encapsulation in a Dynamic Hydrogen-Bonded Capsule

The design of biomimetic models of metalloenzymes needs to take into account many factors and is therefore a challenging task. We propose in this work an original strategy to control the second coordination sphere of a metal centre and its distal environment. A biomimetic complex, reproducing the first coordination sphere, is encapsulated in a self-assembled hydrogen-bonded capsule. The cationic complex is co-encapsulated with its counter-anion or with solvent molecules. The capsule is dynamic, allowing a fast in/out exchange of the co-encapsulated species. It also provides both a hydrogen-bonding site in the second coordination sphere and a source of proton as it can be deprotonated in the presence of the complex, providing a globally neutral host-guest assembly. This simple and broad scope strategy is unprecedented in biomimetic studies. The approach appears to be a very promising method for the stabilisation of reactive species and for the study of their reactivity.     

Transition Metal Cation Salts in Organic Synthesis

Reaction of lithium diisopropylamide (LDA) with (η⁴-1,3-cyclohexadiene)Fe(CO)₃ complexes bearing functionalized side chains at C-5, under an atmosphere of carbon monoxide, gives bridged bicyclo[3,2,1]octene and bicyclo[3,3,1]nonene systems after electrophilic quenching. Under the same reaction conditions, intramolecular cyclization of acyclic (η⁴- 1,3-butadiene)Fe(CO)₃ complexes with functionalized side chains at the terminal position of the diene ligands furnishes fused bicyclo[3.3,0]octanone and bicyclo[4.3.0]nonanone derivatives after acid quenching. The addition of a variety of the highly functionalized zinc-copper reagents RCu(CN)ZnI to the (η⁷-cycloheptatrienyl)Cr(CO) gives (η⁶-cyclohepta-1,3,5-triene)Cr(CO)₃ complexes with a functionalized side-chain at the C-7 position of the ring. Intramolecular cyclization of ester-subsbtuted adducts using lithium diisopropylamide generates fused bicyclo[5.3.0]decane and bicyclo[5.4.0]undecane derivatives. The addition of a variety of the highly functionalized zinc-copper reagents RCu(CN)Znl to the (η⁴-cyclohexa-1,3-diene)Mo(CO)₂(Cp) at the terminus of the coordinated diene ligand gives [Mo(π-allyl)(CO)₂(Cp)](Cp = cyclopentadienyl) complexes with the functionalized side-chain at the C-4 position of the ring. Intramolecular cyclization of the (π-allyl)molybdenum complex containing a pendant propanoic acid unit generates the δ-lactone derivative.     

Quantum-Chemical Analysis of Coordination of Dimethylsulfoxide Molecules to Sodium and Potassium Cations

Coordination of dimethylsulfoxide molecules to the sodium and potassium cations was investigated by HF/6-31G(d)//HF/6-31G(d) and DFT(B3LYP/6-31G(d)) quantum-chemical methods. The coordination numbers of Na⁺ and K⁺ are found to be five and six, respectively. Thermal effects of complexation were calculated for each stage of the process; these were found to be 197.8, 160.1, 106.9, 88.0, 53.9 [HF/6-31G(d)] and 195.0, 158.5, 108.9, 95.7, 60.0 kJ/mole [B3LYP/6-31G(d)] for Na⁺ (one to five DMSO molecules, respectively); 146.6, 118.7, 90.2, 68.9, 70.0, 49.0 [HF/6-31G(d)] and 144.0, 117.4, 91.7, 78.9, 78.6, 56.4 kJ/mole [B3LYP/6-31G(d)] for K⁺ (one to six DMSO molecules, respectively). Structural parameters and charge distributions are given for the complexes. It is shown that solvation of sodium and potassium cations by DMSO molecules is preferable to solvation by water molecules.     

配体数与电子化物的一阶超极化率的碱金属原子序数依赖性

用MP2方法得到单配位电子化物M—X(M=Li, Na, K; X=NH3, NCH, HF)和二配位电子化物M—(FH)2(M=Li, Na, K)的几何结构. 使用高水平的QCISD/6-311++G(3df, 3pd)计算了它们的一阶超极化率β0. 在单配位的电子化物中, 单调的一阶超极化率的碱金属原子序数依赖性未表现出来, 而二配位电子化物 M—(FH)2(M=Li, Na, K)的β0值随着碱金属原子序数的增加而增加, 这与文献报道的四配位相关体系的情况一致. 这表明, 电子化物中配位数与一阶超极化率碱金属原子序数依赖性相关.     

Kinetics of Concerted Processes Occurring in the Coordination Sphere of Polynuclear Complexes

The formal kinetics of concerted processes that occur in the coordination sphere of polynuclear complexes is considered. The kinetics of consumption of one-electron oxidants or reducing agents in many-electron oxidation (reduction) reactions catalyzed by clusters mimics the kinetics of a polymolecular reaction in specific cases. These reactions are analyzed for clusters with different numbers of nuclei, and a comparison with the experimental data is made.     

Phosphorus Ylides in the Coordination Sphere of Transition Metals: An Inventory

Phosphorus ylides are not only classical reagents in organic chemistry, but also play an increasingly important role as novel components in organometallic compounds. These metallic “ylide complexes” are either synthesized from “preformed ylides” and coordination compounds by addition or substitution, on the building block principle, or they are formed, in sometimes complicated reactions, from phosphanes, metal complexes, and C₁ substrates in the coordination sphere of the metals. The resulting metal-carbon bonds are greatly modified in their properties by the immediate presence of the phosphonium center and often belong to the most stable of M-C structural units. The metal can come from any group of the periodic table, including the lanthanoids and actinoids. Numerous preparative and structural studies are gradually enabling us to gain an overall picture of the scope of this area of research.