Water replacement on the decaaqua-di-rhodium(II) cation; synthesis of superoxo and peroxo rhodium(III) complexes with N-donor ligands

The decaaqua-di-rhodium(II) cation has been found to be an interesting starting material in the preparation of dioxygen complexes with different N-donor ligands. Treatment of aqueous HClO₄ solution of [Rh₂(H₂O)₁₀]⁴⁺ with NH₄OH/NH₃, py and/or en results in water exchange and the formation of corresponding [Rh₂^II(H₂O)_10−m(base)_n(OH)_m]^(4−m)+ derivatives. Reaction of the latter with dioxygen afforded superoxo and/or peroxo complexes, depending on reaction conditions: [Rh₂^III(O₂ ⁻)(NH₃)₈(OH)₂](ClO₄)₃ (1), [Rh₂^III(O₂ ⁻)(NH₃)₈(OH)(H₂O)](ClO₄)₄ (2), [Rh₂^III(O₂ ²⁻)(NH₃)₁₀](ClO₄)₄ · 6H₂O (3), [Rh₂^III(O₂ ⁻)(py)₈(H₂O)₂](ClO₄)₅ (4), [Rh₂^III(O₂ ²⁻)(en)₄(H₂O)₂](ClO₄)₄ (5) and [Rh₂^III(O₂ ⁻)(en)₄(H₂O)₂](ClO₄)₅ (6). All the obtained complexes were characterized by elemental analysis, mass spectrometry, UV-Vis, IR and ESR spectroscopies and magnetic measurements.     

Reactions of 2-thiopyridone and related N-, S- and C-methylated derivatives with [Rh2Cl2(CO)4]: crystal and molecular structure of fac-[Rh(MeC5H3NS)3] containing 6-methyl-2-thiopyridonato ligands

[Rh₂Cl₂(CO)₄] reacts with the ligands L (2-pyridone, 2-thiopyridone, and the isomers 6-methyl-2-thiopyridone, 2-methylmercaptopyridine, and N-methylthiopyridone) to give initially, when L/Rh = 1, the bridged-cleaved compounds cis- [RhCl(CO)₂L]. Further additions of 2-methyl- mercaptopyridine, N-methylthiopyridone, or 2-pyridone caused no further change, but 2- thiopyridone and 6-methyl-2-thiopyridone gave new cis-dicarbonyl species (L/Rh = 2) and eventually monocarbonyl species (L/Rh > 3). All these solutions are air-sensitive and air oxidation of a solution of [Rh₂Cl₂(CO)₄] with an excess of 6-methyl-2- thiopyridone gave fac-[Rh(MeC₅H₃NS)₃] the X-ray structure of which shows three equivalent chelating 6-methyl-2-thiopyridonato ligands.     

Rhodium(I) and palladium(II) complexes with the Schiff base 2,2-bis((4S)-4-benzyl-2-oxazoline)

The Schiff base 2,2^′-bis((4S)-4-benzyl-2-oxazoline) (I) and its coordination complexes with rhodium(I) and palladium(II) (and with 1,5-cyclo-octadiene and allyl ligands) have been characterised by single-crystal X-ray diffraction, mass spectrometry, ¹³C and ¹H NMR spectroscopy: [Rh(C₂₀H₂₀N₂O₂)(C₈H₁₂)][Rh₂(C₂₀H₂₀N₂O₂)₂](CF₃SO₃)₃ · (CH₃CH₂O) (II) and [Pd(C₂₀H₂₀N₂O₂)(C₃H₅)]CF₃SO₃ (III). We discuss the reasons for the formation of two complex cations for Rh(I), [Rh(C₂₀H₂₀N₂O₂)(C₈H₁₂)]⁺ (IIa) and [Rh₂(C₂₀H₂₀N₂O₂)₂]²⁺ (IIb), and only one for Pd(II).     

Study of complex formation with 2-hydroxyiminocarboxylates: specific metal binding ability of 2-(4-methylthiazol-2-yl)-2-(hydroxyimino)acetic acid

Complex formation properties of a novel water soluble thiazolyloxime 2-(4-methylthiazol-2-yl)-2-(hydroxyimino)acetic acid (H₃L¹) with Cu²⁺ and Ni²⁺ were investigated in solution by potentiometrical and spectral (UV-Vis, EPR, NMR) methods. All Cu²⁺ and most of Ni²⁺ complex species detected in solution were found to have square-planar MN₄ core with oxime and heterocyclic nitrogen atoms which was rationalized in terms of destabilizing effect of repulsive interaction between oxygen atom of carboxylic group and nitrogen atom of thiazole ring in N,O-coordinated ligand conformation. It has been found that stability of metal complexes in a series of oxime ligands is dependent upon basicity of nitrogen atom of oxime group. The thiazolyloxime forms less stable complexes with Cu²⁺ but stronger ones with Ni²⁺ ions when compared to parent 2-(hydroxyimino)propanoic acid. The lower stability obtained for Cu²⁺ complexes was elucidated in terms of negative inductive effect of the thiazole and nitrile substituents as well as an effect of intramolecular attractive interaction between thiazolyl sulfur and oxime oxygen atoms in thiazolyloxime. In the case of Ni²⁺ the complexes formed are square-planar and it is why thiazolyl ligand is more effective in metal ion binding than simple 2-(hydroxyimino)propanoic acid forming only octahedral species. The solid state structure of the Co³⁺ complex K₃[Co(HL¹)₃]·5.5H₂O (1) was studied by X-ray analysis. The thiazolyloxime ligand is coordinated to Co³⁺ via oxime nitrogen and carboxylate oxygen atoms forming five-membered chelate rings.     

On the nature of mutual inactivation between [Cp*Rh(bpy)(H2O)]2+ and enzymes – analysis and potential remedies

Pentamethylcyclopentadienyl rhodium bipyridine ([Cp*Rh(bpy)(H₂O)]²⁺) is a versatile catalyst to promote biocatalytic redox reactions. However, its major drawback lies in the mutual inactivation of [Cp*Rh(bpy)(H₂O)]²⁺ and the biocatalyst. This interaction was investigated using the alcohol dehydrogenase from Thermus sp. ATN1 (TADH) as model enzyme. TADH binds 4 equiv. of [Cp*Rh(bpy)(H₂O)]²⁺ without detectable decrease in catalytic activity and stability. Higher molar ratios lead to time-, temperature-, and concentration-dependent inactivation of the enzyme suggesting [Cp*Rh(bpy)(H₂O)]²⁺ to function as an ‘unfolding catalyst’. This detrimental activity can be circumvented using strongly coordinating buffers (e.g. (NH₄)₂SO₄) while preserving its activity as NAD(P)H regeneration catalyst under electrochemical reaction conditions.     

Homopolynuclear and heteropolynuclear Rh(III) aqua ions - a review

The kinetic inertness of Rh(III) has facilitated investigations of the early stages of hydrolytic polymerization of [Rh(OH₂)₆]³⁺. These studies have led to the synthesis, solution characterization and determination of the X-ray crystal structure of a series of polynuclear aqua ions, which range in nuclearity from binuclear to tetranuclear. The inertness of Rh(III) has enabled the identification of three structural forms of the trinuclear aqua ion which vary in their degree of condensation as well as detailed kinetic and mechanistic studies of water exchange on the binuclear aqua ion, [Rh₂(μ-OH)₂(OH₂)₈]⁴⁺, applying both ¹⁸O isotopic labeling and ¹⁷O NMR spectroscopy. Strategies have been developed which led to the quite efficient synthesis of heteropolynuclear Rh(III)-Cr(III) aqua ions and a heterobinuclear Rh(III)-Ir(III) aqua ion. Elucidation of the composition, properties and structure of heteropolynuclear aqua ions has been possible by applying techniques that had been instrumental in the development of the chemistry of homometallic aqua ions. Kinetic and thermodynamic studies of the Rh(III)-Cr(III) aqua ions generally revealed thermodynamic and activation parameters that corresponded to those for similar processes occurring at Cr(III), as may have been expected given the greater lability of Cr(III) relative to Rh(III). Inductive effects caused by the Rh(III) centers do, however, influence reactivity as exemplified by the slower than expected rate of cleavage of [CrRh₂(μ-OH)₄(OH₂)₁₀]⁵⁺.     

Chemiluminescence of lucigenin by electrogenerated superoxide ions in aqueous solutions

The chemiluminescence reaction of lucigenin (Luc²⁺?2NO₃^?, N,N′‐dimethyl‐9,9′‐biacridinium dinitrate) at gold electrodes in dioxygen‐saturated alkaline aqueous solutions (pH 10) was investigated in detail by the use of electrochemical emission spectroscopy. We noted that both O₂ and Luc²⁺ are reduced on a gold electrode in aqueous solution of pH 10 in almost the same potential region. From this fact, we expected chemiluminescence based on a radical–radical coupling reaction of superoxide ion (O₂·^?) and one‐electron reduced form of Luc²⁺ (Luc·⁺, a radical cation). Chemiluminescence was actually observed in the potential range where O₂ and Luc²⁺ were simultaneously reduced at the electrodes. The effects were examined upon addition of enzymes, i.e. superoxide dismutase (SOD) and catalase, into the solution and the substitution of heavy water (D₂O) for light water (H₂O) as a solvent on the chemiluminescence. In the presence of native and active SOD, chemiluminescence was completely absent. On the other hand, chemiluminescence was observed, unchanged in the presence of either denatured and inert SOD or catalase. In addition, the amount of chemiluminescence in D₂O solution was about three times greater than that in H₂O solution. These results, together with cyclic voltammetric results, suggest that O₂·^? participates directly in the chemiluminescence but H₂O₂ does not, and the chemiluminescence results from the coupling reaction between O₂·^? and Luc^·+ under the present experimental conditions. These chemically unstable species, O₂·^? and Luc·⁺, are produced during the simultaneous electroreduction of O₂ and Luc²⁺. The coupling reaction between those radical species would lead to the formation of a dioxetane‐type intermediate and, finally, to chemiluminescence. The chemiluminescence reaction mechanism is discussed. Copyright © 2002 John Wiley & Sons, Ltd.     

Computer simulation for effect of Pr(III) on Ca(II) speciation in human interstitial fluid

A multiphase model of metal ion speciation in human interstitial fluid was constructed and the effect of Pr(III) on Ca(II) speciation was studied. Results show that free Ca²⁺, [Ca(HCO₃)], and [Ca(Lac)] are the main species of Ca(II). Because of the competition of Pr(III) for ligands with Ca(II), the percentages of free Ca²⁺, [Ca(Lac)], and [Ca(His)(Thr)H₃] increase gradually and the percentages of CaHPO₄(aq) and [Ca(Cit)(His)H₂] decrease gradually with the increase in the total concentration of Pr(III). However, the percentages of [Ca(HCO₃)] and CaCO₃(aq) first increase and then begin to decrease when the total concentration of Pr(III) exceeds 6.070×10⁻⁴ M.     

One-dimensional chain structures constructed from tetra(acetamidato)dirhodium(II,III) complexes and square planar platinum and palladium complexes

The reaction of [Rh₂(acam)₄(H₂O)₂]ClO₄ (1) (Hacam = acetamide) with K₂PtCl₄ in aqueous solution gave crystals of [Rh₂(acam)₄(H₂O)₂][Rh₂(acam)₄{(μ-Cl)₂PtCl₂}] · 2H₂O (2). The reaction of 1 with K₂PdCl₄ produced the palladium analog [Rh₂(acam)₄(H₂O)₂][Rh₂(acam)₄{(μ-Cl)₂PdCl₂}] · 2H₂O (3) and a small amount of an aquated palladium complex [Rh₂(acam)₄{(μ-Cl)₂PdCl(H₂O)}] · H₂O (4). Complexes 2 and 3 have anionic chains of [Rh₂(acam)₄{(μ-Cl)₂MCl₂}]⁻ (M = Pt, Pd), while 4 includes neutral chains of [Rh₂(acam)₄{(μ-Cl)₂PdCl(H₂O)}]. Although all of the structures include infinite chains of (-Rh-Rh-Cl-M-Cl-)_n (M = Pt, Pd), the chain structures are different; zigzag for 2 and 3 and helical for 4. In the structures of 2 and 3, the counter cation [Rh₂(acam)₄(H₂O)₂]⁺ made a hydrogen-bonded chain with the crystallization water molecules. The cationic chains and the anionic chains are connected with hydrogen bonds. In the structure of 4, the chains are also linked together by direct hydrogen bonds between the chains and those with the crystallization water molecules. ESR spectra of the powdered samples of 2 and 3 at 77 K were consistent with a rhombic structure: for 2, g₁ = 2.111, g₂ = 2.054, g₃ = 2.004; for 3, g₁ = 2.115, g₂ = 2.057, g₃ = 2.007. These results indicate that there is a spin flip-flop exchange between the cations, [Rh₂(acam)₄(H₂O)₂]⁺, and the units in the anionic chains. The electrical conductivities of 2 and 3 were in the order of 10⁻⁷ S cm⁻¹ at room temperature.     

Identity of the rhizotoxic aluminium species

The aluminium (III) released from soil minerals to the soil solution under acid conditions may appear as hexaaquaaluminium (Al(H₂O)₆ ³⁺, or Al³⁺ for convenience) or may react with available ligands to form additional chemical species. That one or more of these species is rhizotoxic (inhibitory to root elongation) has been known for many decades, but the identity of the toxic species remains problematical for the following reasons. 1. Several Al species coexist in solution so individual species cannot be investigated in isolation, even in artificial culture media. 2. The activities of individual species must be calculated from equilibrium data that may be uncertain. 3. The unexpected or undetected appearance of the extremely toxic triskaidekaaluminium (AlO₄Al₁₂(OH)₂₄(H₂O)₁₂ ⁷⁺ or Al₁₃) may cause misatribution of toxicity to other species, especially to mononuclear hydroxy-Al. 4. If H⁺ ameliorates Al³⁺ toxicity, or vice versa, then mononuclear hydroxy-Al may appear to be toxic when it is not. 5. The identity and activities of the Al species contacting the cell surfaces are uncertain because of the H⁺ currents through the root surface and because of surface charges. This article considers the implications of these problems for good experimental designs and critically evaluates current information regarding the relative toxicities of selected Al species. It is concluded that polycationic Al (charge >2) is rhizotoxic as are other polyvalent cations.     

Sugar interaction with uranium ion. Synthesis,spectroscopic and stmctural analysis of UO2-sugar complexes containing D-glucuronate moiety

Interaction between D-glucuronic acid and hydrated uranyl salts has been studied in aqueous solution and solid complexes of the type UO₂(D- glucuronate)X·2H₂0 and UO₂(D-glucuronate)₂·2H₂O, where X = CI⁻, Br⁻ or NO₃⁻, are isolated and characterized by means of FT-IR and proton-NMR spectroscopy.On comparison with the structurally identified Ca(D-glucuronate)Br·3H₂O compound, it is concluded that the UO₂²⁺ cation binds to two D- glucuronate moieties in uranylsugar complexes via O6, O5 oxygen atoms (ionized carboxyl group) of the first and O6′, 04 (non-ionized carboxyl group) of the second sugar moiety, whereas in the UO₂(D- glucuronate)₂·2H₂O salt the uranyl ion is bonded to two sugar anions through O6, O6′ oxygen atoms of the ionized carboxyl group, resulting in a six- coordination geometry around the uranium ion. The strong intermolecular hydrogen bonding network of the free acid is rearranged upon sugar metalation and the sugar moiety showed β-anomer conformation both in the free acid and in these uranylsugar complexes.     

New rhodium complexes of the tetradentate ligand bis(diacetylmonoxime-imino)propane 1,3 (H2dopn): synthesis and crystal structure of trans-[Rh(Hdopn)Cl]2 and trans-[Rh(Hdopn)(I)2]

The reaction between [Rh(H₂O)₆](ClO₄)₃ and the monoanion Hdopn⁻ (H₂dopn=bis(diacetylmonoxime-imino)propane 1,3=3,9-dimethyl-4,8-diazaundeca-3,8-diene-2,10-dione dioxime) afforded a new dimeric rhodium(II) compound of formula [Rh(Hdopn)(H₂O)]₂(ClO₄)₂ · H₂O (1). Treatment of methanolic solution of 1 with NaX (X=Cl⁻, Br⁻, I⁻) results in the replacement of water with halides in 1, leading to the formation of [Rh(Hdopn)X]₂ rhodium(II) dimers. The X-ray crystal structure of [Rh(Hdopn)Cl]₂ · 0.5H₂O (2) was determined showing a [Rh(II)-Rh(II)] core. Upon the reaction of 1 with NaI carried out in air, [Rh(Hdopn)(I)₂] (3) was isolated and characterized by a single-crystal X-ray diffraction analysis.     

A 31P1H NMR study of the reactions of [Rh2(μ-Cl)2(cod)2] with unsymmetrical,bidentate ligands and hydrogen

[Rh₂(μ-Cl)₂(cod)₂] reacts with Ph₂PCH₂CH₂OMe (PC₂O), Ph₂P(CH₂)₃NMe₂ (PC₃N), PBuⁿPh₂ or PPh₃ to give [Rh(cod)L₂]Cl (L = PC₂O, PC₃N, PBuⁿPh₂, PPh₃). In the presence of hydrogen, [Rh(cod)L₂]Cl is converted to [RhClH₂L₃]. In contrast, [Rh(cod)(PC₂O)₂]BPh₄ reacts with H₂ to give [RhH₂(PC₂O)₂S₂]BPh₄ (S = solvent). With Ph₂PCH₂CH₂NMe₂ (PC₂N) or Ph₂PCH₂CH₂SMe (PC₂S), [Rh₂(μ-Cl)₂(cod)₂] reacts to form the chelate complexes cis- [Rh(PC₂N)₂]⁺ or cis-[Rh(PC₂S)₂]⁺, neither of which reacts with hydrogen under ambient conditions. The products of the reactions are characterized in situ by ³¹P¹H NMR spectroscopy.     

Structure of binuclear Rh(II) carboxylato complexes with 2,2-bipyridine and an unprecedented rhodium wire with Rh4 core

Structures of rhodium(II) binuclear complexes [Rh₂(OOCCH₃)₂(bpy)₂(H₂O){(CH₃)₂CHOH}][B(C₆H₅)₄]₂ · H₂O (1), [Rh₂Cl₂(OOCCH₃)₂(bpy)₂] · 2H₂O (2), [Rh₂Br₂(OOCCH₃)₂(bpy)₂] · 3H₂O (3), and [Rh₂I₂(OOCCH₃)₂(bpy)₂] (4), as well as an unprecedented wire with infinite Rh-Rh chain, {[Rh₄(μ-OOCH)₄(bpy)₄](BF₄)}_n · 0.5nC₄H₈O₂ (5), have been determined and discussed. Mass spectra of complexes [Rh₂(OOCMe)₂(bpy)₂(H₂O)₂](MeCOO)₂ and [Rh₂(OOCMe)₂(phen)₂(H₂O)₂](MeCOO)₂ have showed stability of polynuclear cations with rhodium in oxidation states in the range +1.25 to +1.75.     

A Simple Synthetic Strategy toward Defect‐Rich Porous Monolayer NiFe‐Layered Double Hydroxide Nanosheets for Efficient Electrocatalytic Water Oxidation

In this work, porous monolayer nickel‐iron layered double hydroxide (PM‐LDH) nanosheets with a lateral size of ≈30 nm and a thickness of ≈0.8 nm are successfully synthesized by a facile one‐step strategy. Briefly, an aqueous solution containing Ni²⁺ and Fe³⁺ is added dropwise to an aqueous formamide solution at 80 °C and pH 10, with the PM‐LDH product formed within only 10 min. This fast synthetic strategy introduces an abundance of pores in the monolayer NiFe‐LDH nanosheets, resulting in PM‐LDH containing high concentration of oxygen and cation vacancies, as is confirmed by extended X‐ray absorption fine structure and electron spin resonance measurements. The oxygen and cation vacancies in PM‐LDH act synergistically to increase the electropositivity of the LDH nanosheets, while also enhancing H₂O adsorption and bonding strength of the OH* intermediate formed during water electrooxidation, endowing PM‐LDH with outstanding performance for the oxygen evolution reaction (OER). PM‐LDH offers a very low overpotential (230 mV) for OER at a current density of 10 mA cm^?2, with a Tafel slope of only 47 mV dec^?1, representing one of the best OER performance yet reported for a NiFe‐LDH system. The results encourage the wider utilization of porous monolayer LDH nanosheets in electrocatalysis, catalysis, and solar cells.     

Theoretical Studies on α-Helix—DNA Interactions

Abstract

The ¹H NMR relaxation effects produced by paramagnetic Cr(III) complexes on nucleoside 5′-mono- and -triphosphates in D₂O solution at Ph′=3 were measured. The paramagnetic probes were [Cr(III)(H₂O) ₆]³⁺, [Cr(III)(H₂O)₃ (HATP)], [Cr(III)(H₂O)₃(HCTP)] and [Cr(III) (H₂O)₃(UTP)^?, while the matrix nucleotides (0.1 M) were H₂AMP, HIMP^?, and H₂ATP^2-. For the aromatic base protons, the ratios of the transverse to longitudinal paramagnetic relaxation rates (R_2p/R_1p) for the [Cr(III)(H₂O)₆]³⁺/H₂ATP^2-, [Cr(III)(H₂O)₃(HATP)]/H₂ATP^2-, [Cr(III)(H₂O)₃(HCTP)]/H₂ATP² and [Cr(III)(H₂O)₃(UTP)]^?/H₂ATP² systems were below 2.33 so the dipolar term predominates. For a given nucleotide, R_1p for the purine H(8) signal was larger than for the H(2) signal with the [Cr(III)(H₂O)₆]³⁺ probe, while R_1p for the H(2) signal was larger with all the other Cr(III) probes. Molecular mechanics computations on the [Cr(III)(H₂O)₄(HPP)(α,β)], [Cr(III)(NH₃)₄(HPP)(α,β)], [Co(III)(NH₃)₃(H₂PPP)(α,βγ)] and [Co(III)(NH₃)₄(HPP)(α,β)] complexes gave calculated energy-minimized geometries in good agreement with those reported in crystal structures. The molecular mechanics force constants found were then used to calculate the geometry of the inner sphere [Cr(III)(H₂O)₆]³⁺ and [Cr(III)(H₂O)₃(HATP)(α,βγ)] complexes as well as the structures of the outer sphere [Cr(III) (H₂O)₆]³⁺-(H₂AMP) and [Cr(III)(H₂O)₆]-(HIMP)^? species. The gas-phase structure of the [Cr(III)(H₂O)₃(HATP)(α,βγ)] complex shows the existence of a hydrogen bond interaction between a water ligand and the adenine N(7) (O…N = 2.82 Å). The structure is also stabilized by intramolecular hydrogen bonds involving the -O(2′)H group and the adenine N(3) (O…N = 2.80 Å) as well as phosphate oxygen atoms and a water molecule (O…O = 2.47 Å). The metal center has an almost regular octahedral coordination geometry.

The structures of the two outer-sphere species reveal that the phosphate group interacts strongly with the hexa-aquochromium probe. In both complexes, the nucleotides have a similar “anti” conformation around the N(9)-C(l′) glycosidic bond. However, a very important difference characterizes the two structures. For the (HIMP)^? complex, strong hydrogen bond interactions exist between one and two water ligands and the inosine N(7) and O(6) atoms, respectively (O…O = 2.63 Å O…N = 2.72, 2.70 Å). For the H₂AMP complex, the [Cr(III) (H₂O)c]³⁺ cation does not interact with N(7) since it is far from the purine system. Hydrogen bonds occur between water ligands and phosphate oxygens. The Cr-H(8) and Cr-H(2) distances revealed by the energy-minimized geometries for the two outer sphere species were used to calculate the R_1p values for the H(8) and H(2) signals for comparison with the observed R_1p values: 0.92(c), 1.04(ob) (H(8)) and 0.06(c), 0.35(ob) (H(2)) for H₂AMP; and 3.76(c), 4.53(ob) (H(8)) and 0.16(c), 0.77(ob) s^?1 (H(2)) for HIMP^?. These results suggest that the dynamic relaxation effects can be only partially understood with molecular mechanics computations, although the success of the geometry calculations suggests that future efforts in the development of computational methods are justified.     

D-glucose interaction with uranium ion. Synthesis,spectroscopic and structural characterization of uranylglucose adducts and the effect of metal cation binding on the sugar anomeric structures

The interaction of D-glucose with hydrated uranyl salts has been investigated in solution and solid adducts of the type UO₂(D-glucose)X₂·2H₂O, where X = Cl⁻, Br⁻, NO_3⁻ and 0.5 SO_4²⁻ have been isolated. These adducts are characterized by means of FT-IR, ¹H NMR and molar conductivity measurements.Spectroscopic evidence suggested that UO_2²⁺ cation could be bonded to one D-glucose molecule (possibly through O(1)H and O(2)H hydroxyl groups) and to two H₂O, resulting in six-coordination around the uranium ion.The strong sugar H-bonding network is perturbed, on metal ion interaction and the D-glucose α-anomeric structure is favoured, upon uranyl cation coordination.     

Syntheses of linear-type S-bridged trinuclear complexes composed of heavy d metal ions and 2-aminoethanethiolate: comparative characterization by X-ray diffraction, spectroscopy and electrochemistry

The S-bridged trinuclear complexes composed of heavy d⁶ metal ions, [Rh^III{M(aet)₃}₂]³⁺ (M=Ir^III(1), Rh^III(2); aet = 2-aminoethanethiolate), have been prepared by the reactions of fac(S)-[M(aet)₃] with RhCl₃ · 3H₂O. The complexes were separated into meso (1a, 2a) and rac (1b, 2b) isomers by SP-Sephadex C-25 column chromatography. 1b and 2b were optically resolved by the column chromatographic method and characterized by CD spectroscopy. Crystal structures of 1a, 1b and 2a were determined by X-ray diffraction, and it was found that they consist of linear-type trinuclear structures. The central Rh(III) ion in the present complexes has d⁶ electronic configuration with the non-degenerated A-type cubic field term, and showed long Rh?M distances, acute S-M-S angles and obtuse Rh-S-M angles. These are in contrast with the complexes having the degenerated T-type cubic field term such as [M^′{M(aet)₃}₂]ⁿ⁺ (M^′=V^III, Mo^IV and Re^III, M=Ir^III, Rh^III, n=3 or 4). All the isomers have been comparatively characterized and discussed in solid state and the solution for spectrochemical and electrochemical properties.     

Supramolecular assemblies of [Mo3Se4Clx(H2O)9−x] with cucurbituril; complementarity control through the variation of x

From solutions of seleno bridged triangular cluster Mo₃Se₄(aq)⁴⁺ in HCl, crystalline adducts with cucurbituril (Cuc, C₃₆H₃₆N₂₄O₁₂) of different composition, depending on HCl concentration, were isolated. From 2 M HCl, a monosubstituted cationic cluster crystallizes as {[Mo₃Se₄Cl(H₂O)₈]₂(C₃₆H₃₆N₂₄O₁₂)}Cl₆·16H₂O (1). Increase in HCl concentration to 6 M gives a pentasubstituted anionic species, (H₃O)₂[Mo₃Se₄Cl₅(H₂O)₄]₂(C₃₆H₃₆N₂₄O₁₂)·15H₂O (2). The crystal structures of 1 and 2 were determined by X-ray crystallography. Each portal of Cuc in 1 is covered with cluster cations [Mo₃Se₄Cl(H₂O)₈]³⁺ like a ‘lid’ on a ‘barrel’. Six water molecules in the trans position to the core μ₂-Se form complementary hydrogen bonds with oxygen atoms of Cuc (O?O, 2.713-3.067 Å). In 2 the complementarity is lost and the main structure building factor is short Se?Se interactions (Se?Se, 2.96-3.43 Å) between two adjacent anionic clusters. Stereochemistry of halide substitution in the triangular clusters M₃Q₄ is analyzed.     

Computer simulation for effect of Pr(III) on Ca(II) speciation in human interstitial fluid

A mutiphase model of metal ion speciation in human interstitial fluid was constructed and the effect of Pr(III) on Ca(II) speciation was studied. Results show that Ca(II) mainly distributes in free Ca²⁺, [Ca(HCO₃)], and [Ca(Lac)]. Because of the competition of Pr(III) for ligands with Ca(II), with the total concentration of Pr(III) rising, the percentages of free Ca²⁺, [Ca(Lac)] and [Ca(His)(Thr)H₃], gradually increase and the percentages of CaHPO₄(aq) and [Ca(Cit)(His)H₂] gradually decrease. However, the percentages of [Ca(HCO₃)] and CaCO₃(aq) first increase, and then begin to decrease when the total concentration of Pr(III) exceeds 6.070×10⁻⁴ M.