Transition metal-chelating surfactant micelle templates for facile synthesis of mesoporous silica nanoparticles

Highly ordered mesoporous silica nanoparticles with tunable morphology and pore-size are prepared by the use of a transition metal-chelating surfactant micelle complex using Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ ions. These metal ions formed a metal-P123 micelle complex in an aqueous solution, while the metal ions are chelated to the hydrophilic domain such as the poly(ethylene oxide) group of a P123 surfactant. The different complexation abilities of the utilized transition metal ions play an important role in determining the formation of nano-sized ordered MSNs due to the different stabilization constant of the metal-P123 complex. Consequently, from a particle length of 1700 nm in the original mesoporous silica materials, the particle length of ordered MSNs through the metal-chelating P123 micelle templates can be reduced to a range of 180–800 nm. Furthermore, the variation of pore size shows a slight change from 8.8 to 6.6 nm. In particular, the Cu²⁺-chelated MSNs show only decreased particle size to 180 nm. The stability constants for the metal-P123 complex are calculated on the basis of molar conductance measurements in order to elucidate the formation mechanism of MSNs by the metal-chelating P123 complex templates. In addition, solid-state ²⁹Si, ¹³C-NMR and ICP-OES measurements are used for quantitative characterization reveal that the utilized metal ions affect only the formation of a metal-P123 complex in a micelle as a template.     

Hierarchically organized silica monoliths: influence of different acids on macro- and mesoporous formation

The influence of different acids, such as hydrochloric acid, sulfuric acid, nitric acid, hydrobromic acid and acetic acid on the polymerization-induced phase separation process in the formation of hierarchically organized silica monoliths was investigated in detail. Special emphasis is given to systems synthesized from tetrakis(2-hydroxyethoxy)silane (EGMS) or tetramethoxysilane (TMOS) as the silica source in the presence of Pluronic^® P123 serving as structure-directing agent. The obtained silica monoliths exhibited a co-continuous and cellular macroporous structure comprising 2D hexagonally arranged mesopores with high specific surface areas ranging from 320–787 m² g^?1 independent of the applied silane precursor and regardless whether hydrochloric acid or sulfuric acid was used. A drastic change in macropore morphology to closed pores or particulate structures was observed for nitric, bromic as well as acetic acid. For sulfuric and nitric acid, the influence on the mesostructure was not as pronounced and 2D hexagonally arranged mesopores were obtained. With bromic and acetic acid a loss in mesopore ordering has been observed. Best developed hierarchically organized networks with respect to a co-continuous, cellular macroporous network, specific surface area and 2D hexagonally arranged mesopores were obtained for EGMS as well as for TMOS with P123 in sulfuric acid.

     

Investigations of the electronic structure of d transition metal oxides belonging to the perovskite family

Computational and experimental studies using linear muffin tin orbital methods and UV-visible diffuse reflectance spectroscopy, respectively, were performed to quantitatively probe the relationships between composition, crystal structure and the electronic structure of oxides containing octahedrally coordinated d⁰ transition metal ions. The ions investigated in this study (Ti⁴⁺, Nb⁵⁺, Ta⁵⁺, Mo⁶⁺, and W⁶⁺) were examined primarily in perovskite and perovskite-related structures. In these compounds the top of the valence band is primarily oxygen 2p non-bonding in character, while the conduction band arises from the π∗ interaction between the transition metal t_2g orbitals and oxygen. For isostructural compounds the band gap increases as the effective electronegativity of the transition metal ion decreases. The effective electronegativity decreases in the following order: Mo⁶⁺>W⁶⁺>Nb⁵⁺∼Ti⁴⁺>Ta⁵⁺. The band gap is also sensitive to changes in the conduction band width, which is maximized for structures possessing linear M-O-M bonds, such as the cubic perovskite structure. As this bond angle decreases (e.g., via octahedral tilting distortions) the conduction band narrows and the band gap increases. Decreasing the dimensionality from 3-D (e.g., the cubic perovskite structure) to 2-D (e.g., the K₂NiF₄ structure) does not significantly alter the band gap, whereas completely isolating the MO₆ octahedra (e.g., the ordered double perovskite structure) narrows the conduction band width dramatically and leads to a significant increase in the band gap. Inductive effects due to the presence of electropositive “spectator” cations (alkali, alkaline earth, and rare-earth cations) tend to be small and can generally be neglected.     

Metalated Container Molecules

The coordination chemistry of metalated container molecules is currently attracting much interest, because the properties of such compounds are often different from those of their constituent components. By adjusting the size and form of the binding cavity it is often possible to coordinate coligands in unusual coordination modes, to activate and transform small molecules, or to stabilize reactive intermediates. Such compounds also allow for an interplay of molecular recognition and transition‐metal catalysis, and for the construction of more effective enzyme mimics. Consequently, a number of research groups are involved in the development of new supporting ligands that create confined environments about active metal coordination sites. This research report briefly reviews recent progress in this field including the results of my own group. It is shown that N‐functionalized derivatives of Robson‐type macrocyclic hexaaza‐dithiophenolate ligands form bioctahedral transition metal complexes of the type [(L^R)M₂(μ‐L′)]⁺ (M = Mn, Fe, Co, Ni, Zn) with an overall calixarene‐like structure. These complexes are amongst the first prototypes for polynuclear complexes with well defined binding cavities. Since the active coordination site L′ is accessible for a wide range of exogenous coligands, the [(L^R)M₂(μ‐L′)] complexes exhibit a rich coordination chemistry. It is demonstrated that the presence of the binding cavity influences many properties of the binuclear [(L^R)M^II₂]²⁺ complex fragments, including color, molecular and electronic structure, hydrogen bonding interactions, redox potential, complex stability, and reactivity. The unusual properties of the complexes can be traced back to complementary host‐guest interactions and the distinct size and form of the binding pocket of the [(L^Me)M₂]²⁺ fragments.     

溶胶-凝胶伴随相分离制备SiO2多孔块体

以正硅酸甲酯(TMOS)为前驱体, 0.01 mol·L^-1盐酸(HCl)为催化剂, 环氧丙烷(PO)为凝胶促进剂, 粘均分子量(M_v)为10000的聚氧化乙烯(PEO)为相分离诱导剂, 采用溶胶-凝胶伴随相分离制备SiO₂多孔块体材料,利用差热分析(DTA)、傅里叶变换红外(FT-IR)光谱、扫描电镜(SEM)、X射线衍射(XRD)、汞压、N₂吸附/脱附等测试技术对所制得的SiO₂多孔块体进行了表征, 探讨了环氧化物调控溶胶-凝胶以及PEO诱导相分离机理. 结果表明, 加入PEO能诱导SiO₂凝胶发生相分离, 当PEO/TMOS摩尔比为0.0018时, 可以获得共连续多孔结构的SiO₂块体材料, 其大孔孔径分布在1-3 μm之间, 比表面积达719 m²·g^-1, 孔体积为0.48 m³·g^-1. 环氧丙烷因其环氧原子的强亲核性和不可逆的开环反应, 促进溶胶-凝胶转换, 同时借助吸附在SiO₂低聚物上的PEO诱导SiO₂凝胶相分离, 从而制备共连续大孔及骨架结构的多孔块体.     

Ordre local dans quelques verres fluores du systeme PbF2MIItF2MIIItF3 par EXAFS

The local environment of transition metal (M_t) and lead has been studied by EXAFS for some fluoride glasses in the system PbF₂M^II_tF₂M^III_tF₃ (M^II_t = Mn²⁺, Zn²⁺; M^III_t = Fe³⁺, Ga³⁺). Theoretical phase shifts and backscattering amplitude are used after testing with crystallized fluorides of various structures. Transition metals are sixfold coordinated and M_tF distances are very close to those known in crystallized compounds. Lead has eight to nine fluorine neighbors forming a very distorted polyhedra. Radial distributions, partially corrected for phase shifts, show a very weak second peak but the second neighbors nature and the distances cannot be determined without ambiguity.     

三维有序大孔-介孔二氧化硅的可控制备及表征

以聚甲基丙烯酸甲酯(PMMA)胶晶为大孔模板、嵌段共聚物P123为介孔模板,利用双模板剂法进行了三维有序大孔-介孔二氧化硅材料的制备研究。采用SEM、TEM、低角XRD以及N₂吸脱附技术对样品进行了表征。结果表明,通过简单的调控PMMA胶晶模板的组装过程,就可以调变合成材料中的大孔结构,从而轻松地实现可控的制备出具有网状或者层状结构的三维有序大孔-介孔二氧化硅材料,并提出了其可能的形成机理。此外,所制备的三维有序大孔-介孔二氧化硅样品均具有较大的BET比表面积(>550m₂·g^-1),大孔孔径200nm左右,介孔孔径分布集中于3.5nm左右。     

Raman study of cation distribution in the scheelite-like double molybdates and tungstates

Compounds M⁺ M³⁺ (TO₄)₂ have been investigated (M⁺, M³⁺ are alkaline and rare earth metals, respectively; T=Mo, W). The way of cation distribution (statistical or orderec) is given by the ratio of their ionic radii. The boundary between the distributions has been determinea: r _ion (M⁺)/r _ion (M³⁺)=1.3–1.32. In molybdates the cations are partly ordered even when M⁺ and M³⁺ have close dimensions because they interact with each other. The compounds KLa(MoO₄)₂ and KN l(MoO₄)₂ fall within the transition range and have, therefore, a complex polymorphic composition. The phase transition from the high-to low-temperature form of KLa(MoO₄)₂ is identical to the corresponding transition in KEu(MoO₄)₂ known from X-ray studies.Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Struktumoi Khimii, Vol. 34, No. 4, pp. 42–58, July–August, 1993.Translated by L. Smolina     

An investigation of Prussian Blue analogues by Mössbauer spectroscopy and magnetic susceptibility

The Mössbauer spectra and magnetic susceptibilities have been obtained for a series of Prussian Blue analogues of general formula M_j^A[M^B(CN)₆]_k·mH₂O where M^A and M^B are transition metal ions, j and k vary with the oxidation states of M^A and M^B and m typically has values from 8 to 14. The compounds were prepared from the hexacyano acids or with large quaternary ammonium counterions and are therefore not contaminated with alkali cations. In each analogue, A or B is iron and the second metal is Mn, Cu, Co, Cr or Ru. In each case it was possible to assign the site (A or B), oxidation state and spin state to each transition metal ion. This group of compounds are all class II mixed valence species from their colours, but do not show evidence of linkage isomerism or redox changes compared to the starting materials. The Mössbauer linewidths are consistent with the Ludi model of Prussian Blue.     

Mercury(II) oxide as a ligand. III. Far Infrared Spectra of the Addition Compounds of the transition metal sulphates and selenates

A study of the far infrared spectra (700—10 cm^?1) of the divalent transition metal HgO complexes has confirmed the earlier conclusion that the compounds with formula M^IIS(e)O₄ · 2 HgO · (H₂O) resemble HgSO₄ · 2 HgO closely in structure, whereas a lower HgO content indicates a breaking of the HgO framework and coordination of the M²⁺-ions to the oxo anions.     

Ternary Alkali Metal Transition Metal Acetylides

The first alkali metal transition metal acetylides of general composition A₂M⁰C₂ (A = Na ? Cs, M⁰ = Pd, Pt) were obtained by solid state reactions of alkali metal acetylides with palladium and platinum. They are characterized by chains, which are separated by alkali metal ions. Analogous chains also separated by alkali metal ions are the characteristic structural feature of acetylides of composition AM^IC₂, which are accessible by reacting AC₂H with M^II in liquid ammonia (A = Li ? Cs, M^I = Cu, Ag, Au). Despite their structural similarities they possess different properties, as acetylides of composition A₂M⁰C₂ are semiconductors with very small indirect band gaps and slightly extended C–C distances compared to a C–C triple bond, whereas acetylides of composition AM^IC₂ show a typical salt‐like behavior with C–C distances close to the expected value for a C–C triple bond of 120 pm. But with the help of simple chemical models these differences can be made plausible. Furthermore, it is shown that only by a combination of different methods (powder diffraction with X‐rays and neutrons, solid state NMR spectroscopy, Raman spectroscopy) it was possible to characterize this new class of compounds structurally and chemically.     

Molecular-orbital treatment of complex cations of magnesium and beryllium with acetonitrile

Semiempirical MO calculations of the self-consistent charge and configuration (SCCC ) method are reported for the acetonitrile–metal solvated species (CH₃CN)_xMⁿ⁺, where M = Be²⁺ and Mg²⁺. Comparison of the delocalization energies for various chemical structures x = 1, 2, 3, 4, 6 leads to an expectation of a tetrahedral structure for the Be²⁺ species and an octahedral structure for the Mg²⁺ species. The electronic nature of the donor–acceptor interaction is also discussed.     

Exploration of Metal-Metal Charge Transfer (MMCT) and its Effect in Generating New Colored Compounds in Mixed Metal Oxides

Compounds belonging to the palmierite structure, (Zn_3−xM_x)A₂O₈ (M=Co, Ni, Cu and A=V, P) have been prepared employing solid state methods. The transition metal substituted compounds of Zn₃V₂O₈ exhibits colors that are unique varying from mint green to forest green for Co²⁺ ions. The observed colors were understood based on the allowed d-d transitions and metal to metal charge transfer (MMCT) transitions. The MMCT transitions involve partially filled d-orbitals of Co²⁺ (3d⁷), Ni²⁺ (3d⁸), and Cu²⁺ (3d⁹) ions and the V⁵⁺ ions (3d⁰). The spinel compounds, Zn_2−xCo_xMO₄ (M=Ti, Sn) were also prepared to understand the MMCT transitions in the compounds. Band structure calculations were carried out to understand the participating orbitals near the Fermi level and the band gap. The calculations support the idea that the substitution of transition elements in the palmierite structure reduces the overall band gap from 3.18 eV for Zn₃V₂O₈ to 2.61 eV Zn_2.5Co_0.5V₂O₈ compound. This indicates the substitution of transition elements provide a tool towards band gap engineering.     

A Bio‐Inspired Switch Based on Cobalt(II) Disulfide/Cobalt(III) Thiolate Interconversion

Disulfide/thiolate interconversion supported by transition‐metal ions is proposed to be implicated in fundamental biological processes, such as the transport of metal ions or the regulation of the production of reactive oxygen species. We report herein a mononuclear dithiolate Co^III complex, [Co^IIILS(Cl)] ( 1 ; LS=sulfur containing ligand), that undergoes a clean, fast, quantitative and reversible Co^II disulfide/Co^III thiolate interconversion mediated by a chloride anion. The removal of Cl^? from the Co^III complex leads to the formation of a bis(μ‐thiolato) μ‐disulfido dicobalt(II) complex, [Co₂^II,IILSSL]²⁺ ( 2 ²⁺). The structures of both complexes have been resolved by single‐crystal X‐ray diffraction; their magnetic, spectroscopic, and redox properties investigated together with DFT calculations. This system is a unique example of metal‐based switchable Mⁿ₂‐RSSR/2 M⁽ⁿ⁺¹⁾‐SR (M=metal ion, n=oxidation state) system that does not contain copper, acts under aerobic conditions, and involves systems with different nuclearities.     

Voltammetric and potentiometric studies of some sulpha drug-Schiff base compounds and their metal complexes

The electrochemical behavior of some sulpha drug-Schiff bases at a mercury electrode was examined in the Britton-Robinson universal buffer of various pH values (2.5–11.7) containing 20% v/v) of ethanol using DC-polarography, cyclic voltammetry and controlled-potential electrolysis. The DC-polarograms and cyclic voltammograms of the examined compounds exhibited a single, 2-electron, irreversible, diffusion-controlled cathodic step within the entire pH range which is attributed to the reduction of the azomethine group-CH=N- to -CH₂-NH-. The symmetry transfer coefficient (α) of the electrode reaction and the diffusion coefficient (D ₀) of the reactant species were determined. The electrode reaction pathway of the compounds at the mercury electrode was suggested to follow the sequence: H⁺, e⁻, e⁻, H⁺. The dissociation constant of the sulpha drug-Schiff bases, the stability constant and stoichiometry of their complexes with various divalent transition metal ions (Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺) were determined potentiometrically at room temperature.      

Nickel‐Triad Complexes of a Side‐on Coordinating Distannene

NHC adducts of the stannylene Trip₂Sn (Trip=2,4,6‐triisopropylphenyl) were reacted with zero‐valent Ni, Pd, and Pt precursor complexes to cleanly yield the respective metal complexes featuring a three‐membered ring moiety Sn‐Sn‐M along with carbene transfer onto the metal and complete substitution of the starting ligands. Thus the easily accessible NHC adducts to stannylenes are shown to be valuable precursors for transition‐metal complexes with an unexpected Sn? Sn bond. The complexes have been studied by X‐ray diffraction and NMR spectroscopy as well as DFT calculations. The compounds featuring the structural motif of a distannametallacycle comprised of a [(NHC)₂M⁰] fragment and Sn₂Trip₄ represent rare higher congeners of the well‐known olefin complexes. DFT calculations indicate the presence of a π‐type Sn–Sn interaction in these first examples for acyclic distannenes symmetrically coordinating to a zero‐valent transition metal.     

Cobaltocenium Carboxylate Transition Metal Complexes: Synthesis,Structure, Reactivity,and Cytotoxicity

Cobaltocenium carboxylate is an unusual betaine that functions as a formally neutral carboxylate ligand with late transition metal centers comprising Co²⁺, Ni²⁺, Cu²⁺, Ag⁺, Zn²⁺, Cd²⁺, Hg²⁺, and Rh⁺. Structurally, a rich coordination chemistry is observed – from simple monomeric homoleptic complexes to heteroleptic dimeric, trimeric, and polymeric compounds, as shown by X‐ray diffraction of 11 compounds. Chemically, thermal decarboxylation was investigated aiming at the formation of cobaltocenium‐carbene transition metal complexes, in analogy to such chemistry of imidazolium carboxylate betaines. Cytotoxicity studies of cobaltocenium carboxylate transition metal complexes were performed to evaluate the medicinal bioorganometallic potential of these compounds. While cobaltocenium carboxylate was inactive, its complexes with Ag⁺, Cd²⁺, and Hg²⁺ triggered significant cytotoxic effects.     

Paramagnetic probes for the investigation of ordered and disordered perfluorosurfactants,perfluoropolyethers and perfluorinated ionomers

In this review we describe the use of transition metal ions (Cu²⁺, Ti³⁺, VO²⁺, Mn²⁺) and stable nitroxide radicals with different shape, size and charge as paramagnetic probes for the study of perfluorinated compounds in the presence of solvents by electron spin resonance (ESR, ESE, ENDOR) spectroscopy. The physical state of the swelling solvents in perfluorinated ionomers (Nafion and perfluoropolyethers) is deduced by the analysis of the ESR spectral parameters and linewidths as a function of the operating frequency and temperature. The formation of metal aggregates in aqueous and nonaqueous solvents is discussed. The spectral characteristics and relaxation behavior of nitroxides is particularly informative when aggregates such as micelles, lamellar phases and other ordered systems, are formed in solution.     

Fabrication and characterization of hexagonal mesoporous silica monolith via post-synthesized hydrothermal process

Large-sized, optical transparent mesostructured Brij 56/silica monolith has been fabricated using a lyotropic liquid crystal of Brij 56 (C₁₆EO₁₀) as a template and TMOS as a silica source, combined with a optimizing sol-gel process and a hydrothermal aging process. By programmed temperature drying and calcinations, translucent mesoporous silica monolith with two-dimensional hexagonal structure (P6mm) has bee obtained. The ordered mesoporous silica monoliths have been characterized by small-angle X-ray diffraction, transmission electron microscopy (TEM), and nitrogen adsorption, which shows that the materials have a highly ordered two-dimensional hexagonal mesostructure with the high specific surface area of 837 m² · g⁻¹ and narrow pore distribution with a mean BJH pore diameter of 2.73 nm. Based on calculations and differential scanning calorimetry and thermogravimetric analyses, the action mechanism of the hydrothermal aging process has been proposed: the 100°C hydrothermal conditions and autogenous 2.3 atm pressure promote the condensation and dehydration of silanol groups, with the result that cross-linking degree, the flaws and moisture content in gels are reduced notably. Those processes guarantee the integrity of gels in the following drying process.     

Meta‐linked and para‐linked water‐soluble poly(arylene ethynylene)s with amino acid side chains: Effects of different linkage on Hg2+ ion sensing properties in aqueous media

Water‐soluble, meta‐ and para‐linked poly(arylene ethynylene)s containing L ‐aspartic acid‐functionalized fluorene units (P1 and P2) and their model compounds (M1 and M2) have been synthesized, and their photophysical properties and fluorescent sensing properties were investigated in aqueous solution. P1 and M1 with the meta‐linkage show blue‐shifted absorption and emission spectra, and decreased photoluminescence quantum yields compared with those of P2 and M2 with para‐linkage. Their absorption and fluorescence spectra are pH dependent perhaps due to the aggregation of the polymer chains at low pH values. In buffer solutions, both polymers and their model compounds exhibit the excellent selectivity and sensitivity to Hg²⁺ over other common metal ions. Furthermore, the quenching constant and detection limit of P1 are determined to be 1.04 × 10⁷ M^?1 and 10 nM, and show the higher sensitivity compared to P2. Further comparison of their model compounds reveal that the sensitivity and quenching efficiency of M1 is also higher than that of M2, indicating that the meta‐linkage pattern plays a key role in improving their Hg²⁺ ion sensing properties. In addition, both meta‐ and para‐linked polymers exhibit the higher quenching efficiency than their model compounds due to the amplified fluorescence response of conjugated polymer. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012