Polytypism, disorder, and anion exchange properties of divalent ion (Zn, Co) containing bayerite-derived layered double hydroxides

Incorporation of Zn(2+) into bayerite results in the formation of a cation-ordered layered double hydroxide (LDH) of monoclinic symmetry in which about half the vacancies of Al(OH)(3) are occupied by Zn(2+) giving rise to positively charged layers. Charge compensation takes place by the incorporation of sulfate ions in the interlayer region. Structure refinement reveals that the adjacent layers in the crystal are related by a 2(1) axis (we call it 2M(1) polytype) with sulfate coordinating in the D(2d) symmetry in the interlayer region. Another polytype in which adjacent layers are related by a 2-fold axis (2M(2) polytype) can also be envisaged. Faulted crystals arising from intergrowths of the 2M(2) polytype within the 2M(1) structure were also obtained. These bayerite-based LDHs have a distinctly different interlayer chemistry when compared to the better known brucite-based LDHs, in that they have a strong affinity for tetrahedral ions such as SO(4)(2-), CrO(4)(2-), and MoO(4)(2-) and a poor affinity for CO(3)(2-) ions. These observations have implications for the use of LDHs in applications related to chromate sorption.     

Cationic assembly of metal complex aggregates: structural diversity,solution stability,and magnetic properties

The tetradentate imino-carboxylate ligand [L](2)(-) chelates the equatorial sites of Ni(II) to give the complex [Ni(L)(MeOH)(2)] in which a Ni(II) center is bound in an octahedral coordination environment with MeOH ligands occupying the axial sites. Lanthanide (Ln) and Group II metal ions (M) template the aggregation of six [Ni(L)] fragments into the octahedral cage aggregates (M[Ni(L)](6))(x)(+) (1: M = Sr(II); x = 2,2: M = Ba(II); x = 2, 3: M = La(III); x = 3, 4: M = Ce(III); x = 3, 5: M = Pr(III); x = 3, and 6: M = Nd(III); x = 3). In the presence of Group I cations, however, aggregates composed of the alkali metal-oxide cations template various cage compounds. Thus, Na(+) forms the trigonal bipyramidal [Na(5)O](3+) core within a tricapped trigonal prismatic [Ni(L)](9) aggregate to give ((Na(5)O) subset [Ni(L)](9)(MeOH)(3))(BF(4))(2).OH.CH(3)OH, 7. Li(+) and Na(+) together form a mixed Li(+)/Na(+) core comprising distorted trigonal bipyramidal [Na(3)Li(2)O](3+) within an approximately anti-square prismatic [Ni(L)](8) cage in ((Na(3)Li(2)O) subset [Ni(L)](8)(CH(3)OH)(1.3)(BF(4))(0.7))(BF(4))(2.3).(CH(3)OH)(2.75).(C(4)H(10)O)(0.5), 8, while in the presence of Li(+), a tetrahedral [Li(4)O](2+) core within a hexanuclear open cage [Ni(L)](6) in ((Li(4)O) subset [Ni(L)](6)(CH(3)OH)(3))2ClO(4).1.85CH(3)OH, 9, is produced. In the presence of H(2)O, the Cs(+) cation induces the aggregation of the [Ni(L)(H(2)O)(2)] monomer to give the cluster Cs(2)[Ni(L)(H(2)O)(2)](6).2I.4CH(3)OH.5.25H(2)O, 10. Analysis by electronic spectroscopy and mass spectrometry indicates that in solution the trend in stability follows the order 1-6 > 7 > 8 approximately 9. Magnetic susceptibility data indicate that there is net antiferromagnetic exchange between magnetic centers within the cages.     

Topochemical synthesis of co-fe layered double hydroxides at varied fe/co ratios: unique intercalation of triiodide and its profound effect

Co-Fe layered double hydroxides at different Fe/Co ratios were synthesized from brucite-like Co(2+)(1-x)Fe(2+)(x)(OH)(2) (0 ≤ x ≤ 1/3) via oxidative intercalation reaction using an excess amount of iodine as the oxidizing agent. A new redoxable species: triiodide (I(3)(-)), promoted the formation of single-phase Co-Fe LDHs. The results point to a general principle that LDHs with a characteristic ratio of total trivalent and divalent cations (M(3+)/M(2+)) at 1/2 may be the most stable in the oxidative intercalation procedure. At low Fe content, e.g., starting from Co(2+)(1-x)Fe(2+)(x)(OH)(2) (x < 1/3), partial oxidation of Co(2+) to Co(3+) takes place to reach the M(3+)/M(2+) threshold of 1/2 in as-transformed Co(2+)(2/3)-(Co(3+)(1/3-x)-Fe(3+)(x)) LDHs. Also discovered was the cointercalation of triiodide and iodide into the interlayer gallery of as-transformed LDH phase, which profoundly impacted the relative intensity ratio of basal Bragg peaks as a consequence of the significant X-ray scattering power of triiodide. In combination with XRD simulation, the LDH structure model was constructed by considering both the host layer composition/charge and the arrangement of interlayer triiodide/iodide. The work provides a clear understanding of the thermodynamic and kinetic factors associated with the oxidative intercalation reaction and is helpful in elucidating the formation of LDH structure in general.     

Compositional and structural control on anion sorption capability of layered double hydroxides (LDHs)

Layered double hydroxides (LDHs) have shown great promise as anion getters. In this paper, we demonstrate that the sorption capability of a LDH for a specific oxyanion can be greatly increased by appropriately manipulating material composition and structure. We have synthesized a large set of LDH materials with various combinations of metal cations, interlayer anions, and molar ratios of divalent cation M(II) to trivalent cation M(III). The synthesized materials have then been tested systematically for their sorption capabilities for pertechnetate (TcO(-)(4)). It is discovered that for a given interlayer anion (either CO(2-)(3) or NO(-)(3)) the Ni-Al LDH with a Ni/Al ratio of 3:1 exhibits the highest sorption capability among all the materials tested. The sorption of TcO(-)(4) on M(II)-M(III)-CO(3) LDHs may be dominated by the edge sites of LDH layers and correlated with the basal spacing d(003) of the materials, which increases with the decreasing radii of both divalent and trivalent cations. The sorption reaches its maximum when the layer spacing is just large enough for a pertechnetate anion to fit into a cage space among three adjacent octahedra of metal hydroxides at the edge. Furthermore, the sorption is found to increase with the crystallinity of the materials. For a given combination of metal cations and an interlayer anion, the best crystalline LDH material is obtained generally with a M(II)/M(III) ratio of 3:1. Synthesis with readily exchangeable nitrate as an interlayer anion greatly increases the sorption capability of a LDH material for pertechnetate. The work reported here will help to establish a general structure-property relationship for the related layered materials.     

A kinetic study of the intercalation of lithium salts into Al(OH)3

The intercalation of five lithium salts into the gibbsite and bayerite polymorphs of Al(OH)3 has been studied using in situ energy-dispersive X-ray diffraction. The kinetics and mechanisms of the reactions have been modeled using the Avrami-Erofe'ev model. The kinetic data suggest that the reaction mechanisms are predominantly nucleation controlled, although the intercalation of LiNO3 into bayerite and of Li2SO4 into gibbsite proceed via two-stage mechanisms, one part of which is diffusion controlled. All the reactions proceed directly from the host to the product, except for the intercalation of Li2SO4 into gibbsite where a more hydrated intermediate form of [LiAl2(OH)6]2SO4 x yH2O is generated prior to the final product.     

Versatile conversion of N-heterocyclic silylene to silyl metal compounds by insertion of divalent silicon into metal-carbon and metal-hydrogen bonds

The facile one-pot reaction of the stable N-heterocyclic silylene LSi: 1 (L=(ArN)C(=CH(2))CH=C(Me)(NAr), Ar=2,6-iPr(2)C(6)H(3)) with Me(2)Zn, Me(3)Al, H(3)Al-NMe(3), and MeLi has been investigated. The silicon(II) atom in 1 is capable of insertion into the corresponding M-C and Al-H bonds under very mild reaction conditions. Thus, Me(2)Zn furnishes the bis(silyl) zinc complex LSi(Me)ZnSi(Me)L 2 as the sole product, irrespective of the molar ratio of the starting materials applied. Moreover, the reactions of 1 with Me(3)Al, H(3)Al-NMe(3), and MeLi lead directly to the 1,1-addition products LSi(Me)(Al(thf)Me(2)) 3, LSi(H)(AlH(2)(NMe(3))) 4, and LSi(Me)Li(thf)(3) 5, respectively. All new compounds 2-5 were fully characterized by multinuclear NMR spectroscopy, mass spectrometry, elemental analyses, and single-crystal X-ray diffraction analyses.     

Solid-state chelation of metal ions by ethylenediaminetetraacetate intercalated in a layered double hydroxide

The solid-state chelation of transition metal ions (Co(2+), Ni(2+), and Cu(2+)) from aqueous solutions into the lithium aluminum layered double hydroxide ([LiAl(2)(OH)(6)]Cl x 0.5H(2)O or LDH) which has been pre-intercalated with EDTA (ethylenediaminetetraacetate) ligand has been investigated. The intercalated metal cations form [M(edta)](2)(-) complexes between the LDH layers as indicated by elemental analysis, powder X-ray diffraction, and IR and UV-vis spectroscopies. If metal chloride or nitrate salts are used in the reaction with the LDH then co-intercalation of either the Cl(-) or NO(3)(-) anions is observed. In the case of metal acetate salts the cations intercalate without the accompanying anion. This can be explained by the different intercalation selectivity of the anions in relation to the LDH. In the latter case the introduction of the positive charge into LDH structure was compensated for by the release from the solid of the equivalent quantity of lithium and hydrogen cations. Time-resolved in-situ X-ray diffraction measurements have revealed that the chelation/intercalation reactions proceed very quickly. The rate of the reaction found for nickel acetate depends on concentration as approximately k[Ni(Ac)(2)](3).     

Hydrothermal and structural chemistry of the zinc(II)- and cadmium(II)-1,2,4-triazolate systems

Hydrothermal reactions of 1,2,4-triazole with zinc and cadmium salts have yielded 10 structurally unique materials of the M(II)/trz/Xn- system, with M(II)=Zn and Cd and Xn-=F-, Cl-, Br-, I-, OH-, NO3-, and SO(4)2- (trz=1,2,4-triazolate). Of the zinc-containing phases, [Zn(trz)2] (1), [Zn2(trz)3(OH)].3H2O (3.3H2O), and [Zn2(trz)(SO4)(OH)] (4) are three-dimensional, while [Zn(trz)Br] (2) is two-dimensional. All six cadmium phases, [Cd3(trz)3F2(H2O)].2.75H2O (5.2.75H2O), [Cd2(trz)2Cl2(H2O)] (6), [Cd3(trz)3Br3] (7), [Cd2(trz)3I] (8), [Cd3(trz)5(NO3)(H2O)].H2O (9.H2O), and [Cd8(trz)4(OH)2(SO4)5(H2O)] (10), are three-dimensional. In all cases, the anionic components Xn- participate in the framework connectivity as bridging ligands. The structural diversity of these materials is reflected in the variety of coordination polyhedra displayed by the metal sites: tetrahedral; trigonal bipyramidal; octahedral. Structures 3, 5, and 7-9 exhibit two distinct polyhedral building blocks. The materials are also characterized by a range of substructural components, including trinuclear and tetranuclear clusters, adamantoid cages, chains, layers, and complex frameworks.     

Suppression of spinel formation to induce reversible thermal behavior in the layered double hydroxides (LDHs) of Co with Al, Fe, Ga, and In

The layered double hydroxides (LDHs) of Co with trivalent cations decompose irreversibly to yield oxides with the spinel structure. Spinel formation is aided by the oxidation of Co(II) to Co(III) in the ambient atmosphere. When the decomposition is carried out under N2, the oxidation of Co(II) is suppressed, and the resulting oxide has the rock salt structure. Thus, the Co-Al-CO(3)(2-)/Cl- LDHs yield oxides of the type Co(1-x)Al(2x/3) square(x/3)O, which are highly metastable, given the large defect concentration. This defect oxide rapidly reverts back to the original hydroxide on soaking in a Na2CO3 solution. Interlayer NO(3)- anions, on the other hand, decompose generating a highly oxidizing atmosphere, whereby the Co-Al-NO(3)- LDH decomposes to form the spinel phase even in a N2 atmosphere. The oxide with the defect rock salt structure formed by the thermal decomposition of the Co-Fe-CO(3)(2-) LDH under N2, on soaking in a Na(2)CO(3) solution, follows a different kinetic pathway and undergoes a solution transformation into the inverse spinel Co(Co,Fe)(2)O(4). Fe3+ has a low octahedral crystal field stabilization energy and therefore prefers the tetrahedral coordination offered by the structure of the inverse spinel rather than the octahedral coordination of the parent LDH. Similar considerations do not hold in the case of Ga- and In-containing LDHs, given the considerable barriers to the diffusion of M3+ (M=Ga, In) from octahedral to tetrahedral sites owing to their large size. Consequently, the In-containing oxide residue reverts back to the parent hydroxide, whereas this reconstruction is partial in the case of the Ga-containing oxide. These studies show that the reversible thermal behavior offers a competing kinetic pathway to spinel formation. Suppression of the latter induces the reversible behavior in an LDH that otherwise decomposes irreversibly to the spinel.     

Synthesis, structure, and magnetochemical analysis of selected first-row transition-metal anilino- and anisolesquarate compounds

The isomorphous polymeric complexes [M(mu-C(6)H(5)NHC(4)O(3))(2)(CH(3)OH)(2)](n) [M = Mn (1), Co (2), Cu (4), Zn (5)] are produced by reacting the anilinosquarate anion with the appropriate metal nitrates in a methanolic solution. Each of these complexes contains the central metal atom in a slightly distorted octahedral environment, with the coordination polyhedron consisting of four mu-1,2-bridging anilinosquarate ligands and two trans-oriented methanols. The polymer chains propagate to form a two-dimensional net of metal centers, with the conformation of the component sheets in the net being controlled by intramolecular N-H...O and O-H...O hydrogen bonds. Under reaction conditions similar to those used in the synthesis of the polymers 1, 2, 4, and 5, the nickel(II) monomer [Ni(C(6)H(5)NHC(4)O(3))(2)(H(2)O)(4)].2H(2)O (3) is produced in which each nickel center is attached to two cis-coordinated anilinosquarate and four aqua ligands in a distorted octahedral arrangement. The ligand conformation in 3 is stabilized by both intra- and intermolecular hydrogen bonding, which results in the formation of a sheet polymer having distinct hydrophobic and hydrophilic surfaces. Magnetochemical analysis of 1 and 4 reveals normal paramagnetic behavior for 1 and a very weak ferromagnetic interaction in 4; the absence of significant magnetic interactions is attributed to the distortion of the C(4) cycle of the anilinosquarate ligand (lower than C(2)(v) symmetry) in these complexes. Reaction of anisolesquarate with M(NO(3))(2).xH(2)O in acetonitrile produced the set of isomorphous salts [M(H(2)O)(6)][CH(3)OC(6)H(5)C(4)O(3)](2) [M = Mn (6), Co (7), Ni (8), Zn (9)]. The anisolesquarate anions in 6-9 are hydrogen bonded to the [M(H(2)O)(6)](2+) ions to form polymer chains, which are further linked by hydrogen bonds to form complex sheets. Complexation of the anisolesquarate ligand was not observed even when other solvents and reaction conditions were employed.     

Synthesis and Characterization of [Zn‐Al] Layered Double Hydroxides: Effect of the Operating Parameters

In this study, [Zn‐Al] layered double hydroxides (LDHs ) were prepared using the coprecipitation method at constant pH . The synthesis parameters (including the aging time, synthesis pH , nature of the alkali, concentration of metallic salts, and the cationic molar ratio R = Zn/Al) were varied in order to elucidate their effect on the properties of the obtained materials. Different characterization techniques, namely X‐ray diffraction, Fourier transform infrared, thermogravimetric analysis‐differential thermogravimetry, transmission electron microscopy, energy‐dispersive X‐ray, inductively coupled plasma, and photoluminescence, were used in this study. It was found that obtaining well‐crystallized LDHs requires (i) an aging time of 24 h and (ii) a synthesis pH value in the range 8–12. Our results also show that the concentration of the cationic metallic salts has no influence on the structural properties of the LDHs . The use of NH₄OH as alkali for adjusting the pH value during the synthesis favors the formation of nitrated LDH phases while NaOH gives rise to carbonated ones. Moreover, it was found that irrespective of the molar cationic ratio used (between 1 and 5), [Zn‐Al] LDHs could be obtained. The sample synthesized at R = 2 exhibited the best crystallinity.     

Versatile Conversion of N‐Heterocyclic Silylene to Silyl Metal Compounds by Insertion of Divalent Silicon into Metal–Carbon and Metal–Hydrogen Bonds

The facile one‐pot reaction of the stable N‐heterocyclic silylene LSi: 1 (L?(ArN)C(?CH₂) CH?C(Me)(NAr), Ar=2,6‐iPr₂C₆H₃) with Me₂Zn, Me₃Al, H₃Al‐NMe₃, and MeLi has been investigated. The silicon(II) atom in 1 is capable of insertion into the corresponding M? C and Al? H bonds under very mild reaction conditions. Thus, Me₂Zn furnishes the bis(silyl) zinc complex LSi(Me)ZnSi(Me)L 2 as the sole product, irrespective of the molar ratio of the starting materials applied. Moreover, the reactions of 1 with Me₃Al, H₃Al‐NMe₃, and MeLi lead directly to the 1,1‐addition products LSi(Me)(Al(thf)Me₂) 3 , LSi(H)(AlH₂(NMe₃)) 4 , and LSi(Me)Li(thf)₃ 5 , respectively. All new compounds 2 – 5 were fully characterized by multinuclear NMR spectroscopy, mass spectrometry, elemental analyses, and single‐crystal X‐ray diffraction analyses.     

Heterometallic Cu/Co and Cu/Co/Zn complexes bearing rare asymmetric tetranuclear cores: synthesis, structures, and magnetic and catalytic properties toward the peroxidative oxidation of cycloalkanes

The three novel heterometallic complexes [CuCo(III)Co(II)(2)(MeDea)(3)Cl(3)(CH(3)OH)(0.55)(H(2)O)(0.45)](H(2)O)(0.45) (1), [CuCo(III)Zn(2)(MeDea)(3)Cl(3)(CH(3)OH)(0.74)(H(2)O)(0.26)](H(2)O)(0.26) (2), and [CuCo(III)Zn(2)(MeDea)(3)Cl(3)(DMF)] (3) have been prepared using a one-pot reaction of copper powder with cobalt chloride (1) and zinc nitrate (2, 3) in a methanol (1, 2) or dimethylformamide (3) solution of N-methyldiethanolamine. A search of the Cambridge Structural Database shows that the tetranuclear asymmetric cores M(4)(μ(3)-X)(μ-X)(5) of 1-3 represent an extremely rare case of M(4)X(6) arrays. The magnetic investigations of 1 disclose antiferromagnetic coupling in a Co(II)-Cu(II)-Co(II) exchange fragment with J(Co-Cu)/hc = -4.76 cm(-1), J(Co-Co)/hc = -2.76 cm(-1), and D(Co)/hc = +34.3 cm(-1). Compounds 1-3 act as precursors for the mild peroxidative oxidation of cyclohexane to cyclohexanol and cyclohexanone with overall yields up to 23%. The synthetic and structural features as well as the thermogravimetric behavior and electrospray ionization mass spectrometry data are discussed.     

The hydrolysis of lead(II). A potentiometric and enthalpimetric study

The hydrolysis of lead(II) has been investigated by potentiometric titrations (ionic medium 1.0M NaClO(4) and 1.0M KNO(3)) and enthalpimetric titrations (ionic medium 1.0M NaClO(4)) at 25 degrees . The reaction model that gave the best fit to the data for 1.0M NaClO(4) comprised the following five ions: Pb(OH)(+), Pb(3)(OH)(2+)(4), Pb(3)(OH)(+)(5), Pb(4)(OH)(4+)(4) and Pb(6)(OH)(4+)(8). The formation constants, and enthalpy changes (kJ/mol) for these species, defined according to equation (1), have the values log beta(11) = -7.8, DeltaH(0)(11) = 24; log beta(34) = -22.69, DeltaH(0)(34) = 112; log beta(35) = -30.8, DeltaH(0)(35) = 146; log beta(44) = -19.58, DeltaH(0)(44) = 86; log beta(68) = -42.43, DeltaH(0)(68) = 215. Equilibrium constants determined in nitrate medium show good agreement with those pertaining to perchlorate medium if complexation of lead(II) with nitrate is taken into account.     

Thermally Induced Growth of ZnO Nanocrystals on Mixed Metal Oxide Surfaces

An in situ method for the growth of ZnO nanocrystals on Zn/Al mixed metal oxide (MMO) surfaces is presented. The key to this method is the thermal treatment of Zn/Al layered double hydroxides (Zn/Al LDHs) in the presence of nitrate anions, which results in partial demixing of the LDH/MMO structure and the subsequent crystallization of ZnO crystals on the surface of the forming MMO layers. In a first experimental series, thermal treatment of Zn/Al LDHs with different fractions of nitrate and carbonate in the interlayer space was examined by thermogravimetry coupled with mass spectrometry (TG‐MS) and in situ XRD. In a second experimental series, Zn/Al LDHs with only carbonate in the interlayer space were thermally treated in the presence of different amounts of an external nitrate source (NH₄NO₃). All obtained Zn/Al MMO samples were analysed by electron microscopy, nitrogen physisorption and powder X‐ray diffraction. The gas phase formed during nitrate decomposition turned out to be responsible for the formation of crystalline ZnO nanoparticles. Accordingly, both interlayer nitrate and the presence of ammonium nitrate led to the formation of supported ZnO nanocrystals with mean diameters between 100 and 400 nm, and both methods offer the possibility to tailor the amount and size of the ZnO crystals by means of the amount of nitrate.     

Synthesis, characterization, and reactivity studies of heterodinuclear complexes modeling active sites in purple acid phospatases

To model the heterodinuclear active sites in plant purple acid phosphatases, a mononuclear synthon, [Fe(III)(H(2)IPCPMP)(Cl(2))][PF(6)] (1), has been generated in situ from the ligand 2-(N-isopropyl-N-((2-pyridyl)methyl)aminomethyl)-6-(N-(carboxylmethyl)-N-((2-pyridyl)methyl)amino methyl)-4-methylphenol (IPCPMP) and used to synthesize heterodinuclear complexes of the formulas [Fe(III)M(II)(IPCPMP)(OAc)(2)(CH(3)OH)][PF(6)] (M = Zn (2), Co (3), Ni (4), Mn (5)), [Fe(III)Zn(II)(IPCPMP)(mpdp)][PF(6)] (6) (mpdp = meta-phenylene-dipropionate), and [Fe(III)Cu(II)(IPCPMP) (OAc)}(2)(μ-O)][PF(6)] (7). Complexes 2-4, 6, and 7 have been crystallographically characterized. The structure of 6 is a solid state coordination polymer with heterodinuclear monomeric units, and 7 is a tetranuclear complex consisting of two heterodinuclear phenolate-bridged Fe(III)Cu(II) units bridged through a μ-oxido group between the two Fe(III) ions. Mo?ssbauer spectra confirm the presence of high spin Fe(III) in an octahedral environment for 1, 3, and 5 while 2 and 4 display relaxation effects. Magnetic susceptibility measurements indicate weak antiferromagnetic coupling for 3, 4, and 5 and confirm the assignment of the metal centers in 2-5 as high spin Fe(III)-M(II) (M = Zn, Co (high spin), Ni (high spin), Mn (high spin)). Complexes 2-5 are intact in acetonitrile solution as indicated by IR spectroscopy (for 2-4) and electrospray ionization mass spectrometry (ESI-MS) but partly dissociate to hydroxide species and a mononuclear complex in water/acetonitrile solutions. UV-vis spectroscopy reveal pH-dependent behavior, and species that form upon increasing the pH have been assigned to μ-hydroxido-bridged Fe(III)M(II) complexes for 2-5 although 2 and 3 is further transformed into what is propsed to be a μ-oxido-bridged tetranuclear complex similar to 7. Complexes 2-5 enhance phosphodiester cleavage of 2-hydroxy-propyl-p-nitrophenyl phosphate (HPNP) and bis(2,4-dinitrophenyl)phosphate (BDNPP), but the reactivities are different for different complexes and generally show strong pH dependence.     

Poly(pyrazolyl)aluminate complexes containing aluminum-hydrogen bonds

The treatment of LiAlH(4) with 2, 3, or 4 equiv of the 3,5-disubstituted pyrazoles Ph(2)pzH or iPr(2)pzH afforded [Li(THF)(2)][AlH(2)(Ph(2)pz)(2)] (97%), [Li(THF)][AlH(Ph(2)pz)(3)] (96%), [Li(THF)(4)][Al(Ph(2)pz)(4)] (95%), and [Li(THF)][AlH(iPr(2)pz)(3)] (89%). The treatment of ZnCl(2) with [Li(THF)][AlH(Ph(2)pz)(3)] afforded Zn(AlH(Ph(2)Pz)(3))H (70%). X-ray crystal structures of these complexes demonstrated κ(2) or κ(3) coordination of the aluminum-based ligands to the Li or Zn ions. The treatment of [Li(THF)][AlH(Ph(2)pz)(3)] with MgBr(2) or CoCl(2) in THF/Et(2)O solutions, by contrast, afforded the pyrazolate transfer products Mg(2)Br(2)(Ph(2)pz)(2)(THF)(3)·2THF (25%) and Co(2)Cl(2)(Ph(2)pz)(2)(THF)(3)·THF (23%) as colorless and blue crystalline solids, respectively. An analogous treatment of [Li(THF)][AlH(Ph(2)pz)(3)] with MCl(2) (M = Mn, Fe, Ni, Cu) afforded metal powders and H(2), illustrating hydride transfer from Al to M as a competing reaction path.     

Investigation of the zinc(II)-benzoate-2-pyridinealdoxime reaction system

The employment of pyridine-2-carbaldehyde oxime (paoH) in zinc(II) benzoate chemistry, in the absence or presence of azide ions, is described. The syntheses, crystal structures and spectroscopic characterization are reported for the complexes [Zn(O(2)CPh)(2)(paoH)(2)] (1), [Zn(12)(OH)(4)(O(2)CPh)(16)(pao)(4)] (2) and [Zn(4)(OH)(2)(pao)(4)(N(3))(2)] (3). The Zn(II) centre in octahedral 1 is coordinated by two monodentate PhCO(2)(-) groups and two N,N'-chelating paoH ligands. The metallic skeleton of 2 describes a tetrahedron encapsulated in a distorted cube. The {Zn(12)(μ-OH)(4)(μ(3)-ΟR)(4)}(16+) core of the cluster can be conveniently described as consisting of a central {Zn(4)(μ(3)-ΟR)(4)}(4+) cubane subunit (RO(-) = pao(-)) linked to four {Zn(2)(μ-OH)}(3+) subunits via the OH(-) group of each of the latter, which becomes μ(3). The molecule of 3 has an inverse 12-metallacrown-4 topology. Two triply bridging hydroxido groups are accommodated into the metallacrown ring. Each pao(-) ligand adopts the η(1)?:?η(1)?:?η(1)?:?μ coordination mode, chelating one Zn(II) atom and bridging a Zn(II)(2) pair. Complexes 1 and 2 display photoluminescence with maxima at ～355 nm and ～375 nm, upon maximum excitation at 314 nm; the origin of the photoluminescence is discussed.     

Adsorption of Cr(VI) and Se(IV) from their aqueous solutions onto Zr4+-substituted ZnAl/MgAl-layered double hydroxides: effect of Zr4+ substitution in the layer

Hydrotalcite-like compounds (layered double hydroxides, LDHs) containing varying amounts of Al(3+), Zr(4+), and Zn(2+) or Mg(2+) in the metal hydroxide layer have been synthesized and characterized by various physicochemical methods. The adsorption behavior of uncalcined (as-synthesized) and calcined LDHs have been investigated for Cr(2)O(7)(2-) and SeO(3)(2-). The mixed oxides, obtained on calcination at 450 degrees C, exhibit high adsorption capacities for Cr(2)O(7)(2-) (1.6-2.7 meq/g) and SeO(3)(2-) (1.1-1.5 meq/g), where adsorption occurs through rehydration. Substitution of Zr(4+) in the LDHs, for either M(2+) or Al(3+) ions, increases the adsorption capacity up to 20%, thus providing an alternative way to enhance the adsorption capacity of this type of material. The high adsorption capacity of these materials could be successfully used for removal of undesirable anions from water and also for synthesis of intercalated materials with tailored acidobasicity.     

Triimidosulfonic acid and organometallic triimidosulfonates: S(+)-N(-) versus S=N bonding

Sulfonic acids RSO(2)OH and their metal salts MO(3)SR are versatile catalysts in large-scale industrial cyclization and polymerization processes. Isoelectronic replacement of the oxygen atoms by NR imido groups gives triimidosulfonic acid and triimidosulfonates. The salts form nonaggregated soluble molecules rather than infinite solid-state lattices such as their oxo analogues. In this paper, we present the synthesis and structure of the basic starting material MeS(N(t)Bu)(3)H (1), the metal complexes [Me(2)Al(N(t)Bu)(3)SMe] (2) and [Zn[(N(t)Bu)(3)SMe](2)] (3), and the mixed metal adduct [(thf)Li[(N(t)Bu)(3)SMe].ZnMe(2)] (4). The chelating coordination, rather than the tripodal coordination, cannot be attributed to steric effects of the S-bonded methyl group, as the less demanding Ph-C triple bond C-alkynyl substituent at sulfur in [(thf)(2)Li[(N(t)Bu)(3)SCCPh]] (5) causes the same conformation. S-N bond shortening to the pendant imido group has to be attributed to closed-shell electrostatic attraction rather than to S-N double bonding by valence expansion at the central sulfur atom. Coordination to an additional N-->Zn dative bond in 4 widens the bond length to values normally interpreted as S-N single bonds. We take this fact as experimental evidence that S-N bonding is predominantly governed by electrostatic interaction rather than by valence expansion employing d-orbitals. This was predicted by theoreticians more than a decade ago.