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European Journal of Inorganic Chemistry - Current Research Articles

Current research articles: Inorganic Chemistry

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European Journal of Inorganic Chemistry - published by Wiley-VCH

EurJIC is the fastest growing journal in inorganic chemistry. It publishes Full Papers, Short Communications, and Microreviews from the entire spectrum of inorganic, organometallic, bioinorganic, and solid-state chemistry.

Current articles of the journal:

Metallic Charge-Transfer Salts of Bis(ethylenedithio)tetrathiafulvalene with Paramagnetic Tetrachloro(oxalato)rhenate(IV) and Tris(chloranilato)ferrate(III) Anions

The synthesis, crystal structure and physical characterization of three radical salts of the donor bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET) and tetrachloro(oxalato)rhenate(IV) {[ReCl4(C2O4)]2–} or tris(chloranilato)ferrate(III) {[Fe(C6O4Cl2)3]3–} anions are reported. The isolated salts with ReIV are (ET)[ReCl4(C2O4)] [1, monoclinic, space group C2/c with a = 18.3409(3) Å, b = 10.8414(2) Å, c = 11.1285(3) Å, ? = 99.9714(7)°, V = 2179.38(8) Å3, Z = 4] and (ET)4[ReCl4(C2O4)]·C6H5CN [2, monoclinic, space group P21/c with a = 11.8549(2) Å, b = 32.9079(5) Å, c = 36.4154(5) Å, ? = 96.742(2)°, V = 14108.1(4) Å3, Z = 8]. The salt with FeIII is (ET)6[Fe(C6O4Cl2)3]·(H2O)1.5·(CH2Cl2)0.5 [3, triclinic, space group P$\bar {1}$ with a = 20.9489(7) Å, b = 26.7244(8) Å, c = 33.9132(11) Å, ? = 68.262(3)°, ? = 80.632(3)°, ? = 71.172(3)°, V = 16672.2(9) Å3, Z = 6]. Compounds 2 and 3 are two rare examples of paramagnetic molecular metals and the first ones in their respective families. Compound 3 has a very unusual ?21 phase and the largest number of independent ET molecules reported to date (18). Three new paramagnetic molecular conductors have been prepared with the magnetic anions [ReCl4(C2O4)]2– and [Fe(C6O4Cl2)3]3–. ET[ReCl4(C2O4)] [ET = bis(ethylenedithio)tetrathiafulvalene] is a semiconductor that contains ET2+ dications. ET4[ReCl4(C2O4)] is metallic down to 110 K. ET6[Fe(C6O4Cl2)3] has high conductivity and is the first radical salt with a tris(anilato)metalate anion.

Posted on 17 April 2014 | 5:10 pm

Kinetics and Mechanism of the Reduction of mer-Tris-picolinatoruthenium(III) by L-Ascorbic Acid

The kinetics of reduction of the mer-[RuIII(pic)3] complex (pic– = picolinato) by ascorbic acid (AscH2) leading to formation of a red ruthenium(II) species have been studied spectrophotometrically by using both conventional mixing and stopped-flow methods. The reaction was followed as a function of the reductant concentration over a wide pH range (1.0–7.4). Electron transfer proceeds by an outer-sphere mechanism involving three protolytic forms of ascorbic acid, AscH2, AscH– and Asc2–, for which specific rate constants have been determined. The Gibbs' energy of activation was found to correlate linearly with the HOMO energies of the protolytic forms of the reductant. The mer-[RuIII(pic)3] complex is too sparingly soluble in water to inhibit the growth of the Escherichia coli (ATCC 8739) strain. Its cytotoxicity against non-tumorigenic cells precludes its potential use as an anticancer agent. The reduction of mer-tris-picolinatoruthenium(III) by L-ascorbic acid as a function of pH can only be studied under well-selected reaction conditions to prevent the back-oxidation of tris-picolinatoruthenium(II) caused by traces of dioxygen. Under such conditions, the redox activity of L-ascorbic acid (AscH2) follows the sequence AscH2?<<?AscH–?<<?Asc2–.

Posted on 17 April 2014 | 5:10 pm

Graphical Abstract: Eur. J. Inorg. Chem. 12/2014

Posted on 17 April 2014 | 4:42 pm

CuII-Templated Threading of a Bis-amide-tris-amine Macrocycle by Substituted 2,2?-Bipyridyl Derivatives Assisted by Strong ?–? Stacking and Second-Sphere H-Bonding Interactions

Invited for the cover of this issue is the group of Pradyut Ghosh at the Indian Association for the Cultivation of Science (IACS). The cover image shows the [2]pseudorotaxane architecture in which metal coordination, aromatic ?–? stacking, and second-sphere hydrogen-bonding interactions operate between the wheel and the axle simultaneously. We are interested in synthesizing wheels and axles with multiple chemical functionalities for effective threading that can generate new molecules with unexplored features. We feel that there is ample opportunity to develop new smart materials in this area...Read more about the story behind the cover in the Cover Profile and about the research itself on p. 2029 ff.

Posted on 17 April 2014 | 4:42 pm

Masthead: Eur. J. Inorg. Chem. 12/2014

Posted on 17 April 2014 | 4:42 pm

CuII-Templated Threading of a Bis-amide-tris-amine Macrocycle by Substituted 2,2?-Bipyridyl Derivatives Assisted by Strong ?–? Stacking and Second-Sphere H-Bonding Interactions (Eur. J. Inorg. Chem. 12/2014)

The cover picture shows a “wheel” that is composed of (1) a flexible tridentate metal-chelating site, (2) two parallel arene moieties that have potential for aromatic ?–? stacking interactions with the aromatic part of the axle unit, and (3) a bis-amide functionality that can engage in hydrogen-bonding interactions with the suitable functional groups on the axle. The metal ion coordination and other two noncovalent interactions are operative simultaneously to obtain the maximum benefit of the templating strategy in the formation of the pseudorotaxane. Details are discussed in the article by P. Ghosh et al. on p. 2029 ff. For more on the story behind the cover research, see the Cover Profile.

Posted on 17 April 2014 | 4:42 pm

Masthead: Eur. J. Inorg. Chem. 12/2014

Posted on 17 April 2014 | 4:42 pm

Enantiopure Conducting Salts of Dimethylbis(ethylenedithio)tetrathiafulvalene (DM-BEDT-TTF) with the Hexachlororhenate(IV) Anion

The enantiopure radical cation salts [(S,S)-DM-BEDT-TTF]4[ReCl6] ([(S,S)-1]4[ReCl6]) and [(R,R)-DM-BEDT-TTF]4[ReCl6] ([(R,R)-1]4[ReCl6]) [DM-BEDT-TTF = dimethylbis(ethylenedithio)tetrathiafulvalene] have been prepared by electrocrystallization of the chiral precursor DM-BEDT-TTF in the presence of NBu4[ReCl5(pyrazine)] (NBu4 = tetra-n-butylammonium cation; pyz = pyrazine) as supporting electrolyte. The single-crystal X-ray analysis shows that the compounds crystallize in the triclinic system, non-centrosymmetric space group P1, and that the donors arrange in parallel columns. The four independent donor molecules possess approximate charges of +1, +1/2, +1/2 and 0, according to the structural parameter analysis and band-structure calculations, which also support the semiconducting behaviour of the materials. The rhenium(IV) ion in both compounds is six-coordinate with six chloro atoms that describe a slightly distorted octahedral environment with Re–Cl distances that cover the short range 2.348–2.374 Å. Magnetic measurements on polycrystalline samples of [(S,S)-1]4[ReCl6] and [(R,R)-1]4[ReCl6] have been investigated in the temperature range 2–295 K. They are practically identical and confirm the presence of high-spin S = 3/2 [ReCl6]2– isolated monomers together with a Pauli paramagnetism, typical of this kind of system. The magnetic susceptibility data are thoroughly reproduced over the whole temperature range with a simple model of isolated S = 3/2 ions with a zero-field splitting plus a temperature-independent paramagnetism (TIP), and the best-fit parameters being gRe = 1.875(2), |D| = 4.50(3) cm–1 and TIP = 3630(20)×10–6 cm3?mol–1 (2D is the energy gap between the MS = ±3/2 and MS = ±1/2 Kramers doublets). Two enantiomerically pure radical cation salts based on the (S,S)- and (R,R)-dimethylbis(ethylenedithio)tetrathiafulvalene (DM-BEDT-TTF) donor and the paramagnetic [ReCl6]2– dianion show semiconducting behaviour.

Posted on 14 April 2014 | 12:40 pm

Self-Assembly between Dicarboxylate Ions and Dinuclear Lanthanide Complexes: A Surprisingly Complicated Problem

The association between dinuclear lanthanide complexes and dicarboxylate guests has been studied to elucidate the factors that influence the self-assembly of these ternary structures. The self-assembly between ?,??-bis(Eu·DO3A)-m-xylyl (H3DO3A = 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid) host complexes and dicarboxylate guests and the association of a dinicotinate guest and an ?,??-bis(Ln·DO3A)-3,5-dimethylpyridine host in water were demonstrated, and the study of lanthanide-mediated self-assembly and the methods used to investigate the self-assembly are discussed in detail. Furthermore, the self-assembly has been extended to involve five ions from across the lanthanide series, namely, Nd3+, Eu3+, Tb3+, Dy3+ and Yb3+. The self-assembly process, measured by the association constant Ka, is independent of the nature of the lanthanide centre but it is highly solvent dependent. The association constants between a given host–guest pair vary by several orders of magnitude when determined in methanol, methanol/water and water. We conclude that although a lanthanide-centred self-assembly process can be controlled through design, the strength of the association can only be rationalised after the event. The multiple parameters involved in the determination of the value of the association constant appear to be dominated by the solvation contribution to a degree that specific and general solvation has to be understood before we can fully rationalise the association between dinuclear lanthanide complexes and dicarboxylate guests. The forces that control the self-assembly between dicarboxylate guests and dinuclear lanthanide complexes are explored and are more complicated than anticipated.

Posted on 11 April 2014 | 11:20 am

Magnetic Study of a Pentanuclear {Co2IIICo3II} Cluster with a Bent {CoII3} Motif

We have synthesised and structurally characterised a new pentanuclear mixed-valent cobalt cluster of formula [CoII3CoIII2(OH)2(piv)6(L)2(H2O)4] (piv = trimethylacetate, H2L = salicylideneanthranillic acid) from reaction of a dinuclear cobalt pivalate precursor with a Schiff base type ligand under mild reaction conditions. The core structure can be conveniently described as two fused Co3–?3–OH triangles with a strict unique sharing vertex point. A complete picture of the magnetic behaviour of this compound is presented. Through combined use of susceptibility, magnetisation, and EPR data as well as broken-symmetry DFT calculations, we have supported the magnetic data that show weak and anisotropic exchange interaction between CoII ions affording an Seff = 1/2 ground state that is not completely isolated from the low-lying excited doublets at low temperature. Under the optimum applied field of 2 kOe, a frequency-dependent out-of-phase susceptibility signal can be observed below 4 K. However, no reliable relaxation rates could be extracted due to the narrow temperature range in which this behaviour was observed. We report a new pentanuclear mixed-valent cobalt cluster exhibiting a {CoII3CoII2} core that can be conveniently described as two fused Co3–?3–OH triangles with a strict unique sharing vertex point. We have analysed its magnetic behaviour by combining susceptibility, magnetisation and EPR data as well as broken-symmetry DFT calculations.

Posted on 11 April 2014 | 11:20 am

Relative Kinetic Reactivities of Boronic Acids and Boronate Ions toward 1,2-Diols

The following reaction systems, with and without proton ambiguity, were set up for direct measurements of the rate constants of borate and boronate ions: boric acid [B(OH)3] and 4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt (Tiron); 3-nitrophenylboronic acid [3-NO2PhB(OH)2] and Tiron; phenylboronic acid [PhB(OH)2] and 4-nitrocatechol; boric acid and 4-nitrocatechol. Each rate constant for boric or boronic acid is larger than that for the conjugate borate or boronate ion for the reaction systems without proton ambiguity. These results explicitly indicate that the widespread belief that the rate constants of boronate ions are several orders of magnitude larger than those of the conjugate boronic acids is erroneous. The relative kinetic reactivities of RB(OH)2 and RB(OH)3– were investigated in relation to the linear free energy relationships between the rate constants and acidities of the boronic acids and diols. Kinetic results clearly show that boronic acids are more reactive than their respective conjugate boronate ions. This corrects the erroneous conclusion that the boronate ion reacts faster than its conjugate boronic acid by at least several orders of magnitude. The relative kinetic reactivities of boric acid and boronate ions are discussed in terms of mechanistic differences.

Posted on 11 April 2014 | 11:20 am

Nerve Agent Degradation with Polyoxoniobates

Polyoxoniobates are exceptional amongst polyoxometalates in that they can potentially perform base catalysis in water, a process in which a proton is bonded to an oxo ligand, and a hydroxyl is released. Catalytic decomposition of chemical warfare agents such as organofluorophosphates that were used recently in the infamous civilian attacks in Syria is one opportunity to employ this process. Upon evaluation of the polyoxoniobate Lindqvist ion, [Nb6O19]8–, fast neutralization kinetics was discovered for the breakdown of the nerve agent simulant diisopropyl fluorophosphate (DFP). The polyoxoniobates were also tested against the nerve agents Sarin (GB) and Soman (GD). It was determined that different Lindqvist countercations (Li, K, or Cs) affect the rate of decomposition of the organophosphate compounds in both aqueous media (homogeneous reaction), and in the solid state (heterogeneous reaction). Small-angle X-ray scattering analysis of solutions of the Li, K, and Cs salts of [Nb6O19]8– for concentrations at which the experiments were performed revealed distinct differences that could be linked to their relative reaction rates. This study represents the first demonstration of exploiting the unique alkaline reactivity of polyoxoniobates for nerve agent decontamination. Polyoxometalates, like small pieces of metal oxide, can be dissolved or fixed on a surface to perform homogeneous or heterogeneous catalysis, respectively. Here we exploit the alkaline nature of polyoxoniobates to neutralize nerve agents in both solution and the solid state. Solution studies correlate reaction efficacy to the association of the dissolved polyoxoniobate with its counterions.

Posted on 11 April 2014 | 11:20 am

Molecular Conductors with Effectively Half-Filled Electronic States Based on Tetrathiafulvalene Derivatives Condensed with a 2-Isopropylidene-1,3-dithiole Ring

The electron donor 2-isopropylidene-1,3-dithiolo[4,5-d]-4,5-ethylenediselenotetrathiafulvalene (3) provides two new molecular conductors, (3)2[M(CN)2] (M = Ag and Au). These salts crystallize in the triclinic P$\bar {1}$ space group. The donor sheet structure of these salts is the so-called ?-type molecular array, in which the donor molecules form a head-to-tail dimer. The formation of considerable dimerization and the 2:1 donor–anion ratio result in an effectively half-filled electronic nature. These salts show metallic conducting behavior from room temperature. The metallic conducting behavior of (3)2[Ag(CN)2] was retained down to 8 K; however, the resistivity of (3)2[Au(CN)2] increased at around 50 K. The magnetic susceptibility of (3)2[Au(CN)2] suggests that the strength of the electron correlation for this salt is enhanced below 50 K. Molecular conductors (3)2[M(CN)2] (M = Ag and Au) have been successfully prepared and their physical properties and structures have been investigated. The electronic nature of these salts is the effectively half-filled electronic state. (3)2[Au(CN)2] shows nonmetallic behavior below 50 K. These results suggest that the present salts lie on the border between the metallic and insulating phases.

Posted on 10 April 2014 | 12:10 pm

Charge Disproportionation and Magnetoresistivity in a Double Perovskite with Alternate Fe4+(d4) and Mn4+(d3) Layers

An oxygen-stoichiometric, B-site-ordered perovskite Ca2Fe1.1Mn0.9O6 (CFMO) with alternate stacking of Fe and Mn layers was obtained through topochemical oxidation of the corresponding brownmillerite phase under high pressure in the presence of KClO4. The structure crystallizes in the P21/m space group with a doubling of the cell along all three crystallographic axes. Mössbauer spectroscopy, susceptibility, and resistivity measurements suggest ferromagnetic interactions between Fe4+(d4) and Mn4+(d3) along [001] through a double-exchange mechanism, a situation similar to half-doped manganese perovskite oxides. Upon cooling, CFMO exhibits a ferrimagnetic transition below Tc = 90 K, likely accompanied by a charge disproportionation of the iron site, 2Fe4+???Fe3+ + Fe5+. A reasonably good magnetoresistivity of 27?% was observed below Tc. High-pressure oxygen intercalation of a brownmillerite phase Ca2Fe1.1Mn0.9O5 provides a fully oxidized layered double perovskite Ca2Fe1.1Mn0.9O6 with alternate Fe4+(d4) and Mn4+(d3) layers. Ca2Fe1.1Mn0.9O6 exhibits charge disproportionation and magneto-resistivity. Electron hopping through double-exchange ferromagnetic interactions between Fe4+ and Mn4+ is proposed.

Posted on 10 April 2014 | 12:10 pm

Tetrathiafulvalene-Based Phenanthroline Ligands: Synthesis, Crystal Structures, and Electronic Properties

The synthesis and full characterization of three tetrathiafulvalene-based phenanthroline ligands, namely, N-(1,10-phenanthrol-5-yl)-6,7-(ethylenedithio)tetrathiafulvalene-2-carboxamide (1), 2-[(1,10-phenanthrol-5-yl)aminocarbonylmethylthio]-3,6,7-tris(methylsulfanyl)tetrathiafulvalene (2), and 2-[(1,10-phenanthrol-5-yl)iminomethyl]tetrathiafulvalene (3), are described. The electronic absorption properties and the electrochemical behavior of the three ligands have been studied. The UV/Vis absorption spectra of these compounds have been rationalized by time-dependent DFT (TD-DFT) calculations, and the single-crystal X-ray structures of 2 and 3 have been determined. The binding properties of these multifunctional systems for various transition metal ions (Ni2+, Zn2+, Cd2+, and Fe2+) have been analyzed in solution by cyclic voltammetry and UV/Vis spectroscopy. The results show that these ligands are suitable candidates for the preparation of electroactive metal complexes and radical cation salts. Three redox-active phenanthroline–tetrathiafulvalene ligands incorporating different linkers between the accepting and the donating subunits have been synthesized. The critical effect of the linker on the intramolecular charge transfer between both parts is experimentally and theoretically studied.

Posted on 9 April 2014 | 1:10 pm

Chiral Self-Sorting of trans-Chelating ­Chiral Ligands upon Formation of PdII Complexes

Two bis(3-pyridyl) ligands 1 and 2 based on a planar chiral [2.2]paracyclophane scaffold were synthesized in enantiomerically pure forms. These ligands act as trans-chelating ligands for square-planar-coordinated metal centres such as palladium(II) ions. Upon forming mononuclear homochiral [ML2] complexes, they show complete chiral self-sorting in a narcissistic self-recognition manner as proven by NMR spectroscopy, mass spectrometry and single-crystal X-ray diffraction. Two bis(3-pyridyl) ligands based on a planar chiral [2.2]paracyclophane scaffold act as trans-chelating ligands for square-planar-coordinated metal centres such as palladium(II) ions. (Pseudo)racemic ligands undergo complete chiral self-sorting in a narcissistic self-recognition manner upon forming mononuclear homochiral [PdL2] complexes.

Posted on 9 April 2014 | 1:10 pm

Metallic Bi- and Monolayered Radical Cation Salts Based on Bis(ethylenedithio)­tetrathiafulvalene (BEDT-TTF) with the Tris(oxalato)gallate Anion

New metallic triclinic (1) and monoclinic (2) crystals of the (BEDT-TTF)4AI[MIII(C2O4)3]G family of organic molecular conductors have been prepared: ?-“pseudo-?”-(BEDT-TTF)4Kx(H3O)1–x[GaIII(C2O4)3]·1,2-C6H4Br2 (x ? 0.45) (1) and ??-(BEDT-TTF)4Kx(H3O)1–x[GaIII(C2O4)3]·PhBr (x ? 0.33) (2). The triclinic crystals belong to a quite rare type of bilayered radical ion salts and contain alternating BEDT-TTF layers with two distinct packing motifs (?- and “pseudo-?”). The monoclinic crystals contain one kind of BEDT-TTF radical cation layers. The crystal structure, transport, and magnetotransport properties of 1 and 2 have been studied. The Shubnikov–de Haas (SdH) oscillations were found in both phases. The structure and properties of 1 and 2 are compared with another similar phase with M = FeIII. Bilayered and monolayered metallic radical cation salts based on bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) with the [GaIII(C2O4)3]3–· anion have been prepared and investigated. Metallic ? and nonmetallic “pseudo-?” layers of BEDT-TTF alternate in the structure of the bilayered salt, whereas the conducting layers in the monolayered salt have only metallic ??-type packing.

Posted on 9 April 2014 | 1:10 pm

Preparation by Solvothermal Synthesis, Growth Mechanism, and Photocatalytic Performance of CuS Nanopowders

Various CuS nanostructures, including nanoflowers, doughnut-shaped nanospheres, dense nanospheres, and mixtures of nanoneedles, nanoparticles, and nanoplates, were synthesized from different copper and sulfur sources by a solvothermal method. The formation mechanisms along with photocatalytic properties for the degradation of rhodamine B (RhB) under visible-light irradiation were investigated in this study. The experimental results indicate that when the sulfur source is fixed at CS(NH2)2 in the solvothermal reaction, spherical nanoflowers, doughnut-shaped nanospheres, and dense nanospheres could be synthesized by using CuCl2, Cu(NO3)2, and CuSO4 as the copper source, respectively. Furthermore, atypical nanoflowers and a mixture of nanoneedles, nanoparticles, and nanoplates could be obtained when the sulfur source was switched to Na2S2O3 and Na2S with a fixed copper source of CuCl2. The energy gaps calculated from the light absorption spectrum were 1.61, 1.93, 2.01, 1.70, and 1.82 eV for the spherical nanoflowers, doughnut-shaped nanospheres, dense nanospheres, atypical nanoflowers, and the mixture of nanoneedles, nanoparticles, and nanoplates respectively. Among these five samples, three powders composed of spherical nanoflowers, atypical nanoflowers as well as a mixture of nanoneedles, nanoparticles, and nanoplates exhibited excellent photocatalytic properties and can degrade rhodamine B completely in an hour. CuS photocatalysts with various morphologies were synthesized from different copper and sulfur sources by a facile solvothermal method. The formation mechanisms and photocatalytic properties were studied in detail. In the photocatalysis process, CuS powders composed of nanoflowers and mixture of nanoneedles, nanoparticles, and nanoplates showed excellent catalytic activities.

Posted on 9 April 2014 | 1:10 pm

Mixed-Valence Biferrocenium Salts of Xn–TCNQ (X = F, Cl; n = 1, 2): Correlation between Molecular Structures and Assembled Structures

Charge-transfer salts composed of biferrocene derivatives and Xn–TCNQ (X = F, Cl; n = 1, 2; TCNQ = tetracyanoquinodimethane) were prepared and crystallographically characterized. All nine salts exhibited a 1:2 donor/acceptor (D/A) ratio consisting of mixed-valence biferrocenium cations and anions with acceptor dimers. The packing patterns were correlated to the donor substituents. On the basis of the ?–? interactions of the cations, the observed structures were classified into three categories: segregated-stack structures for the biferrocenium and dibromo-biferrocenium salts, mixed-stack structures [···(DA2)n···] for the diiodo-biferrocenium salts, and intermediate structures [···(DDA2A2)n···] for the bromo-biferrocenium salts. Biferrocenium salts with Xn–TCNQ (X = F, Cl; n = 1, 2) exhibit a 1:2 D/A ratio, consisting of mixed-valence cations and anions containing acceptor dimers. These salts exhibit segregated-stack structures, mixed-stack structures, and intermediate structures depending on the donor substituents.

Posted on 9 April 2014 | 1:10 pm

Thermochromic and Piezochromic Effects of CoII–Imidazole-Based Supramolecular Gels as Logic Gates

We demonstrate that the imidazole-based ligand 1 efficiently produces a coordination polymer gel by simple mixing with Co2+ ion. When the molar ratio of CoCl2 to ligand 1 was less < 1, a red sol was obtained, indicating the formation of an octahedral (Oh) complex species as occurs with Co(NO3)2. In contrast to G1, when the amount of CoCl2 employed was more than 1 equiv., the color of the gel changed from red to blue (G2), indicating the formation of mainly a tetrahedral (Td) complex species. The ionochromic and the piezochromic effects of imidazole-based suprmolecular gel with Co2+ were investigated. These effects of supramolecular gel were controlled by various anions of cobalt, which are due to coordination geometric change of gels. Interestingly, the ionochromic and piezochromic effects of G1 act as AND and OR logic gates in the solid and the gel state. The ionochromic and piezochromic effects of an imidazole-based supramolecular gel with Co2+ were investigated. The effects of the supramolecular gel were controlled by various anions of cobalt and are the result of changes in the coordination geometry of the gels. Interestingly, the ionochromic and piezochromic effects act as AND and OR logic gates in the solid and gel states.

Posted on 8 April 2014 | 6:10 pm

The Thermal Stability of Tris(methimazolyl)borates and Their Germanium Complexes

A series of methimazole-based soft scorpionate anions ([RTmMe]–, R = H, Ph, Me, nBu) bearing substitution at the bridgehead boron have been used to produce a series of germanium complexes of general formulae [Ge(RTmMe)2]I2. Structural analyses of the germanium complexes by X-ray crystallography reveal that they all contain an octahedral S6 coordination sphere. The scorpionate anions (as their Li or Na salts) and their germanium complexes have been studied by thermogravimetric analysis. This analysis suggests that the degradation pathway for the free scorpionate anions differs from that of the complexes. Both pathways involve the loss of a methimazole ring thereby supporting the view that cleavage of the boron–nitrogen bonds can occur under thermally aggressive conditions. As expected, the presence of the germanium alters the degradation profile of the anion. In contrast to the free anions, the four complexes all display a similar mechanism for degradation. Although the presence of the germanium enforces a conformational change in the anions, its presence does not significantly increase the stability of the boron–nitrogen bonds. A series of at-boron substituted soft scorpionate ligands ([RTmMe]–) and their germanium(IV) complexes are reported and their thermal degradation explored. Two degradation pathways are observed; it is proposed that one involves alkyl migration (R = Me, nBu) whereas the other pathway proceeds by heterocycle formation (R = H, Ph).

Posted on 8 April 2014 | 6:10 pm

Synthesis and Plasmonic Properties of Core–Shell Bimetallic Silver–Gold Nanoprisms Obtained through an Organometallic Route

Ag–Au core–shell nanoprisms were obtained through the deposition of Au atoms over hexadecylamine-stabilized Ag nanoparticles through the mild decomposition of an organometallic AuI precursor. The effects of the amount of precursor [Au(C6F5)(tht)] (tht = tetrahydrothiophene) added and the reaction time on the size, shape, and composition of the core–shell Ag–Au nanostructures obtained have been studied by TEM, high-angle annular dark field/scanning transmission electron microscopy (HAADF-STEM), EDS, UV/Vis, and 19F NMR spectroscopic analysis. The anisotropic growth of the prismatic metallic shell and its composition has been controlled through the addition of different amounts of AuI precursor, thus leading to a delicate tuning of the plasmonic properties of these nanostructures. Spherical silver nanoparticles serve as the template for the growth of an anisotropic gold prismatic shell through an organometallic approach. TEM, high-angle annular dark field/ scanning transmission electron microscopy (HAADF-STEM) techniques, EDS, UV/Vis, and 19F NMR spectroscopy have been used to explain the formation of these bimetallic core–shell heterostructures.

Posted on 7 April 2014 | 11:40 am

Attachment of Chelating Ligand Pockets to Tinorganyl Moieties

Several approaches have been undertaken to realize the synthesis of a new tinorganyl compound with a 2,2?,6?,2?-terpyridine moiety. A synthesis pathway consisting of five steps with an overall yield of 51?% was successful in producing Ph3Sn(CH2)3OPhttpy [HOttpy = 2,6-bis(2?-pyridyl)-4?-(p-hydroxyphenyl)pyridine], and insight has been gained into (partial) halogenation reactions with this unprecedented tinorganyl compound. Halogenation with hydroiodic acid produced a new dinuclear complex cation that resulted from head-to-tail coordination of two monocations. Furthermore, synthesis and yields of already known intermediates have been optimized. The products were analyzed and identified by 119Sn NMR, 1H NMR, and 13C NMR spectroscopy and ESI mass spectrometry, as well as by means of single-crystal X-ray diffraction. A new compound Ph3SnR, comprising a 2,2?,6?,2?-terpyridine-functionalized ligand R, has been synthesized in a five-step procedure. On attempting to halogenate this compound, a partially iodinated derivative was obtained that forms a head-to-tail connected dimer in the salt [(PhISn(CH2)3OPhttpy)2](I3)2 with the terpyridine units acting as chelating ligands.

Posted on 4 April 2014 | 2:10 pm

Mild Hydrosilylation of Amides by Platinum N-Heterocyclic Carbene Catalysts

The platinum-catalyzed hydrosilylation of amides to afford amines selectively is reported. By using defined platinum/N-heterocyclic carbene complexes, the reduction of secondary and tertiary amines takes place under mild conditions. The selective catalytic hydrosilylation of amides is reported. By using defined platinum/N-heterocyclic carbene (NHC) complexes, the reduction of secondary and tertiary amines proceeds in good yields under mild conditions.

Posted on 4 April 2014 | 2:10 pm

The Synthesis, Structures and Polymorphism of the Dimeric Trivalent Rare-Earth 3,5-Dimethylpyrazolate Complexes [Ln(Me2pz)3(thf)]2

A variety of rare-earth 3,5-dimethylpyrazolate (Me2pz) complexes have been synthesised by (i) the direct reaction of Hg-activated metal with Me2pzH as a pro-ligand at elevated temperatures, (ii) by redox transmetalation/protolysis with the lanthanoid element, Hg(C6F5)2, and Me2pzH, and (iii) by protolysis of tris[bis(trimethylsilyl)amido]cerium(III) with Me2pzH. Each product, upon crystallisation from tetrahydrofuran (thf), formed a dimeric complex, [Ln(Me2pz)3(thf)]2 (Ln = La, Ce, Pr, Nd, Ho, Yb, or Lu). Despite the common formulation, two completely different structures were observed in two distinct crystallographic “domains of existence”, together presumptively spanning the gamut of Ln and Y. For the larger rare-earth ions (La–Pr), there are two terminal ?2-Me2pz ligands and one thf donor on each Ln atom, with the metal atoms being linked by a pair of bridging pyrazolate ligands of an uncommon type (?2:?5), resulting in formal ten-coordination. A Me2pzH complex [Ce(Me2pz)3(Me2pzH)], although not isomorphous, has a similar structure. For the smaller rare-earth elements (Nd–Lu), the bridging is entirely different, with two ?-?1(N):?1(N) pyrazolate and two unusual bridging thf ligands. Each Ln atom also has two chelating Me2pz ligands, resulting in formal eight-coordination. Crystallisation of [Nd(Me2pz)3(thf)]2 from pyridine yields monomeric, nine-coordinate [Nd(Me2pz)3(pyridine)3] with only chelating Me2pz ligands. Contrasting structures and bridging Me2pz groups for Ln = La–Pr and Ln = Nd–Lu are described.

Posted on 4 April 2014 | 2:10 pm

Open-Framework Beryllium Hydrogen Phosphates with (3,4)-Connected Networks

Four beryllium hydrogen phosphates, Be2(Hea)(PO4)(HPO4) (1), Him·Be3(OH)(HPO4)3 (2a), Hpy·Be3(OH)(HPO4)3 (2b), and Hma·Be1.5(HPO4)2·0.5H2O (3) in which ea = ethanolamine, im = imidazole, py = pyridine, and ma = methylamine, were synthesized under solvothermal conditions. All compounds have open-framework structures with (3,4)-connected networks. Compound 1 features a neutral inorganic–organic hybrid framework with an interrupted zeolitic GIS topology. The dual role of the amine molecules as charge-balancing agents and coordinating agents to the beryllium atoms is noteworthy. Compounds 2a and 2b are isostructural, and they have an AFI-related framework with elliptical 12-ring channels. Compound 3 has a 3D structure with 4.82 layers pillared by corner-sharing four-ring chains. It represents the first example of an open-framework beryllium hydrogen phosphate with 16-ring channels. Solvothermal crystallization in the presence of different organic structure-directing agents results in the formation of three kinds of beryllium hydrogen phosphate frameworks that have (3,4)-connected networks with 10-ring, 12-ring, and 16-ring channels, respectively.

Posted on 25 March 2014 | 9:30 am

Selective Synthesis of Stannoles by 1,1-Carboboration of Bis(trimethylsilylethynyl)tin Compounds Using Weakly and Strongly Electrophilic Triorganoboranes: Characterization of a Zwitterionic Intermediate

The triorganoboranes BEt3, BPh3, and B(C6F5)3 were allowed to react with bis(trimethylsilylethynyl)diorganotin compounds [R12Sn(C?C–SiMe3)2; R12 = –(CH2)5– (a), R1 = nBu (b), nOct (c), Ph (d)] to give selectively and quantitatively stannoles. The reactions proceeded by 1,1-carboboration in two consecutive steps (inter- and intramolecular) and intermediates were detected by NMR spectroscopy. In one case, using the strongly electrophilic B(C6F5)3, a zwitterionic intermediate was isolated and structurally characterized by X-ray diffraction analysis. The question of reversibility of the 1,1-carboboration is addressed. Multinuclear magnetic resonance spectroscopy (1H, 11B, 13C, 19F, 29Si, 119Sn NMR) was used to characterize the intermediates and the stannoles as the final products. Some of the NMR parameters (11B, 13C, 29Si) of the intermediates were calculated by DFT methods using the optimized gas-phase geometries. The most important intermediates in the synthesis of stannoles by the reaction of bis(trimethylsilylethynyl)tin compounds with triorganoboranes have been detected, isolated, and structurally characterized.

Posted on 17 March 2014 | 1:10 pm

On the Investigation of the Droplet–Droplet Interactions of Sodium 1,4-Bis(2-ethylhexyl) Sulfosuccinate Reverse Micelles upon Changing the External Solvent Composition and Their Impact on Gold Nanoparticle Synthesis

The effect of the composition of the nonpolar organic media on the properties of sodium 1,4-bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelles (RMs) at a fixed temperature were investigated. To monitor interfacial micropolarity and sequestrated water structure in n-heptane:benzene/AOT/water RMs, the solvatochromic behavior of coumarin 343 (C343) as an absorption and emission probe was studied, and the size of the droplets was measured by dynamic light scattering (DLS). The DLS results confirm the formation of the n-heptane:benzene/AOT/water RMs at every n-heptane mole fraction investigated. The data show that as the n-heptane content increases, the interdroplet attractive interactions and the droplet size both increase. With C343 spectroscopy, we determined the “operational” critical micellar concentration, the interfacial micropolarity of the RMs, the hydrogen-bond ability of the media, and the sequestrated water structure in every RM system studied. To verify the modulation of the interdroplet interactions by the external solvent, we have used a well-known synthetic method to create gold nanoparticles in different RM media. The results support the conclusion that the droplet–droplet interactions are favored with n-heptane as the nonpolar solvent. Thus, the rate of material exchange among micelles increases, and small, monodispersed, and highly concentrated gold nanoparticles are formed. The situation is different for AOT RMs prepared in benzene, in which subnanometer gold clusters are produced. The formation of clusters instead of nanoparticles reflects poor material exchange among the micelles owing to unfavorable droplet–droplet interactions. In this way, our results offer a new appealing way to focus the production of nanoparticles into subnanometer clusters, which is one of the hottest current topics in nanoparticle synthesis. Therefore, it is possible to dramatically affect different properties of the RMs by changing the solvent blend; such effects cannot be obtained with only a single solvent composition and may have a large impact on nanotechnology. We anticipate remarkable effects on nanoparticle sizes and polydispersity with different organic solvent blends. The effect of the nonpolar organic medium on the properties of sodium 1,4-bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelles (RMs) was studied. The organic medium affects the interface composition and interdroplet interactions, which have a great effect on gold nanoparticles synthesized in these media. Therefore, the RM properties can be affected dramatically by changing the solvent blend.

Posted on 13 March 2014 | 11:23 am

Functionalisable N-Heterocyclic Carbene–Triazole Palladium Complexes and Their Application in the Suzuki–Miyaura Reaction

Seven functionalised N-heterocyclic carbene (NHC) ligands and their corresponding palladium(II) complexes have been synthesised with a triazole moiety as a modular and stable linkage between the catalytic centre and the secondary functional group. The complexes were prepared in good yields and fully characterised by NMR spectroscopy, mass spectrometry and X-ray crystallography. The complexes are active in the Suzuki–Miyaura cross-coupling reaction, with catalytic activities maintained whatever the triazolyl substituent. This opens the possibility for various functionalisations of NHC–palladium complexes. New functionalised N-heterocyclic carbene ligands and their corresponding palladium(II) complexes have been synthesised and fully characterised. The use of a triazole moiety as a modular and stable linkage between the catalytic centre and a targeted functionalisation does not damage the catalytic activity.

Posted on 13 March 2014 | 11:23 am

Facile Synthesis of Carbon-Encapsulated Li4Ti5O12@C Hollow Microspheres as Superior Anode Materials for Li-Ion Batteries

An in situ carbon-encapsulating solution route for the synthesis of Li4Ti5O12@C composite hollow microspheres has been developed. The finally obtained Li4Ti5O12@C hollow microspheres possess a microsized spherical shape, embedded Li4Ti5O12 nanocrystals, and fully encapsulating conductive carbon shells, which endow this Li4Ti5O12 anode material with high specific capacity, rate capability, and cycle stability. Owing to their unique microstructure characteristics, these hollow Li4Ti5O12@C microsphere composites are promising anode materials for highly efficient Li-ion batteries with an excellent rate capability (discharge capacity of 169, 152, 130, 116, 93, and 76 mA?h?g–1 at 0.2, 1, 2, 5, 30 and 60C, respectively) and a significantly enhanced cycling performance. A solution-phase self-assembly and solid-phase carbonization route for the synthesis of uniform hollow carbon microspheres embedded with Li4Ti5O12 nanoparticles has been developed. The microsized spherical Li4Ti5O12@C hollow composites have conductive carbon shells, which endow them with high specific capacity, rate capability, electrode density, and cycle stability.

Posted on 13 March 2014 | 11:23 am

Structure Solution from Powder Diffraction of Copper 1,4-Benzenedicarboxylate

In the synthesis of the microporous metal–organic framework copper 1,4-benzenedicarboxylate [Cu(BDC)], solvent exchange with methanol prior to recrystallization lowers the desolvation temperature to 160 °C and produces more crystalline Cu(BDC). The solution to the crystal structure of Cu(BDC) has been determined by using ab initio quantum molecular calculations and refinement with synchrotron X-ray powder diffraction data. This solution is in the P$\bar {1}$ space group with a = 5.25 Å, b = 9.67 Å, c = 10.77 Å, ? = 90.29°, ? = 91.06°, ? = 92.413°, and V = 546.04 Å3. The Brunauer–Emmett–Teller (BET) surface area was 903 m2?g–1 with 777 m2?g–1 of micropore surface area. The uptake of CO2 and CH4 up to 20 bar were 5.2 and 2.7 mmol?g–1, respectively. These values are compared to those of 1,3,5-benzenetricarboxylate [Cu3(BTC)2, HKUST-1] and used to show that the elevated metal-site density per unit volume is responsible for a proportionally higher uptake on the basis of relative surface areas. The platelike particles with perpendicular pores are promising candidates for mixed-matrix membranes. The structure of copper 1,4-benzenedicarboxylate [Cu(BDC)] has been determined by X-ray powder diffraction and ab initio quantum mechanics (QM) calculations (P$\bar {1}$, 546.04 Å3). Extraction with methanol improves the Cu(BDC) crystallite quality. The Brunauer–Emmett–Teller (BET) surface area is 903 cm2?g–1, the CO2 uptake is 5.2 mmol?g–1 at 20 bar, and the selectivity for CO2 over CH4 is 2–3.

Posted on 13 March 2014 | 11:23 am

Structural Characterization, Solution Dynamics, and Reactivity of Palladium Complexes with Benzimidazolin- 2-ylidene N-Heterocyclic Carbene Ligands

Mononuclear and halide-bridged dinuclear palladium(II) complexes with symmetrically (1 and 3) and nonsymmetrically (2, 4–6) substituted benzimidazolin-2-ylidene N-heterocyclic carbene ligands were synthesized and characterized by 1H and 13C NMR spectroscopy, elemental analysis, and X-ray crystallography. The mononuclear complexes exist as a mixture of cis and trans isomers, and the identity of these was ascertained by NMR spectroscopy and structural characterization. The dinuclear complexes 4–6 with nonsymmetrically substituted benzimidazolin-2-ylidene ligands form rotamers (cis/anti, cis/syn, trans/anti, and trans/syn) at room temperature, which can be transformed to a single rotamer at higher temperatures as evidenced by 1H NMR spectroscopy. Crystal structure analyses of representative examples show that the PdII centers are bound in a distorted square-planar environment by halides and carbene C ligands, and the carbene ligands are perpendicular to the Pd–halide plane. All of the complexes were tested for their efficiency as (pre)catalysts in the Suzuki–Miyaura cross-coupling reaction, as well as in hydrodehalogenation reactions, and they show good activity. The Suzuki–Miyaura coupling reactions can be performed under air and in water as an environmentally benign solvent. The most active catalyst for the Suzuki–Miyaura coupling was also used in a sequence together with a “click reaction” to synthesize valuable sterically demanding tripodal triazole ligands. PdII complexes with symmetrically and nonsymmetrically substituted benzimidazolylidene ligands are presented. The complexes exist as various isomers and rotamers in solution and exhibit C–H···Pd interactions in the solid state and in solution. All of the complexes are potent (pre)catalysts for the Suzuki–Miyaura cross-coupling reaction in water and the hydrodehalogenation reactions of haloarenes.

Posted on 13 March 2014 | 11:23 am

A Tripodal Trisilanol Ligand and Its Complexation Behavior towards CuI, CuII, and ZnII

A three-step synthetic route for a new tripodal branched trisilanol ligand PhSi(OSiPh2OH)3 (LH3) was developed. X-ray diffraction analysis revealed that the trisilanol crystallizes as a dimer with a cyclic hydrogen-bonding network. The reaction of LH3 with three equivalents of CunMesn (Mes = mesityl) led to a hexanuclear compound [L2Cu6] (1), which was characterized by single-crystal X-ray diffraction analysis as well as by solution NMR spectroscopy. The crystal structure of 1 revealed that the compound features a hexagonal planar CuI6 ring, which is the first of its kind in an oxygen environment. Deprotonation of the ligand with n-butyllithium and subsequent reaction with CuBr2 resulted in the dinuclear CuII complex [L?2Cu2][Li(THF2)]2 (2, THF = tetrahydrofuran), which contains a new siloxide ligand formed from L3– by the elimination of a SiOPh2 unit, as evidenced by X-ray diffraction analysis. To check if the “Ph2SiO” elimination is a general behavior of this trisilanol, the reaction with ZnBr2 was investigated under analogous conditions. However, this led to the isolation of [L2Zn2][Li(OEt)]2 (3) without any rearrangement of the siloxide ligand. A tripodal branched trisilanol ligand PhSi(OSiPh2OH)3 (LH3) was synthesized. Its reaction with three equivalents of CunMesn (Mes = mesityl) led to a hexanuclear compound [L2Cu6] with a planar CuI6 ring. Deprotonation of LH3 with n-butyllithium and subsequent reaction with either CuBr2 or ZnBr2 resulted in dinuclear complexes. In the case of CuBr2, the original ligand eliminates a “Ph2SiO” unit.

Posted on 12 March 2014 | 1:25 pm

{Cu2+–Co3+–Cu2+} and {Cu2+–Fe3+–Cu2+} Heterobimetallic Complexes and Their Catalytic Properties

We report on the heterobimetallic complexes {Cu+–Co3+–Cu+} (3), {Cu+–Fe3+–Cu+} (4), {Cu2+–Co3+–Cu2+} (5), and {Cu2+–Fe3+–Cu2+} (6) and show their catalytic applications in the oxidation of hindered phenols and the oxidative coupling of terminal alkynes. The former reaction produces C–C-coupled and dealkylated products, whereas the latter leads to the homo- and heterocoupling of terminal alkynes. The facile redox interconversion between Cu+ and Cu2+ for the secondary metal ions in these heterobimetallic complexes appears to be essential for the observed catalysis, and an important design aspect is better substrate accessibility and the use of molecular oxygen as the sole oxidant. Heterobimetallic complexes {Cu+–Co3+–Cu+} (3), {Cu+–Fe3+–Cu+} (4), {Cu2+–Co3+–Cu2+} (5), and {Cu2+–Fe3+–Cu2+} (6) have been used as catalysts for the oxidation of substituted phenols and the oxidative homo- and heterocoupling of terminal alkynes.

Posted on 11 March 2014 | 9:10 am

Acetic Acid Mediated Synthesis of Phosphonate-Substituted Titanium Oxo Clusters

New phosphonate/acetate-substituted titanium oxo/alkoxo clusters were prepared from Ti(OiPr)4 and bis(trimethylsilyl) phosphonates in the presence of acetic acid, which served to generate water in situ through ester formation. The process led to clusters with a higher degree of condensation than in previously known phosphonate-substituted titanium oxo clusters. The clusters [Ti6O4(OiPr)10(OAc)2(O3PR)2] (OAc = acetate) were obtained for a large variety of functional and non-functional groups R under a range of reaction conditions. This cluster type, which is also retained in solution, therefore appears to be very robust. Two other clusters, [Ti5O(OiPr)11(OAc)(O3PCH2CH2CH2Br)3] and [Ti5O3(OiPr)6(OAc)4(O3P-xylyl)2], were only isolated in special cases. Several acetate/phosphonate-substituted titanium cage compounds were obtained from the reaction of titanium isopropoxide with bis(trimethylsilyl) phosphonates in the presence of acetic acid as water generator.

Posted on 11 March 2014 | 9:10 am

Immobilization of 1,5,7-Triazabicyclo[4.4.0]dec-5-ene on Magnetic ?-Fe2O3 Nanoparticles: A Highly Recyclable and Efficient Nanocatalyst for the Synthesis of Organic Carbonates

1,5,7-Triazabicyclo[4.4.0]dec-5-ene was immobilized on magnetic ?-Fe2O3 nanoparticles as a magnetic nanocatalyst. The nanoparticle reagent was obtained with good loading levels and has been successfully used for the efficient and selective synthesis of organic carbonates by the direct condensation of alcohols and diethyl carbonate. The catalyst is quantitatively recovered by an external magnet and can be reused for six cycles with almost consistent activity. 1,5,7-Triazabicyclo[4.4.0]dec-5-ene was immobilized on magnetic ?-Fe2O3 nanoparticles as a magnetic nanocatalyst. The nanoparticle reagent was obtained with good loading levels and has been successfully used for the efficient and selective synthesis of organic carbonates by the direct condensation of alcohols and diethyl carbonate.

Posted on 11 March 2014 | 9:10 am

Binary Lithium Indides Li22–xIn8+x (x = 0.1), Li11–xIn4+x (x = 1.05), and Li10–xIn2+x (x = 1.59) with Clusters

The synthesis, structural characterization, and chemical bonding peculiarities of three new binary Li–In intermetallides are reported. The crystal structures of these compounds were determined by single-crystal X-ray diffraction analysis. The compositions obtained after structure refinements were Li22–xIn8+x (x = 0.1) [new structure type, monoclinic crystal system, Pearson symbol mS30, space group C2/m, a = 14.156(3), b = 4.729(1), c = 8.617(2) Å, ? = 105.89(1)°, R1 = 0.0279, wR2 = 0.0583 for 669 reflections], Li11–xIn4+x (x = 1.05) [new structure type, trigonal, P$\bar {3}$m1, hP15, a = 4.7480(7), c = 14.283(3) Å, R1 = 0.0323, wR2 = 0.0741 for 277 reflections], and Li10–xIn2+x (x = 1.59) [new structure type, hexagonal, P6/mmm, hP12, a = 4.6975(7), c = 11.526(2) Å, R1 = 0.0680, wR2 = 0.1358 for 127 reflections]. The Li22–xIn8+x (x = 0.1) structure is related to the structure of lithium (W-type). The structure of Li11–xIn4+x (x = 1.05) can be described as a derivative of the CdI2 type. Li10–xIn2+x (x = 1.59) can be derived from the Li2Pt structure. [In2@Li20] clusters composed of 20 lithium atoms, which surround a In–In pair, are detected in the structure of all three investigated compounds. TB-LMTO (Tight-Binding Linear Muffin-Tin Orbital) calculations indicate strong covalent In–In interactions and the presence of [In2@Li20] clusters in these new binary indides. Three new binary lithium indides were synthesized, and their crystal structures were studied by single-crystal X-ray diffraction analyses. All compounds crystallize in new structure types. The presence of [In2@Li20] clusters was detected in the structure of all three new compounds. The covalent type of the In–In bonding in the clusters was confirmed by electronic structure calculations.

Posted on 11 March 2014 | 9:10 am

Supramolecular 3-/4-Mercaptobenzoic Acid Complexes of Palladium(II) and Platinum(II) Stabilized by Hydrogen Bonding

The reaction of cis-[Pt(PEt3)2(OTf)2] with 4-mercaptobenzoic acid (4-H2mba) in the presence of sodium methoxide yielded trans-[Pt(SC6H4COOH-4)2(PEt3)2] (1), the simple addition of 3-/4-mercaptobenzoic acid to cis-[Pt(PEt3)2(OTf)2] and cis-[M(PP)2(OTf)2] gave the self-assembled complexes cis-[Pt(?-SC6H4COOH-n)(PEt3)2]2(OTf)2 [n = 3 (2), 4 (3)] and [M(?-SC6H4COOH-n)(PP)]2(OTf)2 [M/n/PP = Pd/3/dppe (4), Pd/4/dppe (5), Pt/4/dppp (6); dppe = 1,2-bis(diphenylphosphino)ethane, dppp = 1,2-bis(diphenylphosphino)propane], respectively, and the reactions of cis-[PtCl2(PR3)2] (R = Et, Ph) and [PtCl2(dppm)] with 3-/4-mercaptobenzoic acids in the presence of triethylamine yielded 1, trans-[Pt(SC6H4COOH-4)2(PPh3)2] (7) and [Pt(SC6H4COOH-n)2(dppm)] [n = 3 (8), 4 (9); dppm = bis(diphenylphosphino)methane], respectively. The complexes 1–4 and 7 form supramolecular assemblies through intermolecular hydrogen bonding in the solid state. A one-dimensional zigzag chain of carboxy dimers is formed in the structures of 1·H2O and 7, whereas methanol-interrupted large-ring formation leads to a 2D network for 1·(MeOH)2. In the cases of 3·(H2O)2 and 4·(H2O)2, water and counter-anions assisted the formation of 1D networks rather than dimers through carboxylic acid groups. 3-/4-Mercaptobenzoic acids have been employed to design Pd/Pt complexes with the general formulae trans-[Pt(SC6H4COOH-4)2(PR3)2], cis-[Pt(?-SC6H4COOH-n)(PEt3)2]2(OTf)2, [M(?-SC6H4COOH-n)(PP)2]2(OTf)2 and cis-[Pt(SC6H4COOH-n)2(dppm)]. The crystal structures and networks of these complexes have been investigated.

Posted on 10 March 2014 | 12:10 pm

The Pentynoate Ligand as a Building Block for Multimetallic Systems

The complexes [RuRCl(CO)(BTD)(PPh3)2] (R = CH=CHtBu, CH=CHC6H4Me-4, CH=CHC5H4FeC5H5; BTD = 2,1,3-benzothiadiazole) and [Ru{C(C?CPh)=CHPh}(CO)(PPh3)2] reacted with pentynoic acid to yield the same complex, [RuCl(O2CCH2CH2C?CH)(CO)(PPh3)2], through cleavage of the vinyl ligand. In contrast, the products [RuR(O2CCH2CH2C?CH)(CO)(PPh3)2] were formed when NaO2CCH2CH2C?CH was used. An osmium example, [Os(CH=CHC6H4Me-4)(O2CCH2CH2C?CH)(CO)(PPh3)2], was also prepared from treatment of [Os(CH=CHC6H4Me-4)Cl(CO)(BTD)(PPh3)2] with NaO2CCH2CH2C?CH. Coupling of the pendant alkyne in [RuCl(O2CCH2CH2C?CH)(CO)(PPh3)2] to yield the homodimetallic complex [{RuCl(O2CCH2CH2C?C)(CO)(PPh3)2}2] was achieved by using [PdCl2(PPh3)2], CuI and NEt3. The reactivity of the alkyne unit was further exploited by the metallation of the alkyne with ClAu(PR3) (R = Ph, Cy) and Co2(CO)8 to yield the multimetallic species [Ru(CH=CHC6H4Me-4)(O2CCH2CH2C?CAuPR3)(CO)(PPh3)2] and [Ru(CH=CHC6H4Me-4)(O2CCH2CH2CC{Co2(CO)6}H)(CO)(PPh3)2]. The structures of the complexes [Ru(CH=CHC6H4Me-4)(O2CCH2CH2C?CH)(CO)(PPh3)2] and [Ru(CH=CHtBu)(O2CCH2CH2C?CH)(CO)(PPh3)2] were determined crystallographically. Organometallic ruthenium and osmium pentynoate complexes were prepared, and the pendant alkyne functionality was used to form homodimetallic and heteronuclear di- and trimetallic complexes.

Posted on 10 March 2014 | 12:10 pm

Speciation of Technetium in Sulfuric Acid/Hydrogen Sulfide Solutions

The reaction between TcVII and H2S(g) in 12 M H2SO4 has been studied. This reaction produced a black solid and a brown supernate. The solid was analyzed by energy dispersive X-ray (EDX) and X-ray absorption fine structure (XAFS) spectroscopy and the results were consistent with the presence of Tc2S7. The speciation of technetium in the supernate was performed by UV/Visible and XAFS spectroscopy. Experiments showed that in 12 M H2SO4 an intermediate TcV sulfate complex was formed. Analysis indicated that the final complex present in solution was a polymeric species with a Tc–O–Tc core coordinated to sulfate ligands. Density Functional Theory (DFT) calculations showed that the proposed complexes were stable and that the theoretical structure was in good agreement with XAFS data. The speciation of technetium after the reaction of KTcO4 in 12 M H2SO4/H2S(g) has been studied. The mechanism of formation can be described as a transformation from the yellow species TcVIIO3(H2O)2(OH) to the green complex TcVO(HSO4)3(OH)– followed by polymerization, leading to precipitation of Tc2S7 and the presence of the polymeric species Tc–O–Tc coordinated to sulfate ligands in solution.

Posted on 7 March 2014 | 10:10 am

Hierarchical N-Doped TiO2 Microspheres with Exposed (001) Facets for Enhanced Visible Light Catalysis

Hierarchical N-doped TiO2 microspheres with exposed (001) facets [N-TiO2-(001)] were synthesized through a simple, fluorine-free solvothermal reaction with subsequent thermal treatment. The results show that the hierarchical N-TiO2-(001) microspheres are made up of numerous TiO2 nanosheets, and that isopropylamine (IPAN) acts as both the nitrogen source and the capping and shape-controlling agent that generates the high-energy (001) facets. In addition, IPAN is also effective in increasing the onset temperature of the phase transformation of TiO2 from anatase to rutile. Compared with the commercially available P25 TiO2, the as-prepared TiO2 microspheres exhibit good photocatalytic activity and high stability under visible-light irradiation. The high photocatalytic performance is derived from the synergy effect of N-doping and the separation of photogenerated electrons and holes among different facets, as evidenced by surface photovoltage spectroscopy. Hierarchical N-doped TiO2 microspheres with exposed (001) facets were successfully synthesized in a fluorine-free solvothermal reaction. Isopropylamine was used as the nitrogen source and as the capping and shape-controlling agent to generate the (001) facets. The hierarchical TiO2 microspheres exhibit good photocatalytic activity and high stability under visible-light irradiation.

Posted on 6 March 2014 | 12:10 pm

CuII-Templated Threading of a Bis-amide-tris-amine Macrocycle by Substituted 2,2?-Bipyridyl Derivatives Assisted by Strong ?–? Stacking and Second-Sphere H-Bonding Interactions

Derivatives of 5,5?-substituted 2,2?-bipyridine (BPy) ligands with bromo-terminated aliphatic side chains with ester functionalities (BPy5Br), hydroxy-terminated aliphatic side chains with amide functionalities (BPy5OH), and benzyl-terminated side chains with amide functionalities (BPy5Bnz) were synthesized. The single-crystal X-ray structure analysis of the axle BPy5Br shows that it has a linear rodlike structure with a length of 15.75 Å. The above three ligands along with a methyl-substituted BPy ligand (BPy5Me) are explored as axles for CuII-templated threading of a bis-amide-tris-amine macrocycle wheel (MC). High-yield (70–80?%) syntheses of the [2]pseudorotaxanes PRT1, PRT2, PRT3, and PRT4 are obtained by reaction of MC with the axles BPy5Me, BPy5Br, BPy5OH, and BPy5Bnz, respectively, in the presence of CuII ions. These complexes were characterized by ESI-MS, UV/Vis and EPR spectroscopy, and single-crystal X-ray diffraction studies. The solution-state binding stoichiometry and the association constants for complex formation between MC–Cu2+ and the axles were studied by UV/Vis absorption titrations. Sigma-fit curves indicate 1:1 stoichiometry, and the association constants range from 1.2?×?103 to 2.6?×?103 M–1. Single-crystal X-ray structure analysis of PRT1, PRT2, and PRT4 confirms the threading of MC by the respective axles, which are coordinated to the CuII center with Cu–N bond lengths of 1.992–2.203 Å. Interestingly, strong aromatic ?–? stacking interactions between two parallel arene moieties of MC and the pyridyl unit of the axle with ?–? interaction distances of 3.402–3.618 Å are observed in all three [2]pseudorotaxanes. However, for PRT4, a strong hydrogen-bonding interaction is also operative between the carbonyl oxygen atom of BPy5Bnz and the amide proton of MC with a N–H···O distance of 2.200 Å. Thus, multiple template interactions such as metal coordination, ?–? stacking, and second-sphere hydrogen-bonding interactions between MC and the axles play crucial roles for facile threading and high-yield syntheses of [2]pseudorotaxanes. Axles with ester functionalities with aliphatic side chains, amide functionalities with aliphatic side chains, and amide functionalities with aromatic side chains show CuII-templated [2]pseudorotaxane formation with an amido–amine macrocycle. Metal coordination, ?–? stacking, and hydrogen-bonding interactions are operative for effective threading.

Posted on 27 January 2014 | 9:10 am

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