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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:

The Ion-Like Supersilylium Compound tBu3Si–F–Al[OC(CF3)3]3

The ion-like silylium compounds tBu3Si–F–Al[OC(CF3)3]3 and Me3Si–F–Al[OC(CF3)3]3 were prepared by degradation of the halonium salts [R3Si–X–SiR3][Al{OC(CF3)3}4] {1a(X): R = tBu, X = Br, I; 1b(X): R = Me, X = Br, I}. The bromonium and iodonium salts 1a(Br), 1a(I), 1b(Br), and 1b(I) were quantitatively obtained from R3SiX (R = Me, tBu) and [Ag][Al{OC(CF3)3}4] in dichloromethane at –50 °C. However, the related fluoronium and chloronium salts, [R3Si–X–SiR3][Al{OC(CF3)3}4] {1a(X): R = tBu, X = F, Cl; 1b(X): R = Me, X = F, Cl}, could not be generated under these conditions. Generally, at low temperatures (< –50 °C) the halonium salts 1a(Br), 1a(I), 1b(Br), and 1b(I) are stable compounds. However, at higher temperatures 1a(Br), 1a(I), 1b(Br), and 1b(I) undergo R3SiX (R = Me, tBu; X = Br, I) elimination to form the highly reactive silyl cations [R3Si]+ (R = Me, tBu). Two different decomposition pathways were observed in the thermolysis of halonium compounds 1a(Br), 1a(I), 1b(Br), and 1b(I): (1) the silylium cations [R3Si]+ reacted with dichloromethane, forming 1a(Cl) as well as 1b(Cl); (2) the silylium cations [R3Si]+ degraded the counteranion to give tBu3Si–F–Al[OC(CF3)3]3 and Me3Si–F–Al[OC(CF3)3]3 along with epoxide C4F8O. Both ion-like silylium compounds could be isolated, and single crystals of tBu3Si–F–Al[OC(CF3)3]3 (orthorhombic, Pnma) as well as Me3Si–F–Al[OC(CF3)3]3 (orthorhombic, P212121) were grown from dichloromethane at room temp. Supersilylium [tBu3Si]+ has higher Lewis acidity than [Me3Si]+, as demonstrated by the reaction of 1a(I) with Me3SiF. Thereby the fluoronium ion 1b(F), along with tBu3SiF and tBu3SiI, was formed. Access to the supersilylated and trimethylsilylated halonium salts [R3Si–X–SiR3]{Al[OC(CF3)3]4} (R = tBu, X = Br, I; R = Me, X = Br, I) was achieved. Degradation of these halonium salts results in the formation of the ion-like silylium compounds tBu3Si–F–Al[OC(CF3)3]3 and Me3Si–F–Al[OC(CF3)3]3.

Posted on 27 April 2015 | 10:21 pm

Carbonylation of Hydrido–Phosphanido-Bridged Dinuclear Platinum Complexes

The carbonylation of the solvento species [(PHCy2)(L)Pt(?-PCy2)(?-H)Pt(PHCy2){?P-P(OH)Cy2}][BF4]2(Pt–Pt) ([1-L]2+, L = CH2Cl2, thf, CH3CN) led to the formation of a singly bridged dicarbonyl PtI compound syn-[(PHCy2)(CO)Pt(?-PCy2)Pt{?P-P(OH)Cy2}(CO)]+(Pt–Pt) (2+). The reaction proceeded in two steps: 1) Substitution of L by CO to give the intermediate syn-[(PHCy2)(CO)Pt(?-PCy2)(?-H)Pt(PHCy2){?P-P(OH)Cy2}]2+(Pt–Pt) ([1-CO]2+) and 2) uptake of a second molecule of CO and elimination of [PH2Cy2]+ (as the BF4– salt) to give 2+. The dicarbonyl complex [2][BF4] was also synthesized starting from the dicyclohexylphosphanido-bridged complex [(PHCy2)Pt(?-PCy2){?2P,O-?-P(O)Cy2}Pt(PHCy2)](Pt–Pt) (5). In this case the first step consisted of the carbonylation of 5 to give [(PHCy2)2Pt(?-PCy2)Pt{?P-P(O)Cy2}(CO)](Pt–Pt) (6), which was transformed into 2+ by protonation with HBF4 under an atmosphere of CO. Prolonged reaction times for the carbonylation of [1-L]2+ in halogenated solvents resulted in the formation of the symmetrical dicarbonyl compound syn-[(CO)(PHCy2)Pt(?-PCy2)Pt(PHCy2)(CO)]+(Pt–Pt) (3+) along with Cy2P(H)OBF3. Complexes 6 and [1-L][BF4]2 were also formed by the carbonylation of 5 and [1-OMe2][BF4]2 in the solid state. The singly bridged dicarbonyl PtI compound 2+ can be obtained, both in solution and in the solid state, either by carbonylation of the solvento species [1-L]2+ or by carbonylation of 5 followed by the addition of HBF4.

Posted on 27 April 2015 | 10:21 pm

Template-Free Synthesis of Three-Dimensional Nanoporous Bulk Graphitic Carbon Nitride with Remarkably Enhanced Photocatalytic Activity and Good Separation Properties

A facile template-free method is presented for the fabrication of three-dimensional (3D) nanoporous bulk graphitic carbon nitride (g-C3N4) with an interconnected framework. Various techniques, namely, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, elemental analysis, specific surface area measurements (Brunauer–Emmett–Teller method), UV/Vis diffuse reflectance spectroscopy, time-resolved fluorescence decay spectroscopy, electron paramagnetic resonance spectroscopy, and photoelectrochemical measurements, were adopted to analyze the structures and physicochemical properties of the as-prpared samples. The results show that the nanoporous bulk g-C3N4 with a particle size of ca. 20 ?m exhibits a high specific surface area, which is ca. 30.9 times higher than that of the original material. The g-C3N4 with such a structure exhibits an improved adsorption capacity for the target pollutants and is readily separable from the photocatalysis reaction system. It is believed that a two-step protonation process plays a key role in the formation of the structure. Furthermore, this 3D nanoporous bulk g-C3N4 also shows more-efficient photogenerated carrier transfer and separation. As a result, the visible-light photocatalytic activity of g-C3N4 is significantly enhanced, and the degradation rates of methyl orange (MO) and rhodamine B (RhB) dyes over the nanoporous bulk g-C3N4 are ca. 5.0 and 22.3 times higher, respectively, than that over the original material. A facile template-free method is presented for the fabrication of nanoporous graphitic carbon nitride (g-C3N4) with a three-dimensional (3D) interconnected framework through a two-step protonation. The material exhibits excellent photocatalytic activity owing to its 3D nanoporous structure and highly efficient charge separation and transfer.

Posted on 27 April 2015 | 10:20 pm

Regioselective Cleavage of Electron-Rich Double Bonds in Dienes to Carbonyl Compounds with [Fe(OTf)2(mix-BPBP)] and a Combination of H2O2 and NaIO4

A method for the regioselective transformation of dienes to carbonyl compounds has been developed. Electron-rich olefins react selectively to yield valuable aldehydes and ketones. The method is based on the catalyst [Fe(OTf)2(mix-BPBP)] with an oxidant combination of H2O2 (1.0 equiv.) and NaIO4 (1.5 equiv.); it uses mild conditions and short reaction times, and it outperforms other olefin cleavage methodologies. The combination of an Fe-based catalyst, [Fe(OTf)2(mix-BPBP)], and the oxidants H2O2 and NaIO4 can discriminate between electronically different double bonds and oxidatively cleave the electron-rich bond in dienes to yield aldehydes and ketones in a regioselective manner. The reaction requires mild conditions (0–50 °C) and short reaction times (70 min).

Posted on 27 April 2015 | 9:50 pm

Dioxomolybdenum(VI) and -Tungsten(VI) Complexes with Multidentate Aminobisphenol Ligands as Catalysts for Olefin Epoxidation

The synthesis of four molybdenum and tungsten complexes bearing tetradentate tripodal amino bisphenolate ligands with either hydroxyethylene (1a) or hydroxyglycolene (1b) substituents is reported. The molybdenum dioxo complexes [MoO2L] (L = 2a, 2b) and tungsten complexes [WO2L] (3a, 3b) were synthesized using [MoO2(acac)2] and [W(eg)3] (eg = 1,2-ethanediolato, ethylene glycolate), respectively, as precursors. All complexes were characterized by spectroscopic means as well as by single-crystal X-ray diffraction analyses. The latter reveal, in all cases, hexacoordinate complexes in which the hydrogen atom of the hydroxy group is involved in hydrogen bonding with one of the metal oxo groups. In the case of the glycol substituent, the ether oxygen atom is coordinated to the metal whereas the hydroxy group remains uncoordinated. The complexes were tested as catalysts in the epoxidation of cyclooctene under eco-friendly conditions, using an aqueous solution of H2O2 as the oxidant and dimethyl carbonate (DMC) as solvent or neat conditions, as substitutes for chlorinated solvents. Molybdenum complexes 2a and 2b showed good catalytic activity using H2O2 without added solvent, and tungsten complexes 3a and 3b showed very high activity in the epoxidation of cyclooctene using H2O2 and DMC as solvents. Four new molybdenum and tungsten complexes bearing tetradentate tripodal amino bisphenolate ligands with either hydroxyethylene or hydroxyglycolene substituents were synthesized and found to catalyze olefin epoxidation reactions under eco-friendly conditions.

Posted on 27 April 2015 | 9:50 pm

Bis(phosphinimino)amide Supported Borondihydride and Heteroleptic Dihalo Compounds of Group 13

The reaction of tetraphenyldiphosphazane (Ph2P)2NH with mesityl azide 2,4,6-Me3C6H2-N3 affords a new [N,N?] chelating ligand, [HN(Ph2PN(2,4,6-Me3C6H2))2] (LH). The ligand can be easily deprotonated by using nBuLi or Li[N(SiMe3)2] in Et2O to yield [{N(Ph2PN(2,4,6-Me3C6H2))2}Li·OEt2] (1). The reaction of LH with AlMe3 and BH3·SMe2, respectively, gives the corresponding mononuclear complexes [{N(Ph2PN(2,4,6-Me3C6H2))2}AlMe2] (2) and a rare borondihydride [{N(Ph2PN(2,4,6-Me3C6H2))2}BH2] (3). Similarly, reaction of 1 with the trihalides, MX3, of group 13 elements afford the corresponding dihalo complexes, [{N(Ph2PN(2,4,6-Me3C6H2))2}MX2] [M = B, X = F (4); M = Al, X = Cl (5); M = Ga, X = Cl (6); M = In, X = Br (7)]. All the complexes reported in this work have been isolated in good yields and are expected to serve as useful synthons in a number of reactions. The solid-state structure of LH and 1–7 have been investigated by single-crystal X-ray structural analysis. Synthesis of a rare borondihydride complex has been made possible through the use of a relatively strong donor monoanionic bis(phosphinimino)amide ligand. Crucially, the ligand backbone is void of any reactive acidic hydrogen. The same ligand has also made feasible the synthesis of some heteroleptic dihalo derivatives of group 13 elements.

Posted on 27 April 2015 | 9:50 pm

Spin Crossover in cis Manganese(III) Quinolylsalicylaldiminates

Two new MnII/III redox pairs, [Mn(qsal-Cl)2]0/+ 10/+ and [Mn(qsal-Br)2]0/+ 20/+ have been synthesized employing the tridentate Schiff base ligands, 5-X–N-(8-quinolyl)salicylaldimine (Hqsal-X, X = Cl and Br). The neutral MnII complexes 1 and 2 were prepared from MnCl2 and Hqsal-Cl and Hqsal-Br while oxidation of 1 or 2 with AgOTf yields the cationic MnIII complexes, [Mn(qsal-Cl)2]OTf, 1+, and [Mn(qsal-Br)2]OTf, 2+. 1 and 2 have been characterized by single-crystal X-ray diffraction as CH2Cl2 solvates. The Mn centres adopt a strongly distorted octahedral geometry with cis O donors due to the pair of meridionally bound qsal-X ligands. Electrochemical studies indicate two reversible one-electron redox processes, Mn2+/3+ and Mn3+/4+. Spectroscopic studies show the LMCT bands move to lower wavelengths by ca. 30 nm while the ?C=N stretches are little changed in the cationic complexes. Variable temperature magnetic susceptibility measurements indicate that 1+ and 2+ undergo gradual half spin crossover, despite having cis O donors. DFT calculations reveal a small HS–LS gap in the MnIII systems consistent with spin crossover and provide insight into the ligand design necessary for spin crossover in cis-N4O2 MnIII compounds. We report the redox pairs [Mn(qsal-X)2]0/+ in which the MnIII cations exhibit spin crossover despite the cis O donors.

Posted on 27 April 2015 | 12:13 pm

Ruthenium Carboxylate Complexes as Efficient Catalysts for the Addition of Carboxylic Acids to Propargylic Alcohols

Ruthenium complexes [Ru(CO)2(PPh3)2(O2CR)2] – 3a (R = CH2OCH3), 3b (R = iPr), 3c (R = tBu), 3d (R = 2-cC4H3O), and 3e (R = Ph) – were synthesized by treatment of Ru(CO)3(PPh3)2 with the corresponding carboxylic acids. The molecular structures of the newly synthesized complexes in the solid state are discussed. Compounds 3a–e were successfully applied as catalysts in the addition of carboxylic acids to propargylic alcohols to give the corresponding ?-oxo esters in good to excellent yields even in air. The different carboxylate ligands do not have an influence on the productivities, because the carboxylates exchange rapidly under the applied reaction conditions, as was confirmed by 31P{1H} NMR spectroscopic studies. The addition of catalytic amounts of Na2CO3 resulted in an increase in ?-oxo ester formation. The reaction is tolerant to the use of versatile functional groups on the propargylic alcohols and carboxylic acids, revealing a broad substrate generality. In contrast to most other known catalytic systems, even sterically hindered substrates, including 2,4,6-trimethylbenzoic acid, 1,1-diphenylprop-2-yn-1-ol, or the biologically active steroid ethisterone, were successfully converted. Ruthenium carboxylate complexes were applied in the synthesis of diverse ?-oxo esters by the addition of carboxylic acids to propargylic alcohols. The catalytic system tolerates a broad range of functional groups and even facilitates the successful conversion of challenging substrates such as sterically demanding steroids.

Posted on 27 April 2015 | 12:13 pm

Syntheses of Ir4(CO)6(?5-C5Me4H)2 and Ir7(?3-CO)3(CO)12(?5-C5Me5) from Pentametallic Molybdenum-Iridium Cluster Precursors

Reaction of Mo2Ir3(?-CO)3(CO)6(?5-C5H5)2(?5-C5Me5) with Ir(CO)2(?5-C5Me4H) afforded the four-valence-electron-deficient butterfly cluster Ir4(CO)6(?5-C5Me4H)2; its stability has been rationalized with the aid of density functional theory calculations, which suggest that significant additional intracluster bonding alleviates the formal electron deficiency. Reaction of MoIr4(CO)10(?5-C5H5)(?5-C5Me5) with [N(PPh3)2][Ir(CO)4] afforded the capped octahedral cluster Ir7(?3-CO)3(CO)12(?5-C5Me5), which possesses three semi-face-capping CO ligands. These outcomes demonstrate that heterometallic clusters may serve as a potential source of new homometallic clusters following appropriate M–M? cleavage. Reactions of molybdenum-iridium clusters with iridium-containing reagents afforded new homometallic clusters. Ir7(?3-CO)3(CO)12(?5-C5Me5) possesses three semi-face-capping CO ligands, while Ir4(CO)6(?5-C5Me4H) is formally very electron-deficient; theoretical studies suggest stabilization by significant intracluster multiple Ir–Ir bonding.

Posted on 27 April 2015 | 12:13 pm

Tin Oxometallates from the Hydrolysis of SnMe22+ in the Presence of 2,6-Lutidine-?2,3-diol and Different Anions

The reaction of the dimethyltin(IV) cation with 2,6-lutidine-?2,3-diol (Lut, 2-hydroxymethyl-3-hydroxy-6-methylpyridine) has been investigated in ethanol/water mixtures (80:20 v/v) containing Cl– and NO3–, NO3– and OAc– or Cl– and OAc– ions in various molar ratios. From these reactions, several tin oxometallates were isolated and characterized by IR, Raman, 1H NMR, 13C NMR and 119Sn NMR spectroscopy as well as ESI-MS. The crystal structures of the compounds [Lut+H]Cl·H2O, [(SnMe2)4O2(Lut-H)2Cl2] (1), [SnMe2(Lut-H)Cl] (2), [(SnMe2)3O(Lut-H)2Cl]Cl (3), [(SnMe2)3O(Lut-H)2Cl2]·H2O (4·H2O) and [(SnMe2)4O2(Lut-H)2(NO3)2] (5) were determined by X-ray diffractometry. The structure of 2 contains dimeric [SnMe2(Lut-H)Cl]2 units based on a central Sn2O2 fragment, the Lut ligand is monodeprotonated, and both the tin atoms are hexacoordinate. The other metallates are all tri- or tetranuclear and show the dimethyltin(IV) unit in several penta- or hexacoordinate environments. The C–OH group of the Lut-H fragment, the Cl atoms, the O atoms of the nitrate group and the water molecules (for 4·H2O) are involved in hydrogen bonds, which modulate the interactions between the units and the packing in the crystal. The NMR and ESI-MS spectra show the existence of complex equilibria in solution. Tin oxometallates incorporating lutidine are synthesized in ethanol/water mixtures containing different anions in various molar ratios. The compounds are liberated from solutions containing several species and show the ability of the tin atom to coordinate to different anions, which are sometimes present in solution at lower concentrations than others.

Posted on 23 April 2015 | 12:40 pm

Synthesis of Binary Sb2E3 (E = S, Se) and Ternary Sb2(S,Se)3 Nanowires Using Tailor-Made Single-Source Precursors

Thermal decomposition of four single-source precursors of the type (Et2Sb)2E and Et3SbE (E = S, Se) at 170 °C in the presence of suitable capping agents yielded binary Sb2S3 and Sb2Se3 nanowires. In addition, simultaneous decomposition of (Et2Sb)2S and(Et2Sb)2Se gave the ternary phase Sb2(S,Se)3 with almost equal S and Se concentrations. The materials were characterized by XRD, REM, EDX, ED and HRTEM. Binary Sb2S3 and Sb2Se3 nanowires as well as ternary Sb2(S,Se)3 nanowires were synthesized by thermal decomposition of four novel single-source precursors of the type (Et2Sb)2E and Et3SbE (E = S, Se) in the presence of suitable capping agents and characterized by XRD, REM, EDX, ED and HRTEM.

Posted on 23 April 2015 | 12:40 pm

Heterocyclic Digallanates, Encapsulation of Lithium Cations in Organometallic Cages and C–H Bond Activation

Hydrogallation of the dialkynylbenzenes 1,3-(R2R?Si-C?C)2C6H4 (3: R = Me, R? = Ph; 4: R = Ph, R? = Me) with dichlorogallane, H-GaCl2, afforded the corresponding dialkenylbenzenes 5 and 6, with GaCl2 groups geminal to the silyl substituents. Compound 6 was characterised by crystal structure determination, which revealed intramolecular bridging of both gallium atoms by two chlorine atoms as a new structural motif. Treatment of 5 and 6 with six equivalents of ethyllithium gave unprecedented heterocyclic digallanates 7 and 8, in which two four-coordinate gallium atoms were bridged by two 1,3-dialkenylbenzene spacer ligands. The obtained large heterocycles encapsulated two lithium counterions in their molecular cavities. The lithium atoms were coordinated in a cryptand-like fashion and showed a variety of short contacts to aromatic rings, alkenyl groups, and ?-carbon atoms of terminal ethyl groups. They could be removed from the molecular cavity by coordination with chelating 1,2-dimethoxyethane ligands. Heating of digallanates 7 and 8 in toluene to more than 100 °C over a period of 5 h resulted in fascinating transformations with C–H bond activation and ortho-metallation. Five-membered GaC4 metallacycles were formed, which had a terminal R2R?Si-CH=CH- group resulting from the formal protolytic cleavage of an alkenyl–gallium bond by the ortho-hydrogen atom. C–H bond activation and ortho-metallation was achieved by heating novel macrocyclic phenylene centered dilithium di(galliumalkenyl) compounds in solution. The products contained five-membered GaC4 heterocycles. Various Li–? interactions resulted in fascinating molecular structures for the digallanate intermediates and the finally isolated metallacycles.

Posted on 23 April 2015 | 12:40 pm

Effects of Co/Ni Ratio on the Supercapacitive Properties of ?-Form Hydroxides

?-Form CoxNi1–x hydroxides with different Co/Ni ratios were synthesized by a chemical co-precipitation method under mild conditions. The effects of Co/Ni ratio on the structure, morphology, and supercapacitive properties of ?-form CoxNi1–x hydroxides were investigated in detail. ?-Form CoxNi1–x hydroxides had structures similar to those of hydrotalcite and ?-Co(OH)2, and they exhibited better electrochemical performance than ?-Co(OH)2 on testing by XRD, FTIR, and electrochemical performance (when x ? 0). The highest specific capacitance at 1 A?g–1 for ?-form CoxNi1–x hydroxides (for x = 0.2) is 1696.7 F?g–1. An asymmetric supercapacitor packaged with Co0.6Ni0.4 hydroxide and activated carbon as positive and negative material, respectively, had an energy density of 23.5 Wh?kg–1 at a power density of 412.5 W?kg–1. ?-Form CoxNi1–x hydroxides have structures similar to that of ?-Co(OH)2, with better electrochemical performance than pure ?-Co(OH)2. The highest specific capacitance at 1 A?g–1 for ?-form CoxNi1–x hydroxides is 1696.7 F?g–1. An asymmetric supercapacitor using Co0.6Ni0.4 hydroxide and activated carbon as electrode materials has an energy density of 23.5 Wh?kg–1 at a power density of 412.5 W?kg–1.

Posted on 23 April 2015 | 12:34 pm

Masthead: Eur. J. Inorg. Chem. 12/2015

Posted on 23 April 2015 | 9:05 am

Potent Reactivity in Solubilised Oxo-Titanium Polymers

Invited for the cover of this issue are Al Nielson and Joyce Waters from Massey University at Auckland, New Zealand. The cover image shows a titanium–salicylaldimine–oxo polymer being chopped up by an aldehyde molecule into a fiery reactive entity, which, on cooling, gives rise to complexes indicating that both polymer degradation and new carbon-based chemistry habe taken place. The titanium–salicylaldimine–oxo complexes can be prepared in large quantities and are very cost-effective when salicyladimine ligands and titanium isopropoxide are the starting materials...Read more about the story behind the cover in the Cover Profile and about the research itself on p. 2028 ff.

Posted on 23 April 2015 | 9:05 am

Potent Reactivity in Solubilised Oxo-Titanium Polymers (Eur. J. Inorg. Chem. 12/2015)

The cover picture shows a titanium–salicylaldimine–oxo polymer being chopped up by an aldehyde molecule into a fiery reactive entity, which, on cooling, gives rise to complexes indicating that both polymer degradation and new carbon-based chemistry have occurred. Details are discussed in the Short Communication by A. J. Nielson and J. M. Waters on p. 2028 ff. For more on the story behind the cover research, see the Cover Profile.

Posted on 23 April 2015 | 9:05 am

Graphical Abstract: Eur. J. Inorg. Chem. 12/2015

Posted on 23 April 2015 | 9:05 am

Synthesis, Structure and Redox Properties of Asymmetric (Cyclopentadienyl)(ene-1,2-dithiolate)cobalt(III) Complexes Containing Phenyl, Pyridyl and Pyrazinyl Units

The compounds [(?5-C5H5)Co{SC(H)CRS}] [R = phenyl (1), pyridin-3-yl (2) or pyrazin-2-yl (3)] have been synthesized and characterized by elemental analysis, 1H NMR, mass spectrometry and X-ray crystallography. The variation in the UV/Vis and redox properties of these compounds alone and upon acidification has been investigated. In CH2Cl2 solution each compound undergoes a reversible one-electron reduction, and the EPR spectrum of each monoanion has been recorded. In the presence of a 5:1 excess of trifluoroacetic acid the one-electron reduction of both 2 and 3 occurs at a less negative potential. The information obtained has been interpreted with the aid of DFT calculations for [1]y, [2]y and [3]y (y = 0 or –1) and the monoprotonated forms [2H]z and [3H]z (z = +1 or 0), and this has provided insight into the nature of the redox-active orbitals in these complexes. The HOMOs and LUMOs of these species are delocalized and each involves contributions from cobalt, ene-1,2-dithiolate and R orbitals. The information from the experimental and theoretical investigations is used to suggest that, for the pyran ring-opened form of the molybdenum cofactor of oxygen-atom-transfer enzymes, the pterin may participate in the redox reactions involved in the catalytic cycle. Structural, electrochemical, spectroscopic and theoretical studies of [(?5-C5H5)Co(dithiolene)] complexes suggest that the pyran ring-opened form of the molybdenum cofactor of Mo- and W-containing oxygen-atom-transfer enzymes may participate in the redox reactions involved in the catalytic cycle.

Posted on 22 April 2015 | 12:50 pm

Unexpected Emission Properties of a 1,8-Naphthalimide Unit Covalently Appended to a Zn–Salophen

We report the synthesis, characterization, and binding properties of a Zn–salophen complex, 1a, functionalized with a 1,8-naphthalimide unit. Unexpectedly, the emission spectrum of 1a shows a remarkable quenching of the band assigned to the naphthalimide unit. To better understand this phenomenon, a supramolecular model system constituted by a symmetric Zn–salophen and a pyridyl derivative of 1,8-naphthalimide, 1b·2a, was investigated. We propose the existence of a photoinduced energy transfer process between the naphthalimide (donor) and the salophen (acceptor) units in 1b·2a. A similar process must be operative in the covalent receptor 1a. Nevertheless, the results deriving from steady-state fluorescence experiments do not rule out the occurrence of a photoinduced electron transfer process as alternative pathway for the quenching. We also describe the chemosensing properties of receptor 1a and the supramolecular system 1b·2a towards acetate. The nonsymmetrically substituted salophen receptor 1a only transduces the binding of the anion to the Zn metal center in significant spectroscopic changes in its absorption spectrum. On the other hand, we exploit the strong emission quenching experienced by the naphthalimide component in the supramolecular complex 1b·2a to detect anions (e.g. acetate) by means of a typical “turn-on” fluorescent indicator displacement assay. Fluorescence switching of 1,8-naphthalimide: A zinc–salophen complex quenches the emission of 1,8-naphthalimide both in the covalently linked and in the supramolecular assembly. The nonfluorescent 1:1 complex was exploited as an on-off-on receptor for anions according to the fluorescent indicator displacement assay approach.

Posted on 22 April 2015 | 12:50 pm

Simple Synthesis of Two-Dimensional Micro/Mesoporous Boron Nitride

Micro/mesoporous boron nitride (BN) nanosheets were synthesized through a simple one-pot procedure using cetyl trimethylammonium bromide (CTAB) and ammonia borane (AB) as a structure-directing agent and a BN precursor, respectively. The pyrolysis of the CTAB/AB hybrid under an ammonia atmosphere at 1150 °C produced a white BN powder. We investigated the effect of the CTAB/AB weight ratio on the morphology and physical properties of the prepared powders. The obtained products were characterized by using X-ray diffraction techniques, X-ray photoelectron spectroscopy, scanning electron microscopy, scanning transmission electron microscopy, transmission electron microscopy, and N2-sorption analysis. We found that increasing the weight ratio of CTAB/AB changed the morphology of the synthesized materials from densely packed porous structures to two-dimentional micro/mesoporous BN powders. The high surface area of 1401 cm2?g–1 and pore volume of 1.56 cm3?g–1 and micropore volume of 0.41 cm3?g–1 were obtained for a CTAB/AB weight ratio of 10:1. Hydrogen sorption analysis revealed that the obtained powder has a hydrogen-adsorption capacity of approximately 1 wt.-% at 77 K and 100 kPa. A facile one-pot synthesis route is presented to prepare micro/mesoporous boron nitride (BN) nanosheets by pyrolysis of cetyl trimethylammonium bromide (CTAB)/ammonia borane (AB) at 1150 °C. Increasing the weight ratio of CTAB/AB changed the morphology of the synthesized materials from densely packed porous structures to micro/mesoporous two-dimensional BN powder.

Posted on 22 April 2015 | 12:50 pm

Viral Nanotemplates Armed with Oxygenic Polyoxometalates for Hydrogen Peroxide Detoxification

Layer-by-layer (LbL) assembly strategies were exploited to decorate wild-type TMV (tobacco mosaic virus) 1D nanoscaffolds with a totally inorganic, multiredox, tetraruthenate complex belonging to the class of polyoxometalate catalysts. The hybrid capsids give rise to an entangled network of fibrils and ribbon-like nanoassemblies, whose functional activity was probed towards H2O2 dismutation in neutral water. Combined solid-state and surface characterization evidence, including Z-potential, electronic microscopy, thermogravimetry and XPS, delineate a favorable tunability of the nanohybrid material as a function of the added cationic binder. A polyoxometalate with oxygenic activity was anchored on the TMV (tobacco mosaic virus). The rod-like biogenic template enables the formation of catalytic nanoarrays for H2O2 dismutation.

Posted on 22 April 2015 | 12:40 pm

Mechanistic Links in the in-situ Formation of Dinuclear Manganese Catalysts, H2O2 Disproportionation, and Alkene Oxidation

The oxidation of substrates, such as alkenes, with H2O2 and the catalyst [MnIV2(?-O)3(tmtacn)2]2+ (1; tmtacn = 1,4,7-trimethyl-1,4,7-triazacyclononane) is promoted by the addition of carboxylic acids through the in situ formation of bis(carboxylato) complexes of the type [MnIII2(?-O)(?-RCO2)2(tmtacn)2]2+. The conversion of 1 to these complexes requires a complex series of redox reactions coupled with the overall exchange of ?-oxido ligands for ?-carboxylato ligands. Here, we show that the mechanism by which this conversion occurs holds implications with regard to the species that is directly engaged in the catalytic oxidation of alkenes. Through a combination of UV/Vis absorption, Raman, resonance Raman and electron paramagnetic resonance (EPR) spectroscopy, it is shown that the conversion proceeds by an autocatalytic mechanism and that the species that engages in the oxidation of organic substrates also catalyses H2O2 decomposition, and the former process is faster. The in situ formation of catalytically active species through the reduction of a precatalyst, H2O2 disproportionation and alkene oxidation are linked to a common active species.

Posted on 21 April 2015 | 12:20 pm

Ultra-Fast Microwave Synthesis of 3D Flower-Like Co9S8 Hierarchical Architectures for High-Performance Supercapacitor Applications

Ultra-fast microwave irradiation is used to synthesize 3D flower-like Co9S8 hierarchical architectures. Based on time-dependent SEM observations, a multistep splitting–growth mechanism is proposed to understand the formation of the observed structures. Moreover, the materials were used as electrodes to fabricate supercapacitors with high specific capacitances of 522, 499, 441, 436, and 397 F?g–1 at current densities of 0.5, 0.8,1.0, 1.5, and 2.0 A?g–1, respectively. The devices also show high charge–discharge reversibility, with an efficiency of 97.7?% after cycling 1000 times at a current density of 1.0 A?g–1. Ultra-fast microwave irradiation is used to synthesize 3D flower-like Co9S8 hierarchical architectures. The materials display both high discharge capacity and long cycle life under charge–discharge cycling for supercapacitors.

Posted on 20 April 2015 | 1:10 pm

Homogeneous Catalysis with AuIII: Insights into the Mechanism of the Alkoxylation of Alkynes

The mechanism of the AuIII-catalyzed nucleophilic addition of a small alkanol to an alkyne, which yields a ketal product, has been investigated computationally by using GGA (BP86), hybrid (PBE0) and double-hybrid (B2-PLYP-D3BJ) density functional theory with the large aug-cc-pVTZ (aug-cc-pVTZ-PP) basis sets of triple-? quality. The importance of hydrogen-bonding networks is highlighted in the mechanism. The nucleophilic attacks possess relatively lower activation barriers than the hydrogen migrations, and the rate-determining step is predicted to be the last hydrogen migration step. A thorough mechanistic study of gold(III)-catalyzed addition of methanol to propyne was carried out by using density functional theory. Each individual process is assisted by explicitly included solvent methanol, which also acts as the nucleophile. Results showed that the double nucleophilic attacks proceed fast over low activation barriers with the last hydrogen migration as the rate-determining step.

Posted on 17 April 2015 | 12:10 pm

Investigations Concerning [Cu4OX6L4] Cluster Formation of Copper(II) Chloride with Amine Ligands Related to Benzylamine

The ?4-oxido motif is well known in copper clusters and often forms spontaneously and unexpectedly; however, little is known about the reaction conditions that generate ?4-oxido clusters. This is surprising because these ?4-oxido copper clusters seem to play an important role in catalysis. Herein, a systematic investigation of ?4-oxido cluster formation is reported. The influence of several factors on cluster formation was studied, namely, the ligand environment, the central chalcogenide atom, and the bridging halido ligands. In this context, the crystal structures of the copper clusters and complexes [Cu4OCl6L24][CuL22Cl2] (L2 = phenethylamine), [CuL32Cl2] (L3 = N-methylbenzylamine), [Cu4OCl6L44] (L4 = N,N-dimethylbenzylamine), [CuL54Cl2] (L5 = cyclohexylamine), and [Cu4OCl6L64]·1.5[CuL62Cl2] (L6 = cyclohexanemethylamine) as well as that of HL4Cl are reported. Furthermore, the acetonitrile complexes [Cu(CH3CN)4][CuBr4], [Cu(CH3CN)Br], and [Cu(CH3CN)Br2] were obtained and characterized within attempts to prepare a ?4-sulfido unit. The reaction conditions that generate ?4-oxido cluster units are discussed in more detail. The ?4-oxido motif is well known in copper clusters and often forms spontaneously and unexpectedly. However, little is known about the reaction conditions that generate ?4-oxido clusters. Here, a systematic investigation of ?4-oxido cluster formation is reported. The effects of the ligand environment, central chalcogenide atom, and bridging halide ligands on cluster formation are investigated.

Posted on 17 April 2015 | 12:10 pm

Two Structure Types Based on Si6O15 Rings: Synthesis and Structural and Spectroscopic Characterisation of Cs1.86K1.14DySi6O15 and Cs1.6K1.4SmSi6O15

The silicate Cs1.86K1.14DySi6O15 represents a mixed tetrahedral-octahedral framework structure type based on roughly circular Si6O15 rings and isolated DyO6 octahedra. The silicate Cs1.6K1.4SmSi6O15 has a layered atomic arrangement built from corrugated Si6O15 layers containing four-, six- and eight-membered rings. The layers are connected by isolated SmO6 octahedra to form a mixed tetrahedral-octahedral framework. This structure shows a close structural relationship to ?-K3NdSi6O15 and a less close one to dehydrated elpidite (Na2ZrSi6O15). In both structures, Cs/K atoms occupy large voids. The silicates were obtained through high-temperature flux syntheses. Their crystal structures have been determined from single-crystal X-ray diffraction data. Cs1.86K1.14DySi6O15 crystallises in R32 (no. 155) with a = 13.896(2), c = 35.623(7) Å and V = 5957.2(17) Å3, whereas Cs1.6K1.4SmSi6O15 crystallises in Cmca (no. 64) with a = 14.474(3), b = 14.718(3), c = 15.231(3) Å and V = 3244.7(11) Å3. The Dy3+ and Sm3+ cations present in the silicates cause PL emission bands in the visible yellow-to-orange spectral range. Two (Cs,K)-REE3+ silicates (REE3+ = Dy or Sm) containing Si6O15 rings represent mixed tetrahedral-octahedral framework structure types. Their crystal structures were characterised by single-crystal X-ray diffraction and photoluminescence spectroscopy. The presence of REE3+ cations in the structures causes emission bands in the visible yellow-to-orange spectral range.

Posted on 16 April 2015 | 9:45 am

Improved Synthesis of a Zirconium(IV) Muconate Metal–Organic Framework: Characterization, Stability and Gas Sorption Properties

The formerly reported ZrIV trans,trans-muconate framework material (1) was synthesized by using an improved synthetic protocol. Instead of using the noncommercial Zr6-methacrylate oxido cluster as the metal source, the same MOF was successfully synthesized by using commercially available ZrCl4 as the Zr source. Small amounts of H2O (1-H2O-AS; AS = as-synthesized) or concd. aqueous HCl (1-HCl-AS) were used as additives in N,N-dimethylformamide (DMF) in order to enhance the crystallinity of the compounds. The guest molecules were removed from the pores by heating the as-synthesized compounds under vacuum, resulting in the empty-pore forms of the compounds. The as-synthesized and thermally activated compounds were characterized by X-ray powder diffraction (XRPD), Fourier transform infrared (FTIR), thermogravimetric (TG) and elemental analyses. Thermogravimetric analyses suggest that the two compounds are stable up to ca. 250 °C in an air atmosphere. As verified by the XRPD experiments, the 1-HCl compounds gradually lose their crystallinity when exposed to water and moisture. As confirmed by the N2 sorption analyses, the optimally activated 1-HCl compound displayed a BET surface area of 557 m2?g–1, which is lower than the isostructural UiO-66 (950 m2?g–1) but it is close to the literature value (705 m2?g–1). The moderate physiochemical stability paired with considerable porosity renders the material a promising candidate for gas storage and separation. The improved synthetic procedure, characterization, thermal and chemical stability and gas adsorption properties of the previously reported ZrIV muconate compound are presented.

Posted on 14 April 2015 | 11:50 am

An Iron-Based Photosensitizer with Extended Excited-State Lifetime: Photophysical and Photovoltaic Properties

Herein, we report a homoleptic iron complex bearing tridentate bis-carbene (CNC) ligands designed for sensitization of TiO2 photoanodes. Its excited state has been characterized by ultra-fast transient spectroscopy and time-dependent density functional theory (TD-DFT) computations, which reveal a record triplet metal-to-ligand charge-transfer (3MLCT) excited-state lifetime (16 ps). The new dye was efficiently chemisorbed on TiO2 and promoted electron injection and photocurrent generation in a dye-sensitized solar cell upon solar irradiation. A new iron(II) complex with a record 16 ps triplet metal-to-ligand charge-transfer (3MLCT) state lifetime has been designed and evaluated as a photosensitizer in a laboratory dye-sensitized solar cell (DSSC), which led to measurable photocurrent and power-conversion efficiency. Such an improvement of the photophysical properties of iron-based complexes opens the way to applications that go far beyond energy production.

Posted on 14 April 2015 | 11:50 am

Hg5AsS2I3 – A Narrow-Band-Gap 2D Layered Compound with Different Trapped I– Anions

A new layered compound, Hg5AsS2I3, has been synthesized in the quaternary system mercury/arsenic/chalcogen/halogen by a moderate-temperature solid-state reaction. The compound crystallizes in the space group C2/c of the monoclinic system, and its structure consists of ?1[Hg(1)2Hg(2)2As2/2S2] eight-membered-ring chains bridged by Hg atoms to form [Hg(1)2Hg(2)2Hg(3)As2/2S2] layers with inner- and interlayer electrostatic interactions between I and Hg. The optical properties were investigated by means of diffuse reflectance and FTIR spectra. The electronic band structures, along with density of states (DOS) calculations by DFT, indicate that the title compound is a semiconductor, and its optical absorption mainly leads to charge transitions from I-5p, As-4p and S-3p states to Hg-6s states, and both I(1) and I(2) atoms contribute to the top of the valence bands. The structure consists of ?1[Hg(1)2Hg(2)2As2/2S2] eight-membered-ring chains bridged by Hg atoms to form [Hg(1)2Hg(2)2Hg(3)As2/2S2] layers with inner- and interlayer electrostatic interactions between I and Hg.

Posted on 14 April 2015 | 11:50 am

Rehydrogenation of Aminoboranes to Amine–Boranes Using H2O: Reaction Scope and Mechanism

Water has been successfully employed as a reagent with which to rehydrogenate aminoboranes (e.g., iPr2N=BH2, 2,2,6,6-Me4C5H6N=BH2, and also transient Me2N=BH2 derived from 1/2[Me2N-BH2]2) to amine–boranes (e.g., iPr2NH·BH3, 2,2,6,6-Me4C5H6NH·BH3, Me2NH·BH3) in approximately 30?% yield. The conversion to amine–boranes from the corresponding aminoboranes using this method represents an example of a metal-free, single-step route for the hydrogenation of the B=N bond. Deuterium labeling studies indicated that the protic hydrogen (N–H) on the rehydrogenated amine–borane was derived from H2O, whereas the third hydridic hydrogen (B–H) on the amine–borane was generated from the formation of a postulated hydride-bridged intermediate H2B(?-H)(?-NR2)B(OH)H (R2 = Me2, iPr2, 2,2,6,6-Me4C5H6), which requires a second equivalent of the starting aminoborane, thus explaining the low yield. Formation of insoluble borates (BxOyHz) provides a driving force for the reaction. Significantly, the yield can be increased by adding a sacrificial source of BH3 (e.g., to ca. 53?% for BH3·THF) or by adding a separate source of H– (e.g., to ca. 95?% for LiBH4) to complement the H+ (from H2O) in a more atom-efficient reaction. The conversion of aminoboranes to amine–boranes using water has been demonstrated and the mechanism investigated using deuterium labeling studies and model reactions.

Posted on 13 April 2015 | 8:30 am

Determining the Ligand Properties of N-Heterocyclic Carbenes from 77Se NMR Parameters

The 1JCSe coupling constants for a range of NHC–selenium adducts have been measured and used to establish a correlation with the ?-donor strength of the respective carbenes. For the subclass of amido-carbenes, the 1JCSe values revealed a high donor capacity, very much in contrast to what the DFT-calculated HOMO energies suggest. The 1JCH coupling constants for the C-2 atoms in azolium-type NHC precursors were more readily obtained and show the same trend as the 1JCSe coupling constants. In addition, the use of 77Se chemical shifts to determine ?-acidity has been extended to a broader range of derivatives, namely 1·Se–22·Se. The superior resolution of the ?(77Se) method in comparison with the Tolman electronic parameters derived from IR spectroscopy is demonstrated for the caffeine-derived bis-carbene 19. The electronic properties of a range of N-heterocyclic carbenes have been evaluated by using the 77Se NMR chemical shifts of NHC–Se adducts, to map the ?-acceptor character, and 1JCSe coupling constants, which provide insights into the ?-donor ability of the respective carbene. DFT calculations were conducted to rationalize the data. The NMR-derived parameters have been compared with TEP values.

Posted on 10 April 2015 | 10:30 am

Hydrogen Bonding and Anticancer Properties of Water-Soluble Chiral p-Cymene RuII Compounds with Amino-Oxime Ligands

An investigation into the effects of hydrogen bonding on the aggregation tendency of ruthenium compounds [(?6-p-cymene)Ru(?NHR,?NOH)Cl]Cl {R = Ph (1a), Bn (1b)} and [(?6-p-cymene)Ru(?2NH(2-pic),?NOH)][PF6]2 (1c), [(?6-p-cymene)Ru(?NHBn,?NO)Cl] (2b), and [(?6-p-cymene)Ru(?NBn,?2NO)] (3b) has been performed by means of concentration-dependence 1H NMR chemical shift and DOSY experiments. The synthesis and full characterization of new compounds 1c, [(?6-p-cymene)Ru(?NPh,?2NO)] (3a) and 3b are also reported. The effect of the water-soluble ruthenium complexes 1a–c on cytotoxicity, cell adhesion, and cell migration of the androgen-independent prostate cancer PC3 cells have been assessed by MTT, adhesion to type-I-collagen, and recovery of monolayer wounds assays, respectively. Interactions of 1a–c with DNA and human serum albumin have also been studied. Together, the properties reported herein suggest that ruthenium compounds 1a–c have considerable potential as anticancer agents against advanced prostate cancer. The ability of water-soluble, chiral arene RuII compounds with amino-oxime ligands to aggregate in solution by means of hydrogen bonding is described. The compounds do not interact with plasmid (pBR322) DNA but display strong cytotoxic and antimetastatic effects in vitro against androgen-unresponsive human prostate cancer PC3 cell line.

Posted on 9 April 2015 | 12:13 pm

Structurally Diverse Manganese(II)–Diclofenac Complexes Showing Enhanced Antioxidant Activity and Affinity to Serum Albumins in Comparison to Sodium Diclofenac­

The interactions of MnII ions with the nonsteroidal anti-inflammatory drug sodium diclofenac in the presence of 1,10-phenanthroline and 2,2?-dipyridylamine lead to the formation of the trinuclear [Mn3(diclofenac)6(1,10-phenanthroline)2(MeOH)] (1) and the mononuclear [Mn(diclofenac)2(2,2?-dipyridylamine)] (2), respectively, which have been characterized by X-ray crystallography. Three different coordination modes of the diclofenac ligands exist in 1, whereas the bidentate chelating mode is observed in 2. In the initial evaluation of their biological properties and potential applications, the complexes exhibited good binding propensity to human or bovine serum albumin proteins and have relatively high binding constants. The ability of the compounds to scavenge 1,1-diphenylpicrylhydrazyl, 2,2?-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), and hydroxyl radicals was evaluated, and 1 was the most-effective scavenger among 1, 2, and sodium diclofenac. The interaction of MnII ions with the nonsteroidal anti-inflammatory drug (NSAID) sodium diclofenac in the presence of 1,10-phenanthroline or 2,2?-dipyridylamine leads to the formation of a trinuclear or a mononuclear complex, respectively. The complexes show noteworthy antioxidant activity and significant binding affinity for serum albumins.

Posted on 9 April 2015 | 12:13 pm

Monomeric or Dimeric Aluminum Complexes as Catalysts for Cycloaddition between CO2 and Epoxides

A monomeric aluminum complex containing aliphatic tetradentate ligand L1 (HOCMe2CH2NMeCH2CH2NMeCH2CMe2OH) was synthesized and used as a catalyst for cycloaddition between CO2 and epoxides in the presence of PPNCl as a cocatalyst. To check the effect of ligand L1, coordinated to the aluminum center, on the activity of cycloaddition, the new ligand HOCMe2CH2NMe2, which corresponds to half of L1, was systematically designed to make monomeric or dimeric aluminum complexes. Comparison of the catalytic properties of the aluminum complex containing the tetradentate ligand with those of the two related aluminum complexes containing the bidentate ligand under the same conditions revealed that the first system showed higher activity than the other two for cycloaddition between CO2 and epoxides in the presence of PPNCl, which was the best cocatalyst out of the six compounds nBu4PBr, nBu4NCl, nBu4NBr, nBu4NI, DMAP, and PPNCl. The aluminum complexes 1–3 demonstrate catalytic activity for cycloaddition between CO2 and epoxides in the presence of cocatalysts.

Posted on 9 April 2015 | 11:43 am

Panchromatic Borane–aza-BODIPY Conjugate: Synthesis, Intriguing Optical Properties, and Selective Fluorescent Sensing of Fluoride Anions

A new triarylborane–aza-BODIPY conjugate is reported. The compound consists of two blue emissive dimesitylarylborane moieties and a near-infrared (NIR) emissive aza-BOIDPY core and shows panchromatic absorption spanning approximately 300–800 nm. DFT computational studies suggest limited electronic communication between the individual fluorophore units. Hence, the partial energy transfer from blue fluorophore triarylborane to NIR chromophore aza-BODIPY unit leads to a broad dual-emissive feature covering a large part of visible and NIR region. Furthermore, the broadband emissive compound can act as a selective sensor for fluoride anion as a result of fluorescence quenching response in both visible and NIR spectral regions. A broadband visible near-IR emissive triarylborane–aza-BODIPY conjugate was synthesized and characterized. The compound shows selective response towards fluoride anions with responses in the both visible and near-IR regions.

Posted on 9 April 2015 | 11:32 am

Hindrance, Donor Ability of MenNN Chelates and Overall Stability of Pentacoordinate [PtCl2(?2-CH2=CH2)(MenNN)] Complexes as Observed by ?2-Olefin 1JPt,C Modulation: An NMR Study

A series of pentacoordinate d8 PtII complexes, of the type [PtCl2(?2-CH2=CH2)(MenNN)], where MenNN = bis-nitrogen ligand, with a variable number of Me groups (i.e., 2,2?-bipyridyl; 1,10-phenanthroline; 6-methyl-2,2?-bipyridyl; 2,9-dimethyl-1,10-phenanthroline; 2,9-dimethyl-1,10-phenanthroline; N,N?-trimethyl-ethylenediamine; N,N,N?,N?-tetramethyl-ethylenediamine; N,N,N?,N?-tetramethyl-1,2-diaminocyclohexane) was studied. The compounds are characterized by variable steric hindrance, due to the variable number (n) of Me substituents, on or ortho to the N-donors of aliphatic diamines or aromatic diimines, respectively. This approach was developed to investigate the interaction of substituents with the metal coordination sphere. With this aim, we analyzed the NMR properties of the considered complexes, with respect to modulation of the metal electron density (195Pt NMR signal frequency) by alkyl groups close to the N-donors. 1H and 13C NMR analysis of the ?2-olefin signals has revealed, for each kind of bis-nitrogen ligand, a positive or negative chemical shift variation that is proportional to the number of Me groups geminal or vicinal to the N-donors. Interestingly, the 1JPt,C values increase by approximately 45 Hz for each additional Me on the series of diamine or diimine bis-nitrogen ligands. A rationale for the stability changes observed in such pentacoordinate complexes is suggested, based on the NMR spectroscopic data analysis. The effect of steric hindrance around bis-nitrogen donors on the metal–olefin bond, according to the Dewar–Chatt–Ducanson model, is described. Low hindrance around bis-nitrogen donors corresponds to a weaker metal–olefin interaction, whereas high steric hindrance around bis-nitrogen donors corresponds to a stronger metal–olefin interaction.

Posted on 9 April 2015 | 11:32 am

A Bioinspired System for Light-Driven Water Oxidation with a Porphyrin Sensitizer and a Tetrametallic Molecular Catalyst

Inspired by natural photosynthesis, the aim of light-driven water splitting is to produce renewable fuels by exploiting solar radiation. Sustained hydrogen production is desirable in such systems, and the oxidation of water to oxygen is currently recognized as the bottleneck of the entire process. Therefore, solutions for this difficult task retain a fundamental interest. In this paper, we present a bioinspired, three-component system for water oxidation that comprises a tetracationic porphyrin ZnII complex as the photosensitizer, a tetraruthenium water-oxidation catalyst, and sodium persulfate as the electron acceptor. An in-depth photophysical study reveals the photogeneration of a pentacation radical of the porphyrin (quantum yield up to ? = 1.01) upon oxidative quenching of the triplet excited state by persulfate. Electron transfer from the water-oxidation catalyst to the pentacation radical (hole scavenging) is slow (bimolecular rate constant, k?<?4?×?107 M–1?s–1), and this is likely the main reason for the low efficiency of the system in photocatalytic tests for water oxidation. Perspectives for improvements of the system and for the development of a light-activated device for water splitting are discussed. The photoinduced events and the light-driven water-oxidation ability of a bioinspired, three-component catalyst/photosensitizer/acceptor molecular system are investigated.

Posted on 8 April 2015 | 12:30 pm

Comparative Study of the Reactivity of Zirconium(IV)-Substituted Polyoxometalates towards the Hydrolysis of Oligopeptides

The hydrolytic activity of the ZrIV-substituted Keggin-type (Et2NH2)8[{?-PW11O39Zr-(?-OH)(H2O)}2]·7H2O (1), Lindqvist-type (Me4N)2[W5O18Zr(H2O)3] (2), and Wells–Dawson-type Na14[Zr4(P2W16O59)2(?3-O)2(OH)2(H2O)4]·57H2O (3) polyoxometalates (POMs) towards the peptide bonds in the oligopeptides triglycine, tetraglycine, glycylglycylhistidine, and glycylserylphenylalanine was investigated by kinetic methods and multinuclear NMR spectroscopy. 31P NMR and UV/Vis spectroscopy showed that 1–3 were stable under the conditions used to study peptide bond hydrolysis. The reactivity of 1–3 towards oligopeptides was compared on the basis of the amount of free glycine produced at a certain time increment. In the presence of 1–3, rate constants in the range 6.25?×?10–7 to 10.14?×?10–7 s–1 were obtained, whereas no hydrolysis was observed after one month in the absence of these POMs. The results showed that the Keggin-type complex 1 was the most active towards peptide bond hydrolysis in tri- and tetrapeptides. 1H and 13C NMR spectroscopy showed that triglycine, tetraglycine, and glycylserylphenylalanine interact with 1 and 2 preferentially through the amine nitrogen atom and the N-terminal amide oxygen atom to activate the peptide bond towards hydrolysis. The coordination of glycylglycylhistidine resulted in multiple complexes with 1–3 as a result of additional imidazole coordination to the ZrIV centers. The hydrolytic activity of ZrIV-substituted Lindqvist-, Keggin-, and Wells–Dawson-type polyoxometalates towards the peptide bonds in tri- and tetrapeptides is investigated by kinetic methods and multinuclear NMR spectroscopy. The peptides are hydrolyzed completely in nearly neutral and neutral pH media. The Keggin complex is the most active towards peptide bond hydrolysis in the studied peptides.

Posted on 8 April 2015 | 12:30 pm

Urea Azines (Bisguanidines): Electronic Structure, Redox Properties, and Coordination Chemistry

Urea azines are a largely neglected class of compounds. We show herein that they can easily be synthesized and sublimed at higher temperatures (90–100 °C) without decomposition. Our discussion includes the derivatives N,N?-diisopropylurea azine (2), tetramethylurea azine (3), and N,N?-dimethylethyleneurea azine (4) as examples. Vibrational spectroscopy and quantum chemical calculations were used to study their electronic structure in detail. A clear trend in the calculated decomposition to N2 and carbene is found, but the analysis reveals that this trend reflects the stability of the carbene decomposition product rather than changes in the electronic structure of the urea azines. Using cyclic voltammetry (CV) measurements we show that the urea azines are strong organic electron donors, which can be oxidized reversibly in two well-separated one-electron steps. The radical salt 4(TCNQ), featuring radical monocations and radical monoanions, which form mixed stacks in the solid state, was prepared by reaction of neutral 4 with tetracyanoquinodimethane (TCNQ). Oxidation of 4 with silver salts Ag+X– (X = BF4 or PF6) was accompanied by dehydrogenation, leading to intensively red-brown colored radical azoimidazolium dyes. Furthermore, urea azines were used as chelating ligands. In the case of 2, coordination to late transition metals initiates tautomerization. Reaction of 2 with boron hydrides leads to hydrogen elimination and formation of new B,N bi-heterocyclic ring structures. Electron donors: This article analyses the electronic structure of urea azines and shows that they are strong organic electron donors and redox-active ligands.

Posted on 8 April 2015 | 12:30 pm

Facile Rearrangement of a Bis(N-heterocyclic carbene)borate Chelate Ligand and Access to [:GeX]+ Complexes (X = H, Cl)

The unexpected isomerization of the potassium bis(N-heterocyclic carbene)borate [BPh2(tBuNHC)2]K (2?) (tBuNHC = 3-tert-butylimidazole-2-ylidene) in toluene, affording the unique potassium imidazolyl–NHC–borate [BPh2(tBuIm)(tBuNHC)]K (2) (tBuIm = 3-tert-butyl-2-imidazolyl), is reported. The latter crystallizes as the centrosymmetric dimer 22. According to the results of DFT calculations, the rearrangement of 2? is basically triggered by the solvation of the K+ ion: while 2? is most stable in THF solutions, the formation of 2 is feasible in least coordinating toluene and drastically favored through dimerization to give 22. The latter reacts with GeCl2·dioxane to form solely the unprecedented chlorogermyliumylideneborate [BPh2(tBuIm)(tBuNHC)]GeCl (3). Treatment of 3 with KHB(sBu)3 furnishes the corresponding hydridogermyliumylideneborate complex [BPh2(tBuIm)(tBuNHC)]GeH (4) in 66?% yield. Flip the chelate: The unexpected solvent-dependent potassium-induced isomerization of a potassium bis(N-heterocyclic carbene)borate in toluene afforded a unique potassium imidazolyl–NHC–borate isomer, which was successfully utilized for the synthesis and isolation of unprecedented chloro- and hydridogermyliumylideneborate complexes.

Posted on 8 April 2015 | 12:30 pm

From Homonuclear Metal String Complexes to Heteronuclear Metal String Complexes

The study of metal string complexes with 1D transition-metal frameworks began in the early 1990s. As these complexes provide great insights into metal–metal multiple bonds and may have potential applications as molecular wires, this field of research has grown in the past 20 years. As such, the electronic structures of the simplest trinuclear complexes, the supporting ligand systems, and the single-molecular conductance of metal string complexes are discussed. This review introduces the development of this field and summarizes some important results in the newly designed heteronuclear metal string complexes (HMSCs). These molecules may be of great interest in studies of the nature of heterometallic electronic effects and molecular electronic applications. This microreview describes the development of metal string complexes, from homonuclear to heteronuclear ones, including their synthesis and physical properties.

Posted on 7 April 2015 | 10:10 am

A Copper Porphyrin for Sensing H2S in Aqueous Solution via a “Coordinative-Based” Approach

A “turn on” fluorescence-based probe for sensing H2S in water via a coordinative-based approach has been successfully devised. The probe can selectively detect H2S in aqueous solutions over other anions, biothiols, and common oxidants such as H2O2. 1H NMR spectroscopy and ESI-MS experiments provide evidence that the turn-on response in the presence of H2S is due to binding of the target anion to the copper center. We devised a new, fast, simple, and cost-effective probe for monitoring hydrogen sulfide. Proof-of-principle results that a copper porphyrin complex can be successfully implemented as a turn-on sensing system for H2S via a coordinative-based approach are reported.

Posted on 7 April 2015 | 10:10 am

Potassium and Magnesium Complexes of the (Iminophosphoranyl)(selenophosphoranyl)methanide Ligand [CH(PPh2Se)(PPh2NSiMe3)]–

The Se,N ligand CH2(PPh2Se)(PPh2NSiMe3) (1e) was prepared in excellent yield by treatment of [CH2(PPh2)(PPh2NSiMe3)] with selenium in hot toluene. Reactions of 1e with a small excess of KH or with Mg[N(SiMe3)2] in a 2:1 molar ratio in boiling THF or toluene produced [K{CH(PPh2Se)(PPh2NSiMe3)}]2 (K3e) or Mg{CH(PPh2Se)(PPh2NSiMe3)}2 [Mg(3e)2], respectively. Compounds 1e, (K3e)2, and Mg(3e)2 were characterized by multinuclear (1H, 13C, 29Si, 31P, 77Se) NMR spectroscopy, and their X-ray structures were determined. In the solid state the N,Se-coordinated potassium salt forms a centrosymmetric dimer via weak K···Se interactions [3.269(1) Å]; the K+ ions also engage in intramolecular (?3 and ?6) interactions with neighboring phenyl groups. The homoleptic magnesium complex Mg(3e)2 is monomeric and exhibits a Se,C,N-bonding mode [Mg–C 2.480(5) and 2.442(5) Å]. (Iminophosphoranyl)(selenophosphoranyl)methanide complexes of K and Mg were synthesized by reactions of the neutral ligand CH2(PPh2Se)(PPh2NSiMe3) with KH or Mg{N(SiMe3)2}2. The N,Se-chelated K complex forms a centrosymmetric dimer through weak K···Se interactions, while the two ligands are Se,C,N-coordinated to the metal in the homoleptic Mg complex.

Posted on 2 April 2015 | 2:20 pm

Controlling the Activities of the Diiron Centre in Bacterial Monooxygenases: Lessons from Mutagenesis and Biodiversity

The soluble diiron monooxygenases (SDIMOs) are a diverse group of bacterial enzymes that possess a deeply buried binuclear iron centre that forms an oxo-diferryl (FeIV) intermediate that is capable of oxygenating a wide range of unfunctionalised hydrocarbons and other hydrophobic organic molecules, ranging in size from methane to diaromatics such as naphthalene and substituted biphenyls. In the environment, these enzymes are important in bioremediation of hydrocarbons and chlorinated hydrocarbons and in mitigation of the greenhouse effect due to methane, and also have numerous potential applications in synthetic organic chemistry. In this review we consider how both natural variations among the enzymes and an increasing body of evidence from mutagenesis studies cast light on how the protein controls the size of substrates that can access the active site, the precision of regio- and stereoselectivity and the oxidising power of the active centre. The soluble diiron monooxygenases (SDIMOs) are a diverse group of enzymes that use a diiron active centre to add oxygen to a wide range of organic molecules. Here we review how natural biodiversity and laboratory mutagenesis studies have revealed how the protein scaffold of SDIMOs controls the activity of the enzymes and the presentation of substrates to the diiron site.

Posted on 2 April 2015 | 2:20 pm

Photoluminescence Tuning and Water Detection of Yttrium Diazinedicarboxylate Materials through Lanthanide Doping

A series of yttrium(III)-based compounds with three diazinedicarboxylate ligands, namely, {[Y2(?-pmdc)2(?-ox)(H2O)6]·4H2O}n (1, pmdc = pyrimidine-4,6-dicarboxylato, ox = oxalato), {[Y2(?-pmdc)3(H2O)6]·2DMF·8H2O}n (2, DMF = N,N-dimethylformamide), {[Y2(?3-pmdc)2(?-ox)(H2O)4]·xH2O}n (3, x ? 4.66), {[Y(?4-pmdc)(NO3)(H2O)]·H2O}n (4), [Y2(?-pddc)3(H2O)6]·7H2O (5, pddc = pyridazine-3,6-dicarboxylato) and {[Y6(?4-pzdc)6(NO3)(H2O)16](NO3)5·2H2O}n (6, pzdc = pyrazine-2,5-dicarboxylato), have been prepared by different synthetic approaches. The crystal structures range from 0D to 3D architectures, and all of the compound show solvent-occupied volumes. The thermal behaviour of these compounds has been analysed, and the open structure of 3 shows a reversible uptake/release of water. Moreover, the yttrium matrix of 3 has been doped with Eu3+ and Tb3+ ions to investigate the photoluminescence response of the hybrid materials. In addition to a tuneable emission colour through the concentration of luminescent ions and the excitation wavelength, these hybrid materials could serve as potential photofluorescent sensors for water detection through the reversible dehydration/rehydration process. Six diazinedicarboxylate-based yttrium(III) coordination compounds are prepared through different synthetic approaches. Activation by lanthanide doping enables the modulation of the emission colour. Coupling the luminescence with reversible water capture/release opens up the way to a functional material that shows promise as a water sensor.

Posted on 2 April 2015 | 2:20 pm

Fluorescence Quenching of a Europium Coordination Compound for the Detection of Trace Amounts of Water: Uncovering the Response Mechanism by Structural Confirmation

The coordination compound Eu(DAF)2(NO3)3 (1, DAF = 4,5-diazafluorene), which shows strong red fluorescence, has been synthesized and characterized. The luminescence-quenching effect of 1 has been applied to the detection of water in CH3CN. For the first time, the response mechanism has been uncovered through the confirmation of the structure of the resultant nonluminous compound [Eu(NO3)2(H2O)5](NO3)(DAF)2·H2O (2). The replacement of the coordinated DAF ligands by the added water led to quenching of the emission of the EuIII ion and the simultaneous enhancement of the ligand emission. X-ray powder diffraction and thermogravimetric analyses also confirmed this mechanism. Theoretical calculations by the semi-empirical method revealed the origin of the absorption spectra of 1. This fluorometric detection of trace amounts of water in CH3CN by 1 is a direct, rapid, and sensitive method. The luminescence-quenching effect of Eu(DAF)2(NO3)3 (1, DAF = 4,5-diazafluorene) is applied to the detection of water in CH3CN. The response mechanism is first uncovered through the confirmation of e structure of the resultant nonluminous compound [Eu(NO3)2(H2O)5](NO3)(DAF)2·H2O (2). Theoretical calculations of the absorption spectra are also reported.

Posted on 2 April 2015 | 2:20 pm

Electronic Fine-Tuning of Oxygen Atom Transfer Reactivity of cis-Dioxomolybdenum(VI) Complexes with Thiosemicarbazone Ligands

A series of six cis-dioxomolybdenum(VI) complexes with thiosemicarbazone ligands was synthesized and characterized. The ligands were obtained by reacting ethyl thiosemicarbazide with salicylaldehydes substituted with a selection of electron-withdrawing and electron-donating groups. The crystal structures, IR, NMR spectroscopic data and oxygen atom transfer activities of the complexes revealed that the electronic effects of the substituents located in the para-position of the phenolate donor are transmitted through to the molybdenum center, as reflected by linear relationships between Hammett constants and key properties of the complexes, including the molybdenum–phenolate bond lengths and the coordination shift of the imine proton resonance. Compared with the unsubstituted catalyst, electron-withdrawing substituents increase the rate of oxygen atom transfer from dimethyl sulfoxide to triphenylphosphine, whereas electron-donating groups have the opposite effect. The highest rate enhancement was achieved through the introduction of a strongly electron-withdrawing NO2 substituent in the p-position of the phenolate donor. Thiosemicarbazone ligands (H2LR) derived from para-substituted salicylaldehydes allow the electronic properties and catalytic activities of cis-dioxo MoVI complexes of composition [MoO2(LR)MeOH] to be fine-tuned by electron-donating or electron-withdrawing groups R.

Posted on 2 April 2015 | 2:20 pm

Catalytic Models of Tyrosinase: Reactivity Differences between Systems Based on Mono- and Binucleating Ligands

A new tyrosinase model based on the binucleating ligand Lpy2 is synthesized and characterized. The ligand Lpy2 contains a combination of an imine and a pyridine function in the sidearms, which are bridged by a flexible alkyl spacer. As shown by UV/Vis and NMR spectroscopy, the Cu2Lpy2 complex catalyzed the conversion of the monophenol 2,4-di-tert-butylphenol (DTBP-H) into the o-quinone 3,5-di-tert-butylquinone (DTBQ) with a turnover number (TON) of 18. The dicopper complex of Lpy2 thus shows monophenolase activity that is comparable to that of the recently developed Lpy1 model of tyrosinase, which is based on a known mononucleating ligand (M. Rolff, J. Schottenheim, G. Peters, F. Tuczek, Angew. Chem. Int. Ed. 2010, 122, 6583). The electron-poor substrate 4-hydroxybenzoic acid methyl ester (MeBA-OH), in contrast, is converted by Cu2Lpy2 into the semiquinone. For both substrates, the oxygenation reactions were also conducted in a stoichiometric fashion to obtain information on the intermediates involved. For the substrate MeBA-OH, we detected a binuclear ?-catecholato copper(II) complex by high-resolution ESI mass spectrometry. These studies were complemented by investigations of deactivation mechanisms that could be invoked to explain the limitation of the TON. To this end, a bis-?-hydroxido Lpy2 dicopper(II) complex as well as a semiquinone Lpy2 complex were prepared. Both complexes may represent decay products of the catalyst. A tyrosinase model based on the binucleating ligand Lpy2 was developed and characterized. The ligand Lpy2 contains a combination of an imine and a pyridine function in the sidearms that are bridged by a flexible alkyl spacer. The Cu2Lpy2 complex catalyzes the conversion of monophenol DTBP-H into the o-quinone DTBQ (TON = 18). An electron-poor substrate is converted into the semiquinone.

Posted on 2 April 2015 | 2:20 pm

One-Pot Synthesis of a 1,2-Diphospholide by Double C–H Deprotonation

The relationship between phosphorus and carbon chemistry has been realized for many years. Phosphorus relatives of classical organic ligands (like cyclopentadienide, Cp–) in which carbon atoms have been substituted for phosphorus atoms are important classes of organometallic ligands, which are relevant to catalysis. Often, however, a limit to applying the phosphorus counterparts is the low-yielding and circuitous nature of their synthesis. A case in point is the 1,2-diphospholide ligand framework, an important analogue of the cyclopentadienyl ligand, which has only been obtained from multistep syntheses. We report in this paper a high-yielding and direct route to this type of framework using a very simple approach. Treatment of MesPHLi (Mes = 2,4,6-trimethylphenyl) with Sb(NMe2)3 generates the 5,7-dimethyl-1,2-benzodiphosphol-1-ide anion (1), the first 1,2-diphospholide analogue of indenyl. Structural and NMR spectroscopic investigations suggest that this unique reaction, involving double C–H deprotonation of a CH3 group of the Mes ligand, occurs through the rearrangement of a tetraphospha-1,4-diide anion. Almost “In-denyl”: 5,7-Dimethyl-1,2-benzodiphosphol-1-ide (1), a species valence-isoelectronic with the indenyl anion, is simply prepared in a one-pot synthesis by treatment of MesPH2 with nBuLi and Sb(NMe2)3. This transformation involves an unprecedented double C–H deprotonation of a CH3 group by a redox-active main group base.

Posted on 31 March 2015 | 10:40 am

Phosphaindazole: A Phosphorus–Carbon Aromatic Heterocycle

A straightforward synthetic route to a novel phosphorus–carbon heterocycle, namely, phosphaindazole, which is the phosphorus analogue of indazole or indene, was developed from sodium tetraphosphanediide [Na2(P4Mes4)](Mes = 2,4,6-Me3C6H2) and nBuLi. A proposed intermediate in this reaction, the dimesityldiphosphanide dianion, could be isolated and structurally characterized as [Na8(thf)8(P2Mes2)4]·2THF. A straightforward synthetic route to a novel phosphorus–carbon heterocycle, phosphaindazole, which is the phosphorus analogue of indazole or indene, was developed from sodium tetraphosphanediide [Na2(P4Mes4)](Mes = 2,4,6-Me3C6H2) and nBuLi.

Posted on 31 March 2015 | 10:30 am

Synthesis, Structure, and Reactivity of Ruthenium(0) Indane Complexes fac-[Ru(NCMe)3(CO)2(InX3)] (X = Cl, Br)

The first ruthenium indane complexes, fac-[Ru(NCMe)3(CO)2(InX3)] (X = Cl: 1, Br: 2), were synthesized in the reaction of triruthenium dodecacarbonyl Ru3(CO)12 with 3 equiv. of InX3 in acetonitrile at 80 °C for 30 min. Reaction of fac-[Ru(NCMe)3(CO)2(InX3)] (X = Cl: 1, Br: 2) with PPh3 at a 1:1 molar ratio in acetonitrile at 50 °C for 5 h afforded cis,cis,trans-[Ru(NCMe)2(CO)2(InX3)(PPh3)] (X = Cl: 3, Br: 4). The structures of 1–4 were determined by using single-crystal X-ray analysis. The first ruthenium indane complexes, fac-[Ru(NCMe)3(CO)2(InX3)] (X = Cl, Br), were synthesized by the reaction of Ru3(CO)12 with 3 equiv. of InX3. Reaction of fac-[Ru(NCMe)3(CO)2(InX3)] (X = Cl: 1, Br: 2) with PPh3 at a 1:1 molar ratio afforded cis,cis,trans-[Ru(NCMe)2(CO)2(InX3)(PPh3)] (X = Cl: 3, Br: 4) as a result of the trans-effect of InX3.

Posted on 31 March 2015 | 10:20 am

Anionic N-Heterocyclic Carbene Complexes of Gold(I) as Precatalysts for Silver-Free Cycloisomerization of Enynes

The anionic malonate-derived N-heterocyclic carbene maloNHC readily and efficiently reacts with AuCl(tht) to generate the corresponding anionic gold(I) complexes of type [(maloNHC)AuCl](M). A stoichiometric reaction of these complexes with triphenylphosphine affords the zwitterionic complex [(maloNHC)Au(PPh3)]. Although totally insoluble in the reaction medium, the [(maloNHC)AuCl](M) salts were shown to be suitable precatalysts for the cycloisomerization of 1,6-enynes through the in situ generation of soluble zwitterionic catalytic species of the type [(maloNHC)Au]. The anionic maloNHC–gold(I) complexes, synthesized as their Li+, K+, and Et4N+ salts, were fully characterized and used as precatalysts in the silver-free Au-catalyzed cycloisomerization reaction of 1,6-enynes. It was revealed that the nature of the countercation has a strong influence on the catalyst efficiency. The potassium salt appeared to be the best catalyst affording yields of up to 99?%.

Posted on 31 March 2015 | 10:20 am

Fabrication and Photocatalytic Properties of TiO2/Reduced Graphene Oxide/Ag Nanocomposites with UV/Vis Response

Novel one-dimensional TiO2 nanofibers/reduced graphene oxide/Ag nanoparticles (TiO2/rGO/Ag) nanocomposite photocatalysts with UV/Vis response properties were fabricated by wrapping rGO sheets around TiO2 nanofibers and then loading Ag nanoparticles onto the surfaces of TiO2/rGO. The prepared samples were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and UV/Vis diffuse reflectance spectroscopy. The photocatalytic activities of the samples were evaluated by photocatalytic degradation of an aqueous solution of rhodamine B (RhB) under UV/Vis light irradiation. The results showed that the introduction of rGO and Ag greatly improved the photocatalytic activity of the TiO2 nanofibers, and this enhancement was attributed to the hybridization of rGO possessing specific electronic effects and Ag nanoparticles showing surface plasmon resonance effects. As a consequence, extension of the absorption spectrum to the visible region and efficient restriction of the recombination of photogenerated carriers were achieved. TiO2·rGO/Ag composite nanofibers are prepared by wrapping reduced graphene oxide (rGO) sheets around TiO2 nanofibers and then loading Ag nanoparticles onto the surfaces of TiO2/rGO. The introduction of rGO and Ag creates a marked improvement in the photocatalytic activity of the TiO2 nanofibers.

Posted on 31 March 2015 | 10:10 am

The Electrically Wired Molybdenum Domain of Human Sulfite Oxidase is Bioelectrocatalytically Active

We report electron transfer between the catalytic molybdenum cofactor (Moco) domain of human sulfite oxidase (hSO) and electrodes through a poly(vinylpyridine)-bound [osmium(N,N?-methyl-2,2?-biimidazole)3]2+/3+ complex as the electron-transfer mediator. The biocatalyst was immobilized in this low-potential redox polymer on a carbon electrode. Upon the addition of sulfite to the immobilized separate Moco domain, the generation of a significant catalytic current demonstrated that the catalytic center is effectively wired and active. The bioelectrocatalytic current of the wired separate catalytic domain reached 25?% of the signal of the wired full molybdoheme enzyme hSO, in which the heme b5 is involved in the electron-transfer pathway. This is the first report on a catalytically active wired molybdenum cofactor domain. The formal potential of this electrochemical mediator is between the potentials of the two cofactors of hSO, and as hSO can occupy several conformations in the polymer matrix, it is imaginable that electron transfer from the catalytic site to the electrode through the osmium center occurs for the hSO molecules in which the Moco domain is sufficiently accessible. The observation of catalytic oxidation currents at low potentials is favorable for applications in bioelectronic devices. Human sulfite oxidase and its catalytic molybdenum-cofactor-containing domain were wired to an electrode with poly(vinylpyridine)–[osmium(N,N?-methyl-2,2?-biimidazole)3]2+/3+, which mediated the electron transfer between either of the enzyme cofactors and the electrode, as demonstrated by electrocatalytic turnover currents.

Posted on 31 March 2015 | 10:10 am

Second-Sphere Complexation of Thorium(IV) by Cucurbit[6]uril with Included Perrhenate Counterions – Crystal Structure and Hirshfeld Surface Analysis

The reaction of thorium(IV) nitrate with cucurbit[6]uril (CB6) in the presence of perrhenic acid in water gives the complex [Th(NO3)(H2O)8][(ReO4)(CB6)](ReO4)2·3H2O (1). Aquated cations are held at both CB6 portals by ion–dipole and hydrogen-bonding interactions, and one of the ReO4– anions is included in the CB6 cavity. The packing displays columns of alternate cations and encapsulated anions. Hirshfeld surfaces are used to visualize short contacts between the species present. Aquated thorium cations are held at both portals of cucurbit[6]uril (CB6) by ion–dipole and hydrogen-bonding interactions, one perrhenate anion being included in the macrocycle cavity. Hirshfeld surfaces are used to visualize short contacts between the species present.

Posted on 30 March 2015 | 1:40 pm

Synthesis, Crystal Structure, and Magnetic Properties of a Family of Undecanuclear [CuII9LnIII2] Nanoclusters

The syntheses, crystal structures, and magnetic properties of a novel family of heterometallic aggregates [CuII9LnIII2(?3-OH)8(mea)4(C3H7COO)4(NO3)2Cl6(MeOH)4(H2O)2]·3MeOH·2H2O [Ln = Eu (1), Gd (2), Tb (3), Dy (4)] are reported. The compounds were obtained by the direct reaction of monoethanolamine (Hmea) with CuCl2·2H2O and Ln(NO3)3·6H2O in the presence of sodium butyrate (C3H7COONa) in MeOH/MeCN solution. Compounds 1–4 are isomorphous and have an intriguing heterometallic undecanuclear [Cu9Ln2] core that contains a [3?×?3] [Cu9] grid and two [LnCu4] tetragonal pyramids that share a common [Cu4] vertex. Compounds 1–4 are the first high-nuclearity 3d-4f aggregates bearing a monoethanolamine (Hmea) ligand to be reported. The magnetic properties of 1–4 have been investigated by dc and ac susceptibility measurements. A detailed magnetic analysis revealed that antiferromagnetic Cu···Cu interactions and ferromagnetic Cu···Gd couplings exist in [Cu9Gd2] (2), which exhibits a significant magnetocaloric effect. Furthermore, [Cu9Tb2] (3) and [Cu9Dy2] (4) display slow relaxation of the magnetization. Four isostructural undecanuclear heterometallic compounds with an unprecedented [Cu9Ln2] core, which can be viewed as a [3?×?3] [Cu9] grid and two [LnCu4] tetragonal pyramids that share a common [Cu4] vertex, have been synthesized. [Cu9Gd2] (2) exhibits a significant magnetocaloric effect, whereas [Cu9Tb2] (3) and [Cu9Dy2] (4) display slow relaxation of the magnetization.

Posted on 30 March 2015 | 1:40 pm

pH-Sensitive Gold Nanorods with a Mesoporous Silica Shell for Drug Release and Photothermal Therapy

A pH-sensitive nanocarrier has been developed for the controlled intracellular release of drugs. The nanocarrier, which is approximately 75 nm in size, is composed of a gold nanorod (GNR) core and mesoporous silica shell (GNR@mSiO2) and shows good stability and biocompatibility, and excellent photothermal effects. Doxorubicin hydrochloride (DOX), a typical anticancer drug, was adopted as the model drug, and was connected to the mesoporous silica through Schiff base bonding. The drug-loading nanocarriers (GNR@mSiO2-DOX) exhibit enhanced drug release under acidic conditions owing to the sensitive Schiff base linker, whereas at high pH values low levels of premature release can be detected. The sensitive release mechanism was further investigated by monitoring the zeta potential before and after drug release. HeLa cells were used as typical cancer cells, and detailed cell experiments were carried out to confirm the good biocompatibility, rapid uptake, and acid-enhanced drug delivery of GNR@mSiO2-DOX. Moreover, the synergistic effect of chemotherapy and hyperthermia (photothermal effect from GNRs) of the nanocarrier can be expected to lead to improved therapy effects on cancer treatment. A pH-sensitive nanocarrier with a gold nanorod (GNRs) core and mesoporous silica shell (GNR@mSiO2) was synthesized. Doxorubicin hydrochloride (DOX) was loaded onto the mesoporous silica with Schiff base bonding, and enhanced drug release was observed under acidic conditions owing to the sensitive Schiff base linker. The synergistic effect of chemotherapy and hyperthermia shown by this nanocarrier can be expected to lead to improved cancer treatment.

Posted on 30 March 2015 | 1:40 pm

Fe,Pd Co-Incorporated LaCoO3 Perovskites: Modification of Thermal Stability and Catalytic Activity for Gasoline Vehicle Exhaust Purification

A series of LaCo0.95–xFexPd0.05O3 (x = 0, 0.1, 0.2, 0.3) perovskite-type catalysts have been prepared by a modified sol–gel method. Their structures and physicochemical properties have been studied by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), the Brunauer–Emmett–Teller (BET) isotherm technique, and temperature-programmed reduction (TPR). Structural characterization showed that Fe had been successfully doped into the perovskite lattice and that Fe doping improves the stability of LaCo0.95Pd0.05O3. A study of the catalysts showed that aged samples maintain the perovskite structure. They all exhibited similar catalytic performance, which has been ascribed to the similar state of palladium at the surface of the catalysts. Of these as-prepared catalysts, the Fe-doped perovskites achieved better catalytic activities than LaCo0.95Pd0.05O3, and LaCo0.65Fe0.3Pd0.05O3 showed the optimal catalytic performance for vehicle emission purification. A series of Fe,Pd co-doped LaCoO3 perovskites have been studied as three-way catalysts. A mechanism is proposed for the enhancement of the stability of the perovskite structure by Fe doping as well as the catalytic performance for the simultaneous elimination of CO, NO, and C3H8.

Posted on 30 March 2015 | 1:40 pm

Influence of Metal Cations and Coordination Modes on Luminescent Group 1 and 2 Metal Sulfonate Complexes Constructed from 4,4?-Dihydroxybiphenyl-3,3?-disulfonic Acid

The reactions of 4,4?-dihydroxybiphenyl-3,3?-disulfonic acid (H4L) with group 1 and 2 metal salts in aqueous solution lead to six metal sulfonate complexes, [K2(H2L)]n (1), {[Cs2(H2L)(H2O)]n·nH2O} (2), 2[Mg(H2O)6]2+·2(H2L)2–·2H2O (3), {[Ca(H2L)(H2O)2]n·4nH2O} (4), {[Sr(H2L)(H2O)4]n·3nH2O} (5), and {[Ba(H2L)(H2O)]n·nH2O} (6), which have been characterized by elemental analysis, IR spectroscopy, thermogravimetry (TG), photoluminescence (PL) spectroscopy, powder XRD, and single-crystal XRD. Complexes 1, 2, and 6 exhibit 3D pillared-layered networks formed by M–O–S layers bridged by the biphenyl rings of H2L2– dianions. The [Mg(H2O)6]2+ cations and sulfonate groups in 3 are held together by second-sphere interactions to generate layer motifs. Complex 4 presents a layer structure formed by Ca–O chains bridged by the biphenyl rings of H2L2– dianions. Complex 5 has a 3D interdigitating architecture (2D + 2D??3D), in which the 44 hydrogen-bonding layer is constructed from linear chains. Meanwhile, the recrystallization of H4L from aqueous solution affords the supramolecular complex 2(H3O+)·(H2L)2–·3H2O (S1), which exhibits a 3D pillared-layered network. The solid-state luminescence properties demonstrate that 1–6 exhibit violet emission at room temperature and can sensitize EuIII and TbIII ions to exhibit their characteristic emissions. The self-assembly of 4,4?-dihydroxybiphenyl-3,3?-disulfonic acid with group 1 and 2 metal salts results in diverse second-coordination-sphere networks, hybrid layers, interdigitating 2D + 2D??3D architectures, and 3D pillared-layered networks tuned by the metal cations and the coordination mode of the ligand.

Posted on 26 March 2015 | 1:10 pm

Ferrocenyl–Bipyridinium Cations and Their Platinum Complexes Related to Viologens – Preparation, Redox Properties, and Crystal Structures

N-R1-N?-R2-4,4?-Bipyridinium and N-R1-4,4?-bipyridinium salts containing ferrocenyl substituents were prepared as donor–acceptor compounds (R1 = ferrocenyl, ferrocenylphenyl; R2 = ferrocenyl, ferrocenylphenyl, phenyl, methyl). Platinum(II)-bridged diferrocene compounds were prepared by using the N-R1-4,4?-bipyridinium ligands. These compounds display multistage redox properties. The redox potentials of the ferrocenyl and bipyridinium moieties in these compounds are independently affected by molecular modifications, which indicates that conjugation between the donor and acceptor moieties is less effective. Single-crystal X-ray diffraction analyses revealed large twist angles between the two moieties in the solid state. The compounds exhibit broad charge-transfer absorption bands in the range 450–800 nm. No electronic communication was observed between the terminal ferrocenes in the diferrocene complexes. 4,4?-Bipyridinium cations bearing ferrocenyl or ferrocenylphenyl substituents at the N-positions were prepared as donor–acceptor compounds. Platinum(II)-bridged diferrocene compounds were also prepared by using bipyridinium cations. These cations display multistage redox properties, and the compounds exhibit broad charge-transfer absorption bands in the range 450–800 nm.

Posted on 26 March 2015 | 1:10 pm

Effects of Big Planar Anions on the Spin Transition of a Mononuclear Manganese(III) Complex with a Hexadentate Schiff-Base Ligand

Two new ion-pair complexes [Mn(3-MeO-sal-N-1,5,8,12)][Ni(dmit)2] (1) and [Mn(3-MeO-sal-N-1,5,8,12)][Pt(mnt)2]·2CH3CN (2), based on the known six-coordinate mononuclear Schiff-base manganese(III) spin-crossover complex [Mn(3-MeO-sal-N-1,5,8,12)]NO3, have been synthesized and structurally characterized. Their crystal structures indicate that increasing the size of the anion from NO3– to [Pt(mnt)2]– and [Ni(dmit)2]– leads to the dimerization of the cations and formation of alternating cation–anion stacks with loss of the most effective cation–anion interactions; only weak short contacts exist between the cations and anions. Magnetic measurements and variable-temperature single-crystal X-ray crystallography analysis provided firm evidence for spin-crossover (SCO) effects in 1. The magnetic susceptibility of compound 2 is typical of a simple paramagnet, and the manganese(III) complex cations remain in the high-spin state in the temperature range 2–300 K. Spin-crossover in d4 ions is a most rare event. Changing the size of the anion from NO3– to [Pt(mnt)2]– and [Ni(dmit)2]– leads to significant changes in the overall crystal packing of Mn ion-pair complexes and furthermore in the spin state of the MnIII center.

Posted on 26 March 2015 | 1:10 pm

Potent Reactivity in Solubilised Oxo-Titanium Polymers

[TiO(salen)]n polymers are solubilised in aldehyde solution giving highly reactive entities. Unprecedented carbon-based chemistry is demonstrated by the formation of new ligands about the titanium centre. Identified by X-ray crystallography are a polymer deconstructed [Ti(salen)] oxo dimer, a [Ti(salen)] catecholato complex and an unusual [Ti(salen)] diolato complex. Formation of the new ligands appears to be related to the salicylidene ligand aromatic ring ortho substituent and the aldehyde used. [TiO(salen)]n polymers solubilised in aldehyde solution show potent activity when ortho substituents are present on the salicylidene ligand aromatic rings. Unprecedented carbon-based chemistry is demonstrated by the formation of new ligands about the titanium centre.

Posted on 25 March 2015 | 11:40 am

Monoclinic Copper(I) Selenide Nanocrystals and Copper(I) Selenide/Palladium Heterostructures: Synthesis, Characterization, and Surface-Enhanced Raman Scattering Performance

We have developed a simple and facile approach to the fabrication of monoclinic Cu2Se nanocrystals and Cu2Se/Pd heterostructures. [(C2H5)4N]2[CuCl4] was chosen as the copper source and SeO2/terpineol was used as the Se–II precursor for the generation of hexagonal CuSe and cubic Cu2–xSe through the “hot-injection” and “one-pot” methods, respectively. Both CuSe and Cu2–xSe could be further transformed into monoclinic Cu2Se through heat treatment with trioctylphosphine (TOP) at 220 °C. Cu2Se/Pd as well as CuSe/Pd and Cu2–xSe/Pd were readily obtained by simply mixing copper selenides and Pd(NO3)2 in a 2-propanol solution. The Pd nanoparticles were distributed on the surface of the copper selenides. The effect of certain reaction parameters on the formation of copper selenides was studied. The amount of terpineol used played an important role in the phase-selective synthesis of CuSe and Cu2–xSe. The surface-enhanced Raman scattering (SERS) performance of the heterostructures was investigated with 4-mercaptopyridine (4-Mpy) as a probe molecule. Owing to the strong synergistic effects between Cu2Se and Pd, Cu2Se/Pd showed greater SERS performance than pure Pd or Cu2Se. Moreover, compared to those of CuSe/Pd and Cu2–xSe/Pd, Cu2Se/Pd exhibited the highest SERS sensitivity to 4-Mpy with a detection limit as low as 1.0?×?10–9 M, which revealed its phase- and composition-dependent characteristics. This Cu2Se/Pd heterostructure exhibits potential applications in the chemical and biological sensing fields. Monoclinic Cu2Se nanocrystals and Cu2Se/Pd heterostructures have been synthesized by simple and facile methods. Owing to strong synergistic effects and phase-dependent characteristics, the surface-enhanced Raman scattering performance of the Cu2Se/Pd heterostructure is superior to those of Cu2Se, Pd, CuSe/Pd, and Cu2–xSe/Pd.

Posted on 25 March 2015 | 11:40 am

Phenylpyrazole-Based Hypervalent Phosphorus Compounds: From Positional Isomerism to Stacking Interactions

The lithium salt of 3,5-dimethyl-1-phenyl-1H-pyrazole (PyrC6H4Li) reacts with (Et2N)2PCl to give the precursor [PyrC6H4P(NEt2)2] (2), which, after reaction with PCl3, affords PyrC6H4PCl2 (3) in 79?% yield. The phosphorus atom in 3 has four-coordinate disphenoidal geometry with an axial arrangement of Cl atoms. The length of the hypervalent N–P bond in this compound [1.775(1) Å] is comparable to that of common single bonds. The structure of 3 is better described by canonical formulae containing charges on the N, P, and Cl atoms. The 1H NMR spectrum of 3 in CDCl3 shows five pairs of nonequivalent Me groups, which correspond to the positional isomers that exist in the equilibrium mixture. Compound 3 easily exchanges chlorine with methyl iodide to form the diiodo derivative 4 (PyrC6H4PI2) with nonequivalent P–I bonds. The reduction of 3 with aluminium foil or [GeCl2(diox)] gave cationic diphosphines [(PyrC6H4P)2(?-Cl)][AlCl4] (8) and [(PyrC6H4P)2(?-Cl)][GeCl3] (9), respectively, with a chloride bridge between the phosphorus atoms. Compounds 4, 8 and 9 show a disphenoidal arrangement around the hypervalent phosphorus atoms. The dichloro and diiodo derivatives 3 and 4 are destroyed on heating in pyridine to give diphosphines [(PyrC6H4PCl)2] (10) and [(PyrC6H4P)2(?-I)]+[I] (12), respectively, containing hypervalent (trivalent four-coordinate) phosphorus. The crystal structure of 10 shows multiple C···C, C···Cl, H···H, and C···H short contacts between the adjacent molecules. Compound 3 exchanges chlorine for oxygen atoms on heating in dimethylformamide to give the dioxide PyrC6H4PO2 (13) with an N–PV distance [1.808(1) Å] even longer than that in 3. The dichlorophosphino derivative of 3,5-dimethyl-1-phenyl-1H-pyrazole exists in solution as an equilibrium mixture of positional isomers. Its reduction leads to cationic diphosphines with a chloride bridge between the phosphorus atoms. The hypervalent N···P (1.774–1.885 Å) and Hal···P interactions influence the behavior in solution and the arrangement of molecules in the crystal form.

Posted on 24 March 2015 | 1:10 pm

External-Template-Assisted Formation of Octacyanometalate-Based MV–MnII (M = W, Mo) Bimetallic Coordination Polymers with Magnetic Properties

Three manganese–molybdenum/tungsten bimetallic coordination polymers, two 2D {{[?4-M(CN)8]2[Mn(dmf)3]2[Mn(dmf)4]}·2DMF}n (M = W 1, Mo 2) and a 1D {{[?4-Mo(CN)8][Mn(dmf)4]2}·(ClO4)}n (3), were constructed from the reaction of the (Bu3NH)3[M(CN)8] (M = W, Mo) and Mn(ClO4)2·6H2O molecular building blocks in DMF solvent in the presence (for 1 and 2) or absence (for 3) of the organic ligand bis(benzimidazol-2?-yl)pyridine. Single-crystal X-ray diffraction structure analysis indicated that compounds 1 and 2 both crystallize in the monoclinic crystal system with the P21/c space group and possess the same 2D network. The 2D layer structures of 1 and 2 have a (3,4)-connected 2-nodal topology with the point symbol {42·63·8}{42·6}. Compound 3 crystallizes in the tetragonal crystal system with the P42/m space group. All three compounds are further assembled into 3D supramolecular structures through intermolecular C–H···N or C–H···O hydrogen bonds. The magnetic susceptibility of compounds 1 and 3 was investigated in the temperature range of 2–300 K; these compounds exhibit typical ferrimagnetic properties. 2D coordination polymers {{[?4-M(CN)8]2[Mn(dmf)3]2[Mn(dmf)4]}·2DMF}n (M = W, Mo) and a 1D chain compound {{[?4-Mo(CN)8][Mn(dmf)4]2}·(ClO4)}n are constructed by external-template-assisted formation in the presence and absence of bis(benzimidazol-2?-yl)pyridine. All three compounds can be assembled into 3D supramolecular structures, and two of the compounds exhibit typical ferrimagnetic properties.

Posted on 24 March 2015 | 1:10 pm

Facile Preparation of Ammonium Molybdophosphate/Al-MCM-41 Composite Material from Natural Clay and Its Use in Cesium Ion Adsorption

Ordered hexagonal mesoporous aluminosilicate matrix (Al-MCM-41) with incorporated ammonium molybdophosphate (AMP) was successfully synthesized by a one-pot synthesis method with natural clay from low-grade potash ores of Qinghai salt lake as the silica and aluminum source. We introduced a modified “liquid-phase transport” step, which allowed the use of impure natural clay as a starting material to directly produce pure product without sedimentation pretreatment. The resultant product was characterized by X-ray fluorescence (XRF) spectroscopy, FTIR spectroscopy, XRD, TEM, 27Al and 31P magic-angle spinning (MAS) NMR spectroscopy, and N2 adsorption/desorption, which indicated that the AMP was immobilized in the mesoporous structure of Al-MCM-41. The adsorption capacity of the final product for the removal of cesium ions in solution was also investigated. The results suggested that salt lake clay is a promising low-cost precursor for the production of mesoporous aluminosilicate supports through one-pot syntheses, and the final composite material is effective for the adsorption of cesium ions from solutions containing other alkali metal ions. A composite ammonium molybdophosphate/Al-MCM-41 material is synthesized by a one-pot method with natural clay as the silica and aluminum source. A modified “liquid-phase transport” step allows the use of impure natural clay as the starting material to produce pure product without sedimentation pretreatment. The composite material is effective for the adsorption of cesium ions from brine.

Posted on 23 March 2015 | 11:10 am

Thymol Bromination – A Comparison between Enzymatic and Chemical Catalysis

The catalytic activity of the vanadium-dependent bromoperoxidase isolated from the brown alga Ascophyllum nodosum is compared with the activity of a cheap, commercially available V-catalyst precursor in the bromination of thymol. Organic solvents have been avoided to make the system appealing from a sustainable chemistry point of view. It is noteworthy that, notwithstanding the low solubility of the substrate, the thymol bromination reactions were performed in water, with a safe brominating source, under mild conditions, and with relatively inexpensive reagents. In this regard, the greenness of the systems was evaluated by the estimation of the E-factor value; the result is that the chemical reaction has a lower environmental impact than the enzymatic process, with an E-factor in the range of eco-friendly processes. Catalysis of thymol bromination by vanadium derivatives is directly compared to catalysis by a V-dependent bromoperoxidase. All reactions were performed under mild and sustainable conditions with relatively inexpensive reagents. Appealing results were obtained in terms of selectivity and sustainability.

Posted on 20 March 2015 | 12:10 pm

Flux Crystal Growth of the Ternary Polygermanide LaPtGe2, a p-Type Metal

Large plate crystals of LaPtGe2 have been grown by using an inert indium metal flux. This compound crystallizes in the CeNiSi2-type structure (orthorhombic space group Cmcm) with lattice parameters a = 4.3770(9) Å, b = 17.186(3) Å, and c = 4.3942(9) Å. The structure of LaPtGe2 is a three-dimensional framework with alternating PbO-type layers of PtGe and infinite Ge chains, separated by La atoms. Electrical resistivity and Hall effect measurements characterize LaPtGe2 as a metal with holes that act as the charge carriers. Strong temperature dependence of the Hall coefficient and a violation of Kohler's rule (from magnetoresistance data) both indicate possible multiband effects. The electronic structure calculations suggest the metallic nature of LaPtGe2 and show that the strongest bonding exists between Pt and Ge within the PbO-type layers. Plate crystals of LaPtGe2 have been grown from a molten indium flux. This compound crystallizes in the CeNiSi2-type structure. Electrical resistivity, Hall effect, and thermopower measurements have shown that LaPtGe2 exhibits p-type metallic behavior, which is consistent with electronic band structure calculations.

Posted on 20 March 2015 | 12:10 pm

Room-Temperature Hydrogenation of Citral Catalyzed by Palladium–Silver Nanocrystals Supported on SnO2

We have developed two strategies to optimize Pd catalysts. On one hand, Ag was introduced into Pd and then they were applied to the selective hydrogenation of citral under mild conditions. The addition of metallic Ag could tune the selectivity of Pd and made it suitable for the selective hydrogenation of the conjugated double bond. The selectivity of citronellal increased from 0 (for Pd/C and Pd0.7Ag0.3/C) to 96?% (for Pd0.4Ag0.6/C) as the Ag content increased. On the other hand, the addition of SnO2 made the Pd catalysts more inclined to activate the C=O bond and gave better performance for the hydrogenation of the conjugated double bond compared with the corresponding Pd–Ag catalysts. The selectivity of citronellal increased from 0 (for Pd0.7Ag0.3/C) to 76?% (for Pd0.7Ag0.3–SnO2/C was used) after the addition of SnO2. On the basis of these results, we developed a catalyst (Pd0.6Ag0.4–SnO2/C) with the best catalytic performance for the selective hydrogenation of citral (the conversion of citral reached 99?%, and the selectivity was up to 96?%). We have developed two strategies to optimize Pd catalysts for the selective hydrogenation of citral and exploited a catalyst (Pd0.6Ag0.4–SnO2/C) with the best catalytic performance (the conversion of citral reached 99?%, and the selectivity was up to 96?%).

Posted on 20 March 2015 | 12:10 pm

Synthesis, Crystal Structures, Molecular Docking, and Urease Inhibitory Activities of Transition-Metal Complexes with a 1,2,4-Triazolecarboxylic Acid Derived Ligand

Four novel complexes, [Cu(L)2(NH3)2(H2O)2] (1), {[Cu(L)2(H2O)2]·2H2O}n (2), {[Zn(L)2(H2O)2]·2H2O}n (3), and {[Fe(L)2(H2O)2]·2H2O}n (4) (HL = 2-{[4-amino-3-(pyridin-4-yl)-4,5-dihydro-1H-1,2,4-triazol-5-yl]thio}acetic acid) were synthesized and characterized by single-crystal X-ray diffraction analysis. Complex 1 exhibited a mononuclear structure. Complexes 2, 3, and 4 featured 2D networks. The crystal structures were stabilized by intermolecular hydrogen bonds to generate 3D supramolecular frameworks. The inhibitory activity was tested in vitro against jack bean urease. Among the four complexes, the two CuII complexes 1 and 2 exhibited better inhibitory activity than the positive reference acetohydroxamic acid, with IC50 values of 4.052 and 6.868 ?M, respectively, whereas the ZnII and FeII complexes showed no activity. To explore the mechanism of inhibition of the enzyme, kinetics studies were carried out; the results indicated that both the activated complexes 1 and 2 operated through a mixed-competitive inhibitory mechanism. Molecular docking was used to insert the most active complex 1 into the crystal structure of jack bean urease at the active site to determine the probable mode of binding. Four novel crystals of copper, zinc, and iron complexes based on 1,2,4-triazole carboxylic acid derivatives were determined by single-crystal X-ray diffraction. The inhibitory activity and kinetic studies were tested in vitro against jack bean urease. The computational predications, biological evaluation, and mechanism study will help in the discovery of new urease inhibitors.

Posted on 20 March 2015 | 12:10 pm

Synthesis and Characterization of 4-, 5-, and 6-Coordinate Tris(1-ethyl-4-isopropylimidazolyl-?N)phosphine Cobalt(II) Complexes

The synthesis and characterization of [Co(T1Et4iPrIP)X2] {T1Et4iPrIP = tris(1-ethyl-4-isopropylimidazolyl)phosphine; X = OTf– (1), Cl– (2), Br– (3)} and [Co(T1Et4iPrIP)(CH3CN)3](OTf)2 (4) were investigated. In compounds 1 and 4, T1Et4iPrIP binds in a tridentate fashion, whereas 2 and 3 feature bidentate ligation. Compound 1 additionally coordinates two triflate ligands to complete a distorted square pyramidal geometry. Compound 4 also binds three acetonitrile ligands to afford a distorted octahedral geometry. Compounds 2 and 3 exhibit a distorted tetrahedral geometry for which the ligands comprise two imidazole nitrogen atoms and two halides. Bidentate coordination by using a tris(imidazolyl)phosphine ligand is unprecedented. Compounds 2 and 3 can be derived from 1 by the addition of either Cl– or Br– salts, respectively, whereas 4 can be generated by dissolving 1 in acetonitrile. DFT studies indicate that the HOMO–LUMO gaps of all compounds are comparable; however, steric factors stabilize the formation of 2 and 3 over 1 in the presence of halide ligands. [Co(T1Et4iPrIP)X2] {T1Et4iPrIP = tris(1-ethyl-4-isopropylimidazolyl)phosphine; X = OTf– (1), Cl– (2), Br– (3)}, and [Co(T1Et4iPrIP)(CH3CN)3](OTf)2 (4) are reported. Dissolution of 1 in MeCN affords 4. Reaction of 1 with Cl– or Br– yields 2 or 3, respectively. DFT studies indicate that 1 has the largest HOMO–LUMO gap, which suggests that the formation of 2 or 3 from 1 is primarily sterically driven.

Posted on 20 March 2015 | 12:10 pm

Pentanuclear and Octanuclear Manganese Helices

Two helical manganese complexes, [Mn5(L)3(?3-O)(NO3)(OMe)2(MeOH)](NO3)·4MeOH·H2O (1) and [Mn8(L)6(?3-Cl)2]Cl2·3C2H4Cl2·60H2O·2DMF (2, DMF = N,N-dimethylformamide), were obtained by the reaction of the multidentate polypyridine ligand 2,6-bis[5-(2-pyridinyl)-1H-pyrazole-3-yl]-pyridine (H2L) with manganese nitrate and chloride, respectively. The compounds were characterized by elemental analyses and single-crystal X-ray structural analyses. The pentanuclear complex 1 is composed of three ligands and five manganese ions with ?3-oxido bridges, whereas the octanuclear complex 2 is constructed from six ligands and eight manganese ions with two ?3-chlorido bridges. Both compounds have helix-type structures. The manganese ions in 1 are present in a mixture of +2 and +3 valence states, whereas 2 is homovalent and contains only +2 ions. The magnetic properties of both compounds were investigated in the temperature range 1.8–300 K, and antiferromagnetic interactions between the manganese ions are dominant in both complexes. Pentanuclear and octanuclear manganese helices are obtained by the reactions of a multidentate polypyridine ligand with manganese nitrate and chloride. The Mn ions in the pentanuclear complex are in a mixture of +2 and +3 valence states, whereas those of the octanuclear complex are homodivalent. Both compounds show antiferromagnetic interactions.

Posted on 19 March 2015 | 12:14 pm

Chiral Ruthenium Catalyst Immobilized within Magnetically Retrievable Mesoporous Silica Microcapsules for Aqueous Asymmetric Transfer Hydrogenations

The preparation of magnetically separable silica microcapsules that incorporate in their inner shell a chiral catalyst and their application in asymmetric transfer hydrogenation reactions are described. The preparation method is based on the emulsification of an oil phase containing chloroform, a modified Noyori Ru-TsDPEN catalyst, tetraethoxysilane (TEOS), and hydrophobic magnetic nanoparticles in water in the presence of an appropriate surfactant, followed by an interfacial polycondensation process under basic conditions to generate a silica shell around the oil droplets. The resulting catalytic microreactors can be considered a “quasi-homogeneous” system because the immobilized chiral catalyst reacts in a homogeneous zone, the microcapsule core filled with an organic solvent. The catalytic activity was tested in the asymmetric transfer hydrogenation of ketones in an aqueous medium. The catalytic reactions took place only in the presence of surfactants. In addition, the judicious selection of the surfactant plays a crucial role in enhancing the reaction progress through the emulsion-solid transfer (EST) approach. The catalytic activity of the Ru-TsDPEN catalyst immobilized within the silica microcapsules was superior to the same catalyst supported on silica microspheres or linked to the backbone of a silica sol–gel matrix, which indicates the importance of the homogeneous zones for the reactions. We report the design of a “quasi-homogeneous” catalytic system, based on a modified Noyori Ru-TsDPEN catalyst confined within mesoporous silica-based microreactors, for the efficient asymmetric transfer hydrogenation of ketones in water. The new system demonstrates excellent reactivity and enantioselectivity characteristic of homogeneous catalysts, but can be easily recovered.

Posted on 19 March 2015 | 12:13 pm

The Effects of Alkaline-Earth Counterions on the Architectures, Band-Gap Energies, and Proton Transfer of Triazole-Based Coordination Polymers

Three coordination polymers based on alkaline-earth metals (Ca, Sr, and Ba) have been synthesized with 3-amino-1,2,4-triazole-5-carboxylic acid (3-AmTrZAc). Structural analysis reveals that the Ca-based structure [Ca(3-AmTrZAc)(5-AmTrZAc)(H2O)] (1) is two-dimensional, and the Sr- and Ba-based structures [Sr(3-AmTrZAc)2(H2O)] (2) and [Ba(3-AmTrZAc)2(H2O)] (3) are three-dimensional. In the Ca-based structure 1, the 3-AmTrZAc reactant converts to 5-AmTrZAc. The relative stability of the two isomers is controlled by a dipole–ion interaction between the triazole ring and the carboxylate group. We have measured the band-gap energies, and the Ca-based structure has the largest band-gap energy. Density functional theoretical investigations showed that internal electric fields generated by the alkaline-earth counterions increase the band gap in the 5-AmTrZAc anion and lower it in the 3-AmTrZAc anion. The effects of alkaline-earth ions on the architectures, band-gap energies, and proton transfer of triazole-based coordination polymers are investigated.

Posted on 19 March 2015 | 12:13 pm

Accessible Syntheses of Late Transition Metal (Pre)Catalysts Bearing N-Heterocyclic Carbene Ligands

This microreview details and discusses some selected examples of the accessible syntheses of useful complexes bearing N-heterocyclic carbenes (NHCs). The term “accessible”, as used here, is defined as a synthetic route that does not require the isolation of the free NHC. These routes typically rely on either the generation of low equilibrium concentrations of the free NHC, which is then trapped by a metal centre, the deprotonation of the azolium salt by a suitable ligand or the activation of the C–H bond. These approaches can help to overcome a key weakness of NHCs in that they must be handled under stringently inert conditions. Studies of complexes based on metal centres from groups 8–11 are presented and discussed. Selected examples of the synthesis of useful (pre)catalysts bearing N-heterocyclic carbenes (NHCs) are discussed. All of these examples avoid the generation and isolation of free carbenes and the use of strong, sensitive bases; therefore, they are presented as useful preparative methods that can allow these catalysts to be utilised more widely.

Posted on 18 March 2015 | 2:10 pm

Retention of the Cluster Core Structure during Ligand Exchange Reactions of Carboxylato-Substituted Metal Oxo Clusters

The exchange of the carboxylato ligands of Zr4O2(methacrylato)12 in reactions with carboxylic acids proceeds with retention of the composition and structure of the cluster core. This was concluded from exchange/re-exchange experiments and from comparison of the IR bands of the cluster core of the original and ligand-exchanged clusters. The IR bands were assigned on the basis of DFT calculations. Scrambling reactions between two Zr4O2(OOCR)12 clusters with different carboxylato ligands are a new way to prepare mixed-ligand oxo clusters. Ligand exchange in Zr4O2(OOCR)12 clusters proceeds with retention of the cluster core. A new scrambling reaction is introduced for the preparation of mixed-ligand clusters.

Posted on 18 March 2015 | 2:10 pm

Molecular Rectangles with Rod-Shaped Disulfonic Acids

Polysulfonic acids and their compounds have been scarcely investigated, despite the huge knowledge that we have of the respective polycarboxylic acids and polycarboxylates. This is because of the limited availability of polysulfonic acids, for which reliable synthetic protocols are often lacking. Here, we present the first compound of the recently reported disulfonic acid 1,4-bis(4-sulfophenyl)butadiyne (H2DPBDS) prepared in our groups and a new compound of the commercially available 4,4?-biphenyldisulfonic acid (H2BPDS). The zinc sulfonates [Zn2(BPDS)2(NMP)6]·2NMP [I, NMP = N-methylpyrrolidone; triclinic, P$\bar {1}$, Z = 2, a = 972.8(2), b = 981.5(2), c = 1915.2(2) pm, ? = 87.73(3)°, ? = 77.68(3)°, ? = 89.36(3)°, V = 1785.0(6) Å3] and [Zn2(DPBDS)2(DMA)6]·2DMA [II, DMA = dimethylacetamide; triclinic, P$\bar {1}$, Z = 2, a = 973.79(2), b = 1347.53(2), c = 1411.08(2) pm, ? = 110.531(1)°, ? = 92.445(1)°, ? = 101.931(1)° V = 1683.11(5) Å3] display rigid molecular rectangles constructed from two zinc atoms and two sulfonate ligands. The rectangles are assembled through weak interactions to form soft host lattices that incorporate the solvent DMA or NMP molecules, partly through Zn2+ coordination. Thermal analysis shows that the solvent molecules can be completely removed without decomposition of the coordination polymers. Rod-shaped disulfonic acids are suitable for the construction of zinc-based molecular rectangles. These rectangles form flexible lattices that incorporate solvent molecules. The removal of the solvent molecules leads to disulfonates of astonishingly high thermal stability, in strong contrast to the behavior of comparable polycarboxylates.

Posted on 18 March 2015 | 2:10 pm

Modulating Sonogashira Cross-Coupling Reactivity in Four-Coordinate Nickel Complexes by Using Geometric Control

Herein, we present the synthesis of nickel complexes with tripodal phosphine ligands, CH3Si(CH2PPh2)3 and CH3C(CH2PPh2)3, and their application as catalysts in Sonogashira cross-coupling reactions in water. Although both types of nickel complexes are based on similar tripodal ligands, the Si-derived compounds adopt stable tetrahedral coordination geometries, whereas the C-derived counterparts adopt a square-planar coordination environment. This structural and electronic difference has an important effect on the catalytic properties of the complexes. Our study demonstrates that C-derived complexes are catalytically inactive, whereas the complexes [CH3Si(CH2PPh2)3NiX2] (X = Cl–, Br–) are competent catalysts for cross-coupling reactions of aryl halides with phenylacetylenes. This investigation reveals the importance of structural tuning on catalysis and strongly supports the theory that tetrahedral (PR3)2NiCl2 complexes are the active species in Sonogashira cross-coupling reactions. Two tripodal phosphines CH3E(CH2PPh2)3 (E = C, Si) are applied as ligands in Ni-catalyzed cross-coupling reactions; various coordination modes at the Ni center can be achieved. For the first time, experimental evidence is provided to prove that tetrahedral instead of planar (PR3)2NiCl2 moieties are required to perform effective Sonogashira coupling reactions.

Posted on 17 March 2015 | 12:30 pm

Oxide-Bridged Heterobimetallic Aluminum/Zirconium Catalysts for Ethylene Polymerization

A bimetallic aluminum/zirconium complex Cp*2Zr(Me)OAl(DIPH) [DIPH-H2 = 3,3?-bis(2-methylallyl)-(1,1?-biphenyl)-2,2?-diol; Cp* = C5Me5] was prepared in good yield by the reaction of (DIPH)AlMe with Cp*2Zr(Me)OH. In contrast to Roesky's catalyst, Cp2Zr(Me)O(Me)Al(DIPP-nacnac) {DIPP-nacnac = CH[(CMe)(2,6-iPr2C6H3N)]2}, it contains no Al–Me functionality and has increased Lewis acidity at Al. Crystal structures and the NMR spectra of the aluminum complex (DIPH)AlMe and the bimetallic Al/Zr species reveal in both cases dimeric complexes. The crystal structure of [Cp*2Zr(Me)OAl(DIPH)]2 shows a planar Al2O2 core and a terminal Cp*2Zr(Me)O group. Ethylene polymerization in toluene was studied for the bimetallic complex with a variety of scavengers. Under comparable polymerization conditions, the methylalumoxane-activated species show high activities that are similar to those obtained with Cp*2ZrCl2 and Roesky's bimetallic complex Cp2Zr(Me)OAl(Me)(DIPP-nacnac), with a relatively narrow polydispersity index (2.47). The targeted synthesis of a new bimetallic aluminum/zirconium species with remaining Lewis acidity on aluminum gives a dimeric Al–O–Zr complex. In the presence of methylalumoxane, this ?-oxo complex is able to activate ethylene to produce polyethylene with high activity.

Posted on 17 March 2015 | 12:30 pm

Germanium(II) and Tin(II) Halide Complexes Containing the Triimido Sulfur(VI) Phosphanyl Ligand

The monomeric compounds [GeCl{(NtBu)3SCH2PPh2}] (1) and [SnBr{(NtBu)3SCH2PPh2}] (2) have been synthesized from equimolar reactions of [(tmeda)Li{(NtBu)3SCH2PPh2}] and GeCl2·dioxane or SnBr2, respectively, to introduce the N,N?-chelating triimidosulfonate anion Ph2PCH2S(NtBu)3–. The complexes were fully characterized by single-crystal X-ray structural analysis, NMR spectroscopy, and mass spectrometry. The P-functionalized triimido sulfur ligand [(NtBu)3SCH2PPh2]– can be used without ligand scrambling to stabilize synthetically useful group 14 metal(II) halides. It chelates the metal through two S-bound imido nitrogen atoms only. The additional coordination site is provided by the phosphorus atom; although with germanium the P side-arm is pendant, it forms a long-range interaction with tin.

Posted on 17 March 2015 | 12:20 pm

Niobium–Containing Lindqvist Isopolyanions [NbxW6–xO19](2+x)– Used as Precursors for Hydrodesulfurization Catalysts with Isomerization Properties

Lindqvist isopolyanions [NbxW6–xO19](2+x)– (x = 0–4 and 6) were prepared and their spectroscopic and thermal properties were determined by Raman and IR spectroscopy as well as TGA/DSC. The structure of the [NbW5O19]3– anion obtained as single crystal was determined. Ni-promoted alumina-supported hydrodesulfurization (HDS) catalysts were prepared from the best soluble NbW polyoxometalates. In the calcined catalysts, better dispersion of the metallic species is observed when using NbW isopolyanions instead of the conventional ammonium metatungstate. The presence of niobium was expected to introduce acidity leading to isomerization property in classical NiW HDS catalysts. In HDS reaction conditions (under hydrogen pressure and sulfided environment) the cyclohexane isomerization into methylcyclopentane activity of niobium-based catalysts was found up to 5 times superior to that of conventional NiW catalyst, showing the beneficial effect of niobium for this reaction. [NbxW6–xO19](2+x)– Lindqvist type isopolyanions were synthesized and characterized to prepared NbWNi-based alumina-supported hydrodesulfurization catalysts. Nb-containing catalysts showed improved CC6 isomerization properties under HDS conditions (H2 pressure and H2S presence) compared to those of a reference NiW catalyst related to the acid properties induced by niobium.

Posted on 13 March 2015 | 11:10 am

On the Reactivity of RSnCl and RSiMe3 {R = 4-tBu-2,6-[P(O)(OiPr)2]2C6H2} towards BF3·OEt2: Competing Lewis Acidities

The reactions of boron trifluoride with the organostannylene RSnCl {R = 4-tBu-2,6-[P(O)(OiPr)2]2C6H2} and the organosilane RSiMe3 provided the corresponding 1:1 and 1:2 complexes, respectively, through the formation of P=OB interactions. In the former reaction, even with excess BF3·OEt2, no SnB complexation involving the lone electron pair at the tin(II) center was observed. The experimental results are supported by DFT calculations. The reactions of boron trifluoride with the organostannylene RSnCl {R = 4-tBu-2,6-[P(O)(OiPr)2]2C6H2} and the organosilane RSiMe3 provided the corresponding 1:1 and 1:2 complexes, respectively, through the formation of P=OB interactions. The experimental results are supported by DFT calculations.

Posted on 11 March 2015 | 10:20 am

Synthesis, Characterization, and Stereoselective Oxidations of the Dinuclear Copper(II) Complex Derived from a Chiral Diamino-m-xylenetetra(benzimidazole) Ligand

Recent advances in dinuclear copper complexes as mimics of the catalytic centers of tyrosinase and catechol oxidase allowed the reproduction of the structural and mechanistic aspects of the enzymes. However, a challenging objective is the development of chiral complexes for bioinspired enantioselective oxidation reactions. Here, we report the synthesis and characterization of a dinuclear copper(II) complex with a new chiral diamino-m-xylenetetra(benzimidazole) ligand (L55Bu4), which has chiral centers at the four 2-methylbutyl substituents of the benzimidazole rings. The spectral characteristics, ligand binding properties, and reactivity of [CuII2L55Bu4]4+ in the catalytic oxidations of several biogenic catechols (L-/D-dopa, L-/D-DopaOMe, and L-/D-norepinephrine) and thioanisole are reported. The best discriminating properties are displayed towards the DopaOMe derivatives, for which the oxidation rate of the L enantiomer is approximately one order of magnitude larger than that of the opposite D isomer. A dinuclear copper(II) complex derived from a chiral hexadentate nitrogen ligand is reported as a new catalyst for asymmetric oxidations. For biogenic catechols as model substrates, the best enantioselectivity is obtained in the oxidation of the methyl esters of L-/D-Dopa, for which 70?%?ee is obtained in favor of the L enantiomer.

Posted on 9 March 2015 | 12:10 pm

Mononuclear Iron(III) Complexes as Functional Models of Catechol Oxidases and Catalases

Mononuclear amino triphenolate iron(III) complexes have been synthesized and characterized (UV/Vis spectroscopy, cyclic voltammetry, ESI-MS, 1H NMR spectroscopy, X-ray diffraction). These complexes act as biomimetic catalysts promoting the aerobic auto-oxidation of 3,5-di-tert-butylcatechol to the corresponding o-benzoquinone at room temperature and displaying catalase activity for the hydrogen peroxide dismutation with remarkable activity (TON up to 4000). Amino triphenolate iron(III) complexes promote effectively, at room temperature, the aerobic auto-oxidation of 3,5-di-tert-buthylcatechol to the corresponding o-benzoquinone (oxidase mimicking) and hydrogen peroxide dismutation (catalase mimicking).

Posted on 16 February 2015 | 4:50 pm

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