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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:



Sn6[P12N24] – A Sodalite-Type Nitridophosphate

Sn6[P12N24] was synthesized from Sn and HPN2 at 820 °C in an evacuated silica glass ampoule. According to powder X-ray diffraction investigations and Rietveld refinement [space group I$\bar {4}$3m (no. 217), a = 8.2882(2) Å, RP = 0.03645, wRP = 0.04613], Sn6[P12N24] crystallizes with a sodalite-type structure with a reduced occupation factor of 3/4 for the Sn atom at Wyckoff site 8c and an empty Wyckoff site 2a at the center of the ?-cages. The structural results are further corroborated by energy-dispersive X-ray spectroscopy (EDX) analyses, solid-state NMR spectroscopy, and theoretical investigations (DFT), including density of states (DOS), energy/volume, and electron localization (ELF) calculations. The 119Sn Mössbauer spectrum shows a single, quadrupole-split signal for SnII at an isomer shift of 3.05 mm/s. In addition to SiPN3 with a defective wurtzite type of structure, the nitridophosphate sodalite Sn6[P12N24] represents the second ternary nitridophosphate containing only p-block elements. The new pseudobinary nitridophosphate Sn6[P12N24] is synthesized and investigated. The ?-cage of this compound, which crystallizes with the sodalite type of structure, is partially empty, as shown by several experimental and theoretical methods.

Posted on 22 December 2014 | 12:10 pm


Hybrid Material Constructed from Hg(NCS)2 and 2,4,6-Tris(2-pyrimidyl)-1,3,5-triazine (TPymT): Coordination of TPymT in a 2,2?-Bipyridine-Like Mode

A unique HgII coordination polymer has been synthesized through the reaction of 2,4,6-tris(2-pyrimidyl)-1,3,5-triazine (TPymT) with a stoichiometric mixture of HgCl2 and NH4NCS, thus leading to the formation of a 1D polymeric heteroleptic hybrid material [{Hg(NCS)2}2TPymT]n (1). Two coordination pockets of TPymT in 1 are each coordinated to two HgII cations in an unprecedented 2,2?-bipyridine-like mode. Reaction of 2,4,6-tris(2-pyrimidyl)-1,3,5-triazine (TPymT) with a mixture of HgCl2 and NH4NCS leads to the formation of a polymeric heteroleptic hybrid material [{[Hg(NCS)2]2TPymT}n], in which two coordination pockets of TPymT are each coordinated to two HgII cations in an unprecedented 2,2?-bipyridine-like mode.

Posted on 22 December 2014 | 12:10 pm


Computational Insights into the Isomerism of Hexacoordinate Metal–Sarcophagine Complexes: The Relationship between Structure and Stability

The hexacoordinate complexes that the macrobicyclic ligands {(NH3)2sar}2+ and {(NMe3)2sar}2+ (sar = 3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane) form with transition metals such as CoIII, CoII and CuII can adopt several isomeric structures. In this article, we have firstly employed DFT methods to compute the relative stability of their ?-ob3, ?-ob2lel, ?-lel2ob and ?-lel3 isomers, as well as the activation barriers for their interconversion. In agreement with the experimental data, the results show that, in general, the different isomers of the CoIII and CoII complexes present similar free energies, whereas the CuII complexes show a strong tendency towards the lel3 form. In addition, the interplay between the structure and stability of these species has been studied by combining shape maps with a distortion/interaction energy analysis. In contrast to the geometries close to the ideal octahedron that all the studied Co complexes present, the lel3 structures of [Cu{(NH3)2sar}]4+ and [Cu{(NMe3)2sar}]4+ are better described as trigonal prisms. In such structures the ligand adopts a conformation significantly more stable than in the other isomers, and this drives the formation of lel3-[Cu{(NH3)2sar}]4+ and lel3-[Cu{(NMe3)2sar}]4+. Overall, the results show a clear relationship between the stability of a given isomer and its degree of distortion with respect to the ideal octahedron (or trigonal prism), with the latter being ultimately dependent on the transition metal and its radius. The relative stability of the isomers of {M(NR3)2sar}2+ (M = CoIII, CoII, CuII; R = H, Me; sar = 3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane) was studied by means of DFT calculations. Further combination of distortion/interaction analysis and shape maps revealed its relationship with the degree of distortion with respect to the ideal octahedron, which is ultimately dictated by the metal.

Posted on 22 December 2014 | 12:10 pm


Biomimetic Hydroxylation Catalysis Through Self-Assembly of a Bis(pyrazolyl)methane Copper–Peroxo Complex

We synthesised and characterised four copper complexes (with copper in the oxidation states I and II) with the bis(pyrazolyl)methane ligands HC(3-tBuPz)2(Py) and HC(3-tBuPz)2(Qu). With the quinolinyl ligand (2-quinolinyl)bis(3-tert-butylpyrazolyl)methane [HC(3-tBuPz)2(Qu)] we obtained the tetrahedral monofacial complex [CuCl{HC(3-tBuPz)2(Qu)}] (C1) and with the pyridinyl ligand (2-pyridinyl)bis(3-tert-butylpyrazolyl)methane [HC(3-tBuPz)2(Py)] we obtained the three complexes [CuCl{HC(3-tBuPz)2(Py)}] (C2), [CuBr2{HC(3-tBuPz)2(Py)}] (C3) and [CuCl2{HC(3-tBuPz)2(Py)}] (C4), which are also monofacially coordinated. The molecular structures were analysed and compared with density functional theory calculations, which included natural bond orbital (NBO) analysis. C1 can, when generated in situ, serve as part of a precursor, used for the activation of oxygen as tyrosinase model. We observe the self-assembly of a peroxo–dicopper complex P with the HC(3-tBuPz)2(Qu) ligand, which is able to perform catalytic hydroxylation catalysis with phenols. DFT calculations were also carried out to understand the electronic transitions responsible for the UV/Vis bands in the corresponding spectra of the peroxo species. Herein, we present four new bis(pyrazolyl)methane–copper complexes. Furthermore, we studied the self-assembly of a peroxo–dicopper species with catalytic hydroxylation activity of phenols by UV/Vis spectroscopy. The donor competition between pyrazolyl and pyridinyl units as well as the UV transitions of the tyrosinase model have been investigated by density functional theory.

Posted on 22 December 2014 | 12:10 pm


A Technique to Fabricate La2O2CN2:Tb3+ Nanofibers and Nanoribbons with the Same Morphologies as the Precursors

Terbium(III)-doped lanthanum dioxymonocyanamide (La2O2CN2:Tb3+) nanofibers and nanoribbons were fabricated, by the cyanamidation technique, from precursor La2O3:Tb3+ nanofibers and nanoribbons prepared by electrospinning. The morphology of the final products were the same as those of the precursors. X-ray powder diffraction analysis indicated that the crystal phase of La2O2CN2:Tb3+ is tetragonal in space group I4/mmm. SEM analysis revealed that the thickness and width of the La2O2CN2:Tb3+ nanoribbons is about 184 nm and 3.53?±?0.37 ?m, respectively, and the diameter of the La2O2CN2:Tb3+ nanofibers is 175.87?±?16.23 nm at a 95?% confidence level. When excited with a 274 nm ultraviolet light source, the La2O2CN2:Tb3+ nanostructures emit predominantly at 543 nm; this emission originates from the 5D47F5 energy level transition of the Tb3+ ion. It was found that the optimum molar concentration of Tb3+ ions for doping La2O2CN2:Tb3+ nanostructures is 3?%. The La2O2CN2:Tb3+ nanofibers exhibit a higher photoluminescence (PL) intensity than that exhibited by nanoribbons for the same doping concentration. Commission International de l'Eclairage (CIE) analysis demonstrated that color-tuned luminescence can be obtained by changing the concentration of the doping activator ions and the nanostructure morphology. Possible formation mechanisms for the La2O2CN2:Tb3+ nanofibers and nanoribbons are also proposed. More importantly, the new technique employed in this paper and the preparation method are of universal significance for providing other rare earth oxycyanamide nanostructures with various morphologies. Tb3+-doped La2O2CN2 nanofibers and nanoribbons were fabricated by cyanamidation from precursor La2O3:Tb3+ nanofibers and nanoribbons made by electrospinning. The morphologies of the final products were the same as those of their respective precursors. The La2O2CN2:Tb3+ nanostructures are tetragonal in structure with space group I4/mmm and exhibit excellent luminescence performance.

Posted on 22 December 2014 | 12:10 pm


A Click-Functionalized Single-Molecule Magnet Based on Cobalt(II) and Its Analogous Manganese(II) and Zinc(II) Compounds

A mononuclear CoII single-molecule magnet suitable for click chemistry was investigated. [M(oda)(aterpy)] complexes (oda2– = oxodiacetate, aterpy = 4?-azido-2,2?:6?,2?-terpyridine) with M = MnII, ZnII, and CoII were synthesized as azide-functionalized building blocks for the copper-catalyzed azide–alkyne cycloaddition reaction. The required structural integrity of the complexes in solution was proven in great detail by using ESI-MS and NMR spectroscopy. For the six-coordinate [Co(oda)(aterpy)] complex, single-molecule magnet behavior was confirmed with an effective energy barrier of 4.2 cm–1. An azide-functionalized single-molecule magnet suitable for click reactions is reported. The solution stability of three novel building blocks containing single CoII, MnII, and ZnII metal ions is proven in great detail by using ESI-MS and NMR spectroscopy. Remarkably, alternating current susceptibility data of the six-coordinate cobalt(II) complex reveal single-molecule magnet behavior.

Posted on 22 December 2014 | 12:10 pm


S = 2 Spin Ladders in the Sulfide Oxide BaFe2S2O (Eur. J. Inorg. Chem. 36/2014)

The cover picture shows globular grains within the particles of BaFe2S2O and their pleochroitic behavior, as seen with polarized light. Superimposed on this background is a part of the BaFe2S2O crystal structure, where the corner- and edge-sharing FeS3O tetrahedra are drawn as polyhedra. The spin ladders are emphasized solemnly by extending the magnetic Fe lattice. The interladder couplings are marked with dashed lines. Details are discussed in the article by M. Valldor et al. on p. 6150 ff. For more on the story behind the cover research, see the Cover Profile.

Posted on 18 December 2014 | 8:59 pm


S = 2 Spin Ladders in the Sulfide Oxide BaFe2S2O

Invited for the cover of this issue is the group of Martin Valldor at MPI CPfS, Dresden, Germany. The cover image shows globular grains within the particles of BaFe2S2O and their pleochroitic behavior, as seen with polarized light. Superimposed on this background is a part of the crystal structure of the title compound. These low-symmetry sites for magnetically active or highly oxidized cations could result in magnetoelectric coupling or strong nonlinear optical activity, respectively, both of which are interesting for fundamental and applied science...Read more about the story behind the cover in the Cover Profile and about the research itself on p. 6150 ff.

Posted on 18 December 2014 | 8:59 pm


Graphical Abstract: Eur. J. Inorg. Chem. 36/2014

Posted on 18 December 2014 | 8:59 pm


Masthead: Eur. J. Inorg. Chem. 36/2014

Posted on 18 December 2014 | 8:59 pm


1,8-Disubstituted Xanthylidene-Based Remote Carbenes: Photolytic Generation and Isolation of Low-Coordinate Palladium(II) Complex

The isolation and study of carbenes with ?-donating and ?-accepting properties stronger than those of N-heterocyclic carbenes (NHCs) have been regarded as one of the big challenges in carbene chemistry. We have investigated the properties of 1,8-disubstituted xanthylidene-based compounds by using two different approaches: The photolysis-induced formation of free carbenes and the synthesis of the corresponding metal–carbene complexes by oxidative addition. The former study revealed that the carbene unsubstituted at the 1- and 8-positions is kinetically more reactive than the parent xanthylidene and that the substituents at the 1- and 8-positions are less effective in generating carbenes by photolysis. However, oxidative addition of palladium(0) to the 1,8-diphenyl-substituted precursor successfully afforded a low-coordinate 14-electron palladium(II)–carbene complex. This unusual complex is stabilized by agnostic interactions involving an adjacent phenyl group. This complex is the second example of a stable cationic 14-electron palladium(II)–carbene complex to have been reported so far. The photolysis-induced formation of 1,8-disubstituted xanthylidene-based remote carbenes from tosylhydrazone lithium salts has been investigated. The 1,8-unsubstituted carbene was found to be kinetically more reactive than the parent xanthylidene. Oxidative addition of palladium(0) to the chloride precursor facilitated the isolation of a low-coordinate 14-electron palladium(II)–carbene complex.

Posted on 18 December 2014 | 8:41 pm


Catalytic Synthesis of Bi- and Teraryls in Aqueous Medium with Palladium(II) Complexes of 2-(Pyridine-2-ylmethylsulfanyl)benzoic Acid

Suzuki–Miyaura coupling reactions of phenylboronic and 1,4-phenylenediboronic acid with ArBr to form bi- and teraryls have been efficiently catalyzed by the air- and moisture-insensitive complexes [PdCl2L1] [1, L1 = 2-(pyridine-2-ylmethyl)sulfanylbenzoic acid; 0.05–0.5 mol-%] and [Pd(L2-H)2] (2, L2-H = 2-pyridin-2-yl-benzo[b]thiophen-3-ol; 0.01–0.5 mol-%). The complexes were formed by the reaction of [Pd(CH3CN)2Cl2] with L1, and the catalysis proceeds in water for 1. The loading of 0.1–0.5 mol-% of Pd is very promising for the coupling reactions to form teraryls. The COOH group imparts solubility to 1 in water. Ligand L2 is formed by the unprecedented cyclization of L1 in the course of the complexation reaction. The yield of 2 increases with the reaction time (5 h: 70?%; 24 h: 85?%). The two complexes and L1 have been characterized by NMR spectroscopy (1H and 13C{1H}). The single-crystal structures of 1 and 2 have been solved, and the Pd–S, Pd–N, and Pd–O bond lengths are 2.269(2), 1.999(6)–2.057(2), and 1.9787(17) Å, respectively. Nanoparticles (NPs) with a narrow size distribution (ca. 3.0–5.5 nm for 80–85?% of the particles) formed at the start of these reactions and appear to be important for the catalytic coupling. Poisoning experiments and a two-phase test have shown that the catalysis is largely homogeneous and involves [Pd0–PdII] processes. The bond lengths and angles calculated by DFT are consistent with the experimental ones. Complexes [PdCl2L1] [1, L1 = 2-(pyridine-2-ylmethyl)sulfanylbenzoic acid] and [Pd(L2-H)2] (2, L2-H = 2-pyridin-2-yl-benzo[b]thiophen-3-ol) catalyze Suzuki coupling (1 in water) reactions to form bi- and teraryls. L2 forms by an unprecedented cyclization of L1. Pd nanoparticles (NPs) generated in situ play a role in the catalysis, which is a combination of homogeneous and heterogeneous processes.

Posted on 18 December 2014 | 8:41 pm


1,2-Dithiooxalato-Bridged Heterobimetallic Complexes as Single-Source Precursors for Ternary Metal Sulfide Semiconductors

The new 1,2-dithiooxalato-bridged bimetallic Cu–Ga, Cu–In, and Cu–Sn complexes [{(Ph3P)2Cu(?-S2C2O2)}3Ga] (1), [{(Ph3P)2Cu(?-S2C2O2)}3In] (2), [(Ph3P)2Cu(?-S2C2O2)In(S2CNEt2)2] (3), and [{(Ph3P)2Cu(?-S2C2O2)}2Sn(S2C2O2)] (4) were prepared and spectroscopically fully characterized. The crystal structures of 2–4 are presented. Complexes 3 and 4 are potential molecular single-source precursors (SSP) for the ternary semiconductors CuInS2 and Cu2SnS3, respectively, which can be manipulated under ambient conditions. Indeed, a study of the thermal degradation of 3 and 4 revealed that 3 affords pure nanoscaled CuInS2 (mean diameter ca. 2 nm) when the decomposition is carried out in an oleylamine solution by using a hot-injection or arrested-precipitation technique at temperatures well below 250 °C. In contrast, 4 decomposes under the same reaction conditions in an ambiguous manner and forms mixed binary chalcogenide phases. This can be explained by a subtle influence of the relative stability of possible SnII and SnIV intermediates in the case of SSP [{(Ph3P)2Cu(?-S2C2O2)}2Sn(S2C2O2)] (4). Bimetallic single-source precursor complexes for ternary metal sulfide semiconductors are presented. The 1,2-dithiooxalato ligand serves as a linker, complexation site, and molcular source of sulfur in the formation of CuInS2 nanoparticles.

Posted on 18 December 2014 | 8:40 pm


Structural Variation in [PdX2{RE(CH2)nNMe2}] (E = Se, Te; X = Cl, OAc) Complexes: Experimental Results, Computational Analysis, and Catalytic Activity in Suzuki Coupling Reactions

A series of chalcogenoether ligands RE(CH2)nNMe2 (1) [E = Se or Te; R = Ph, o-tol (o-tol = ortho-tolyl), Mes (Mes = 2,4,6-trimethylphenyl); n = 2 or 3] and their palladium complexes [PdX2{RE(CH2)nNMe2}]m [X = Cl (2) or OAc (3); m = 1, 2] were synthesized. Complexes [PdCl2(RECH2CH2NMe2)] [R/E = Ph/Se (2a), Mes/Se (2b), Mes/Te (2c)] were isolated as monomers. Complexes [PdCl2(RECH2CH2CH2NMe2)]m [R/E = Ph/Se (2d), Ph/Te (2e), o-tol/Te (2f)] exist in one monomeric and two dimeric forms in solution; their ratio depends on E and R as revealed by NMR spectroscopic data. Crystal structures of monomeric 2a, 2b, 3b, 2d, 2f, and dimeric 2e were established. Compounds 2a, 2d, 2e, and 2f were also investigated by means of density functional theory (DFT)-based quantum chemical calculations to understand structural variation. The complexes that contained acetate or chalcogenoether ligands with n = 3 showed higher catalytic activity than other derivatives in Suzuki C–C cross-coupling reactions. Complexes [PdX2{RE(CH2)nNMe2}]m (X = Cl, OAc) exist in one monomeric and two dimeric forms in solution depending on E and n. Molecular structures were established by X-ray structural analyses and supported by DFT calculations. These complexes act as catalyst in Suzuki coupling reactions.

Posted on 18 December 2014 | 8:40 pm


Synthesis, Stability and Sensitised Lanthanide Luminescence of Heterobimetallic d/f Terpyridine Complexes

The synthesis, solution behavior and photophysical properties of several heteronuclear bimetallic d/f complexes that utilise a RuII bis-terpyridine moiety as the sensitiser for EuIII, NdIII and YbIII luminescence are reported and compared to a GdIII analogue. The former compounds display sensitised emission in the visible and near-infrared (NIR) regions depending on the choice of the LnIII cation. We illustrate that sensitised lanthanide emission can operate by two distinctly different pathways that involve either the triplet ligand-centred (3LC) excited state of the organic ligand or the triplet metal-to-ligand charge transfer (3MLCT) excited state of the RuII complex. Owing to the electronic structure of this antenna and the higher density of metal-centred accepting states, a higher sensitization efficiency with NdIII was observed than with YbIII and EuIII. Lastly, we have observed unusual sensitised emission from the upper (4F5/2, 2H9/2) excited state of NdIII at approximately 800 nm, which we report here for the first time from a molecular species in solution. The synthesis and solution properties for a series of heterobimetallic RuII–LnIII complexes are reported. These compounds demonstrate the use of a RuII bis-terpyridine unit as the sensitiser for LnIII-based near-infrared emission for the first time. Energy transfer is shown to operate through both the triplet ligand-centred and triplet metal-to-ligand charge-transfer pathways.

Posted on 16 December 2014 | 5:40 pm


Structures and Properties of Luminescent Pentanitratoeuropate(III) Ionic Liquids

A series of luminescent ionic liquids based on pentanitratoeuropate(III) anions combined with imidazolium cations, namely, 1,2,3-trimethylimidazolium {[MC1mim]2[Eu(NO3)5] (1)}, 1,3-dimethylimidazolium {[C1mim]2[Eu(NO3)5] (2)}, 1-ethyl-3-methylimidazolium {[C2mim]2[Eu(NO3)5] (3)}, 1-butyl-3-methylimdazolium {[C4mim]2[Eu(NO3)5] (4)}, 1-hexyl-3-methylimidazolium {[C6mim]2[Eu(NO3)5] (5)}, and 1-methyl-3-octylimidazolium {[C8mim]2[Eu(NO3)5] (6)}, were synthesized. These complexes were characterized by NMR and IR spectroscopy as well as elemental analysis. They exhibit high thermostability and wide liquidus ranges of more than 300 °C. Colorless plate crystals of 1 were isolated, and the crystal structure was determined by single-crystal X-ray diffraction [monoclinic system, C2/c space group with the cell parameters a = 21.6870(6) Å, b = 9.9807(4) Å, c = 15.0267(6) Å, ? = 131.140(4)°, Z = 4]. In the [Eu(NO3)5]2– anion, the 10-coordinate EuIII ion is coordinated by five bidentate nitrate ligands and has a highly symmetrical trigonal-bipyramidal geometry. Compounds 1–6 exhibit bright red luminescence of high colorimetric purity. Only two characteristic narrow monochromatic bands, arising from the 5D07FJ (J = 1 and 2) intraconfigurational f–f transitions, were clearly observed in their emission spectra at 298 K. The intense red photoluminescence is still stable at 150 °C. These 10-coordinated EuIII complexes are of interest as potential thermally stable luminescent soft materials. A series of luminescent ionic liquids based on pentanitratoeuropate (III) anions are synthesized and characterized. These complexes exhibit high thermostability and a wide liquidus range. The 10-coordinate [Eu(NO3)5]2– anion has a highly symmetric trigonal-bipyramidal structure. Complexes 1–6 exhibit bright red luminescence with narrow-band and intense emission of high colorimetric purity.

Posted on 16 December 2014 | 5:40 pm


Iron(II) Spin-Crossover Complexes with Schiff Base Like Ligands and N-Alkylimidazoles

Three new iron(II) spin-crossover complexes with N2O2-coordinating Schiff base like equatorial ligands and alkylimidazole ligands in the axial positions were synthesised. The chain length of the alkylimidazole was varied from the previously published 1 to 5, 7 and 10 carbon atoms to investigate the influence of the alkyl chain length on the spin-transition behaviour in solution and in the solid state. The crystal structures of [1(HeptIm)2] and [1(DecIm)2] (1 = Fe complex with equatorial Schiff base like ligand; HeptIm = N-heptylimidazole, DecIm = N-decylimidazole) and the packing of the molecules in the crystals are discussed. Iron(II) spin-crossover complexes with Schiff base like equatorial ligands and alkylimidazole axial ligands are synthesised. The alkyl chain length is varied from 5 to 7 and 10 carbon atoms. The crystal structures of the C7 and C10 compounds are described. There is an increased cooperativity in spin-crossover behaviour for the compound with the longer C10 alkyl chain than for the C5 compound.

Posted on 16 December 2014 | 12:10 pm


Three Polyoxometalate-Based Coordination Polymers Constructed from the Same Dimetallic Cyclic Building Block

The reactions of silicotungstate, 2,5-bis(3-pyridyl)-1,3,4-oxadiazole (3-bpo), and copper, cobalt, or nickel acetate under hydrothermal condition yield the three compounds [(SiW12O40)Cu2(3-bpo)2(C5H4NCOOH)2]·H2O (1), [(SiW12O40)Co2(3-bpo)2(C5H4NCOOH)2(H2O)2]·2H2O (2), and [(SiW12O40)Ni2(3-bpo)2(C5H4NCOOH)2(H2O)2]·3H2O (3), respectively, in which the nicotinic acid ligands are generated from the in situ decomposition of 3-bpo during the hydrothermal process. In the three structures, the polyoxometalate (POM) serves as the center and is imbedded within the dimetallic cyclic [M2(3-bpo)2(C5H4NCOOH)2]4+ moiety through coordination bonds to form infinite one-dimensional (1D) supramolecular snadwich-like structures. Owing to the difference in the metal ions, the packing style of [Cu2(3-bpo)2(C5H4NCOOH)2]4+ is different from that of [M2(3-bpo)2(C5H4NCOOH)2]4+ (M = Co, Ni). The electrochemical behaviors of compounds 1–3 were studied by cyclic voltammetry. Three polyoxometalate-based (POM-based) coordination polymers containing a similar type of building block, [M2(3-bpo)2(C5H4NCOOH)2]4+ [M = Cu, Co, Ni; 3-bpo = 2,5-bis(3-pyridyl)-1,3,4-oxadiazole], are hydrothermally synthesized. These polymers are characterized, and their electrochemical behaviors are studied by cyclic voltammetry.

Posted on 15 December 2014 | 11:23 am


Synthesis and Reactions of PdII Complexes with Aryl, Aroyl, and Iminoaroyl Ligands – Insertion of CO and RNC into the Pd–Ar Bond and Intermolecular Coupling of the Ligands

The arylpalladium(II) complexes [PdIAr(bpy)] (Ar = Ph, C6H3-3,5-Me2, C6H4-4-OMe, C6H4-2-OMe, C6H4-4-C6H4-4-I, 1-naphthyl; bpy = 2,2?-bipyridine) undergo insertion of CO and CNR (R = tBu, C6H3-2,6-Me2) into the Pd–aryl bond to produce [PdI(COAr)(bpy)] and [PdI{C(=N–R)Ar}(bpy)]. The dinuclear complex [C6H3-3,5-{(OCH2CH2)2C6H4-3-PdI(bpy)}2] is synthesized by the oxidative addition reaction of 1,3-bis[(3-iodophenyl)-1,4,7-trioxaheptyl]benzene to [Pd(dba)2] (dba = dibenzylideneacetone). The addition of AgBF4 to the arylpalladium(II) complexes [PdIAr(bpy)] (Ar = C6H4-4-OMe, C6H4-2-OMe, 1-naphthyl) produces the intermolecular coupling products of the aryl ligands, Ar–Ar. The reactions of AgBF4 with the aroylpalladium(II) complexes [PdI(COAr)(bpy)] (Ar = C6H3-3,5-Me2, C6H4-2-OMe) result in decarbonylation and intermolecular coupling of the ligands to yield the diarylketones. The iminoaroylpalladium(II) complex [PdI{C(=NtBu)C6H3-3,5-Me2}(bpy)] undergoes hydrolysis of the ligand to yield tBuNHCO(C6H3-3,5-Me2). The addition of AgBF4 to the dinuclear complex [C6H3-3,5-{(OCH2CH2)2C6H4-3-PdI(bpy)}2] yields a mixture of the cyclic oligomers cyclo-[C6H3-3,5-{(OCH2CH2)2C6H4-3-}2]n (n = 1–4) by inter- and intramolecular coupling of the aryl ligands. Aryl-, aroyl-, and iminoaroyl iodidopalladium(II) complexes with a 2,2?-bipyridine ligand react with AgBF4 and H2O to afford biaryls, diarylketones, and arylamides by labilization of the iodido ligand.

Posted on 15 December 2014 | 11:23 am


Synthesis of Monodisperse SrTi1–xZrxO3 Nanocubes in Oleate by a Two-Phase Solvothermal Method

Nanocubes of mixed-crystal perovskites SrTi1–xZrxO3 (x = 0.25–0.6) were obtained in a two-phase oil/water solvothermal environment. In an optically transparent autoclave, the evolution of an alkali metal oleate phase at the oil/water interface was monitored; this phase is the environment for nucleation and growth of the nanocrystals. The typical synthesis yields monodisperse nanocubes with an edge length of 10 nm. The size and shape of the nanoparticles do not depend on the Zr content and, most remarkably, do not vary with reaction time. We propose a growth mechanism that depends on the accessibility of the metal hydroxyalkanoate monomers to the growing crystal: after the formation of {100} facets, they are densely capped by oleate ion surfactants, and monomers are no longer able to attach. Increasing the reaction time only increases the amount of nanoparticles formed. As determined by Raman spectroscopy and energy-dispersive X-ray spectroscopy, the nanoparticles have the cubic (Pm$\bar {3}$m) perovskite structure and have an excess of B-site ions (Ti + Zr), which is explained by a terminating Ti/Zr + O surface layer of the nanocubes. The monodisperse particles self-assemble to form monolayers on a support. Alkali metal oleate formed in situ in an oil/water solvothermal process is a suitable reaction medium for the synthesis of monodisperse SrTi1–xZrxO3 perovskite nanoparticles, which are characterized in detail by TEM methods as well as XRD and Raman spectroscopy to provide information on their crystal structure and surface termination.

Posted on 12 December 2014 | 11:40 am


Hexagonal-Prism-Shaped Optical Sensor/Captor for the Optical Recognition and Sequestration of PdII Ions from Urban Mines

In this work, we have developed a hexagonal-prism-shaped optical sensor/captor (OSC) based on the immobilization of an organic probe into hexagonal, micrometric monoliths of mesoporous aluminosilica scaffolds for the colorimetric monitoring, selective sequestering, and effective recovery of PdII ions from urban mines as a promising technology for industrial applications. In such a solid OSC, H-type aggregation and face-to-face (?–?* stacking) interactions between the heteroatoms-coordinated organic probe and the active acid sites of the scaffolds lead to the formation of 1D molecular probe assemblies parallel to the interior pore walls. The design patterns of hexagonal-prism-shaped and open cylindrical pores (ca. 4 nm) exhibited suitable accommodation to protect the organic probe from extra H-aggregates, as evidenced by the high affinity of the PdII–probe binding events. The OSC shows evidence of controlled PdII ion assessment in terms of the optical recognition of PdII ions down to sub-nanomolar concentrations (3.3?×?10–9 mol/L). Our study shows that the developed OSC can be used as an effective tool for urban mining development, particularly for secondary resources in industrial countries. We report the pressure-assisted fabrication of a hexagonal-prism-shaped optical sensor/captor (OSC) based on monolithic aluminosilica scaffolds. The H-aggregates of the probe might lead to the formation of 1D molecular probe assemblies parallel to the interior pore walls. This OSC is a promising technology for the efficient recognition, removal, and recovery of PdII ions from urban mines.

Posted on 12 December 2014 | 11:40 am


Photo- and Electrocatalytic Reduction of CO2 by [Re(CO)3{?,??-Diimine-(4-piperidinyl-1,8-naphthalimide)}Cl] Complexes

The effects of the highly fluorescent 4-piperidinyl-1,8-naphthalimide (PNI) chromophore on the CO2 reduction catalytic properties of rhenium-based catalysts are investigated herein. In particular, the electro- and photocatalytic CO2 reduction features of [Re(CO)3(bpy)Cl] (bpy = 2,2?-bipyridine) are compared with the activity of [Re(CO)3(phen–PNI)Cl] (phen = 1,10-phenanthroline), which is known for its long excited-state lifetime. Moreover, another Re complex, namely [Re(CO)3(bpy–Ph–PNI)Cl], has been synthesized and tested as an electro- and photocatalyst. The catalytic properties of the selected compounds were studied by means of electrochemical (cyclic voltammetry and controlled-potential electrolysis) and photophysical measurements together with DFT calculations. [Re(CO)3(bpy–Ph–PNI)Cl] showed good electrocatalytic efficiency toward selective CO2 reduction to CO, as well as reduced electrocatalytic overpotential. The efficiency and stability of a series of [Re(?,??-diimine)(CO)3Cl] complexes suitable for catalytic photo- and electrochemical selective reduction of CO2 to CO has been investigated. The introduction in the diimine part of the fluorescent moiety 4-piperidinyl-1,8-naphthalimide provides new insights into designing catalysts with improved performance.

Posted on 12 December 2014 | 11:40 am


Pentafluorosulfanyltrimethylsilane: A Nonexistent Molecule?

From a medicinal chemistry standpoint, the pentafluorosulfanyl (SF5) group is justifiably viewed as a “super-trifluoromethyl” group. Unfortunately, synthetic routes to this remarkable, strongly electron-withdrawing, highly lipophilic substituent are limited. In this study, DFT calculations with large basis sets indicate that reagents of the form MSF5, where M = Me3Si, Li, Cu, MeZn, MeCd, and MeHg, are both thermodynamically and kinetically unstable. Attempts to synthesize reagents such as pentafluorosulfanyltrimethylsilane (TMSSF5) and pentafluorosulfanylcopper (CuSF5) are therefore likely to fail. According to DFT calculations, reagents such as Me3SiSF5, LiSF5 and CuSF5 are all thermodynamically and kinetically unstable. Attempts to synthesize them are therefore doomed to failure.

Posted on 11 December 2014 | 1:10 pm


Methylalumoxane – History, Production, Properties, and Applications

Since its discovery, methylalumoxane (MAO) has become of great importance as a cocatalyst in homogeneous olefin polymerization. The working principles of single-site polymerization catalysts are well-understood, but those of the cocatalyst MAO itself are not. Thus far structural and functional investigations have yielded limited insights and often give contradicting results. MAO's complex nature is due to multiple equilibria between undefined oligomers and “free” trimethylaluminum. Fundamental studies do not clearly portray the molecular structure, and the exact functioning of MAO remains a topic of debate. This comprehensive overview starts with the historical background of MAO and then focuses on its synthesis and large-scale production, structural characterization, properties, and different roles in the activation of olefin polymerization catalysts. Also given is an overview of potential modifications, immobilization on surfaces, and other alternative applications that have been reported for MAO. This is a comprehensive overview on methylalumoxane (MAO). After presenting its historical discovery and development, the review focuses on the synthesis and large-scale production of MAO, its structural characterization, properties, and different roles in the activation of olefin polymerization catalysts. Potential modifications, immobilization on surfaces, and other applications are also mentioned.

Posted on 11 December 2014 | 12:20 pm


Reactivity of Aromatic Phosphorus Heterocycles – Differences Between Nonfunctionalized and Pyridyl-Substituted 2,4,6-Triarylphosphinines

Detailed studies on the reactivity of 2-(2?-pyridyl)-4,6-diphenylphosphinine (2) towards CF3SO3H and sulfur have been performed, and the results were compared with those for nonfunctionalized 2,4,6-triphenylphosphinine derivatives. Substantial differences between these heterocycles were observed, and the reaction products could be characterized crystallographically. The reactions of 2,4,6-triarylphosphinine sulfides with methanol led to different products, which could be characterized by NMR spectroscopy and X-ray crystal structure analysis. Interestingly, the outcomes of these transformations strongly depend on the presence of an additional donor functionality within the phosphorus heterocycle as well as the nature of the solvent and the reaction temperature. DFT calculations were performed to rationalize the different reaction pathways. Substantial differences in reactivity towards methanol have been observed for 2,4,6-triarylphosphinine derivatives. The outcomes of the transformations strongly depend on the presence of additional donor functionalities within the phosphorus heterocycle as well as the nature of the solvent and the reaction temperature. DFT calculations were performed to rationalize the observed reaction pathways.

Posted on 11 December 2014 | 12:20 pm


Structural Diversity in Sterically Demanding Diiminophosphinato Alkali Metal Complexes

We have prepared the new aminophosphine Ph2PNHMes 2 [Mes = mesityl (2,4,6-Me3C6H2)], and the aminoiminophosphorane Ph2P(=NMes)NHMes 4 (MesLH), and obtained the new alkali metal complexes [(DipLLi)2] 5 [DipL = Ph2P(NDip)2, Dip = 2,6-iPr2C6H3], [(MesLLi)2] 6, [(DipL)(DipN2L)Li2] 7 [DipN2L = Ph2P(NDip)(N3Dip)], [(DipN2L)2Li2] 8, [DipLLi(THF)] 9, [DipLLi(THF)2] 10, [(DipLNa)2] 11, [(MesLNa)n] 12, [DipLNa(THF)2] 13, [{MesLNa(THF)}2] 14 and [MesLK] 16 by deprotonation of their respective ligand precursors with standard strong alkali metal bases in various solvents. The crystal structures of 2, 4–6, 7·8, 9–14, and 16 are reported. The different coordination modes in their solid-state structures are discussed and generally compared to the solution behavior of those species. We report on the synthesis of a new aminoiminophosphorane and a range of homoleptic alkali metal complexes of sterically demanding diiminophosphinate ligands, plus a series of related THF-solvated alkali metal complexes that show a rich structural diversity between them and underpin the flexible coordination properties of that ligand class.

Posted on 11 December 2014 | 12:20 pm


Influence of Ligand Substitution Pattern on Structure in Cobalt(II) Complexes of Bulky N,N?-Diarylformamidinate N-Oxides

Cobalt(II) complexes of bulky N,N?-diarylformamidinate N-oxide ligands were synthesized and structurally characterized. The cobalt(II) bis(chelates) are square-planar (low spin) in the solid state, according to XRD and magnetic measurements (?eff = 1.8 to 2.1 ?B), but show square-planar (low spin) to tetrahedral (high spin: ?eff = 3.5 to 4.7 ?B) isomerization in solutions of noncoordinating solvents, as demonstrated by different spectroscopic techniques. The isomerization equilibrium is highly sensitive to the substitution pattern on the ligand due to a combination of steric and electronic influences. Cobalt(II) bis(chelates) of bulky N,N?-diarylformamidinate N-oxide ligands show isomerization from square-planar low-spin (in the solid state) to tetrahedral high-spin (in solutions of noncoordinating solvents).

Posted on 10 December 2014 | 10:10 am


Synthesis, Structure, and Luminescence of Rare Earth Cyanurates

Rare earth cyanurates were prepared by exothermic solid-state metathesis reactions of appropriate proportions of A(OCN) (A = K, Rb, Cs) and RECl3 (RE = La, Ce, Pr) at 500 °C. A DTA study of this mixture revealed the reaction to occur around 450 °C. The crystal structure of RbLa2Cl(O3C3N3)2 was refined from a powder X-ray diffraction pattern. Homologous ARE2Cl(O3C3N3)2 compounds with A = K, Rb, Cs and RE = La, Ce, Pr were indexed isotypically. Photoluminescence and reflection properties of doped samples and an infrared study are reported. Rare earth metal cyanurates were prepared by solid-state metathesis reactions and characterized as ARE2Cl(O3C3N3)2 (A = K, Rb, Cs and RE = La, Ce, Pr). Photoluminescence properties of Eu3+ and Tb3+ doped RbRE2Cl(O3C3N3)2 samples were studied by means of luminescence and reflection spectroscopy.

Posted on 10 December 2014 | 10:10 am


Slow Magnetic Relaxation in Mononuclear Octahedral Manganese(III) Complexes with Dibenzoylmethanide Ligands

The structural characterization and magnetic studies of three mononuclear MnIII complexes based on the dibenzoylmethanido (dbm–) ligand, Mn(dbm)3 (1) and [Mn(dbm)2(L)2](ClO4) (L = dimethyl sulfoxide, 2; L = pyridine, 3), are reported. The MnIII ions are in an axially elongated octahedral coordination geometry. The axial zero-field-splitting parameters D, ranging from –3.42 to –4.52 cm–1 for the three complexes, were obtained by fitting magnetic-susceptibility and magnetization data. Ab initio calculations also show the axial magnetic anisotropy in the molecules of 1–3. With an applied dc field, the ac susceptibility measurements reveal slow magnetic relaxation in 1–3. The possible relationship between the structures and the magnetic properties in these complexes are discussed. Three mononuclear MnIII complexes based on the dibenzoylmethanido ligand and having negative zero-field-splitting parameters D exhibit field-induced slow relaxation behavior.

Posted on 9 December 2014 | 1:10 pm


Uranyl–Organic Hybrids Designed from Hydroxyphosphonate

A series of phosphonate-based uranyl–organic hybrids has been assembled based on the reaction of uranyl cations with 2,5-dihydroxy-1,4-benzenediphosphonic acid in the presence of a variety of alkali metal and organoammonium cations: K[(UO2)2F2{H0.5O3PC6H2(OH)2PO3H0.5}](H2O)2 (1), Cs[(UO2)2{H0.75O3PC6H2(OH)2PO3H0.75}](H2O)4·2H2O (2), [(CH3)4N]2[UO2{HO3PC6H2(OH)2PO3H}2] (3), [(CH3CH2)4N][UO2F{HO3PC6H2(OH)2PO3H}] (4), and [(CH3CH2)2N(CH3)2][UO2F{HO3PC6H2(OH)2PO3H}] (5). In compounds 1, 4, and 5, chains of UO5F2 pentagonal bipyramids are linked by the hydroxyphosphonate moiety into three-dimensional frameworks, and compound 4 is isostructural with 5. However, the structures of 2 and 3 are composed of monomeric UO7 pentagonal bipyramids assembled to form layered structural units. Additional steric influences from the –OH groups appended on the diphosphonate species play a vital role in directing the structure topologies. Five new phosphonate-based uranyl–organic hybrids were crystallized in the presence of a variety of alkali and organoammonium cations using hydroxyphosphonate ligands. They represent the first examples of such hybrids constructed in this way. The steric effects from the phenyl ring and the –OH groups of the hydroxyphosphonate moiety play major roles in directing the structure topologies.

Posted on 9 December 2014 | 1:10 pm


Perfluorinated Cobalt Phthalocyanine Effectively Catalyzes Water Electrooxidation

Efficient electrocatalysis of water oxidation under mild conditions at neutral pH was achieved by a fluorinated cobalt phthalocyanine immobilized on fluorine-doped tin oxide (FTO) surfaces with an onset potential at 1.7 V vs. RHE. Spectroscopic, electrochemical, and inhibition studies indicate that phthalocyanine molecular species are the operational active sites. Neither free cobalt ions nor heterogeneous cobalt oxide particles or films were observed. During long-term controlled-potential electrolysis at 2 V vs. RHE (phosphate buffer, pH 7), electrocatalytic water oxidation was sustained for at least 8 h (TON ? 1.0?×?105), producing about 4 ?mol O2 h–1 cm–2 with a turnover frequency (TOF) of about 3.6 s–1 and no measurable catalyst degradation. Water oxidation is efficiently electrocatalyzed by a fluorinated cobalt phthalocyanine (CoFPc) immobilized on fluorine-doped tin oxide surfaces. CoFPc molecular species are revealed as the operational active sites. At 2 V (vs. RHE, pH 7), electrocatalytic water oxidation is sustained for at least 8 h (TON ? 1.0?×?105), producing about 4 ?mol O2 h–1 cm–2 with no measurable catalyst degradation.

Posted on 8 December 2014 | 11:40 am


Using Click Chemistry to Tune the Properties and the Fluorescence Response Mechanism of Structurally Similar Probes for Metal Ions

Four cyclam-based fluorescent molecular probes were prepared using “click” chemistry and investigated to determine the effect of the triazole connectivity and fluorophore substitution on the photophysical properties and metal-ion response mechanism. The fluorescence of the ligands is turned on in the presence of ZnII but varies in intensity depending on the solvent; the highest signal changes are found in MeCN. Complexation with CuII leads to fluorescence quenching, but only in the aqueous solvent, in which the triazole is involved in coordination of the metal. The length of the pendant triazole arm influences the ligand field around pentacoordinate CuII to yield a distorted square-planar coordination geometry in the ligands with an ethylene linker. The quantum yield (QY) of the emission intensity can be tuned by the triazole substitution, thereby resulting in increases in QY of more than one order of magnitude (ligand 1 versus 3). Changing the fluorophore opens up alternative radiative processes, thus leading to phosphorescence-like behavior in coumarin probe 2. Steady-state fluorescence emission spectra of the free ligands and their respective CuII complexes in a “glass environment” reveal two different inherent fluorescence quenching mechanisms. In the free ligands an electron-transfer deactivates the excited chromophore, whereas in the CuII complexes it is energy transfer that results in complete quenching of the emission of the ligands. In these scorpionand molecular probes, the triazole connectivity, the carbon linker, and the fluorescent tail all combine to modulate photophysical behavior and metal responsiveness.

Posted on 5 December 2014 | 12:40 pm


Alkaline-Earth (Mg–Ba) Coordination Networks Built Around the Tris(dipicolinato)cerate(3–) Ion: Highly Hydrated Networks That Survive Dehydration

Alkaline-earth (AE)/cerium(III)-based heterometallic coordination compounds of the biologically important ligand dipicolinic acid (dipicH2), namely [Mg(H2O)6]2[Ce(dipic)3][Ce(dipic)2(H2O)3]·2H2O (1), [Ca3(H2O)12Ce2(dipic)6]·6H2O (2), [Sr3(H2O)16Ce2(dipic)6]·4H2O (3) and [Ba2(H2O)7Ce(dipic)3NO3]·H2O (4), have been obtained by the reduction of an aqueous solution of (NH4)2Ce(NO3)6·6H2O in the presence of dipicH2 and alkaline-earth oxides or carbonates. This series demonstrates the role of AE ions in controlling the topology of coordination networks based on the [Ce(dipic)3]3– anion. Compound 1 is a zero-dimensional ionic compound, the crystal structure of compound 2 is based on a mixed four-connected 3D network, compound 3 presents ladder-shaped chains running along a crystallographic axis, and layers of squeezed CeBa6 pentagonal pyramids interconnected by nitrates generate a mixed five- and six-connected network in 4. A thermal analysis showed that all four compounds exhibit reversible water-uptake capacity and the basic nature of the frameworks could be intact up to at least 120 °C. The CeIII–dipic–AE–H2O system generates microporous coordination networks of various dimensionalities in the Mg–Ba series.

Posted on 5 December 2014 | 12:30 pm


Formation and Stability of Gaseous Ternary Oxides of Group 14–16 Elements and Related Oxides of Group 15 Elements: Mass Spectrometric and Quantum Chemical Study

The formation of four hitherto unknown lead tellurium oxides – PbTeO3, PbTe2O5, Pb2TeO4 and Pb2Te2O6 – was observed in the gas phase by means of a mass-spectrometric Knudsen-cell method. Other ternary oxides of group 14–16 elements were not observed in the gas phase. The enthalpies of formation for these oxides were obtained experimentally by means of a mass-spectrometric Knudsen-cell method and confirmed theoretically by using quantum chemical (QC) calculations. Appearance potential measurements were conducted for PbTeO3 and Pb2TeO4. The structures of the ternary oxides that represent the minima on the potential-energy surfaces were found by using QC calculations. The behaviour of the related compounds PbTeO3, X2O3, Pb2Te2O6 and X4O6 in the gas phase has been discussed (for which X = P, As, Sb, Bi). The formation of four hitherto unknown lead tellurium oxides – PbTeO3, PbTe2O5, Pb2TeO4 and Pb2Te2O6 – was observed in the gas phase by means of a mass-spectrometric Knudsen-cell method. The enthalpies of formation for these oxides were obtained experimentally by means of a mass-spectrometric method and confirmed theoretically using quantum chemical calculations.

Posted on 4 December 2014 | 12:13 pm


Coordination of Alkaline-Earth Metal Ions in Inverted Cucurbit[6]uril Supramolecular Assemblies Formed in the Presence of Tetrachloride Zincates

Coordination in supramolecular assemblies in aqueous HCl solutions was investigated by reacting alkaline-earth cations (AE2+) and inverted cucurbit[6]uril (iQ[6]) in the presence of the structure-directing agent, tetrachloride zincate ion. Single-crystal X-ray diffraction analysis revealed that the iQ[6]–Mg2+–[ZnCl4]2––HCl interaction system yielded a supramolecular assembly of iQ[6] and [ZnCl4]2– without forming coordination complexes of Mg2+ or Zn2+ with iQ[6]. In contrast, interaction of Ca2+ or Sr2+ with iQ[6] in the presence of [ZnCl4]2– gave rise to linear coordination polymers, which formed a honeycomb-like framework in which the linear polymers occupy cells of the framework. The iQ[6]–Ba2+–[ZnCl4]2––HCl interaction system immediately produced precipitates, thus preventing isolation of single crystals under similar synthetic conditions. Coordination in supramolecular assemblies in aqueous HCl solutions was investigated by reacting alkaline-earth cations and inverted cucurbit[6]uril in the presence of the structure-directing agent, tetrachloride zincate ion.

Posted on 3 December 2014 | 9:10 am


A Simple Fluorescent Probe Derived from Naphthylamine for Selective Detection of HgII, FeII and FeIII Ions in Mixed Aqueous Media: Applications in Living Cells and Logic Gates

A naphthylamine-based probe was utilized for the detection of HgII, FeII and FeIII in mixed aqueous media by fluorescence quenching. These sensitive metal ions bind with the probe by forming a 1:1 complex. The time-resolved fluorescence and quantum yield of the probe in the absence as well as in the presence of metal ions were investigated. The extent of binding of the probe with sensitive metal ions was calculated. The sensitivity of the probe in the presence of other metal ions was examined using competitive binding studies. The probe displayed sensitivity towards HgII during in vitro as well as in vivo studies. This multianalyte probe has potential biological applications in cell imaging and in logic gates. A naphthylamine-based fluorescence probe was used for sensing of HgII, FeII, and FeIII by a chelation-enhanced quenching mechanism and could be utilized for in vivo application and in logic gates.

Posted on 3 December 2014 | 9:10 am


Photochemical Carbon–Carbon Bond Cleavage of CF3-Substituted (dppbe)Pt0(?2-tolane) Complexes

Three different complexes of the (dppbe)Pt(?2-tolane) [dppbe = 1,2-bis(diphenylphosphino)benzene] type bearing CF3 groups at the 2,2?- (4a), 3,3?- (4b), and 4,4?-positions (4c) of the tolane ligand were synthesized. A one-pot procedure for the synthesis of the tolane ligands from 2-methyl-3-butyn-2-ol as the acetylene derivative was developed. To investigate their selective photochemical carbon–carbon bond cleavage, 4a–4c were exposed to UV light (1 W, 356 nm) in the solid state and in solution. The oxidative addition of the C(sp)–C(sp2) bond to the (dppbe)Pt0 complex fragment to form the corresponding CF3-substituted (dppbe)Pt(ethynylphenyl)(phenyl) complex was followed by 31P{1H} NMR spectroscopy. The reactivity of 4a–4c relative to the position of the CF3 substituent and the torsion angle between the substituted phenyl rings is discussed. All of the complexes were isolated and characterized by various spectroscopic methods and additionally by single-crystal X-ray diffractometry. (dppbe)Pt(?2-tolane) [dppbe = 1,2-bis(diphenylphosphino)benzene] complexes with CF3 groups at various positions (ortho, meta, and para) of the tolane ligand are synthesized. This type of complex undergoes photochemical carbon–carbon bond cleavage of the C(sp)–C(sp2) atoms in solution and in the solid state. Additionally, this remarkable reaction is reversible under thermal conditions in solution.

Posted on 3 December 2014 | 9:10 am


Unexpectedly Complex Crystalline Phases in the MSO3F–Ag(SO3F)2 Phase Diagram (M = Na, K, Rb, Cs)

The syntheses and characterizations of mixed-cation fluorosulfates containing AgII ions are reported and add to the moderately well-known chemistry of AgII compounds. The compounds synthesized mostly show different structures and compositions. The mixed sodium–silver fluorosulfate is isostructural with Ag3(SO3F)4 (monoclinic P21/c, a = 5.2812 Å, b = 13.0473 Å, c = 19.3557 Å, and ? = 100.970°) and has the composition (Ag0.05Na0.95)(Ag0.65Na0.35)AgII(SO3F)4. The mixed potassium–silver fluorosulfate does not correspond to KI2AgII(SO3F)4 but rather to KAgI2AgII(SO3F)5 [orthorhombic P2221, a = 6.4736(3) Å, b = 7.3915(4) Å, and c = 17.7736(10) Å]. Two rubidium–silver fluorosulfates form as a mixture, one corresponds to RbAgI2AgII(SO3F)5 [orthorhombic P2221, a = 6.4828(6) Å, b = 7.3551(7) Å, c = 18.0262(17) Å], and the other corresponds to RbAgII(SO3F)3 [monoclinic P21/m, a = 15.8152(14) Å, b = 15.4861(13) Å, c = 17.0211(14) Å, and ? = 101.513(5)°]. The cesium fluorosulfate/silver(II) fluorosulfate phase diagram is exemplified by the CsAgII(SO3F)3 salt [triclinic P$\bar {1}$, a = 14.9241(5) Å, b = 9.7046(3) Å, c = 17.8465(7) Å, ? = 109.116(2)°, ? = 84.655(3)°, and ? = 119.171(3)°]. The IR and Raman spectra of the compounds were measured, and their thermal stability and magnetic properties have been determined. The MAgI2AgII(SO3F)5 systems show antiferromagnetic behavior with absolute superexchange constants of up to 19.1 meV for M = K, and ferromagnetism can be observed below 20–40 K for the MAg(SO3F)3 derivatives (M = Rb, Cs). The ability of the fluorosulfate anion to form complex paramagnetic salts with alkali metal and AgII cations has been scrutinized. The SO3F– anion efficiently transfers magnetic superexchange between AgII centers in complex MAgI2AgII(SO3F)5 antiferromagnets, and the superexchange constant reaches –19.1 meV for the K salt.

Posted on 2 December 2014 | 2:20 pm


Solvent-Free Hydrosilylation of Terminal Alkynes by Reaction with a Nonclassical Ruthenium Hydride Pincer Complex

Upon the simple addition of substrates, the ruthenium pincer complex [Ru(tBuPNP)(H2)(H)2] [1; tBuPNP = 2,6-bis(di-tert-butylphosphinomethyl)pyridine] is an active and selective catalyst system for the hydrosilylation of terminal alkyl alkynes under mild, solvent-free conditions. The reactivity of this system for other functionalized terminal alkynes was also investigated, and we observed competing catalytic cycles that produce both alkyne dimers and dehydrogenative silylation products. Kinetic measurements for the hydrosilylation of 1-octyne show that the catalyst has an initial turnover frequency of 121 h–1 at room temperature. The stoichiometric reaction between 1 and H2SiPh2 yields [Ru(tBuPNP)(H)2(H2SiPh2)], which undergoes Si–H bond activation to yield the catalytically active species [Ru(tBuPNP)(HSiPh2)(H)]. The reaction of 1 with phenylacetylene yielded [Ru(tBuPNP)(H)2(HC?CPh)] and [Ru(tBuPNP)(H)(C?CPh)(HC?CPh)], and we propose that the latter is the active species in the dimerization reaction. A selective catalyst system for the hydrosilylation of alkyl alkynes under mild, solvent-free conditions has been developed with the ruthenium pincer complex [Ru(tBuPNP)(H2)(H)2] [tBuPNP = 2,6-bis(di-tert-butylphosphinomethyl)pyridine].

Posted on 2 December 2014 | 2:20 pm


Homometallic FeIII4 and Heterometallic {FeIII4LnIII2} (Ln = Dy, Tb) Complexes – Syntheses, Structures, and Magnetic Properties

The sequential reaction of the multisite coordination ligand 2-methoxy-6-{[2-(2-hydroxyethylamino)ethylimino]methyl}phenol (LH2) with Fe(ClO4)2·4H2O or a combination of Fe(ClO4)2·4H2O and Ln(NO3)3·5H2O [DyIII and TbIII] in the presence of tetramethylammonium hydroxide and pivalic acid (pivH) under ambient conditions afforded a homometallic tetranuclear FeIII complex and heterometallic hexanuclear FeIII/LnIII complexes, namely, [Fe4(?3-O)2(L)4]·3CH3CN·2CH3OH (1), [Fe4Dy2(?3-O)2(L)2(O2CCMe3)10(MeOH)]·2CH3CN (2), and [Fe4Tb2(?3-O)2(L)2(O2CCMe3)10(HO2CCMe3)]·H2O (3). Compounds 1–3 crystallize in the monoclinic system in space group P21/n (Z = 4). The homometallic tetranuclear derivative 1 possesses three contiguous four-membered Fe2O2 rings in a ladderlike configuration. Each of the iron centers is hexacoordinate (2N, 4O) in a distorted octahedral geometry. On the other hand, 2 and 3 contain two symmetrically related Fe2Ln units that are joined to each other through oxygen atoms from the ethoxide side arms of the ligand L2–; the two lanthanide ions are located at the opposite ends of the hexanuclear core. In 2 and 3, the lanthanide centers are eight- (distorted trigonal dodecahedron) and nine-coordinate (distorted monocapped square antiprism), respectively, and the iron centers are hexacoordinate (distorted octahedral). Magnetic studies on 2 and 3 reveal the presence of weak antiferromagnetic coupling between the FeIII and LnIII ions. The reactions of the multisite ligand 2-methoxy-6-{[2-(2-hydroxyethylamino) ethylimino]methyl}phenol with Fe(ClO4)2·4H2O or a combination of Fe(ClO4)2·4H2O and Ln(NO3)3·5H2O [DyIII and TbIII] in the presence of Me4NOH and pivalic acid afford a tetranuclear Fe4 complex and hexanuclear FeIII4LnIII2 complexes. Magnetic studies reveal weak antiferromagnetic coupling between the FeIII and LnIII ions.

Posted on 2 December 2014 | 2:10 pm


Chromium Tricarbonyl and Chromium Benzene Complexes of Graphene, Their Properties, Stabilities, and Inter-Ring Haptotropic Rearrangements – A DFT Investigation

The structures, electronic properties, stabilities, mechanisms, and activation barriers of the intramolecular inter-ring haptotropic rearrangements (?6,?6-IRHRs) of chromium tricarbonyl and chromium benzene complexes of graphene were modeled by DFT calculations. All of the above calculated characteristics are in good agreement with the experimental data for related complexes with ultralarge, large, and medium-sized polyaromatic ligands (PALs). Generally ?6,?6-IRHRs between isomer complexes with organometallic groups (OMGs) in different positions in graphene ligand proceeds via ?3-transition states with activation barriers considerably lower (<25 kcal/mol) than those of the corresponding rearrangements in medium-sized PALs (>30 kcal/mol). This could be explained by the reduction of electron density and the increase of electron mobility inside graphene molecules, which weaken metal–ligand bonds and facilitate rearrangements. DFT calculations show that organometallic moieties such as Cr(CO)3 or Cr(benzene) can move easily on large polyaromatic hydrocarbons.

Posted on 2 December 2014 | 2:10 pm


Synthesis, Molecular Structure and Properties of a Ferrocene-Based Difluoropyrrolo-Oxaborole Derivative

Reaction of 1,1?-ferrocenedicarbonyl chloride with 3-ethyl-2,4-dimethylpyrrole in DCM produced the half-way product, namely, the ferrocene bis(2-ketopyrrole) derivative 2 and not the expected bis(dipyrromethene) compound. The 2-ketopyrrole compound readily reacted with BF3·Et2O to produce the bis(difluoropyrrolo)-oxaborole compound, FBF, as a red/brown solid which was characterised by X-ray crystallography. 57Fe Mössbauer spectra for 2 and FBF were consistent with low-spin iron(II) (d6) ferrocene derivatives. A cyclic voltammogram for 2 in acetonitrile revealed a reversible wave at +0.31 V vs. Fc+/Fc (ferrocene-based) and an irreversible wave at –2.38 V vs. Fc+/Fc (ketopyrrole-based). The electrochemical behaviour is severely perturbed by the chelation of the BF2 groups. Alterations to the electronic properties of 2 by formation of FBF are also evident in the absorption profiles. DFT calculations [B3PW91, 6-31G(3df)] support the observed changes in the electrochemistry findings and the Mössbauer spectroscopic data. Reaction of 1,1?-ferrocenedicarbonyl chloride with 3-ethyl-2,4-dimethylpyrrole produces the bis(ketopyrrole) compound. Chelation of BF2 to the ketopyrrole units forms the difluoropyrrolo-oxaborole.

Posted on 2 December 2014 | 2:10 pm


Structure and Microwave Dielectric Properties of Ultralow-Temperature Cofirable BaV2O6 Ceramics

A new ultralow-temperature-sinterable BaV2O6 ceramic was prepared through a conventional solid-state ceramic method. Thermogravimetric and differential-scanning-calorimetry analyses were performed to confirm the phase formation of BaV2O6. Phase purity and crystal structure of the ceramic material were studied by using X-ray diffraction analysis and Raman spectroscopic studies. BaV2O6 crystallizes in an orthorhombic unit cell, and the calculated lattice parameters are a = 8.532 Å, b = 12.583 Å, and c = 7.554 Å. BaV2O6 ceramic was well sintered at 550 °C for 1 h and exhibited a dense microstructure with excellent microwave properties, for example, a dielectric constant of 11.2, a Qxf value of 42790 GHz, and a temperature coefficient of resonant frequency of 28.2 ppm/°C. The BaV2O6 ceramic exhibits a linear coefficient of thermal expansion of 10 ppm/°C in the range 30–350 °C. The BaV2O6 ceramic shows good chemical compatibility with Al electrodes, which makes it as a suitable candidate material for ULTCC technology. Ceramics that can be sintered at temperatures lower than the melting point of aluminum (660 °C) are classified as ULTTC ceramics. In the present work, a BaV2O6 microwave ceramic suitable for ULTCC applications was sintered at 550 °C, and phase formation was confirmed by DSC/TGA, X-ray diffraction, and Raman spectroscopic studies. The sintered ceramic has excellent compatibility with Al electrodes.

Posted on 28 November 2014 | 11:40 am


Synthesis and Conformational Study of Bioconjugates Derived from 1-Acetyl-1?-aminoferrocene and ?-Amino Acids

1,1?-Disubstituted ferrocene conjugates present useful and efficient bioorganometallic constraint design to reduce the conformational flexibility of small peptides. In this study we present the first systematic conformational analysis of nonsymmetric ferrocene peptidomimetics (Boc-AA-NH-Fn-COMe; Boc = tert-butoxycarbonyl; AA = Gly, L-Ala, L-Val; Fn = 1,1?-ferrocenylene) and their monosubstituted analogues (Boc-AA-NH-Fc; Fc = ferrocenyl; AA = Gly, L-Ala, L-Val). The spectroscopic data (IR, NMR and CD) were corroborated by DFT calculations and indicated the engagement of the NH group closest to the ferrocene unit in intrachain hydrogen bonds. This medium-strength bond is not disrupted by the introduction of a hydrogen-bonding acceptor on the other ferrocene ring, but rather is accompanied by an additional interchain hydrogen bond, which causes the restricted rotation of ferrocene rings and gives rise to a chiral arrangement of the ferrocene core in a P helical manner. Conformational analysis (IR, NMR,CD and DFT) revealed that nonsymmetric bioorganometallics [Boc-AA-NH-Fn-COMe; Boc = tert-butoxycarbonyl; AA = Gly, L-Ala, L-Val; Fn = 1,1?-ferrocenylene] adopt helically ordered conformations supported by intramolecular hydrogen bonds.

Posted on 27 November 2014 | 1:20 pm


Substitutional Lability of Diphosphine Ligands in Tetrahedral Iron(II) Chloro Complexes

A series of iron(II) dihalogenide complexes with two different bisphosphinoethane ligands is reported. In the case of 1,2-bis(diphenylphosphanyl)ethane (dppe), depending on the stoichiometry, the tetrahedral [(?-dppe)FeCl2]n and octahedral trans-[(dppe)2FeCl2] complexes are formed. The polymeric complex [(?-dppe)FeCl2]n, with iron in a tetrahedral environment, preferentially reacts with chelating amines to give the octahedral diphosphine complex, trans-[(dppe)2FeCl2], and different octahedral amine complexes. With the sterically more demanding 1,2-bis(diisopropylphosphanyl)ethane (dippe), the monomeric and tetrahedral halogen complexes [(dippe)FeX2] are exclusively obtained (X = Cl, Br). These complexes react with chelating amines in a similar manner, to give free ligand and the corresponding octahedral amine complex. The present results suggest that the diphosphines in the investigated iron(II) complexes are bound too weakly to form productive catalyst precursors. The synthesis and reactivity of iron diphosphine complexes towards chelating amines is described. The results illustrate the fundamental difference with respect to the corresponding ruthenium complexes and demonstrate that the investigated diphosphine ligands are bound too weakly in iron(II) complexes to be used for active iron-based catalysts.

Posted on 27 November 2014 | 1:20 pm


An Efficient Catalytic Approach for the Synthesis of Unsymmetrical Siloxanes

The potential for expanding the variety of catalytic methods for siloxane bond formation is explored. Alkoxysilanes react with methylallylsilanes in the presence of scandium(III) trifluoromethanesulfonate to yield disiloxanes and isobutene. The reaction proceeds through one-pot hydrolysis/O-silylation of alkoxysilanes with allylsilanes (via silanol intermediates) under mild conditions. Unsaturated siloxane products are used as substrates for further functionalization through the catalytic hydrosilylation reaction. An efficient methodology for the synthesis of unsymmetrical disiloxanes by means of catalytic one-pot hydrolysis/O-silylation of alkoxysilanes with allylsilanes (via silanol intermediates) in the presence of scandium(III) trifluoromethanesulfonate under mild conditions is described. Unsaturated siloxane products are used as substrates for further functionalization through the catalytic hydrosilylation reaction.

Posted on 27 November 2014 | 1:20 pm


Cyclizations of 1,2-Bis(pinacolylboryl)acetylene at Zirconocene

In the reaction of Cp2Zr(py)(?2-Me3SiC2SiMe3) (1Zr) (Cp = ?5-cyclopentadienyl) with the bis-BPin-substituted alkyne (2) (BPin = pinacolylboryl = 4?,4?,5?,5?-tetramethyl-[1?,3?,2?]dioxaborolan-2?-yl) via the zirconacyclopropene Cp2Zr(py)(?2-PinBC2BPin) (3), or alternatively by the reduction of Cp2ZrCl2 with magnesium in the presence of two equivalents of 2, the zirconacyclopentadiene Cp2Zr[C4(BPin)4] (4) was obtained. It was of interest to see how substituents influence the special side reactions of metallacyclopentadienes and if those would limit their synthetic application. Complex 4 reacts with (Ph3P)2NiCl2 and 3-hexyne to give the hexasubstituted benzene 1,2-ethyl-3,4,5,6-pinacolylboryl-benzene (6). During this procedure the heterometallic ferrol-type complex CpZr[CpNiC4(BPin)4]Cl2 (7) is observed as a side product. In this complex, one Cp ligand moves from Zr to Ni, from which the Ph3P ligands are eliminated. The nickelacyclopentadiene is ?4-bonded to the vacant site of the former zirconocendichloride. The formation of 7 is connected with the inhibition for the formation of 6. Compounds 7 and 6 were characterized by NMR spectroscopy and X-ray crystal structure analysis. In the reaction of [Cp2Zr] with 1,2-bis(pinacolylboryl)acetylene, zirconacyclopentadiene 4 was obtained. It reacts with (Ph3P)2NiCl2 and 3-hexyne to give the hexasubstituted benzene, 1,2-ethyl-3,4,5,6-pinacolylborylbenzene (6), and a heterometallic ferrol-type complex 7. The formation of 7 is the inhibition process for the synthesis of 6.

Posted on 27 November 2014 | 1:20 pm


The Synthesis, Structure, and Electrical Characterization of (SnSe)1.2TiSe2

(SnSe)1.2TiSe2 was found to self-assemble from a precursor containing modulated layers of Sn–Se and Ti–Se over a surprisingly large range of layer thicknesses and compositions. The constituent lattices form an alternating layer superstructure with rotational disorder present between the layers. This compound was found to have the highest Seebeck coefficient measured for analogous TiX2 containing misfit layered compounds to date, suggesting potential for low-temperature thermoelectric applications. Electrical characterization suggests that electrons transferred from SnSe to TiSe2 are responsible for the higher carrier concentration observed relative to bulk TiSe2. The transfer of charge from one constituent to the other may provide a mechanism for doping layered dichalcogenides for various applications without negatively affecting carrier mobility. The first intergrowth compound in the Sn–Ti–Se system was synthesized from modulated elemental reactants and was found to have a large negative Seebeck coefficient for 1021 carriers. Electrical characterization suggests that charge transfer occurs between layers to stabilize the superstructure and provides conducting electrons to the TiSe2 layer.

Posted on 27 November 2014 | 1:10 pm


Unexpected Strong Antiferromagnetic Interaction in [CuCyclam][Ni(1,2-benzenedithiolate)2]2

Two new molecule-based magnetic materials were prepared, namely, [CuCyclam(CH3CN)2][Ni(bdt)2]2 and [CuCyclam][Ni(bdt)2]2 (bdt = 1,2-benzenedithiolate). The former compound is characterized by a two-dimensional layer structure, in which axially coordinated acetonitrile molecules prevent cation–anion stacking. The weak antiferromagnetic interaction of 2J/kB = –6.2 K between the adjacent [CuCyclam(CH3CN)2]+ (S = 1/2) and [Ni(bdt)2]– (S = 1/2) moieties leads to a ferrimagnetic transition at 2.6 K. In contrast to the structure of [CuCyclam(CH3CN)2][Ni(bdt)2]2, the crystal structure of [CuCyclam][Ni(bdt)2]2 is characterized by alternately stacked [CuCyclam]2+ and [Ni(bdt)2]– units, and another [Ni(bdt)2]– anion bridges the chain to form a two-dimensional ferrimagnetic layer. The magnetic susceptibility of [CuCyclam][Ni(bdt)2]2 reveals a quite strong intrachain antiferromagnetic interaction of 2J/kB = –66 K between the [CuCyclam]2+ and [Ni(bdt)2]– ions. The weak interchain and interlayer interactions make the crystals antiferromagnetic below 3.2 K. New molecule-based magnetic materials containing quasiplanar [CuCyclam]2+ cations and planar [Ni(bdt)2]– anions (bdt = 1,2-benzenedithiolate) are prepared. Magnetic measurements reveal the existence of a rather strong exchange interaction of 2J/kB = –66 K, which is caused by the face-to-face stacking of the planar molecules in [CuCyclam][Ni(bdt)2]2.

Posted on 27 November 2014 | 1:10 pm


Understanding the Dynamics of Eu3+ Ions in Room-Temperature Ionic Liquids – Electrochemical and Time-Resolved Fluorescence Spectroscopy Studies

To understand the oxidation state, coordination geometry, and physicochemical behavior of the Eu3+ complex with dihexyl N,N-diethylcarbamoylmethylphosphonate (DHDECMP) in the ionic liquid (IL) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][NTf2]), the spectroscopic and electrochemical properties of the system were investigated. The electrochemical behavior of Eu3+–DHDECMP in [bmim][NTf2] was studied by cyclic voltammetry (CV) and chronoamperometry at a glassy carbon (GC) electrode. The reduction of Eu3+ to Eu2+ in [bmim][NTf2] is quasireversible and controlled by diffusion as well as charge-transfer kinetics. Photoluminescence spectroscopy confirms that the symmetry around the europium ions in Eu3+–DHDECMP in the room-temperature IL (RTIL) is relatively low; this is further supported by calculations of the Judd–Ofelt parameters (?2 higher than ?4). On the basis of fluorescence lifetime measurements, the number of water molecules in the inner sphere is six for uncomplexed europium ions, and practically no water molecules are retained in the presence of the complexing extractant DHDECMP. The present work deals with the extraction of Eu3+ ions (as a surrogate for Am3+ ions) from acidic feed solutions with dihexyl N,N-diethylcarbamoylmethylphosphonate (DHDECMP) in the ionic liquid (IL) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][NTf2]). The electrochemical and spectroscopic properties of Eu3+–DHDECMP in [bmim][NTf2] are investigated.

Posted on 27 November 2014 | 1:10 pm


Photoactive Hybrid Polymer Films Incorporated with Lanthanide Complexes and ZIF-8 for Selectively Excited Multicolored Luminescence

A series of photoactive polymer hybrid films fabricated with both lanthanide complexes and ZIF-8 [zeolite imidazole framework, a kind of metal organic framework, Zn(MeIM)2, MeIM = 2-methylimidazole] was prepared. ZIF-8 and the lanthanide complexes Ln-L [Ln = Eu, Tb; L = AA (acetylacetonate), phen (1,10-phenanthroline), TAA (trifluoroacetylacetonate), TTA (trifluoroacetylacetonate)] were assembled with the the monomers 4-vinyl pyridine (VPD) and ethylene-methyl acrylate (EMA), forming the final hybrid polymer films after initiation with benzoyl peroxide (BPO). The products are are indicated as PEMA-PVPD?Ln-L/ZIF-8 [PEMA-PVPD: copolymer of poly 4-vinyl pyridine (PVPD) and polyethylene-methyl acrylate (PEMA)]. The SEM images of these hybrid films indicate homogeneous dense packing and a high degree of coverage of the crystals on the ITO glass. The luminescent behavior of all the hybrid films was studied in detail. Discrete luminescence of the ZIF-8 unit and the lanthanide complexes was observed in which energy coupling between the two emissive centers does not exist. Therefore, by selectively exciting these hybrid films with different wavelengths, the luminescence colors of them can be tuned from blue (for ZIF-8) to red (for Eu3+), green (for Tb3+), yellow (for Eu3+/Tb3+) and even to white by integrating the emission of both Eu3+/Tb3+ into the polymer unit (PEMA-PVPD). These results are useful and have potential application in optical devices for displays or encoding. A series of photoactive polymer hybrid films fabricated with both Ln complexes and ZIF-8 is described. The films show discrete luminescence from ZIF-8 and the Ln complexes, and there is no energy coupling between the two emissive centers. By selective excitation with different wavelengths, the luminescence can be tuned from blue (ZIF-8) to red (Eu3+), green (Tb3+) or yellow (Eu3+/Tb3+) and even white by integrating the emission of both Eu3+ and the polymer unit.

Posted on 26 November 2014 | 12:20 pm


Cinnamate-Functionalized Cage Silsesquioxanes as Photoreactive Nanobuilding Blocks

Starting from potassium cinnamate, photoreactive mono-, octa-, and deca(propyl cinnamate)-functionalized cage silsesquioxanes were synthesized by simple nucleophilic substitution reactions with chloropropyl-substituted octasilsesquioxanes. Among them, octa(propyl cinnamate)silsesquioxane exhibited some remarkable behavior, including high photopolymerization conversion of double bonds under UV irradiation and thermal stability. These compounds can act as pure photoreactive nanobuilding blocks for the preparation of hybrid nanocomposites with specific properties. From potassium cinnamate, photoreactive mono-, octa-, and deca(propyl cinnamate)-functionalized cage silsesquioxanes are synthesized by simple nucleophilic substitution reactions with chloropropyl-substituted octasilsesquioxanes. Among them, octa(propyl cinnamate)silsesquioxane exhibits excellent properties such as high photopolymerization conversion of double bonds and thermal stability.

Posted on 26 November 2014 | 12:20 pm


NMR Spectroscopic Studies on the 1:1 Interaction of Tris(hydroxymethyl)phosphine with Cinnamic Acids

A 1:1 reaction of (HOCH2)3P with the cinnamic acids ArCH=CHCO2H (Ar = Ph, o- and p-C6H4OH) in acetone at 60 °C affords a phosphobetaine of the type (HOCH2)3P+CH(Ar)CH2CO2– in 70–80?% yields; the products were characterized by 31P{1H}-, 1H-, and 13C{1H}-NMR spectroscopy, and mass spectrometry. In methanol, the compounds decompose partially to a tertiary phosphine of the type (HOCH2)2PCH(Ar)CH2CO2H; the degree of decomposition decreases in the order Ar = o-C6H4OH > p-C6H4OH > C6H5. The 1:1 reaction of (HOCH2)3P with cinnamic acid in CD3OD generates (DOCH2)3P+CH(Ph)CH(D)CO2– and (DOCH2)2PCH(Ph)CH(D)CO2D, whereby addition of a deuteron to the ?-C atom is stereospecific and leads to (R,S)- and (S,R)-stereoisomers. A 1:1 reaction of (HOCH2)3P with cinnamic acids in acetone at 60 °C affords a phosphobetaine in 70–80?% yields. In methanol, the compounds decompose partially to a tertiary phosphine; the degree of decomposition decreases in the order Ar = o-C6H4OH > p-C6H4OH > C6H5.

Posted on 26 November 2014 | 12:20 pm


Synthesis and Characterization of Barium Tetrafluoridobromate(III) Ba(BrF4)2

Alkali and alkaline earth metal tetrafluoridobromates MIBrF4, MII(BrF4)2 (MI = Na–Cs, MII = Sr, Ba) can be synthesized from the respective fluorides and BrF3. The reaction of BaF2 with liquid BrF3 under Freon-113 leads to the formation of Ba(BrF4)2 as a colorless microcrystalline powder. Here, we discuss its formation kinetics and thermodynamics. The compound crystallizes in the tetragonal space group I$\bar {4}$ with a = 9.65081(11) Å, c = 8.03453(13) Å, V = 748.32(2) Å3, and Z = 4 at 27 °C, and it is isotypic to Ba(AuF4)2. The structure contains square planar BrF4– anions. The compound is stable at ambient conditions excluding moisture and at temperatures up to approximately 200 °C. Solid-state computational calculations of the Raman and IR spectra are in good agreement with the experimentally obtained ones, and in combination with its powder X-ray diffraction pattern, density measurement, thermodynamics, elemental and EDXRF analyses, this shows that the compound is pure. The synthesis of Ba(BrF4)2 and its characterization by various methods is presented. Tetrafluoridobromates(III) may be promising materials for the dry-chemical recycling of solid noble-metal wastes.

Posted on 26 November 2014 | 12:20 pm


trans-1,2-Cyclohexanedisulfonic Acid: An Optically Active Linker for Coordination Polymers

Racemic 1,2-cyclohexanedisulfonic acid was prepared from cyclohexene oxide via the cyclic trithiocarbonate and isolated as its barium salt. Optical resolution was achieved by crystallization with (–)-(R,R)-1,2-cyclohexane diamine; the absolute configuration was established by X-ray crystallography of this salt, [C6H10(NH3)2][C6H10(SO3)2]. Solid-state structures were investigated of the racemic acidic sodium disulfonate Na(H5O2)[C6H10(SO3)2] and the optically active disulfonates Na2[C6H10(SO3)2]·1.8H2O and Ag(NH2Me2)[C6H10(SO3)2]. Optically active trans-1,2-cyclohexanedisulfonic acid was prepared in four steps from cyclohexene oxide.

Posted on 26 November 2014 | 12:20 pm


Four Cobalt(II)-Containing Coordination Polymers: Effects of pH Value and Temperature on Synthesis, Gas-Sorption, and Magnetic Properties

Four 3D CoII-containing coordination polymers – namely, [Co2(L)(OH)(H2O)]·1.5H2O (1), [Co(HL)(H2O)] (2), [Co4(HL)(L)(trz)3(H2O)]·6H2O (3), and [Co3(HL)2(trz)2(H2O)2] (4) {H3L = 5-(benzonic-4-ylmethoxy)isophthalic acid; Htrz = 1,2,4-triazole} – based on a semirigid carboxylate ligand have been successfully synthesized under hydrothermal conditions. Compounds 1/2 and 3/4 were obtained by using the pH value and temperature as the only independent variable, respectively. Compound 1 possesses a (4,8)-connected net based upon tetranuclear CoII clusters, whereas 2 shows a (3,6)-connected net based on binuclear CoII units. Compound 3 displays a 4-nodal (3,4,7)-connected framework with 1D channels, whereas 4 reveals a (3,10)-connected net based upon trinuclear CoII clusters. The CO2-selective adsorption property of compound 3 was studied. In addition, the variable-temperature magnetic susceptibilities of compounds 1–4 were also investigated. Four 3D CoII-containing coordination polymers (CPs) based on a semirigid trigonal carboxylic acid have been synthesized under hydrothermal conditions. The CP that is formed is influenced by the pH value, reaction temperature, and auxiliary ligand. Variable-temperature magnetic susceptibilities of compounds 1–4 were also investigated.

Posted on 25 November 2014 | 12:10 pm


Fluorescence Detection of Anilines and Photocatalytic Degradation of Rhodamine B by a Multifunctional Metal–Organic Framework

A multifunctional transition metal CdII coordination polymer based on an amide-inserted flexible multicarboxylate ligand, bis(3,5-dicarboxyphenyl)terephthalamide (H4L), [CdL]·[+H2N(CH3)2] (DMF)(H2O)3 (MOF1) was synthesized by the solvothermal method. Its structure was determined by single-crystal X-ray diffraction analysis and it was characterized by elemental analysis, IR spectroscopy and thermogravimetric analysis. MOF1 shows selective sensitivity to detecting aniline pollutants in both aqueous media and as vapors due to its strong fluorescence emission and microporous structure. In addition, the visible-light-driven photocatalytic degradation of Rhodamine B (RhB) by MOF1 and polyaniline (PANI) composite material (named PANI/MOF1), which was prepared by loading PANI onto the surface of MOF1, was also studied. The results obtained illustrate that PANI/MOF1 exhibits improved photocatalytic activity over MOF1, which could be used to effectively treat wastewater containing organic dyes in the future. A multifunctional metal–organic framework for determination of toxic aromatic amines has been constructed and it shows photocatalytic degradation of organic dyes due to the combination of luminescence and accessible porosity within the MOF.

Posted on 25 November 2014 | 12:10 pm


Metal Complexes of Very Bulky N,N?-Diarylimidazolylidene N-Heterocyclic Carbene (NHC) Ligands with 2,4,6-Cycloalkyl Substituents

1,3,5-Tricycloalkylbenzene (cycloalkyl = C5H9, C6H11) was converted into the respective anilines (by means of nitration and reduction) and then into the corresponding diimines (with glyoxal), the cyclization of which with (HCHO)n/ZnCl2 provided the respective 1,3-bis(2,4,6-tricyclopentylphenyl)imidazolium salt in modest yields. An analogous reaction sequence that employed acenaphthene-1,2-dione instead of glyoxal yielded the two azolium salts in good yields, which were converted into the respective N-heterocyclic carbene (NHC) complexes [(NHC)AgCl], [(NHC)AuCl], [(NHC)RhCl(cod)] (cod = cyclooctadiene), and [(NHC)RhCl(CO)2]. Sterically very demanding N-heterocyclic carbenes and metal complexes thereof were synthesized by means of a classic sequence of Friedel–Crafts alkylation, nitration, and nitro-to-amine reduction to lead to the respective anilines, which were then converted into the respective azolium salts through established synthetic routes.

Posted on 25 November 2014 | 12:10 pm


The Unexpected Reactions of Boron Trihalides with 7-Phosphanorbornadiene Complexes

The reactions of BX3 (X = Cl, Br) with 7-R-7-phosphanorbornadiene–M(CO)5 (M = Mo, W) complexes (1) yields products 2 and 4 in which the RP–M(CO)5 unit is inserted into one of the carboxyl units of the phthalic derivative as a result of the collapse of the bridge. When X = Br, 4 cyclizes to give new six-membered heterocycles 5 with quasiplanar structures. When treated by an excess of BBr3, heterocycles 5 undergo ring contraction to afford five-membered oxocyclic products 6. The reactions of BX3 (X = Cl, Br) with 7-R-7-phosphanorbornadiene–M(CO)5 (M = Mo, W) complexes yield products in which the RP–M(CO)5 unit is inserted into one of the carboxyl units of the phthalic derivatives through the collapse of the bridge. Six-membered heterocycles with quasiplanar structures can form from these derivatives, and ring contraction leads to five-membered oxocyclic products.

Posted on 25 November 2014 | 12:10 pm


Glycoconjugated Rhenium(I) and 99m-Technetium(I) Carbonyl Complexes from Pyridyltriazole Ligands Obtained by “Click Chemistry”

A series of pyridyltriazole ligands containing sugar moieties have been prepared by copper(I)-mediated 1,3-dipolar cycloaddition (“click” reaction) of azides functionalized with D-glucose, D-galactose, D-mannose, D-xylose as well as D-maltose residues, and 2-ethynylpyridine as alkyne. The peracetylated saccharide residues as well as their water-soluble deprotected derivatives were treated with Re(CO)5Cl to obtain the corresponding mononuclear rhenium(I) carbonyl complexes [LRe(CO)3Cl]. For comparison, one ReI complex bearing a tert-butylbenzyl residue instead of a sugar moiety as well as two dinuclear rhenium complexes derived from a branched ligand containing two pyridyltriazole units were prepared. The structure and integrity of the ligands and complexes was established by NMR, IR, UV/Vis and fluorescence spectroscopy, mass spectrometry, and by elemental analysis. Coordination of the metal ion occurred by both the pyridyl nitrogen atoms and one of the triazole nitrogen atoms. Upon treatment with an excess of histidine, the ReI complexes were stable for only 2.5 h. After a longer period (24 h) ligand exchange was detected by HPLC measurements. In contrast, a complex labeled with 99mTc was found to be stable for up to 24 h against an excess of histidine. Cytotoxicity was screened for all ReI complexes against HepG2 cells using a concentration of 100 ?M. All sugar-functionalized complexes were found to be nontoxic, except for the complex derived from the pyridyl (tert-butylbenzyl)-triazole, which exhibited remarkable toxicity. A series of pyridyltriazole ligands containing sugar moieties and their corresponding Re(I) complexes were synthesized and characterized. Stability tests against histidine showed that the complexes are stable up to 2.5 h; the 99mTc-labeled complex was stable up to 24 h. All sugar-based ReI complexes were nontoxic against HepG2 cells; in contrast, the ReI complex without a carbohydrate moiety was toxic.

Posted on 25 November 2014 | 12:10 pm


[IrCp*(NCMe)2(PPh2Me)][PF6]2 as Catalyst for the Meyer–Schuster Rearrangement of Arylpropargylic Alcohols under Mild Conditions

The novel iridium complex [IrCp*(NCMe)2(PPh2Me)][PF6]2 (I) efficiently catalyzed the Meyer–Schuster rearrangement of selected arylpropargylic alcohols into ?,?-unsaturated aldehydes under mild conditions and without the need of a co-catalyst. A mechanism involving a (hydroxy)alkenylcarbene intermediate is proposed. [IrCp*(NCMe)2(PPh2Me)][PF6]2 efficiently catalyzes the rearrangement of propargylic alcohols into ?,?-unsaturated aldehydes under mild conditions and without the need of a co-catalyst.

Posted on 25 November 2014 | 12:10 pm


C–O Bond Activation by a Tantalum-Bonded Pincer Ligand – Ligand Modification Effects on the Selectivity of C–H Bond Cleavage Processes

The tantalum complexes [TaCp*Me{(OCH2)(OCHCO2)py-?4-N,O,O,O}]2 (2, Cp* = ?5-C5Me5, py = pyridyl) and [TaCp*Me{(OCH2)(OCHCONAr)py-?4-N,O,O,O}]2 (3, Ar = p-tolyl) have been synthesized by the reactions of [TaCp*Me{(OCH2)(OCH)py-?3-N,O,O}] (1) with CO2 and p-tolyl isocyanate, respectively. The reaction of 3 with an excess of water renders the corresponding tantalum hydroxide [TaCp*Me(OH){(OCH2)(OCHCONHAr)py-?3-N,O,O}] (4). Compound 1 reacts with pyridyl triflate (pyOTf) to afford the new pyridyl-functionalized pincer derivative [TaCp*Me{(OCH2)(OCHpy)py-?3-N,O,O}(OTf)] (5). Compound 5 reacts with water to yield the aqua adduct [TaCp*Me(OH2){(OCH2)(OCHpy)py-?3-N,O,O}]OTf (6). The reaction of 5 with LiN(SiMe3)2 gives rise to the new tantalum compound [TaCp*Me{(OCH2)(OCpy)py-?3-N,O,O}] (7). Complex 7 reacts with pyOTf to give the dipyridyl-functionalized pincer derivative [TaCp*Me{(OCH2)(OCpy2)py-?3-N,O,O}(OTf)] (8). The molecular structures of complexes 2, 4 and 6 have been established by single-crystal X-ray diffraction studies. The cooperative metal–ligand activation of C–O bonds allows the functionalization of the pincer moiety to yield a variety of tantalum-bonded tetradentate ligands. We study the role of the ligand substituents on the selectivity of C–H bond cleavage processes.

Posted on 25 November 2014 | 12:10 pm


Electrospinning of Ionogels: Current Status and Future Perspectives

Ionogels (IGs), also termed ion gels, are functional hybrid materials based on an ionic liquid (IL) and a polymeric, hybrid, or inorganic matrix. IGs combine the properties of the matrix such as mechanical strength with IL properties like high ionic conductivity, high thermal stability, or catalytic activity. IGs are thus attractive for many applications, but the vast majority of IGs made and published so far are bulk materials or dense films. Applications like sensing or catalysis, however, would benefit from IGs with high surface areas or defined surface morphologies or architectures. In spite of this, only relatively few examples of high-surface-area IGs have been made so far; this has mostly been achieved by electrospinning, which has proven to be a promising strategy towards advanced IGs. The current review discusses first developments and outlines the future potential of electrospun ionogels, predominantly from a materials and inorganic chemistry perspective. Spin it: Electrospinning is a useful and low-cost approach towards high-surface-area nanofibrous ionogels, that is, multifunctional hybrid materials based on ionic liquids, with tremendous application potential from catalysis to energy, healthcare, and beyond. The article provides an overview of the field and discusses the future potential of these promising materials.

Posted on 25 November 2014 | 12:10 pm


Mechanism of Nitric Acid Reduction and Kinetic Modelling

In France, the recycling of nuclear waste fuels involves the use of hot concentrated nitric acid. The understanding and prediction of the behaviour of the structural materials (mainly austenitic stainless steels) requires the determination and modelling of the nitric acid reduction process. Nitric acid is indirectly reduced by an autocatalytic mechanism depending on the cathodic overpotential and acid concentration. This mechanism has been widely studied. All the authors agree on its autocatalytic nature, characterized by the predominant role of the reduction products. It is also generally admitted that neither nitric acid nor the nitrate ion is the electroactive species. However, the nature of the electroactive species, the place where the catalytic species regenerates and the thermodynamic and kinetic behaviour of the reaction intermediates remain uncertain. The aim of this study was to clarify some of these uncertainties by performing an electrochemical investigation of the reduction of 4 M nitric acid at 40 °C at an inert electrode (platinum or gold). An inert electrode was chosen as the working electrode in a first step to avoid its oxidation and focus the research on the reduction mechanism. This experimental work enabled us to suggest a coherent sequence of electrochemical and chemical reactions. Kinetic modelling of this sequence was then carried out for a gold rotating disk electrode. A thermodynamic study at 25 °C allowed the composition of the liquid and gaseous phases of nitric acid solutions in the concentration range 0.5–22 M to be evaluated. The kinetics of the reduction of 4 M nitric acid was investigated by cyclic voltammetry and chronoamperometry at an inert electrode at 40 °C. The coupling of chronoamperometry and FTIR spectroscopy in the gaseous phase led to the identification of the gaseous reduction products as a function of the cathodic overpotential. The results showed that the reduction process is autocatalytic for potentials between 0.6 and 1.15 V/NHE. The electroactive species may be regenerated at the surface of the electrode for lower potentials, otherwise this regeneration process occurs in solution by a homogeneous chemical reaction. When the potential is less than 0.6 V/NHE, the fast reduction of nitrogen oxide may lead to rupture of the autocatalytic cycle. The kinetics of the reduction of 4 M nitric acid has been investigated at an inert electrode at 40 °C. The results show that the reduction process is autocatalytic for potentials between 0.6 and 1.15 V/NHE. HNO2 is the electroactive species and is regenerated at or near the electrode surface by a chemical reaction between HNO3 and NO(ads). Kinetic modelling of this mechanism was carried out.

Posted on 25 November 2014 | 12:10 pm


Platinum Diolefin Complexes – Synthesis, Structures, and Cytotoxicity

The synthesis, spectroscopy, structures and chemical reactivity of platinum(II) diolefin complexes cis-[(???)PtCl2], cis-[(???)PtCl(R)] and cis-[(???)Pt(R)2] [??? = chelate diolefin ligand: 1,5-cyclooctadiene (COD), 1,5-dimethylocta-1,5-diene (Me2COD), norbornadiene (NBD), 1,5-hexadiene (HEX), 3-allyloxypropene (All2O, diallyl ether), diallylamine (All2NH); R = Me, Bn, C6F5, C6F4H-4 (or -5), or C?C(4-Me)Ph] have been explored. The relative exchange rates of the cis-[(???)PtCl2] complexes towards the diimine ligand diisopropyl-1,4-diazabutadiene (iPr-DAB) increased along the series COD?< Me2COD?< NBD?< HEX?< All2O by a factor of 4. The presumably dimeric complex [(All2NH)PtCl2]2 undergoes a unique rearrangement process in dimethyl sulfoxide (DMSO) solution to yield the dimeric piperazine complex [PtCl(dmso)(C6H10N)]2, which has been characterised by single-crystal XRD. For selected platinum complexes, cytotoxic effects in HT-29 colon carcinoma and MCF-7 breast cancer cell lines were evaluated. For comparison, the dicationic complexes [(COD)Pt(Bn)(L)][PF6]2 with the very labile coligands N-methyl-4,4?-bipyridinium (MQ+) and N-methyl-1,4-pyrazinium (Mpz+) were added to the study. Although the hexadiene complexes [(HEX)Pt(C6F4H-4)2] and [(HEX)Pt(C6F4H-5)2] show strong cytotoxicity, the introduction of labile diolefin ligands or the labile cationic MQ+ or Mpz+ coligands does not generally lead to markedly increased cytotoxicity. Organometallic diolefin platinum(II) complexes [(???)PtCl2], [(???)Pt(R)(L)] and [(???)Pt(R)2] are synthesised and characterised. Cytotoxicity experiments (HT-29 and MCF-7 cancer cell lines) show that the introduction of labile diolefin ligands ??? or labile coligands does not lead to increased cytotoxicity compared with that of the established 1,5-cyclooctadiene derivatives.

Posted on 24 November 2014 | 10:10 am


Synthesis and Characterization of ortho-Thio-Functionalized Triarylmethyl Palladium Complexes

A series of triarylmethyl palladium complexes with ortho coordination sites were synthesized. Thereby, the palladium atom exhibits various inter- and intramolecular binding modes towards the organic ligand. Further, the first crystallographically proven, exclusively ?-coordinated triarylmethyl palladium complexes, stabilized by ortho-thio-substituents, were discovered. The NMR spectra of the palladium complexes indicate temperature-dependent dynamic behavior. Various inter- and intramolecular binding modes between palladium salts and ortho-thio-substituted triarylmethyl ligands are detected in the solid state. The corresponding dynamic behavior in solution is studied by temperature-dependent NMR spectroscopy.

Posted on 21 November 2014 | 3:20 pm


Structural and Morphological Transformations of In–MIL-68-Based Hexagonal Lumps to QMOF-2-Based Pointed Hexagonal Rods by Means of Destruction and Reconstruction Processes

Simple thermal treatment of three-dimensional Kagomé-like [In(OH)(BDC)]n (In–MIL-68) hexagonal lumps in the presence of an extra amount of 1,4-benzenedicarboxylic acid (H2BDC) induces structural and morphological transformations of the hexagonal lumps into three-dimensional quartz-structured [InH(BDC)2]n (QMOF-2) pointed hexagonal rods. Transformation processes have been monitored by scanning electron microscopy to verify the destruction of the In–MIL-68-based hexagonal lumps and the simultaneous reconstruction of QMOF-2-based pointed hexagonal rods. We have also discovered the production of In–MIL-68-based hexagonal wires as early-stage kinetic products and the generation of QMOF-2-based pointed hexagonal rods as final-stage thermodynamic products from one-step solvothermal reaction of In(NO3)3 with an excess amount of H2BDC. Simple thermal treatment of In–MIL-68-based three-dimensional Kagomé-like structured hexagonal lumps in the presence of an excess amount of 1,4-benzenedicarboxylic acid (H2BDC) induces structural and morphological transformations into quartz-structured QMOF-2-based pointed hexagonal rods.

Posted on 21 November 2014 | 3:20 pm


Synthesis of Multifunctional Fe3O4@mSiO2@Au Core–Shell Nanocomposites for pH-Responsive Drug Delivery

A multifunctional nanocomposite has been successfully prepared for pH-responsive and magnetic-targeting drug delivery. First, Fe3O4@mesoporous silic (mSiO2) core–shell nanoparticles were synthesized as the nanocapsules. Doxorubicin hydrochloride was adopted as the model drug; after drug loading, gold nanoparticles (5 nm) were connected to block the mesopore through the hydrazone linkage. The hydrazone bond, a typical acid-sensitive bond, could undergo hydrolysis in an acidic environment to induce the release of the capping agent, so that the multifunctional nanocomposite revealed acid-enhanced release performance. What's more, before reaching acid conditions, little premature release was found to take place. Cell experiments were also carried out to reveal the good biocompatibility, fast uptake, and improved toxicity toward HeLa cells. Thus, in association with the magnetic target, the multifunctional nanocomposite shows the potential application for some low-pH tissue-targeted therapy, such as for inflammation and tumors. A pH-responsive and magnetic-targeted drug-delivery system was prepared with a Fe3O4@mesoporous silica core–shell nanostructure as host. Au nanoparticles were used as the capping agent. These were connected to the surface of the mesopore through the hydrazone linkage to restrict the drug release. The system has potential applications in low-pH tissue-targeted therapy.

Posted on 21 November 2014 | 3:20 pm


Two-Photon Absorption Properties of Eu3+-DPA-Triazolyl Complexes and the Derived Silica Nanoparticles Embedding These Complexes

Several complexes and silica-based nanohybrids of rare-earth ions (Eu3+, Gd3+) have been synthesized from dimethyl 4-azidopyridine-2,6-dicarboxylate (4) following the Click chemistry approach. A complete spectroscopic study indicates that such compounds exhibit strong sensitization by the antenna effect from both UV and NIR excitations. The Gd3+-based materials show phosphorescence under ambient conditions, which originates from the lowest-energy intra-ligand triplets. Fine analysis of the NIR excitation spectra using time resolved photoluminescence spectroscopy (TRS) indicates that the spectral repartition of the triplet T1 state differs notably between the complexes and the NPs embedding the complexes. Moreover the dependence of Eu3+ luminescence vs. incident beam power in the NIR region diverges from pure quadratic dependence expected in the framework of the two-photon absorption process. The results are discussed considering the occurrence of a direct singlet-to-triplet optical absorption transition (S0T1) upon NIR excitation. The TRS technique is used at 300 K to analyze the phosphorescence and the NIR excitation spectra of Gd3+-, Eu3+-DPA-triazolyl complexes and derived NPs embedding them. The TPA excitation spectra of the NPs are located on the low-energy side of the phosphorescence spectrum and consist of narrow bands attributed to the S0(0)T1(0–2) pure electronic transition.

Posted on 21 November 2014 | 3:20 pm


Quenching of Fluorescence in Bodipy-Derived Trifluoromethyl Enaminone Ligands upon Coordination to Copper(II)

The synthesis of two trifluoromethyl-derived enaminone ligands, L1H (bidentate) and L2H2, (tridentate), which bear a fluorescent 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (Bodipy) moiety, leads to the preparation and characterization of two CuII complexes {[Cu(L1)2]·2(CH2Cl2) (A) and [Cu4(L2)4]·4(C4H8O2) (B)} that exhibit different architectures. The magnetic properties of the cubane-like complex B evidence a dominant ferromagnetic behavior characterized by exchange coupling constants J1 = +20.56(3) cm–1 and J2 = –10.29(2) cm–1. Indeed, whereas the luminescence properties of the Bodipy-derived trifluoromethyl enaminones L1H and L2H2 are typical of the Bodipy skeleton, the emission is totally quenched in both mononuclear (A) and cubane (B) CuII complexes. To elucidate this quenching phenomenon, the Rehm–Weller equation has been used based on experimental cyclic voltammetry redox potential measurements. The result remains ambiguous for complexes A and B, and the origin of the quenching phenomenon, photoinduced electron transfer (PET) versus energy transfer (Förster or Dexter), cannot be deduced. Syntheses of two derived enaminone ligands bearing a fluorescent 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (Bodipy) moiety lead to two mono- and tetranuclear CuII complexes with redox and magnetic properties, respectively. Whereas the luminescence properties of the ligands are typical of the Bodipy skeleton, the emission is quenched in the complexes.

Posted on 21 November 2014 | 3:20 pm


Glycine–Nitrate Process for the Elaboration of Eu3+-Doped Gd2O3 Bimodal Nanoparticles for Biomedical Applications

Monoclinic and cubic europium-doped Gd2O3 structures were selectively synthesized by the glycine–nitrate process by fine control of the synthesis temperature through the crucial fuel/oxidant ratio. The cubic phase is obtained under fuel-rich conditions, whereas stoichiometric conditions induce the simultaneous formation of cubic and monoclinic polymorphs. The samples were subjected to appropriate sintering to obtain highly crystalline and carbon-free materials. The average nanoparticle (NP) size determined by TEM for these nanopowders (23 nm) agrees with the average crystallite sizes obtained from XRD Rietveld analysis; therefore, the particles are monocrystalline. Both electron energy loss spectroscopy (EELS) and photoluminescence studies showed that the europium-doped NPs are highly luminescent, and the Eu3+ ions are homogeneously distributed over the whole material as well as over the two gadolinium crystallographic sites of the cubic phase. These fluorescent NPs exhibit relaxivities that define them as potential T1 contrast agents for further biomedical applications. By fine control of the flame temperature in the glycine–nitrate process, highly crystalline Eu3+-doped and undoped Gd2O3 nanoparticles are obtained. In the doped samples, the Eu3+ ions are homogeneously distributed over the whole material. The Eu:Gd2O3 NPs are highly luminescent and exhibit relaxivities that define them as potential T1 contrast agents for biomedical applications.

Posted on 18 November 2014 | 10:23 am


Lanthanide(III) Nitride Bismuthides M2NBi (M = La–Nd) and Their Potential as Topological Insulators

Four lanthanide(III) nitride bismuthides of the new class M2NBi (M = La–Nd) have been synthesized by the reaction of the respective lanthanide metal (M) with caesium azide (CsN3), elemental bismuth (Bi), the corresponding lanthanide trichloride (MCl3), and caesium chloride (CsCl) as flux in evacuated silica tubes for 7 days at 900 °C. The M2NBi compounds crystallize tetragonally in the space group P4/nmm with Z = 2 with the lattice parameters a = 480.61(4) pm, c = 948.34(9) pm (M = La), a = 475.48(4) pm, c = 938.76(9) pm (M = Ce), a = 471.80(4) pm, c = 929.51(9) pm (M = Pr), and a = 468.13(4), c = 921.08(9) pm (M = Nd). As the main structural feature of the crystal structures, ?2{[NM2]3+} layers of condensed nitride-centered square pyramids of M3+ cations dominate. These pyramids, in which the base is built of (M1)3+ and the top of terminal (M2)3+ cations (t), are connected by all four basal edges (e) to form a two-dimensional network according to ?2{[N(M1)e4/4(M2)t1/1]3+} that is separated by square double layers of Bi3– anions. Both crystallographically independent M3+ cations bear two types of anions (N3– and Bi3–) as ligands. (M1)3+ is coordinated in the shape of a square antiprism by four N3– and four Bi3– anions, and (M2)3+ is surrounded by a distorted octahedron consisting of one N3– and five Bi3– anions. The Bi3– anions reside in capped square antiprisms of nine M3+ cations. The partial density of states (PDOS) and the band structure of La2NBi show that this compound has to be considered as a zero-band-gap semiconductor with a nontrivial topology and a high potential as a topological insulator. Four lanthanide(III) nitride bismuthides of the class M2NBi (M = La–Nd) were synthesized and characterized by X-ray diffraction. All four compounds crystallize tetragonally in the space group P4/nmm and anti-isotypically with KCoO2 or BaNiS2. The partial density of states and the band structure of La2NBi show that this compound has to be considered a zero-band-gap semiconductor.

Posted on 17 November 2014 | 11:10 am


ZrIV Coordination Polymers Based on a Naturally Occurring Phenolic Derivative

The reactivity under solvothermal conditions of the ZrIV ion with the naturally occurring gallic acid ligand has been evaluated in depth. The study led to the isolation of four microcrystalline hydroxycarboxylate-based coordination polymers (MIL-151 to -154). Through the use of a combination of solid-state NMR and high-resolution X-ray powder diffraction analyses, the structures of two of these phases (MIL-153, MIL-154) were solved. In both cases, the gallol motifs favour the formation of rod-like inorganic units built up from ZrO8 polyhedra. Although one compound (MIL-151) was found to be microporous (SBET ? 470 m2?g–1), its poor crystallinity prevented comprehensive structural analysis. Nevertheless, a comparison of its physicochemical features with those of the fully characterized solids allows a plausible structural model to be proposed. An investigation into the reactivity of carboxyphenolic gallic acid with the ZrIV ion led to the isolation of four microcrystalline solids, amongst which one was found to be microporous. Such ligand/cation pairing strongly favours the formation of chain-like inorganic motifs.

Posted on 14 November 2014 | 1:23 pm


Highly Stable Complexes of Divalent Metal Ions (Mg2+, Ca2+, Cu2+, Zn2+, Cd2+, and Pb2+) with a Dota-Like Ligand Containing a Picolinate Pendant

The stability constants of complexes of the macrocyclic ligand do3a-pic4– (H4do3a-pic = 2,2?,2?-{10-[(6-carboxypyridin-2-yl)methyl]-1,4,7,10-tetraazacyclododecane-1,4,7-triyl}triacetic acid) with several divalent metal ions (Pb2+, Cd2+, Zn2+, Cu2+, Ca2+, and Mg2+) have been determined by using pH-potentiometric titrations (I = 0.1 M KCl, 25 °C). The stability of these complexes follows the trend Cu2+?> Cd2+???Pb2+???Zn2+?>>?Ca2+?>>?Mg2+. A particularly high stability constant has been determined for the Cu2+ complex [log?KCuL = 23.20(4)]. Analysis of the titration curves indicate the presence of protonated forms of the complexes in solution, with protonation constants of log?KM(HxL) = 6.9–2.0 (x = 1, 2, or 3). The structure of the complexes in solution has been investigated by using 1H and 13C NMR spectroscopy and DFT calculations performed in aqueous solution at the TPSSh/6-31G(d) level. In the case of the Pb2+ and Cd2+ complexes, relativistic effects were considered with the use of relativistic effective core potentials. Calculations show that the complexes with the largest metal ions (Pb2+ and Ca2+) are nine-coordinate, with their coordination polyhedra being best described as capped twisted square antiprisms. The Cd2+ and Mg2+ complexes are seven-coordinate, with the metal ions being bound to the four nitrogen atoms of the cyclen unit and the three acetate pendant arms. Finally, in the Cu2+ and Zn2+ complexes, the metal ions are six-coordinated, with the metal ions being asymmetrically placed inside the macrocyclic cavity of the ligand, and the coordination polyhedra can be described as an octahedron and a trigonal prism, respectively. A detailed study of the thermodynamic stability of complexes formed by divalent metal ions with a macrocyclic ligand containing a picolinate arm is reported. The complexes of Cu2+, Zn2+, Cd2+, and Pb2+ present high stability constants [log?KML?> 20]. DFT calculations and NMR spectroscopy point to variable coordination numbers and geometries for this series of metal complexes.

Posted on 13 November 2014 | 2:10 pm


Tuning the Morphology of GeS2 Hybrid Materials Using Ionic Liquids as Structuring Agents

Control of the surface chemistry and morphology of chalcogenide materials, which are highly polarizable, is a very interesting challenge as it might lead to breakthroughs in various fields such as electrochemistry, catalysis, and gas-phase separation. With this in mind, a new approach to synthesize structured Ge-based chalcogenide products has been investigated. It involves the use of tetraethoxygermanium (TEOG) and thioacetamide with an ionic liquid (IL) as structuring agent. This innovative synthesis process has two main advantages: it is performed under soft conditions, and it also enables the morphological control of the obtained hybrid organic–GeS2 particles. In the absence of the IL, the synthesis leads to an agglomeration of nanospheres, whereas the introduction of the ionic liquid leads either to microspheres or to gypsum rosette-like particles. It has been clearly highlighted that the morphology of the hybrid organic–GeS2 particles strongly depended on the nature of the cationic part of the IL. Hybrid organic–GeS2 particles, the morphology of which depended upon the cationic part of an ionic liquid that was added as structuring agent, were prepared by means of an innovative nonhydrolytic soft-chemistry route at room temperature at atmospheric pressure.

Posted on 13 November 2014 | 1:30 pm


Molecular Mechanisms of [Bi6O4(OH)4](NO3)6 Precursor Activation, Agglomeration, and Ripening towards Bismuth Oxide Nuclei

Molecular dynamics simulations have been employed to characterize the role of [Bi6O4(OH)4](NO3)6 cage structures in DMSO solution as precursors to larger bismuth oxide aggregates. We find that the nitrate ions play a twofold role: (i) the association of [Bi6O4(OH)4](NO3)6 clusters – which are fully coordinated by six nitrate ligands – is electrostatically disfavored giving rise to stable [Bi6O4(OH)4](NO3)6 solutions; (ii) in contrast, the dissociation of a single nitrate ligand results in attractive cluster–cluster interactions. This results in the formation of oligomers, which are initially bridged by one to three nitrate ions, but then form Bi–O contacts by sharing common edges and faces and eventually ripen into nuclei of bismuth oxide. Strikingly, this process may be induced by a single activated species, the [Bi6O4(OH)4](NO3)5+ cluster, which may bind several [Bi6O4(OH)4](NO3)6 clusters. Molecular dynamics simulations unravel the early steps of bismuth oxide precursor association and ripening into larger aggregates. Nitrate ions play a twofold role in the process by preventing the association of Bi6O4(OH)4(NO3)6 clusters but at the same time inducing the formation of oligomers comprising under-coordinated Bi ions.

Posted on 13 November 2014 | 1:30 pm


Possible Roles of the Spatial Distribution of Organic Guest Species in Mesoporous Silicas to Control the Properties of the Hybrids

Mesoporous silicas are promising materials for the construction of host–guest hybrids by the accommodation of functional unit/guest species into the mesopore, and moreover, by hierarchical assembly with controlled location, density, and orientation. Precisely designed structures open up the versatile functions of mesoporous silicas and their host–guest systems. In this microreview, the spatial distribution (location, density, and orientation) of the organic functional units/guest species in mesoporous silicas (mainly one-dimensional cylindrical) is discussed to highlight the present status of the host–guest chemistry of mesoporous silicas. The spatial distribution (location, density, and orientation) of the functional units (guest species) attached/included on/in mesoporous silicas are discussed to highlight the status of the host–guest chemistry of mesoporous silicas.

Posted on 12 November 2014 | 12:40 pm


Synthesis of Advanced Nanoreinforced Polyurethane with Thiolene Photografted Organo-Modified Layered Double Hydroxide

New bionanocomposites with strongly intertwined structures based on polyurethane and layered double hydroxides (LDH) were obtained by using two different intermolecular thiolene coupling strategies in which the modification of LDH with oleic acid was either performed first and then followed by the thiolene photografting using 2-mercaptoethanol, or the initial thiolene photografted oleic acid/2-mercaptoethanol product was subsequently used to modify the LDH platelets. The resultant photografted oleate/LDH was condensed with diisocyanate and the addition of poly(ethyleneglycol) yielded a final hybrid polymer. The interleaved LDH materials were characterized by X-ray diffraction and thermogravimetric analysis, underlining the possible commutative steps between photografting and organo-modification processes. The resultant polyurethanes were characterized by FTIR spectroscopy, nuclear magnetic resonance, differential scanning calorimetry and rheology. Furthermore, the durability of the resultant polymers was assessed by photo-FTIR. The results showed that strongly intermingled polyurethanes were processed by both strategies. Enhanced mechanical properties as well as more prolonged durability were found after anchoring LDH sheets and this was even more amplified when using the photografted acid direct intercalation into the LDH during the first synthesis step. Successive processes to yield layered double hydroxide filled polyurethane nanocomposite including (1) organo-modification of LDH platelets, (2) functionalization using UV thiolene coupling and (3) monomer addition.

Posted on 12 November 2014 | 12:40 pm


Hybrid Polymer Electrolytes Based on a Poly(vinyl alcohol)/Poly(acrylic acid) Blend and a Pyrrolidinium-Based Ionic Liquid for Lithium-Ion Batteries

Polymer blends of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA) were prepared with different molar ratios by a solvent-casting technique. The XRD patterns of the blends show that the degree of crystallinity of the PVA membranes decreases with the addition of PAA owing to the formation of interpenetrating polymer chains. The vibrational spectra of the blend membranes reveal the formation of strong hydrogen bonding between PVA and PAA. Dynamic mechanical analysis (DMA) reveals that the storage modulus of a 25 mol-% PAA sample is comparable to that of pure PVA and, therefore, confirms the mechanical stability of the blend membranes. Significant changes in the peak areas and chemical shifts of the PVA hydroxyl signal (? = 4–5 ppm) in the 1H NMR spectra of the blend membranes confirm the strong hydrogen bonding between the OH groups of PVA and PAA. The ionic liquid (IL) 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) with 0.2 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added to the polymer blend to prepare flexible, nonvolatile hybrid polymer electrolytes for lithium-ion batteries. A maximum ionic conductivity of 1 mS?cm–1 is observed at 90 °C for the membrane with 70 mol-% IL. Mechanically stable polymer membranes for lithium-ion batteries consist of 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (PYR14TFSI) doped with 0.2 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

Posted on 11 November 2014 | 2:10 pm


Mechanistic Insights into Phenol Oxidation by a Copper(II) Complex of a Pyridine- and Amide-Containing Copolymer in an Aqueous Medium

A CuII complex of a pyridine- and amide-containing copolymer (Cu-P1) exhibits effective activity toward phenol hydroxylation in 50?% aqueous methanol solution at apparent pH 8.0 and 25 °C. The complex shows significant first-order rate accelerations of 4.2?×?105 and 1.4?×?105 relative to phenol autoxidation in air and in the presence of 20 mM H2O2, respectively. The reaction mechanisms with H2O2 and air are different on the basis of (a) the different activity profiles for Cu binding, (b) the different deuterium kinetic isotope effects (2.8 in 20 mM H2O2 and 1.2 aerobically), and (c) the formation of a dinuclear substrate–(Cu-P1) complex with H2O2 but a mononuclear one aerobically. The mechanism in the presence of H2O2 is consistent with that of the type-3 dicopper tyrosinase. Although oxidized di-CuII tyrosinase can only use H2O2 for phenol hydroxylation, CuII-P1 can use either air or H2O2 for this process. The studies herein introduce a versatile chemical system for the further exploration of Cu–oxygen chemistry and other types of metal-centered chemistry and for the aerobic degradation of aromatic compounds in environmental and green chemistry. A CuII complex of a pyridine- and amide-containing copolymer catalyzes phenol hydroxylation/oxidation in aqueous methanol at pH 8.0 and 25 °C. First-order rate accelerations by factors of 4.2?×?105 and 1.4?×?105 and deuterium kinetic isotope effects of 2.8 and 1.2, respectively, were observed with and without H2O2. The results suggest that different mechanisms apply for oxidation by O2 and H2O2.

Posted on 7 November 2014 | 11:40 am


Hydrolytic Stability and Hydrogen Peroxide Activation of Zirconium-Based Oxoclusters

The hydrolytic stability of [Zr6(OH)4O4{O(O)CC(CH3)=CH2}12] (Zr6), and [Zr6O4(OH)4{O(O)CCH2CH=CH2}12]2·6[CH2=CHCH2C(O)OH] (Zr12) oxoclusters in different environments was thoroughly investigated by FTIR, Raman, and X-ray photoelectron spectroscopy (XPS). Specific information about the local structures around the Zr centers during the stability tests was achieved by in situ extended X-ray absorption fine structure (EXAFS) measurements, and the exact compositions were determined by inductively coupled plasma MS (ICP-MS) and elemental analysis. By this multidimensional spectroscopic approach, an overview on the structures formed after different treatments could be gained. The stability of the oxoclusters was then investigated in the presence of hydrogen peroxide, and the formation of peroxo–metal complexes was detected. Thus, a kinetic study was performed in acetonitrile to evaluate the performances of the oxoclusters as oxygen transfer catalysts. The oxidation of methyl p-tolyl sulfide to the corresponding sulfoxide and sulfone was chosen as a model reaction; in some cases, an interesting selectivity towards the formation of the sulfone was found over more than 4700 catalytic cycles. The hydrolytic stability and reactivity of Zr6 and Zr12 oxoclusters are investigated by FTIR, Raman, and extended X-ray absorption fine structure (EXAFS) spectroscopy. The clusters are stable in water at neutral pH, and peroxo complexes are detected in the presence of hydrogen peroxide. A kinetic study highlights the catalytic potential of the clusters for the oxidation of methyl p-tolyl sulfide.

Posted on 6 November 2014 | 9:33 am


Synthetic Strategies for Variably Substituted Ruthenium–Imidazophenanthrolinium Complexes

The synthesis of several symmetric and asymmetric substituted imidazophenanthrolinium ligands and their corresponding ruthenium polypyridyl complexes was achieved by applying a newly designed synthetic concept. By testing different moieties, the advantages and limits of the synthetic approach could be defined. The substitution pattern on the imidazolium moiety has no significant influence on the structural aspects of the imidazophenanthrolinium backbone or on the photophysical properties of the ruthenium compounds. Given that imidazolium salts act as precursors for N-heterocyclic carbenes, the reported results provide the basis for the design of highly efficient oligonuclear photocatalysts. Different synthetic strategies are investigated for the synthesis of variably substituted ruthenium–imidazophenanthrolinium complexes. Structural and preliminary photochemical characterizations suggest that substitution patterns can be altered without influencing the photochemical properties.

Posted on 28 October 2014 | 10:11 pm


S = 2 Spin Ladders in the Sulfide Oxide BaFe2S2O

Pure powder and small single crystals of BaFe2S2O were obtained by solid-state reaction between BaO, Fe, and S in closed silica ampoules. The crystal structure contains a magnetic ladderlike sublattice of high-spin Fe2+ (d6) tetrahedrally coordinated by three S and one O atoms. Strong antiferromagnetic spin interactions are observed far above the Néel transition (TN = 260 K). 57Fe Mössbauer spectra show typical features of Fe2+ as a doublet with large quadrupole splitting above TN and combined electric and magnetic hyperfine interaction in the magnetically ordered phase. A structural transition upon the magnetic order is discussed. The sulfide oxide BaFe2S2O contains spin ladders of tetrahedrally coordinated high-spin Fe2+ (d6). The Fe ion is thereby surrounded by three S and one O atoms. Below the Néel transition (TN = 260 K), it is assumed that the crystal lattice distorts and the geometrical frustration between the spin ladders is cancelled.

Posted on 21 October 2014 | 10:10 am





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