A novel Ni(4) complex exhibiting microsecond quantum tunneling of the magnetization

A highly asymmetric Ni(II) cluster [Ni(4)(OH)(OMe)(3)(Hphpz)(4)(MeOH)(3)](MeOH) (1) (H(2)phpz=3-methyl-5-(2-hydroxyphenyl)pyrazole) has been prepared and its structure determined by means of single-crystal X-ray diffraction by using synchrotron radiation. Variable-temperature bulk-magnetization measurements show that the complex exhibits intramolecular-ferromagnetic interactions leading to a spin ground state S=4 with close-lying excited states. Magnetization and high-frequency EPR measurements suggest the presence of sizable Ising-type magnetic anisotropy, with zero-field splitting parameters D=-0.263 cm(-1) and E=0.04 cm(-1) for the spin ground state, and an isotropic g value of 2.25. The presence of both axial and transverse anisotropy was confirmed through low-temperature specific heat determinations down to 300 mK, but no slow relaxation of the magnetization was observed by AC measurements down to 1.8 K. Interestingly, AC susceptibility measurements down to temperatures as low as 23 mK showed no indication of slow relaxation of the magnetization in 1. Thus, despite the presence of an anisotropy barrier (U approximately 4.21 cm(-1) for the purely axial limit), the magnetization relaxation remains extremely fast down to the lowest temperatures. The estimated quantum tunneling rate, Gamma>0.667 MHz, makes this complex a prime candidate for observation of coherent tunneling of the magnetization.     

Direct observation of the primary bond-twisting dynamics of stilbene anion radical

The anion radicals of stilbenes in the collisionless isolated phase were synthesized by electron attachment, and their dynamics were observed in real time on the femtosecond time scale. The observed coherent vibrational motion (approximately 42 cm(-1)) and the primary bond-twisting dynamics (approximately 650 fs) for the D2 state are on a vastly different time scale from that reported (approximately 10 ns) in solution.     

Synthesis, structural characterization, and ligand replacement reactions of gem-dithiolato-bridged rhodium and iridium complexes

The reaction of gem-dithiol compounds R 2C(SH) 2 (R = Bn (benzyl), (i) Pr; R 2 = -(CH 2) 4-) with dinuclear rhodium or iridium complexes containing basic ligands such as [M(mu-OH)(cod)] 2 and [M(mu-OMe)(cod)] 2, or the mononuclear [M(acac)(cod)] (M = Rh, Ir, cod = 1,5-cyclooctadiene) in the presence of a external base, afforded the dinuclear complexes [M 2(mu-S 2CR 2)(cod) 2] ( 1- 4). The monodeprotonation of 1,1-dimercaptocyclopentane gave the mononuclear complex [Rh(HS 2Cptn)(cod)] ( 5) that is a precursor for the dinuclear compound [Rh 2(mu-S 2Cptn)(cod) 2] ( 6). Carbonylation of the diolefin compounds gave the complexes [Rh 2(mu-S 2CR 2)(CO) 4] ( 7- 9), which reacted with P-donor ligands to stereoselectively produce the trans isomer of the disubstituted complexes [Rh 2(mu-S 2CR 2)(CO) 2(PR' 3) 2] (R' = Ph, Cy (cyclohexyl)) ( 10- 13) and [Rh 2(mu-S 2CBn 2)(CO) 2{P(OR') 3} 2] (R' = Me, Ph) ( 14- 15). The substitution process in [Rh 2(mu-S 2CBn 2)(CO) 4] ( 7) by P(OMe) 3 has been studied by spectroscopic means and the full series of substituted complexes [Rh 2(mu-S 2CBn 2)(CO) 4- n {P(OR) 3} n ] ( n = 1, 4) has been identified in solution. The cis complex [Rh 2(mu-S 2CBn 2)(CO) 2(mu-dppb)] ( 16) was obtained by reaction of 7 with the diphosphine dppb (1,4-bis(diphenylphosphino)butane). The molecular structures of the diolefinic dinuclear complexes [Rh 2(mu-S 2CR 2)(cod) 2] (R = Bn ( 1), (i) Pr ( 2); R 2 = -(CH 2) 4- ( 6)) and that of the cis complex 16 have been studied by X-ray diffraction.     

Versatile scorpionates and new developments in the denticity changes of NNCp hybrid scorpionate/cyclopentadienyl ligands in Sc and Y compounds: from kappa1-Neta5-Cp to kappa2-NNeta5-Cp

Reaction of hybrid scorpionate/cyclopentadienyl ligands in the form of the lithium derivatives [Li(bpzcp)(THF)] [bpzcp=2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethylcyclopentadienyl], [Li(bpztcp)(THF)] [bpztcp=2,2-bis(3,5-dimethylpyrazol-1-yl)-1-tert-butylethylcyclopentadienyl], and the in situ-generated "Li(bpzpcp)" [bpzpcp=2,2-bis(3,5-dimethylpyrazol-1-yl)-1-phenylethylcyclopentadienyl] with MCl3(THF)3 afforded the group 3 halide compounds [MCl2(bpzcp)(THF)] (M=Sc, 1; Y, 2), [MCl2(bpztcp)(THF)] (M=Sc, 3; Y, 4), and [MCl2(bpzpcp)(THF)] (M=Sc, 5; Y, 6). The H2O adduct of 4, [YCl2(bpztcp)(H2O)] (7), was formed when a solution of 4 was allowed to stand at room temperature in the presence of moisture. Complexes 1-7 adopt a pseudo-octahedral structure with heteroscorpionate ligands kappa2-NNeta5-Cp coordinated to the metal through the cyclopentadienyl group and two imino nitrogens of pyrazole rings. The alkyl heteroscorpionate scandium and yttrium complexes recently reported by our group, [M(CH2SiMe3)2(bpzcp)], react with 2,6-dimethylphenol and 3,5-dimethylphenol to give the bis(aryloxide) derivatives [M(OAr)2(bpzcp)] (M=Sc, OAr=2,6-dimethylphenoxide, 8; M=Y, OAr=2,6-dimethylphenoxide, 9; M=Y, OAr=3,5-dimethylphenoxide, 10). Complex 9 underwent an interesting hydrolysis process to give the tetranuclear complex [{Y(bpzcp)}(micro-OH)2(micro3-OH){Y(OAr)2}]2 (11). Variable-temperature 1H NMR experiments on 9 and 10 revealed a rapid fluxional exchange between coordinated and noncoordinated pyrazolyl rings, producing interconversion between the two enantiomers in which the scorpionate ligand can be coordinated in a kappa1-Neta5-Cp form. The structures of the complexes were determined by spectroscopic methods and the X-ray crystal structures of 2, 7, and 11 were also established. Complexes 1 and 2 are active olefin polymerization catalysts after activation with methylaluminoxane. These compounds gave atactic polystyrenes with narrow molecular weight distribution (Mn/Mw 1.26-1.91) and with low molecular weights.     

Continuum percolation of long lifespan clusters in a simple fluid

We present results on the percolation loci for chemical clusters and physical clusters of long lifespan. Chemical clusters are defined as sets of particles connected through particle-particle bonds that last for a given time tau. Physical clusters are sets of particles that remain close together at every instant for a given period of time tau. By using molecular dynamics simulations of a Lennard-Jones system we obtain the percolation loci at different values of tau as the lines in the temperature-density plane at which the system presents a spanning cluster in 50% of the configurations. We find that the percolation loci for chemical clusters shifts rapidly toward high densities as tau is increased. For moderate values of tau this line converges to the low-density branch of the liquid-solid coexistence curve. This implies that no stable chemical clusters can be found in the fluid phase. In contrast, the percolation loci for physical clusters tend to a limiting line, as tau tends to infinity, which is far from the liquid-solid transition line.     

NHC-Adducts of Cyclopentadienyl-Substituted Alanes

The mono- and bis-iodo-substituted NHC-stabilized alanes (NHC) ⋅ AlH₂I and (NHC) ⋅ AlHI₂ offer a convenient entry for further substitution reactions at aluminum. Reactions of (NHC) ⋅ AlH₂I 1 – 4 with one equivalent of NaCp afforded the adducts (NHC) ⋅ AlH₂Cp 9 – 12 (NHC=Me₂Im^Me ( 9 ), iPr₂Im^Me ( 10 ), iPr₂Im ( 11 ), Dipp₂Im ( 12 )). Alane adducts with two Cp substituents (NHC) ⋅ AlHCp₂ 13 – 16 (NHC=Me₂Im^Me ( 13 ), iPr₂Im^Me ( 14 ), iPr₂Im ( 15 ), Dipp₂Im ( 16 )) were prepared by the analogous reaction of (NHC) ⋅ AlHI₂ 5 – 8 using two equivalents of NaCp. The unusual dimeric adducts ((NHC) ⋅ AlH₂Cp ⋅ CpMgI)₂ 17 – 19 (NHC=Me₂Im^Me ( 17 ), iPr₂Im^Me ( 18 ), iPr₂Im ( 19 )) were obtained from the reaction of 1 – 3 with MgCp₂.     

Ionic liquids versus ionic liquid-based surfactants in dispersive liquid–liquid microextraction for determining copper in water by flame atomic absorption spectrometry

This work compares the performance of dispersive liquid–liquid method (DLLME) as a prior step for determining copper by flame atomic absorption spectrometry (FAAS), when using the ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate (C₄MIm-PF₆) or the IL-based surfactant 1-hexadecyl-3-butylimidazolium bromide (C₁₆C₄Im-Br) as extractant solvents. For the water-insoluble C₄MIm-PF₆, the most conventional DLLME mode using acetonitrile as dispersive solvent was employed. For the water-soluble C₁₆C₄Im-Br, the in situ DLLME mode with lithium bis[(trifluoromethane)sulfonyl]imide (Li-NTf₂) as metathesis reagent was employed. In both approaches, some effective parameters such as volumes of extractant and dispersive solvents, concentration of complexing agent, pH of sample solution, salting-out effect and final diluting solvent to ensure compatibility with FAAS, were properly optimised. The optimum conditions for the IL-DLLME method using C₄MIm-PF₆ were: 100 μL of neat C₄MIm-PF₆, 1 mL of acetonitrile, 10 mL of water, no control of pH for environmental waters, NaCl content of 23 g L^?1, diethyl dithiocarbamate (DDTC) as complexing agent at 10 mg L^?1 and final dilution of the micro-droplet with acetonitrile up to 70 µL. The optimum conditions for the in situ IL-DLLME method using C₁₆C₄Im-Br were: 0.8 mL of acetonitrile, 10 mL of water containing C₁₆C₄Im-Br at 25.2 mmol L^?1, final dilution step of the micro-droplet with 200 µL of acetonitrile and remaining conditions as those of C₄MIm-PF₆. The analytical performance of both methods was similar, being slightly better for the IL-DLLME method using C₄MIm-PF₆, with limits of detection (LOD) of 3.3 µg L^?1 (versus 5.1 µg L^?1 when using C₁₆C₄Im-Br), precision values as intraday relative standard deviation (RSD in %) lower than 8.8% (being of 10% for the C₁₆C₄Im-Br method) and an enrichment factor of 54 (being 27 when using C₁₆C₄Im-Br). The DLLME-FAAS method with C₄MIm-PF₆ was used in the analysis of environmental waters with successful performance, with relative recoveries of 110% and 105%, and interday precision with RSD values of 21% and 7.4% for spiked levels of 60 and 160 µg L^?1, respectively. The results obtained when analysing an urban wastewater sample coming from an inter-laboratory exercise was comparable to those obtained for other 93 laboratories. The method was also valid for the determination of Cu²⁺ in presence of foreign ions commonly found in natural waters.     

Fensterbierscheiben in the Pena National Palace collection – chemical and iconographic relations

The stained‐glass collection from the Pena National Palace (Sintra, Portugal) includes around 130 ‘rural panels’, also known as Fensterbierscheiben, that were produced between the 16th and 19th centuries. The aim of this investigation is to characterise the glass composition of this collection of Fensterbierscheiben and relate it with the iconographic research made on these panels, in order to establish possible provenance of production. This is the first study on Fensterbierscheiben, where the chemical information of the glass is considered and related with historical information. The micro‐energy dispersive X‐ray fluorescence allowed performing non‐invasive analysis, mostly performed in situ. Micro‐particle‐induced X‐ray emission analysis was performed on the cross section of a small group of fragmented panels for obtaining quantitative chemical composition of the glass. Through the analysis of the colourless glass, and the comparison of micro‐energy dispersive X‐ray fluorescence and micro‐particle‐induced X‐ray emission data, it was concluded that the majority of the panes have a high lime low alkali glass composition. Furthermore, the Fensterbierscheiben panes form a cohesive group in terms of composition, suggesting that they were all manufactured with raw materials from the same region. This study also allowed one to observe the chronological evolution in terms of treatments applied to the used raw materials. Copyright © 2016 John Wiley & Sons, Ltd.     

Relative Gorenstein Dimensions

In the last years (Gorenstein) homological dimensions relative to a semidualizing module C have been subject of several works as interesting extensions of (Gorenstein) homological dimensions. In this paper, we extend to the noncommutative case the concepts of G _C -projective module and dimension, weakening the condition of C being semidualizing as well. We prove that indeed they share the principal properties of the classical ones and relate this new dimension with the classical Gorenstein projective dimension of a module. The dual concepts of G _C -injective modules and dimension are also treated. Finally, we show some interesting interactions between the class of G _C -projective modules and the Bass class associated to C on one side, and the class of G\({_{C^{\vee}}}\) -injective modules (C ^∨ = Hom _R (C, E) where E is an injective cogenerator in R-Mod) and the Auslander class associated to C in the other.     

Magnetic ionic liquids as non-conventional extraction solvents for the determination of polycyclic aromatic hydrocarbons

This work describes the applicability of magnetic ionic liquids (MILs) in the analytical determination of a group of heavy polycyclic aromatic hydrocarbons. Three different MILs, namely, benzyltrioctylammonium bromotrichloroferrate (III) (MIL A), methoxybenzyltrioctylammonium bromotrichloroferrate (III) (MIL B), and 1,12-di(3-benzylbenzimidazolium) dodecane bis[(trifluoromethyl)sulfonyl)]imide bromotrichloroferrate (III) (MIL C), were designed to exhibit hydrophobic properties, and their performance examined in a microextraction method for hydrophobic analytes. The magnet-assisted approach with these MILs was performed in combination with high performance liquid chromatography and fluorescence detection. The study of the extraction performance showed that MIL A was the most suitable solvent for the extraction of polycyclic aromatic hydrocarbons and under optimum conditions the fast extraction step required ∼20 μL of MIL A for 10 mL of aqueous sample, 24 mmol L⁻¹ NaOH, high ionic strength content of NaCl (25% (w/v)), 500 μL of acetone as dispersive solvent, and 5 min of vortex. The desorption step required the aid of an external magnetic field with a strong NdFeB magnet (the separation requires few seconds), two back-extraction steps for polycyclic aromatic hydrocarbons retained in the MIL droplet with n-hexane, evaporation and reconstitution with acetonitrile. The overall method presented limits of detection down to 5 ng L⁻¹, relative recoveries ranging from 91.5 to 119%, and inter-day reproducibility values (expressed as relative standard derivation) lower than 16.4% for a spiked level of 0.4 μg L⁻¹ (n = 9). The method was also applied for the analysis of real samples, including tap water, wastewater, and tea infusion.