First-row transition-metal complexes based on a carboxylate polychlorotriphenylmethyl radical: trends in metal-radical exchange interactions

We report the synthesis, crystal structures, and magnetic properties of a series of mononuclear, metal-radical complexes with first-row transition-metal ions using a new class of radical-based ligands, the polychlorinated triphenylmethyl (PTM) radicals. Crystal structures of three new PTM-based complexes of general formula M(PTMMC)2(py)4-x(H2O)x [PTMMC = PTM radical functionalized at the para position with one carboxylic group; M = Zn(II), x = 2 (1); M = Ni(II), x = 1 (2); M = Co(II), x = 1 (3)] show similar molecular structures in which mononuclear complexes are formed by an octahedral metal ion coordinated by two monodentated PTMMC units. From a magnetic point of view, these similar configurations describe a quasilinear, trimeric magnetic model (PTMMC-M(II)-PTMMC), in which the metal [Ni(II) or Co(II)]-radical magnetic-exchange coupling constants have been determined for the first time. In all of these complexes, the temperature dependence of the magnetic susceptibility reveals moderate antiferromagnetic-exchange coupling constants between the PTMMC radicals and Ni(II) (2J/kB = -47.1 K) and Co(II) ions (2J/kB = -15.2 K) based on the exchange Hamiltonian H = -2JSM(Srad1 + Srad2).     

Merging multiconfigurational wavefunctions and correlation functionals to predict magnetic coupling constants

We study the performance of different approaches that combine multiconfigurational wavefunctions with correlation functionals for the calculation of magnetic coupling constants of several materials and molecules. The systems under study include four antiferromagnetic materials: NiO, KNiF(3), K(2)NiF(4) and La(2)CuO(4); two biradicals: alpha-4-Dehydrotoluene and 1,1',5,5'-Tetramethyl-6,6'-dioxo-3,3'-biverdazyl; two molecular complexes: [Cu(2)Cl(6)](-2) and Copper(II) acetate monohidrate; and the prototypical H-He-H system. On average, the best results are obtained with a recently proposed method [Phys. Rev. A 75, 012503 (2007)] that estimates the correlation energy of density functionals from a pair of alternative spin densities built from the natural orbitals and occupation numbers of the multiconfigurational wavefunction.     

Different strategies for the preconcentration and separation of parabens by capillary electrophoresis

Several strategies, namely, large volume sample stacking (LVSS), field‐amplified sample injection (FASI), sweeping, and in‐line SPE‐CE, were investigated for the simultaneous separation and preconcentration of a group of parabens. A BGE consisting of 20 mM sodium dihydrogenphosphate (pH 2.28) and 150 mM SDS with 15% ACN was used for the separation and preconcentration of the compounds by sweeping, and a BGE consisting of 30 mM sodium borate (pH 9.5) was used for the separation and preconcentration of the compounds by LVSS, FASI, and in‐line SPE‐CE. Several factors affecting the preconcentration process were investigated in order to obtain the maximum enhancement of sensitivity. The LODs obtained for parabens were in the range of 18–27, 3–4, 2, and 0.01–0.02 ng/mL, and the sensitivity evaluated in terms of LODs was improved up to 29‐, 77‐, 120‐, and 18 400‐fold for sweeping, LVSS, FASI, and in‐line SPE‐CE, respectively. These preconcentration techniques showed potential as good strategies for focusing parabens. The four methods were validated with standard samples to show the potential of these techniques for future applications in real samples, such as biological and environmental samples.     

Determination of volatile organic compounds in industrial wastewater plant air emissions by multi-sorbent adsorption and thermal desorption-gas chromatography-mass spectrometry

This paper describes the process of determining the presence of volatile organic compounds in air emissions from industrial wastewater treatment plants (WWTP). The analytical method, based on thermal desorption-gas chromatography-mass spectrometry, was developed to simultaneously determine of 99 volatile organic compounds (VOCs) in air samples. This method is rapid, environmentally-friendly (since no organic solvents are used to extract the analytes) and compatible with a large range of thermally stable polar and apolar compounds. The target VOCs were selected on the basis of their occurrence in real samples and their adverse effects on the environment and human health. To cover the wide range of target compounds, multisorbent tubes filled with Tenax TA and Carbograph 1TD were used. Method validation showed good repeatabilities, low detection limits, a high linear range and good recoveries. At a fixed sample volume of 600?mL no significant losses for any of the target compounds were found in the samples. Stability during storage indicated that samples must be keep refrigerated at 4°C and analysed within three days of collection. Real samples were taken from air emissions of an industrial wastewater treatment plant located in the Southern Industrial Area of Tarragona (Spain) with the aim of studying its contribution as a source of atmospheric VOCs. This WWTP collects wastewater from several chemical factories which produce isocyanates, polyurethanes, chlorinated organics and functional chemicals among other products. Samples from the collecting tank after the primary sedimentation showed higher VOC concentrations than samples from the secondary treatment tank. The most abundant VOCs found in these emissions are included in the USEPA List of Hazardous Air Pollutants. The highest values correspond to acrylonitrile (up to 1843?µg?m^?3) and styrene (up to 573.70?µg?m^?3). The levels of chloroform, 1,4-dioxane, ethylbenzene, 1,2,3-trimethylbenzene and 1,4-diethylbenzene were also high.     

A Versatile Methodology for the Controlled Synthesis of Photoluminescent High‐Boron‐Content Dendrimers

Fluorescent star‐shaped molecules and dendrimers with a 1,3,5‐triphenylbenzene moiety as the core and 3 or 9 carborane derivatives at the periphery, have been prepared in very good yields by following different approaches. One procedure relies on the nucleophilic substitution of Br groups in 1,3,5‐tris(4‐(3‐bromopropoxy)phenyl)benzene with the monolithium salts of methyl and phenyl‐o‐carborane. The second method is the hydrosilylation reactions on the peripheral allyl ether functions of 1,3,5‐tris(4‐allyloxy‐phenyl)benzene and 1,3,5‐tris(4‐(3,4,5‐trisallyloxybenzyloxy)phenyl)benzene with suitable carboranyl‐silanes to produce different generations of dendrimers decorated with carboranyl fragments. This approach is very versatile and allows one to introduce long spacers between the fluorescent cores and the boron clusters, as well as to obtain a high loading of boron clusters. The removal of one boron atom from each cluster leads to high‐boron‐content water‐soluble macromolecules. Thermogravimetric analyses show a higher thermal stability for the three‐functionalized compounds than for those containing 9 clusters. All compounds exhibit photoluminescent properties at room temperature under ultraviolet irradiation with high quantum yields; these depend on the nature of the cluster and the substituent on the C_cluster. Cyclic voltammetry indicates that there is no electronic communication between the core and the peripheral carboranyl fragments. Due to the high boron content of these molecules, we currently focus our research on their biocompatibility, biodistribution in cells cultures, and potential applications for boron neutron capture therapy (BNCT).     

Design of dinuclear copper species with carboranylcarboxylate ligands: study of their steric and electronic effects

A series of new mononuclear and carboranylcarboxylate‐bridged dinuclear copper(II) compounds containing the 1‐CH₃‐2‐CO₂H‐1,2‐closo‐C₂B₁₀H₁₀ carborane ligand ( L H) has been synthesized. Reaction of different copper salts with L H at room temperature leads to dinuclear compounds of the general formula [Cu₂(μ‐ L )₄( L_t )₂] ( L_t =thf ( 1 ), L_t =H₂O ( 1′ )). The reaction of 1 and 1′ with different terminal pyridyl (py) ligands leads to the formation of a series of structurally analogous complexes by substitution of the terminal ligand thf or H₂O ( L_t =py ( 2 ), p‐CF₃‐py ( 3 ), p‐CH₃‐py ( 4 ), pz ( 6 ), and 4,4′‐bpy ( 7 )), which maintain the structural Cu₂(μ‐O₂CR)₄ core in the majority of the cases except for o‐(CH₃)₂‐py, where a mononuclear compound ( 5 ) is exclusively obtained. These compounds have been characterized through analytical, spectroscopic (NMR, IR, UV‐visible, ESI‐MS) and magnetic techniques. X‐ray structural analysis revealed a paddle‐wheel structure for the dinuclear compounds, with a square‐pyramidal geometry around each copper ion and the carboranylcarboxylate ions bridging two copper atoms in syn–syn mode. The mononuclear complex obtained with the o‐(CH₃)₂‐py ligand presents a square‐planar structure, in which the carboranylcarboxylate ligand adopts a monodentate coordination mode. The magnetic properties of the dinuclear compounds 1 , 3 , 4 , and 6 show a strong antiferromagnetic coupling in all cases (J=?261 ( 1 ), ?255 ( 3 ), ?241 ( 4 ), ?249 cm^?1 ( 6 )). Computational studies based on hybrid density functional methods have been used to study the magnetic properties of the complexes and also to evaluate their relative stability on the basis of the strength of the bond between each Cu^II and the terminal ligand.     

Uncommon coordination behaviour of P(S) and P(Se) units when bonded to carboranyl clusters: experimental and computational studies on the oxidation of carboranyl phosphine ligands

Oxidation of closo-carboranyl diphosphines 1,2-(PR(2))(2)-1,2-closo-C(2)B(10)H(10) (R=Ph, iPr) and closo-carboranyl monophosphines 1-PR(2)-2-R'-1,2-closo-C(2)B(10)H(10) (R=Ph, iPr, Cy; R'=Me, Ph) with hydrogen peroxide, sulfur and elemental black selenium evidences the unique capacity of the closo-carborane cluster to produce uncommon or unprecedented P/P(E) (E=S, Se) and P=O/P=S chelating ligands. When H(2)O(2) reacts with 1,2-(PR(2))(2)-1,2-closo-C(2)B(10)H(10) (R=Ph, iPr), they are oxidized to 1,2-(OPR(2))(2)-1,2-closo-C(2)B(10)H(10) (R=Ph, iPr). However, when S and Se are used, different reactivity is found for 1,2-(PPh(2))(2)-1,2-closo-C(2)B(10)H(10) and 1,2-(PiPr(2))(2)-1,2-closo-C(2)B(10)H(10). The reaction with sulfur produces mono- and dioxidation products for R=Ph, whereas Se produces the mono-oxidation product only. For R=iPr, only monooxidation takes place with S, and the second C(c)-PiPr(2) bond breaks to yield 1-SPiPr(2)-1,2-closo-C(2)B(10)H(11). When Se is used, only 1-SePiPr(2)-1,2-closo-C(2)B(10)H(11) is formed. The potential of the mono-chalcogenide carboranyl diphosphines 1-EPPh(2)-2-PPh(2)-1,2-closo-C(2)B(10)H(10) (E=S, 9; Se, 15) to behave as unsymmetric chelating bidentate ligands was studied for different metal complexes, different solvents and in the solid state. Dechalcogenation takes place in each case. Computational studies provided information on the P=E (E=S, Se) bonds. Steric effects block the bonding ability of the P=E group due to interactions between the chalcogen and the neighbouring hydrogen atoms (three from the phenyl rings and one from the carborane cluster). The electronic effects originate from the strongly electron-withdrawing character of the closo carborane cluster, which polarizes the P=E (E=S, Se) bond towards the phosphorus atom. As a consequence, the E atom is the electron-poor site and the P atom the electron-rich site in the P=E bond.     

A trinuclear copper(II) cryptate and its μ3-CO3 cascade complex: thermodynamics, structural and magnetic properties

The 2,4,6-triethylbenzene-capped hexaamine macrobicycle with pyridyl spacers (pyr) was able to coordinate three copper(II) ions within its cavity. Potentiometric studies performed at 298.2 K in MeOH/H(2)O (50:50 v/v) and at ionic strength 0.10 mol dm(-3) in KNO(3) revealed that trinuclear species predominate in solution from pH 5.0, the hydroxo complexes being the main species, which start forming at unusual very low pH values. The single-crystal X-ray determination of the trinuclear complex showed that the three copper centres have square-planar geometry, arranged in an almost equilateral triangle, and have carbonate bridging the three metal centres. The presence of carbonate resulted from fixation of atmospheric CO(2). The present study represents the first μ(3)-CO(3)-bridged trinuclear copper(II) complex located in the interior of a macrobicyclic cavity. The magnetic data of [Cu(3)(pyr)(μ(3)-CO(3))]·(ClO(4))(4) showed ferromagnetic intramolecular interactions [J=3.80 cm(-1), based on the Hamiltonian H=-J(S(1)S(2)+S(2)S(3)+S(1)S(3))] yielding a spin quartet, S=3/2, ground state. Density functional calculations on the experimental geometry of the trinuclear complex showed that the ferromagnetic nature of the magnetic coupling can be attributed to the syn-anti conformation of the carbonato bridge, and a magneto-structural correlation, based on the different conformations (syn-anti, syn-syn and anti-anti), is presented. The interesting properties observed, namely the lowering of the pK(a) of coordinated water molecules to unusual values and the good fit of the carbonate anion between the copper centres, derive from the special architecture of pyr.     

Determination of Organophosphate Ester Metabolites in Seafood Species by QuEChERS-SPE Followed by LC-HRMS

Organophosphate triesters are compounds widely used in industries and are ubiquitous in the environment, where they can be transformed into organophosphate diesters. Some organophosphate diesters are also used by industry. Several studies suggest organophosphate diesters can have toxic effects for reproduction, and hazardous and mutagenic properties. Due to the impact these compounds can have on marine biota and human beings through the consumption of fish and shellfish, it is necessary to study their presence in widely consumed seafood species. We therefore developed an analytical method for determining six of the most common organophosphate diesters in seafood. The procedure is based on the Quick, Easy, Cheap, Effective, Rugged and Safe extraction method and a solid phase extraction clean-up, followed by liquid chromatography coupled to high-resolution mass spectrometry. The method was optimised and validated for seafood with different lipid content, providing satisfactory relative recoveries (from 89 to 138%) and limits of detection (1.0–50 ng g⁻¹ dry weight), as well as repeatability values (RSD% (n = 5, 100 ng g⁻¹ (dry weight)) lower than 15%. Eight seafood species were analysed using this method and two organophosphate diesters were detected and quantified in all the samples, demonstrating the suitability of the method.