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Rocio-Bautista P.,University of La Laguna | Gonzalez-Hernandez P.,University of La Laguna | Pino V.,University of La Laguna | Pasan J.,University of La Laguna | And 2 more authors.
TrAC - Trends in Analytical Chemistry | Year: 2017

This review provides a critical overview on the current state of the use of MOFs as sorbents in dispersive-based microextraction methods, not only classifying the different MOFs used in these methods and highlighting the advantages of these materials in terms of stability, analytical performance, and reuse in some cases; but also insightfully describing the analytical applications reported. A description of the current methods described in literature to prepare bare MOFs, hybrid/functionalized MOFs, and different magnetic composites based on MOF, is also included. © 2017 Elsevier B.V.

Gonzalez J.,Institute Ciencia Molecular ICMOL | Llinares J.M.,Institute Ciencia Molecular ICMOL | Belda R.,Institute Ciencia Molecular ICMOL | Pitarch J.,Institute Ciencia Molecular ICMOL | And 3 more authors.
Organic and Biomolecular Chemistry | Year: 2010

The synthesis of two new tritopic double-scorpiand receptors in which two equivalent 5-(2-aminoethyl)-2,5,8-triaza[9]-(2,6)-pyridinophane moieties have been linked with 2,6-dimethylpyridine (L1) or 2,9-dimethylphenanthroline (L2) units is reported for the first time. Their acid-base behaviour and Zn 2+ coordination chemistry have been studied by pH-metric titrations, molecular dynamic calculations, NMR, UV-Vis and steady-state fluorescence techniques. L1 and L2 behave, respectively, as hexaprotic and heptaprotic bases in the experimental conditions used (298.1 ± 0.1 K, 0.15 mol dm -3 NaCl, pH range under study 2.0-11.0). These ligands are able to form mono-, bi- and trinuclear Zn2+ complexes depending on the Zn2+-receptor molar ratio. Interaction of L1 and L2 with pyrophosphate (PPi), tripolyphosphate (TPP) and adenosine 5′-triphosphate (ATP) has been followed by pH-metric titrations, 1H and 31P NMR techniques and molecular dynamic analysis. Finally, formation of mixed complexes Zn2+-L-PPi, Zn2+-L-TPP and Zn 2+-L-ATP has been studied for both receptors by potentiometric titrations. © 2010 The Royal Society of Chemistry.

Deniz M.,University of La Laguna | Hernandez-Rodriguez I.,University of La Laguna | Pasan J.,University of La Laguna | Fabelo O.,University of Zaragoza | And 6 more authors.
CrystEngComm | Year: 2014

Five new manganese(ii)-based complexes of general formula [Mn(Rmal)(H 2O)]n with Rmal = methylmalonate (Memal) (1), dimethylmalonate (Me2mal) (2), diethylmalonate (Et2mal) (3), butylmalonate (Butmal) (4) and benzylmalonate (Bzmal) (5) were synthesized and their structures characterized by single crystal X-ray diffraction. 1 and 2 are three-dimensional compounds whereas 3-5 exhibit two-dimensional networks. The structure of 1 consists of chains of μ-κO:κO bridged aquamanganese(ii) ions which are interlinked through anti-anti carboxylate bridges. The structure of 2 is built by double μ-κO:κO bridged bis[aquamanganese(ii)] entities which are linked to six other dimanganese(ii) units through oxo- and anti-syn carboxylate bridges. These dinuclear entities also occur in 4 and 5. They are interconnected by anti-anti and anti-syn carboxylate bridges to four other units, leading to neutral layered structures. Finally, compound 3 consists of aqua-bridged chains of manganese(ii) ions connected through tetrakis(monodentate) Et2mal ligands leading to a sheet-like structure. The topological representation of the crystal structures shows the of four different nets: (10,3)-d utp (1), 6-connected crs (2), gek2 (3) and the square-grid sql topology (4-5). The magnetic properties of 1-5 were investigated in the temperature range 2.0-300 K. Overall antiferromagnetic behavior occurs in 1, 2, 4 and 5 with susceptibility maxima in the range 3.6-17.0 K. Compound 3 exhibits an overall antiferromagnetic behaviour in the high temperature range with a weak spin canting in the low temperature domain and magnetic ordering below ca. 32 K. This journal is © 2014 The Royal Society of Chemistry.

Rocio-Bautista P.,University of La Laguna | Pacheco-Fernandez I.,University of La Laguna | Pasan J.,University of La Laguna | Pasan J.,Institute Ciencia Molecular ICMol | Pino V.,University of La Laguna
Analytica Chimica Acta | Year: 2016

Solid-phase microextraction (SPME) is a powerful technique commonly used in sample preparation for extraction/preconcentration of analytes from a wide variety of samples. Among the trends in improving SPME applications, current investigations are focused on the development of novel coatings able to improve the extraction efficiency, sensitivity, and thermal and mechanical stability, within other properties, of current commercial SPME fibers. Metal-organic frameworks (MOFs) merit to be highlighted as promising sorbent materials in SPME schemes. MOFs are porous hybrid materials composed by metal ions and organic linkers, presenting the highest surface areas known, with ease synthesis and high tuneability, together with adequate chemical and thermal stability. For MOF based-SPME fibers, it results important to pretreat adequately the SPME supports to ensure the correct formation of the MOF onto the fiber or the attachment MOF-support. This, in turn, will increase the final stability of the fiber while generating uniform coatings. This review provides a critical overview of the current state of the use of MOFs as SPME coatings, not only highlighting the advantages of these materials versus commercial SPME coatings in terms of stability, selectivity, and sensitivity; but also insightfully describing the current methods to obtain reproducible MOF-based SPME coatings. © 2016 Elsevier B.V.

Deniz M.,University of La Laguna | Hernandez-Rodriguez I.,University of La Laguna | Pasan J.,University of La Laguna | Fabelo O.,University of La Laguna | And 9 more authors.
Crystal Growth and Design | Year: 2012

Six new manganese(II) complexes of formulas [Mn 2(Rmal) 2(H 2O) 2(azpy)] n (1-3), [Mn(Phmal)(H 2O)(azpy)] n (4), [Mn 2(Et 2mal) 2(H 2O) 4(azpy) 2] n (5), and [Mn(Bzmal)(H 2O) 3(azpy)] (6) [azpy = 4,4′-azobispyridine (1-6), Rmal = methylmalonate (Memal) (1), dimethylmalonate (Me 2mal) (2), and butylmalonate (Butmal) (3), Phmal = phenylmalonate (4), Et 2mal = diethylmalonate (5), and Bzmal = benzylmalonate (6)] were synthesized and structurally characterized by single-crystal X-ray diffraction. Complexes 1-3 are three-dimensional compounds whose structure consists of corrugated layers of manganese(II) linked through syn-anti carboxylate (Rmal) bridges, which are pillared through the bis-monodentate azpy molecule. Complex 4 has a layered structure of manganese(II) ions connected by carboxylate (Phmal) bridges in the syn-anti coordination mode as in 1-3, the azpy group acting here as a terminally bound monodentate ligand. The structure of 5 consists of Et 2mal-Mn(II) neutral chains linked through the azpy ligand, giving rise to a complex three-dimensional network. Complex 6 is constituted by neutral [Mn(Bzmal)(H 2O) 3(azpy)] mononuclear units, which are interlinked through O-H•••O, O-H•••N, and π-π type intermolecular interactions to afford a three-dimensional supramolecular structure. The topological analysis of these crystallographic structures shows the occurrence of four different nets: a (3,4)-connected InS-type (1-3), a binodal layered hcb (4), a uninodal CdS-type (5), and a (4,5)-connected tcs topology (6). The magnetic properties of 1-5 were investigated in the 2.0-300 K temperature range. Overall antiferromagnetic behavior occurs in 1-4 with susceptibility maxima in the range 2.8-5.5 K, the exchange pathway being provided by the syn-anti carboxylate (substituted malonate) bridge [manganese-manganese separation in the range 5.4365(3)-5.5274(1) Å]. Very weak antiferromagnetic interactions are observed in 5 through the trans-bis-monodentate Et 2mal ligand, the intrachain manganese-manganese separation being 7.328(3) Å. The much larger manganese-manganese separation through the bis-monodentate azpy ligand in 1-5 (values greater than 13.5 Å) accounts for the lack of any significant magnetic interaction though this extended bridge. © 2012 American Chemical Society.

Nastase S.,University of Bucharest | Maxim C.,University of Bucharest | Andruh M.,University of Bucharest | Cano J.,Institute Ciencia Molecular ICMol | And 5 more authors.
Dalton Transactions | Year: 2011

Three MnIII-MIII (M = Cr and Fe) dinuclear complexes have been obtained by assembling [MnIII(SB)(H2O)] + and [MIII(AA)(CN)4]- ions, where SB is the dianion of the Schiff-base resulting from the condensation of 3-methoxysalicylaldehyde with ethylenediamine (3-MeOsalen2-) or 1,2-cyclohexanediamine (3-MeOsalcyen2-): [Mn(3-MeOsalen)(H 2O)(-NC)Cr(bipy)(CN)3]·2H2O (1), [Mn(3-MeOsalen)(H2O)(-NC)Cr(ampy)(CN)3][Mn(3-MeOsalen) (H2O)2]ClO4·2H2O (2) and [Mn(3-MeOsalcyen)(H2O)(-NC)Fe(bpym)(CN)3]·3H 2O (3) (bipy = 2,2′-bipyridine, ampy = 2-aminomethylpyridine and bpym = 2,2′-bipyrimidine). The [M(AA)(CN)4]- unit in 1-3 acts as a monodentate ligand towards the manganese(iii) ion through one of its four cyanide groups. The manganese(iii) ion in 1-3 exhibits an elongated octahedral stereochemistry with the tetradentate SB building the equatorial plane and a water molecule and a cyanide-nitrogen atom filling the axial positions. Remarkably, the neutral mononuclear complex [Mn(3-MeOsalen)(H2O)2]ClO4 co-crystallizes with the heterobimetallic unit in 2. The values of the MnIII-M III distance across the bridging cyanide are 5.228 (1), 5.505 (2) and 5.265 Å (3). The packing of the neutral heterobimetallic units in the crystal is governed by the self-complementarity of the [Mn(SB)(H 2O)]+ moieties, which interact each other through hydrogen bonds established between the aqua ligand from one fragment with the set of phenolate- and methoxy-oxygens from the adjacent one. The magnetic properties of the three complexes have been investigated in the temperature range 1.9-300 K. Weak antiferromagnetic interactions between the MnIII and M III ions across the cyanido bridge were found: JMnM = -5.6 (1), -0.63 (2) and -2.4 cm-1 (3) the Hamiltonian being defined as H = -JSMn·SM. Theoretical calculations based on density functional theory (DFT) have been used to substantiate both the nature and magnitude of the exchange interactions observed and also to analyze the dependence of the magnetic coupling on the structural parameters within the MnIII-N-C-MIII motif in 1-3. © 2011 The Royal Society of Chemistry.

Inglis R.,University of Edinburgh | Houton E.,University Road | Liu J.,Florida State University | Liu J.,University of Florida | And 7 more authors.
Dalton Transactions | Year: 2011

The serendipitous self-assembly of the complex [Mn III 2Zn II 2(Ph-sao) 2(Ph-saoH) 4(hmp) 2] (1),whose magnetic core consists solely of two symmetry equivalent Mn(iii) ions linked by two symmetry equivalent -N-O- moieties, provides a relatively simple model complex with which to study the magneto-structural relationship in oxime-bridged Mn(iii) cluster compounds. Dc magnetic susceptibility measurements reveal ferromagnetic (J = +2.2 cm -1) exchange resulting in an S = 4 ground state. Magnetisation measurements performed at low temperatures and high fields reveal the presence of significant anisotropy, with ac measurements confirming slow relaxation of the magnetisation and Single-Molecule Magnetism behaviour. Simulations of high field, high frequency EPR data reveal a single ion anisotropy, D(Mn III)= -3.83 cm -1. DFT studies on a simplified model complex of 1 reveal a pronounced dependence of the exchange coupling on the relative twisting of the oxime moiety with respect to the metal ion positions, as suggested previously in more complicated [Mn III 3] and [Mn III 6] clusters. © The Royal Society of Chemistry 2011.

Pennon D.,University of Valencia | Koshevoy I.O.,University of Valencia | Estevan F.,University of Valencia | Sanau M.,University of Valencia | And 2 more authors.
Organometallics | Year: 2010

A novel C3-symmetric tetradentate tripodal ligand with phosphorus as coordinating atoms has been synthesized in good yields. Its coordination ability through the four phosphorus atoms, three at the arms and one at the bridging position, is shown by formation of rigid Pd(II) and Rh(I) complexes. These C3-iymmetric complexes are intrinsically chiral; experimental evidence for their configurational stability is included. © 2010 American Chemical Society.

Yahlali N.,University of Valencia | Fernandes L.M.P.,University of Coimbra | Gonzalez K.,University of Valencia | Garcia A.N.C.,University of Coimbra | Soriano A.,Institute Ciencia Molecular ICMOL
Journal of Instrumentation | Year: 2013

Silicon photomultipliers (SiPMs) are photosensors widely used for imaging in a variety of high energy and nuclear physics experiments. In noble-gas detectors for double-beta decay and dark matter experiments, SiPMs are attractive photosensors for imaging. However they are insensitive to the VUV scintillation emitted by the noble gases (xenon and argon). This difficulty is overcome in the NEXT experiment by coating the SiPMs with tetraphenyl butadiene (TPB) to convert the VUV light into visible light. TPB requires stringent storage and operational conditions to prevent its degradation by environmental agents. The development of UV sensitive SiPMs is thus of utmost interest for experiments using electroluminescence of noble-gas detectors. It is in particular an important issue for a robust and background free ββ0ν experiment with xenon gas aimed by NEXT. The photon detection efficiency (PDE) of UV-enhanced SiPMs provided by Hamamatsu was determined for light in the range 250-500 nm. The PDE of standard SiPMs of the same model (S10362-33-50C), coated and non-coated with TPB, was also determined for comparison. In the UV range 250-350 nm, the PDE of the standard SiPM is shown to decrease strongly, down to about 3%. The UV-enhanced SiPM without window is shown to have the maximum PDE of 44% at 325 nm and 30% at 250 nm. The PDE of the UV-enhanced SiPM with silicon resin window has a similar trend in the UV range, although it is about 30% lower. The TPB-coated SiPM has shown to have about 6 times higher PDE than the non-coated SiPM in the range 250-315 nm. This is however below the performance of the UV-enhanced prototypes in the same wavelength range. Imaging in noble-gas detectors using UV-enhanced SiPMs is discussed. © 2012 IOP Publishing Ltd and Sissa Medialab srl.

Sarwar M.,University of Bucharest | Madalan A.M.,University of Bucharest | Lloret F.,Institute Ciencia Molecular ICMol | Julve M.,Institute Ciencia Molecular ICMol | Andruh M.,University of Bucharest
Polyhedron | Year: 2011

The mononuclear high-spin iron(III) complexes [Fe(3-MeOsalpn)Cl(H 2O)] (1) and [Fe(3-MeOsalpn)(NCS)(H2O)]·0.5CH 3CN (2) and the tetranuclear oxo-bridged compound [{Fe(3-MeOsalpn)Gd(NO3)3}2(μ-O)] ·CH3CN (3) [3-MeOsalpn2- = N,N′- propylenebis(3-methoxysalicylideneiminate)] have been prepared and magneto-structurally characterised. The iron(III) ion in 1 and 2 is six-coordinated in a somewhat distorted octahedral surrounding with the two phenolate-oxygens and two imine-nitrogens from the Schiff-base building the equatorial plane and a water (1 and 2) and a chloro (1)/thiocyanate-nitrogen (2) in the axial positions. The neutral mononuclear units of 1 and 2 are assembled into centrosymmetric dinuclear motifs through hydrogen bonds between the axially coordinated water molecule of one iron centre and methoxy-oxygen atoms from the Schiff-base of the adjacent iron atom. The values of the intradimer metal-metal distance within the supramolecular dimers are 4.930 (1) and 4.878 (2). The tetranuclear of 3 can be described as two {FeIII(3-MeOsalpn)} units connected through an oxo-bridge, each one hosting a [GdIII(NO 3)3] entity in the outer cavity defined by the two phenolate- and two methoxy-oxygen atoms. The values of the intramolecular Fe⋯Fe and Fe⋯Gd distances in 3 are 3.502 and 3.606 , respectively. The analysis of the magnetic data of 1-3 in the temperature range 1.9-300 K shows the occurrence of weak intermolecular antiferromagnetic interactions in 1 and 2 [J = -0.76 (1) and -0.75 cm-1 (2) with the Hamiltonian defined as H = -JSFe1·SFe1] whereas two intramolecular antiferromagnetic interactions coexist in 3, one very strong between the two iron(III) ions (J1) through the oxo bridge and the other much weaker between the iron(III) and the Gd(III) ions (J2) across the double phenoxo oxygens [J1 = -275 cm-1 and J2 = -3.25 cm-1, the Hamiltonian being defined as H=-J1SFe 1·SFe1′-J2(SFe1· SGd1+SFe1′·SGd1′)]. These values are analysed in the light of the structural data and compared with those of related systems. © 2011 Elsevier Ltd. All rights reserved.

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