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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. Source

Abalos T.,Unidad University | Abalos T.,Polytechnic University of Valencia | Abalos T.,CIBER ISCIII | Moragues M.,Unidad University | And 18 more authors.
European Journal of Inorganic Chemistry | Year: 2012

A family of dyes (L1-L6) that contain a thiazolylazo group as signalling subunit and several macrocyclic cavities with different ring sizes and type and number of heteroatoms as binding sites has been synthesized and characterized. Solutions of L1-L6 in acetonitrile show broad and structureless absorption bands in the 554-577 nm range with typicalmolar absorption coefficients that range from 20000 to 32000 M -1 cm-1. A detailed protonation study was carried out with solutions of L1, L2 and L5 in acetonitrile. Addition of one equivalent of protons to L1 and L2 resulted in the development of a new band at 425 and 370 nm, respectively, which was ascribed to protonation in the aniline nitrogen. In contrast, protonation of L5 resulted in a bathochromic shift of 25 nm of the absorption band that was conceivable with protonation of one of the nitrogen atoms of the azo moiety. These results were in agreement with 1H NMR spectroscopic data. Theoretical studies on the model ligand L1 and on different possible protonation species were also performed by using density functional theory (DFT) quantum mechanical calculations. Colour modulations in solutions of L1-L6 in acetonitrile in the presence of the metal cations Fe3+, Ni2+, Zn2+, Cd2+, Pb2+ and Hg2+ have been studied. A selective chromogenic response of L4 in the presence of Pb2+ and L5 in the presence of Hg2+ was observed. To get a better insight into the chromophoric nature in the presence of metal cations, the interaction of Hg2+ with the model compound L1 in two different coordination modes was studied theoretically by using density functional theory (DFT) quantum mechanical calculations. Source

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. Source

Barros W.P.,Federal University of Minas Gerais | Da Silva B.C.,Federal University of Minas Gerais | Reis N.V.,Federal University of Minas Gerais | Pereira C.L.M.,Federal University of Minas Gerais | And 7 more authors.
Dalton Transactions | Year: 2014

Two new trinuclear copper(ii) complexes without end-capping ligands, (Bu4N)2[Cu(dmso)2{Cu(dnopba)(dmso)}2] (1) and (Bu4N)2[Cu(dmso)2{Cu(dcopba)(dmso)}2] (2) [dnopba = 4,5-dinitro-ortho-phenylenebis(oxamate), dcopba = 4,5-dichloro-ortho-phenylenebis(oxamate), Bu4N+ = tetra-n-butylammonium and dmso = dimethylsulfoxide], were synthesized and their structures were determined by single crystal X-ray diffraction. The crystal structures of 1 and 2 consist of two outer bis(oxamato)(dmso)cuprate(ii) units which act as bidentate ligands toward a trans-bis(dmso)copper(ii) inner entity leading to centrosymmetric tricopper(ii) complexes with copper-copper separations across the oxamate bridges of 5.1916(3) (1) and 5.1776(3) Å (2). The peripheral copper(ii) ions in 1 and 2 are five-coordinate in somewhat distorted square pyramidal environments with a dmso molecule filling the apical position whereas the inner copper(ii) ion is six-coordinate in an elongated octahedral environment with two dmso molecules in the axial sites. The investigation of their magnetic properties in the temperature range 2.0-300 K shows the occurrence of a strong intramolecular antiferromagnetic coupling between the copper(ii) ions through the oxamate bridges [J1 = -296(1) (1) and -334(1) cm-1 (2), the Hamiltonian being defined as H = -J1(SCu2·SCu1 + SCu2·SCu1′)], which leads to a low-lying spin doublet at low temperatures. Density functional theory calculations (DFT) have been used to substantiate these magnetic couplings and also to analyse the influence exerted on these interactions by the type of substituent at the 4,5-positions from the phenylene ring of the bis(oxamate) ligand. This journal is © the Partner Organisations 2014. Source

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. Source

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