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Hazari A.,University of Calcutta | Kanta Das L.,University of Calcutta | Kadam R.M.,Bhabha Atomic Research Center | Bauza A.,University Of Les Illesbalears | And 2 more authors.
Dalton Transactions | Year: 2015

Three new mixed valence trinuclear Co(ii/iii) compounds cis-[Co3L2(MeOH)2(N3)2(μ1,1-N3)2] (1), trans-[Co3L2(H2O)2(N3)2(μ1,1-N3)2]·(H2O)2 (2) and [Co3LR 2(N3)3(μ1,3-N3)] (3) have been synthesized by reacting a di-Schiff base ligand (H2L) or its reduced form [H2LR] (where H2L = N,N′-bis(salicylidene)-1,3-propanediamine and H2LR = N,N′-bis(2-hydroxybenzyl)-1,3-propanediamine) with cobalt perchlorate hexahydrate and sodium azide. All three products have been characterized by IR, UV-Vis and EPR spectroscopies, ESI-MS, elemental, powder and single crystal X-ray diffraction analyses. Complex 1 is an angular trinuclear species in which two terminal octahedral Co(iii)N2O4 centers coordinate to the central octahedral cobalt(ii) ion through μ2-phenoxido oxygen and μ1,1-azido nitrogen atoms along with two mutually cis-oxygen atoms of methanol molecules. On the other hand, in linear trinuclear complex 2, in addition to the μ2-phenoxido and μ1,1-azido bridges with terminal octahedral Co(iii) centres, the central Co(ii) is bonded with two mutually trans-oxygen atoms of water molecules. Thus the cis-trans configuration of the central Co(ii) is solvent dependent. In complex 3, the two terminal octahedral Co(iii)N2O4 centers coordinate to the central penta-coordinated Co(ii) ion through double phenoxido bridges along with the nitrogen atom of a terminal azido ligand. In addition, the two terminal Co(iii) are connected through a μ1,3-azido bridge that participates in pnicogen bonding interactions (intermolecular N-N interaction) as an acceptor. Both the cis and trans isomeric forms of 1 and 2 have been optimized using density functional theory (DFT) calculations and it is found that the cis configuration is energetically more favorable than the trans one. However, the trans configuration of 2 is stabilized by the hydrogen bonding network involving a water dimer. The pnicogen bonding interactions have been demonstrated using MEP surfaces and CSD search which support the counter intuitive electron acceptor ability of the μ1,3-azido ligand. Complexes 1-3 exhibit catecholase-like activities in the aerial oxidation of 3,5-di-tert-butylcatechol to the corresponding o-quinone. Kinetic data analyses of this oxidation reaction in acetonitrile reveal that the catecholase-like activity follows the order: 1 (kcat = 142 h-1) > 3 (kcat = 99 h-1) > 2 (kcat = 85 h-1). Mechanistic investigations of the catalytic behaviors by X-band EPR spectroscopy and estimation of hydrogen peroxide formation indicate that the oxidation reaction proceeds through the reduction of Co(iii) to Co(ii). This journal is © The Royal Society of Chemistry 2015.


Mahmoudi G.,Islamic Azad University at Maragheh | Bauza A.,University Of Les Illesbalears | Rodriguez-Dieguez A.,University of Granada | Garczarek P.,Wroclaw University of Technology | And 2 more authors.
CrystEngComm | Year: 2015

In this manuscript we report the synthesis and X-ray characterization of five complexes of Zn(ii) based on a N4O core carbohydrazone ligand (H2L); i.e. {[Zn4(HL)4](CH3OH)4(NO3)4} (1), {[Zn4(HL)4](ClO4)4} (2) {[Zn4(HL)4][Zn(SCN)4](NO3)2} (3) {[Zn(SCN)4](H4L)(CH3OH)2} (4) and {[Zn4(HL)4](NO3)4(H2O)} (5). Structurally characterized tetranuclear Zn(ii) complexes, as those reported herein, are scarcely found in the literature. In the crystal structures of several compounds, N-H⋯S hydrogen bonds, anion-π and π-hole interactions are described and analysed by means of density functional theory (DFT) calculations since they play an important role in the construction of three-dimensional supramolecular frameworks. Moreover, the noncovalent interactions have been also analysed using Hirshfeld surface analysis. © The Royal Society of Chemistry.


Hazari A.,University of Calcutta | Hazari A.,Government General Degree College Singur | Das L.K.,Government General Degree College Kharagpur II Ambigeria | Bauza A.,University Of Les Illesbalears | And 2 more authors.
Dalton Transactions | Year: 2016

Three new trinuclear hetero-metallic complexes [(CuL)2Zn(NCS)2] (1), [(CuLR)2Zn(NCS)(μ1,1-NCS)] (2) and [(CuLR)2Cd(μ1,3-NCS)2] (4) have been synthesized using [CuL] and [CuLR] as "metalloligands" (where H2L = N,N′-bis(salicylidene)-1,3-propanediamine and H2LR = N,N′-bis(2-hydroxybenzyl)-1,3-propanediamine). All three complexes are characterized by elemental analysis, spectroscopic methods and single crystal XRD. Complex 1 is an angular trinuclear species, in which two terminal four-coordinate square planar "metalloligands" [CuL] are coordinated to a central Zn(ii) through double phenoxido bridges along with two mutually cis nitrogen atoms of terminal isothiocyanate ions as is usually found in such complexes. In contrast, in complex 2, the two terminal "metalloligands" [CuLR] are square pyramidal, as one of the SCN- ions makes an unusual μ1,1-NCS bridge between copper centers while the other one coordinates to Zn(ii) through a N atom in a usual fashion making its geometry also square pyramidal. For 4 which possesses an angular trinuclear structure, in addition to double phenoxido bridges from two terminal [CuLR], both the SCN- ions are S-bonded to Cd(ii) and form a bridge (cis-μ1,3-SCN) between Cd(ii) and each of the terminal Cu(ii) ions. This structure is different from its unreduced analogue in which NCS- was N-terminal coordinated to Cd(ii) (3/3′). All the structures have been optimized using density functional theory (DFT) calculations. It has been found that for H2L, optimized structures like 1 and 2 differ only by 0.4 kcal mol-1 but the H2LR structure 2 is more stable by 5.5 kcal mol-1 than the structure resembling 1. For Cd(ii) complexes also, H2L optimized structures such as 3 and 4 do not differ significantly in energy (1.0 kcal mol-1) but the H2LR structure 4 is more stable than that of 3 by 4.6 kcal mol-1. In fact, structure 4 has been found to be the most stable one among the other possible isomers of H2LR. © 2016 The Royal Society of Chemistry.


Mirzaei M.,Ferdowsi University of Mashhad | Eshtiagh-Hosseini H.,Ferdowsi University of Mashhad | Lotfian N.,Ferdowsi University of Mashhad | Salimi A.,Ferdowsi University of Mashhad | And 5 more authors.
Dalton Transactions | Year: 2014

In this paper we report the synthesis and X-ray characterization of four novel hybrid inorganic-organic assemblies generated from H4SiW 12O40 as Keggin-type polyoxometalates (POM) and, in three of them, a trinuclear lanthanide cluster of type {Na(H2O) 3[Ln(HCAM)(H2O)3]3}4+ is formed, where Ln metal is La in compound 1, Ce in compound 2, and Eu in compound 3 (H3CAM = chelidamic acid or 2,6-dicarboxy-4-hydroxypyridine). These compounds represent the first POM-based inorganic-organic assemblies using chelidamic acid as an organic ligand. The thermal stability of the organic ligand is crucial, since pyridine-2,6-bis(monothiocarboxylate) instead of chelidamic acid is used (compound 4) under the same synthesis conditions, the decomposition of the ligand to pyridine was observed leading to the formation of colorless crystals of a pseudo hybrid inorganic-organic assembly. In compound 4 the hybrid inorganic-organic assembly is not formed and the organic part simply consists of four molecules of protonated pyridine acting as counterions of the [SiW12O40]4- counterpart. The luminescent properties of compounds 1 and 3 have been investigated and their solid state architectures have been analyzed. Whereas compound 1 only shows ligand emission, the Eu3+ emission in compound 3 is discussed in detail. We have found that unprecedented anion-π interactions between the POM, which is a tetra-anion, and the aromatic rings play a crucial role in the crystal packing formation. To the best of our knowledge, this is the first report that describes and analyzes this interaction in Keggin-type POM based inorganic-organic frameworks. The energetic features of these interactions in the solid state have been analyzed using DFT calculations in some model systems predicted by us. This journal is © The Royal Society of Chemistry.


Barman N.,Jadavpur University | Banerjee S.,Jadavpur University | Brandao P.,University of Aveiro | Bauza A.,University Of Les Illesbalears | And 2 more authors.
Journal of Coordination Chemistry | Year: 2016

Four complexes based on N,N′-bis(2-pyridylmethylene)-1,3-propanediamine (L) and different Cd(II) salts have been synthesized and characterized by single-crystal X-ray diffraction analysis. The complexes are [Cd2(L)2(μ-Cl)2](ClO4)2 (1), [Cd2(L)2(μ-Br)2](ClO4)2 (2), [Cd(L)I](ClO4) (3), and [Cd(L)(NCS)2] (4). L exhibits the same coordination mode in 1-4. The radius of each anion plays a role in affecting the structures and luminescent intensities of the final products. CdCl2, CdBr2, and CdI2 react with L to produce chloride or bromido-bridged binuclear complexes and mononuclear iodido complex, respectively, whereas an unusual mononuclear trigonal prismatic (TP) 4 is obtained when thiocyanate was used as a coligand. Photoluminescence properties of all the complexes show that the trend of fluorescence intensity is 1 > 4 > 2 > 3. All four complexes exhibit different supramolecular interactions such as C-H/σ, π-π, and C-H/π and hydrogen bonding interactions. The experimental findings are complemented by density functional theory (DFT) calculations. (Graph Presented). © 2016 Informa UK Limited, trading as Taylor & Francis Group.


Picos R.,University Of Les Illesbalears | Papadopoulos N.P.,University of Waterloo | Lee Z.-H.,University of Waterloo | Lopez-Grifol A.,University Of Les Illesbalears | And 4 more authors.
Proceedings of the 2015 10th Spanish Conference on Electron Devices, CDE 2015 | Year: 2015

In this paper we analyze the effects of X-ray irradiation on a-Si:H TFTs. We have irradiated at low doses, up to 1 krad, and we have measured several transistors, obtaining coherent behaviors. The main effect is a shifting of the threshold voltage, as well as a change in the Ioff current and a change in the mobility. We discuss these effects, and find them to be around three orders of magnitude higher than in an equivalent bulk CMOS technology. © 2015 IEEE.


Mirzaei M.,Ferdowsi University of Mashhad | Eshtiagh-Hosseini H.,Ferdowsi University of Mashhad | Karrabi Z.,Ferdowsi University of Mashhad | Notash B.,Shahid Beheshti University | And 2 more authors.
Journal of Molecular Structure | Year: 2014

One-dimensional coordination polymer, i.e., {(Hampy)[Cu(chel)(H2O)]2H2O}n (1, ampy = 2-amino-6-methylpyridine, H3chel = chelidamic acid), has been synthesized and characterized by elemental analysis, IR spectroscopy, solution studies and X-ray single-crystal diffraction. In the monomeric unit of compound 1 the metal center exhibits a distorted square-pyramidal coordination sphere. The Cu(II) ion is coordinated to chelidamic acid and water. These monomers are interlinked generating a 1D polymer by means of the para hydroxyl group of the ligand. Protonated 2-amino-6-methylpyridine rings act as counter cations. The crystal lattice is aggregated through intermolecular interactions, such as electrostatic attraction, N-H⋯O, O-H⋯O and C-H⋯O hydrogen bonding and aromatic π stacking interactions. Hydrogen bond interactions between the water molecules led to formation of six-membered rings with chair conformation. These assemblies are described and analyzed by means of density functional theory (DFT) calculations since they play an important role in the construction of three-dimensional supramolecular frameworks. © 2014 Elsevier B.V. All rights reserved.


Mahmoudi G.,Islamic Azad University at Maragheh | Castineiras A.,University of Santiago de Compostela | Garczarek P.,Wroclaw University of Technology | Bauza A.,University Of Les Illesbalears | And 3 more authors.
CrystEngComm | Year: 2016

Two new pyridine-based heterocyclic thiosemicarbazone ligands and their Ni(ii), Cd(ii), Mn(ii), Co(iii) and Cu(ii) complexes have been synthesized and characterized by structural, analytical and spectroscopic methods. The monodeprotonated anionic forms of the ligands coordinate in a tridentate fashion via two nitrogen and one sulphur donor atoms to yield seven complexes in which metal centres vary from four-coordinated square planar to six-coordinated distorted octahedral geometries. Single-crystal X-ray crystallography showed that the molecular complexes can aggregate into larger entities depending on the anion coordinated to the metal centre. We have analysed the interesting supramolecular assemblies observed in the solid state of some complexes by means of DFT calculations. These assemblies are formed by a combination of several noncovalent interactions, including chelate ring-π, π-π, and chalcogen bonding interactions, that have been characterized using Bader's Theory of "atoms-in-molecules". © The Royal Society of Chemistry 2016.


Fornos J.J.,University Of Les Illesbalears | Gomez-Pujol L.,University Of Les Illesbalears | Gomez-Pujol L.,CSIC - Mediterranean Institute for Advanced Studies | Cifre J.,University Of Les Illesbalears | Hierro F.,University Of Les Illesbalears
Acta Carsologica | Year: 2011

A combined atomic force microscope (AFM) and scanning electron microscope (SEM) experiment examining the first steps in limestone weathering and erosion is presented. The experiment deals with the exposure of polished limestone rock tablets to a Western Mediterranean coastal environment and with the rate and patterns of weathering addressed by roughness quantification and qualitative assessment of nanoforms. Observations show how rock surface roughness increases at high rates after four and six months of exposure, passing from initial roughness RMS values between 14 and 32 μm to values between 396 to 492 μm. From the qualitative SEM approach, it can be concluded that the roughness increase relates with the widening of the space between rock grains and results in the isolation and detaching of rock grains.

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