One pot solvothermal synthesis of organic acid coated magnetic iron oxide nanoparticles

Indexación: ScieloABSTRACT In this work we present the synthesis and characterization of iron oxide nanoparticles (IONPs), which were structurally and magnetically characterized. The use of iron salts and an organic acid (l-serine or ascorbic acid) as precursors under solvothermal conditions yielded these coated IONPs. The powder X-ray diffraction pattern of FeO-1 and FeO-2 is consistent with hematite (α-Fe2O3) and hematite-maghemite ((α-Fe2O3/γ-Fe2O3) respectively. The TEM analysis permits to estimate an average size of 10 nm for the FeO-1 sample. The magnetic characterization of the samples through the M(H) plots showed a very low coercivity value for both samples, being 53 Oe for FeO-1 and 10 Oe for FeO-2, indicating the very weak ferromagnetic character of the synthesized iron oxide species. Even though both organic acids under solvothermal conditions permit to obtain coated IONPs in one pot reaction, l-serine produces a more narrow-size distribution

Single-molecule magnet properties of transition-metal ions encapsulated in lacunary polyoxometalates: a theoretical study

Single-molecule magnet (SMM) properties of transition-metal complexes coordinated to lacunary polyoxo-metalates (POM) are studied by means of state of the art ab initio methodology. Three [M(gamma-SiW10O36)(2)] (M =Mn-III Fe-III, Co-II) complexes synthesized by Sato et al. (Chem. Commun. 2015, 51, 4081-4084) are analyzed in detail. SMM properties for the Coll and Mninnsystems can be rationalized due to the presence of low-energy excitations in the case of Co-II, which are much higher in energy in the case of Mn-II. The magnetic behavior of both cases is consistent with simple d-orbital splitting considerations. The case of the Fe-III complex is special, as it presents a sizable demagnetization barrier for a high-spin d(5) configuration, which should be magnetically isotropic. We conclude that a plausible explanation for this behavior is related to the presence of low-lying quartet and doublet states from the iron(III) center. This scenario is supported by ab initio ligand field analysis based on complete active space self-consistent field results, which picture a d-orbital splitting that resembles more a square-planar geometry than an octahedral one, stabilizing lower multiplicity states. This coordination environment is sustained by the rigidity of the POM ligand, which imposes a longer axial bond distance to the inner oxygen atom in comparison to the more external, equatorial donor atoms

Exchange interactions on the highest-spin reported molecule: the mixed-valence Fe-42 complex

The finding of high-spin molecules that could behave as conventional magnets has been one of the main challenges in Molecular Magnetism. Here, the exchange interactions, present in the highest-spin molecule published in the literature, Fe-42, have been analysed using theoretical methods based on Density Functional Theory. The system with a total spin value S = 45 is formed by 42 iron centres containing 18 high-spin Fe-III ferromagnetically coupled and 24 diamagnetic low-spin Fe-II ions. The bridging ligands between the two paramagnetic centres are two cyanide ligands coordinated to the diamagnetic Fe-II cations. Calculations were performed using either small Fe-4 or Fe-3 models or the whole Fe-42 complex, showing the presence of two different ferromagnetic couplings between the paramagnetic Fe-III centres. Finally, Quantum Monte Carlo simulations for the whole system were carried out in order to compare the experimental and simulated magnetic susceptibility curves from the calculated exchange coupling constants with the experimental one. This comparison allows for the evaluation of the accuracy of different exchange-correlation functionals to reproduce such magnetic properties

Análise da contribuição financeira para o esporte de elite no Chile

Funding is one of the most controversial areas when analyzing the likelihood of performance in elite sports. In order to establish the level of funding available in this area, it was necessary to establish certain conceptual margins with respect to elite sport and to determine the different sectors of sport that fit the proposed conceptual definition. Using a non-experimental descriptive method, based on empirical research in sports sciences and a meta-analysis strategy secondary information available on various websites of public services of Chile, together with yearbooks and information requested from entities linked to elite sport, Secondary information was collected that allowed knowing the different lines of funding from each of the factors and sub-factors of pillar 1 of the SPLISS model, proposed by De Bosscher et al. (2006) for the achievement of elite sport achievement that was part of the study. In conclusion, it can be established that a permanent increase in funding does not guarantee performance in elite sports.El financiamiento es uno de los aspectos más controvertidos a la hora de analizar la probabilidad de rendimiento en el deporte de élite. Para establecer el nivel de financiación disponible, fue necesario establecer ciertos márgenes conceptuales con respecto al deporte de élite y determinar los diferentes sectores del deporte que se ajustan a la definición conceptual propuesta. Se utilizó un método descriptivo no experimental basado en la investigación empírica en ciencias del deporte. Se empleó una estrategia de meta-análisis y se obtuvo información secundaria disponible en los sitios web de servicios públicos chilenos, además de anuarios e información solicitada a entidades vinculadas al deporte de élite. Esta información secundaria permitió conocer las diferentes líneas de financiamiento de cada uno de los factores y subfactores del pilar 1 del modelo SPLISS, propuesto por De Bosscher et al. (2006) para la consecución del deporte de élite que formaron parte del estudio. En conclusión, se puede establecer que un aumento permanente en la financiación no garantiza el rendimiento en el deporte de elite.O financiamento é uma das áreas mais controversas ao analisar a probabilidade de desempenho no esporte de elite. Para estabelecer o nível de financiamento disponível nesta área, foi necessário estabelecer certas margens conceituais a respeito do esporte de elite e determinar os diferentes setores do esporte que se encaixam na definição conceitual proposta. Utilizou-se um método descritivo não experimental, baseado em pesquisa empírica em ciências do esporte e uma estratégia de meta-análise, informações secundárias disponíveis em vários sites de serviços públicos do Estado do Chile, juntamente com anuários e informações solicitadas de entidades ligadas ao esporte de elite. Foram coletadas informações secundárias que permitiram conhecer as diferentes linhas de financiamento de cada um dos fatores e subfatores do pilar 1 do modelo SPLISS, proposto por De Bosscher et al. (2006) para a ocorrência de realizações esportivas de elite que fizeram parte do estudo. Em conclusão, pode-se estabelecer que um aumento permanente no financiamento não garante o desempenho no esporte de elite

Models to predict the magnetic properties of single- and multiple-bridged phosphate Cu-II systems: a theoretical DFT insight

Copper(II) phosphate bridged compounds have been studied by DFT methods in order to gain a better understanding of the magnetic exchange interactions through 1,1 and 1,3-bridges, which vary with the bonding modes of the ligand. In many cases phosphate is only one among several bridging ligands making it difficult to identify the predominant exchange pathway. This work proposes a graphical analysis, based on the unrestricted corresponding orbitals (UCO), and the derived 'magnetic orbitals' to identify the predominant exchange pathway. Models for the 1,1- and 1,3-bridging modes allow establishing the angle or dihedral dependence of the J values. For the 1,1-bridging mode the theta Cu-O-Cu angle was used. For the 1,3-phosphate the correlation was established with a D-P-O-i-Cu-i dihedral angle (tau) where D is a dummy atom. Using models with different D-P-O-i-Cu-i dihedral angles a predictive scheme was generated. Eleven copper(II) phosphate bridged structures were used to validate the proposed model. The study has shown that antiferromagnetic exchange interactions are primarily produced by phosphate bridges due to the possibility of this ligand that always enables a degree of overlap between the magnetic orbitals

[μ-10,21-Dimethyl-3,6,14,17-tetra­za­tricyclo­[17.3.1.18,12]tetra­cosa-1(23),2,6,8,10,12 (24),13,17,19,21-deca­ene-23,24-diolato-κ4 N 3,N 6,O 23,O 24:κ4 N 14,N 17,O 23,O 24]bis­(perchlorato-κO)dimanganese(II)

In the centrosymmetric and dinuclear title complex, [Mn2(C22H22N4O2)(ClO4)2], the two Mn atoms are bridged by two phenolate O atoms of the N4O2 macrocycle with an Mn⋯Mn distance of 2.9228 (11) Å. The distorted square–pyramidal N2O3 coordination geometry is completed by an O atom derived from a perchlorate anion

Catena-(bis((1,10-Phenanthroline-N,N')-copper(II)) hydroxy-bis( phosphato)-tris(dioxo-vanadium(v))): a polymorphic phase driven by disorder.

International audienceIn the present paper a copper(II) phosphovanadate is presented and formulated as [Cu6(phen)6(VVO2)6(PO4)6(VVO2HO)3] (1a). This compound was obtained by hydrothermal synthesis and crystallizes in the triclinic group P-1, with a = 10.6290(5), b = 17.4275(8), c = 23.6151(11) Å; α = 92.888(4)°, β = 98.910(4)° and γ = 91.995(4)°. The leitmotif in (1a) is almost identical to some previously reported ones, viz. [Cu(phen)(VVO2)(PO4)]2[VVO2(OH)] (2); [Cu(phen)(VVO2)(PO4)]2[VIVO2(H2O)] (3) except for the fact that the small cells found in (2)-(3) are tripled in (1a). The reasons driving to these differences are subtle, and reside in the way in which the disorder in some vanadate groups takes place, viz., completely at random in (2)-(3) thus leading to a small "average" cell, while keeping some systematics in (1a) thus needing for a larger motif to take account of its repetition scheme in the crystal. The magnetic unit in the structure of (1a) is defined by a dinuclear system of CuII bonded by a μ2,η1-PO4 bridge. A fit of the corresponding magnetic data of (1a) was done, using the van Vleck equation for two S = ½ centres View the MathML source. The parameters obtained by the fit of the experimental data were g = 2.1 and J = −3.5 cm−1

New highly charged iron(III) metal-organic cube stabilized by a bulky amine.

In this work, we report a new octanuclear cluster based on FeIII and the ligand 1H-imidazole-4,5-dicarboxylic acid, [Et3NH]12[Fe8(IDC)12]·10DMF·13H2O (1), with a metal core containing eight FeIII connected by only one type of organic ligand. A peak at 573 m/z in the mass spectra of the compound suggests the adduct species {[Fe8(IDC)12]+8H}4-. By X-ray photoelectron spectroscopy, the oxidation state of the iron cation was confirmed to be 3+, also identifying the presence of a quaternary nitrogen species, which act as a countercation of the anionic metal core [Fe8(IDC)12]12-. Mössbauer spectra recorded at different temperatures show an isomer shift and quadrupole splitting parameters that confirm the existence of only FeIII-HS in the structure of 1. X-ray analysis reveals that compound 1 crystallizes in the orthorhombic system space group Ibam, confirming a molecular cluster structure with an almost regular cube as geometry, with the FeIII atoms located at the corners of the cube and connected by μ-1κ2 N,O:2κ2 N',O‴-IDC3- bridges. Additionally, the magnetic measurements reveal a weak antiferromagnetic coupling in the Fe8 III coordination cluster (J = -3.8 cm-1). To the best of our knowledge, 1 is the first member of the family of cubes assembled with 1H-imidazole-4,5-dicarboxylic acid and FeIII cation, exhibiting high pH stability over a broad pH range, making it an ideal candidate for the design of supramolecular structures and metal-organic frameworks

2-(2-Pyridylamino)pyridinium tetra­chlorido­zincate(II)

The structure of the title compound, (C10H10N3)2[ZnCl4], is composed of C10H9N3H+ (DPAH+) cations and [ZnCl4]2− anions. The two pyridyl rings of DPAH+ are approximately coplanar, with a dihedral angle of 7.2 (2)° between their corresponding least-squares planes. The proton is disordered in a one-to-one ratio over the two chemically equivalent pyridyl N atoms. An intra­molecular hydrogen bond is formed between the pyridinium H atom and the pyridyl N atom of the other pyridyl ring. The Zn atom lies on a twofold rotation axis. There are also some weak N—H⋯Cl hydrogen bonds. These inter­actions lead to the formation of an alternating zigzag chain in the solid state. The results clearly show that reducing agents normally used in hydro­thermal syntheses, such as metallic zinc employed here, are also active in terms of coordination chemistry

Functionalization using biocompatible carboxylated cyclodextrins of iron-based nanoMIL-100

Here we report the first example of nanoMIL-100 particles modified with monomeric cyclodextrin derivatives of different length by exploiting strong interactions between non-saturated iron trimers at the external surface and carboxylate functionalities located at the end of biocompatible and flexible linkers of cyclodextrins. The main results revealed that, after the functionalization, the cyclodextrins are selectively located at the external surfaces covering the nanoparticles. Z potential measurements show that this functionalization induced changes respect to the bare nanoMIL-100 particles, however, the presence of the cyclodextrins does not modify the size neither porosity of the nanoparticles. The amount of cyclodextrins attached, investigated by thermogravimetry, increases with the length of the linker between CD cavity and nanoparticle surface, reaching up a 9 % wt. Auger spectroscopy suggested a clear predominant sp3 character after the functionalizations (vs. sp2 predominance in the unmodified nanoMIL-100). This study supposes the creation of an alternative family of hybrids based on carboxylated monomeric cyclodextrins