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1.
ChemistryOpen ; 8(9): 1204-1208, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31523608

RESUMO

The synthesis of a Cu4(OH)4 cube which is coordinated by four molecules of the dipyridyl ligand 1,6-[di(pyridin-4-yl)hex-3-ene] is reported. This compound has a trans double bond which restricts the conformational freedom of the ligand and favours coordination within a unique copper cube. The structure was solved by an X-Ray single crystal structure determination and low temperature magnetic susceptibility measurements examined its magnetic properties. The cube classification corresponds to the type I classification of Mergehenn and Haase and the short/long distribution of Cu ⋅⋅⋅ Cu separations in the cube as defined by Ruiz. The magnetic susceptibility measurements show paramagnetic behaviour down to 50 K but below this the copper cube shows weak ferromagnetic exchange interactions. The low temperature magnetic susceptibility characteristics are examined in detail then modelled and compared to other similar Cu4O4 copper cubes.

2.
J Comput Chem ; 39(22): 1815-1827, 2018 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-30141533

RESUMO

We present a FORTRAN code based on a new powerful and efficient computational approach to solve multidimensional dynamic Jahn-Teller and pseudo Jahn-Teller problems. This symmetry-assisted approach constituting a theoretical core of the program is based on the full exploration of the point symmetry of the electronic and vibrational states. We also report some selected examples of increasing complexity aimed to display the theoretical background as well as the advantages and capabilities of the program to evaluate of the energy pattern, magnetic and optical properties of large multimode vibronic systems. © 2018 Wiley Periodicals, Inc.

3.
Front Chem ; 6: 231, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-29971232

RESUMO

A synthetic procedure is presented to construct new magnetic polyoxometalates (POMs) containing one or two subunits of '[CoIIICo 3II (OH)3(H2O)6-m(PW9O34)]3-' (m = 3 or 5). The substitution of the water ligands present in these subunits by oxo or hydroxo ligands belonging to other POM fragments, gives rise to four, larger POM anions: [Co7(OH)6(H2O)6(PW9O34)2]9- (2), [Co7(OH)6(H2O)4(PW9O34)2] n9n- (2'), [Co11(OH)5(H2O)5(W6O24)(PW9O34)3]22- (3) and [{Co4(OH)3(H2O)(PW9O34)}2{K⊂(H2W12O41)2}{Co(H2O)4}2]17- (4). The crystal structures, magnetic characterization and stabilities in aqueous solutions of these POM derivatives are also presented.

4.
Dalton Trans ; 47(34): 11788-11805, 2018 Aug 29.
Artigo em Inglês | MEDLINE | ID: mdl-29855645

RESUMO

In this article, we report our development of a vibronic model for the electric-field control of antiferromagnetic superexchange in the mixed-valence (MV) triferrocenium complex FeIII-FeII-FeIII proposed as a possible candidate for the molecular implementation of a quantum logic gate. Along with the electronic interactions, such as electron transfer between the iron ions in different oxidation degrees and Coulomb repulsion of the extra holes, the proposed model of the triferrocenium complex also takes into account the vibronic coupling as an inherent ingredient of the problem of mixed valency. The latter is described by the conventional Piepho-Krauzs-Shatz (PKS) model adapted to the linear disposition of the redox sites in the trimeric FeIII-FeII-FeIII complex, which gives a clear insight into the degree of delocalization in mixed-valence compounds. By introducing symmetry adapted molecular vibrations composed of the local "breathing" displacements, the three-mode vibronic problem is reduced to a two-mode problem involving interaction with the even and odd molecular vibrations of the linear centrosymmetric complex. The vibronic coupling was shown to play a key role in the degree of localization of the two holes among the three iron centers. This was shown to produce a pronounced influence on the electric-field dependences of the electronic-density distributions and electrically switchable magnetic exchange in the considered linear triferrocenium complex. In particular, it was shown that the vibronic coupling significantly influences the field-induced stepwise transformation FeIII-FeII-FeIII ↔ FeIII-FeIII-FeII, increasing the abruptness of the field dependencies of the singlet-triplet gap and the hole densities, which are of primary importance for the switching function.

5.
Chem Sci ; 8(1): 305-315, 2017 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-30294411

RESUMO

A new photoresponsive molecular polyanion in which two Fe(iii) ions are simultaneously coordinated by two [A-α-PW9O34]9- polyoxometalate units and two oxalato ligands has been obtained. When irradiated with UV light its potassium salt, 1, exhibits a remarkable photocoloration effect, attributable to the partial reduction of the POM units to give rise to a mixed-valence species. The photoinduced process is intramolecular and involves electron transfer from the oxalato ligands, which partially decompose releasing CO2, towards the Fe(iii) and the POM. This mechanism has been confirmed by DRS, IR, XPS and Mössbauer spectroscopy, magnetism and elemental analysis. An analogous derivative of 1 containing malonato ligands does not exhibit such photoactive behaviour, which is evidence that the oxalate ligand is essential for the photoactivity of 1. To our knowledge, 1 represents the first POM-based compound in which the photocoloration effect does not require the presence of intermolecular short interactions.

6.
Chem Commun (Camb) ; 52(90): 13245-13248, 2016 Nov 03.
Artigo em Inglês | MEDLINE | ID: mdl-27774535

RESUMO

Partial reductive hydrolysis of a penta-CoII/III cluster [Co(H2O)2(CoIIIW9O34)(PW9O34)]12- (1) leads to the formation of [Co2{Co3(H2O)(Co(OH)2W7O26)(PW9O34)}2]22- (2). This polyoxometalate is made up of two capping [PW9O34]9- units and two bridging [W7O26]10- units that assemble to encapsulate a novel deca-CoII cluster core comprising octahedral and tetrahedral CoII ions.

7.
Dalton Trans ; 45(42): 16653-16660, 2016 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-27778004

RESUMO

Polyoxometalate (POM) chemistry has recently offered excellent examples of single ion magnets (SIMs) and molecular spin qubits. Compared with conventional coordination compounds, POMs provide rigid and highly symmetric coordination sites. However, all POM-based SIMs reported to date exhibit a very limited range of possibilities for chemical processability. We present herein two new families of POM-based SIMs which are soluble in organic solvents: [Ln(ß-Mo8O26)2]5- {LnIII = Tb, Dy, Ho, Er, Tm and Yb} and the functionalised POMs [Ln{Mo5O13(OMe)4NNC6H4-p-NO2}2]3- {LnIII = Tb, Dy, Ho, Er, Yb and Nd}. In addition, these two families represent the first SIMs based on polyoxomolybdates. A magneto-structural analysis of these families is presented, which is based on an effective crystal field model, and compared with the results reported in analogous lanthanoid SIMs based on polyoxotungstates.

8.
J Comput Chem ; 37(13): 1238-44, 2016 05 15.
Artigo em Inglês | MEDLINE | ID: mdl-26833799

RESUMO

SIMPRE is a fortran77 code which uses an effective electrostatic model of point charges to predict the magnetic behavior of rare-earth-based mononuclear complexes. In this article, we present SIMPRE1.2, which now takes into account two further phenomena. First, SIMPRE now considers the hyperfine and quadrupolar interactions within the rare-earth ion, resulting in a more complete and realistic set of energy levels and wave functions. Second, and to widen SIMPRE's predictive capabilities regarding potential molecular spin qubits, it now includes a routine that calculates an upper-bound estimate of the decoherence time considering only the dipolar coupling between the electron spin and the surrounding nuclear spin bath. Additionally, SIMPRE now allows the user to introduce the crystal field parameters manually. Thus, we are able to demonstrate the new features using as examples (i) a Gd-based mononuclear complex known for its properties both as a single ion magnet and as a coherent qubit and (ii) an Er-based mononuclear complex. © 2016 Wiley Periodicals, Inc.

9.
Inorg Chem ; 55(2): 925-38, 2016 Jan 19.
Artigo em Inglês | MEDLINE | ID: mdl-26731303

RESUMO

Four novel cobalt-substituted polyoxometalates having cobalt cores exhibiting cubane or dicubane topologies have been synthesized and characterized by IR, elemental analysis, electrochemistry, UV-vis spectroscopy, X-ray single-crystal analysis, and magnetic studies. The tetracobalt(II)-substituted polyoxometalate [Co4(OH)3(H2O)6(PW9O34)](4-) (1) consists of a trilacunary [B-α-PW9O34](9-) unit which accommodates a cubane-like {Co(II)4O4} core. In the heptacobalt(II,III)-containing polyoxometalates [Co7(OH)6(H2O)6(PW9O34)2](9-) (2), [Co7(OH)6(H2O)4(PW9O34)2]n(9n-) (3), and [Co7(OH)6(H2O)6(P2W15O56)2](15-) (4), dicubane-like {Co(II)6Co(III)O8} cores are encapsulated between two heptadentate [B-α-PW9O34](9-) (in 2 and 3) or [α-P2W15O56](15-) (in 4) ligands. While 1, 2, and 4 are discrete polyoxometalates, 3 exhibits a polymeric, chain-like structure that results from the condensation of polyoxoanions of type 2. The magnetic properties of these complexes have been fitted according to an anisotropic exchange model in the low-temperature regime and discussed on the basis of ferromagnetic interactions between Co(2+) ions with angles Co-L-Co (L = O, OH) close to orthogonality and weakly antiferromagnetic interactions between Co(2+) ions connected through central diamagnetic Co(3+) ion. Moreover, we will show the interest of the unique spin structures provided by these cubane and dicubane cobalt topologies in molecular spintronics (molecular spins addressed though an electric field) and quantum computing (spin qu-gates).

10.
Chemistry ; 21(2): 763-9, 2015 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-25430555

RESUMO

Herein we evaluate the influence of an electric field on the coupling of two delocalized electrons in the mixed-valence polyoxometalate (POM) [GeV14 O40 ](8-) (in short V14 ) by using both a t-J model Hamiltonian and DFT calculations. In absence of an electric field the compound is paramagnetic, because the two electrons are localized on different parts of the POM. When an electric field is applied, an abrupt change of the magnetic coupling between the two delocalized electrons can be induced. Indeed, the field forces the two electrons to localize on nearest-neighbors metal centers, leading to a very strong antiferromagnetic coupling. Both theoretical approaches have led to similar results, emphasizing that the sharp spin transition induced by the electric field in the V14 system is a robust phenomenon, intramolecular in nature, and barely influenced by small changes on the external structure.

11.
Inorg Chem ; 53(20): 11323-7, 2014 Oct 20.
Artigo em Inglês | MEDLINE | ID: mdl-25271391

RESUMO

Simple electrostatic models have been shown to successfully rationalize the magnetic properties of mononuclear single molecule magnets based on f-elements and even to predict the direction of the magnetic anisotropy axis in these nanomagnets. In this Article, we go a step forward by showing that these models, conveniently modified to account for the covalency effects, are able to predict not only the easy axis direction but also the three components of the magnetic anisotropy. Thus, by using a lone pair effective charge (LPEC) model we can fully reproduce the angular dependence of the magnetic susceptibility in single crystals of pentamethylcyclopentadienyl-Er-cyclooctatetraene single-ion magnet. Furthermore, the parametrization of the ligands obtained in this study has been extrapolated to successfully reproduce spectroscopic data of a set of mononuclear lanthanoid complexes based on the same kind of ligands, thus emphasizing the predictive character of this model.

12.
Inorg Chem ; 53(18): 9976-80, 2014 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-25156530

RESUMO

This paper belongs to a series of contributions aiming at establishing a general library that helps in the description of the crystal field (CF) effect of any ligand on the splitting of the J ground states of mononuclear f-element complexes. Here, the effective parameters associated with the oxo ligands (effective charges and metal-ligand distances) are extracted from the study of the magnetic properties of the first two families of single-ion magnets based on lanthanoid polyoxometalates (POMs), formulated as [Ln(W5O18)2](9-) and [Ln(ß2-SiW11O39)2](13-) (Ln = Tb, Dy, Ho, Er, Tm, Yb). This effective CF approach provides a good description of the lowest-lying magnetic levels and the associated wave functions of the studied systems, which is fully consistent with the observed magnetic behavior. In order to demonstrate the predictive character of this model, we have extended our model in a first step to calculate the properties of the POM complexes of the early 4f-block metals. In doing so, [Nd(W5O18)2](9-) has been identified as a suitable candidate to exhibit SMM behavior. Magnetic experiments have confirmed such a prediction, demonstrating the usefulness of this strategy for the directed synthesis of new nanomagnets. Thus, with an effective barrier of 51.4 cm(-1) under an applied dc field of 1000 Oe, this is the second example of a Nd(3+)-based single-ion magnet.

13.
J Comput Chem ; 35(26): 1930-4, 2014 Oct 05.
Artigo em Inglês | MEDLINE | ID: mdl-25087575

RESUMO

The crystal field approach used by SIMPRE is analyzed, verifying the exactness of the results concerning energy levels and magnetic properties calculated by the package. To coincide with the prevailing conventions, we reformulate the presentation of the crystal field parameters, so that the results are now, also from a formal point of view, strictly correct. New calculations are presented to test the influence of neglecting the excited J states, a common but critical approximation employed by SIMPRE. For that, we examine the case of Er(trensal) complex (H3 trensal = 2,2',2″-tris(salicylideneimino)triethylamine) where the influence of this approximation is found to be minimal. A patched version of the code, SIMPRE 1.1, and an updated version of the user manual are now available. Finally, we comment on "Software package SIMPRE - revisited," which apparently revisits a software package without inspecting or using the code.

14.
Inorg Chem ; 53(5): 2441-9, 2014 Mar 03.
Artigo em Inglês | MEDLINE | ID: mdl-24552535

RESUMO

Three new heterometallic copper(II)-cobalt(II) complexes [(CuL(2))2Co{dca}2]·H2O(1), [(CuL(1))2Co{dca}2]n (2a), and [(CuL(1))2Co{dca}2]n (2b) [dca(-) = dicyanamide = N(CN)2(-)] have been synthesized by reacting the "metallo-ligand" [CuL(1)] or [CuL(2)] with cobalt(II) perchlorate and sodium dicyanamide in methanol-water medium (where H2L(1) = N,N'-bis(salicylidene)-1,3-propanediamine and H2L(2) = N,N'-bis(α-methylsalicylidene)-1,3-propanediamine). The three complexes have been structurally and magnetically characterized. Complex 1 is a discrete trinuclear species in which two metallo-ligands coordinate to a cobalt(II) ion through the phenoxido oxygen atoms along with two terminally coordinated dicyanamide ions. On the other hand, complexes 2a and 2b are one of the very scarce examples of supramolecular isomers since they present the same [(CuL(1))2Co{dca}2] trinuclear units (very similar to the trinuclear core in 1) and differ only in their superstructures. Thus, although each Cu2Co trimer in 2a and 2b is connected to four other Cu2Co trimers through four µ1,5-dca(-) bridges, 2a presents a square two-dimensional structure (each Cu2Co trimer is connected to four in-plane Cu2Co trimers); whereas, 2b shows a triangular three-dimensional lattice (each Cu2Co trimer is connected to three in-plane and one out-of-plane trimers). Variable-temperature magnetic susceptibility measurements show the presence of moderate antiferromagnetic exchange interactions (ferrimagnetic) in all the cases mediated through the double phenoxido bridges that have been fitted with an anisotropic model including spin-orbit coupling in the central Co(II) ion.

15.
Chemistry ; 19(48): 16394-402, 2013 Nov 25.
Artigo em Inglês | MEDLINE | ID: mdl-24151048

RESUMO

Two cobalt phosphonates, [Co2(2,2'-bpy)2(H2O)(pbtcH)] (1) and [Co2(H2O)(pbtcH)(phen)2] (2; pbtcH5=5-phosphonatophenyl-1,2,4-tricarboxylic acid, 2,2'-bpy=2,2'-bipyridine, phen=1,10-phenanthroline), with layer structures are reported. Compound 1 contains O-C-O and O-P-O bridged tetramers of Co4, which are further connected by pbtcH(4-) units to form a layer. In compound 2, the cobalt tetramers made up of water-bridged Co2 dimers and O-P-O linkages are connected into a layer by pbtcH(4-) units. Upon dehydration, compounds 1 and 2 experience single-crystal-to-single-crystal (SC-SC) structural transformations to form [Co2(2,2'-bpy)2(pbtcH)] (1 a) and [Co2(pbtcH)(phen)2] (2 a), respectively. The process is reversible in each case. Notably, a breathing effect is observed for 1, accompanied by pore opening and closing due to the reorientation of the coordinated 2,2'-bpy molecules. The transformation was also monitored by in situ IR measurements. Magnetic studies reveal that antiferromagnetic interactions are mediated between the magnetic centers in compounds 1 and 1 a, whereas ferromagnetic interactions are dominant in compound 2.

16.
J Comput Chem ; 34(22): 1961-7, 2013 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-24000391

RESUMO

This work presents a fortran77 code based on an effective electrostatic model of point charges around a rare earth ion. The program calculates the full set of crystal field parameters, energy levels spectrum, and wave functions, as well as the magnetic properties such as the magnetization, the temperature dependence of the magnetic susceptibility, and the Schottky contribution to the specific heat. It is designed for real systems that need not bear ideal symmetry and it is able to determine the easy axis of magnetization. Its systematic application to different coordination environments allows magneto-structural studies. The package has already been successfully applied to several mononuclear systems with single-molecule magnetic behavior. The determination of effective point charge parameters in these studies facilitates its application to new systems. In this article, we illustrate its usage with two example studies: (a) an ideal cubic structure coordinating a lanthanoid ion and (b) a system with slow relaxation of the magnetization, LiHo(x)Y((1-x))F(4).


Assuntos
Complexos de Coordenação/química , Elementos da Série dos Lantanídeos/química , Teoria Quântica , Software , Fenômenos Magnéticos , Eletricidade Estática , Temperatura
17.
Chem Commun (Camb) ; 49(83): 9621-3, 2013 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-24022124

RESUMO

The two-electron reduced mixed-valence polyoxometalate [GeV14O40](8-) presents an unusual paramagnetic behaviour as a consequence of the partial trapping of these electrons. The effect of applying an electric field is that of inducing antiferromagnetic coupling between the two delocalized electronic spins.

18.
Chem Commun (Camb) ; 49(79): 8922-4, 2013 Oct 11.
Artigo em Inglês | MEDLINE | ID: mdl-23955315

RESUMO

Polyoxometalate single ion magnet [GdW30P5O110](14-) (1) has been studied by generalized Rabi oscillation experiments. It was possible to increase the number of coherent rotations tenfold through matching the Rabi frequency with the frequency of the proton. Achieving high coherence with polyoxometalate chemistry, we show its excellent potential not only for the storage of quantum information but even for the realization of quantum algorithms.

19.
Chemistry ; 19(4): 1457-65, 2013 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-23197446

RESUMO

A series of homoleptic ([Tb(III)(Pc)(2) ]) and heteroleptic ([Tb(III)(Pc)(Pc')]) Tb(III) bis(phthalocyaninate) complexes that contain different peripheral substitution patterns (i.e., tert-butyl or tert-butylphenoxy groups) have been synthesized in their neutral radical forms and then reduced into their corresponding anionic forms as stable tetramethylammonium/tetrabutylammonium salts. All of these compounds were spectroscopically characterized and their magnetic susceptibility properties were investigated. As a general trend, the radical forms exhibited larger energy barriers for spin reversal than their corresponding reduced compounds. Remarkably, heteroleptic complexes that contain electron-donor moieties on one of the two Pc ligands show higher effective barriers and blocking temperatures than their homoleptic derivatives. This result is assigned to the elongation of the N-Tb distances in the substituted macrocycle, which brings the terbium(III) ion closer to the unsubstituted Pc, thus enhancing the ligand-field effect. In particular, heteroleptic [Tb(III) (Pc)(Pc')] complex 4, which contains one octa(tert-butylphenoxy)-substituted Pc ring and one bare Pc ring, exhibits the highest effective barrier and blocking temperature for a single-molecule magnet reported to date.

20.
Inorg Chem ; 51(22): 12565-74, 2012 Nov 19.
Artigo em Inglês | MEDLINE | ID: mdl-23102271

RESUMO

Here we develop a general approach to calculating the energy spectrum and the wave functions of the low-lying magnetic levels of a lanthanoid ion submitted to the crystal field created by the surrounding ligands. This model allows us to propose general criteria for the rational design of new mononuclear lanthanoid complexes behaving as single-molecule magnets (SMMs) or acting as robust spin qubits. Three typical environments exhibited by these metal complexes are considered, namely, (a) square antiprism, (b) triangular dodecahedron, and (c) trigonal prism. The developed model is used to explain the properties of some representative examples showing these geometries. Key questions in this area, such as the chemical tailoring of the superparamagnetic energy barrier, tunneling gap, or spin relaxation time, are discussed. Finally, in order to take into account delocalization and/or covalent effects of the ligands, this point-charge model is complemented with ab initio calculations, which provide accurate information on the charge distribution around the metal, allowing for an explanation of the SMM behavior displayed by some sandwich-type organometallic compounds.

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