Publications by authors named "Dante Gatteschi"

79 Publications

Study of manganese binding to the ferroxidase centre of human H-type ferritin.

J Inorg Biochem 2018 05 9;182:103-112. Epub 2018 Feb 9.

INSTM, Department of Physics and Astronomy, University of Florence, Via Sansone 1, 50019 Sesto Fiorentino, Florence, Italy. Electronic address:

Ferritins are ubiquitous and conserved proteins endowed with enzymatic ferroxidase activity, that oxidize Fe(II) ions at the dimetal ferroxidase centre to form a mineralized Fe(III) oxide core deposited within the apo-protein shell. Herein, the in vitro formation of a heterodimetal cofactor constituted by Fe and Mn ions has been investigated in human H ferritin (hHFt). Namely, Mn and Fe binding at the hHFt ferroxidase centre and its effects on Fe(II) oxidation have been investigated by UV-Vis ferroxidation kinetics, fluorimetric titrations, multifrequency EPR, and preliminary Mössbauer spectroscopy. Our results show that in hHFt, both Fe(II) and Mn(II) bind the ferroxidase centre forming a Fe-Mn cofactor. Moreover, molecular oxygen seems to favour Mn(II) binding and increases the ferroxidation activity of the Mn-loaded protein. The data suggest that Mn influences the Fe binding and the efficiency of the ferroxidation reaction. The higher efficiency of the Mn-Fe heterometallic centre may have a physiological relevance in specific cell types (i.e. glia cells), where the concentration of Mn is the same order of magnitude as iron.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.jinorgbio.2018.02.003DOI Listing
May 2018

Adding remnant magnetization and anisotropic exchange to propeller-like single-molecule magnets through chemical design.

Chemistry 2014 Oct 8;20(42):13681-91. Epub 2014 Sep 8.

Departamento de Química, Universidade Federal do Paraná, Centro Politécnico, 81530-900, Curitiba-PR (Brazil).

The selective replacement of the central iron(III) ion with vanadium(III) in a tetrairon(III) propeller-shaped single-molecule magnet has allowed us to increase the ground spin state from S=5 to S=13/2. As a consequence of the pronounced anisotropy of vanadium(III), the blocking temperature for the magnetization has doubled. Moreover, a significant remnant magnetization, practically absent in the parent homometallic molecule, has been achieved owing to the suppression of zero-field tunneling of the magnetization for the half-integer molecular spin. Interestingly, the contribution of vanadium(III) to the magnetic anisotropy barrier occurs through the anisotropic exchange interaction with iron(III) spins and not through single ion anisotropy as in most single-molecule magnets.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/chem.201403361DOI Listing
October 2014

The emergence of complex behaviours in molecular magnetic materials.

Phys Chem Chem Phys 2014 Sep;16(34):18076-82

1. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70550, Stuttgart, Germany.

Molecular magnetism is considered an area where magnetic phenomena that are usually difficult to demonstrate can emerge with particular clarity. Over the years, however, less understandable systems have appeared in the literature of molecular magnetic materials, in some cases showing features that hint at the spontaneous emergence of global structures out of local interactions. This ingredient is typical of a wider class of problems, called complex behaviours, where the theory of complexity is currently being developed. In this perspective we wish to focus our attention on these systems and the underlying problematic that they highlight. We particularly highlight the emergence of the signatures of complexity in several molecular magnetic systems, which may provide unexplored opportunities for physical and chemical investigations.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c4cp01413hDOI Listing
September 2014

Circular magnetoplasmonic modes in gold nanoparticles.

Nano Lett 2013 Oct 24;13(10):4785-9. Epub 2013 Sep 24.

Department of Chemistry, University of Florence & INSTM , 50019 Florence, Italy.

The quest for efficient ways of modulating localized surface plasmon resonance is one of the frontiers in current research in plasmonics; the use of a magnetic field as a source of modulation is among the most promising candidates for active plasmonics. Here we report the observation of magnetoplasmonic modes on colloidal gold nanoparticles detected by means of magnetic circular dichroism (MCD) spectroscopy and provide a model that is able to rationalize and reproduce the experiment with unprecedented qualitative and quantitative accuracy. We believe that the steep slope observed at the plasmon resonance in the MCD spectrum can be very efficient in detecting changes in the refractive index of the surrounding medium, and we give a simple proof of principle of its possible implementation for magnetoplasmonic refractometric sensing.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/nl402394pDOI Listing
October 2013

Kineococcus radiotolerans Dps forms a heteronuclear Mn-Fe ferroxidase center that may explain the Mn-dependent protection against oxidative stress.

Biochim Biophys Acta 2013 Jun 8;1830(6):3745-55. Epub 2013 Feb 8.

Department of Biochemical Sciences A. Rossi Fanelli, Sapienza University of Rome, Italy.

Background: The ferroxidase center of DNA-binding protein from starved cells (Dps) is a major player in the iron oxidation/detoxification process that leads to a decreased reactive oxygen species production. The possible Mn(II) participation in this process has been studied in Dps from Kineococcus radiotolerans, a radiation-resistant bacterium with a high cytosolic Mn/Fe ratio and a high capacity to survive ionizing and stress conditions.

Methods: The X-ray structure of recombinant K. radiotolerans Dps loaded with Mn(II) has been solved at 2.0Å resolution. Mn(II) binding to K. radiotolerans Dps and its effect on Fe(II) oxidation have been characterized in spectroscopic measurements.

Results: In K. radiotolerans Dps, the Fe-Fe ferroxidase center can have a Mn-Fe composition. Mn(II) binds only at the high affinity, so-called A site, whereas Fe(II) binds also at the low affinity, so-called B site. The Mn-Fe and Fe-Fe centers behave distinctly upon iron oxidation by O2. A site-bound Mn(II) or Fe(II) plays a catalytic role, while B site-bound Fe(II) behaves like a substrate and can be replaced by another Fe(II) after oxidation. When H2O2 is the Fe(II) oxidant, single electrons are transferred to aromatic residues near the ferroxidase center and give rise to intra-protein radicals thereby limiting OH release in solution. The presence of the Mn-Fe center results in significant differences in the development of such intra-protein radicals.

Conclusions: Mn(II) bound at the Dps ferroxidase center A site undergoes redox cycling provided the B site contains Fe.

General Significance: The results provide a likely molecular mechanism for the protective role of Mn(II) under oxidative stress conditions as it participates in redox cycling in the hetero-binuclear ferroxidase center.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.bbagen.2013.02.003DOI Listing
June 2013

Dinuclear Cu(II) complexes of isomeric bis-(3-acetylacetonate)benzene ligands: synthesis, structure, and magnetic properties.

Inorg Chem 2012 May 19;51(9):5409-16. Epub 2012 Apr 19.

Istituto di Scienze e Tecnologie Molecolari, Consiglio Nazionale delle Ricerche and Consorzio Interuniversitario per la Scienza e Tecnologia dei Materiali, Dipartimento di Scienze Chimiche, Università di Padova, Via F. Marzolo, 1-35131, Padova, Italy.

Highly versatile coordinating ligands are designed and synthesized with two β-diketonate groups linked at the carbon 3 through a phenyl ring. The rigid aromatic spacer is introduced in the molecules to orient the two acetylacetone units along different angles and coordination vectors. The resulting para, meta, and ortho bis-(3-acetylacetonate)benzene ligands show efficient chelating properties toward Cu(II) ions. In the presence of 2,2'-bipyridine, they promptly react and yield three dimers, 1, 2, and 3, with the bis-acetylacetonate unit in bridging position between two metal centers. X-ray single crystal diffraction shows that the compounds form supramolecular chains in the solid state because of intermolecular interactions. Each of the dinuclear complexes shows a magnetic behavior which is determined by the combination of structural parameters and spin polarization effects. Notably, the para derivative (1) displays a moderate antiferromagnetic coupling (J = -3.3 cm(-1)) along a remarkably long Cu···Cu distance (12.30 Å).
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/ic3003806DOI Listing
May 2012

Exploring the no-man's land between molecular nanomagnets and magnetic nanoparticles.

Angew Chem Int Ed Engl 2012 May 4;51(20):4792-800. Epub 2012 Apr 4.

Department of Chemistry and RU INSTM, University of Florence, Italy.

The comparison of the structural and magnetic properties of molecular nanomagnets (MNM) and magnetic nanoparticles (MNP) can be instructive to get a deeper understanding of the magnetic behavior on the intermediate scale between molecular and bulk objects. In this respect iron oxo based clusters are particularly interesting, since they provide an increasing number of molecular systems with sizes close to that of iron oxide MNP. In this Minireview we report a survey of literature data aimed at improving our understanding of the emergence of MNP properties from MNM ones.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/anie.201105428DOI Listing
May 2012

Interpretation of cw-ESR spectra of p-methyl-thio-phenyl-nitronyl nitroxide in a nematic liquid crystalline phase.

Phys Chem Chem Phys 2012 Mar 27;14(9):3200-7. Epub 2012 Jan 27.

Dipartimento di Scienze Chimiche, Università degli Studi di Padova, Via Marzolo, I-35131 Padova, Italy.

In this paper we report on the characterization by continuous wave electron spin resonance spectroscopy (cw-ESR) of a nitronyl nitroxide radical in a nematic phase. A detailed analysis is performed by exploiting an innovative modeling strategy alternative to the usual spectral simulation approach: most of the molecular parameters needed to calculate the spectrum are evaluated a priori and the ESR spectrum is obtained by direct application of the stochastic Liouville equation. Allowing a limited set of fitting parameters it is possible to reproduce satisfactorily ESR spectra in the temperature range 260 K-340 K including the nematic-to-isotropic phase transition (325.1 K). Our results open the way to a more quantitative understanding of the ordering and mobility of nitronyl nitroxide radicals in nanostructured environments.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c2cp23079hDOI Listing
March 2012

Molecular (nano) magnets as test grounds of quantum mechanics.

Angew Chem Int Ed Engl 2011 Dec 7;50(50):11852-8. Epub 2011 Nov 7.

Dipartimento di Chimica U. Schiff and UdR INSTM, Università di Firenze, Via della Lastruccia, 3, 50019 Sesto Fiorentino, Firenze, Italy.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/anie.201100818DOI Listing
December 2011

Anisotropic dysprosium.

Authors:
Dante Gatteschi

Nat Chem 2011 Sep 23;3(10):830. Epub 2011 Sep 23.

Department of Chemistry, University of Florence, Polo Scientifico Universitario, Via della Lastruccia 3, 50019 Sesto Fiorentino, Italy.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/nchem.1157DOI Listing
September 2011

Synergistic role of B and F dopants in promoting the photocatalytic activity of rutile TiO2.

Chemphyschem 2011 Aug 22;12(12):2221-4. Epub 2011 Jun 22.

INSTM and Department of chemistry U. Shiff, Firenze University, Sesto Fiorentino (FI), Italy.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/cphc.201100254DOI Listing
August 2011

Water-dispersible sugar-coated iron oxide nanoparticles. An evaluation of their relaxometric and magnetic hyperthermia properties.

J Am Chem Soc 2011 Jul 16;133(27):10459-72. Epub 2011 Jun 16.

Institut Charles Gerhardt Montpellier, UMR 5253 CNRS-UM2, Chimie Moléculaire et Organisation du Solide, Université Montpellier II, Place E. Bataillon, 34095 Montpellier Cedex 5, France.

Synthesis of functionalized magnetic nanoparticles (NPs) for biomedical applications represents a current challenge. In this paper we present the synthesis and characterization of water-dispersible sugar-coated iron oxide NPs specifically designed as magnetic fluid hyperthermia heat mediators and negative contrast agents for magnetic resonance imaging. In particular, the influence of the inorganic core size was investigated. To this end, iron oxide NPs with average size in the range of 4-35 nm were prepared by thermal decomposition of molecular precursors and then coated with organic ligands bearing a phosphonate group on one side and rhamnose, mannose, or ribose moieties on the other side. In this way a strong anchorage of the organic ligand on the inorganic surface was simply realized by ligand exchange, due to covalent bonding between the Fe(3+) atom and the phosphonate group. These synthesized nanoobjects can be fully dispersed in water forming colloids that are stable over very long periods. Mannose, ribose, and rhamnose were chosen to test the versatility of the method and also because these carbohydrates, in particular rhamnose, which is a substrate of skin lectin, confer targeting properties to the nanosystems. The magnetic, hyperthermal, and relaxometric properties of all the synthesized samples were investigated. Iron oxide NPs of ca. 16-18 nm were found to represent an efficient bifunctional targeting system for theranostic applications, as they have very good transverse relaxivity (three times larger than the best currently available commercial products) and large heat release upon application of radio frequency (RF) electromagnetic radiation with amplitude and frequency close to the human tolerance limit. The results have been rationalized on the basis of the magnetic properties of the investigated samples.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/ja111448tDOI Listing
July 2011

Molecule-based magnets.

Chem Soc Rev 2011 Jun 9;40(6):3065-6. Epub 2011 May 9.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c1cs90019fDOI Listing
June 2011

Lanthanides in molecular magnetism: old tools in a new field.

Chem Soc Rev 2011 Jun 9;40(6):3092-104. Epub 2011 Mar 9.

Dipartimento di Chimica U. Schiff and UdR INSTM, Università di Firenze, Sesto Fiorentino(FI), Italy.

In this tutorial review we discuss some basic aspects concerning the magnetic properties of rare-earth ions, which are currently the subject of a renovated interest in the field of molecular magnetism, after the discovery that slow relaxation of the magnetization at liquid nitrogen temperature can occur in mononuclear complexes of these ions. Focusing on Dy(III) derivatives a tutorial discussion is given of the relation of the crystal field parameters, which determine the anisotropy of these systems and consequently their interesting magnetic properties, with the geometry of the coordination sphere around the lanthanide centre and with the pattern of f orbitals. The problem of systems of low point symmetry is also addressed by showing how detailed single crystal investigation, coupled to more sophisticated calculation procedures, is an absolute necessity to obtain meaningful structure-property relationships in these systems.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c0cs00185fDOI Listing
June 2011

A periodic mixed gaussians-plane waves DFT study on simple thiols on Au(111): adsorbate species, surface reconstruction, and thiols functionalization.

Phys Chem Chem Phys 2011 Mar 5;13(9):3886-95. Epub 2011 Jan 5.

Dipartimento di Chimica, Polo Scientifico, INSTM Università degli Studi di Firenze, via della Lastruccia 3, 50019 Sesto fiorentino, Italy.

Here we present DFT calculations based on a periodic mixed gaussians/plane waves approach to study the energetics, structure, bonding of SAMs of simple thiols on Au(111). Several open issues such as structure, bonding and the nature of adsorbate are taken into account. We started with methyl thiols (MeSH) on Au(111) to establish the nature of the adsorbate. We have considered several structural models embracing the reconstructed surface scenario along with the MeS˙-Au(ad)-MeS˙ type motif put forward in recent years. Our calculations suggest a clear preference for the homolytic cleavage of the S-H bond leading to a stable MeS˙ on a gold surface. In agreement with the recent literature studies, the reconstructed models of the MeS˙ species are found to be energetically preferred over unreconstructed models. Besides, our calculations reveal that the model with 1:2 Au(ad)/thiols ratio, i.e. MeS˙-Au(ad)-MeS˙, is energetically preferred compared to the clean and 1:1 ratio models, in agreement with the experimental and theoretical evidences. We have also performed Molecular Orbital/Natural Bond Orbital, MO/NBO, analysis to understand the electronic structure and bonding in different structural motifs and many useful insights have been gained. Finally, the studies have then been extended to alkyl thiols of the RSR' (R, R' = Me, Et and Ph) type and here our calculations again reveal a preference for the RS˙ type species adsorption for clean as well as for reconstructed 1:2 Au(ad)/thiols ratio models.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c0cp02042gDOI Listing
March 2011

Photocoercivity of nano-stabilized Au: Fe superparamagnetic nanoparticles.

Adv Mater 2010 Sep;22(36):4054-8

1. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70550, Stuttgart, Germany.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/adma.201002295DOI Listing
September 2010

Single molecule magnet behaviour in robust dysprosium-biradical complexes.

Chem Commun (Camb) 2010 Sep 17;46(35):6458-60. Epub 2010 Aug 17.

L.A.M.M, Department of Chemistry Ugo Schiff and INSTM Research Unit, Università di Firenze, Via Della Lastruccia 3, 50019 Sesto Fiorentino, Italy.

A Dy-biradical complex was synthesized and characterized down to very low temperature. ac magnetic measurements reveal single molecule magnet behaviour visible without any application of dc field. The transition to the quantum tunneling regime is evidenced. Photophysical and EPR measurements provide evidence of the excellent stability of these complexes in solution.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c0cc00966kDOI Listing
September 2010

Dynamical formation of spatially localized arrays of aligned nanowires in plastic films with magnetic anisotropy.

ACS Nano 2010 Apr;4(4):1873-8

Center for Bio-Molecular Nanotechnologies (CBN) of IIT@NNL-UniLe-Lecce, via Barsanti c/o STAMMS, Arnesano 73010 Lecce, Italy.

We present a simple technique for magnetic-field-induced formation, assembling, and positioning of magnetic nanowires in a polymer film. Starting from a polymer/iron oxide nanoparticle casted solution that is allowed to dry along with the application of a weak magnetic field, nanocomposite films incorporating aligned nanocrystal-built nanowire arrays are obtained. The control of the dimensions of the nanowires and of their localization across the polymer matrix is achieved by varying the duration of the applied magnetic field, in combination with the evaporation dynamics. These multifunctional anisotropic free-standing nanocomposite films, which demonstrate high magnetic anisotropy, can be used in a wide field of technological applications, ranging from sensors to microfluidics and magnetic devices.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/nn901597aDOI Listing
April 2010

Synthesis of iron oxide nanoparticles in Listeria innocua Dps (DNA-binding protein from starved cells): a study with the wild-type protein and a catalytic centre mutant.

Chemistry 2010 Jan;16(2):709-17

C.N.R. Institute of Molecular Biology and Pathology, Department of Biochemical Sciences A. Rossi-Fanelli, Sapienza, University of Rome, 00185 Rome, Italy.

A comparative analysis of the magnetic properties of iron oxide nanoparticles grown in the cavity of the DNA-binding protein from starved cells of the bacterium Listeria innocua, LiDps, and of its triple-mutant lacking the catalytic ferroxidase centre, LiDps-tm, is presented. TEM images and static and dynamic magnetic and electron magnetic resonance (EMR) measurements reveal that, under the applied preparation conditions, namely alkaline pH, high temperature (65 degrees C), exclusion of oxygen, and the presence of hydrogen peroxide, maghemite and/or magnetite nanoparticles with an average diameter of about 3 nm are mineralised inside the cavities of both LiDps and LiDps-tm. The magnetic nanoparticles (MNPs) thus formed show similar magnetic properties, with superparamagnetic behaviour above 4.5 K and a large magnetic anisotropy. Interestingly, in the EMR spectra an absorption at half-field is observed, which can be considered as a manifestation of the quantum behaviour of the MNPs. These results indicate that Dps proteins can be advantageously used for the production of nanomagnets at the interface between molecular clusters and traditional MNPs and that the presence of the ferroxidase centre, though increasing the efficiency of nanoparticle formation, does not affect the nature and fine structure of the MNPs. Importantly, the self-organisation of MNP-containing Dps on HRTEM grids suggests that Dps-enclosed MNPs can be deposited on surfaces in an ordered fashion.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/chem.200901138DOI Listing
January 2010

Density functional studies on the exchange interaction of a dinuclear Gd(iii)-Cu(ii) complex: method assessment, magnetic coupling mechanism and magneto-structural correlations.

Dalton Trans 2009 May 13(17):3153-61. Epub 2009 Mar 13.

Università degli Studi di Firenze, INSTM, Polo Scientifico, Dipartimento di Chimica, via della Lastruccia 3, 50019, Sesto F.no, Italy.

Density functional calculations have been performed on a [Gd(iii)Cu(ii)] complex [L(1)CuGd(O(2)CCF(3))(3)(C(2)H(5)OH)(2)] () (where L(1) is N,N'-bis(3-ethoxy-salicylidene)-1,2-diamino-2-methylpropanato) with an aim of assessing a suitable functional within the DFT formalism to understand the mechanism of magnetic coupling and also to develop magneto-structural correlations. Encouraging results have been obtained in our studies where the application of B3LYP on the crystal structure of yields a ferromagnetic J value of -5.8 cm(-1) which is in excellent agreement with the experimental value of -4.42 cm(-1) (H = JS(Gd).S(Cu)). After testing varieties of functional for the method assessment we recommend the use of B3LYP with a combination of an effective core potential basis set. For all electron basis sets the relativistic effects should be incorporated either via the Douglas-Kroll-Hess (DKH) or zeroth-order regular approximation (ZORA) methods. A breakdown approach has been adopted where the calculations on several model complexes of have been performed. Their wave functions have been analysed thereafter (MO and NBO analysis) in order to gain some insight into the coupling mechanism. The results suggest, unambiguously, that the empty Gd(iii) 5d orbitals have a prominent role on the magnetic coupling. These 5d orbitals gain partial occupancy via Cu(ii) charge transfer as well as from the Gd(iii) 4f orbitals. A competing 4f-3d interaction associated with the symmetry of the complex has also been observed. The general mechanism hence incorporates both contributions and sets forth rather a prevailing mechanism for the 3d-4f coupling. The magneto-structural correlations reveal that there is no unique parameter which the J values are strongly correlated with, but an exponential relation to the J value found for the O-Cu-O-Gd dihedral angle parameter is the most credible correlation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/b817540cDOI Listing
May 2009

Magnetic anisotropy of dysprosium(III) in a low-symmetry environment: a theoretical and experimental investigation.

J Am Chem Soc 2009 Apr;131(15):5573-9

Department of Chemistry, University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino, Italy.

A mixed theoretical and experimental approach was used to determine the local magnetic anisotropy of the dysprosium(III) ion in a low-symmetry environment. The susceptibility tensor of the monomeric species having the formula [Dy(hfac)(3)(NIT-C(6)H(4)-OEt)(2)], which contains nitronyl nitroxide (NIT-R) radicals, was determined at various temperatures through angle-resolved magnetometry. These results are in agreement with ab initio calculations performed using the complete active space self-consistent field (CASSCF) method, validating the predictive power of this theoretical approach for complex systems containing rare-earth ions, even in low-symmetry environments. Susceptibility measurements performed with the applied field along the easy axis eventually permitted a detailed analysis of the temperature and field dependence of the magnetization, providing evidence that the Dy ion transmits an antiferromagnetic interaction between radicals but that the Dy-radical interaction is ferromagnetic.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/ja8100038DOI Listing
April 2009

Organizing and addressing magnetic molecules.

Inorg Chem 2009 Apr;48(8):3408-19

Department of Chemistry and INSTM (UdR Firenze), University of Florence, via della Lastruccia 3, 50019 Sesto Fiorentino (FI), Italy.

Magnetic molecules ranging from simple organic radicals to single-molecule magnets (SMMs) are intensively investigated for their potential applications in molecule-based information storage and processing. The goal of this Article is to review recent achievements in the organization of magnetic molecules on surfaces and in their individual probing and manipulation. We stress that the inherent fragility and redox sensitivity of most SMM complexes, combined with the noninnocent role played by the substrate, ask for a careful evaluation of the structural and electronic properties of deposited molecules going beyond routine methods for surface analysis. Detailed magnetic information can be directly obtained using X-ray magnetic circular dichroism or newly emerging scanning probe techniques with magnetic detection capabilities.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/ic8013283DOI Listing
April 2009

Thermal deposition of intact tetrairon(III) single-molecule magnets in high-vacuum conditions.

Small 2009 Jun;5(12):1460-6

Department of Chemistry, University of Firenze INSTM Research Unit, ISTM-CNR (URT Firenze), Via della Lastruccia 3, 50019 Sesto Fiorentino, Italy.

A tetrairon(III) single-molecule magnet is deposited using a thermal evaporation technique in high vacuum. The chemical integrity is demonstrated by time-of-flight secondary ion mass spectrometry on a film deposited on Al foil, while superconducting quantum interference device magnetometry and alternating current susceptometry of a film deposited on a kapton substrate show magnetic properties identical to the pristine powder. High-frequency electron paramagnetic resonance spectra confirm the characteristic behavior for a system with S = 5 and a large Ising-type magnetic anisotropy. All these results indicate that the molecules are not damaged during the deposition procedure keeping intact the single-molecule magnet behavior.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/smll.200801594DOI Listing
June 2009

Magnetic memory of a single-molecule quantum magnet wired to a gold surface.

Nat Mater 2009 Mar 1;8(3):194-7. Epub 2009 Feb 1.

Department of Chemistry and INSTM research unit, University of Florence, 50019, Sesto Fiorentino, Italy.

In the field of molecular spintronics, the use of magnetic molecules for information technology is a main target and the observation of magnetic hysteresis on individual molecules organized on surfaces is a necessary step to develop molecular memory arrays. Although simple paramagnetic molecules can show surface-induced magnetic ordering and hysteresis when deposited on ferromagnetic surfaces, information storage at the molecular level requires molecules exhibiting an intrinsic remnant magnetization, like the so-called single-molecule magnets (SMMs). These have been intensively investigated for their rich quantum behaviour but no magnetic hysteresis has been so far reported for monolayers of SMMs on various non-magnetic substrates, most probably owing to the chemical instability of clusters on surfaces. Using X-ray absorption spectroscopy and X-ray magnetic circular dichroism synchrotron-based techniques, pushed to the limits in sensitivity and operated at sub-kelvin temperatures, we have now found that robust, tailor-made Fe(4) complexes retain magnetic hysteresis at gold surfaces. Our results demonstrate that isolated SMMs can be used for storing information. The road is now open to address individual molecules wired to a conducting surface in their blocked magnetization state, thereby enabling investigation of the elementary interactions between electron transport and magnetism degrees of freedom at the molecular scale.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/nmat2374DOI Listing
March 2009

Magnetic interactions and magnetic anisotropy in exchange coupled 4f-3d systems: a case study of a heterodinuclear Ce3+-Fe3+ cyanide-bridged complex.

Chemistry 2009 ;15(6):1377-88

UdR INSTM and Dipartimento di Chimica, Università di Firenze, Via della Lastruccia 3, 50019 Sesto Fiorentino (FI), Italy.

We report here a detailed single-crystal EPR and magnetic study of a homologous series of complexes of the type Ln-M (Ln = La(III), Ce(III); M = Fe(III), Co(III)). We were able to obtain a detailed picture of the low-lying levels of Ce(III) and Fe(III) centres through the combined use of single-crystal EPR and magnetic susceptibility data. We show that classical ligand field theory can be of great help in rationalising the energies of the low-lying levels of both the transition-metal and rare-earth ions. The combined analysis of single-crystal EPR and magnetic data of the coupled system Ce-Fe confirmed the great complexity of the interactions involving rare-earth elements. With little uncertainty, it turned out clearly that the description of the interaction involving the lowest lying spin levels requires the introduction of the isotropic, anisotropic and antisymmetric terms.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/chem.200801638DOI Listing
March 2009

XAS and XMCD investigation of Mn12 monolayers on gold.

Chemistry 2008 ;14(25):7530-5

Department of Chemistry and INSTM Research Unit, Università di Firenze, Via della Lastruccia 3, Sesto Fiorentino, Florence, Italy.

The deposition of Mn(12) single molecule magnets on gold surfaces was studied for the first time using combined X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) methods at low temperature. The ability of the proposed approach to probe the electronic structure and magnetism of Mn(12) complexes without significant sample damage was successfully checked on bulk samples. Detailed information on the oxidation state and magnetic polarization of manganese ions in the adsorbates was obtained from XAS and XMCD spectra, respectively. Partial reduction of metal ions to Mn(II) was clearly observed upon deposition on Au(111) of two different Mn(12) derivatives bearing 16-acetylthio-hexadecanoate and 4-(methylthio)benzoate ligands. The average oxidation state, as well as the relative proportions of Mn(II), Mn(III) and Mn(IV) species, are strongly influenced by the deposition protocol. Furthermore, the local magnetic polarizations are significantly decreased as compared with bulk Mn(12) samples. The results highlight an utmost redox instability of Mn(12) complexes at gold surfaces, presumably accompanied by structural rearrangements, which cannot be easily revealed by standard surface analysis based on X-ray photoelectron spectroscopy and scanning tunnelling microscopy.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/chem.200800693DOI Listing
October 2008

Electron paramagnetic resonance and density-functional theory studies of Cu(II)-bis(oxamato) complexes.

Inorg Chem 2008 Aug 2;47(15):6633-44. Epub 2008 Jul 2.

Department of Chemistry, Chemnitz University of Technology, 09107 Chemnitz, Germany.

In this work we present the investigation of the influence of electronic and structural variations induced by varying the N,N'-bridge on the magnetic properties of Cu(II)- bis(oxamato) complexes. For this study the complexes [Cu(opba)] (2-) ( 1, opba = o-phenylene- bis(oxamato)), [Cu(nabo)] (2-) ( 2, nabo = 2,3-naphthalene- bis(oxamato)), [Cu(acbo)] (2-) ( 3, acbo = 2,3-anthrachinone- bis(oxamato)), [Cu(pba)] (2-) ( 4, pba = propylene- bis(oxamato)), [Cu(obbo)] (2-) ( 5, obbo = o-benzyl- bis(oxamato)), and [Cu(npbo)] (2-) ( 6, npbo = 1,8-naphthalene- bis(oxamato)), and the respective structurally isomorphic Ni(II) complexes ( 8- 13) have been prepared as ( (n)Bu 4N) (+) salts. The new complex ( (n)Bu 4N) 2[Cu(R-bnbo)].2H 2O ( 7, R-bnbo = (R)-1,1'-binaphthalene-2,2'- bis(oxamato)) was synthesized and is the first chiral complex in the series of Cu(II)-bis(oxamato) complexes. The molecular structure of 7 has been determined by single crystal X-ray analysis. The Cu(II) ions of the complexes 1- 7 are eta (4)(kappa (2) N, kappa (2) O) coordinated with a more or less distorted square planar geometry for 1- 6 and a distorted tetrahedral geometry for 7. Using pulsed Electron Nuclear Double Resonance on complex 6, detailed information about the relative orientation of the hyperfine ( A) and nuclear quadrupole tensors ( Q) of the coordinating nitrogens with respect to the g tensor were obtained. Electron Paramagnetic Resonance studies in the X, Q, and W-band at variable temperatures were carried out to extract g and A values of N ligands and Cu ion for 1- 7. The hyperfine values were interpreted in terms of spin population on the corresponding atoms. The obtained trends of the spin population for the monomeric building blocks were shown to correlate to the trends obtained in the dependence of the exchange interaction of the corresponding trinuclear complexes on their geometry.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/ic702460tDOI Listing
August 2008

Solvent effects on the adsorption and self-organization of Mn12 on Au(111).

Langmuir 2007 Nov 16;23(23):11836-43. Epub 2007 Oct 16.

Dipartimento di Chimica, Università di Firenze and INSTM, Via della, Lastruccia 3, 50019 Sesto Fiorentino, Italy.

A sulfur-containing single molecule magnet, [Mn12O12(O2CC6H4SCH3)16(H2O)4], was assembled from solution on a Au(111) surface affording both submonolayer and monolayer coverages. The adsorbate morphology and the degree of coverage were inspected by scanning tunneling microscopy (STM), while X-ray photoelectron spectroscopy (XPS) allowed the determination of the chemical nature of the adsorbate on a qualitative and quantitative basis. The properties of the adsorbates were found to be strongly dependent on the solvent used to dissolve the magnetic complex. In particular, systems prepared from tetrahydrofuran solutions gave arrays of isolated and partially ordered clusters on the gold substrate, while samples prepared from dichloromethane exhibited a homogeneous monolayer coverage of the whole Au(111) surface. These findings are relevant to the optimization of magnetic addressing of single molecule magnets on surfaces.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/la7016837DOI Listing
November 2007

The origin of transverse anisotropy in axially symmetric single molecule magnets.

J Am Chem Soc 2007 Sep 9;129(35):10754-62. Epub 2007 Aug 9.

Grenoble High Magnetic Field Laboratory-CNRS, 38042 Grenoble, France.

Single-crystal high-frequency electron paramagnetic resonance spectroscopy has been employed on a truly axial single molecule magnet of formula [Mn(12)O(12)(tBu-CH(2)CO(2))16(CH(3)OH)4].CH(3)OH to investigate the origin of the transverse magnetic anisotropy, a crucial parameter that rules the quantum tunneling of the magnetization. The crystal structure, including the absolute structure of the crystal used for EPR experiments, has been fully determined and found to belong to I4 tetragonal space group. The angular dependence of the resonance fields in the crystallographic ab plane shows the presence of high-order tetragonal anisotropy and strong dependence on the MS sublevels with the second-highest-field transition being angular independent. This was rationalized including competing fourth- and sixth-order transverse parameters in a giant spin Hamiltonian which describes the magnetic anisotropy in the ground S = 10 spin state of the cluster. To establish the origin of these anisotropy terms, the experimental results have been further analyzed using a simplified multispin Hamiltonian which takes into account the exchange interactions and the single ion magnetic anisotropy of the Mn(III) centers. It has been possible to establish magnetostructural correlations with spin Hamiltonian parameters up to the sixth order. Transverse anisotropy in axial single molecule magnets was found to originate from the multispin nature of the system and from the breakdown of the strong exchange approximation. The tilting of the single-ion easy axes of magnetization with respect to the 4-fold molecular axis of the cluster plays the major role in determining the transverse anisotropy. Counterintuitively, the projections of the single ion easy axes on the ab plane correspond to hard axes of magnetization.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/ja0717921DOI Listing
September 2007

Polyfunctional inorganic-organic hybrid materials: an unusual kind of NLO active layered mixed metal oxalates with tunable magnetic properties and very large second harmonic generation.

J Am Chem Soc 2007 Aug 7;129(30):9410-20. Epub 2007 Jul 7.

Dipartimento di Chimica Inorganica, Metallorganica e Analitica, Università di Milano, Centro CIMAINA, UdR di Milano INSTM and Centro ISTM-CNR, Via Venezian 21, Milano, Italy.

Mixed M(II)/M(III) metal oxalates, as "stripes" connected through strong hydrogen bonding by para-dimethylaminobenzaldeide (DAMBA) and water, form an organic-inorganic 2D network that enables segregation in layers of the cationic organic NLO-phore trans-4-(4-dimethylaminostyryl)-1-methylpyridinium, [DAMS+]. The crystalline hybrid materials obtained have the general formula [DAMS]4[M2M'(C2O4)6].2DAMBA.2H2O (M = Rh, Fe, Cr; M' = Mn, Zn), and their overall three-dimensional packing is non-centrosymmetric and polar, therefore suitable for second harmonic generation (SHG). All the compounds investigated are characterized by an exceptional SHG activity, due both to the large molecular quadratic hyperpolarizability of [DAMS+] and to the efficiency of the crystalline network which organizes [DAMS+] into head-to-tail arranged J-type aggregates. The tunability of the pairs of metal ions allows exploiting also the magnetic functionality of the materials. Examples containing antiferro-, ferro-, and ferri-magnetic interactions (mediated by oxalato bridges) are obtained by coupling proper M(III) ions (Fe, Cr, Rh) with M(II) (Mn, Zn). This shed light on the role of weak next-nearest-neighbor interactions and main nearest-neighbor couplings along "stripes" of mixed M(II)/M(III) metal oxalates of the organic-inorganic 2D network, thus suggesting that these hybrid materials may display isotropic 1D magnetic properties along the mixed M(II)/M(III) metal oxalates "stripes".
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/ja0710712DOI Listing
August 2007