Silvia Titos-Padilla

University of Granada, Granada, Andalusia, Spain

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Publications (7)26.9 Total impact

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    ABSTRACT: New types of linear tetranuclear Ln(III)-Ni(II)-Ni(II)-Ln(III) (Ln(III) = Dy (1), Gd (2)) complexes have been prepared using the multidentate ligand N,N'-bis(3-methoxysalicylidene)-1,3-diaminobenzene, which has two sets of NO and OO' coordination pockets that are able to selectively accommodate Ni(II) and Ln(III) ions, respectively. The X-ray structure analysis reveals that the Ni(II) ions are bridged by phenylenediimine groups forming a 12-membered metallacycle in the central body of the complex, whereas the Ln(III) ions are located at both sides of the metallacycle and linked to the Ni(II) ions by diphenoxo bridging groups. Phenylenediimine and diphenoxo bridging groups transmit ferromagnetic exchange interactions between the two Ni(II) ions and between the Ni(II) and the Ln(III) ions, respectively. Complex 1 shows slow relaxation of the magnetization at zero field and a thermal energy barrier Ueff = 7.4 K with HDC = 1000 Oe, whereas complex 2 exhibits an S = 9 ground state and significant magnetocaloric effect (-ΔSm = 18.5 J kg(-1) K(-1) at T = 3 K and ΔB = 5 T).
    Inorganic chemistry. 10/2014;
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    ABSTRACT: Thermochromic thin films of the spin crossover (SCO) polymer [Fe(NH2trz)3](BF4) are prepared using a variety of organic polymers as hosts. The formation of different polymeric networks is confirmed macroscopically by the colour changes related to an SCO phenomenon induced by thermal variation, and the results are correlated with electron microscopy and energy dispersive X-ray spectroscopy. Large particles of the SCO material are observed in SCO/polymer hybrid systems with hydrophobic polymers, while more dispersed nano-crystals appear in the hydrophilic matrices, leading to the transformation of the particles into fibrous structures. Subsequently, submicrometer-size SCO fibrous nanoparticles undergo colourimetric spin transitions near room temperature while grains with sizes larger than several microns move their transitions to lower temperatures. The difference in properties between the SCO/ polymer hybrid materials is not only due to the differences in the size and shape of the SCO crystals in each polymer but also to the nature of the polymer and solvent interactions. The optical changes obtained for each SCO/polymer hybrid material are related to the microscopic origin of the cooperative interactions tracked by using a photographic digital camera. A linear correlation is obtained (colour values versus temperature) when processing all the colourimetric data by artificial neural networks, thus avoiding the uncertainty inherent in the hysteresis loop.
    Journal of Materials Chemistry C. 07/2014;
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    ABSTRACT: There were new dinuclear Zn(II)-Ln(III) complexes of general formulas [Zn(μ-L)(μ-OAc)Ln(NO3)2] (Ln(III) = Tb (1), Dy (2), Er (3), and Yb (4)), [Zn(μ-L)(μ-NO3)Er(NO3)2] (5), [Zn(H2O)(μ-L)Nd(NO3)3]·2CH3OH (6), [Zn(μ-L)(μ-9-An)Ln(NO3)2]·2CH3CN (Ln(III) = Tb (7), Dy (8), Er (9), Yb(10)), [Zn(μ-L)(μ-9-An)Yb(9-An)(NO3)3]·3CH3CN (11), [Zn(μ-L)(μ-9-An)Nd(9-An)(NO3)3]·2CH3CN·3H2O (12), and [Zn(μ-L)(μ-9-An)Nd(CH3OH)2(NO3)]ClO4·2CH3OH (13) prepared from the reaction of the compartmental ligand N,N',N″-trimethyl-N,N″-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylenetriamine (H2L), with ZnX2·nH2O (X = NO3(-) or OAc(-)) salts, Ln(NO3)3·nH2O, and, in some instances, 9-anthracenecarboxylate anion (9-An). In all these complexes, the Zn(II) ions invariably occupy the internal N3O2 site whereas the Ln(III) ions show preference for the O4 external site, giving rise to a Zn(μ-diphenoxo)Ln bridging fragment. Depending on the Zn(II) salt and solvent used in the reaction, a third bridge can connect the Zn(II) and Ln(III) metal ions, giving rise to triple-bridged diphenoxoacetate in complexes 1-4, diphenoxonitrate in complex 5, and diphenoxo(9-anthracenecarboxylate) in complexes 8-13. Dy(III) and Er(III) complexes 2, 8 and 3, 5, respectively, exhibit field induced single molecule magnet (SMM) behavior, with Ueff values ranging from 11.7 (3) to 41(2) K. Additionally, the solid-state photophysical properties of these complexes are presented showing that ligand L(2-) is able to sensitize Tb(III)- and Dy(III)-based luminescence in the visible region through an energy transfer process (antenna effect). The efficiency of this process is much lower when NIR emitters such as Er(III), Nd(III), and Yb(III) are considered. When the luminophore 9-anthracene carboxylate is incorporated into these complexes, the NIR luminescence is enhanced which proves the efficiency of this bridging ligand to act as antenna group. Complexes 2, 3, 5, and 8 can be considered as dual materials as they combine SMM behavior and luminescent properties.
    Inorganic Chemistry 12/2013; · 4.59 Impact Factor
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    ABSTRACT: The synthesis, structure, magnetic, and luminescence properties of the Zn2Dy2 tetranuclear complex of formula {(μ3-CO3)2[Zn(μ-L)Dy(NO3)]2}·4CH3OH (1), where H2L is the compartmental ligand N,N',N″-trimethyl-N,N″-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylenetriamine, are reported. The carbonate anions that bridge two Zn(μ-L)Dy units come from the atmospheric CO2 fixation in a basic medium. Fast quantum tunneling relaxation of the magnetization (QTM) is very effective in this compound, so that single-molecule magnet (SMM) behavior is only observed in the presence of an applied dc field of 1000 Oe, which is able to partly suppress the QTM relaxation process. At variance, a 1:10 Dy:Y magnetic diluted sample, namely, 1', exhibits SMM behavior at zero applied direct-current (dc) field with about 3 times higher thermal energy barrier than that in 1 (Ueff = 68 K), thus demonstrating the important role of intermolecular dipolar interactions in favoring the fast QTM relaxation process. When a dc field of 1000 Oe is applied to 1', the QTM is almost fully suppressed, the reversal of the magnetization slightly slows, and Ueff increases to 78 K. The dilution results combined with micro-SQUID magnetization measurements clearly indicate that the SMM behavior comes from single-ion relaxation of the Dy(3+) ions. Analysis of the relaxation data points out that a Raman relaxation process could significantly affect the Orbach relaxation process, reducing the thermal energy barrier Ueff for slow relaxation of the magnetization.
    Inorganic Chemistry 08/2013; · 4.59 Impact Factor
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    ABSTRACT: In this study, we report the synthesis and characterization of phosphorescent silica nanoparticles doped with the blue-greenish emitting Ir-tpy complex [Ir(tpy)2]X3 (tpy = 2,2′:6′,2′′-terpyridine; X = PF6− or NO3−). Depending on the type of counterion and the solubility of the complex, three different kinds of Ir(tpy)-doped silica nanoparticles were prepared by the Stöber, water-in-oil and direct micelle synthetic approaches. The materials prepared through the Stöber and the water-in-oil approaches showed enhanced photochemical stability and higher luminescence efficiency compared to the free Ir-tpy complex. In these cases, the silica matrix hampers the diffusion of O2 and restrains the mobility of the complexes resulting in a decrease of the vibration relaxation and restraining the nonradiative decay. Conversely, for the material prepared by the direct micelle method, in which the structure of silica shows some degree of mesoporosity, the luminescence properties of the Ir-tpy complex remained almost unchanged after silica encapsulation. Additionally, the nanoparticles prepared by the Stöber method were chosen to functionalize their surface with a red-emitting Eu(hfac)3-alkoxysilane derivative leading to multicoloured luminescent silica nanoparticles in which the colour of the emission could be tuned by changing the excitation wavelength and where an Ir → Eu energy transfer was evidenced.
    J. Mater. Chem. C. 05/2013; 1(24):3808-3815.
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    ABSTRACT: We introduce the first method for imaging colour changes related to a spin crossover phenomenon induced by thermal variation which can be determined with the naked eye or with a photographic digital camera in a solid phase sensor.
    Chemical Communications 11/2012; · 6.38 Impact Factor
  • Angewandte Chemie International Edition 03/2011; 50(14):3290-3. · 11.34 Impact Factor