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1.
Inorg Chem ; 58(1): 52-56, 2019 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-30550268

RESUMO

The design of a coordination complex that involves a ligand combining both a tetrathiafulvalene core and a helicene fragment was achieved thanks to the reaction between the new 2-{1-[2-methyl[6]helicene]-4,5-[4,5-bis(propylthio)tetrathiafulvalenyl]-1 H-benzimidazol-2-yl}pyridine ligand (L) and the Dy(hfac)3·2H2O metalloprecursor. Magnetic investigations showed field-induced single-molecule-magnet (SMM) behavior under an applied magnetic field of 1000 Oe for [Dy(hfac)3(L)]·0.5CH2Cl2, while experimentally oriented single-crystal magnetic measurements allowed for determination of the magnetic anisotropy orientation. The magnetic behavior was rationalized through ab initio CASSCF/SI-SO calculations. This redox-active chiral-field-induced SMM paves the way for the design of switchable-multiproperty SMMs.

2.
Front Chem ; 6: 552, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-30483497

RESUMO

Tetrathiafulvalene and 1,10-phenanthroline moieties present, respectively remarkable redox-active and complexation activities. In this work, we investigated the coordination reaction between the bis(1,10-phenanthro[5,6-b])tetrathiafulvalene triad (L) and the Dy(hfac)3·2H2O metallo precursor. The resulting {[Dy2(hfac)6(L)]·CH2Cl2·C6H14}3 (1) dinuclear complex showed a crystal structure in which the triad L bridged two terminal Dy(hfac)3 units and the supramolecular co-planar arrangement of the triads is driven by donor-acceptor interactions. The frequency dependence of the out-of-phase component of the magnetic susceptibility highlights three distinct maxima under a 2000 Oe static applied magnetic field, a sign that 1 displays a Single-Molecule Magnet (SMM) behavior with multiple magnetic relaxations. Ab initio calculations rationalized the Ising character of the magnetic anisotropy of the DyIII ions and showed that the main anisotropy axes are perpendicular to the co-planar arrangement of the triads. Single-crystal rotating magnetometry confirms the orientation of the main magnetic axis. Finally combining structural analysis and probability of magnetic relaxation pathways through Quantum Tunneling of the Magnetization (QTM) vs. excited states (Orbach), each DyIII center has been attributed to one of the three observed magnetic relaxation times. Such coordination compound can be considered as an ideal candidate to perform redox-magnetic switching.

3.
Acc Chem Res ; 48(11): 2834-42, 2015 Nov 17.
Artigo em Inglês | MEDLINE | ID: mdl-26492407

RESUMO

The synthesis of molecules featuring different properties is a perpetual challenge for the chemists' community. The coexistence and even more the synergy of those properties open new perspectives in the field of molecular devices and molecular electronics. In that sense, coordination chemistry contributed to the development of new functional molecules through, for instance, single-molecule magnets (SMMs) and light emitting molecules with potential applications in high capacity data storage and OLEDs, respectively. The appealing combination of both electronic properties into one single object may offer the possibility to have magnetized luminescent entities at nanometric scale. To that end, lanthanides seem to be one of the key ingredients since their peculiar electronic structures endow them with specific magnetic and luminescence properties. Indeed, lanthanides cover a wide range of emission wavelengths, from infrared to UV, which add up to a large variety of magnetic behaviors, from the fully isotropic spin (e.g., Gd(III)) to highly anisotropic magnetic moments (e.g., Dy(III)). In lanthanide complexes, ligands play a fundamental role because on one hand they govern the orientation of the magnetic moment of anisotropic lanthanides and on the other hand they can sensitize efficiently the luminescence. The design of appropriate organic ligands to elaborate such chemical objects with the desired property appears to be essential but remains a perpetual challenge. In this Account, we describe the design of lanthanide-based complexes that emit light, behave as SMMs, or combine both properties. We have paid peculiar attention to the design of ligands based on the tetrathiafulvalene (TTF) moiety. TTF and its derivatives are well-known chemical entities, stable at different oxidation states, and employed mainly in the synthesis of molecular conductors and superconductors. In addition to their redox properties, TTF-based derivatives act as organic chromophores for the sensitization of visible and near-infrared (NIR) luminescence of lanthanides. The mechanism of sensitization involves either antenna effect (energy transfer from the excited state) or photoinduced electron transfer. TTF-based ligands act also as structural agents in the conception of SMM in crystals. Such objects are obtained with the highly anisotropic Dy(III) ion in crystalline phase as well as in frozen solution with magnetic memory at helium-4 temperature (4 K). We highlight the influence of the magnetic dilution (both in amorphous solution and in diamagnetic crystalline matrix) and, particular case of dysprosium based SMMs, the effect of metal-centered isotope enrichment on the SMM properties. Our aim is not only to realize functional molecules but to rationalize both luminescence and magnetic properties on the basis of the structure of the molecules. These two properties are intimately intricate and governed by the electronic structure, which can be calculated and interpreted using modern quantum chemistry tools.

4.
Inorg Chem ; 54(11): 5232-8, 2015 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-25974728

RESUMO

One-dimensional coordination polymer [Co(Piv)2(4-ptz)(C2H5OH)2]n (compound 1, Piv(-) = pivalate, 4-ptz = 2,4,6-tris(4-pyridyl)-1,3,5-triazine) was synthesized by interaction of Co(II) pivalate with 4-ptz. Desolvation of 1 led to formation of [Co(Piv)2(4-ptz)]n (compound 2), which adsorbed N2 and H2 at 78 K as a typical microporous sorbent. In contrast, absorption of methanol and ethanol by 2 at 295 K led to structural transformation probably connected with coordination of these alcohols to Co(II). Formation of 2 from 1 was accompanied by change of color of sample from orange to brown and more than 2-fold decrease of molar magnetic susceptibility (χM) in the temperature range from 2 to 300 K. Resolvation of 2 by ethanol or water resulted in restoration of spectral characteristics and χM values almost to the level of that of 1. χMT versus T curves for 1 and samples, obtained by resolvation of 2 by H2O or C2H5OH, were fitted using a model for Co(II) complex with zero-field splitting of this ion.

5.
Inorg Chem ; 54(11): 5384-97, 2015 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-25965094

RESUMO

The reaction between the TTF-fused dipyrido[3,2-a:2',3'-c]phenazine (dppz) ligand (L) and 1 equiv of Ln(hfac)3·2H2O (hfac(-) = 1,1,1,5,5,5-hexafluoroacetyacetonate) or 1 equiv of Ln(tta)3·2H2O (tta(-) = 2-thenoyltrifluoroacetonate) (Ln(III) = Dy(III) or Yb(III)) metallic precursors leads to four mononuclear complexes of formula [Ln(hfac)3(L)]·C6H14 (Ln(III) = Dy(III) (1), Yb(III) (2)) and [Ln(tta)3(L)]·C6H14 (Ln(III) = Dy(III) (3), Yb(III) (4)), respectively. Their X-ray structures reveal that the Ln(III) ion is coordinated to the bischelating nitrogenated coordination site and adopts a D4d coordination environment. The dynamic magnetic measurements show a slow relaxation of the Dy(III) magnetization for 1 and 3 with parameters highlighting a slower relaxation for 3 than for 1 (τ0 = 4.14(±1.36) × 10(-6) and 1.32(±0.07) × 10(-6) s with Δ = 39(±3) and 63.7(±0.7) K). This behavior as well as the orientation of the associated magnetic anisotropy axes have been rationalized on the basis of both crystal field splitting parameters and ab initio SA-CASSCF/RASSI-SO calculations. Irradiation of the lowest-energy HOMO → LUMO ILCT absorption band induces a (2)F5/2 → (2)F7/2 Yb-centered emission for 2 and 4. For these Yb(III) compounds, Stevens operators method has been used to fit the thermal variation of the magnetic susceptibilities, and the resulting MJ splittings have been correlated with the emission lines.

6.
Inorg Chem ; 54(8): 4021-8, 2015 Apr 20.
Artigo em Inglês | MEDLINE | ID: mdl-25831451

RESUMO

The reaction between the 2-(1-(2,6-di(pyrazol-1-yl)-4-methylpyridyl)-4,5-(4,5-bis(propylthio)-tetrathiafulvalenyl)-1H-benzimidazol-2-yl)-pyridine ligand (L) and 2 equiv of Dy(hfac)3·2H2O (hfac(-) = 1,1,1,5,5,5-hexafluoroacetylacetonate) and 1 equiv each of Dy(hfac)3·2H2O and Dy(tta)3·2H2O (tta(-) = 2-thenoyltrifluoroacetonate) metallic precursors leads to two dinuclear complexes, [Dy2(hfac)6(L)]·(CH2Cl2)2·C6H14 (1) and [Dy2(hfac)3(tta)3(L)] (2), respectively. Their X-ray structures reveal that the two coordination sites are occupied by one Dy(III) ion. The Dy(III) ion coordinated to the benzoimidazolylpyridine (bzip) moiety adopts a D4d coordination sphere, while the Dy(III) ion coordinated to the 2,6-di(pyrazol-1-yl)-4-pyridine (dpp) moiety is in a D3h surrounding. In a zero dc field, the dynamic magnetic measurements show a slow relaxation for the D4d eight-coordination Dy(III) magnetization for 1 and 2. Application of an external dc field induces multirelaxation signals of the magnetic susceptibility for both compounds. The low frequency and high frequency of the out-of-phase magnetic signals are attributed to the Dy(III) ion in D4d and D3h surroundings, respectively. The two complexes can be described as double induced-field mononuclear single-molecule magnets.

7.
Angew Chem Int Ed Engl ; 54(5): 1504-7, 2015 Jan 26.
Artigo em Inglês | MEDLINE | ID: mdl-25486900

RESUMO

The influence of nuclear spin on the magnetic hysteresis of a single-molecule is evidenced. Isotopically enriched Dy(III) complexes are synthesized and an isotopic dependence of their magnetic relaxation is observed. This approach is coupled with tuning of the molecular environment through dilution in an amorphous or an isomorphous diamagnetic matrix. The combination of these approaches leads to a dramatic enhancement of the magnetic memory of the molecule. This general recipe can be efficient for rational optimization of single-molecule magnets (SMMs), and provides an important step for their integration into molecule-based devices.

8.
Chem Asian J ; 9(10): 2814-25, 2014 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-25087945

RESUMO

Ligand L was synthesized and then coordinated to [Ln(hfac)3]⋅2 H2O (Ln(III)=Tb, Dy, Er; hfac(-)=1,1,1,5,5,5-hexafluoroacetylacetonate anion) and [Ln(tta)3]⋅2 H2O (Ln(III)=Eu, Gd, Tb, Dy, Er, Yb; tta(-)=2-thenoyltrifluoroacetonate) to give two families of dinuclear complexes [Ln2(hfac)6(L)]⋅C6H14 and [Ln2(tta)6(L)]⋅2 CH2Cl2. Irradiation of the ligand at 37,040 cm(-1) and 29,410 cm(-1) leads to tetrathiafulvalene-centered and 2,6-di(pyrazol-1-yl)-4-pyridine-centered fluorescence, respectively. The ligand acts as an organic chromophore for the sensitization of the infrared Er(III) (6535 cm(-1)) and Yb(III) (10,200 cm(-1)) luminescence. The energies of the singlet and triplet states of L are high enough to guarantee an efficient sensitization of the visible Eu(III) luminescence (17,300-14,100 cm(-1)). The Eu(III) luminescence decay can be nicely fitted by a monoexponential function that allows a lifetime estimation of (0.49±0.01) ms. Finally, the magnetic and luminescence properties of [Yb2(hfac)6(L)]⋅C6H14 were correlated, which allowed the determination of the crystal field splitting of the (2)F(7/2) multiplet state with M(J)=±1/2 as ground states.

9.
Chem Commun (Camb) ; 49(99): 11632-4, 2013 Dec 25.
Artigo em Inglês | MEDLINE | ID: mdl-24177382

RESUMO

Lanthanide dinuclear complexes involving tetrathiafulvalene-based ligands in their radical cation form were synthesised and crystallised by a galvanostatic procedure. Dynamic magnetic measurements reveal an unprecedented slow magnetic relaxation for the Dy(III) analogue in this kind of molecular edifice.

10.
J Am Chem Soc ; 135(44): 16332-5, 2013 Nov 06.
Artigo em Inglês | MEDLINE | ID: mdl-24127637

RESUMO

The [Dy(tta)3(L)] complex behaves as a single ion magnet both in its crystalline phase and in solution. Experimental and theoretical magnetic anisotropy axes perfectly match and lie along the most electro-negative atoms of the coordination sphere. Both VSM and MCD measurements highlight the robustness of the complex, with persistence of the memory effect even in solution up to 4 K.

11.
Inorg Chem ; 52(17): 9711-3, 2013 Sep 03.
Artigo em Inglês | MEDLINE | ID: mdl-23944607

RESUMO

The galvanostatic reaction of the [4,5-bis(2-pyridyl-N-oxidemethylthio)]-4',5'-methyldithiotetrathiafulvalene ligand with lanthanide ions in the presence of hexafluorophosphate (PF6(-)) anions afforded the highest-nuclearity lanthanide clusters decorated by tetrathiafulvalene-based ligands thanks to the original partial hydrolysis of the PF6(-) anions in difluorodioxophosphate (PO2F2(-)) bridging ligands.

12.
J Phys Chem A ; 117(25): 5241-50, 2013 Jun 27.
Artigo em Inglês | MEDLINE | ID: mdl-23768132

RESUMO

Polarized reflectivity spectra versus temperature of two isostructural charge-transfer salts κ-(ET)4[M(CN)6][N(C2H5)4]·2H2O (M = Co(III) and Fe(III)) (ET = bis(ethylenedithio)tetrathiafulvalene) were studied. The electronic and vibrational spectra exhibit a drastic change at around 150 K. On the basis of the spectral analysis, we deduced the nature of the phase transition. The phase transition at 150 K is due to a charge ordering; above this temperature, strong charge fluctuations are observed.

13.
Inorg Chem ; 52(11): 6543-50, 2013 Jun 03.
Artigo em Inglês | MEDLINE | ID: mdl-23675959

RESUMO

Preparations, crystal structure analyses, and magnetic property investigations on a new Cu(II)(hfac)2 complex coordinated with two TTF-CH═CH-BTA ligands, where hfac is hexafluoroacetylacetonate, TTF is tetrathiafulvalene, and BTA is 1,3-benzothiazole, are reported together with those of its dicationic AsF6(-) salt, [Cu(hfac)2(TTF-CH═CH-BTA)2](AsF6)2, in which each TTF part is in a radical cation state. In these Cu(II)(hfac)2 complexes, two ligands are bonded to the central Cu atom of the Cu(hfac)2 part through the nitrogen atom of the 1,3-benzothiazole ring and occupy the two apical positions of the Cu(hfac)2 complex with an elongated octahedral geometry. These two ligands are located parallelly in a transverse head-to-tail manner, and the Cu(hfac)2 moiety is closely sandwiched by these two ligands. In the AsF6(-) salt of the Cu(hfac)2 complex, each TTF dimer is separated by the AsF6(-) anions and has no overlap with each other within the one-dimensional arrays, resulting in an insulating behavior. Both Cu(hfac)2 complexes showed the simple Curie-like temperature dependence of paramagnetic susceptibilities (χM), indicating that no interaction exists between the paramagnetic Cu(II) d spins. Furthermore, crystal structure analysis and magnetic/conducting properties of a radical cation ReO4(-) salt of the Cu(I) complex with two TTF-CH═CH-BTA ligands, [Cu(TTF-CH═CH-BTA)2](ReO4)2, are also described. Two nitrogen atoms of the ligands are connected to the central Cu(I) in a linear dicoordination with a Cu-N bond length of 1.879(9) Å. Two TTF parts of the neighboring complexes form a dimerized structure, and such a TTF dimer forms a one-dimensional uniform array along the a direction with a short S-S contact of 3.88 Å. Magnetic property measurement suggested the existence of a strongly antiferromagnetic one-dimensional uniform chain of S = 1/2 spins that originate from the radical cation states of the TTF dimers. Due to the construction of the one-dimensional uniform array of the radical cation state of the TTF dimer along the a axis, a semiconducting behavior is observed with σ(rt) = of 6 × 10(-5) S cm(-1) and an activation energy of E(a) = 0.16 eV.


Assuntos
Benzotiazóis/química , Cobre/química , Compostos Organometálicos/química , Cátions/química , Radicais Livres/química , Ligantes , Modelos Moleculares , Estrutura Molecular , Compostos Organometálicos/síntese química , Sais/química
14.
Inorg Chem ; 52(10): 5978-90, 2013 May 20.
Artigo em Inglês | MEDLINE | ID: mdl-23659581

RESUMO

The reaction between (4,5-bis(2-pyridyl-N-oxidemethylthio)-4',5')-ethylenedithiotetrathiafulvene (L(1)) or -methyldithiotetrathiafulvene (L(2)) ligands and Ln(hfac)3·nH2O precursors (Ln(III) = Pr, Tb, Dy, Er, and Yb) leads to the formation of seven dinuclear complexes of formula [Ln2(hfac)6(H2O)x(L(y))2] (x = 2 and y = 1 for Ln(III) = Pr (1); x = 0 and y = 1 for Ln(III) = Tb (2), Dy (3), Er (4) and Yb (5); x = 0 and y = 2 for Ln(III) = Tb (6) and Dy (7)). Their X-ray structures reveal that the coordination environment of each Ln(III) center is filled by two N-oxide groups coming from two different ligands L(y). UV-visible absorption properties have been experimentally measured and rationalized by TD-DFT calculations. The temperature dependences of static magnetic measurements have been fitted. The ground state corresponds to the almost pure |M(J) = ±13/2〉 while the first excited state (±0.77|±11/2〉 ± 0.50|±3/2〉 ± 0.39|±5/2〉) is located at 19 cm(-1) and 26.9 cm(-1) respectively for 3 and 7. Upon irradiation at 77 K and at room temperature, in the range 25,000-20,835 cm(-1), both compounds 4 and 5 display a metal-centered luminescence attributed to (4)I(13/2) → (4)I(15/2) (6660 cm(-1)) and (2)F(5/2) → (2)F(7/2) (9972 cm(-1)) transitions, respectively. Emission spectroscopy provides a direct probe of the |±5/2〉 ground state multiplet splitting, which has been confronted to magnetic data. The energy separation of 225 cm(-1) between the ground state and the first excited level (M(J) = ±3/2) fits exactly the second emission line (234 cm(-1)). While no out-phase-signal is detected for 3, the change of ligand L(1) → L(2) induces a change of coordination sphere symmetry around the Dy(III) increasing the energy splitting between the ground and first excited states, and 7 displays a single molecule magnet behavior.


Assuntos
Compostos Heterocíclicos/química , Elementos da Série dos Lantanídeos/química , Luminescência , Imãs/química , Compostos Organometálicos/química , Cristalografia por Raios X , Modelos Moleculares , Estrutura Molecular , Compostos Organometálicos/síntese química , Processos Fotoquímicos
15.
Chemistry ; 19(24): 7895-903, 2013 Jun 10.
Artigo em Inglês | MEDLINE | ID: mdl-23589325

RESUMO

Reaction of the ligands 4,5-bis(propylthio)tetrathiafulvalene-2-(2-pyridyl)benzimidazole (L(1)) and 4,5-bis(propylthio)tetrathiafulvalene-2-(2-pyridyl)-3-(2-pyridinylmethyl)benzimidazole (L(2)) with Dy(hfac)3⋅2 H2O (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonate) gave mononuclear complexes [Dy(hfac)3(L(1))] (1) and [Dy(hfac)3(L(2))] (2). In both compounds the Dy(III) ion is surrounded by six oxygen and two nitrogen atoms. Complex 1 displays single-ion magnet (SIM) behaviour only in solution (Δ=12(1) K and τ0 =1.9(4)×10(-6)  s), while complex 2 is a SIM in both solution (Δ=15(2) K and τ0 =1.5(3)×10(-6)  s) and solid state (Δ=17(2) K and τ0 =9.5(2)×10(-6)  s). The SIM behaviour is obtained if the hydrogen bond is broken by dissolution (1 in solution) or by alkylation (2). Multiple relaxation processes were identified for 2 with two competing processes: a fast one in zero field and a slow one for fields higher than 500 Oe. The two processes coexist for intermediate applied magnetic field. Magnetic-dilution and frozen-solution measurements led to the conclusion that the origin of these multiple relaxation processes is not due to the property of a single molecule.

16.
Chemistry ; 19(18): 5742-57, 2013 Apr 26.
Artigo em Inglês | MEDLINE | ID: mdl-23447398

RESUMO

Treatment of [Cp*(dppe)Fe-C≡C-TTFMe3] (1) with Ag[PF6] (3 equiv) in DMF provides the binuclear complex [Cp*(dppe)Fe=C=C=TTFMe2 =CH-CH=TTFMe2 =C=C=Fe(dppe)Cp*][PF6]2 (2[PF6 ]2) isolated as a deep-blue powder in 69 % yield. EPR monitoring of the reaction and comparison of the experimental and calculated EPR spectra allowed the identification of the radical salt [Cp*(dppe)Fe=C=C=TTFMe2 =CH][PF6]2 ([1-CH][PF6]) an intermediate of the reaction, which results from the activation of the methyl group attached in vicinal position with respect to the alkynyl-iron on the TTF ligand by the triple oxidation of 1 leading to its deprotonation by the solvent. The dimerization of [1-CH][PF6] through carbon-carbon bond formation provides 2[PF6]2. The cyclic voltammetry (CV) experiments show that 2[PF6]2 is subject to two sequential well-reversible one-electron reductions yielding the complexes 2[PF6] and 2. The CV also shows that further oxidation of 2[PF6]2 generates 2[PF6]n (n=3-6) at the electrode. Treatment of 2[PF6]2 with KOtBu provides 2[PF6] and 2 as stable powders. The salts 2[PF6] and 2[PF6]2 were characterized by XRD. The electronic structures of 2(n+) (n=0-2) were computed. The new complexes were also characterized by NMR, IR, Mössbauer, EPR, UV/Vis and NIR spectroscopies. The data show that the three complexes 2[PF6]n are iron(II) derivatives in the ground state. In the solid state, the dication 2(2+) is diamagnetic and has a bis(allenylidene-iron) structure with one positive charge on each iron building block. In solution, as a result of the thermal motion of the metal-carbon backbone, the triplet excited state becomes thermally accessible and equilibrium takes place between singlet and triplet states. In 2[PF6], the charge and the spin are both symmetrically distributed on the carbon bridge and only moderately on the iron and TTFMe2 electroactive centers.

17.
Inorg Chem ; 52(3): 1398-408, 2013 Feb 04.
Artigo em Inglês | MEDLINE | ID: mdl-23339398

RESUMO

Centro-symmetric dinuclear complexes of formula [Ln(tta)(3)(L)](2)·xCH(2)Cl(2), (tta(-) = 2-thenoyltrifluoroacetonate anion, x = 0.5 for Ln = Eu (1a), Tb (3), and Dy (4) and x = 0 for Ln = Eu (1b) and Nd (2)) have been synthesized using the tetrathiafulvalene-3-pyridine-N-oxide as a bridging ligand (L). X-ray structures have shown the formation of channels with CH(2)Cl(2) solvent inside. 1 is stable with both filled channels (at 150 K) and empty channels (at room temperature). The Dy(III) analogue displays a complex butterfly like hysteresis loop at 1.5 K. Photophysical properties of the coordination complexes have been studied by solution and solid-state absorption spectroscopy. Time-dependent density functional theory (TD-DFT) calculations have been carried out on the diamagnetic Y(III) derivative to shed light on the absorption spectrum. For 2, the excitation of the charge transfer transitions induces line shape emission in the near-infrared spectral range assigned to (4)F(3/2) → (4)I(9/2), (4)F(3/2) → (4)I(11/2), and (4)F(3/2) → (4)I(13/2) neodymium centered transitions. The reversible redox-activity of the ligand L makes possible an original sensitization process involving a ligand centered charge separation followed by energy transfer to the Nd(III) ion upon recombination.


Assuntos
Óxidos N-Cíclicos/química , Elementos da Série dos Lantanídeos/química , Compostos Organometálicos/química , Radicais Livres/química , Ligantes , Campos Magnéticos , Modelos Moleculares , Estrutura Molecular , Compostos Organometálicos/síntese química , Processos Fotoquímicos , Teoria Quântica , Sais/química , Semicondutores
18.
Inorg Chem ; 52(3): 1610-20, 2013 Feb 04.
Artigo em Inglês | MEDLINE | ID: mdl-23323869

RESUMO

The reaction between the tetrakis(2-pyridyl-N-oxidemethylthio)tetrathiafulvalene ligand (L) and Ln(hfac)(3)·2H(2)O precursors (where hfac(-) = 1,1,1,5,5,5-hexafluoroacetylacetonate anion and Ln = Tb(III) (1), Dy(III) (2), Er(III) (3), and Yb(III) (4) and (4b)) leads to the formation of five tetranuclear complexes of formula [Ln(4)(hfac)(12)(L)(2)](n)·xCHCl(3)·yC(6)H(14) (n = 1, x = 2, y = 0 for (1), (2), and (4), n = 1, x = 4 for (3), and n = 2, x = 2.5, y = 1 for (4b)). Their X-ray structures reveal that the surrounding of each Ln(III) center is filled by two N-oxide groups coming from two different ligands L. These tetranuclear complexes have the highest nuclearity which is reported until now for coordination compounds of lanthanide involving TTF-based ligands. Direct current (dc) measurements highlight the paramagnetic behavior of the compounds with a significant crystal field effect. The temperature dependences of static magnetic measurements for 4 have been fitted. The ground state corresponds to M(J) = ±5/2 while the first excited state (M(J) = ±3/2) was localized at +214 cm(-1) which was well correlated with the luminescence transition. UV-visible absorption properties have been experimentally measured and rationalized by time-dependent density functional theory (TD-DFT) calculations. Upon irradiation at 77 K and room temperature, in the range 24390-20835 cm(-1), both compounds 3 and 4 display a metal-centered luminescence attributed to (4)I(13/2) → (4)I(15/2) (6660 cm(-1)) and (2)F(5/2) → (2)F(7/2) (signal centered around the value of 9966 cm(-1)) transitions, respectively. The observed six transitions could be attributed to the M(J) state splitting due to the existence of two Yb1 and Yb2 ions with slightly different polyhedra in 4.


Assuntos
Compostos Heterocíclicos/química , Elementos da Série dos Lantanídeos/química , Compostos Organometálicos/química , Ligantes , Campos Magnéticos , Modelos Moleculares , Estrutura Molecular , Compostos Organometálicos/síntese química , Processos Fotoquímicos
19.
Chem Commun (Camb) ; 49(6): 615-7, 2013 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-23223163

RESUMO

A redox active dinuclear complex [Yb(tta)(2)(L(1))(L(2))](2)·1.4(CH(2)Cl(2)) displays single molecule magnet behaviour with M(J) = ±7/2 ground state. The anisotropic barrier Δ is evaluated by the three dc data fit, ac analysis and emission spectrum demonstrating the correlation between magnetic and optical properties.

20.
Dalton Trans ; 42(6): 1949-60, 2013 Feb 14.
Artigo em Inglês | MEDLINE | ID: mdl-23208602

RESUMO

The elaboration of multifunctional materials is a great challenge for the physical chemistry community and the studies of molecular materials exhibiting coexistence or synergy between two or more properties are very active. In particular, molecular compounds displaying electrical conductivity and magnetic interactions are currently the subject of intensive studies. Two approaches are now well-known and are explored. On the one hand, the interactions between mobile electrons of the organic network (π electrons) and localized electrons of paramagnetic transition metal (d electrons) take place through space. On the other hand, these interactions take place through covalent chemical bonds. In the latter, the probability to have significant interaction between π and d electrons is enhanced compared to the first approach. In this perspective article, we will give an overview of the known coordination complexes involving tetrathiafulvalene derivatives as ligands for paramagnetic 3d ions and we will describe their physical properties. If necessary, the coexistence or synergy between electrical conductivity, magnetism and other properties will be highlighted.

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