A field‐induced chiral YbIII Single‐Molecule Magnet (SMM) displayed an unprecedented near‐infrared circularly polarized luminescence (NIR‐CPL) in the solid‐state. The bridging bis(1,10‐phenantro[5,6b])tetrathiafulvalene triad (L) allowed an efficient sensitization of the NIR 2F5/2→2F7/2 emission while the NIR‐CPL is associated to the f‐f transitions of the YbIII ion bearing chiral β‐diketonate derived‐camphorate ancillary ligands.

A triclinic polymorph Dy(t) and a monoclinic polymorph Dy(m) of [Dy(tta)(L)] with L = 4-[6-(1,3-benzothiazol-2-yl)pyridin-3-yl]-4',5'-bis(methylthio)tetrathiafulvene behave as Single-Molecule Magnets with hysteresis loops opened at zero field. Magnetic properties were enhanced through magnetic dilution and Dy isotopic enrichment which definitively support the importance of isotopes for the control of quantum magnets.

International audienceThree lanthanide-based complexes involving a tetrathiafulvalene deriv. (L) in which the lanthanide ion has a pseudo-D4d symmetry have been reported. One is a dinuclear compd. of formula [Dy(hfac)3(L)]2 (1) while the two others are isostructural and described as mononuclear complexes of formulas [Ln(tta)3(L)]·xCH2Cl2 (LnIII = Dy and x = 1.41 (2); Yb and x = 2 (3)). The nuclearity of the species is driven by the nature of the ancillary ligands. Magnetic properties revealed that 1 and 3 behave as single mol. magnets, while 2 does not. The crystal field splitting of the ground multiplet state has been theor. detd. as well as the orientation of the easy axis of the ground MJ state. The results of ab initio calcns. are in agreement with the exptl. detns. of the anisotropy axis. Irradn. of the lowest-energy charge transfer bands of 3 led to an intense and resolved Yb-centered emission which can be correlated to the magnetic data. Thus 3 can be described as a redox-active luminescent field-induced single-mol. magnet

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.

International audienceThe reaction between the 2-_TTF-fused-1H-benzimidazol-2-yl_ pyridine alkylated with either the di-( pyrazol-1-yl)-4-pyridyl (L-1) or dimethyl-2,2'-bipyridine (L-2) moiety and 1 equiv. of L-n(hfac)(3).2H(2)O (Ln(III) = Dy-III and Yb-III) leads to three dinuclear complexes of formula [Yb-2(hfac)(6)(L-1)].2(CH2Cl2).C6H14 (1) and [Ln(2)(hfac)(6)(L-2)].CH2Cl2 (Ln(III) = Yb-III (2) and Dy-III (3)). The X-ray structures highlight square antiprism (D-4d symmetry) and spherical tricapped trigonal prism (D-3h) for the eight-and nine-coordinated lanthanide ions, respectively. Irradiation of the lowest-energy HOMO -> LUMO ILCT absorption band induced a F-2(5/ 2) -> F-2(7/ 2) Yb-centered emission for 1 and 2. Both Yb-III ions displayed similar emissions in 2 while two distinct emissions, attributed to the two YbIII ions because of their different coordination environments, were observed in 1. Slow magnetic relaxation is detected by dynamic magnetic measurements for 3 with a measured relaxation time tau(0) = 3.7(1.3) x 10(-7) s and an energy barrier Delta = 39.6(2) cm(-1). Taking into account the environment of both DyIII ions in 3, it was expected that both metallic centers displayed similar dynamic magnetic behavior. The latter was rationalized by ab initio CASSCF/SI-SO calculations

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.

The rational synthesis of the 2-{1-methylpyridine-N-oxide-4,5-[4,5-bis(propylthio)tetrathiafulvalenyl]-1H-benzimidazol-2-yl}pyridine ligand (L) is described. It led to the tetranuclear complex [Dy4(tta)12(L)2] (Dy-Dy2-Dy) after coordination reaction with the precursor Dy(tta)3⋅2 H2O (tta(-) = 2-thenoyltrifluoroacetonate). The X-ray structure of Dy-Dy2-Dy can be described as two terminal mononuclear units bridged by a central antiferromagnetically coupled dinuclear complex. The terminal N2O6 and central O8 environments are described as distorted square antiprisms. The ac magnetism measurements revealed a strong out-of-phase signal of the magnetic susceptibility with two distinct sets of data. The high- and low-frequency components were attributed to the two terminal mononuclear single-molecule magnets (SMMs) and the central dinuclear SMM, respectively. A magnetic hysteresis loop was detected at very low temperature. From both structural and magnetic points of view, the tetranuclear SMM Dy-Dy2-Dy is a self-assembly of two known mononuclear SMMs bridged by a known dinuclear SMM.

The interest for lanthanide circularly polarized luminescence (CPL) has been quickly growing for 10 years. However, very few of these studies have involved correlation between the dissymmetry factor (g lum ) and the chemical modifications in a series of chiral ligands. Four polymeric compounds of Eu(III) were prepared by using a series of binaphtyl derivatives for which the size of the π system as well as the number of stereogenic elements (i.e., the binaphtyl moiety) are modulated. The resulting {[Eu(hfac) 3 ((S)/(R)-L x )]} n (x = 1 and 3) and {[Eu(hfac) 3 ((S,S,S)/(R,R,R)-L x )]} n (x = 2 and 4) have been characterized by powder X-ray diffraction by comparison with the X-ray structures on single crystal of the Dy(III) analogs. In solution, the structure of the complexes is deeply modified and becomes monomeric. The nature of the ligand induces change in the shape of the CPL spectra in CH 2 Cl 2 solution. Furthermore, a large jg lum j = 0.12 of the magnetic-dipole transition for the [Eu(hfac) 3 ((S,S,S)/ (R,R,R)-L 2 )] complex involving the ligand with three stereogenic elements and an extended π system has been measured. This report also shows CPL measurements in solid state for the series of {[Eu(hfac) 3 ((S)/(R)-L x )]} n (x = 1 and 3) and {[Eu(hfac) 3 ((S,S,S)/(R,R,R)-L x )]} n (x = 2 and 4) polymers.