4-(2-Tetrathiafulvalenyl-ethenyl)pyridine (TTF−CH═CH−Py) Radical Cation Salts Containing Poly(β-diketonate) Rare Earth Complexes: Synthesis, Crystal Structure, Photoluminescent and Magnetic Properties

Bulky anion effect on the architecture of chiral dysprosium single-molecule magnets

The interest for chiral tris(β-diketonato)lanthanide complexes in coordination chemistry is huge due to its Lewis acid character, optical activity, and the control of the final compound architecture. The reaction of equimolar quantities of [Dy((-)/(+)hfc)₃ (H₂ O)] (hfc^-  = 3-(heptafluoropropylhydroxymethylene)-(+/-)-camphorate) and L led to the formation of a pair of enantiomers for dinuclear complexes [Dy((-)/(+)hfc)₃ (L)]₂ ⋅C₇ H₁₆ ([(-)/(+)1]⋅C₇ H₁₆ ) (L = 4'-(4'''-pyridyl-N-oxide)-1,2':6'1''-bis-(pyrazolyl)pyridine]). Starting from the previous experimental protocol with the addition of bulky BArF anions, a partial dissociation of the chiral [Dy((-)/(+)hfc)₃ (H₂ O)] was observed leading to the isolation of a mono-dimensional cationic chiral polymer {[Dy((-)/(+)hfc)₂ (L)][BarF]}_n ⋅nCH₃ NO₂ ([(-)/(+)2]_n ⋅nCH₃ NO₂ ). Natural circular dichroism (NCD) highlighted an exciton CD couplet for [(-)/(+)2]_n but not for (-)/(+)1. The latter behaves as a single-molecule magnet (SMM) with a blocking temperature up to 4 K, whereas [(-)/(+)2]_n is a 1D assembly of field-induced SMMs with a magnetic relaxation occurring through a Raman process only.

Influence of the Increasing Number of Organic Radicals on the Structural, Magnetic, and Electrochemical Properties of the Copper(II)-Dioxothiadiazole Family of Complexes

The preparation, structures, and electrochemical and magnetic properties supported by density functional theory (DFT) calculations of three new copper(II) compounds with [1,2,5]thiadiazolo[3,4-f][1,10]phenanthroline 1,1-dioxide (td) and its radical anion (td·-) are reported: {[CuIICl(td)](μ-Cl)2[CuIICl(td)]} (1), which incorporates only neutral td ligands; [CuIICl(td·-)(td)]·2MeCN (2), which comprises one neutral td and one radical td·-; and PPN[CuIICl(td·-)2]·2DMA (3), where CuII ions are coordinated by two radical anions td·- (DMA, dimethylacetamide; PPN+, the bis(triphenylphosphine)iminium cation). All three compounds show interesting paramagnetic behavior with low-temperature features indicating significant antiferromagnetic coupling. The magnetic properties of 1 are dominated by CuII···CuII interactions (JCuCu) mediated through the Cl- bridges, while the magnetic properties of 2 and 3 are governed mainly by the td·-···td·- (Jtdtd) and CuII-td·- (JCutd) exchange interactions. The structure of 2 features only two major magnetic coupling pathways enabling the fitting of experimental data with Jtdtd = -36.0(5) cm-1 and JCutd = -12.6(2) cm-1 only. Compound 3 exhibits a complex network of magnetic contacts. Attempt to approximate its magnetic behavior using only a local magnetic contacts model resulted in Jtdtd = -5.6(1) cm-1 and two JCutd constants, -12.4(2) and -22.6(4) cm-1. The experimental fitting is critically compared with the results of broken symmetry density functional theory (BS DFT) calculations for inter- and intramolecular contacts. More consistent results were obtained with the M06 functional as opposed to popular B3LYP, which encountered problems reproducing some of the experimental intermolecular exchange interactions. Electrochemical measurements of 2 and 3 in MeCN showed three reversible nearly overlapping redox peaks appearing in a narrow potential range of -600 to -100 mV vs Fc/Fc+. Small differences between the redox events suggest that such compounds may be good candidates for new switchable materials, where the electron transfer between the metal and the ligand center is triggered by temperature, pressure, or light (valence tautomerism).

Synthesis, structural characterization and electrochemical and magnetic studies of M(hfac)2 (M = CuII, CoII) and Nd(hfac)3 complexes of 4-amino-TEMPO

Three mononuclear complexes [M(hfac)x(ATEMPO)y], where M = Cu (11) and Co (12), x = y = 2; M = Nd (13), x = 4, y = 1, and two polynuclear complexes [{Cu(hfac)2(ATEMPO)}n], where n = 2 (14) and 4 (15), were obtained by the reaction of M(hfac)x (M = CuII, CoII, NdIII; x = 2, 3) with 4-amino-TEMPO (4-amino-2,2,6,6-tetramethylpiperidin-N-oxyl) in good yields and their structural, electrochemical and magnetic properties were examined. In all cases, the radical is coordinated to the metal through the amino group, except 15, and the metal ions have an octahedral geometry, except 13. Different coordination architectures of the copper complexes were obtained as a function of the stoichiometry and solvents used. In complexes 11 and 12 the radicals show an equatorial-equatorial and axial-equatorial arrangement, respectively, giving rise to two distinct 2D supramolecular systems through intermolecular interactions. Compound 13 is the first example of a lanthanide complex of the ATEMPO radical. The NdIII ion adopts a rare nine-coordination via binding to four hfac ligands and the radical. The dinuclear complex 14 shows a (Cu-O)2 core in which the CuII ions are bridged by the oxygen atoms from the hfac ligands. In compound 15 the ATEMPO radical acts as a bidentate ligand through the amino and nitroxyl groups leading to an unprecedented tetranuclear square-shaped framework. Cyclic voltammetry showed redox processes associated with the copper and TEMPO moieties. Electrochemical impedance spectroscopy revealed the temperature dependence of the conductivity for compound 15 with a maximum of 2.09 × 10-5 S cm-1 at 408 K. The magnetic behavior of complexes 11-15 is determined by metal-radical interactions. Ferromagnetic interaction has been observed for complex 11 due to the existence of two different exchange pathways arising from the conformational arrangement of the radicals around the metal center, whereas the single conformation of the radical in complex 14 resulted in a weak antiferromagnetic coupling. In complex 15 both O-Cu and N-Cu contacts are present giving rise to ferromagnetic and antiferromagnetic interactions, respectively.

Lanthanide complexes involving multichelating TTF-based ligands

The TTF-based skeleton could be alkylated with either the di(pyrazol-1-yl)-4-pyridyl (L1) or dimethyl-2,2′-bipyridine (L2) to design multichelating ligands. The ([Yb₂(hfac)₆(L1)]·2(CH₂Cl₂)·C₆H₁₄ (1) and [Ln₂(hfac)₆(L2)]·CH₂Cl₂ (Ln = Yb (2) and Dy (3)) complexes which display either SMM behaviour with the hysteresis loop at 0.5 K or multi-NIR emissions.

Carbazole functionalized new bipolar ligand for monochromatic red light-emitting europium(iii) complex: combined experimental and theoretical study

Complete energy transfer observed from carbazole functionalized bipolar ligand as well as β-diketonate to Eu(iii) ion and Eu(iii) complex shows efficient PLQE (41.4%) with appropriate CIE color coordinates (x = 0.64, y = 0.36).

Lanthanide ion and tetrathiafulvalene-based ligand as a "magic" couple toward luminescence, single molecule magnets, and magnetostructural correlations

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.

Homogeneous liquid–liquid extraction of neodymium(iii) by choline hexafluoroacetylacetonate in the ionic liquid choline bis(trifluoromethylsulfonyl)imide

Choline hexafluoroacetylacetonate diluted in the ionic liquid choline bis(trifluoromethylsulphonyl)imide has been used as an extractant for the homogeneous liquid–liquid extraction of neodymium(iii) ions.

Tetrathiafulvalene-tetracarboxylate: an intriguing building block with versatility in coordination structures and redox properties

The synthesis of the transition metal coordination polymers containing a tetrathiafulvalene (TTF) moiety substituted with a tetracarboxylate group of the formulas [Mn(L)(0.5)(phen)(H(2)O)(2)](n).nH(2)O (1), [Mn(L)(0.5)(bpy)](n).nH(2)O (2), [Mn(L)(0.5)(bpy)(CH(3)OH)](n).2nH(2)O (3), and [Cu(L)(0.5)(bpy)(DMF)](n).n(DMF) (4) (L(4-) = TTF-tetracarboxylate; phen = 1,10-phenanthroline; bpy = 2,2'-bipyridine) is reported. Complex 1 is a two-dimensional (2-D) coordination polymer constructed of infinite carboxylate bridged Mn(II) chains and TTF moiety linkages. Complex 2 possesses a 3-D polymeric structure formed by infinite -Mn-(O-C-O)(2)-Mn- bridged one-dimensional (1-D) chains, which are further coordinated by TTF-tetracarboxylate ligands of two different orientations. Both complexes 3 and 4 show 1-D extended chain structures but are constituted by different dinuclear metal(II) units with a -Mn-(O-C-O)(2)-Mn- bridge in 3 and a -Cu-(O)(2)-Cu- bridge in 4. Electrochemical study of the solid-state compounds attests to the redox activity of the coordination system. Magnetic investigations reveal the existence of antiferromagnetic interactions between magnetic centers in complexes 3 and 4, while in 1, the paramagnetic metallic centers are isolated, in agreement with the solid-state structure.