Easy-plane to easy-axis anisotropy switching in a Co(ii) single-ion magnet triggered by the diamagnetic lattice

Single ion magnets SIMs with large magnetic anisotropy are promising candidates for realization of single molecule based magnetic memory and qubits. Creation of materials with magnetically uncoupled spatially separated SIMs requires dilution in a diamagnetic matrix. Herein, we report that progressive dilution of paramagnetic Co II by diamagnetic Zn II in the SIM [CoxZn 1 amp; 8722;x piv 2 2 NH2 Py 2], x 1 0 beyond a threshold of 50 reveals an abrupt structural change, where the distorted tetrahedral Zn coordination structure is superimposed on the remaining Co ions, which were initially in a distorted octahedral environment. Dilution induced structure modification switches the magnetic anisotropy from easy plane D 36.7 cm amp; 8722;1 to easy axis type D amp; 8722;23.9 cm amp; 8722;1 , accompanied by a fivefold increase of the magnetic relaxation time at 2 K. Changes of the static and dynamic magnetic properties are monitored by electron paramagnetic resonance spectroscopy and AC susceptibility measurements. Complementary quantum chemical ab initio calculations quantify the influence of structural changes on the electronic structure and the magnetic anisotropy. Thus, magnetic dilution hits two goals at once, the creation of isolated magnetic centres and an improvement of their SIM propertie

Coordination polymers based on trinuclear heterometallic pivalates and polypyridines: Synthesis, structure, sorption and magnetic properties

International audienceIt was shown that interaction of trinuclear pivalates Fe2MO(Piv)6(Hpiv)3 (M = NiII or CoII, Piv = (CH3)3CCO2−) with pyridine-containing ligands - trans-bis-1,2-(4-pyridyl)ethylene (trans-dpe), bis-1,3-(4-pyridyl)propane (py2Pn) resulted in formation of 2D porous coordination polymers [Fe2NiO(Piv)6(trans-dpe)1.5]n (1), [Fe2CoO(Piv)6(trans-dpe)1.5]n (2) and 1D polymers [{Fe2CoO(Piv)6(cis-dpe)}2(trans-dpe)]n (3), [Fe2NiO(Piv)6(py2Pn)(DMF)]n (4), where cis-dpe is cis-bis-1,2-(4-pyridyl)ethylene, formed due to in situ isomerization of trans-dpe. Interaction of Fe2NiO(Piv)6(Hpiv)3 with bis-2,3-(4-pyridyl)-2,3-dihydroxybutane led to in situ destruction of this ligand and isolation of trinuclear complex Fe2NiO(Piv)6(pyCOCH3)3 (5). X-ray structures of all five complexes were determined; compounds 1 and 2 were found to be isostructural. It was shown that crystal structures of [Fe2MO(Piv)6(trans-dpe)1.5]n complexes significantly changed at temperature variation. Sorption capacity of 1 and 2 on N2, H2 at 78 K (total volume of pores VT less than 0.045 cm3/g) was much lower than sorption capacity on methanol and ethanol at 293 K (VT from 0.16 cm3/g to 0.37 cm3/g), which can be explained by flexibility of crystal structure of these coordination polymers. Magnetic properties of 1 and 2 were simulated taking into account exchange interactions between metal ions and zero-field splitting of NiII or CoII. Exchange coupling between trinuclear units Fe2MO(Piv)6 was negligibly small

Halogen-free GeO2 conversion electrochemical reduction vs. complexation in (DTBC)(2)Ge[Py(CN)(n)] (n=0...2) complexes

International audience3,5-di-tert-Butylcatecholate (DTBC) germanium complexes (DTBC)2Ge[Py(CN)n]2 (n = 0…2) have been synthesized from GeO2, 3,5-di-tert-butylcatechol and cyano-substituted pyridines Py(CN)n and characterized by elemental analysis, NMR, IR and UV-VIS spectroscopy. The structure of 1 (with 4-cyanopyridine) has been determined by X-ray single crystal analysis. UV-VIS spectra have shown that these complexes are stable in CH3CN, toluene and CH2Cl2 solutions; in contrast, they are rapidly decomposed by dimethylformamide and tetrahydrofuran. Complexes 1 and 2 (with 4-cyano and 3-cyanopyridine) are electrochemically reducible in toluene/1 M Bu4NPF6 at E = -1.3…-1.7 V vs. AgCl. The quantum-chemical study of these complexes is in accordance with the unsuccessful attempts to obtain analogous derivatives with 2-cyanopyridine and 2,6-dicyanopyridine

Mono- and Mixed Metal Complexes of Eu3+, Gd3+, and Tb3+ with a Diketone, Bearing Pyrazole Moiety and CHF2-Group: Structure, Color Tuning, and Kinetics of Energy Transfer between Lanthanide Ions

Three novel lanthanide complexes with the ligand 4,4-difluoro-1-(1,5-dimethyl-1H-pyrazol-4-yl)butane-1,3-dione (HL), namely [LnL3(H2O)2], Ln = Eu, Gd and Tb, were synthesized, and, according to single-crystal X-ray diffraction, are isostructural. The photoluminescent properties of these compounds, as well as of three series of mixed metal complexes [EuxTb1-xL3(H2O)2] (EuxTb1-xL3), [EuxGd1-xL3(H2O)2] (EuxGd1-xL3), and [GdxTb1-xL3(H2O)2] (GdxTb1-xL3), were studied. The EuxTb1-xL3 complexes exhibit the simultaneous emission of both Eu3+ and Tb3+ ions, and the luminescence color rapidly changes from green to red upon introducing even a small fraction of Eu3+. A detailed analysis of the luminescence decay made it possible to determine the observed radiative lifetimes of Tb3+ and Eu3+ and estimate the rate of excitation energy transfer between these ions. For this task, a simple approximation function was proposed. The values of the energy transfer rates determined independently from the luminescence decays of terbium(III) and europium(III) ions show a good correlation

Self-Assembly of a Two-Dimensional Coordination Polymer Based on Silver and Lanthanide Tetrakis-Acylpyrazolonates: An Efficient New Strategy for Suppressing Ligand-to-Metal Charge Transfer Quenching of Europium Luminescence

A new strategy for the easy polymerization of anionic [Ln(Qcy)4]− (HQcy-4-(cyclohexanecarbonyl)-5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one) into two-dimensional layers of [AgLn(Qcy)4]n (Ln = Sm, Eu, Gd, Tb and Dy) is proposed by binding the single molecular anions [Ln(Qcy)4]− to silver cations through the coordination of the pyridinic nitrogen atoms of the pyrazolonate rings. The luminescent properties of [AgLn(Qcy)4]n have been studied in detail, and it was shown that the previously described low photoluminescence quantum yield (PLQY) of [Eu(Qcy)4]− is due to Ligand-To-Metal Charge Transfer (LMCT) quenching, which is effectively suppressed in the heterometallic [AgEu(Qcy)4]n polymer. Sensibilization coefficients for H3O[Eu(Qcy)4], [AgEu(Qcy)4]n, and H3O[Sm(Qcy)4] complexes (n ≈ 1) were estimated via theoretical analysis (also by using Judd-Ofelt theory for Sm3+) and PLQY measurements

Easy-plane to easy-axis anisotropy switching in a Co(ii) single-ion magnet triggered by the diamagnetic lattice

Single-ion magnets (SIMs) with large magnetic anisotropy are promising candidates for realization of single-molecule based magnetic memory and qubits. Creation of materials with magnetically uncoupled spatially separated SIMs requires dilution in a diamagnetic matrix. Herein, we report that progressive dilution of paramagnetic Co(ii) by diamagnetic Zn(ii) in the SIM ([CoxZn(1−x)(piv)2(2-NH2-Py)2], x = 1 ÷ 0) beyond a threshold of 50% reveals an abrupt structural change, where the distorted tetrahedral Zn coordination structure is superimposed on the remaining Co ions, which were initially in a distorted octahedral environment. Dilution-induced structure modification switches the magnetic anisotropy from easy-plane (D = 36.7 cm−1) to easy-axis type (D = −23.9 cm−1), accompanied by a fivefold increase of the magnetic relaxation time at 2 K. Changes of the static and dynamic magnetic properties are monitored by electron paramagnetic resonance spectroscopy and AC susceptibility measurements. Complementary quantum chemical ab initio calculations quantify the influence of structural changes on the electronic structure and the magnetic anisotropy. Thus, magnetic dilution hits two goals at once, the creation of isolated magnetic centres and an improvement of their SIM properties

Rational synthesis and dimensionality tuning of MOFs from preorganized heterometallic molecular complexes

International audienceRational synthesis of a series of new heterometallic MOFs was carried out by the judicious choice of the corresponding pivalate complexes [Li2M2(piv)(6)(py)(2)] (M = Zn2+, Co2+, piv(-) = pivalate anion and py = pyridine) as a source of secondary building units, {LiM(O2CR)(3)} and an organic tricarboxylate linker as a node defining the dimensionality of the framework by the orientation of the carboxylic group in or out of the central aromatic ring plane. Thus the trimesate (btc(3-)) linker results in 3D srs topology frameworks with intersecting systems or isolated channels, and 1,3,5-benzenetribenzoate (btb(3-)) results in layered hcb isostructural compounds additionally stabilized with H-pi interactions between the layers. The layered compounds demonstrate a permanent porosity with a BET surface area of up to 688 m(2)center dot g(-1) with the possibility of selective gas adsorption (CO2 over N-2 and CH4). Zn-Based coordination polymers show notable color changes and drastic (up to 30 times) quenching of luminescence upon inclusion of different nitroaromatics

Probing Spin Crossover in a Solution by Paramagnetic NMR Spectroscopy

Spin transitions in spin-crossover compounds are now routinely studied in the solid state by magnetometry; however, only a few methods exist for studies in solution. The currently used Evans method, which relies on NMR spectroscopy to measure the magnetic susceptibility, requires the availability of a very pure sample of the paramagnetic compound and its exact concentration. To overcome these limitations, we propose an alternative NMR-based technique for evaluating spin-state populations by only using the chemical shifts of a spin-crossover compound; those can be routinely obtained for a solution that contains unknown impurities and paramagnetic admixtures or is contaminated otherwise

Synthesis, Structure and Photoluminescence Properties of Cd and Cd-Ln Pentafluorobenzoates with 2,2′:6′,2′-Terpyridine Derivatives

Six new complexes [Cd(tpy)(pfb)2] (1, tpy = 2,2′:6′,2″-terpyridine), [Ln2Cd2(tpy)2(pfb)10] (Ln = Eu (2Eu), Tb (2Tb)), [Ln2Cd2(tbtpy)2(pfb)10]·2MeCN (Ln = Eu (3Eu), Tb (3Tb), tbtpy = 4,4′,4″-tri-tert-butyl-2,2′:6′,2″-terpyridine), [Eu2Cd2(tppz)(pfb)10]n (4, tppz = 2,3,5,6-tetra-(pyridin-2-yl)pyrazine) based on pentafluorobenzoic acid (Hpfb) have been prepared and investigated. The effect of tridentate ligands on geometry heterometallic scaffolds synthesized complexes is discussed. The supramolecular crystal structures of the new compounds are stabilized by π-π, C-F···π, C-H···O, C-H...F, F….F interactions. Non-covalent interactions have been studied using Hirschfeld surface analysis. The obtained compounds were characterized by single-crystal and powder X-ray diffraction, luminescence spectroscopy, IR spectroscopy, CHN analysis. Complexes 2Ln and 3Ln exhibit metal-centered photoluminescence, but the presence of ligand luminescence bands indicates incomplete energy transfer from the d-block to the lanthanide ion

Synthesis, structure, and physical properties of new rare earth ferrocenoylacetonates

New ferrocenoylacetonate complexes of several rare earth elements, [Ln(fca)3(bpy)]·MeC6H5 (Ln = Pr (1), Eu (2), Gd (3), Tb (4), Dy (5), Ho (6), Y (7); bpy – 2,2’-bipyridine; Hfca – FcCOCH2COMe) as well as scandium ferrocenoylacetonate [Sc(fca)3]·0.5MeC6H5 (8), were synthesized and characterized by single crystal X-ray diffraction analysis. In the crystal lattice of the isostructural complexes 1–7, two [Ln(fca)3(bpy)] molecules form a pair due to stacking interactions between the bpy ligands. The Ln3+ ions are coordinated in a square antiprism geometry with a coordination number of 8. The Sc3+ ions in complex 8 are coordinated in an octahedral geometry. Thermolysis of complexes 1–7 was studied under air and argon atmospheres; in the first case, it affords perovskites LnFeO3 as one of the products. Complexes 4–6 display single-molecule magnet properties, and the effective relaxation barrier for the Dy complex 5, was found to be Δeff/kB = 241 K, which is one of the highest values obtained for a mononuclear β-diketonate lanthanide complex