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

Dynamics of the Ligand Excited States Relaxation in Novel β-Diketonates of Non-Luminescent Trivalent Metal Ions

Complexes emitting in the blue spectral region are attractive materials for developing white-colored light sources. Here, we report the luminescence properties of novel coordination compounds based on the trivalent group 3, 13 metals, and the 1-phenyl-3-methyl-4-cyclohexylcarbonyl-pyrazol-5-onate (QCH) ligand. [M(QCH)3] (M = Al, Ga, and In), [M(QCH)3(H2O)] (M = Sc, Gd, and Lu), [Lu(QCH)3(DMSO)], and [La(QCH)3(H2O)(EtOH)] complexes were synthesized and structurally characterized by a single-crystal X-ray diffraction study. It has been found that the luminescence quantum yields of the ligand increase by one order of magnitude upon metal coordination. A significant correspondence between the energies of the ligand’s excited states and the luminescence quantum yields to the metal ion’s atomic numbers was found using molecular spectroscopy techniques. The replacement of the central ion with the heavier one leads to a monotonic increase in singlet state energy, while the energy of the triplet state is similar for all the complexes. Time-resolved measurements allowed us to estimate the intersystem crossing (ISC) rate constants. It was shown that replacing the Al3+ ion with the heavier diamagnetic Ga3+ and In3+ ions decreased the ISC rate, while the replacement with the paramagnetic Gd3+ ion increased the ISC rate, which resulted in a remarkably bright and room-temperature phosphorescence of [Gd(QCH)3(H2O)]

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

Cobalt(II) Complexes Based on Benzylmalonate Anions Exhibiting Field-Induced Single-Ion Magnet Slow Relaxation Behavior

The reaction of (NBu4)2Bzmal (where Bzmal2− is benzylmalonate dianion) with Co(OAc)2∙4H2O gives the [Co(Bzmal)(EtOH)(H2O)]n 2D-polymer (1). The addition of 2,2′-bipyridine (bpy) to the starting system results in the [Co(Bzmal)(bpy)2]·H2O·EtOH molecular complex (2). Their molecular and crystal structures were analyzed by single-crystal X-ray crystallography. An analysis of the static magnetic data supported by the SA-CASSCF/NEVPT2 calculations revealed the presence of easy-plane magnetic anisotropy in both complexes. The AC susceptibility data confirm that both complexes show a slow field-induced (HDC = 1000 Oe) magnetic relaxation behavior

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

Structure and emission properties of dinuclear copper(i) complexes with pyridyltriazole

A new series of five highly emissive binuclear heteroleptic pyridyltriazole-Cu(i)-phosphine complexes 1-5 was synthesized and examined by different experimental (IR, elemental and thermogravimetric analysis, single crystal X-ray diffraction technique, UV-vis and fluorescence spectroscopy) and quantum chemical aproaches. Complexes 1-5 exhibited excellent stimuli-responsive photoluminescent performance in the solid state at room temperature (quantum yield (QY) = 27.5-52.0%; lifetime (tau) = 8.3-10.7 mu s) and when the temperature was lowered to 77 K (QY = 38.3-88.2; tau = 17.8-134.7 mu s). The highest QY was examined for complex 3 (52%) that can be explained by the small structural changes between the ground S-0 and exited S-1 and T-1 states leading to the small S-1-T-1 triplet gap and efficient thermally-activated delayed fluorescence. Moreover, complex 4 demonstrates reversible mechanochromic and excitation dependent luminescence.Funding Agencies|Russian Science Foundation [22-73-00043]; Ministry of Education and Science of Ukraine [0121U107533, 0122U000760]; Swedish Research Council [2020-04600]</p

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