Stéphane Soriano

New Families of Hetero-tri-spin 2p−3d−4f Complexes: Synthesis, Crystal Structures, and Magnetic Properties

In this work we report the synthesis, crystal structures, and magnetic behavior of 2p-3d-4f heterospin systems containing the nitroxide radical 4-azido-2,2,6,6-tetramethylpiperidine-1-oxyl radical (N3tempo). These compounds were synthesized through a one-pot reaction by using [Cu(hfac)2], [Ln(hfac)3] (hfac = hexafluoroacetylacetonate, Ln = Dy(III), Tb(III) or Gd(III)), and the N3tempo radical. Depending on the stoichiometric ratio used, the synthesis leads to penta- or trimetallic compounds, with molecular formulas [Cu3Ln2(hfac)8(OH)4(N3tempo)] (Ln = Gd, Tb, Dy) and [CuLn2(hfac)8(N3tempo)2(H2O)2] (Ln = Gd, Dy). The magnetic properties of all compounds were investigated by direct current (dc) and alternating current (ac) measurements. The ac magnetic susceptibility measurements of Tb(III)- and Dy(III)-containing compounds of both families revealed slow relaxation of the magnetization, with magnetic quantum tunneling in zero field.

New Synthetic Route toward Heterometallic 3d–3d′ and 3d–4f Single-Molecule Magnets. The First CoII–MnIII Heterometallic Complex

Four tetranuclear heterometallic complexes, [Co(II)2Mn2(III)(dpm)4(MeO)6] (1) and [Ln(III)2Mn(III)2(dpm)6(MeO)6(MeOH)n], where Ln = Gd (2, n = 2), Tb (3, n = 2), and Dy (4, n = 0), have been obtained following the same general synthetic route, namely, the one-pot reaction between 2,2,6,6-tetrametil-3,5-heptanodione (Hdpm), MnCl2 and CoCl2 or Ln(NO3)3 in the presence of sodium methoxide. Within the four compounds, the metal ions bridged by methoxide ligands display a defect-diheterocubane core. Compounds 1, 3, and 4 show slow relaxation of the magnetization below 4 K.

New copper(II)-radical one dimensional chain: Synthesis, crystal structure, EPR, magnetic properties and DFT calculations

The novel chain compound [Cu(Phtfac)(2)(NITpPy)](n) (where NITpPy = 4-pyridyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and Phtfac = 4,4,4-trifluoro-1-phenylbutane-1,3-dione) was synthesized and characterized structurally, magnetically and by EPR. The compound contains two non equivalent Cu(II) ions, Cu1 and Cu2, located at inversion centers and bridged by a NITpPy ligand coordinating Cu1 through the pyridine donor atom, and Cu2 through a N-O group, resulting in a head-to-head chain structure. The chain exhibits an unusual spin topology with two alternating pairs of magnetic coupling constants. The magnetic behavior was modeled considering a 16-membered ring with alternating exchange couplings. The best fit parameters indicate a ferromagnetic (J(1) = 29.4 cm(-1)), and antiferromagnetic (J(2) = -4.6 cm(-1)) couplings and an average g = 2.05, corresponding to a ground state with three parallel and one anti-parallel spin for each Cu(2)NITpPy(2) unit. DFT calculations allowed assigning the ferromagnetic coupling to Cu-O-NITpPy and the antiferromagnetic coupling to Cu-N(Py)-NITpPy. Single crystal EPR spectra display only one resonance for most field orientations, as a consequence of the collapse of the signals of the different spins produced by the exchange interactions. The observed g-tensor of this resonance is related to those expected for the Cu(II) and radical ions. Comparison of this compound with other Cu-NIT radicals chains bearing different substituents in the organic radicals, highlights that the beta-diketonate ligand plays an important role in determining the final architecture. Moreover, we show how a knowledge of the spin density distribution in the initial building blocks is essential to rationalize the magnetic behavior of the resulting product.

One-dimensional coordination polymers constructed from binuclear 3d–4f nodes and isonicotinato spacer

Three new 1-D coordination polymers, [Co(valpn)Gd(hfac)2(IN)]n (1), [Ni(valpn)Gd(hfac)2(IN)]n (2), and [Ni(valpn)Dy(hfac)2(IN)]n (3), were constructed by connecting {MII(valpn)LnIII(hfac)2} nodes through isonicotinato spacers (IN−), with hexafluoroacetylacetonato being hfac and 1,3-propanediylbis(2-iminomethylene-6-methoxy-phenol) (H2valpn) being the Schiff base obtained from the condensation reaction between o-vanillin and 1,3-diaminopropane. The synthetic approach relied on the substitution of the acetate ligands from the binuclear precursors [MII(CH3OH)(valpn)LnIII(hfac)2(CH3COO)] with the isonicotinato ligand. The investigation of the magnetic properties of all compounds showed a ferromagnetic interaction attributed to the intranode exchange interaction between the 3d and 4f metal ions. For compound 3, the AC magnetic measurements indicated a field-induced slow relaxation of the magnetization of the [NiIIDyIII] nodes.

Synthesis, Crystal Structures, and EPR Studies of First MnIIILnIII Hetero-binuclear Complexes

A new family of binuclear complexes [MnIIILnIII(dpm)4(MeO)2(MeOH)2] is reported (where Ln = LaIII (1), PrIII (2), and EuIII(3)). These compounds were obtained from a one-pot reaction between 2,2,6,6-tetramethyl-3,5-heptanodione (Hdpm), MnII, and the respective LnIII salt in the presence of sodium methoxide. The derivative containing the diamagnetic ion LaIII has been synthesized in order to characterize the local anisotropy of the MnIII ion. High-field electron paramagnetic resonance (HFEPR) spectroscopy shows that the MnIII ion, with an elongated octahedral geometry in all compounds, has a significant axial zero-field splitting and a small rhombic anisotropy. Additionally, the HFEPR measurements indicate that there is almost no exchange between the spin carriers in these compounds, all of which exhibit field-induced slow relaxation of the magnetization.