Synthesis, Magnetic and High-Field EPR Investigation of Two Tetranuclear NiII-Based Complexes.

Two tetranuclear compounds with a cubane-like structure were synthesized from a one-pot reaction between NiII and 2,2,6,6-tetramethyl-3,5-heptanedione (Hdpm) for 1 or 4,4,4-trifluoro-1-phenyl-1,3-butanedione (Hbta) for 2 in the presence of sodium methoxide. The crystal structures of both compounds have been determined by single-crystal X-ray diffraction, and their magnetic properties have been studied by SQUID magnetometry as well as by high-field electron paramagnetic resonance (HFEPR) spectroscopy. For 1, the temperature dependence of the magnetic susceptibility can be fitted by taking into account Ni···Ni ferromagnetic interactions, which leads to an S = 4 ground-state spin. For 2, both antiferromagnetic and ferromagnetic interactions are present. However, the latter are dominant, which also leads to an S = 4 ground-state spin, in good agreement with the HFEPR study.

SMM Behavior Tuned by an Exchange Coupling LEGO Approach for Chimeric Compounds: First 2p-3d-4f Heterotrispin Complexes with Different Metal Ions Bridged by One Aminoxyl Group.

Coordination compounds containing three different spin carriers (2p, 3d, and 4f), with the general formula [MIIDyIII(LH)(hfac)5] (M = Co, Ni, Mn, Zn), have been obtained using Mannich ligands decorated with a nitronyl-nitroxide fragment. The synthetic approach is general and leads to binuclear 3d-4f complexes, the two metal ions being bridged by one aminoxyl group and by one oxygen atom arising from a hfac- ligand. Triangular spin topology affords significant 2p-3d, 3d-4f, and 2p-4f exchange interactions. For the [CoIIDyIIIRad] derivative obtained using a nitronyl-nitroxide chiral ligand, a high energy barrier (∼200 cm-1) and a slow relaxation behavior below 30 K were found and rationalized by ab initio calculations. The improvement of magnetic properties comes from the synergy of optimal single ions properties and exchange couplings contributions where the CoII-Rad interaction becomes the leading one. The role played by this interaction is clearly proved by the investigation of the magnetic properties of the [ZnIIDyIIIRad] derivative, with a much lower energy barrier (12.7 cm-1) and by the lack of SMM behavior of the previously reported [CoIIDyIIIRad] compound ( Chem. Commun . 2017 , 53 , 6504 ), with a linear topology of spin carriers and a negligible CoII-Rad interaction.

Magnetic Cationic Copper(II) Chains and a Mononuclear Cobalt(II) Complex Containing [Ln(hfac)4]- Blocks as Counterions.

Four new heterospin compounds with molecular formula {[Cu2(hfac)3(TlTrzNIT)2][Ln(hfac)4]} n·C7H16 (LnIII = Gd (1), Tb (2), or Dy (3)) and [Co(hfac)(TlTrzNIT)2][Dy(hfac)4] (4), where hfac is hexafluoroacetylacetonato and TlTrzNIT is the nitronylnitroxide radical 1-( m-tolyl)-1 H-1,2,3-triazole-4-(4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide), were obtained. All structures were determined by single-crystal X-ray diffraction. In compounds 1-3, the TlTrzNIT radical is bridge-coordinated to copper(II) ions, leading to positively charged copper(II)-radical chains containing [Ln(hfac)4]- as counterions. In compound 4, the cobalt(II) ion is coordinated to two TlTrzNIT radicals and one hfac ligand in bidentate mode leading to a mononuclear cationic complex that contains [Dy(hfac)4]- as counterion. Magnetic measurements of all complexes were performed. Magnetic data were fit considering the contributions of the copper(II)-radical chain and a paramagnetic gadolinium(III) ion for 1. The sign and magnitude of the magnetic coupling constants extracted from the fit were confirmed by density functional theory calculations. The obtained spin topology shows an alternated ferro-antiferromagnetic chain. Field-induced single molecule magnet behavior was observed for the Dy derivatives 3 and 4, in agreement with CASSCF calculations performed for the latter system.

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.

Binuclear Lanthanide-Radical Complexes Featuring Two Centers with Different Magnetic and Luminescence Properties.

Binuclear complexes with general formula [Ln2(hfac)6(H2O)2(dppnTEMPO)] (LnIII = Gd, Tb, and Dy) have been obtained using the paramagnetic ligand 1-piperidinyl-4-[(diphenylphosphinyl)amino]-2,2,6,6-tetramethyl (dppnTEMPO) as a bridge. One of the lanthanide ions is ferromagnetically coupled with the TEMPO moiety. Two of the complexes (Dy and Tb) show slow relaxation of the magnetization, and the non-magneto-equivalence of the two LnIII ions was clearly observed. The ab initio CASSCF calculations were employed to confirm this behavior, as well as to rationalize the Ln-Rad interaction. The simulations of the magnetic properties were allowed by the insights given by the calculations. The inequivalence of the TbIII ions was also proved by emission spectroscopy.

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 Co(II)-Mn(III) 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.

A chimeric design of heterospin 2p-3d, 2p-4f, and 2p-3d-4f complexes using a novel family of paramagnetic dissymmetric compartmental ligands.

End-off bicompartmental ligands bearing a nitronyl-nitroxide arm have been designed for synthesizing various heterospin molecular systems. These ligands can selectively interact with 3d and 4f metal ions, leading to 2p-4f, 2p-3d, and 2p-3d-4f complexes. The magnetic properties of the 2p-4f and 2p-3d-4f complexes have been investigated and rationalized by theoretical calculations.

First coordination compounds based on a bis(imino nitroxide) biradical and 4f metal ions: synthesis, crystal structures and magnetic properties.

The synthesis, crystal structures and magnetic properties of two families of heterospin complexes containing lanthanide ions and a bis(imino nitroxide) biradical (IPhIN = 1-iodo-3,5-bis(4',4',5',5'-tetramethyl-4',5'-dihydro-1H-imidazole-1'-oxyl)benzene) are reported: in [Ln2(hfac)6(IPhIN)(H2O)2] compounds, two lanthanide ions [Ln = Gd(III) (1) and Dy(III) (2)] are coordinated to the biradical, and in [Ln(hfac)3(IPhIN)(H2O)] compounds, one lanthanide ion (Ln = Tb(III) (3), Gd(III) (4) or Dy(III) (5)) is coordinated to the biradical. Ferromagnetic intramolecular magnetic interactions between Gd(III) and the biradical were found for 1 and 4, while intramolecular magnetic interactions between the radicals were ferro- and antiferromagnetic, respectively. Compound 2 shows a field induced slow relaxation of magnetization, which (under an external applied field of 2 kOe) exhibits an activation energy barrier of ΔE/kB = 27 K and a pre-exponential factor of 1.4 × 10(-8) s. To support the magnetic characterization of compound 3ab initio calculations were also performed.

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.