Pablo Alborés

We report the synthesis, structure, and magnetic properties of a novel Co/Dy heterometallic complex, [Co^III ₄Co^II ₂Dy^III ₂(tea)₄(CH₃COO)₄(OH)₂(NO₃)₄]·2H₂O (1), the first structurally characterized example of a mixed-valent {Co^III ₄Co^II ₂Dy^III ₂} motif. It comprises two butterfly-like {Co^III ₂Co^IIDy^III} units linked by carboxylate and alkoxide bridges. X-ray diffraction shows unique Dy(III) and Co(II) sites, with Dy(III) nine-coordinated and Co(II) in a rhombic tetrahedral geometry. Magnetic data and quantum chemical calculations reveal weak Co(II)–Co(II) antiferromagnetic exchange, negligible Co(II)–Dy(III) interactions, and moderate Co(II) zero-field splitting (D ≈ 12–20 cm⁻¹), which drives single-molecule magnet behavior below 14 K. AC studies indicate multiple tunneling pathways and an Orbach barrier (U_eff ≈ 65 cm⁻¹) arising from Co(II), while Dy(III) ions remain largely magnetically decoupled.

In this work we report the synthesis, structural characterization and magnetic properties of a family of butterfly complexes {Cr₂Ln₂} with Ln = Tb (4), Ho (5), Er (6), Tm (7) and Yb (8), extending the family of previously reported isostructural compounds with Gd (1), Dy (2) and Y (3). As in 1 and 2, an anti-ferromagnetic Cr(III)–Ln(III) exchange interaction is found. For oblate ions 4 and 5, SMM behavior with a purely Orbach relaxation mechanism is observed with thermal barriers of 38 cm⁻¹ (4) and 32 cm⁻¹ (5). Complex 4 displays hysteresis opening up to 2.4 K with loss of magnetization at zero field. The prolate complex ions 6 and 7 are field-induced SMM's with dominant Orbach, direct and QTM relaxation mechanisms. Compound 8 did not show SMM properties.

A new series of Co(iii)/Dy(iii) complexes bearing long C_nH_2n+1 alkyl chains (n = 3, 4, 6, 8 and 10) at a diethanolamine ligand, and exhibiting an hexanuclear core, shows SMM behavior with chain length relaxation times dependency.

We report the synthesis, structural characterization and SMM behaviour of a new mixed valence Co(II)/Co(III) dinuclear complex bearing the H₂pmide ligand. Well defined molecule pairs are observed in the crystal structure, bound through H-bond interactions directed by aqua ligands. From DC magnetometry data, a spin-only Hamiltonian approach including an axial zero-field splitting term seems to be enough for reasonable modelling, with a sizeable D parameter close to 40 cm⁻¹. The first order orbital contribution is extensively quenched due to strong distortion from octahedral symmetry of the Co(II) site. Quantum computation at the CASSCF level supports this interpretation. To model low temperature magnetization data, the H-bond intermolecular exchange interaction is required, with a magnitude close to −1 cm⁻¹, well supported by broken-symmetry DFT computation. This exchange is highly anisotropic due to the existence of a well isolated Kramers doublet at the Co(II) site. AC magnetic susceptibility shows field-induced SMM behaviour with competing Orbach and Raman relaxation pathways as well as a quantum tunnelling process at the lowest probed temperatures. The Orbach thermal barrier agrees with the expected one from combined experimental and quantum computed DC magnetometry analysis.

We report a combined computational and experimental study of efficient QTM suppression in {Cr₃Dy₃} triangle-in-triangle SMMs.

We are reporting the synthesis and structural characterization of a new family of butterfly complexes with formula [Co₂^IIILn₂^III−(μ₃−(OR))₂] where −OR is an alcohol‐amine type ligand, in this case N‐methyldiethanolamine (H₂mdea) with Ln=Tb, Dy, Ho, Er and Yb. This new family adds to the previously reported one, where the alcohol‐amine ligand is triethanolamine (H₃tea), and allows a one‐to‐one comparison between them. From a combined experimental study, that included DC and AC magnetometry as well as HF‐EPR measurements, and a theoretical approach based on Broken‐Symmetry DFT and CASSCF‐SA‐SOC ab‐initio computations, we discuss the single molecule magnet (SMM) performance in these complexes. We focus in a few key structural parameters that correlate with the magnetization relaxation behaviour observed along the different explored lanthanide ions.

We are reporting the synthesis and structural characterization of a new hexanuclear Co(II)/Co(III) complex starting from a versatile pivalate cobalt precursor and the racemic mixture of a chelating Schiff base type ligand. The main [Co^II ₄Co^III ₂(μ₃-OH)₂(μ-OR)₂(μ-OR′)₂(μ-OR′′)₂]⁶⁺ core is unprecedented and exhibits an inversion center that affords only two unique Co(II) sites. We performed DC and AC magnetic measurements and analysed them in terms of the anisotropic exchange of ground Kramers doublets at each Co(II) site due to their unquenched angular orbital contribution to the magnetic moment. Quantum computations support the experimental data treatment. The interplay of dominant antiferromagnetic exchange, inversion symmetry and a non-collinear main quantization axis affords an exchange energy spectrum with mostly non-magnetic states. Nevertheless, field induced SMM behaviour is observed at 1500 Oe and below 3 K which might be explained by the relaxation of the first excited magnetic state (which is populated enough) through the next closest excited state. The Orbach and/or Raman mechanism could be operative from the experimental and quantum computed results.

The formation of the symmetrical μ₃-carbonate-bridged self-assembled trinuclear Ni^II complex Na₂{[Ni(LO)₂(H₂O)]₃(μ₃-CO₃)} (LO is the carboxylate anion of a L-tyrosine derivative), involves atmospheric CO₂ uptake. The asymmetric unit of the complex comprises an octahedral coordination for the Ni^II with two L-tyrosine-based ligands, a water molecule and one O atom of the carbonate bridge. The Ni₃–μ₃-CO₃ core in this compound is the first reported of this kind according to the Cambridge Structural Database (CSD). The supramolecular structure is mainly sustained by hydrogen bonds developed by the phenolic functionality of the L-tyrosine moiety of one ligand and the carboxylate group of a neighbouring ligand. The crystal packing is then characterized by three interpenetrated supramolecular helices associated with a diastereoisomer of the type R-^sup P, which is essential for the assembly process. Magnetic susceptibility and magnetization data support weak ferromagnetic exchange interactions within the novel Ni₃–μ₃-CO₃ core. The Ni^II complex obtained under the same synthetic conditions but using the analogous ligand derived from the amino acid L-phenylalanine instead of L-tyrosine gives rise to to a mononuclear octahedral system. The results obtained for the different complexes demonstrate the role of the supramolecular structure regarding the CO₂ uptake property for these Ni^II–amino-acid-based systems.

We report a combined computational and experimental study of magnetic behaviour in a mixed valence {Co^IIICo^II4} complex with a tetrahedral μ₄O-CoII4 core.