Danielle Cangussu

Dicopper(ii) metallacyclophane enables long-distance ferromagnetic coupling via spin polarization and potential selective catalyst for hydroquinone oxidation.

Herein, we present the synthesis and characterization of a series of isostructural lanthanide(III) compounds with the N-(4-carboxyphenyl)oxamic acid (H₃pcpa) ligand of the general formula as {[Ln₂(Hpcpa)₃(H₂O)₅]}_n [Ln = Dy(III) 1, Ho(III) 2, Er(III) 3]. The structure of 3 consists of neutral zig–zag chains of Er(III) ions, with Hpcpa^2– ligands acting as bridges in a bidentate/monodentate coordination mode with five water molecules achieving the eight-coordination around the two Er(III) ions within the repeating bis(carboxylate)-bridged dinuclear units along the chain. The magnetic and magnetocaloric properties were studied for 1–3. Compound 1 presents a field-induced slow relaxation of the magnetization with a “reciprocating thermal behavior” below 5 K for H = 0.25 T, while 2 shows maxima of the magnetic entropy from 3 up to 6 K for ΔH > 2 T.

Designing and implementing multielectron transfer and single-molecule magnet properties in spin crossover compounds constitute a promising way to obtain a new class of multiresponsive and multifunctional materials. This contribution uses N-phenyl-substituted pyridine-2,6-diimine (PDI) ligands to explore a novel family of spin-crossover cobalt(II) complexes, with general formula [CoL₂](ClO₄)₂·xH₂O [L = 4-MePhPDI (1, x = 1), 4-MeOPhPDI (2, x = 0), 4-MeSPhPDI (3, x = 0), 4-Me₂NPhPDI (4, x = 0.5), and 2,4-Me₂PhPDI (5, x = 0)]. These mononuclear six-coordinate octahedral cobalt(II) bis(chelating) complexes incorporate tridentate PDI derivatives with various electron-donating substituents at para (X₄ = Me, OMe, SMe, and Me₂N) or ortho and para positions (X₂, X₄ = Me) of terminal phenyl rings. Our investigations reveal that these complexes exhibit both thermally-induced low-spin (LS)/high-spin (HS) transition and field-induced slow magnetic relaxation in the LS (S = 1/2) and HS (S = 3/2) states. Moreover, they display a dual multiredox behaviour featuring one-electron oxidation of the paramagnetic Co^II ion to the diamagnetic Co^III ion and stepwise two-electron reduction of each PDI ligand to the corresponding imine-type PDI˙⁻ π-radical anion and diimine-type PDI²⁻ dianion, which positions them as candidates for prototypes of spin quantum transistors and capacitors, offering potential applications in quantum information processing.

Coexistence of tunable spin-crossover and field-dependent single-molecule magnet behaviours in cobalt( ii )-pyridine-2,6-diiminephenyl complexes.

A new metallosupramolecular compound of formula Na₆Ni₃(dabtzox)₃·10H₂O (1) was prepared by the metal-mediated self-assembly of the potentially tris(chelating) N,N′-2,2′-(4,4′-bithiazole)bis(oxamate) (dabtzox) ligand and its structure was determined by single-crystal X-ray diffraction. The structure of 1 comprises linear centrosymmetric helicate-type [Ni^II ₃(dabtzox)₃]⁶⁻ complex anions which are interconnected through hydrated Na^I cations. The two crystallographically independent nickel(II) ions [Ni(1) and Ni(2)] are six-coordinate in distorted octahedral geometries with Ni(1)N₃O₃ and Ni(2)N₆ chromophores. The value of the intra-helicate Ni(1)⋯Ni(2) separation is 4.082(2) Å. The investigation of the static (dc) magnetic properties of 1 in the temperature range 1.9–300 K reveals the occurrence of weak intramolecular ferro- [J₁ = +0.6 cm⁻¹ for Ni(1)⋯Ni(2)] and antiferromagnetic interactions [J₂ = −0.9 cm⁻¹ for Ni(1)⋯Ni(1)ⁱ] together with a moderate zero-field splitting (|D| = 2.3 cm⁻¹), the Hamiltonian being defined as DFT- and CASSCF/NEVPT-type theoretical calculations were carried out to substantiate these parameters and illustrate the occurrence of the strict orthogonality between the d_z² [Ni(1)] and d_(x²−y²) [Ni(2)] magnetic orbitals and the spin polarisation mechanism [Ni(1) and Ni(1)ⁱ] accounting for the unusual intramolecular ferro- and antiferromagnetic interactions, respectively. Dynamic (ac) magnetic susceptibility measurements in the temperature range 2.0–10.0 K showed the lack of any out-of-phase signal for 1, unlike what is observed for the previously reported triple helicate of formula K₆Co₃(dabtzox)₃·8H₂O·MeOH (2) which exhibits intramolecular antiferromagnetic coupling and field-induced slow magnetic relaxation. A detailed magneto-structural comparison between 1 and 2 is carried out to elucidate their different magnetic behaviours.

Field-induced SMM behaviour in a series of tetrahedral 1,2-disubstituted benzimidazole cobalt( ii ) complexes and their catalytic properties for an eco-friendly cycloaddition of CO ₂ with epoxides.

The cobalt(II)-mediated self-assembly of the potentially tris(chelating) N,N′-2,2′-(4,4′-bithiazole)bis(oxamate) (dabtzox) ligand gives a new metal–organic supramolecular nanomagnet of formula K₆Co₃(dabtzox)₃·8H₂O·MeOH (1) featuring a unique linear triple-stranded trinuclear structure of the helicate type.

The reaction of aqueous solutions of Eu^III, Tb^III, and Gd^III ions with Na₂Hpcpa [H₃pcpa = N-(4-carboxyphenyl)oxamic acid] afforded three new isostructural oxamate-containing lanthanide(III) coordination polymers of general formula {Ln^III₂(Hpcpa)₃(H₂O)₅·H₂O}_n [Ln = Eu (1),Tb (2), and Gd(3)]. Their structure is made up of neutral zigzag chains running parallel to the [101] direction where double syn–syn carboxylate(oxamate)-bridged dilanthanide(III) pairs (Ln1 and Ln2) are linked by three Hpcpa^2– ligands, one of them with the μ–κ²O,O′:κO″ coordination mode and the other two with the μ₃-κ²O,O′:κO″:κO′′′. Additionally, two of those chains are interlinked through hydrogen bonding and π–π type interactions, resulting in a porous structure with channels where water molecules are hosted. The emission properties of 1 and 2 are evaluated as a function of the temperature, exhibiting an emission in red and green, respectively. The external quantum yield for 2 is approximately 7 times that obtained for 1, indicating that the oxamate ligand is a better sensitizer for Tb^III ions. The temperature dependence of the dc magnetic properties of 1–3 reveals a different magnetic behavior depending on the nature of the Ln^III ion. A continuous decrease of χ_MT occurs for 1 upon cooling, and finally χ_MT tends to vanish, as expected for the thermal depopulation of the six magnetic ⁷F_J excited states (J = 1–6) of the Eu^III ion with a nonmagnetic ⁷F₀ ground state. χ_MT for 2 decreases sharply with decreasing the temperature due to the depopulation of the splitted m_J levels of the ⁷F₇ ground state of the magnetically anisotropic Tb^III ion. A very weak antiferromagnetic interaction between the magnetically isotropic Gd^III ions across the double carboxylate(oxamate) bridge is responsible for the small decrease of χ_MT at low temperatures for 3. The dynamic (ac) magnetic properties of 2 and 3 reveal a slow magnetic relaxation with very incipient frequency-dependent χ_M″ signals below 6.0 K (2) and frequency-dependent χ_M″ peaks below 10.0 K (3) under nonzero applied dc magnetic fields, being thus new examples of field-induced single molecule magnets (SMMs).

Molecular magnetism has made a long journey, from the fundamental studies on through-ligand electron exchange magnetic interactions in dinuclear metal complexes with extended organic bridges to the more recent exploration of their electron spin transport and quantum coherence properties. Such a field has witnessed a renaissance of dinuclear metallacyclic systems as new experimental and theoretical models for single-molecule spintronics and quantum computing, due to the intercrossing between molecular magnetism and metallosupramolecular chemistry. The present review reports a state-of-the-art overview as well as future perspectives on the use of oxamato-based dicopper(II) metallacyclophanes as promising candidates to make multifunctional and multiresponsive, single-molecule magnetic (nano)devices for the physical implementation of quantum information processing (QIP). They incorporate molecular magnetic couplers, transformers, and wires, controlling and facilitating the spin communication, as well as molecular magnetic rectifiers, transistors, and switches, exhibiting a bistable (ON/OFF) spin behavior under external stimuli (chemical, electronic, or photonic). Special focus is placed on the extensive research work done by Professor Francesc Lloret, an outstanding chemist, excellent teacher, best friend, and colleague, in recognition of his invaluable contributions to molecular magnetism on the occasion of his 65th birthday.