Marco Evangelisti

Polymetallic clusters of Fe ^III constructed without organic bridging ligands are an emerging class of molecules with structures akin to iron oxide minerals, possessing large spin ground states and/or displaying spin frustration effects. All previous examples, [Fe ₈ ], [Fe ₁₇ ], [Fe ₃₀ ] and [Fe ₃₄ ], have been isolated from pyridine or analogous heterocyclic amine solvents. Here, we report the isolation of an [Fe ₁₆ ] cluster from dmf. The complex is ‘isostructural’ with the previously reported [Fe ₁₇ ] molecular metal oxide, but with the central, tetrahedral Fe ^III ion absent. Antiferromagnetic exchange interactions between the tetrahedral and octahedral Fe ^III ions in [Fe ₁₆ ] lead to a spin ground state of S = 20, the highest yet for this family of materials, consistent with the S = 35/2 found for [Fe ₁₇ ] containing an additional (antiferromagnetically coupled) s = 5/2 ion. Dissolution of [Fe ₁₆ ] in pyridine regenerates [Fe ₁₇ ] or the larger [Fe ₃₀ ], depending on reaction conditions, demonstrating for the first time that these species can be interconverted.

In amorphous elastomers with liquid-crystal mesogens, variable-temperature elastocaloric measurements uncover a kinetic optimum where molecular relaxation and mechanical cycling synchronize to maximize cooling performance.

Correction for ‘Dodecanuclear [NiII8Ln ₄ ] clusters and rings of corner-sharing {NiII2Ln ₂ } cubanes (Ln = Dy, Gd, Y); magnetic and magnetothermal properties’ by Thomais G. Tziotzi et al. , Dalton Trans. , 2025, 54 , 4664–4671, https://doi.org/10.1039/D5DT00175G.

We report a comprehensive magnetothermal study of the classical gadolinium salt [Gd(NO3)3] · 6H2O at temperatures approaching absolute zero. Despite its long-standing availability as a commercial compound, its magnetocaloric properties have remained unexplored. Using electron paramagnetic resonance, magnetic susceptibility, heat capacity, and direct measurements of the magnetocaloric effect, we reveal that weak dipolar interactions combined with axial crystal-field anisotropy drive antiferromagnetic ordering at TN = 0.21 K. Remarkably, [Gd(NO3)3] · 6H2O exhibits an isothermal magnetic entropy change of −ΔSm = 26.1 J K−1 kg−1 at T = 0.6 K for a modest field variation of ΔB = 1 T and an adiabatic temperature change of ΔTad = 5.0 K at T = 1.6 K for the same ΔB, placing its performance among the strongest reported for Gd-based refrigerants under comparable low-field and sub-Kelvin conditions. These results provide a reference for understanding magnetocaloric behavior in hydrated salts and highlight the interplay between dipolar coupling and crystal-field anisotropy.

Incorporating 4d and 5d metal ions into coordination frameworks offers a powerful route to quantum materials where orbital delocalization and spin-orbit coupling reshape magnetic and electronic ground states. However, such systems remain difficult to access synthetically. Here we report Mo(pyz)₂I₂, the first pyrazine-bridged square-lattice framework featuring a paramagnetic 4d metal center, obtained using a new organometallic precursor route that enables Mo incorporation. Structural and spectroscopic data establish a Mo^III({pyz₂}^•-)I₂ formulation and reveal pronounced ligand redox non-innocence accompanied by local symmetry breaking arising from a disordered distribution of neutral and reduced pyrazine linkers─the first experimental observation of local symmetry lowering in a pyrazine-based coordination solid. Magnetic measurements show strong antiferromagnetic interactions without clear evidence of long-range order, and electrical transport indicates narrow-gap semiconducting behavior. Extending pyrazine framework chemistry to the 4d block thus requires new synthetic strategies and reveals new local structural and magnetic degrees of freedom, positioning Mo(pyz)₂I₂ as a prototype for designing correlated and spin-orbit-entangled states in molecule-based quantum materials based on heavier transition metals.

We show that [choline] ₂ CoCl ₄ and [choline] ₂ ZnCl ₄ show competitive reversible adiabatic temperature and entropy changes at low working pressures due to hydrogen bonding competition in the disordered orthorhombic and ordered monoclinic phases.

We report a highly symmetric {Gd₉} molecular nanocage with the formula [Gd₉(BA)₁₆(OH)₁₀]Cl·3(C₂H₅OH)·4(H₂O), which crystallizes in the cubic space group Pn3̅n. The structure features two crystallographically distinct Gd³⁺ ions, forming highly regular triangular Gd³⁺ arrangements leading to a geometrically frustrated magnetic network. Magnetization measurements at 2 K reveal a broad plateau between 1.5 and 4 T, while zero-field heat capacity shows a Schottky anomaly centered at 0.6 K─indicative of low-lying excited states and competing magnetic interactions. The magnetocaloric effect, evaluated through both direct and indirect methods, exhibits a re-entrant profile in the isentropic curves, pointing to a nontrivial evolution of magnetic entropy under applied fields. To probe the origin of this behavior, we employed the finite-temperature Lanczos method on a model spin Hamiltonian. The results reveal that the antiferromagnetic exchange between Gd³⁺ ions, combined with the frustration inherent to the {Gd₉} geometry, leads to a degenerate ground state. An external field lifts this degeneracy, producing a regime with a sharply reduced density of states between 1.5 and 4 K, which underlies the unconventional magnetocaloric response. The {Gd₉} cage thus represents a rare example of a spin-frustrated arrangement arising from competing antiferromagnetic interactions between the Gd³⁺. These findings demonstrate how frustrated topologies and tunable low-energy excitations can be exploited to modulate the magnetothermal properties, with potential implications for cryogenic magnetic cooling technologies.

Incorporating 4d and 5d metal ions into coordination frameworks offers a powerful route to quantum materials where orbital delocalization and spin–orbit coupling reshape magnetic and electronic ground states. Yet, such systems remain largely unexplored. We introduce Mo(pyz)2I2, a pyrazine-linked square-lattice material that uniquely couples a paramagnetic heavy transition metal center with ligand-radical character, opening access to spin–orbit-entangled ground states in molecular frameworks. Structural and spectroscopic analyses establish a MoIII({pyz2}⦁−)I2 formulation, revealing pronounced ligand redox non-innocence and local symmetry breaking arising from a disordered distribution of neutral and reduced pyrazine linkers. Magnetization measurements reveal dominant antiferromagnetic interactions, while the electrical transport follows semiconducting Arrhenius behavior. Density functional calculations confirm strong Mo–pyz exchange and weak interlayer coupling. These results demonstrate how extending pyrazine frameworks to the 4d block profoundly modifies their redox and magnetic landscapes, establishing Mo(pyz)2I2 as a prototype for designing correlated and spin–orbit-entangled states in molecule-based quantum materials.

The need of operating molecular spin qubits at very low temperatures constitutes a technological limitation. This challenge is addressed by integrating, in the same material and at the molecular scale, quantum processing and magnetic refrigeration capabilities. The molecular unit is a [GdEr] heterolanthanide coordination complex, where Er(III) encodes a qubit while Gd(III) provides a large magnetocaloric effect. The properties of each component are separately studied in isostructural [LaEr] and [GdLu] complexes, where each functional ion lies next to a diamagnetic metal. All complexes are characterized by magnetic, heat capacity, and EPR measurements. The results show that the presence of both ions in the same molecule has a synergic effect on both functionalities. Thus, the coupling between Er(III) and Gd(III) spins lifts any level degeneracies even close to zero magnetic field, leading to a d = 16 set of spin states that, as revealed by pulse EPR measurements, can be coherently manipulated. In turn, Er(III) enhances the magnetocaloric effect compared to [GdLu], extending it to lower temperatures. This is corroborated by direct magnetocaloric measurements, which show the ability of this material to cool itself, and a device, down to temperatures as low as 0.4 K.