Synthesis, Structure, and Spectroscopic and Magnetic Characterization of [Mn12O12(O2CCH2But)16(MeOH)4]·MeOH, a Mn12 Single-Molecule Magnet with True Axial Symmetry

Spectroscopic Investigation of a Metal-Metal-Bonded Fe6 Single-Molecule Magnet with an Isolated S = 19/2 Giant-Spin Ground State

The metal-metal-bonded molecule [Bu₄N][(^HL)₂Fe₆(dmf)₂] (Fe₆) was previously shown to possess a thermally isolated spin S = ¹⁹/₂ ground state and found to exhibit slow magnetization relaxation below a blocking temperature of ∼5 K [J. Am. Chem. Soc. 2015, 137, 13949-13956]. Here, we present a comprehensive spectroscopic investigation of this unique single-molecule magnet (SMM), combining ultrawideband field-swept high-field electron paramagnetic resonance (EPR) with frequency-domain Fourier-transform terahertz EPR to accurately quantify the spin Hamiltonian parameters of Fe₆. Of particular importance is the near absence of a 4th-order axial zero-field splitting term, which is known to arise because of quantum mechanical mixing of spin states on account of the relatively weak spin-spin (superexchange) interactions in traditional polynuclear SMMs such as the celebrated Mn₁₂-acetate. The combined high-resolution measurements on both powder samples and an oriented single crystal provide a quantitative measure of the isolated nature of the spin ground state in the Fe₆ molecule, as well as additional microscopic insights into factors that govern the quantum tunneling of its magnetization. This work suggests strategies for improving the performance of polynuclear SMMs featuring direct metal-metal bonds and strong ferromagnetic spin-spin (exchange) interactions.

Porous substrates as platforms for the nanostructuring of molecular magnets

This article highlights recent advances in the newly emerging field on the nanostructuration of molecular magnets using porous substrates.

Magnetic Exchange Interactions in the Molecular Nanomagnet Mn_{12}

The discovery of magnetic bistability in Mn_{12} more than 20 years ago marked the birth of molecular magnetism, an extremely fertile interdisciplinary field and a powerful route to create tailored magnetic nanostructures. However, the difficulty to determine interactions in complex polycentric molecules often prevents their understanding. Mn_{12} is an outstanding example of this difficulty: although it is the forefather and most studied of all molecular nanomagnets, an unambiguous determination of even the leading magnetic exchange interactions is still lacking. Here we exploit four-dimensional inelastic neutron scattering to portray how individual spins fluctuate around the magnetic ground state, thus fixing the exchange couplings of Mn_{12} for the first time. Our results demonstrate the power of four-dimensional inelastic neutron scattering as an unrivaled tool to characterize magnetic clusters.

Photoluminescence and magnetic analysis of a family of lanthanide(iii) complexes based on diclofenac

A family of ten isostructural complexes based on the diclofenac ligand exhibiting interesting magnetic and luminescence properties has been prepared.

Enhancing the Magnetic Anisotropy of Linear Cr(II) Chain Compounds Using Heavy Metal Substitutions

Magnetic properties of the series of three linear, trimetallic chain compounds Cr2Cr(dpa)4Cl2, 1, Mo2Cr(dpa)4Cl2, 2, and W2Cr(dpa)4Cl2, 3 (dpa = 2,2'-dipyridylamido), have been studied using variable-temperature dc and ac magnetometry and high-frequency EPR spectroscopy. All three compounds possess an S = 2 electronic ground state arising from the terminal Cr(2+) ion, which exhibits slow magnetic relaxation under an applied magnetic field, as evidenced by ac magnetic susceptibility and magnetization measurements. The slow relaxation stems from the existence of an easy-axis magnetic anisotropy, which is bolstered by the axial symmetry of the compounds and has been quantified through rigorous high-frequency EPR measurements. The magnitude of D in these compounds increases when heavier ions are substituted into the trimetallic chain; thus D = -1.640, -2.187, and -3.617 cm(-1) for Cr2Cr(dpa)4Cl2, Mo2Cr(dpa)4Cl2, and W2Cr(dpa)4Cl2, respectively. Additionally, the D value measured for W2Cr(dpa)4Cl2 is the largest yet reported for a high-spin Cr(2+) system. While earlier studies have demonstrated that ligands containing heavy atoms can enhance magnetic anisotropy, this is the first report of this phenomenon using heavy metal atoms as "ligands".

Dodenuclear [Mn(III)(8)Ln(III)(4)] clusters with 2-(hydroxymethyl)pyridine: syntheses, structures, and magnetic properties

A new family of isostructural Mn/Ln dodenuclear clusters: [Mn8Ln4(O)8(hmp)4(O2CPh)12(NO3)4(PhCO2H)(C2H5OH)] [Ln = La (1), Pr (2), Nd (3), Gd (4), Dy(5), hmpH = 2-(hydroxymethyl)pyridine] have been synthesized by the reaction of Mn(NO3)2 and Ln(NO3)3·6H2O with hmpH and benzoic acid as co-ligands. Compounds 1-5 possess a spindle-shaped core of [MnLn(μ4-O)4(μ3-O)4(μ3-OR)2(μ2-OR)8](10+), which is composed of six face-sharing defected cubane units and two square-pyramidal units. The compounds represent the highest nuclearity Mn/Ln clusters with the use of hmpH to date. That the ferromagnetic interactions dominated within complexes 1-4 were suggested by solid-state dc magnetic susceptibility analyses. Compound 4 displays a magnetic-caloric effect (MCE) with 13.94 J kg(-1) K(-1) as the entropy change at 6 K for ΔH = 8 T. Compounds 1 and 5 exhibit an out-of-phase χ''M peak maximum above 2.0 K. Fitting of the ac susceptibility data to an Arrhenius law gives an energy barrier Ueff = 6.88/7.44 K for compounds 1 and 5 respectively.

Synthesis, crystal structures and magnetic properties of a family of manganese phosphonate clusters with diverse structures

Four manganese clusters containing tert-butylphosphonate ligands with diverse structures have been synthesized and characterized.

Geometric-phase interference in a Mn12 single-molecule magnet with fourfold rotational symmetry

We study the magnetic relaxation rate Γ of the single-molecule magnet Mn(12)-tBuAc as a function of the magnetic field component H(T) transverse to the molecule's easy axis. When the spin is near a magnetic quantum tunneling resonance, we find that Γ increases abruptly at certain values of H(T). These increases are observed just beyond values of H(T) at which a geometric-phase interference effect suppresses tunneling between two excited energy levels. The effect is washed out by rotating H(T) away from the spin's hard axis, thereby suppressing the interference effect. Detailed numerical calculations of Γ using the known spin Hamiltonian accurately reproduce the observed behavior. These results are the first experimental evidence for geometric-phase interference in a single-molecule magnet with true fourfold symmetry.