Chem

We have determined by polarized neutron diffraction (PND) the low-temperature molecular magnetic susceptibility tensor of the anisotropic low-spin complex PPh₄[Fe^III(Tp)(CN)₃]⋅H₂O. We found the existence of a pronounced molecular easy magnetization axis, almost parallel to the C₃ pseudo-axis of the molecule, which also corresponds to a trigonal elongation direction of the octahedral coordination sphere of the Fe^III ion. The PND results are coherent with electron paramagnetic resonance (EPR) spectroscopy, magnetometry, and ab initio investigations. Through this particular example, we demonstrate the capabilities of PND to provide a unique, direct, and straightforward picture of the magnetic anisotropy and susceptibility tensors, offering a clear-cut way to establish magneto-structural correlations in paramagnetic molecular complexes.

Molecular Magnetism: The low-temperature molecular magnetic susceptibility tensor of the anisotropic low-spin [Fe^III(Tp)(CN)₃]⁻ complex (Tp=tris(pyrazolyl)borate; see picture) was determined by polarized neutron diffraction (PND). PND provided a unique, direct, and straightforward picture of the magnetic anisotropy and susceptibility tensors.

Elaborate chemical design is of utmost importance in order to slow down the relaxation dynamics in single-molecule magnets (SMMs) and hence improve their potential applications. Much interest was devoted to the study of distinct relaxation processes related to the different crystal fields of crystallographically independent lanthanide ions. However, the assignment of the relaxation processes to specific metal sites remains a challenging task. To address this challenge, a new asymmetric Dy₂ SMM displaying a well-separated two-step relaxation process with the anisotropic centers in fine-tuned local environments was elaborately designed. For the first time a one-to-one relationship between the metal sites and the relaxation processes was evidenced. This work sheds light on complex multiple relaxation and may direct the rational design of lanthanide SMMs with enhanced magnetic properties.

One-to-one correspondence: Employing a new hydrazone ligand resulted in the self-assembly of an asymmetric Dy₂ single-molecule magnet (SMM) displaying well-separated two-step relaxation with the anisotropic centers in fine-tuned local environments where the correspondence between the metal sites and the relaxation processes was evidenced (QTM=quantum tunneling of magnetization).

Invited for the cover of this issue are the groups of Maylis Orio at the Aix-Marseille University and Carole Duboc at the University of Grenoble Alpes. The image depicts the magnetic behavior dependence to the halide nature in Co^III species represented by ribbons as “double-well” diagrams, which are traditionally used to depict magnetization processes. Read the full text of the article at 10.1002/chem.201502997.

“The magnetic anisotropy of these complexes, the zero field splitting parameter (D), shows a dependence on the nature of the halide: the largest D value was obtained for the chloride compound and the smallest for the iodide one.” Read more about the story behind the cover in the Cover Profile and about the research itself on page ▪▪ ff. (DOI: 10.1002/chem.201502997).

Novel cubic perovskites SrFe_1−xNi_xO₃ (0≤x≤0.5) with unusual high-valence iron(IV) and nickel(IV) ions were obtained by high-pressure and high-temperature synthesis. Substantial magnetic moments of Ni^IV, which is intrinsically nonmagnetic with a nominal d⁶ electron configuration, were induced by the large magnetic moments of Fe^IV through orbital hybridization with oxygen. As a result, ferromagnetism with the transition temperature (T_c) above room temperature could be induced.

Under pressure: Cubic perovskite derivatives SrFe_1−xNi_xO₃ (0≤x≤0.5) with unusual high-valence Fe^IV and Ni^IV ions are obtained by high-pressure synthesis. In these compounds, the Ni^IV ion, which is intrinsically nonmagnetic, has a substantial magnetic moment, and ferromagnetism with a transition temperature (T_c) greater than room temperature is induced.

Invited for the cover of this issue is the group of Emilio Pardo at the University of València and his collaborators. The image depicts the solid-state incorporation of a metalloporphyrin within the pores of a magnetic metal–organic framework. Read the full text of the article at 10.1002/chem.201504176.

“Many single-ion magnets, which are the smallest possible magnetic devices, need the application of an external magnetic field in order to avoid the presence of undesired quantum tunneling effects.” Read more about the story behind the cover in the Cover Profile and about the research itself on page ▪▪ ff. (DOI: 10.1002/chem.201504176).

Heteroleptic iron(III) complexes of formula [Fe(qsal)(thsa)]⋅solvent have been synthesized: [Fe(qsal)(thsa)]⋅0.4 BuOH (1), [Fe(qsal)(thsa)]⋅0.5 MeCN (2) and [Fe(qsal)(thsa)]⋅0.5 THF, (3). The latter two show partial solvent loss at room temperature to yield [Fe(qsal)(thsa)]⋅0.1 MeCN (2′) and [Fe(qsal)(thsa)]⋅0.1 THF (3′), respectively. This family maintains a structural integrity which is analogous over different degrees of solvation, a rare occurrence in discrete molecular species. Uniquely, removal of MeCN from compound 2 leads to retention of crystallinity yielding the isostructural, fully desolvated compound [Fe(qsal)(thsa)] (2′′) and a new high spin polymorph, 4. To the best of our knowledge, this is the first compound that forms polymorphs through a desolvation process. The desolvated mixture, 2′′ and 4, is porous and can reabsorb MeCN and give rise to 2′ again. This illustrates the reversible single-crystal-to-single-crystal transformation of two polymorphs back to a purely original phase, 2′′+42′. The structural, magnetic and Mőssbauer features of the various samples are described in terms of spin crossover.

Sign of the cross: [Fe(qsal)(thsa)]⋅solvent complexes, where solvent is MeCN or THF, have been characterized. For MeCN compounds, spin crossover properties are observed in both the solvated and non-solvated compounds (see scheme). Interestingly, the desolvation process in [Fe(qsal)(thsa)]⋅n MeCN resulted in two new polymorphs of Fe^III spin crossover systems, for the first time. The desolvated material is porous to liquid MeCN.