Gabriel Brunet

Significant Enhancement of Energy Barriers in Dinuclear Dysprosium Single-Molecule Magnets Through Electron-Withdrawing Effects

The effect of electron-withdrawing ligands on the energy barriers of Single-Molecule Magnets (SMMs) is investigated. By introducing highly electron-withdrawing atoms on targeted ligands, the energy barrier was significantly enhanced. The structural and magnetic properties of five novel SMMs based on a dinuclear {Dy2} phenoxo-bridged motif are explored and compared with a previously studied {Dy2} SMM (1). All complexes share the formula [Dy2(valdien)2(L)2]·solvent, where H2valdien = N1,N3-bis(3-methoxysalicylidene) diethylenetriamine, the terminal ligand L = NO3(-) (1), CH3COO(-) (2), ClCH2COO(-) (3), Cl2CHCOO(-) (4), CH3COCHCOCH3(-) (5), CF3COCHCOCF3(-) (6), and solvent = 0.5 MeOH (4), 2 CH2Cl2 (5). Systematic increase of the barrier was observed for all complexes with the most drastic increase seen in 6 when the acac ligand of 5 was fluorinated resulting in a 7-fold enhancement of the anisotropic barrier. Ab initio calculations reveal more axial g tensors as well as higher energy first excited Kramers doublets in 4 and 6 leading to higher energy barriers for those complexes.

Slow Magnetic Relaxation Observed in Dysprosium Compounds Containing Unsupported Near-Linear Hydroxo- and Fluoro-Bridges

The encapsulating N1,N3-bis(3-methoxysalicylidene)diethylenetriamine (H2valdien) ligand was employed to isolate two novel Dy(III) compounds which contain rare bridging pathways for lanthanide systems. Compound 1, [Na2Dy(III)2(valdien)2(μ-OH)(dbm)2(H2O)2][Na2Dy(III)2(valdien)2(μ-OH)(NO3)2(dbm)2], where dbm(-) is dibenzoylmethanido, and compound 2, [Na3Dy(III)2(valdien)2(μ-F)(μ3-F)2(Cl)2(MeOH)2]n·0.5(MeOH)·(H2O), both exhibit linear lone hydroxo- and fluoro-bridges, respectively, between the metal centers. The unit cell of 1 comprises two discrete dinuclear molecules, which differ slightly, forming a cation-anion pair, while 2 forms a coordination polymer. The magnetic investigations indicate that both compounds display ferromagnetic coupling between the Dy(III) ions. Magnetic susceptibility measurements in the temperature range 1.8-300 K reveal that the Dy(III) ions in 1 are weakly coupled, resulting in a mononuclear single-molecule magnet-like behavior under an applied field. In the case of 2, the stronger coupling arising from the fluoride-bridge, leads to zero-field single-molecule magnet (SMM) behavior with a non-negligible anisotropy barrier (Ueff) of 42 K.

Terminal solvent effects on the anisotropy barriers of Dy2 systems

A family of three dinuclear dysprosium complexes have been successfully synthesized and studied in terms of their magnetic properties. Complexes 1 and 2 share the formula [Dy2(ovph)2Cl2(solvent)2], where H2ovph = pyridine-2-carboxylic acid [(2-hydroxy-3-methoxyphenyl)methylene] hydrazide, and solvent = DMF (1), i-PrOH (2), while complex 3, [Dy2(ovph)2Cl2(H2O)3(EtOH)], exhibits differences in terms of the identity and number of coordinated solvent molecules. Thus, we investigate the impact of terminally bonded solvent molecules on the slow relaxation dynamics of {Dy2} SMMs, a parameter which can sometimes be overlooked in the quest to attain higher energy barriers. Notably, the exchange of DMF for i-PrOH, both of which coordinate through a single oxygen atom, results in a near 2-fold increase in Ueff, from 58 to 98 K, for 1 and 2, respectively.

Turning on Single-Molecule Magnet Behavior in a Linear {Mn3} Compound

The synthesis, structure, and magnetic properties are reported for a new manganese compound with a mixed-valent {Mn(3)} core arranged in a linear fashion. The previously reported complex 1, [Mn(IV)(3)(dpo)(6)]·2MeCN, where H(2)dpo is (E)-1-hydroxy-1,1-diphenylpropan-2-one oxime, served as a starting point for the isolation of a {Mn(3)} compound with an analogous core arrangement through the reaction of Mn(OAc)(2)·4H(2)O, H(3)oxol ((E)-2,5-dihydroxy-2,5-dimethylhexan-3-one oxime), and NaOH in MeOH and MeCN. By using these reaction conditions, compound 2, Na[Mn(IV)(2)Mn(III)(Hoxol)(6)](n)·MeOH·H(2)O, was successfully isolated revealing a central Mn(III) ion thereby introducing structural and magnetic anisotropy to the system. The structure of 2 reveals linear trinuclear Mn(IV)-Mn(III)-Mn(IV) units connected through Na(+) ions forming a linear one-dimensional coordination polymer. The Jahn-Teller axes of each trinuclear unit are aligned parallel within the same chain and form a 75° angle between the two symmetry related chains. Magnetic susceptibility measurements of 1 and 2 in the temperature range 1.9-300 K reveal that only the reduced compound, 2, is a single-molecule magnet (SMM) largely due to the anisotropy introduced by the Jahn-Teller distortions on the Mn(III) ions, which effectively induce this magnet behavior. Weak antiferromagnetic interactions along the chains through the Na(+) cations lead to a modulation of the intrinsic properties of the Mn(IV)-Mn(III)-Mn(IV) SMMs.

Single-molecule magnetism arising from cobalt(II) nodes of a crystalline sponge

The remarkable Metal–Organic Framework (MOF), {[(Co(NCS)2)3(κ3-TPT)4]·a(H2O)·b(MeOH)}n (1), which is used in the revolutionary crystalline sponge method, displays characteristic Single-Molecule Magnet (SMM) behaviour under applied static fields. We report the subtle effects of changes in the coordination environment of the CoII ions in 1, leading to drastically different magnetic behaviors of two additional related compounds, {[(Co(NCS)2)3(κ0–3-TPT)4]·c(H2O)}n (2) and {[(Co(NCS)2(H2O)0.65(MeOH)0.35)3(κ3-TPT)2]·2.4(H2O)}n (3). Magnetic measurements reveal unquenched first order orbital angular momentum, leading to significant magnetic anisotropy in all compounds, which was corroborated through CASSCF-type calculations. Notably, the crystalline sponge is the first example of a 3D network built from CoII Single-Ion Magnets (SIMs) as nodes.