Halobenzene Adducts of a Dysprosocenium Single-Molecule Magnet

Abstract

Dysprosium complexes with strong axial crystal fields are promising candidates for single-molecule magnets (SMMs), which could be used for high-density data storage. Isolated dysprosocenium cations, [Dy(Cp R ) 2 ] + (Cp R = substituted cyclopentadienyl), have recently shown magnetic hysteresis (a memory effect) above the temperature of liquid nitrogen. Synthetic efforts have focused on reducing strong transverse ligand fields in these systems as they are known to enhance magnetic relaxation by spin-phonon mechanisms. Here we show that equatorial coordination of the halobenzenes PhX (X = F, Cl, Br) and o-C 6 H 4 F 2 to the cation of a recently reported dysprosocenium complex [Dy(Cp ttt )(Cp*)][Al{OC(CF 3 ) 3 } 4 ] (Cp ttt = C 5 H 2 t Bu 3 -1,2,4; Cp* = C 5 Me 5 ) reduces magnetic hysteresis temperatures compared to that of the parent cation. We find that this is due to increased effectiveness of both one-(Orbach) and two-phonon (Raman) relaxation mechanisms, which correlate with the electronegativity and number of interactions with the halide despite κ 1coordination of a single halobenzene having a minimal effect on the metrical parameters of [Dy(Cp ttt )(Cp*)(PhX-κ 1 -X)] + cations vs the isolated [Dy(Cp ttt )(Cp*)] + cation. We observe unusual divergent behavior of relaxation rates at low temperatures in [Dy(Cp ttt )(Cp*)(PhX)][Al{OC(CF 3 ) 3 } 4 ], which we attribute to a phonon bottleneck effect. We find that, despite the transverse fields introduced by the monohalobenzenes in these cations, the interactions are sufficiently weak that the effective barriers to magnetization reversal remain above 1000 cm −1 , being only ca. 100 cm −1 lower than for the parent complex, [Dy(Cp ttt )(Cp*)]-[Al{OC(CF 3 ) 3 } 4 ].

Synthesis and Magnetic Properties of Bis-Halobenzene Decamethyldysprosocenium Cations

“…For 3-Dy , there are four ion pairs within the P unit cell; thus, the atomic coordinates of the two least disordered ion pairs were used for comparative purposes and for subsequent calculations. Increasing the size of the halogen in the coordinated solvent leads to increased mean Dy–X distances [ 2-Dy : 2.358(12) Å; 4-Dy : 2.920(3) Å; 5-Dy : 3.064(3) Å] as expected; subtracting the covalent radii of the halogens (F: 0.64 Å; Cl: 0.99 Å; Br: 1.14 Å) from these distances gives a value of ca . 1.93 Å for both X = Cl and Br.…”

“…During various attempts to isolate 2-Dy , 3-Dy , 4-Dy , and 5-Dy , the unintentional introduction of trace amounts of coordinating solvents led to the formation of oxygen-bound adducts that could be identified by SCXRD, including [Dy­(Cp*) 2 (DME)]­[Al­{OC­(CF 3 ) 3 } 4 ] ( 10-Dy ) and [Dy­(Cp*) 2 (PhBr-κ- Br )­(THF)]­[Al­{OC­(CF 3 ) 3 } 4 ] ( 11-Dy ). A small portion of “[{Dy­(Cp*) 2 }­{Al­[OC­(CF 3 ) 3 ] 4 }]” dissolved in THF, layered with n -hexane, and stored at −30 °C gave several crystals of [Dy­(Cp*) 2 (THF) 2 ]­[Al­{OC­(CF 3 ) 3 } 4 ] ( 12-Dy ); the two bound THF molecules are akin to the closely related analog [Dy­(Cp ttt )­(Cp*)­(THF) 2 ]­[Al­{OC­(CF 3 ) 3 } 4 ] and the comparable group 3 complex [Sc­(Cp*) 2 (THF) 2 ]­[BPh 4 ] …”

“…Following our recent reports of the heteroleptic dysprosocenium complex [Dy­(Cp ttt )­(Cp*)]­[Al­{OC­(CF 3 ) 3 } 4 ] and its monohalobenzene-solvated adducts, we resolved to apply these methods to {Dy­(Cp*) 2 } analogues. Here, we report the synthesis of the putative WCA-bound complexes “[{Ln­(Cp*) 2 }­{Al­[OC­(CF 3 ) 3 ] 4 }]” (Ln = Y, Dy), together with a family of bis-halobenzene-bound {Dy­(Cp*) 2 } + cations with the same WCA derived from this starting material.…”

A photochromic trinuclear dysprosium(iii) single-molecule magnet with two distinct relaxation processes

“…This is due to the incomplete photocyclization in the solid state as well as the remote character of these changes with respect to the ligand eld of the Dy III centers. This suggests that the dte-type ligands should be attached to a high-performance SMM such as dysprosocenium- [53][54][55] or lanthanide-bisamide-type 56 complexes to achieve substantial light-switchable magnetic properties. Most importantly, in the linear molecule of 1 it was possible to distinguish two processes of slow relaxation of the magnetization associated with the central and peripheral dysprosium ions.…”

Ligand–Metal Complementarity in Rare-Earth and Actinide Chemistry

“…In their contribution, Chilton, Mills, and colleagues demonstrated that the sought-after SMM candidate [Dy­(Cp*) 2 ] + (Cp* = {C 5 Me 5 }) cannot be isolated free of equatorial donor coordination, even when extremely weakly donating haloarenes are used, resulting in the first f-block bis-haloarene adducts [Dy­(Cp*) 2 (PhX-κ-X) 2 ]­[Al­{OC­(CF 3 ) 3 } 4 ] (X = F, Cl, Br) . Even when the size of the supporting ligands is increased, as in a second paper by Chilton and Mills that features [Dy­(Cp*)­(Cp ttt )­(X n C 6 H 6– n )] + (Cp ttt = {C 5 H 2 -1,2,4- t Bu 3 }), equatorial haloarene adducts could be isolated, although this class has better SMM characteristics than the previous due to the reduced equatorial donation . Roesky and co-workers have explored the influence of arsolyl ligands, {η 5 -AsC 4 R 4 }, on the coordination environment and magnetic properties of several Ln III ions (Sm, Dy, and Er), finding that the nuclearity of [RE­(η 8 -COT)­(η 5 :μ n -AsC 4 R 4 )] n (Ln = Sm, Dy, Er; n = 1, 2; COT = {C 8 H 8 }) complexes depends on the steric protection at the 2,5 positions of the {AsC 4 R 4 } ring with large Sm III ions, but with small Dy III and Er III ions, monomeric complexes are obtained even with small R groups such as in {AsC 4 Me 4 }.…”