Tetraanionic Biphenyl Lanthanide Complexes as Single-Molecule Magnets

Abstract

Inverse sandwich biphenyl complexes [(NNTBS)Ln]2(μ-biphenyl)[K(solvent)]2 [NNTBS = 1,1′-fc(NSitBuMe2)2; Ln = Gd, Dy, Er; solvent = Et2O, toluene; 18-crown-6], containing a quadruply reduced biphenyl ligand, were synthesized and their magnetic properties measured. One of the dysprosium biphenyl complexes was found to exhibit antiferromagnetic coupling and single-molecule-magnet behavior with U eff of 34 K under zero applied field. The solvent coordinated to potassium affected drastically the nature of the magnetic interaction, with the other dysprosium complex showing ferromagnetic coupling. Ab initio calculations were performed to understand the nature of magnetic coupling between the two lanthanide ions bridged by the anionic arene ligand and the origin of single-molecule-magnet behavior.

Cycloheptatrienyl trianion: an elusive bridge in the search of exchange coupled dinuclear organolanthanide single-molecule magnets

“…31 In regard to compound 3 , the intramolecular Er–Er distance of 3.9580(7) Å is slightly shorter than the distance observed in a COT″ (1,4-bis(trimethylsilyl)cyclooctatetraenyl dianion) bridged Er 2 dimer (4.1109(5) Å) or an arene bridged Er 2 compound (4.067(1) Å). 21,22 A similar Sm 2 inverse sandwich analogue was reported with a bridging COT and terminal [N(SiMe 3 ) 2 ] – ligands with a Sm–Sm distance of 4.308(1) Å. 32 However, the larger distance in the case of the Sm example is primarily due to the larger ionic radii of the Sm III ion.…”

“…42 Similar arrangements of the local magnetic axes were revealed with the previously studied Er 2 C 6 (η 6 -C 6 R 6 ) compounds. 22 Parameters of the ab initio calculated crystal field for the investigated Ln sites in 2–4 are given in Table S2 †…”

“…While many different bridging systems exist, 14,18,19 few examples have demonstrated the importance of planar aromatic organometallic ligands towards garnering favourable magnetic interactions. 20–22 These systems are an appealing design strategy as they may be employed as building blocks to generate higher nuclearity compounds, while they are more notably effective in harnessing the inherent magnetic anisotropy of 4f and 5f ions. 13,15–17,23,24 Our recent reports with cyclooctatetraenyl 20,21 and arene-bridged 22 systems shows that a weak, yet non-negligible, interaction can be observed with coupling constants between Gd III ions of –0.644 cm –1 and –0.488 cm –1 respectively, utilizing the isotropic spin Hamiltonian ( H = –2 JS a S b , S a = S b = 7/2) for each system respectively.…”

“…20–22 These systems are an appealing design strategy as they may be employed as building blocks to generate higher nuclearity compounds, while they are more notably effective in harnessing the inherent magnetic anisotropy of 4f and 5f ions. 13,15–17,23,24 Our recent reports with cyclooctatetraenyl 20,21 and arene-bridged 22 systems shows that a weak, yet non-negligible, interaction can be observed with coupling constants between Gd III ions of –0.644 cm –1 and –0.488 cm –1 respectively, utilizing the isotropic spin Hamiltonian ( H = –2 JS a S b , S a = S b = 7/2) for each system respectively. Herein, the role of the 7-membered cycloheptatrienyl ring in the magnetic exchange between lanthanide ions will be examined and compared with its counterparts, the 6- and 8-membered rings (Chart 1).…”

Aromatic C–F Bond Activation by Rare-Earth-Metal Complexes

“…As part of our group's continuing efforts to explore the chemistry of rare-earth metals and actinides supported by ferrocene-derived ligands, [55][56][57][58][59][60][61][62] especially redox reactions in the presence of arenes, [63][64][65][66][67][68][69][70][71] we discovered a bimetallic cleavage of the C-H bond of benzene by (NN TBS ) . In addition, the C-H bond activation of a naphthalene dianion sandwiched between two lutetium ions in the previously isolated [(NN TBS )Lu(THF)]2(μ-C10H8) (4-Lu2) was observed upon moderate heating (Scheme 2c).…”