A Local D_4h Symmetric Dysprosium(III) Single‐Molecule Magnet with an Energy Barrier Exceeding 2000 K**

Abstract

Three six‐coordinate DyIII single‐molecule magnets (SMMs) [Dy(OtBu)2(L)4]+ with local D4h symmetry are obtained by optimizing the equatorial ligands. One of the compounds with L=4‐phenylpyridine shows an energy barrier (Ueff) of 2075(11) K, which is the third largest Ueff, and the first Ueff>2000 K for SMMs with axial‐type symmetry so far. Ab initio analysis indicates that the exceptional uniaxial magnetic anisotropy is deeply related to the axially compressed octahedral geometry. This work provides a new insight into the local D4h symmetry for high‐performance SMMs.

Mononuclear Dysprosium Alkoxide and Aryloxide Single‐Molecule Magnets

“…Complex 6.1 [41] has one of the shortestD y ÀOd istances,aDy-O-Dy angle of 1808 and four weak equatorial donors; to date, this complex shows the highest U eff value as well as the biggest GS-ES 1 energy gapf or any Ln alkoxide or aryloxide SMM. However,h aving ah igh energy barrier is not the sole requirement to provide improved SMMs, and this is when the effects of co-ligands can help.…”

“…Ideal axially elongated-Oh, PB and HB geometries would generate D 4h , D 5h and D 6h local symmetries, respectively. [13,17,41] If these ideal local symmetries can be achieved they can create highly axial ligand fields and increase U eff by restricting some degrees of freedom responsible for generating the transverse CF (eliminating B q6 ¼0 k terms) thereby suppressing QTM. [13,17,35,41] Unfortunately no molecules have been reported that have such ideal symmetry,and indeed strictly D 5h symmetry cannot be found in acrystalline material.…”

“…[41] The Dy III ions in 6.1-6.3 have octahedral geometries with two mutually transalkoxides and four equivalent neutralc o-ligands at the equatorial positions, alongw ith aB Ph 4 À counter anion for chargeb alance (Figure 11). [41] These complexesw ere synthesised via salt metathesis protocols by refluxing DyCl 3 with 2NaOtBu and NaBPh 4 in THF overnight, then adding sixe quivalents of respectiveco-ligands (Phpy (6.1), Pdpy (6.2), Plpy (6.3)) after concentrating the THF solution to saturation. [41] The O-Dy-Oa ngles [68] and has the Dy III centre in at rigonal prismatic geometry (Figure 11).…”

“…[41] These complexesw ere synthesised via salt metathesis protocols by refluxing DyCl 3 with 2NaOtBu and NaBPh 4 in THF overnight, then adding sixe quivalents of respectiveco-ligands (Phpy (6.1), Pdpy (6.2), Plpy (6.3)) after concentrating the THF solution to saturation. [41] The O-Dy-Oa ngles [68] and has the Dy III centre in at rigonal prismatic geometry (Figure 11). It showedm agnetic hysteresis up to 3Kin the absence of an external magneticf ield, with a U eff of 190 K. Giansiracusa et al reported 6.5 recently.…”

“…The use of symmetry in lowc oordinate Ln SMMs to modulate the CF to achievei mprovedS MM behaviour has been discussed exhaustively in the literature. [14,17,35,41] From group theory,ageneral form of the CF within the J multiplets of the 4f ions can be expressed via the Hamiltonian,…”