A hundredfold enhancement of relaxation times among Er(iii) single-molecule magnets with comparable energy barriers

Abstract

Magneto-structural correlations are of great importance in developing single-molecule magnets (SMMs) for storage and quantum processing of information. In this work, three cyclooctatetraenylido (COT) ligands, namely COTTMS1, COTTMS2, and COTTMS3...

Substituent Positioning Effects on the Magnetic Properties of Sandwich-Type Erbium(III) Complexes with Bis(trimethylsilyl)-Substituted Cyclooctatetraenyl Ligands

“…The energy gaps between the first excited state and the ground state are 202.10 and 174.36 K for Er1 and Er2, respectively. These values are comparable to those reported for analogous sandwich-type Er-COT SMMs 19,20,23,34,45,48 and also in agreement with the results from a theoretical investigation. 68 The g x and g y values are in the range between 1.40 × 10 −3 and 2.18 × 10 −3 for Er1 and Er2, indicating that the two complexes may undergo quantum tunneling of magnetization (QTM) with comparable relaxation times.…”

“…Complexes Er1 and Er2 with the crystallographically determined formulas [Li(DME)Er(COT 1,5-TMS2 ) 2 ] n and [Na(DME) 3 ][Er-(COT 1,3-TMS2 ) 2 ], respectively, were prepared by a slightly modified literature procedure previously used for the preparation of [Li(DME) 3 ][Er(COT 1,4-TMS2 ) 2 ] (A) 23 and [K(DME) 2 ][Er(COT 1,4-TMS2 ) 2 ] (B). 48 These complexes share a common feature of an Er(III) ion being sandwiched by two TMS-disubstituted COT ligands, differing from one another in the specific form of their countercation and more interestingly in the position of the two TMS substituents on the COT ring. COT 1,5-TMS2 and COT 1,3-TMS2 are positional isomers of the most commonly obtained and researched COT 1,4-TMS2 , and they can be obtained via formal migration of one of the TMS substituents to a neighboring position on the ring, but in opposite directions (Figure 2).…”

“…These metric values are in good agreement with those reported for A, 20 B, 45 and other analogous sandwich-type Er(III) complexes with COT-based ligands. 19,20,23,34,45,48 It is interesting to note that with the two COT 1,3-TMS2 ligands of Er2 being centrosymmetrically related, the COT ring skeletons are in a perfect eclipsed conformation, producing a rare example of D 8h symmetry in the local coordination among the large number of Er−COT complexes. CASSCF-SO Calculations.…”

“…As a recent example, we showed that the relaxation times (τ) of three closely related Er(III) complexes with trimethylsilylated (TMS) COT ligands depend sensitively on the degree of substitution, so much so that even with comparable energy barriers, a 100-fold enhancement of τ between the mono-and trisubstituted complexes was observed. 48 modifying a common parent ligand with the same number but different types of substituents had already been established. 49,50 Having studied the effects of the type and number of COT ring-bound substituents on the magnetic properties of the resulting Er(III) SMM complexes, we explored the influence possibly arising from the disparate positioning of substituents of a particular type on the parent COT platform.…”

“…In this vein, a large number of sandwich-type Er(III) SMMs with disubstituted COT ligands are of interest, but most of these complexes are with 1,4-disubstituted COT ligands. 23,24,30,40,[42][43][44][45]48 A small number of complexes with 1,3-and 1,5-disubstituted COT ligands indeed exist, including 52 Ce(COT 1.3-BIG2 ) 2 [COT 1.3-BIG2 = 1,3-bis(triphenylsilyl)-substituted cyclooctatetraenyl dianion], 53 (COT 1.4-TMS2 )Ln(COT 1.3-TMS2 )Ln-(COT 1.4-TMS2 ) (Ln = Y, Tb, Ho, Tm, or Lu) [COT 1.3-TMS2 = 1,3-bis(trimethylsilyl)-substituted cyclooctatetraenyl dianion; COT 1.4-TMS2 = 1,4-bis(trimethylsilyl)-substituted cyclooctatetraenyl dianion], 54,55 and (COT 1.4-TMS2 )Pu(COT 1.3-TMS2 ); 56 however, they are not Er(III) complexes. And the occurrence of the 1,3-and 1,5-disubstituted COT ligands in these complexes appears to be unexpected and synthetically elusive.…”