Single-molecule magnets: control by a single solvent molecule of Jahn–Teller isomerism in [Mn₁₂O₁₂(O₂CCH₂Bu^t)₁₆(H₂O)₄]

Abstract

Faster- and slower-relaxing versions of the title Mn12 compound have been obtained in pure forms that crystallize in the same space group and differ only in the identity of one lattice solvent molecule; solvent loss causes isomerization from the faster- to the slower-relaxing form.

Anisotropy barrier reduction in fast-relaxingMn12single-molecule magnets

“…In all cases where the FR species are obtained in single-crystal form, X-ray studies show that one or more of the Jahn-Teller (JT) elongation axes associated with the Mn III atoms are abnormally oriented 18,19,21,24,25,33 in comparison to the usual SR form of Mn 12 . 26,27,[34][35][36][37] This is illustrated in Fig.…”

“…Furthermore, the spacing between the QMT steps associated with the FR species (~0.4 T) is not all that dissimilar to those of the SR species (~0.45 T), suggesting that they possess similar uniaxial anisotropy constants D. [14][15][16] Subsequently, detailed synthetic work by Christou, Hendrickson and co-workers, involving ligand substitution and crystallization from a variety of solvents, resulted in the discovery of many different forms of Mn 12 possessing essentially the same neutral Mn 12 O 12 core. 11,12,[17][18][19][20][21][22][23][24][25][26][27] However, important differences have been inferred from X-ray and magnetic studies. Most notably, the various Mn 12 complexes can be grouped broadly into two categories, i.e.…”

“…Subsequent recrystallization of dry FR-Mn 12 tBuAc from a CH 2 Cl 2 /MeCN mixture gives good crystals of the pure SR form (hereon SR-Mn 12 tBuAc) and Xray studies indicate that the JT axes are now in their normal orientations. 25 It should be emphasized that there are relatively few examples of truly high-symmetry Mn 12 , 26,[34][35][36][37] the acetate 9 being the best known. However, when crystallized with acetic acid solvent, the resulting samples are rather disordered: not only are FR molecules randomly distributed throughout the crystal, but the acetic acid is also disordered and this is known to influence the SR species as well; this point has been discussed at length by several authors.…”

“…25 This conversion has been monitored for FR-Mn 12 tBuAc via ac susceptibility measurements performed on a single crystal at regular time intervals. 25 Measurements performed on the fresh (wet) crystals removed directly from the mother liquor reveal a single, sharp LT χ˝ peak at ~2 K. As the sample ages, this peak diminishes in intensity, but does not shift.…”

“…25 This conversion has been monitored for FR-Mn 12 tBuAc via ac susceptibility measurements performed on a single crystal at regular time intervals. 25 Measurements performed on the fresh (wet) crystals removed directly from the mother liquor reveal a single, sharp LT χ˝ peak at ~2 K. As the sample ages, this peak diminishes in intensity, but does not shift. Meanwhile, a broader HT χ˝ peak appears at ~7 K. This behavior signifies the slow conversion between the two forms, which is attributed to the loss of volatile CH 2 Cl 2 /MeNO 2 solvents from the structure (also confirmed via elemental analysis).…”