Twisting, bending, stretching: strategies for making ferromagnetic [MnIII3] triangles

Abstract

The synthesis and characterisation of a large family of trimetallic [Mn(III)(3)] Single-Molecule Magnets is presented. The complexes reported can be divided into three categories with general formulae (type 1) [Mn(III)(3)O(R-sao)(3)(X)(sol)(3-4)] (where R = H, Me, (t)Bu; X = (-)O(2)CR (R = H, Me, Ph etc); sol = py and/or H(2)O), (type 2) [Mn(III)(3)O(R-sao)(3)(X)(sol)(3-5)] (where R = Me, Et, Ph, (t)Bu; X = (-)O(2)CR (R = H, Me, Ph etc); sol = MeOH, EtOH and/or H(2)O), and (type 3) [Mn(III)(3)O(R-sao)(3)(sol)(3)(XO(4))] (where R = H, Et, Ph, naphth; sol = py, MeOH, beta-pic, Et-py, (t)Bu-py; X = Cl, Re). We show that deliberate structural distortions of the molecule can be used to tune the observed magnetic properties. In the crystals the ferromagnetic triangles are involved in extensive inter-molecular H-bonding which is clearly manifested in the magnetic behaviour, producing exchange-biased SMMs. These interactions can be removed by ligand replacement to give "simpler" SMMs.

Magnetic quantum tunneling: insights from simple molecule-based magnets

“…one anticipates only a moderate increase in the barrier (a factor of ~1.45 -1.75) upon switching from low-to high-spin, and a factor of less than two upon doubling the nuclearity (spin). The concept of D decreasing as S increases is not new [16][17][18][19][20][26][27][28]. However, our results paint a slightly more optimistic view in comparison to two previous works suggesting that U does not increase upon increasing S [26,27].…”

“…In this way, we can for example relate D mol (or E mol ) to J and d ion (as well as e ion ). At every step, our findings are informed by real molecules that have been extensively characterized by magnetic and spectroscopic (EPR) techniques which are published elsewhere [12][13][14][15][16][17][18][19]22,25]. We focus primarily on the III 3 Mn and III 6 Mn SMMs, with occasional reference to II 4 Ni .…”

“…Before summarizing the main findings of these studies, we point out several approximations and simplifying assumptions that were made in refs. [16][17][18][19]. Our main goal here was not to achieve precise agreement with experiment, but rather to provide a general understanding of the factors that contribute to the molecular axial anisotropy, D mol , in polynuclear clusters, using III 3 Mn and III 6 Mn as examples.…”

“…1), i.e. they may be viewed as a ferromagnetic III 3 2 [Mn ] dimer; (3) extensive families of both molecules exist (20-30 members in each case), differing only in the peripheral ligands and solvent molecules, resulting in relatively minor, albeit controllable perturbations to the structures [18][19][20]22,25]; and, most importantly, (4) one can vary the magnitude and sign of the exchange within the oxocentered III 3 Mn triangles [19], enabling studies of both low-and high-spin molecules (S = 2 and 6 in the case of III 3 Mn , S = 4 and 12 for III 6 Mn ). Before summarizing the main findings of these studies, we point out several approximations and simplifying assumptions that were made in refs.…”

“…These solvents are often disordered and are easily lost via evaporation [42,43], leading to considerable strains in the molecular ZFS parameters [44]. Furthermore, in cases where intermolecular interactions are present, solvent disorder can give rise to additional complexity [19]. In contrast, a few smaller molecules (e.g.…”