Meta-Atom Behavior in Clusters Revealing Large Spin Ground States

Abstract

The field of single molecule magnetism remains predicated on super- and double exchange mechanisms to engender large spin ground states. An alternative approach to achieving high-spin architectures involves synthesizing weak-field clusters featuring close M–M interactions to produce a single valence orbital manifold. Population of this orbital manifold in accordance with Hund’s rules could potentially yield thermally persistent high-spin ground states under which the valence electrons remain coupled. We now demonstrate this effect with a reduced hexanuclear iron cluster that achieves an S = 19/2 (χMT ≈ 53 cm3 K/mol) ground state that persists to 300 K, representing the largest spin ground state persistent to room temperature reported to date. The reduced cluster displays single molecule magnet behavior manifest in both variable-temperature zero-field 57Fe Mössbauer and magnetometry with a spin reversal barrier of 42.5(8) cm−1 and a magnetic blocking temperature of 2.9 K (0.059 K/min).

Maximizing Electron Exchange in a [Fe3] Cluster

“…1 Nonetheless, when the temperature of acquisition is lowered to 4.2 K, a multiline spectrum for ( tbs L)Fe 3 (thf) is obtained (Figure S8), as observed in other molecular species. 24,37 The spectral features are broad and unresolved, consistent with overlapping sextets, indicative of a slowly relaxing internal magnetic field ( H int ). However, the magnetic relaxation rate exceeds that which is needed to display an out-of-phase ${\chi }_{\mathrm{M}}^{″}$ signature in the ac magnetic susceptibility under zero-applied dc field since no maximum is observed, even at the lowest temperatures achievable (1.8 K).…”

“…In related mixed-valent hexairon clusters embedded within similar weak-field ligand environments, the contraction in the Fe–N avg distance correlates linearly with a decrease in the spin ground state. 24 …”

“…Finally, future work will target understanding the origins of magnetic anisotropy exhibited by strongly delocalized mixed-valent clusters typified by [( tbs L)Fe 3 ] − and other high-spin systems. 24 …”

Strong Electronic and Magnetic Coupling in M4 (M = Ni, Cu) Clusters via Direct Orbital Interactions between Low-Coordinate Metal Centers

“…Recently, however, a number of clusters exhibiting strong ferromagnetic direct exchange, mediated by direct metal-metal orbital overlap, have been reported. [6][7][8][9][10][11][12] These complexes have motivated a new design paradigm for accessing single-molecule magnets with thermally isolated large-spin ground states. 11,12 For example, the tetranuclear iron cluster Fe4(N=CPh2)6 was recently shown to exhibit an S = 7 ground state and consequently slow magnetic relaxation with a spin relaxation barrier of Ueff = 29 cm −1 .…”

Alkene Hydrogenations by Soluble Iron Nanocluster Catalysts

“…[19] Thecomposition of the cluster mixture was further verified by X-ray analysis,elemental analysis,and LIFDI-MS (m/z 1301.2287, 1358.1793). TheF e 4 ,F e 6 ,and Fe 7 nanocluster architectures contain multiple iron centers in low oxidation states (formally Fe 0 ,F e I ,F e II )a nd constitute ad istinct class of metallic cluster complexes [20] that adopt…”