Studies of an Fe₉ Tridiminished Icosahedron

Abstract

The synthesis and structural characterization of a nonanuclear FeIII cage complex is reported. The nine iron centers in [Fe9(mu3-O)4(O3PPh)3(O2CCMe3)13] lie on the vertices of an incomplete icosahedron, with the P atoms of triphenylphosphonate at the other three vertices. The paramagnetic core therefore describes a tridiminished icosahedron. Magnetic studies suggest an S=1/2 ground state for the molecule. Analysis of exchange paths and the susceptibility data point to the interpretation that the cluster can be divided into two nearly decoupled sections: an {Fe6O3} section, with an S=0 ground state, in which three oxo-centered triangles bound a central triangle that is not oxo-centered; and an {Fe3O} triangle with S=1/2. The analysis of the susceptibility data leads to a Heisenberg model based on three significant antiferromagnetic exchange interactions, with values of 173.7 cm-1 in the {Fe3O} triangle, and 30.9 and 19.1 cm-1 within the {Fe6O3} section, while the exchange between them is <1 cm-1. With these assignments, the theoretical low-temperature differential susceptibility is also in very good agreement with measurements up to 50 T. Magnetic measurements in the milli-kelvin range reveal striking hysteresis loops and magnetization reversals associated with a Landau-Zener-Stückelberg (LZS) transition as enhanced by the occurrence of a phonon bottleneck.

Linkage Isomerism and Spin Frustration in Heterometallic Rings: Synthesis, Structural Characterization, and Magnetic and EPR Spectroscopic Studies of Cr7Ni, Cr6Ni2, and Cr7Ni2 Rings Templated About Imidazolium Cations

“…In antiferromagnetically coupled iron triangles and in a triangle within a {Fe 9 } cage unusual EPR spectra have been observed from spin-frustrated ground doublets. [28,29] Antisymmetric DzyaloshinskyMoria (DM) interactions can lift the degeneracy of the doublets and lead to mixing of the associated wave functions. Consequently, EPR transitions are no longer intradoublet transitions and, hence, the assigned "g values" are not genuine molecular g values and can be significantly more anisotropic than usual.…”

Heterospin Single‐Molecule Magnets Based on Terbium Ions and TCNQF4 Radicals: Interplay between Single‐Molecule Magnet and Phonon Bottleneck Phenomena Investigated by Dilution Studies

“…[31] The PB effect was detected for fields higher than the exchange fields and temperatures above the ordering temperature of about 0.25 K for all fields except H = 0.…”

“…In general, due to its molecular origin, the slow relaxation of SMMs is characterized by an increase in coercivity for increasing field sweep rates; which is in strikingly contrast to the phonon bottleneck (PB) effect, which leads to a decrease in coercivity with increasing field sweep rate. [31] This is easily explained by the fact that, for phonon bottlenecks, very fast field scans overcome the rate of exchange of phonons with the cryostat, and the hysteresis loop collapses. Compound 1 exhibits a butterfly-shaped hysteresis loop, and a monotonical increase of the coercivity is observed when the rate of the applied field increases, an indication of SMM behavior arising from ligand field effects of the Tb ion.…”

Magneto-Structural Analysis of Iron(III) Keggin Polyoxometalates

“…3 Discrete magnetic 4 clusters and nanoclusters (magnetite in particular) respectively have enormous potential as spintronic-based molecular devices for memory storage. 5 The interpretation of susceptibility data of these discrete magnetic clusters is extremely challenging due to their high nuclearity, 6 and the number of valence electrons per metallic unit. Several mixed addenda Keggin structures have been characterised with the general aim of creating new magnetic materials.…”