The rational design of 3d-metal-based single-molecule magnets (SMM) requires a fundamental understanding of their intrinsic electronic and structural properties and how they translate into experimentally observable features. Here, we determined the magnetic properties of the linear iron(I) silylamides K{crypt}[FeL2] and [KFeL2] (L = -N(Dipp)SiMe3; crypt = 4,7,13,16,21,24-Hexaoxa-1,10-diazabicyclo[8.8.8]hexacosan). For the former, slow-relaxation of the magnetization with a spin reversal barrier of Ueff = 152 cm-1 as well as a closed-waist magnetic hysteresis and magnetic blocking below 2.5 K are observed. For the more linear [KFeL2], in which the potassium cation is encapsulated by the aryl substituents of the amide ligands, the relaxation barrier and the blocking temperature increase to Ueff = 184 cm-1 and TB = 4.5 K, respectively. The increase is rationalized by a more pronounced axial anisotropy in [KFeL2] determined by dc-SQUID magnetometry. The effective relaxation barrier of [KFeL2] is in agreement with the energy spacing between the ground and first-excited magnetic states, as obtained by field-dependent IR-spectroscopy (178 cm-1), magnetic measurements (208 cm-1), as well as theoretical analysis (212 cm-1). In comparison with the literature, the results show that magnetic coercivity in linear iron(I) silylamides is driven by the degree of linearity in conjunction with steric encumbrance, whereas the ligand symmetry is a marginal factor.

Department of Chemistry Philipps University Marburg Hans Meerwein Straße 4 35043Marburg Germany

Institute of General and Inorganic Chemistry Bulgarian Academy of Sciences Akad Georgi Bontchev Street Bl 11 1113Sofia Bulgaria

Institute of Inorganic Chemistry University of Göttingen Tammannstr 4 D 37077Göttingen Germany

Institute of Physics Charles University Prague Ke Karlovu 5 CZ 12116Prague Czech Republic

LAB National des Champs Magnétiques Intenses LNCMI─CNRS 25 Martyrs Avenue BP 166 38042Grenoble Cedex 9 France

Max Planck Institut für Kohlenforschung Kaiser Wilhelm Platz 1 45470Mülheim an der Ruhr Germany

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