High-Spin [Fe<sup>I</sup><sub>3</sub>] Cluster Capable\nof Pnictogen Atom Capture

Using a new hexanucleating anildophosphine ligand <sup><i>t</i>Bu</sup>LH<sub>3</sub> (1,3,5-C<sub>6</sub>H<sub>9</sub>(NHC<sub>6</sub>H<sub>3</sub>–5-F–2-P(<i>t</i>Bu)<sub>2</sub>)<sub>3</sub>), the all-monovalent [Fe<sup>I</sup><sub>3</sub>] compound (<sup><i>t</i>Bu</sup>L)Fe<sub>3</sub> (<b>1</b>) was isolated and characterized by X-ray\ndiffraction\nanalysis, SQUID magnetometry, <sup>57</sup>Fe Mössbauer spectroscopy,\nand cyclic voltammetry. The molecular structure of <b>1</b> reveals\nvery close Fe–Fe distances of 2.3825(7), 2.4146(8), and 2.3913(8)\nÅ which results in significant Fe–Fe interactions and\na maximum high-spin <i>S</i> = <sup>9</sup>/<sub>2</sub> spin state as determined by SQUID magnetometry and further supported\nby quantum chemical calculations. Compound <b>1</b> mediates\nthe multielectron, oxidative atom transfer from inorganic azide ([Bu<sub>4</sub>N][N<sub>3</sub>]), cyanate (Na[NCO]), and phosphonate (Na(dioxane)<sub>2.5</sub>[PCO]) to afford the [Fe<sub>3</sub>]-nitrido (N<sup>3–</sup>) and [Fe<sub>3</sub>]-phosphido (P<sup>3–</sup>) pnictides,\n(<sup><i>t</i>Bu</sup>L)Fe<sub>3</sub>(μ<sup>3</sup>–N) (<b>2</b>) and [(<sup><i>t</i>Bu</sup>L)Fe<sub>3</sub>(μ<sup>3</sup>–P)(CO)]<sup>−</sup> (<b>3</b>), respectively. Compounds <b>1</b>–<b>3</b> exhibit rich electrochemical behavior with three (for <b>1</b>), four (for <b>2</b>) and five (for <b>3</b>) distinct redox events being observed in the cyclic voltammograms\nof these compounds. Finally, the all–monovalent <b>1</b> and the formally Fe<sup>II</sup>/Fe<sup>II</sup>/Fe<sup>I</sup> compound <b>3</b>, were investigated by alternating current (ac) SQUID magnetometry,\nrevealing slow magnetic relaxation in both compounds, with <b>3</b> being found to be a unique example of a [Fe<sub>3</sub>]-phosphido\nsingle-molecule magnet having an energy barrier relaxation reversal\nof <i>U</i> = 30.7(6) cm<sup>–1</sup> in the absence\nof an external magnetic field. This study demonstrates the utility\nof an all low-valent polynuclear cluster to perform multielectron\nredox chemistry and exemplifies the redox flexibility and unique physical\nproperties that are present in the corresponding midvalent oxidation\nproducts.