Hernández Sánchez Raúl, Betley Theodore A
Department of Chemistry and Chemical Biology, Harvard University , 12 Oxford Street, Cambridge, Massachusetts 02138, United States.
J Am Chem Soc. 2015 Nov 4;137(43):13949-56. doi: 10.1021/jacs.5b08962. Epub 2015 Oct 21.
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 (χ(M)T ≈ 53 cm(3) 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 (57)Fe 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).
单分子磁体领域仍然依赖于超交换和双交换机制来产生大的自旋基态。实现高自旋结构的另一种方法是合成具有紧密M-M相互作用的弱场簇，以产生单个价轨道流形。根据洪德规则填充这个轨道流形可能会产生热稳定的高自旋基态，在这种基态下价电子保持耦合。我们现在用一个还原的六核铁簇证明了这种效应，该簇实现了一个S = 19/2（χ(M)T ≈ 53 cm³ K/mol）的基态，该基态持续到300 K，代表了迄今为止报道的在室温下持续存在的最大自旋基态。还原簇在变温零场（57）Fe穆斯堡尔谱和磁测量中均表现出单分子磁体行为，自旋反转势垒为42.5(8) cm⁻¹，磁阻塞温度为2.9 K（0.059 K/min）。
