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

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Strong Electronic and Magnetic Coupling in M4 (M = Ni, Cu) Clusters via Direct Orbital Interactions between Low-Coordinate Metal Centers
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2020-10-28 , DOI: 10.1021/jacs.0c08460
Khetpakorn Chakarawet , Mihail Atanasov _{1,

2} , Jonathan Marbey ₃ , Philip C. Bunting , Frank Neese ₁ , Stephen Hill ₃ , Jeffrey R. Long ₄

Affiliation

We present an extensive study of tetranuclear transition-metal cluster compounds M4(NPtBu3)4 and [M4(NPtBu3)4][B(C6F5)4] (M = Ni, Cu; tBu = tert-butyl), which feature low-coordinate metal centers and direct metal-metal orbital overlap. X-ray diffraction, electrochemical, magnetic, spectroscopic, and computational analysis elucidate the nature of the bonding interactions in these clusters and the impact of these interactions on the electronic and magnetic properties. Direct orbital overlap results in strongly coupled, large-spin ground states in the [Ni4(NPtBu3)4]+/0 clusters and fully delocalized, spin-correlated electrons. Correlated electronic structure calculations confirm the presence of ferromagnetic ground states that arise from direct exchange between magnetic orbitals, and, in the case of the neutral cluster, itinerant electron magnetism similar to that in metallic ferromagnets. The cationic nickel cluster also possesses large magnetic anisotropy exemplified by a large, positive axial zero-field splitting parameter of D = +7.95 or +9.2 cm-1, as determined by magnetometry or electron paramagnetic resonance spectroscopy, respectively. The [Ni4(NPtBu3)4]+ cluster is also the first molecule with easy-plane magnetic anisotropy to exhibit zero-field slow magnetic relaxation, and under a small applied field, it exhibits relaxation exclusively through an Orbach mechanism with a spin relaxation barrier of 16 cm-1. The S = 1/2 complex [Cu4(NPtBu3)4]+ exhibits slow magnetic relaxation via a Raman process on the millisecond time scale, supporting the presence of slow relaxation via an Orbach process in the nickel analogue. Overall, this work highlights the unique electronic and magnetic properties that can be realized in metal clusters featuring direct metal-metal orbital interactions between low-coordinate metal centers.

中文翻译：

通过低配位金属中心之间的直接轨道相互作用在 M4 (M = Ni, Cu) 簇中产生强电子和磁耦合

我们对四核过渡金属簇化合物 M4(NPtBu3)4 和 [M4(NPtBu3)4][B(C6F5)4]（M = Ni、Cu；tBu = 叔丁基）进行了广泛的研究，它们具有低坐标金属中心和直接金属-金属轨道重叠。X 射线衍射、电化学、磁性、光谱和计算分析阐明了这些簇中键合相互作用的性质以及这些相互作用对电子和磁特性的影响。直接轨道重叠导致 [Ni4(NPtBu3)4]+/0 簇中的强耦合、大自旋基态和完全离域的自旋相关电子。相关的电子结构计算证实了由磁轨道之间的直接交换产生的铁磁基态的存在，并且在中性星团的情况下，流动的电子磁性类似于金属铁磁体。阳离子镍簇还具有大的磁各向异性，例如分别由磁力测定法或电子顺磁共振光谱确定的大的正轴向零场分裂参数 D = +7.95 或 +9.2 cm-1。[Ni4(NPtBu3)4]+ 团簇也是第一个具有易平面磁各向异性的分子，表现出零场慢磁弛豫，并且在小外加场下，它完全通过具有自旋弛豫势垒的奥尔巴赫机制表现出弛豫16 cm-1。S = 1/2 复合物 [Cu4(NPtBu3)4]+ 通过拉曼过程在毫秒时间尺度上表现出缓慢的磁弛豫，支持通过镍类似物中的奥尔巴赫过程存在缓慢的弛豫。全面的，

更新日期：2020-10-28

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