Synthesis and computational study of an unprecedented low-valence iron cluster with icosahedral [Fe@Fe12]16+ core and multicenter iron-iron bonding

The study was directed by Prof. Xu-Dong Chen (Nanjing Normal University) and Prof. Jun Li (Tsinghua University). Synthesis of the cluster was conducted by Gan Xu at Nanjing Normal University, directed by Xu-Dong Chen. After repeated optimizations, they rationalized the synthesis and identified the structure of the cubic-shaped black crystals to contain an icosahedral [Fe@Fe₁₂]¹⁶⁺ core, where an interstitial iron is surrounded by 12 peripheral irons (see the image below). The interactions between the interstitial and the peripheral irons are not bridged by any ligands. Successful incorporation of an interstitial iron with unsupported iron-iron boding paves the way toward building other high nuclear iron clusters. “It is exciting. The synthetic strategy could be extended to other scenarios,” Prof. Chen says.

Yun-Shu Cui, Xue-Lian Jiang, and Cong-Qiao Xu, together with lab director Jun Li, carried out a systematic theoretical study of this fascinating iron cluster. They found that the interstitial and peripheral irons are assembled through multi-center iron-iron bonding, while the peripheral irons interact with each other via ferromagnetic coupling. Quantum chemistry studies also revealed that the stability of the tridecanuclear cluster arises from the 18-electron shell-closing of the cluster core, which is further stabilized by bonding interactions with the surrounding ligands through Fe-S coordination and W-Fe bonding (see the image below). The ground-state spin quantum number of the cluster was predicted to be S=32/2. “This is a unique cluster comprising a series of intriguing bonding modes,” Prof. Li says.

The team also disclosed that the oxidation states of the irons are extremely low. Both experimental and theoretical evidence are in good support of the average iron oxidation states at about +1.23, and the cluster represents a very rare example of low-valence iron compound. “This case provides a good reference to understanding the role of metal oxidation state in a series of natural and industrial processes that may correlate with low-valence irons,” Prof. Li says.

The successful synthesis of the [Fe@Fe₁₂]¹⁶⁺ cluster enriched the family of high-nuclear transition metal clusters, complementing the modes of iron-iron bonding in iron clusters. The rational construction of high-nuclear clusters and the study of their electron structures and bonding nature are the keys to understanding the intrinsic rule that guides the evolution of physical/chemical properties from atom to bulk materials.

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See the article:

Synthesis and characterization of iron clusters with an icosahedral [Fe@Fe₁₂]¹⁶⁺ core

https://doi.org/10.1093/nsr/nwad327

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