Magnetically induced Binary Ferrocene with Oxidized Iron*

Our understanding of ferrocene—a cornerstone of organometallic chemistry—has remained largely unchanged in terms of its structure and electronic properties for over seven decades. In particular, all previous attempts to oxidize the iron center in ferrocene were unsuccessful. We report results that challenge this understanding by utilizing a metal-organic framework (Co-MOF-74) as a host material. This combination transforms ferrocene into a previously unobserved high-spin Fe(II) state with a stretched and bent conformation, significantly different from its traditional structure [1]. Remarkably, in this new state, the iron readily accepts oxygen from the air, transitioning it from Fe(II) to Fe(III)—a feat previously considered impossible due to the 18-electron rule. Moreover, our study suggests the reversibility of the iron-oxygen binding, as suggested by temperature swing experiments, highlighting the system's dynamic nature. Our analysis is based on Mößbauer spectroscopy, extended X-ray absorption fine structure (EXAFS), in situ infrared spectroscopy (IR), SQUID magnetometry, thermal gravimetric analysis, energy dispersive X-ray fluorescence spectroscopy, and ab initio calculations. These techniques provide an exhaustive view of the structural, electronic, and magnetic changes within ferrocene when placed inside Co-MOF-74. Our multifaceted approach opens new frontiers in organometallic chemistry, unveiling the potential of ferrocene for novel oxygen storage/delivery mechanisms, medical and drug-related applications, and iron catalysts.

 

[1]      S. Ullah et al., J. Am. Chem. Soc. 145, 18029 (2023).