Is Introducing Crystal Structures of Ferrocene in Cyclodextrin into Learning Materials for STEM Education Possible?

Abstract

This study aimed to critically verify the validity of the widely used "Ferrocene in Cyclodextrin" (Fc in CyD) model in inquiry-based education within Science, Technology, Engineering, and Mathematics (STEM) fields, by examining available crystallographic data for inclusion compounds between Cyclodextrin (CyD) and Ferrocene (Fc). The methodology relied on a systematic review of scientific literature and a search of the Cambridge Crystallographic Data Centre (CCDC) database to verify reported molecular structures. The results revealed that the simplified educational model, which assumes specific inclusion ratios (e.g., 2:1 for α-CyD and 1:1 for β- and γ-CyD), is not conclusively supported by comprehensive crystallographic evidence; confirmed crystal structures exist only for α-CyD with Fc (2:1 ratio) and its oxidized form Fc⁺, and for β-CyD with Fc but in a complex 4:5 ratio, whereas no X-ray crystallographic analysis confirming Fc inclusion within γ-CyD was found, despite spectroscopic and theoretical evidence suggesting their interaction. The study concludes that relying on the simplified model as an absolute truth in educational curricula may convey inaccurate information, and instead proposes using well-documented inclusion compounds of Fc/Fc⁺ with α-CyD as alternative educational materials, given their support by robust structural and experimental data, thereby enhancing the accuracy of inquiry-based learning in organometallic chemistry and host-guest chemistry. The originality of this study lies in its being the first systematic critical review to verify the actual crystallographic support for the widely cited "Fc in CyD model" in education.