The borderline: exploring the structural landscape of triptycene in cocrystallization with ferrocene

Abstract

Cocrystallization of the geometrically demanding triptycene (TripH) with the compact and electron-rich ferrocene (FcH) and its derivatives afforded C–H---π_Cp assembled supramolecular chains of alternating (C₅H₅)(C₅H₄R)Fe and TripH molecules in a series of binary crystals: FcH/TripH (1), (C₁₀H₉)FeCHO/TripH (2), diferrocenyldiacetylene/TripH (3), paracyclophane-CC–Fc/TripH (4), and (C₁₀H₉)₂Fe₂/TripH (5). Analysis of the structure of cocrystals 1–5 (single crystal XRD) showed significant H_bridgehead---π_Cp interaction along with C–H---π and π---π interactions. Upon varying the groups on FcH, the appreciable H_bridgehead---π_Cp interaction remains in action to maintain the efficient packing and dense arrangement in the form of properly crystallized chains among the TripH and FcH derivatives mostly. In the case of 5, the effective close packing of such chain oligomers could not be achieved, so at this point, we reached a borderline at the structural landscape of TripH. This borderline can be described as an intermediate area between the native TripH and co-crystals domains, where TripH and Fc₂ molecules form 2D ribbons, which are packed closely by T-shaped C–H---π_Ph interactions between TripH molecules which exactly reproduce the geometry of TripH---TripH interaction in the TripH native crystal.