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The reactivity of solid rubrene with potassium: competition between intercalation and molecular decomposition

DOI: 10.1021/jacs.8b11231 DOI Help

Authors: Jiliang Zhang (University of Liverpool) , George F. S. Whitehead (University of Liverpool) , Troy D. Manning (University of Liverpool) , David Stewart (University of Liverpool) , Craig I. Hiley (University of Liverpool) , Michael J. Pitcher (University of Liverpool) , Susanna Jansat (University of Liverpool) , Kosmas Prassides (Osaka Prefecture University; Tohoku University) , Matthew J. Rosseinsky (University of Liverpool)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of The American Chemical Society

State: Published (Approved)
Published: November 2018

Abstract: We present the synthesis and characterization of the K+ intercalated rubrene (C42H28) phase, K2Rubrene (K2R) and identify the co-existence of amorphous and crystalline materials in samples where the crystalline component is phase pure. We suggest this is characteristic of many intercalated alkali metal-polyaromatic hydrocarbon (PAH) systems, including those for which superconductivity has been claimed. The systematic investigation of K-rubrene solid state reactions using both K and KH sources reveals complex competition between K intercalation and the decomposition of rubrene, producing three K-intercalated compounds, namely, K2R, K(RR*), and KxRʹ (where R* and Rʹ are rubrene decomposition derivatives C42H26 and C30H20, respectively). K2R is obtained as the major phase over a wide composition range and is accompanied by the formation of amorphous by-products from the decomposition of rubrene. K(RR*) is synthesized as a single phase and KxRʹ is obtained only as a secondary phase to the majority K2R phase. The crystal structure of K2R was determined using high resolution powder X-ray diffraction, revealing that the structural rearrangement from pristine rubrene creates two large voids per rubrene within the molecular layers in which K+ is incorporated. K+ cations accommodated within the large voids interact strongly with the neighbouring rubrene via η6, η3 and η2 binding modes to the tetracene cores and the phenyl groups. This contrasts with other intercalated PAHs where only a single void per PAH is created and the intercalated K+ weakly interact with the host. The decomposition products of rubrene are also examined using solution NMR, highlighting the role of the breaking of C-CPhenyl bonds. For the crystalline decomposition derivative products K(RR*) and KxRʹ, a lack of definitive structural information with regards to R* and Rʹ prevents the crystal structures being determined. The study illustrates the complexity in accessing solvent-free alkali metal salts of reduced PAH of the type claimed to afford superconductivity.

Journal Keywords: intercalation; crystal structure; rubrene; decomposition

Subject Areas: Materials, Chemistry

Instruments: I11-High Resolution Powder Diffraction