Reactivity of Solid Rubrene with Potassium: Competition between Intercalation and Molecular Decomposition

Zhang, Jiliang, Whitehead, George FS, Manning, Troy D ORCID: 0000-0002-7624-4306, Stewart, David, Hiley, Craig I, Pitcher, Michael J, Jansat, Susanna, Prassides, Kosmas and Rosseinsky, Matthew J ORCID: 0000-0002-1910-2483 (2018) Reactivity of Solid Rubrene with Potassium: Competition between Intercalation and Molecular Decomposition JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 140 (51). pp. 18162-18172. ISSN 0002-7863, 1520-5126

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Abstract

We present the synthesis and characterization of the K ⁺ -intercalated rubrene (C <inf>42</inf> H <inf>28</inf> ) phase, K <inf>2</inf> Rubrene (K <inf>2</inf> R), and identify the coexistence 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 a complex competition between K intercalation and the decomposition of rubrene, producing three K-intercalated compounds, namely, K <inf>2</inf> R, K(RR∗), and K <inf>x</inf> R′ (where R∗ and R′ are rubrene decomposition derivatives C <inf>42</inf> H <inf>26</inf> and C <inf>30</inf> H <inf>20</inf> , respectively). K <inf>2</inf> R is obtained as the major phase over a wide composition range and is accompanied by the formation of amorphous byproducts from the decomposition of rubrene. K(RR∗) is synthesized as a single phase, and K <inf>x</inf> R′ is obtained only as a secondary phase to the majority K <inf>2</inf> R phase. The crystal structure of K <inf>2</inf> R 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 neighboring rubrene via η ⁶ , η ³ , and η ² 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 interacts with the host. The decomposition products of rubrene are also examined using solution NMR, highlighting the role of the breaking of C-C <inf>phenyl</inf> bonds. For the crystalline decomposition derivative products K(RR∗) and K <inf>x</inf> R′, a lack of definitive structural information with regard to R∗ and R′ prevents the crystal structures from being determined. The study illustrates the complexity in accessing solvent-free alkali metal salts of reduced PAH of the type claimed to afford superconductivity.

Item Type:	Article
Additional Information:	No access restrictions: data can be made immediately available.
Uncontrolled Keywords:	3402 Inorganic Chemistry, 34 Chemical Sciences
Depositing User:	Symplectic Admin
Date Deposited:	06 Dec 2018 10:46
Last Modified:	16 Jun 2026 13:19
DOI:	10.1021/jacs.8b11231
Open Access URL:	https://pubs.acs.org/doi/pdf/10.1021/jacs.8b11231
Related Websites:	Author Publisher
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3029622
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