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

Jiliang Zhang, George F.S. Whitehead, Troy D. Manning, David Stewart, Craig I. Hiley, Michael J. Pitcher, Susanna Jansat, Kosmas Prassides, Matthew J. Rosseinsky

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)

Abstract

We present the synthesis and characterization of the K + -intercalated rubrene (C 42 H 28 ) phase, K 2 Rubrene (K 2 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 2 R, K(RR∗), and K x R′ (where R∗ and R′ are rubrene decomposition derivatives C 42 H 26 and C 30 H 20 , respectively). K 2 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 x R′ is obtained only as a secondary phase to the majority K 2 R phase. The crystal structure of K 2 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 phenyl bonds. For the crystalline decomposition derivative products K(RR∗) and K x 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.

Original languageEnglish
Pages (from-to)18162-18172
Number of pages11
JournalJournal of the American Chemical Society
Volume140
Issue number51
DOIs
Publication statusPublished - 2018 Dec 26

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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