Sarah N. Spisak

A Main Group Metal Sandwich: Five Lithium Cations Jammed Between Two Corannulene Tetraanion Decks

Characterization of the lithium-ion arrangement between two carbon sheets may ultimately aid in the design of battery electrodes. Lithium-coordinated polyaromatic anions such as tetrareduced corannulene, C20H104− (14−), are useful substrates to model and ultimately improve the graphitic electrodes in lithium-ion (Li+) batteries. Previous studies suggested that 14− forms dimers encasing four Li+ ions in solution. Here, we report a single-crystal x-ray diffraction analysis confirming the formation of a sandwich-type supramolecular aggregate with a high degree of alkali metal intercalation. In contrast to the prior model, our data reveal that five Li+ ions are sandwiched between the two tetrareduced corannulene decks, and 7Li nuclear magnetic resonance spectroscopy delineates a conserved structure in tetrahydrofuran solution. Remarkably, the sandwich is robust in both solution and solid states even in the presence of crown ethers that compete for Li+ coordination. These results should help elucidate Li+ intercalation motifs between curved carbon surfaces more broadly.

Selective endo and exo binding of alkali metals to corannulene.

The ion size matters: the structures of corannulene monoanions crystallized with Cs(+) and Rb(+) ions in the presence of [18]crown-6 reveal the intrinsic binding preferences of alkali metals and allow evaluation of the bowl deformation caused by negative charge distribution and metal binding. The large cesium cation coordinates exclusively to the concave face of C(20) H(10)(-), whereas the smaller rubidium cation exhibits convex binding.

A Buckybowl with a Lot of Potential: C5-C20H5(CF3)5†

Lots of potential: a trifluoromethylated corannulene, C(5)-C(20)H(5)(CF(3))(5), has been prepared and characterized spectroscopically and by X-ray crystallography. The structure exhibits a highly ordered bowl stacking that is unusual for corannulenes with acyclic substituents. The first reduction of C(5)-C(20)H(5)(CF(3))(5) is anodically shifted by 0.95 V, making it the strongest corannulene-based electron acceptor to date.

How Charging Corannulene with One and Two Electrons Affects Its Geometry and Aggregation with Sodium and Potassium Cations

Bowl-shaped mono- and dianions are prepared by reduction of corannulene (C(20)H(10), 1) with sodium and potassium metals in the presence of [18]crown-6 ether. Single-crystal X-ray diffraction studies of two sodium salts, [Na(THF)(2)([18]crown-6)](+)[1(-)] (2a) and [Na([18]crown-6)](+)[1(-)] (2b), reveal the presence of naked corannulene monoanions 1(-) in both cases. In contrast, the potassium adduct, [K([18]crown-6)](+)[1(-)] (3), shows an η(2)-binding of the K(+) ion to the convex face of 1(-). For the first time, corannulene dianions have been isolated as salts with sodium, [Na(2)([18]crown-6)](2+)[1(2-)] (4a) and [Na(THF)(2)([18]crown-6)](+)[Na([18]crown-6)](+)[1(2-)] (4b), and potassium counterions, [K([18]crown-6)](2)(+)[1(2-)] (5). Their structural characterization reveals geometry perturbations upon addition of two electrons to a bowl-shaped polyarene. It also demonstrates η(5)- or η(6)-binding of metals to the curved carbon surface of 1(2-), depending on the crystallization conditions. Both mono- and doubly-charged corannulene bowls show the preferential exo binding of Na(+) and K(+) ions in all investigated compounds. Various types of C-H···π interactions are found in the crystals of 2-5. The UV/Vis, ESR, and (1)H NMR spectroscopic studies of 2-5 indicate different coordination environment of corannulene anions in solution, depending on the metal ion.

A Strain‐Releasing Trap for Highly Reactive Electrophiles: Structural Characterization of Bowl‐Shaped Arenium Carbocations

In addition toits own unique properties, corannulene serves as a primarymodel for both theoretical and experimental studies for avariety of curved carbon networks ranging from fullerenes tonanotubes.Todate,theorganicreactionsofcorannulenehavebeen mainly limited tothe derivatization of its exteriorand tosynthetic transformations of rim-bound functional groups.

Clamshell Opening in the Mixed‐Metal Supramolecular Aggregates Formed by Fourfold Reduced Corannulene for Maximizing Intercalated Metal Content

The first members of a new class of supramolecular organometallic compounds with mixed-alkali-metal cluster cores, LiK5 and Li3 K3 , sandwiched between two four-fold reduced corannulene decks are prepared and fully characterized. The triple-decker supramolecular anions, [(C20 H10 (4-) )(LiK5 )(6+) (C20 H10 (4-) )](2-) and [(C20 H10 (4-) )(Li3 K3 )(6+) (C20 H10 (4-) )](2-) , illustrate a record ability of bowl-shaped and highly charged corannulene to provide all its sites, five benzene rings fused to a central five-membered ring, for binding of six alkali-metal ions. The previously unseen engagement of the hub-site of C20 H10 (4-) in lithium binding is accompanied by unprecedented shifts up to -24 ppm in (7) Li NMR spectra. The discussion of product formation mechanism, augmented by calculations, is provided.

Jahn–Teller Effect in Circulenes: X‐ray Diffraction Study of Coronene and Corannulene Radical Anions

Single-crystal X-ray diffraction studies of two polyaromatic radical anions crystallized as sodium salts, namely [Na(DME)(3) ](+)[C(20) H(10)(-)] (1) and [Na(DME)(3)](+)[C(24)H(12)(-)] (2) are reported. This allowed the first structural evaluation of Jahn-Teller (JT) effects for monoreduced circulenes and a comparison between bowl-shaped corannulene and planar coronene. The C(s) and D(2h) symmetrical distortions are found to fit the experimental data for C(20)H(10)(·-) and C(24)H(12)(·-), respectively. The continuous symmetry measure (CSM) analysis was carried out to provide a quantitative measure of the JT distortions in 1 and 2. In addition, the X-ray crystallographic results were fully supported by DFT calculations.

A Biradical Balancing Act: Redox Amphoterism in a Diindenoanthracene Derivative Results from Quinoidal Acceptor and Aromatic Donor Motifs

The reduced and oxidized states of an open-shell diindeno[b,i]anthracene (DIAn) derivative have been investigated by experimental and theoretical techniques. As a result of moderate biradical character and the ability of cyclopenta-fused scaffolds to stabilize both positive and negative charges, DIAn exhibits rich redox chemistry with four observable and isolable charged states. Structural and electronic properties of the DIAn system are brought to light by UV-vis-NIR and Raman spectroelectrochemical measurements. Aromatization of the diindeno-fused anthracene core upon successive single-electron injections is revealed through single-crystal X-ray diffraction of radical anion and dianion salts. We present a rare case where the pseudoaromatic/quinoidal ground state of a neutral biradical polycyclic hydrocarbon leads to a stable cascade of five redox states. Our detailed investigation of the transformation of molecular structure along all four redox events provides a clearer understanding of the nature of charge carriers in ambipolar organic field-effect transistors.

Convex and Concave Encapsulation of Multiple Potassium Ions by Sumanenyl Anions

Herein we report the novel complex consisting of di- and tripotassiumsumanenide, K7(C21H10(2-))2(C21H9(3-))·8THF (2), which was prepared by the treatment of sumanene (C21H12, 1) with excess K metal in THF. The X-ray structural determination revealed unique self-assembly of six potassium ions sandwiched by convex faces of two sumanenyl trianions in addition to novel interaction involving all 15 carbon atoms of three Cp-like moieties on the concave surface of the sumanenyl bowls outside the sandwich. The unique structural features of 2 are rationalized with the help of DFT calculations.

Double Concave Cesium Encapsulation by Two Charged Sumanenyl Bowls

The controlled reaction of Na and Cs, two alkali metals of different ionic sizes and binding abilities, with sumanene (C21 H12 ) affords a novel type of organometallic sandwich [Cs(C21 H11- )2 ]- , which crystallized as a solvent-separated ion pair with a [Na(18-crown-6)(THF)2 ]+ cation (where THF=tetrahydrofuran). The unprecedented double concave encapsulation of a metal ion by two bowl-shaped sumanenyl anions in [Cs(C21 H11- )2 ]- was revealed crystallographically. Evaluation of bonding and energetics of the remarkable product was accomplished computationally (B2PLYP-D/TZVP/ZORA), providing insights into its formation.