Dianion and Dication of Tetracyclopentatetraphenylene as Decoupled Annulene-within-an-Annulene Models.

The dianion and dication of tetramesityl-substituted tetracyclopentatetraphenylene, a circulene consisting of alternating five- and six-membered rings, have been generated by reduction with alkali metals and oxidation with antimony(V) halides, respectively. They are theoretically predicted to adopt double annulenoid structures called annulene-within-an-annulene models in which the outer and inner conjugation circuits are significantly decoupled. The theoretical structures were experimentally proven by X-ray crystallographic analyses and the electronic configurations were supported by MCD spectra.

Stepwise Generation of Mono-, Di-, and Triply-Reduced Warped Nanographenes: Charge-Dependent Aromaticity, Surface Nonequivalence, Swing Distortion, and Metal Binding Sites.

The stepwise chemical reduction of a molecular warped nanographene (WNG) having a negatively curved π-surface and defined C H composition with Cs metal used as the reducing and complexing agent allowed the isolation of three different reduced states with one, two, and three electrons added to its π-conjugated system. This provided a unique series of nanosized carbanions with increasing negative charge for in-depth structural analysis of consequences of controlled electron charging of non-planar nanographenes, using X-ray crystallographic and computational tools. The 3D molecular electrostatic potential (MEP) maps identified the negative charge localization at the central part of the WNG surface where selective coordination of Cs ions is confirmed crystallographically.

Mono-reduced Corannulene: To Couple and Not to Couple in One Crystal.

One-electron reduction of corannulene, C H , with Li metal in diglyme resulted in crystallization of [{Li (diglyme) } (C H ) (C H -C H ) ] (1), as revealed by single-crystal X-ray diffraction. This hybrid product contains two corannulene monoanion-radicals along with a dianionic dimer, crystallized with four Li ions wrapped by diglyme molecules. The dimeric (C H -C H ) anion provides the first crystallographically confirmed example of spontaneous radical dimerization for C H .

Structural and Electronic Effects of Stepwise Reduction of a Tetraaryl[3]Cumulene.

The chemical reduction of a [3]cumulene ([3]TrTol) has been explored using alkali metals. Mono- and doubly reduced forms of [3]TrTol were isolated as solvent-separated ion pairs with {Na(18-crown-6)THF } and {K(18-crown-6)THF } counterions and crystallographically characterized. This allowed analysis of structural parameters of the "naked" anions of [3]TrTol without interference from metal binding.

Highly strained [6]cycloparaphenylene: crystallization of an unsolvated polymorph and the first mono- and dianions.

An X-ray diffraction study of [6]cycloparaphenylene (1), crystallized under solvent-free conditions, revealed a unique solid state structure with tight packing of individual molecules that minimizes empty internal space. The controlled chemical reduction of this highly strained nanohoop with Group 1 metals resulted in the first isolation and structural characterization of its mono- and dianions, allowing for the evaluation of core transformations for the series ranging from 10 to 11- and 12-.

Record Alkali Metal Intercalation by Highly Charged Corannulene.

The need for advanced energy storage technologies demands the development of new functional materials. Novel carbon-rich and carbon-based materials of different structural topologies attract significant attention in this regard. Attractive systems include a unique class of bowl-shaped polycyclic aromatic hydrocarbons that map onto fullerene surfaces and are thus often referred to as fullerene fragments, buckybowls, or π-bowls.

Site-Directed Dimerization of Bowl-Shaped Radical Anions to Form a σ-Bonded Dibenzocorannulene Dimer.

Designed site-directed dimerization of the monoanion radicals of a π-bowl in the solid state is reported. Dibenzo[a,g]corannulene (C H ) was selected based on the asymmetry of the charge/spin localization in the C H anion. Controlled one-electron reduction of C H with Cs metal in diglyme resulted in crystallization of a new dimer, [{Cs (diglyme)} (C H -C H ) ] (1), as revealed by single crystal X-ray diffraction study performed in a broad range of temperatures.

Fusing a Planar Group to a π-Bowl: Electronic and Molecular Structure, Aromaticity and Solid-State Packing of Naphthocorannulene and its Anions.

Molecular and electronic structure, reduction electron transfer and coordination abilities of a polycyclic aromatic hydrocarbon (PAH) having a planar naphtho-group fused to the corannulene bowl have been investigated for the first time using a combination of theoretical and experimental tools. A direct comparison of naphtho[2,3-a]corannulene (C H , 1) with parent corannulene (C H , 2) revealed the effect of framework topology change on electronic properties and aromaticity of 1. The presence of two reduction steps for 1 was predicted theoretically and confirmed experimentally.

Experimental and DFT Studies of the Electron-Withdrawing Ability of Perfluoroalkyl (R ) Groups: Electron Affinities of PAH(R ) Increase Significantly with Increasing R Chain Length.

Two series of aromatic compounds with perfluoroalkyl (R ) groups of increasing length, 1,3,5,7-naphthalene(R ) and 1,3,5,7,9-corannulene(R ) , have been prepared and their electronic properties studied by low-temperature photoelectron spectroscopy (PES) (for gas-phase electron affinity measurements). These and many related compounds were also studied by DFT calculations. The data demonstrate unambiguously that the electron-withdrawing ability of R substituents increases significantly and uniformly from CF to C F to n-C F to n-C F .

Synthesis of the Unknown Indeno[1,2-a]fluorene Regioisomer: Crystallographic Characterization of Its Dianion.

Of the five possible indenofluorene regioisomers, examples of a fully conjugated indeno[1,2-a]fluorene scaffold have so far remained elusive. This work reports the preparation and characterization of 7,12-dimesitylindeno[1,2-a]fluorene as a highly reactive species. Experimental and computational data support the notion of a molecule with pronounced diradical character that exists in a triplet ground state.

Tuning the separation and coupling of corannulene trianion-radicals through sizable alkali metal belts.

The first heterobimetallic sandwich-type aggregate formed by bowl-shaped corannulene trianion-radicals, CH˙, has been synthesized using mixed-metal reduction of CH. The product was crystallographically characterized to reveal the self-assembly of [Cs//(CH)/4K/(CH)//Cs], in which two triply-charged corannulene decks encapsulate a rectangle of four potassium ions (the K···K separations are 4.212(4) and 5.

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 (C H ) affords a novel type of organometallic sandwich [Cs(C H ) ] , which crystallized as a solvent-separated ion pair with a [Na(18-crown-6)(THF) ] cation (where THF=tetrahydrofuran). The unprecedented double concave encapsulation of a metal ion by two bowl-shaped sumanenyl anions in [Cs(C H ) ] was revealed crystallographically. Evaluation of bonding and energetics of the remarkable product was accomplished computationally (B2PLYP-D/TZVP/ZORA), providing insights into its formation.

Mixing Li and Cs in the reduction of corannulene for the assembly of a cesium-capped sandwich with a hexanuclear heterometallic core.

The use of two alkali metals having the greatest ion size mismatch, Li and Cs, in the reduction of bowl-shaped corannulene (CH, 1), results in the preparation of a heterobimetallic organometallic self-assembly, [Cs(diglyme)]//[LiCs(CH)(diglyme)] (2). The X-ray crystallographic investigation of 2 revealed the formation of a triple-decker sandwich having a highly-charged hexanuclear core, (LiCs), held between two tetrareduced corannulene decks. The sandwich is capped by external cesium ions filling the concave cavities of corannulene bowls.

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.

Supramolecular trap for a transient corannulene trianion.

The first structural characterization of the transient triply-reduced state of corannulene (CH) is accomplished. The X-ray crystallographic study reveals that the CH˙ trianions, generated by corannulene reduction with metallic cesium, form a novel type of supramolecular sandwich-type assembly, [Cs//(CH)/4Cs/(CH)//Cs]. In the product, two triply-charged corannulene decks encapsulate a rectangle of four cesium ions with the external concave bowl cavities being filled by one cesium ion each.

Monoreduced 1,2-dihydrocorannulene versus the parent corannulene.

The monoanion of dihydrogenated corannulene isolated in the form of its potassium salt, namely tris(diglyme-κ(3)O,O',O'')potassium hexacyclo[11.5.2.

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.

Self-assembly of tetrareduced corannulene with mixed Li-Rb clusters: dynamic transformations, unique structures and record Li NMR shifts.

Self-assembly processes of the highly reduced bowl-shaped corannulene generated by the chemical reduction with a binary combination of alkali metals, namely Li-Rb, have been investigated by variable-temperature H and Li NMR spectroscopy. The formation of several unique mixed metal sandwich products based on tetrareduced corannulene, CH (), has been revealed followed by investigation of their dynamic transformations in solutions. Analysis of NMR data allowed to propose the mechanism of stepwise alkali metal substitution as well as to identify experimental conditions for the isolation of intermediate and final supramolecular products.

An unsolvated buckycatcher and its first dianion.

The X-ray crystallographic study of C60H28 consisting of two tethered corannulene bowls revealed a unique solid-state packing based on tight convex-concave π-π interactions. The controlled reduction of C60H28 resulted in the isolation and structural characterization of its dianion in the form of the rubidium salt that shows an entrapment of counterions by an anionic pincer.

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.

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.

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(-).

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.

A main group metal sandwich: five lithium cations jammed between two corannulene tetraanion decks.

Lithium-coordinated polyaromatic anions such as tetrareduced corannulene, C(20)H(10)(4-) (1(4-)), are useful substrates to model and ultimately improve the graphitic electrodes in lithium-ion (Li(+)) batteries. Previous studies suggested that 1(4-) 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.