Mark Sievert

Single crystals of an ionic anthracene aggregate with a triplet ground state

Crystalline supramolecular aggregates consisting of charged organic molecules, held together through metal-cluster-mediated Coulomb interactions, have attracted interest owing to their unusual structural, chemical and electronic properties. Aggregates containing metal cation clusters ‘wrapped’ by lipophilic molecular anions have, for example, been shown to be kinetically stable and soluble in nonpolar liquids such as saturated hydrocarbons. The formation of supramolecular aggregates can even be exploited to generate aromatic hydrocarbons that carry four negative charges and crystallize in the form of organic poly(metal cation) clusters or helical polymers. Here we report the anaerobic crystallization of an ionic organic aggregate—a contact ion septuple consisting of a fourfold negatively charged ‘tripledecker’ of three anthracene molecules bridged by four solvated potassium cations. Its electronic ground state is shown experimentally, using temperature-dependent electron paramagnetic resonance spectroscopy, to be a triplet. Although the spins in this biradical ionic solid are separated by a considerable distance, density functional theory calculations indicate that the triplet ground state is 84 kJ mol -1 more stable than the first excited singlet state. We expect that the successful crystallization of the ionic solid we report here, and that of a covalent organic compound with a triplet ground state at room temperature, will stimulate further attempts to develop new triplet-ground-state materials for practical use.

STRUCTURAL DISTORTIONS IN DIIODINE-SUBSTITUTED UNSATURATED HYDROCARBONS

The novel compound 1,10-diiodophenanthrene (right) is twisted by 68° owing to I–I repulsion. Density functional calculations with basis sets augmented by iodine pseudopotentials have been performed for this compound and for 2,2′diiodobiphenyl and 1,8-diiodonaphthalene, and the distortion of their structures caused by the presence of the iodine atoms discussed.

The Li+-Initiated Twofold Dehydrogenation and C−C Bond Formation of Hexaphenylbenzene to the Dilithium Salt of the 9,10-Diphenyltetrabenz[a,c,h,j]anthracene Dianion

Partly solvent-separated and partly solvent-shared, the contact ion triple of the 9,10-diphenyltetrabenz[a,c,h,j]anthracene dianion is formed by the ultrasonically activated reaction of hexaphenylbenzene with lithium metal powder in 1,2-dimethoxyethane (dme) [Eq. (1)]. The proposed microscopic pathway for this reaction-twofold dehydrogenation and C-C bond formation-is supported by quantum-chemical calculations.

Die Li+-initiierte zweifache Dehydrierung und C-C-Verknüpfung von Hexaphenylbenzol zum Dilithium-Salz des 9,10-Diphenyltetrabenzo[a,c,h, j]anthracen-Dianions

Teils Solvens-getrennt, teils Solvens-umhullt ist das Kontaktionen-Tripel des 9,10-Diphenyltetrabenzo[a,c,h,j]anthracen-Dianions, das unter Ultraschalleinwirkung bei der Umsetzung von Hexaphenylbenzol mit Lithiumpulver in 1,2-Dimethoxyethan (dme) entsteht [Gl. (1)]. Der vorgeschlagene mikroskopische Reaktionspfad – zweifache Dehydrierung und Bildung zweier neuer C-C-Bindungen – wird durch quantenchemische Rechnungen gestutzt.

Wechselwirkungen in Kristallen, 176. Mitteilung , Redox‐Reaktionen von Hexahydropyren: Kristallstrukturen seiner Radikalanion‐Salze sowie von Trihydropyrenylium‐tetrachloroaluminat und Dichtefunktionaltheorie‐Berechnungen

Redox Reactions of Hexahydropyrene: Crystal Structures of Its Radical-Anion Salts as well as of Trihydropyrenylium Tetrachloroaluminate and Density-Functional-Theory Calculations Hexahydropyrene 1, a doubly propane-1,3-diyl-bridged peri-naphthalene derivative wtih 10 π-electrons allows both oxidation to its cation as well as reduction to its radical-anion salts, which could be crystallized and structurally characterized – a rather rare case for small unsaturated hydrocarbons. The unexpected formally threefold dehydrogenation by the oxidizing system AlCl3/H2CCl2 (Bocks reagent) generated the hitherto unknown 1,2,3-trihydropyrene cation in two polymorphic crystals, which contain 12 π-electrons delocalized over three anellated six-membered rings comprising 13 π-centers. Structural comparison of the altogether four crystallized redox products [K+solv][M.−] 2a, [K+solv][M.−]∞2b, [Na+solv][M.−] 2c, and [(M−3 H)+][AlCl−4] 3 with the neutral hydrocarbon 1 reveals only small differences in bond lengths and angles, but establishes solvation contacts, π(η6)⋅⋅⋅K+ coordination in the polymer 2b, the flattening of one molecular half in the trihydropyren cation of 3 and ten H-bonds CH⋅⋅⋅Cl to the AlCl4− counter anion of 3. DFT/NBO Charge distributions, calculated based on the experimental structural parameters, show charge accumulation in the propanediyl bridges as well as in the peripheral naphthalene C−C bonds of the radical anions. The largest changes result expectedly for the formally triply dehydrogenated 1, i.e. the trihydropyren cation of 3, with two slightly positive and partly considerably less negative π-centers.

Wechselwirkungen in Molekülkristallen, 163 [1, 2]. Einfluß der Alkalimetall-Reduktionspotentiale auf die Bildung ihrer Kontaktionenmultipel mit Tetracen- und Decacylen-Polyanionen / Interaction in Molecular Crystals, 163 [ 1,2]. The Influence of Alkaline Metal Reduction Potentials on the Formation of their Contaction Multiples with Tetracene and Decacyclene Polyanions

The reduction of selected π-hydrocarbons tetracene and decacyclene by various alkaline metals allowed the crystallization and structure determination of the following five solvent separated or solvent shared contaction multiples: [Tetracene⊖⊖ (Na⊕Diglyme)2], [Tetracene⊖⊖ - (K⊕ Triglyme)2], [Decacyclene• ⊖] [Cs⊕ (Triglyme)2], [Decacyclene•⊖⊖⊖] [Na⊕ (DME)3]3, [Decacyclene⊖⊖⊖⊖ (K⊕Diglyme)4]. These alkaline salts contain a radicalanion M• ⊖ , dianions M⊖⊖ , a radicaltrianion M•⊖⊖⊖ , and a tetraanion M⊖⊖⊖⊖ generated by single or multiple electron transfer. Their structures are discussed in terms of the difference in alkaline metal reduction potentials, the powerful cation solvation, the effects of the anion charges and of the cation radii. Further aspects concern the solvent-shared or solvent-separated cation coordination to the anions, the polyion aggregation and for the radical trianion the experimentally proven and quantumchemically simulated Jahn/Teller distortion. Altogether the investigation adds facets to the knowledge of multielectrontransfer reactions and of selforganisation phenomena of alkaline salts.

Wechselwirkungen in Kristallen, 89 [1 - 3] Donator/Akzeptor-Komplexe von Alkyl- und Aminobenzolen, Anthracen oder Pyren mit 1,3,5-Cyan-/Nitro-benzolen: Kristallisation, Strukturen und Elektronenspektren / Interactions in Crystals, 89 [ 1 - 3] Donor/Acceptor Complexes of Alkyl and Aminobenzenes, Anthracene or Pyrene and 1,3,5-Cyano/nitro-benzenes: Crystallisation, Structures and Electronic Spectra

The following mixed-stack donor/acceptor complexes {D···A}∞ have been crystallized and their structures determined: {hexamethylbenzene···3,5-dicyano-1-nitrobenzene hexamethylbenzene···3,5-dinitro-1-cyanobenzene}∞, {pyrene···3,5-dinitro-1-cyanobenzene}∞, {anthracene···(3,5-dinitro-1-cyanobenzene)2}∞, {N,N-dimethylanilin···3,5-dinitro- 1-cyanobenzene}∞ and { 1-3-phenylenediamine···3,5-dinitro-1-cyanobenzene}∞. Their lattice packing consists of parallel layers, which contain either donors and acceptors as for hexamethylbenzene and pyrene or composite ones as in the 1:2 complex of anthracene with each one of the acceptors above and below its peripheral rings. The isostructural hexamethylbenzene complexes exhibit almost identical packing coefficients as well as a hexagonal coplanar arrangement of the C6(CH3)6 donors. Weak intermolecular van der Waals interactions are also observed between antiparallel cyano substituents. The interplanar n distances range between 334 and 353 pm, i. e. around 340 pm of two van der Waals n radii. In none of the complexes, however, significant structural changes in either the donor or the acceptor components due to the complex formation are observed. In both the crystals as well as in solution, the donor/acceptor complexes exhibit colours between yellow and red; their long-wavelength charge transfer absorption maxima, therefore, correspond to a lowering in excitation energy of only up to 1 eV relative to that of the components. The different charge transfer in the ground and the CT excited states is also discussed referring to other data such as vertical first ionization energies or interplanar distances {D···A}, as well as to results from semiempirical calculations based on the crystal structure data determined and including approximate configuration interaction.

Wechselwirkungen in Kristallen, 88 [1 - 3] Donator/Akzeptor - Komplexe von Alkylbenzolen, Pyren oder Perylen mit Tetrahalogen-p-benzochinonen: Strukturen und Eigenschaften / Interactions in Crystals, 88 [1 -3] Donor/Acceptor Complexes of Alkylbenzenes, Pyrene or Perylene and Tetrahalogen-p-benzoquinones: Structures and Properties

The following mixed-stack donor/acceptor complexes {D · · · A }∞ have been crystallized and their structures determined: { 1 ,2,4,5-tetramethylbenzene · · · tetrabromo-p -benzoquinone}∞ , {hexamethylbenzene · · · tetrabromo-p-benzoquinone}∞ , { ( 1 ,2 ,4,5-tetramethyl-benzene)2 · · · tetrachloro -p -benzoquinone}∞ , {pyrene · · · tetrafluoro-p-benzoquinone}∞ , {pyrene · · · tetrabromo-p-benzoquinone}∞ and {perylene · · · tetrabromo-p-benzoquinone}∞ . They exhibit an interesting lattice packing, especially the 2:1 tripeldecker sandwich of tetrachloro-p-benzoquinone, which crystallizes in a herringbone pattern. Their interplanar distances are around 340 pm, i. e. two van der Waals π radii. None of them , however, exhibits in neither the donor nor the acceptor components significant structural changes due to complex formation. Their colours range from orange-red to black in the crystal and to green in H2CCl2 solution. Their long-wavelengths charge transfer absorption maxim a correspond to a lowering in excitation energy of up to 2 eV relative to that of the components. The different charge transfer in the ground and excited states of the donor/acceptor complexes investigated is further discussed referring to data such as cyclovoltammetric reduction potentials as w ell as to results from semiempirical calculations based on the crystal structure data determined and including configuration interaction.

Wechselwirkungen in Molekülkristallen, 155 [1, 2]. Kristallzüchtung und Strukturbestimmung des Radikalkation-Salzes [Tetrahydrotetrathiafulvalenium●⊕] [AlCl4⊖]/Interaction in Molecular Crystals, 155 [1,2]. Crystallization and Structure Determination of the Radicalcation Salt [Tetrahydrotetrathiafulvalenium●⊕][AlCl4⊖]

The dark red tetrahydrotetrathiafulvalenium radical cation has been generated 20 years ago by iodine oxidation of hexathia-dispiro[4.0.4.4]decane and characterized in solution by its temperature-dependent ESR spectrum. Here we report the single crystal growth of its tetrachloroaluminate salt as well as its low temperature structure determination, which proves the C=C double bond to be elongated to 140 pm length and one molecular half to be twisted by 7°. The assumed slight cyanine type distortion is supported by structural comparison with tetrakis(dimethylamino)ethene dication salts and with the 1:3 complex of tetrahydrotetrathiafulvalene mercury dichloride. Unrestricted Density Functional Theory calculations predict both the spin as well as the positive charge to be distributed predominantly within the π molecular center {S2C=CS2}.

Kristallstrukturen von 6,7-Dimethyl-2,3-bis(2-pyridyl)chinoxalin-tetraphenylborat und -dihydrochlorid: Von einer intramolekularen Wasserstoffbrücke bei Einfachprotonierung zu einem intermolekularen Netzwerk bei Zweifachprotonierung

Summary. 6,7-Dimethyl-2,3-bis(2-pyridyl)quinoxaline presents another example for structural distortions upon protonation and for the dominating influence of the anion on the crystal packing: An intramolecular hydrogen bridge forms upon monoprotonation and with the sterically wrapped tetraphenyloborate anion, whereas upon diprotonation in concentrated HCl a dichloride dihydrate with an interamolecular H-bridge network crystallizes.