Claudia Arad

The structures of solvent-separated naphthalene and anthracene radical anions

Reduction of naphthalene and anthracene in diglyme, a thermodynamically favourable chelate ether for Na+ solvation, with sodium metal gave the crystalline solvent-separated radical anion salts, [C10H8·–][Na+(diglyme)2] and [C14H10·–][Na+(diglyme)2] whose structures were determined.

Wechselwirkungen in Kristallen 99. Alkalimetall-Kontaktionenmultipel von acenaphthylen- und Fluoranthen-Dianionen: Fünfring- und Sechsring-Koordination

Abstract Stimulated by qualitative MO considerations, the non-alternant π-hydrocarbons acenaphthylene and fluoranthene have been reduced in their ether solutions under aprotic conditions by alkali metals to their dianions. These crystallize as contact ion multiples of different structures: the (15-crown-5)-solvated sodium salt of acenaphthylene is a monomeric contact ion triple [(H2CH2CO)5Na⊕C12H8⊝⊝Na⊕-(OCH2CH2)5]1 with the ten-fold coordinated Na⊕ counter cations above and below the cyclopentadienyl ring. In contrast, the DME- or diglyme-solvated Na⊕- and Li⊕-salts of fluoranthene dianion [(R2O)2Me⊕C16H10⊝⊝Me⊕(OR2)2]∞ crystallize in polymer strings containing eight-fold coordinated Li⊕ or ten-fold coordinated Na⊕ counter cations above and below different of the two naphthalene six-membered rings. For these rather unexpected coordination differences, MNDO calculations based on the structural data provide a plausible rationale: the negative charge in the acenaphthylene dianion is predominantly located within the five-membered ring and in the fluoranthene dianion within the naphthalene six-membered rings.

Carbazole deprotonation by sodium metal mirror in various ethers: Structures with Na + -coordination numbers 3 and 4 to 7

Abstract Solutions of carbazole anions and sodium cations in aprotic ethers such as tetrahydrofuran, dimethoxyethane, diglyme, triglyme, tetraglyme, 15-crown-5 or 2.2.1-cryptand form a cation solvation system with a shallow potential and numerous local minima. Its experimental exploration allows to crystallize and structurally characterize contact ion multiples of Na+-solvated carbazole anion M− salts comprising polyether-solvated monomers [M−Nasolv+]1, solvent-shared dimers [M−Nasolv+]2 and solvent-separated polyions [(M−)nNasolv+](n − 1)−[Nasolv+](n − 1). Their Na+ coordination numbers stretch from 3 to 7. Series of compounds, shape-selected from the same crystallization batch such as 3- and 7-coordinate [(M−)3Na+]2−[Na+(2.2.1-cryptand)]2, 4- and 7-coordinate [(M−)2Na+(THF)2]−[Na+(2.2.1-cryptand)] as well as solvent-separated [M−][Na+(2.2.1-cryptand)] suggest potential cation solvation equilibria in the reductive deprotonation mixtures. The seven different carbazolate sodium salts presented, therefore, demonstrate the delicate energy balance, by which cation solvation can influence the crystallization of individual molecular crystals.

Strukturen ladungsgestörter oder räumlich überfüllter Moleküle, 108 [1] Strukturänderungen bei der Zweifach-Reduktion von Tetraphenyl-p-chinodimethan zu seinem Dianion / Structures of Charge-Perturbed or Sterically Overcrowded Molecules, 108 [1] Structural Changes of Tetraphenyl-p-quinodim ethane on Twofold Reduction to its Dianion

The two-electron reduction of tetraphenyl-p-quinodimethane M via its radical anion M⊖ to its dianion M⊖⊖ is explored both by cyclovoltammetry and ESR/ENDOR spectroscopy. Contact of the diglyme solution with added 15-crown-5 under aprotic conditions with a sodium metal mirror yields black crystals of a solvent-separated contact ion triple [M⊖⊖][Na⊕(OCH2CH2)5(H3CO(CH2CH2O)2CH3)]2. The two-electron-insertion into the pquinodimethane derivative R2C⊖=C(HC=CH)2C=CR2 changes its structure drastically to that of a twofold carbanion substituted benzene, R2C⊖ -(C6H4)- ⊖CR2. MNDO calculations provide a rationale for both the tremendous solvation of a Na⊕ center coordinated to seven oxygen centers of 15-crown-5 and of one diglyme molecule and the structural changes as well as the charge distribution in the unique Tetraphenyl-p-quinodimethane dianion (H5C6)2C⊖-(C6H4)- ⊖C(C6H5)2, in which the two negative charges are largely localized at the carbanion center of the benzene -substituents.

Elektronentransfer und Kontaktionen-Bildung, 45 [1, 2] Strukturänderungen bei der Einelektronen-Reduktion von Tetraphenylbutatrien zum Radikalanion und bei der Zweifach-Deprotonierung von Tetraphenyl-butin-2 zum Tetraphenylbutatrien-Dianion / Electron Transfer and Contact Ion Pair Formation, 45 [1,2] Structural Changes on Single Electron Reduction of Tetraphenylbutatriene to its Radical Anion and on Twofold Deprotonation of Tetraphenylbutyne-2 to the Tetraphenylbutatriene Dianion

Tetraphenylbutatriene is reduced under aprotic conditions to its ESR/ENDOR-spectroscopically characterized radical anion and to its dianion, with both electron transfers quasireversible according to cyclovoltammetric measurements. The alkali cation salts, the red contact ion pair [(H5C6)4C4·⊖][Na⊕ (H3COCH2CH2OCH3)3] and the dark violet contact ion triple [(H5C6)4C4⊖⊖][Li⊕(H3COCH2CH2OCH3)3]2 can be prepared by single electron reduction at a sodium metal mirror or by twofold de-protonation of 1,1,4,4-tetraphenylbutyne-2 using lithium-n-butyl. Their single crystal structures as well as that of the parent acetylene have been determined at low temperatures. The essential structural changes observed are the twisting of both molecular halves (H5C6)2CC relative to each other with increasing negative charge. The simultaneously resulting bond alternancy >C = C = C = C< → >C⊖ - C ≡ C⊖ - C < within the cumulene chain is discussed based on MNDO calculations for the structures determined.