Structure of the 10.pi. electron cyclooctatetraene dianion in potassium diglyme 1,3,5,7-tetramethylcyclooctatetraene dianion, [K((CH3OCH2CH2)2O)]2[C8H4(CH3)4]

Abstract

The structure of the potassium salt of a cyclooctatetraene dianion has been determined. As predicted by the Hiickel theory this 10t electron system is aromatic with eightfold molecular symmetry and average C-C bond lengths of 1.407 (6) A. Yellow air-sensitive crystals of potassium diglyme bis(l,3,5,7-tetramethylcyclooctatetraene) dianion, [K((CH3OCH2CH2)20)]2[C8H4(CH3)4], crystallize in space group FI (C,1) with a =9 .757 (3), b = 10.026 (4), c = 8.793 (3) A, a = 97.15 (1)°, ß = 112.35 (1)°, and y = 109.95 (1)°w ith pcalcd = 1.16 g cm-3 for Z = 1. All atoms, including hydrogen atoms, have been located and their positions and thermal parameters refined by full-

Paramagnetic alkali-aromatic ion-pair structures. The crystal structure of bis[1,2-bis(2-methoxyethoxy)ethane]sodium biphenylide

“…2Tg (Mooij, Klaassen, de Boer, Degens, van den Hark & Noordik, 1976)and KBp.2Ttg (Noordik, Schreurs, Gould, Mooij & de Boer, 1978). Crystal structures of some diamagnetic aromatic ion-pairs in which tetramethylethylenediamine or bis-quinuclidine are the coordinating molecules (Rhine, Davis & Stucky, 1975;Walczak & Stucky, 1976) and crystal structures of alkali complexes of cyclooctatetraene (Goldberg, Raymond, Harmon & Templeton, 1974;Noordik, Degens & Mooij, 1975) have been reported to belong to the class of contact ion-pair structures. All of these crystal structure determinations firmly underline the existence of two distinct types of ion-pairs in the solid state, demonstrating that the concept of solvent-separated and contact ion-pairs, which descends from spectroscopic experiments in solution, also holds in the solid state.…”

“…After the successful preparation of single crystals of alkali-biphenyl ion-pairs (Canters, Klaassen & de Boer, 1970), X-ray crystal structure determinations have shown that the structures of aromatic ion-pair containing complexes in the solid state can also be characterized as belonging to the solvent-separated or the contact ion-pair category (Brooks & Stucky, 1972;Brooks, Rhine & Stucky, 1972a,b;Noordik, van den Hark, Mooij & Klaassen, 1974;Noordik, Degens & Mooij, 1975;Goldberg, Raymond, Harmon & Templeton, 1974;Mooij, Klaassen, de Boer, Degens, van den Hark & Noordik, 1976;Noordik, Schreurs, Gould, Mooij & de Boer, 1978). The structures of the paramagnetic complexes rubidium and potassium biphenyl, crystallized from tetraglyme [CH30(CH2CH20)4CHal and having the composition RbBp.2Ttg and KBp.2Ttg (Bp --biphenyl; Ttg = tetraglyme), may be considered to be built up from solvent-separated ion-pairs.…”

An experimental and theoretical study of the low temperature E.S.R. of the cyclooctatetraene and tetramethylcyclooctatetraene anion radicals-in single crystal environments

“…The crystal structures of M2COT 9 dg (M= K, or Rb) and K2TMCOT 9 2dg are known and have been reported [6,8,9]. K2COT.…”

“…spectroscopy of cyclooctatetraene (COT) and 1,3,5,7-tetramethylcyclooctatetraene (TMCOT) monoanion radicals oriented in single crystals of dialkali metal cyclooctatetraene diglyme (M2COT 9 dg) [6][7][8], where M= K, Rb or Cs, and dipotassium 1,3,5,7-tetramethylcyclooctatetraene bis(diglyme) (K~TMCOT 2. dg) [9], respectively. In particular, we present theoretical calculations which explain why, as previously found experimentally, the equilibrium position of the COT monoanion in single crystals of M2COT 9 dg at low temperatures is rotated about its D s symmetry axis by an angle of 22.5 ~ relative to the equilibrium position of the COT dianion [7].…”

“…But no matter how fruitful the results of such studies, there is always the element of uncertainty because the studies have been performed in solution and on species whose exact structures can not be known precisely. Therefore, recent studies of aromatic hydrocarbon anions in the solid state, especially in single cr)rsta!s [2][3][4][5][6][7][8][9][10][11][12][13], are of considerable significance. An important result of the single crystal studies is that the conclusions derived from them are consistent with the conclusions drawn from previously reported investigations of ion pair phenomena in solution.…”