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.

COMMUNrCATlONS P/ii..\. 1973. 2. 41; G. te Velde. E. J. Baerends, J. Compuf. P h w . 1992. 99, 84. Computational details: A local spin density approximation (S. H. Vosko, L. Wilk. M. h'usair, Cun. J Phw. 1980,58, 1200) was used in connection with the self-interaction correction ofStoll et al. (H. Stoll, C. M. E. Pavlidou, H. Preuss, 7/1ror. C / I I~. A r f u 1978.49, 143) and a gradient correction to the exchange part of the potcntial (A D. Becke, Phys. Rev A 1988, 38, 3098). Frozen core approximntion with the following Slater-type-orbital (STO) basis sets for the valence shell$. V. double.< for 3s. 3p. and 4s and triple-< for 3d, 0, N. and C, double.; for 7s and 2p: H double.; for Is. A set of auxiliary s. p, d, f. and g type STOa centered on the different atoms was used to fit the electronic density [15] a ) L. Noodleman.

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.

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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.