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

Abstract

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.

1,2‐Diphenylbenzene Dianion: Alkali‐Metal Salts with Drastically Spread C6 Rings

“…Both DFT calculations and ESR experiments confirm a triplet ground state (S = 1) which is of interest for the development of new materials. [16] Received: December 23, 2002 Revised: June 11, 2003 [Z50841] . Keywords: alkaline metals · carbanions · density functional calculations · hydrocarbons · reduction…”

“…This formation of contact-ion multiples is a consequence of strong Coulombic interactions M + ···C 6 2À is a general phenomenon, [3,13] covers a multitude of different contact-ion structures, [3][4][5][6] demonstrates essential effects of cation size as well as solvation, [14,15] and provides information on reduction pathways [6] or on promising novel materials. [16] Three examples of C 6 2À dianions illustrate some Angewandte Chemie of these aspects: Lithium-metal reduction of hexakis(trimethylsilyl)benzene (Scheme 4, left) [15] generates at strongly distorted C 6 2À dianion in boat-conformation, which can host two [Li(thf)]…”

C30H126−: Self‐Aggregation, High Charge Density, and Pyramidalization in a Supramolecular Structure of a Supercharged Hemifullerene

“…[14,15] Polycyclic aromatic hydrocarbons (PAHs) constructed in a stack are held together by countercharged metal ions that stabilize high negative charges on the anions. As the total electrostatic interaction between PAH anions and alkali metal cations depends on the square of the degree of reduction, it is clear why some PAHs show an inclination to aggregate only at high charges.…”

“…As the total electrostatic interaction between PAH anions and alkali metal cations depends on the square of the degree of reduction, it is clear why some PAHs show an inclination to aggregate only at high charges. [16] The PAH anions that do aggregate are typically unstable in solution and tend to precipitate, [14] so higher order stable aggregates with Li + ions, even more so with K + ions, are scarce.…”

Spin alignment of extra electrons in K-phenanthrene clusters taken from the crystalline tripotassium-intercalated phenanthrene structure

“…A similar result was already reported in 2000 by Bock et al for a tetrapotassium trianthracene crystal stabilized by THF (tetrahydrofuran). 37 A large calculated singlet-triplet splitting of 0.87 eV was obtained in this case. 38 Although it is a different system where cells interact very weakly, it shares with potassium intercalated phenanthrene the doping mechanism.…”