Abstract
Cocrystallization of 7,7',8,8'-tetracyanoquinodimethane radical anion (TCNQ-•) and 3-methylpyridinium-1,2,3,5-dithiadiazolyl radical cation (3-MepyDTDA+•) afforded isostructural acetonitrile (MeCN) or propionitrile (EtCN) solvates containing cofacial π dimers of homologous components. Loss of lattice solvent from the diamagnetic solvates above 366 K affords a high-temperature paramagnetic phase containing discrete TCNQ-• and weakly bound π dimers of 3-MepyDTDA+•, as evidenced by X-ray diffraction methods and magnetic susceptibility measurements. Below 268 K, a first-order phase transition occurs, leading to a low-temperature diamagnetic phase with TCNQ-• σ dimer and π dimers of 3-MepyDTDA+•. This study reveals the first example of cooperative interactions between two different organic radical ions leading to magnetic bistability, and these results are central to the future design of multicomponent functional molecular materials.
Highlights
Cocrystallization of 7,7′,8,8′-tetracyanoquinodimethane radical anion (TCNQ−) and 3-methylpyridinium-1,2,3,5dithiadiazolyl radical cation (3-MepyDTDA+) afforded isostructural acetonitrile (MeCN) or propionitrile (EtCN) solvates containing cofacial π dimers of homologous components
Stable organic radicals that exhibit a hysteretic response to an external stimulus display physical properties such as magnetic bistability that are promising for use in nanotechnology devices.[1−6] Neutral organic π radicals have been extensively studied because their electron-exchange interactions can lead to dynamic structures weakly coupled; in which interconversion between radicals (S = 1/2) and π or σ dimers (S = 0) is possible.[7−20] These cooperative solid-state interactions between different centers allow variation of the crystalline lattice such that hysteretic first-order phase transitions can arise
Common Modes of Dimerization in Substituted 1,2,3,5-Dithiadiazolyl (DTDA) Radicals and 7,7′,8,8′Tetracyanoquinodimethane (TCNQ) Radical Anion tetracyanoquinodimethane (TCNQ) was chosen as a partner for MepyDTDA+ because it forms stable π radical anions (TCNQ−) and its cyanido substituents can act as structuredirecting groups
Summary
Cocrystallization of 7,7′,8,8′-tetracyanoquinodimethane radical anion (TCNQ−) and 3-methylpyridinium-1,2,3,5dithiadiazolyl radical cation (3-MepyDTDA+) afforded isostructural acetonitrile (MeCN) or propionitrile (EtCN) solvates containing cofacial π dimers of homologous components. Thermogravimetric analysis (TGA) of crystalline samples indicated the onset of desolvation of 1·EtCN at 365 K, while the loss of lattice solvent from 1·MeCN occurred with a noticeably higher onset temperature of 396 K.
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