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.

Condensation of persilylated nicotinimideamide and isonicotinimideamide with sulfur monochloride affords double salts of the 3-,4-pyridyl-subtituted 1,2,3,5-dithiadiazolylium DTDA cations of general formula [3-, 4-pyDTDA][Cl][HCl], in which the pyridyl nitrogen serves as a non-innocent base. Reduction of these salts with triphenylantimony followed by deprotonation of the intermediate protonated radical affords the free base radicals [3-, 4-pyDTDA], the crystal structures of which, along with those of their diselenadiazolyl analogues [3-, 4-pyDSDA], have been characterized by powder or single crystal X-ray diffraction. The crystal structures consist of "pancake" -dimers linked head-to-tail into ribbon-like arrays by η 2-S2-N(py) intermolecular secondary bonding interactions. Methylation of the persilylated (iso)nicotinimide-amides prior to condensation with sulfur monochloride leads to N-methylated double chloride salts Me[3-, 4-pyDTDA][Cl]2, which can be converted by metathesis into the corresponding triflates Me[3-, 4-pyDTDA][OTf]2 and then reduced to the N-methylated radical triflates Me[3-, 4-pyDTDA][OTf]. The crystal structures of both the N-methylated double triflate and radical triflate salts have been determined by single crystal X-ray diffraction. The latter consist of transcofacial -dimers strongly ion-paired with triflate anions. Variable temperature magnetic susceptibility measurements on both the neutral and radical ion dimers indicate that they are diamagnetic over the temperature range 2-300 K.

The design of molecular containers capable of selectively binding specific guest molecules presents an interesting synthetic challenge in supramolecular chemistry. Here, we report the synthesis and structure of a coordination cage assembled from Cu 3 I 4 À clusters and tripodal cationic N-donor ligands. Owing to the localized permanent charges in the ligand core the cage binds iodide anions in specific regions within the cage through ionic interactions. This allows the selective binding of bromomethanes as secondary guest species within the cage promoted by halogen bonding, which was confirmed by single-crystal X-ray diffraction.

The synthesis, structural, thermal, and magnetic properties of a series of simple binary organic salts based on the radical anion of 7,7,8,8-tetracyanoquinodimethane (TCNQ) and 4-(N-alkylpyridinium-3-yl)-1,2,3,5-dithiadiazolyl (DTDA), 1 R (R = Et, Pr, Bu), radical cations and their heavier selenium analogues (DSDA), 2 R , are described. Single-crystal X-ray structural analyses reveal that short alkyl substituents on the pyridinium moiety of DTDA/DSDA cations lead to crystallization of isostructural acetonitrile (MeCN) solvates 1 Et •MeCN, 1 Pr •MeCN, 2 Et •MeCN, and 2 Pr •MeCN with trans-cofacial DTDA radical cation and eclipsed-cofacial TCNQ radical anion dimers. A slight increase in the substituent chain length to butyl affords the solvate 1 Bu • 0.5MeCN or the nonsolvate 1 Bu . The nonsolvate 1 Bu can be exclusively isolated using propionitrile (EtCN), whereas the isostructural selenium analogue 2 Bu crystallizes from MeCN. The crystal packing in 1 Bu •0.5MeCN and 1 Bu /2 Bu is distinctively different: rare one-dimensional (1D) columnar π-stacks of evenly spaced TCNQ radical anions with periodic distortions along the vertical stacking direction and cis-cofacial DTDA dimers in 1 Bu •0.5MeCN vs discrete, non-eclipsed-cofacial TCNQ dimers and transantarafacial DTDA/DSDA dimers in 1 Bu /2 Bu . The nonsolvated structure 1 Pr with trans-cofacial DTDA and non-eclipsed-cofacial TCNQ dimers can be isolated from EtCN. Single-crystal and powder X-ray diffraction methods confirmed a thermally driven, irreversible, single-crystal-to-single-crystal structural transformation between 1 Pr •MeCN and 1 Pr . Thermogravimetric analyses of all nonsolvated salts show varied, yet robust, thermal behavior, while the thermal behavior of the solvates is consistent with more facile lattice solvent loss from structures with longer N-alkyl chains. Variable-temperature magnetic susceptibility measurements indicate that all structures are diamagnetic at low temperatures. However, thermally populated magnetic states could be observed for

The design of molecular containers capable of selectively binding specific guest molecules presents an interesting synthetic challenge in supramolecular chemistry. Here, we report the synthesis and structure of a coordination cage assembled from Cu 3 I 4 À clusters and tripodal cationic N-donor ligands. Owing to the localized permanent charges in the ligand core the cage binds iodide anions in specific regions within the cage through ionic interactions. This allows the selective binding of bromomethanes as secondary guest species within the cage promoted by halogen bonding, which was confirmed by single-crystal X-ray diffraction.