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 1