Structural Variations in the Dithiadiazolyl Radicals <i>p</i>‑ROC₆F₄CNSSN (R = Me, Et, ^<i>n</i>Pr, ^<i>n</i>Bu): A Case Study of Reversible and Irreversible Phase Transitions in <i>p</i>‑EtOC₆F₄CNSSN

The 4′-alkoxy-tetrafluorophenyl dithiadiazolyls, ROC₆F₄CNSSN [R = Me (<b>1</b>), Et (<b>2</b>), ^<i>n</i>Pr (<b>3</b>), ^<i>n</i>Bu­(<b>4</b>)] all adopt <i>cis-oid</i> dimers in the solid state. The methoxy derivative <b>1</b> adopts a π-stacked AA’AA’ motif, whereas propoxy (<b>3</b>) and butoxy (<b>4</b>) derivatives exhibit an AA’BB’ stacking. The ethoxy derivative (<b>2</b>) is polymorphic. The α-phase (<b>2α</b>) adopts an AA’BB’ motif comparable with <b>3</b> and <b>4</b>, whereas <b>2β</b> and <b>2γ</b> are reminiscent of <b>1</b> but combine a mixture of both monomers and dimers in the solid state. The structure of <b>2β</b> exhibits <i>Z</i>’ = 6 with two dimers and two monomers in the asymmetric unit but undergoes a thermally induced phase transition upon cooling below −25 °C to form <b>2γ</b> (<i>Z</i>’ = 14) with six dimers and two monomers in the asymmetric unit. The transition is associated with both rotation and translation of the dithiadiazolyl ring. Detailed differential scanning calorimetry and variable temperature powder X-ray diffraction studies coupled with SQUID magnetometry have been used to show that <b>2α</b> converts irreversibly to <b>2β</b> upon heating and that <b>2β</b> and <b>2γ</b> interconvert through a reversible phase transition with a small thermal hysteresis in its magnetic response