Structural Variations in the Dithiadiazolyl Radicals <i>p</i>-ROC<sub>6</sub>F<sub>4</sub>CNSSN (R = Me, Et, <sup><i>n</i></sup>Pr, <sup><i>n</i></sup>Bu): A Case Study of Reversible and Irreversible Phase Transitions in <i>p</i>-EtOC<sub>6</sub>F<sub>4</sub>CNSSN
作者:Yassine Beldjoudi、Rui Sun、Ana Arauzo、Javier Campo、Robert J. Less、Jeremy M. Rawson
DOI:10.1021/acs.cgd.7b01065
日期:2018.1.3
The 4′-alkoxy-tetrafluorophenyl dithiadiazolyls, ROC6F4CNSSN [R = Me (1), Et (2), nPr (3), nBu(4)] all adopt cis-oid dimers in the solid state. The methoxy derivative 1 adopts a π-stacked AA’AA’ motif, whereas propoxy (3) and butoxy (4) derivatives exhibit an AA’BB’ stacking. The ethoxy derivative (2) is polymorphic. The α-phase (2α) adopts an AA’BB’ motif comparable with 3 and 4, whereas 2β and 2γ are reminiscent of 1 but combine a mixture of both monomers and dimers in the solid state. The structure of 2β exhibits Z’ = 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 2γ (Z’ = 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 2α converts irreversibly to 2β upon heating and that 2β and 2γ interconvert through a reversible phase transition with a small thermal hysteresis in its magnetic response.
4′-烷氧基-四氟苯基二噻二唑基ROC6F4CNSSN [R = Me (1), Et (2), nPr (3), nBu(4)]在固态时均采用顺式二聚体。甲氧基衍生物1采用π堆积的AA’AA’基序,而丙氧基(3)和丁氧基(4)衍生物则呈现AA’BB’堆积。乙氧基衍生物(2)是多晶型的。 α相 (2α) 采用与 3 和 4 类似的 AA'BB' 基序,而 2β 和 2γ 让人想起 1,但在固态下结合了单体和二聚体的混合物。 2β的结构表现出Z' = 6,不对称单元中有两个二聚体和两个单体,但在冷却至-25°C以下时会发生热诱导相变,形成2γ(Z' = 14),其中有六个二聚体和两个单体。不对称单位。该转变与二噻二唑基环的旋转和平移相关。详细的差示扫描量热法和变温粉末 X 射线衍射研究与 SQUID 磁力测定相结合,表明 2α 在加热时不可逆地转化为 2β,并且 2β 和 2γ 通过可逆相变相互转化,其磁响应具有小的热滞后。