Thermal behaviour and electrochemical properties of bis(trifluoromethanesulfonyl)amide and dodecatungstosilicate viologen dimers
Thermal behaviour and electrochemical properties of bis(trifluoromethanesulfonyl)amide and dodecatungstosilicate viologen dimers
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DOI：
10.1039/c2cp23580c
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发表时间：
2012-01-01
影响因子：
3.3
通讯作者：
Saielli, Giacomo
中科院分区：
文献类型：
--
作者：
Bonchio, Marcella;Carraro, Mauro;Saielli, Giacomo
本文报道了以双三氟甲磺酰胺（bistriflimide，Tf ~ 2N ~-）为抗衡阴离子的二聚紫精盐（1 '，1“-（烷烃-1，n-二基）双（1-乙基-4，4'-联吡啶），n = 4-10）的合成和表征。对于n = 4，5和6，以及对于壬基紫精阳离子（1，1 '-二壬基-4，4'-联吡啶），我们还制备了具有完全无机的十二钨硅酸盐阴离子SiW 12 O 4 O 4-的盐，其具有多电荷表面和纳米尺寸。该材料已被其特征在于通过量热技术，X-射线衍射和固态NMR和比较与类似的单体紫精盐表现出近晶中间相。一个强大的奇-偶效应中观察到的熔点和热行为的bistriflimide二聚体系统，类似于所报道的偶极棒状液晶二聚体，虽然所研究的紫精二聚体是不介晶。通过增加抗衡阴离子的大小，我们已经观察到有利于玻璃无定形状态的晶相和中间相的不稳定。新型离子液体晶体的设计的影响进行了讨论。溶液中的电化学行为已经通过循环伏安法测量进行了研究：有趣的是，奇偶效应在氧化还原电位中也清晰可见。在二聚体的每个末端形成的紫精自由基阳离子的自旋配对负责观察到的氧化还原趋势。通过密度泛函理论计算得到了自旋配对二聚体的结构。
We report the synthesis and characterization of dimeric viologen salts (1',1 ''-(alkane-1,n-diyl)bis (1-ethyl-4,4'-bipyridinium) with n = 4-10) with bis(trifluoromethanesulfonyl) amide (bistriflimide, Tf2N-) as a counteranion. For n = 4, 5 and 6, and for the nonylviologen cation (1,1'-dinonyl-4, 4'-bipyridinium) we also prepared salts with the totally inorganic dodecatungstosilicate anion, SiW12O404-, featuring a poly-charged surface and nanosized dimensions. The materials have been characterized by means of calorimetric techniques, X-ray diffraction and solid state NMR and a comparison is made with analogous monomeric viologen salts exhibiting smectic mesophases. A strong odd-even effect is observed in the melting points and in the thermal behaviour of the bistriflimide dimeric systems, similar to what was reported for dipolar calamitic liquid crystal dimers, although the studied viologen dimers are not mesomorphic. By increasing the size of the counteranion we have observed a destabilization of the crystal phases and of the mesophases in favour of a glassy amorphous state. Implications on the design of novel ionic liquid crystals are discussed. The electrochemical behaviour in solution has been investigated by cyclic voltammetry measurements: interestingly, the odd-even effect is clearly visible also in the redox potentials. The spin-pairing of the viologen radical cations formed at each end of the dimer is responsible for the observed redox trend. Insights on the structure of the spin-paired dimer have been obtained by DFT calculations.