Mittapalli Sudhir, Perumalla D Sravanakumar, Nanubolu Jagadeesh Babu, Nangia Ashwini
School of Chemistry, University of Hyderabad, Professor C. R. Rao Road, Gachibowli, Hyderabad 500 046, India.
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bengaluru 500 016, India.
IUCrJ. 2017 Oct 27;4(Pt 6):812-823. doi: 10.1107/S2052252517014658. eCollection 2017 Nov 1.
The design and synthesis of mechanically responsive materials is interesting because they are potential candidates to convert thermal energy into mechanical work. Reported in this paper are thermosalient effects in a series of halogen derivatives of salinazids. The chloro derivative, with higher electronegativity and a weaker inter-halogen bond strength (Cl⋯Cl) exhibits an excellent thermal response, whereas the response is weaker in the iodo derivative with stronger I⋯I halogen bonding. 3,5-Di-chloro-salinazid (Compound-A) exists in three polymorphic forms, two room-temperature polymorphs (Forms I and II) and one high-temperature modification (Form III). The transformation of Form I to Form III upon heating at 328-333 K is a reversible thermosalient transition, whereas the transformation of Form II to Form III is irreversible and non-thermosalient. 3,5-Di-bromo- (Compound-B) and 3-bromo-5-chloro- (Compound-C) salinazid are both dimorphic: the Form I to Form II transition in Compound-B is irreversible, whereas Compound-C shows a reversible thermosalient effect (362-365 K). In the case of 3,5-di-iodo-salinazid (Compound-D) and 3,5-di-fluoro-salinazid (Compound-E), no phase transitions or thermal effects were observed. The thermosalient behaviour of these halosalinazid molecular crystals is understood from the anisotropy in the cell parameters (an increase in the axis and a decrease in the and axes upon heating) and the sudden release of accumulated strain during the phase transition. The di-halogen salinazid derivatives (chlorine to iodine) show a decrease in thermal effects with an increase in halogen-bond strength. Interestingly, Compound-B shows solid-state photochromism in its polymorphs along with the thermosalient effect, wherein Form I is cyan and Form II is light orange.
机械响应材料的设计与合成很有趣，因为它们是将热能转化为机械功的潜在候选材料。本文报道了一系列沙利那嗪卤代衍生物中的热突出效应。氯衍生物具有较高的电负性和较弱的卤素间键强度（Cl⋯Cl），表现出优异的热响应，而碘衍生物中I⋯I卤素键较强，其响应较弱。3,5-二氯沙利那嗪（化合物A）以三种多晶型形式存在，两种室温多晶型（I型和II型）和一种高温变体（III型）。在328 - 333 K加热时，I型向III型的转变是可逆的热突出转变，而II型向III型的转变是不可逆的且非热突出的。3,5-二溴-（化合物B）和3-溴-5-氯-（化合物C）沙利那嗪都是二晶型的：化合物B中I型向II型的转变是不可逆的，而化合物C表现出可逆的热突出效应（362 - 365 K）。对于3,5-二碘沙利那嗪（化合物D）和3,5-二氟沙利那嗪（化合物E），未观察到相变或热效应。这些卤代沙利那嗪分子晶体的热突出行为可从晶胞参数的各向异性（加热时a轴增加，b轴和c轴减小）以及相变过程中积累应变的突然释放来理解。二卤代沙利那嗪衍生物（从氯到碘）随着卤素键强度的增加，热效应降低。有趣的是，化合物B在其多晶型中除了热突出效应外还表现出固态光致变色，其中I型为青色，II型为浅橙色。
