Zero in-Plane Thermal Expansion in Guest-Tunable 2D Coordination Polymers

Zero
in-plane thermal expansion (TE) in a two-dimensional (2D) coordination
polymer is demonstrated. The combination of components that expand
and those that shrink into zigzag layers results in no net area change
in the 2D materials with temperature. Single crystals of [Mn­(salen)]2­[Mn­(N)­(CN)4(guest)] (salen = N,N′-ethylenebis­(salicylideneaminato), guest = MeOH
and MeCN) were prepared, and variable-temperature single-crystal X-ray
structural analyses demonstrated that these compounds exhibited both
anisotropic positive and negative thermal expansion depending on the
guest species. The TE behavior results from distortions of the octahedral
coordination geometry of [Mn­(salen)]+ units in the zigzag
layers. When both guests MeOH and MeCN were incorporated into one
material, [Mn­(salen)]2­[Mn­(N)­(CN)4(MeOH)0.25­(MeCN)0.75], zero in-plane
TE resulted in a range of temperature between 380 and 440 K.

本研究证实二维（2D）配位聚合物可实现面内零热膨胀（in-plane thermal expansion，TE）特性。通过将热膨胀组分与热收缩组分结合构筑锯齿状层，该二维材料的净面积随温度变化为零。本研究成功合成了[Mn(salen)]₂[Mn(N)(CN)₄(客体)]（salen = N,N'-亚乙基双(水杨醛亚胺合基)，客体为甲醇（MeOH）与乙腈（MeCN））的单晶，并通过变温单晶X射线结构分析证实，这类化合物的热膨胀行为取决于客体种类，可分别表现出各向异性正热膨胀与负热膨胀。该热膨胀行为源于锯齿状层中[Mn(salen)]⁺单元的八面体配位几何构型发生畸变。当将甲醇与乙腈两种客体同时引入同一材料，即得到[Mn(salen)]₂[Mn(N)(CN)₄(MeOH)₀.₂₅(MeCN)₀.₇₅]时，在380 K至440 K的温度区间内，该材料呈现出面内零热膨胀特性。