MOF-74(Zn,Ni)的各向异性负热膨胀

Anisotropic Negative Thermal Expansion in MOF-74(Zn,Ni)

金属有机框架材料(MOF)结构简单、孔径大,在分离、催化、吸附等领域有很好的应用前景,其结构的柔软性和可调性为MOF的热膨胀调控提供了可能。以MOF-74(Zn,Ni)化合物为研究对象,通过变温X射线衍射研究晶体结构,发现化合物在a(b)方向上表现出负热膨胀,而在c轴方向表现出正热膨胀。在(373~448)K的温度区间内,Zn-MOF-74表现出体积的正热膨胀,Ni-MOF-74则因更强的a轴负热膨胀而表现出体积的负热膨胀,这说明金属中心对负热膨胀具有显著影响。同时,负热膨胀起源于配体的桥链结构单元横向热运动。

Metal organic framework(MOF)compounds with simple structure and large pores show the promising applications in chemical separation,catalysis,adsorption,etc.Its flexible structure and divers bonding permit one to tailor thermal expansion to desired level.In the present paper,we studied the structure of MOF-74(Zn,Ni)with variable temperature X-ray diffraction and showed anisotropic negative thermal expansion,negative thermal expansion(NTE)along a(b)plane and positive thermal expansion(PTE)along c axis.Further structure refinements revealed that Zn-MOF-74 exhibits volumetric positive thermal expansion in the temperature range from 373 to 448 K,while Ni-MOF-74 behaviors volumetric negative thermal expansion due to stronger NTE in a-axis,indicating that the metal center plays a key role in the negative thermal expansion.Such NTE in MOF-74 is attributed to the transverse thermal vibration of the ligand linkage block.