Network-Forming Liquids from Metal-Bis(acetamide) Frameworks with Low Melting Temperatures
Network-Forming Liquids from Metal-Bis(acetamide) Frameworks with Low Melting Temperatures
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DOI：
10.1021/jacs.0c11718
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发表时间：
2021-02-11
影响因子：
15
通讯作者：
Mason, Jarad A.
中科院分区：
文献类型：
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作者：
Liu, Mengtan;McGillicuddy, Ryan D.;Mason, Jarad A.
金属有机网络的熔融相为利用配位化学原理获得具有独特和可调结构和性质的液体和玻璃提供了令人兴奋的机会。在这里，我们讨论了一般的热力学策略，以提供一个增加的可逆的，低温熔融过渡在扩展的配位固体和熵的驱动力，并说明这种方法通过系统的研究一系列的双（乙酰胺）为基础的网络与创纪录的低熔点温度。这些化合物的低熔融温度是弱配位键、构象上灵活的桥接配体以及空间上分离的阳离子和阴离子之间的弱静电相互作用的结果，这些共同降低了焓并增加了熔融熵。通过晶体学，光谱学和量热法的组合，双晶趋势被发现由每个化合物内的配位键和氢键的强度决定，而熵的趋势受到残余运动和位置无序在结晶状态下受到限制的程度的强烈影响。Co（bba）（3）[CoCl_4] [bba = N，N '-1，4-丁烯双]的扩展X射线吸收精细结构（EXAFS）和对分布函数（PDF）分析（乙酰胺）]，其特征在于124摄氏度的三维金属-有机网络的创纪录低熔融温度，提供了液相中金属-配体配位的直接证据，以及支持其网络形成性质的中间和扩展范围秩序。此外，流变学测量还用于合理化玻璃形成能力和松弛动力学的差异。这些结果提供了新的见解的结构和化学因素，影响扩展的配位固体的熔融转变的热力学，以及配位网络形成液体的结构和性质。
Molten phases of metal-organic networks offer exciting opportunities for using coordination chemistry principles to access liquids and glasses with unique and tunable structures and properties. Here, we discuss general thermodynamic strategies to provide an increased enthalpic and entropic driving force for reversible, low-temperature melting transitions in extended coordination solids and illustrate this approach through a systematic study of a series of bis(acetamide)-based networks with record-low melting temperatures. The low melting temperatures of these compounds are the result of weak coordination bonds, conformationally flexible bridging ligands, and weak electrostatic interactions between spatially separated cations and anions, which collectively reduce the enthalpy and increase the entropy of fusion. Through a combination of crystallography, spectroscopy, and calorimetry, enthalpic trends are found to be dictated by the strength of coordination bonds and hydrogen bonds within each compound, while entropic trends are strongly influenced by the degree to which residual motion and positional disorder are restricted in the crystalline state. Extended X-ray absorption fine structure (EXAFS) and pair distribution function (PDF) analysis of Co(bba)(3)[CoCl4] [bba = N,N'-1,4-butylenebis(acetamide)], which features a record-low melting temperature for a three-dimensional metal-organic network of 124 degrees C, provide direct evidence of metal-ligand coordination in the liquid phase, as well as intermediate- and extended-range order that support its network-forming nature. In addition, rheological measurements are used to rationalize differences in glass-forming ability and relaxation dynamics. These results provide new insights into the structural and chemical factors that influence the thermodynamics of melting transitions of extended coordination solids, as well as the structure and properties of coordination network-forming liquids.