碱金属、碱土金属准二维多碳化物的高压合成、结构与相关反应机理

Metal polycarbide has extensive applications in the research of high-temperature superconductivity and Li-battery materials. It is also an important precursor to synthesize carbon materials like porous carbon and nano-diamond et al.. However, compared to elemental carbon and hydrocarbon, the types of carbide structures are still very limited, and it is of great significance to synthesize metal carbides with novel structures. Recently, metal carbides with different carbon structures were predicted by theoretical calculations, among which the quasi-2D nano-ribbon structure, such as polyacenide, attracts most attention. In this proposal, we focus on the synthesis of alkaline, alkaline earth metal polycarbides with quasi-2D nano-ribbon structure under high pressure and high temperature conditions (up to 60 GPa and 2000 K), as well as the crystal structure and the relationship between the structure and synthetic conditions. We will track intermediates in the reaction to understand the reaction process, and also explore the protonation, demetallization and polymerization reaction of the quasi-2D polycarbide. Through these reactions, carbon materials like nano-ribbon with controllable width, porous carbon structure and 3D metal carbides are likely to be obtained. By combining the novel synthetic methods (high pressure and high temperature) with multiple cutting-edge analysis methods, the synthesis, structure and the reaction rules of metal polycarbide under extreme conditions will be systemically investigated. It will provide an important reference for poly-carbonic chemistry and synthesis of novel carbon materials under extreme conditions.

金属多碳化物在高温超导研究与锂电池电极材料方面具有重要的应用，同时是合成多孔碳材料、纳米金刚石等多种碳材料的重要前体。与碳单质和烃类相比，多碳化物的结构类型相当单调，具有新型骨架结构的金属多碳化物亟需实验探索。近年来人们预测了大量在高压下稳定的多碳化物，其中最典型的是含有准二维超窄碳纳米带的聚并苯盐系列。本项目即以碱金属、碱土金属准二维多碳化物作为核心研究内容，运用极端条件（至60GPa，2000K）探索合成新型多碳化物，并测定其晶体结构，研究合成-结构的关系。同时一方面追踪合成过程的中间产物，研究高压反应机理；另一方面研究多碳化物的化学反应性，包括质子化反应、脱金属反应和聚合反应，尝试合成规则碳纳米带、碳骨架孔道材料及三维多碳化物。本项目将极端合成条件与多种前沿表征手段相结合，系统研究多碳化物的合成、结构与反应规律，为极端条件下的多碳离子化学与新型碳结构的合成建立研究基础。

本项目主要致力于运用高压手段合成具有新颖骨架结构的碳基材料，并探究其合成过程中的化学反应机理，总结反应规律。在项目执行期间，我们研究了多个离子型金属多碳化物、中性炔类分子、芳香分子在高温高压条件下的化学反应，合成了多个准二维多碳化物，如聚丁炔二酸、聚二苯基丁二炔、聚均三炔基苯、氟掺杂石墨烷等，并通过晶体学、谱学、计算化学等多方面的分析与研究得到了化学反应机理。我们发现Diels-ALder反应和脱氢Diels-Alder反应这一类协同反应是芳香类、炔类化合物高压聚合的重要机理。另外通过总结大量分子晶体在高压反应前的晶体结构，我们发现炔类和芳香类分子晶体中相邻分子的不饱和碳原子受高压驱动成键时存在一定的距离阈值，低于该阈值即可反应成键。该阈值在室温下约为3.0A，芳香分子稍小，约为2.8A；炔类稍大，可达3.2A；带电荷的多碳离子阈值较小，中性分子阈值较大；具有协同反应路线的体系阈值较大。这些发现使得我们对高压下不饱和分子合成高聚碳材料的过程有了理性认识，可以作为参考基础，通过理性设计和理论模拟精准合成新型碳基材料，极大地拓展了合成材料化学的工具箱。