物理化学学报 >> 2021, Vol. 37 >> Issue (11): 2009039.doi: 10.3866/PKU.WHXB202009039

所属专题: 能源与材料化学

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吡咯锂的合成、表征及晶体结构

荆子君1,2, Khai Chen Tan1,2, 何腾1,*(), 于洋1,2, 裴启俊1,2, 王金涛1,2, Wu Hui3,*(), 陈萍1   

  1. 1 中国科学院大连化学物理研究所,辽宁 大连 116023
    2 中国科学院大学,北京 100049
    3 美国国家标准技术研究所中子研究中心,马里兰州 盖瑟斯堡 20899-6012,美国
  • 收稿日期:2020-09-10 录用日期:2020-10-19 发布日期:2020-10-23
  • 通讯作者: 何腾,Wu Hui E-mail:heteng@dicp.ac.cn;huiwu@nist.gov
  • 基金资助:
    国家重点研发计划(2018YFB1502100);国家重点研发计划(2019YFE0103600);国家自然科学基金(51671178);国家自然科学基金(51472237);中国科学院大连化学物理研究所光源基金(DICP DCLS201701);辽宁省兴辽人才计划(XLYC1807157);王宽诚教育基金会(GJTD-2018-06)

Synthesis, Characterization, and Crystal Structure of Lithium Pyrrolide

Zijun Jing1,2, Chen Tan Khai1,2, Teng He1,*(), Yang Yu1,2, Qijun Pei1,2, Jintao Wang1,2, Hui Wu3,*(), Ping Chen1   

  1. 1 Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, Liaoning Province, China
    2 University of Chinese Academy of Sciences, Beijing 100049, China
    3 NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899-6102, USA
  • Received:2020-09-10 Accepted:2020-10-19 Published:2020-10-23
  • Contact: Teng He,Hui Wu E-mail:heteng@dicp.ac.cn;huiwu@nist.gov
  • About author:Email: huiwu@nist.gov (H.W.)
    Email: heteng@dicp.ac.cn (T.H.), Tel.: +86-411-84379583 (T.H.)
  • Supported by:
    the National Key R&D Program of China(2018YFB1502100);the National Key R&D Program of China(2019YFE0103600);the National Natural Science Foundation of China(51671178);the National Natural Science Foundation of China(51472237);the Light Source Fund of Dalian Institute of Chemical Physics, Chinese Academy of Sciences(DICP DCLS201701);the Liaoning Revitalization Talents Program(XLYC1807157);the K. C. Wong Education Foundation(GJTD-2018-06)

摘要:

高效储氢材料的缺乏是制约氢能大规模应用的主要瓶颈之一。有机液态储氢材料是一类具有前景的体系,但是仍然面临吸放氢热力学性质差等难题。作者在前期提出了一种金属取代策略,即碱(土)金属取代有机物中的活泼氢,优化了有机储氢材料的热力学性质。基于此,我们开发了一系列金属有机氢化物储氢材料。然而在这些材料中,金属吡咯盐的合成方法及性质并没有被详细地研究,同时吡咯锂这种新物质的晶体结构尚未解析。在本工作中,我们采用球磨法和湿化学法两种合成方法制备了吡咯锂和吡咯钠两种物质,并利用核磁共振、X射线衍射、紫外可见吸收光谱等技术对材料进行了详细的表征。晶体结构解析发现,吡咯锂为单斜晶系,P21/c (14)空间群,晶胞参数为a = 4.4364(7)Å、b = 11.969(2) Å、c = 8.192(2) Å、β = 108.789(8) °和V = 411.8(2) Å3。在晶体结构中,每个锂离子被三个吡咯离子包围,其中包括两个Li-N形成的σ键和一种阳离子–π相互作用,并由此形成了三维网络结构。这些特征不同于文献中对咔唑锂的理论预测。

关键词: 吡咯锂, 晶体结构, 金属取代, 液态有机储氢材料, 金属氮杂环化合物, 储氢

Abstract:

Development of clean energy is an urgent requirement because of the depletion of fossil energy sources and increasingly severe environmental pollution. However, the lack of safe and efficient hydrogen storage materials is one of the bottlenecks in the implementation of hydrogen energy. Liquid organic hydrogen carriers (LOHCs) have been recognized as potential materials for the storage and transportation of hydrogen owing to their high gravimetric and volumetric hydrogen densities, reversible hydrogen absorption and desorption ability, and ease of widespread implementation with minimal modification on the existing fueling infrastructure. While some LOHCs such as cycloalkanes and N-heterocycles have been developed for hydrogen storage, they require a high hydrogen release temperature due to the large enthalpy change of dehydrogenation. In our previous work, a metallation strategy was proposed to improve the thermodynamic properties of liquid organic hydrogen carriers for hydrogen storage, and a series of metalorganic hydrides were synthesized and investigated. Among them, sodium phenoxide-cyclohexanolate pair, lithium carbazolide-perhydrocarbazolide, and sodium anilinide-cyclohexylamide pair showed promising dehydrogenation thermodynamics and improved hydrogen storage properties. Sodium pyrrolide and sodium imidazolide were also synthesized. However, pyrrolides were not well characterized, and the structure of lithium pyrrolide was not resolved. In the present study, we synthesized sodium and lithium pyrrolides by ball milling and wet chemical methods. One equivalent of hydrogen could be released from the reaction of pyrrole and metal hydrides, indicating the replacement of H by metal. The formation of pyrrolides was confirmed by nuclear magnetic resonance (NMR), X-ray diffraction (XRD) and ultraviolet-visible spectroscopy analyses. The 1H signals attributed to C-H in the NMR spectra of the alkali metal pyrrolides shifted upfield due to the replacement of the H of N-H with a stronger electron-donating species (Li or Na), resulting in a greater shielding environment upon metallation. The absorption peaks of lithium and sodium pyrrolides showed red shifts, and the intensities became obviously stronger in the UV-Vis spectra, suggesting an enhancement of the conjugation effect, in accordance with theoretical calculations. The structure of lithium pyrrolide was determined by the combined direct space method and first-principles calculations on XRD data and Rietveld refinement. This molecule crystallizes in the monoclinic P21/c (14) space group, with lattice parameters of a = 4.4364(7) Å, b = 11.969(2) Å, c = 8.192(2) Å, β = 108.789(8)°, and V = 411.8(2) Å3 (1 Å = 0.1 nm). Each Li+ cation is surrounded by three pyrrolides via cation-N σ bonding with two pyrrolides and a cation–π interaction with the third pyrrolide, where the Li+ is on the top of the π face. Our experimental findings are different from the theoretical prediction in the literature.

Key words: Lithium pyrrolide, Crystal structure, Metal replacement, Liquid organic hydrogen carrier, Metallo-N-heterocycle, Hydrogen storage

MSC2000: 

  • O641