Ge Zhongxue, Ding Kewei, Li Yisu, Xu Hongguang, Chen Zhaoqiang, Ma Yiding, Li Taoqi, Zhu Weiliang, Zheng Weijun
State Key Laboratory of Fluorine & Nitrogen Chemicals Xi'an 710065 China.
Xi'an Modern Chemistry Research Institute Xi'an 710065 China
RSC Adv. 2019 Feb 26;9(12):6762-6769. doi: 10.1039/c9ra00439d. eCollection 2019 Feb 22.
Mixed nitrogen-lithium cluster cations LiN were generated by laser vaporization and analyzed by time-of-flight mass spectrometry. It is found that LiN has the highest ion abundance among the LiN ions in the mass spectrum. Density functional calculations were conducted to search for the stable structures of the Li-N clusters. The theoretical results show that the most stable isomers of LiN clusters are in the form of Li(N) , and the order of their calculated binding energies is consistent with that of Li-N bond lengths. The most stable structures of LiN evolve from one-dimensional linear type ( , = 2; , = 4), to two-dimensional branch type ( , = 6), then to three-dimensional tetrahedral ( , = 8) and square pyramid ( , = 10) types. Further natural bond orbital analyses show that electrons are transferred from the lone pair on N of every N unit to the empty orbitals of lithium atom in LiN , while in LiN , electrons are transferred from the bonding orbital of the Li-N bonds to the antibonding orbital of the other Li-N bonds. In both cases, the N units become dipoles and strongly interact with Li. The average second-order perturbation stabilization energy for LiN is the highest among the observed LiN clusters. For neutral LiN clusters, the most stable isomers were also formed by a Li atom and /2 number of N units, while that of LiN is in the form of Li(N)(η-N).
通过激光汽化产生混合氮 - 锂团簇阳离子LiN ，并采用飞行时间质谱法进行分析。结果发现，LiN 在质谱图中的LiN 离子中具有最高的离子丰度。进行了密度泛函计算以寻找Li - N团簇的稳定结构。理论结果表明，LiN 团簇最稳定的异构体为Li(N) 形式，其计算的结合能顺序与Li - N键长顺序一致。LiN 的最稳定结构从一维线性类型（ ， = 2； ， = 4）演变为二维分支类型（ ， = 6），然后变为三维四面体（ ， = 8）和方锥（ ， = 10）类型。进一步的自然键轨道分析表明，在LiN 中，每个N单元上孤对电子从N转移到锂原子的空轨道，而在LiN 中，电子从Li - N键的成键轨道转移到其他Li - N键的反键轨道。在这两种情况下，N单元都成为偶极子并与Li强烈相互作用。LiN 的平均二阶微扰稳定能在观察到的LiN 团簇中最高。对于中性LiN团簇，最稳定的异构体也由一个Li原子和 /2个N单元形成，而LiN的最稳定异构体为Li(N)(η - N)形式。
