On the Composition and Crystal Structure of the New Quaternary Hydride Phase Li₄BN₃H₁₀

X-ray data on single crystals of the quaternary metal hydride near the composition LiB0.33N0.67H2.67, previously identified as “Li3BN2H8”, reveal that its true composition is Li4BN3H10. The structure has body-centered-cubic symmetry [space group I213, cell parameter a = 10.679(1)−10.672(1) Å] and contains an ordered arrangement of BH4- and NH2- anions in the molar ratio 1:3. The borohydride anion has an almost ideal tetrahedral geometry (∠H−B−H ∼ 108−114°), while the amide anion has a nearly tetrahedral bond angle (∠H−N−H ∼ 106°). Three symmetry-independent Li atom sites are surrounded by BH4- and NH2- anions in various distorted tetrahedral configurations, one by two B and two N atoms, another by four N atoms, and the third by one B and three N atoms. The Li configuration around B is nearly tetrahedral, while that around N resembles a distorted saddlelike configuration, similar to those in LiBH4 and LiNH2, respectively.针对组分近似为LiB0.33N0.67H2.67的四元金属氢化物单晶所采集的X射线数据（此前该化合物被鉴定为“Li3BN2H8”），揭示其真实组分为Li4BN3H10。该晶体结构具有体心立方对称性[空间群I213，晶胞参数a = 10.679(1)−10.672(1) Å]，其中BH4-与NH2-阴离子以1:3的摩尔比呈有序排布。BH4-阴离子具有近乎理想的四面体几何构型（∠H−B−H约为108°~114°），而NH2-阴离子的键角也接近四面体构型（∠H−N−H约为106°）。存在三个独立于对称性的锂原子位点，周围被BH4-与NH2-阴离子以不同畸变四面体构型配位：其中一个位点由2个B原子与2个N原子配位，另一个由4个N原子配位，第三个则由1个B原子与3个N原子配位。锂原子围绕B原子的配位构型近似四面体，而围绕N原子的配位构型则呈畸变鞍状，这分别与LiBH4和LiNH2中的配位构型相似。