title: Stepwise phase transition in the formation of lithium amidoborane.
abstract: A stepwise phase transition in the formation of lithium amidoborane via the solid-state reaction of lithium hydride and ammonia borane has been identified and investigated. Structural analyses reveal that a lithium amidoborane-ammonia borane complex (LiNH(2)BH(3).NH(3)BH(3)) and two allotropes of lithium amidoborane (denoted as alpha- and beta-LiNH(2)BH(3), both of which adopt orthorhombic symmetry) were formed in the process of synthesis. LiNH(2)BH(3).NH(3)BH(3) is the intermediate of the synthesis and adopts a monoclinic structure that features layered LiNH(2)BH(3) and NH(3)BH(3) molecules and contains both ionic and dihydrogen bonds. Unlike alpha-LiNH(2)BH(3), the units of the beta phase have two distinct Li(+) and [NH(2)BH(3)](-) environments. beta-LiNH(2)BH(3) can only be observed in energetic ball milling and transforms to alpha-LiNH(2)BH(3) upon extended milling. Both allotropes of LiNH(2)BH(3) exhibit similar thermal decomposition behavior, with 10.8 wt % H(2) released when heated to 180 degrees C; in contrast, LiNH(2)BH(3).NH(3)BH(3) releases approximately 14.3 wt % H(2) under the same conditions.
authors.affiliation: Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, People's Republic of China.
authors.forename: Chengzhang
authors.initials: C
authors.lastname: Wu
authors.forename: Guotao
authors.initials: G
authors.lastname: Wu
authors.forename: Zhitao
authors.initials: Z
authors.lastname: Xiong
authors.forename: William I F
authors.initials: WI
authors.lastname: David
authors.forename: Kate R
authors.initials: KR
authors.lastname: Ryan
authors.forename: Martin O
authors.initials: MO
authors.lastname: Jones
authors.forename: Peter P
authors.initials: PP
authors.lastname: Edwards
authors.forename: Hailiang
authors.initials: H
authors.lastname: Chu
authors.forename: Ping
authors.initials: P
authors.lastname: Chen
mesh_terms: D000641:Ammonia / Q000737:chemistry*; D001880:Boranes / Q000737:chemistry*; D008094:Lithium / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D044367:Phase Transition
chemical_list: D001880:Boranes; D009942:Organometallic Compounds; D000641:Ammonia; D008094:Lithium