Bonding and stability of the hydrogen storage material Mg(2)NiH(4).
Bonding and stability of the hydrogen storage material Mg(2)NiH(4).
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DOI：
10.1021/ic0201046
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发表时间：
2002-06
影响因子：
4.6
通讯作者：
U. Häussermann;H. Blomqvist;D. Noréus
中科院分区：
文献类型：
--
作者：
U. Häussermann;H. Blomqvist;D. Noréus
采用从头算密度泛函方法研究了储氢材料Mg（2）NiH（4）（单斜晶系，C2/c，Z = 8）的结构稳定性和成键性质，并与Ba（2）PdH（4）（正交晶系，Pnma，Z = 8）的结构稳定性和成键性质进行了比较.这两种化合物都属于复杂的过渡金属化合物家族。它们的晶体结构为不连续的四面体18电子配合物T（0）H（4）（4-）（T = Ni，Pd）。然而，在两个系统中的键合情况被发现是完全不同的。对于Ba（2）PdH（4），电子态密度完美地反映了络合物PdH（4）（4-）的分子态，而对于Mg（2）NiH（4），TH（4）（4-）的分子态和固态化合物的态密度之间没有明确的关系。Ba（2）PdH（4）和Mg（2）NiH（4）的键合差异源于T-H相互作用的不同强度（Pd[键]H相互作用比Ni[键]H相互作用强得多）和碱土金属组分与H之间相互作用的不同强度（Ba[键]H相互作用比Mg[键]H相互作用弱得多）。为了降低Mg（2）NiH（4）的氢脱附温度，建议通过在四面体Ni（0）H（4）（4-）配合物周围的互补基质中引入缺陷来使该化合物不稳定。这可以通过用Mg代替Al来实现。
Structural stability and bonding properties of the hydrogen storage material Mg(2)NiH(4) (monoclinic, C2/c, Z = 8) were investigated and compared to those of Ba(2)PdH(4) (orthorhombic, Pnma, Z = 8) using ab initio density functional calculations. Both compounds belong to the family of complex transition metal hydrides. Their crystal structures contain discrete tetrahedral 18 electron complexes T(0)H(4)(4-) (T = Ni, Pd). However, the bonding situation in the two systems was found to be quite different. For Ba(2)PdH(4), the electronic density of states mirrors perfectly the molecular states of the complex PdH(4)(4-), whereas for Mg(2)NiH(4) a clear relation between molecular states of TH(4)(4-) and the density of states of the solid-state compound is missing. Differences in bonding of Ba(2)PdH(4) and Mg(2)NiH(4) originate in the different strength of the T-H interactions (Pd[bond]H interactions are considerably stronger than Ni[bond]H ones) and in the different strength of the interaction between the alkaline-earth metal component and H (Ba[bond]H interactions are substantially weaker than Mg[bond]H ones). To lower the hydrogen desorption temperature of Mg(2)NiH(4), it is suggested to destabilize this compound by introducing defects in the counterion matrix surrounding the tetrahedral Ni(0)H(4)(4-) complexes. This might be achieved by substituting Mg for Al.