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Unusual and Conventional Dative Bond Formation by s2 Lone Pair Donation from Alkaline Earth Metal Atoms to BH3, AlH3, and GaH3.
The Journal of Physical Chemistry A ( IF 2.9 ) Pub Date : 2020-06-04 , DOI: 10.1021/acs.jpca.0c03432
Iwona Anusiewicz 1 , Dawid Faron 1 , Piotr Skurski 1, 2 , Jack Simons 2
Affiliation  

Using ab initio electronic structure methods with flexible atomic orbital basis sets, we examined the nature of the bonding arising from donation of an ns2 electron pair on an alkaline earth atom (Mg or Ca) into a vacant n′p orbital on the group 13 atom of BH3, AlH3, or GaH3. We also examined what happens when an excess electron is attached to form corresponding molecular anions. Although the geometries of MgBH3, MgAlH3, MgGaH3, and CaBH3 are found to be much as one would expect for datively bound molecules, CaAlH3 and CaGaH3 were found to have very unusual geometries in that their Al–H or Ga–H bonds are directed toward the Ca atom rather than away, as in the other compounds. Internal electrostatic Coulomb attractions between the partially positively charged Ca center and the partially negatively charged H centers were suggested as a source of these unusual geometries. The other novel finding is that the electron affinities (EAs) of all six M′–MH3 species lie in the 0.7–1.0 eV range, which is suggestive of ionic electronic structures for the neutrals even though the partial charges on the alkaline earth centers are as low as 0.3 atomic units. Partial positive charge on the alkaline earth atoms combined with substantial electron affinities of the BH3, AlH3, and GaH3 groups, but only when distorted from planar geometries, were suggested to be the primary contributors to the large EAs.

中文翻译:

由碱性金属原子向BH3,AlH3和GaH3的s2孤对捐赠形成了不寻常的常规键合。

使用具有灵活原子轨道基础集的从头算电子结构方法,我们研究了由碱土原子(Mg或Ca)上的ns 2电子对捐赠给第13组空位n'p轨道而产生的键的性质BH 3,AlH 3或GaH 3的原子。我们还研究了当多余的电子附着形成相应的分子阴离子时会发生什么。尽管发现MgBH 3,MgAlH 3,MgGaH 3和CaBH 3的几何形状与固定结合分子CaAlH 3和CaGaH 3的几何形状一样。被发现具有非常不寻常的几何形状,因为它们的Al–H或Ga–H键与其他化合物一样指向Ca原子而不是指向Ca原子。建议将部分带正电的Ca中心与部分带负电的H中心之间的内部库仑引力作为这些异常几何形状的来源。另一个新颖的发现是,所有六个M'-MH 3物种的电子亲和力(EAs)都在0.7-1.0 eV范围内,这暗示着中性分子的离子电子结构,即使碱土中心的部分电荷低至0.3原子单位。碱土原子上的部分正电荷与BH 3,AlH 3和GaH 3的大量电子亲和力结合 小组建议,但只有当它们偏离平面几何形状时,才是大型EA的主要贡献者。
更新日期:2020-07-02
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