Charge Densities and Chemical Bonding of CaSi2
Charge Densities and Chemical Bonding of CaSi2
复制标题
CaSi2 的电荷密度和化学键
DOI：
10.7567/jjaps.38s1.504
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发表时间：
1999
影响因子：
1.5
通讯作者：
M. Imai
中科院分区：
文献类型：
--
作者：
E. Nishibori;D. Saso;M. Takata;M. Sakata;M. Imai
利用同步辐射粉末衍射数据，通过最大熵法（MEM）得到了CaSi 2的电荷密度分布图。MEM电荷密度图揭示了在单元电池中存在两种类型的Si层。在两层中，Si原子形成较强的共价键。然而，它们并不完全相同。在键中点的电子密度在每层上略有不同，即一层为0.62[e/m3]，另一层为0.52[e/m3]。这些值表明前一层的共价键明显强于后一层。对于键长，前一层的Si-Si键长为2.32 μ m，后一层的Si-Si键长为2.40 μ m。目前对键电子的直接观察给出了一个例子，即键长越长，共价键越弱。Ca-Ca原子间存在共价性的观点尚未得到公认。由于MEM电荷密度显示Ca-Si之间的电子云非常轻微的重叠，CaSi 2中Ca的化学键的性质几乎是离子的。
The charge density distribution map of CaSi2 was obtained by the Maximum Entropy Method(MEM) using synchrotron powder diffraction data. The MEM charge density map reveals that there are two types of Si layers in a unit cell. In both layers, Si atoms form rather strong covalent bond. However, they are not identical. Electron density at bond mid point are slightly different at each layer, i.e. 0.62[e/Å3] for one layer, and 0.52[e/Å3] for the other. These values shows covalent bond of the former layer is considerably stronger than that of the latter layer. As for the bond lengths, the Si-Si bond length of the former layer is 2.32 Å and that of the latter is 2.40 Å, respectively. The present direct observation of bond electrons gives one of the examples that the longer the bond length, the weaker the covalent bond. It is not recognized that there exists covalency between Ca-Ca atoms. Since the MEM charge density shows very slight overlap of electron clouds between Ca-Si, the nature of chemical bond of Ca in CaSi2 is almost ionic.