Frustrated Packing in Simple Structures: Chemical Pressure Hindrance to Isolobal Bonds in the TiAl 3 type and ZrAl 2.6 Sn 0.4
Frustrated Packing in Simple Structures: Chemical Pressure Hindrance to Isolobal Bonds in the TiAl 3 type and ZrAl 2.6 Sn 0.4
复制标题
简单结构中的受阻堆积：化学压力对 TiAl 3 型和 ZrAl 2.6 Sn 0.4 中同位素键的阻碍
DOI：
10.1021/acs.inorgchem.0c03740
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发表时间：
2021
影响因子：
4.6
通讯作者：
Fredrickson, Daniel C.
中科院分区：
文献类型：
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作者：
Kamp, Kendall R.;Fredrickson, Daniel C.
虽然简单的紧凑安排传达了一种优化的感觉，但实际上，它们可能导致不同类型的交互之间的竞争。例如，tial3结构类型代表了面心立方结构的一系列有序te3变体（T =过渡金属，E =主族元素）中的一种，旁边还有aucu3和zral3类型。这些结构的T-T连通性不同于18-n规则：电子赝隙发生在电子浓度为18-n /T的原子上，这是每个T原子在T-T等球键中与其他T原子共享的电子对的数量。简单的堆叠变化使这些结构相互关联，可能为电子精确的系列奠定了基础。然而，tial3型的原型本身违反了18 - n规则，它的13个电子/Ti原子的计数称为form = 5，而不是该类型中可用的4个等球体T-T键/T原子。在这里，我们研究了导致这种偏离18-nrule的因素，以及它们与新tial3型化合物ZrAl3-xSnx （x ~ 0.4）的关系。首先，比较了tal3化合物（T = Zr和Ti）的tial3和zral3类型的相对稳定性。当T = Zr时，结构更倾向于遵循18-nrule，而当T = Ti时，能量差基本消失。通过dft化学压力（CP）分析，这一趋势与tial3中出现的张力有关，该张力出现在T-T等球形键的优化与其他地方Al-Al接触的空间要求之间。该图说明了ZrAl2.6Sn0.4中部分Sn取代后zral3从自身型转变为TiAl3型的过程：Sn的加入使电子计数更接近TiAl3型的预测值，而电负性和CP将较大的Sn原子引导到抵抗TiAl3中等球形键形成的位置。
While simple close-packed arrangements convey a sense of optimization, they can, in fact, host competition between different types of interactions. The TiAl3structure type, for example, represents one of a series of ordered TE3variants (T = transition metal, E = main group element) of the face-centered cubic structure, alongside the AuCu3and ZrAl3types. These structures differ in their T-T connectivity corresponding to the 18–nrule: electronic pseudogaps occur at electron concentrations of 18–n/T atom, wherenis the number of electron pairs each T atom shares with other T atoms in T-T isolobal bonds. Facile stacking variations interrelate these structures, presumably setting the stage for an electronically precise series. However, the prototype of the TiAl3type itself violates the 18–nrule, with its count of 13 electrons/Ti atom calling forn= 5 rather than the 4 isolobal T-T bonds/T atom available in this type. Here, we investigate the factors underlying this deviation from the 18–nrule and their relation to the new TiAl3-type compound ZrAl3–xSnx(x∼ 0.4). First, the relative stabilities of the TiAl3and ZrAl3types are compared for TAl3compounds (T = Zr and Ti). While for T = Zr, the structure adhering to the 18–nrule is highly preferred, for T = Ti, the energy difference essentially vanishes. This trend is connected through DFT-Chemical Pressure (CP) analysis to a tension that emerges in TiAl3between the optimization of the T-T isolobal bonds and the space requirements of Al-Al contacts elsewhere. This picture elucidates the transition of ZrAl3from its own type to the TiAl3-type upon partial Sn substitution in ZrAl2.6Sn0.4: the incorporation of Sn brings the electron count closer to that predicted for the TiAl3type, while electronegativity and CP direct the larger Sn atoms to the site that resists isolobal bond formation in TiAl3.