Abstract Magnesium dichloride and titanium tetrachloride are key components of Ziegler–Natta polymerization catalysts. We report a systematic computational study at M06-2X/def-TZVP level, thus accounting for dispersion, on saturation of magnesium dichloride crystallites by titanium tetrachloride. The crystallites are represented by (MgCl2)n clusters of various sizes and shapes, with n = 4–94, and they show preference for (104)-type edges with five-coordinate Mg atoms. Preferred adsorption modes of TiCl4 upon full saturation of crystallite edges are identified, alongside with adsorption strengths and relative stabilities of the (MgCl2)n-(TiCl4)m products. Consistent with previous literature, both Ti and Mg have tendency of favoring octahedral six-coordination, which can be achieved at all surface sites, including corners, serving as representatives of defect sites on the MgCl2 surfaces. The adsorption strengths of TiCl4 are the strongest for crystallites having (110)-type edges with four-coordinate Mg atoms. The much higher reactivity of (110)-type edges compared to (104)-type edges leads to reversal of the stability order of the crystallites upon TiCl4 adsorption. Saturated (MgCl2)n-(TiCl4)m crystallites thus favor shapes rich in (110)-type edges.

中文翻译：

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四氯化钛对二氯化镁微晶的饱和

摘要 二氯化镁和四氯化钛是齐格勒-纳塔聚合催化剂的关键组分。我们报告了 M06-2X/def-TZVP 水平的系统计算研究，从而解释了四氯化钛对二氯化镁微晶的饱和度的分散。微晶由各种尺寸和形状的 (MgCl2)n 簇表示，n = 4-94，并且它们显示出对具有五个配位 Mg 原子的 (104) 型边缘的偏好。确定了在微晶边缘完全饱和时 TiCl4 的优选吸附模式，以及 (MgCl2)n-(TiCl4)m 产品的吸附强度和相对稳定性。与之前的文献一致，Ti 和 Mg 都有利于八面体六配位的趋势，这可以在所有表​​面位点实现，包括角、作为 MgCl2 表面缺陷位点的代表。TiCl4 的吸附强度对于具有四配位 Mg 原子的 (110) 型边缘的微晶最强。与 (104) 型边缘相比，(110) 型边缘的高得多的反应性导致 TiCl4 吸附后微晶的稳定性顺序发生逆转。因此，饱和的 (MgCl2)n-(TiCl4)m 微晶有利于富含 (110) 型边缘的形状。