Institute of Molecular Science, Shanxi University, Taiyuan, 034000, China.
Nanoscale. 2018 Apr 26;10(16):7451-7456. doi: 10.1039/c8nr01087k.
Inspired by recent observations of the highest coordination numbers of CN = 10 in planar wheel-type complexes in D10h Ta@B10- and CN = 20 in double-ring tubular species in D10d Ta@B20- and theoretical prediction of the smallest endohedral metalloborospherene D2 Ta@B22- (1) with CN = 22, we present herein the possibility of larger endohedral metalloborospherenes C2 Ta@B23 (2), C2 Ta@B24+ (3), C2v Ta@B24- (4), C1 Ta@B25 (5), D2d Ta@B26+ (6), C2 Ta@B272+ (7), and C2 Ta@B283+ (8) based on extensive first-principles theory investigations. These cage-like Ta@Bqn complexes with B6 pentagonal or B7 hexagonal pyramids on their surface turn out to be the global minima of the systems with CN = 23, 24, 24, 25, 26, 27, and 28, respectively, unveiling the highest coordination number of CN = 28 in spherical environments known in chemistry. Detailed bonding analyses show that 1-8 as superatoms conform to the 18-electron configuration with a universal σ + π double delocalization bonding pattern. They are effectively stabilized via spd-π coordination interactions between the Ta center and ηn-Bn ligand which match both geometrically and electronically. Such complexes may serve as embryos of novel metal-boride nanomaterials.
受最近在 D10h Ta@B10- 中的平面轮式配合物中观察到的最高配位数 CN = 10 和 D10d Ta@B20- 中的双环管状物种中观察到的最高配位数 CN = 20 的启发，以及对具有 CN = 22 的最小内笼金属硼烷球 D2 Ta@B22-（1）的理论预测，我们提出了更大的内笼金属硼烷球 C2 Ta@B23（2）、C2 Ta@B24+（3）、C2v Ta@B24-（4）、C1 Ta@B25（5）、D2d Ta@B26+（6）、C2 Ta@B272+（7）和 C2 Ta@B283+（8）的可能性。这些笼状 Ta@Bqn 配合物表面具有 B6 五边形或 B7 六边形金字塔，是具有 CN = 23、24、24、25、26、27 和 28 的系统的全局最小值，分别揭示了在化学中已知的球形环境中的最高配位数 CN = 28。详细的键分析表明，1-8 作为超原子符合 18 电子构型，具有通用的 σ+π 双重离域键合模式。它们通过 Ta 中心和 ηn-Bn 配体之间的 spd-π 配位相互作用得到有效稳定，这些相互作用在几何和电子上都匹配。这些配合物可能成为新型金属硼化物纳米材料的胚胎。
