Overgaard Jacob, Clausen Henrik F, Platts Jamie A, Iversen Bo B
Department of Chemistry and the Interdisciplinary Nanoscience Center, University of Aarhus, Langelandsgade 140, 8000 Aarhus C, Denmark.
J Am Chem Soc. 2008 Mar 26;130(12):3834-43. doi: 10.1021/ja076152c. Epub 2008 Mar 4.
The charge density of Co2(CO)6(HC[triple bond]CC6H10OH) (1) in the crystalline state has been determined using multipolar refinement of single-crystal X-ray diffraction data collected (i) with a synchrotron source at very low temperatures (15 K) and (ii) using a conventional source with the crystal at intermediate temperature (100 K). The X-ray charge density model is augmented by complete active space and density functional theory calculations. Topological analyses of the different charge distributions show that the two Co atoms are not bonded to each other in the quantum theory of atoms in molecules (QTAIM) sense of the word. However, the behavior of the source function and the total energy density indicate that there is some bond-like character in the Co-Co interaction. The bridging alkyne fragment provides an unusual bonding situation, with extremely small electron density differences between the two Co-C bond critical points and the "CoC2" ring critical point. Thus, the structure is close to a topological catastrophe point. Comparison of the results obtained from the two diffraction data sets and ab initio theory suggests that the topology of the experimental electron density in this special atomic environment is highly sensitive to subtle effects of measurement errors and potential shortcomings of the multipole model, or to effects of the crystal field. Thus, even the two identical molecules in the asymmetric unit show altered bonding patterns.
已通过对单晶X射线衍射数据进行多极精修来确定Co2(CO)6(HC≡CC6H10OH) (1) 在晶体状态下的电荷密度，这些数据是：(i) 在极低温度（15 K）下使用同步辐射源收集的，以及(ii) 在中间温度（100 K）下使用传统源并以晶体收集的。通过完全活性空间和密度泛函理论计算增强了X射线电荷密度模型。对不同电荷分布的拓扑分析表明，在分子中原子的量子理论（QTAIM）意义上，两个Co原子彼此不键合。然而，源函数和总能量密度的行为表明，Co-Co相互作用中存在一些类似键的特征。桥连炔烃片段提供了一种不寻常的键合情况，两个Co-C键临界点与“CoC2”环临界点之间的电子密度差异极小。因此，该结构接近拓扑灾难点。对从两个衍射数据集和从头算理论获得的结果进行比较表明，在这种特殊原子环境中，实验电子密度的拓扑对测量误差的细微影响和多极模型的潜在缺点非常敏感，或者对晶体场的影响非常敏感。因此，即使不对称单元中的两个相同分子也显示出改变的键合模式。
