Department of Chemistry & Centre for Materials Crystallography, Aarhus University, Langelandsgade 140, DK-8000 Aarhus C, Denmark.
Inorg Chem. 2011 Sep 5;50(17):8418-26. doi: 10.1021/ic2009946. Epub 2011 Aug 2.
The experimental electron density of the only known example of a four-membered Ga(I) N-heterocyclic carbene analogue has been determined by multipole modeling of 90 K X-ray diffraction data and compared to theoretical data. In order to obtain a satisfactory model, it is necessary to modify the radial dependency of the core electrons of Ga using two separate scaling parameters for s,p- and d-electrons. Evidence for significant lone-pair density on Ga is found in the electron density and derived properties despite the partial positive charge of this atom. Static deformation density and molecular electrostatic potential clearly show a directional lone pair on Ga, whereas the Laplacian of the total electron density does not; this feature is, however, present in the Laplacian of the valence-only density. The Ga center also acts as an acceptor in four intramolecular C-H···Ga contacts, whose nature is probed by density properties. Substantial covalent character is apparent in the Ga-N bonds, but no sign of donation from filled N p-orbitals to empty Ga p-orbitals is found, whereas π-delocalization over the organic ligand is evident. This study highlights the utility of experimental charge density analysis as a technique to investigate the unusual bonding and electronic characteristics of low oxidation state/low coordinate p-block complexes.
唯一已知的四元 Ga(I) N-杂环卡宾类似物的实验电子密度已通过 90 K X 射线衍射数据的多极建模确定，并与理论数据进行了比较。为了获得令人满意的模型，有必要使用两个单独的 s、p-和 d 电子的缩放参数来修改 Ga 的核电子的径向依赖性。尽管 Ga 原子带部分正电荷，但在电子密度及其衍生性质中发现了 Ga 上显著的孤对电子密度的证据。静态变形密度和分子静电势清楚地显示了 Ga 上的定向孤对电子，而总电子密度的拉普拉斯算子则没有；然而，这个特征存在于价电子密度的拉普拉斯算子中。Ga 中心在四个分子内 C-H···Ga 接触中充当受体，其性质通过密度性质进行探测。Ga-N 键中明显存在共价特征，但没有发现填充的 N p 轨道向空的 Ga p 轨道供电子的迹象，而有机配体上的π离域则很明显。这项研究强调了实验电荷密度分析作为一种技术的实用性，用于研究低氧化态/低配位数 p 区配合物的不寻常成键和电子特性。
