Charge Transfer via the Dative N鈭払 Bond and Dihydrogen Contacts. Experimental and Theoretical Electron Density Studies of Four Deltahedral Boranes

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• 作者：Stefan Mebs ; Roman Kalinowski ; Simon Grabowsky ; Diana Fo虉rster ; Rainer Kickbusch ; Eugen Justus ; Wolfgang Morgenroth ; Carsten Paulmann ; Peter Luger ; Detlef Gabel ; Dieter Lentz
• 刊名：Journal of Physical Chemistry A
• 出版年：2011
• 出版时间：March 3, 2011
• 年：2011
• 卷：115
• 期：8
• 页码：1385-1395
• 全文大小：1001K
• 年卷期：v.115,no.8(March 3, 2011)
• ISSN：1520-5215

文摘

In an approach combining high resolution X-ray diffraction at low temperatures with density functional calculations, two closo-borates, B₁₂H₁₂^{2鈭?/sup> (1) and B₁₀H₁₀2鈭?/sup> (2), and two arachno-boranes, B₁₀H₁₂L₂ (L = amine (3) or acetonitrile (4)), are studied by means of Atoms In Molecules (AIM) theory and Electron Localizability Indicator (ELI-D). The charge transfer via the dative N鈭払 bonds in the arachno-boranes and via dihydrogen contacts in the closo-borates is quantified. The dative N鈭払 bond in 4 is significantly shorter and stronger than that in 3 and in small N鈭払 Lewis acid base adducts from the literature. It is even shorter in the gas phase than in the crystal environment in contrast to the bond shortening in the crystal generally found for N鈭払 Lewis acid鈭抌ase adducts. Furthermore, the calculated charge transfer in terms of AIM charges is opposite to the expected N 鈫?B direction but still weak as found for all other N鈭払 bonds. The intramolecular charge redistributions due to intermolecular interactions are quantified by the AIM and ELI-D analysis of contact ion pairs. The latter method gives a deeper understanding of delocalization effects in the borane cages as well as in the counterions. Since dihydrogen bonds are rarely found in crystal structures, one focus was directed to the topologies of the large number of 58 experimentally found contacts of this type. The analysis reveals that the electron density at the bond critical point, the corresponding Laplace function, and the curvature along the bond path (位₃) show a behavior that clearly discriminates these interactions from classical hydrogen bonds, confirming earlier theoretical findings.}