A Crystallographic Charge Density Study of the Partial Covalent Nature of Strong N⋅⋅⋅Br Halogen Bonds |
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Authors: | Mihael Erakovi Dominik Cin
i Kreimir Mol
anov Vladimir Stilinovi |
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Institution: | Mihael Erakovi?,Dominik Cin?i?,Kre?imir Mol?anov,Vladimir Stilinovi? |
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Abstract: | The covalent nature of strong N?Br???N halogen bonds in a cocrystal ( 2 ) of N‐bromosuccinimide ( NBS ) with 3,5‐dimethylpyridine ( lut ) was determined from X‐ray charge density studies and compared to a weak N?Br???O halogen bond in pure crystalline NBS ( 1 ) and a covalent bond in bis(3‐methylpyridine)bromonium cation (in its perchlorate salt ( 3 ). In 2 , the donor N?Br bond is elongated by 0.0954 Å, while the Br???acceptor distance of 2.3194(4) is 1.08 Å shorter than the sum of the van der Waals radii. A maximum electron density of 0.38 e Å?3 along the Br???N halogen bond indicates a considerable covalent contribution to the total interaction. This value is intermediate to 0.067 e Å?3 for the Br???O contact in 1 , and approximately 0.7 e Å?3 in both N?Br bonds of the bromonium cation in 3 . A calculation of the natural bond order charges of the contact atoms, and the σ*(N1?Br) population of NBS as a function of distance between NBS and lut , have shown that charge transfer becomes significant at a Br???N distance below about 3 Å. |
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Keywords: | Ladungstransfer Nichtkovalente Wechselwirkungen Quantenchemie Rö ntgenbeugung Supramolekulare Chemie |
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