Interaction between amines and N-haloimides: a new motif for unprecedentedly short Br⋯N and I⋯N halogen bonds

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Abstract
The complexes of N-bromosuccinimide or N-iodosuccinimide with a halogen bond acceptor, either 1,4-diazabicyclo[2.2.2]octane (DABCO), hexamethylenetetramine (HMTA) or 1,3,5-triazine (TRZ), led to an unprecedentedly strong (CO)2N–X⋯N halogen bond synthon (X = Br or I) determined from crystal structures of [DABCO]·[NBS]22, [HMTA]·[NBS]22, [TRZ]·[NIS]22 and [HMTA]·[NIS]44. The Br⋯N distances with DABCO and with HMTA donors were 2.347 Å and 2.414 Å being remarkably shorter (31% and 29%) than the sum of the VDW radii of nitrogen and bromide atoms, respectively. The corresponding I⋯N distances with HMTA and TRZ were 2.549 Å and 2.596 Å (27.8% and 26.4% less than the sum of the VDW radii of N and I). Moreover, the tetrahedral complex of [HMTA]·[NIS]44 forms a stable halogen bond based organic framework structure (XBOF) with 7.31 Å × 6.74 Å diameter channels filled with disordered acetonitrile solvent. The total volume of the channels, four in each unit cell, was 1130.5 Å3 which covers 28% of the unit cell volume.

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