ORIGINAL PAPER How do halogen bonds (S – O ⋯ I, N – O ⋯ I and C – O ⋯ I) and halogen – halogen contacts (C – I ⋯ I – C, C – F ⋯ F – C) subsist in crystal structures? A quantum chemical insight B. Vijaya Pandiyan 1 & P. Deepa 2 & P. Kolandaivel 1 Received: 27 September 2016 /Accepted: 28 November 2016 /Published online: 29 December 2016 # Springer-Verlag Berlin Heidelberg 2016 Abstract Thirteen X-ray crystal structures containing various non-covalent interactions such as halogen bonds, halogen – halogen contacts and hydrogen bonds (I ⋯ N, I ⋯ F, I ⋯ I, F ⋯ F, I ⋯ H and F ⋯ H) were considered and investigated using the DFT-D3 method (B97D/def2-QZVP). The interac- tion energies were calculated at MO62X/def2-QZVP and MP2/aug-cc-pvDZ level of theories. The higher interaction and dispersion energies (2nd crystal) of − 9.58 kcal mol − 1 a n d − 7 . 1 0 k c a l m o l − 1 o b s e r v e d f o r 1 , 4 - d i - iodotetrafluorobenzene bis [bis (2-phenylethyl) sulfoxide] structure indicates the most stable geometrical arrangement in the crystal packing. The electrostatic potential values cal- culated for all crystal structures have a positive σ -hole, which aids understanding of the nature of σ -hole bonds. The signif- icance of the existence of halogen bonds in crystal packing environments was authenticated by replacing iodine atoms by bromine and chlorine atoms. Nucleus independent chemical shift analysis reported on the resonance contribution to the interaction energies of halogen bonds and halogen – halogen contacts. Hirshfeld surface analysis and topological analysis (atoms in molecules) were carried out to analyze the occur- rence and strength of all non-covalent interactions. These analyses revealed that halogen bond interactions were more dominant than hydrogen bonding interactions in these crystal structures. Keywords Halogen bond . Stabilization energy . Hirshfeld surface . Nucleus independent chemical shift (NICS) . Atoms inmolecules(AIM) . Molecular electrostatic potential(MESP) map Introduction Many scientists nowadays have focused their attention towards halogen bonds, which play a vital role in crystal packing. Halogen bonds can stabilize inter- and intra- molecular interactions in proteins and nucleic acid struc- tures [ 1 ], help to form four-stranded DNA junctions [ 2 ], transport anions in a lipid layer [ 3 ], can be used to rec- ognize anions in fluorescence microscopy [ 4 ], and play pivotal role in the interactions of halogen atoms inside a molecular container [ 5 ]. For the above reasons, halogen bonds have been utilized in drug design with increased efficiency [ 6 ]. In material engineering, thin film struc- tures [ 7 ], liquid crystals [ 8 ], and gels [ 9 , 10 ] can be formed by halogen bonds. Halogen bonds form between the charge depleted region of a electronegative atom R – X (X = Halogen), and charge intense regions (e.g., lone pairs) [ 11 , 12 ]. As a result, X continues to be nucleo- philic in character [ 13 ] by proceeding as an electron ac- ceptor, and R – X ⋯ B is found to be about 180° [ 14 ].
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