1 Overall resonance is the major source of stabilizing the molecule with

1 overall resonance is the major source of

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1 ). Overall, resonance is the major source of stabilizing the molecule with halogen bond interactions. Fig. 4 Two-dimensional (2D)-fingerprint plot for all non-covalent interactions in all 13 crystal structures J Mol Model (2017) 23: 16 Page 15 of 22 16
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Fig. 4 continued. 16 Page 16 of 22 J Mol Model (2017) 23: 16
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Fig. 4 continued. J Mol Model (2017) 23: 16 Page 17 of 22 16
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Hirshfeld surface analysis From single crystal X-ray diffraction studies, different kinds of non-covalent interactions, particularly hydrogen bonding and σ -hole interactions, were identified and ana- lyzed through Hirshfeld surface analysis, which is mapped with the function of d norm . Such analysis yields three re- sults: a Hirshfeld surface map, a two-dimensional (2D)- fingerprint, and the percentage contribution for different kinds of non-covalent interactions. The Hirshfeld surface map has three regions: a red region indicates the short contacts between the corresponding two atoms, a white region represents moderate short contacts, and a blue re- gion lacks short contacts [ 48 ]. Figure 3 gives a Hirshfeld surface map depicting the distinct region of contacts for all the crystal structures except the 3rd structure due to poor resolution in crystal packing. From the figures, the red spots confirm the presence of I O contacts in the crystal structures. The size of the red spots describes the strength of the interaction. For multifurcated interactions, the red regions were merged. Red spots of hydrogen bond interactions were dominated by halogen bond interactions, revealing that the strength of the halogen bonds is higher as compared with hydrogen bonds in these crystal struc- tures. Also, halogen bond interactions occur predominant- ly in crystal structures over other non covalent interactions. To provide evidence for the occurrence of halogen bond interactions existing in crystal structures, the inter contacts were plotted with 2D-fingerprint plots. This gives a novel visual Fig. 4 continued. 16 Page 18 of 22 J Mol Model (2017) 23: 16
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representation for all intermolecular non-covalent interactions. The fingerprint plots of the unit cell containing molecule show spikes of various lengths and thickness, as shown in Fig. 4 . The percentage contribution of all the interactions existing in the crystal structures was estimated through a 2D fingerprint. The characteristic B wings ^ present at the top left and bottom right of the fingerprint plot are a sign of non- covalent interactions. All I O interactions show the presence of the iconic wings characteristics. The donor and acceptor of halogen halogen interactions have a center of middle line fingerprints, which is shown in Fig. 4 for the 5th crystal. For I H interactions, the wings characteristics are not as perfect as those of the I O interaction existing in the 1st and 4th crystal structure. Table 3 lists the percentage contri- bution to the halogen bond interaction. Comparing all the structures, I N halogen bond interactions in the 6th crystal make a higher contribution (9.6%) than other halogen bond interactions (I
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