Abstract
5-Iodo-1-arylpyrazoles are interesting templates for investigating the halogen bond propensity in small molecules other than the already well-known halogenated molecules such as tetrafluorodiiodobenzene. Herein, we present six compounds with different substitution on the aryl ring attached at position 1 of the pyrazoles and investigate them in the solid state in order to elucidate the halogen bonding significance to the crystallographic landscape of such molecules. The substituents on the aryl ring are generally combinations of halogen atoms (Br, Cl) and various alkyl groups. Observed halogen bonding types spanned by these six 5-iodopyrazoles included a wide variety, namely, C–I⋯O, C–I⋯π, C–I⋯Br, C–I⋯N and C–Br⋯O interactions. By single crystal X-ray diffraction analysis combined with the descriptive Hirshfeld analysis, we discuss the role and influence of the halogen bonds among the intermolecular interactions.
Highlights
The central concept of the halogen interactions is the so-called sigma-hole [33,34,35,36,37,38,39,40,41], which is briefly a formal positive potential on the extremity of the halogen atom that is more likely to interact with nucleophilic entities
Halogen bonding was first investigated in the case of halogen–halogen interactions which were defined as type I and type II [1,2,42], and more recently an unconventional type III halogen or di-σ-hole [43] has been reported (Figure 1b)
We recently discovered that halogenated sydnones [44,45] and pyrazoles [46] are molecules with investigating the propensity propensity of halogen bonding and its contribution among the high potential for investigating interactions
Summary
The propensity and utility of the halogen bond [1,2] is already well established in materials chemistry [3,4,5,6], many applications from crystal engineering [7,8,9,10,11,12] to halogen-bonded catalyzed reactions [12,13,14,15,16,17,18] and even more to smart materials [3,4,5,6] or medicinal chemistry [19,20,21,22,23,24,25,26,27] being currently reported Both in solution [28,29,30,31,32] and in the solid state, halogen bonding seems to be developing into a promising field. Halogen–oxygen, halogen–nitrogen or halogen–π (Figure 1c) interactions were reported both in liquid and solid state
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