Acta Crystallographica Section B research papers IMPORTANT: this document contains embedded data - to preserve data integrity, please ensure where possible that the IUCr Word tools (available from http://journals.iucr.org/services/docxtemplate/) are installed when editing this document. 1 Crystal packing and theoretical analysis of halogen- and hydrogen- bonded hydrazones from pharmaceuticals. Evidence of type I and II halogen bonds in infinite chains of dichloromethane Authors Gilles Berger a , Jalal Soubhye b , René Wintjens a , Koen Robeyns c and Franck Meyer a * a Microbiology, Bioorganic and Macromolecular Chemistry, Faculty of Pharmacy, Université Libre de Bruxelles (ULB), Bruxelles, 1050, Belgium b Pharmacognosy, Bioanalysis and Drug Discovery Unit, Faculty of Pharmacy, Université Libre de Bruxelles (ULB), Bruxelles, 1050, Belgium c Institute of Condensed Matter and Nanosciences (IMCN), Bâtiment Lavoisier - Place Louis Pasteur 1, Louvain-la-Neuve, 1348, Belgium Correspondence email: franck.meyer@ulb.ac.be Synopsis Supramolecular assemblies of halogenated and hydroxyl hydrazones derived from pharmaceuticals are governed by I···N and I···π halogen bonds or O-H···N hydrogen bonds. An unexpected linear arrangement of clathrated dichloromethane molecules bound through type I and II halogen bonds is observed. Theoretical calculations support the crystallographic study. Abstract The supramolecular assembly of halogenated and hydroxyl hydrazones derived from two well-known pharmaceuticals, i.e. isoniazid (IsX with X = I, Br, OH) and hydralazine (HyX with X = I, Br, OH), were studied by X-ray crystallography and theoretical methods. Crystal packing of IsI and HyI shows weak I···N and I···π halogen bonds, whereas the hydrogen bonds are dominant in the brominated scaffolds IsBr and HyBr. While the calculated I···N interaction strength appears almost three times weaker than the O-H···N contacts in the isoniazid-based hydrazones, the higher directionality of the halogen bonds induces a linear and planar architecture of self-complementary tectons, that is observed only with the help of a bridging water molecule in the case of IsOH. Finally, the X-ray structure of HyOH is characterized by an unexpected linear arrangement of clathrated dichloromethane molecules bound through type I and II halogen bonds. This rare phenomenon, only observed in less than ten structures, was studied by coupled cluster-based energy decomposition. Keywords: Halogen bond, pharmaceuticals, dichloromethane, hydrazones 1. Introduction