Crystal structures and Hirshfeld surface analyses of N,N-di­methyl­acetamide-1-(dimethyl-λ4-aza­nyl­idene)ethan-1-ol tribromide (1/1), N,N-di­methyl­acetamide-1-(dimethyl-λ4-aza­nyl­idene)ethan-1-ol di­bromido­iodate (1/1) and N,N-di­methyl­acetamide-1-(dimethyl-λ4-aza­nyl­idene)ethan-1-ol di­chlorido­iodate (1/1)

In the title compounds, N,N-di­methyl­acetamide-1-(dimethyl-λ4-aza­nyl­idene)ethan-1-ol tribromide (1/1), C4H9NO·C4H10NO+·Br3 - or [(C4H9NO)·(C4H10NO)](Br3), (I), N,N-di­methyl­acetamide-1-(dimethyl-λ4-aza­nyl­idene)ethan-1-ol di­bromido­iodate (1/1), C4H9NO·C4H10NO+·Br2I- or [(C4H9NO)·(C4H10NO)](Br2I), (II), and N,N-di­methyl­acetamide-1-(dimethyl-λ4-aza­nyl­idene)ethan-1-ol di­chlorido­iodate (1/1), C4H9NO·C4H10NO+·Cl2I- or [(C4H9NO)·(C4H10NO)]·(Cl2I), (III), all the anions are almost linear in geometry and all the cations, except for the methyl H atoms, are essentially planar. In the crystal structure of (I), the cations are linked by pairs of C - H⋯O hydrogen bonds, forming inversion dimers with an R 2 2(8) ring motif. These dimers also exhibit O - H⋯O hydrogen bonding. Dimerized cation pairs and anions are arranged in columns along the a axis. In the crystal of (II), the cations are linked by pairs of O - H⋯O and C - H⋯O hydrogen bonds, forming an R 4 4(14) ring motif. These groups of cations and the anions form individual columns along the a axis and jointly reside in planes roughly parallel to (011). In the crystal of (III), cations and anions also form columns parallel to the a axis, resulting in layers parallel to the (020) plane. Furthermore, the crystal structures of (I), (II) and (III) are consolidated by strong halogen (Br and/or I and/or Cl)⋯H and weak van der Waals inter­actions. In addition to the structural evaluation, a Hirshfeld surface analysis was carried out. © 2023 International Union of Crystallography. All rights reserved.