Crystal structures and Hirshfeld surface analyses of N,N-di­methyl­acetamide–1-(dimethyl-λ(4)-aza­nyl­idene)ethan-1-ol tribromide (1/1), N,N-di­methyl­acetamide–1-(dimethyl-λ(4)-aza­nyl­idene)ethan-1-ol di­bromido­iodate (1/1) and N,N-di­methyl­acetamide–1-(dimethyl-λ(4)-aza­nyl­idene)ethan-1-ol di­chlorido­iodate (1/1)

In the title compounds, N,N-di­methyl­acetamide–1-(dimethyl-λ(4)-aza­nyl­idene)ethan-1-ol tribromide (1/1), C(4)H(9)NO·C(4)H(10)NO(+)·Br(3) (−) or [(C(4)H(9)NO)·(C(4)H(10)NO)](Br(3)), (I), N,N-di­methyl­acetamide–1-(dimethyl-λ(4)-aza­nyl­idene)ethan-1-ol di­bromido­iodate (1/1), C(4)H(9)NO·C(4)H(10)NO(+)·Br(2)I(−) or [(C(4)H(9)NO)·(C(4)H(10)NO)](Br(2)I), (II), and N,N-di­methyl­acetamide–1-(dimethyl-λ(4)-aza­nyl­idene)ethan-1-ol di­chlorido­iodate (1/1), C(4)H(9)NO·C(4)H(10)NO(+)·Cl(2)I(−) or [(C(4)H(9)NO)·(C(4)H(10)NO)]·(Cl(2)I), (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.