Crystal structures and Hirshfeld surface analyses of N , N -di-methyl-acetamide-1-(dimethyl-λ 4 -aza-nyl-idene)ethan-1-ol tribromide (1/1), N , N -di-methyl-acetamide-1-(dimethyl-λ 4 -aza-nyl-idene)ethan-1-ol di-bromido-iodate (1/1) and N , N -di-methyl-acetamide-1-(dimethyl-λ 4 -aza-nyl-idene)ethan-1-ol di-chlorido-iodate (1/1).

In the title compounds, N , N -di-methyl-acetamide-1-(dimethyl-λ 4 -aza-nyl-idene)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 -di-methyl-acetamide-1-(dimethyl-λ 4 -aza-nyl-idene)ethan-1-ol di-bromido-iodate (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 -di-methyl-acetamide-1-(dimethyl-λ 4 -aza-nyl-idene)ethan-1-ol di-chlorido-iodate (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 inter-actions. In addition to the structural evaluation, a Hirshfeld surface analysis was carried out.