[CuCl₃(H₂O)]⁻ complexes aggregated to form hydrate columns in methyl-substituted pyridinium or piperidinium salts

1,2,3-Trimethylpyridinium aquatrichloridocuprate(II), (C₈H₁₂N)[CuCl₃(H₂O)], (I), 3,4-dimethylpyridinium aquatrichloridocuprate(II), (C₇H₁₀N)[CuCl₃(H₂O)], (II), and 2,3-dimethylpyridinium aquatrichloridocuprate(II), (C₇H₁₀N)[CuCl₃(H₂O)], (III), exhibit the same fundamental structure, with (I) and (II) isomorphous and with the unit-cell constants of (III) similar to the reduced unit-cell constants of (I) and (II). The distorted square-planar [CuCl₃(H₂O)]⁻ complex [mirror symmetric in (I) and (II)] forms two semicoordinate Cu...Cl bonds to a neighboring complex to produce a dimer with 2/m symmetry [only inversion symmetry in (III)]. The semicoordinate Cu...Cl bond length of the dimer shows significant elongation at 295 K compared with that at 100 K, while the coordinate Cu—Cl bond lengths are slightly contracted at 295 K compared with those at 100 K. The inorganic dimers are linked by eight hydrogen bonds to four neighboring dimers to establish a checkerboard network layer in the ab plane, with voids between the dimers that accommodate, on both sides, inversion-related organic cation pairs. The organic cations are required by mirror-plane symmetry to be disordered in (I) and (II). The organic cations and [CuCl₃(H₂O)]⁻ complexes are nearly coplanar and tilted out of the layer plane to establish a hybrid organic–inorganic layer structure parallel to (202) [(11) in (III)], with hydrate columns (defined by water molecules) and hydrophobic columns (defined by methyl groups) parallel to each other [and along the 2₁ axes in (I) and (II)]. In 1,1-dimethylpiperidinium aquatrichloridocuprate(II), (C₇H₁₆N)[CuCl₃(H₂O)], (IV), the bulkier organic cation prevents semicoordinate bonding between complexes, which are hydrogen bonded side-to-side in zigzag chains that place water molecules in columns along half of the 2₁ axes.