Hydrates of N‑((10-Chloroanthracen-9-yl)methyl)-3-(1H-imidazol-1-yl)propan-1-ammonium\nCobalt(II), Copper(II), and Zinc(II) 2,6-Pyridinedicarboxylate:\nReversible Crystallization

In a quest to explore interconvertible assemblies of\nhydrates of\ncobalt(II), copper(II), and zinc(II) 2,6-pyridine­dicarboxylate\n(<b>26-pdc</b>), complexes having cation of a chloro-substituted\nanalogue N-{(10-chloroanthracen-9-yl)methyl}-3-(1H-imidazol-1-yl)propan-1-amine\nwere investigated. In the case of cobalt and copper complexes, a crystallized\nstable hydrate and a less stable methanol hydrate were guided by concentration-dependent\ncrystallizations. The unit-cells of the crystals of the methanol hydrates\nof the two cobalt and copper complexes each belong to the P1̅\nspace group but have different stoichiometries as well as large differences\nin packing. These hydrates could be reversibly crystallized in a predictable\nmanner. The unit-cell volumes of the methanol hydrate of the cobalt\ncomplex were four-times smaller than that of the respective stable\nform (<i>C</i>2/<i>c</i> space group), whereas\nsimilar hydrates of the copper complex had a two-times smaller unit-cell\nvolume than that of the stable form. The cations of the stable forms\nassembled together and formed zigzag ladder-like chains. The spaces\npresent in between the assembled chains were filled with clusters\nof face to face stacked anions. The transformation to stable form\nrequired a bottom-up building process of the unit-cell starting from\na smaller unit-cell of the less stable hydrates. Fluorescence spectroscopic\nstudies showed the possibility of two forms of assemblies of the zinc-complex\nin solution, but crystallization had yielded only the stable form.