Solvent-Induced Reversible Crystal-to-Amorphous Transformation Properties of Cobalt(II) 4-Aminomethylpyridine-Sulfate with Chromotropism

The crystalline Co-II coordination compound with empirical formula [Co(Hampy)(2)(H2O)(4)](SO4)(2)(H2O)(3) (1); ampy = 4-aminomethylpyridine was obtained. The structure contains a mononuclear [Co(Hampy)(2)(H2O)(4)](4+) cation unit, two sulfate ions, and three lattice water molecules. The Co2+ cation shows an elongated octahedral geometry comprised of four oxygen atoms from water molecules at equatorial positions and two nitrogen atoms from Hampy ligands which are protonated at NH2. Each mononuclear cation unit is assembled by intermolecular hydrogen bonding and pi-pi stacking interactions by the coordinated and lattice water molecules, amino group, and sulfate anions to form a 3D supramolecular network. Investigations of the dynamic structural behaviour demonstrate that the title compound exhibits a solvent-induced reversible crystal-to-amorphous transformation with chromotropism when exposed to water and methanol vapour. This indicates that the dehydrated amorphous form, [Co(Hampy)(2)(SO4)(2)] 1A, may be utilised as an indicator for humidity and methanol vapour.