Flexible metal supramolecular framework of 2D cobalt(II) coordination polymer with water-induced reversible crystal-to-amorphous transformation

A new flexible 3D supramolecular framework, [Co(4,4′-bipy)(pro)2(H2O)] (1) (4,4′-bipy=4,4′-bipyridine and pro=propionate) has been prepared and structurally characterized. This compound crystallizes in monoclinic, space group P21/c. Each Co(II) cation shows an octahedral geometry. The Co(II) ions are assembled by the bridging propionate and 4,4′-bipyridine ligands in c and a axes, generating an infinite 2D layer. These 2D layer networks are further linked to one another by hydrogen bonding interactions, leading to a 3D supramolecular framework. Interestingly, compound 1 exhibits water-induced reversible crystal-to-amorphous transformation with chromotropism confirmed by spectroscopic techniques, elemental analysis, TGA, and XRPD. Thus, dehydrated amorphous form, Co(4,4′-bipy)(pro)2 (1A), may be utilized as an indicator for humidity.