Humidity-Induced Structural Transformation in Pseudopolymorph Coordination Polymers.

Three cadmium coordination polymers, namely, {[CdL(OAc)2](C2H5OH)}n (1), {[CdL(OAc)2](CH3CN)}n (2), and [CdL(OAc)2(H2O)]n (3), were synthesized by an exoditopic 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene Schiff base ligand (L) and cadmium acetate in the presence of different solvent systems. Single-crystal X-ray diffraction, powder X-ray diffraction, and thermogravimetric analysis showed that 1D ladder pseudopolymorphic compounds (1 and 2) transformed to the solvent-free 1D linear compound 3 through a rare case of water absorption from air at room temperature. Interestingly, compound 3 was transformed to compound 1 through a dissolution-recrystallization structural transformation process. The results illustrated that solvents and humidity have an important role in the formation of pseudopolymorphs with the same or different structural motifs.