Syntheses, structures, and magnetic properties of two unique Cu(ii)-based coordination polymers involving a crystal-to-crystal structural transformation from a 1D chain to a 3D network.

Two new coordination polymers, Cu(Hbsal)(4,4'-bpy) (1) and Cu(bsal)(4,4'-bpy)·DMF (2), have been synthesized from 5-bromosalicylic acid (Hbsal) and the auxiliary ligand 4,4'-bipyridine (4,4'-bpy) through a slow diffusion method. Compound 1 is composed of parallel 1D linear chains, whereas compound 2 represents a non-interpenetrated 3D sod net which is constructed from left and right-handed helical chains alternately separated by 4,4'-bpy. The most interesting finding is that compound 1 can be irreversibly transformed into 2 in a crystal-to-crystal manner in the case that compound 1 is immersed in the DMF solvent. Particularly, the 1D-to-3D crystal-to-crystal structural transformation also incurs a drastic change in the magnetic properties of 1 and 2.