A layered copper/bis(4-pyridylformyl)piperazine coordination polymer with cyclic water molecule octamers and reversible structural reorganization

The layered coordination polymer {[Cu(4-bpfp)2(NO3)](NO3)•8H2O}n (1, 4-bpfp = bis(4-pyridylformyl)piperazine) has been prepared by hydrothermal methods and characterized by single-crystal X-ray diffraction. Rare hydrogen-bonded R8 cyclooctane-like octameric water molecule clusters, in an unprecedented twist-chair-chair conformation, are stabilized within the coordination polymer network. Dehydration of 1 results in the crystalline green phase {[Cu(4-bpfp)2(NO3)](NO3)}n 2, which regenerates purple crystalline 1 upon rehydration.