Hydrous salts of 1-aminoethylidenediphosphonic acid and piperazidine: temperature induced reversible structural transformation in a humid environment

Abstract

A series of hydrous salts constructed using 1-aminoethylidenediphosphonic acid (AEDPH₄) and piperazidine (pip) were synthesized and structurally characterized, namely (AEDPH₃)·(pipH₂)_0.5·0.5H₂O (1), (AEDPH₃)·(pipH₂)_0.5·2H₂O (2), and (AEDPH₃)·(pipH₂)_0.5·3H₂O (3). Compounds 1–3 all contain porous [(AEDPH₃)·(pipH₂)_0.5]_n supramolecular hosts with the same components, but illustrate different host structures, which allow different numbers of water molecules to lie inside. Moreover, a reversible structural transformation circle is observed among the single crystals of the three hydrous salts, that is, compounds 1–3 through changing the temperature, can transform into each other in a humid environment.