Crystal structure, phase transition and thermal decomposition of a copper (II) sulfate dihydrate containing a chiral organic ammonium cation

The directed synthesis of a new organically templated copper sulfate has been achieved through the use of chiral organic amine. Reaction containing S-2-methylpiperazine, CuSO4·5H2O, H2SO4 and H2O were subjected to the slow evaporation conditions, resulting in the growth of single crystals of [(S)-C5H14N2][Cu(SO4)2(H2O)4]·(H2O)2. At room temperature, it crystallises in the non-centrosymmetric space group P21, Z = 2, a = 7.5583(5), b = 10.1721(6), c = 10.7974(7) Å, β = 94.425(4)° and V = 827.67(9) Å3. The structure consists of trimeric units [Cu(SO4)2(H2O)4]2−, [(S)-C5H14N2]2+ cations and free water molecules, donating hydrogen bonds that stabilize the three-dimensional structure and filling space. The title compound undergoes a reversible phase transition of first-order, which is detected by differential-scanning calorimetry at 347.2 K in the heating cycle and at 318.9 K in the cooling cycle. The evolution of the dielectric constant as a function of frequency and temperature revealed this transition to be ferro-paraelectric. Thermogravimetric analyses indicate that its decomposition proceeds through three stages giving rise to the copper oxide.