Crystal growth, thermal and magnetic characterizations of a new ferromagnetic Ni(II) dimer

Single crystals of 1-methylpiperazine-1,4-diium hexaaquatetrachlorodinickel(II) dichloride, (C5H14N2) [Ni2Cl4(H2O)6]Cl2, were grown by hydrothermal techniques in aqueous solution. The compound was characterised by differential thermal analysis (TG-TDXD), single crystal X-ray diffraction, and variable temperature magnetic susceptibility. The compound crystallizes in the triclinic system (space group P-1, Z = 2) with the following unit cell dimensions: a = 6.611(3) A, b = 8.776 (4) A, c = 17.457(8) A, a = 101.34(2) , b = 96.31(2) , and c = 105.38(2) . The structure was solved using 4,243 independent reflections and refined to R = 0.024. The structure of (C5H14N2)[Ni2Cl4(H2O)6]Cl2 can be described as mixed organic–inorganic layers along the [-101] direction. The Ni dimers show ferromagnetic exchange (J * 15 K), while the interactions between the dimers are antiferromagnetic (J * -3 K). The 3D network is further linked by three types of hydrogen bonds (N–H Cl, OW– H Cl, and N–H O), in order to build cation–anion cohesion. Dehydration of the precursor proceeds through three stages, leading to crystalline intermediary hydrate phases and an anhydrous compound.