Synthesis, crystal structure, phase transition and thermal behaviour of a new dabcodiium hexaaquanickel(II) bis(sulphate), (C6H14N2)[Ni(H2O)6](SO4)2

A new dabcodiium-templated nickel sulphate, (C6H14N2)[Ni(H2O)6](SO4)2, has been synthesised and characterised by single-crystal X-ray diffraction at 20 and −173 °C, differential scanning calorimetry (DSC), thermogravimetry (TG) and temperature-dependent X-ray powder diffraction (TDXD). The high temperature phase crystallises in the monoclinic space group P21/n with the unit-cell parameters: a = 7.0000(1), b = 12.3342(2), c = 9.9940(2) Å; β = 90.661(1)°, V = 862.82(3) Å3 and Z = 2. The low temperature phase crystallises in the monoclinic space group P21/a with the unit-cell parameters: a = 12.0216(1), b = 12.3559(1), c = 12.2193(1) Å; β = 109.989(1)°, V = 1705.69(2) Å3 and Z = 4. The crystal structure of the HT-phase consists of Ni2+ cations octahedrally coordinated by six water molecules, sulphate tetrahedra and disordered dabcodiium cations linked together by hydrogen bonds. It undergoes a reversible phase transition (PT) of the second order at −53.7/−54.6 °C on heating–cooling runs. Below the PT temperature, the structure is fully ordered. The thermal decomposition of the precursor proceeds through three stages giving rise to the nickel oxide.

Graphical abstractA new transition metal sulphate in the presence of dabco amine, (C6H14N2)[Ni(H2O)6](SO4)2, was prepared and characterised. The structural arrangement is pointed out, in which dabco plays a templating role. A structural phase transition was detected at −53.7/−54.6 °C on heating–cooling runs and the thermal decomposition of the precursor, at high temperature, was discussed.Figure optionsDownload full-size imageDownload as PowerPoint slide