Structural and thermal properties of NaMn(SO)·4HO and NaNi(SO)·10HO.

The title compounds were prepared a wet chemistry route and their crystal structures were determined from single crystal X-ray diffraction data. NaMn(SO)·4HO crystallizes with a monoclinic symmetry, space group 2/, with = 5.5415(2), = 8.3447(3), = 11.2281(3) Å, = 100.172(1)°, = 511.05(3) Å and = 2. NaNi(SO)·10HO also crystallizes with a monoclinic symmetry, space group 2/, with = 12.5050(8), = 6.4812(4), = 10.0210(6) Å, = 106.138(2)°, = 780.17(8) Å and = 2. NaMn(SO)·4HO is a new member of the blödite family of compounds, whereas NaNi(SO)·10HO is isostructural with NaMg(SO)·10HO. The structure of NaMn(SO)·4HO is built up of [Mn(SO)(HO)] building blocks connected through moderate O-H⋯O hydrogen bonds with the sodium atoms occupying the large tunnels along the axis and the manganese atom lying on an inversion center, whereas the structure of NaNi(SO)·10HO is built up of [Ni(HO)] and [Na(SO)(HO)] layers. These layers which are parallel to the (100) plane are interconnected through moderate O-H⋯O hydrogen bonds. The thermal gravimetric- and the powder X-ray diffraction-analyzes showed that only the nickel phase was almost pure. At a temperature above 300 °C, all the water molecules evaporated and a structural phase transition from 2/-NaNi(SO)·10HO to 2/-NaNi(SO) was observed. 2/-NaNi(SO) is thermally more stable than NaFe(SO) and therefore it would be suitable as the positive electrode for sodium ion batteries if a stable electrolyte at high voltage is developed.