Variable temperature powder diffraction investigations also explained the origin of some unusual sample variability in Cr[Bi(SCN) 6 ] [Fig. ]. Despite its apparently dense structure Cr[Bi(SCN) 6 ] can play host to guests and form a hydrate, Cr[Bi(SCN) 6 ] • H 2 O. This hydrate is formed when the synthesis of Cr[Bi(SCN) 6 ] is carried out in more acidic solution, and also slowly forms from Cr[Bi(SCN) 6 ] at room temperature and ambient humidity over a period of weeks. When Cr[Bi(SCN) 6 ] • H 2 O is heated above 150 • C, this guest water is lost, leading to a reduction in cell volume by 19 Å 3 and a mass loss of 3 % [Fig. ].