On the (non-)existence of Tutton salts with formula types [M(H2O)6](ClO4)2(H2O)2 and Na2M(SO4)2(H2O)6 (M is a first-row transition metal).

Two structures of the Tutton salt family, originally reported with composition [Cu(H2O)6](ClO4)2(H2O)2 and Na2Cu(SO4)2(H2O)6, have been redetermined based on the original intensity data. With respect to the original [Cu(H2O)6](ClO4)2(H2O)2 model, the perchlorate anion and the noncoordinating water molecule are replaced by a sulfate anion and an ammonium cation. With respect to the original Na2Cu(SO4)2(H2O)6 model, the sodium site is replaced by a mixed-occupancy potassium/ammonium site. The resulting revised formulae are (NH4)2Cu(SO4)2(H2O)6 [diammonium hexaaquacopper(II) disulfate] and [(NH4)1.176K0.824]Cu(SO4)2(H2O)6, respectively. In both cases, the redetermination led to chemically more sensible structure models, accompanied by lower reliability factors. Three other reported structures with formula types [M(H2O)6](ClO4)2(H2O)2 or Na2M(SO4)2(H2O)6 (M is a first row transition metal) have also been re-examined. From crystal-chemical considerations, their existence is likewise questioned. It is shown that the deposition of structure factors is beneficial for detailed re-examinations of problematic structure models.