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)62(H2O)2 and Na2Cu(SO4)2(H2O)6, have been redetermined based on the original intensity data. With respect to the original Cu(H2O)62(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)62(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.