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

Abstract

Two structures of the Tutton salt family, originally reported with composition [Cu(H 2 O) 6 ](ClO 4 ) 2 (H 2 O) 2 and Na 2 Cu(SO 4 ) 2 (H 2 O) 6 , have been redetermined based on the original intensity data. With respect to the original [Cu(H 2 O) 6 ](ClO 4 ) 2 (H 2 O) 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 Na 2 Cu(SO 4 ) 2 (H 2 O) 6 model, the sodium site is replaced by a mixed-occupancy potassium/ammonium site. The resulting revised formulae are (NH 4 ) 2 Cu(SO 4 ) 2 (H 2 O) 6 [diammonium hexaaquacopper(II) disulfate] and [(NH 4 ) 1.176 K 0.824 ]Cu(SO 4 ) 2 (H 2 O) 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 (H 2 O) 6 ](ClO 4 ) 2 (H 2 O) 2 or Na 2 M (SO 4 ) 2 (H 2 O) 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.