Two Isotypic Transition Metal Germanophosphates M^II₄(H₂O)₄[Ge(OH)₂(HPO₄)₂(PO₄)₂] (M^II = Fe, Co): Synthesis, Structure, Mössbauer Spectroscopy, and Magnetic Properties

Synthetic, structural, thermogravimetric, Mössbauer spectroscopic, and magnetic studies were performed on two new isotypic germanophosphates, M^II₄(H₂O)₄[Ge­(OH)₂(HPO₄)₂(PO₄)₂] (M^II = Fe, Co), which have been prepared under hydro-/solvo-thermal conditions. Their crystal structures, determined from single crystal data, are built from zigzag chains of M^IIO₆-octahedra sharing either trans or skew edges interconnected by [GeP₄O₁₄(OH)₄]^8– germanophosphate pentamers to form three-dimensional neutral framework structure. The edge-sharing M^IIO₆-octahedral chains lead to interesting magnetic properties. These two germanophosphates exhibit a paramagnetic to antiferromagnetic transition at low temperatures. Additionally, two antiferromagnetic ordering transitions at around 8 and 6 K were observed for cobalt compound while only one at 19 K for the iron compound. Low-dimensional magnetic correlations within the octahedral chains are also observed. The divalent state of Fe in the iron compound determined from the Mössbauer study and the isothermal magnetization as well as thermal analyses are discussed.