A new pseudo-polymorph in mineral sphenicidite family (NH4)[Fe2(OH)(H2O)(PO4)2]·1.5H2O exhibiting spontaneous magnetization below 25 K

The hydrothermal synthesis and structure for a new iron phosphate based open-framework solid, (NH4)[Fe2(OH)(H2O)(PO4)2]·1.5H2O, is presented. The three-dimensional (3-D) framework is built from butterfly-shaped tetranuclear iron-oxygen clusters, which are coordinated by eight PO4 tetrahedra to create 8-membered windows along the a-, b- and c-axes; the lattice water molecules as well as the counter NH4+ cations reside in the cross channels. The new open-framework solid is a pseudo-polymorph with the known structure of the mineral sphenicidite, and exhibits spontaneous magnetization in the low temperature regime with TN ≈ 25 K, which is a result of canted spin antiferromagnetism.

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