Divalent metal incorporation in MIL-74, the super-sodalite aluminum phosphates M3M3Al6(PO4)12⋅4tren⋅17H2O (M =Mg, Mn, Co) and its gallium phosphate analogs M3′Ga6(PO4)12⋅4tren⋅17H2O (M′=M′=Mg, Mn, Co, Fe, Zn)

The mixed metal(II)–aluminum phosphates M3M3Al6(PO4)12⋅4tren⋅17H2O (M=Mg2+, Mn2+, Co2+) and its gallium phosphate analogs M3′Ga6(PO4)12⋅4tren⋅17H2O (M′=M′=Mg2+, Mn2+, Fe2+, Co2+, Zn2+) have been hydrothermally synthesized with the tris(2-aminoethyl)amine (tren  ) as a structure-directing agent (453 K, 36 hours, autogenous pressure). The solids were characterized by single-crystal X-ray diffraction. Their crystal structures are cubic, a≈16.8 Åa≈16.8 Å and may be described in I-43m. The open-framework is built up from an enneameric unit (T  =Al or Ga / Mg, Mn, Fe, Co, Zn) containing five TO4TO4 and four PO4 tetrahedra (one of the PO bonding is terminal). A central TO4TO4 tetrahedral unit shares all the corners with four phosphate groups. Two phosphate groups are connected to two other peripheral TO4TO4 units. It results in the formation of a “pseudo” planar building block T5P4T5P4 consisting of four square 4-rings. The connection of the T5P4T5P4 units generates a three-dimensional framework, which defines a super-sodalite topology. The resulting cavities (diameter of 10 Å) are bound by 12-ring windows in which are located the tren species in interaction with the phosphate groups (mainly terminal PO bonding) through hydrogen bond. A (H2O)17 cluster is encapsulated in the super-sodalite cages. The TO distances are discussed according to the ionic radii of the trivalent cations (Al, Ga) and the different divalent cations (Mg, Mn, Fe, Co, Zn).

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