Four new hydroxymonophosphates with closely related intersecting tunnels structures: The series AMIII(PO3(OH))2 with A=Rb, Cs; M=Fe, Al, Ga, In

The family of hydroxymonophosphates of generic formula AMIII(PO3(OH))2 has been revisited using hydrothermal techniques. Four new phases have been synthesized: CsIn(PO3(OH))2, RbFe(PO3(OH))2, RbGa(PO3(OH))2 and RbAl(PO3(OH))2. Single crystal diffraction studies show that they exhibit two different structural types from previously observed other phases with A=H3O, NH4, Rb and M=Al, V, Fe. The “Cs–In” and “Rb–Fe” phosphates crystallize in the triclinic space group image, with the cell parameters a=7.4146(3) Å, b=9.0915(3) Å, c=9.7849(3) Å, α=65.525(3)°, β=70.201(3)°, γ=69.556(3)° and V=547.77(4) Å3 (Z=3) for CsIn(PO3(OH))2 and a=7.2025(4) Å, b=8.8329(8) Å, c=9.4540(8) Å, α=65.149(8)°, β=70.045(6)°, γ=69.591(6)° and V=497.44(8) Å3 (Z=3) for α-RbFe(PO3(OH))2. The “Rb–Al” and “Rb–Ga” phosphates crystallize in the Rimagec space group, with a=8.0581(18) Å and c=51.081(12) Å (V=2872.5(11) Å3 and Z=18) for RbAl(PO3(OH))2 and a=8.1188(15) Å and c=51.943(4) Å (V=2965(8) Å and Z=18) for RbGa(PO3(OH))2. These two structural types are closely related. Both are built up from MIIIO6 octahedra sharing their apices with PO3(OH) tetrahedra to form [M3(PO3OH)6] units, but the latter exhibits a different configuration of their tetrahedra. The three-dimensional host-lattices result from the connection of the [M3(PO3OH)6] units and they present numerous intersecting tunnels containing the monovalent cations.