Synthesis and characterisation of MIL-43 and MIL-44, two new layered templated tetravalent phosphates: Zr(PO4)2·N2C2H10 and Ti2(PO4)2(HPO4)2·N2C2H10

Abstract

Zr(PO4)2·N2C2H10 or MIL-43 and Ti2(PO4)2(HPO4)2·N2C2H10 or MIL-44 were prepared hydrothermally (20 or 4 days, 473 or 453 K, respectively, autogenous pressure) in the presence of ethylenediamine. Their structures have been determined by single-crystal X-ray diffraction. MIL-43 crystallises in the monoclinic space group P21 (No. 4) with a=11.0722(1), b=10.6631(1), c=16.4642(2) Å, β=95.991(1)° and V=1933.21(3) Å3 (final agreement factors R1(F)=0.0466, wR2(F2)=0.1096). Due to the very poor quality of the crystal, only an approached structure of MIL-44 is given; it crystallises in the triclinic space group P1 (No. 1) with a=5.0845(4), b=6.3097(5), c=12.6111(9) Å, α=77.454(1), β=78.926(2), γ=89.986(1)° and V=387.21(5) Å3. Both solids are two-dimensional and are the ion-exchanged equivalents of the layered solids αZrP and γTiP. Inorganic sheets of MIL-43 are built up from pseudo-hexagonal arrays of ZrO6 octahedra surrounded by PO4 tetrahedra pointing their terminal oxygen alternatively up and down at the interlayer space. Layers of MIL-44 are made of double (TiOP) chains built from TiO6 octahedra and PO4 tetrahedra on which HPO4 groups are grafted pointing towards the interlayer space. In both cases, diprotonated organic templates, located between the layers, interact with terminal phosphate groups and ensure via hydrogen bonds the stability of the structures.