Synthesis and characterisation of MIL-43 and MIL-44, two new layered templated tetravalent phosphates: Zr(PO_4)_2 centre dot N_2C_2 H_(10) and Ti_2(PO_4)_2(HPO_4)_2 centre dot N_2C_2H_(10)

摘要

Zr(PO_4)_2 centre dot N_2C_2H_(10) or MIL-43 and Ti_2(PO_4)_2(HPO_4)_2 centre dot N_2C_2H_(10) 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 P2_1 (No.4) with a = 11.0722(1), b = 10.6631(1), c = 16.4642(2) A, #beta# = 95.991(1) deg and V = 1933.21(3) A~3 (final agreement factors R_1(F) = 0.0466, #omega# R_2(F~2) = 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) A, #alpha# = 77.454(1), #beta# = 78.926(2), #gamma# = 89.986(1) deg and V = 387.21(5) A~3. Both solids are two-dimensional and are the ion-exchanged equivalents of the layered solids #alpha#ZrP and #gamma#TiP. Inorganic sheets of MIL-43 are built up from pseudo-hexagonal arrays of ZrO_6 octahedra surrounded by PO_4 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 TiO_6 octahedra and PO_4 tetrahedra on which HPO_4 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.