Hydrothermal synthesis and structure of organically templated chain, layered and framework scandium phosphates

Four scandium phosphate-based structures have been prepared hydrothermally in the presence of the primary diamines ethylenediamine and diaminobutane and the primary amine cyclohexylamine and characterised by single crystal and powder X-ray diffraction, ³¹P and ⁴⁵Sc solid-state MAS NMR and chemical analysis. Charge balancing protons in the structures are located using bond valence sum calculations and postulated hydrogen bonding networks. Compound 1, (H₃NC₂H₄NH₃)₃]Sc₃(OH)₂(PO₄)₂(HPO₄)₃(H₂PO₄)], , a=5.4334(6), b=8.5731(9), , α=79.732(4), β=83.544(4), γ=80.891(5)°, Z=2, is built up of scandium phosphate ribbons, based on trimers of ScO₆ octahedra linked by OH groups. These trimers are joined through phosphate groups bound through three oxygens, and are decorated by phosphate groups linked by a single oxygen atom. The ribbons are arranged parallel to the a-axis and linked one to another by fully protonated ethylenediammonium ions. Compounds 2, (H₃NC₄H₈NH₃)₃](Sc(OH₂))₆Sc₂(HPO₄)₁₂(PO₄)₂], , a=13.8724(3), , Z=1, and 3, (H₃NC₄H₈NH₃)₂(H₃O)]Sc₅F₄(HPO₄)₈], C2/m, a=12.8538(4), b=14.9106(4), , β=101.17(9)°, Z=2, were prepared using diaminobutane as the organic template in the absence and presence, respectively, of fluoride ions in the gel. Compound 2 has a pillared layered structure, in which ScO₆ octahedra are linked by three vertices of hydrogenphosphate groups into sheets and the sheets pillared by ScO₆ octahedra to give a three-dimensionally connected framework isostructural with a previously reported iron(III) hydrogenphosphate. The protonated diaminobutane molecules occupy cavities between the layers. Compound 3 has a layered structure in which isolated ScO₆ octahedra and tetrameric arrangements of ScO₄F₂ octahedra, the latter linked in squares through fluoride ions, are connected by phosphate tetrahedra that share two or three oxygens with scandium atoms. In this structure, the protonated diaminobutane molecules connect the layers, the -NH₃⁺ groups fitting into recesses in the layers. Compound 4, (C₆H₁₁NH₃)]ScF(HPO₄)(H₂PO₄)], Pbca, a=7.650(3), b=12.867(5), , Z=8, the first scandium phosphate to be prepared with a monoamine, is also a layered solid. In this case, the layers contain single chains of ScO₄F₂ octahedra which share fluoride ions in trans positions. Phosphate tetrahedra bridge across scandiums via two of their four oxygens, both within the same chain and also to neighbouring chains to make up the layer. The protonated amine groups of the cyclohexylamine molecules achieve close contact with phosphates of the layer, while the cyclohexyl moieties, which are in the chair configuration, project into the interlayer space.