Hydrothermal Synthesis and Structural Characterization of Four Scandium Phosphate Frameworks

The recent expansion of zeolitic synthesis toward mixed geometry frameworks reflects
their potential applications in shape-selective catalysis and absorption. Four scandium
phosphates with three-dimensional frameworks have been hydrothermally synthesized. All
structures were solved from single-crystal X-ray diffraction and were supported by 31P MAS
NMR and infrared spectroscopy. Structure 1 ((C2N2H10)8Sc8(ScO2)4(PO4)4(HPO4)12·12H2O)
consists of a novel framework with 14-membered rings (MRs) and 10-MR channels along
the a and c axes, respectively. Ethylenediamine and water reside in the resulting supercage.
Structure 2 ((C2N2H10)2Sc4(HPO4)8) consists of a framework built from the corner-sharing of
ScO6 octahedra with HPO4 tetrahedra whose connection results in a 8-MR channel down
the a axis, where hydrolyzed cyclam resides. This compound is isostructural to a number of
existing synthetic materials including a scandium phosphate, an indium phosphate, and an
iron phosphate. Structure 3 (Sc4(HPO4)8·4(H3O)) is a framework built in the same way as
structure 2 but is described by a 12-MR channel down the a axis in which hydronium resides.
This structure is isostructural to a ferric oxonium bis(hydrogenphosphate). Structure 4
(Sc4(PO4)4·8H2O) is a framework built by the corner-sharing of PO4 tetrahedra with ScO4·2H2O octahedra to form 8-MR channels down the a-axis. This structure occurs in nature as
sterrettite, a scandium-bearing phosphate mineral, and has an isostructural indium
phosphate. Crystal data:  structure 1, P21/n, a = 8.603(2) Å, b = 15.476(3) Å, 16.504(4) Å,
and β = 96.877(5)°, structure refinement converged at R = 0.0443; structure 2, P2/n, a =
9.4111(15) Å, b = 9.1066(15) Å, c = 9.6950(15) Å, and β = 117.272(3)°, structure refinement
converged at R = 0.032; structure 3, P2/n, a = 5.3048(11) Å, b = 8.8230(18) Å, c = 14.779(3)
Å, and β = 96.685(5)°, structure refinement converged at R = 0.0433; structure 4, P2(1)/n,
a = 5.4429(8) Å, b = 10.2513(15) Å, c = 8.9094(11) Å, and β = 90.253(7)°, structure refinement
converged at R = 0.063.