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New Series of Layered Vanadyl Phosphates with Varied Polyamine Templates

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posted on 31.05.2005, 00:00 by Ya-Ching Yang, Ling-I Hung, Sue-Lein Wang
Four two-dimensional vanadyl phosphates, (H3dien)[(VOPO4)2(OH)]·H2O (dien = diethylenetriamine) (1), (H2dach)1.5[(VOPO4)2(OH)]·2H2O (dach = 1,4-diaminocyclohexane) (2), (H2tmdpp)[V3O4(OH)(PO4)2]·3H2O (tmdpp = 4,4‘-trimethylenedipiperidine) (3), and (H2tmdpp)(H1.5tmdpp)K0.5[V5O7(H2O)2(PO4)4]·H2O (4), with clearly distinct but orderly increasing layer separations from 7.75 to 18.07 Å, have been prepared via hydrothermal routes and characterized by single-crystal X-ray diffraction, thermogravimetric analysis, and magnetic susceptibility or ion-exchange studies. The series possesses three unique layer topologies, but all contain VIVO5 square pyramid, PO4 tetrahedron, discrete dimers of V−O polyhedra, and 3-, 4-, 5-, and 8-membered rings. Structures 1 and 2 are VIV species, having the same layer topology but different amine cations. Compounds 3 and 4 are VIV/VV mixed valent, holding the same amine templates in varied inclined angles. Being similar to 1 and 2, the layer of 3 contains extra vanadate groups. In contrast, the layers in 4 are distinct and contain VVO6 and VIVO6 octahedra besides VIVO5 square pyramid. It exhibits an interlayer d-spacing of 18.07 Å, the largest propped up by noncovalent intermediates between VPO layers. With an extremely low density of 1.71 g·cm-3, compound 4 also demonstrates the lightest layered material ever prepared in the V/P/O system. Structural relationship, template effect, factors controlling layer gaps, ion exchange, thermal stability, and magnetic properties are discussed.