SMCr. VIII Congreso Nacional de Cristalografía
II Reunión Latinoamericana de Cristalogfrafía
VI Reunión de Usuarios de Luz Sincrotrón
23-27 de octubre del 2016. Mérida, Yucatán, México.
2D and 3D Titanium Phosphate Materials:
Crystal Structure and Properties
Jorge García-Glez,1 Camino Trobajo,1 Zakariae Amghouz,2 Sergei A. Khainakov,2 Conchi
O. Ania,3 José B. Parra,3 Artem A. Babaryk,4 Iván da Silva,5 Germán R. Castro,6 and
Santiago García-Granda.7,*
1
Department of Organic and Inorganic Chemistry, University of Oviedo-CINN, 33006 Oviedo, Spain.
Scientific and Technical Services, University of Oviedo, 33006 Oviedo, Spain.
3
INCAR-CSIC, 33080 Oviedo, Spain.
4
Faculty of Chemistry, Taras Shevchenko National University of Kyiv, 01601 Kyiv, Ukraine.
5
ISIS Facility, Rutherford Appleton Laboratory, Chilton, Oxfordshire OX11 0QX, UK.
6
SpLine, Spanish CRG Beamline, ESRF, BP 220, 38043 Grenoble, France.
7
Department of Analytical and Physical Chemistry, University of Oviedo-CINN, 33006 Oviedo, Spain.
*e-mail: [email protected]
2
Abstract. Layered α-Ti(HPO4)2·H2O (α-TiP) and its propylamine intercalation product, αTi(HPO4)2·2C3H7NH2·H2O, have been synthesized and characterized, their sorption capacity for
europium(III) was investigated, and the crystal structure of a hypothetical final product, α[Eu(H2O)6]2/3Ti(PO4)2·[(H2O)6]1/3, has been proposed by DFT calculations. Tri-dimensional
Ti2O(PO4)2·2H2O polymorphs (ρ-TiP and π-TiP) with fibrous morphologies were prepared
hydrothermally. The crystal structure of π-phase was solved ab initio from synchrotron X-ray powder
diffraction data, and the thermal transformation of ρ-Ti2O(PO4)2·2H2O to ρ-Ti2O(PO4)2, was monitored
by HT-PXRD. The coordination environment of the hydrated titanium changes from octahedral to
distorted tetrahedral, which explains the measurable thermally activated nitrogen-adsorption observed for
the anhydrous phase.
Keywords: Titanium, phosphate, crystallography.
Metal salts of phosphoric acid have been known for over a century. However, research into layered tetravalent metal
phosphates and their relatives only began in the late 1950’s due to the recognition of the application of some of these
salts as cation exchangers in radioactive waste streams. Intially, tetravalent metal phosphates were only available as
amorphous gels as consequence of their low solubility. In 1964, Clearfield and Stynes prepared the first crystalline
compound, α-Zr(HPO4)2·H2O, which made its layered structure and chemical reactivity clearly understood,
including its titanium analogous. Since then, the possibility of relating the properties of these metal acid salts to their
crystalline structures and the many potential applications in the fields of ion exchange, intercalation, catalysis and
ionic conductivity prompted the comprehensive study of these classes of compounds. The existence of the γ-layered
compound was also reported by Clearfield et al., who prepared Zr(PO4)(H2PO4)·2H2O and Zr(PO4)(H2PO4). The
prefix γ was assigned to the dihydrate and the prefix β to the anhydrous compound. The formula was originally
given as γ-Zr(HPO4)2·2H2O. However, 31P MAS NMR studies performed by Clayden showed that γ-ZrP contains
tertiary phosphate groups and dihydrogen phosphate groups in equal amounts. In 1990 Christensen et al. proposed
an essentially correct structure for the titanium parent compound, Ti(PO4)(H2PO4)·2H2O, from powder diffraction
data that was in accordance with the results of Clayden, although later the combined SS-NMR and powder
synchrotron X-ray diffraction data showed that the unit cell was inadequately selected [1]. In 1995, the structure of
γ-ZrP was solved from powder X-ray diffraction by Poojary et al., and the data confirmed the model reported by
Christensen. Later, the structure determination of β-TiP showed that the structure of the γ-type layer is retained in
the anhydrous compound. Layered titanium phosphate compounds intercalated with amines may be used as
precursors in pillaring reactions, because of their water stability, suitable interlayer distance, moderate affinity of the
intercalated species towards the host active centers, and an adequate occupied interlayer volume [2]. Despite the
many potential applications of these materials, including the synthesis of organic-inorganic nanotubes based on γ-
SMCr. VIII Congreso Nacional de Cristalografía
II Reunión Latinoamericana de Cristalogfrafía
VI Reunión de Usuarios de Luz Sincrotrón
Mérida, Yucatán, México 23-27 de octubre del 2016