Bartley, J.

Budroni, G.

Conte, M.

Dong, W.

Girgsdies, F.

Hutchings, G.

Ressler, T.

Schlögl, R.

Schneider, M.

Wolf, G.

English

MPG.PuRe

 α family β family δ family  αI αII β ε δ ω    Relative chain arrangement parallel only parallel only parallel & perpendicular    No. of chains linked by PO4 4 3 4    Dimensionality (pyramidal view) 2D 3D 3D    Chain directionality anti-parallel anti-parallel anti-parallel parallel anti-parallel (disordered)    Chain shape straight straight zigzag zigzag zigzag straight  β sub-family ε sub-familyδ structure familyβ structure familyNew Contributions to the Structural Chemistry of Vanadyl Orthophosphate VOPO4F. Girgsdies 1, T. Ressler 1 *, R. Schlögl 1, W.-S. Dong 2, G. Budroni 2, M. Conte 2, J.K. Bartley 2, G.J. Hutchings 2, G.-U. Wolf 3, M. Schneider 31 Abteilung Anorganische Chemie, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany2 School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff, CF10 3AT, UK3 Leibniz-Institut für Katalyse e.V. an der Universität Rostock, Außenstelle Berlin, Postfach 96 11 56, 12474 Berlin, Germany* current address: Institut für Chemie, Technische Universität Berlin, Sekretariat C2, Straße des 17. Juni 135, 10623 Berlin, GermanyThe Crystal Structure of ε-VOPO4 [1] The Crystal Structure of δ-VOPO4 [6]Backgroundε-VOPO4 is the most recently described polymorph of VOPO4 [2]. Based on the chemical behavior and similarities in the X-ray diffraction patterns, it was proposed that the structure of ε-VOPO4 should be both related to monoclinic VPO4·H2O and similar to β-VOPO4. A Rietveld refinement of the monoclinic VPO4·H2O structure (space group C2/c) to the ε-VOPO4 data was only of limited success [2]. Recently, a structure model derived from monoclinic VPO4·H2O was successfully refined in the lower symmetry space group P21/n [3].ExperimentalSamples of ε-VOPO4 were prepared at Cardiff University in the course of searching for potential VPO catalyst precursors by means of hydrothermal synthesis [4]. The X-ray diffraction pattern was subjected to ab initiostructure solution attempts in various monoclinic and orthorhombic space groups using the TOPAS [5] software, employing a rigid body approach [1].ResultsThe crystal structure of ε-VOPO4 was successfully solved and refined in the monoclinic space group Cc (a = 7.266 Å, b = 6.893 Å, c = 7.265 Å, β = 115.34°; because a ≈ c, the unit cell is pseudo-orthorhombic). This solution was found to be in better agreement with the experimental data than the previously published P21/n model. Both models differ in the general orientation of the VO5 pyramids. While the direction of pyramid stacks would alternate in the centrosymmetric space group P21/n (Fig. 1, right), they all point into the same general direction in the acentric space group Cc (Fig. 1, left).Fig. 1: Pyramidal representation of two structure models for ε-VOPO4 in the space groups Cc (this work, left) and P21/n (after reference [3], right), respectively.Backgroundδ-VOPO4 was described in 1985 by Bordes and Courtine [7] as one of the minority phases found in activated (VO)2P2O7 catalysts for the selective oxidation of n-butane to maleic anhydride. Since then, several unit cells and two structure hypotheses ("Bordes model" [8] and "Benabdelouahab model" [9, 10]) have been proposed. The reason for this uncertainty is that the material obtained is usually badly crystallized and often contaminated with other phases, yielding a diffraction pattern with rather broad, overlapping peaks. Only recently, well crystallized single phase material was obtained and investigated by means of TEM and powder XRD [11]. The diffraction pattern proved to be incompatible with the unit cells proposed until then, resulting in a new unit cell proposal of orthorhombic symmetry. Despite the high quality of the diffraction pattern, the crystal structure of δ-VOPO4could not be determined at that time.ExperimentalThe preparation of well crystallized δ-VOPO4 and the collection of the corresponding X-ray diffraction pattern were conducted at the former ACA Berlin (now Berlin branch of the Leibniz Institute for Catalysis at University Rostock), as previously published [11]. The structure solution described here is based on a re-investigation of aforementioned diffraction data. The program TOPAS [5] was used for all steps of the ab initio structure determination and subsequent refinement.ResultsA Le Bail pattern decomposition proved that the δ-VOPO4 unit cell could be equally well described as tetragonal instead of orthorhombic. Thus, the higher (tetragonal) symmetry was assumed to be more probable. Structure solution attempts in various tetragonal space groups yielded an initial structure model in the space group P42bc, which was subsequently transferred into the higher symmetry space group P42/mbc and refined. The obtained crystal structure of δ-VOPO4 is found to be very similar to that of ω-VOPO4, thus disproving both traditional structure hypotheses. The unit cell of δ-VOPO4 (a = 9.055 Å, c = 8.608 Å) corresponds to a quadruple (2×2×1) unit cell of ω-VOPO4 (see below).The Polymorphs of VOPO4 – Structural SystematicsIntroductionSeven polymorphs of VOPO4 have been described so far: αI, αII, β, γ, δ, ε, and ω. With the work presented here, only the crystal structure of γ-VOPO4 remains unknown. Now that six of seven polymorphs are characterized in sufficient detail, the general structure building principles of VOPO4 can be discussed systematically.Common featuresAll structurally characterized polymorphs of VOPO4 share some common characteristics:  Each vanadium atom is surrounded by six oxygen atoms with• one particularly short distance (vanadyl bond V=O),• four medium distances (V−O bonds to phosphate groups),• one rather long distance (V···O contact to next vanadyl group). V···O is always trans-positioned to V=O. Depending on whether V···O is considered a bond or not, the  coordination geometry of vanadium can be described as a distorted VO6 octahedron (⇒ "octahedral  representation") or a VO5 pyramid (⇒ "pyramidal representation"), respectively. Each VO6 octahedron shares two trans-positioned corners with two other octahedra, forming infinite chains with [V=O···V=O···]∞ backbone. Each VO6 octahedron shares four corners with four different PO4 tetrahedra. Each PO4 tetrahedron shares corners with four  different VO6 octahedra.Distinguishing and grouping charactersThe polymorphs of VOPO4 can be characterized and grouped into three structure families according to the following characters:  Three-dimensional arrangement of VO6 chains (parallel only vs. parallel & perpendicular). Number of different VO6 chains linked by a single PO4 tetrahedron (3 vs. 4). Dimensionality of structure network in pyramidal representation (2D vs. 3D).Further distinguishing (but non-grouping) characters: Relative directionality of adjacent chains (parallel vs. anti-parallel). Shape of [V=O···V=O···]∞ backbone (straight vs. zigzag).Octahedral (top) and pyramidal representation (bottom). Unit cell viewed along a (top) and c axis (bottom).Quadruple (2×2×1) unit cell viewed along a (top) and c axis (bottom).related structures: related structures:β-VOPO4 [16] ε-VOPO4 [1]δ-VOPO4 [6] ω-VOPO4 [23]Octahedral (top) and pyramidal representation (bottom).orthorhombic β-LiVOPO4 [17] triclinic α-LiVOPO4 [19]Octahedral (left) and pyramidal representation (right). Li atoms omitted for clarity.VOHPO4 [18]Same space group and [VOPO4] host lattice structure as β-VOPO4 and β-LiVOPO4 (no picture).Octahedral (left) and pyramidal representation (right). Li atoms omitted for clarity.NaVOPO4 [20, 21]Monoclinic. Same [VOPO4] host lattice structure as α-LiVOPO4 (no picture)."New phase" of Lim et al. [2] ?Crystal structure unknown. Prepared by (topotactic?) hydrogen-spillover reduction from β-VOPO4 [2]. Could be a new polymorph of VPO4·H2O with the same connectivity as β-VOPO4.monoclinic VPO4·H2O [22]Symmetric V−O−V chains, undistorted octahedra. ReferencesαI-VOPO4 [12] αII-VOPO4 [13][1] F. Girgsdies, T. Ressler, R. Schlögl, W.-S. Dong, J.K. Bartley, G.J. Hutchings; submitted for publication in Solid State Sciences.[2] S.C. Lim, J.T. Vaughey, W.T.A. Harrison, L.L. Dussac, A.J. Jacobson, J.W. Johnson; Solid State Ionics 84 (1996) 219.[3] Y. Song, P.Y. Zavalij, M.S. Whittingham; J. Electrochem. Soc. 152 (2005) A721.[4] W.-S. Dong, J.K. Bartley, N.F. Dummer, F. Girgsdies, D. Su, R. Schlögl, J.-C. Volta, G.J. Hutchings; J. Mater. Chem. 15 (2005) 3214.[5] Topas v2.1, copyright 1999, 2000 Bruker AXS[6] F. Girgsdies, T. Ressler, R. Schlögl, G.-U. Wolf, M. Schneider; in preparation.[7] E. Bordes, P. Courtine; J. Chem. Soc., Chem. Commun. (1985) 294.[8] E. Bordes; Catal. Today 1 (1987) 499.[9] F. Ben Abdelouahab, R. Olier, N. Guilhaume, F. Lefebvre, J.-C. Volta; J. Catal. 134 (1992) 151.[10] G.F. Benabdelouahab, J.-C. Volta, R. Olier; J. Catal. 148 (1994) 334.[11] M. Schneider, M. Pohl, G.-U. Wolf, F. Krumeich; Mater. Sci. Forum 321-323 (2000) 960.[12] M. Willinger, pers. communication.[13] C. Calvo, B. Jordan; Canad. J. Chem. 51, 2621. [ICSD-2889][14] N. Dupré, G. Wallez, J. Gaubicher, M. Quarton; J. Solid State Chem. 177 (2004) 2896.[15] H.R. Tietze; Austral. J. Chem. 34 (1981) 2035. [ICSD-200884][16] R. Gopal, C. Calvo; J. Solid State Chem. 5 (1972) 432. [ICSD-9413][17] K.H. Lii, C.H. Li, C.Y. Cheng, S.L. Wang; J. Solid State Chem. 95 (1991) 35. [ICSD-80613][18] L. Wilde, J. Trommer, U. Steinike, H. Worzala, G.-U. Wolf; Mater. Sci. Forum 278 (1998) 704. [ICSD-86824][19] A.V. Lavrov, V.P. Nikolaev, G.G. Sadikov, M.A. Porai-Koshits; Phys. Dokl. 27 (1982) 680. [ICSD-20537][20] K.H. Lii, C.H. Li, T.M. Chen, S.L. Wang; Z. Krist. 197 (1991) 67. [ICSD-33944][21] L. Benhamada, A. Grandin, M.M. Borel, A. Leclaire, B. Raveau; C.R. Acad. Sci. Ser. II 314 (1992) 585. [ICSD-66355][22] J.T. Vaughey, W.T.A. Harrison, A.J. Jacobson; Inorg. Chem. 33 (1994) 2481. [ICSD-67996][23] P. Amorós, M.D. Marcos, M. Roca, J. Alamo, A. Beltrán-Porter, D. Beltrán-Porter; J. Phys. Chem. Solids 62 (2001) 1393.View along a axis in octahedral (left) and pyramidal representation (right).View along a axis in octahedral (left) and pyramidal representation (right).related structures:tetragonal LiVOPO4 [14]View along a axis in octahedral (left) and pyramidal representation (right). Li atoms omitted for clarity.Same [VOPO4] host lattice structure as in αI-VOPO4, but can be obtained from both αI- and αII-VOPO4 by lithiation.VOPO4·2H2O [15]View along a axis in octahedral (left) and pyramidal representation (right).Of the two water molecules per formula unit, one is coordinating to vanadium (oxygen atom shown), while the second one is crystal water (omitted for clarity).Same [VOPO4] host lattice structure as in αI-VOPO4, but can be obtained from both αI- and αII-VOPO4 by hydration.Remark:The layered α-VOPO4 structures show a rich intercalation chemistry with organic donor molecules (especially amides) instead of water.One important additional property (which cannot be coded by simple characters) is the connectivity pattern, i.e. the possibility of different "stacking" of otherwise equivalent building blocks ⇒ distinction of sub-families (ε vs. β).α structure family

New Contributions to the Structural Chemistry of Vanadyl Orthophosphate VOPO<sub>4</sub>

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New Contributions to the Structural Chemistry of Vanadyl Orthophosphate VOPO<sub>4</sub>

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