Solid State Sciences 4 (2002) 233–238www.elsevier.com/locate/ssscie

Crystal structure of a rubidium zinc oxovanadium phosphateHRb3ZnV2P4O17 with open structure containing PO4, HPO4 and P2O7

E. Le Fur, J.Y. Pivan∗

Institut de Chimie de Rennes, Laboratoire de Physicochimie, UPRES 1795-ENSCR, Ecole Nationale Supérieure de Chimie de Rennes,Campus de Beaulieu, av. du Général Leclerc, 35700 Rennes, France

Received 26 July 2001; received in revised form 11 October 2001; accepted 15 October 2001

Abstract

A new rubidium zinc oxovanadium phosphate Rb3Zn(VO)2(PO4)(HPO4)(P2O7) has been obtained under hydrothermal conditions. Itcrystallizes in theP212121 space group with parametersa = 7.0989(2) Å, b = 9.5374(2) Å, c = 23.3016(8) Å. The structure consists ofcorner-sharing VO6 octahedra, PO4, HPO4, ZnO4 tetrahedra and P2O7 groups leading to layers parallel to(110) interconnected with chainsrunning alonga. The open framework that results shows tunnels alonga and b where the rubidium atoms are located. 2002 Éditionsscientifiques et médicales Elsevier SAS. All rights reserved.

1. Introduction

Numerous oxovanadium phosphate hydrates MVPO’swith M as inorganic or organic cations have been syn-thesized during the last decade since the discovery of theefficient catalyst (VO)2(P2O7). When prepared under hy-drothermal conditions, these solids are fundamentally basedon the linking of elemental polyhedra (EP’s) such as pyra-mids VL5, octahedra VL6 and tetrahedra PL4 where L=O2−, OH−, F− or H2O and in contrast with the limited num-ber of EP’s, the obtained frameworks show a very importantvariability [1–3]. Terminal V=O (V4+, V5+), V· · ·(H2O)(V5+, V4+, V3+), P=O or P· · ·OH govern the dimension-ality of the solids as they are disrupting the connectiv-ity. Whether the number and/or the arrangement of thesedisrupting groups, one-dimensional, layered or tunnelledframeworks are obtained with a limited number of structuralbuilding units (SBU’s) based onµ2- and µ3-oxo bridges[1]. For the solids we are dealing with, i.e., oxovanadiumphosphate hydrates, theµ2-oxo links are widespread andhetero-condensation leads to V–O–P bridges while homo-condensation results in V–O–V and P–O–P links. Our re-cent works have shown that Zn2+ can replace disrupt-ing groups and the new solids NaZnVO(PO4)(HPO4) [4],

* Correspondence and reprints.E-mail address: jean-yves.pivan@ensc-rennes.fr (J.Y. Pivan).

MZn(H2O)(VO)2(PO4)2(H2PO4) [5] with M+ =K+, Rb+and Cs+ and (NH4)Zn(H2O)(VO)2(PO4)2(H2PO4) [6] havebeen described.

In this context, we describe herein the synthesis andthe crystal structure of a new zinc oxovanadium phosphateRb3Zn(VO)2(PO4)(HPO4)(P2O7) that contains simultane-ously PO3−

4 , HPO2−4 and P2O4−

7 species.

2. Experimental section

Synthesis. Mixtures of V2O5 (0.1535 g), Rb2CO3(0.500 g), 85% H3PO4 (1 ml), tetraethylammonium chlo-ride (1 g) and water (∼ 3.6 ml) were introduced togetherwith reducing Zn0 (0.10 g) in a Teflon acid digestion bomb(23 ml) then heated at different temperatures (180< T <

245◦C) for different times (24 h< t < 7 days). The fi-nal products were filtered off and dried in air and ap-peared either as mono- or multi-component phases depend-ing on the conditions used. So, V3+ containing phasessuch asα-RbV(HPO4)2 andβ-RbV(HPO4)2, previously re-ported by Haushalter [7], were obtained as roughly 50%–50% mixtures after hydrothermal treatments at 245◦C for7 days. Other experiments (24< reaction time<48 h) ledto the less reduced Rb∼ 5(VO)∼ 10(PO4)∼ 4(HPO4)∼ 8 andRb6(V2O3)2(VO)2(PO4)4(HP2–xVxO7) solids [8,9]. In caseof long reaction time, few curiously drop-like green “sin-

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234 E. Le Fur, J.Y. Pivan / Solid State Sciences 4 (2002) 233–238

gle crystals” of the title compound were frequently present.Attempts to obtain pure samples of this new phase were un-successful.

X-ray diffraction. Single crystals data were recorded atroom temperature on an Enraf–Nonius diffractometer with aCCD detector using MoKα radiation (graphite monochro-mated). The experiment was run using the software packageimplemented by Nonius. The intensity data collection wasperformed in theω–φ scanning mode with a crystal/detectordistance of 25 mm and COLLECT [10] was used to optimisethe goniometer and detector angular settings. The diffractionspots were measured with a high accuracy as indicated bythe statistical indicators (χ2 < 1) obtained with COLLECT.The set of data was scaled using SCALEPACK, Lorentz-polarization correction and peak integration were made withDENZO [10]. The main crystallographic features and con-ditions for structure analysis are listed in Table 1. Fromthe systematic absences, the only possible space group wasthe non-centrosymmetricP212121. Direct methods usingSIR97 [11] were used to obtain the starting structure modeland the refinements were made onF 2

o with SHELXL 97 [12].Successive difference Fourier maps lead to the entire struc-ture model (non-hydrogen atoms). At the end of refinement,anisotropic displacement and extinction parameters were al-lowed to vary and the residuals given in Table 1 resulted.The lack of∼ 0.77 electrostatic valence units (e.v.u.) forO15 clearly indicates the presence of an OH group at thissite instead of an oxygen atom and so, the true formula isRb3Zn(VO)2(PO4)(HPO4)(P2O7).

Table 1Crystal data and summary of data collection, structure solution andrefinement for Rb3Zn(VO)2(PO4)(HPO4)(P2O7)

Empirical formula Rb3Zn(VO)2(PO4)(HPO4)(P2O7)Color; habit green; ‘drops’Crystal system orthorhombicSpace group P212121 (No 19)Unit cell dimensions a = 7.0989(2) Å

b = 9.5374(2) Åc = 23.3016(8) Å

Volume V = 1577.6(2) Å3

Z 4Formula weight 3278.16 g·mol−1

Density (calc) 3.451 g·cm−3

Absorption coefficient 123.6 cm−1

Maximum 2θ 2θ � 76◦Data collected h: 0,+9

k: 0,+13l: 0,+32

Unique data after merging 2626Observed data (> 2.0σ(F2)) 2506Free parameters 245Flack parameter 0.0(1)Rint 0.022ResidualsR (F2 > 2.0σ(F2)) 0.033wR 0.066Min., max. (e Å−3) −1.39,+1.19G.o.f. 3.14

3. Results and discussion

The atomic coordinates are listed in Table 2. The struc-ture (Fig. 1) is based on the linking of vanadium octahe-dra with phosphorus and zinc tetrahedra. Fig. 2 shows theconnectivity for the assymetric unit. Both monophosphateand diphosphate species are present throughout the struc-ture that can be described as a vanadium phosphorus ox-ide framework (VPO) with zinc atoms making additionallinks. The framework VPO consists of layers [VOP2O7] par-allel to (1 1 0) connected throughµ2-oxo bridges to chains[VO(PO4)(HPO4)] that run alonga (Fig. 3). The diphos-phate species are located in the layers while only monophos-phate (PO4 and HPO4) are present along the chains. TheVO6 are isolated from each other in the layers while theyare corner connected with alternated bonds V=O· · ·V alongthe chains and the V–O–V bond angle at the shared oxygenO9, α = 134.89(3)◦. At this stage of assembling, a three-dimensional framework results (Fig. 3) that is made morerigid through the links provided by zinc atoms between onelayer and two chains (Fig. 1). As a result, 8-membered tun-nels with approximate areaS ∼ 5.6× 5.2 Å2 develop alonga that interconnect tunnels with smaller aperture runningalongb. The rubidium ions are inside the tunnels (Fig. 1).The vanadium atoms show the classical distorted octahedralcoordination with four equatorial bonds atd ∼ 2.008 Å, oneshort bond atd ∼ 1.628 Å characteristic of the vanadyl ionplus a longer distance at the opposite apex atd ∼ 2.179 Å.The vanadium V2 in the layer is connected to three diphos-phate and one monophosphate, the free apex of the V=Obond is oriented towards the centre of the tunnels alonga.On the contrary, the vanadium V1 in the chains shares itsequatorial oxygen atoms with two PO4 and two HPO4, thelatter two apices are part of “homo-nuclear” bondings be-tween adjacent VO6 octahedra. Different kinds of phosphatespecies are present in the structure as PO3−

4 , HPO2−4 and

P2O4−7 . The P–O bond lengths (dP–O = 1.53(3) Å) and O–

P–O bond angles (αO–P–O = 109(3)◦) are almost similarwhatever the nature of the phosphate species though somedifferences are normally visible associated with the pres-ence of hydrogen phosphate (bond P2–O17) or diphosphategroups (bridge P3–O15–P4). Every phosphate group con-nect throughµ2-oxo bridge to vanadium and zinc polyhedra.So, the PO3−

4 shares its four apices with three VO6 and oneZnO4, the HPO2−

4 shares three apices with two VO6 andone ZnO4, the latter apex O17 is directed towards the cen-tre of the tunnels alongb whereas the diphosphate connectto two VO6 and one ZnO4. The geometry of the ZnO4 tetra-hedron is quite regular withdZn–O = 1.932 Å and O–Zn–Obond anglesαO–Zn–O = 109.0◦ consistent with known data.Each Zn tetrahedron connects the planes [VOP2O7] to thechains [VO(PO4)(HPO4)] via µ2-oxo bridges Zn–O–P in-volving one PO3−

4 , one HPO2−4 and one P2O4−

7 . Accord-ing to Figs. 1 and 3, the ZnO4 makes the overall topologymore rigid. The rubidium atoms are surrounded by 7 (Rb1)or 10 oxygen atoms (Rb2 and Rb3) at distances in the range

E. Le Fur, J.Y. Pivan / Solid State Sciences 4 (2002) 233–238 235

Table 2Atomic coordinates and equivalent isotropic displacement coefficientsU(eq) (Å2 ×100) for Rb3Zn(VO)2(PO4)(HPO4)(P2O7)

Atoms x y z U(eq)

V1 0.0430(1) 0.7454(1) 0.99106(5) 1.02(2)V2 0.7752(1) 0.52114(8) 0.75576(4) 1.02(2)Zn 0.77986(9) 0.22126(6) 0.90180(3) 1.25(1)P1 0.7411(2) 0.6109(1) 0.90231(7) 0.87(3)P2 0.7819(2) 0.0252(1) 0.99561(7) 0.93(3)P3 0.5018(2) 0.7463(1) 0.69548(7) 0.89(3)P4 0.9162(2) 0.7965(1) 0.69503(7) 1.01(3)O1 0.9263(4) 0.6995(4) 0.7464(2) 1.30(9)O2 0.9898(5) 0.9407(4) 0.7084(2) 1.60(9)O3 0.9330(5) 0.6735(4) 0.9185(2) 1.47(9)O4 0.0835(5) 0.7946(4) 0.0732(2) 1.22(9)O5 0.9387(5) 0.9357(4) 0.9698(2) 1.26(9)O6 0.7178(6) 0.6073(4) 0.8380(2) 1.83(9)O7 0.0916(5) 0.5438(4) 0.0118(2) 1.44(9)O8 0.3729(5) 0.8533(4) 0.7198(2) 2.6(1)O9 0.2565(5) 0.7848(3) 0.9712(2) 1.33(8)O10 0.7121(6) 0.4636(4) 0.9281(2) 1.63(9)O11 0.5671(6) 0.1920(4) 0.8619(2) 1.91(9)O12 0.5386(5) 0.6278(4) 0.7373(2) 1.49(9)O13 0.7862(5) 0.1726(3) 0.9716(2) 1.58(9)O14 0.0040(5) 0.2344(4) 0.8595(2) 2.1(1)O15 0.6946(5) 0.8246(4) 0.6825(2) 2.4(1)O16 0.8094(6) 0.4630(4) 0.6910(2) 2.6(1)O17 0.8218(5) 0.0412(4) 0.0625(2) 1.55(9)Rb1 0.26985(6) 0.10223(6) 0.94212(3) 2.02(1)Rb2 0.26362(8) 0.65975(6) 0.83811(3) 2.20(1)Rb3 0.7794(1) 0.92493(6) 0.83670(3) 3.60(2)

2.884(2)–3.346(2) Å. The calculated valence sums [13] are,respectively,Σs = 1.02, 1.02 and 0.82 for Rb1, Rb2 andRb3. Similarly, the interatomic distances reported in Table 3lead toΣs = 4.04, 4.10 for V1 and V2,Σs = 5.03, 5.00,5.15, 4.98 for P1, P2, P3, P4 andΣs = 2.16 for Zn that giveformal oxidation states in good agreement with the expectedvalues for V4+, P5+ and Zn2+.

The structure of Rb3Zn(VO)2(PO4)(HPO4)(P2O7) is anew example of phases MZnVPO’s. It is worthwhile not-ing that the framework of these MZnVPO’s is built upfrom vanadium phosphorus oxide structural building unitsalready found for pure MVPO’s that are linked togetherby zinc atoms in tetrahedral coordination. So, the two-dimensional structure of Na3VO(PO4)(HPO4) [14], closelyrelated to the layered oxovanadium phosphate hydratesM(VOPO4)24H2O, transforms into the three-dimensionalNaZnVO(PO4)(HPO4) for ZnO4 tetrahedra connect togetheradjacent layers [VO(PO4)(HPO4)] through µ2- and µ3-oxo bridges. In the same manner, the 2D structure of thehemihydrate VO(HPO4)0.5H2O [15] transforms into the3D structures MZn(H2O)(VO)2(PO4)2(H2PO4) (M =K+,Rb+, Cs+, NH+

4 ) for Zn(H2O)O3 and H2PO4 tetrahedra en-sure additional connectivity between the layers [5,6]. Birc-sack et al. [16] reported recently on another representa-tive of MZnVPO’s, namely (NH4)3Zn2V(PO4)2(HPO4)2,where the unique 1D chains [V(PO4)2(HPO4)2] are linkedtogether by tetrahedral zinc atoms to form the 3D frame-work [Zn2V(PO4)2(HPO4)2]. To conclude, the fact that

Fig. 1. The structure of Rb3Zn(VO)2(PO4)(HPO4)(P2O7) viewed along[100]. Black spheres are rubidium, grey ones are oxygen. V, P and Zn atomsare not shown for clarity. Hatched polyhedra: VO6, open polyhedra: ZnO4,light grey polyhedra: P2O7 and dark grey polyhedra: PO4/HPO4.

236 E. Le Fur, J.Y. Pivan / Solid State Sciences 4 (2002) 233–238

Fig. 2. Asymmetric unit for Rb3Zn(VO)2(PO4)(HPO4)(P2O7) showing theconnectivity. The thermal ellipsoids are drawn at the 95% level.

MZnVPO’s are obtained after a long reaction time (t > 1week), that MVPO’s and MZnVPO’s show the same vana-dium phosphorus oxide structural building units, brings tothe following comments: (i) the contribution of the Zn2+atoms to the building of the framework necessitates a thresh-old value of aqueous Zn2+ to be present into the reac-tor, (ii) Zn0 seemingly dissolves in water more slowly thanthe other reactants, (iii) the oxovanadium monomers reactpreferably with the phosphate species to achieve first a vana-dium phosphorus oxide framework VPO involving mainlyµ2-oxo bridges V–O–V, P–O–P or V–O–P, (iv) the self-assembly of the VPO framework generates tetrahedral voidsthat are well suited for the Zn2+ atoms inducing additionallinks and forming the final ZnVPO framework.

(a)

(b) (c)

Fig. 3. The vanadium phosphorus oxygen framework (VPO) of Rb3Zn(VO)2(PO4)(HPO4)(P2O7) showing the structural building units (SBU) (a). Views ofthe layer [VOP2O7] (b) and of the chain [VO(PO4)(HPO4)] (c).

E. Le Fur, J.Y. Pivan / Solid State Sciences 4 (2002) 233–238 237

Table 3Selected bond lengths (Å), bond angles (deg) with their standard deviation in brackets and bond valence sum values (Σs) for Rb3Zn(VO)2(PO4)(HPO4)(P2O7)

Distance AnglesV1 O9 1.629(4)

O3 1.984(4) 101.8(2)O4 1.990(4) 94.8(2) 163.1(2)O7 2.013(4) 97.4(2) 86.7(2) 88.2(2)O5 2.021(4) 93.7(2) 87.5(2) 94.4(2) 168.3(1)O9 2.234(4) 171.4(1) 86.1(2) 77.5(2) 86.5(2) 83.0(2)

Σs(V1)= 4.04

V2 O16 1.627(4)O8 1.998(4) 94.0(2)O12 2.010(4) 95.7(2) 91.5(2)O2 2.018(4) 97.6(2) 90.7(2) 166.4(2)O1 2.023(4) 96.2(2) 169.6(2) 89.7(2) 85.7(2)O6 2.124(4) 176.1(2) 87.3(2) 80.6(2) 86.1(2) 82.7(2)

Σs(V2)= 4.1

P1 O6 1.508(4)O3 1.534(4) 110.5(2)O10 1.542(4) 110.6(2) 112.2(2)O4 1.546(4) 107.5(2) 108.9(2) 106.9(2)

Σs(P1)= 5.03

P2 O7 1.512(4)O13 1.513(4) 112.4(2)O5 1.527(4) 111.3(2) 111.1(2)O17 1.592(4) 108.2(2) 105.6(2) 108.0(2)

Σs(P2)= 5.00

P3 O8 1.483(4)O11 1.515(4) 111.9(2)O12 1.515(4) 111.9(2) 111.6(2)O15 1.588(4) 106.3(2) 105.7(2) 108.9(2)

Σs(P3)= 5.15

P4 O2 1.504(4)O14 1.512(4) 113.7(2)O1 1.515(4) 112.2(2) 114.0(2)O15 1.622(4) 102.8(2) 106.1(2) 106.8(2)

Σs(P4)= 4.99

Zn O10 1.906(4)O14 1.924(4) 125.8(2)O13 1.930(4) 103.0(2) 106.7(2)O11 1.967(4) 110.7(2) 107.0(2) 100.6(2)

Σs(Zn) = 2.16

Rb1 O7 2.882(4)O5 2.908(4)O13 2.943(4)O11 2.946(4)O14 2.973(4)O9 3.104(3)O10 3.114(4)O17 3.416(4)O16 3.418(5)

Rb2 O2 2.960(4)O3 3.007(4)O16 3.018(4)O17 3.047(4)O12 3.069(4)O4 3.101(4)O1 3.232(4)O15 3.245(4)O6 3.264(4)

238 E. Le Fur, J.Y. Pivan / Solid State Sciences 4 (2002) 233–238

Table 3 (Continued)

Distance

Rb3 O16 3.013(5)O11 3.016(4)O6 3.064(4)O1 3.185(4)O3 3.253(4)O4 3.273(4)O5 3.302(4)O2 3.344(4)O14 3.398(4)

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