~~ Layered structures of hydrated vanadium oxides. Part 5:-Single-crystal structure of RbJZ05 and phase changes of rubidium intercalate Takeshi Yao,a Yoshio Oka*band Naoichi Yamamotoc "Division of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 606, Japan bDepartment of Natural Environment Sciences, Faculty of Integrated Human Studies, Kyoto University, Kyoto 606, Japan 'Graduate School of Human and Environmental Studies, Kyoto University, Kyoto 606, Japan Rbo.,V205, an anhydrous phase of the rubidium intercalate, has been synthesized in hydrothermal VO(OH),-RbCl system. It crystallizes in the monoclinic system C2/m: a = 11.596(2), b = 3.6908(9), c = 9.723(1)A, fi = 100.93( 1)" and 2 = 4.A single-crystal study (R/R,= 0.069/0.079) revealed that the V205 layers are isostructural with those of K0.5V205 in Part 4 which consist of zigzag chains of edge-sharing VO, octahedra.The interlayer Rb atom forms an RbOs rectangudar prism with the apical oxygens of the VO, octahedra in contrast to the KO7coordination in Ko.,V405. Rb0.,V20, with 9.55 A spacing was oxidized by hydrogen peroxide to a hydrated phase, Rbo~,V205~0.8H20 with 10.85 A spacing. This compound was reduced by rubidium iodide to a less hydrated phase, Rbo~,V205~0.5H20 with 10.41 A spacing, rather than to Rb0.,V20,. Interlayer sites for monovalent cations in anhydrous phases are suggested to be correlated with cationic sizes and contents. ., phase vanadium bronzes such as 6-Ag,V205 In Part 4' we reported the crystal structure of the anhydrous potassium intercalate (K intercalate) Ko.sV205, where our previously proposed model of the double-sheet type V20, layer2v3 was proved to be the same as the V205 layer of the 6 Phase conver- sions between hydrated and anhydrous phases were also studied for the K intercalate.' The anhydrous phase Ko.sVz05 is changed into the hydrated phase K0.,V2O5-H2O by the oxidation of the V205 layer or, in other words, by the partial extraction of K+ ions.The reverse process occurs by the reduction of the V205 layer or by the uptake of K+ ions using a potassium iodide solution. This suggests that the hydration process depends strongly on the interlayer cation content. For further understanding of the structures and reactivities of the alkali-metal intercalates we need more information about other intercalates, especially those containing larger cations.In the present study we have achieved the hydrothermal synthesis of single crystals of the rubidium intercalate (Rb intercalate) in an anhydrous phase, Rb0.5V205. The structural analysis dis- closed an interlayer cationic site which was different from that found in K0.5V205. The phase changes of the Rb intercalate were also found to be somewhat different from those of the K intercalate. Experimenta1 Sample preparation The anhydrous and hydrated Rb intercalates were prepared using hydrothermal systems of VO(OH),-RbCl and VOS0,-Rb2S04, respectively. The preparation methods and sample characterization were essentially the same as those used in Part 4 for the K intercalate.' In brief, a suspension of 0.25-0.30 g VO(OH)2 powder in RbCl solution (80 ml, 0.1 mol 1-I) or a solution of VOSO, and Rb2S0, (80 ml, V and Rb each 0.015mol I-') was sealed in a Pyrex ampoule and was treated in an autoclave at 220-280°C for 24-48 h.The com- positions of the anhydrous and hydrated phases were Rb0.48(1)V205and Rbo~30~l~V205-0.8H20,respectively, and therefore they were formulated as Rbo.,V20, and t Part 4 = ref. 1. Rb0.,V2O, .0.8H20, respectively. When treated at 280 "C, single crystals of the anhydrous phases were obtained which exhibited a thin plate-like shape. Powder X-ray diffraction patterns were recorded by using monochromated Cu-Ka radiation.Layer spacings of the layered phases were calculattd from diffraction angles of 001 reflections to an error of 0.01 A. Single-crystal structure determination Data collection was performed on a Rigaku AFC-7R diffractometer using Mo-Ka radiation. The crystallographic and experimental parameters are listed in Table 1. The mono- clinic space group C2/m was chosen and the lattice parameters were determined from 22 reflections of 21.2 < 28/degrees < 27.1. The intensity data with I >3o(I) were used in the structural analysis. An empirical absorption correction of the $-scan method was applied resulting in min./max. transmission fac- tors = 0.53/1.00. The structural analysis was performed by using the TEXSAN software package.' An initial model based on the 6-phase V205 layer of Part 4' was applied successfully to determine the V and 0 atomic sites and subsequently the Rb atom was located in a differential Fourier map.The occupancy of Rb site was determined as 0.956(8) leading to x=0.478(4) Table 1 Crystallographic data and experimental parameters for Rbo 5VP5 composition crystal dimensions/mm3 sp$ce group 44 bI4 CIA Pltegrees VIA3 Z DJg cmP3 scan technique scan width Awldegrees maximum 28ldegrees no. of reflections (I >O) no. of reflections [Z > 3o(I)] no. of variables absorption correction RIRW Rbo 48V205 0.25 x 0.15 x 0.01 C2/m 11.596(2) 3.6908( 9) 9.723( 1) lOo.93( I) 408.6(1 ) 4 3.651 28-1.21+0.30 tan 8 80 1451 857 49 I) scan 0.069/0.079 J.Muter. Chem., 1996, 6(7), 1195-1198 1195 in Rb,V205, in good agreement with x =0.48( 1) determined by chemical analysis; full occupancy gives a stoichiometric composition of Rbo,5Vz05. The structure refinements finally led to RIR, =0.069/0.079. Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC). See Information for Authors, J. Mater. Chem., 1996, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 1145/5. Results and Discussion Crystal structure of Rbo.sVz05 The crystal structure of Rbo,,V205 is depicted in Fig. 1.Selected bond distances for the V-0 and Rb-0 coordination polyhedra and V-V distances are listed in Table 2. The VZO, Fig. 1 Crystal structure of Rb,,sV20s viewed along the 6 axis. Rb and V atoms positioned at y=O and 0.5 are indicated by full and empty circles, respectively. Table 2 Selected bond distances/A in Rbo,SV,Os V( 1)06 octahedron V( 1 )-O( 1)a,b 1.906(2) V(1)-0(2) 2.049(9) V( 1)-0(3)e 1.800(9) V(l)-0(3)d 2.388(9) V( 1)-0(4) 1.61(1) V(2)--0(1) 1.97(1) V(2)06 octahedron V(2)-0(2)'sf 1.914(2) V(2)-0(2)d 2.57(1) V(2)-0(3) 1.840(9) V(1)-0(5) 1.61( 1) Rb-0(4)',fJ,h 2.934(7) RbO, rectangular prism Rb-O(5)".bsis's 2.954(8) metal-metal V( 1)-V(2Y,b 2.977( 3) Symmetry codes: "x-4, -y-$, z; "-4, -y+), z; 'x-1, y, z; d-x+1, -y, -z; ex++, -y+& 2; fx++, -y-4, 2.; Z-Xf), y-4, z+l; *-x++, --y+), z+l; l-x+ j, -y-& z+l; '-x+ j, -y++, z+ 1.\ a Fig. 2 RbO, rectangular prism coordination layers of the double-sheet typezs3 consist of zigzag chains of edge-sharing V( 1)06and V(2)06 octahedra running along the b axis, which are isostructural with those of Ko.sVz05 in Part 4.' As shown in Fig. 2, the interlayer Rb atom in an equatorial plane at z=OS is surrounded by, eight apical oxygevs of V06 octahedra [0(4) x 4 at 2.934 A, O(5) x 4 at 2.954 41 forming an Rb08 rectangular prism (3.081, 3.691, 3.399A along the a, b and c axes, respectively). This type of coordination is formed as a result of the relative location of adjacent Vz05 layers expressed by the monoclinic angle b= 100.93'.In the case of KO,~VZO~,~ the interlayer K atom is coordinated by seven apical oxygens, i.e. four oxygens of one Vz05 layer and three oxygens of the opposite layer in the manner of a KO, monocapped trigonal prism. The K atom is attracted to the four-oxygen side and consequently shifts slightly from an equatorial plane to z=O.476. This type of coordination corresponds to the monoclinic angle ,B =92.24' (or 87.76' relative to the p value of Rbo,,V205). There are two main types of A-0 coordination for monovalent At ions in A,V205, namely, A08 rectangular prism and A07 monocapped trigonal prism. Table 3 presents the relationship between the ionic radius of A' and the A-0 coordination for isomorphous A,Vz05 (x 0.5) compounds.There is a clear boundary at the size of K+ ion, i.e. A07 for A+ smaller than Kt and A08 for A' larger than K'; both types of coordination are found in polymorphs of Ko,,VzO, (Table 3). Note that the top member, cu0,85vzo5,6 has different types of coordination, i.e. A06 octahedra and A04 rectangular planes. Note that Strobel13 reported a v'-phase RbO,,V,0, synthe- sized by the cathodic reduction of the reaction products of Rb2C03 and VZO,. The compound crystallizes in the mono: clinic system C2/m with a= 11.63(4), b=3.664(8), c=9.75(3) A and p= 101.2( 5). Although its structure remains undetermined, it is quite possible that V'-R~~,~V,O~ is the same as Rbo,,V20,. Galy14 sorted the layered bronzes A,V205 into several groups where V'-R~~,~V~O~ is grouped into the v phase together with A=Ca, K and NH4 and therefore Rb0,,V205 should be designated v-RbO,,V,O5. Among the v-phase members, Table3 Ionic radius" (R,) of A+ ion, layer spacing (dWl), space group (SG), monoclinic angle (B) and coordination number (CN) of A for A,V205 with monovalent A ions ~~~ ~ _____~~ A,V*OS R, of A+/,& dWJA SG /?/degrees CN of A ref.c~o.ssv2os 0.96 8.24 Cm 111.804:6' 6 Na0.56V205 1.02 8.92 C2/m 90.91 7 7 A&.68V205 1.12 8.74 C2/m 90.48 7 4 KOSV2OS 1.38 9.50 C2/m 92.24 7 1 Ko.5V20sb 1.38 9.32 Cmcm 90 Xf 89 RbOSVZOS 1.49 9.5s C2/m 100.93 X this work T10.,,VzO,' 1.50 9.46 C2/m 100.90 8 10 "Taken from ref. 11 for Na', Ag', K+, Rb', T1' and ref. 12 for Cu'. bOrthorhombic system.'Analysed from powder X-ray diffraction data. dRectangular plane. 'Octahedron. /Ref. 9 gives additional coordination of KO6 trigonal prism for 20% of the K atoms, 1196 J. Muter. Chem., 1996, 6(7), 1195-1198 Ca0.,V2O5 with a divalent cation is the only one to have been characterized by a single-crystal study.15 It was revealed that two-thirds of the Ca atoms form a CaO, trigonal prism and the rest form a CaO, rectangular prism. This cation distri- bution over the interlayer sites is somewhat different from those observed for A+ cations in other v-phas? members (Table 3). It is presumed that the Ca2+ ion (1.00 A radius"), being smaller than the K+ ion, should prefer CaO, c?ordi- nation which determines both the layer spacing of 9.072 A and the monoclinic angle of 101.87", and the rectangular prism site which is formed concomitantly is occupied to some extent.In fact, the layer spacing of Ca0.,V2O5 is rather smaller than those of the other v-phase members of A+ cations (Table 3). On the other hand, in Rbo.5V205 the larger Rb+ ion occupies exclusively RbO, sites resulting in a phase similar to Cao.,V205; the Rb+ ion must be too large to occupy the trigonal-prism site and in fact the trigonal-prism site was proved to be vacant in this study. Rb0.5V205 is the first example of a single-crystal structure for a v phase with A+ cations, and it is found to be isostructural with T10.48V205 which was characterized by the X-ray Rietvelt method." Hydrated and anhydrous phases of the Rb intercalate Phase changes caused by redox reactions were examined for the Rb intercalate in a similar manner to that described in Part 4 for the K intercalate.' The results are shown in Fig.3 by the changes in the X-ray diffraction patterns. The anhydrous phase Rbo5V205 was oxidized by soaking in a hydrogen peroxide solution, and was transformed into a hydrated phase accompapied by an expansion of the layer spacing from 9.55 to 10.85 A [Fig. 3(u)]. This hydrated phase is formulated as Rbo~3V205-0.8H20,and it seems to be the same as the phase obtained from the hydrothermal VOS04-Rb2S04 system.2,16 Next the hydrated phase Rbo.3V205.0.8H20 of the VOS04-Rb2S04 system was reduced by soaking in a rubidium iodide solution, leading to another hydrated phase, Rb,V20, .nH20 (xz 0.4, n z0.5) [Fig.3(b)], with a contraction of the layer spacing from 10.85 to 10.41 A. Note that the Rb interylate shows two more hydrated phases with 10.70 and 10.15 A spacings which appeared in the VO(OH),-RbCl system but have not been characterized yet because no single- phase sample was obtained. This is not the case for the K intercalate, which has one hydrated phase. The oxidation process leading to RbO.,V2O5.O.8H2O is parallel to that of the K intercalate' but the reduction process stops at Rbo.4V205*0.5H20,part of the way to Rb0.5V205, in contrast to that of the K intercalate which leads to the ultimate phase K0.5V205-' As reported in Part 1,2 the anhydrous phase Rbo.3V205 was obtained by heating Rbo~,V2O5.O.8H20 to 150°C; it shows 9.80 A spacing which is significantly larger than the 9.55 A spacing found for Rb0.,V2O5, and it returns immediately to Rb0.,V2O5.0.8H2O when cooled in air.The difference in layer spacing must be attributed to the difference in Rb-0 coordi-nation, namely RbO, for Rb0.3V205 and RbO, for Rb0.5V205, for the following reason. As reported previously,'6 the layer spacings of Ao.3V205 for A=Na, K, Rb and Cs derived from A0.3V205*nH20increase linearly with the ionic radii of the A+ ions, which suggests the same type of A-0 coordination for all A0.3V205 compounds, particularly for K0.3V205 and Rb0,,V2O5. Ko.3V205 must havc the AO, coordination judging from the layer !pacing (9.49A) which is equal to that of Ko.54, 205(9.50 A),' and consequently AO, coordination is expefted in Rbo.3V205. In fact, the orthorhombic KO.~V&)~ with the AO, coordination exhibiots a spacing of 9.32 which is smaller than that of 9.50 A for K0.5V205 with A0, coordination (Table 3); this cFrresponds to the relatio!ship between the spacings of 9.55 A for Rbo.,V205 and 9.80 A for 001 003 treated in a hydrogen peroxide solution J C 002 I\ c 004 005 A I I I I I I I I I I I 10 20 30 40 50 001 (b) 004 005 002 Fig.3 Phase changes of the Rb intercalate demonstrated by the changes in X-ray diffraction patterns: (a) from Rbo.,V205 to Rbo.3V205-0.8H20formed in 3% hydrogen peroxide solution at room temperature for 3 min; (b) from Rb0,,V2O5.0.8H20 to Rbo,V205~0.5H20 formed in 0.1 mol dm-3 rubidium iodide solution at 85 "C for 28 h Rb0.3V205.The phase changes of the Rb intercalate are summarized in Fig. 4. Conclusion The structural and phase changes of the Rb intercalate have been investigated and the results are compared with those for the K intercalate in Part 4.' The anhydrous phase Rb0.,V2O5 adopts a structure related to that of K0.5V205, but the inter- stitial Rb site has Rb0, coordination, different from the KO, coordination. It is considered that the A-0 coordination in A0.5V205 changes from A07 to AOs with increasing size of the A+ ion and the boundary is at A =K. The phase conversion J. Muter. Chem., 1996, 6(7), 1195-1198 1197 4 dehydration1 Fig.4 Diagram of the phase relation for the hydrated and anhydrous phases of the Rb intercalate into the hydrated phase Rbo3V205 0 8H20was achieved by oxidizing the V205 layer However, the reverse process from RbO3V2O508H20 led to a less hydrated phase, Rb, 4V205 0 5H20,instead of Rb, 5v205 The Rb-0 coordi-nation of the anhydrous phase changes with the Rb content, namely Rb08 for RbO5V2O5 and Rb07 for Rb,,V205 The Rb intercalate consequently exhibits various layer spacings, depending more strongly on the Rb content and on the extent of hydration than the K intercalate The present work is supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan References 1 Y Oka, T Yao and N Yamamoto, J Muter Chem, 1995,5,1423 2 T Yao, Y Oka and N Yamamoto, J Muter Chem , 1992,2,331 3 T Yao, Y Oka and N Yamamoto, J Muter Chem , 1992,2,337 4 S Anderson, Acta Chem Scand, 1965,19, 1361 5 TEXSAN Crystal Structure Analysis Package, Molecular Structure Corp ,The Woodland, TX, 1985,1992 6 J Galy, D Lavaud, A Casalot and P Hagenmuller, J Solid State Chem, 1970,2,531 7 Y Kanke, K Kato, E Takayama-Muromachi and M Isobe, Acta Crystallogr Sect C, 1990,46,536 8 Y Kanke, K Kato, E Takayama-Muromachi and M Isobe, Acta Crystallogr Sect C, 1990,46, 1590 9 J-M Savariault and J Galy, J Solid State Chem ,1992, 101, 119 10 M Ganne, A Jouanneaux, M Trournoux and A LeBail, J Solid State Chem ,1992,97,186 11 R D Shannon and C T Prewitt, Acta Crystallogr Sect B, 1969, 25,925 12 L H Ahrens, Geochim Cosmochim Acta, 1952,2, 155 13 R Strobel, J Solid State Chem ,1987,66,95 14 J Galy, J Solid State Chem , 1992, 100,229 15 A Kutoglu, Z Kristallogr ,1983, 162,263 16 Y Oka, T Yao and N Yamamoto, Seramikkusu Ronbunshi (J Ceram SOC Jpn ),1990,98, 1365 Paper 6/00349D, Received 16th January, 1996 1198 J Muter Chem, 1996, 6(7), 1195-1198