J. MATER. CHEM., 1994,4( 121, 1889-1892 Two New Diphosphates with SrV,(P,O,), Structure: Mercury and Lead Phases S. Boudin, A. Grandin, A. Leclaire,” M. M. Bore1 and B. Raveau Laboratoire CRISMAT, ISMRA et Universite de Caen Bd.du Marechal Juin, 14050-Caen Cedex, France Two new diphosphates of the AV2(P207)2series involving a trans configuration of the bidentate P207groups have been synthesized for A =Hg or Pb. Their structure, determined from a single-crystal X-ray diffraction study is similar to that of the Sr-phase. They crystallize in the Pi space group, 2 = 1,u =4.848(1) A, b =6.892(1)A, c =8.077(2) A, CI =92.65(1)’,b =93.26(1)”,7 =106.23(1)”, for the Hg phase and a =4.804(1) A, b =7.1 13(1) A, c =7.898(2) A, x =89.78(1)”, ,!I=92.62(1)”, ;1=106.10(2)“, for the Pb phase.The crystal structures, solved by the heavy-atom method, were refined. The final agreement factors are R=0.027 and 0.033 for the Hg and Pb phases, respectively. A comparison with the other isotypic members of this series A =Sr, Cd and Na,MoP,O, (0.25 <x <0.50) is presented. The great similarity between the lead and strontium phases is shown, demonstrating the absence of a lone-pair effect of Pb” in this structure. The particular behaviour of the Hg phase is emphasized, due to the ability of this element to adopt the dumbbell (or 2+4) coordination; the strong covalent character of Hg” induces a significant distortion of the PO4 tetrahedra, rarely observed to date in transition-metal phosphates. The studies performed on V”’ diphosphates with the general pounds are isotypic of the mixed valent molybdenum diphos- formula AV,( P207),allow two different structural types to phate Na,MoP,O, (0.25dxd0.50, x =0.30? x =0~0~~).The be distinguished according to the nature of the divalent recent synthesis of the cadmium diphosphate CdV2( P,0,)26 cation A.For a large A cation, like barium, the [V2P401,], confirms the great flexibility of this [V2P2014]m host lattice. framework consists of VO, octahedra linked to two bidentate In fact, the stability of this second structural form seems to P207 groups in a cis configuration [Fig. l(a)] so that be governed by the ability of the ‘interpolated’ cations (sodium, BaV,( P207),’ exhibits tunnels where barium cations are strontium, calcium or cadmium) to adopt a more or less located.This kind of framework is very stable. It was observed distorted octahedral coordination. In this respect, the study for the first time for BaTi,(P207)22 and has also been seen of the behaviour of Hg” and Pb” in these phosphates is of for BaMo,( P207),., interest, since the first species is known for its ‘2+4‘ coordi-When the size of the bivalent cation is smaller, the nation, whereas the second is intermediate in size between [V2P201,], framework is also built up from V06 octahedra strontium and barium and often exhibits a lone-pair effect. and diphosphate groups, forming tunnels. However, in this We report here the synthesis and single-crystal study of two case the two P207 groups linked to one V06 octahedron are new isotypic diphosphates, HgV,( P207),and PbV,( P207)2 in a trans configuration [Fig. l(b)].This was shown by Hwu with a trans configuration of the P207 groups. and Willis, for SrV,( P207),. These authors could also prepare the isotypic phosphate CaV,( P,0,)2.4 In fact these two com- Experimental The crystal growth of the title compounds was performed in two steps. An intermediate mixture, with the compo-sition ‘V2P4015’ and ‘Pb2V1,2P4014’ for the Hg and the Pb phases, respectively, was first prepared, starting from the appropriate molar ratios of V205, H(NH4),P04 and Pb(CH3CO2)-2.3H2O. The ‘V2P4015’ mixture was he.ited at 653 K, and the ‘PbV1.2P4014’ mixture was heated at 773 K for 2 h in order to eliminate CO,, NH,, H,O and CH,.An appropriate amount of HgO and V was added to the ‘V2P4015’ mixture in a second step in order to obtain the ‘Hg,V,P4OI7’ composition. In the same way, 0.8 mol of V was added per ‘PbV,,,P,O,~ formula unit to reach the composition PbV2P4OI4. These mixtures were placed in an alumina crucible and heated in an evacuated silica ampoule for 24 h at 1073 and 1373 K, respectively. They were cooled to 1073 K at a rate of 1K h-’ and to 873 K at a rate of 0.5 K h-’, respectively, and finally quenched to room tem- perature. Under these conditions yellow-green crystals of the mercury phosphate and green crystals of the lead phase were extracted. Their composition, HgV2( P,0,)2 and PbV2( P207),, was confirmed by microprobe analysis. The lead diphosphate PbV,( P207),could be synthesized as a pure phase in the form of polycristalline samples by a similar method.It was heated at 1223 K for 24 h and quenched Fig. 1 VP,O1, unit with two bidentate PzO, groups in (a) cis to room temperature. The X-ray powder diffractogram configuration, (b) trans configuration (Table 1) was recorded on a Philips diffractometer with J. MATER. CHEM., 1994, VOL. 4 Table 1 Intereticular distances in PbV,( P,O,), Table 2 Positional parameters and their estimated standard deviations h k 1 dob,/A d,,,,/A I h k 1 dobslA dcalc/A I 00 1 7.8588 7.8890 33 220 2.2192 2.2176 8 ~~ ~ ~ 0 10 0 1 1 1 0 0 1 T o 1 oi 1 Ti I T I 1 1 i 1 12 12 i 1 2 0 021 1 0 2 6.8229 5.1276 4.6071 4.4381 4.0552 3.9295 3.8095 3.1802 3.0016 2.9918 3.2020 3.1295 3.0641 6.8334 5.1418 4.6108 4.435 1 4.0637 3.93 15 3.8038 3.2031 3.1743 3.1248 3.0685 3.0057 2.9925 16 5 30 12 13 8 33 30 24 34 8 100 41 201 2'21 113 2i2 122 113 20-2 123 132 032 202 22 2 014 2.1863 2.1556 2.1201 2.0907 2.0457 2.04 13 2.0357 2.0061 1.9818 1.9640 1.9516 1.9015 1.8878 2.1857 2.1566 2.1224 2.0932 2.0469 2.0440 2.0319 2.0074 1.9831 1.9647 1.9513 1.9019 1.8903 7 5 2 6 9 12 12 5 10 5 2 4 2 Hg V(1) V(2) 0 0 0.5 0.38 1 7( 1) 0.9714(1') 0.1755(4) -0.1218(4) -0.3752(4) 0.1 322(4) 0.7310(4) 0.4739( 4) 0.2071(4) 0 0 0.5 0.75873(8) 0.35984(8) 0.18 12(3) 0.3041( 3) 0.4425(3) 0.7447( 3) 0.5318(3) -0.1107(3) -0.1916( 3) 0.5 0 0.5 0.80628(8) 0.74191(8) -0.1913( 3) -0.1 584( 3) -0.0624( 3) 0.5893(3) 0.6837( 3) 0.6283(3) 0.8472( 3) 1.5 15( 2) 0.395( 6) 0.399( 6) 0.463 (7 0.425( 7 0.77(2) 0.82(2) 0.78(2) 0.77(2) 0.86(2) 0.77( 2) 0.71(2) 10 2 2.9358 2.9309 7 130 1.8481 1.8486 6 1 T 2 00 3 2.8884 2.6272 2.8925 2.6297 26 13 231 123 1.8418 1.8154 1.8401 1.8171 9 3 atom X 4' 7 B,,lA2 0 2 -2 0 2 2 1 12 12 2 12 2 12 0 21 o 121 12 1 2 00 2.5929 2.5691 2.5288 2.5127 2.4568 2.4404 2.3939 2.3470 2.3119 2.3051 2.5944 2.5709 2.5309 2.5 158 2.4583 2.4403 2.3950 2.3520 2.31 11 2.3054 8 11 5 4 5 11 4 3 13 14 131 if4 212 133 113 033 040 132 114 124 1.7894 1.7758 1.7675 1.7472 1.7358 1.7133 1.7080 1.6904 1.6789 1.6604 1.7895 1.7768 1.7679 1.7488 1.7366 1.7139 1.7083 1.6909 1.6790 1.6620 3 4 6 3 3 4 4 5 2 2 0 0 0.5 0.38 17(4) 0.9728( 4) -0.088( 1) 0.125( 1) 0.178( 1) -0.376( 1) 0 0 0.5 0.7706(2) 0.3842( 2) 0.2023( 7) 0.3514( 7) -0.0956(7) -0.1764(7) 0.5 0 0.5 0.7978(2) 0.7490(2) -0.2047(7) -0.1474(7) -0.0709( 7) 0.5892( 7) 1.503( 7) 0.47( 2) 0.50(2) 0.49( 3) 0.48(3) 0.89(8) 0.92(8) 0.98( 9) 0.88(8) 0.703( 1) 0.4457( 7) 0.7066( 7) 0.97(8)0 3 0 2.2765 2.2778 2 132 1.6096 1.6098 3 0.474(1) 0.7565( 7) 0.6163(6) 0.79(8)2 i 1 2.2633 2.2636 3 240 1.6012 1.6015 3 10 3 2.2401 2.24 5 22'2 1.5867 1.5871 1 0.197( 1) 0.5567( 6) 0.8519(6) 0.69(8) 1 i 3 2.2258 2.2246 8 042 1.5727 1.5729 4 Anisotropically refined atoms are given in the form of the isotropic equivalent displacement parameter defined as: Cu-Ka radiation and indexed in a triclinic cell, in agreement Be, =4/3 [Plla**+P22b*2+p33c*2+Plza* b* cos ;I*with the parameters obtained from the single-crystal study.Attempts to synthesize pure HgV,( P,O,), were unsuccessful +PI3a*b* cos P* +P2,b*c* cos a*]. using the previous experimental procedure; only the vanadium phosphate V( PO,), and metallic Hg were obtained as major products. The [V,P,O,,], framework of these two diphosphates is very similar to that previously described for SrV,( P,O,),,, Results and Discussion Na,MoP,O, (0.25 <x<0.50, x =0.30,5a x =0.5OSb) and CdV2(P20,),.6 A projection of the structure onto the (100) Two crystals of HgV,(P,O,), ad PbV2(P,0,), with dimen- plane (Fig. 2) shows that the latter can be described by the sions 0.116 mm x 0.077 mm x 0.051 mm and 0.026 mm x 0.026 mm x 0.026 mm, respectively, were selected for the struc- tural determination.The cell parameters were determined at 294 K from a least-squares refinement based upon 25 reflec-tions with 18"<0<25". The intensities were measured on a CAD-4 Enra!-Nonius diffractometer, using Mo-Ka radiation (i=0.71069 A) in the range -9 <h <9; -13 <k <13;0 <E <16, and, -9<h<9; -14<k<14; 0<1<15, for the Hg and Pb phases, respectively. Three reflections were periodically meas- ured in order to confirm that there were no significant vari- ations. A total of 4456 reflections for the Hg phase (4475 for the Pb phase) were collected. The structure determinations were carried out with 2725 reflections having I >341) for the Hg phase and 1205 for the Pb phase.The data were corrected for Lorentz and polarization effects. No absorption were per- formed and secondary extinction corrections were calculate? for the Hg ehase only. Th? crystal data are a =4.848( 1) A, h =6.892( 1) A, c =8.07'g2) A, a =92.65( l)", p =93.26( l)G,y 7 106.23( l)', Vo=258( 1) A3 for the Hg phase and a =4.804( 1) A, b =7.113( 1) A, c =7.898( 2) A, cc =89.78( 1)", p =92.62( l)G, y = 106.10(2)", V =259.0( 9) A3 for the Pb phase, triclinic Pi space group. The structures were solved by the heavy- atom method using the SDP chain program., The refinement of the atomic coordinates and the anisotropic thermal factors, listed in Table 2, led to R=0.027, R,=0.029 and R=0.033 and R,=0.036 for the Hg and Pb phases, respectively. Fig.2 Projection of the structure AM,(P,O,), slightly inclined to a J. MATER. CHEM., 1994, VOL. 4 stacking along b of [VP,O1l], mixed layers of V06 octahedra A second important feature of this study deals with the and PO, tetrahedra with [VO,], layers of VO, octahedra. distortion of the PO, tetrahedra in the Hg phase. Each P(2)This framework forms tunnels where the mercury and lead tetrahedron of this phas?, exhibits one abnormally long ions are located. P(2)-0(4) bond, of 1.58 A, in addition to that corresponding The examination of the interatomic distances (Table 3) to the bridging oxygen of the P207 group. This is easily shows the VO, octahedra of the two compounds are not very explained by the fact that O(4) is also linked to mercury, distorted. The amplitude of V( 1)-0 distances is slightly more forming a rather strongly covalent Hg-0 bond.importaqt for the Pb phase, wit! distances ranging from 1.94 It is worth comparing these structural distortions with to 2.07 A against 1.95 to 2.02 A for the Hg phase. On th,e those of the other isotypic phosphates of strontium, cadmium other hand, the V(2)-0 distances range from 1.93 to 2.10 A and sodium (Table4). Except for the Hg phase, all the for the Hg phase and are $ghtly more spread than those of compounds exhibit the same distortion of the PO4 tetra-the Pb phase (1.95-2.07 A). The most striking difference hedron, i.e. Lhree normal P-0 bonds ranging fromc 1.480(2) between the two structures is the coordination of mercury to 1.548(6)A, and a longer one of 1.572(2)-1.616(2) A charac-compared to lead.Lead exhibits a distorted octahe(ra1 coordi- teristic of the bridging oxygen of the diphosphate group. Thus, nation, Pb-0 distances ranging from 2.50 to 2.81 A (Table 3), mercury appears as one of the rare elements that is able to whereas mercury is characterized by its classical '2+4' coordi-distort the phosphate matrix. Considering the four vmadium nation, i,e. a dumbbell coordination with two oxygens located diphosphates AV2(P207),, one observes from the evolution at 2.09A, yith four additional oxygens much further away of the A-0 distances that the amplitude of the distortion of (2.79-2.93 A), forming a very flattened HgO, octahedron. the AO, octahedron is very similar for cadmium, strontium Table 3 Distances (/A)and angles (/degrees) in polyhedra HgV,( P207)2 structure PbV,( P,0,)3 structure V(1) 0(1) O(1') O(2) O(2') O(3) O(3') 0(1) O(1') O(2) O(2') O(3) O(3') O(I) 2.024(2) 4.028(3) 2.794(3) 2.902(3) 2.839(3) 2.780(3) 2.072(5) 4.144(8) 2.815(7) 2.907(8) 2.816(8) 2.864(8) O(1') 180.0(0) 2.024(2) 2.902(3) 2.794(3) 2.780(3) 2.839(3) 180.0(0) 2.072(5) 2.907(8) 2.815(8) 2.864(8) 2.816(8) O(2) 87.83(8) 92.17(8) 2.004(2) 4.009(3) 2.691(3) 2.897(3) 88.2(2) 91.9(2) 1.973(5) 3.945(8) 2.748(7) 2.788(8) O(2') 92.17(8) 87.83(8) lSO.O(O) 2.004(2) 2.897(3) 2.691( 3) 91.9( 2) 88.2(2) lSO.O(O) 1.973(5) 2.788( 8) 2.748(7) O(3) 91.22(8) 88.78(8) 85.77(8) 94.23(8) 1.949(2) 3.897(3) 89.0(2) 91.0(2) 89.2(2) 90.8(2) 1.942(6) 3.884(8) O(3') 88.78(8) 91.22(8) 94.23(8) 85.77(8) lSO.O(O) 1.949(2) 91.0(2) 89.0(2) 90.8(2) 89.2(2) 180.0(0) 1.942(6) V(2) O(4) O(4") O(5) O(5") O(6) O(6") V(2) O(4) O(4") O(5) O(5") O(6) O(6") O(4) 2.101(2) 4.202(3) 2.838(3) 2.869(3) 3.018(3) 2.745(3) O(4) 1.969(6) 3.937(8) 2.774(8) 2.766(8) 2.900(7) 2.818(8) O(4i) 180.0(0) 2.101(2) 2.869(3) 2.838(3) 2.745(3) 3.018(3) O(4") 180.0(0) 1.969(6) 2.766(8) 2.774(8) 2.818(8) 2.900(7) O(5) 89.38(9) 90.62(9) 1.931(2) 3.861(3) 2.751(3) 2.775(3) O(5) 90.2(2) 89.9(2) 1.949(5) 3.897(8) 2.794(7) 2.896(8) O(5") 90.62(9) 89.38(9) 180.0(0) 1.931(2) 2.775(3) 2.751(3) O(5") 89.9(2) 90.2(2) lSO.O(O) 1.949(5) 2.896(8) 2.794(7) O(6) 95.43(8) 84.57(8) 89.50(9) 90.50(9) 1.977(2) 3.954(3) O(6) 91.7(2) 88.3(2) 87.9(2) 92.1(2) 2.073(5) 4.147(8) O(6") 84.57(8) 95.43(8) 90.50(9) 89.50(9) lXO.O(O) 1.977(2) O(6") 88.3(2) 91.7(2) 92.1(2) 87.9(2) 180.0(0) 2.073(5) O(li") 1.521(2) 2.572(3) 2.474(3) 2.544(3) O(1'l') 1.527(6) 2.554(8) 2.486(8) 2 529(7) O(3lv) 117.1(1) 1.494(2) 2.546(3) 2.412(3) O(3"') 114.9(3) 1.502(6) 2.563(8) 2441(7) O(6) 108.0(1) 114.3( 1) 1.536(2) 2.528(3) O(6) 107.9(3) 114.3(3) 1.548(6) 2 542(7) O(7) 108.3( 1) 101.6(1) 106.6( 1) 1.616(2) O(7) 107.9( 3) 103.7( 3) 107.7( 3) 1.600(5) O(2') 1.480(2) 2.500(3) 2.491(3) 2.492(3) WV) 1.489(6) 2.463(8) 2.492(8) 2.509( 7) O(4") 109.3( 1) 1.584(2) 2.532(3) 2.495(3) 0(4") 108.7(3) 1.543(6) 2.527(8) 2.193(7) O(6) 113.7( 1) 110.6( 1) 1.495(2) 2.496(3) O(6).112.6(3) 111.9(3) 1.507(6) 2.512(8) 0(7"') 109.4(1) 104.5(1) 108.9(1) 1.572(2) O(7") 109.3(3) 105.6(3) 108.5(3) 1.587(5) Hg-0(4), 2.093(2)A; Hg-O(4"'"), 2.093(2) A; Hg-O( 1'1, Pb-0(4], 2.506(5) A; Pb-0(4"I1:), 2.506(5) A; Pb-O( 1'1,2.796(2) A; Hg-O(J"'), 2.796(2) A; Hg-0(6"), 2.939(2) A, 2.605(5) A; Pb-O(~"'), 2.605(5) A; Pb-O(6"), 2.817(5) A,Hg-O(6'"), 2.939(2) A.Pb-0(6'"), 2.817(5) A. Symmetry codes: -7i -x -y ii 1-x 1-y 1 -z ... 111 x l+Y lsz iv l+x 1+y l+z v l+x 4' 1+z vi l+x y l+z vii x Y z+l ... Vlll -x -Y 1-z ix x-1 y-1 Z J. MATER. CHEM., 1994, VOL. 4 Table 4 Comparison of the interatomic distances in the diphosphates AV,( PZO7),and Na,MoP,O, compounds CdV,(P,O,), HgV,(P,O7)2 SrV,(P,O,), PbV2.(P207)2 Na,MoP,O," NaMo,P,O,,b Sloping characters: Mo " Ref. 5(a). Ref.5(b). d (A-O)/A 2.307( 1)-2.586( 1) 2.093(2)-2.93( 2) 2.48 1(2)-2.761(2) 2.506(5)-2.817( 5)2.331 (6)-3.205(6)" 2.335(7)-3.20( l)b -0 distances. lq v -O)/A 2.005( 1) 1.998(2) 2.000(2) 1.996(5) 2.046 (2)" 2.043 (3)b d [V( 1)-O]/A 1.914(1)-2.148( 1) 1.949( 2)-2.024( 2) 1.944(2)-2.069( 2) 1.942(6)-2.072( 5) 1.972(2)-2.022(2)' 1.973(3)-2.014(3)b ti[V(2)--O]/A 1.932(1)-2.070( 1) 1.9i1(2)-2.101(2) 1.952(2)-2.092( 2) 1.949(S)-2.073( 5) 2.060 (2)-2.115 (2)" 2.0.~7(3)-2.111(3)b and lead in spite of the different sizes of these cations. Note the striking similarity between lead and strontium whose SrO, and PbO$ octahedra exhibit distances of 2.48-2.76 and 2.50-2.81 A, respectively. This shows that there is no lone-pair effect of Pb" in PbV,(P,O,),.As pointed out above, mercury exhibits a different behaviour owing to its tendency to adopt the dumbbell coordination. The size of the VO, octahedron, charactFristic by the aveJage V-0 distances, ranging from 2.006 A for Cd to 1.996 A for Pb is not signifi- cantly affected by the size of the A cation. On the other hand, the distortion of the VO, octahedra is closely related to the nature of the A cations. The Sr and Pb phosphates that are characterized by similar A -0 distances exhibit very similar VO, octahedra; the latter are not stron8ly distorted, with V-0 distances ranging from 1.94 to 2.09 A (Table 4). On the other hand, cadmium, probably because of its smaller size, induces a larger distortion of the VO, octahedra, especially for the V(l) octahFdra for which V-0 distances ranging from 1.91 to 2.14A are seen.In the same way, the V(2) octahedra of the Hg phase are slightly more distorted than those of the Sr and the Pb phases; nevertheless the V(l) octahedra are less distorted compared to Sr and Pb phases because of the strong anisotropic coordination of the mercury. It is difficult to compare the molybdenum phosphate Na,MoP,O, (0.25 <x <0.50, x =0.30,5" x =0.505') with the vanadium diphosphates because of the existence of the mixed valency of the molybdenum MO"'-MO'~.Nevertheless it is worth pointing out that the NaO, octahedra exhibit a much greater distortion than the other A cations with Na-0 distances ranging from 2.33 to 3.20 A.This is due to the fact that sodium does not sit on the symmetry centre as it does in the vanadium diphosphates. Note that the M 00,octahedra are almost regular. Two new members of the series of vanadium diphosphates AV,(P,O,), with a trans configuration of the PzO, groups have been synthesized. The large size range of the A cations and their various electronic configurations show the high flexibility of this structure. Among these compounds, the mercury phase is remarkable for the ability of mercury to induce a distortion of the PO4 tetrahedra that has rarely been observed to date. These results encourage us to study the behaviour of mercury in other phosphates of transition elements. References 1 L. Benhamada, A. Grandin, M. M. Borel, 4. Leclaire and B. Raveau, Acta Crystallogr., Secl. C, 1991,47, 2437. 2 S. Wang and S. J. Hwu, J. Solid State Chem., 1991.90, 31. 3 A. Leclaire, J. Chardon, M. M. Borel, A. Grand~nand B. Raveau, 2.Anorg. Allg. Chem., 1992,617, 127. 4 S. J. Hwu and E. Willis, J. Solid State Chem., 1991, 93, 69. 5 (a) A. Leclaire, M. M. Borel, A. Grandin and B. Raveau, 2. Kristallogr., 1988, 184, 247; (b) K. L. Lii and J. J. Chen J. Solid State Chem., 1989,78, 178. 6 S. Boudin, A. Grandin, M. M. Borel, A. Leclaire and B. Raveau,Acta Crystallogr., Sect. C, 1994,50, 840. 7 B. A. Frenz and Associates, Inc., 1982, SDP Structure Determination Package College Station, Texas, I JSA. Paper 4104146A; Received 7th July, 1994