Double molybdates of composition CsR - Springer Link

5. 6. 7. 8. 9. I0. ii. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.

H. G. Hertz, in: Teorie der Electrolyte, S. Hirzel Verlag, Leipzig (1971), pp. 479-543. A. P. Sadovskii, L. N. Mazalov, T. I. Guzhavina, et al., Zh. Strukt. Khim., 14, No. 4, 667 (1973). A. K. Lyashchenko and A. S. Lieev, Koord. Khim., iO, 1607 (1984). A. Tramer, Chimie Phys. Physicochim. Biol., 59, No, 3, 232 (1962). Yu. Ya. Kharitonov, in: Vibrational Spectra in Inorganic Chemistry [in Russian], Nauka, Moscow (1971), pp. 139-181. I. Padova, J. Chem. Phys., 39, No. 5, 1552 (1963). D. Paoli, M. Lucson, and M. Chabanel, Spectrochim. Acta, 34A, 1087 (1978). P. Bacelon and I. Corset, J. Sol. Chem., 9, No. 2, 401 (1980). P. Mitchel and P. Williams, J. Chem. Soc., 1912 (1960). L. Jones, Inorg. Chem., ~, 777 (1963). C. B. Baddiel and G. I. lanz, Trans. Faraday Soc., 60, 2009 (1964). A. A. Vashman and I. S. Pronin, Nuclear Magnetic Relaxation and Its Application in Chemical Physics [in Russian], Nauka, Moscow (1979). R. K. Mazitov, O. Ya. Samoilov, and N, V. Bryushkova, Zh. Strukt. Khim., i_~6, No. 4, 564 (1975). R. G. Bryant, J. Phys. Chem., 73, No. 4, 1153 (1969). D. E. Wossner, B. S. Showden, and A. G. Ostroff, J. Chem. Phys., 49, No. I, 376 (1968). H. Frank and J. G. Sketchard, J. Chim. Engn. Data, No. 3, 295 (1975). G. N. Mikulin and I. E. Vosnesenskaya, in: Aspects of the Physical Chemistry of Electrolyte Solutions [in Russian], Khimiya, Leningrad (1968), p. 305. L. S. Lilich, Author's Abstract of Doctoral Dissertation [in Russian], Izd-vo LGU, Leningrad (1966).

DOOBLE MOLYBDATES OF COMPOSITION CsR~+(MoO4)3

(R = Ni, Co, Mg, Mn, Cd)

AND THE CRYSTAL STRUCTURE OF Cs2Co2(Mo04) 3 S. F. Solodovnikov, R. F. Klevtsova, V. G. Kim, and P. V. Klevtsov

UDC 548.736

Double molybdates Cs=R2(Mo04) 3 (R = Ni, Co, Mg, Mn, Cd) having the langbeinite K=Mg=(S04) 3 structure were synthesized, and the parameters of the (pseudo) cubic unit cells were determined together with their melting characteristics. The crystal structure of Cs2Co2(MoO~) 3 was solved [a = 10.832(5), b = 10.829(5), c = 10.830(5) ~, space group P212121, Z = 4, Syntex P21 automatic diffractometer, MoK=-radiation, 3881 independent reflections, R = 0.069]. In the structure, alternating Mo tetrahedra and Co octahedra, linked by common vertices, form a three-dimensional network, similar to the langbeinite one, in whose large ellipsoidal interstices the cesium atoms are distributed. The deviation of the structure from a cubic one is caused by small mutual rotations of the Mo tetrahedra. This implies the existence of a number of phase transitions in the double molybdates investigated.

Previously, double molybdates of alkali (Li, Na, K) and of divalent (Mg, Co, Ni, Cu, Zn) metals of composition M2+R~+(MoO~)3 [i-4] have been studied. Compounds with M + = Li, Na are related to the structural type Li=Fe2(Mo04) 3 [5], whereas double molybdate K2R~+(MoO~)3 crystallize in the structural type K2Zn2(Mo04) s [2]. Also, KaMg2(Mo04) 3 has a high-temperature pseudocubic (orthorhombic) modification [4] with a structure of the langbeinite type K2Mg2(SO4) 3 [6]. One would therefore expect that this type of structure could occur in compounds M~R~+(MoO~)3 with ions more strongly electropositive than K. The aim of the present Institute of Inorganic Chemistry, Siberian Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 27, No. 6, pp. 100-106, November-December, 1986. Original article submitted October 14, 1985. 928

0022-4766/86~2706-0928512.50

9 1987 Plenum Publishing Corporation

TABLE i.

X-Ray Photographic Data for Cs2Cd2(MoO~) 3

hkz

d, ?~

21i 220 22t 310 3tt 320 32t 410, 322 33i 420 42t 332 422 510, 43t 51t, 333 520, 432 52t 522,44t 530, 433 53i 6O0 6t0 6tl, 532 62O 62t, 540, 443 54t 630, 542 63t 444 632

4,596 3,980 3,753 3,560 3,392. 3,121 3,006 2,729 2,58t 2,5t5 2,456 2,398 2,296 2,206 .2,t66 2,089 2,055 1,959 1,930 i,902 t,876 t,850 t,825 t,779 t,757 91,736 t,679 t ,659 t ,624 1,607

hkl

8

2 4 t )0 }0 }0 ~0 1t 4 8 4 2 20 20 2 1t 5 t2 6 6 2 t5 3~ tt t3 t7. t2 4 3

7t0, 550, 543 720, 64i 721,633, 552 642 722, 544 730 73t, 553 650, 643 732, 651 8i0, 740, 652 81t, 74t, 554 733 820,644 82t, 742 653 822, 660~. 83t, 750, 743 75t, 555 752 841,744, 663 910, 833 91t, 753 842' 920, 760 92t, 761,655 664 922, 850, 843 930, 851,754 852 932, 763

a,

I

t,59t3 1,5455 1,5308 t,5027 1,490i 1,4777 t,4647 t,44i0 t,429t 1,3954 i,3847 t,3746 1,3646 i,3545 t,3446 t,3262 1,3078 i,2992 1,2740 !,2498 t,2423 t,2348 t,2276 t,2206 t,2132 t,t997 t,t926 t,186t t,1669 1,1607

7 3 4 4 2 2 8 3 5 4 3 2 1

5 4 5 7 i 4 2 t

3 3 1

2 1 6 4 1

3

TABLE 2. Unit Cell Parameters, Densities, and Melting Points (decomposition) of Double Molybdates Cs2R2(Mo04) a (R = Ni, Co, Mg, Mn, Cd) .Parameter of I

Compound

Cs2Ni~(MoO4)s C%Co2(MoOi)a C%Mg~(MoO4)a Cs2Mn~(MoO4)a C%Cd2(MoO4)a

(l~eudo) c@~ic i unit cell A

z

t0,75 10,830 * t0,85 1t,05 tl,25

4 4 4 4 4

Melting Point pCALC, (dec~

4,61 4,5t ? ; 4,t3 4,21 4,54

700 750 905 820 870

*Mean value of the three parameters of the orthorhombic unit cell, measured on a Syntex P2 z automatic diffractometer. %When measured by pycnometry, density = 4.33 g/cm 3. work was to clarify the possibility of synthesizing double molybdates CsaR2(MoO~) 3 (R = Ni, Co, Mg, Mn, Cd) and to investigate them. Compounds of composition CsaR2(MoO~) 3 in powder form were prepared by the method of solid phase reactions from mixtures Cs2MoO 4 + 2RMo04, which we heated (with grinding at frequent intervals) at temperatures of 450-500~ The double molybdates obtained were investigated by methods of thermal analysis (curvilinear heating and cooling and differential thermal analysis using the NTR-70 apparatus with a rate of heating of i0 deg/mm) and x-ray diffraction (diffractometer DRON-2, CuKa-radiation). All the compounds synthesized under the above conditions of type Cs2Ra(Mo04) 3 were isostructural and related to the structural type of cubic langbeinite Cs2Co2(MoO~)a, space group P2z3 [6] by use of powder diffraction photographs [x-ray photographic data for Cs2Co2(Mo04) 3 are given in Table i]. X-ray photographic investigation of the tempered samples showed that the cesium-nickel molybdate dissociated in the solid phase into a mixture of cesium and nickel molybdates. The remaining double molybdates fused incongruently. The unit cell parameters and melting points (with decomposition) of Cs2R2(MoOq) 3 are given in Table 2. 929

TABLE 3. Coordinates and Isotropic Temperature Parameters of Principal Atoms in the Structure Cs2Co=(Mo04) a (standard deviations in brackets) A tom

x/a

y/b

z/e

B* ,r

cs(t) Cs(2)

0,32.09(1) o,542o(t) o,6236(1) 0,1954(1) 0,4741(1) 0,t125(1) o,8373(1) 0,6705(10) 0,4840(9) 0,6013(11) 0,7382(IOI 0,0425(7) 0,2263(11) 0,2535(t0) 0,2873(i0) 0,4844(9) 0,55t8(10) 0,3193(9) 0,5486(10)

0,3209(1) 0,54t9(1) 0,4741(1) 0,6236(1) 0,1983(1) 0;1123(1) o,s374(t) 0,4842(tt) 0,555601) 0,3203(9) 0,5486(I0) 0,6703(11.) 0,4825(9) 0,60t8(9) 0,7363(10) o,o44o(8) 0,2269(12) 0,2459(t2) 0,2871(10)

0,3209(1) 0,54t9(1) o,19s4(i) 0,4741(t) 0,6236(1) 0,1t27(1) o,8372(1) 0,0442(8) 0,2244(10) 0,2474(10) 0,2873(I0) o,4839(lO) o,5534(1o) 0,3206(9), 0,5585(10) 0,6706(ti) 0,5828(9) 0,605600) 0,7384(ti)

1,20 1,88 0,59 0,59 0,59 0,56 0,53 1,30 1,45 1,31 f ,39 f,27 1,44 i,t6 1,39 i,28 1,56 1,45 1,34

Mo(l) Mo(2) Mo(3) Co(i) Co(2)

0(1) O(Z) 0(3) 0(4) 0(5) 0(6) 0(7) 0(8) 0(9) o(to) 0(tl) 0(12)

*Calculated using the equation Bequ = 4(B11a 2 + B22b 2 + B33c2)/3. Single crystals of the compounds investigated were obtained by the method of spontaneous crystallization from a solution in molten Cs2Mo207 by slowly lowering the temperature. As charges we used both double molybdates previously prepared by solid phase synthesis, and mixtures of molybdates Cs2MoO 4 + 2RMo04. The temperature of homogenization of the solutionmelt was set 50-100 ~ lower than the melting point (decomposition) of Cs2Ra(MoO~) 3. Isothermal conditions were maintained for a period of 20-30 h. The ratio charge:solution was 1:2 in all cases. The solution-melt was cooled at a speed of 3-5 deg/h down to 400~ Under the conditions described we obtained single crystals of double molybdates measuring up to 3 m m w h i c h had the isometric features typical of cubic crystals. The structure determination was carried out on CsaCo2(MoO~) 3. A preliminary x-ray investigation (RKOP camera, Weissenberg x-ray goniometer) of single crystals of the cesium-cobalt molybdate did not reveal any noticeable deviations from cubic symmetry. However, in polarized light (MPS-2Y4.2 microscope) the crystals exhibited slight double-refraction. In the absence of adequate evidence of any greater lowering of the symmetry from the prototype cubic langbeinite cell, an orthorhombic system for Cs=Co2(MoO4) 3 was implied for subsequent work. For the x-ray structural investigation a spherical sample was used of diameter approximately 0.3 mm. Refinement of the unit cell parameters [a = 10.832(5), b = i0.829(5), c = 10.830(5) ~, V = 1270 ~s, Z = 4] and measurement of the intensities of 4423 independent reflections (MoKa radiation, 8/2e scanning, sin 8/~ ~ 0.90 ~-i) was carried out on a Syntex P21 automatic diffractometer. The conversion of the intensities to Fhks values was carried out using absorption corrections (u = 112.6 cm -I, ~R = 1.7) in the spherical crystal approximation with the aid of the Syntex XTL Suite, The remaining calculations were carried out using the YANX suite of programs [7], and STRUCTURA [8], using 3881 reflections with I ~ 3a (I). The resulting systematic absences in the bulk of the reflections agree with the space group D~ = P21212 I. The solution of the structure of Cs2Co2(MoO~) ~ was effected by analysis of a three-dimensional Patterson function. The course of the analysis was followed by comparing the atomic coordinates thus obtained with those in the prototype structures K2Mg2(SO~) 3 and ~-K2Mg 2" (MoO~)s. Fourier syntheses, Constructed using the set of heavy atoms which had been found, enabled us to identify all 12 independent oxygen atoms with certainty. Isotropic refinement by the method of least squares of the model in space group P212121 led to R = 0.087, and using anisotropy for all atoms we obtained an R value of 0.069. 930

TABLE 4. Principal Interatomic Distances (~) in the Structure of Cs2Co2(Mo04) 3

MOO)-tetrahedron

MoO)--o(t) 0(3) 0(4) 0(2) o(t)-o(4) 0(2)-0(4) 0(2)--0(3) 0(1)--0(2) 0(3)-0(4), o(1)--o(3)

t,75 t,76 1,77 1,77 t,76 2,82 2,84 2,86 2,9t 2,92 2,92 2,88

Mo(2)-tetrahedron Mo(2)'0(7) 0(8) 0(5) 0(6) 0(6)--0(8) 0(5)--0(8) 0(6)--0(7) 0(5)--0(7) 0(7)--0(8) 0(5)--0(6)

co(t)-octaheAron Co(1)--0(4) 0(i2) 0(5) 0(8) 0(9) 0(I) 0(5)--0(12) 0(4)--0(9) 0(t)--0(8) 0(t)--0(5) 0(5)--0(9) 0(I)--0(9) 0(4)--002) 0(5)--0(8) 0(8)--0(12) 0(9).0(12) 0(1)--0(4) 0(4)--0(8)

.0(tt) 0(t0) 0(6) 0(8) 0(4) 0(12) 0(2).

0(2') 0(6') "

o(to')

i,75 t,75 ~t,77 !,78 1,76 2,83 2,83 2,84 2,90 2,90 2,94 2,87

Mo(3)--0(9) o(tt) o(t2) o(t0) 0(9)--0(t2) 0(10)--002) 0(10)--0(tt) 0(tt)--0(12) 0(9)--0(tt) o(9)-o(to)

1,75 t,76 1,76 1,77 1,76 2,82 2,84 2,86 2,90 2,9t 2,93 2,88

co(2)-octahcdron 2,06 2,07 2,08 2,09 2,09 2,09 2,08 2,87 2,89 2,90 2,92 2,93 2,94 2,96 2,96 2,97 2,97 2,97 2,98 2,94

cs( i)-polyhedmn

Cs(l)--o(3) 0(7)

Mo(3)-tctrahedron

Co(2)--0(ti) 0(3) 0(2) 0(6) 0(7) o(to) 0(3)--o(10) o(6)--o(1t) 0(2)--0(7) 0(7)--0(11) 0(2)--0(1t) 0(2)--0(10) 0(2)--0(6) 0(6)--0(10) 0(3)--0(7) 0(2)--0(3) 0(6)--0(7) o(to)-o(1t)

2,06 2,07 2,08 2,09 2,09 2,t0 2,08 2,80 2,81 2,85 2.93 .2,94 2,94 2,96 2,98 2,99 3,03 3,05 3,07 2,94

cst2)-polyhedron

3,t4 3,t5 3,t9 3,22 3,23 3,24 3,24 3,24 3,27 3,60 3,63 3,84

Cs(2)--0(9) o(1) 0(5) o(8) o(to) o(6). o(4)

0(12> 0(2) o(t25

0(4') 0(8')

3,t3 3,t3 3,13 3,47 3,47 3,48 3,48 3,49. 3,50 3,70 3,70 3,7t

Shortest intercation distances (less than 5.0 ~0

Mo--Mo 4,38"~'64 (isohted tet, ai~e&a) Mo--Co 3,49--3,89(polyhedra with general peaks/ Mo--Cs 3,8i--4,00 [ Cs(l)--Cs(2) 4,t5 Cs(1)--Co(t) 3,92 t Cs(2)--Co(1) 4,17 Cs(t)--Co(2) 4;08 Cs(2)--Co(2) 4,85 Note. Atoms related by principal symmetry elements are indicated by brackets. Standard deviations for metal-oxygen distances are O.Ol ~ and those for oxygen-oxygen are 0.01-0.02 ~. 931

71

Fig. i. View of the structure of Cs2Co2(Mo04) 3 along the [111] direction illustrating the pseudocubic arrangement of the atoms in the crystal. The number of the atoms is as in Table 3. Controlled isotropic refinement of the structure in space group P2z3 gave an R value of 0.092, which was virtually unchanged using anisotropy, but in both cases we obtained significantly worse temperatureparameters compared with the orthorhombic alternative. In addition the preference for the orthorhombic alternative over the cubic was confirmed with the aid of Hamilton's R test [9]. Final coordinates and isotropic temperature parameters of the principal atoms are given in Table 3 (anisotropic temperature parameters can be obtained from the authors). The principal interatomic distances in the structure of Cs2CO2(Mo04) 3 are given in Table 4. All three crystallographically independent Mo atoms are characterized by perfectly regular tetrahedral coordination with standard mean distances < Mo-O> = 1.76 ~. Two nonequivalent cobalt atoms are situated within slightly distorted oxygen octahedra with = 2.08 ~ throughout. The coordination of the two independent Cs atoms is rather abnormal and is confined to a sphere of radius 4 ~, CN = 12. To a large degree this is appropriate for Cs(2) which has a comparatively uniform environment, whereas the coordination of Cs(1) can be seen rather as 9 + 3. This difference is probably explained by the fact that the value of the temperature factor of Cs(2) is less than that of Cs(1). The essence of the structure of CsaCo2(Mo04) 3 is an open three-dimensional framework made up of alternating Mo tetrahedra and Co tetrahedra, joined together by general peaks (see Fig. i). The manner of this linking is such that large ellipsoidal cavities are formed in the framework, in each of which two cesium atoms are situated. The same kind of principle governing the composition of the structure is observed both in cubic langbeinite and orthorhombic 8-K2Mg2(Mo04)3.* The pseudocubic structure is in evidence aSove all in the arrangement of the metal atoms, which to a high degree of accuracy (within the range Io) are subject to the rules of cubic symmetry (see Table 3). However, the difference in the coordinates of some of the oxygen eThe unit cells in the structures of CsaCo2(MoO4) 3 and ~-K2Mg2(MoO4) 3 were chosen identically and the arrangement of the atoms in them was directly comparable. For a comparison between them and the structure of langbeinlte it is necessary to transform the origin of coordinates by 1/4, 1/4, 1/4 and to relabel the cell axes.

932

atoms related by the pseudo-threefold axis, for example 0(2) and O(i0), 0(3) and 0(7), etc., exceeds at least 3a. This could indicate small relative rotations of the MoO 4 tetrahedra (the displacement of the oxygen atoms does not exceed 0.05 ~), symmetrically equivalent in space group P213, which would also result in orthorhombic distortion of the structure of Cs2Co2(MoO4) 3. An analogous mechanism of orthorhombic distortion of the prototype cubic langbeinite structure related to a rotation of the tetrahedral oxygen anions is found in K2Cd2(SO4) 3 [i0]. An investigation of the phase transitions for crystals of the langbeinite family using the tool of group theory [Ii, 12] has shown that, for the space group P213 of langbeinite, transitions to the space groups P21, PI, P3, P212121 are possible. Here the first three transitions are improper ferroelectric and the last is proper ferroelastic. Examples of such transitions are well known for double sulfates, for example TI2Cd2(SO4) 3 (P213 + P21 + PI § P212121), K2Cd2(SO4) s, K2Mn2(SO4) 3 (P213 § P212121) [I0, 13]. It is obvious that analogous phase transitions can be expected also in a number of langbeinite double molybdates studied in the present investigation, Cs2R2(Mo04) 3 (R = Ni, Co, Mg, Mn, Cd), and also in $-K2Mg2(MoO4) 3 . The authors wish to express their gratitude to N. V. Podberezskaya for obtaining and processing experimental data on the automatic diffractometer and to V. F. Krivoshapov for his help in carrying out crystal optics observations. LITERATURE CITED i. 2. 3. 4. 5. 6. 7. 8. 9. i0. ii. 12. 13.

V. A. Efremov and V. K. Trunov, Izv. Akad. Nauk SSSR, Ser~ Neorg. Mater., l_!, 273 (1975). C. Gicquel-Mayer and G. Perez, Rev. Chim. Minerale, 12, 537 (1975). V. G. Penkova and P. V. Klevtsov, Zh. Neorg. Khim., 2-2, 1713 (1977). P. V m Klevtsov, V. G. Kim, and R~ F. Klevtsova, Kristallografiya, 25, 301 (1980). R. F. Klevtsova and S. A. Magarill, Kristallografiya, 15, 710 (1970). A. Zemann and J. Zemann, Acta Crystallogr., i0, 409 (1957). R. G. Gerr, A. I. Yanovskii, and T. Yu. Struchkov, Kristallografiya, 28, 1029 (1983). L. P. Solov'eva, V. E. Ovchinnikov, E. N. Ipatova, and V. I. Andrianov, Kristallografiya, 24, 821 (1979). W. C. Hamilton, Acta Crystallogr., 18, 502 (1965). S. C. Abrahams, F. Lissalde, and J. L. Bernstein, J. Chem. Phys., 68, 1926 (1978). V. Dvorak, Phys. Status Solidi, b52, 93 (1972). V. Dvorak, Phys. Status Solidi, 66, 87 (1974). T. Hikita, H. Sekiguchi, and T. ikeda, J. Phys. Soc. Jpn., 43, 1327 (1977).

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