~ Pergamon

Po(vhedron Vol. 17, Nos 13-14, pp. 2301 2307. 1998 ~ 1998 Elsevier Science Ltd

All rights reserved. Printed in Great Britain PII : S0277-5387(98)00001-1 0277 5387/98 $19.00 ÷0.00

The anions [(ZrOH(COa)a)z] 6- and [(ZrOH(C204)a)z]6- : single crystal X-ray

diffraction studies of the complexes guanidinium zirconium carbonate

[(C(NH2)a)3ZrOH(CO3)3" H20]2 and sodium zirconium oxalate Na6(ZrOH(C204)3)2" 7H20

Susan Morris, Matthew J. Almond,* Christine J. Cardin, Michael G. B. Drew, David A. Rice and Yan Zubavichus

Department of Chemistry, The University of Reading, P.O. Box 224, Whiteknights, Reading RG6 6AD, U.K.

(Received 20 October 1997; accepted 18 December 1997)

Abstract--The complex [(C(NH2)3)3ZrOH(CO3) 3 • H20]2 (A) has been shown by means of a single crystal X- ray diffraction study to contain [C(NH2)3] + cations and dimeric anions of formulation [(ZrOH(CO3)~)2] 6- . The anion is centrosymmetric with each metal being bonded to two bridging OH groups and three chelating CO~ ions. The Zr atoms are thus eight coordinate with a dodecahedral environment. The Zr - -O distances formed by the bridging OH groups are shorter than those formed through zirconium carbonate interactions. The non-bonded Zr . . • Zr distance is 3.47(2) A,. An infrared spectroscopic investigation of A provides data which support the findings of the crystallographic study. Likewise the complex Na6(ZrOH(CEO4)3)2" 7HzO (B) contains the anion [(ZrOH(C204)3)2] 6-. This anion is structurally related to the anion in A as each Zr atom has an eight-coordinate dodecahedral environment being bonded to two bridging OH groups and three chelating oxalate ligands, but has no imposed crystallographic symmetry. The Zr . . • Zr non-bonded distance is 3.50(1) A,. The O - - Z r - - O bridge angles are 69.7(4) ~ in A and 67.4(3):' in B. ~;) 1998 Elsevier Science Ltd. All rights reserved

Keywords: anions ; single crystal X-ray diffraction.

Zirconia (ZrO2) is a material which finds a wide range of industrial applications. These range from use as a light scatterer in ophthalmic glasses [1,2], as a tough- ener in composite ceramics [3], in X-ray photography [2], as heat shields, in the high temperature filtration of corrosive liquids [4] and in the production of cru- cibles and furnace cores [4]. Some of these industrial uses require zirconia in a particular phase. For exam- ple the cubic phase is often required for optical appli- cations since it has a refractive index of 2.4 and is thus efficient at scattering light [1]. By contrast the tetragonal phase is normally required when zirconia is used to toughen composite ceramics. These phases

* Author to whom correspondence should be addressed.

are only stable at high temperatures (cubic above 2370°C; tetragonal between 1170 and 2370'C) and unfortunately cannot normally be retained by rapid quenching. According these phases are typically stabilised by adding a dopant to the ZrO2 e.g. the addition of small amounts of yttria (Y200 to the ZrO2 may stabilise the cubic or tetragonal forms [3,5]. Adding yttria (or other dopants e.g. CaO) to ZrO2 also has the effect of increasing the electrical con- ductivity of the material (pure ZrO2 is an insulator with a resistivity of about 10 ~2 f~m at room tem- perature) allowing its use as an electrolyte [6].

In our current investigations one aim is to search for coordination compounds of zirconium, typically containing oxo ligands, which readily yield zirconia upon calcination. Thus we hope to find routes, not

2301

2302 S. Morris et al.

only to ZrO2 itself, but a lso--by forming complexes which contain alongside Zr other metal ions e.g. y3+ or Ca2+--to doped zirconia. Various complexes have been suggested and used as precursors to zirconia by calcination. Two such classes of compounds are the carbonates and oxalates. Thermal decomposition experiments [7-11] have shown that oxalate com- plexes of zirconium decompose via carbonates to yield ultimately oxide products.

We have synthesised three closely related zirconium carbonate complexes--[(C(NH2)3) 3ZrOH (CO3) 3 • HzO]2 (A), [(NH4)3ZrOH(CO3)3"2H20]2 (C) and [K3ZrOH(CO3)3"3H20]2 (D)--during the course of our investigations. C [12] and D [13] have previously been the subject of single crystal X-ray diffraction studies. Both crystallise in the monoclinic space group P2~. However, it is quite likely that subtle differences in structure may arise between A and the other two compounds when it is borne in mind that hydrogen bonding involving the guanidinium cation and water molecules will doubtless play an important role in A. We also noted from a preliminary X-ray powder diffraction study that, unlike C and D, A crystallises in the triclinic space group P-I. Previous comments regarding the possible structure A [14] have not been based upon any structural data. Indeed in proposing structures for A, Dervin et al. [14] appeared to be unaware of the earlier X-ray work performed on single crystals of C [12] and D [13] since no reference is made to these structures. Accordingly we have carried out a single crystal X-ray diffraction study of A. We have supported these data by an infrared spectroscopic investigation of the three compounds A, C and D.

Our interest in oxalato complexes of zirconium is driven partly by the scarcity of published work detail- ing such compounds since the pioneering work of Venables and Baskerville in 1897 [15]. There have been two single crystal X-ray diffraction studies of monomeric zirconium oxalate complexes : KaZr(C204)4"5H20 [16] and NaaZr(C204)4"3H20 [17]. Our synthesis of B was, however, quite fortu- itous. We were attempting to follow the method of Blumental [2] for the preparation of a mixed car- bonate/oxalate of zirconium. A small number of crys- tals were isolated which were shown to be B by means of a single crystal X-ray diffraction study.

EXPERIMENTAL

Compound A was prepared following the method described by Pospelova and Zaitsev [18]. Saturated aqueous ammonium carbonate solution (9 cm 3) and guanidinium carbonate (4 g, 0.02 mol in l0 cm 3 water) were mixed and solid zicronyl chloride (2 g, 0.01 mol) was added. The mixture was filtered to remove any solid residue and the filtrate was left in a desiccator over H2SO4 (conc). After a few days tiny, rod-shaped crystals formed. These were isolated by filtration. The zirconium content of A was found by direct calci-

nation. C, H and N analysis was performed using a Perkin-Elmer 240B microanalyser by Medac Ltd at Brunel University. Found: Zr, 19.7%, C, 15.0%, H, 4.2%, N, 26.3%; Calc.: Zr, 19.1%, C, 15.1%, H, 4.4%, N, 26.4%.

A small number of crystals of B were prepared during the attempted preparation of a mixed car- bonate/oxalate of zirconium following the method of Blumental [2]. "Hydrous carbonated zirconia" [18] was first prepared by adding zirconyl chloride (10 g, 0.04 tool) to sodium carbonate (5 g, 0.05 mol) in aqueous solution. The product (1 g, 0.002 mol) was dissolved in the minium of water and crystals of oxalic acid were added until the solution was saturated. The solution effervesced upon addition of the acid. The residue was filtered and the filtrate set aside. After a few days a micro-crystalline precipitate had formed together which a small quantity of needle-shaped crys- tals of B. The precipitate was found to be mul- ticrystalline and analysis suggested that it consisted of a mixture of compounds which proved impossible to separate. This finding endorses a point made pre- viously by Solovkin and Tsvetkova that "a charac- teristic feature of (the chemistry of) zirconium is the formation of precipitates of indefinite composition" [19]. The needle-shaped crystals of B were studied by single crystal X-ray diffraction. Unfortunately the small quantity of crystals produced did not allow any other form of analysis to be performed.

Crystal data for A and B are given in Table 1 tog- ether with refinement details. For both compounds data were collected with Mo-K, radiation using the MAR research image plate system. The crystals were positioned at 75 mm from the image plate. Ninety- five frames were measured at 2 intervals, each with a counting time of 2 rain. Data analyses were carried out with the XDS program [20]. The structures were solved by the Patterson method using the program Shelx 86 program [21]. In both cases the non-hydro- gen atoms were refined anisotropically. Hydrogen atoms on the cations in A were included in geometric positions, but those on oxygen could not be located. Hydrogen atoms on the bridging hydroxide in B were located in a different Fourier map and refined inde- pendently. However, hydrogen atoms in the water molecules could not be located. The structures were then refined on F 2 using SHELXL [22]. Bond lengths and angles in the metal coordination spheres for A and B are given in Tables 2 and 3. Crystallographic data for A and B have been deposited at the Cam- bridge Crystallographic Database. Infrared spectra were recorded on samples of A in pressed KBr discs using a Perkin-Elmer model 1720-X Fourier trans- form spectrometer.

RESULTS AND DISCUSSION

Single crystal X-ray d(ff?action study of A

A is an ionic compound and contains [C(NH2)3] + cations and dimeric anions of formulation

The anions [(ZrOH(CO3)~)2] 6 and [(ZrOH(C204)02] {'

Table 1. Crystal data and structure refinement for A and B

2303

Empirical tbrmula Ch2H36N~O20Zr2 C~2H ~6Na603~Zr2 Formula weight 935.04 10(18.63 Temperature (K) 293(2) 293(2) Wavelength (A) 0.71070 0.71073 Crystal system triclinic triclinic Space group P- 1 P- I Unit cell dimensions a {A) 6.842(5) 8.094(6) h {A) 10.706(81 10.984(6) c (A) 11.801(8) 18.409(6)

( ) 109.08(51 91.91{6) [~ ( I 94.50(5) 96.78(6) 7( } 104.86(5) 109.92(6) V (A'} 777.0 1523.2 Z I 2 D,,t~ (Mgm ~) 1.998 2.199 Absorption coefficient (mm ~) 0.785 0.900 F(000 ) 474 996 Crystal size 0.1 x0.1 x0.15 mm 0.1 ×0.1 ×0.3 mm 0 range for data collection ( ) 1.86 to 24.97 2.19 to 24.60 Index range 0 < h < 7 , - 1 2 < k < 12, - 1 2 < 1 < 13 0 < h < 9 , - 1 2 < k < 1 2 , 2 1 < / < 2 1 Reflections collected 2079 424 I Data/parameters 2079/247 4219,,545 Goodness-of fit on F -~ 1.023 1.320 Final R indices [I > 40-(/)] R~ = 0.0605, wR~ = 0.1889 R~ = 0.0814, wR2 = 0,1922 R indices (all data) R~ = 0.1184, wR, = 0.3098 RL = 0.1180, wR~ = 0,2480 Largest diff. peak and hole (e A 3) 1.743 and -2.454 1.280 and - 1.173

[(ZrOH(CO3)3)2] ~- . The anion is the most interesting moiety in the structure and it is depicted in Fig. 1 together with the atom numbering scheme. The anion is centrosymmetric with each metal a tom being bonded to two bridging OH groups and three chel- ating CO 2- ions. Thus the zirconium atoms are eight coordinate. The Z r - - O distances formed by the bridg- ing OH groups [2.112(8) A (Zr - -O(1 ) ) ; 2.119(91 A (Zr - -O(I )*) ] are shorter than those formed through zirconium-carbonate interactions. Of these latter the Z r - - O bond formed with O(12) [2.162(11) A] appears shorter than the others that span the range 2.204(9) A [Zr--O(22)] to 2.252(10) A [Zr--O(31)]. The struc- ture of the anion found in A has been previously reported as part of a study of (NH4)6[Zr(OH)(CO3)a]2 (C) [I 2]. The data reported in this earlier study are of poorer quality than are those given here. However, the Z r - - O bridging distances in C were found to be 2. I 1 ( 1 ) A with the Z r - - O (carbonate) distances rang- ing from 2.18(21 A to 2.25(2) A. Thus the distances from the two structure determinations are in accord. The angles in A subtended by the chelating carbonate groups range from 57.6(3) [O(32)- -Zr- -O(31)] to 59.7(4) ~ [O(12 ) - -Z r - -O( I 1)] and these are the smal- lest angles subtended at the metal centre. The next smallest angle is that formed by the two bridging OH groups; an angle of 69.7(4) ~ is found at the metal centre and the dependent Z r - - O ( 1)--Zr* angle is thus 110.3(4)". The geometry of the metal coordination

sphere can best be considered to be a slightly distorted dodecahedron. The Z r . . . Zr* distance is 3.471(21 A which is shorter than that previously reported for C [3.498(2) A,] [12]. Each of the 18 hydrogen atoms from the amine groups in the three guanidinium cations form a hydrogen bond to a carbonate oxygen atom with distances ranging from 2.67(I ) to 3.15111/k.

Single crystal X-ray d([]?action study orb

In the unit cell of B there are two Na6[Zr(OH)(C204)3]2" 7H20 moieties which contain the anion [(Zr(OH)(C204)312] 6 which has no crys- tallographically imposed symmetry. This anion is depicted in Fig. 2 where the atom numbering scheme is also given. One of the sodium ions (Na(5)) is dis- ordered over two sites (SA and 5B), as is the oxygen atom of one water molecule (2W). The anion, [(ZrOH(C20413)2] 6 is non-centrosymmetric. The two metal centres in the anion have similar but not ident- ical coordinat ion geometries. Each metal a tom is eight coordinate being bonded to three chelating oxalate groups and two bridging OH anions. Thus the coor- dination geometries found here are similar to those seen in A. The Z r - - O distances formed with the che- late oxalate anions range from 2.178(91 A to 2.239(9) A for Zr ( l ) and 2.185(9) A to 2.224(8) A for Zr(2) and cover a similar range to those formed by the

2304 S. Morris et al.

Table 2. Bond lengths (A) and angles C) for A

Zr--O(l)* 2.112(8) Zr--O(1) 2.119(9) Zr--O(l 2) 2.162(11) Zr--O(22) 2.204(9) Zr--O(11) 2.213(7) Zr--O(32) 2.231 (8) Zr--O(21 ) 2.240(8) Zr--O(31) 2.252(10)

O(1)*--Zr--O(1) 69.7(4) O(1)*--Zr--O(12) 82.8(4) O(l)--Zr--O(12) 132.5(3) O(1)*--Zr--O(22) 95.5(4) O(l)--Zr--O(22) 87.3(3) O(12)--Zr--O(22) 134.6(3) O(l)*--Zr--O(l 1) 98.4(4) O(1)--Zr--O(11) 86.2(4) O(12)--Zr--O(11) 59.7(4) O(22)--Zr--O(11) 161.6(4) 0(1)*--Zr--0(32) 156.4(4) O( 1 )--Zr--O(32) 133.9 (3) 0(12)--Zr--0(32) 79.3(3) 0(22)--Zr--0(32) 86.3(4) O(1 l)--Zr--O(32) 85.9(3) O(1)*--Zr--O(21) 83.0(3) O(1)--Zr--O(21) 134.4(4) O(12)--Zr--O(21) 75.8(4) O(22)--Zr--O(21 ) 59.0(4) O(11)--Zr--O(21) 134.8(4) O(32)--Zr--O(21) 77.8(3) O(l)*--Zr--O(31) 146.0(3) O(1)--Zr--O(31) 76.3(3) O(12)--Zr--O(31) 123.1(4) O(22)--Zr--O(31) 81.4(4) O(11)--Zr--O(31) 80.3(4) O(32)--Zr--O(31) 57.6(3) 0(21 )--Zr--O(31 ) 122.0(4) Zr*--O(1)--Zr 110.3(4)

* Symmetry transformations used to atoms : X~ - - y , - -Z ,

Table 3. Bond lengths (A) and angles (') for B

generate equivalent

Zr(I)--O(2) 2.098(8) Zr( 1 )--O(1 ) 2.122 (8) Zr(!)--O(14) 2.178 (9) Zr(l)--O(21) 2.191(9) Zr(1)--O(34) 2.193 (8) Zr(l)--O(31 ) 2.202(8) Zr( 1)--O ( 11 ) 2.236(8) Zr(1)--O(24) 2.239(9)

chelating carbonate groups [2.162(11) A to 2.252(10) A]. The two metal centres are linked by two OH bridges. The uncertainties in the OH distances are, as expected, large [1.0(2) A O(I) - -H(1) ; 0.9(2) A O(2)--H(2)] but the hydrogen atoms were detectable. The Zr(I)--O(1) and Zr(I)--O(2) distances are 2.122(8) /k and 2.098(8) A respectively while the related distances for Zr(2) are 2.111(8) A [to O(1)] and 2.110(9) A [to 0(2)]. Thus all the zirconium- oxygen bridging bonds are equal and of equivalent length to the bridging bonds found in A [2.112(8) and 2.119(9) /k]. The zirconium-zirconium distance [3.501(1) A] is longer than the metal metal distance in A [3.471(2) ,~].

The angles subtended at the metal centres by the chelating oxalate fragments range from 69.5(3) ° to

O(2)--Zr(l)--O(l) 67.4(3) O(2)--Zr(1)--O(14) 99.1(3) O(1)--Zr(1)--O(14) 80.7(3) O(2)--Zr(1)--O(21) 95.3(3) O(1)--Zr(1)--O(21) 80.1(3) O(14)--Zr(1)--O(21) 149.3(3) O(2)--Zr(1)--O(34) 148.3(3) O(l)--Zr(l )--0(34) 144.2(3) O(14)--Zr(1)--O(34) 88.5(3) 0(2 l)--Zr(1 )--0(34) 93.3 (4) O(2)--Zr(1)--O(31) 139.9(3) O(l)--Zr(1)--O(31) 72.6(3) O(14)--Zr(1)--O(31) 76.9(3) O(21)--Zr(1)--O(31) 74.6(3) 0(34)--Zr(1)--0(31) 71.8(3) O(2)--Zr(l)--O(l 1) 78.1(3) O(l)--Zr(l)--O(l l) 130.5(3) O(14)--Zr(1)--O(I 1) 70.6(3) O(21)--Zr(I)--O(I 1) 139.4(3) O(34)--Zr(1)--O(l 1) 75.5(3) O(31)--Zr(1)--O(11) 134.0(3) O(2)--Zr(1)--O(24) 79.1 (3) O(1)--Zr(1)--O(24) 132.0(3) O(14)--Zr(1)--O(24) 139.8(3) O(21)--Zr(1)--O(24) 69.5(3) O(34)--Zr(1)--O(24) 75.5(3) O(31)--Zr(1)--O(24) 129.1(3) O(11)--Zr(1)--O(24) 69.8(3)

Zr(2)--O(2) 2.110(9) Zr(2)--O(l ) 2.111 (8) Zr(2)--O(41) 2.185(9) Zr(2)--O(61) 2.190(8) Zr(2)--O(54) 2.204(8) Zr(2)--O(51) 2.211 (9) Zr(2)--0(44) 2.212(9) Zr(2)--0(64) 2.224(8)

O(2)--Zr(2)--O(l) 67.4(3) O(2)--Zr(2)--O(4 l) 118.0(4) O(1)--Zr(2)--O(41) 76.1(3) O(2)--Zr(2)--O(61) 77.8(3) O(l)--Zr(2)--O(61) 140.8(3) O(41)--Zr(2)--O(61) 139.1(3) O(2)--Zr(2)--O(54) 82.9(3) O(1)--Zr(2)--O(54) 84.0(3) O(41)--Zr(2)--O(54) 141.1 (3) 0(61)--Zr(2)--0(54) 74.0(3) 0(2)--Zr(2)--0(51) 138.6(3) 0(1)--Zr(2)--0(51) 78.7(3) 0(41)--Zn(2)--0(51) 73.2(3) 0(61)--Zr(2)--0(51) 121.4(3) 0(54)--Zr(2)--0(51) 70.3(3) 0(2)--Zr(2)--0(44) 77.8(3)

The anions [(ZrOH(CO3)0:] ~' and [(ZrOH(C204)~)2] ~

Table 3. Continued

O11 )--Zr(2)--O(44) 110.3(4) O(41)--Zr(2)--O(41) 70.1(3) O(61)--Zr12)--O(44) 78.0(4) O(54)--Zr12)--O144) 148.7(3) O(51)--Zr(2)--O144) 138.413) O12)--Zr12)--O164) 144.213) O( 1 )--Zr(2)--0(64) 147.2(3) 0(41 )--Zr(2)--0(64) 78.0(3) 0(61 )--Zr(2)--0(64) 71.1 (3) 0(54)--Zr(2)--0(64) 104.6(3) O(51 )--Zr(2)--0(64) 74.9(3) O(44)--Zr12)--O164) 78.7(4) Zr(2)--O( 1 )--Zr( 1 ) 111.614) Zr(I )--O(2)--Zr(2) 112.614)

2305

hedral. The five-membered oxalato chelate ligands are, within experimental error, planar while the uncer- tainties associated with the C- -O distances are such that no significant difference was detected in the bond distances between the bonded and non-bonded C- -O groups. The sodium ions are coordinated to oxygen atoms from both the oxalate groups and water mol- ecules. The two bridging OH anions form hydrogen bonds to adjacent dimers O(1)" . 0(65) ( . \ -1 , v,-) 2.7511) A and 0 (2 ) . . . 0 (35 ) ( x + l , y , z ) 2.6911) A. In addition each water molecule forms at least two hydrogen bonds to oxygen atoms in the oxalate anions or to other water molecules.

Inf}'ared spectroscopic study qf'A

71.813) for Zr(l) and 70.113) to 71.1(3) for Zr(2). These angles being part of five-membered rings are, as expected, larger than the angles subtended at the zirconium centres by the chelating carbonate ions in A which range from 57.6(3) ° to 59.7(4) and are part of four-membered rings. The geometry of the metal coordination spheres are slightly distorted dodeca-

A shows infrared absorptions at the following wav- enumbers (v/cm i): 1684 (br), 1559 (br), 1361 (s), 1318 (m), 1303 (m), 1051 (w), 1036 (w), 1008 (w), 945 (w), 858 (w), 847 (m), 783 (m), 758 (s), 690 (w), 622 (vw), 554 (br) and 355 (m). Features are also seen in the regions 1680-1720 cm t [attributable to v(C---N) vibrations] and 2900-3600 cm ~ [attributable to v(C--H), v(O--H) and v(N--H) vibrations]. However, bands in these last two regions were

023

C20

o21 111%% °22

032

033 C30 o31 \

01;

CI0 011

O1

013

Fig. I. The [(ZrOH(CO3)a)2] 6 anion showing the atomic numbering scheme. Ellipsoids are shown at 50% probability.

2306 S. Morris et al.

015

C13 016 056

C33

014 W $ C12

055

C53 054

034 C52 06 ! O65 02 ~ nq ~ mTn C62

036 _~r2 C32 031

035 0~L24 ,4"- i C63 iC23 041 064

021 044 066

C221 " g 025 C42 ¢ ' ~ C43

Fig. 2. The [(ZrOH(C204)02] 6- anion showing the atom numbering scheme. Ellipsoids are shown at 50% probability.

extremely broad and its is difficult to make a detailed analysis or to draw definite conclusions from them. Some points of interest emerge, however, from the infrared data which is listed above, although the situ- ation is necessarily complicated by overlapping of bands and by coupling of vibrations within the molecule. It is possible to distinguish between bands arising from the guanidinium cation or from the anion by a comparison of the spectrum of A with spectra of the related compounds C and D which contain the same anion [12,13]. In order to allow a direct com- parison between the infrared spectra of A, C and D spectra of C and D were recorded as part of our study under identical conditions used for obtaining the spec- trum of A. Vibrations which arise from the anion give rise to bands in very similar positions in the spectra of each of the three compounds. The bands of A at 1559, 1318 and 1051 cm -I may thus be assigned to stretching vibrations of the coordinated carbonato groups (C shows corresponding bands at 1559, 1330 and 1050; D at 1560, 1324 and 1048 cm '). The pos- ition of these bands is typical of chelatinq CO~- [23,24]. In particular the presence of one higher fre- quency mode (in A at 1559 cm-~) allows an assign- ment to be made to chelating bidentate as opposed to monodentate CO~- [23,24]. The feature at 1008 cm- most probably arises from the Z r - -O(H) - -Z r bend-

ing mode. C and D show corresponding features at 997 and 1004 cm -j respectively. This vibration has been found to occur typically in the range ca 950- 1000 cm i for a wide range of complexes [23,25], although Tarte has reported values from 677 to 1000 cm-~ for a number of copper compounds [26]. The combination of infrared spectroscopic and single crys- tal X-ray diffraction data allow us to confirm that compounds A, C and D have similar structures, although in A and C (but not D) the structure is somewhat complicated by the presence of hydrogen bonding involving the guanidinium (A) or ammonium (C) cations and water molecules.

Acknowledgements--We are grateful to Cookson's Ltd., Yarnton, Oxon., U.K. and SERC for the provision of a CASE award for S.M. We thank the Rotary Club of Caver- sham, Berks., U.K. and Sun Microsystems for financial help in supporting a visit of Y.Z. from the Russian Academy of Sciences, Moscow, Russia during which this work was completed.

REFERENCES

1. Singer, F. and German, W. L., Ceramic Glasses. Borax Consolidated, London, 1960.

The anions [(ZrOH(CO~)02] ~' and [(ZrOH(C204)J_~] 6-

2. Blumenthal, W. B., The Chemical Behavior of Zir- conium. Van Nostrand, New Jersey, 1958,

3. Heuer, A. H. and Hobbs, L. W., eds, Advances in Ceramics, 1984, 3, I

4. Greenwood, N. N. and Earnshaw, A., ChemistD, (?/the Elements. Pergamon, Oxford, 1984.

5. McDougall, A., Fuel Cells. Macmillan, London, 1976.

6. Liebhasky, H. A. and Cairns, E. J., Fuel Cells and Fuel Batteries. J. Wiley, New York, 1968.

7. Gangadevi, T., Subba Row, M. and Kutty, T. R. N., Ind. J. Chem., 1980, 19A, 303, 309.

8. Gangadevi, T., Muraleedharan, K. and Kannan, M. P., Thermochim. Acta, 1989, 144, 109.

9. Sheinkman, A. P., Yunusova, N. V., Osachev. V. P. and Kondrashenkov, A. A., Russ. J. Inor#. ('hem., 1974, 19, 206.

10. Gangadevi, T., Muraleedharan, K. and Kannan, M. P., Thermochim. Acta, 1989, 146, 225.

1 I. Gangadevi, T., Muraleedharan, K. and Kannan, M. P., Thermochim. Acta, 1991, 191, 105.

12. Clearfiekt, A., lnorq. Chim, Acta, 1970, 3, 166.

13. Gorbunova. Y. E., Zh. Stukt. Khim., 1968, 9, 918.

2307

14. Dervin, J., Faucherre, J. and Prusek, H., Rev. Chim. Min., 1974, 11,372.

15. Venables, F. P. and Baskerville, C.. J. Am. Chem. Sot., 1897, 19, 13.

16. Kojic-Prodic, B., Ruzic-Toros, Z. and Sljukic, M,, Acta Co'st., 1978, B34, 2001.

17. Glen, G. L., Silvertom J. V. and Hoard, J. L., lnorg. Chem., 1963, 2, 250.

18. Pospelova, L. A. and Zaitsev, L, M., Russ..I. hu~r 9. Chem., 1966, 11,996.

19. Solovkin, A. S. and Tsvetkowt, S. V., Russ. Chem. Rer., 1962, 31,655.

20. Kabsch, W., J. Appl. Crvst., 1988, 21,916. 21. Sheldrick, G. M., SHELX86, Acta Crvst.. 1990,

A46, 467. 22. Sheldrick, G. M., SHELXL93, program for crys-

tal structure refinement, University of Gotlingen. 23. Nakamoto, K., In/?ared and Raman Spectra o[

Inorganic and Coordination Compounds, 4th edn, J. Wiley, Ne~ York, 1986.

24. Fujita, J., Martell, A. E. and Nakamoto, K., J. Chem. Phys., 1962, 36, 339.

25. Scavgill, D., J, Chem. Sot., 1961, 4444. 26. Tarte. P., Spectrochim. Acta, 1958, 13, 107.