948 J.C.S. DaltonReactions of Tellurium Oxides with Alkali-metal Oxides and HydroxidesBy E. Gutierrez-Rios, M. L. Veiga, and Carlos Pico," Departamento de Qulmica Inorgdnica, Facultad deCiencias Quimicas, Universidad Complutense, Madrid-3, SpainThe double oxides Na,TeO,, K2Te0,, K2Te0,, and the triple oxides Na,Te207 and K,Te207 have been prepared bysolid-state reactions of TeO, and TeO,*H,O with M20 and M[OH] (M = Na or K) and have been characterised bytheir X-ray diffraction patterns. The transformations and structures of the products obtained are discussed.TELLURIUM differs from the other elements of Group 6Bin its tendency to form mixed oxides with metallicelements. These compounds have typically ionic crystal-line structures in which tellurium is present in its VIand/or IV oxidation states1, Relatively few studieshave been carried out on the mixed anhydrous oxides oftellurium and alkali metals obtained by solid-statereaction^.^-^ The methods of synthesis used in thisstudy avoid high temperatures or pressures and permitpolycrystalline compounds to be obtained which arenormally pure and from which it is hoped to producesingle crystals, to enable a complete structural charac-terisation to be achieved.The solid phases obtainedwhich correspond to the mixed oxides of tellurium-(vI)and -(Iv) have not previously been described in theliterature.In previous studies, ' tellurates-(vI) and -(Iv) ' wereprepared in good yield by other synthetic methods fromorthotelluric acid, H,TeO,, and alkali-metal hydroxides.These preliminary results allowed the prediction of theexperimental conditions and processes described in thispaper.6 Thus the solid-state reactions have been studiedto characterise the stable compounds in the M,O (M =Na or K)-Te0,-TeO, ternary system.The reactions ofTeO,*H,O (usually called metatelluric acid) with sodiumand potassium hydroxides at intermediate temperatures,and the reactions of TeO, with alkali-metal oxides in aira t up to 700 "C, have also been studied and the reactionproducts have been identified. The synthesised com-pounds can be represented as solid phases of doubleoxides : TeO,*M,O, Te02*M,0, and Te20,*2M,0.RESULTS AND DISCUSSIONThe reaction characteristics and conditions togetherwith the structures of the products obtained are given inTable 1.Reactions of Te0,-H,O.-The synthesis of Na,TeO,and K,TeO, from a mixture of TeO,*H,O(s) and M[OH](s)(M = Na or K) in 1 : 2 molar ratio has been verified byheating to constant weight at 400 and 300 "C (forNa,TeO, and K,TeO, respectively) in air for 24 h.J .Galy, Nut. Bur. Stand. Special Publ., 1972, 364, 29.P. Tarte and J. Preudhomme, Compt. rend., 1971, C272, 212.R. Julien, P. Khodada, and J . DuguC, Bull. Soc. chim.5 W. A. Hart and F. Beumel, ' Pergamon Texts in Inorganic2 G. Bayer, Fortschr. Mineral., 1969, 48, 42.France, 1971, 10, 3418.Chemistry,' Pergamon Press, Oxford, 1975, vol. 18.The preliminary operations were carried out in an inertatmosphere. The process [Table 1, reactions (i) and (ii)]can be represented by equation (1).TeO,*H,O(s) + 2 M[OH](s) +M2Te04(s) + H2°(g)Quantitative chemical analysis carried out on the solidNa,TeO, phase (whitish yellow, microcrystalline) andK,TeO, (white, microcrystalline) and the parametersTABLE 1Reactions of tellurium oxides with alkali-metal oxidesand hydroxidesReac-tion Reactants Conditions Product System(i) Te03*H20 + 400 "C, in air Na,TeO, Orthorhombic(ii) TeO,*H,O + 300 "C, in air K,TeO, Monoclinic(iii) TeO, + Na20 650 OC, in air Na,Te207 Orthorhombic(iv) TeO, + K20 500 OC, in air K4Te207 Orthorhombic(v) TeO, + K,O 700 "C, in air K,Te03 Tetragonal2 Na[OH]2 KCOH]deduced for the unit cell are listed in Table 2.Thesystematic absences observed in the X-ray photographsindicated that Na,TeO, belongs to the P222 or Pmmmspace groups while that of K,TeO, is P2/m.Although some of these compounds with alkalimetals have been known for a long time (supposedly asderivatives of polymetatelluric acid, H,TeO,) , thecrystallographic data published are not reliable since theresults of P a t r ~ , ~ who suggested isomorphism betweenK,[SO,], K,SeO,, and K,TeO,, are not considered to beconsistent.The four-co-ordination of tellurium in thesecompounds seems to be supported by spectroscopic dataI8although in Na,TeO, tellurium should be six-co-ordinate,as is customary for tellurium(v1) compounds. Moss-bauer spectroscopic results for Na,TeO, are compatiblewith six-co-ordination for tellurium, and the existence ofpolymeric anions formed by Te'IO, octahedrons joinedat two vertices has been suggested by analogy with otheralkali-metal oxo-derivatives whose structures are wellknown.1°However, no substantial differences were observed inthe i.r.spectra of Na,TeO, and K,TeO, obtained in this6 C. Pic0 and E. Gutierrez-Rios, Anales de Quim., in the press.* P. Tarte and F. Leyder, Compt. rend., 1971, C273, 852.0 N. E. Erickson and A. G. Maddock, J . Chern. SOC. ( A ) , 1970,M. Patry, Compt. rend., 1936, 202, 1518.1665.lo 0. Lindqvist, A d a Chem. Scand., 1972, 26, 41071978 949study, and these compounds will be subjected to furtherresearch to clarify their structural nature.Reactions of TeO,.-The reactions of amorphous tel-lurium trioxide with sodium and potassium oxides giveWhen a mixture of TeO,(s) and K,O(s) is heated a t700 "C under the same conditions as those previouslydescribed [Table 1, reaction (v)] the compound K,TeO,is obtained, while the reaction with sodium oxide at thisProductNa,TeO,K,TeO,Na,Te,07K4Te207K,TeO,TABLE 2Analytical, crystallographic, and density resultsAnalysis (yo) * * Cell constant r- 7TeO, M,O TeO, (473.6 (73.9) 26.2 (26.1) a 5.19 (4)G 5.97 (2)64.8 (65.1) 34.7 (34.9) a 5.47 (5)b 6.32 (2)b 10.55 (2)c 4.62 (0)(3 = 93.6"37.9 (38.2)33.2 (33.5)27.3 (27.0) 35.0 (34.8)35.8 (36.0) 30.2 (30.5)37.0 (37.1) 62.8 (62.9)a 7.37 (6)b 5.50 (2)c 6.16 (3)a 7.23 (2)b 5.72 (1)c 6.92 (0)a 7.88 (2)c 7.45 (1)Density (g ern-,)Crystallographic Expi.5.00 4.985.05 5.013.22 3.113.04 2.973.64 3.46* Calculated values are given in parentheses.solid products containing Tel" and Texrl.The prepar-ation of compounds of stoicheiometry M,Te,O, has beencarried out using a method similar to that previouslydescribed, but by heating in air at 650 and 500 "C (forsodium and potassium derivatives respectively) mixturesof TeO,(s) and M,O(s) in 1 : 1 molar proportions [Table 1 ,reactions (iii) and (iv)]. The process can be representedby equation (2).2TeO,(s) + 2M,O(s) -w M,Te,O,(s) + 0.5 O,(g)The chemical analysis of Na,Te,O, (whitish, poly-crystalline) and K,Te,O, (whitish yellow) and their unit-cell parameters are listed in Table 2. The possible spacegroups deduced for both compounds are P222 and Pmmmand P222, Pmm2, and Pmmm respectively.The densi-ties determined by picnometry are in satisfactory agree-ment with those obtained crystallographically.The existence of double oxides of tellurium of stoicheio-metry M14Te207 was demonstrated by Moret et a2.11 withthe Li,O-TeO, system. Only Li,Te,O,, which has atriclinic structure, has been described. These com-pounds can be considered to be derivatives of ditelluriumpentaoxide Te205 (TeVIO,*TeIVO,) l2 and the correspond-ing alkali-metal oxide M20 in a 1 : 2 molar ratio. Thestructural data reported here give further information onthis new type of oxide. The characteristics of lithium,principally those related to its small size and high charged e n ~ i t y , ~ could make the crystalline symmetry ofLi,Te,O, very different from that of its sodium andpotassium analogues.The sodium and potassium com-pounds possess similar unit-cell parameters and theirdifferences can be attributed to the different sizes of theatoms.(2)l1 J. Moret, A. Norbert, and D. Cachau-Herreillat, Compt.le 0. Lindqvist and J. Moret, Acta Cryst., 1973, B29, 643.rend., 1973, C278, 677.temperature gives the double oxide Na,Te,O, togetherwith another possible phase which could not be identified.The reaction with K,O can be represented by equation(3).Teo,(s) + K2°(s) * K2Te03(s) + 0*5 O,(g) (3)The analytical, crystallographic, and density data forK,TeO, are in Table 2. The c/a quotient is 0.946 and thepossible space group P4m2.The structural aspects of the double oxides of TeIVwith alkali metals have been little studied with the excep-tion of Li,Te0,,13 which has orthorhombic symmetry,space group P222, and parameters a = 8.79, b = 10.52,and c = 7.10 A; its structure is probably of the sametype as Li,SeO,.However, these results are not inagreement with those obtained by Moret et aZ.14 forLi,TeO, synthesised by solid-state reaction, which hadmonoclinic symmetry with cell parameters a = 5.064,b = 9.540, c = 13.630 A, and p = 95.35". The telluritesNa,TeO, and K,TeO, have been known for a long timeand their respective d values are found in the A.S.T.M.card index, but neither their structures nor their unit-cell parameters have been determined. The d valuesobtained in this study for K,TeO, do not coincide withthose mentioned in the A.S.T.M.index, and so mustrelate to a different solid phase. The rubidium andcaesium tellurites have also been described l5 althoughtheir crystallographic parameters have not been pub-lished. The cause of these inaccuracies lies in thedifficult and laborious crystallisation of the productsobtained by solid-state reactions or in solution.An interesting structural variation can be observed in13 0. N. Breusov, T. V. Revzina, and N. A. Druzn, Zhur.l4 J. Moret, D. Cachau-Herreillat A. Norbert, and M. Maurin,l5 J. Dobrowolski, Roczniki Chem., 1966, 40, 1813.neorg. Khim., 1965, 10, 1990.Compt. rend., 1971, C272, 1971950 J.C.S. Daltonthe potassium compounds studied, where there is a pro-gressive increase in crystal symmetry : K,TeO, (mono-clinic) - K,Te,O, (orthorhombic) --+ I<,TeO, (tetra-gonal).A cubic modification of K,TeO, or a non-stoicheiometric derivative of this compound is thought toexist and the preparation of this material is being studied.EXPERIMENTALReagents and Techniques -The compound TeO,*H,O wasobtained by thermal decomposition of H,TeO, ( AnalaR,B.D.H.) to constant weight a t 200 "C. The solid product isamorphous to X-rays and was characterised by the usualtechniques of chemical anslysis l6 (Found: Te, 65.8.* For details see Notices to Authors No. 7, J.C.S. Dalton, 1977,Index issue.Calc. : Te, 65.9%) and thermal analysis (Found: weightloss, 15.7. Calc. : 15.8%). Tellurium trioxide, a yellowishamorphous solid, was prepared by complete dehydration ofH,TeO, by heating at 300 "C. Alkaline-metal hydroxideswere supplied by Scharlau p.a.The X-ray diffraction patterns were obtained using aPhilips PW-I 310 generator equipped with a chart recorderand cylindrical cameras of 114.6-mm internal diameter.Nickel-filtered Cu-h', radiation was used. The patternsare available as Supplementary Publication No. SUP 22252The densities were determined by solid picnometric[7/1493 Received, 17th August, 19771K. Kodama, ' Methods of Quantitative Inorganic Analysis,'(6 PP.).*methods, using CCI, as the dispersant liquid.Interscience, New York, 1963