Solubility of rubidium tetrahydrogallate in diglyme

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  • INORGANIC CHEMISTRY SOLUBIL ITY OF RUBID IUM TETRAHYDROGALLATE IN DIGLYME T . N . Dymova and Yu . M. Dergachev UDC 541.8:532.739 2:546.35'681 Complex hydr ides of gal l ium MGaH4(M = L i -Cs ) a re new and l itt le studied compounds . On ly qualita- tive data a]:e known on the solubility of L iGaH 4 in diethyl ether, THF , and d ig lyme (DO); NaGaH 4 in THF and d ig lyme. For the lower members of the series MGaH 4 (M = K-Cs) , only one solvent is known - di- g lyme. These solvents have been used as the react ion med ium in the synthesis of hydridogal lates by ex- change rea3tions [1-3]. The synthesis and purification of hydridogal lates require quantitative data on their solubility ia d ig lyme. The solubility of [{bGaH 4 was studied in this work . EXPERIMENTAL METHOD The ~:eaction of gal l ium with rub id ium and hydrogen in a mel t [4] at increased temperature and pres - sure was used for the product ion of RbGaH 4. RbGaH4 was extracted with DG f rom the reaction mass , re - present ing a solid melt , readily pulver ized in the mor tar . For the decompos i t ion of perox ides in water , DG was boiled with KOH, redistilled over Na, collect- ing the fraction at 162 ~ and stored in a covered flask over Na w i re in an a tmosphere of d ry argon. RbGaH 4 was isolated f rom solution in d ig lyme, by distilling off the solvent in a vacuum (I mm Hg) at 105-110 ~ . The precipitated white crystals were separated f rom the mother liquor on the filter, washed with pentane, and dr ied for 3 h at 90-100 ~ Found: Ga 43.75; H 2.49%. RbGaH 4. Calculated: Ga 43.97; H 2.51%. In the; region of positive temperatures (0-115~ the solubility in the sys tem RbGaH4 - DG was studied by an i sothermal method, us ing the usual technique of [5, 6]. Equ i l ib r ium was establ ished in the solution in 2-3 h with intensive mix ing. The samples were collected in an a tmosphere of Ar with a pipette with a dense filter at the; end. The concentrat ion of the investigated solutions of RbGaH 4 in d ig lyme was establ ished ac- cord ing to gal l ium by determinat ion of the optical density of aqueous solutions of complexes of gal l ium with xylene orange [7] on an SF -4A spect rophotometer . When solid RbGaH 4 is d issolved in DG (20 ~ and samples of the solution are ana lyzed for a long t ime (~ i00 h), a supersaturated metastab le state is establ ished in the sys tem. Initially the concentrat ion of the solution reached 18-22 mole %, then decreas ing with t ime to 9.2 mole %, and subsequent ly remain ing con- stunt. In the interval f rom -66 to -35 ~ the solubility was s ind iedby differential thermal and visual-poly- thermal methods . The liquidus line was constructed accord ing to the data of visual observat ions and estab- l i shment of the temperatures of d i sappearance of the last crystal. The points of the solidus line were de- te rmined accord ing to the curves of heating of a solution cooled to -1O0 ~ Stepanov vessels with the solution and standard (A1203), p laced in the seat of a mass ive copper block, were cooled with liquid nitrogen, wh ich was introduced into a r ing -shaped space between the b lock and the wal ls of the; outer cas ing of the instrument, made of stainless steel [8]. S imple and differential thermo- couples wece introduced f rom be low into the seat of the block. The heating curves were recorded on a Kurnakov pyrometer . N. S. Kurnakov Institute of Genera l and Inorganic Chemis t ry , Academy of Sciences of the USSR. T rans la ted f rom Izvestiya Akademi i Nauk SSSR, Ser iya Kh imicheskaya , No. 12, pp. 2659-2661, December , 1973. Original article submit ted Apr i l 3, 1973. �9 1974 Consultants Bureau, a division of Plenum Publishing Corporation, 227 Test 17th Stre~et, New York, N. Y. 10011. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission of the publisher. A copy of tiiis article is available from the publisher for $15.00. 2597
  • %, ffO gO Og 0 -30 8 I I D z ,'s 2o z,~ 28 ,.,,z ,.,'~ c,~_ RbGaHs RbCaH4,2DG Liq B E J ~qL+' I RbGaH4.6DG A R.bGaH,.6DG I ,1 7 s N 19 DG Fig. i. Liq + RbGaH 4 800 H Liq + RbGaH42DG -35 ~ g cl Rb Gall4. 6DG + RbGaH4.2 DG ~, I I I a, - 78 ZZ ZF JO C, mole % Solubility d iagram of RbGaH 4 - Diglyme DISCUSSION OF RESULTS The po ly therm of the solubility of RbGaH 4 in DG (Fig. i) consists of four branches. The first b ranch cor responds to the crystallization of pure d ig lyme. The branch AB in the interval 1.8-9.2 mo le ~0 cor re - sponds to crystallization of the hexasolvate RbGaH 4 �9 6DG, wh ich mel ts ineongruently at -36 ~ The hexaso l - vate, wh ich splits out four mo lecu les of d ig lyme, is converted to the disolvate RbGaH 4 �9 2DG, the solubility of wh ich changes negligibly in a b road range of temperatures (-36 to + 80~ The nonvar iant point C at 80 ~ and a RbGaH 4 concentrat ion of 8.0 mo le % cor responds to the equi l ibr ium RbGaH 4 �9 2DG ~ RbGaH4 + 2DG. The solubility of the nonsolvated RbGaH 4 drops to 3.14 mole % when the temperature is raised to 115 ~ and at 130 ~ it is evidently close to zero. The nature of the change in the solubility in the sys tem RbGaH4-DG and of the convers ions of the sol- rates is analogous to that noted on the fusibility d iagrams of Na2SO4-H20 [9-11], NaBH4-pyr id ine [5], and C sGaH 4 - d ig lyme. CONCLUSIONS i. The solubility in the sys tem RbGaH 4 -d ig lyme was studied in the interval f rom -66 to + 115 ~ by isothermal , v isual -polythermal , and differential thermal methods . 2. The existence of the solvates RbGaH 4 �9 6DG and RbGaH 4 �9 2DG, wh ich mel t incongruently at -36 and 807, respectively, was established. 3. Above 80 ~ nonsolvated RbGaH 4 is at equi l ibr ium with the solution. L ITERATURE C ITED 1. A .E . Finholt, A. C. Bond, and H. J. Schlesinger, J. Amer. Chem. Soc., 69, 1199 (1947). 2. V . I . Mikheeva and S. M. Arkhipov, Zh. Neorgan. Khimii, 12, 1142 (1967). 3. L . I . Zakhark in , V. V. Gavr i lenko, and Yu. N. Karaks in , Synth. in Inorgan. and Metal lorgan. Chem. , I, 37 (1971). 4. T .N . Dymova and Yu. M. Dergaehev , USSR Patent No .364562 (1972); Byull. Izobr., No. 5 (1973). 5. V . I . M ikheeva and L. V. Titov, Dokl. Akad . Nauk SSSR, 149, 609 (1963). 6. T .N . Dymova, S. I. Bakum, S. S. Grazhulene, and M. Mukhid inov, Izv. Akad . Nauk SSSR, Set. Kh im. , 1892 (1970). 7. P .P . K i sh and M. I. Golovei, Zh. Analit. Kh im. , 20, 794 (1965). 8. G .B . Ravieh, V. A. Vol 'nova, and G. G. Tsur inov, Izv. Sektora F i z . -Kh im. Anal iza, IONKh AN SSSR, 25, 41 (1954). 9. N .S . Kurna--kov and S. Z. Makarov , Izv. I FKh AN SSSR, 4, 329 (1930). 2598
  • 10. E~ I. Akhumov and E. V. Pylkova, Zh. Neorgan. Khimii, 3, 2180 (1958). 11. V. V, Vyazov and A. D. Pel 'esh (editors), Handbook of Solubility of Salt Systems [in Russian], Vol. 3, Gcskhimizdat, Leningrad (1961). 2599

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