INORGANIC CHEMISTRY

SOLUBILITY OF RUBIDIUM TETRAHYDROGALLATE

IN DIGLYME

T. N. Dymova and Yu. M. Dergachev UDC 541.8:532.739 2:546.35'681

Complex hydrides of gallium MGaH4(M = Li-Cs) are new and l i t t le studied compounds. Only qualita-

tive data a]:e known on the solubility of LiGaH 4 in diethyl ether, THF, and diglyme (DO); NaGaH 4 in THF

and diglyme. For the lower members of the series MGaH 4 (M = K-Cs), only one solvent is known - di-

glyme. These solvents have been used as the reaction medium in the synthesis of hydridogallates by ex-

change rea3tions [1-3]. The synthesis and purification of hydridogallates require quantitative data on their solubility ia diglyme. The solubility of [{bGaH 4 was studied in this work.

EXPERIMENTAL METHOD

The ~:eaction of gallium with rubidium and hydrogen in a melt [4] at increased temperature and pres-

sure was used for the production of RbGaH 4. RbGaH4 was extracted with DG from the reaction mass, re- presenting a solid melt, readily pulverized in the mortar.

For the decomposition of peroxides in water, DG was boiled with KOH, redistilled over Na, collect-

ing the fraction at 162 ~ and stored in a covered flask over Na wire in an atmosphere of dry argon.

RbGaH 4 was isolated from solution in diglyme, by distilling off the solvent in a vacuum (I mm Hg) at

105-110 ~ . The precipitated white crystals were separated from the mother liquor on the filter, washed with pentane, and dried 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 system RbGaH4 - DG was studied

by an isothermal method, using the usual technique of [5, 6]. Equilibrium was established in the solution in

2-3 h with intensive mixing. The samples were collected in an atmosphere of Ar with a pipette with a dense

filter at the; end. The concentration of the investigated solutions of RbGaH 4 in diglyme was established ac-

cording to gallium by determination of the optical density of aqueous solutions of complexes of gallium with xylene orange [7] on an SF-4A spectrophotometer.

When solid RbGaH 4 is dissolved in DG (20 ~ and samples of the solution are analyzed for a long time

(~i00 h), a supersaturated metastable state is established in the system. Initially the concentration of the

solution reached 18-22 mole %, then decreasing with time to 9.2 mole %, and subsequently remaining con-

stunt. In the interval from -66 to -35 ~ the solubility was sindiedby differential thermal and visual-poly-

thermal methods. The liquidus line was constructed according to the data of visual observations and estab-

lishment of the temperatures of disappearance of the last crystal. The points of the solidus line were de- termined according to the curves of heating of a solution cooled to -1O0 ~

Stepanov vessels with the solution and standard (A1203), placed in the seat of a massive copper block,

were cooled with liquid nitrogen, which was introduced into a ring-shaped space between the block and the

walls of the; outer casing of the instrument, made of stainless steel [8]. Simple and differential thermo-

couples wece introduced from below into the seat of the block. The heating curves were recorded on a Kurnakov pyrometer.

N. S. Kurnakov Institute of General and Inorganic Chemistry, Academy of Sciences of the USSR.

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2659-2661, December, 1973. Original article submitted April 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.

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%,

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 diagram of RbGaH 4 - Diglyme

DISCUSSION OF RESULTS

The polytherm of the solubility of RbGaH 4 in DG (Fig. i) consists of four branches. The first branch corresponds to the crystallization of pure diglyme. The branch AB in the interval 1.8-9.2 mole ~0 corre- sponds to crystallization of the hexasolvate RbGaH 4 �9 6DG, which melts ineongruently at -36 ~ The hexasol- vate, which splits out four molecules of diglyme, is converted to the disolvate RbGaH 4 �9 2DG, the solubility of which changes negligibly in a broad range of temperatures (-36 to + 80~ The nonvariant point C at 80 ~ and a RbGaH 4 concentration of 8.0 mole % corresponds to the equilibrium 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 system RbGaH4-DG and of the conversions of the sol- rates is analogous to that noted on the fusibility diagrams of Na2SO4-H20 [9-11], NaBH4-pyridine [5], and

C sGaH 4- diglyme.

CONCLUSIONS

i. The solubility in the system RbGaH 4-diglyme was studied in the interval from -66 to + 115 ~ by isothermal, visual-polythermal, and differential thermal methods.

2. The existence of the solvates RbGaH 4 �9 6DG and RbGaH 4 �9 2DG, which melt incongruently at -36 and 807, respectively, was established.

3. Above 80 ~ nonsolvated RbGaH 4 is at equilibrium with the solution.

L I T E R A T U R E C I T E D

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. Zakharkin, V. V. Gavrilenko, and Yu. N. Karaksin, Synth. in Inorgan. and Metallorgan. 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. Mikheeva and L. V. Titov, Dokl. Akad. Nauk SSSR, 149, 609 (1963). 6. T.N. Dymova, S. I. Bakum, S. S. Grazhulene, and M. Mukhidinov, Izv. Akad. Nauk SSSR, Set.

Khim., 1892 (1970). 7. P.P. Kish and M. I. Golovei, Zh. Analit. Khim., 20, 794 (1965). 8. G.B. Ravieh, V. A. Vol'nova, and G. G. Tsurinov, Izv. Sektora Fiz.-Khim. Analiza, IONKh AN

SSSR, 25, 41 (1954). 9. N.S. Kurna--kov and S. Z. Makarov, Izv. IFKh AN SSSR, 4, 329 (1930).

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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).

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