THEBIS-(ACETYLACETONATO)-URANIUM(~I) S O L V A T E S
Sept., 1960
count for their magnitudes in a realistic way. The systeins involved are unusual in that the fundamental sorbate-solid interactions are small, and comparable Ivith the heats of liquefaction of the gases involved. This being the case, it is reasonable to expect that the linear analysis of enthalpies employed in this work would be unusually successful, even more so than in the case of graphite, where the gas-solid interactions tend to be higher. Having arrived at these conclusions,
1289
it would seem possible to be able to calculate the enthalpy-coverage plots, and hence the isotherms, for a number of similar systems, provided some weighting factor can be introduced for topographical heterogeneities and that the gas-solid dispersion constant is accessible. Acknowledgments.-I wish to thank Miss A. D. Warner for assistance with the calculations, and Dr. A. M. Bueche for critical comments on several occasions during this work.
THE CHEMISTRY OF THE SOLVATED METAL CHELATES. 111. THE BIS- (ACETYLACETONATO)-URAKIUR.I(VI) SOLVATES' BY
llrERLEY
17'.
JVENDLANDT,
JOHN L. BEARAND G. ROBERT HORTON
Department of Chemistry, Texas Technological College, Lubbock, T ~ x a s Receiued March 1 g t 1960
The bis-( acety1acetonato)-uranium(V1)solvates with water, n-propyl alcohol, n-butyl alcohol, ethyl alcohol, acetone, acetophenone, acetylacetone, dioxane, ammonia and pyridine were studied by calorimetric and thermogravimetric methods and by differential thermal analysis (DT.4). The heats of solvation, AH,, for the reaction (where AA is acetylacetone) U02(.\.4),(s) solvate(1) = UOz(AA)?.solvate(s)were found to be from -3.22 to -20.7 kcal. mole-'. All of the complexes r i t h oxygen-containing solvate molecules were much less stable thermally than those containing nitrogen. In the case of the former, the desolvation was generally a one-step process, followed by the decomposition of the anhydrous complex. With the latter, total disruption of the anhydrous complex immediately followed the desolvation reaction. The DTA thermograms showed that in many of the desolvation reactions, two or more endothermic energy changes took place.
+
Introduction
Bis-(acety1acetonato)-uranium(V1) readily forms solvates m-ith compounds such as water, ammonia, acetylacetone, pyridine, the alcohols, acetone and others.2,3 In an effort to elucidate the structure of these solvates, particularly in reference to the coordination number of uranium(V1) , Sacconi and co-workers4-6 and Comyns and c o - ~ o r k e r studied s~ the complexes by ultraviolet and infrared spectroscopy, magnetic susceptibility and conductivity measurements. It was concluded that the 0-U-0 group in the complex was coordinatively unsaturated and t,hat t,he solvate molecules n-ere attached directly by U-0 or U-S bonds, giving uranium a coordination number greater than six. In an ef'fort to elucidate further the nature of the interaction between t,he solvate molecule and the metal complexes, the solvated complexes mere prepared and subject'ed to thermal decomposition on the thermobalance and by differential thermal analysis (DTA). Further information on this interaction was obtained by measuring t'he heat.s of solvation using an indirect calorimetric procedure. Experimental
All other chemicals used were of C.P. quality. Preparation of Solvated Complexes.-The bis-(acetylacetonat0)-uranium(V1) and its solvates were prepared as previously described.6~7 The compounds were analyzed by ignition to UaOs in porcelain crucibles a t 800". The metal oxide contents were within 0.5y0of that required by theory. Calorimeter.-The calorimeter used has been previously desrrilsed.8 The finely powdered complexes or the liquid solvate compounds were allowed to react with 250 ml. of 11.7 N hydrochloric acid contained in the Dewar calorimeter flask. Duplicate and in some cases triplicate runs were made on each compound. Thermoba1ance.-The automatic recording thermobalance and its modification previously have been described.gv10 Sample sizes ranged in weight from 50 t o 90 mg. and were run in duplicate or triplicate. The furnace heating rate was linear with time a t 6.6" per min. A slow stream of air was permitted to flow through the furnace during the pyrolyses. DTA Apparatus.-The D T 4 apparatus has been described previously.ll The platinum-platinum-lO~o rhodium alloy thermocouples were replaced by thermocouples made of chrome1 and alumel alloys to achieve greater sensitivity. Samples ranged in weight from 0.10 to 0.18 g. and were run in duplicate or triplicate. The furnace heating rate was 6.5" per min. with a recorder chart speed of 6 in. per hr.
Experimental Results Heat of Solvation Studies.-The heats of solvaReagents.-The uranium(V1) nitrate 6-hydrate --as ob- tion were calculated indirectly by measuring the tained from l r e r c k and Co., Rahway, N.J. The acetylacetone wa.s obtained from Eastman Organic Chemicals, heats of solution of the anhydrous bis-(acetylRochester, S . 'Ir. It was distilled just prior to use; the acetonato)-uranium(V1) complex, the solvated fraction used had a boiling point of 133-135". metal complex, and the Folvate compound in 11.7 N hydrochloric acid a t 25.0". These heats of so(1) Presented a t the 15th Southwest Regional Meeting of the American Chemical Society, Baton Rouge, Louisiana, December 3-5, lution reactions can be illustrated by the example 1959. of U02(C5H702)2.H20; it is assumed that the ( 2 ) W. Bilta and J. A. Clinch, Z . a n o ~ g .allgem. Ckem., 40, 221 complexes are completely dissociated in the acid. (1904). (3) IC. Ha!:er, ibid., 168, 85 (1927). (4) L. Sacmni and G. Giannoni, J . Chem. Soc., 2368 (1954). (5) L. Sacconi and G. Giannoni, ibid., 2751 (1954). (6) L. Sacconi, G. Caroti and P. Paoletti, ibid., 4257 (1958). (7) A. E. Comyns, B. M.Gatehouse and E. Wait, ibid., 4655 (1958).
(8) J. H. Van Tassel and FV. W. Wendlandt, J . A m . Chem. Soc., 81, 813 (1959): (b) 82, 4821 (1960). (9) W. W. Wendlandt, Anal. Chem., 30, 56 (1958). (10) W. W. Wendlandt, ibid., 32, 848 (1960) (11) W. W. Wendlandt, J . Chem. Educ., 37, 94 (1960).
W.W. WENDLAKDT, J. I,. REARAXD G . R. HORTOX
1290
Tol. 64
TABLE I HEATS
OF
SOLUTION
OF
BIS-(ALI:TYLACETOXATO)11.7 A' HYDROCHLORIC LACII) 25.0" THE
LVZANILr?J(~TI) COMPLEXES I N AT
AH,
Compounds
EO2(AA)?,wat'er(8) U02(AA)2.ammonia(s)
C02(AA)2.pyridine(P) UOz(AA)z,acetophenone(s) U02(i\A)2.acetylacetone(s) TEMP ' C
Fig. 1.-Thermogravimetric curves for the his-(acetylacetonato)-iiranium(VI) solvates: A, uO~(-IA)+.xater; 'B, r02(AA)~.acetophenone; C, UO,(AA)?.pyridine; I), t-02(.4-4)2.1 25-dioxane; E, UO?(.I;\)? acetylacetone; F, ~ ' J O r ( i l A ) ? . n - ~ ) u1 talcohol ~
UO, (.4.4)2,acet#one(x) UO, (BA)*.I .25-dioxane(s) tJOs(AA)2~n-but~yl alcohol(s) UOz(AA)2.n-propyl alcohol(s)
U 0 2(AA)?.ethyl alcohol (p) UO?(AA)?(s) Water (1) Pyridine(1) Acetylacetone(1)
I
Acetophenone (1)
LTEMP
'C
Fig. 2.-Thermogravimetric curves for the bis-(acetj 1acetonatol-uranium(V1) solvates: A, U02(AA)2.n-propyl alcohol, B, TTO2(.4.4)2 .acetone, C, UO?(AA), .ethyl alcohol, 11, V02( AA)?.ammonia
+
+
LT01(C~H702)2(s) 2H+(aq) 2CI-(aq) = cOz++(aq) i- 2C,&Oz(aq) 2C1-(ay) 1701(C,H,0,)?II>O(s) 2H+(aq) 2Cl-(aq) UO.++iaq) 2C,H802(aqj H,O(aq) 2Cl-(aq) H20(1) = H20(aq)
+
+
+
+ +
n-Propyl alcohol(1) n-Butyl alcohol(1)
=
+ AH2 ( 2 )
AHo ( 3 )
+
ITO?(C'HiO?)>(q) H20(1) LO,(C,H,OJ)i H?O(i) AH4 AH4 = AH,
Dioxane(1)
AH1 (1)
The heat of solvation, AHd, is represented by
niid is equal to
Acetone(1)
(4)
+ AH8 - AH1
The heats of solution of all of the compounds studied are given in Table I; the average heats of solvation are given in Table 11. Since the heats of solution values were independent of sample size, they were considered to be equal to the values a t infinite dilution. The interaction between mater and the alcohols with bis- (acety1acetonato)-uranium (VI) had the smallest heat of solvation, followed by the ketones and then the ether type compounds, This increase
Saiiiple wt., L.
1.2922 0.9095 0.4477 1.0044 0.3847 0.4744 1.3799 1.1946 0,9343 1.1065 1.0422 0.9945 ,5352 ,3458 ,7378 ,5663 .4239 .5150 .9380 1.0100 1.4177 0.9865 ,4204 ,2433 ,0946 ,1552 ,6114 ,6015 ,9046 ,8045 ,5618
Av. - A H ,
kcal.
kcal. mole-'
'7.31 "50 4.74 4.54 10.20 10.53 0.89 .71 .01 .00 3.38 3.36 0.87 0.93 2.35 2.36 2.49 2.64 2.49 2.44
2.40
mole-'
4,i2
4.G1 0.95 0.97 14.33 14.30 2.07 2 11 0.73 0.76 3.10 3.30 ,3485 3.76 ,2929 3 . 4 3 ,6882 1 . 4 9 ,6094 1.35 ,9976 1 . 3 : 3 ,6490 1 . 2 0
4.64 10.36
0,80 0.00 3.37 0.90 2.35
2.57 2.46 4.66 0.96 14.36
2.013
0.75 3.20
3.60 1.42 1.27
20. io" ,2748 1 70 1 .79 ,4893 1 88 Calculated from selected values taken from the Sational Bureau of Standards, Circular 500, 1952. Animonia(g) Ethyl alcohol(1)
in the heats of solvation is in accord with the increased electron donor ability of the oxygen in the solvate molecule. Since nitrogen has a greater electron donor ability than oxygen, it is to be expected that the heats of solvation mould be greater than those found for solvate molecules containing oxygen atoms. This was indeed found to be the case. From ultraviolet and infrared spectroscopy data, it was found that the solvated uranium complexes contained C-0 and U-N bonds5s6 If the heats of solvation can be construed as the "binding en-
Sept., l!IAO TABLE
Hkxm
OB
~C)LVATIOS OF
11
THE
BIS-(ACETYLACETONATO)-
URAXIUX(VI) COMPLEX AT 25.0' Solvate molecule
a
V'ater n-.Propyl :dcohol E - ~ I l t alf
