Jan. 5 , 1954
THERMAL DECOMPOSITION OF cOPPER(I1) FLUORIDE DIHYDRATE [CONTRIBUTION FROM THE DEPARTMENT OF CHEMISTRY, UNIVERSITY OF NEW
263
HAMPSHIRE]
The Thermal Decomposition of Copper (11) Fluoride Dihydrate1 BY CHARLES M. WHEELER,JR.,
AND
HELMUT M. HAENDLER
RECEIVED JULY 24, 1953 The thermal decomposition of copper(I1) fluoride dihydrate has been studied by differential thermal analysis, X-ray diffraction and chemical analysis. It undergoes a two-stage decomposition, forming CuOHF.CuF2 a t 132O, followed by decomposition to the oxide and fluoride a t 420'. The related basic fluoride, CuOHF, also undergoes a two-stage decomposition, first forming CuOHF.CuF2 a t 345'.
Introduction An indication of the unusual behavior of copper(I1) fluoride dihydrate on heating was first given by Berzelius,2who reported the formation of a basic salt when an aqueous suspension of the hydrate was boiled. Balbiano3 prepared this basic salt, CuOHF, and reported the formation of the oxide on heating it in air. A similar observation was made on the hydrate by Kurtenacker, Finger and Hey. This is in sharp contrast to the behavior of copper(I1) chloride dihydrate, which loses its water of hydration above 130") forming the anhydrous chloride. The fluoride hydrate loses water and hydrogen fluoride, and the anhydrous fluoride cannot be prepared by this method. A study of the action of fluorine on copper compounds has shown the fluorination of anhydrous copper(I1) sulfate or of the sulfides t o be an effective method of preparation. Because of these peculiarities this study of the thermal decomposition of copper(I1) fluoride dihydrate was undertaken as part of a general investigation of decompositions of complex fluorides and hydrates. Experimental Copper( 11) Fluoride Dihydrate .-The dihydrate was prepared by adding basic copper(I1) carbonate, Cu(OH)2. CuCOa, with stirring, to a twofold excess of 40% hydrofluoric acid.4~6 Polyethylene apparatus was used to prevent formation of fluosilicate. After standing several hours with occasional stirring the precipitated hydrate was filtered, washed with ethanol, air dried briefly and stored in platinum. It was found advisable to use freshly prepared material since the hydrate slowly reacts on standing, presumably forming the basic fluoride. Anal. Calcd. for CuF2.2H20: Cu, 46.20; F, 27.62. Found: Cu, 45.78, 45.82, 45.86; F,27.16, 27.16, 27.20. The X-ray powder pattern of the material was in agreement with that of a sample made by hydrating anhydrous copper(I1) fluoride by the method suggested by Walton.0 The weight gain of the anhydrous fluoride was within 1% of the theoretical value for dihydrate formation. Basic Copper(I1) Fluoride.-The basic fluoride, CuOHF, was prepared by boiling an aqueous suspension of the dihy(1) This work is from a program of research on inorganic fluorides supported in part by the Research Corporation and the Atomic Energy Commission. (2) J. J. Berzelius, P o g g . Ann., 1 , 28 (1824); A n n . chim. phrs., [2J 2 4 , 61 (1823); J. W. Mellor, "A Comprehensive Treatise on Inorganic and Physical Chemistry," Vol. 111, Longmans, Green and Co., London, 1923, p. 155. (3) L. Balbiano, Gaez. chim. ilal., 1 4 , 74 (1884); Chcm. Cenlr., 56, 931 (1885). (4) H . Kurtenacker, W. Finger and F. Hey, Z . anorg. Chem., 211,83 (1933). (5) F. H . Edmister and H. C. Cooper, THISJOURNAL, 42, 2419 (1920). (6) H. F. Walton, "Inorganic Preparations," Prentice- Hall, Inc., New York, N. Y,, 1948,p. 24.
drate.7 Boiling over an extended period of time seemed to have no effect on the composition. The filtered fluoride was mashed with alcohol and ether, and air-dried. Anal. Calcd. for CuOHF: Cu, 63.84; F , 19.08. Found: Cu, 62.88, 62.99, 63.14; F , 18.57, 18.81, 18.95. General.-The procedure for the thermal decomposition has been reported previously.8 All runs were made a t atmospheric pressure. The X-ray powder diffraction photographs were made with copper radiation, filtered by nickel, using a 114.59-mm. Phillips camera. Samples lvere mounted on Pyrex fibers, in the dry-box if necessary, using Formvar "T" in ethylene chloride and were then coated with Formvar for protection against atmospheric moisture. Intensities were estimated visually by comparison with a film of known intensity. Copper was determined electrolytically.9 and fluorine was determined by the volumetric lead bromofluoride method
Results and Discussions Differential heating curves (Fig. 1) obtained during the thermal decomposition of the hydrate, a t atmospheric pre+ sure and without free access to air, 4how two mauima, corresponding to the reactions
132O
+ H F + 3Hz0 CuOHF.CuFz +CUO + CuFz + H F + H?O
2[CuF*.2H?O]
___f
CuOHF.CuF2
(1)
420'
(2)
A weighed sample of the hydrate, heated in a stream of drv nitrogen to 150", came to constant weight with a weight loss corresponding to that expected for equation 1 . Anal. Calcd. for CuOHF.CuF2: Cu, 63.21; F , 28.34. Found: Cu, 63.00, 62.87, 62.72; F. 28.30, 28.50, 28.63.
Fig.
150 200 250 300 350 400 450 Sample temperature, 'C. 1.-Thermal decomposition of CuF2.2H20, CUOHF, -.-; CUOHF CuF2'2H20, -.
+
- - -.
(7) H. Martin, R. L. Wain and E. H . Wilkinson, A n n . Applied Bioi.,
ae, 412 (1942). ( 8 ) H . M. Haendler, C. M. Wheeler, Jr., and D. W. Robinson, THIS JOURNAL, 74,
2353 (1952). (9) I. M. Kolthoff and E. B. Sandell, "Textbook of'auantitative Inorganic Analysis," The Macmillan Co., New York, N. Y., 1952, p. 407. (10) P.Ehrltch and 0. Pietzka, Z.anal. Chcm., 138. 84 (1961).
CH.IRLFSAT TYHEELER,JR.,
2ii3
1
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2
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I ,I
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1
1
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Yol. 70
HELMVT 11. HAENDLER
show three maxima: the first, a t 125-130”, corresponds t o the initial decomposition of the dihydrate as in equation 1; the second to the decomposition of CuOHF as in equatiotl 3 and the third t o the decomposition of the CuOHF.CuI: formed in the first two stages. The nature of the decompositions depends on the presciice or absence of air. I n the presence of air, copper(I1) oxide is the final product and no well-defined steps in the decomposition series can be observed. If the decompositions are carried out, however, in a closed system, so that the hydrogen fluoride produced prevents contact with the air, the final products : r e the oxide and fluoride, and the stages are shown clearly. The uew X-ray powder data are given in ‘ h b l e I. I t i5 of interest t o note that the “d”-spacings listed for the tlihydrate in the ASTM diffraction catalog1’ appear t o include values for the basic fluoride, CuOHF. This illustrates the difficulty of preparing and keeping a pure sample of the hydrate. An attempt is being made to grow single crystals of the hydrate for X-ray structural studies.
/ # 1 1 1 1 1
4
5
.\XD
I I
TABLEI
111
S-R.417 POWDER DATA
I 1
6
7
It
I
I
/ I
CuF~2H20 Relative intenqity
I,
I I I I I I I
8 1
.
Fig. 2.-Diffraction diagrams: 1, CuFz,2H!O; 2, CuF2.2He0 heated a t 132’ (CuOHF.CuF2); 3, CuOHF.CuF? CuF2); 4, CuO; 5 , CuF?; 6, Cuheated a t 420” (CuO OHF; 7, CuOHF heated a t 345” (CuOHF.CuF2 CuO).
+
+
The related basic fluoride also undergoes a two-step decomposition, as shown by the differential data and the Xray patterns, with the reaction 4CuOHF
345O
---+
+
CUOHF.CUF? 2CuO
4-H F + H?O (3)
being following by decomposition of the CuOHF.CuF2 a t 410-420°, as in equation 2. The first decomposition product of the dihydrate, white CuOHF.CuF2, reacts with atmospheric moisture t o form an equimolar mixture of CuOHF and CuF2.2H20, as shown by X-ray patterns taken during the reaction. A sample of CuOHF.CuF2 was exposed t o water vapor until the weight gained indicated absorption of two moles of water per mole of starting material. The mixture was placed in a desiccator over anhydrous CuOHF.CuF2 and allowed t o reach constant weight. Hydrogen fluoride evolves s l o ~ l yon standing, presumably because of decomposition of the dihydrate to the basic fluoride. Anel. Calcd. for [CuOHF C U F V ~ H Z O CU, ] : 53.61; F, 24.03. Found: Cu, 53.67, 58.33, 53.59; F, 23.47, 23.93, 23.93. Differential heating curves of the “hydrate” mixture
+
4.78 3.71 3.15 3.10 2.98 2.71 2.55 2.35 2.29 2.18 2.02 1.96 1.92 1.85 1.75 7 .70 1.60 1.58 1.55 1.53 1.49 1.43 1.33
CuOHF .CuFs Relative n’ intensity
100
4 22
25 12 12 12 45 18 15 38
3 54 3 43 2 71 2 61 2 58 2 47 2 34 2 25 2 20 2 10 1 99 1 87 1 84 1 79 1 77 1 72 1 70 1 63 1 55 1 51 1 43 1 41
9
15 12 17 13 8 8 20 3
1
5 5 6 8
100 85 70 70 30 20 12 45 12 25
3 3 12 18 6 45 30 45 6 25 12 G 3
CuOHF Relative intensity d
4.68 2.65 2.55 2.43 2.34 2.14 1.97 1.88 1.63 1.59 1.56 1.54 1.51 1.49 1.48 1.44 1.43 1.36 1.33 1.30 1.28 1.26 1.24 1.21 1.17
ion 8 40 25 >
15 3 ti 20 3 15 3 10 5
9 9 3
1 1 1 2 1 1 1 2 1
DURHAM, S. H . (11) “X-Ray Diffraction Data Cards,” American Society for Testing Materials,” Philadelphia, Pa.
