The crystal structure of uranyl chloride-bis-triethylammonium chloride

J. inorg,nucLChem.,1974,Vol. 36, pp. 791-794. PergamonPress. Printed in Great Britain.

THE CRYSTAL STRUCTURE OF URANYL CHLORIDE-BIS-TRIETHYLAMMONIUM CHLORIDE

H. BRUSSET, NGUYEN-QUY-DAO and F. H A F F N E R Ecole Centrale des Arts et Manufactures, Institut de Chimie, Grande voie des Vignes, 92-Chatenay Malabry, France and the Universit6 de Paris VI, Laboratoire de Chimie syst6matique, 9, quai St. Bernard, Pads, France

(Received 12 January 1973) Abstract--The structure of uranyl chloride-bis-triethylammonium chloride, U O 2 C I 2 . 2 [ C 2 H s ) 3 N H C 1 ] has been determined from three-dimensional single-crystal X-ray data. Space group is I41/a with unit cell dimensions a = 13.55 fit (5), c = 24.32 fit (5). The measured and calculated densities are, respectively 1.79 (5) and 1.84 g/cm 3 for eight molecules per unit cell. The uranium atom has octahedral coordination in the UO2CI 2- anion, with four chlorine atoms at the corners of a rectangular plane while the uranyl group UO2z + is linear and almost perpendicular with regard to the rectangular plane The approximate symmetry of the ion is D,th. The chains (C2Hs)3NH are very similar to those which are found in the structure of triethylammonium chloride. The cohesion in the molecule U O 2 C I 2 . 2[C2Hs)3NHCI] is assured by weak hydrogen bonds N . . . H . . . Cl of length 3-6(1) fit. Two of the four chlorine atoms are linked to the nitrogen.

INTRODUCTION IN ORDER to understand the extraction mechanism of a dissolved uranyl salt in an aqueous phase by a dissolved tertiary a m m o n i u m salt in a n organic phase, it is necessary to k n o w beforehand the chemical species which can be formed. W h e n ' u r a n y l chloride UO2C12 has been extracted by tertiary a m m o n i u m salts, the uranyl chloride bis-trialkylammonium chloride complex which has the formula UO2C12 . 2(RaNHC1 ), is formed in a wide range of initial aqueous acid concentration[l]. R y a n [ l c ] has shown the formation of UO2C12- a n i o n a n d the general formula of the complex in the organic phase (R3NH)2UO2CI 4 for several tertiary a n d secondary amines. It seemed interesting to us to determine the structure of the uranyl chloride bis-triethylammonium chloride c o m p o u n d by single-crystal X-ray diffraction, to correlate with our results obtained previously during water a n d acid extraction by a tertiary amine[2], and during u r a n i u m extraction by the a m m o n i u m salt[3].

EXPERIMENTAL

Preparation of UO2Cl 2 . 2[(C2Hs)3NHC1 ] The alkyl ammonium salt is obtained by shaking two equal volumes of pure amine (CzHs)N and of hydrochloric acid in 12 M HCl (solution 1). The uranyl salt is dissolved in a solution of hydrochloric acid of the same molarity (solution

2). The mixture of the two solutions (1 and 2) leads to the formation of the fluorescent truncated prismatic crystals of light yellow-greenish color. The crystals obtained are relatively unstable. They decompose slowly when submitted to X-rays and heat and they change color (orange). The analytical data are UO2 (43.8 per cent); C1 (23.0 per cent); N (4.54 per cent); organic (32.8 per cent); calcd (43.8; 23.0; 4.54; 32.5).

Crystallographic data The UO2C12.2[(C2Hs)aNHC1] compound crystallizes in the quadratic system (space group 14~/a) with unit cell dimensions a = 13.55 (5) A ; c = 24-32 (5) A. The molecular weight is 651.8, the unit cell volume V = 4442 fit3. The observed density 1.79 (5) g/cm 3, the calculated density 1.844 g / e r a 3, with eight molecules per unit cell. The reflections were recorded with a Weissenberg camera using a superposed photographic film technique (CuK. radiation = 1.5418 A) and by the precession method. The rotation takes place along the crystal axis (110). It was not possible to use a molybdenum anticathode because of great unit cell dimensions which bring the reflections too close together. The set of inllependent intensity data was collected using a Joyce integrating microdensitometer. The intensity of the measured 1043 reflections was corrected for the usual Lorentz and polarization effects. The absorption correction was carried out taking into account that the linear absorption coefficient/~ was 322 cm- 1 (Cur" radiation). Because of the irregular shape of the crystal, the statistical method used for the absorption correction was to divide the reciprocal space into regions as a function of the diffraction angle and of the plane for which the average value of the 791

792

H. BRUSSET,NGUYEN-QuY-DAO and F. HAFFNER

modulus of the factor depends only on the crystal content [4]. The corrective coefficients for each region are calculated using curves F J F o = k(sin 0) and the reflection values are then brought individually closer to the values of the average corresponding curve. The least-squares refinements of the structure were carried out using the SAPHIR program of the Centre de calcul du CNRS, Orsay, France. DETERMINATION OF THE STRUCTURE The structure was solved by the usual heavy-atom methods. The uranium atom was located on the 8 (e) positions: _+ (0, g, 1 z~), (0, ~, x ¼ - z~} with z~ = 0.92. The scale factor coefficients, the Z, coordinate and the isotropic thermal parameter have been refined. The conventional R factor defined by E = ~ l l F o l - IF~ll/IFol, reached the value 0.23 in this first least-squares calculation. The location of the chlorine atoms was carried out

using a three-dimensional difference Fourier synthesis map where the contributions of the uranium atom added to the structure factors were subtracted. A second least-squares refinement was carried out on the coordinates of the uranium and chlorine atoms according to three cycles. The R factor converged on 0-20. A second three-dimensional difference Fourier synthesis obtained after subtracting the contributions of the uranium and chlorine atoms, permitted the oxygen atoms to be located easily. The nitrogen and carbon atoms were located by marking the barely visible peaks caused by these atoms on this second threedimensional difference Fourier synthesis. The determination of the carbon chain was facilitated even more by the knowledge of the crystal structure of triethylammonium chloride[5]. Three refinement cycles were carried out on the coordinates of all the atoms on the uranium and chlorine isotropic temperature factor, and on the scale factors while the temperature factors relative to those of

Table 1. Positional parameters (a, b) and thermal parameters for UO2C12.2((C2Hs)3NHC1) Species U CII CIu O N C1 C'1 C~ C2 C~ C~

x/a

0 0.070 (2)~ 0.072 (2) 0-112 (5) 0.312 (7) 0.330 (8) 0.387 (8) 0.314 (8) 0.327 (8) 0.354 (8) 0-198 (8)

y/b

z/c

0.25* 0.377 (2) 0.375 (2) 0.161 (5) 0.441 (7) 0.388 (8) 0.420 (8) 0-534 (8) 0.286 (8) 0.523 (8) 0-583 (8)

0.3303 (1) 0.404 (1) 0-254 (1) 0.334 (3) 0.358 (3) 0-326 (4) 0.396 (4) 0.355 (4) 0.319 (4) 0.453 (4) 0.384 (4)

B(Az) 0.70 (6) 4.4 (5) 4.0 (5) 4.0 5.0 5.0 5-0 5.0 5.0 5-0 5.0

*Parameters for which no standard deviations are given, are fixed by symmetry considerations. l'Numbers in parentheses are estimated standard deviations of the last significant digit. Table 2. Bond distances (A)* for U O 2 C I 2 . 2((C2Hs)aNHC1)

Atoms

Bonds in compound Distances

U-Oa ; U-O2 U-CII. 1; U-CII, 2 U-CIn, 1 ; U-Cln. 2 Clt, t - N 1 ; Cll.2-N 2 NI-C1 ; N2-C1 Na-C~ ; Nz-C'I NI-C~ ; N2-C"1 C1-C 2 C~-C~ C~-Cg

*See footnote (?) in Table 1.

1-94 (10) 2.67 (5) 2.70 (5) 3.57 (15) 1.08 (24) 1.42 (24) 1.26 (24) 1-40 (26) 2.00 (26) 1-73 (26)

Bonds in octahedron UO2CI 2 Atoms Distances Cln, I-CIa, 2 Clii,1-Clll,2

Cll.l-Clna ; Cll,2-Clu. 2 Ot-C1L1 ; O2-C11. 2

Ol-Clll,1 ; O2-C111,2 O1-Clu.2 ; O2-Cln, 1 O I - C I I . 2 ; O2-CII. 1

O1-O2 N1-CIII, 1;N2-Cln. 2 N1-O~ ; N2-O2 N1-O2 ; N2-O1 Na-U ; N2-U N1-N 2

3.94 (6) 3.91 (6) 3.66 (6) 3.44 (12) 3.54 (12) 3.20 (12) 3.05 (12) 3.88 (16) 4.22 (16) 4-70 (19) 5.93 (19) 5-00 (15) 9.92(21)

Crystal structure of UO2CI 2 . 2[(C2Hs)3NHC1]

the light atoms remain fixed. The R factor changes to a final value R = 0-15. We stopped at this stage of the refinement of the structure because of the imprecision of the experimental results which was due to the use of a copper anticathode (whose K, wavelength is thoroughly absorbed by the compound) and also due to the instability of the compound. Observed and calculated structure factor amplitudes for 1043 reflections used for the refinement are listed in the Table 4. The final atomic parameters of the atoms are given in Table 1. Tables 2 and 3 give bond distances and bond angles of the compound.

Table 3. Bond angles (deg)* for UO2C12 . 2((C2H5) 3 NHC1)

Octahedral group O2-U-O~ CII,2-U-Cll, 1 CII1,2-U-CII,2 ; CIII,1-U-Cll, 1 CIlI,2-U-CIII,1 CII,2-U-O2 , CIL1-U-O 1 CII, 1 - U - O 2 ; Cll,2-U-O t CII],I-U-O2; Clll,2-U-O 1 CIlI,2-U-O 2 ; CIlI,1-U-O 1 CI~,2-U-CIIL~. C1L~-U-Clm2

793

175 (5) 95 (2) 86 (2) 93 (2) 95 (3) 81 (3) 85 (3) 98 (3) 178 (2)

Selected angles U - O 1 - N 1; U - O 2 - N 2 U-O1-N 2; U-O2-N 1 N1-U-N 2 U-CI~,2-N2 ; U-CI~, ~-N ~ U-CI:L~-N ~; U-CIn,2-N 2 C1L~-N~-C ~ CI~a-N~-C' ~ CIL~-N~-C ~

DESCRIPTION OF THE STRUCTURE AND DISCUSSION

87 (4) 53 (3) 165 (3) 106 (3) 90 (2) 106 (10) 114 (10) 107 (10)

Figure 1 represents a general view of the molecular structure of the compound and Fig. 2 the projection of the crystal structure on the (a, e) plane. According to the views we have of the structure, it appears that the uranium atom has octahedral coordination, which is made up of four chlorine atoms and two oxygen atoms. The calculation of the plane containing the uranium

*See footnote (t) in Table 1.

Table 4. Observed and calculated structure amplitudes in electrons . m

•

H

ic.~c

: 1: . . . . io

meJ,

•

iss

•

7

': i=

s i ~

m

111

z~4 zz~

n

--

~

all

m

s

ra

~

ae

a=a

lie

141 2711 lee ~ 1~e 4~

,

I18 I H

101 m

~; ,",~ i

'°~

z~

,m

10

z~

," ~ ~,

~,.: :~ 1; =

lez

m

I ~

:g

~n

=a

-- -~e

"~=.

i °'*

m

m i

~

........................

..,|| 4m

tl4

2

21g

1~4

•

s

i

~e~ 4 ~

lee

!111| •

zls

~e

1~."

11s l m

am am ae4

04 tu " a t teT ~ee *Ts

am

~

l I ~ l ~I0 ~ l mlO

l~

s ii alO e m l e l~aae

elamll I al~ a l e e II ll~

e a m ~

* ~i

s

ip

lql

lille

•

Im

lle

l~lle

~o l ~ t~ l i e

ale m

:~:~

~e e all

:

ll~

g=

,, '2

i!ii e

4~

s

~

~l~ 410

Ill

m

ewoan

0

L'~

l

i ~

. 7

am m see

,41 t ~mt

*

i

414 m

,: • = te e a

,'--b"

...................... ~

m

~a m

.... • i

leo ~es

I 4tl ~

I" 11|

*N

~m

io ~se ~m ~m ~e4

n m~s z m s~ ~o

1.~ ' '

2~

m

L,.~o m

~z 4os ~ 1o as, ~ e

}

,_-_.

L.m

Ila ~s

:~: m

,o ~ 111 I14

am all

1; .~; g .......

i

~1

al* am m ~ 7 m sm

d

~o~ l z ~ ~so

Zel z ~

~e~

....

~

m

{} . . . . .

a~t~,=

t

o 1~*

i

t=

•

In

io

m ~z

~n m

o

e

mr

e~

nl

m

~l~

~

s

*lq

~e

~ ~es

~e

a

~es ~

~e

s

~

~

ee ~

w

~e

794

H. BRUSSET,NGUYEN-QuY-DAoand F. HAFFNER

c~

c)

Chr~

Ctx,~

Fig. 1. A general view of the molecular structure of the UO2C12 • 2((C2Hs)aNHCI ) compound.

side of the rectangular plane at the distance of U - O = 1.94 (10),~ and the UO22÷ group is linear. This distance is of the same order as those found in the literature for the uranyl group. Since the axis represented by the uranyl group is inclined at about 8 ° to the plane of the chlorine atoms, we can thus observe the formation of a slightly deformed octahedron. As a first approximation, the anionic group UO2CI~- possesses D+h symmetry, if we admit that the chlorine atoms are distributed at the corners of a square. An examination of the interatomic positions and distances of the a m m o n i u m cation (C2Hs)3NH + shows that, the ethyl groups distribute themselves about the valence axis N-C1, according to local ternary symmetry. This distribution is identical to that observed in the triethylammonium chloride compoundE5]. Let us examine the bond between the group (C2Hs)3NH + and the octahedron UO2C12-. If we compare the distances N1-C111, NI-Clu 1, we notice that the distance N1-CI t 1 is 3.6' (1)A while the distance N1-ClnA is 4.2 (1) A. We are thus led to conclude that the Cll, t atom and the C1L2 atom, which is symmetrical with the C1Lt atom with regard to the binary axis through the uranium atom, are linked to the anionic group. The N-C1 bonds are not coplanar with the chlorine and uranium atoms; in fact N1, C1Lt, Cln, t, C1~,2, Clli.2 , and N2 atoms have a chair shaped conformation. We can note that the N - H - C 1 bond lengths indicate that the hydrogen bonds are weak. The crystal structure of the compound UO2C12 . 2((C2Hs)3NHC1 ) can be described as a molecular structure. In conclusion, the structural study of the compound UO2C12.2((C2Hs)3NHCI) constitutes the first stage of our investigation of the association mechanism in the extraction phenomenon of uranyl salts using ammonium salts. Our next investigation will be a study of the different characteristic vibrations of this molecule with i.r. and Raman spectroscopy methods.

REFERENCES Fig. 2. Projection of the structure parallel to the h axis. Q , uranium atom; O, nitrogen atom: O. chlorine atom; O, carbon atom; ©, oxygen atom. and four chlorine atoms indicates, taking into account random errors, that these atoms are coplanar and that this plane in particular is parallel to the crystallographic axis c. The four chlorine atoms are situated at the corners of a rectangle with the following dimensions Clx 1 - Cln, t = 3.66 (6) A and Cll l-Clt 2 = 3-94 (6) ). "i'he average distances for U - C I t anci U - C l n are 2.68 (5) A. According to Tables 2 and 3 the oxygen atoms of the uranyl group UO22÷ are situated on either

1. (a) T. Sato, J. inorg, nucl. Chem. 28, 1461 (1966); (b) J. Bizot and B. Tremillon, Bull. Soc. chim. Ft. 122 (1959); (c) J. L. Ryan, Inorg. Chem. 2, 348 (1963); (d) A. S. Vieux, Bull. Soc. chim. Ft. 4281 (1968). 2. (a) H. Brusset, C. Duboc and F.Haffner, Bull. Soc. chim. Fr. 3546 (1968); (b) H. Brusset and F. Haffner, Bull. Soc. chim. Fr. 1829 (1969). 3. (a) H. Brusset, L. Matutano, A. Coulon and F. Haffner, 37th Congresso International de Quimica Industrial, Memoria Tomo, Madrid 525 (1968); (b) H. Brusset, L. Matutano and F. Haffner, An. R. Soc. esp. Fis. Quire. 67, 365 (1871). 4. A. J. C. Wilson, Nature, Lond. 150, 152 (1942). 5. F. Genet, Bull. Soc. fr. Mindr. Cristallogr. 88, 463 (1965).