Crystal structure of the double salt (NH4)2SiF6·NH4NO3

I

Mat. R e s . B u l l . , Vol. 23, p p . 755-758, 1988. Printed in the USA. 0025-5408/88 $3.00 + .00 C o p y r i g h t (c) 1988 Pergamon P r e s s plc.

CRYSTAL THE

DOUBLE

STRUCTURE SALT

OF

(NH4)2SiF6"NH4NO 3

N. B u c h h o l z and R. Mattes A n o r g a n i s c h - C h e m i s c h e s I n s t i t u t der W e s t f a l i s c h e n W i l h e l m s - U n i v e r s i t a t M~nster, W i l h e l m - K l e m m - S t r a ~ e 8, 4400 M{]nster, B u n d e s r e p u b l i k D e u t s c h l a n d

( R e c e i v e d F e b r u a r y 16, 1988; Communicated b y A. Rabenau)

ABSTRACT The d o u b l e salt (NH4) SiF , NH NO was prepared from 2 6 4 3 solution. It c r y s t a l i i z e s in the h e x a g o n a l space group P 6 3 / m m c with a = 5.860(2), c = 14.754(4) ~ and Z = 2. The s t r u c t u r e c o n s i s t s of h e x a g o n a l layers, w h i c h contain the f l u o r i n e and o x y g e n atoms, and the ammonium ions. The s t a c k i n g of the layers is i d e n t i c a l to the C s 3 C r 2 C l 9 s t r u c t u r e type. MATERIALS

INDEX

:

ammonium,

hexafluorosilicates,

nitrates

Introduction

During a t t e m p t s to p r e p a r e single c r y s t a l s of (NH4)]VgO4F 5 in glass vessels, we i s o l a t e d well formed, c o l o u r l e s s He~a~ofiaI platelike or prismatic crystals of an unknown substance. W e i s s e n b e r g films h e r e f r o m showed that it had similar lattice c o n s t a n t s as the o x i d e f l u o r i d e s R b 3 V . O 4 F . and Cs3V.O.F., which z D z crystallize n the C s 3 F e 2 F 9 type s t r u c t u r e (I-3). G u i ~ e ~ by our i n t e r e s t in h e x a g o n a l f l u o r i d e layer s t r u c t u r e s (3) we d e t e r m i n e d the s t r u c t u r e of the u n k n o w n substance.

Experimental

After identification by (NH4)2SiF6. N H 4 N O 3 could be p r e p a r e d

755

crystal structure analysis as follows: 1.54 g of a

756

N. BUCHHOLZ, et al.

Vol. 23, No. 5

saturated aquous solution of a m m o n i u m n i t r a t e (12.1 mmol) were c a r e f u l l y c o v e r e d in a test tube first w i t h 0.5 ml w a t e r and then with 12.16 g of a saturated aquous solution of ammonium hexafluorosilicate (12.1 mmol). Hexagonal crystals of ( N H 4 ) ~ S i F 6 - N H 4 N O ~ grew w i t h i n 20 h in high yield b e t w e e n these lay4r~. A ~ s e l 4 c t ~ d crystal was m o u n t e d in a glass capillary. The d i f f r a c t i o n study was p e r f o r m e d on a S y n t a x (Nicolet) P21 four c i r c l e a u t o m a t e d d i f f r a c t o m e t e r with a Mo X - r a y source equipped with a g r a p h i t e m o n o c h r o m a t o r and a low t e m p e r a t u r e device. The final o r i e n t a t i o n m a t r i x and unit cell p a r a m e t e r s were d e t e r m i n e d at 140 K by least-s~uares treatment of 13 machine-centered reflections having 17 ~ < 2 @ < 3 3 ° . The intensity of one check reflection revealed no s i g n i f i c a n t change in intensity during data a c q u i s i t i o n . C r y s t a l data: H , ~ F c N A O ~ S i , M = 258.2, h e x a g o n a l , space g r o u p P6~/mmc, a = 5 . 8 6 0 ( 2 ) ~ ~ ~ ~4.754(4) ~, V = 436.8 ~, Z ~I 2, Dm = 7.94, D = 1.96 g cm-~, F(000) = 282, ~(Mo-K~) = 3.9 cm . c From a Guinier p o w d e r d i a g r a m lattice c o n s t a n t s at room t e m p e r a t u r e a = 5.866(2) and c = 14.769(5) ~ were c a l c u l a t e d . A total of 442 r e f l e c t i o n s were m e a s u r e d at 140 K by the e/28 scan m o d e with v a r i a b l e scan speed from 2.0 to 2 9 . 3 ~ / m i n and 28ma x = 54 ° . The data were c o r r e c t e d for a b s o r p t i o n (empirical ~ -scan c o r r e c t i o n ) , L o r e n t z and p o l a r i z a t i o n factors. E q u i v a l e n t ref l e c t i o n s were m e r g e d to give a total of 220 u n i q u e reflections, from w h i c h 168 had I > 1.96 ~ (I). The s t r u c t u r e was solved by P a t t e r s o n m e t h o d s and s u b s e q u e n t d i f f e r e n c e F o u r i e r syntheses. H y d r o g e n atoms could not be localized. ~ r e f i n e m e n t of ~0 p a r a m e t e r s with the w e i g h t i n g scheme I/w = o ) + 0.0008 F c o n v e r g e d at R = 0.061, R w = 0.056; g o o d n e s s o~ fit S = 1.75~. The f i n ~ 1 3 e l e c t r o n d e n s i t y map showed several r a n d o m features ( < 0 . 7 6 e A- ) in the v i c i n i t y of NI and N2. S H E L X p r o g r a m m s have been used t h r o u g h o u t .

Results

and D i s c u s s i o n

T a b l e I c o n t a i n s the final atomic p a r a m e t e r s , some intera t o m i c angles and d i s t a n c e s , Fig. I shows the s e q u e n c e of the h e x a g o n a l layers along c. The s t r u c t u r e of the double salt (NH4)2SiF6. N H 4 N O q can e a s i l y be d e r i v e d from the C s 3 C r 2 C l 9 type struc£ure: Bo£h ~ t r u c t u r e s c o n t a i n a A B A C B C series of six layers; in Cs3Cr2Cl 9 each layer consists of Cs and 3 Cl, in (NH)2SiF .NH4NO~_ the A and C layers have the c o m p o s i t i o n NH 4 (N19 and ~ F, the B layers the c o m p o s i t l o n NH 4 (N2) and 3 0 . Each pair of Cr atoms, w h i c h fill the Cl 6 o c t a h e d r ~ s h a r i n g a face, is r e p l a c e d in the p r e s e n t s t r u c t u r e by a single N atom (N3). This is located in the center of a t r i a n g l e of three o x y g e n atoms, thus f o r m i n g the NO~ion. The silicon atoms fill the F6 o c t a h e d r a a b o v e the o ~ i g i n along z, w h i c h are empty in C s ~ C r 2 C l a [ The Si-F bond distance of 1.681(3) ~ agrees well w~th t6e l i t e r a t u r e data for the cubic m o d i f i c a t i o n of (NHA)gSiF ~ (4). The SiF6 =- o c t a h e d r o n is r e g u l a r w i t h i n the standard ~ e ~ i a t [ o n s . The

Vol.

23,

No.

5

DOUBLE SALTS

757

N-O bond length in the NO 3- ion, 1.256(6) ~, is similar to the a v e r a g e values w h i c h have Seen found in several m o d i f i c a t i o n s of N H 4 N O 3 (5,6). The NH4 + ions are twelve c o o r d i n a t e d . The hydrogen atoms are d i s o r d e r e d and form r a n d o m l y o r i e n t e d h y d r o g e n bonds to o x y g e n and fluorine atoms. The N - H " . N and N-H'..O d i s t a n c e s are in the range 2.956(6) to 3.155(5) ~.

C}-

. . . . . . . . . . .

' p

•

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P

©

q

-'

p

[001]

•

5'

t_

.

.

.

C) .

.

C

o

©

I

.

.

.

.

.

.

.

J

r'

C

I

,

I

,

'

i

©-

'

-0

0

i

l

o

(~

i

' i

A

~

-

i

I

--+[ml1

0

Cs

• Cr

ONH4

o

Si

• N

FIG. I C o m p a r i s o n of the sequence of the h e x a g o n a l layers in the s t r u c t u r e s of Cs3Cr2Cl 9 and ( N H 4 ) 2 S i F 6 - N H 4 N O 3 v i e w e d along I110].

The v i b r a t i o n a l f r e q u e n c i e s of (NH4)2SiF~6"NH4NO"7 ~j are very similar to the values o b s e r v e d for the lnalvlaual compounds (NHa)pSiF 6 and N H 4 N O ~. V SiFt is slightly broadened in the as ~ douBl~ saIt and V NO~-is inactive in the infrared due to different selection ru~es in the respective structures. Very probably N H 4 N O R forms similar double salts with a m m o n i u m salts of other d i V a l ~ n t h e x a f l u o r o a n i o n s . But s y s t e m a t i c studies have not yet been performed.

758

N. BUCHHOLZ, et al.

TABLE

Fractional atom

site

Si F O NI N2 N3

2a 12k 6h 4f 2b 2d

site

3m m mm 3m 6m2 6m2

Thermal

Si F O NI N2 N3

I

Atomic

symmetry

Vol. 23, No. 5

Coordinates

x.104

y.104

z.104

0 1356(4) 5427(6) I/3 0 I/3

0 2711 10853 2/3 0 2/3

0 - 658(2) I/4 916(6) I/4 3/4

Parameters

U11

U22

U33

U23

19(I) 34(2) 32(3) 21(3) 27(4) 39(5)

19 27(2) 26(4) 21 27 30

17(2) 30(2) 44(4) 35(5) 22(6) 18(6)

0 11(2) 0 0 0 0

(x 103 ) U13

U12

Ueq

0 5 0 0 0 0

9 13 13 11 14 15

18(I) 31(I) 35(3) 26(3) 25(4) 26(4)

o

Interatomic

Distances

(in A) and Angles

Si - F N3 - O

1.681(3) 1.256(6)

(6x) (3x)

Fi - Si - F

NI NI NI

2.965(5) 3.066(6) 3.155(5)

(6x) (3x) (3x)

N2 - O N2 - F

- F - F - 0

(in deg)

90.0(2)

2.956(6) 3.044(5)

(6x) (6x)

References

I. F. Wall, G. P a u s e w a n g 257 (1971). 2. R. Mattes

and D.J.

and H. F~rster,

3. N. Buchholz, M. Leimkuhler, Chem. in press.

Babel,

J. L e s s - C o m m o n

J.Less-Common L. Kiriazis

Met.

87,

Met.

227

(1982).

and R. Mattes,

Hamilton

5. C.S. Choi, J.E. 1357 (1972).

and E. Prince,

Acta

Crystallogr.

B28,

and A.W. Hewat, 2005 (1980).

Acta

Crystallogr.

B25,

6. B.W. Lucas, 1038 (1979)

M. Ahtee and B26,

Rush,

J. Chem.

Inorg.

4. E.O. Schlemper, W.C. 44, 2499 (1966). Mapes

and J.J.

25,

Phys.