The polymorphism of protactinium pentabromide

INORG. NUCL. CHEM. L E T T E R S V o l . 1 5 , pp. 2 1 9 - 2 2 3 P e r g a m o n P r e s s Ltd. 1979. P r i n t e d in G r e a t B r i t a i n

The

Polymorphism

of Protactinium

Pentabromide

D. B R O W N Chemistry

Division,

A.E.R.E., Harwell, Oxon, E n g l a n d .

(Received

26

March

1979)

ABSTRACT X-ray polymorph

powder

data

of this

PTwith

a = 7.52

117.55

(6) ° , X =

morphism

are

reported

compound. (i), b = 109.01

of P a B r 5

for y - P a B r s, a p r e v i o u s l y

It c r y s t a l l i s e s 10.21

(I),

i n the

c = 6.74

unidentified

triclinic

space

(i) ~, a = 8 9 . 2 7

(5) ° , a n d is i s o s t r u c t u r a l

with

group

(5) ° , 8 =

8-UC15.

The poly-

is d i s c u s s e d .

INTRODUCTION The reported

structure by

determined

Brown from

of t h i s

c = 9.92

~,

~-PaBrs,

e t al 2 w h o

single

crystals

which

crystal

modification

subsequently

unpublished

is i s o s t r u c t u r a l

also presented data, (space

~ = 108.0 ° ) , h o w e v e r ,

determination, UBr 5 with

of

group

data

P21/c

to ~ - P a B r 5, l e d to t h e d e d u c t i o n 3, r e p o r t e d isostructural study

has

10.127

108.87

~ - P a B r 5.

However,

shown 5 UBr 5 prepared

8-modification b =

with

of UCI56,

(14),

in the

crystallising

c = 6.686

cell

~ - P a B r 5.

The

b =

for

a complete

structure

powder were

photographs

believed

L u x e t al 4, t h a t

a recent

neutron

same way

to b e

in s p a c e

dimensions,

a = 12.69,

which by

unit

with

of X - r a y

for PaBrs,

~ - U C I 5 I, w a s

polymorph,

unsuitable

a comparison

powder

preliminary

for a s e c o n d

were

with

UBr 5 was

diffraction

PT with

(4) ~, ~ = 8 9 . 2 5

(12) ° , 8 =

117.56

are n o w

for ~{-PaBrs,

of

to c o r r e s p o n d

isostructural

group

12.82,

powder with

a = 7.449

situation

with

respect

data

reported

to p o l y m o r p h i s m

in t h i s

compound

219

and

(7),

(4) ° a n d ~( =

(9) ° .

Crystallographic

the

the p r e s e n t

is d i s c u s s e d .

220

The P o l y m o r p h i s m

of P r o t a c t i n i u m

Pentabromide

EXPERIMENTAL Preparation

of PaBrs:

which

X-ray p o w d e r

X-Ray

Powder

Details

of the p r e p a r a t i o n

Samples

were mounted

capillaries

(i.d. 0.01

- 0.015

< 20 ppm).

Films w e r e

recorded

CuK

radiation

The ~I and ~2 r e f l e c t i o n s intensities

were

An absorption intensities, coefficient were

generated

correction

programme 0.0004

in order

derived

fory~aBrs.

refined by

~m :

have yielded

patterns.

This d i m o r p h i s m was

on a c c o u n t

of the single

~-PaBr5 data was

which

could r e a d i l y b e i n d e x e d

t h a t of ~ - P a B r 5. intensities

addition,

the s i n g l e

It w a s

since

be

subsequently,

15 mA).

and r e f l e c t i o n H I N T E N 9.

to the relative

films method

agreement

absorption results

of UBr5 II, and u s i n g the

limit w a s set at

data were

treated

in the same

of the u n i t cell p a r a m e t e r s

in the o r i g i n a l

to the c a l c u l a t e d

therefore

of P a B r 5 in this

one of two d i s t i n c t

on the basis

X-ray p o w d e r

communication 7

13

One of the

intensity

pattern

of the p r e l i m i n a r y

assumed

that this p o w d e r

it w a s n o t p o s s i b l e

pattern

to c a l c u l a t e

powder In

u s e d for the unit cell d e t e r m i n a t i o n

were

in evacuated,

data were

sealed

preparation

on the b a s i s

capillaries for w h i c h

and w e r e

powder

of the s i m i l a r i t i e s

for

unit cell

n o t available.

as p a r t of a l a r g e r - s c a l e

recorded,

(35 Kv,

The PaBr5 p o w d e r

then in p r o g r e s s

full s t r u c t u r a l

crystals

grown 2'13 on the ~ g m scale available

studies

Unfortunately

applied

preparations

not reported

crystal

16 h

AND DISCUSSION

exhibiting

did not correspond

for ~ - P a B r s 2'13.

pattern

products

(H20 and 02

camera w i t h

~ is the linear

the r e l i a b i l i t y

the n u m e r o u s

laboratory

patterns,

The

or L i n d e m a n n

u s i n g the p r o g r a m m e was

for

.

pattern

d a t a a n d new

The U B r 5 p o w d e r

15 yr.

12 -

a least-squares

1.5418 ~.

to e s t a b l i s h

the p a s t

samples

of the c y l i n d e r I0.

RESULTS During

structure

these

of

7,8

box

Scherrer

The p o w d e r

of ~r = 5.0, w h e r e

of Sin2O.

fashion

n o t resolved.

comparison with

C O H E N 12, w i t h

times

o f PaBrs

silica

atmosphere

using a Ig cm Debye

for c y l i n d r i c a l

unit cell was

for values

in a n i t r o g e n

for the UBr5

and r the radius

then i n d e x e d b y

cm)

.

prevlous±y

in t h i n - w a l l e d

and e x p o s u r e

were

u s i n g a value

the r e s u l t i n g

•

d a t a are r e p o r t e d w e r e p u b l i s h e d

Studies:

nickel-filtered

of the samples

only

not

d a t a could

between

this

The P o l y m o r p h i s m of P r o t a c t i n i u m P e n t a b r o m i d e

p o w d e r p a t t e r n of PaBr 5 and t h a t of UBr 5 the l a t t e r w a s isostructural with ~-PaBr53'4

This has

the r e c e n t d e t e r m i n a t i o n 5 of the

of U B r 5 and the structural

therefore,

now b e e n s h o w n to be e r r o n e o u s b y

full s t r u c t u r e

o f the PaBr s p o w d e r d a t a w i t h calculated intensity pattern

results,

PaBr5 w h i c h

of UBr5, w h i c h

is, in fact,

new, b e t t e r q u a l i t y p a t t e r n s

for this

c o m p o u n d b a s e d on the

now c o n f i r m that these c o r r e s p o n d to a p o l y m o r p h

is i s o s t r u c t u r a l w i t h UBr 5 and 8-UC15. was

r e p o r t e d to be

~-UCI56.

isostructural with Comparisons

221

associated with

of

The o r i g i n a l error,

i n d e x i n g the p o w d e r p a t t e r n on the b a s i s

d - P a B r 5 u n i t cell in the a b s e n c e of s t r u c t u r a l p a r a m e t e r s

of the

to p e r m i t i n t e n s i t y

calculations. This new p o l y m o r p h w i l l be d e s i g n a t e d ~ - P a B r 5 . the p o w d e r p a t t e r n calculated intensity

can r e a d i l y be

for the U B r 5 s t r u c t u r e , ~ i0 b e i n g o b s e r v e d .

unit cell d i m e n s i o n s 6.74

in space

(i) ~, ~ = 89.27

volume,

427.9 ~3,

is s l i g h t l y

c a l c u l a t e d d e n s i t y is 4.89 reflections have been results

= 108.77

(7) ° .

possible

117.55

refinement yields

a = 7.52

(i), b = 10.21

(6), ~ = i09.01

(5) ° .

lines

of r e l a t i v e the

following

(I), c =

The u n i t cell

l a r g e r than that of UBr s and w i t h

gm/cm 3.

Z = 2, the

A l t h o u g h o n l y a l i m i t e d n u m b e r of

to be r e a s o n a b l y

10.15

(i),

reliable

gave the

c = 6.71

since

(i) ~, ~ : 89.32

(see above).

r e f i n e m e n t of U B r 5

(6), ~ = 117.68

agreement with

those r e p o r t e d

u n i t cell d i m e n s i o n s w i t h i n

(6), from

R e f i n e m e n t of the PaBr 5 p o w d e r

of the s t r o n g lines only r a t h e r t h a n the c o m p l e t e

contributing reflections

the

f o l l o w i n g u n i t cell d i m e n s i o n s :

T h e s e are in r e a s o n a b l e

the n e u t r o n d i f f r a c t i o n study d a t a on the b a s i s

m o s t of the r e f l e c t i o n s

g r o u p P[:

p o w d e r data of the same q u a l i t y (i), b =

with

of the s t r o n g e s t

m e a s u r e d and u s e d in the unit cell d e t e r m i n a t i o n ,

are c o n s i d e r e d

a : 7.47

i n d e x e d on the b a s i s

Least squares

(5), ~ =

As shown in the Table

set of

as s h o w n in the Table did n o t c h a n g e

the

the q u o t e d e r r o r limits.

It is now e v i d e n t t h a t there are two r e l i a b l y i d e n t i f i e d p o l y m o r p h s , andy,

ofprotactinium

w i t h ~- and 8-UCIs. on the b a s i s

p e n t a b r o m i d e w h i c h are, The e x i s t e n c e

respectively,

of ~ - P a B r s has

of the s m a l l e r d i m e r u n i t v o l u m e

s h o w n o r i g i n a l l y 13 that the c r y s t a l s

c o u l d be

isostructural

recently been questioned 5

(383 ~3). transformed

H o w e v e r it w a s c o m p l e t e l y to 8-

222

The Polymorphism of Protactinium Pentabromide

PaBr5 on heating at 400 - 410°C and that this transformation was reversible at c_aa390°C.

At these temperatures the capillaries invariably contained a

single phase rather than mixtures of ~- and 8-PaBrs.

It is hoped that work

currently in progress will clarify the situation concerning ~-PaBr 5 and provide information on polymorphism in UBr5.

TABLE 1 Partial X-Ray Powder Diffraction Data For 7-PaBr 5 Sin2@obs.

Sln2@cal.

h,k ,i

a Ica I.-

b Iobs .--

0.0150

0.0150

T i 0

29

M

0.0174

[ 0.0171 0.0175

T 0 1 0 0 1

26 ] 17

W+

0.0199

[ 0.0199

T 1 1

15 ]

0.0206

0 1- 1

11

W

0.0266

0.0267

0 2 0

17

W

0.0593

0.0593 0.0594 0.0596

T 1 2 2 2 0 0 3 0

5 1 5 2

[ 0.0651

T 3 1

0.0653

2 1 ~-

99 ? 100

0.0688

[0.0687 0.0691

0]"2 0 0 2

48 1 1

0.0925

0.0920

0.0971

[0.0968 0.0973

0.1090

0.1087 0. 1090 0. 1091 0.1091 0. 1093

~ 4 2 2 7 0 "2- 4 0 2

0.iiii

0.1108 0.1109 0.1112

201 121-i T3 2

34] 14 7

0.1137

0.1133 0.1133 0.1138

731 -3-0 2 172

7] 13 47

0.1398

0. 1393 0.1399 0. 1401 0. 1402

300 2 3T ~2 3 131

0.3] i0 3 3

0.1502

0.1500

1 4 0

27

0.0651

W+

S

M+

T40

2

W-

130 ~- 1 1

5 1 3

W-

1 7 1 0 2

41 2 36 4 3

M+

M

The Polymorphism of Protactinium Pentabromide

223

TABLE 1 (cont) Sin2Oobs.

0.1561

Sin2Ocal.

h,k, 1

a Ica I --

[0.1556 0.1563

T2 3 2 2 3

63 28

1

0 . 1642 0. 1643

1 4 2 1 5" 1

10 4

]

0.1646 0. 1648

0 5 0 2 3 0

4 3

0.1718 0.1719 0.1724

4" 2 2 0 1 3 1 3 "3

0.4 6 10

0.1646 _

O. 1723

W+

I 0.1821 0.1825 0. 1825

~I i ~ 3 2 0 ~ 3

1 ] 44 i

0 1849 •

[ 0.1849 0.1849

3 1 1 2 5- 1

49

i 0.2219

2 1 2 ~ 1 4

1 38

/

0.2230

0.2353 0.2355 0.2356 0.2359

3 ~ -3 4

5 8 1 21

1

0.2355

1 2 6 4

M(d)

W+

0.1819

0.2223

b Iobs ~-

M

]

47

1 4 1 0

M+

7 W+

J

M+

Calculated using positional parameters reported 5 for UBr 5 b --Visually

estimated:- S, strong; M, medium; W, weak, d, diffuse

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G.S. SMITH, Q. JOHNSON and R.E. ELSON, Acta. Cryst.

22, 300

2.

D. BROWN, T.J. PETCHER and A.J. SMITH, Acta. Cryst. B25,

3.

D. BROWN, Private communication to F. Lux et al

4.

F. LUX, G. WIRTH and K.W. BAGNALL, Chem. Ber.

5.

J.H. LEVY, J.C. TAYLOR and P.W. WILSON, J. Inorg. Nucl. Chem. 40, 1055 (1978).

6.

U. M~LLER and W. KOLITSCH, Z. Anorg. Allg. Chem. 410, 32 (1974).

7.

D. BROWN and P.J. JONES, J. Chem. Soc.

8.

D. BROWN, T.C. TSO and B. WHITTAKER, J. Chem. Soc. Dalt. Trans., 2291 (1976).

9.

P.E. KNOTT and J.A.C. MARPLES, Brit. Rep. AERE-M 2531

(see Ref.

103, 2807,

(A), 262

(1967).

178 (1969). [4]). (1970).

(1966).

(1972).

10.

H.S. PIESER, H.P. ROOKSBY and A.J.C. WILSON (Eds.), "X-ray Diffraction of Polycrystalline Materials", Inst. of Phys., London, p. 665 (1955).

ii.

D. BROWN, B. WHITTAKER and T.C. TSO - unpublished observations

12.

J.A.C. MARPLES and J.L. SHAW, Brit. Rep. AERE-R 5210

13.

T.J. PETCHER, Thesis, Sheffield University (1967).

(1966).

(1978).