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Reference
High temperature single crystal x-ray diffraction: structure of cubic manganese iodine and manganese bromine boracites
CROTTAZ, Olivier, KUBEL, Frank, SCHMID, Hans
Abstract
The structural parameters of optically controlled cubic Mn I boracite, Mn3B7O13I, and Mn Br boracite, Mn3B7O13Br, were refined on single crystals at 421 and 580 K, resp. (space group F.hivin.43c, Z = 8). To perform these measurements, a low-cost heating device, based on a soldering Fe heating element, was used. Cell parameters are 12.3404(3) .ANG. for Mn I boracite and 12.3100(9) .ANG. for Mn I boracite and 12.3100(9) .ANG. for Mn Br boracite.
The cell parameters and the deviation from planarity of the O environment around the metal ion are greater in Mn boracites than in other known cubic boracites. At. coordinates are given.
CROTTAZ, Olivier, KUBEL, Frank, SCHMID, Hans. High temperature single crystal x-ray diffraction: structure of cubic manganese iodine and manganese bromine boracites. Journal of Solid State Chemistry , 1995, vol. 120, no. 1, p. 60-63
DOI : 10.1006/jssc.1995.1376
Available at:
http://archive-ouverte.unige.ch/unige:31185
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l O U R N A L O F S O L I D S T A T E C H E M I S T R Y 1 2 0 , 60-63 (1995)
High Température Single Crystal X-Ray Diffraction: Structure of Cubic Manganèse lodine and Manganèse Bromine Boracites
O . C r o t t a z / F . K u b e l , a n d H . S c h m i d
Department of Minerai, Analylical. and Applied Chemistry, University of Geneva, 30 quai E. Ansermef, 1211 Geneva 4, Switzerland Received March 31, 1995; in rcviscd form Junc 19, 1995; accepted June 20, 1995
The structural parameters of optically controlled cubic man- ganèse iodine boracite, MnîByOoI, and manganèse bromine bo- racite, MnjBTOiîBr, have been refined on single crystals at 421 and 580 K, respectively (space group F43c, Z = 8). I n order to perform thèse measurements, a low-cost heating device, based on a soldering Iron heating élément, has been used. Cell parameters were found to be 12.3404(3) A for manganèse lodine boracite and 12.3100(9) A for manganèse bromine boracite. The cell parameters and the déviation from planarity of the oxy- gen environment around the métal ion are found to be greater in manganèse boracites than in other known cubic boracites. © 1W5 Académie Press, Inc.
I . I N T R O D U C T I O N
Boracites o f chemical c o m p o s i t i o n M^-jOx^X (hereafter M-X, w h e r e M stands for a b i v a l e n t m é t a l i o n and X f o r a halogen i o n ) t e n d t o undergo first order structural phase transitions f r o m a h i g h - t e m p e r a t u r e cubic s t r u c t u r ^ ( p o i n t g r o u p 4 3 m , n o n - c e n t r o s y m m e t r i c space g r o u p F 4 3 ç ) t o noncubic l o w - t e m p e r a t u r e structures ( m m 2 , m , 3 m , 4 2 m ) . I n o r d e r t o study t h è s e transitions, s t r u c t u r a l data o f cubic boracites are r e q u i r e d . T h e chemical e n v i r o n m e n t o f the m é t a l ions i n cubic boracites is s h o w n i n F i g . 1. T h e m é t a l atoms are s u r r o u n d c d b y four n e a r b y o x y g e n atoms ( 0 ( 1 ) ) w h i c h are nearly coplanar a n d t w o m o r e distant halogen atoms located o n an axis p e r p e n d i c u l a r t o the i d é a l M- 0 ( 1 ) plane. T h i s r é g i o n o f the structure is supposed t o be responsible for t h e phase transitions (see R é f . ( 1 ) ) a n d can be described as an elongated o c t a h e d r a l e n v i r o n m e n t o f the m é t a l i o n w i t h a tendency t o a t e t r a h e d r a l a r r a n g e m e n t of the f o u r nearly coplanar o x y g e n ( l ) ions (i.e., an octahe- d r a l e n v i r o n m e n t w i t h a t e t i a g o n a l a n d a s m a l l t e t r a h e d r a l d é f o r m a t i o n ) . T h e d é f o r m a t i o n o f the o x y g e n p l a n e varies w i t h the m é t a l and the halogen atoms p r é s e n t i n t h e b o r a - cites. T h e d é v i a t i o n f r o m p l a n a r i t y was i n t r o d u c e d i n t h e f o r m o f a p a r a m e t e r e (defined as e ( A ) ^ x ( 0 ( l ) ) x a{A))
' To whom correspondence shnuld be addressed.
by N e l m e s ( 2 ) . T h i s p a r a m e t e r is r e l a t e d t o the magnitude o f the planar t o t e t r a g o n a l d é f o r m a t i o n o f the oxygen i o n arrangement and is m o r e casily calculated t h a n the
" o u t o f p l a n a r i t y " angle ( t h a t is, the angle between the i d é a l m é t a l plane a n d the 0 ( 1 ) ions). T o o b t a i n correct rcsults i t is h e l p f u l t o standardize the structures using t h e " s t r u c t u r e t i d y " p r o g r a m ( 3 ) . H o w e v e r , i t should be n o t e d that t h e n u m é r a t i o n s o f the o x y g e n a n d b o r o n atoms are opposite t o n o n s t a n d a r d i z e d a t o m i c positions p u b l i s h e d previousiy.
So far the cubic phase has been characterized for boracites w i t h M g , C r , Fe, C o , N i , C u , a n d Z n as the M^"^ i o n [see ( 4 ) a n d Réf. t h e r e i n , (5) f o r F e - I , a n d ( 6 ) for Z n - C l ] . E x c e p t for M g ^ ^ a n d Z n ^ ^ ail t h è s e ions m a y p r é s e n t a J a h n - T e l l e r effect, e i t h e r i n octahedral o r i n t e t r a h e d r a l e n v i r o n m e n t ( 7 ) . w h i c h may make the u n d e r s t a n d i n g o f the d é f o r m a t i o n difficult. Since Mn^+
is a 3rf^ i o n , w h e r e n o J a h n - T e l l e r effect is expected i n the g r o u n d state for o c t a h e d r a l o r t e t r a h e d r a l c o o r d i n a t i o n , a study o f the cubic phase o f boracites w i t h manganese(II) m a y a l l o w a better u n d e r s t a n d i n g o f the cubic structures o f boracites a n d o f t h e c u b i c - o r t h o r h o m b i c phase-transi- t i o n t e m p é r a t u r e s i n the boracites. Consequently, we have chosen t o refine the cubic structures o f M n - I and M n - B r boracites.
2. E X P E R I M E N T A L 2.1. Apparatus
T h e data c o l l e c t i o n s were m a d e o n a C A D - 4 diffrac- t o m e t e r .
_ F o r M n - I a n d M n - B r , the t e m p é r a t u r e s o f the m m 2 =>
4 3 m phase transitions are 407 a n d 543 K , respectively (8).
I n o r d e r t o p e r f o r m X - r a y data collections, an optical con- t r o l device a n d a l o w cost h e a t i n g device, a l l o w i n g single crystal studies i n t h e range 320-520 K , have been de- v e l o p e d .
T h e o p t i c a l c o n t r o l device is needed t o assure that the crystal is i n the cubic a n d o p t i c a l l y isotropic phase. T h i s a t t a c h m e n t consists o f a p o l a r i z e r , an analyzer, a n d a m i c r o -
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S T R U C T U R E O F M A N G A N E S I Z H A L I D E B O R A C I T E S 61 the site o f the crystal, before and afler the data collection.
T h e t e m p é r a t u r e was set t o 421 ± 1 K for M n - I and 580 ± 5 K for M n - B r . T h e crystals were fixed w i t h stan- d a r d A r a l d i t glue o n q u a r t z fibers.
F I G . 1. Environment of thc métal ions in cubic boracites.
scope. T h e crystal can be observed in situ i n t r a n s m i t t e d Ught, d u r i n g heating.
T h e heating device consists o f the h e a t i n g é l é m e n t o f a soldering i r o i i ( 0 = 4.5 m m , T = 20 W ) w h i c h is i n t r o d u c e d i n t o a T Pyrex t u b e = 5.0 m m ) . T h e t u b e is i n s u l a t e d by A l foils. T h e soldering i r o n was connected to a variable voltage generator set t o 3 V f o r M n - I a n d t o 6 V f o r M n - B r . A n air stream is i n t r o d u c e d l a t e r a l l y i n t o the T Pyrex tube. T h e air stream is p r o v i d e d b y a compressed air System connected t o a pressure reducer and a P o r t e r flux r e g u l a t o r system. T h e flow rate was set to 9 l i t e r / m i n . A sketch o f this system is s h o w n i n F i g . 2. T h c t e m p é r a t u r e was measured w i t h a F t - P t / R h t h e r m o c o u p l e , placed at
0-12V
— air stream with constant pressure 'AI foils
_ crystal
quartz fiber
F I G . 2. Schematic sketch of Ihe heating device used for thc X-ray mcasurements at 421 ± 1 and 580 ± 5 K.
2.2. Data Colleaion and Refinemeni
M n - 1 : b r i g h t p i n k dodecahedral crystal = 0.1 m m ) o b t a i n e d by chemical v a p o r t r a n s p o r t ( 9 ) . L a t t i c e parame- ter a = 12.3403(3) Â a n d K - 1879.29(5) at 421 ± 1 K . C A D - 4 a u t o m a t i c f o u r - c i r c l e diffractometer, A ( C u Ka) = 1.5418 A , Z = 8, g r a p h i t e m o n o c h r o m a t o r , a c o m - p l è t e s p h è r e measured w i t h —15 < h < 15, —\5<k<
15, - 1 5 < / < 15, [(sin 0)1 k]^^^ = 0.606 Â - \ 8 integrated intensities, co - 20 scan, 2 standard reflections, m a x i m u m i n t e n s i t y change 6%, spherical a b s o r p t i o n c o r r e c t i o n {fxR = 0.59), lattice parameters d e t e r m i n e d f r o m 24 reflec- t i o n s w i t h 44" < 20 < 10°; structure refinement by f u l l - m a t r i x least squares, f u n c t i o n m i n i r a i z c d 1^w(\Fj^ - u n i t weights: scattering factors for n e u t r a l atoms and a n o m - alous-dispersion c o r r e c t i o n (International Tables for X-ray Crystallography, 1974, V o l . Ï V ) , 20 parameters refined [one scale factor, 4 p o s i t i o n a l parameters, 3 isotropic, 9 aniso- t r o p i c , a n d one o v e r a l l displacement parameters, one ex- t i n c t i o n p a r a m e t e r a n d one absolute structure param- eter ( 1 0 ) ] . using t h c X T A L 3.2 p r o g r a m system (11).
(A/(r)nitix = 3 X 10 T h e refmed value f o r the absolute s t r u c t u r e p a r a m e t e r was 0.025(25). A value close to 0 or 1 was expected f o r a cubic single crystal, as l o n g as i t is n o t m i m e t i c a l l y t w i n n e d . F i n a l R values are R - 2.0%
a n d = 2.7% for 99 c o n t r i b u t i n g reflections.
T w o measurements were made f o r M n - B r ; D u r i n g a first a t t e m p t a data set was coUected o n a crystal w h i c h was m i m e t i c a l l y t w i n n e d i n t h e cubic phase due t o g r o w t h t w i n s . T h i s type o f t w i n (see, c.g., F i g . 16 i n R é f . ( 1 2 ) ) cannot be analvzed o p t i c a l l y . T h e r c f i n e m e n t a l l o w e d t h e c a l c u l a t i o n o f a n absolute structure p a r a m e t e r o f 0.58(3) w i t h R = 5.2% and R^ = 4.9%. T h e second measurement was m a d e o n a single crystal w h i c h was n o t t w i n n e d i n thc cubic phase.
C o n d i t i o n s for data c o l l e c t i o n were t h e samc as for M n - I , except: b r i g h t p i n k dodecahedral crystal ((f) = 0.3 m m ) w i t h lattice p a r a m e t e r a = 12.3100(9) A and V = 1865.4(4) Â^ a t 580 ± 5 K . - 1 5 < / Ï , A < 15, - 5 < / < 5.
[(sin y)/A]max = 0.634 A-\8 i n t e g r a t e d intensifies, co — 28 scan, 2 standard reflections, m a x i m u m intensity change 5%, spherical a b s o r p t i o n c o r r e c t i o n {^R = 0.39), l a t t i c e p a r a m e t e r s d e t e r m i n e d f r o m 25 reflections w i t h 32°
<2B< 86". ( A/ a) n . , ^ - 0.5 X I Q - * . T h e refined value for t h e absolute s t r u c t u r e parameter was - 0 . 0 0 1 8 ( 2 ) . F i n a l R values are R ^ 3.7% a n d R^, = 4.8% for 90 c o n t r i b u t i n g re- flections.
T h e standardized a t o m i c c o o r d i n a t e s o f M n - I and M n - B r are listed i n T a b l e 1.
62 C R O T T A Z . K U B E L , A N D SCHMID T A B L E 1
Standardized Fractional Atomic Coordinates and Equivalent Isotropic Displacement Parameters (A^ x ICH) of M n - I and M n - B r Boracites
Wyckoff
Atom notation X y z TT a
L'cq
Mn - I (421 ± 1 K ) : a = 12.3404(3) À
Mn 24(c) 0 0.25 0.25 1.07(4)
I m 0.25 0.25 0.25 0.83(4)
B ( l ) 32(e-) 0.0797(4) 0.0797(4) 0.0797(4) 0,9(1)
3(2) 24{d) 0.25 0 0 01(3)
0{11 96{h) 0,0230(1) 0.0'^42(1) 0.1807(1) 041(5)
0(2} 8(«) 0 0 0 1,0(2)
Mn-•Br (580 ± S K ) : a = 12.3100(9) A
Mn 24(0 0 0.25 0.25 3.23(7)
Br m 0.25 0.25 0.25 2,47(8)
B ( l ) 0.nS14(5) 0.0814(5) 0.0814(5) 2,0(2)
B(2) 24(d) 0.25 0 0 1,2(4)
0(1) %(/i) 0.0234(2) 0.0950(2) 0.1814(2) 1.1(7)
0(2) 8(«) 0 0 0 2,1(2)
" t/eq is deJined as one-lhird of Ihe trace of tlic nrthogonalized L',, tensor.
3. RESULTS A N D DISCUSSION
The main interatomic distances i n cubic iodine and b r o - mine boracites are presented i n Table 2. T h e last hne (i.e., A^ijia^) shows the différence b e t w c c n e x t r ê m e values. I t can be noted that there is a significant change o f the M-X, A / - 0 ( 1 ) , and B ( l ) - 0 ( 2 ) b o n d distances when metals and halogens are varied. O t h e r distances like the 0 ( 1 ) - 0 ( 1 ) , B ( l ) - 0 ( 1 ) and B ( 2 ) - 0 ( l ) are not influenced. Except for the letrahedrally coordinated B ( l ) atoms the b o r o n - oxygen dislances show only little change w i t h the type o f boracite and t e m p é r a t u r e , thus contirming the picture o f a rigid b o r o n - o x y g e n n e t w o r k . D u e to this rigidity consid- é r a b l e modifications may mainly be expected i n the m é t a l environment which therefore is discussed i n d é t a i l .
T h e M n - O ( l ) and M n - A ' bonds are longer in M n - I and M n - B r than any o l h c r m e t a l - o x y g e n ( l ) or metal-halogen b o n d i n the other k n o w n cubic boracites, as reflected by the larger unit cell parameters of t h è s e compounds. The out o f planarity angles are equal t o 7.68(1)" i n M n - I and 7.85(3)° i n M n - B r while the d é v i a t i o n f r o m planarity pa- rameters (e) are 0.2834(12) Â in M n - I and 0.2881(24) À i n M n - B r . Similarly to other cubic boracites, the m é t a l i o n v i b r â t e s mainly i n the direction parallel to thc weak m é t a l halogen b o n d [{u)f!(Mf_ - 3.9(2) i n M n - I and 5.2(4) i n M n - B r ] rather than in the direction o f thc strong m e t a l - oxygcn bonds. T h e values obtained for the [{u}j/{u}i ra- tios are i n agrccment w i t h those of other boracites, found t o be between 2.7(3) for C r - I and 5.1(3) for C r - C l [see R e L ( 4 ) ] .
T h e d é v i a t i o n from planarity of the A/ O 4 group, e, as a function of the cubic cell parameters is shown i n Fig. 3.
T h e overail t r c n d of e to increase w i t h the cell parameter, as suggested by M o n n i c r et al. (13), is respected as M n - 1 and M n - B r show greater d é f o r m a t i o n s than other bora- cites. I t can be noted that the Z n - C l boracite does not foUow thc g ê n e r a i trend as i t is m u c h more planar than expected by the value o f Ihe lattice parameter. This may be due t o the d^^ configuration o f the Zn^"" atoms. T h e fact that e x t r ê m e values are observed for boracites w i t h Z m ^ (d^'^) and M n - " (d^) is another indication of thc i m - portance o f the clcctronic configuration o f the transition m é t a l o n the structure o f cubic boracites.
W h e n the e parameter is p l o t t e d as a function of the M - O ( l ) b o n d length i t appears that the largest s corre- sponds to the longest M - O ( l ) b o n d . B u t i f the geometry around the M ions is governed mainly by sterical effects, the largest e should correspond t o the shortest M-0{1) bond. This suggests that. as the M - O ( l ) distance gets shorter, the bond strength increases, thus leading to a more planar environment. T h i s effect may be in relation w i t h the sp'^ hybridization o f the 0( 1 ) ions w h î c h may lead to an interaction between the M ^ " empty 4d shell and the 0(1) é l e c t r o n lone pair. T h i s interaction could tend to
T A B L E 2
Interatomic Distances (A) in Cubic M n - B r , M n- 1 , and i n Other Cubic lodine Boracites
Name M-X M-0{ 1 ) O(l)-O(l)shortest B(1)~0(1) B ( 2 ) - 0 ( l ) B ( l ) - 0 ( 2 ) Réf.
C r - l 3,0520(2) 2.075(2) 2.393(2) 1.439(3) 1.479(2) 1.682(2) (13)
Fc-I(373 K) 3.06 2.10 -2.3 -1.5 -1.4 -1,5
C o - I 3.030(1) 2.056(2) 2.390(2) 1,434(3) 1.463(1) 1.673(3) (14)
N i - 1 3.011(1) 2.053(3) 2.390(4) 1.433(4) 1.465(3) 1,673(5) (15)
C u - I 3.005(1) 2.008(4) 2.389(5) 1 431(8) 1.469(4) 1,692(7) (16)
Mn-I (471 K ) 3.0851(1) 2.1233(12) 2.3872(17) 1.441(5) 1.4708(12) 1.703(3)
Mn-Br (580 K) 3.0775(2) 2.107(2) 2.386(4) 1.433(7) 1.471(3) 1.736(6)
A/niax (without F c - l ) 0.0801(2) 0.115(5) 0,006(3) 0,010(13) 0.016(3) 0.063(11)
S T R U C T U R E OF M A N G A N E S E H A L I D E B O R A C I T E S 63
12.5 12.41-
^ 12.3
1 12.2 -
o
Û .
s 12.1
12.0 11.9
ô N
— l O
0.12 0.14 Q16 ai8 0.20 022
Epsilon (Â)
Q24 0.26 0.28 0.30
F I G . 3. Déviation from planarity, e (for définition see text), of the O-atom environment around the métal atoms (site symmetry of métal atoms 4) i n cubic boracites as a function of cubic celL parameter, a. Data include Refs. (4-6 and 13-20). Error bars + 1 e.s.d. Dashed régions inciude ( i ) N i - I (77 and 293 K ) , Cu-Cl (390 K ) , Cu-Br, and C u - I and ( i i ) C r - C I , C r - B r (113 and 293 K ) . C r - I , and C o - I . See Réf. (3) for détails.
p r é s e r v e a planar e n v i r o n m e n t . T h i s hypothesis can aiso h e l p t o e x p l a i n the great d i f f é r e n c e o f p l a n a r i t y b e t w c c n the M g - C I and Z n - C l boracites, as the i n t e r a c t i o n b e t w c c n the o x y g e n lone pairs and t h e e m p t y d shell arc w c a k c r i n M g - C l {3d shell) t h a n i n Z n - C l (4d s h e l l ) .
M o r e t h e o r e t i c a l studies are necessary i n o r d e r t o under- stand the effect o f the e l e c t r o n i c c o n f i g u r a t i o n o f t h e m é t a l ions on the structure o f cubic boracites. T h e possible i n t e r - actions b e t w e e n the m é t a l ions and t h e sp^ 0 ( 1 ) ions also r e m a i n unclear.
A C K N O W L E D G M E N T
The authors are grateful for the support of the Swiss National Sci- ence Foundation.
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