The crystal structure of the weberite Na2MgInF7

Article abstract of DOI:10.1006/jssc.2001.9184

The fluoride Na₂MgInF₇ is orthorhombic: a = 10.435(1) A, b = 7.345(1) A, c = 7.553(1) A, Z = 4. Its crystal structure was solved in the space group Pnma (No. 62), from X-ray single crystal data using 1879 unique reflections (1183 with F_o/σ(F_o)>4). The three-dimensional network is built up from tilted chains of trans corner-sharing [MgF₆] octahedra running along the shortest axis of the cell. These chains are linked together through four corners of [InF₆] octahedra. The sodium ions are 8 and 7 coordinated to fluorine. The [NaF₈] polyhedron can be described as a distorted cube, whereas the [NaF₇] polyhedron is a pentagonal bipyramid. Despite a different space group, the crystal structure of Na₂MgInF₇ can be easily related to the orthorhombic body-centered weberite-type structure.

Full text of DOI:10.1006/jssc.2001.9184

Journal of Solid State Chemistry 159, 234}238 (2001)
doi:10.1006/jssc.2001.9184, available online at http://www.idealibrary.com on
The Crystal Structure of the Weberite Na MgInF7
2
Armen Caramanian, Jean-Paul Souron, Patrick Gredin, and Ariel de Kozakꢀ
Laboratoire de Cristallochimie du Solide, Universit e& Pierre-et-Marie-Curie, 4 place Jussieu, case courrier 176, 75252 Paris Cedex 05, France
Received December 1, 2000; in revised form March 13, 2001; accepted March 26, 2001
had to be improved. In 1982 a paper entitled &&What Is the
The 6uoride Na
2
MgInF
7
is orthorhombic: a ؍ 10.435(1)A
, Z ؍ 4. Its crystal structure was
>
,
True Space Group of Weberite?'' (8) reviewed all the pos-
sible space groups, trying to answer this question and con-
cluded that the noncentrosymmetric Imm2 was probably
the best space group for Weberite in the absence of a proof
of achirality. In the late 1980s, the crystal structure of
Na NiFeF was reexamined, concluding this time that the
b ؍ 7.345(1)A, c ؍ 7.553(1) A
>
>
solved in the space group Pnma (No. 62), from X-ray single
crystal data using 1879 unique re6ections (1183 with
F
o
/r(F
tilted chains of trans corner-sharing [MgF
along the shortest axis of the cell. These chains are linked
together through four corners of [InF ] octahedra. The sodium
ions are 8 and 7 coordinated to 6uorine. The [NaF ] polyhedron
can be described as a distorted cube, whereas the [NaF ] poly-
o
) > 4). The three-dimensional network is built up from
6
] octahedra running
ꢁ
ꢂ
true space group is Imma despite weak re#ections observed
for hk0: h"2n#1, attributed to the Renninger e!ect (9).
The space group Imma was also attributed to Na NiCrF
6
8
7
ꢁ
ꢂ
hedron is a pentagonal bipyramid. Despite a di4erent space by the same authors (10). The problem is that a primitive
group, the crystal structure of Na MgInF can be easily related space group was never considered for orthorhombic
2
7
to the orthorhombic body-centered weberite-type structure. weberite until the structure determinations of Na CuCrF
ꢁ
ꢂ
(
2001 Academic Press
(
11), Na NiInF (12), and Na CuInF (13), because all pre-
ꢁ
ꢂ
ꢁ
ꢂ
Key Words: weberite; Na
2
MgInF ; crystal structure.
7
vious reports agreed with a body-centered cell. As we had
the opportunity to prepare a powder of Na MgInF for
ꢁ
ꢂ
optical studies, we observed on its X-ray di!ractogram
many lines of weak intensity which could not be indexed in
an orthorhombic body-centered cell, but only in a primitive
one. Therefore we decided to determine the crystal structure
of Na MgInF , starting from a single crystal. The problems
mentioned before were resolved when re"ning the structure
in the space group Pnma (the cell parameters a and b are
here reversed for a conventional space group, No. 62). It is
valuable to mention that weberite-type #uorides crystallize
also with monoclinic and trigonal symmetries and that all
weberite variants were abundantly studied for several years
by D. Babel's group (14}16 and references therein).
INTRODUCTION
The crystal structure of the mineral called &&Weberite,''
Na MgAlF , discovered in Ivigtut (Greenland), was deter-
ꢁ
ꢂ
ꢁ
ꢂ
mined by Bystro
techniques, in 1978 (2). Both investigations led to the same
body-centered orthorhombic cell: a+7.05(1) A
b+9.98(2) A, c+7.29(1)A, but disagreed in the choice of
K m in 1944 (1) and again, using modern
>
,
>
>
the space group: Imm2 (No. 44), non-centrosymmetric for (1)
and Imma (No. 74), centrosymmetric for (2). Nevertheless,
the two structure descriptions are nearly the same. Since
then many synthetic analogs were discovered by substitu-
tion of Mg and/or Al by other bivalent and/or trivalent
cations (3}6) and the crystal structure of one of them:
Na NiFeF was determined precisely in 1978 (7). The
SYNTHESIS OF Na MgInF
2
7
The starting #uorides NaF and MgF used in the syn-
ꢁ
ꢂ
ꢁ
authors solved the structure in the space group Imm2, as thesis of Na MgInF are commercial products, while InF
ꢁ
ꢂ
ꢃ
Bystro
remained: a very short Na}F distance of 2.160A
impossibility of re"ning the anisotropic displacement para-
meters of the later #uorine atom, showing that something state at 7003C, by annealing for 15 h a stom
K m did it for Weberite (1). However, some problems was prepared in the laboratory by #uoridation of In O in
ꢁ
ꢃ
>
and the an anhydrous hydrogen #uoride stream at 7503C in 6 h.
The synthesis of Na MgInF was performed in the solid
ꢁ
ꢂ
K
chiometric mix-
ture of the three elementary #uorides placed in a platinum
crucible under inert argon atmosphere. Its powder pattern,
recorded on a 17-cm vertical Philips PW 1050/25 di!rac-
tometer (copper anti-cathode), is globally similar to that
ꢀ
To whom correspondence should be addressed. Fax: 33 1 44 27 25 48.
E-mail: adk@ccr.jussieu.fr.
2
34
0
022-4596/01 $35.00
Copyright ( 2001 by Academic Press
All rights of reproduction in any form reserved.

CRYSTAL STRUCTURE OF Na MgInF
235
ꢁ
ꢂ
TABLE 1
X-ray Powder Pattern of Na MgInF
2
7
dꢀ%!ꢁ(A
>
)
d#!ꢂ# (A
>
)
h
k
l
I/I (peak height)
dꢀ%!ꢁ (A
>
)
d#!ꢂ# (A
>
)
h
k
l
I/I (peak height)
ꢄ
ꢄ
6
5
5
4
4
3
3
3
3
3
3
3
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
1
.110
.260
.215
.290
.252
.776
.705
.670
.197
.151
.057
.003
.632
.608
.459
.446
.395
.382
.349
.337
.268
.216
.166
.146
.126
.060
.039
.015
.888
.853
6.118
5.266
5.217
4.293
4.254
3.777
3.706
3.672
3.197
3.149
3.059
3.003
2.633
2.609
2.458
2.447
2.395
2.382
2.350
2.338
2.268
2.216
2.167
2.146
2.127
2.060
2.039
2.016
1.888
1.853
1
0
2
2
2
0
2
0
1
1
2
2
0
4
4
1
3
0
2
4
2
2
2
4
4
4
3
1
0
4
0
1
0
0
1
0
1
2
1
2
0
2
2
0
1
0
2
1
2
1
0
3
1
0
2
1
0
3
0
2
1
1
0
1
0
2
1
0
2
1
2
0
2
0
0
3
1
3
2
1
3
0
3
2
0
2
3
2
4
2
4
100
36
1
1.836
1.775
1.759
1.737
1.732
1.693
1.679
1.663
1.651
1.614
1.599
1.580
1.574
1.544
1.530
1.502
1.480
1.456
1.451
1.442
1.424
1.412
1.405
1.394
1.390
1.385
1.365
1.359
1.316
1.836
1.775
1.759
1.737
1.732
1.692
1.679
1.664
1.651
1.614
1.599
1.580
1.574
1.544
1.530
1.502
1.480
1.456
1.451
1.442
1.424
1.412
1.405
1.394
1.390
1.385
1.365
1.359
1.316
0
2
4
4
2
6
0
2
6
4
2
6
2
6
4
4
0
4
6
0
2
4
6
6
2
1
3
7
0
4
0
1
3
4
1
2
3
1
3
2
0
4
1
0
4
1
3
2
5
1
2
1
3
5
2
4
2
4
0
4
3
1
0
0
4
3
1
2
4
2
2
2
4
0
5
3
2
1
5
4
3
1
1
5
3
1
4
14
3
10
12
4
2
7
4
8
3
14
76
14
1
3
2
96
66
12
9
1
5
12
15
19
10
1
2
10
2
29
5
8
2
13
61
25
11
20
2
7
3
2
6
4
3
4
1
2
4
4
1
1
1
5
given by Chassaing (3), reported on PDF 22-0894, and The scattering factors and anomalous dispersion correc-
indexed in a body-centered orthorhombic cell. Nevertheless, tions were taken from the &&International Tables for X-ray
many weak lines (one was also observed by (3) for
d"4.27 A
>
) could not be indexed with a body-centered con-
TABLE 2
dition: (hkl): h#k#l"2n. Therefore a primitive cell had
to be considered for indexing the powder pattern (Table 1).
Singles crystals of Na MgInF were obtained after
Crystal Data, Data Collection, and Re5nement Characteristics
Formula: Na MgInF
ꢁ
ꢂ
ꢁ
ꢂ
Symmetry: Orthorhombic
Cell parameters: a"10.435(1)A
Volume: 578.9(1)A Formula weight: 318.1 g mol\ꢀ
Space group: Pnma (No. 62)
melting at 8603C the #uoride, followed by a slow cooling.
Weissenberg and Buerger X-ray photographs of one of these
single crystals con"rmed the orthorhombic symmetry and Density (calculated): 3.65 g cm\ꢃ
>
, b"7.345(1) A
>
, c"7.553(1)A
>
>
ꢃ
Z"4
Radiation: MoKa (j"0.71069 A
>
)
F (0 0 0)"584
the re#ections conditions: hkl, no condition; hk0, h"2n;
Linear absorption coe$cient: 4.4 mm\ꢀ
and 0kl, k#l"2n are in agreement with two space groups:
Crystal size: 0.2;0.2;0.2 mm\ꢃ (parallelepiped shape)
Theta range for data collection: 3 to 403
Colorless
Pnma (No. 62) and Pn2 a (No. 33). The measured cell
ꢀ
parameters are given in Table 2.
Index range: 04h418; 04k413; 04l413; 2053 re#ections collected,
1
879 unique, 1183 with F /p(F )'4
ꢃ ꢃ
Re"nement method: full-matrix least-squares on Fꢁ; 62 Re"ned parameters
STRUCTURE DETERMINATION
Weighting scheme: w"1/[pꢁ(Fꢁ)#(0.0479;Pꢁ)#0;P], where
ꢃ
P"[Max (Fꢁ, 0)#2;Fꢁ]/3
One single crystal of Na MgInF was mounted on an
ꢃ
#
Extinction coe$cient: x"0.020(1)
Electron density in Fourier di!erence map: Max. height: 1.64 e\ A
ꢁ
ꢂ
Enraf-Nonius CAD4 four-circle di!ractometer. A total of
053 intensities were measured and the conditions of the
s
\ꢃ
2
Min. height: !3.30 e\ A
s
\ꢃ
Reliability factors:
Goodness-of-"t on Fꢁ"1.008
data collection are gathered in Table 2. The data were
corrected for Lorentz and polarization e!ects and a method
based on psi-scans was used for the absorption correction.
Final R indices (F /p(F )'4)
R "0.034
wR "0.096
ꢃ
ꢃ
ꢀ
ꢁ
R indices (all data)
R
"0.062
wR "0.106
ꢀ
ꢁ

2
36
CARAMANIAN ET AL.
TABLE 3
4
Atomic coordinates (؋ 10 ) and Anisotropic Displacement
2
3
Parameters in A
Na MgInF
>
(؋ 10 ) (with e.s.d. in Parentheses) for
2
7
Atom
Site
x
y
z
;ꢀꢀ ;ꢁꢁ ;ꢃꢃ ;ꢁꢃ ;ꢀꢃ ;ꢀꢁ ;%ꢄ
Na(1)
0
0
0
31
(1)
22
(1)
21
(1)
4
54
(2)
18
(1)
8
(1)
12
(1)
13
(1)
12
(1)
36
(2)
3
(1)
0
!5
(1)
!8
(1)
0
(1)
0
(1)
2
(1)
3
(1)
15
(1)
7
(1)
0
36
(1)
24
(1)
6
4
a
Na(2) 2680
ꢀ
ꢅ
2372 35
(2)
4
c
(2)
0
(1)
5
(1)
Mg(1)
0
ꢀ
!1
(1)
0
1
(1)
0
ꢁ
4
b
(1)
9
(1)
10
(1)
19
(1)
20
(1)
27
(1)
21
(1)
22
(1)
In(1)
2619
(1)
3574
(3)
1625
(3)
4706
(3)
3738
(2)
3648
(2)
ꢀ
ꢅ
7495 11
(1) (1)
5082 24
(3) (1)
9834 21
(3) (1)
0569 36
(5) (2)
8029 21
(3) (1)
1750 21
(3) (1)
4
c
(1)
21
(1)
28
(1)
9
(1)
20
(1)
15
(1)
F(1)
ꢀ
ꢅ
0
0
0
0
0
0
4
c
F(2)
ꢀ
ꢅ
4
c
F(3)
ꢀ
ꢅ
4
c
F(4)
0241
(3)
9501
(2)
23 !3 !8
(1)
31
(1)
7
(1)
8
d
(1)
3
(1)
(1)
13 !4
(1) (1)
F(5)
8
d
Crystallography'' (17). First a statistical test for centrosym-
metry (Howells, Phillips, and Rogers test (18)) was per-
formed on the structure factor's intensities of the X-ray data
collection: it showed unambiguously the centrosymmetry of
FIG. 2. (010) Projection of the structure of Na MgInF (magnesium
octahedra are light gray and indium octahedra dark gray; sodium atoms
ꢁ
ꢂ
the crystal structure. Therefore, the structure was solved in are represented as circles).
the space group Pnma (No. 62). All the re"nement calcu-
lations were performed with the SHELX-97 programs (19).
Sodium, magnesium, and indium atoms were "rst located
using the direct method analysis (TREF instruction), and
FIG. 3. (001) Projection of the structure of Na MgInF (magnesium
octahedra are light gray and indium octahedra dark gray; sodium atoms
are represented as circles).
FIG. 1. The unit cell of Na MgInF (magnesium octahedra are light
gray and indium octahedra dark gray; sodium atoms are represented as
black circles).
ꢁ
ꢂ
ꢁ
ꢂ

CRYSTAL STRUCTURE OF Na MgInF
237
ꢁ
ꢂ
TABLE 4
TABLE 6
Interatomic Na+F Distances (A
Coordination Polyhedra
Interatomic Distances (A
>
) and Bond Angles (3)
>
) in the Sodium
in the [MgF ] Octahedron
6
Mg(1)
F(3)
F(3)
F(5)
F(5)
F(4)
F(4)
Na(1) polyhedron
(CN"8)
Na(2) polyhedron
(CN"7)
F(3)
F(3)
F(5)
F(5)
F(4)
F(4)
1.911(1) 3.821
2.860
2.620
2.860
2.730
2.795
2.739
2.795
2.730
2.864
2.739
F(1)
F(1)
F(2)
F(2)
F(4)
2.364(2)
2.364(2)
2.503(2)
2.503(2)
2.646(2)
2.646(2)
2.855(2)
2.855(2)
F(2)
F(1)
F(5)
F(5)
F(3)
F(4)
F(4)
2.211(3)
2.249(3)
2.468(2)
2.468(2)
2.515(4)
2.547(3)
2.547(3)
180.0
95.0
85.0
88.7
91.3
1.911(1) 2.620
85.0
95.0
91.3
88.7
1.968(2) 3.935
180.0
87.5
92.5
1.968(2) 2.864
92.5
87.5
1.995(2) 3.991
180.0
1.995(2) F(4)
F(5)
F(5)
>
Note. Mean 1Mg}F2"1.958 A.
Note. Mean: 1Na(1)}F2"2.592 A
>
;
1Na}F2"2.49 A
>
[21]. Mean:
1
Na(2)}F2"2.429 A. 1Na}F2"2.43A
>
>
[21].
then the positions of the "ve independent #uorine atoms
were found by successive di!erence Fourier syntheses. The
re"nement of all anisotropic thermal parameters for all octahedra running along the b axis of the cell. These chains
atoms leads to R (F )"0.034 and wR (Fꢁ)"0.096 for 1183 are linked with each other roughly in the [101] and [101
ꢀ
]
ꢀ
ꢃ
ꢁ ꢃ
unique re#ections with F '4p(F ) and 62 re"ned para- directions through corners of [InF ] octahedra, as shown
ꢃ
ꢃ
ꢇ
meters. The atomic coordinates and the anisotropic dis- on the (010) projection of the structure (Fig. 2). Each [InF ]
ꢇ
placement parameters are listed in Table 3. In opposition to octahedron connects two chains of [MgF ] octahedra via
ꢇ
the crystal structure determination of Na NiFeF (7), all four of its corners (Fig. 3). The magnesium and indium
ꢁ
ꢂ
atoms, including #uorine, have here suitable anisotropic #uorine octahedra are fairly regular, with mean Mg}F and
displacement parameters. The simulated powder pattern of In}F distances (1.958 and 2.062 A) shorter than the sum of
Na MgInF , using the atomic coordinates of the crystal the ionic radii calculated with Shannon's table (2.03 and
>
) (21). Bond lengths and angles observed in the
similar to the observed one (Table 1). One can also observe [MgF ] and [InF ] octahedra are gathered in Tables 4
that the strong and medium lines are all indexed with and 5. The sodium atoms, inserted between the chains,
a body-centered condition: (hkl): h#k#l"2n. The nine ensure the electroneutrality and the cohesion of the struc-
lines indexed with a body-centered absence condition are ture. They exhibit 8 and 7 coordination (Table 6). The
weak; therefore, these lines could have been ignored in the sodium polyhedra can be described as a distorted cube for
>
ꢁ
ꢂ
structure determination (program Fullprof (20)), is 2.11A
ꢇ
ꢇ
indexation of weberite-type compounds by previous [Na(1)F ] (Fig. 4) and as a pentagonal bipyramid for
ꢆ
ꢂ
authors.
[Na(2)F ] (Fig. 5). It is useful to observe that the shortest
A list of structure factors may be obtained from the Na}F bond is now 2.211 A
>
, instead of 2.160 A
>
in
authors on request.
Na NiFeF (7), but remains very short.
ꢁ
ꢂ
DESCRIPTION OF THE STRUCTURE AND DISCUSSION
The three-dimensional network of Na MgInF (Fig. 1) is
ꢁ
ꢂ
built up from tilted chains of trans corner-sharing [MgF ]
ꢇ
TABLE 5
>
Interatomic Distances (A) and Bond Angles (3)
in the [InF ] Octahedron
6
In(1)
F(2)
F(5)
F(5)
F(4)
F(4)
F(1)
F(2)
F(5)
F(5)
F(4)
F(4)
F(1)
2.049(3)
84.9
84.9
96.8
96.8
2.769
2.055(2) 2.939
91.3
171.9
81.0
2.769
3.078
4.114
3.078
2.677
4.114
4.125
3.021
3.021
2.782
2.055(2) 2.677
81.0
171.9
93.9
2.069(2) 3.318
106.7
84.3
2.069(2) 2.782
84.3 2.077(3)
178.3
93.9
Note. Mean 1In}F2"2.062 A
>
.
FIG. 4. The [Na(1)F ] distorted cube in Na MgInF .
ꢆ
ꢁ
ꢂ

2
38
CARAMANIAN ET AL.
cation. Copper weberites are isostructural, due to the
Jahn}Teller e!ect (11,13).
REFERENCES
1
2
. A. Bystro
. G. Giuseppetti and C. Tadini, ¹schermaks Mineral. Petrogr. Mitt. 25,
7 (1978).
. J. Chassaing, C.R. Acad. Sci. Paris 268C, 2188 (1969).
. R. Hansler and W. Rudor!, Z. Naturforsch. B 25, 1305 (1970).
K m, Ark. Kemi Mineral. Geol. 18(10), 1 (1944).
5
3
4
5
K
K
. R. Cosier, A. Wise, A. Tressaud, J. Grannec, R. Olazcuaga, and
J. Portier, C.R. Acad. Sci. Paris 271C, 142 (1970).
6
7
8
9
. A. Tressaud, J. M. Dance, J. Portier, and P. Hagenmuller, Mater. Res.
Bull. 9, 1219 (1974).
. R. Haegele, W. Verscharen, D. Babel, J. M. Dance, and A. Tressaud,
J. Solid State Chem. 24, 77 (1978).
. O. Knop, T. S. Cameron, and K. Jochem, J. Solid State Chem. 43,
2
13 (1982).
. Y. Laligant, Y. Calage, G. Heger, J. Pannetier, and G. Fe
State Chem. 78, 66 (1989).
H
rey, J. Solid
FIG. 5. The [Na(2)F ] pentagonal bipyramid in Na MgInF .
ꢂ
ꢁ
ꢂ
1
1
1
0. Y. Laligant, G. Fe
Chem. 553, 163 (1987).
1. S. Kummer, W. Massa, and D. Babel, Z. Naturforsch. B 43, 694
(1988).
2. G. Frenzen, W. Massa, D. Babel, N. Ruchaud, J. Grannec, A. Tressaud,
and P. Hagenmuller, J. Solid State Chem. 98, 121 (1992).
H
rey, G. Heger, and J. Pannetier, Z. Anorg. Allg.
The crystal structure of Na MgInF (space group Pnma)
ꢁ
ꢂ
and of its homologs, Na CuCrF , Na NiInF , and
ꢁ
ꢂ
ꢁ
ꢂ
Na CuInF , can be considered as a new structure-variant
ꢁ
ꢂ
13. N. Ruchaud, J. Grannec, P. Gravereau, P. Nun
W. Massa, G. Frenzen, and D. Babel, Z. Anorg. Allg. Chem. 610, 67
1992).
14. B. Peschel, M. Molinier, and D. Babel, Z. Anorg. Allg. Chem. 621,
573 (1995).
5. D. Babel and B. Peschel, Z. Anorg. Allg. Chem. 623, 1614 (1997).
16. P. Dahlke, B. Peschel, and D. Babel, Z. Anorg. Allg. Chem. 624,
003 (1998).
ꢁ ez, A. Tressaud,
for weberite, if it is admitted that a body-centered cell is well
assumed for the hitherto resolved structures of Na MgAlF
1, 2, 8) and Na NiFeF (7, 9).
(
ꢁ
ꢂ
(
ꢁ
ꢂ
1
It is here useful to mention for comparison that the
1
RE NbO oxides (RE"La, Nd, Sm) have the weberite
ꢃ
ꢂ
structure (space group Imm2) for (22) and an orthorhombic
cell (nonconventional space group Pnam) for (23). In addi-
tion, a series of niobium}samarium oxides Sm RENbO
1
1
1
1
2
7. J. A. Ibers and W. C. Hamilton (Eds.), &&International Tables for X-Ray
Crystallography'' Vol. IV, Kynoch Press, Birmingham, (1974).
8. E. R. Howells, D. C. Phillips, and D. Rogers, Acta Crystallogr. 3,
ꢁ
ꢂ
was found to be orthorhombic, with weberite-type cell para-
meters, space group Pnam (24). Unfortunately, the X-ray
powder patterns of all these compounds are not available
2
10 (1950).
9. G. M. Sheldrick, &&SHELX-97: A Program for Crystal Structure
Determination.'' Gottingen, Germany, 1997.
K
(
23,24).
0. J. Rodriguez-Carjaval, &&FULLPROF: Rietveld, Pro"le Matching and
Integrated Intensity Re"nement of X-ray and/or neutron Data,'' 3.2
version. L eH on-Brillouin Laboratory, CEA, Saclay, France, 1997.
1. R. D. Shannon, Acta Crystallogr. A 32, 751 (1976).
2. A. J. Dyer and E. A. D. White, ¹rans. Br. Ceram. Soc. 63, 301 (1964).
3. G. Tilloca, M. Perez-y-Jorba, and F. Queyroux, C. R. Acad. Sci. Paris
Discussion is open to answer two queries: Is the crystal
structure of orthorhombic weberite well body-centered? and
Do di!erent space groups exist for the orthorhombic
weberite structure? A partial response was given by Frenzen
et al. (12), who conclude that the indium weberites are
2
2
2
2
71C 134 (1970).
di!erent from the others, due to the large size of the trivalent 24. G. Baud and J. P. Besse, C. R. Acad. Sci. Paris 272C, 1222 (1971).