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On the existence of lower hydrates of M(OH)X(M is Sr, Ba; X is Cl, Br, I)
thermochimica acta ELSEVIER
Thermochimica Acta 258 (1995) 189 195
On the existence of lower hydrates of M(OH)X(M is Sr, Ba; X is C1, Br, I) K. B e c k e n k a m p , H . D . L u t z * Universitdt Sieqen. Anor#anische Chemie l, D-57068 Sie#en, Germany
Received 17 June 1994; accepted 12 November 1994
Abstract Preparation of the lower hydrates of M(OH)X(M is Ba, Sr; X is C1, Br, I) was attempted both by dehydration experiments of Ba(OH)X'2H20(X is CI, Br), Ba(OH)I-4H20, and Sr(OH)X'4H20 (X is CI, Br), and by rehydration of the anhydrous salts using infrared, Raman, and high-temperature Raman spectroscopic methods. Thus, the hitherto unknown compound Ba(OH)I'2H20 has been established and Ba(OH)CI.0.5 H20, but not Ba(OH)Br. 0.5H20, has been confirmed. Ba(OH)I.0.5 H20 and lower hydrates of Sr(OH)X were not obtained. Ba(OH)I2H20 is isostructural with Ba(OH)X.2 H20 (X is CI, Br). The crystal structure of Ba(OH)CI0.5H20 is not known so far. The dehydration and fusing temperatures of M(OH)X.4H20 and M (OH)X, respectively, are presented. Keywords: Dehydration; Halide; Hydration; IRS; Raman
1. Introduction The higher hydrates of the barium and strontium hydroxy halides Ba(OH)X. 2 H2O (X is CI, Br), S r ( O H ) X - 4 H 2 0 (X is CI, Br), and B a ( O H ) I - 4 H 2 0 are well established [1 6]. The crystal structures of these compounds are noteworthy in so far as that the former belong to the very few structures in which O H - ions are not coordinated to metal ions [3, 4, 7]. The latter possess water molecules which are the most distorted ones known so far. This is due to the extremely differently strong hydrogen bonds formed [6, 8]. Literature data on the lower hydrates of these basic salts are scarce [1, 5]. The only compounds mentioned are Ba(OH)X.0.5 H 2 0 with X being C1 and Br, apart from the well-established anhydrous salts [1,5, 9, 10]. * Corresponding author. 0040-6031/95/$09.50 i ' 1995 ElsevierScience B.V. All rights reserved SSDI 0040-6031(94)02213-5
190
K. Beckenkamp, H.D. Lutz/Thermochimica Acta 258 (1995) 189 195
In this paper, we demonstrate the existence of lower hydrates of M(OH)X (M is Ba, Sr; X is C1, Br, I) by means of IR, Raman, and high-temperature Raman spectroscopic methods, and by thermoanalytical (DTA, TG, DTG) measurements. 2. E x p e r i m e n t a l
The starting materials were Ba(OH)X.2 H20 (X is C1, Br) and Ba(OH)[-4 H20. They (as well as deuterated specimens) were prepared by crystallization of aqueous solutions of the respective halides and hydroxides in molar ratios of 10:1; for details, see Refs. [3,9, 10]. Preparation of the lower hydrates of the title compounds was attempted by dehydration of the higher hydrated hydroxide halides and by rehydration of anhydrous M(OH)X, respectively.
I
I+II
3527
3588 /~ 34,90
' '
36'00
'
Wavenumber
35'00
'
3400
in 1 / c m
Fig. 1. High-temperature Raman spectroscopic dehydration studies of Ba(OH)I'4H20 (closed tube): l, Ba(OH)I.4H20; II, Ba(OH)I.
K. Beckenkamp, H.D. Lutz/Thermochimica Acta 258 (1995) 184 195
191
DTA (difference thermal analysis), TG (thermogravimetry) and DSC (differential scanning calorimetry) measurements were carried out on Linseis L 62, Mettler TA 4000, and Perkin-Elmer DSC 7 systems, using silica tubes and gold crucibles as sample holders, respectively. Heating rates were 5-10°C min- ~. AlzO 3 was used as reference. IR spectra of dehydrated and rehydrated samples, respectively, were recorded on a Perkin-Elmer model 580 spectrophotometer (resolution < 1 cm- ~) using KBr and CsI discs as well as Nujol and Fluorolub mulls. Raman spectra, with the samples in
..~i~.,, B a ( O H ) B r • 2H20
..'I~o
,,, ".
3(~59 ~ ~ ' o
1o:;o',,l
!
4~;51 I;
~
~s7
tl
t
,..'
2320202o 177o162o~
~
---,., ,.,
1010
3o2o'~'..-/2~'~2050 -'~
853
421
2700
P 280
/"4
•" ~ - ' ,
,,"t" 50~': ' "°
Ba(OH)I • 2H20 ......
..,,.3440
,,..."TilSs 7°
~/"
~/--~,,,o,~35
1,[35
]
.^.V'~1"e/'~¥679
,~,,\/,;~17
36683410
854 5 %
D
...---,,,"i?~",~
; 1010 1310/; ; .-," 1195
85% D
.
.
.
.
.
.
.
.
.
-3~9~ 3669
.
.
" .
.
.
.
176o -
2600 2709
I 3000
282
1
/ ~ ~
, ;,,,
~"'1]l
I 11450 ===686' ' ' / "" ~=nn ~w ; 946 , 1740 ~ / t ~ I/"~ ;';
-3450 T --2200 / 3662 -3000 '~', ,,-. I - ..
Y I
/470
5% D
'
83~1273~
4;
2700
-
~!37g: I
. ....
..'"23~0 2020
3~,~....~-~5o
.........
/
, iq i
l
, ~ II
:o
67~-5
~LI~ ~
3J~,
2030 I 2000
I 1,500
Wavenumber
I 1000
I 500
in l / e m
Fig. 2. Infrared spectra (Csl discs) of Ba{O(H, D)}X.2(H, D ) 2 0 (X is Br, 1) at ambient (-) and liquid nitrogen temperature ( ). Assignment of the observed bands (cm - 1) [3] : 3662 and 2703, stretches of OH and O D - ; 2700 3000, stretches of H 20; 846 and 630, librations of H 2O and D 2 0 ; 430 and 334, librations of OH - and O D - ; < 3 0 0 c m - 1, translational modes (data for X is I).
192
K. Beckenkamp, H.D. Lutz/Thermochimica Acta 258 (1995) 189 195
glass capillaries, were measured on a Dilor O M A R S 89 multichannel Raman spectrograph (resolution < 4 c m - 1 ) with the usual right-angle geometry. For excitation, the 514.5 nm line of an Ar + ion laser was employed. Further details, especially with respect to high-temperature Raman measurements, are given elsewhere [9, 11]. 3. Results and discussion 3,1. B a ( O H ) I ' 2 H z O
The existence of the hitherto unknown Ba(OH)I.2 H 2 0 compound was first detected by dehydration o f B a ( O H ) I . 4 H 2 0 in a Csl matrix in the course of IR spectroscopic measurements [9]. The tetrahydrate dehydrates very easily to the anhydrous salt. With
3593
a
T[K]
T[K]
3656
3564
3592
I ÷ II + III
3478
..~ ~..__
I + II 3563
415
-3478 1398 3566
'
3doo
Wavenumber
'
3~00
'
in 1 / c m
3476
3doo'3s'oo' Wavenumber
in 1 / c m
Fig. 3. High-temperature Raman spectroscopicdehydration studies of Ba(OH)CI'2H20: a, closed tube; b, open tube I. Ba(OHJC1.2H20; II, Ba(OH)CI-0.5H 20; III, Ba(OH)CI;'r,OH stretchingmode (OH ions)of Ba(OH)CI-0.5H20.
K. Beckenkamp, H.D. Lutz/Thermochimica Acta 258 (1995) 184 195
193
thermal analyses (DTA, etc.), dehydration starts at 348 K (onset, Tma~, 368 K; open crucible). The dihydrate is obtained if the disc is produced with a pressure of l09 Pa (10 t cm 2) using a cooled mortar. High-temperature Raman studies, however, do not reveal the existence of this compound, either on dehydration of the tetrahydrate or on rehydration of Ba(OH)I (see Fig. 1). IR spectra of Ba {O(H, D)} 1.2 H20 are shown in Fig. 2. The spectra are very similar to those of Ba(OH)Br-2H20 [3] indicating that the hydrogen bonds formed are very similar in these compounds. Obviously, the hydrogen bond system present in Ba(OH)CI. 2 H20-type structures cannot be further expanded on substitution of Br by I without destabilization of the structure. This also explains the low stability of the iodide under discussion.
3600
l + III
T[K]
J 3 53
398
'...~ 3654
I
i
~ , ~
Ij,
393
I
I 3658
I
J
295
'
as'oo
'
Wavenumber
a oo
'
in 1/cm
Fig. 4. High-temperature Raman spectroscopic dehydration studies of Ba(OH)Br-2H20 (closed tube): l, Ba(OH)Br.2H20: III, Ba(OH)Br.
194
K. Beckenkamp. H.D. Lutz/Thermochimica Acta 258 (1995) 189 195
Table 1 Fusing temperatures(K) and fusingenergies(kJ mol- 1)of M(OH)X (DSC measurements,Au crucibles)
To.set Tmn x
HM
Ba(OH)CI
Ba(OH)Br
Ba(OH)I
Sr(OH)CI
Sr(OH)Br
Sr(OH)I
805 814 21.4
850 863 22
937 949 36.5
782 793 22.4
848 863 17.2
934 943 29.0
3.2. B a ( O H ) X . O . 5 H20 ( X is CI, Br)
Unlike Ba(OH)Br.0.5 H20, Ba(OH)CI.0.5 H20 can be prepared by both dehydration of the dihydrate at ambient temperature over P205 and by rehydration of the anhydrous compound with stoichiometric amounts of H 2 0 [3, 5]. On dehydration of Ba(OH)CI'2H20 at higher temperatures (DTA and DSC studies [2,3,9, 12]), the two water molecules are usually emitted in one step. These findings were confirmed by high-temperature Raman experiments (see Figs. 3 and 4), which indicate that Ba(OH)C1.0.5 H20, but not Ba(OH)Br-0.5 H20, is a real compound. Formation of Ba(OH)CI-0.5 H20 starts at 390 K, and that of Ba(OH)C1 starts at 410 K (closed tube). The hemihydrate can be detected and distinguished from other barium hydroxide chlorides by the Raman band at 3564 cm- 1 which is due to the stretching mode of the OH ions. 3.3. Lower hydrates of Sr( OH ) X
Compounds like Sr(OH)X.0.5 H20 and Sr(OH)X-2 HzO (X is C1, Br) have not been established. Sr(OH)X.4 H20 (X is C1, Br) dehydrate to the anhydrous compounds in one step. Dehydration starts at 321 and 335 K, respectively (onset, Tm,x, 351 and 361 K, open tube, DTA) [9]. In the case of the iodide, the tetrahydrate reported in Refs. [1,5] could not be prepared. Therefore, its existence is debatable. 3.4. M ( O H ) X ( M is Ba, Sr; X is C1, Br, l )
Anhydrous Ba(OH)X (X is CI, Br, I) and Sr(OH)I (all laurionite type [9, 10, 13, 14]), Sr(OH)Br (space group P213 [13]), and Sr(OH)CI, Cd(OH)Cl-type [13], melt undecomposed at 780-940 K (see Table 1). On further heating, decomposition to MO and M4OX 6 [15] occurs.
Acknowledgments The authors thank the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie for financial support.
K. Beckenkamp, H.D. Lutz/Thermochimica Acta 258 (1995) 184-195
195
References [1] Gmelins Handbuch der anorganischen Chemie, Barium, 8. Aufl., No. 30, Teil B, Verlag Chemie, Weinheim, 1960. [2] T.V. Mozharova and E.N. Pavlyuchenko, Zh. Neorg. Khim., 24 (1979) 2522; Russ. J. Inorg. Chem., 24 (1979) 1401. [3] H.D. Lutz, Th. Kellersohn and K. Beckenkamp, Z. Naturforsch. Sect. b, 44 (1989) 928. [4] Th. Kellersohn, K. Beckenkamp, H.D. Lutz and E. Jansen, Acta Crystallogr. Sect. C, 47 (1991)483. [5] H. Aspelund, Acta Acad. Abo. Ser. B, 7 (1933) (5) 1 and (6) 1. [6] Th. Kellersohn, K. Beckenkamp and H.D. Lutz, Z. Naturforsch. Sect. b, 46 (1991) 1279. [7] H.D. Lutz, Struct. Bonding (Berlin), H 82 (1995) 85. [8] H.D. Lutz, Struct. Bonding (Berlin), 69 (1988) 79. [9] K. Beckenkamp, Doctoral Thesis, University of Siegen, 1991. [10] H. M611er, K. Beckenkamp, Th. Kellersohn, H.D. Lutz and J.K. Cockcroft, Z. Kristallogr., 209 (1994) 157. [11] J. Henning and H.D. Lutz, Thermochim. Acta, 150 (1989) 141. [12] O.A. Markova, Zhur. Fiz. Khim., 48 (1975) 38; Russ. J. Phys. Chem., 49 (1975) 21. [13] St. Peter, K. Beckenkamp and H.D, Lutz, unpublished results. [14] H. M611er, Doctoral Thesis, University of Siegen, 1993, [15] A.F. Wells, Structural Inorganic Chemistry, 5th edn. Clarendon Press, Oxford, 1984, p. 488.
Thermochimica Acta 258 (1995) 189 195
On the existence of lower hydrates of M(OH)X(M is Sr, Ba; X is C1, Br, I) K. B e c k e n k a m p , H . D . L u t z * Universitdt Sieqen. Anor#anische Chemie l, D-57068 Sie#en, Germany
Received 17 June 1994; accepted 12 November 1994
Abstract Preparation of the lower hydrates of M(OH)X(M is Ba, Sr; X is C1, Br, I) was attempted both by dehydration experiments of Ba(OH)X'2H20(X is CI, Br), Ba(OH)I-4H20, and Sr(OH)X'4H20 (X is CI, Br), and by rehydration of the anhydrous salts using infrared, Raman, and high-temperature Raman spectroscopic methods. Thus, the hitherto unknown compound Ba(OH)I'2H20 has been established and Ba(OH)CI.0.5 H20, but not Ba(OH)Br. 0.5H20, has been confirmed. Ba(OH)I.0.5 H20 and lower hydrates of Sr(OH)X were not obtained. Ba(OH)I2H20 is isostructural with Ba(OH)X.2 H20 (X is CI, Br). The crystal structure of Ba(OH)CI0.5H20 is not known so far. The dehydration and fusing temperatures of M(OH)X.4H20 and M (OH)X, respectively, are presented. Keywords: Dehydration; Halide; Hydration; IRS; Raman
1. Introduction The higher hydrates of the barium and strontium hydroxy halides Ba(OH)X. 2 H2O (X is CI, Br), S r ( O H ) X - 4 H 2 0 (X is CI, Br), and B a ( O H ) I - 4 H 2 0 are well established [1 6]. The crystal structures of these compounds are noteworthy in so far as that the former belong to the very few structures in which O H - ions are not coordinated to metal ions [3, 4, 7]. The latter possess water molecules which are the most distorted ones known so far. This is due to the extremely differently strong hydrogen bonds formed [6, 8]. Literature data on the lower hydrates of these basic salts are scarce [1, 5]. The only compounds mentioned are Ba(OH)X.0.5 H 2 0 with X being C1 and Br, apart from the well-established anhydrous salts [1,5, 9, 10]. * Corresponding author. 0040-6031/95/$09.50 i ' 1995 ElsevierScience B.V. All rights reserved SSDI 0040-6031(94)02213-5
190
K. Beckenkamp, H.D. Lutz/Thermochimica Acta 258 (1995) 189 195
In this paper, we demonstrate the existence of lower hydrates of M(OH)X (M is Ba, Sr; X is C1, Br, I) by means of IR, Raman, and high-temperature Raman spectroscopic methods, and by thermoanalytical (DTA, TG, DTG) measurements. 2. E x p e r i m e n t a l
The starting materials were Ba(OH)X.2 H20 (X is C1, Br) and Ba(OH)[-4 H20. They (as well as deuterated specimens) were prepared by crystallization of aqueous solutions of the respective halides and hydroxides in molar ratios of 10:1; for details, see Refs. [3,9, 10]. Preparation of the lower hydrates of the title compounds was attempted by dehydration of the higher hydrated hydroxide halides and by rehydration of anhydrous M(OH)X, respectively.
I
I+II
3527
3588 /~ 34,90
' '
36'00
'
Wavenumber
35'00
'
3400
in 1 / c m
Fig. 1. High-temperature Raman spectroscopic dehydration studies of Ba(OH)I'4H20 (closed tube): l, Ba(OH)I.4H20; II, Ba(OH)I.
K. Beckenkamp, H.D. Lutz/Thermochimica Acta 258 (1995) 184 195
191
DTA (difference thermal analysis), TG (thermogravimetry) and DSC (differential scanning calorimetry) measurements were carried out on Linseis L 62, Mettler TA 4000, and Perkin-Elmer DSC 7 systems, using silica tubes and gold crucibles as sample holders, respectively. Heating rates were 5-10°C min- ~. AlzO 3 was used as reference. IR spectra of dehydrated and rehydrated samples, respectively, were recorded on a Perkin-Elmer model 580 spectrophotometer (resolution < 1 cm- ~) using KBr and CsI discs as well as Nujol and Fluorolub mulls. Raman spectra, with the samples in
..~i~.,, B a ( O H ) B r • 2H20
..'I~o
,,, ".
3(~59 ~ ~ ' o
1o:;o',,l
!
4~;51 I;
~
~s7
tl
t
,..'
2320202o 177o162o~
~
---,., ,.,
1010
3o2o'~'..-/2~'~2050 -'~
853
421
2700
P 280
/"4
•" ~ - ' ,
,,"t" 50~': ' "°
Ba(OH)I • 2H20 ......
..,,.3440
,,..."TilSs 7°
~/"
~/--~,,,o,~35
1,[35
]
.^.V'~1"e/'~¥679
,~,,\/,;~17
36683410
854 5 %
D
...---,,,"i?~",~
; 1010 1310/; ; .-," 1195
85% D
.
.
.
.
.
.
.
.
.
-3~9~ 3669
.
.
" .
.
.
.
176o -
2600 2709
I 3000
282
1
/ ~ ~
, ;,,,
~"'1]l
I 11450 ===686' ' ' / "" ~=nn ~w ; 946 , 1740 ~ / t ~ I/"~ ;';
-3450 T --2200 / 3662 -3000 '~', ,,-. I - ..
Y I
/470
5% D
'
83~1273~
4;
2700
-
~!37g: I
. ....
..'"23~0 2020
3~,~....~-~5o
.........
/
, iq i
l
, ~ II
:o
67~-5
~LI~ ~
3J~,
2030 I 2000
I 1,500
Wavenumber
I 1000
I 500
in l / e m
Fig. 2. Infrared spectra (Csl discs) of Ba{O(H, D)}X.2(H, D ) 2 0 (X is Br, 1) at ambient (-) and liquid nitrogen temperature ( ). Assignment of the observed bands (cm - 1) [3] : 3662 and 2703, stretches of OH and O D - ; 2700 3000, stretches of H 20; 846 and 630, librations of H 2O and D 2 0 ; 430 and 334, librations of OH - and O D - ; < 3 0 0 c m - 1, translational modes (data for X is I).
192
K. Beckenkamp, H.D. Lutz/Thermochimica Acta 258 (1995) 189 195
glass capillaries, were measured on a Dilor O M A R S 89 multichannel Raman spectrograph (resolution < 4 c m - 1 ) with the usual right-angle geometry. For excitation, the 514.5 nm line of an Ar + ion laser was employed. Further details, especially with respect to high-temperature Raman measurements, are given elsewhere [9, 11]. 3. Results and discussion 3,1. B a ( O H ) I ' 2 H z O
The existence of the hitherto unknown Ba(OH)I.2 H 2 0 compound was first detected by dehydration o f B a ( O H ) I . 4 H 2 0 in a Csl matrix in the course of IR spectroscopic measurements [9]. The tetrahydrate dehydrates very easily to the anhydrous salt. With
3593
a
T[K]
T[K]
3656
3564
3592
I ÷ II + III
3478
..~ ~..__
I + II 3563
415
-3478 1398 3566
'
3doo
Wavenumber
'
3~00
'
in 1 / c m
3476
3doo'3s'oo' Wavenumber
in 1 / c m
Fig. 3. High-temperature Raman spectroscopicdehydration studies of Ba(OH)CI'2H20: a, closed tube; b, open tube I. Ba(OHJC1.2H20; II, Ba(OH)CI-0.5H 20; III, Ba(OH)CI;'r,OH stretchingmode (OH ions)of Ba(OH)CI-0.5H20.
K. Beckenkamp, H.D. Lutz/Thermochimica Acta 258 (1995) 184 195
193
thermal analyses (DTA, etc.), dehydration starts at 348 K (onset, Tma~, 368 K; open crucible). The dihydrate is obtained if the disc is produced with a pressure of l09 Pa (10 t cm 2) using a cooled mortar. High-temperature Raman studies, however, do not reveal the existence of this compound, either on dehydration of the tetrahydrate or on rehydration of Ba(OH)I (see Fig. 1). IR spectra of Ba {O(H, D)} 1.2 H20 are shown in Fig. 2. The spectra are very similar to those of Ba(OH)Br-2H20 [3] indicating that the hydrogen bonds formed are very similar in these compounds. Obviously, the hydrogen bond system present in Ba(OH)CI. 2 H20-type structures cannot be further expanded on substitution of Br by I without destabilization of the structure. This also explains the low stability of the iodide under discussion.
3600
l + III
T[K]
J 3 53
398
'...~ 3654
I
i
~ , ~
Ij,
393
I
I 3658
I
J
295
'
as'oo
'
Wavenumber
a oo
'
in 1/cm
Fig. 4. High-temperature Raman spectroscopic dehydration studies of Ba(OH)Br-2H20 (closed tube): l, Ba(OH)Br.2H20: III, Ba(OH)Br.
194
K. Beckenkamp. H.D. Lutz/Thermochimica Acta 258 (1995) 189 195
Table 1 Fusing temperatures(K) and fusingenergies(kJ mol- 1)of M(OH)X (DSC measurements,Au crucibles)
To.set Tmn x
HM
Ba(OH)CI
Ba(OH)Br
Ba(OH)I
Sr(OH)CI
Sr(OH)Br
Sr(OH)I
805 814 21.4
850 863 22
937 949 36.5
782 793 22.4
848 863 17.2
934 943 29.0
3.2. B a ( O H ) X . O . 5 H20 ( X is CI, Br)
Unlike Ba(OH)Br.0.5 H20, Ba(OH)CI.0.5 H20 can be prepared by both dehydration of the dihydrate at ambient temperature over P205 and by rehydration of the anhydrous compound with stoichiometric amounts of H 2 0 [3, 5]. On dehydration of Ba(OH)CI'2H20 at higher temperatures (DTA and DSC studies [2,3,9, 12]), the two water molecules are usually emitted in one step. These findings were confirmed by high-temperature Raman experiments (see Figs. 3 and 4), which indicate that Ba(OH)C1.0.5 H20, but not Ba(OH)Br-0.5 H20, is a real compound. Formation of Ba(OH)CI-0.5 H20 starts at 390 K, and that of Ba(OH)C1 starts at 410 K (closed tube). The hemihydrate can be detected and distinguished from other barium hydroxide chlorides by the Raman band at 3564 cm- 1 which is due to the stretching mode of the OH ions. 3.3. Lower hydrates of Sr( OH ) X
Compounds like Sr(OH)X.0.5 H20 and Sr(OH)X-2 HzO (X is C1, Br) have not been established. Sr(OH)X.4 H20 (X is C1, Br) dehydrate to the anhydrous compounds in one step. Dehydration starts at 321 and 335 K, respectively (onset, Tm,x, 351 and 361 K, open tube, DTA) [9]. In the case of the iodide, the tetrahydrate reported in Refs. [1,5] could not be prepared. Therefore, its existence is debatable. 3.4. M ( O H ) X ( M is Ba, Sr; X is C1, Br, l )
Anhydrous Ba(OH)X (X is CI, Br, I) and Sr(OH)I (all laurionite type [9, 10, 13, 14]), Sr(OH)Br (space group P213 [13]), and Sr(OH)CI, Cd(OH)Cl-type [13], melt undecomposed at 780-940 K (see Table 1). On further heating, decomposition to MO and M4OX 6 [15] occurs.
Acknowledgments The authors thank the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie for financial support.
K. Beckenkamp, H.D. Lutz/Thermochimica Acta 258 (1995) 184-195
195
References [1] Gmelins Handbuch der anorganischen Chemie, Barium, 8. Aufl., No. 30, Teil B, Verlag Chemie, Weinheim, 1960. [2] T.V. Mozharova and E.N. Pavlyuchenko, Zh. Neorg. Khim., 24 (1979) 2522; Russ. J. Inorg. Chem., 24 (1979) 1401. [3] H.D. Lutz, Th. Kellersohn and K. Beckenkamp, Z. Naturforsch. Sect. b, 44 (1989) 928. [4] Th. Kellersohn, K. Beckenkamp, H.D. Lutz and E. Jansen, Acta Crystallogr. Sect. C, 47 (1991)483. [5] H. Aspelund, Acta Acad. Abo. Ser. B, 7 (1933) (5) 1 and (6) 1. [6] Th. Kellersohn, K. Beckenkamp and H.D. Lutz, Z. Naturforsch. Sect. b, 46 (1991) 1279. [7] H.D. Lutz, Struct. Bonding (Berlin), H 82 (1995) 85. [8] H.D. Lutz, Struct. Bonding (Berlin), 69 (1988) 79. [9] K. Beckenkamp, Doctoral Thesis, University of Siegen, 1991. [10] H. M611er, K. Beckenkamp, Th. Kellersohn, H.D. Lutz and J.K. Cockcroft, Z. Kristallogr., 209 (1994) 157. [11] J. Henning and H.D. Lutz, Thermochim. Acta, 150 (1989) 141. [12] O.A. Markova, Zhur. Fiz. Khim., 48 (1975) 38; Russ. J. Phys. Chem., 49 (1975) 21. [13] St. Peter, K. Beckenkamp and H.D, Lutz, unpublished results. [14] H. M611er, Doctoral Thesis, University of Siegen, 1993, [15] A.F. Wells, Structural Inorganic Chemistry, 5th edn. Clarendon Press, Oxford, 1984, p. 488.