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Synthesis, structure and properties of a new intermetallic compound, Ca7Ni4Sn13
Journal of the Less-Common LCM 1269
Metals,
175 (1991)
339-346
339
Synthesis, structure and properties of a new intermetallic compound, Ca,Ni,Sn, 3 Deborah A. Vennos, Michael E. Badding and F. J. DiSalvo Department (Received
of Chemistry,
Cwnell
University,
Ithaca, NY 14853 (U.S.A.)
April 5, 1991)
Abstract Crystals of a new intermetallic compound, Ca,Ni,Sn,,, have been prepared. The refined structure was solved in the P4/m space group, 2 = 1, with lattice constants a = 11.200(l) %,and c=4.594(1) A, R= 2.8% and %=2.4%. This new structure type consists of an Sn-Ni network forming channels parallel to the c axis which are filled with calcium atoms. Temperature-dependent magnetic and conductivity studies show Ca7Ni4Sn13to be Pauli paramagnetic with simple metallic behavior.
1. Introduction We have previously reported that ternary metal nitrides of the general composition Ca,M,N,, where M is a transition metal or post-transition metal, are readily prepared as polycrystalline powders by reaction of Ca,N, and M under N2 at temperatures on the order of 1000 “C [l-3]. When the structures are relatively simple, we have been able to determine them by X-ray or neutron powder diffraction [ 41. In only a few instances have we obtained single crystals [ 51. In order to prepare single crystals of materials with more complicated structures, we have been attempting to develop general methods of nitride crystal growth using molten salts or metal fluxes. Initial attempts to grow crystals of CaNiN from a tin flux resulted in the loss of nitrogen and the growth of crystals of a new ternary inter-metallic, Ca7Ni4Sni3. Herein we report the synthesis, structure and properties of this new phase.
2. Synthesis The title compound was first discovered by heating an intimate mixture of CaNiN (0.3579 g, 3.18 mmol) and tin (0.6699 g, 5.64 mmol) in a sealed niobium tube under an argon atmosphere at 1000 “C for 24 h, followed by cooling to 500 “C in 15 h and finally cooling to room temperature in 6 h. The majority phase consisted of metallic needle-shaped crystals up to 4 mm in length which were used for the structure determination. The remaining
0022-5088/91/$3.50
0 1991 -
Elsevier
Sequoia. Lausanne
340
nickel from the CaNiN (three-sevenths of the nickel initially included) must have alloyed with the niobium tube since it was not observed in the product by X-ray powder diffraction. After the structure determination, Ca,Ni,Sn,, was synthesized by heating a pressed pellet of a stoichiometric mixture of the metals in an alumina crucible sealed in an evacuated quartz tube at the heating schedule mentioned above. X-ray powder diffraction indicated nearly pure Ca,Ni,Sn,, with a small unidentified impurity phase. The intensity of the strongest impurity diffraction peak was 2% of that of the strongest peak of the bulk phase. 3. Structure
determination
Unit cell symmetry and approximate lattice constants were obtained from rotation and axial photographs of a crystal mounted along the needle axis. Data were collected on a Syntex P2, diffractometer using MO Ka radiation and a graphite monochromator. Since no systematic absences were observed, the choice of space groups was reduced to P4, P4 and P4/m and the structure was solved by direct methods in the P4/m space group. Solution of the structure in either non-centrosymmetric space group resulted in no significant change in R. An analytical absorption correction was performed and four o&ants of data were merged to improve the data set. The largest peak in the difference Fourier map was 1.8e- and was 0.8 %,from a tin atom. Final values ofR = 2.8% and R, = 2.4% were obtained after refinement. The structure determination and refinement were performed using Nicolet SHELXTL Plus software running on a Microvax computer. Table 1 summarizes the data collection parameters. Atomic positions are listed in Table 2. Anisotropic thermal parameters are summarized in Table 3. 4. Magnetic
susceptibility
measurement
The magnetic susceptibility was measured on a previously calibrated system [ 61 by the Faraday technique. The susceptibility of a sample contained in a thin-walled quartz tube was determined to be field independent at room temperature, showing that no ferromagnetic impurities were present. The temperature-dependent susceptibility data were fit well by the following form: x=x0+
c T+O
where x0= -2.53~10~~ and 0=6 K. 5. Conductivity
e.m.u. mole-‘,
C=1.98X10W2
e.m.u. K mole-’
measurement
The resistance of a sintered pellet (0.5 in diameter, 0.035 in thick) was measured by the four-probe method at 40 Hz by lock-m detection. Four
341 TABLE 1 Summary of crystal and diffraction data for CarNi,Sn,a P4tm (no. 83) 1 11.200(l), 4.594(l) 576 55, w-20
Space group
a, c
(%i>
v (A4
20 maximum (deg), scan type Octants measured X-ray radiation Monochromator Measured reflections Observed reflectionsa Independent reflections Number of parameters Absorption coefficient CL(mm-‘) Rb, R,q= (%)
hkl,
-hkl,
-h-k-L,
h-k-I
MO Kru Graphite 3950 869 947 40 19.68 2.8, 2.4
=Fo2> 3s(F,,‘). bR=X(IFc,l - IF,I)~(lF,I). =R,={Z[w(lF,I - IF~i)2]E(wlF~12>}‘n,
w=s(F,,)-‘.
TABLE 2 Positional parameters for Ca$Ji,Sn,, Atom
Site
5
Y
z
Snl Sn2 Sn3 Sn4 Cal Ca2 Ca3 Nil
4k
0.21629(3) 0.42478(4) 0.28533(3) 0 0.5 0.16284(10), 0.5 0.77594(6)
0.38922(3) 0.30952(3) 0.01751(3) 0 0.5 0.17058(10) 0 0.38068(7)
0.5 0 0.5 0.5 0.5 0 0 0.5
4i 4k lb Id e’ 2e 4k
TABLE 3 Anisotropic displacement parameters (A2X 103) Atom
Ul,
u 22
ff33
u23
u*3
u,2
Snl Sn2 Sn3 Sn4 Cal ca2 Ca3 Nil
10.7(2) 16.2(2) 13.1(2) 15.4(2) 12.4(5) 13.7(5) 14.5(7) 11.7(3)
10.6(Z) 13.2(Z) 9.9(2) 15.4(4) 12.4(5) 13.7(5) 20.7(8) 12.9(3)
l&6(2) 10.7(2) 14.2(Z) l&4(4) 13*2(l) 16.0(5) 16.3(g) 11.8(4)
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
-OS(l) -2.8(l) 0.4(l) i.9(2) 1.8(3) - 2.5(6) 0.9(2)
The anisotropic displacement exponent takes the form - 2r2(hZa*2U1, + _._+ Bhka*b*U,z).
342
,I,,., 0
ItItII 50
100
150
200
I.,,
250
1 300
T (K) Fig. 1.
Temperature
dependence
of the resistivity of Ca,Ni,Sn13.
spring-loaded pins arranged in a collinear configuration were pressed against the face of the pellet to serve as contacts and were shown to be low resistance (less than 0.2 Q) and ohmic from the linearity of the I-V behavior (from 10 to 70 mA). The resistivity of the sample was determined by measuring the resistance of a solid molybdenum pellet (0.5 in diameter). A proportionality constant between the resistivity and resistance was then calculated [7] and this value was used to determine the resistivity of Ca,Ni,Sn,,. F’igure 1 shows the results of a temperat~e-dependent resistivity study between 4 and 300 K. The shape of the curve and the magnitude of the resistivity are characteristic of a metallic system with R(295 KjYR(4.2 K) = 11.2. The somewhat noisy behavior between 140 and 190 K is attributed to slightly shifting voltage contacts as the system contracted on cooling.
6. Discussion The structure of CaTNi,Sn,a can be visualized as sheets of tin and nickel atoms forming channels filled by calcium atoms. The central channel is composed of a square of tin atoms and a calcium-centered octagon of alternating tin and nickel atoms. The square and octagonal units stack alternately along the c axis (Fig. 2; bonds to calcium are omitted for clarity). This central channel structure is linked by calcium-centered pentagonal and hexagonal arrays of tin and nickel as shown in Fig. 3.
343
Fig. 2. A view perpendicular 3.
to the c axis indicates
the labels
used to identify
atoms
in Table
The shortest Sn-Sn distance (2.87 .& SnlSn3) is close to that in LYSn (four at 2.81 A) and Ni3Snq (2.93 A) [8], indicating a strong bonding interaction, whereas the remaining Sn-Sn distances (3.20-3.27 A) are longer than in either cy-Sn or /3-Sn(four at 3.02 A and two at 3.18 %,respectively), suggesting much weaker Sn-Sn interactions. The range of Sn-Ca distances (3.18-3.57 &I falls within the range found in CazSn (3.13-3.71 A) [9]. The average Sn-Ni distance (2.54 ;i> is comparable to that in Ni3Sn, (2.65 A). The shortest Ni-Ca distance (3.37 ;I> is larger than that found in Ca-Ni binary compounds (2.85-3.15 A) [ 10 J, indicating weaker Ca-Ni bonding interactions. Relevant. bond distances are listed in Table 4. The atoms in Ca,Ni,$& possess high coordination numbers typical of intermetallics. The coordination environment of the tin atoms ranges from 9 to 12, ~c~ud~g bonds to calcium atoms. The nickel is likewise in a tenfold coordinate position. Cal has an unusual 16-fold coordination: 12 bonds to tin atoms and four bonds to nickel atoms (Fig. 4). Although this is a new structure type, some features of the BaNiSn, and SrNiSn, [ 1 l] structures can be seen in Ca7Ni4Sn13. The four layers of atoms spanned by the bracket in Fig. 5 are compressed into three layers after the indicated tin layer is rotated by 45”. This leaves the central alkaline earth atom in the same 16-coordinate position found in Ca7Ni,Sn,,. The magnetic properties are consistent with a low density-of-states metallic system. The weakly diamagnetic x0 is more positive than the predicted core
Fig. 3. A view of the structure down the c axis. Open circles represent calcium atoms, dotted circles nickel atoms and hatched circles tin atoms.
Imports& bond distances (angstroms) for CqNi,Sn,, SnlSn2 Cal-Snl Cal-%:! Snl-Ca2 Snl-Ca3 Snl-Nil
3.272(l) 3.411(l) 3.246(l) 3.410(l) 3.561(l) 2.610(l) 2.579(l)
Sn2-Sn2 Sn2-Ca2 SnZ-Ca3 Sn3-Sn4 Sn3-Ca2 Sn3-Ca3 Snl-Sn3
3.244(l) 3.321(l) 3.568(l) 3.202(l) 3.318(l) 3.331(l) 2.865(l)
Sn4-Ca2 Cal-Nil Ca3-Ni 1 Nil-SnZ NilSn3 Nil-Ca3 Ni l-Ca2
3.500(l) 3.367(l) 3.655(l) 2.537(l) 2.548(l) 3.655(l) 3.404(l)
di~a~et~rn &core= 3.64~ 10V4 e.m.u. mol-’ assuming positive ion cores of Sn2+, Ni2+ and Ca2’) [ 121 owing to the presence of Pauli paramagnetism. No evidence for local moment formation on the nickel atoms was observed. A small increase in the susceptibility at low temperatures (the “Curie tail”)
345
Fig. 4. The unusual coordination
environment
of Cal
Fig. 5. A possible transformation of the Ba(Sr)NiSn, environment of Cal in the Ca7Ni,Sn,B structure.
structure to produce
the coordination
is consistent with a low level of paramagnetic impurities (e.g. 270 ppm Fe with a moment of 5 pB, which is consistent with 99.9% pure Ni used in the synthesis). The electrical resistivity data are in accord with a simple metallic system and the room temperature resistivity is typical of that of many inter-metallic compounds containing transition metals (i.e. on the order of 100 fl cm).
Acknowledgments The authors would like to thank Greg VanDuyne of the Cornell Chemistry Single Crystal X-ray Facility for aid with the structure determination. Funding for this work through the Oflice of Naval Research is greatly appreciated.
346
References I 2 3 4 5 6 7 8 9 10 11 12
M. Y. Chem and F. J. DiSalvo, J. Solid State Chem., 88 (1990) 459. M. Y. Chem and F. J. DiSaivo, J. Sotid State Chem., 88 (1990) 528. M. Y. Chem, D. A. Vennos and F. J. DiSalvo, J. Solid State Cha., in the press. M. Y. Chem and F. J. DiSalvo, Solid State Commun., in the press. D. A. Vennos, M. E. Badding and F. J. DiSalvo, Iwg. &em., 29 (1990) 4059. J. K. Vassiliou, M. Hornbostel, R. Ziebarth and F. J. DiSalvo, J. Solid State Chem., (1989) 208. J. D. Wasscher, Phitips Res. Rep., 16 (1961) 301. W. Jeitschko and B. Jaberg, Acta. Crystal&p-. B, 38 (1982) 598. V. P. Eckerlin, E. Leicht and E. Wolfel, 2. Awg. A.!&. C&em., 307 (1961) 10. H. Nowotny, 2. Metal&, 34 (1942) 247. W. D. Orrsheidt and H. Schafer, J. Less-Common Met., 58 (1978) 209. P. W. Selwood, Magnetochernistvy, Wiley Interscience, New York, 1979, p. 186.
81
Metals,
175 (1991)
339-346
339
Synthesis, structure and properties of a new intermetallic compound, Ca,Ni,Sn, 3 Deborah A. Vennos, Michael E. Badding and F. J. DiSalvo Department (Received
of Chemistry,
Cwnell
University,
Ithaca, NY 14853 (U.S.A.)
April 5, 1991)
Abstract Crystals of a new intermetallic compound, Ca,Ni,Sn,,, have been prepared. The refined structure was solved in the P4/m space group, 2 = 1, with lattice constants a = 11.200(l) %,and c=4.594(1) A, R= 2.8% and %=2.4%. This new structure type consists of an Sn-Ni network forming channels parallel to the c axis which are filled with calcium atoms. Temperature-dependent magnetic and conductivity studies show Ca7Ni4Sn13to be Pauli paramagnetic with simple metallic behavior.
1. Introduction We have previously reported that ternary metal nitrides of the general composition Ca,M,N,, where M is a transition metal or post-transition metal, are readily prepared as polycrystalline powders by reaction of Ca,N, and M under N2 at temperatures on the order of 1000 “C [l-3]. When the structures are relatively simple, we have been able to determine them by X-ray or neutron powder diffraction [ 41. In only a few instances have we obtained single crystals [ 51. In order to prepare single crystals of materials with more complicated structures, we have been attempting to develop general methods of nitride crystal growth using molten salts or metal fluxes. Initial attempts to grow crystals of CaNiN from a tin flux resulted in the loss of nitrogen and the growth of crystals of a new ternary inter-metallic, Ca7Ni4Sni3. Herein we report the synthesis, structure and properties of this new phase.
2. Synthesis The title compound was first discovered by heating an intimate mixture of CaNiN (0.3579 g, 3.18 mmol) and tin (0.6699 g, 5.64 mmol) in a sealed niobium tube under an argon atmosphere at 1000 “C for 24 h, followed by cooling to 500 “C in 15 h and finally cooling to room temperature in 6 h. The majority phase consisted of metallic needle-shaped crystals up to 4 mm in length which were used for the structure determination. The remaining
0022-5088/91/$3.50
0 1991 -
Elsevier
Sequoia. Lausanne
340
nickel from the CaNiN (three-sevenths of the nickel initially included) must have alloyed with the niobium tube since it was not observed in the product by X-ray powder diffraction. After the structure determination, Ca,Ni,Sn,, was synthesized by heating a pressed pellet of a stoichiometric mixture of the metals in an alumina crucible sealed in an evacuated quartz tube at the heating schedule mentioned above. X-ray powder diffraction indicated nearly pure Ca,Ni,Sn,, with a small unidentified impurity phase. The intensity of the strongest impurity diffraction peak was 2% of that of the strongest peak of the bulk phase. 3. Structure
determination
Unit cell symmetry and approximate lattice constants were obtained from rotation and axial photographs of a crystal mounted along the needle axis. Data were collected on a Syntex P2, diffractometer using MO Ka radiation and a graphite monochromator. Since no systematic absences were observed, the choice of space groups was reduced to P4, P4 and P4/m and the structure was solved by direct methods in the P4/m space group. Solution of the structure in either non-centrosymmetric space group resulted in no significant change in R. An analytical absorption correction was performed and four o&ants of data were merged to improve the data set. The largest peak in the difference Fourier map was 1.8e- and was 0.8 %,from a tin atom. Final values ofR = 2.8% and R, = 2.4% were obtained after refinement. The structure determination and refinement were performed using Nicolet SHELXTL Plus software running on a Microvax computer. Table 1 summarizes the data collection parameters. Atomic positions are listed in Table 2. Anisotropic thermal parameters are summarized in Table 3. 4. Magnetic
susceptibility
measurement
The magnetic susceptibility was measured on a previously calibrated system [ 61 by the Faraday technique. The susceptibility of a sample contained in a thin-walled quartz tube was determined to be field independent at room temperature, showing that no ferromagnetic impurities were present. The temperature-dependent susceptibility data were fit well by the following form: x=x0+
c T+O
where x0= -2.53~10~~ and 0=6 K. 5. Conductivity
e.m.u. mole-‘,
C=1.98X10W2
e.m.u. K mole-’
measurement
The resistance of a sintered pellet (0.5 in diameter, 0.035 in thick) was measured by the four-probe method at 40 Hz by lock-m detection. Four
341 TABLE 1 Summary of crystal and diffraction data for CarNi,Sn,a P4tm (no. 83) 1 11.200(l), 4.594(l) 576 55, w-20
Space group
a, c
(%i>
v (A4
20 maximum (deg), scan type Octants measured X-ray radiation Monochromator Measured reflections Observed reflectionsa Independent reflections Number of parameters Absorption coefficient CL(mm-‘) Rb, R,q= (%)
hkl,
-hkl,
-h-k-L,
h-k-I
MO Kru Graphite 3950 869 947 40 19.68 2.8, 2.4
=Fo2> 3s(F,,‘). bR=X(IFc,l - IF,I)~(lF,I). =R,={Z[w(lF,I - IF~i)2]E(wlF~12>}‘n,
w=s(F,,)-‘.
TABLE 2 Positional parameters for Ca$Ji,Sn,, Atom
Site
5
Y
z
Snl Sn2 Sn3 Sn4 Cal Ca2 Ca3 Nil
4k
0.21629(3) 0.42478(4) 0.28533(3) 0 0.5 0.16284(10), 0.5 0.77594(6)
0.38922(3) 0.30952(3) 0.01751(3) 0 0.5 0.17058(10) 0 0.38068(7)
0.5 0 0.5 0.5 0.5 0 0 0.5
4i 4k lb Id e’ 2e 4k
TABLE 3 Anisotropic displacement parameters (A2X 103) Atom
Ul,
u 22
ff33
u23
u*3
u,2
Snl Sn2 Sn3 Sn4 Cal ca2 Ca3 Nil
10.7(2) 16.2(2) 13.1(2) 15.4(2) 12.4(5) 13.7(5) 14.5(7) 11.7(3)
10.6(Z) 13.2(Z) 9.9(2) 15.4(4) 12.4(5) 13.7(5) 20.7(8) 12.9(3)
l&6(2) 10.7(2) 14.2(Z) l&4(4) 13*2(l) 16.0(5) 16.3(g) 11.8(4)
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
-OS(l) -2.8(l) 0.4(l) i.9(2) 1.8(3) - 2.5(6) 0.9(2)
The anisotropic displacement exponent takes the form - 2r2(hZa*2U1, + _._+ Bhka*b*U,z).
342
,I,,., 0
ItItII 50
100
150
200
I.,,
250
1 300
T (K) Fig. 1.
Temperature
dependence
of the resistivity of Ca,Ni,Sn13.
spring-loaded pins arranged in a collinear configuration were pressed against the face of the pellet to serve as contacts and were shown to be low resistance (less than 0.2 Q) and ohmic from the linearity of the I-V behavior (from 10 to 70 mA). The resistivity of the sample was determined by measuring the resistance of a solid molybdenum pellet (0.5 in diameter). A proportionality constant between the resistivity and resistance was then calculated [7] and this value was used to determine the resistivity of Ca,Ni,Sn,,. F’igure 1 shows the results of a temperat~e-dependent resistivity study between 4 and 300 K. The shape of the curve and the magnitude of the resistivity are characteristic of a metallic system with R(295 KjYR(4.2 K) = 11.2. The somewhat noisy behavior between 140 and 190 K is attributed to slightly shifting voltage contacts as the system contracted on cooling.
6. Discussion The structure of CaTNi,Sn,a can be visualized as sheets of tin and nickel atoms forming channels filled by calcium atoms. The central channel is composed of a square of tin atoms and a calcium-centered octagon of alternating tin and nickel atoms. The square and octagonal units stack alternately along the c axis (Fig. 2; bonds to calcium are omitted for clarity). This central channel structure is linked by calcium-centered pentagonal and hexagonal arrays of tin and nickel as shown in Fig. 3.
343
Fig. 2. A view perpendicular 3.
to the c axis indicates
the labels
used to identify
atoms
in Table
The shortest Sn-Sn distance (2.87 .& SnlSn3) is close to that in LYSn (four at 2.81 A) and Ni3Snq (2.93 A) [8], indicating a strong bonding interaction, whereas the remaining Sn-Sn distances (3.20-3.27 A) are longer than in either cy-Sn or /3-Sn(four at 3.02 A and two at 3.18 %,respectively), suggesting much weaker Sn-Sn interactions. The range of Sn-Ca distances (3.18-3.57 &I falls within the range found in CazSn (3.13-3.71 A) [9]. The average Sn-Ni distance (2.54 ;i> is comparable to that in Ni3Sn, (2.65 A). The shortest Ni-Ca distance (3.37 ;I> is larger than that found in Ca-Ni binary compounds (2.85-3.15 A) [ 10 J, indicating weaker Ca-Ni bonding interactions. Relevant. bond distances are listed in Table 4. The atoms in Ca,Ni,$& possess high coordination numbers typical of intermetallics. The coordination environment of the tin atoms ranges from 9 to 12, ~c~ud~g bonds to calcium atoms. The nickel is likewise in a tenfold coordinate position. Cal has an unusual 16-fold coordination: 12 bonds to tin atoms and four bonds to nickel atoms (Fig. 4). Although this is a new structure type, some features of the BaNiSn, and SrNiSn, [ 1 l] structures can be seen in Ca7Ni4Sn13. The four layers of atoms spanned by the bracket in Fig. 5 are compressed into three layers after the indicated tin layer is rotated by 45”. This leaves the central alkaline earth atom in the same 16-coordinate position found in Ca7Ni,Sn,,. The magnetic properties are consistent with a low density-of-states metallic system. The weakly diamagnetic x0 is more positive than the predicted core
Fig. 3. A view of the structure down the c axis. Open circles represent calcium atoms, dotted circles nickel atoms and hatched circles tin atoms.
Imports& bond distances (angstroms) for CqNi,Sn,, SnlSn2 Cal-Snl Cal-%:! Snl-Ca2 Snl-Ca3 Snl-Nil
3.272(l) 3.411(l) 3.246(l) 3.410(l) 3.561(l) 2.610(l) 2.579(l)
Sn2-Sn2 Sn2-Ca2 SnZ-Ca3 Sn3-Sn4 Sn3-Ca2 Sn3-Ca3 Snl-Sn3
3.244(l) 3.321(l) 3.568(l) 3.202(l) 3.318(l) 3.331(l) 2.865(l)
Sn4-Ca2 Cal-Nil Ca3-Ni 1 Nil-SnZ NilSn3 Nil-Ca3 Ni l-Ca2
3.500(l) 3.367(l) 3.655(l) 2.537(l) 2.548(l) 3.655(l) 3.404(l)
di~a~et~rn &core= 3.64~ 10V4 e.m.u. mol-’ assuming positive ion cores of Sn2+, Ni2+ and Ca2’) [ 121 owing to the presence of Pauli paramagnetism. No evidence for local moment formation on the nickel atoms was observed. A small increase in the susceptibility at low temperatures (the “Curie tail”)
345
Fig. 4. The unusual coordination
environment
of Cal
Fig. 5. A possible transformation of the Ba(Sr)NiSn, environment of Cal in the Ca7Ni,Sn,B structure.
structure to produce
the coordination
is consistent with a low level of paramagnetic impurities (e.g. 270 ppm Fe with a moment of 5 pB, which is consistent with 99.9% pure Ni used in the synthesis). The electrical resistivity data are in accord with a simple metallic system and the room temperature resistivity is typical of that of many inter-metallic compounds containing transition metals (i.e. on the order of 100 fl cm).
Acknowledgments The authors would like to thank Greg VanDuyne of the Cornell Chemistry Single Crystal X-ray Facility for aid with the structure determination. Funding for this work through the Oflice of Naval Research is greatly appreciated.
346
References I 2 3 4 5 6 7 8 9 10 11 12
M. Y. Chem and F. J. DiSalvo, J. Solid State Chem., 88 (1990) 459. M. Y. Chem and F. J. DiSaivo, J. Sotid State Chem., 88 (1990) 528. M. Y. Chem, D. A. Vennos and F. J. DiSalvo, J. Solid State Cha., in the press. M. Y. Chem and F. J. DiSalvo, Solid State Commun., in the press. D. A. Vennos, M. E. Badding and F. J. DiSalvo, Iwg. &em., 29 (1990) 4059. J. K. Vassiliou, M. Hornbostel, R. Ziebarth and F. J. DiSalvo, J. Solid State Chem., (1989) 208. J. D. Wasscher, Phitips Res. Rep., 16 (1961) 301. W. Jeitschko and B. Jaberg, Acta. Crystal&p-. B, 38 (1982) 598. V. P. Eckerlin, E. Leicht and E. Wolfel, 2. Awg. A.!&. C&em., 307 (1961) 10. H. Nowotny, 2. Metal&, 34 (1942) 247. W. D. Orrsheidt and H. Schafer, J. Less-Common Met., 58 (1978) 209. P. W. Selwood, Magnetochernistvy, Wiley Interscience, New York, 1979, p. 186.
81