Synthesis and structures of new layered ternary manganese tellurides: AMnTe2 (A = K, Rb, Cs), Na3Mn4Te6, and NaMn1.56Te2

Article abstract of DOI:10.1021/ic980805w

The synthesis and crystal structures of new ternary manganese tellurides, AMnTe₂ (A = K, Rb, Cs), Na₃Mn₄Te₆, and NaMn_1.56Te₂, are reported. These compounds are synthesized by solid-state reaction and cation exchange techniques in sealed Nb tubes. The single-crystal structures of AMnTe₂ (A = K, Rb), Na₃Mn₄Te₆, and NaMn_1.56Te₂ have been determined; KMnTe₂: a = 4.5110(4) ?, c = 14.909(2) ?, I4m2 (No. 119, Z = 2); RbMnTe₂: a = 4.539(1) ?, c = 15.055(2) ?, I4?m2 (No. 119, Z = 2); Na₃Mn₄Te₆: a = 8.274(4) ?, b = 14.083(6) ?, c = 7.608(6) ? β = 91.97(4)°, C2/m (No. 12, Z = 2); NaMn_1.56Te₂: a = 4.4973(8) ?, c = 7.638(2) ?, P3?m1 (No. 164, Z = 1). The fundamental building blocks of the title compounds are MnTe₄ tetrahedra. AMnTe₂ (A = K, Rb, Cs) are isostructural with TlFeS₂, consisting of layers built up by four corner-shared MnTe₄ tetrahedra. Manganese telluride layers in Na₃Mn₄Te₆ consist of two hexagonal nets of Te atoms between which two-thirds of the tetrahedral interstices are filled with Mn atoms to form two 6³ honeycomb nets. NaMn_1.56Te₂ adopts a defective CaAl₂Si₂ structure type, in which Mn atoms partially and randomly occupy 78% of tetrahedral sites. Temperature-dependent magnetic susceptibilities measurements show that AMnTe₂ (A = K, Rb, Cs) exhibit Curie-Weiss paramagnetism, whereas Na₃Mn₄Te₆ and NaMn_1.56Te₂ show paramagnetism with a weak dependence on temperature.

Full text of DOI:10.1021/ic980805w

Inorg. Chem. 1999, 38, 235-242
235
Synthesis and Structures of New Layered Ternary Manganese Tellurides: AMnTe2 (A ) K,
Rb, Cs), Na3Mn4Te6, and NaMn1.56Te2
†
Joonyeong Kim, Chwanchin Wang, and Timothy Hughbanks*
Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77842-3012
ReceiVed July 15, 1998
The synthesis and crystal structures of new ternary manganese tellurides, AMnTe2 (A ) K, Rb, Cs), Na3Mn4Te6,
and NaMn1.56Te2, are reported. These compounds are synthesized by solid-state reaction and cation exchange
techniques in sealed Nb tubes. The single-crystal structures of AMnTe2 (A ) K, Rb), Na3Mn4Te6, and NaMn1.56-
Te2 have been determined; KMnTe2: a ) 4.5110(4) Å, c ) 14.909(2) Å, I 4h m2 (No. 119, Z ) 2); RbMnTe2: a
)
4.539(1) Å, c ) 15.055(2) Å, I 4h m2 (No. 119, Z ) 2); Na3Mn4Te6: a ) 8.274(4) Å, b ) 14.083(6) Å, c )
7
.608(6) Å, â ) 91.97(4)°, C2/m (No. 12, Z ) 2); NaMn1.56Te2: a ) 4.4973(8) Å, c ) 7.638(2) Å, P 3h m1 (No.
64, Z ) 1). The fundamental building blocks of the title compounds are MnTe4 tetrahedra. AMnTe2 (A ) K,
1
Rb, Cs) are isostructural with TlFeS2, consisting of layers built up by four corner-shared MnTe4 tetrahedra.
Manganese telluride layers in Na3Mn4Te6 consist of two hexagonal nets of Te atoms between which two-thirds
3
of the tetrahedral interstices are filled with Mn atoms to form two 6 honeycomb nets. NaMn1.56Te2 adopts a
defective CaAl2Si2 structure type, in which Mn atoms partially and randomly occupy 78% of tetrahedral sites.
Temperature-dependent magnetic susceptibilities measurements show that AMnTe2 (A ) K, Rb, Cs) exhibit Curie-
Weiss paramagnetism, whereas Na3Mn4Te6 and NaMn1.56Te2 show paramagnetism with a weak dependence on
temperature.
Introduction
such A-M-Q ternary systems have concentrated on sulfides
and selenides; with less attention paid to tellurides. Some notable
There is much current interest in ternary systems with
A-M-Q compositions (A ) alkali metals; M ) Mn, Fe, Co,
Ni; Q ) chalcogen). This has led to the synthesis of many new
exceptions to this generalization include contributions by
1
,4,15,16,18
Bronger and Klepp.
Our interest in layered ternary manganese tellurides was
sparked by the serendipitous discovery of the polar layered
materials with unusual structural features and physical properties
that deserve further investigation.1
-17
Most investigations of
19
compounds, LiMnTe2 and NaMnTe2. We believe that layered
compounds with intrinsic polarity to be interesting potential
hosts for composite materials prepared by intercalation of
*
To whom correspondence should be addressed.
†
Present address : Department of Chemistry, Princeton University,
Princeton, NJ 08544.
2
0,21
nonlinear optical chromophores.
In these compounds, there
(
(
(
(
(
(
1) Klepp, K. O.; Sparlinek, W.; Boller, H. J. Alloys Compd. 1996, 238,
-5.
2) Huan, G.; Greenblatt, M.; Croft, M. Eur. J. Solid State Inorg. Chem.
989, 26, 193-220.
3) Bronger, W.; Rennau, R. M.; Schmitz, D. Z. Anorg. Allg. Chem. 1996,
also exists the possibility that interesting magnetic properties
might accompany such behavior. Bronger and co-workers
reported the only other ternary manganese tellurides known,
1
1
all of which fall into three types: A2MnTe2 (A ) K, Rb, Cs),
622, 627-629.
A6MnTe4 (A ) Na, K), and A2Mn3Te4 (A ) Rb, Cs).4
,15,16
In
4) Bronger, W.; Hardtdegen, H.; Kanert, M.; Schmitz, D. Z. Anorg. Allg.
Chem. 1996, 622, 313-318.
the first of these structure classes, one-dimensional chains,
MnTe2] , built up by edge-sharing of MnTe4 tetrahedra are
found. Discrete [MnTe4] tetrahedra are found in the second
structure class. The third series of compounds possess layered
structures, ∞[Mn3Te4] , as will more fully described below.
We have uncovered several new layered compounds, AMnTe2
(A ) K, Rb, Cs), Na3Mn4Te6, and NaMn1.56Te2 and this paper
report the synthesis and structures of these new compounds.
We also discuss structural relationships between the title
compounds and other related compounds. A preliminary com-
munication of some of this work has been published.19
5) Bronger, W.; Koelman, W.; Schmitz, D. Z. Anorg. Allg. Chem. 1995,
1
∞
2-
[
621, 405-408.
6
-
6) Bronger, W.; Bomba, C.; Koelman, W. Z. Anorg. Allg. Chem. 1995,
621, 409-411.
(
(
7) Bronger, W.; Muller, P. Z. Anorg. Allg. Chem. 1995, 621, 412-416.
2
2-
8) Bronger, W.; Ruschewitz, U.; M u¨ ller, P. J. Alloys Compd. 1995, 218,
2
2-27.
(
9) Bronger, W.; Balk-Hardtdegen, H.; Ruschewitz, U. Z. Anorg. Allg.
Chem. 1992, 616, 14-18.
(
(
(
10) Bronger, W.; Ruschewitz, U.; M u¨ ller, P. J. Alloys Compd. 1992, 187,
9
5-103.
11) Bronger, W.; Rennau, R.; Schmitz, D. Z. Anorg. Allg. Chem. 1991,
97, 27-32.
12) Bronger, W.; Kyas, A.; M u¨ ller, P. J. Solid State Chem. 1987, 70, 262-
70.
5
2
(
13) Bronger, W.; Schmitz, D. Z. Kristallogr. 1988, 183, 201-205.
(18) Bronger, W.; Bonsmann, B. Z. Anorg. Allg. Chem. 1995, 621, 2083-
(14) Bronger, W.; Hendriks, U.; M u¨ ller, P. Z. Anorg. Allg. Chem. 1988,
2088.
5
59, 95-105.
15) Bronger, W.; Balk-Hardtdegen, H. Z. Anorg. Allg. Chem. 1989, 574,
9-98.
16) Bronger, W.; Balk-Hardtdegen, H.; Schmitz, D. Z. Anorg. Allg. Chem.
989, 574, 99-106.
17) Bronger, W.; Bomba, C. J. Less-Common Met. 1990, 158, 169-176.
(19) Kim, J.; Wang, C.; Hughbanks, T. Inorg. Chem. 1998, 37, 1428-
(
(
(
1429.
8
(20) Lacroix, P. G.; Cl e´ ment, R.; Nakatani, K.; Zyss, J.; Ledoux, I. Science
1994, 263, 658-660.
1
(21) Lagadic, I.; Lacroix, P. G.; Cl e´ ment, R. Chem. Mater. 1997, 9, 2004-
2012.
1
0.1021/ic980805w CCC: $18.00 © 1999 American Chemical Society
Published on Web 12/30/1998

236 Inorganic Chemistry, Vol. 38, No. 2, 1999
Kim et al.
Experimental Section
Na2.90(3)Mn3.95(2)Te
elements heavier than Na, including Nb, were found in either case.
Atomic absorption measurements for both compounds gave the
6
and Na1.01(1)Mn1.54(1)Te
2
, respectively. No other
Materials and Instrumentation. As the compounds described herein
are sensitive to both moisture and oxygen, experimental operations were
carried out under an inert gas atmosphere. Elemental starting materials
were Mn (99.99%, Johnson Matthey), Te (99.997% Aldrich), Li (99.0%,
Aldrich), Na (99.0%, Aldrich), and K (99.0%, Aldrich). LiCl (>99.0%,
Aldrich), KCl (>99.0%, Aldrich), RbCl (>99.0%, Aldrich), and CsCl
respective compositions Na2.91(2)Mn4.02(1)Te
X-ray Crystallography. X-ray diffraction data of KMnTe
MnTe , Na Mn Te , and NaMn1.56Te were collected on a Siemens
R3m/V diffractometer with graphite-monochromated Mo KR radiation
λ ) 0.710 73 Å) at 20 °C. Structure refinements of these compounds
6 2
and Na0.99(1)Mn1.57(1)Te .
2
, Rb-
2
3
4
6
2
(
(
>99.0%, Aldrich) were sublimed at least twice before use. Li
Na Te, and K Te were synthesized in liquid NH as described in the
literature and purity was confirmed by examination of Guinier X-ray
powder patterns. LiMnTe was prepared by loading a 1:1:2 ratio of
Li/Mn/Te in a sealed Nb tube which was in turn sealed in an evacuated
2
Te,
2
25
were based on F with the use of the SHELX-93 package of programs.
2
2
3
A dark-red platelike crystal of KMnTe having approximate dimen-
2
22,23
sions 0.12 × 0.10 × 0.03 mm was mounted in a glass capillary.
Tetragonal cell constants and an orientation matrix were obtained from
a least-squares refinement using the setting angles from 15 centered
reflections. This cell was refined by centering on 24 reflections in the
range 15 e 2θ e 35°. Intensity data were collected by use of θ-2θ
scans for reflections with 2θ < 60°. Three check reflections monitored
every 97 reflections throughout the data collection process showed no
significant trends. A hemisphere of the data was collected (+h, (k,
2
-
4
(
∼10 Torr) and flame-baked silica tube as described in a previous
19
communication; its identity was confirmed by measuring the Guinier
X-ray powder pattern before use. All compounds were synthesized by
-
4
the use of Nb tubes that were in turn sealed in an evacuated (∼10
Torr) silica tube. Atomic absorption (AA) measurements were per-
formed on a Varian SpectrAA 250 Plus instrument after dissolution of
products in 20% (w/w) nitric acid. Standard solutions for AA
measurements are purchased from Aldrich. For each element, measure-
ments on at least three standard solutions were taken with different
concentrations to obtain a linear calibration plot. Wavelength-dispersive
X-ray spectrometry (WDS) analyses were performed using a Cameca
SX 50 scanning electron microscope. Samples for AA and WDS
measurements were gathered by selecting crystals from the reaction
products.
(
l) to gain the advantage of averaging. The data were corrected for
absorption using the ψ scan technique based on five reflections. 166
reflections were unique, and 158 reflections with I > 2σ(I) were used
in the refinements. Systematic absences (h + k + l ) 2n + 1), Guinier
X-ray diffraction data, and elemental analysis suggested that KMnTe
is isostructural with the known phase TlFeS , with tetragonal space
group I 4h m2, so the atomic positions of TlFeS were used to begin
refinement of the KMnTe
structure.26 Isotropic refinement of the
structure with all K, Mn, and Te positions fully occupied resulted in a
residual (R) of 6.96%. Final anisotropic refinement of KMnTe gave
.86 and 10.34% for final R(F) and wR2(F ) with I > 2σ(I). The largest
2
2
2
2
Temperature-dependent magnetic susceptibilities were measured with
a LakeShore 7229 AC susceptometer with an external field strength
2
2
4
1
0 Oe over the temperature range 4-300 K for selected crystals of
3
remaining peaks in the final Fourier difference map were 1.265 e/Å
located close to Te in the framework of the structure.
A dark-red platelike crystal of RbMnTe with approximate dimen-
2
sions 0.08 × 0.08 × 0.04 mm was selected and mounted in a glass
capillary. Preliminary Guinier X-ray powder patterns were used to
establish tetragonal unit cells and to obtain lattice parameters. Cell
constants and an orientation matrix were obtained from a least-squares
refinement using 24 centered reflections in the range of 15 e 2θ e
title compounds. Data were corrected for the diamagnetic contributions
2
4
of the atomic cores and sample holder.
Synthesis. AMnTe (A ) K, Rb, Cs) compounds were synthesized
by mixing LiMnTe , LiCl, and ACl (A ) K, Rb, Cs) in 1:2:2 mole
2
2
ratios in a sealed Nb tube. In each case, the temperature was uniformly
raised from room temperature to 750 °C over 4 days, held at that
temperature for 200 h, and finally cooled to room temperature at a
rate of 2 °C/h. All products contained dark-red single crystals suitable
for X-ray crystallography. Excess ACl (A ) K, Rb, Cs) and LiCl were
removed from the desired products by washing with dried methanol
under a nitrogen atmosphere. Microprobe analysis on selected crystals
3
5°. Intensity data were collected in the θ-2θ scanning mode for
reflections with 5 e 2θ e 50°. A hemisphere (+h, (k, (l) of data
was collected. Three check reflections were monitored periodically and
showed no significant change during the data collection process. The
data set was corrected for absorption using the ψ scan technique based
on five reflections. All data except those for which h + k + l ) 2n +
showed the compositions K0.93(1)Mn1.09(3)Te
2
, Rb0.91(1)Mn1.05(1)Te
2
, and
. No other elements heavier than Na were found.
Atomic absorption analyses were carried out to independently determine
compositions and yielded the following results: K0.97(1)Mn1.08(3)Te
. AA measurements showed
Cs0.88(1)Mn1.04(1)Te
2
1
1
were observed, consistent with a body centered tetragonal space group.
09 reflections were unique, and 105 reflections with I > 2σ(I) were
2
,
2 2
Rb0.98(1)Mn1.01(1)Te , and Cs1.00(1)Mn0.94(1)Te
used in the refinements. RbMnTe
atomic positions of KMnTe
RbMnTe structure. Isotropic refinement of RbMnTe
able thermal coefficients for all atoms. Final anisotropic refinement of
2
is isostructural with KMnTe
were used to begin refinement of the
showed reason-
2
so the
no detectable Li in these compounds.
Na Mn Te and NaMn1.56Te were first found in our attempts to
synthesize NaMnTe
directly from the elemental starting materials.19
2
3
4
6
2
2
2
2
A reaction loaded using elemental sodium, manganese, and tellurium
combined in a 3:4:6 ratio was conducted in a sealed Nb capsule which
2
RbMnTe
2
gave 4.07 and 9.25% for final R(F) and wR2(F ) with I >
2
σ(I). The largest residual peak in the final Fourier difference map
-4
was in turn sealed in an evacuated (∼10 Torr) and flame-baked silica
3
was 1.395 e/Å located close to Te in the framework of the structure.
tube. The temperature of the reaction vessel was uniformly raised to
Elemental analyses and Guinier X-ray powder diffraction patterns
4
50 °C over 2 days, maintained at 450 °C for 2 days, uniformly
of CsMnTe
2
showed that it is isostructural with AMnTe
2
(A ) K, Rb).
increased to 600 °C for 2 days, and then maintained at that temperature
for 1 week. It was then cooled to room temperature at a rate of 1 °C/h.
Cell parameters of CsMnTe
powder patterns. Cell parameters and volumes of AMnTe
Rb, Cs) are listed in Table 1.
2
were refined by use of Guinier X-ray
2
(A ) K,
Red crystals of Na
found. NaMn1.56Te
3
Mn
4 6
Te suitable for X-ray crystallography were
2
was synthesized by mixing elemental Na, Mn, and
3 4 6
A red platelike crystal of Na Mn Te with approximate dimensions
Te in stoichiometric proportions in Nb tubes. The temperature of
reaction vessel was uniformly raised to 450 °C for 2 days, maintained
at 450 °C for 2 days, uniformly increased to 850 °C over 3 days, held
at that temperature for 200 h, and finally cooled to room temperature
at a rate of 2 °C/h. Dark-red platelike crystals suitable for X-ray studies
were found. Microprobe analysis on selected crystals from the products
0
.16 × 0.10 × 0.02 mm was selected and mounted in a glass capillary.
Indexing of Guinier X-ray powder patterns had established a monoclinic
unit cell and lattice parameters. Monoclinic cell constants and an
orientation matrix were also obtained from a least-squares refinement
using 24 centered reflections in the range of 15 e 2θ e 35°. Intensity
data were collected in the θ-2θ scanning mode for reflections with 5
e 2θ e 50°. Data were collected over one quadrant ((h, +k, +l).
3 4 6 2
of both Na Mn Te and NaMn1.56Te showed approximate compositions
(
(
(
22) Feher, F. In Handbuch der PreparatiVen Anorganischen Chemie;
Brauer, G., Ed.; Ferdinand Enke Verlag: Stuttgart, Germany, 1954.
(25) (a) Sheldrick, G. M. SHELXTL-93 User Guide; Crystallography
Department: University of G o¨ ttingen, Germany, 1993. (b) SHELXTL-
93 User Guide, version 3.4; Nicolet Analytical X-ray Instruments:
G o¨ ttingen, Germany, 1993.
23) Klemm, W.; Sodomann, H.; Langmesser, P. Z. Anorg. Allg. Chem.
1939, 241, 281.
24) Mulay, L. N., Boudreaux, E. A., Eds. Theory and Application of
Molecular Diamagnetism; Wiley-Interscience: New York, 1976.
(26) Kutoglu, A. Naturwissenschaften 1974, 61, 125-126.

New Layered Ternary Manganese Tellurides
Inorganic Chemistry, Vol. 38, No. 2, 1999 237
a
3
Table 1. Lattice Parameters (Å) and Cell Volumes (Å ) of
Table 2. Crystallographic Data for KMnTe
2
, RbMnTe
2
,
AMnTe
with a Space Group I 4h m2
2
(A ) K, Rb, Cs) with TlFeS
2
Structure Type Compounds
Na Mn Te , and NaMn1.56Te
3
4
6
2
chemical KMnTe
formula
2
RbMnTe
4.539(1)
15.055(2)
2
Na Mn Te
3
4
6
NaMn1.56Te
4.4973(8)
7.638(2)
2
KMnTe
2
RbMnTe CsMnTe
2
2
a, Å
4.5110(4)
8.274(4)
14.083(6)
7.608(6)
91.97(4)
a (Å)
c (Å)
V (Å )
c/a
4.5110(4)
14.909(2)
303.39(6)
3.305
4.539(1)
15.055(2)
310.17(11)
3.317
4.5711(4)
15.527(2)
324.44(6)
3.397
b, Å
c, Å
â, deg
V, Å3
Z
14.909(2)
3
303.39(6)
2
349.24
310.17(11) 886.0(9)
2
133.77(5)
1
363.90
P 3h m1
a
Lattice parameters refined from Guinier powder diffraction patterns
using Si as an internal standard.
2
fw
395.61
I 4h m2
1054.33
C2/m
space group I 4h m2
(No. 119)
(No. 119)
(No. 12)
(No. 164)
Three check reflections every 97 reflections were monitored and showed
no significant change during the data collection process. The data set
was corrected for absorption using the ψ scan technique based on five
reflections. All reflections except those for which h + k ) 2n were
absent, consistent with C-centering. An initial structural model for
T (°C)
λ (Å)
20
0.710 73
20
20
20
0.710 73
4.236
18.983
4.07
0.710 73
3.952
12.503
5.41
0.710 73
4.517
14.314
4.35
3
F
calcd (g/cm ) 3.823
-1
µ (mm
)
12.123
4.86
10.34
a
R1 (%)
refinement of Na
were unique, and 480 reflections with I > 2σ(I) were used in the
refinements. Isotropic refinement of Na Mn Te showed reasonable
thermal coefficients for all atoms. Anisotropic refinement of Na Mn
Te showed reasonable thermal parameters and gave 5.41 and 11.01%
Mn Te
3 4 6
was found by direct methods. 567 reflections
b
wR2 (%)
9.25
11.01
6.03
a
b
2
2
2
2
R1(F) ) ∑(|F
o
| - |F
c
|)/∑(|F
o
|). wR2(F ) )[∑|w(F
o
- F
c
) |/
3
4
6
2
2
1/2
2
2
2
2
∑
+
|w(F
o
) |] , w ) 1/[σ (F
o
) + (xP) + yP], where P ) (Max(F
o
,0)
3
4
-
2
2F )/3.
c
6
2
for final R(F) and wR2(F ) with I > 2σ(I). The largest remaining peaks
in the final Fourier difference map were 1.740 e/Å close to a Mn atom
in the framework of the structure.
2
A dark-red platelike crystal of NaMn1.56Te with approximate
dimensions 0.20 × 0.18 × 0.06 mm was selected and mounted in a
glass capillary. Indexing of Guinier X-ray powder patterns enabled us
to establish the hexagonal unit cell and to obtain lattice parameters.
Cell constants and an orientation matrix were obtained from a least-
squares refinement using 24 centered reflections in the range of 15 e
Table 3. Atomic Coordinates and Equivalent Isotropic
3
Displacement Parameters
a
U
eq
2
3
atom position
x/a
y/b
z/c
(Å × 10 )
KMnTe
0.0
2
K
Mn
Te
2a
2c
4e
0.0
0.0
0.0
0.0
42(2)
25(1)
22(1)
1
1/2
0.0
/
4
0.3592(1)
2
θ e 35°. Intensity data were collected in the θ-2θ scanning mode
for reflections with 5 e 2θ e 50°. Data ranging over the indices (+h,
k, (l) were collected. Three check reflections every 97 reflections
RbMnTe
2
Rb
Mn
Te
2a
2c
4e
0.0
0.0
0.0
0.0
0.0
/
4
0.3563(1)
27(1)
11(2)
16(1)
1
1
+
/
2
0.0
were monitored periodically and showed no significant change during
the data collection process. The data set was corrected for absorption
using the ψ scan technique based on five reflections. 111 reflections
were unique and used in the refinements. No systematic absences were
Na Mn Te
3
4
6
Na1
Na2
Mn
Te1
Te2
4g
2a
8j
4i
8j
0.0
0.0
0.3422(16) 0.0
0.0
0.1668(8) 0.1646(3)
0.3022(5) 0.0
0.1524(4) 0.1763(2)
68(9)
58(11)
35(2)
42(1)
35(1)
0.0
observed. An initial structural model for refinement of NaMn1.56Te
was found by direct methods. Isotropic refinement of the structure with
all Na, Mn, and Te positions fully occupied (corresponding to a
2
0.6279(7)
0.7673(6)
0.2612(3)
2 2
“NaMn Te ” composition) resulted in a residual (R) of 6.17%. However,
NaMn1.56Te2
the thermal parameter of Mn (Uiso ) 0.053) was about 2 times larger
than that of Te (Uiso ) 0.027). When the thermal parameter of the Mn
was fixed to be same as the Te atom, the refinement of the Mn site
occupancy factor yielded 0.76(1) with a residual R ) 4.64%. This result
was comparable to the composition obtained from WDS and AA
measurements. In subsequent refinement cycles, both site occupancy
and temperature parameters of Mn were refined simultaneously, which
yielded in reasonable isotropic thermal parameters and a fractional site
occupancy of 0.78(1). In the last cycle, the site occupancy of Mn was
fixed and structure was refined anisotropically to yield respective
Na b
Mn
Te
1b
2d
2d
0.0
0.0
1/2
0.8753(8)
0.2429(4)
55(6)
31(2)
31(1)
2
1
/
/
3
/
/
3
2
1
3
3
a
Equivalent isotropic U defined as one-third of the trace of the
orthogonalized Uij tensor. b Occupancy 0.783(3).
) K, Rb, Cs) flux, but the quality of crystals obtained from
lower temperature reactions was not adequate for X-ray studies.
Well-developed crystals of these compounds are obtained when
the reaction temperature is 750 °C and cooling speed is slow
2
residuals of 4.35 and 6.03% for final R(F) and wR2(F ) with I > 2σ(I).
(
2 °C/h). Huan et al. used this method to synthesize ternary
The largest remaining peak in the final Fourier difference map was
transition metal chalcogenides, AM2Q2 (A ) Rb, Cs; M ) Ni,
3
1
.405 e/Å located near Te in the framework of the structure.
Co; Q ) S, Se), from the corresponding Tl compounds, TlM2Q2
A summary of crystal and data collection parameters of KMnTe
2
,
2
(
M ) Ni, Co; Q ) S, Se). Attempts to synthesize KMnTe2 by
2 3 4 6 2
RbMnTe , Na Mn Te , and NaMn1.56Te are listed in Table 2, and final
loading either elements or K2Te, Mn, and Te as starting materials
in stoichiometric proportions at 750 °C resulted in the formation
of a mixture of K2MnTe2 and KMnTe2. To optimize synthetic
conditions for the synthesis of KMnTe2, several reactions were
attempted in which parameters such as loading composition,
reaction time, temperature, and cooling speed were varied; in
each case, a mixture of K2MnTe2 and KMnTe2 was obtained.
2
atomic coordinates are shown in Table 3.
Results and Discussion
Syntheses. Recently, new ternary manganese tellurides,
1
9
AMnTe2 (A ) Li, Na), were discovered in our laboratories.
As these new compounds have unusual polar layers,
2
∞
-
[
MnTeTe3/3] , we investigated the possibility that corre-
KMnTe was generally found as a minor product. It appears
sponding AMnTe2 (A ) K, Rb, Cs) would adopt the same
structure type. However, these compounds proved to be iso-
structural with TlFeS2.
AMnTe2 (A ) K, Rb, Cs) can be synthesized at temperatures
as low as 450 °C by reaction of LiMnTe2 with a LiCl/ACl (A
that KMnTe is a thermodynamically stable phase in the 450-
2
800 °C temperature range, but that K MnTe , once formed, is
2
2
unreactive and equilibrium is not attained in direct reactions.
As the colors of K2MnTe2 and KMnTe2 are similar (dark-red),
it is impossible to physically separate KMnTe2 from a reaction

238 Inorganic Chemistry, Vol. 38, No. 2, 1999
Kim et al.
mixture. The indirect cation exchange method described above
proves to be the best means of obtaining KMnTe2.
synthesis of NaMn1.56Te2 at 850 °C. It seems likely that Nb-
Te compound (NbTe and Nb5Te4) formation reduces the
tellurium activity to an extent sufficient that manganese rich
compounds such as NaMn1.56Te2 can be formed at higher
reaction temperature (>750 °C). Preheating at 450 °C for 1 or
2 days reduces the reaction between Te and Nb container;
presumably because Te activity is lowered by formation of
binary tellurides such as Na2Te and MnTe.
Na3Mn4Te6 and NaMn1.56Te2 can be synthesized directly from
elemental starting materials in sealed Nb tubes. Na3Mn4Te6 and
NaMn1.56Te2 were originally discovered in a reaction designed
to directly synthesize NaMnTe2.19 A mixture of Na, Mn, and
Te in a 1:1:2 ratio was loaded into a Nb reaction vessel that
-
4
was in turn sealed in an evacuated (∼10 Torr) and flame-
baked silica tube. The temperature of the reaction vessel was
uniformly raised to 450 °C for 2 days, maintained at that
temperature for 2 days, uniformly increased to 600 °C for 2
days, held at that temperature for 1 week, and finally cooled to
room temperature at a rate of 2 °C/h. Powder diffraction data
showed that there were at least two different phases and no
detectable NaMnTe2. X-ray single-crystal structure determina-
tions and elemental analyses (AA and WDS) showed that one
of these phases was Na3Mn4Te6.
To further explore the role of containers in these reactions,
we conducted additional experiments using silica tubes for the
synthesis of NaMn1.56Te and Na Mn Te . We could synthesize
2
3
4
6
NaMn1.56Te2 and Na Mn Te from loading stoichiometric
3
4
6
proportions of starting materials (Na Te, Mn, and Te) in silica
2
tubes which were evacuated and sealed. These silica tubes were
heated to 450 °C for 2 days, kept at that temperature for 2 days,
then heated to 600, 650, 750, and 850 °C at a rate of 10 °C/h
in separate experiments, then held at each reaction temperature
for 7 days, and slowly cooled to room temperature at a rate of
10 °C/h. Guinier X-ray diffraction patterns of the products of
reactions designed to yield NaMn1.56Te2 showed that NaMn1.56-
Te2 was the predominant product, but the patterns exhibited
unidentified lines as well. Unlike the situation when a Nb
container was used, no MnTe was detected. Diffraction patterns
observed when Na3Mn4Te6 was the target product indicated the
presence of mainly Na3Mn4Te6, MnTe2, and lesser amounts of
unidentified phases. No MnTe and NaMnTe2 were detected. This
result contrasts with the results carried out in Nb container, in
which no MnTe2 was formed and NaMn1.56Te2 was formed at
higher reaction temperature (>750 °C). A white reaction product
stuck on inside of the silica tube after reaction probably results
from a reaction between the silica tube and Na2Te to form
ternary sodium silicate compounds, but we did not identify them.
From the results of these reactions, we could conclude that
the formation of NaMn1.56Te2 is favored by loading stoichio-
metric amounts of starting materials in either Nb or silica tubes.
Na3Mn4Te6 can be synthesized at temperatures ranging from
600 to 850 °C in silica tubes by loading stoichiometric
proportions of starting materials. We also observed that Na3-
Mn4Te6 was formed at 600 °C by loading stoichiometric
amounts of starting materials in a Nb container, but NaMn1.56-
Te2 forms instead at temperatures higher than 750 °C. Although
silica tubes can be used for the synthesis of Na3Mn4Te6 and
NaMn1.56Te2, reaction products stick to the container walls and
single crystals are not readily obtained.
NaMn1.56Te2 was first identified from the reaction product
designed to synthesize Na3Mn4Te6 at 850 °C. A mixture of Na,
Mn, and Te in a 3:4:6 ratio was loaded into a Nb reaction vessel
-4
that was in turn sealed in an evacuated (∼10 Torr) and flame-
baked silica tube. The temperature of the reaction vessel was
uniformly raised to 450 °C for 2 days, maintained at that
temperature for 2 days, uniformly increased to 850 °C for 4
days, held at that temperature for 1 week, and finally cooled to
room temperature at a rate of 2 °C/h. Powder diffraction data
showed that there was a predominant unknown phase which
has similar X-ray powder pattern as NaMnTe2. Subsequent
X-ray single-crystal structure determination and elemental
analyses (AA and WDS) showed that this unknown phase was
NaMn1.56Te2.
After we determined structures and compositions of Na3Mn4-
Te6 and NaMn1.56Te2, we attempted to find the optimum reaction
conditions for both compounds by changing reaction parameters
such as temperature, loading conditions, heating and cooling
speed, and reaction container. Na3Mn4Te6 can be made by
loading stoichiometric proportions of elemental starting materials
in a Nb capsule. The temperature of the reaction vessel was
uniformly raised to 450 °C for 2 days, maintained at that
temperature for 2 days, uniformly increased to 600 °C for 2
days, held at that temperature for 1 week, and finally cooled to
room temperature at a rate of 1 °C/h. Well-developed dark-red
platelike crystals of Na3Mn4Te6 were observed.
NaMn1.56Te2 can be synthesized directly: stoichiometric
proportions of elemental starting materials were loaded into a
Nb capsule, heated to 450 °C for 2 days, stayed at that
temperature for 2 days, heated to 850 °C for 4 days, then stayed
at 850 °C for 10 days, and slowly cooled to room temperature
at a rate of 2 °C/h after reaction. The Guinier X-ray powder
pattern shows that the major product was NaMn1.56Te2, a small
amount of MnTe was also formed.
NaMnTe2 was not observed in several reaction attempts
described above, but Na6MnTe4 was detected in reaction
products when excess Na and Te (loading ratios of Na/Mn/Te
were 3:1:4, 2:1:3, and 2:1:2) were used in reactions carried out
from 600 to 850 °C in either Nb or silica tubes.
Structure. With the inclusion of larger alkali metal cations,
-
[MnTe ] layers are formed by condensation of MnTe tetra-
2
4
The synthesis of compounds NaMnxTe2 (x ) 1.5, 1.7, 2.0)
was attempted by mixing elemental starting materials, Na, Mn,
and Te in stoichiometric proportions and heating at 850 °C for
hedra at every vertex and Te atoms are arranged in tetragonal
layers (square nets). Thus, the AMnTe2 (A ) K, Rb, Cs)
2
6
-
compounds are isostructural with TlFeS2. The [MnTe2] layers
in these compounds are essentially the same as layers found in
2
00 h. Elemental analyses (WDS and AA) of products from
27
each reaction container showed that the Mn composition (x) in
each case was close to 1.56. Cell parameters for NaMn1.56Te2
determined for each sample were unchanged within experimental
error. But MnTe and unidentified lines in the Guinier X-ray
diffraction pattern indicated that the synthesis of pure NaMn1.56-
Te2 was elusive.
Incorporation of Te into the Nb containers to form binary
compounds such as NbTe and Nb5Te4 was confirmed by WDS
analyses on the inside wall of Nb tubes that were used in the
red HgI2, though the layer stacking differs. A thermal ellipsoid
plot of KMnTe2 is shown in Figure 1. Selected bond distances
and angles for KMnTe2 and RbMnTe2 are listed in Table 4. In
this tetragonal structure, each layer is separated by alkali metals
that center slightly compressed square prisms formed by 8 Te
atoms. Distances to the surrounding Te atoms are 3.819(1) Å
(× 8) for KMnTe2 and 3.871(1) Å (× 8) for RbMnTe2,
(27) Jeffrey, G. A.; Vlasse, M. Inorg. Chem. 1967, 6, 396-399.

New Layered Ternary Manganese Tellurides
Inorganic Chemistry, Vol. 38, No. 2, 1999 239
2
Figure 1. Thermal ellipsoid plot of KMnTe . 70% probability ellipsoids
are shown.
Table 4. Selected Interatomic Distances (Å) and Angles (deg)
KMnTe
2
Mn-Te (×4)
2.782(1) K-Te (×8)
3.819(1)
4.5110(4)
Mn-Mn
4.5110(4) Te-Te
Te-Mn-Te (×4) 110.03(3)
Te-Mn-Te (×2) 108.35(6)
Mn-Te-Mn
108.35(6)
RbMnTe
2
Mn-Te (×4)
Mn-Mn
2.777(1)
4.539(1)
Rb-Te (×8)
3.871(1)
4.539(1)
Te-Te
Te-Mn-Te (×4) 109.39(3)
Te-Mn-Te (×2) 109.64(7)
Mn-Te-Mn
109.64(7)
Na
3
Mn
4
Te
6
Mn-Te1 (×2)
Mn-Te1
2.806(7)
2.793(7)
3.29(2)
3.25(2)
Mn-Te2
2.770(6)
3.113(4)
3.560(4)
3.397(3)
]3-
Figure 2. (Top) Polyhedral representation of two-dimensional [Mn
layer viewed on the ab plane. MnTe
are shown as open circles, Na atoms as gray circles. (Bottom) Thermal
ellipsoid (70% probability) plot of Na Mn Te along the c axis. Na
4 6
Te
Na2-Te2 (×2)
Na1-Te1 (×2)
Na2-Te1 (×4)
4
tetrahedra are shown and Te atoms
Na1-Te1 (×2)
Na1-Te2 (×2)
3
4
6
Mn-Te1-Mn
Mn-Te1-Mn
Te2-Mn-Te1
Te2-Mn-Te1
Te1-Mn-Te1
72.8(2)
117.0(2)
115.7(2)
110.4(2)
104.9(2)
Mn-Te1-Mn
Mn-Te2-Mn
Te2-Mn-Te1
Te1-Mn-Te1
Te1-Mn-Te1
75.1(2)
113.6(3)
107.9(2)
106.8(2)
111.1(2)
atoms within the unit cell are shown for clarity. The octahedral
surroundings of one Na atom is with dashed lines.
filled with Mn atoms and octahedral interstices filled with Na
atoms in a manner that generates a layered structure. A
polyhedral representation of the Na3Mn4Te6 layer viewed on
the ab plane and a thermal ellipsoid plot projected approximately
down the a axis are shown in Figure 2. Selected bond distances
and angles for this compound are listed in Table 4. Mn atoms
occupy tetrahedral sites between alternate Te layers into a pair
of honeycomb (graphite-like) networks that comprise two-thirds
of the tetrahedra that “point up” and two-thirds of tetrahedra
that “point down”. Consistent with this connectivity, each MnTe4
tetrahedron shares Te vertexes with three adjacent tetrahedra
in the same network. Within each ∞[Mn4Te6] layer, the
paired honeycomb nets are arranged so that each MnTe4
tetrahedron shares two edges with tetrahedra in the other
honeycomb net. The MnTe4 tetrahedra are slightly distorted;
Mn-Te bond distances in the tetrahedron fall into the range
between 2.793(7) and 2.806(6) Å, and Te-Mn-Te angles are
between 104.9(2) and 115.7(2)°. There are two crystallographi-
NaMn1.56Te
2.749(3)
2.808(7)
2
Mn-Te (×3)
Mn-Te
Te-Na (×6)
3.255(2)
3.220(8)
Mn-Mn (×3)
Mn-Te-Mn (×3) 109.8(2)
Mn-Te-Mn (×3)
70.8(2)
Te-Mn-Te (×3) 109.8(2)
Te-Mn-Te (×3) 109.2(2)
respectively. In contrast, Na atoms in NaMnTe2 sit on trigonal
antiprismatic sites surrounded by 6 Te atoms, a difference that
is clearly attributable to the increased size of the heavier alkali
metal cations. The MnTe4 tetrahedra in KMnTe2 and RbMnTe2
are quite regular with Mn-Te distances of 2.782(2) Å (× 4)
and 2.777(1) Å (× 4), respectively. The Te-Mn-Te angles
are 108.35(6)° (× 2) and 110.03(3)° (× 4) in KMnTe2 and
2
3-
1
09.39(3)° (× 4) and 109.64(7)° (× 2) in RbMnTe2. It is notable
that AMnTe2 (A ) K, Rb, Cs) as well as AMnTe2 (A ) Li,
Na) are the first compounds among the known ternary manga-
III
cally distinct Te atoms in the Na Mn Te ; Te1 is bonded to
nese tellurides that contain exclusively Mn .
The Na3Mn4Te6 structure may be described as a hexagonal
close-packed array of Te atoms with tetrahedral interstices
3
4
6
2
∞
two Mn atoms and Te2 is bonded to three (
[Mn4Te6] )
2
[MnTe3/3Te1/2]; Figure 2). There are two crystallographically
∞

240 Inorganic Chemistry, Vol. 38, No. 2, 1999
Kim et al.
distinct Na atoms, all of which are coordinated to six Te atoms.
2
Na atoms fill the octahedral interstices between ∞[Mn4Te6]
layers. Na-Te bond distances range from 3.113(4) to 3.560(4)
III
II
Å. Na3Mn4Te6 is formally a Mn /Mn mixed valence com-
pound assuming all tellurium are Te2 (the shortest Te-Te
contact is 4.495 Å).
-
XPS studies were attempted to determine whether the formal
“
mixed-valence” description we have used for Mn in Na3Mn4-
Te6 might have some basis in observable properties. Unfortu-
nately, we observed that the Mn 2p3/2 binding energy of
Na3Mn4Te6, 640.80 eV, was very close to the 640.67 eV found
III
II
for Mn in NaMnTe2 and 640.87 eV for Mn in MnTe. As a
II
III
result, the investigation of Mn valency (Mn vs Mn ) in Na3-
Mn4Te6 by comparison of Mn 2p3/2 binding energies was
inconclusive. On the basis of the crystallographic equivalence
of the all the Mn sites, we can only conclude that if there is
mixed valency, no long-range order results from it.
The honeycomb net that is characteristic of the layers in
Na3Mn4Te6 is also observed a high-pressure form of B2O3.
2
8
Figure 3. Thermal ellipsoid plot of NaMn1.56Te
thermal ellipsoids are shown.
2
. 70% probability
Unlike the fusion of two nets in Na3Mn4Te6, such nets in B2O3
are stacked up the c axis and linked together by fusion of
corners. In Figure 2, it is clear that there are four empty
tetrahedral sites within the unit cell. If these empty tetrahedral
sites are filled up with Mn atoms, this would lead to the formula
+1.5
of the hypothetical compound, “NaMn2Te2”, having all Mn
.
The crystal structure of Na3Mn4Te6 can be traced back to a
distorted close packed arrangement of Te atoms with hexagonal
stacking sequence ABABAB, the stacking direction is perpen-
dicular to ab plane. For an undistorted structure, the cell
parameters should be related to those of a simple hcp unit cell
(a′, c′) by
c′ ) c sin â
a′ ) a/
a′ ) b/3
(1)
x
3
(2)
(3)
The deviation of the actual structure from this idealized model
is due to the fact that slightly different values for a′ are obtained
from eqs 2 and 3; 4.777 and 4.694, respectively. The cell
parameters obtained from the eqs 1-3 are similar to those of
NaMn1.56Te2 and NaMnTe2, and the axial ratio c′/a′ (1.59-
1
.62) is close to the ideal value 1.63 for simple hexagonal unit
cell.
The structure of NaMn1.56Te2, projected approximately along
the c axis, is shown in Figure 3. Selected bond distances and
angles are listed in the Table 4. NaMn1.56Te2 is found to adopt
a defective CaAl2Si2 structure type.29 Again, fairly regular
MnTe4 tetrahedra are the building blocks of the structure having
Mn-Te bond distances in the range of 2.749(3) to 2.808(7) Å
and Te-Mn-Te angles 109.2(2) and 109.8(2)°. These tetrahedra
Figure 4. Structural relationships between [M
2
Q
2
2
] in AM
] () [Mn
2
Q
2
(A )
]) in
K, Rb, Cs; M ) Ni, Co; Q ) S, Se), [Mn3/2Te
3
Te
4
A Mn Te where A ) Rb, Cs, and [MnTe ] in AMnTe (A ) K, Rb,
2
3
4
2
2
Cs). If one metal atom in every two is removed in [M
2 2
Q ] layer, one
obtains [MnTe ] layer. [Mn3/2Te ] layer is formed if one metal atom is
2
2
removed every four in a specific way.
share three edges in the formation of two-dimensional
-
Structural Relationships. There are close structural relation-
ships between the title compounds and other compounds. The
TlFeS2 structure type adopted by the AMnTe2 (A ) K, Rb, Cs)
compounds is closely related to A2Mn3Te4 (A ) Rb, Cs), and
AM2Q2 (A ) K, Rb, Cs; M ) Ni, Co; Q ) S, Se).2 The
manganese telluride layers in these compounds and their
interrelationship are shown in Figure 4. Although “AMn2Te2”
[
Mn1.56Te2] layers that are held together by ionic bonding to
Na cations. There is one crystallographically unique Na atom
in the structure which is coordinated to six Te atoms at a distance
of 3.255(2) Å. Mn atoms partially occupy in the tetrahedral sites
within layers and have an average formal charge of slightly less
than +2. If these empty tetrahedral sites are filled up with Mn
atoms, this again yields to the hypothetical compound, “NaMn2-
Te2”.
,4
(
A ) alkali metal) with ThCr2Si2 structure type is not known,
ternary cobalt and nickel selenides and sulfides with ThCr2Si2
structure type have been reported. Ternary manganese silicides,
2
(
28) Prewitt, C. T.; Shannon, R. D. Acta Crystallogr. 1968, B24, 869-
74.
29) Gladyskevskii, E. I.; Kripajakevic, P. I.; Bodak, O. I. Ukr. Fiz. Zh.
Russ. Ed.) 1967, 12, 447.
8
(
(30) Siek, S.; Szytula, A.; Leciejewicz, L. Phys. Stat. Sol. 1978, 46A,
K101-K105.
(

New Layered Ternary Manganese Tellurides
Inorganic Chemistry, Vol. 38, No. 2, 1999 241
Figure 5. Structural relationships between the hypothetical compound
“
NaMn
2
Te
2
” ()Na
()Na
()Na Mn
are randomly removed from “NaMn
one-third of Mn atoms are removed from each Mn layer in two different
ways, Na Mn Te and Na Mn
3
Mn
Mn4.7
Te
3 6
6
Te
6
), and the real structures of Na
), Na Mn ()Na Mn ; Q ) S, Se), and
). If approximately one-quarter of the Mn atoms
Te ”, NaMn1.56Te is formed. If
3 4 6
Mn Te ,
NaMn1.56Te
NaMnTe
2
3
Q
6
2
2
Q
3
4
4 6
Q
2
3
2
2
2
3
4
6
2
2 3
Q (Q ) S, Se) are obtained. If all Mn
atoms from one layer removed, NaMnTe
2
is formed. Dark tetrahedra
point up, pale gray down.
RMn2Si2 (R ) Ce, Tb, Dy, Er, Th, Pr, Nd, Y), germanides,
RMn2Ge2 (R ) La, Ce, Pr, Nd, Sm, Y, Th), and a pnictide,
30-34
BaMn2Sb2, with the ThCr2Si2 structure type are also known.
The fundamental building blocks of these compounds are
MX4 (X ) S, Se, Si, Ge, Sb) tetrahedra. In the AM2Q2 (A )
K, Rb, Cs; M ) Ni, Co; Q ) S, Se) type, each transition metal
atom is tetrahedrally coordinated to chalcogen, and in turn each
chalcogen is bonded to 4 metal atoms. Consequently, four edges
of the MQ4 tetrahedra are shared with adjacent tetrahedra to
2
-
form a 2-dimensional layer, ∞[Mn4/4Q4/4] . The alkali metal
atom is located in the center of a compressed cube formed by
8
chalcogen atoms. If every second Mn atom is removed, one
2
-
obtains [Mn4/4Te4/2] layers in AMnTe2 (A ) K, Rb, Cs). As
∞
a result, metal-metal contacts observed in of AM2Q2 (A ) K,
Rb, Cs; M ) Ni, Co; Q ) S, Se), are comparatively short and
range between 2.634 and 2.761 Å, while the shortest Mn-Mn
distances in AMnTe2 (A ) K, Rb, Cs) range between 4.511
Figure 6. (a) Observed molar magnetic susceptibilities of AMnTe
A ) K, Rb, Cs). (b) Inverse susceptibilities of AMnTe (A ) K, Rb,
Cs). (c) Observed molar magnetic susceptibilities of NaMn1.56Te and
Na Mn Te
2
(
2
6
3
4
6
.
(3) and 4.569 (1) Å. This difference may be responsible for the
metallic character of AM2Q2 (A ) K, Rb, Cs; M ) Ni, Co; Q
formation of hypothetical compound with composition “NaMn2-
Te2” (CaAl2Si2 structure type). This can also be viewed as parent
compound of AMnTe2 (A ) Li, Na). This type of structure is
2
)
S, Se). A2Mn3Te4 (A ) Rb, Cs) structures are obtained if
one Mn atom in every four is removed in a specific way to
2
∞
3- 4
form another layer, [MnTe4/3] . Mn-Mn contacts in these
37
observed in the ternary silver sulfide, BaAg2S2 and ternary
compounds range from 3.269(1) to 3.346(4) Å.
manganese pnictides, AMn2Pn2 (A ) Ca, Sr, Ba, Pn ) P, As;
We can also compare Na3Mn4Te6, NaMn1.56Te2, AMnTe2 (A
34,38,39
A ) Ca, Sr, Pn ) Sb).
Each layer in “NaMn2Te2” has a
35,36
)
Li, Na), and Na2Mn2Q3 (Q ) S, Se).
Relationships
[
Te-Mn-Mn-Te] stacking sequence. If approximately one-
quarter of the Mn atoms are randomly removed from the [Mn2-
between these compounds are illustrated in Figure 5. As was
also mentioned above, a complete filling of the tetrahedral sites
with Mn atoms in Na3Mn4Te6 and NaMn1.56Te2 results in the
Te2] layer, NaMn1.56Te2 (tNa3Mn4.7Te6) results. The layer in
Na3Mn4Te6 can be obtained from those in “NaMn2Te2” by
1
removing /3 of the Mn atoms (
x
3 ×
x
3 superlattice) from the
(
31) Siek, S.; Szytula, A.; Leciejewicz, J. Solid State Commun. 1981, 39,
63-866.
32) Ban, Z.; Omejec, L.; Szytula, A.; Tomkowicz, Z. Phys. Stat. Sol. 1975,
two hexagonal sheets within such layers ([Mn4/3Te2] ) [Te-
8
1
(
Mn2/3-Mn2/3-Te]). In Na2Mn2Q3 (Q ) S, Se), /3 of the Mn
2
7A, 333-339.
35,36
atoms are removed with a different ordering (zigzag).
(
(
33) Szytula, A.; Szott, I. Solid State Commun. 1981, 40, 199-202.
34) Brechtel, E.; Cordier, G.; Sch a¨ fer, H. Z. Naturforsch 1978, 33B, 820-
8
22.
(37) Bronger, W.; Lenders, B.; Huster, J. Z. Anorg. Allg. Chem. 1997, 623,
1357-1360.
(38) Cordier, G.; Sch a¨ fer, H. Z. Naturforsch 1976, 31b, 1459-1461.
(39) Mewis, A. Z. Naturforsch 1978, 33B, 606-609.
(
35) Klepp, K.; B o¨ ttcher, P.; Bronger, W. J. Solid State Chem. 1983, 47,
01-306.
36) Kim, J.; Hughbanks, T. Unpublished results.
3
(

242 Inorganic Chemistry, Vol. 38, No. 2, 1999
Kim et al.
Finally, if all atoms from one Mn layer are removed, one obtains
the polar [MnTe2] layer which we recently reported.
tibility of Na3Mn4Te6 decreases slightly from 0.00497 emu/mol
at 30 K to 0.00421 emu/mol at 300 K, whereas the magnetic
susceptibility of NaMn1.56Te2 increases slightly from 0.00565
emu/mol at 30 K to 0.00604 emu/mol at 300 K. The magnitude
of these compounds’ room-temperature susceptibilities are
comparable to those measured for the A MnTe2 (A ) K, Rb,
Cs) compounds, but the deviation from Curie Law behavior
suggests even stronger interaction between moments.
1
9
The size of alkali metal cations plays a key role in structural
transition from CaAl2Si2 type to ThCr2Si2 type in a series of
compounds AMnTe2 (A ) Li, Na, K, Rb, Cs). Larger alkali
metal cations destabilize the “NaMn2Te2” (CaAl2Si2 structure
type) in favor of ThCr2Si2 type structure. This trend is also
evident in a series of compounds CaMn2As2, SrMn2As2, and
BaMn2As2;3 the former two compounds adopt CaAl2Si2
structure type, whereas the last one adopts the ThCr2Si2 type
structure.
I
4
Concluding Remarks. The layered compounds, AMnTe2 (A
)
K, Rb, Cs), Na3Mn4Te6, and NaMn1.56Te2, have been
synthesized and characterized by the use of single-crystal and
powder X-ray diffraction, microprobe analysis, atomic absorp-
tion spectroscopy, and temperature-dependent magnetic studies.
The proper choice of reaction condition parameters such as
temperature and cooling speed, reaction vessels, starting materi-
als, and their stoichiometry are important for successful
syntheses. Close structural relationships are observed between
title compounds and other compounds which are already known.
All title compounds form layered structures with the MnTe4
tetrahedron as the fundamental building block. All compounds
Magnetic Measurements. The temperature-dependent molar
magnetic susceptibilities for AMnTe2 (A ) K, Rb, Cs) are
shown in Figure 6a and b. The reciprocal magnetic susceptibili-
ties of these compounds show nearly linear temperature varia-
tion. For T > 40 K, these data were fit to a modified Curie-
2
Weiss expression (ø ) ø0 + Nµeff /(T - θ), where ø0 accounts
for temperature-independent contributions, θ is the Weiss
constant, µeff is the effective magnetic moment per Mn center,
and N and kB are Avogadro’s and Boltzmann’s constants). The
following parameters were obtained: for KMnTe2, ø0 ) 2.53
III
have different formal oxidation states, Mn in AMnTe2 (A )
-
5
×
10 emu/mol, θ = -420 K, and µeff ) 4.31 µB; for
2.25+
II
K, Rb, Cs), Mn
in Na3Mn4Te6, and Mn in NaMn1.56Te2.
-
5
RbMnTe2, ø0 ) 2.38 × 10 emu/mol, θ = -420 K, and µeff
Temperature-dependent magnetic susceptibilities measurements
show that AMnTe2 (A ) K, Rb, Cs) exhibit Curie-Weiss
paramagnetism, whereas Na3Mn4Te6 and NaMn1.56Te2 show
paramagnetism with a weak dependence on temperature.
-5
)
4.71 µB; for CsMnTe2, ø0 ) 7.26 × 10 emu/mol, θ = -510
K, and µeff ) 4.86 µB. The effective magnetic moments are in
reasonable agreement with the value of 4.90 µB (S ) 2) expected
III
for a free high-spin Mn ion in a tetrahedral field. The large
negative values of the Weiss constants for each of these
compounds probably indicate strong antiferromagnetic interac-
tions between localized Mn ions. This result is consistent with
Acknowledgment. This research was generously supported
by the Texas Advanced Research Program through Grant
010366-097 and National Science Foundation through Grant
DMR-9215890. The R3m/V single-crystal X-ray diffractometer
and crystallographic computing system were purchased from
funds provided by the National Science Foundation (Grant CHE-
8513273). We thank Dr. Renald Guillemette, Dr. Anatoly
Bortun, and Mr. Aaron Dumar for their assistance with the
microprobe analyses, atomic absorption measurements, and
magnetic susceptibilities measurements.
III
other 2-dimensional ternary manganese selenides with tetragonal
4
arrangements of Mn ions, e.g., A2Mn3Se4 (A ) Rb, Cs).
Neutron diffraction studies for these ternary selenide examples
revealed that the Mn spins were antiferromagetically arranged
within layers. The low-temperature upturns in our measured
magnetic susceptibilities might be due to the presence of
paramagnetic impurities which were not detectable by X-ray
diffraction analysis.
Supporting Information Available: Tables of anisotropic displace-
Temperature-dependent magnetic susceptibilities for NaMn1.56-
Te2 and Na3Mn4Te6 over the temperature range 4-300 K are
plotted in Figure 6c. Magnetic susceptibilities of both com-
pounds exhibit nearly temperature-independent paramagnetism
over the temperature range 30-300 K. The magnetic suscep-
2 2 3 4 6
ment parameters for KMnTe , RbMnTe , Na Mn Te , and NaMn1.56-
Te (1 page). Ordering information is given on any current masthead
2
page.
IC980805W