Synthesis, crystal structures and properties of the polychalcogenides manganese-tris(1,2-ethanediamine)-triselenide [Mn(en)3]Se3 and manganese-tris(1,2-ethanediamine)-monotellurodiselenide[Mn(en) 3]TeSe2

Article abstract of DOI:10.1515/znb-2000-0911

The reaction of manganese (II)-chloride-tetrahydrate, caesium triselenide and elemental selenium or tellurium in 1,2-ethanediamine (en) under solvothermal conditions leads to the formation of two new isostructural compounds [Mn(en)₃]Se₃ (1) and [Mn(en)₃]TeSe₂ (2). The compounds crystallize in the orthorhombic space group Pbcn with the lattice parameters a = 1149.39(9), b = 1506.83(11), c = 935.96(6) pm for 1 and a = 1184.1(2), b = 1495.3(2), c = 949.8(1) pm for 2. Their crystal structures are built up of [Mn(en)₃]²⁺ cations and Se₃^2- or TeSe₂^2- anions, respectively. Each cation is surrounded by six next neighbouring anions, and vice versa. Between the cations and the anions hydrogen bonding is observed. The thermal behaviour was investigated using differential thermal analysis, thermogravimetry as well as X-ray powder diffraction. Completely different properties were found. Compound 1 decomposes in two distinct endothermic steps, while compound 2 shows only one endothermic peak. The weight loss for 1 corresponds roughly to the emission of all en molecules, whereas the weight loss for 2 is significantly lower. The final products are composed of MnSe₂ and elemental Se or Te, respectively, and an unknown crystalline phase which is different for the two samples.

Full text of DOI:10.1515/znb-2000-0911

Synthesis, Crystal Structures and Properties of the Polychalcogenides
Manganese-tris(l,2-ethanediamine)-triselenide [Mn(en)3]Se3and
Manganese-tris(l,2-ethanediamine)-monotellurodiselenide [Mn(en)3]TeSe2
Frank Wendland, Christian Näther, and Wolfgang Bensch
Institut für Anorganische Chemie der Christians-Albrechts-Universität Kiel, Olshausenstraße
40, D-24098 Kiel, Germany
Reprint requests to Prof. Wolfgang Bensch. Fax: +49 (0)431-8801520.
E-mail: wbensch@ac.uni-kiel.de
Z. Naturforsch. 55 b, 871-876 (2000); received May 12, 2000
Solvothermal Synthesis, Polychalcogenides
The reaction of manganese(II)-chloride-tetrahydrate, caesium triselenide and elemental se-
lenium or tellurium in 1,2-ethanediamine (en) under solvothermal conditions leads to the
formation of two new isostructural compounds [Mn(en)3]Se3 (1) and [Mn(en)3]TeSe2 (2). The
compounds crystallize in the orthorhombic space group Pbcn with the lattice parameters a =
1149.39(9),
b = 1506.83(11), c = 935.96(6) pm for 1 and a = 1184.1(2), b = 1495.3(2), c =
949.8(1) pm for 2. Their crystal structures are built up of [Mn(en)3]2+cations and Se}2~ or
TeSe22~ anions, respectively. Each cation is surrounded by six next neighbouring anions, and
vice versa. Between the cations and the anions hydrogen bonding is observed. The thermal
behaviour was investigated using differential thermal analysis, thermogravimetry as well as X-
ray powder diffraction. Completely different properties were found. Compound 1 decomposes
in two distinct endothermic steps, while compound 2 shows only one endothermic peak. The
weight loss for 1 corresponds roughly to the emission of all en molecules, whereas the weight
loss for 2 is significantly lower. The final products are composed of MnSe2 and elemental Se
or Te, respectively, and an unknown crystalline phase which is different for the two samples.
Introduction
the K2 S3 structure type [4a, b], as well as BaSe3
[4c] were reported. The conditions for the synthe-
ses of Na2 Se3 [lc] and [(CH3 )3N(CH2)i5 CH3 ]2 Se3
[5] were published but no structural details were re-
ported. For mixed Se/Te trichalcogenides only the
compound (2 ,2 ,2 -crypt-K)2 TeSe2 was structurally
characterized [6 ].
For the synthesis of polychalcogenide anions
different methods can be applied. Using the so-
called mild solvothermal conditions (temperature
range 350 -450 K, autogeneous pressure of p =
105 - 106 Pa) polychalcogenide anions of variable
lengths can be trapped and isolated using appro-
priate cations as counterions. Alkali polychalco-
genides can alsobepreparedunder ammonothermal
conditions by reacting the elemental alkali metals
and stoichiometric amounts ofelemental chalcogen
attemperatures ranging from213to600K andpres-
suresvaryingfromatmosphericpressure(105 Pa) up
to 3-108 Pa (see [la- f]). In addition, other routes
like the reaction of an aqueous solution of NaoCC^
with H2 Se and Se [2] or the reduction of Se with
NaBH4 in boiling ethanol weresuccessfully applied
for the preparation of compounds containing poly-
chalcogenide anions [3].
For the formation of telluroselenide TeSe2- and
selenotelluride TeSe3 2_ in the reaction of alkali
monoselenides ordiselenides withtellurium (eq. (1 )
and (2 )) or alkali polytellurides with selenium in an
aqueous solution at 353 K under an atmosphere
of purified nitrogen (eq. (3)) the following mecha-
nisms were proposed by I. G. Zaitseva et al. [7]:
Na2Se +Te ^
2 Na2 Se2 +Te ^ 2 Na2TeSe3 +Na2TeSe
Ten2- +3 Se TeSe32~+(n -1) Te
Na2TeSe • 10H20
(1)
(2)
(3)
In our own research on the synthesis of salts with
With respect to trichalcogenide anions only the
triselenides of K, Rb, and Cs, all crystallizing in new polychalcogenide anions applying solvother-
0932-0776/00/0900-0871 $ 06.00 (c) 2000 Verlag der Zeitschrift für Naturforschung, Tübingen •www.znaturforsch.com
K
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F. Wendland et al. •The Polychalcogenides [Mn(en)3]Se3 and [Mn(en)3]TeSe2
Table 1. Se-Q bond lengths [pm] and Se-Q-Se angles [°]
(Q = Se, Te) in the title compounds as well as in elemental
selenium and other trichalcogenides extracted from the
literature (*: this work).
Se-Q
Se-Q-Se
Compound
Lit.
Q
*
233.96(4)
238.3(2)
238.3(7)
235.8(1)
235(6)
104.65(2) Se
102.5(1) Se
103.1(3) Se
[Mn(en)3]Se3
K2Se3
Rb2Se3
Cs2Se3
BaSe3
[4al
I4b]
103.6(5) Se [4b]
Se [4c]
103.1(2) Se
237.3(5)
250.25(6)
250.1,250.4
[4d]
*
Q-Se
[Mn(en)3]TeSe2
(2,2,2-crypt-K)2TeSe2
Te
Te
102.6(1)
111.3(1)
[6]
MnCl2 •4H20 +K2Te3/Rb2Te3/Cs2Te3 +3 Se
[Mn(en)3]TeSe2+2 AC1
(5)
Fig. 1. Crystal structure of [Mn(en)3]TeSe2viewed along
the a-axis (hydrogen bonding is shown as dotted lines).
It is difficult to decide whether the formation of the
TeSe2 2_ anion is only favoured by the solvother-
mal conditions or due to the presence of the com-
ponents manganese(II) and en. Results of experi-
ments in which the reactions according to eqs (1 -
3) were carried out under solvothermal conditions
do not allow a definite conclusion. If Li2 Se2 and
tellurium (eq. (1)) or K2Te3 and selenium (eq. (2))
were reacted in H2O under solvothermal conditions
thealkali chalcogenides weredissolved whereas the
elemental chalcogen was not attacked. Using en in-
steadof H2 O asthe solvent thealkali chalcogenides
as well as the elemental chalcogen were dissolved
but no crystalline product was obtained.
mal conditions we investigate the influence of the
size of the cations on the length of the poly-
chalcogenide fragments. During these investiga-
tions we have prepared the new trichalcogenides
[Mn(en)3 ]Se3 (1 ) and [Mn(en)3 ]TeSe2 (2 ). 1 and 2
are the first examples of chelated transition metal
triselenides and diselenomonotellurides. Here we
reportontheirsyntheses, crystal structures andther-
mal properties.
Results and Discussion
Syntheses
Crystal structures
The title compounds were prepared by the re-
action of manganese(II)-chloride-tetrahydrate, cae-
sium triselenide and elemental selenium or tel-
lurium (molar ratio 1:1:3) under solvothermal con-
ditions. We note that under solvothermal condi-
tions the reaction of alkali selenides with tellurium
leads to the formation of TeSe22~anions instead of
TeSe2- or TeSe3 2_ anions (see introduction). This
is also the case if other alkali selenides like Li2 Se2 ,
Rb2Se3 orCs2 Se3 areused in the synthesis (eq. (4)).
EveniftellurideslikeK2Te3 ,Rb2Te3 orCs2Te3 were
reacted with selenium (eq. (5)) always dark rednee-
dles and polyhedra of compound 2 plus the alkali
halide AC1 (A = alkali) were obtained.
Thecompounds [Mn(en)3]Se3 (1)and [Mn(en)3]-
TeSe2 (2) are isostructural and crystallize in the
orthorhombic space group Pbcn with four crystal-
lographically independent formula units in the unit
cell. Both compounds are composed of [Mn(en)3 ]2+
cations which are located on a centre of inversion
and trichalcogenide anions with the central chalco-
genide atom located on a twofold axis (Fig. 1). The
Mn2+cations are in a sixfold coordination of ni-
trogen atoms of three chelating en ligands forming
distorted octahedra (Fig. 1). The Mn-N distances
are between 226.0(2) and 228.8(2) pm for 1 and
226.7(3) and 228.9(3) pm for 2 and are in the nor-
mal range of 223.5 -228.6 pm asfound for example
in [Mn(en)3 ]SbSe4 -enH [8] and 226.1 -229.0 pm in
MnCh 4 H2O +Li2Se2/Rb2Se3/Cs2 Se3 +3Te
[Mn(en)3]TeSe2+2 AC1
(4) [Mn(en)3]Te4 [9].
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873
F. Wendland et al. •The Polychalcogenides [Mn(en)3]Se3 and [Mn(en)3]TeSe2
Table 2. Se • H distances [pm] and Se -H-N angles [°] in
[Mn(en)3]Se3.
Se(2)-H6N
Se(l)-H5N
Se(2)-H3N
275.1(3) Se(2)-H1N
274.3(2)
273.9(3)
Se(2)-H2N
271.8(2)
272.1(2)
Se(2)-H1N-N(l) 162.3(1)
Se(2)-H2N-N(l) 161.0(10)
Se(2)-H6N-N(3) 154.8(1)
Se(l)-H5N-N(3) 175.4(1)
Se(2)-H3N-N(2) 158.3(1)
Table 3. Se -Hand Te-H distances [pm] and Se-H-N /
Te--H-N angles [°] in [Mn(en)3]TeSe2.
Se-HIN
Se-H3N
Te-H5N
284.1(3)
274.4(3)
284.7(3)
Se-H2N
Se-H6N
277.0(3)
270.8(4)
Se-H2N-N(l)
Se-H6N -N(3)
159.7(1)
160.2(1)
Se-HIN-N(l)
Se-H3N-N(2)
Te-H5N-N(3)
158.2(1)
159.4(1)
172.2(1)
arranged in such away, thattheQ-Sebonds (Q = Se,
Te) are eclipsed by two ofthe threeen molecules of
the pseudo C3 symmetric cation (Fig. 2).
Fig. 2. Crystal structure of [Mn(en)3]TeSe2 viewed on
(001) (hydrogen atoms are omitted for clarity).
The Se32~ anions and [Mn(en)3 ]2+cations are
connected via Se -Hbonds as suggested by the rel-
atively shortSe •Hcontacts andbythelargeSe H-
N angles (Table 2). Every terminal atom of a Se32-
anion is connected totwo cations while the inner Se
atom has acontact to only one cation.
In Table 1 the Se-Se bond lengths and Se-Se-
Se angles of 1 as well as data reported for other
triselenides and elemental selenium extracted from
the literature are listed. The Se-Se distance of
233.96(4) pm observed in 1is very short compared
tothe values found in other Se32~anions. As acon-
sequence of the short bond the Se-Se-Se angle of
104.65(2)° is somewhat larger than in other trise-
lenide anions.
For2 short contacts between theTeand Se atoms
andthehydrogenatomsoftheaminogroupsarealso
found, indicative of hydrogen bonding (Table 3).
The distances Se -H(between 270.8 and 284.1 pm)
and Te H (284.7 pm) are significantly shorter than
those reported for (2 ,2 ,2 -crypt-K)2 TeSe2 which are
between 341 -356 pm for Te -Hand 290 -349 pm
for Se-H [6 ],
The Se-Te bond length in 2 of 250.25(6) pm
is comparable to that reported for (2 ,2 ,2 -crypt-
K)2TeSe2 (crypt = 4,7,13,16,21,24-hexaoxa-l,10-
diazabicyclo[8 .8 .8 ]hexacosane) [6 ], but the angle
Se-Te-Seof 102.59(3)° is significantly smaller than
in (2 ,2 ,2 -crypt-K)2 TeSe2 of 111.3(1)° (Table 1). We
note that structural data for a TeSe22~ anion was
only reported for (2 ,2 ,2 -crypt-K)2 TeSe2 .
Thermoanalytical experiments on [Mn(en)s]Ses (1)
All DTA-TG experiments were conducted on se-
lected single crystals because the material sponta-
neously decomposes when powdered (see experi-
mental part). On heating a broad endothermic sig-
The anions and cations are arranged in apseudo-
hexagonal packing (Fig. 2). Each cation is sur-
roundedby sixanions andeach anion by sixcations.
Thebestplanecalculatedfortheatomsoftheanions nal (Tonset= 421 K) composed oftwo distinct peaks
is observed which is accompanied by a mass loss
between the chalcogen atoms amounts to 596.4 pm of 34.3% in the TG curve (Fig. 3). The experiments
is parallel to (010). The shortest interionic contact
wereperformed several times andthesplittingofthe
peak in the DTA curve was reproduced. Therefore,
it must be assumed that the decomposition reaction
proceeds in two different steps that cannot be re-
solved. Upon further heating a second endothermic
for 1 and 602.9 pm for 2 and the interplanar angle
between the planes of neighbouring anions is 1 1 °
for 1 and 13.8° for 2. Parallel to the
c axis stacks
of alternating cations and anions are found. Within
these stacks cations and anions are synperiplanarly
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F. Wendland et al. •The Polychalcogenides [Mn(en)3]Se3 and [Mn(en)3]TeSe2
mension perpendicular to the reflecting planes is
about 40 nm for MnSe2 and about 100 nm for Se.
The thermal decomposition was also studied by
thermomicroscopy. At 303 K the crystal is dark red
and the surface is smooth. At 453 K the colour
changes from red to black and the surface becomes
rough. Further heating to 512 K leads to a partial
melting of the material.
Thermoanalytic experiments on
[Mn(en)3]TeSe2(2)
T[K]
The decomposition of [Mn(en)3]TeSe2 single
Fig. 3. DTA-TG curves for [Mn(en)3]Se3 (argon atmo-
sphere; heating rate: 3 K/min).
crystals starts at Tonset = 438 K. In contrast to 1
only one sharp endothermic signal isobserved. The
weight loss of 19.5% (Fig. 5) is close to the weight
change fortheelimination oftwo enmolecules (cal-
culated: 23.1%). A valueof34.6%iscalculatedifall
en molecules were emitted. The second endother-
mic signal atTonset= 714.9 K isduetothemeltingof
elemental tellurium (literature value: 725 K [11]).
In the X-ray powder pattern of the dark grey de-
composition product reflections of MnSe2 and Te
aswell asfour additional reflections ofan unknown
compound (marked with “X” in Fig. 6 ) are seen.
An estimation of the composition leads to aratio of
29:47:24 (in %) for MnSe2 :Te :unknown phase.
In contrast to the decomposition product of 1
the reflections of MnSe2 are significantly smaller
than those of the elemental chalcogen. Applying
the Scherrerformula (nocorrection forinstrumental
broadening) the average crystal dimension perpen-
dicular to the reflecting planes is about 53 nm for
MnSe2 and about 35 nm for Te.
2en
Fig. 4. X-ray diffraction pattern of the product obtained
after the DTA-TG measurement of single crystals of
[Mn(en)j]Se3. The Bragg reflections of Se are marked,
those marked with an “X” could not be identified. The
remaining reflections originate from MnSe2.
Identification of the unknown phase was at-
tempted with an EDX mapping analysis, but no
signal at TonSet = 485 K is observed which corre-
sponds to the melting of elemental selenium (liter-
ature value: 490 K [10]). The weight loss of 34.3%
is in rough agreement with the emission of all 3 en
molecules (calculated: 38.2%).
After decomposition a dark grey powder is ob-
tained. In the X-ray powder pattern MnSe2 and Se
could be identified (Fig. 4) as well as four reflec-
tions of an yet unknown phase (marked with “X” in
Fig. 4). A rough estimate using the area of the most
intense reflections yields a ratio of 31:52:17 (in %)
for MnSe2 :Se:unknown phase. It is noteworthy that
the reflections of Se are significantly smaller than
those of MnSe2 indicative of a better crystallinity
of Se. Applying the Scherrer formula (no correction
for instrumental broadening) the average crystal di-
T [K]
Fig. 5. DTA-TG curves for [Mn(en)3]TeSe2 (argon atmo-
sphere; heating rate: 3 K/min).
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875
F. Wendland et al. ■The Polychalcogenides [Mn(en)3]Se3 and [Mn(en)3]TeSe2
Table 4. Crystallographic data, details of the data collec-
tion and selected results of the structure refinement for
[Mn(en)3]Se3 (1) and [Mn(en)3]TeSe2 (2).
[Mn(en)3]Se3
[Mn(en)3]TeSe2
1184.1(2)
1495.3(2)
949.8(1)
1681.7
1149.39(9)
1506.83(11)
935.96(6)
1621.0
Unit cell:
a
b
[pm]
[pm]
c[pm]
V [106pm3]
Z
4
4
orthorhombic
Pbcn (IT 60)
2.057
orthorhombic
Pbcn (IT 60)
Crystal system
Space group
Density (calcd) [g-cm-3] 1.935
6.80
7.54
/j. [mm-1]
Wavelength
2en
Mo-Kq (71.073 pm, graphite
monochromated)
Fig. 6. X-ray diffraction pattem of the product obtained
after the DTA-TG measurement of single crystals of
[Mn(en)3]TeSe2. The Bragg reflections of Te are marked,
those marked with an “X” could not be identified. The
remaining reflections originate from MnSe2.
3° < 29 < 52c3 3° < 29 < 56°
Scan range
T [K]
Refls measured
Independent refls
Refls with F0> 4a(F0)
Data
273
2138
273
3144
2034
1428
1592
1209
2036
2.9
1596
1.39
evidence for the presence of a mixed MnSexTey
compound or a Se-Te phase was obtained.
flint [%]
Min./max. transm.
Indices (F0> 4cr(F0) [%]
0227/0.496
fil =2.84
wR2 = 6.35
R\=5.66
wR2 = 7.3
0.43/-0.45
0.328/0.438
Rl =2.19
wR2 = 4.73
Rl =4.37
wR2 = 5.88
0.25/—0.31
In a series of test experiments single crystals of
[Mn(en)3]Se
ence of elemental Te. Surprisingly, a similar be-
haviour as for [Mn(en) ]TeSe is observed. The
3
were also decomposed in the pres-
Indices (all data) [%]
Residual electron
density [e/106pm3]
3
2
DTA signal shows only one broad endothermic
peak instead of a split signal as found for pure
red needles and polyhedra of 1(yield about 28% based on
MnCb •4 H2O). The product was washed with degassed
ethanol and dried in vacuo. As a by-product CsCl was
formed. [Mn(en)3]Se3 could also be prepared using the
alkali polyselenides Li2Se2, Na2Se3, Rb2Se3 or K2Se5 as
starting materials. The reaction of MnCl2 • 4 H2O with
selenium or alkali polyselenides leads to the formation of
MnSe2.
[Mn(en)
3
]Se3 and the mass loss is only 2/3 of the
calculated value for the emission of all three en
molecules. Again, in the X-ray powder pattern of
the grey reaction product MnSe2 and Te could be
identified. In addition three strong reflections of an
unknown phase were observed which are not iden-
tical to those observed for the decomposition prod-
ucts of pure [Mn(en)
3
]Se
3
or [Mn(en)
3
]TeSe2 .
[Mn(en)3]TeSe2:49.5 mg (0.25 mmol) manganese(II)-
chloride-tetrahydrate, 125.7 mg (0.25 mmol) caesium
triselenide and 95.7 mg (0.75 mmol) tellurium were re-
acted in 2 cm3of 1,2-ethanediamine in teflon lined steel
autoclaves at 433 K for 7 d to give dark red needles and
polyhedra of 2 (yield 99%). The product was washed
with degassed ethanol and dried. As a by-product CsCl
was formed. [Mn(en)3]TeSe2 can also be obtained in the
same yield from the reaction of MnCh •4 H2O with ei-
ther Li2Se2 or Rb2Se3and tellurium (1:1:3) or potassium,
rubidium, or caesium tritelluride and selenium (1:1:3) ap-
plying the same conditions as described above.
It appears that the mechanism of the decompo-
sition reaction is completely different when Te is
involved. The experiments performed on the pure
selenide suggest that the en ligands are eliminated
completely, while in the presence of tellurium these
ligands are involved in afurther reaction. The inves-
tigations on the meachnism of this unusual reaction
will be the subject of further experiments.
Experimental
Both compounds are air-sensitive and decompose
within a few days to give MnSe? and Se (Te). It must
be noted that the compounds are spontaneously de-
composed when pulverised in a dry nitrogen atmo-
sphere.
Syntheses: [Mn(en)3]Se3: 49.5 mg (0.25 mmol) man-
ganese(II)-chloride-tetrahydrate, 125.7 mg (0.25 mmol)
caesium triselenide and 59.2 mg (0.75 mmol) elemental
selenium were reacted in 2 cm3of 1,2-ethanediamine in
teflon lined steel autoclaves at 433 K for 7 d to give dark
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Single crystal X-ray diffractometry: The intensities
F. Wendland et al. ■The Polychalcogenides [Mn(en)3]Se3 and [Mn(en)3]TeSe2
X-ray powder diffractometry: The X-ray powder pat-
terns were recorded with a STOE Stadi-P diffractometer
(Cu-Kq radiation, A = 154.056 pm) in transmission ge-
ometry and with aSiemens D5000 diffractometer (Cu-KQ
radiation, A = 154.056 pm) in Bragg-Brentano geometry.
DTA-TG: The DTA-TG data were recorded using a
Netzsch STA 429. All measurements were performed un-
der an argon atmosphere in alumina crucible using AI2O3
as the inert reference. Heating rate: 3 K/min.
were collected using a Philips PW1100 diffractometer
([Mn(en)3]Se3) and an Enraf-Nonius CAD4 diffractome-
ter([Mn(en)3]TeSe2). The data were corrected for Lorentz
and polarisation effects and empirical absorption cor-
rections using psi-scans were applied. All non-hydrogen
atoms were refined with anisotropic displacement param-
eters. The hydrogen atoms were positioned with idealized
geometry and refined with fixed isotropic displacement
parameters.
Thermomicroscopy: Thermomicroscopy was per-
formed with an Olympus BX60M microscope which is
equipped with a Sony DXC-950P 3CCD colour video
camera and a heating stage from Raczek DSC600 sys-
tem.
Crystallographic data (excluding structure factors) for
the structures reported in this paper have been de-
posited with the Cambridge Crystallographic Data Cen-
tre as supplementary publication no. CCDC 141230 for
[Mn(en)3]Se3 and CCDC 141231 for [Mn(en)3]TeSe2.
Copies of the data can be obtained, free of charge,
on application to CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK. (fax: +44-(0)1223-336033 or email:
deposit@ccdc.cam.ac.uk).
Acknowledgements
We gratefully acknowledge the financial support by
the state of Schleswig-Holstein and the Deutsche For-
schungsgemeinschaft (DFG).
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