Thermal analysis of manganese (II) complexes of general formula (Et 4N)2[MnBrnCl4?n]

Article abstract of DOI:10.1016/j.tca.2010.03.001

Thermal decomposition of compounds consisting of tetrahalogenomanganates(II) anions, [MnBr_nCl_4?n] ^2? (n = 0-4), and a tetraethylammonium cation has been studied using the DSC and TG techniques. The measurements were carried out in an argon atmosphere over the temperature ranges 173-500K (DSC) and 300-1073K (TG). Products of the thermal decomposition were identified by MS, FTIR, Far-FTIR spectroscopy as well as X-ray powder diffractometry.

Full text of DOI:10.1016/j.tca.2010.03.001

Thermochimica Acta 503–504 (2010) 21–27
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Thermal analysis of manganese(II) complexes of general formula
(
Et N) [MnBr Cl
]
4
2
n
4−n
a
b
a,∗
E. Stycze n´ , M. Gazda , D. Wyrzykowski
a
Faculty of Chemistry, University of Gda n´ sk, Sobieskiego 18, 80-952 Gda n´ sk, Poland
Faculty of Physics and Mathematics, Technical University of Gda n´ sk, Narutowicza 11/12, 80-952 Gda n´ sk, Poland
b
a r t i c l e i n f o
a b s t r a c t
Thermal decomposition of compounds consisting of tetrahalogenomanganates(II) anions, [MnBr Cl ]2
(
−
Article history:
n
4−n
Received 18 January 2010
Received in revised form 25 February 2010
Accepted 1 March 2010
n = 0–4), and a tetraethylammonium cation has been studied using the DSC and TG techniques. The
measurements were carried out in an argon atmosphere over the temperature ranges 173–500 K (DSC)
and 300–1073 K (TG). Products of the thermal decomposition were identified by MS, FTIR, Far-FTIR
spectroscopy as well as X-ray powder diffractometry.
Available online 6 March 2010
©
2010 Elsevier B.V. All rights reserved.
Keywords:
Tetrahalogenomanganates(II)
Thermal decomposition
DSC
1
. Introduction
[11–14]. Knowledge of thermal characteristics of a large group of
compounds would enable to determine the influence of the organic
cation, the metal and the halide ligand on thermal stability of com-
In 1992, Peter Day and associates from the University College,
n−
London, published the first report on utilization of the (BEDT-
pounds with an [MX4] anion.
TTF) CuCl ·H O compounds as magnetic molecular conductors [1].
2
4
2
Successive investigations have shown that these systems, owing to
interaction of alternate organic–inorganic sheets have interesting
physical properties such as superconductivity [2–4]. In respect of
high-spin configurations of d electrons, the inorganic sheet in the
conductors can be formed by paramagnetic complex anions of gen-
eral formula [MX4] where M = Mn, Fe, Co, Ni, Cu; X = Cl, Br; n = 1, 2.
As such, tetraalkylammonium salts of tetrahalogenometallates(II)
have been subsequently used to synthesize those compounds
2. Experimental
2.1. Synthesis
n−
The manganese(II) complex salts were obtained by a procedure
described in the literature, by mixing together stoichiometric quan-
tities of a manganese(II) halide with tetraethylammonium chloride
and/or bromide in ethanol [15].
[
1,5–10]. The complexes constitute thus an exciting area of explo-
ration aimed principally at elucidation of their structure as well as
magnetic and spectroscopic properties including infrared spectra
(Et N) [MnCl ]. MnCl (0.05 mol) was dissolved in a small
quantity of ethanol and the solution was added to ethanolic solu-
4
2
4
2
(
FTIR and Far-FTIR), reflection spectra, and EPR. From the point of
tion of Et NCl (0.1 mol). (Found: C, 42.02; N, 6.11; H, 8.98. Calcd. for
4
view of application of the magnetic molecular conductors inter-
esting are also their as yet poorly explored thermal characteristics.
Stability characteristics of the systems at various temperatures may
be useful for designing magnetic molecular conductors. Further-
more, knowledge of their thermal decomposition products may
be helpful for working out procedures for utilization of appliances
containing the conductors.
(Et N) [MnCl ], C, 42.03; N, 6.13; H, 8.82%).
4
2
4
(Et N) [MnBr ] was also prepared as described, by using MnBr
4
2
4
2
(0.05 mol) and Et NBr. (Found: C, 30.35; N, 4.39; H, 6.32. Calcd. for
4
(Et N) [MnBr ], C, 30.26; N, 4.41; H, 6.35%).
4
2
4
(Et N) [MnBrCl ]. MnCl (0.05 mol) was dissolved in a small
4
2
3
2
quantity of ethanol and the solution was added to an equimolar
mixture (0.05 mol each) of Et NCl and Et NBr in ethanol. (Found:
4
4
This contribution is a continuation of our studies on thermal
analysis of bis(tetraalkylammonium) tetrahalogenometallates(II)
C, 38.89; N, 5.74; H, 8.31. Calcd. for (Et N) [MnBrCl ], C, 38.30; N,
4 2 3
5.58; H, 8.04%).
Et N) [MnBr Cl] was prepared as described, but MnBr2
(
4
2
3
(0.05 mol) was used as a manganese halide. (Found: C, 32.78; N,
∗ Corresponding author. Tel.: +48 523 53 94.
E-mail address: daro@chem.univ.gda.pl (D. Wyrzykowski).
4.79; H, 7.02. Calcd. for (Et N) [MnBr Cl], C, 32.54; N, 4.74; H,
6.83%).
4
2
3
0
040-6031/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.tca.2010.03.001

2
2
E. Stycze n´ et al. / Thermochimica Acta 503–504 (2010) 21–27
Table 2
(
Et N) [MnBr Cl ]. MnCl (0.05 mol) was dissolved in a small
4 2 2 2 2
Results of analysis of the decomposition products.
quantity of ethanol and the solution was added to an ethanolic solu-
tion of Et NBr (0.01 mol). (Found: C, 35.25; N, 5.27; H, 7.52. Calcd.
4
Complex
Step
Temp. range (K)
DTGmin (K)
Mass loss (%)
for (Et N) [MnBr Cl ], C, 35.19; N, 5.13; H, 7.38%).
4
2
2
2
(Et N) [MnCl ]
1
2
3
573–643
643–688
858–968
599
665
61
11
12
4
2
4
2.2. Instrumental
(
Et4N)2[MnBrCl3]
Et4N)2[MnBr2Cl2]
1a
2
553–693
733–943
601
66
16
The Far-FTIR spectra were recorded on a BRUKER IFS 66 spec-
−1
trophotometer in PE over the 650–50 cm range.
(
1
2
3
548–628
628–683
728–866
585
639
56
10
20
The DSC measurements were carried out in an argon (Ar 5.0) on a
NETZSCH DSC 204 apparatus (range 173–500 K, aluminum crucible,
sample mass ca. 10 mg, heating rate 10 K/min).
(
Et4N)2[MnBr3Cl]
Et4N)2[MnBr4]
1
2
3
563–608
608–658
758–958
584
636
36
25
26
The TG-FTIR analyses in argon (Ar 5.0) were run on a Netzsch TG
2
09 apparatus coupled with a Bruker FTIR IFS66 spectrophotome-
ter (range 298–1073 K, corundum crucible, sample mass ca. 12 mg,
heating rate 15 K/min, flow rate of the carrier gas 18 mL/min).
The TG–MS measurements in argon were carried out on a
Netzsch STA 449 F3 Jupiter apparatus (TA Instruments) (range
(
1
2
3
538–603
603–653
763–983
583
633
968
35
25
30
a
Split into steps at a slower rise in temperature.
2
90–1273 K, corundum crucible, sample mass ca. 5–10 mg, heating
rate 1–10 K/min). The thermal analysis instrument was connected
on-line with the quadrupole mass spectrometer QMS 403C Aëolos.
The course of thermal analysis was broken at points correspond-
ing to the main steps of decomposition and the residues in the
crucible were quickly cooled in the stream of argon. This enabled
to analyze the residues at strictly pre-determined steps of decom-
position. The analysis was carried out using the FTIR spectroscopic
techniques as well as the X-ray powder diffractometry.
transformations, most probably owing to transformation of one
polymorphic form to another. Upon cooling of the compound down
to 173 K (cooling 1), a peak below 273 K appears in the DSC curve
assigned to another phase transformation that is also reversible as
demonstrated by a peak at similar temperature and of similar sur-
face area recorded upon reheating the sample (heating 2). As in the
case of (Et N) [MnCl ], the transformation could also be attributed
4
2
4
The presence of crystalline phases was checked by X-ray diffrac-
tion with the use of Philips X’Pert diffractometer system. The XRPD
patterns were recorded at room temperature with CuK␣ radiation
to small movements of the ions. The DSC curves of (Et N) [MnBr ]
4 2 4
recorded upon heating the sample from ambient temperature up
to 500 K (heating 1) followed by its cooling down to 173 K (cooling
1) and reheating up to 500 K (heating 2) are shown in Fig. 1.
The greatest number of transformations occurring upon
changes of temperature among the bis(tetraethylammonium)
tetrahalogenmanganates(II) was noticed with (Et N) [MnBr Cl].
(
ꢀ = 1.540 Å). Qualitative analysis of the diffraction spectra was car-
ried out with the ICDD PDF database [16].
3
. Results and discussion
4
2
3
Apart from analogous ones recorded with (Et N) [MnBrCl ],
4
2
3
Results of the thermal analysis of the complexes are compiled
(Et N) [MnBr Cl ] and (Et N) [MnBr ], such as the reversible
4 2 2 2 4 2 4
in Tables 1 and 2.
endothermic one occurring upon heating the sample, and the
reversible exothermic one upon cooling, an additional peak
emerges at 389 K assignable to irreversible endothermic transfor-
mation. Its origin is based on lack of a similar peak upon reheating
the sample (heating 2, Fig. 2).
There are no changes in the DSC curve of (Et N) [MnCl ] upon
4
2
4
raising temperature up to that close to the decomposition point
573 K). They emerge only upon cooling the sample down to
73 K. Peaks appearing at 221 and 189 K are assigned to reversible
(
1
exothermic transformations. They origin can be attributed to
small movements of the ions resulting in the change of their
mutual position. As a consequence, parameters of the elemen-
tary cell of (Et N) [MnCl ] can be changed as was the case with
A common feature of the (Et N) [MnBrnCl
their thermal dissociation occurring in the solid state. This means
that they have no melting point prior to decomposition.
] compounds is
4
2
4−n
4
2
4
(
Me N) [MnCl ] [17].
4 2 4
The (Et N) [MnBrCl ], (Et N) [MnBr Cl ] and (Et N) [MnBr ]
4
2
3
4
2
2
2
4
2
4
complexes (Fig. 1), upon heating up to their decomposition points
ca. 523 K) (heating 1), undergo reversible endothermic phase
(
Table 1
Temperature and enthalpy changes for physical transformations of the man-
ganese(II) complex as taken from the DCS curve.
Complexes
T␴ (K)
ꢁH␴ (kJ/mol)
R
(
(
(
(
Et4N)2[MnCl4]
221
1
−3.2
−4.4
1.7
R
89
R
R
R
R
I
Et4N)2[MnBrCl3]
Et4N)2[MnBr2Cl2]
Et4N)2[MnBr3Cl]
462
22
432
36
389
2
−2.5
2.5
2
−2.8
8.1
2.3
−3.3
11.0
−4.6
R
R
R
R
4
2
30
60
443
55
(
Et4N)2[MnBr4]
2
T␴: temperature of phase transformation; ꢁH␴: enthalpy of phase transformation;
R: reversible; I: irreversible.
Fig. 1. DSC curves of (Et4N)2[MnBr4], ˇ = 10 K/min.

E. Stycze n´ et al. / Thermochimica Acta 503–504 (2010) 21–27
23
Fig. 4. FTIR spectrum of the volatile decomposition products of (Et4N)2[MnCl4], at
30 K, together with theoretical harmonic transitions for Et3N (squares) and EtCl
circles) [18].
6
(
Fig. 2. DSC curves of (Et4N)2[MnBr3Cl], ˇ = 10 K/min.
A closer inspection of the results of the thermal decomposition
of bis(tetraethylammonium) tetrahalogenomanganates(II) reveals
the influence of anion identity on the pathways of their thermal
dissociation. The differences lie in the formation of various solids
during the first step.
The presence of these volatiles released during thermal
decomposition of bis(tetraethylammonium) tetrahalogenoman-
ganates(II) has also been confirmed by the FTIR spectra. For
instance, in a FTIR spectrum of the volatiles from (Et N) [MnCl ],
4
2
4
−
1
−1
bands were recorded around 660 cm (ꢂ C–Cl), 740–1210 cm
(ı C–C–H), 1290–1390 cm (ı H–C–N), 1470 cm (ı H–C–H) and
2800–2980 cm (ꢂ C–H). These bands are compatible with those of
the theoretical IR spectra of ethylamine and ethyl chloride (Fig. 4).
Formation of the volatiles containing halogen ions triggers some
changes in the coordination sphere of Mn(II). In the Far-FTIR
− −1
1
In spite of the differences in the solids’ composition, simi-
lar volatile products are released. For instance, upon heating of
−
1
(
Et N) [MnCl ], Et N and EtCl are released (Fig. 3), whereas in the
4 2 4 3
case of (Et N) [MnBr ]–Et N and EtBr. Fig. 3 represents a TG curve
4
2
4
3
of an exemplary compound, (Et N) [MnCl ], with superimposed
4
2
4
curves of ionic currents for selected m/z values corresponding
spectrum of (Et N) [MnCl ] there are bands assigned to bending
4 2 4
+
+
+
+
−1
to EtCl {m/z = 26 (C H ), 27 (C H3 ), 28 (C H ), 29 (C H5 ), 49
vibrations of Cl–Mn–Cl (at 79 and 118 cm ) and to the stretching
2
2
2
2
4
2
3
5+
35+
37+
−1
(
CH Cl ), 64 (C H5Cl ) and 66 (C H5Cl )}. The variations in
ones of Mn–Cl at 282 cm . These bands are absent in the spectrum
2
2
2
the ionic current intensity correspond to the temperature ranges
over which the loss in weight is recorded in the TG curve.
of the sinter, this indicating destruction of the tetrahedral geometry
of the manganese(II) complex upon heating up to 648 K.
Complexes containing both the chloride and bromide ligands
in the coordination sphere of manganese(II) release simultane-
Juxtaposition of the spectra of the sinters obtained at 648 K
(first step) and 693 K (second step), represented in Fig. 5(2) and
(3), resp., reveals that they have a similar structural unit. For com-
parison of the band frequencies, a standard spectrum of anhydrous
manganese(II) chloride has been recorded (Fig. 5(1)).
ously Et N, EtCl and EtBr during decomposition as evidenced by
3
+
variations in the ionic currents of the m/z values of 26 (C H ),
2
2
+
+
+
+
35+
2
5
(
7 (C H ), 28 (C H ), 29 (C H5 ), 30 (C H ), 49 (CH Cl ),
2
3
2
4
2
2
6
2
+
+
35+
37+
8 (C H N ), 64 (C H5Cl ), 66 (C H5Cl ), 86 (C5H12N ), 100
A closer inspection of the position and relative intensities of the
absorption bands in the spectra represented in Fig. 5 shows that the
3
8
+
2
2
+
79+
81+
C6H14N ), 101 (C H N ), 108 (C H5Br ) and 110 (C H5Br ).
6
15
2
2
Fig. 3. TG curve of (Et4N)2[MnCl4] (ˇ = 1 K/min over the range 523–723 K) and ionic currents for m/z assigned to EtCl recorded during decomposition of the complex.

2
4
E. Stycze n´ et al. / Thermochimica Acta 503–504 (2010) 21–27
Fig. 5. Far-FTIR spectra of the (Et4N)2[MnCl4] sinters obtained at 648 K (2) and 693 K
3), and the spectrum of MnCl2 (1).
(
Fig. 7. TG curves of (Et4N)2[MnBrCl3], ˇ = 15 K/min (1) and 1 K/min (2), in argon.
product of the first (648 K) and second (693 K) decomposition steps
of (Et N) [MnCl ] is MnCl . Also the X-ray diffraction results show
4
2
4
2
that MnCl2 is one of the crystalline phases present in the sinter. As
can be seen in Fig. 6, part of the XRD reflexes of the sinter left after
combustion of (Et N) [MnCl ] at 693 K may be attributed to MnCl .
4
2
4
2
Manganese(II) chloride was also found at the second step of
decomposition of (Et N) [MnBrCl ] as indicated by the position
4
2
3
of relative band intensities in the Far-FTIR spectrum of a sinter
obtained at 703 K.
The difference in the thermal decomposition patterns of the
(
Et N) [MnBrnCl ] compounds is due to the fact that MnCl left at
4 2 4-n 2
the first step of decomposition of (Et N) [MnCl ], (Et N) [MnBrCl ]
4
2
4
4
2
3
The loss in weight due to formation of MnCl during the first two
decomposition steps (72%, TG curve, Table 2) is compatible with the
theoretical one (72%). This indicates a total release of the organic
and (Et N) [MnBr Cl ] probably reacts with Et N being released
2
4
2
2
2
3
to form an Et N:MnCl2 adduct which undergoes thermal decom-
3
position during the next step. This can be seen at a slow rate
of temperature increase (Fig. 7). A slower diffusion of the gases
fragment as Et N and EtCl. However, in the final decomposition
3
product, non-decomposed organic matter (CxHyNz) has been found.
Analogous decomposition pattern can also be suggested for
Et N) [MnBrCl ]:
4 2 3
(
at ˇ = 1 K/min) from the sample facilitates formation of the
Et N:MnCl adduct which undergoes decomposition at higher tem-
3
2
(
perature to release Et N.
3
Knowledge of the volatile and solid decomposition products
of (Et N)[MnBrnCl
the first step of decomposition of the compound to be suggested:
] (n = 0–2) allows the following pathway of
4
4−n
Here, the calculated loss in weight due to formation of MnCl2 is
4%. On the other hand, that taken from the TG curve is smaller (66%,
7
Table 2, Fig. 7). This difference can be attributed to the formation
of MnBr2 as well. Assuming that during the second step equimolar
quantity of MnCl2 and MnBr2 is being formed, the theoretical loss
in weight would be just 66%. However, the presence of MnBr in the
2
residue (703 K) has been ruled out by its Far-FTIR spectrum whose
shape suggests that MnCl is the sole decomposition product. It can
2
thus be concluded that the smaller than theoretical loss in weight
can be explained in terms of the presence of the non-decomposed
organic matter. Its presence would also affect the course of the final
decomposition step of the compound.
The most intricate decomposition pattern among the
(Et4N)2[MnBrnCl4−n] (n = 0–2) compounds has been exhibited
Fig. 6. X-ray diffraction pattern of the sinter left after combustion of (Et4N)2[MnCl4]
at 693 K (second decomposition step) together with X-ray reflexes assigned to
MnCl2.

E. Stycze n´ et al. / Thermochimica Acta 503–504 (2010) 21–27
25
Fig. 8. Far-FTIR spectrum of the sinter of (Et4N)2[MnBr2Cl2] left at 693 K (1) super-
imposed with those of MnBr2 (2) and MnCl2 (3).
Fig. 9. TG and DTG curves of (Et4N)2[MnBr3Cl], ˇ = 15 K/min, in argon.
the stretching vibrations of Mn–Br decreases while that of Mn–Cl
disappears. There are also changes over the range of the bending
vibrations of Br–Mn–Br.
by (Et N) [MnBr Cl ]. A sinter left at 693 K (second decomposition
4
2
2
2
step) has been shown to contain both MnCl2 and MnBr . In its
2
Far-FTIR spectrum (Fig. 8) bands at identical positions to those
of MnBr2 (gray arrow) and MnCl2 (light gray arrow) have been
found. An additional proof in favour of those halides is an X-ray
diffraction pattern of the sinter in which the most intense peaks
correspond to X-ray reflexes of MnCl2 and MnBr2.
The loss in weight in the TG curve (66%) corresponds roughly to
an equimolar mixture of MnCl2 and MnBr2 (69%). On this basis the
following pathway can be suggested for the first two decomposition
Manganese(II) bromide is the product of the next step of decom-
position of (Et N) [MnBr Cl] and (Et N) [MnBr ], at 663 K. This
4
2
3
4
2
4
conclusion is based on similarity of the Far-FTIR spectra of the cor-
responding sinters and anhydrous manganese(II) bromide as well
as the X-ray diffraction patterns of the samples.
A
careful scrutiny of the results of experiments with
this class of compounds revealed a difference between the
decomposition patterns of (Et N) [MnCl ], (Et N) [MnBr Cl]
4
2
4
4
2
3
steps of (Et N) [MnBr Cl ]:
4
2
2
2
and (Et N) [MnBr Cl ] on the one hand, and the remain-
4
2
2
2
ing two bis(tetraethylammonium) tetrahalogenomanganates(II),
Et N) [MnBrCl ] and (Et N) [MnBr ], on the other hand. During
(
4
2
3
4
2
4
thermal decomposition of the first-named compounds, MnCl2 is
left at the first step which subsequently forms a stable Et N:MnCl2
3
adduct. With the two last-named compounds, initially only small
changes take place in the coordination sphere of Mn(II), and MnBr2
is formed at the next step. Furthermore, MnBr , in contrast to
2
MnCl , does not react wit the volatiles Et N. The poorer capacity
2
3
of MnBr2 to form adducts can be due to a lower electronegativity
of bromine as compared to that of chlorine on the one hand, and
to the steric hindrance of the former, on the other hand. The more
electronegative chlorine atom increases the positive charge on the
metal cation to enhance its interaction with the lone electron pair
on the nitrogen atom of the triethylamine molecule.
Slightly different are the decomposition patterns of complexes
with a higher number of bromide ligands. Thus, the nature
of ligands in the coordination sphere of manganese(II) has an
influence on the character of thermal transformations of the
bis(tetraethylammonium) tetrahalogenomanganates(II).
As the compiled results do not warrant certainty as to the chem-
ical composition of the first decomposition product (“?” in the
scheme), it is rather difficult to write a stoichiometric equation
for the processes progressing during the first step of the thermal
dissociation. This notwithstanding, having in hand composition of
the released gases and of the solid product of the second step, the
following scheme can be suggested for the first two steps of the
decomposition of (Et N) [MnBr Cl]:
The shapes of the TG curves of (Et N) [MnBr Cl] (Fig. 9) and
4
2
3
(
Et N) [MnBr ] suggest a two-step decomposition of the com-
4 2 4
pounds.
The clear-cut extrema in the DTG curves corresponding to the
first step of decomposition indicate two separate reactions to
occur. During those two steps, identical volatiles were released
as indicated by variations in the ionic current intensities for the
same m/z values. During decomposition of (Et N) [MnBr Cl] and
4
2
3
4
2
3
(
Et N) [MnBr ], Et N, EtCl and EtBr as well as Et N and EtBr, respec-
4 2 4 3 3
tively, were formed.
Due to high transformation rate taking place and consecutive
reactions, it was difficult to collect samples during the first step of
decomposition. Heating of (Et N) [MnBr Cl] up to 613 K gave a sin-
4
2
3
ter whose Far-FTIR spectrum allowed only to rule out the presence
of either manganese(II) halide. A comparison of the Far-FTIR spec-
trum of (Et N) [MnBr Cl] and of its sinter reveals some changes
4
2
3
in the coordination sphere of the Mn(II) ion. Thus, the intensity of

2
6
E. Stycze n´ et al. / Thermochimica Acta 503–504 (2010) 21–27
and, by analogy, for (Et N) [MnBr ]:
4. Conclusions
4
2
4
The bis(tetraethylammonium) tetrahalogenomanganates(II)
undergo, as a rule, reversible phase transformations associated
with small movements of ions. It should be emphasized that
the compounds do not melt. Decomposition of the complexes
takes place in the solid phase in two or three steps depend-
ing on the identity of the anion. Compounds with identical
tetraethylammonium cation are characterized by comparable
decomposition points and release similar volatile products. In
the case of (Et N) [MnBrnCl ] these are ethyl halides and
4
2
4−n
triethylamine. However, both the nature of the ligand in the
coordination sphere of manganese(II) and the size of the organic
cation have a significant influence on temperature and character of
the thermal transformations of the compounds. Decomposition of
The loss in mass in the TG curve of (Et N) [MnBr Cl] assigned
4
2
3
to the formation of MnBr2 is 61% (Table 2, Fig. 9), whereas the
theoretical one is 63%. With (Et N) [MnBr ] respective losses are
4
2
4
(
Et N) [MnCl ], (Et N) [MnBrCl ] and (Et N) [MnBr Cl ] results
4 2 4 4 2 3 4 2 2 2
6
0% (Table 2) and 66%. The differences are most probably due to
in a stable adduct, Et N:MnCl , formed at the first step. This
3
2
non-decomposed organic cations of the compounds, CxHyNz.
Irrespective of the identity of anion, the final step of the thermal
decomposition of the bis(tetraethylammonium) tetrahalogeno-
manganates(II) leaves identical product, manganese(II) halide. This,
being the solid product of the last but one step undergoes con-
version to manganese(II) carbide and small amounts of elemental
manganese. The presence of the latter in sinters obtained around
adduct is analogous to Bu N:MnCl2 formed at the second step of
3
decomposition of (Bu N) [MnCl ] and (Bu N) [MnBrCl ] [14]. The
4
2
4
4
2
3
two remaining compounds, (Et N) [MnBr Cl] and (Et N) [MnBr ]
4
2
3
4
2
4
leave behind only a manganese(II) halide during the second
step. However, irrespective of the nature of the organic cation or
complex anion, the final step of thermal decomposition of the
bis(tetralkylammonium) tetrahalogenomangananates(II) affords
identical products. A manganese(II) halide, being the solid product
of the last but one decomposition step of the compounds under-
goes conversion to a manganese carbide and small amounts of
elemental manganese.
1
000 K has been confirmed by X-ray diffraction patterns. A sim-
ilar result was previously reported for the (Bu N) [MnBrnCl
n = 0–4) counterparts [14].
The final step of the thermal decomposition of the compounds
]
4−n
4
2
(
is not quite clear. Without any doubt, the final decomposition
products are manganese carbides. Unfortunately, it is difficult
to precisely determine their composition solely on the basis
of X-ray analysis of the polycrystalline samples. The products
may be either a carbide of definite composition or a mixture
of carbides. There are five manganese carbides described in the
literature, namely Mn15C4, Mn23C , Mn C, Mn5C , and Mn7C
The results of this contribution, as compared to those previously
reported for compounds of general formula (Et N) [MBrnCl4-n],
4
2
where M = Fe, Co, Cu; n = 0–4 [11–13] reveal the influence of the
central ion identity on the course of thermal decomposition of the
complexes. Only during decomposition of compounds of the least
electronegative element, manganese(II), stable adducts are formed
between the solid MnCl2 and the volatile amines, Et N and Bu N.
6
3
2
3
3
3
[
19,20].
There are also some difficulties in the identification of the
Finally, depending on the identity of the metal, the final products
of the thermal decomposition in an inert atmosphere are metal
carbides and/or elemental metal.
volatiles undoubtedly released at that step (see loss in weight in
the TG curve). Most probably these are inorganic compounds and
this makes the FTIR spectral analysis difficult. Identification of the
gases could be possible from analysis of variations in the intensi-
ties of the ionic currents. However, the variations are missing for
Acknowledgement
This research was supported by the Polish State Committee for
Scientific Research under grant DS/8232-4-0088-9.
the m/z values corresponding to Cl , Br , HCl and HBr. This indi-
2
2
cates that either the products are not released at all during thermal
degradation of a manganese(II) halide or their concentration is too
low to be recorded by the detector. It can also be speculated that the
halide ions react with the incompletely combusted organic residue,
CxHyNz, to form intricate systems. The residue is also a source of
carbon for the manganese carbides being formed. Furthermore,
decomposition of the residue at high temperature (around 1000 K)
can afford elemental carbon which subsequently can reduce man-
ganese(II) to elemental manganese that can be seen with naked eye
both in the combusted samples as well as in the X-ray diffraction
patterns.
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