Heteroleptic tri-tert-butoxysilanethiolate complexes of manganese(II): Thermal studies

Article abstract of DOI:10.1007/s10973-007-8088-6

The thermal behavior of Mn(II) silanethiolate series [Mn(SR) ₂L(MeOH)_n], where R=SSi(OBut)₃, L=heterocyclic nitrogen base and n=0, 1 or 2 has been comparatively investigated using differential scanning calorimetry (DSC), t

Full text of DOI:10.1007/s10973-007-8088-6

Journal of Thermal Analysis and Calorimetry, Vol. 88 (2007) 2, 463–470
HETEROLEPTIC TRI-TERT-BUTOXYSILANETHIOLATE COMPLEXES
OF MANGANESE(II)
Thermal studies
1
Anna KropidÓowska , M. Strankowski , Maria Gazda and Barbara Becker
*
2
3
1
1
Inorganic Chemistry Department, GdaÕsk University of Technology, Narutowicza Str. 11/12, 80-952 Gdañsk, Poland
Polymer Technology Department, Chemical Faculty, GdaÕsk University of Technology, Narutowicza Str. 11/12
2
8
0-952 Gdañsk, Poland
3
Faculty of Applied Physics and Mathematics, GdaÕsk University of Technology, Narutowicza Str. 11/12, 80-952 Gdañsk, Poland
t
], where R=SSi(OBu )
The thermal behavior of Mn(II) silanethiolate series [Mn(SR)
2
L(MeOH)
n
3
, L=heterocyclic nitrogen base and
n=0, 1 or 2 has been comparatively investigated using differential scanning calorimetry (DSC), thermogravimetry (TG) and
TG-infrared spectoscopy (IR) techniques. The TG curves indicate the differences in the thermal decomposition due to presence of
distinct N-donor ligands and labile MeOH molecules coordinated to the central atom. The first step on the TG curves (60–110°C)
corresponds to the elimination of alcohol from respective complexes. The main step (150–350°C) can be assigned to the decomposi-
3 4
tion of the complexes yielding Mn O and silica as the main final products, identified by X-ray diffraction patterns.
Keywords: manganese(II) complexes, metal thiolates, pyridine, silanethiolate, thermal analysis
Introduction
by the ‘a’ class metals which show greater affinity to
ligands with hard oxygen than soft sulfur atom. The
thermal behavior of complexes (mainly with
O-donors) based on Mn(II) is widely discussed in the
literature [6–8] what is in sharp contrast to Mn(II)
thiolate complexes. Till now, the conditions of
thermal decomposition of various complexes of
manganese(II) with such rests as thiolate have not
been studied. A survey of the available literature also
shows that relatively little work on thermal
decomposition of other complexes with Mn–S bond
[9–14], as well as silanethiolates [15] has been done
so far. Recently, we have reported on syntheses of a
series of heteroleptic manganese(II) tri-tert-butoxy-
silanethiolates incorporating solvent molecules
(MeCN, MeOH) [16], chelating N-donors (phen,
bipy, neo) [17] and monodental N-donor ligands (Py,
MePy, ImH, etc.) [18, 19] as coligands. What more,
we have found that the complex with
2-methylimidazole is in fact a N–H···S hydrogen
Thiolate complexes still attract much attention, since
they can be widely used in medicine, agriculture, in-
dustry or analytical and organic chemistry [1]. Model
compounds of several biologically relevant
species [2] should be also mentioned. The knowledge
of thermal behavior is a very important feature espe-
cially in industry since a given substance must be suf-
ficiently stable for an effective action. Therefore, the
interest in the stability of thiolates has been recently
greatly enhanced because of their utilization as cata-
lysts [3] or precursors of sulfides thin films [4].
TG is the simplest method that can be utilized to
determine the compound stability within the given
temperature range or the mode of its thermal
decomposition. Not only the well-established
thermogravimetry but also DSC techniques have been
reliably used over last decades in characterization of
many organic compounds (particularly solids) as well
as studying the thermal behavior and properties of
various types of complexes and evaluating the
thermal parameters for their degradation processes
bonded
[Mn{SSi(OBu ) } (2-MeIm)]
assembly
of
two
complexes
and
[Mn{SSi(OBu ) } (2-MeIm)(MeOH)] [18]. The last
t
3
2
t
3
2
[
5]. Numerous coordination compounds of transition
one has MnNOS core closely related to the ZnNOS
2 2
metals with S-donor ligands have been investigated
nevertheless the thermal analysis in the case of earlier
kernel of horse liver alcohol dehydrogenase catalytic
site. Now, we have focused our attention on thermal
properties of these species, since this is one of the
most important factors, which have to be considered
if we want to think about application of these
st
transition elements comparing to the later 1 row ones
seems to be undeveloped. It is associated with a small
number of known S-donor ligated complexes formed
*
Author for correspondence: anna@urethan.chem.pg.gda.pl
1
388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
©
2007 Akadémiai Kiadó, Budapest

KROPID˜OWSKA et al.
complexes. This work presents the results obtained
The final products of thermal decomposition
process were obtained in an oven at the same temper-
ature and atmosphere that they appeared in the TG
curves. After 15 min they were cooled down and kept
in a desiccator under vacuum. The X-ray patterns of
the crystalline residues were recorded in the room
temperature using X’Pert Philips diffractometer
when a series of 11 manganese(II) silanethiolate
complexes (2–12) with various additional N-donor
ligands have been investigated using TG, DSC and
TG coupled with IR.
Experimental
(source radiation: CuK , l=0.1546 nm, 40 kV,
3
a1
0 mA). For characterization and qualitative analysis
the results were compared with standard data from the
International Centre for Diffraction Data [20].
Complete details of the syntheses and characteriza-
tion of the title complexes as well as their structure
are published elsewhere [16–19]. Table 1 presents the
formulae of studied compounds.
Thermal analysis (TG and DTG curves) was per-
formed using PerkinElmer Thermogravimetric Ana-
Results and discussion
–
1
lyzer TGA Pyris 1 at a heating rate of 20°C min un-
der nitrogen flow and heating program 25–600°C.
DSC measurements were made using
PerkinElmer DSC 7 for encapsulated (aluminum
pans) samples of ca. 3–10 mg at a heating rate of
Recently we synthesized and described the structure
of a series of manganese(II) silanethiolate complexes,
among them species with solvent molecules as
t
coligands, e.g., [Mn{SSi(OBu ) } (MeOH) ] 1. Un-
4
3
2
fortunately 1 was extremely unstable and quickly de-
composed, what actually can be considered as a typi-
cal property of a hitherto sparse Mn(II) thiolates. In
the search of a more stable species we decided to syn-
thesize complexes with additional N-donor ligands
such as bipyridine, imidazole or pyridine and their de-
rivatives. Here we discuss the thermal stability of
complexes 2–12 and describe their thermal decompo-
sition with emphasis on dependence between struc-
ture and thermal stability, what is a key factor for ap-
plicability of these systems.
–
1
2
0°C min under nitrogen flow. Samples were heated
to melting point (pre-determined using automatic Stu-
art MP3 device) and then cooled. The second melting
scan was also performed. The calibration of the tem-
perature and heat flow scales at the same heating rate
was performed with In and Zn.
Thermal analysis coupled with IR was per-
formed in a flow of argon using Netzsch thermo-
balance TG 209 coupled with Bruker IFS66 FTIR
spectrometer. Approximately, 10 mg samples were
contained in an Al O crucible. The volatiles evolving
2 3
from the heated sample were transported to the spec-
trometer chamber via thermostated pipe in the stream
of argon.
Heteroleptic Mn(II) silanethiolates with chelating
heterocyclic bases as coligands
Infrared spectra of solid residues were recorded
on a FTIR Mattson Genesis II Gold, externally con-
trolled by WinFirst software. Spectra were registered
The TG-DTG curves, which characterize the thermal
decomposition of the heteroleptic Mn(II) silane-
thiolate complexes 2–5 are given in Fig. 1 (a, b re-
spectively). The results are summarized in Table 2.
The differences in the thermal decomposition behav-
–
1
in solid state (KBr pellet) in the range 4000–400 cm .
Fig. 1 a – TG and b – DTG curves for 2–5 measured in dynamic nitrogen atmosphere
464
J. Therm. Anal. Cal., 88, 2007

HETEROLEPTIC TRI-TERT-BUTOXYSILANETHIOLATE COMPLEXES OF MANGANESE(II)
J. Therm. Anal. Cal., 88, 2007
465

KROPID˜OWSKA et al.
Table 2 Comparison of main thermal parameters of compounds 2–5
DSC
DSC
T range/°C
DSC
DH/kJ kg
DTGmax
°C
/
DTG Total mass
T range/°C loss found/%
Solid decomposition
products
Complex
–1
Tmax/°C
2
301.1
01.4
297–303
44.91
349.6
211–386
64–130
84.4
84.0
SiO , Mn
2
3
O
4
, MnS, Mn
1
56–105
242-260
36.78
27.37
89.8
250.4
3
258.1
SiO
2
, Mn
3
O
4
, MnS, SiS
2
2
73.4
146–347
175–280
157–376
4
5
260.4
335.7
256–262
334–337
79.4
263.3
351.7
83.6
82.4
SiO
2
136.8
SiO
, Mn
3 4
O
2
Changes in the heat flow during process of con-
trolled heating were studied by means of Differential
Scanning Calorimetry. The first heating scan, cooling
and the second heating run were registered. In Fig. 2
the first heating scan is presented since all examined
compounds melt with decomposition and recorded
sharp peaks refer to slopes on TG curve.
Thermal stability of [Mn{SSi(OBu )
t
}
(N–N)]
3
2
series (where N–N=phen, bipy, neo) can be thus or-
dered in relation to the heterocyclic bases (N–N) used
as: neo (5)>phen (2)>bipy(4). In the case of com-
pound with MeOH molecule coordinated to manga-
nese (3) the process takes place in lower temperature
range and a peak with maximum at about 101°C rep-
resents endothermic process of MeOH evolving.
For compounds 2, 4 and 5 also mass spectra were
recorded [17]. Although parent ions could not be
seen, the spectra give us some insight into the possi-
ble fragmentation pattern through elimination of
Fig. 2 DSC curves for 2–5 recorded in dynamic nitrogen at-
mosphere
ior of these complexes are evident. Close examination
of the TG-DTG curves (Fig. 1) reveals that in the case
of 2, 4 and 5 a decomposition process proceeds in
one-step (at the 211–386°C range for 2, at the
t
t
OBu and Si–OBu fragments from tri-tert-
butoxysilanethiolate ligand. It is worth mentioning
that such fragmentation mode is different from that
observed for closely related complexes but with Cd
1
75–280°C range for 4 and at the wide 157–376°C
range in the case of 5). In the case of methanol con-
taining compound 3 its decomposition proceeds in
two consecutive steps. In the first step elimination of
approximately 1 mol of MeOH per 1 mol of 3 (mass
loss found 3.6%; calculated 3.88%) is observed using
not only TG, but also DSC measurements (Fig. 2).
The maximum rate of alcohol detach takes place at
about 100°C. Decomposition of the complex contin-
ues in the second step, represented by a sharp slope on
the TG curve. It should be noted that complex 3 dried
at room temperature in a stream of argon simply elim-
inates methanol and yields complex 2 [17]. It is evi-
dent that under applied thermal conditions the elimi-
nation of methanol from 3 does not simply lead to the
transient formation of 2 since the second decomposi-
tion step of 3 is different from that observed for 2.
[
21] and Zn [22] in the metallic center, where the
main fragmentation pattern is characterized by
stepwise elimination of butene (m/z 56) molecules.
XRD measurement have shown that the final
products of thermal decomposition of manganese(II)
silanethiolate complexes containing chelating bases
as additional ligands consists mainly of manganese
oxide and silica. This corresponds well with strong IR
absorption (v(Si–O) 1080 cm ) found in spectra of
the solid residues. Small quantities of sulfur, silicon
disulfide, manganese sulfide and metallic Mn are also
present (Fig. 3).
Thermobalance coupled with FTIR spectrometer
allowed the recording of IR spectra of volatiles
released during decomposition process (Figs 4, 5).
One can see, e.g., that during the initial steps of
thermogravimeric analysis methanol released in the
case of 3 can be found in IR spectra (v(O–H)
–
1
The curve
Mn{SSi(OBu ) } (neo)] 5 is very similar to the one
3 2
TG
recorded
for
t
[
–
1
–1
–1
for phenanthroline derivative 2, but the thermal deg-
radation starts at slightly lower temperature.
3
temperatures fragments of heterocyclic bases (about
2
650 cm , v(C–H) 2983 cm , 2888 cm ). At higher
–
00°C, v(C–H) 3022 cm ) and tri-tert-butoxysilyl
1
466
J. Therm. Anal. Cal., 88, 2007

HETEROLEPTIC TRI-TERT-BUTOXYSILANETHIOLATE COMPLEXES OF MANGANESE(II)
in the first decomposition steps. Table 3 compares
characteristic thermal parameters taken from the TG,
DTG and DSC curves. Mass losses obtained from the
TG curves and those calculated for the corresponding
molecules are in relatively good agreement as is the
case of all investigated species 2–12. The XRD mea-
surements confirmed that compounds 6–8 decompose
with the formation of silica and manganese oxide as
the main end product.
Heteroleptic Mn(II) silanethiolates with pyridine and
picolines as coligands
Fig. 3 XRD patterns for products of thermal decomposition of
, 4 and 5
The process of decomposition of manganese(II)
silanethiolate complexes incorporating pyridine and
its methyl substituted derivatives is presented in
Fig. 8. In the case of methanol containing complexes
9 and 10 the first steps of decomposition indicate the
loss of alcohol molecules. It is observed in the TG
curves of 9 and 10 at 60–80°C range with the maxi-
mum rate of mass loss in the DTG curves at tempera-
tures of 70.3 and 65.5°C respectively. In the first step
2
–
1
–1
rest (v(C–H) 2981 cm , v(Si–OC) 1078 cm , Fig. 5)
are evolved from 3 and 5. IR spectra of volatiles
evolving during TG analysis of all three
t
[
Mn{SSi(OBu ) } (N–N)] complexes are in fact quite
3
2
similar (Fig. 4) suggesting an analogous decompo-
sition pathway.
t
Fig. 4 3D IR spectra of volatiles evolving during TG analysis in the function of temperature for a – [Mn{SSi(OBu )
3
}
2
(phen)] 2,
t
t
t
3 2 3 2 3 2
b – [Mn{SSi(OBu ) } (phen)(MeOH)] 3, c – [Mn{SSi(OBu ) } (bipy)] 4 and d – [Mn{SSi(OBu ) } (neo)] 5
Heteroleptic Mn(II) silanethiolates with molecules
possessing imidazole ring as coligands
Manganese(II) silanethiolate complexes incorporat-
ing imidazole and its methyl derivatives (6–8) decom-
pose progressively (Fig. 6). First, within the tempera-
ture range 45–80°C, methanol molecules are
eliminated from 7 and 8. The corresponding endother-
mic peaks in the DSC curve are visible at 65–75°C
range. Due to the presence of distinct alcohol types –
only solvating in 7 but one solvating and one ligating
in 8 – both compounds lose methanol differently. The
alcohol-free complex 6 begins to decompose at higher
temperature range 150–310°C, with slow elimination
of N-donor molecules coordinated to metallic center
Fig. 5 IR spectra of volatiles evolving during TG analysis of
t
[Mn{SSi(OBu ) } (phen)(MeOH] 3 and
3
2
t
[Mn{SSi(OBu )
3
}
2
(neo)] 5
J. Therm. Anal. Cal., 88, 2007
467

KROPID˜OWSKA et al.
Fig. 6 a – TG and b – DTG curves for 6–8 measured in dynamic nitrogen atmosphere
(
1
up to 75°C) approximately 0.5 mol of MeOH per
mole of 10 is eliminated (mass loss found 2.1%; cal-
higher temperature range (146–256°C for 11 and
172–272°C in the case of 12) what is connected with
the simultaneous release of picoline and fragments of
tri-tert-butoxysilyl group. In fact one can notice a
small inflexion on registered DTG curve for 11 and
12 (at 210–215°C range) and then the main step of de-
composition with a large and sharp peak. It indicates a
rapid and vigorous decomposition feature. The IR
analysis of volatiles evolving during decomposition
as well as the analysis of solid residues indicated that
again similar products as described earlier for other
Mn(II) silanethiolates were formed. The main decom-
position product in the case of 12 was silica while for
culated 2.07%). The following mass loss is most
probably connected with further alcohol release com-
pleted at ca. 150°C. The release of methanol molecule
from both compounds is confirmed also in DSC ex-
periments (Fig. 9).
In the case of complexes without coordinated
solvent molecule the decomposition takes place at
9
–11 manganese oxide, however presence of some
manganese(II) silicate cannot be excluded. Changes
in the heat flow during controlled heating were stud-
ied also by means of DSC. In Fig. 9 the first heating
scan is presented. Peaks on DCS curve represent
melting with decomposition of respective com-
pounds. Performed measurements thus indicate that
the stability
Mn{SSi(OBu ) } (N)(MeOH) ] series depends pri-
3 2 n
thermal
of
t
[
marily on presence of alcohol molecules and then
N-donor ligand used.
Fig. 7 DSC curves for 6–8 recorded in dynamic nitrogen at-
mosphere
Fig. 8 a – TG and b – DTG curves for 9–12 measured in dynamic nitrogen atmosphere
468
J. Therm. Anal. Cal., 88, 2007

HETEROLEPTIC TRI-TERT-BUTOXYSILANETHIOLATE COMPLEXES OF MANGANESE(II)
Table 3 Comparison of main thermal parameters of compounds 6–8
DSC
DSC
T range/°C
DSC
DH/kJ kg
DTGmax
°C
/
DTG
T range/°C
Total mass
loss found/%
Solid decomposition
products
Complex
–1
Tmax/°C
*
6
226.0
5.4
21.7
223–228
41.0
292.6
152–311
87.2
87.1
2 3 4
SiO , Mn O , MnS
6
2
44–68
202–224
28.4
29.4
72.6
212.9
64–76
156–241
7
SiO
2
2
, Mn
, Mn
3
3
O
4
4
7
3.2
30.5
45–76
208–235
63.1
49.3
78.8
274.1
58–72
206–338
8
82.0
SiO
O
2
*
–1
Crystallization parameters for 6: DSC Tmax=171.9°C; DSC DH=–13.4 kJ kg
Table 4 Comparison of main thermal parameters of compounds 9–12
DSC
DSC
T range/°C
DSC
DH/kJ kg
DTGmax
°C
/
DTG
T range/°C
Total mass loss
found/%
Solid decomposition
products
Complex
–1
Tmax/°C
6
2.7
37–65
177–191
22.6
57.5
70.3
245.6
67–79
134–260
9
83.5
81.2
Mn
3
O
4
, SiO
2
189.1
6
4.4
51–66
173–189
53.4
68.6
65.5
248.9
61–77
108–264
1
0
Mn
3
O
4
, SiO
, SiO
2
2
187.6
1
1
1
2
186.1
211.1
178–192
197–213
43.1
70.2
240.5
260.5
146–256
172–272
83.5
83.5
Mn
3
O
4
SiO
2
stoichiometry of the prepared metal complexes. In the
investigated case of metal complexes with
silanethiolate being S-donor ligand and a group of
mutually related N-donor co-ligands, various thermal
decomposition behavior and thermal stability are
clearly observed. This may be attributed to the differ-
ences in N-donors used as well as to the different
mode of silanethiolate coordination capable to serve
as S-donor, but also as S,O-chelating donor. The
shape of endotherms for melting, recorded for manga-
nese(II) silanethiolate species with additional N-do-
nor ligands suggests also, that those compounds can
be easily prepared as crystals of good quality and pu-
rity. The results obtained using Differential Scanning
Calorimetry were compared with those obtained with
standard automatic apparatus for melting point deter-
mination (again in inert gas atmosphere). Therefore it
was possible to confirm finally that changes regis-
tered by DSC correspond to the melting of examined
species.
Fig. 9 DSC curves for 9–12 recorded in dynamic nitrogen at-
mosphere
Conclusions
Thermal stability and changes occurring during con-
trolled heating of manganese(II) tri-tert-butoxy-
silanethiolates were investigated by thermogravi-
metric and calorimetric methods. The measurements
revealed that thermal decomposition of manga-
nese(II) silanethiolate complexes containing addi-
tional ligands such as N-donor heterocyclic bases and
methanol is multistage. Generally the process of
methanol elimination occurs in the first step and the
decomposition of organic ligands in the next one. The
results obtained from the TG and DTG curves con-
firm therefore the presence of MeOH and the
Thermal measurements revealed also that man-
ganese(II)
1
silanethiolate
,10-phenathroline, 2,2’-bipiridine and 2,9-di-
complexes
with
methyl-1,10-phenanthroline as coligands are espe-
cially stable – also in air. These are the first known
manganese(II) thiolate complexes exhibiting such
high stability in normal conditions. This prompted us
to check their applicability in sol-gel related proce-
dures [23] and the vulcanization process of natural
rubber systems [24]. Related work is now in progress.
J. Therm. Anal. Cal., 88, 2007
469

KROPID˜OWSKA et al.
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DOI: 10.1007/s10973-007-8088-6
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