Luminescence and thermal behavior by simultaneous TG/DTG-DTA coupled with MS of neutral copper (I) complexes with heterocyclic thiones

Article abstract of DOI:10.1007/s10973-010-0974-7

Copper(I) halide complexes formulated as [(L)CuX(μ₂-L) ₂CuX(L)] (X = Cl, Br and L = pyridine-2-thione (py2SH), or 4,6-dimethylpyrimidine-2-thione (dmpymtH)) were prepared, and their photoluminescence and thermal properties were investigated. The complexes are strongly emissive in the solid state, with the emissions being dominated by large Stokes shifts (>200 nm), which are depending on both the heterocyclic thione and the nature of the halogen. These emissions can be assigned to MLCT with some mixing of the halide-to-ligand (XL) CT characters. Simultaneous TG/DTG-DTA technique, coupled with MS for the analysis of the gaseous decomposition products, was used for two complexes with the dmpymtH ligand to determine their thermal degradation, which was found to be very complicated. In inert atmosphere the residues at 1,000 °C (verified with PXRD) were a mixture of Cu₂S and CuX, while at 1,300 °C a mixture of Cu ₂S and Cu. In oxygen atmosphere the residues were CuO.

Full text of DOI:10.1007/s10973-010-0974-7

J Therm Anal Calorim (2011) 103:525–531
DOI 10.1007/s10973-010-0974-7
Luminescence and thermal behavior by simultaneous
TG/DTG–DTA coupled with MS of neutral copper (I)
complexes with heterocyclic thiones
P. Aslanidis
M. Lalia-Kantouri
•
V. Gaki
•
K. Chrissafis
•
Received: 23 April 2010 / Accepted: 19 July 2010 / Published online: 11 August 2010
Ó Akad e´ miai Kiad o´ , Budapest, Hungary 2010
Abstract Copper(I) halide complexes formulated as
(L)CuX(l -L) CuX(L)] (X = Cl, Br and L = pyridine-
Introduction
[
2
2
2
-thione (py2SH), or 4,6-dimethylpyrimidine-2-thione
Heterocyclic thiones have attracted considerable interest in
the last three decades because of their relevance in bio-
logical systems [1, 2]. Specific attention has been given to
the study of their binding properties in complexes with
(
dmpymtH)) were prepared, and their photoluminescence
and thermal properties were investigated. The complexes
are strongly emissive in the solid state, with the emissions
being dominated by large Stokes shifts ([200 nm), which
are depending on both the heterocyclic thione and the
nature of the halogen. These emissions can be assigned to
MLCT with some mixing of the halide-to-ligand (XL) CT
characters. Simultaneous TG/DTG–DTA technique, cou-
pled with MS for the analysis of the gaseous decomposition
products, was used for two complexes with the dmpymtH
ligand to determine their thermal degradation, which was
found to be very complicated. In inert atmosphere the
residues at 1,000 °C (verified with PXRD) were a mixture
of Cu S and CuX, while at 1,300 °C a mixture of Cu S and
1
0
closed-shell d metal ions, mainly copper (I) and silver (I).
The metal–ligand interaction in such complexes has been
found to be highly flexible, resulting in an extraordinary
variety of molecular structures [3–5]. However, our long
standing investigations within this field of research resulted
almost exclusively in the isolation of pseudo-tetrahedrally
coordinated symmetrical doubly bridged dicopper species
of the general type [CuX(thione) ] , where X = Cl, Br, I
2
2
[6, 7], or of dinuclear mixed-ligand copper(I) complexes
[CuX(phosphine)(thione)] [7–9].
2
It is recently mentioned, however, the preparation and
structural characterization of two isostructural tetranuclear
2
2
Cu. In oxygen atmosphere the residues were CuO.
complexes [CuX(pymtH)] , where X = Cl, Br [10]. It is
4
Keywords Copper(I) complexes Á Heterocyclic thiones Á
Luminescence Á TG/DTG–DTA Á Coupled TG–MS Á PXRD
interesting that Cu centers have two different coordination
environments, that is CuNSCl in a distorted planar trigonal
geometry and CuNS Cl in a distorted tetrahedral geome-
2
try. The mixed coordinated tetranuclear complex [CuCl
(dmpymtH)] has also been obtained from CuCl with the
4 2
thione ligand in a molar ratio 1:2 [11].
Electronic supplementary material The online version of this
article (doi:10.1007/s10973-010-0974-7) contains supplementary
material, which is available to authorized users.
Much attention has also been paid to emissive copper (I)
complexes in view of practical applications in solar-energy
conversion systems, chemical sensors, or display devises
P. Aslanidis Á V. Gaki Á M. Lalia-Kantouri (&)
Laboratory of Inorganic Chemistry, Department of Chemistry,
Faculty of Sciences, Aristotle University of Thessaloniki,
P.O. Box 135, 54124 Thessaloniki, Greece
[
12–14]. However, most of the studies about copper (I)
complexes with thiones as ligands, are limited to the struc-
tural aspects, and reports on their photochemical properties
are scarce [10]. The computational (DFT and TD-DFT)
methodologies in conjunction with single crystal X-ray
studies have been used to explore the relationship between
structure and luminescence in thione-S ligated copper (I)
e-mail: lalia@chem.auth.gr
K. Chrissafis
Solid State Physics Department, School of Physics,
Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece
123

5
26
P. Aslanidis et al.
complexes bearing tertiary arylphosphanes as bulky spec-
tator ligands [15]. Since it is very interesting to reveal the
impact of the thione ligands on the luminescence properties
of such complexes, four neutral dimeric copper(I) halide
complexes, formulated as [(L)CuX(l -L) CuX(L)], where
X = Cl, Br and L = pyridine-2-thione (py2SH), or 4,6-
dimethylpyrimidine-2-thione (dmpymtH) were studied.
A further important scope of this article pertains to the
study of the thermal properties of the two neutral [CuX
(6.0 ± 0.2 mg) were placed in alumina crucibles. An empty
alumina crucible was used as reference. The compounds
were heated from ambient temperature to 1,400 °C in a
-
1
50 mL/min flow of N or O at heating rate 20 °C min
.
2
2
Continuous recordings of sample temperature, sample
weight, its first derivative, and heat flow were taken.
The structure identification is performed with X-ray dif-
2
2
?
fraction (XRD) analysis using a 2-cycles Rigaku Ultima
diffractometer (40 kV, 30 mA, Cu Ka radiation) with
Bragg–Brentano geometry.
(
dmpymtH)2]2 complexes (X = Cl, Br), by using the
simultaneous TG/DTG–DTA technique in inert and oxi-
dative atmospheres. Simultaneous TG-DTA coupled with
MS was used for the analysis of the gaseous decomposition
products in argon atmosphere, while Powder XRD was
used for the verification of the final solid residues.
General procedure for the synthesis of the neutral
Cu(I) complexes [CuXL ] (1–4)
2
2
The complexes were prepared according to published
procedures [6, 7], in some cases slightly modified. A sus-
pension of 0.5 mmol of copper(I) halide (49.5 mg for
3
Experimental section
CuCl, 71.7 mg for CuBr) in 50 cm of dry acetonitrile was
stirred for 2 h at 50 °C. The resulting clear solution was
filtered off and then treated with a solution of the appro-
priate thione (0.5 mmol) dissolved in a small amount
Materials and instrumentation
3
Commercially available copper (I) halides were purchased
as reagent grade from Aldrich and were used without fur-
ther purification, while the thione ligands were re-crystal-
lized from hot ethanol prior to their use. All the solvents
were purified by respective suitable methods and allowed
to stand over molecular sieves.
(*20 cm ) of ethanol or methanol, and the new reaction
mixture was stirred for additional 30 min at 50 °C. Slow
evaporation of the clear solution at ambient temperature
afforded a microcrystalline solid, which was filtered off
and dried in vacuum. The compounds are moderately sol-
uble in CH CN, CH COCH , and CHCl .
3
3
3
3
Stoichiometric analyses (C, H, and N) were performed
on a Perkin-Elmer 240B elemental analyzer. Metal content
was determined by EDTA titration after decomposition
with nitric acid, using mourexide as indicator. Molar con-
(
(
(
(
1) [CuCl(py2SH) ] : yellow microcrystalline solid, yield
2 2
4
4.5%. Stoichiometry calculated for C H Cl Cu
20 20 2 2
N S : C, 37.38; H, 3.13; Cu, 19.78; N, 8.72. Found: C,
4 4
3
2) [CuBr(py2SH) ] : yellow microcrystalline solid,
7.81; H, 3.14; Cu, 19.87; N, 8.71%.
ductivities were measured in CH CN solutions, employing
3
2
2
a WTW conductivity bridge and a calibrated dip-type cell.
yield 55.0%. Stoichiometry calculated for C H Br
20 20 2
-
1
Infrared spectra in the region of 4,000–200 cm were
obtained in KBr disks with a Nicolet FT-IR 6700 spec-
trophotometer, while a Shimadzu 160A spectrophotometer
and a Hitachi F-700 fluorescence spectrometer were used
to obtain the electronic absorption and emission/excitation
spectra, respectively.
Cu N S : C, 32.83; H, 2.75; Cu, 17.37; N, 7.65.
2
4 4
Found: C, 33.26; H, 3.04; Cu, 17.85; N, 8.11%.
3) [CuCl(dmpymtH) ] : orange microcrystalline solid,
2
2
yield 55.0%. Stoichiometry calculated for C H Cl
2
24
32
Cu N S : C, 37.99; H, 4.25; Cu, 16.75; N, 14.77.
2
8 4
Found: C, 38.25; H, 4.35; Cu, 16.27; N, 14.82%.
4) [CuBr(dmpymtH) ] : orange microcrystalline solid,
The simultaneous TG/DTG–DTA curves were obtainedona
SETARAM thermal analyzer, model SETSYS-1200. The
samples of approximately 10 mg were heated in platinum
crucibles, in nitrogen or argon atmosphere at a flow rate of
2
2
yield 46.4%. Stoichiometry calculated for C H
4 32
2
Br Cu N S : C, 34.0; H, 3.80; Cu, 14.99; N, 13.22.
2
2 8 4
Found: C, 35.25; H, 3.93; Cu, 14.79; N, 12.85%.
8
0 mL/min, within the temperature range 30–950 °C, at a
-1
heating rate of 10 °C min . Mass spectra (MS) of the gaseous
evolved moiety during the experiments were recorded since the
TG apparatus was coupled with a Quadrupole Mass Spec-
trometer (QMS) model Thermostar. The TG was linked to a
heated gas cell of the MS by means of a heated transfer line, at
temperature 180 °C. Data were processed using on-line con-
nected computer system with commercial software Quadstar.
Thermogravimetric analysis was also carried out
with a SETARAM SETSYS TG-DTA 16/18. Samples
Results and discussion
General considerations
The heterocyclic thiones (pyridine-2-thione (py2SH), pyr-
imidino-2-thione (pyrmtH), and 4,6-dimethylpyrimidine-2-
thione (dmpymtH)) are depicted in Scheme 1.
1
23

Luminescence and thermal behavior by simultaneous TG/DTG–DTA
527
4
2
0
0
CH3
0
–
.0
100
DTG
DTA
N
N
80
N
H
S
N
S
N
S
H C
3
H
H
0.2
60
dmpymtH
py2SH
pymtH
Scheme 1 The heterocyclic thiones with their abbreviations
40
TG
0
–0.4
20
355 nm
560 nm
0
200
400
600
800
1000
1200
Temperature/°C
Fig. 3 Thermoanalytical curves (TG/DTG–DTA) of the compound
-
1
[
CuBr(dmpymtH)
2
]
2
in N
2
atmosphere with heating rate 20 °C min
2
50
300
350
400
450
500
550
600
650
analysis, gave good correlation. In this complex, the
dmpymtH thione behaves as monodentate ligand, through
the exocyclic sulfur, in two coordination modes (as bridging
to the two copper atoms and as free neutral thione)
Wavelength/nm
Fig. 1 Room temperature solid state excitation and emission spectra
of [CuCl(py2SH)
2 2
]
(
Scheme 2). This compound is similar with the [CuBr
pymtH) ] [7], possessing a trans Cu-halide configuration,
(
2
2
0
–
–
–
.0
100
DTG
while in [CuI(py2SH) ] [6] and [CuI(pymtH) ] [10] the
2
2
2 2
Cu–I configuration is cis. This knowledge provides a useful
basis, for predicting the structure of the yet unknown
analogous complexes.
2
0
80
60
40
20
DTA
0.2
0.4
0.6
Spectroscopy (UV–Vis and IR)
TG
The electronic absorption spectra of the complexes,
recorded in chloroform at room temperature, showed three
intense broad bands with maxima in the 227–241, 286–318,
and 353–383 nm regions, respectively. With reference to
the absorption spectra of the uncoordinated thiones, the two
high energy bands can be attributed to intraligand p ? p*
transitions on the phenyl groups of the thiones, whereby the
lower energy band should be considered as a p ? p*
transition located at the C=S bond of the thiones [6, 7, 16].
The infrared spectra, recorded in the range
0
0
200
400
600
800
1000
1200
Temperature/°C
Fig. 2 Thermoanalytical curves (TG/DTG–DTA) of the compound
-
1
[
CuCl(dmpymtH)
2
]
2
in N
2
atmosphere with heating rate 20 °C min
All the complexes are air stable, yellow to orange
-
1
microcrystalline solids. They were characterized as neutral
diamagnetic compounds with the formula [CuX(thione)2]2
by means of elemental analysis, conductivity measure-
4,000–250 cm , contain the characteristic four ‘‘thioamide
-
1
bands’’ (1562, 1825, 985, and 732 cm ), required by the
presence of the heterocyclic thione ligands, with shifts due
to coordination indicative of an exclusive S-coordination
ments (they show no conductance in CH CN solutions),
3
-
1
and FT-IR spectra. The Powder XRD of all the studied
compounds was recorded and their patterns are given as
supplementary materials in Figs. 1, 2, 3, 4.
mode, as well as a broad band in the 3,100–2,900 cm
region assigned to the m(NH) stretching vibration, over-
lapped with aliphatic CH stretching.
The crystal structure of the studied compound [CuCl
(
dmpymtH) ] (3) was recently confirmed, by single crystal
2
Luminescence
2
X-ray diffraction analysis, as dinuclear copper(I) com-
pound, [(thione)CuCl(l -thione) CuCl(thione)] [16]. Com-
parison of the experimental XRD pattern of the complex
Room temperature photoexcitation at 350–390 nm of solid
samples of the investigated complexes containing py2SH
and dmpymtH thiones produces an intense broad emission
2
2
(
3) with the theoretical one, derived from the crystal
123

5
28
P. Aslanidis et al.
of type Cu(I) ? halogen. However, the participation of the
halogen in the emissive excited states, in the form of a
ligand-to-metal charge-transfer (XMCT) or an interligand
charge-transfer (VLCT, X ? thione) cannot be excluded.
In fact, according to recent results [17], a redistribution of
charge in terms of transfer from the halogen to the thione
unit appears likely in the complexes under investigation. In
this respect, there is a dependence of the emission maxima
on the kind of the halide present, with a remarkable red
shift in the order Br ? Cl. The differences in the Stokes
shifts observed for the compounds with the same halogen
could be attributed to the electronic properties of the
respective thione, which considerably affect the Cu–S bond
strength. Recent studies on complexes of the type CuXL
Cu S
2
*
CuBr
#
* #
*
*
*
*
*
*
*
*
*
*
*
*#
*
*
#
*
20
30
40
50
60
70
80
2
θ/°
(L = heteroaromatic unit) revealed that the emissive
excited state strongly depends on the electrophilic char-
acter of L [18], while on polynuclear copper(I) complexes
with chalcogen ligands the emission at *570 nm could be
ascribed as an LMCT (S ? Cu) [10].
Fig. 4 Powder XRD diffraction pattern of compound [CuBr(dm-
pymtH) under N
atmosphere at 1,000 °C. Cu–S phases: PDF #72-
966 (Cu7.2 ), 29-0578 (Cu1.96S), 72-1071 (Cu S), 65-3816 (Cu S),
2
]
2
2
1
S
4
2
2
and CuBr phases: PDF #82-2120 (CuBr) [26]
The fluorescence observed in a number of dimeric or
tetrameric complexes of copper(I) halides with metal–metal
distances lower than the sum of the van der Waals radii (2.8
˚
A) has been often assigned to metal–metal bonding inter-
NH
actions [19–21]. The CuÁÁÁCu separation in the studied
compounds is clearly above this limit; thus, inter-metallic
interactions are quite unlikely to participate in any excited
states responsible for the observed emissions.
S
S
S
X
S
HN
Cu
Cu
NH
X
HN
Thermal decomposition
TG/DTG–DTA in nitrogen
Scheme 2 Structure of the neutral copper(I) complexes [(L)CuX
-L) CuX(L)] (X = Cl, Br)
(
l
2
2
The thermal decomposition for two compounds under
investigation [CuCl(dmpymtH) ] and [CuBr(dmpymtH) ] ,
2
2
2 2
Table 1 Solid state excitation and emission maxima for Cu(I)
compounds at R.T
was studied in N and O atmospheres by TG-DTA. The
2 2
released gaseous products were examined by coupled
TG–MS, while the solid residues by powder XRD.
Compound
Excitation, kmax/nm
Emission, kmax/nm
Thermoanalytical curves (TG/DTG–DTA) for the com-
pounds [CuCl(dmpymtH) ] and [CuBr(dmpymtH) ] in
1
2
3
4
[CuCl(py2SH)
[CuBr(py2SH)
[CuCl(dmpymtH)
2 2
[CuBr(dmpymtH) ]
2
]
2
355
371
350
332
560
545
572
546
2
2
2 2
2 2
]
nitrogen atmosphere are given in Figs. 2 and 3, respectively.
The shape of the mass loss is very complicated. It pre-
sents three different areas of mass loss, and each area starts
before the ending of the previous one. For this reason it is
very difficult to correspond to different areas of mass loss
in a specific way of decomposition of the compound.
Using mass loss and derivative mass loss plots (TG/DTG)
we can conclude that: under nitrogen, in the first stage
(110–470 °C), the compound [CuCl(dmpymtH) ] (Fig. 2)
2 2
]
band with peak maxima for the neutral complexes in the
region 545–572 nm (Table 1). The representative excita-
tion and emission spectra of [CuCl(py2SH) ] is depicted
2
2
in Fig. 1. The most characteristic feature of the emission
spectra is the large Stokes shifts ([200 nm), much larger
than the ones observed for the free thiones. These emis-
sions cannot be considered as one of pure intraligand ori-
gin, because of their significant red shifts relative to the
solid state R.T. emission spectra of the free ligands, but
appear to be more compatible with an MLCT excited state
2
2
shows sudden mass loss (DTG peak at 264 °C) of 47.5%,
which coincides with the release of two thione ligands with
a theoretical mass loss of 36.9% plus a moiety that it was
not possible to be identified due to the continuing decom-
position. The DTA curve shows one sharp endothermic
1
23

Luminescence and thermal behavior by simultaneous TG/DTG–DTA
529
peak at 238 and a broader one (as shoulder) at 290 °C. The
first peak is attributed to simultaneous melting and
decomposition of the compound, as it was evidenced with
automated melting point capillary tube system in static air
It is also referred, according to XRD measurements, that
the residues at 1,200 °C for Cu(I) thiocarbamates in inert
atmospheres were consisted from Cu S and Cu [23, 24],
2
while a more recent study on mixed valence copper (I, II)
salt gave both copper sulfides (Cu1.8S and CuS) [25].
(mp. at 233–236 °C), while the next one to further
decomposition.
Upon increasing the temperature, the unstable interme-
diates undergo further decompositions with gradually mass
loss during the second and third stages (470–790 and
TG/DTG–DTA in oxygen
The shape of mass loss plots is quite different in the two
atmospheres, while the decomposition in both atmospheres
is very complicated. Thermoanalytical curves (TG/DTG–
DTA) for the compounds [CuCl(dmpymtH)2]2 and
[CuBr(dmpymtH) ] in oxygen atmosphere are given in
7
90–1,300 °C) of 27.7%, which could be attributed to
further elimination of the remaining thione molecules.
Efforts to isolate the intermediates were not successful due
to their continuous decomposition, as it was evidenced
from the TG curves, while the mass losses at these stages
cannot be attributed to certain species. The amount of the
solid residue, estimated from the TG curve (found 24.8%),
2
2
Figs. 5 and 6, respectively. The decomposition rate of the
compounds under O atmosphere becomes larger than the
2
one under N atmosphere, and at around 600 °C they have
2
with the calculated value for Cu S 21.0% and metallic
2
lost the major quantity of their mass. In details, in the first
stage (100–445 °C), the compound [CuCl(dmpymtH)2]2
(Fig. 5) shows sudden mass loss (DTG peak at 300 °C) of
32.4%, which is lower than the release of two thione ligands
(calc. 36.9%). The DTA curve shows one small endothermic
peak at 235 °C, which is attributed to the melting and further
decomposition of the compound.
copper 16.7% denotes that the decomposition of this
compound at 1,300 °C was not completed.
For the compound [CuBr(dmpymtH) ] (Fig. 3), in the
2
2
first stage (120–480 °C) with DTG peaks at 260 and
90(sh) °C, the sudden mass loss of 47.4% coincides with
2
the release of two dmpymtH ligands with a theoretical
mass loss of 33.1% plus a moiety that it was not possible to
be identified due to the continuing decomposition. The
DTA curve shows a sharp endothermic peak at 235 °C,
which is attributed to simultaneous melting and decom-
position of the compound.
In the second stage (445–610 °C), the decomposition
rate (DTGmax at 390 °C) is higher than in N with a sudden
2
mass loss of 35.5% denoting the elimination of two thione
ligands. This decomposition is strongly exothermic with
DTA peaks at 425 and a doublet at 490, 520 °C, which
means that maybe an oxidation takes place along with the
decomposition. The residue at 1,300 °C, as it is measured
by TG, coincides well with the theoretical amount of CuO
(found 20.7%, calc. 20.9%).
The second and third stages (480–720 and 720–1,300 °C)
with mass loss of 36.0% found contribute to the further
decomposition of the possible intermediates [CuBr(dm-
pymtH) ] and [Cu(dmpymtH) ]. The final solid residue at
2
2
2
1
1
1
,300 °C in nitrogen, estimated from the TG curve (found
7.6.0%) cannot be attributed only to metallic copper (calc.
The thermal decomposition profile of the compound
[CuBr(dmpymtH) ] under O (Fig. 6) is quite similar with
2
2
2
5.0%) or to Cu S (calc. 18.8%), and there is no evidence on
2
the profile of the compound [CuCl(dmpymtH) ] . The only
2 2
the DTA curve for melting of copper at 1,084 °C. On the
other hand, there is a small, well-defined endothermic peak
at 1,100 °C for both studied copper compounds under
nitrogen, which is probably due to the melting point of Cu2S
difference is that it presents a large plateau in the range
0.0
100
1
1
60
20
(
1,130 °C).
In order to verify the solid residues, as they deduced and
DTG
8
6
4
0
0
0
–
0.4
estimated from the TG and DTG curves of the studied
copper compounds, powder XRD studies were used in the
case of the compound [CuBr(dmpymtH) ] . It was found
80
40
0
2
2
–0.8
that the solid material, at 1,000 °C during decomposition in
N , consists mainly of Cu S, while some peaks could also
2
2
–
1.2
TG
DTA
be assigned to CuBr (Fig. 4). Analogous intermediates
were found in the literature, according to their TG curves,
I
on complexes of the type [Cu XL] (L = heteroaromatic
20
n
–1.6
0
200
400
600
800
1000
1200
unit) where the residue above 400 °C corresponds to CuCl
Temperature/°C
[
10], while for the Cu(I) complexes of type [(tpp)Cu
(
m-Cl) Cu(tppp)] (tpp = triphenylophospine) corresponds
2
Fig. 5 Thermoanalytical curves (TG/DTG–DTA) of the compound
-1
0
to metallic copper (Cu ) at 600 °C [22].
[CuCl(dmpymtH)
2
]
2
in air with heating rate 20 °C min
123

5
30
P. Aslanidis et al.
TG–MS
DTG
100
0.0
By the analysis of the evolved gases, performed by on-line
coupling an MS spectrometer to the thermobalance, the
proposed decomposition stages can be confirmed. Exami-
nation of the ionic current profiles during decomposition in
inert, under argon atmosphere of the investigated com-
pounds, has shown the presence of small molecules released
at the 200–480 and 480–700 °C temperature ranges, which
correspond to the decomposition stages I and II, respectively.
In the MS spectra of the thermal decomposition released
gases of the copper (I) complexes, the detected masses for
the first stage (DTGmax 260 °C) with m/z: 17, 28, 32 and 44
are assigned to ammonia (NH ), nitrogen (N ) or ethylene
4
2
0
0
0
8
6
4
0
0
0
–
–
0.2
0.4
TG
DTA
800
20
0
200
400
600
1000
1200
Temperature/°C
3
2
Fig. 6 Thermoanalytical curves (TG/DTG–DTA) of the compound
-
1
[
CuBr(dmpymtH)
2
]
2
in air with heating rate 20 °C min
(CH =CH ), sulfur (S) or hydrazine (NH –NH ) and car-
2 2 2 2
bon monosulfide (CS), respectively. The fragments with
m/z: 16(CH ) and 42 (CH –CH=CH ) are also detected,
4
3
2
giving evidence for the rupture of the bonds inside the
dimethyl-pyrimidino thione ligand. All the detected ions
derived from the fragmentation of the thione ligands, after
the break of the coordination bonds between copper and
ligands (Cu–S bonds) and the rupture of bonds inside the
ligands, confirmed the proposed fragmentation pattern with
the elimination of the ligand molecules, estimated by the
mass loss on the TG/DTG curves.
CuO
*
*
*
For the second stage (DTGmax 690 °C) the masses m/z:
7, 18, and 28 could be assigned to ammonia, water
*
1
*
*
*
*
*
*
vapor(H O), and nitrogen or ethylene, respectively, giving
2
*
*
evidence for the elimination of further fragments of the
2
0
30
40
50
60
70
80
2
θ/°
NH
Fig. 7 Powder XRD diffraction pattern of compound [CuBr(dm-
pymtH) under O
268 (CuO) [26]
2
]
2
2
atmosphere at 1,300 °C. CuO phase PDF #80-
1
S
S
S
X
S
HN
Cu
Cu
NH
6
10–1,100 °C, which could be attributed to the intermediate
X
Cu S (found 25.1%, calculated 18.8%) or to CuS (calcu-
2
lated 22.5%) or to CuBr (calculated 26.4%). Evidence for
2
HN
the presence of Cu S gives the small sharp endothermic
2
peak on the DTA curve at 1,100 °C, although the XRD gave
only CuO.
S
–2
HN
The final residue at 1,300 °C as it is measured by TG
coincides well with the theoretical amount of CuO (found
1
8.8%, calc. 18.8%) and verified from the results of the
S
X
X
powder XRD analysis (Fig. 7), in accordance with the lit-
erature findings [23].
HN
Cu
Cu
NH
S
Decomposition mechanism Taking into account the
results coming from the TG/DTG measurements and the
XRD analysis of the solid intermediate and residue mate-
rials, of the thermal decomposition in nitrogen atmosphere,
we propose a general decomposition pathway for the
complexes under investigation in Scheme 3.
Cu S + CuX
2
Cu S + Cu
2
Scheme 3 Proposed decomposition pathway in nitrogen atmosphere
1
23

Luminescence and thermal behavior by simultaneous TG/DTG–DTA
531
ligands. Beyond 790 °C, the detected mass (m/z: 44),
obtained in broad temperature range, is assigned to carbon
monosulfide (CS).
thione ligands: crystal and electronic structures (DFT) of [CuCl(py-
2
mtH)(dppp)], [CuBr(dppp)], [Cu(l-I)(dppp)] . Inorg Chem. 2002;41:
6875–86.
1
1
0. Li D, Shi W-J, Hou L. Coordination polymers of copper(I)
halides and neutral heterocyclic thiones with new coordination
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1. Mandal TN, Roy SN, Barik AK, Gupta S, Butcher RJ, Kar SK.
Unusual complexation of Cu(II) by pyrimidine/pyridine-pyrazole
derived ligands exploiting the molecular function of 2-mercapto-
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2. Scaltrino DV, Thompson DW, O’Callaghan JA, Meyer GJ.
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13. Mc Millin DR, McNett KM. Photoprocesses of copper complexes
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Conclusions
The determination of the emissive excited states in the
compounds under investigation is a difficult task, with
research in this area being yet in the beginnings. The results
of this study provide some promising qualitative trends that
could be useful as a basis for further investigations. The
complexes are strongly emissive in the solid state at ambient
temperature, with the emissions being dominated by large
Stokes shifts ([200 nm), which are depending on both the
heterocyclic thione and the nature of the halogen. The
emissions of these compounds can be assigned to metal-to-
ligand charge-transfer (MLCT) excited states with some
mixing of the halide-to-ligand (XL) CT characters. The
thermal decomposition of the title compounds under both
atmospheres is very complicated giving multi-step TG/DTG
curves. The decomposition starts with the elimination of the
thione ligands in small fragments proved by the coupled
1
1
16. Falcomer VAS, Lemos SS, Batista AA, Ellena J, Castellano EE.
Mono- and dinuclear copper(I) complexes with methyl substi-
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1
1
1
7. Pawlowsky V, Kn o¨ r G, Lennartz C, Vogler A. Luminescence and
theoretical studies of Cu(tripod)X [tripod = 1,1,1-tris(diphenyl-
TG–MS. The XRD gave mainly Cu S and traces of CuBr as
2
-
phosphanylmethyl)ethane; X = halide, thiophenolate, phenyl-
acetylide]. Eur J Inorg Chem. 2005;15:3167–71.
intermediates at 1,000 °C. The final residue at 1,300 °C is a
mixture of Cu S and metallic Cu, as it was calculated by TG
2
8. Araki H, Tsuge K, Sasaki Y, Ishizaka S, Kitamura N. Lumines-
cence ranging from red to blue: a series of copper(I)–halide
complexes having rhombic Cu (l - X) (X = Br and I) units
measurements. In the case of O atmosphere the final residue
2
of all the compounds, as verified from the results of the
powder XRD analysis, is CuO and its value, as it is measured
by TG, coincides well with the theoretical amount of CuO.
2
2
with N-heteroaromatic ligands. Inorg Chem. 2005;44:9667–75.
9. Rath NP, Holt EM, Tanimura K. Fluorescent copper(I) com-
plexes: structural and spectroscopic characterization of bis
(
p-toluidine)bis(acetonitrile) tetraiodotetracopper and bis[p-chlo-
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123