Luminescence and thermal behavior of copper (I) complexes with heterocyclic thiones. Part II: Cationic complexes

Article abstract of DOI:10.1007/s10973-010-1077-1

Copper (I) halide complexes formulated as [(L) ₂Cu(μ₂-L)₂Cu(L)₂]²⁺ 2Χ^-, (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 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 mainly Cu₂S, while at 1,300 °C a mixture of Cu₂S and Cu. In oxygen atmosphere the residues were CuO.

Full text of DOI:10.1007/s10973-010-1077-1

J Therm Anal Calorim (2011) 103:797–803
DOI 10.1007/s10973-010-1077-1
Luminescence and thermal behavior of copper (I) complexes
with heterocyclic thiones. Part II: cationic complexes
P. Aslanidis
•
K. Chrissafis M. Lalia-Kantouri
•
Received: 25 July 2010 / Accepted: 22 September 2010 / Published online: 7 October 2010
Ó Akad e´ miai Kiad o´ , Budapest, Hungary 2010
Abstract Copper (I) halide complexes formulated as
2
Introduction
?
-
[
(L) Cu(l -L) Cu(L) ] 2V , (X = Cl, Br and L = pyr-
2
2
2
2
idine-2-thione (py2SH) or 4,6-dimethylpyrimidine-2-thione
The past three decades heterocyclic thiones have attracted
considerable interest due to their relevance in biological
systems [1, 2]. Specific attention has been given to the
study of their binding properties in complexes with 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 in the isolation of pseudo-tetrahedrally
coordinated symmetrical doubly bridged dinuclear species
of the general type [CuX(thione) ] , where X = Cl, Br, I
(
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 charac-
ters. Simultaneous TG/DTG–DTA technique was used for
two complexes with the dmpymtH ligand to determine their
thermal degradation, which was found to be very compli-
cated. In inert atmosphere the residues at 1,000 °C (verified
2
2
[6, 7] or of mixed-ligand copper (I) complexes
with PXRD) were mainly Cu S, while at 1,300 °C a mixture
[CuX(phosphine)(thione)] [7], or of the general type
2
2
2
?
-
of Cu S and Cu. In oxygen atmosphere the residues were
[Cu (thione) ] 2X (X = Cl, Br) [8, 9]. The stoichi-
2 6
2
CuO.
ometry of these complexes strongly depends on the
molecular ratio of the starting materials. Recently, it is
also referred the preparation and structural characteriza-
tion of two polymers with tetrameric structural units
Keywords Cationic copper (I) complexes Á Heterocyclic
thiones Á Luminescence Á TG/DTG–DTA Á PXRD
[CuX(pymtH)] , (X = Cl, Br) [10], where the Cu centers
4
have two different coordination environments, that is
CuNSCl in a distorted planar trigonal geometry and
CuNS Cl in a distorted tetrahedral geometry. The mixed
2
coordinated cyclic tetramer [CuCl(dmpymtH)] has also
4
Electronic supplementary material The online version of this
article (doi:10.1007/s10973-010-1077-1) contains supplementary
material, which is available to authorized users.
been obtained from CuCl with the thione ligand in a
2
molar ratio 1:2 [11].
In view of practical applications in solar-energy con-
version systems, chemical sensors, or display devises [12–
P. Aslanidis Á M. Lalia-Kantouri (&)
Laboratory of Inorganic Chemistry, Department of Chemistry,
Faculty of Sciences, Aristotle University of Thessaloniki,
P.O. Box 135, 541 24 Thessaloniki, Greece
e-mail: lalia@chem.auth.gr
14], attention has been paid to emissive copper (I) com-
plexes with thiones as ligands, although reports on their
photochemical properties are scarce [10]. The computa-
tional (TD–DFT) methodologies in conjunction with single
crystal X-ray studies have been used to explore the rela-
tionship between structure and luminescence in thione-S
K. Chrissafis
Solid State Physics Department, School of Physics, Aristotle
University of Thessaloniki, 541 24 Thessaloniki, Greece
123

7
98
P. Aslanidis et al.
ligated copper (I) complexes bearing tertiary arylphos-
phanes as bulky spectator ligands [15].
The structure identification is performed with X-ray
diffraction analysis (XRD) using a 2-cycles Rigaku
?
Ultima diffractometer (40 kV, 30 mA, CuK radiation)
In this study, the photoluminescence properties of four
a
cationic dimeric copper (I) halide complexes, formulated
2
with Bragg-Brentano geometry.
?
-
as [(L) Cu(l -L) Cu(L) ] 2V , where X = Cl, Br and
2
2
2
2
L = pyridine-2-thione (py2SH), or 4,6-dimethylpyr-
imidine-2-thione (dmpymtH) were studied. A further
important scope of the present paper was the study of the
General procedure for the synthesis of the Cu(I)
2
complexes [Cu L ] 2X (1–4)
?
-
2
6
2
?
thermal properties of the two cationic [Cu (dmpymtH) ]
2
The complexes were prepared according to the following
procedure [8]. A solution of 0.5 mmol of copper (II)
chloride or bromide in 10 mL of water was treated with an
ethanolic solution of the appropriate thione (2.5 mmol in
20 mL) and the resulting mixture was stirred for 30 min at
ambient temperature. The resulting clear solution was kept
at 5 °C until a microcrystalline solid was formed, which
was filtered off and dried in vacuum. The compounds are
soluble in CH NO , CH OH, CH COCH , and CH Cl .
6
-
X complexes (X = Cl, Br), by using the simultaneous
2
TG/DTG–DTA technique in inert and oxidative atmo-
spheres. Powder XRD was used for the verification of the
final solid residues.
Experimental section
3
2
3
3
3
2
2
2
?
-
Materials and instrumentation
[Cu (py2SH) ]
2
2Cl (1): yellow to orange micro-
crystalline solid, yield 44.5%. Stoichiometry calculated for
C30 H30 Cl Cu N S : C, 41.65; H, 3.49; Cu, 14.70; N, 9.71.
6
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.
2
2 6 6
Found: C, 41.80; H, 3.53; Cu, 15.02; N, 10.02%. Con-
ductivity in CH NO and in MeOH (K = 142.0 and
3
2
183.0 lS/cm, respectively).
2
?
-
2Br (2): yellow to orange micro-
[Cu (py2SH) ]
2
6
crystalline solid, yield 55.2%. Stoichiometry calculated for
C30 H30 Br Cu N S : C, 37.77; H, 3.17; Cu, 13.33; N, 8.81.
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 murexide as indicator. Molar con-
ductivities were measured in CH NO and CH OH solu-
2
2 6 6
Found: C, 38.08; H, 3.21; Cu, 13.65; N, 8.70%. Conduc-
tivity in CH NO and in MeOH (K = 145.3 and 168.0 lS/
3
2
cm, respectively).
2
?
-
2Cl (3): orange to red micro-
[Cu (dmpymtH) ]
2
3
2
3
6
tions, employing a WTW conductivity bridge and a
calibrated dip type cell.
crystalline solid, yield 68.0%. Stoichiometry calculated for
C H Cl Cu N S : C, 41.60; H, 4.62; Cu, 12.23; N,
3
6
48
2
2 12 6
-
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.
16.17. Found: C, 40.99; H, 4.74; Cu, 12.43; N, 15.85%.
Conductivity in CH NO and in MeOH (K = 151.3 and
3
2
194.0 lS/cm, respectively).
2
?
-
2Br (4): orange to red micro-
[Cu (dmpymtH) ]
2
6
crystalline solid, yield 60.6%. Stoichiometry calculated for
C H Br Cu N S : C, 38.33; H, 4.38; Cu, 11.27; N,
3
6
48
2
2 12 6
The simultaneous TG/DTG–DTA curves were obtained
on a SETARAM thermal analyzer, model SETSYS-1200.
The samples of approximately 10 mg were heated in
platinum crucibles, in nitrogen or argon atmosphere at a
14.90. Found: C, 38.08; H, 3.99; Cu, 11.38; N, 14.67%.
Conductivity in CH NO and in MeOH (K = 148.7 and
3
2
204.0 lS/cm, respectively).
-
1
flow rate of 80 ml min , within the temperature range
-
1
3
0–950 °C, at a heating rate of 10 °C min
Thermogravimetric analysis was also carried out with a
SETARAM SETSYS TG–DTA 16/18. Samples
6.0 ± 0.2 mg) were placed in alumina crucibles. An
.
Results and discussion
General considerations
(
empty alumina crucible was used as reference. The com-
The heterocyclic thiones (pyridine-2-thione (py2SH) and
4,6-dimethylpyrimidine-2-thione (dmpymtH)), are depic-
ted in Scheme 1.
pounds were heated from ambient temperature to 1,300 °C
in a 50 ml/min flow of N or O2 at heating rate
-
2
1
2
0 °C min . Continuous recordings of sample tempera-
ture, sample mass, its first derivative and heat flow were
All the complexes are air stable, orange microcrystalline
solids. They were characterized as 1:2 electrolytes with the
2
?
-
2X by means of elemental
taken.
formula [Cu (thione) ]
2
6
1
23

Luminescence and thermal behavior of Cu(I) complexes
799
Spectroscopy (UV–Vis and IR)
CH3
N
The electronic absorption spectra of the complexes,
recorded in chloroform at room temperature, show 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].
The infrared spectra, recorded in the range
N
H
S
N
H
S
H C
3
py2SH
dmpymtH
Scheme 1 The heterocyclic thiones with their abbreviations
analysis, conductivity measurements, and FT-IR spectra.
2
?
The powder XRD of the compounds [Cu (dmpymtH) ]
6
2
-1
-
Cl and [Cu (dmpymtH) ]
2?
-
2Br was recorded, and
4,000–250 cm contain the characteristic four ‘‘thioamide
2
2
6
-
1
bands’’ (1,562, 1,825, 985, and 732 cm ), required by the
presence of the heterocyclic thione ligands, with shifts due
to coordination indicative of an exclusive S-coordination
their patterns are given as supplementary materials in Figs.
s1 and s2.
The crystal structures of the studied compounds
-
Cu (py2SH) ] 2Cl (1) and [Cu (py2SH) ] 2Br (2)
2 6 2 6
-
1
2
?
-
2?
mode, as well as a broad band in the 3,100–2,900 cm
[
region assigned to the m(NH) stretching vibration,
overlapped with aliphatic CH stretching. The FT-IR spec-
were previously confirmed by single crystal X-ray dif-
fraction analysis, as dinuclear copper (I) compound, [(thi-
2
?
-
2?
tra of the complexes [Cu
2
(py2SH)
6
]
2Cl and [Cu
2
one) Cu(l -thione) Cu(thione )] [8]. In these complexes,
2
2
2
2
2
py2SH)6] 2Br are given as supplementary material in
?
-
(
the thione(py2SH) behaves as monodentate ligand, through
the exocyclic sulfur, in two coordination modes (as bridging
to the two copper atoms and as free neutral thione)
2
Fig. s3, while for the complexes [Cu (dmpymtH) ] 2Cl
?
-
2
6
2
?
-
and [Cu (dmpymtH) ] 2Br in Fig. s4. The pair-wise
2
6
presentation of the spectra shows strong similarities of
isomorphous compounds.
(
Scheme 2).
Crystal structures of Cu(I) complexes having the molar
ratio Cu-thione 1:3, have been early reported as 1:1 elec-
?
trolytes for [Cu(py2SH) ] NO [16] and recently for the
-
Luminescence
3
3
?
isomorphous anhydrous monomeric compounds [Cu(tu) ]
3
-
Room temperature photoexitation at 350–365 nm of solid
samples of the investigated complexes containing py2SH
and dmpymtH thiones produces an intense broad emission
band with peak maxima for the cationic complexes in the
region 540–585 nm (Table 1). The representative excita-
X
(tu = thiourea and X = Cl, Br), while as 1:2 electro-
lytes for the isomorphous hydrated dimeric compounds
2
?
-
[
Cu (tu) ]
2
2X Á2H O. The structure of the thiourea
6
2
complexes depends on the molar ratio of copper halide and
the sulfur containing ligand, as well as on the number of
crystallization water molecules [9].
2
?
-
tion and emission spectra of [Cu (dmpymtH) ] 2Br is
6
2
depicted 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 emissions cannot be considered as one of pure intra-
ligand origin, 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 a metal-to-ligand
charge-transfer (MLCT) excited state 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
It is also referred a third isomorphous pair of these
complexes with copper-thiourea stoichiometric ratio 1:1,
[
Cu(tu)]XÁ0.5H O, behaved as 1:1 electrolyte [9].
2
2
+
NH
Cu
NH
S
S
S
S
S
(
VLCT, X ? thione) cannot be excluded. In fact, accord-
N
X–
Cu
2
H
H
ing 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
N
S
HN
HN
2 2
Scheme 2 Structure of the cationic copper (I) complexes [(L) Cu(l -
2?
-
L)
2 2
Cu(L) ]
2V
123

8
00
P. Aslanidis et al.
0.0
0.2
0.4
100
80
Table 1 Solid-state excitation and emission maxima for cationic
Cu(I) compounds at R.T.
–
–
6
4
2
0
0
0
Compound
Excitation,
max/nm
Emission,
k
kmax/nm
–4L (53.9%)
Cu2S Cu S + Cu
2
2
?
?
-
-
(
15.3% + 12.2%)
1. [Cu
2. [Cu
3. [Cu
4. [Cu
2
2
2
2
(py2SH)
6
]
]
2Cl
330
355
365
350
584
576
543
559
8
4
0
2
(py2SH)
6
2Br
2?
-
-
(dmpymtH)
6
]
]
2Cl
2?
(dmpymtH)
6
2Br
–4
0
200
400
600
800 1,000 1,200
Temperature/°C
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 (L = het-
eroaromatic unit) revealed that the emissive excited state
strongly depends on the electrophilic character 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. 2 Thermoanalytical curves (TG/DTG–DTA) of the compound
2?
-
[
Cu
2
(dmpymtH)
-
6
]
2
2Cl in N atmosphere with heating rate
1
20 °C min
53.5%, which coincides with the release of four thione
ligands with a theoretical mass loss of 53.9%. The DTA
curve shows one sharp endothermic peak at 227 and a
second overlapped one (as shoulder) at 255 °C. The first
peak is attributed to simultaneous melting and decompo-
sition of the compound, as it was evidenced with auto-
mated melting point capillary tube system in static air (mp.
at 225–227 °C), while the next one to further decomposi-
tion as the DTG curve implies.
Thermal decomposition
TG/DTG–DTA in nitrogen
The thermal decomposition for two compounds under inves-
2
?
-
tigation, [Cu (dmpymtH) ] 2Cl and [Cu (dmpymtH) ]
2?
Upon increasing the temperature, the unstable interme-
diates undergo further decompositions with gradually and
successive mass loss in the temperature range 460–1,300 °C
of 28.8%, 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 17.7%), with the calculated value
2
6
2
6
-
2
Br , was studied in N and O atmospheres by TG–DTA.
2 2
The solid residues were examined by powder XRD.
Thermoanalytical curves (TG/DTG–DTA) for the com-
2?
2
?
-
pounds [Cu (dmpymtH) ] 2Cl and [Cu (dmpymtH) ]
2
6
2
6
-
Br in nitrogen atmosphere are given in Figs. 2 and 3,
2
respectively.
The shape of the mass loss is very complicated and
resembles the shape of the corresponding neutral com-
pounds [Cu X (dmpymtH) ] [19]. Each area of mass loss
2
2
4
for Cu S 15.3% and metallic copper 12.2% denotes that the
2
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
decomposition of this compound at 1,300 °C was not
completed.
2
?
For the compound [Cu (dmpymtH) ] 2Br (Fig. 3), in
-
2
6
the first stage (130–490 °C) with DTG peak at 264 °C, the
sudden mass loss of 49.9% coincides well with the release
of four dmpymtH ligands with a theoretical mass loss of
2?
-
(
120–460 °C), the compound [Cu (dmpymtH) ]
2Cl
2
6
(
Fig. 2) shows sudden mass loss (DTG peak at 257 °C) of
Fig. 1 Room temperature
solid-state excitation and
emission spectra of
350 nm
559 nm
2?
-
[
Cu
2
(dmpymtH)
6
]
2Br
3
00
350
400
450
500
550
600
650
Wavelength/nm
1
23

Luminescence and thermal behavior of Cu(I) complexes
801
1
8
00
0
100
80
0
.0
0
.0
–
–
0.2
0.4
6
0
–
–
0.2
0.4
60
4
2
0
0
40
20
–4L (49.7%)
–0.6
Cu S
2
(15.3%)
CuO
(15.3%)
Cu S + Cu
(
2
2
1
0
0
0
80
14.1 + 11.2%)
4
0
0
–10
0
200
400
600
800 1,000 1,200
0
200
400
600
800 1,000 1,200
Temperature/°C
Temperature/°C
Fig. 3 Thermoanalytical curves (TG/DTG–DTA) of the compound
[
2
Fig. 4 Thermoanalytical curves (TG/DTG–DTA) of the compound
-
2?
6
]
-
2Br in N
2?
]
-1
Cu
0 °C min
2
(dmpymtH)
-
2
atmosphere with heating rate
[Cu
2
(dmpymtH)
6
2Cl in oxygen with heating rate 20 °C min
1
4
2
9.7%. The DTA curve shows a sharp endothermic peak at
0
.0
100
80
47 °C, which is attributed to simultaneous melting and
–
–
0.2
0.4
6
0
decomposition of the compound.
40
The second and third stages (490–700 and 700–1,300 °C),
with mass loss of 37.6% found, contribute to the further
decomposition of the possible intermediates [CuX(dm-
2
0
–0.6
Cu2S
(14.1%)
CuO
(14.1%)
6
4
2
0
0
0
0
pymtH) ]. The final solid residue at 1,300 °C in nitrogen,
estimated from the TG curve (found 12.5%), could be
2
attributed to metallic copper (calc. 11.2%) but not to Cu2S
0
200
400
600
800 1,000 1,200
(
calc. 14.1%). The DTA curves do not clearly show the
Temperature/°C
endothermic peaks due to the melting of copper at 1,084 °C
or to the melting of Cu S at 1,130 °C.
2
Fig. 5 Thermoanalytical curves (TG/DTG–DTA) of the compound
-
2?
]
-1
In order to verify the solid residues, as they deduced and
estimated from the TG and DTG curves of the studied
copper compounds, powder XRD studies were used in the
[
Cu
2
(dmpymtH)
6
2Br in oxygen with heating rate 20 °C min
2
?
-
case of the compound [Cu (dmpymtH) ] 2Br . It was
2
compounds under O atmosphere becomes larger than the
2
6
found that the solid material, at 1,000 °C during decom-
position in N consists mainly of Cu S, while at 1,300 °C
to metallic copper.
one under N atmosphere, and at around 600 °C they have
2
lost the major quantity of their mass. In details, in the first
?
2
2
2
stage (120–385 °C), the compound [Cu (dmpymtH) ]
2
6
-
It is known that for Cu(I) complexes of type [(tpp)Cu
2Cl (Fig. 4) shows sudden mass loss (DTG peaks at
240(sh) and 270 °C) of 36.9%, which is lower than the
release of three thione ligands (calc. 40.5%). The DTA
curve shows one small endothermic peak at 240 °C, which
is attributed to the melting and further decomposition of the
compound.
(
l-Cl) Cu(tppp)] (tpp = triphenylophospine) the residue at
2
0
600 °C corresponds to metallic copper (Cu ) [20]. It is also
referred, according to XRD measurements, that the resi-
dues at 1,200 °C for Cu(I) thiocarbamates in inert atmo-
spheres consisted of Cu S and Cu [21, 22]. A more recent
2
study on mixed valence copper (I, II) thiosulfate salt gave
both copper sulfides (Cu1.8S, digenite and CuS, covellite) at
about 300 °C range even in flowing air atmosphere [23].
Similarly both sulfides are formed from thiourea solution
In the second and third stages (385–450 and
450–612 °C), the decomposition rate (DTG peaks at 440 and
490 °C) is higher than in N with sudden mass losses of 6.2
2
and 34.2%. These decompositions are strongly exothermic
with DTA peaks at 440 and 490 °C, which means that maybe
an oxidation takes place along with the decomposition.
Finally, an endothermic fourth stage takes place
[
24].
TG/DTG–DTA in oxygen
(612–1,300 °C) with DTG peak at 1,100 °C. The residue at
The shape of mass loss plots is quite different in the two
atmospheres. Thermoanalytical curves (TG/DTG–DTA)
1,300 °C, as it is measured by TG, coincides well with the
theoretical amount of CuO (found 15.9%, calc. 15.3%). For
an analogous copper-thiourea compound [Cu (tu) ]Cl Á
2
for the compounds [Cu (dmpymtH) ] 2Cl and [Cu2
?
-
2
6
2
6
2
2
dmpymtH)6] 2Br in oxygen atmosphere are given in
?
-
(
2H O, the main degradation step in static air led to the for-
2
Figs. 4 and 5, respectively. The decomposition rate of the
mation of Cu1.8S (digenite) at 300 °C, while stoichiometric
123

8
02
P. Aslanidis et al.
amount of the oxides CuO and Cu O was formed at
2
in nitrogen atmosphere, we propose a general decomposi-
tion pathway for the cationic complexes under investiga-
tion in Scheme 3.
*
1,000 °C, proved by powder XRD [25].
The thermal decomposition profile of the compound
2
?
-
[
Cu (dmpymtH) ] 2Br under O (Fig. 5) is quite sim-
2 6 2
2
?
ilar with the profile of the compound [Cu (dmpymtH) ]
2
6
-
2
Cl . The first stage (120–420 °C, with DTG peak at
50 °C) shows sudden mass loss of 32.4%, which is lower
Conclusions
2
than the release of three thione ligands (calc. 37.3%). The
DTA curve shows one small endothermic peak at 250 °C,
which is attributed to the melting and further decomposi-
tion of the compound. The second stage (420–650 °C, with
DTG peak at 520 and DTA exothermic peak at 525 °C)
shows even larger mass loss of 48.5%. A large plateau in
the range 650–1,100 °C with an intermediate solid found
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 investi-
gations. 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 MLCT excited states with some mixing of the
halide-to-ligand (XL) CT characters. The thermal decom-
position 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
1
8.0% could be attributed to the intermediate Cu S (cal-
2
culated 14.1%) or to CuS (calculated 16.9%) or to CuBr2
(
calculated 19.8%) although the XRD gave only CuO.
The final residue at 1,300 °C as it is measured by TG
coincides well with the theoretical amount of CuO (found
1
4.3%, calc. 14.1%) and verified from the results of the
powder XRD analysis, in accordance with the literature
findings [21].
ligands in small fragments. The XRD gave mainly Cu S as
2
Decomposition mechanism
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
2
Taking into account the results coming from the TG/DTG
measurements and the XRD analysis of the solid interme-
diate and residue materials, of the thermal decomposition
TG measurements. In the case of O atmosphere the final
2
residue 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+
NH
Cu
Acknowledgements The authors are grateful to Dr. G. Vourlias,
Department of Physics, AUTH, for collecting the powder XRD data.
NH
S
S
S
S
S
N
X–
2
H
N
Cu
H
S
HN
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