Copper(I) halide complexes of 2-thiohydantoin and 5,5-diphenyl-2- thiohydantoin

Article abstract of DOI:10.1016/j.poly.2012.08.065

A series of copper(I) halide complexes formulated as [CuX(L)₂] [X = Cl, Br; L = 2-thiohydantoin (th) and 5,5-diphenyl-2-thiohydantoin (dpth)] were prepared and their photophysical and thermal (TG-DTA) behaviour was investigated. Further treatment of these complexes with triphenylphosphane gave mixed-ligand compounds [CuX(L)(PPh₃)₂]. Solutions of the complexes are emissive in the solid state and in solution at ambient temperature, with the lowest energy emitting excited states assigned to MLCT/XLCT transitions. The crystal structures of [CuBr(th)₂] and [CuCl(PPh₃)₂(th)] revealed planar trigonal and distorted tetragonal coordination environment around the Cu(I) centres, respectively.

Full text of DOI:10.1016/j.poly.2012.08.065

Polyhedron 48 (2012) 140–145
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Copper(I) halide complexes of 2-thiohydantoin and 5,5-diphenyl-2-thiohydantoin
a
a
b
b
P. Aslanidis a, , S. Kyritsis , M. Lalia-Kantouri , B. Wicher , M. Gdaniec
⇑
a Aristotle University of Thessaloniki, Faculty of Sciences, Department of Chemistry, Laboratory of Inorganic Chemistry, P.O. Box 135, Thessaloniki 54124, Greece
b Adam Mickiewicz University, Faculty of Chemistry, 60-780 Poznan, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of copper(I) halide complexes formulated as [CuX(L)2] [X = Cl, Br; L = 2-thiohydantoin (th) and
5,5-diphenyl-2-thiohydantoin (dpth)] were prepared and their photophysical and thermal (TG–DTA)
behaviour was investigated. Further treatment of these complexes with triphenylphosphane gave
mixed-ligand compounds [CuX(L)(PPh3)2]. Solutions of the complexes are emissive in the solid state
and in solution at ambient temperature, with the lowest energy emitting excited states assigned to
MLCT/XLCT transitions. The crystal structures of [CuBr(th)2] and [CuCl(PPh3)2(th)] revealed planar trigo-
nal and distorted tetragonal coordination environment around the Cu(I) centres, respectively.
Ó 2012 Elsevier Ltd. All rights reserved.
Received 19 July 2012
Accepted 28 August 2012
Available online 7 September 2012
Keywords:
Copper(I) complexes
Thiohydantoins
Triphenylphosphane
Luminescence
TG/DTG–DTA
1. Introduction
them reported so far. In this work we report on the synthesis
and characterization of the copper(I) chloride and bromide com-
The coordination chemistry of heterocyclic thioamides has seen
spectacular expansion in the recent past mainly because of the rel-
evance of these compounds to biological systems [1,2]. The key
feature of this class of compounds, with respect to their ligating
properties, is the ability to bind to a metal centre adopting several
coordination modes, thus giving rise to a rich variety of complexes
with variable nuclearities and often unusual geometries [3].
Univalent coinage metals are typical soft acids and their chem-
istry is largely based upon coordination to ligands containing sul-
fur donor atoms. In this sense, copper(I) complexes containing
heterocyclic thioamides have received a great deal of attention
during the past few decades. In the course of our long-standing
investigations in this area we obtained a large number of interest-
ing structures in which the neutral thioamide molecules were gen-
erally found to bind the metal through the exocyclic sulfur atom in
either a terminal or bridging mode [4].
Among the numerous molecules containing the thioamide moi-
ety, 2-thiohydantoin and 5,5-diphenyl-2-thiohydantoin, hereafter
abbreviated as th and dpth respectively, have received some atten-
tion in the past, mainly because of their use for medical purposes
as anticonvulsant [5], antimutagenic [6], anticarcinogenic [7], anti-
androgen [8] and antiviral [9] agents, but also recently as polymer-
ization catalysts [10], as corrosion inhibitors [11] and as analytical
reagents [12]. However, in view of such a potential importance, re-
ports on the coordination chemistry of these two compounds are
unexpectedly rare, and to the best of our knowledge, there are
no structurally characterized copper(I) compounds bearing any of
plexes of 2-thiohydantoin and 5,5-diphenyl-2-thiohydantoin from
type [CuX(thiohydantoin)2] and [CuX(thiohydantoin)(PPh3)2] and
the structural characterization of one representative compound
of each type. Further we investigate the luminescence properties
of the new compounds as well as their thermal behaviour.
2. Experimental
2.1. Materials and instrumentation
Commercially available copper(I) halides and triphenylphos-
phane were used as received while 2-thiohydantoin and 5,5-diphe-
nyl-2-thiohydantoin were re-crystallized from hot ethanol prior to
their use. All the solvents were purified by respective suitable
methods and allowed to stand over molecular sieves. Infra-red
spectra in the region of 4000–200 cmꢀ1 were obtained in KBr discs
with a Nicolet FT-IR 6700 spectrophotometer, while a Shimadzu
160A spectrophotometer and a Hitachi F-7000 fluorescence spec-
trometer were used to obtain the electronic absorption and emis-
sion/excitation spectra respectively. The simultaneous TG/DTG–
DTA curves were obtained on a SETARAM thermal analyzer, model
SETSYS-1200. The samples of approximately 10.0 mg, were heated
in platinum crucibles, in nitrogen atmosphere with heating rate
10 °C minꢀ1, at a flow rate of 80 ml minꢀ1, within the temperature
range 30–800 °C.
2.2. Crystal structure determination
⇑
Single crystals of [CuBr(th)2] (2) and [CuCl(PPh3)2(th)] (5) suit-
able for X-ray structure analysis were obtained at room tempera-
Corresponding author.
E-mail address: aslanidi@chem.auth.gr (P. Aslanidis).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.08.065

P. Aslanidis et al. / Polyhedron 48 (2012) 140–145
141
Table 2
ture by slow evaporation method. The diffraction data were col-
Selected bond distances (Å) and angles (°) in [CuBr(th)2] (2).
lected at room temperature with an Oxford Diffraction Xcalibur E
CCD diffractometer. Data collection and reduction were performed
with the CrysAlis Pro software [13]. The structures were solved by
direct methods with the SHELXS-97 program [14] and refined by full-
matrix least-squares method on F2 with SHELXL-97 [15]. The hydro-
gen atoms from C–H groups, and N–H groups in 2, were placed in
idealized positions and refined using riding model. The hydrogen
atoms from N–H groups in 5 were located in electron-density dif-
ference maps and freely refined. Additional details concerning
crystal data and structure refinement are given in Table 1. Selected
bond lengths and angles are listed in Table 2. Molecular graphics
were generated with ORTEP-3 for Windows [15] and Mercury 3.0
software [16].
Bond lengths
Cu1–Br1
Cu1–S11
S11–C21
C21–N11
C21–N31
C41–N31
C41–C51
N11–C51
C41–O11
2.3984(5)
2.2348(9)
1.676(3)
1.315(4)
1.374(3)
1.367(3)
1.491(4)
1.451(3)
1.210(3)
Cu1–S12
S12–C22
C22–N12
C22–N32
C42–N32
C42–C52
C22–N12
C42–O12
2.2407(8)
1.684(3)
1.313(4)
1.374(3)
1.365(3)
1.494(4)
1.313(3)
1.209(3)
Bond angles
Br1–Cu1–S11
S11–Cu1–S12
Cu1–S12–C22
S11–C21–N11
N11–C21–N31
O11–C41–N31
N31–C41–C51
C22–N12–C52
S12–C22–N32
C22–N32–C42
O12–C42–C52
N12–C52–C42
120.72(3)
119.81(3)
108.81(9)
129.5(2)
108.0(2)
126.5(2)
106.3(2)
112.5(2)
122.1(2)
111.8(2)
127.6(3)
101.7(2)
Br1–Cu1–S12
Cu1–S11–C21
C21–N11–C51
S11–C21–N31
C21–N31–C41
O11–C41–C51
N11–C51–C41
S12–C22–N12
N12–C22–N32
O12–C42–N32
N32–C42–C52
119.44(3)
107.61(9)
112.2(2)
122.5(2)
111.6(2)
127.2(2)
101.8(2)
130.2(2)
107.7(2)
126.2(3)
106.2(2)
2.3. General procedure for the synthesis of complexes 1–4
A suspension of 0.5 mmol of copper(I) halide (49.5 mg for CuCl,
71.7 mg for CuBr) in 50 cm3 of dry acetonitrile was stirred for 2 h at
50 °C. The resulting clear solution was filtered of and then treated
with a solution of the appropriate hydantoine (1 mmol) dissolved
in a small amount (ꢁ20 cm3) 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 afforded a micro-
crystalline solid, which was filtered off and dried in vacuo.
2.3.2. [CuBr(th)2] (2)
Red-brown crystals (103 mg, 55%), m.p. 196 °C; Anal. Calc. for
C6H8N4CuBrO2S2: C, 19.18; H, 2.15; N, 14.91. Found: C, 20.01; H,
2.38; N, 15.02. IR (cmꢀ1): 3175s, 3102s, 3034w, 2914w, 1781vs,
1749vs, 1536vs, 1425vs, 1353m, 1289vs, 1173s, 1154vs, 884m,
2.3.1. [CuCl(th)2] (1)
726m, 682s, 530s, 504s; UV–Vis (kmax, log
e): 222 (4.43), 263 (4.75).
Brown crystals (94 mg, 57%), m.p. 170 °C; Anal. Calc. for C6H8N4-
CuClO2S2: C, 21.75; H, 2.43; N, 16.91. Found: C, 21.63; H, 2.68; N,
17.13%. IR (cmꢀ1): 3096s, 3044m, 2893m, 1770vs, 1739s, 1535vs,
1479s, 1432vs, 1381m, 1282vs, 1163vs, 1153vs, 1094s, 744vs,
695vs, 518vs, 508vs, 488s; UV–Vis (kmax, loge): 221 (4.72), 262
(4.90), 310 (4.15).
2.3.3. [CuCl(dpth)2] (3)
Pale yellow crystals (216 mg, 68%), m.p. 164 °C; Anal. Calc. for
C
30H24N4CuClO2S2: C, 56.68; H, 3.81; N, 8.81. Found: C, 56.73; H,
4.17; N, 9.09%. IR (cmꢀ1): 3096m, 3044m, 2893m, 1770vs, 1739s,
1536vs, 1479s, 1432vs, 1282s, 1162vs, 1094s, 871m, 744vs,
695vs, 518vs, 507vs, 488s; UV–Vis (kmax, loge): 223 (4.88), 270
(4.94), 311sh (3.77).
Table 1
Crystallographic data and refinement details for [CuBr(th)2] (2) and [CuCl(PPh3)2(th)]
(5).
2.3.4. [CuBr(dpth)2] (4)
Pale yellow crystals (211 mg, 62%), m.p. 181 °C; Anal. Calc. for
2
5
C
30H24N4CuBrO2S2: C, 52.98; H, 3.57; N, 8.24. Found: C, 53.23; H,
CCDC
892470
[CuBr(th)2]
375.73
monoclinic
293
892471
[CuCl(PPh3)2(th)]
739.67
orthorhombic
293
4.13; N, 8.33%. IR (cmꢀ1): 3163s, 3056w, 1771vs, 1749s, 1514vs,
1448vs, 1407s, 1226m, 1162vs, 1005s, 938m, 726s, 694vs, 529s;
Empirical formula
Formula weight
Crystal system
T (K)
UV–Vis (kmax, loge): 224 (4.90), 270 (5.07), 313sh (3.92).
Radiation
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
Mo K
P21/c
a
Mo Ka
Pbca
2.4. General procedure for the synthesis of complexes 5–8
7.2568(3)
12.3226(6)
13.4493(7)
90
97.566(4)
90
1192.2(1)
4, 1
5.523
14.8243(8)
18.7041(9)
25.663(1)
90
90
90
7115.7(6)
8, 1
0.871
43424
6725
A suspension of copper(I) halide (0.5 mmol) and triphenylphos-
phane (262 mg, 1 mmol) in 50 cm3 acetonitrile was stirred until a
white precipitation was formed. A solution of the appropriate thi-
ohydantoin (0.5 mmol) in methanol was then added and the mix-
ture was stirred to clearness. The resulting solution was filtered of
and kept at room temperature, whereupon crystals of the respec-
tive product were obtained after few days, which were filtered of
and dried in vacuo.
a
(°)
b (°)
c
(°)
V (Å3)
Z, Z0
Absorption coefficient
Reflections collected
Independent reflections (Rint
5379
2169
)
Completeness up to hmax = 25°
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
99.50%
5379/0/145
1.066
R1 = 0.0266,
wR1 = 0.0593
R2 = 0.0343,
wR2 = 0.0625
0.33, ꢀ0.60
99.67%
6725/0/432
1.062
R1 = 0.0264,
wR1 = 0.0695
R2 = 0.0307,
wR2 = 0.0723
0.31, ꢀ0.30
2.4.1. [CuCl(th)(PPh3)2] (5)
Red crystals (225 mg, 61%), m.p. 162 °C; Anal. Calc. for C39H34N2-
P2CuClOS: C, 63.32; H, 4.63; N, 3.79. Found: C, 63.37; H, 4.66; N,
3.98%. IR (cmꢀ1): 3098s, 3039m, 2894m, 1770vs, 1739s, 1536vs,
1478s, 1433vs, 1382s, 1282vs, 1163vs, 1153vs, 1094s, 1027m,
870s, 744vs, 695vs, 674s, 518vs, 508vs, 488vs; UV–Vis (kmax, loge):
222 (4.72), 270 (4.94), 312 (3.95).
Final R indices [I > 2
r(I)]
R indices (all data)
Largest difference in peak and
hole (e Åꢀ3
)

142
P. Aslanidis et al. / Polyhedron 48 (2012) 140–145
2.4.2. [CuBr(th)(PPh3)2] (6)
H
N
O
Brown crystals (219 mg, 56%), m.p. 174 °C; C39H34N2P2CuBrOS:
C, 59.74; H, 4.37; N, 3.57. Found: C, 59.37; H, 3.66; N, 3.68%. IR
(cmꢀ1): 3100s, 3040w, 2916s, 1716vs, 1529vs 1411vs, 1380s,
1297vs, 1156vs, 1045s, 964s, 891vs, 759vs, 685vs, 626s, 529vs,
H
N
O
S
S
N
H
N
H
486s; UV–Vis (kmax, loge): 221 (4.96), 262 (4.91).
5,5-Diphenyl-2-thiohydantoin (dpth)
2-Thiohydantoin (th)
2.4.3. [CuCl(dpth)(PPh3)2] (7)
Yellow crystals (272 mg, 61%), m.p. 128 °C; Anal. Calc. for C51-
H42N2P2CuClOS: C, 68.68; H, 4.74; N, 3.14. Found: C, 67.38; H,
4.40; N, 3.08%. IR (cmꢀ1): 3161m, 3058m, 2866m, 1759vs,
1584m, 1525vs, 1448vs, 1434s, 1401m, 1230s, 1164vs, 1090s,
1002s, 941m, 743s, 730s, 694vs, 660m, 618m, 520s, 501s; UV–
Scheme 1. The thiohydantoins used as ligands.
bands with maxima in the range ꢁ220 and ꢁ270 nm. With refer-
ence to the absorption spectra of the uncoordinated thiohydanto-
ins, these two bands, which remain practically unshifted upon
coordination, can be attributed to CT transitions at the C@S bond
[18]. Exact assignment of the bands due to the presence of triphen-
ylphosphine in the spectra of compounds 5–8 is difficult since both
the thiohydantoin ligands and triphenylphosphine strongly ab-
sorbs in the same regions.
Vis (kmax, loge): 224 (4.93), 269 (4.91).
2.4.4. [CuBr(dpth)(PPh3)2] (8)
Yellow crystals (271 mg, 58%), m.p. 195 °C; C51H42N2P2CuBrOS:
C, 65.42; H, 4.52; N, 2.99. Found: C, 66.88; H, 4.76; N, 2.97%. IR
(cmꢀ1): 3168s, 3057w, 2875w, 1757vs, 1729vs, 1526vs, 1494s,
1446s, 1434s, 1384s, 1226m, 1163vs, 1093m, 1001s, 941s, 909m,
743s, 726vs, 696vs, 659s, 529s, 520s, 501 m; UV–Vis (kmax, loge):
225 (4.97), 270 (5.02).
The infra-red spectra, recorded in the range 4000–250 cmꢀ1
contain all the characteristic bands required by the presence of
the thiohydantoin ligands. In particular, the N–H stretching vibra-
tion appears in the 3100–3170 cmꢀ1 region as a broad split band of
quite strong intensity, whereas the very strong band assigned to
the C@O stretching vibration, appears in the 1760–1790 cmꢀ1 re-
gion. Shifts of the four ‘‘thioamide bands’’ due to coordination
are indicative of an exclusive S-coordination mode. Thus, ‘‘thioam-
ide III’’, containing contribution from the C@S stretching vibration,
generally appears red shifted by 15–25 cmꢀ1 in the spectra of the
complexes, compared to the spectra of the respective uncoordi-
nated thiohydantoin, whereas shift of ‘‘thioamide I’’ and ‘‘thioam-
ide II’’, containing contributions from the C@N and C–N
stretching vibrations are, as expected, less intense and not always
in the same direction.
3. Results and discussion
3.1. General considerations
Treatment of copper(I) chloride or bromide with three equiva-
lents of 2-thiohydantoin or 5,5-diphenyl-2-thiohydantoin in dry
acetonitrile/methanol solution at 50 °C afforded microcrystalline
air stable solids which, on analysis, were found to be of the compo-
sition [CuX(thiohydantoin)2] (compounds 1–4) (see Scheme 1).
As this composition cannot be derived from the stoichiometry
of the reactants chosen, the reaction procedure was repeated using
the two reactants in 1:2 ratio but keeping the other conditions un-
changed. In doing so, the same compounds were once more ob-
tained, this time in considerably increased yields. According to
the analytical data, the formation of a doubly bridged dimer, bear-
ing either a Cu2S2 or a Cu2X2 core, seemed to be obvious, however
the structure determination of [CuBr(2-thiohydantoin)2] (com-
pound 2) by X-ray diffraction revealed the presence of three-coor-
dinated mononuclear species.
3.3. Description of the structures
An ORTEP presentation of the molecular structure of [CuBr(th)2]
(2) is shown in Fig. 1 Selected bond lengths and angles are given in
Table 2 and hydrogen-bonding geometry is given in Table 3. Or-
ange-red crystals of [CuBr(th)2] have been obtained on slow evap-
oration of a saturated acetonitrile solution.
The metal ion is surrounded by the two S atoms of two thiohyd-
antoin ligands and the bromide ion to attain a trigonal planar coor-
dination geometry. Deviations of the bond angles around the metal
centre from the ideal value of 120° for planar trigonal geometry do
not exceed 0.8°. The five-membered rings of thioamide ligands are
virtually planar and coplanar with the CuBrS2 core. Noteworthy,
the molecule adopts a frequently encountered for trigonal Cu(I)
thioamide complexes ‘w-shape’ geometry that is stabilized by
two intramolecular N–HꢂꢂꢂBr hydrogen bonds (Table 3). The bond
distances and angles are not altered significantly upon coordina-
Although the coordination number three is not the most fa-
voured one for CuI, it can be often realized, usually in conjunction
with ‘‘soft’’ sulfur and phosphorus donors. The majority of known
+
trigonal planar copper(I) complexes are cations of type CuL3
,
while the reported neutral complexes, usually of the formula
CuXL2, are relatively rare. Most of these compounds are formed
by bulky ligands, which is not surprising since the steric hindrance
plays a major role in stabilizing the coordination number three
[17]. On the other hand, electronic factors should be additionally
considered in the case of the thiones, which are regarded as typical
p-acceptor ligands and as such capable of a multiple bonding to the
d10 metal. With this in mind, the observed three-coordination in
complexes 1–4 can be considered as quite unexpected, the more
so as during our hitherto studies on coordination of thiones to cop-
per(I), we only have isolated examples with tetrahedral coordina-
tion around copper. Similarly, it contradicts to the formation of
tetrahedral complexes bearing the same thione ligands in conjunc-
tion with triphenylphosphine (compounds 5–8).
3.2. Spectroscopy
The electronic absorption spectra of complexes 1–8, recorded in
Fig. 1. A view of compound 2 with atom labels. Displacement ellipsoids are shown
dichloromethane at room temperature, show two intense broad
in the 50% probability level.

P. Aslanidis et al. / Polyhedron 48 (2012) 140–145
143
Table 3
Hydrogen bond geometry in [CuBr(th)2] (2) and [CuCl(th)(PPh3)2] (5).⁄
D—HꢂꢂꢂA
D—H (Å)
HꢂꢂꢂA (Å)
DꢂꢂꢂA (Å)
<D—HꢂꢂꢂA (°)
[CuBr(th)2] (2)
N11—H11ꢂꢂꢂBr1
N11—H12ꢂꢂꢂBr1
N31—H31ꢂꢂꢂO11i
N31—H32ꢂꢂꢂO12ii
0.86
0.86
0.86
0.86
2.49
2.52
1.99
1.99
3.320(2)
3.350(2)
2.816(3)
2.805(3)
163
161
161
159
[CuCl(th)(PPh3)2] (5)
N1—H1ꢂꢂꢂCl1
0.83(2)
0.82(2)
2.37(2)
2.40(2)
3.1806(17)
3.2026(17)
167(2)
166(2)
N3—H3ꢂꢂꢂCl1
Table 4
Selected bond distances (Å) and angles (°) in [CuCl(th)(PPh3)2] (5).
Cu1–Cl1
Cu1–P11
Cu1–P12
Cu1–S1
S1–C2
2.3893(5)
2.2786(5)
2.2542(4)
2.4016(5)
1.6694(18)
O1–C4
N1–C2
N1–C5
C2–N3
N3–C4
C4–C5
1.202(2)
1.322(2)
1.444(2)
1.371(2)
1.376(3)
1.509(3)
P12–Cu1–P11
P12–Cu1–Cl1
P11–Cu1–Cl1
P12–Cu1–S1
P11–Cu1–S1
Cl1–Cu1–S1
C2–S1–Cu1
C2–N1–C5
128.971(17)
109.333(17)
100.550(18)
105.220(17)
102.226(18)
109.575(18)
108.25(6)
N1–C2–N3
N1–C2 –S1
N1– C2–S1
C2–N3–C4
O1–C4–N3
O1–C4–C5
N3–C4–C5
N1–C5–C4
107.80(16)
127.94(14)
124.26(14)
112.13(16)
126.82(19)
127.91(19)
105.28(15)
102.03(15)
Fig. 2. A view of compound 5 with atom labels. Displacement ellipsoids are shown
in the 50% probability level.
112.52(16)
Cu–Cl bond length of 2.3893(5) Å, as well as the two individual
Cu–P distances of 2.2786(5) and 2.2542(4) Å, are comparable to
the corresponding values previously found in related four coordi-
nate complexes with terminal chlorine and thione-S donors
[24–26]. In the crystal the complex molecules are connected via
N–HꢂꢂꢂCl interactions into chains extending along the a axis.
tion, except for the expected moderate lengthening of the C@S
bond [19]. The Cu–Br bond length of 2.3985(5) Å, as well as the
two individual Cu–S distances of 2.2348(8) and 2.2407(9) Å, are
similar to the corresponding values previously found in related
three-coordinate complexes with terminal bromide and thione-S
donors [20,21]. In the crystal, the complex molecules are con-
nected into tapes extending along the a axis via N–HꢂꢂꢂO hydrogen
bonds generating centrosymmetric R22 (8) ring motifs.
Violet crystals of the complex [CuCl(th)(PPh3)2] (5) have been
obtained on slow evaporation of an acetonitrile/methanol solution.
Selected bond lengths and angles are given in Table 4 and a per-
spective drawing showing the atom numbering is shown in
Fig. 2. The geometrical characteristics of this four-coordinate
monomer generally refer to those of other copper(I) halide com-
plexes tetrahedrally coordinated by thione and phosphane ligands.
Each of the interbond angles around the central copper atom show
moderate deviations from the idealized tetrahedral geometry ex-
cept for the P12–Cu1–P11 angle which value of 128.971(17)° rep-
3.4. Luminescence
Room temperature photoexcitation at 310–370 nm of degassed
10ꢀ5 M acetonitrile solutions of the complexes produces a broad
emission band with peak maxima in the 383–416 nm region. The
excitation and emission spectrum of [CuCl(th)2], representative
for the series of complexes 1–8, is depicted in Fig. 3.
As can be seen from the data listed in Table 4, for all four com-
plexes bearing 2-thiohydantoin, the maxima of the emission bands
are red shifted by 6–20 nm relative to the emission spectrum of the
free ligand (394 nm). On the other hand, the maxima of the emis-
sion bands for the four 5,5-dipheny-thiohydantoin complexes are
blue shifted by 11–34 nm, when compared to the emission maxi-
mum of 427 nm in the free ligands spectrum. These differentia-
tions of the emission bands are obviously associated with the
electronic characteristics of the thiohydantoin ligands which
determine the strength of the Cu–S bond [27], however precise
statements cannot be made on the basis of the compounds under
investigation. Although these shifts are relatively small, to be con-
sidered as evidence for participation of S ? Cu charge transfer in
the emissive excited state [28], the emissions cannot be considered
as one of pure thione centred intraligand origin because of a possi-
ble participation of the halogen in the emissive excited states, in
the form of a ligand-to-metal charge-transfer (XMCT) or an interli-
gand charge-transfer (XLCT, X ? thione) [29]. In this respect, there
is a dependence of the emission maxima on the kind of the halide
present, with a small red shift in the order Cl ? Br (see Table 5).
In conclusion, the determination of the emissive excited states
in the compounds under investigation is a difficult task, with re-
search in this area being yet in the beginnings. The emissive states
are most likely of mixed MLCT/XLCT/IL character, and this applies
all the more for the mixed-ligand complexes in which the presence
resents the most significant distortion as
a result of steric
imposition of the bulky phosphine ligands. The arrangement of
the thiohydantoin ligand within the complex is dictated by the
intramolecular N–HꢂꢂꢂCl hydrogen bond (Table 3), an interaction
observed in all known complexes of formula [CuX(HL)(PPh)3]
where X is halogen and HL is a thioamide ligand [22]. As an inter-
esting feature of the present structure, the five-membered thi-
ohydantoin ring and the C(131)–C(181) benzene ring have their
planes in an almost parallel arrangement, promoting an intramo-
lecular p–p stacking interaction. The centroid-to-centroid distance
between the two rings is 3.619 Å. This geometrical adaptation
could be considered as contributing to some degree to the overall
stabilization of the molecule in the solid state. Similar arrangement
of the ligands was recently observed in the closely related
[CuX(HL)(PPh)3] complex with 1,4-dihydro-tetrazole-5-thione as
thioamide ligand [23].
The Cu–S distance of 2.4016(5) Å is close to the mean value of
2.38 Å reported for [CuX(HL)(PPh)3] complexes [23]. Both, the

144
P. Aslanidis et al. / Polyhedron 48 (2012) 140–145
Table 5
of triphenylphosphane also affects in some degree the energy of
the emission.
Room temperature excitation and emission maxima for compounds 1–8 in CH3CN
solution.
a/a Compound
kexc (nm)
kem (nm)
3.5. Thermal decomposition studies
1 [CuCl(th)2]
2 [CuBr(th)2]
3 [CuCl(dpth)2]
4 [CuBr(dpth)2]
5 [CuCl(th)(PPh3)2]
6 [CuBr(th)(PPh3)2]
7 [CuCl(dpth)(PPh3)2]
8 [CuBr(dpth)(PPh3)2]
307
343
330
347
362
368
360
367
400
411
383
402
410
414
413
416
The thermal decomposition for two simple [CuBr(th)2] (2),
[CuBr(dpth)2] (4), and two mixed-ligand [CuBr(th)(PPh3)2] (6),
[CuCl(dpth)(PPh3)2] (7) compounds under investigation was stud-
ied in N2 atmosphere by simultaneous TG–DTA. Thermoanalytical
curves (TG/DTG–DTA) for the compounds [CuBr(dpth)2] (2) and
[CuBr(th)(PPh3)2] (6), in nitrogen atmosphere are representatively
given in Figs. 4 and 5, respectively.
The shape of the mass loss is complicated. It presents different
areas of mass loss and each area starts before the ending of the pre-
vious one. For this reason it is very difficult to correspond to differ-
ent areas of mass loss in a specific way of decomposition of the
compound. In the first stage (180–320 °C), the compound
[CuBr(th)2](2), (Fig. 4) shows sudden mass loss (DTG peak at
255 °C) of 31.0%, which coincides with the release of one thione li-
gand with theoretical mass loss of 30.9%. The DTA curve shows one
sharp endothermic peak at 206 °C, and moreover two broader ones
at 230 and 274 °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,
while the next ones to further decomposition.
Upon increasing the temperature, the unstable intermediates
undergo further decompositions with gradually mass loss during
the second and third stages (320–500 and 500–800 °C), which
could be attributed to further elimination of the bromine atom
and the remaining thione molecule. The amount of the solid resi-
due, estimated from the TG curve (found 30%), with the calculated
value for Cu2S 21.2% and metallic copper 16.9% denotes that the
decomposition of this compound at 800 °C was not completed.
The mixed-ligand compounds, an example is given for
[CuBr(th)(PPh3)2] (6) in Fig. 5, are stable up to ꢁ100 °C, where
the elimination of absorbed solvent takes place and the decompo-
sition starts with sudden mass loss at 200 °C in one stage (200–
400 °C, with DTG max at 264 and 335 °C. The experimental mass
loss of 54.5% coincides with the release of one thione and one tri-
phenylphosphane ligands with a theoretical mass loss of 54.3%,
leaving as possible intermediates Cu2S and CuBr. Upon further
heating up to 800 °C, the decomposition continues with gradual
mass loss, while the final solid residue (found 30.0%) cannot be
attributed only to metallic copper (calc. 8.1%) or to Cu2S (calc.
10.1%).
Fig. 4. Thermoanalytical curves (TG/DTG–DTA) of [CuBr(th)2] in nitrogen atmo-
sphere, with heating rate 10 °C minꢀ1
.
The thermal decomposition of the compounds bearing the thi-
one ligand 5,5-diphenyl-2-thiohydantoin (dpth) (compounds 4
and 7) instead of the 2-thiohydantoin (th) mentioned above, is
Fig. 5. Thermoanalytical curves (TG/DTG–DTA) of [CuBr(th)(PPh3)2] in nitrogen
atmosphere, with heating rate 10 °C minꢀ1
.
completed at 800 °C (experimental mass loss ꢁ93.0%), giving as so-
lid residue metallic copper (calculated value 9.3% for the simple
compound 4 and 7.1% for the mixed-ligand compound 7).
Analogous intermediates were found in the literature, according
to their TG curves, on complexes of the type [CuIXL]n (L = heteroar-
omatic unit) where the residue above 400 °C corresponds to CuCl
[30], while for the Cu(I) complexes of type [(tpp)Cu(m-Cl)2-
Cu(tppp)] (tpp = triphenylophosphane) corresponds to metallic
copper (Cu0) at 600 °C [31]. It is also referred, according to XRD
Fig. 3. Room temperature excitation and emission spectrum of [CuCl(th)2] in
CH3CN solution.

P. Aslanidis et al. / Polyhedron 48 (2012) 140–145
145
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