The influence of benzaldehyde-N-alkyl-thiosemicarbazones on the synthesis of gold(I) ionic complexes: Spectroscopy, ESI-mass, structures and variable H-bonded polymeric networks

Article abstract of DOI:10.1016/j.poly.2015.01.029

The effect of the substituents at the N¹/C² atoms of the thiosemicarbazones R¹R²C² = N³-N²H-C¹(=S)-N¹HR³ on the type of gold(I) complexes is inve

Full text of DOI:10.1016/j.poly.2015.01.029

Polyhedron 91 (2015) 89–97
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
The influence of benzaldehyde-N-alkyl-thiosemicarbazones
on the synthesis of gold(I) ionic complexes: Spectroscopy,
ESI-mass, structures and variable H-bonded polymeric networks
Tarlok S. Lobana a, , Rekha Sharma a,1, Shikha Indoria , Ray J. Butcher b
⇑
a
a
Department of Chemistry, Guru Nanak Dev University, Amritsar 143 005, India
Department of Chemistry, Howard University, Washington, DC 20059, USA
b
a r t i c l e i n f o
a b s t r a c t
1
2
1
2
2
3
2
1
Article history:
The effect of the substituents at the N /C atoms of the thiosemicarbazones R R C = N -N H-C (=S)-
Received 13 October 2014
Accepted 17 January 2015
Available online 26 February 2015
1
3
N HR on the type of gold(I) complexes is investigated. Direct reaction of gold(I) chloride with
1
1
2
3
benzaldehyde-N-methyl thiosemicarbazones (HL : R = Ph, R = H, R = Me) in a 1:2 M ratio in acetoni-
1
1
trile has yielded an ionic complex, [Au(
j
-S-HL )
2
]Cl (1). Similarly, the reaction of benzaldehyde-N-ethyl
2
1
2
3
1
2
thiosemicarbazone (HL : R = Ph, R = H, R = Et) has formed another ionic complex, [Au(
2
j -S-HL ) ]Cl (2).
Keywords:
The complexes have been characterized using analytical data, spectroscopy (IR, 1H, C NMR, UV–Vis),
13
Gold(I) chloride
Thiosemicarbazones
Structures
ESI-mass
Spectroscopy
fluorescence, ESI-mass and X-ray crystallography. Complexes 1 and 2 represent the first examples
obtained from the direct reactions of gold(I) chloride with a thio-ligand without the presence of PPh
or the use of any intermediate substrate, as has normally been used. Complex 1, with a methyl sub-
stituent at N , has two independent molecules in the crystal lattice, while complex 2, with an N-ethyl
3
1
substituent, has only one type of molecule in the crystal lattice. ESI-mass studies reveal the formation
I
+
I
1
+
I
1
+
I
2
+
of the species: [Au Cl+H] (A), [Au Cl
D) (complex 2). Interestingly both complexes have shown intense fluorescence bands in the wide region
40–540 nm, corresponding to the excitation wavelength of 308 nm.
Ó 2015 Elsevier Ltd. All rights reserved.
2 2 2
(HL )+2H] (B), [Au (HL ) ] (C) (complex 1) and [Au (HL ) -4H]
(
3
1
. Introduction
Gold-sulfur compounds find applications in medicine and mod-
compared to other metals [6]. Apart from supramolecular net-
works, the interest in gold–thiosemicarbazone chemistry has
focused on the biochemical and luminescent properties [8–16].
Some of gold(III) complexes have been tested for their in vitro
cytotoxic activity against tumor cell lines [18]. Likewise, gold(I)-
thiosemicarbazone complexes have been tested for their in vitro
cytotoxic activity against tumor cell lines [8], human leukemia
and solid tumor cell lines [13], and the human cervix carcinoma
cell line [10,15]. It is noted that gold(I) complexes have greater
activity than the corresponding gold(III) complexes [10,15].
We have been interested in the coordination chemistry of
thiosemicarbazones [22–24] and it has been observed that the sub-
ern technology. In this respect, gold(I) compounds are found to be
suitable in rheumatoid arthritis and anticancer treatments, used in
the photographic industry [1], rich in luminescent properties [2]
and act as optical [3] and chemosensors [4]. Further, it is found that
gold(III) compounds also display antitumor properties similar to
cisplatin [5]. Gold(I) compounds display intra- and/or inter-
molecular d –d interactions that assist in modulating their
luminescent {due to the metal-centered Au(5d) ? Au(6p) transi-
tion} and solid state behavior [1–5].
1
0
10
2
1
The chemistry of N, S-donor ligands based on thiosemicar-
stituents at the C and N atoms, as well as variations in the halide
ions, the nature of the co-ligand and solvents, all play an important
role in controlling the bonding and nuclearity of the resulting com-
plexes. Some of the novel features observed are cyclometallation
1
2
2
3
2
1
1 3 4
bazones {(R R C = N -N H-C (=S)-N R R }, an important class of
biochemically active molecules [6,7], with gold(I) [8–16] and
gold(III) [10,12,17–21] has been investigated to a limited extent
(
Pd, Pt, Ru), variable bridge bonding between metal centers, bond
isomerism, multiple bridging, formation of cis–trans isomers, furan
oxygen coordination etc [22–24]. In continuation of our interest in
metal-thiosemicarbazone chemistry, we reported the first ionic
⇑
Corresponding author. Fax: +91 183 2 258820.
E-mail address: tarlokslobana@yahoo.co.in (T.S. Lobana).
Present address: Department of Chemistry, Lovely Professional University,
1
1
3
2
gold(I) complex, [Au(j -S-HL ) ]Cl, formed from the direct reaction
Phagwara 144402, India.
http://dx.doi.org/10.1016/j.poly.2015.01.029
0
277-5387/Ó 2015 Elsevier Ltd. All rights reserved.

9
0
T.S. Lobana et al. / Polyhedron 91 (2015) 89–97
of gold(I) chloride with 3-nitrobenzaldehyde thiosemicarbazone
Chart 1) in the presence of PPh [9]. However, in the literature,
complexes have been prepared using different methods that have
electrically heated Gallenkamp apparatus. The 1H NMR spectra
were recorded on a Bruker Avance-III 500 spectrometer operating
(
3
3
at a frequency of 500 MHz using CHCl -d as the solvent with
1
3
involved the reaction of a thiosemicarbazone with: (a) AuCl(PEt
3
)
TMS as the internal standard and C NMR spectra were recorded
at an operating frequency of 125 MHz in the same solvent as above
(see Chart 2 for the numbering of the C and H atoms). The mass
spectra were recorded using DMSO solvent on a Bruker Daltonik
LS–MS high resolution microTOF-Q II 10356. The UV–Vis spectra
of the ligands and complexes were recorded in methanol solvent
with the help of a UV-1601 PC Shimadzu spectrophotometer.
Fluorescence spectra of complexes were recorded in methanol
solvent with a Varian Cary Eclipse Fluorescence spectrophotometer.
0
[
8], (b) [AuCl(2,2 -thiodiethanol)] [11,12,15,16], (c) HAuCl
4
[13]
III
and [Au (damp-C,N)Cl
2
] [10,14] as intermediate substrates. The
complexes are ionic or neutral and their central cores are enumer-
n+
ated as follows: [S-Au-P] (n = 1, mononuclear [8], n = 2, dinuclear
n+
[
(
15]), [S-Au-S] {n = 1, mononuclear [9,12,14], n = 3, mononuclear
n+
pyridyl protonated) [12], n = 2, dinuclear [10]}, [S-Au-Cl] {n = 0,
mononuclear [13], n = 1, mononuclear (pyridyl protonated) [13]},
\
\
\
[
P
Cl-Au-S P-Au-Cl] [11], [Cl-Au-P S-Au-S P-Au-Cl] [11] and [S-Au-
\
2
S-Au-P
2
] [16]. In view of our interest in preparing gold(I) ionic
1
1
2
complexes, the N -substituted thiosemicarbazones HL and HL ,
as shown in Chart 1, were reacted directly with gold(I) chloride,
without using an intermediate substrate [12,14] or the presence
Table 1
Crystallographic data of complexes 1 and 2.
3
of PPh [9].
Empirical formula
C
18
H22AuN
6 2
S Cl
20 6 2
C H26AuN S Cl
M
T (K)
618.95
110 (2)
647.00
110 (2)
2
. Materials and techniques
Gold(I) chloride, benzaldehyde, 3-methyl thiosemicarbazide
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
monoclinic
P2 /c
monoclinic
P2 /n
1
1
and 3-ethyl thiosemicarbazide were procured from Aldrich
Chemicals Ltd., and used as received. Benzaldehyde-N -methyl
15.111
12.921
25.343
90.00
105.97
90.00
4757.1
8
1.728
6.488
15600
8688 [Rint = 0.0000]
8688
12.2045 (2)
12.8030 (2)
15.8333 (3)
90.00
95.1806 (16)
90.00
2463.91 (7)
4
1.744
6.267
17474
8176 [Rint = 0.0253]
6103
R = 0.0232
1
thiosemicarbazone and benzaldehyde-N-ethyl thiosemicarbazone
were prepared by refluxing benzaldehyde with the respective
thiosemicarbazide in methanol for 8–10 h. 2-Acetylpyridine
thiosemicarbazone and salicylaldehyde thiosemicarbazone were
prepared using literature methods [25]. The gold(I) complex
a
(°)
b (°)
(°)
c
3
V (Å )
Z
D
l
calc (g cmꢀ3)
[
Au(PPh
and
FLASHEA1112 CHNS analyzer. Infrared spectra were recorded from
3
)Cl] was prepared by a literature method [26]. The C, H
ꢀ
1
(mm
)
N
analyses were obtained with Thermoelectron
a
Reflections collected
Unique reflections
Reflections with [I > 2
ꢀ1
KBr pellets in the range 4000–200 cm on a Pye–Unicam SP-3-300
spectrophotometer. Melting points were determined with an
r
(I)]
(I)]
Final R indices [I > 2
r
R = 0.0483
wR = 0.0884
wR = 0.0431
R1
R2
Table 2
R3
Abbrev,
Important bond parameters {bond lengths (Å) and bond angles (°)}.
1
S
HL1
[Au(g
-S-Hbtsc-N-Me) ]Cl (1)
H
2
2
Me
R1
Au(1)–S(1B)
Au(1)–S(1A)
Au(2)–S(1D)
Au(2)–S(1C)
S(1A)–C(2A)
S(1B)–C(2B)
S(1C)–C(2C)
S(1D)–C(2D)
N(1A)–C(2A)
2.2760(14)
2.2839(14)
2.2686(15)
2.2717(16)
1.729(6)
1.722(5)
1.727(5)
1.731(5)
1.313(6)
N(1A)–C(1A)
1.442(6)
2
C
3
N
NH C1
S(1B)–Au(1)–S(1A)
S(1D)–Au(2)–S(1C)
C(2A)–S(1A)–Au(1)
C(2B)–S(1B)–Au(1)
C(2C)–S(1C)–Au(2)
C(2D)–S(1D)–Au(2)
C(2A)–N(1A)–C(1A)
C(2A)–N(2A)–N(3A)
171.80(5)
170.95(6)
104.87(17)
106.80(19)
105.13(19)
109.57(18)
123.3(5)
N HR3
1
R2
HL2
Et
H
H
HL3 [9]
HL4 [12]
H
O N
2
NH2
Me
H
119.1(4)
N
Cl
Cl
2
[Au(g ]Cl (2)
1-S-Hbtsc-N-Et)
Au–S(1A)
Au–(S1B)
S1A–C(3A)
S1B–C(3B)
N1A–C(3A)
N1A–(C2A)
HL5 [14]
2.2822(6)
2.2828(6)
1.730(2)
1.727(2)
1.327(3)
1.472(3)
S1(A)–Au–S(1B)
C(3A)–S(1A)–Au
C(3B)–S(1B)–Au
C(3A)–N(1A)–C(2A)
C(4A)–N(3A)–N(2A)
168.33(2)
106.38(8)
106.54(8)
125.5(2)
H
H
HL5
[14]
Me
Br
115.74(17)
Chart. 1. Thiosemicarbazone ligands under study.
H
C
NHR
NH
1
C
S
H
2
NH
AuCl
N
1
NHR
4
2
3
N
3
C
C
CH CN
3
5
+
-
Au Cl
2
x
S
8
7
S
C
7
N
RHN
NH
C
H
Chart. 2. Synthesis of complexes, R = Me, 1; Et, 2.

T.S. Lobana et al. / Polyhedron 91 (2015) 89–97
91
2
2
2
.1. Synthesis of the complexes
m
8
(C@S) 832s. 1H NMR (d, ppm; d-CHCl
3
): 10.15 (s, 1H, –N H),
2
4,8
1
.03 (s, 1H, –C H), 7.81 (m, 2H, C H), 7.68 (b, 1H, N H), 7.43 (m,
2H, C H), 3.30 (d, 3H, CH ). C NMR (d, ppm; d-CHCl ): 177.36
3 3
(C ), 143.64 (C ), 133.64 (C ), 130.53 (C ), 128.66 (C ), 127.10
1
1
5–7
13
.1.1. Synthesis of [Au(
j
-S-HL )
2
]Cl (1)
1
2
3
6
4,8
Gold(I) chloride (0.025 g, 0.107 mmol) was suspended in 15 mL
of acetonitrile, the thio-ligand HL1 (0.041 g, 0.214 mmol) was
added and the reaction mixture was stirred for 2 h. The light
yellow clear solution that formed was filtered and kept for crystal-
lization. Slow evaporation at room temperature yielded crystals of
5,7
3
(C ), 31.99 (CH ).
1
2
2
.1.2. Synthesis of [Au(
2
j -S-HL ) ]Cl (2)
Gold(I) chloride (0.025 g, 0.107 mmol) was suspended in 15 mL
1
1
2
[
Au(
for C18
H, 3.56; N, 13.71%. Main IR bands (KBr, cm ):
j
-S-HL )
2
]ꢁCl (1) (0.042 g, 63%; mp 202–204 °C). Anal. Calc.
of acetonitrile, the thio-ligand HL (0.044 g, 0.214 mmol) was
added and the reaction mixture was stirred for 1 h. The light yel-
low solution that formed was filtered and kept for crystallization.
Slow evaporation at room temperature yielded crystals of
22 6 2
H N S AuCl: C, 34.92; H, 3.55; N, 13.60. Found: C, 34.86;
ꢀ1
1
m
(N –H) 3371m,
(C–H) 3071br, 2975m, 2940m;
(C–C) 1531s, 1516s; (C–N) 1084m, 1029m, 951m;
2
3
273m;
m(–N H–) 3122m; m
m
1
2
m
(C@N) +
m
[
2
Au(j -S-HL ) ] Cl (2) (0.045 g, 65%; mp 196–198 °C). Anal. Calc.
Fig. 1. Molecular structure of [Au(
j
1-S-HL1)
2
]ꢁCl (1) with the numbering scheme.
Fig. 2. Molecular structure of [Au(
j
1-S-HL2)
2
]ꢁCl (2) with the numbering scheme.

9
2
T.S. Lobana et al. / Polyhedron 91 (2015) 89–97
1
2
3
6
for C20
H
26
N
6
S
2
AuCl: C, 37.12; H, 4.02; N, 12.99. Found: C, 37.26; H,
d-CHCl
3
): 177.95 (C ), 143.34 (C ), 133.06 (C ), 130.83 (C ),
ꢀ1
1
4,8
5,7
4
.13; N, 12.76%. Main IR bands (KBr, cm ):
m
(N –H) 3350m,
(C–H) 3061br, 2955m, 2920m;
(C–C) 1536s, 1521s; (C–N) 1076m, 1029m, 954m;
128.96 (C ), 127.76 (C ), 39.72 (CH ), 14.27 (CH ).
2 3
2
3
243m;
m(N –H) 3100m; m
m
m(C@N) +
m
2.2. X-ray data collection, structure solution and refinement
1
2
m(C@S) 822s. H NMR (d, ppm; d-CHCl
3
): 9.74 (s, 2H, –N H), 7.93
2
4,8
1
(
C
s, 2H, –C H), 7.67 (m, 4H, C H), 7.47 (b, 1H, N H), 7.43 (m, 2H,
Prismatic crystals of complexes 1 and 2 were mounted on a
Gonimeter Xcalibur diffractometer equipped with a graphite
5
–7
13
H), 3.80 (m, 2H, CH
2
–), 1.35 (t, 3H, CH
3
). C NMR (d, ppm;
Fig. 3. Interactions between twin molecules of complex 1.
Fig. 4. Interactions between two sets of twin molecules of complex 1.

T.S. Lobana et al. / Polyhedron 91 (2015) 89–97
93
monochromator and Mo K
a
radiation (k = 0.71073 Å). The unit cell
3. Results and discussion
dimensions and intensity data were measured at 110 K. The struc-
tures were solved by direct methods and refined by full matrix
least squares based on F2 using SHELXLS-97 [27]. Structure refine-
ment has been done using SHELXL-97 [28]. The weighted R-factor
3.1. Synthesis and IR spectroscopy of the complexes
Direct reaction of gold(I) chloride with benzaldehyde-N-methyl
2
1
wR and goodness of fit S are based on F , conventional R-factors
thiosemicarbazone (HL ) in a 1:2 M ratio (M:L) in acetonitrile has
2
1
1
2
are based on F, with F set to zero for negative F . The threshold
yielded an ionic complex of the stoichiometry, [Au(
j
-S-HL ) ]Cl
2
2
2
expression of F > 2
r
(F ) was used only for calculating R-factors(gt)
(1). Similarly, benzaldehyde-N-ethyl-thiosemicarbazone (HL ) has
1
2
etc. and is not relevant to the choice of reflections for refinement.
2
also formed a similar ionic complex, [Au(j -S-HL ) ]Cl (2) (Chart 2).
2
R-factors based on F are statistically about twice as large as those
It is added here that earlier in the direct reaction of gold(I) chloride
with 3-nitrobenzaldehyde thiosemicarbazone (Chart 1, R = 3-NO -
1
based on F, and R factors based on all data will be even larger.
2
Fig. 5. Interaction between different sets of twin molecules to form a zig–zag 1D chain.
Fig. 6. Interaction of chloride ions with different hydrogen atoms in complex 1.

9
4
T.S. Lobana et al. / Polyhedron 91 (2015) 89–97
Fig. 7. Interlinking of two zig–zag chains to form the 2D sheet of complex 1.
triphenyl phosphine, despite using a variety of solvent com-
binations [9]. The formation of complexes 1 and 2 in the present
investigation strongly supports the role of the substituents
1
(
methyl, ethyl) at N in the formation of ionic complexes, rendering
the presence of triphenyl phosphine unnecessary, unlike the
formation of complex 3 [9]. The gold(I) ionic complexes 1 and 2
represent the first examples obtained by the direct reaction of
gold(I) chloride with a thio-ligand without the presence of PPh
9] or the use of any intermediate substrate [12,14]. The IR spectral
bands shown by complexes 1 and 2 are listed in the experimental
3
[
1
section. In complex 1, the bands due to
m
(N –H) at 3371 and
(–N H–) at 3122 cm suggest that the thio-ligand
HL is coordinating to the gold metal center as a neutral ligand. The
ꢀ
1
2
ꢀ1
2
3273 cm and m
Fig. 8. The N ꢁ ꢁ ꢁH–CPh interaction in complex 2.
1
diagnostic
m(C@S) bands in the complexes appear at 832 and
3
1-S-HL3)
ꢀ1
C H
6
4
-; HL ), an ionic complex [Au(
j
2
]Cl (3) was reported
822 cm in complexes 1 and 2 respectively which are at lower
energy relative the free thio-ligands (See ESI).
by this laboratory, but the presence of triphenyl phosphine was
necessary to obtain a crystalline product [9]. However, the benzalde-
1
hyde thiosemicarbazone with two hydrogen atoms at the N atom
3.2. Molecular structures
1
(
2
–N H ) did not yield a crystalline product, even in the presence of
The crystallographic data of complexes 1 and 2 are given in
Table 1, while important bond parameters are placed in Table 2.
The molecular structures, along with numbering scheme, are given
2
Fig. 9. Interactions between chains (via N ꢁ ꢁ ꢁH–CPh interactions) in complex 2.
Fig. 10. Interactions of the chloride ion of complex 2.

T.S. Lobana et al. / Polyhedron 91 (2015) 89–97
95
Fig. 11. Packing diagram of complex 2.
bonding and other interactions are discussed in a stepwise fashion
Figs. 3–7). The hydrogen atoms of the methyl group at the N1
(
atom of the thiosemicarbazone ligand of one molecule showed
an interaction with the thione carbon atom of the second molecule
(
Fig. 3). In addition, there are C–H(Ph)ꢁ ꢁ ꢁ
p(Ph) interactions between
the two molecules (2.745 and 2.831 Å). These interactions appear
to be responsible for the formation of two molecules. Fig. 4 shows
the interaction between two sets of independent molecules
wherein the methyl group of one set has agostic interactions with
Fig. 12. Electronic absorption spectra of complexes 1 and 2 along with the spectra
of the ligands (HL1 and HL ).
2
in Figs. 1 and 2 respectively. Both complexes crystallized in the
1
monoclinic crystal system with the space group P2 /n. In complexes
1
and 2, two thiosemicarbazone moieties bind to the gold center via
+
the thione sulfur to form a [S-Au-S] core. For complex 1, two mole-
cules crystallized in the asymmetric unit, which interact with one
another, and the bond parameters of these molecules are slightly
different from each other (Fig. 1 and Table 2). The Au–S bond
distances are Au(1)–S(1B) 2.2760(14), Au(1)–S(1A) 2.2839(14),
Au(2)–S(1D) 2.2686(15) and Au(2)–S(1C) 2.2717(16) Å. These
Au–S distances are comparable to those found in the literature
[
9,12,14]. The Au–S bond distances are smaller than the sum of
the covalent radii of Au and S, 2.36 Å [29,30]. The C–S bond lengths
in 1 {1.729(6), 1.722(5); 1.727(5), 1.731(5) Å} are comparable to
those reported in the literature [9,12,14]. The S–Au–S bond angles
in complex 1 are 171.80(5) and 170.95(6)°, which indicate
distortion from linearity. The Au–S–C bond angles of 1 are in
the range 104.87(17)–109.57(18)° and are similar to literature
reports [9,12,14]. The Au–S {Au–S(1A) 2.2822(6) and Au–S(1B)
2
.2828(6) Å} and C–S {1.727(2) and 1.730(2) Å} bond distances
in 2 are also comparable to those found in the literature [9,12,14].
The S–Au–S bond angle is more distorted in complex
2
1
(
168.33(2)°) than in 1 due to the bulkier ethyl group at N atom
in 2.
3.3. H-bonded polymeric networks
In order to understand how complex 1, with a methyl sub-
stituent at the N atom, has two independent molecules in the unit
1
Fig. 13. (a) Fluorescence spectra of the ligands HL1 and HL2; (b) fluorescence
cell unlike only one molecule in case of complex 2, hydrogen
spectra of complexes 1 and 2.

9
6
T.S. Lobana et al. / Polyhedron 91 (2015) 89–97
I
1
]+ (C) (m/z = 583.11 obsd; 583.10 calcd.).
2
Fig. 14. ESI mass peaks for [Au (HL )
4
the methyl group of the second set (C–Hꢁ ꢁ ꢁ
r
electrons interact
C–Hꢁ ꢁ ꢁHCH
1 shows one absorption band at kmax = 308 nm (
e
= 6.02 ꢂ 10
ꢀ1
ꢀ1
with the C–H hydrogen atoms of the second set; H
2
1
2
,
L M cm ), while complex 2 also shows one band at kmax = 312 nm
4
ꢀ1
ꢀ1
2
.335 Å and
H
2
C–Hꢁ ꢁ ꢁCH
3
,
2.898 Å) and its N –H moiety
(e
= 7.70 ꢂ 10 L M cm ). The ligands also show absorption
4 ꢀ1 1
ꢀ1
1
(
N Hꢁ ꢁ ꢁHCH2, 2.348 Å). These types of interactions continue to
maxima at 307 nm (
e
= 2.71 ꢂ 10 L M cm , HL ) and 311 nm
4
ꢀ1
ꢀ1
2
form a zig–zag 1D chain (Fig. 5). Various interactions of the chlo-
(e
= 2.97 ꢂ 10 L M cm
,
HL ). These electronic absorption
⁄
ride ion are shown in Fig. 6. Two zig–zag chains are inter-linked
bands are assigned to n,
p
?
p
transitions. It can be noted that com-
1
via H
2
C–Hꢁ ꢁ ꢁCH
3
(2.898 Å), H
3
Cꢁ ꢁ ꢁCH
3
(3.602 Å) and N Hꢁ ꢁ ꢁHCH
2
plexation has enhanced the molar absorptivity by a factor of more
than two, though the band positions are essentially unchanged.
The solutions of the ligands in methanol show weak emissions in
the region 315–520 nm (maximum FI = 95 HL at k = 343 nm, 180
HL at k = 344 nm) (k = 308 nm), while both complexes show
intense fluorescence bands in the wide region 325–625 nm (maxi-
mum FI = 230 1 at k = 367 nm, 270 2 at k = 365 nm) (k = 308 nm)
(Fig. 13). The interaction of the ligands with gold(I) ions has signifi-
cantly enhanced the fluorescence intensity and thus the origin of the
fluorescence appears to be based on the thio-ligands (Fig. 13).
(
2.348 Å) interactions, along with chloride interactions, to form a
sheet-like structure (Fig. 7).
2
1
The interactions are different in complex 2. Here the N atom of
one of the thiosemicarbazone ligands of one molecule shows a
weak interaction with the phenyl ring of a thiosemicarbazone
2
ex
2
ex
ligand of a second molecule, N ꢁ ꢁ ꢁHCph 2.658 Å. These interactions
2
are repeated to form a 1D chain (Fig. 8). The N atom of this mole-
cule also shows a similar interaction with the phenyl ring of a
thiosemicarbazone ligand of second chain to form 2D sheet-like
structure (Fig. 9). The interactions of the chloride ion are shown
in Fig. 10. Finally Fig. 11 represents the combined packing, which
includes various interactions. It is added here that in complex 2
the ethyl group does not show any type of interaction, unlike
complex 1 wherein the methyl group at the N1 atom appears
instrumental in forming a pair of two independent molecules with
different intermolecular interactions.
3.5. ESI-mass studies
ESI-mass spectral data for both complexes have been obtained.
Complex 1 showed three lines at m/z values of 231.1, 461.2 and
583.1, which suggest the species as [Au Cl+H] (A) (calcd.
I
+
I
1
+
m/z = 232.9), [Au Cl
2
(HL )+2H] (B) (calcd. m/z = 461.9) and
I
1
+
[
Au (HL )
2
] (C) (calcd. m/z = 583.1). Complex 2 showed one signal
I
2
-4H]+ (D)
at m/z = 607.1, corresponding to the species [Au (HL )
2
1
13
3
.4. NMR ( H and C), electronic absorption and fluorescence
(calcd. m/z = 607.1). For complex 1, species C is in conformity with
the solid state molecular structure (Fig. 14). It also shows species A,
with no thio-ligand coordinated, and species B, which shows that
gold is bonded to a neutral thio-ligand and two halogen atoms.
With regards to complex 2, only one species, D, was identified
(see supplementary for more details of ESI-mass with isotopic
patterns).
spectroscopy
The 1H NMR spectrum of complex 1 shows an –N H proton
signal at 10.15 ppm and likewise complex 2 shows this signal at
2
9
.74 ppm, which are at lower fields relative to the free ligands
1
2
(
HL , 9.81 ppm; HL , 9.50 ppm). This strongly supports that both
the thio-ligands coordinate to the metal center as neutral ligands
2
in their complexes. Various other proton signals due to –C H,
4
. Conclusion
phenyl ring protons, methyl and ethyl protons are either
1
3
marginally low field or are unaffected. The C NMR spectra of
From this study it is concluded that the use of suitable thio-li-
1
2
1
2
complexes 1 and 2 show signals due to C , C , phenyl ring carbons,
methyl and ethyl carbons. The C1 carbons are upfield, C2 carbons
low field and the others are minimally affected (see experimental
gands, namely HL and HL , have made it possible to prepare
gold(I) ionic complexes 1 and 2 by the direct reaction of a metal
salt with the thiosemicarbazone ligand. It is important to know
that benzaldehyde thiosemicarbazone, with two hydrogen atoms
⁄
section and ESI ).
The electronic absorption spectra of 10ꢀ5M solutions of the
ligands and complexes in methanol are shown in Fig. 12. Complex
at the N atom (–N H
in the presence of triphenyl phosphine, despite using a variety of
1
1
), did not yield a crystalline product, even
2

T.S. Lobana et al. / Polyhedron 91 (2015) 89–97
97
solvent combinations [9]. The formation of complexes 1 and 2 in
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77;
9
the present investigation strongly supports the role of the sub-
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1
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(
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[9]. Complex 1, with a methyl substituent at the N atom, has two
(
independent molecules in the crystal lattice, while complex 2, with
an N-ethyl substituent, has only one type of molecule in the crystal
lattice. Both complexes have shown intense fluorescence bands
in the wide region 340–540 nm corresponding to an excitation
wavelength of 308 nm. The synthesis of gold(I) ionic complexes
might be useful from a bio-chemical point view as such complexes
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3
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(
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Financial assistance from Council of Scientific and Industrial
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8] J.S. Casas, E.E. Castellano, M.D. Couce, J. Elena, A. Sanchez, J. Sordo, C. Taboada,
J. Inorg. Biochem. 100 (2006) 1858.
[
[
0
5/EMRII) is gratefully acknowledged.
9] T.S. Lobana, Sonia Khanna, R.J. Butcher, Inorg. Chem. Commun. 11 (2008) 1433.
[
10] A. Castineiras, S. Dehnen, A. Fuchs, I. Garcia-Santos, P. Sevillano, Dalton Trans.
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Appendix A. Supplementary data
[
[
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N.L. Speziali, E.M.S. Fagundes, H. Beraldo, J. Inorg. Biochem. 105 (2011) 1729.
CCDC 1017811 and 1017812 contains the supplementary crys-
tallographic data for 1 and 2. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336 033; or e-mail:
deposit@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at http://dx.doi.org/10.
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