Synthesis, characterization and antimicrobial studies of mixed ligand silver(I) complexes of thioureas and triphenylphosphine; crystal structure of {[Ag(PPh3)(thiourea)(NO3)]2·[Ag( PPh3)(thiourea)]2(NO3)2}

Article abstract of DOI:10.1016/j.poly.2009.12.037

Mixed ligand silver(I) complexes of triphenylphosphine and thioureas (thiourea (Tu), N-methylthiourea (Metu), N,N′-dimethylthiourea (Dmtu) and N,N′-diethylthiourea (Detu)) with the general formulae, [(Ph₃P)₂Ag(thione)]NO₃ and [(Ph₃P)Ag(thione)₂]NO₃, have been prepared and characterized by elemental analysis, IR and NMR (¹H, ¹³C and ³¹P) spectroscopic methods. The crystal structure of one of them has been determined by X-ray crystallography. The spectral data of the complexes are consistent with sulfur coordination of the thiones to silver(I). The single crystal X-ray structure of complex 1, {[Ag(PPh₃)(thiourea)(NO₃)]₂·[Ag( PPh₃)(thiourea)]₂(NO₃)₂}, shows that the complex consists of two independent centrosymmetric binuclear units, each having the silver atoms coordinated to one PPh₃ and two bridging thiourea molecules. In one of the independent units the silver atom is additionally bound to a nitrate ion, leading to a tetrahedral geometry, while in the other unit the silver atom adopts a trigonal planar environment. Antimicrobial activities of the complexes were evaluated by their minimum inhibitory concentration and the results showed that the complexes show a wide range of activity against two gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa) and molds (Aspergillus niger, Penicillium citrinum), while the activities were poor against yeasts (Candida albicans, Saccharomyces cerevisiae). However, the title complex did not show activity against any tested microorganism.

Full text of DOI:10.1016/j.poly.2009.12.037

Polyhedron 29 (2010) 1251–1256
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, characterization and antimicrobial studies of mixed ligand silver(I)
complexes of thioureas and triphenylphosphine; crystal structure
of {[Ag(PPh3)(thiourea)(NO3)]2ꢀ[Ag(PPh3)(thiourea)]2(NO3)2}
Anvarhusein A. Isab a, Sidra Nawaz b, Muhammad Saleem c, Muhammad Altaf d,
d
Muhammad Monim-ul-Mehboob a, Saeed Ahmad b, , Helen Stoeckli Evans
*
a Department of Chemistry, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
b Department of Chemistry, University of Engineering and Technology, Lahore 54890, Pakistan
c KINPOE, KNPC, PAEC, P.O. Box # 3183, Karachi 29, Pakistan
d Institute of Physics, University of Neuchâtel, CH-2009 Neuchâtel, Switzerland
a r t i c l e i n f o
a b s t r a c t
Article history:
Mixed ligand silver(I) complexes of triphenylphosphine and thioureas (thiourea (Tu), N-methylthiourea
(Metu), N,N0-dimethylthiourea (Dmtu) and N,N0-diethylthiourea (Detu)) with the general formulae,
[(Ph3P)2Ag(thione)]NO3 and [(Ph3P)Ag(thione)2]NO3, have been prepared and characterized by elemental
analysis, IR and NMR (1H, 13C and 31P) spectroscopic methods. The crystal structure of one of them has
been determined by X-ray crystallography. The spectral data of the complexes are consistent with sulfur
coordination of the thiones to silver(I). The single crystal X-ray structure of complex 1, {[Ag(PPh3)(thio-
urea)(NO3)]2ꢀ[Ag(PPh3)(thiourea)]2(NO3)2}, shows that the complex consists of two independent centro-
symmetric binuclear units, each having the silver atoms coordinated to one PPh3 and two bridging
thiourea molecules. In one of the independent units the silver atom is additionally bound to a nitrate
ion, leading to a tetrahedral geometry, while in the other unit the silver atom adopts a trigonal planar
environment. Antimicrobial activities of the complexes were evaluated by their minimum inhibitory
concentration and the results showed that the complexes show a wide range of activity against two
gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa) and molds (Aspergillus niger, Penicillium
citrinum), while the activities were poor against yeasts (Candida albicans, Saccharomyces cerevisiae). How-
ever, the title complex did not show activity against any tested microorganism.
Received 11 November 2009
Accepted 30 December 2009
Available online 14 January 2010
Keywords:
Silver(I) complexes
Thiourea
Triphenylphosphine
Spectroscopy
Crystal structure
Antimicrobial activity
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
ver(I) and gold(I) complexes with phosphines and thiones
[5,9,24–29]. In this work, our study is continued with the prep-
The coordination chemistry of silver(I) complexes with phos-
phorus and sulfur donor ligands has attracted great interest in
recent years because of the biological relevance of metal–sulfur
interactions in the living systems and the potential applications
of silver–phosphine complexes as antitumor/antibacterial agents
[1–15]. In view of this, the crystal structures of several silver(I)
complexes of phosphines and thioamides have been reported,
which describe that these complexes are either mononuclear or
dinuclear with the silver atom showing a distorted tetrahedral
or trigonal configuration [2,3,9,16–23]. We are particularly inter-
ested in the spectral and structural chemistry of M–P and M–S
complexes, and in this regard we have already reported the
spectroscopic and structural characterization of a number of sil-
aration, characterization and biological properties of silver(I)
complexes of the general formula, [Ag(PPh3)n(thioamide)n]NO3,
including the crystal structure of a tetranuclear silver(I) complex,
{[Ag(PPh3)(thiourea)(NO3)]2ꢀ[Ag(PPh3)(thiourea)]2(NO3)2}.
The
structures of the thiourea ligands used in this study are given
in Scheme 1.
2. Experimental
2.1. Materials
Silver nitrate (AgNO3) was obtained from Panreac, Spain and tri-
phenylphosphine (PPh3) from Alfa Aesar, USA. Thiourea was a
product of Merck, Germany. Other thiourea derivatives were pur-
chased from Acros Organics, Belgium.
* Corresponding author. Tel.: +92 333 5248570.
E-mail address: saeed_a786@hotmail.com (S. Ahmad).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.12.037

1252
A.A. Isab et al. / Polyhedron 29 (2010) 1251–1256
CH
H C
3
3
CH
NH
CH
3
3
CH
NH
3
P
NH
NH
H N
HN
H N
HN
2
2
2
S
S
S
S
Thiourea
N-Methylthiourea N,N/-Dimethylthiourea N,N/-Diethylthiourea Triphenylphosphine
Scheme 1. Structures of the ligands used in this study.
2.2. Synthesis of the complexes
F2. An empirical absorption correction was applied using the MUL-
scanABS routine in PLATON [32]; transmission factors: Tmin
/
The complexes were prepared by adding one or two equivalents
of a thione dissolved in 15–20 mL methanol (Detu was taken in
water) to a 1:1 mixture of AgNO3 and PPh3 in methanol–acetoni-
trile medium (10 mL and 15 mL, respectively). In each case, mixing
resulted in a clear solution that was stirred for a further 30 min.
The solutions were filtered and the filtrates were kept at low tem-
perature for crystallization. The white crystalline products ob-
tained were isolated and air-dried. The elemental analyses and
melting points of the complexes are given in Table 1.
Tmax = 0.685/0.849. Crystal data and details of the data collection
are summarized in Table 2.
2.5. Antimicrobial studies of the complexes
Antimicrobial activities of the silver(I) compounds prepared
here were estimated by the minimum inhibitory concentration
(MIC;
l
g mLꢁ1) [33]. Standard culture media of bacteria, Esche-
richia coli, (ATCC 13706) and Pseudomonas aeruginosa (MTCC
424), molds, Aapergillus niger (MTCC 1349) and Penicillium citrinum
(MTCC 5215), and yeast, Candida albicans (MTCC 183) and Saccha-
romyces cerevisiae (MTCC 463), were obtained from Qingdao Yijia
Huuyi Co., China. Bacteria were inoculated into 5 mL of liquid
SCD medium (soybean, casein and digest) and cultured for 24 h
at 35.5 °C. The cultured fluids were diluted, adjusted to a concen-
tration of 105–106 microorganisms per mL and used for inoculation
in the MIC test. In the case of the mold culture, the agar slant (po-
tato and dextrose) medium for one week cultivation at 27 °C was
gently washed with saline containing 0.05% Tween 80. The spore
suspension obtained was adjusted to the concentration of 105
microorganisms per mL and used for inoculation in the MIC test.
Yeast were inoculated into 5 mL of glucose polypeptone (GP) med-
ium and cultured for 48 h at 30 °C. The cultured fluids were di-
luted, adjusted to a concentration of 106–107 mLꢁ1 and used for
inoculation in the MIC test. The test materials (silver(I) complexes)
were suspended in water, and solutions were then diluted with
SCD medium for bacteria and with GP medium (glucose and poly-
peptone) for mold and yeast. Using them, two-fold diluted solu-
tions with concentrations of 1000–10 mg mLꢁ1 were prepared.
Each 1 mL of culture medium containing various concentrations
of the test materials was inoculated with 0.1 mL of the microorgan-
ism suspension prepared above. Bacteria were cultured for one day
at 35.5 °C, mold for 7 days at 25 °C and yeast for 2 days at 30 °C.
Growth of the microorganisms was monitored during this period.
When no growth of microorganism was observed in the medium
containing the lowest concentration of test materials, the MIC of
the test material was defined as being at this point of dilution.
2.3. IR and NMR measurements
The IR spectra of the complexes were recorded on a Perkin–
Elmer FTIR 180 spectrophotometer using KBr pellets over the range
4000–400 cmꢁ1. The 1H NMR spectra of the complexes in DMSO-d6
were obtained on a Jeol JNM-LA 500 NMR spectrometer operating
at a frequency of 500.00 MHz at 297 K using 0.10 M solution. The
13C NMR spectra were obtained at a frequency of 125.65 MHz with
1H broadband decoupling at 298 K. The spectral conditions were:
32 K data points, 0.967 s acquisition time, 1.00 s pulse delay and
45° pulse angle. The 13C chemical shifts were measured relative
to TMS.
2.4. X-ray structure determination
Single crystal data collection for complex 1 was performed at
173 K (ꢁ100 °C) on a Stoe Mark II-Image Plate Diffraction System
[30] equipped with a two-circle goniometer and using Mo K
a
graphite monochromated radiation. Image plate distance
100 mm, rotation scans: = 0–180° at u = 0° and = 0–150°
at u = 90.0°, step = 1.0°, exposures of 2 min per image, 2h
x
x
x
D
x
range = 2.29–59.53°, dmin ꢁ dmax = 17.779 ꢁ 0.716 Å. The structure
was solved by direct methods using the program SHELXS-97 [31].
The refinement and all further calculations were carried out using
SHELXL-97 [31]. The H-atoms were included in calculated positions
and treated as riding atoms: N–H = 0.88 Å, C–H = 0.95 Å and
Uiso(H) = 1.2Ueq (parent N or C-atom). The non-H atoms were re-
fined anisotropically, using weighted full-matrix least-squares on
Table 1
Elemental analysis and melting points of silver(I) complexes of phosphines and thiones, [(R3P)xAg(thione)y].
Complex
Found (Calc.) (%)
C
M.p. (°C)
H
N
S
[Ag(PPh3)1]NO3
50.24 (50.03)
44.41 (44.90)
56.97 (58.18)
44.70 (43.14)
55.94 (58.65)
45.46 (45.00)
48.42 (48.95)
58.95 (57.64)
3.39 (3.47)
3.66 (3.74)
4.33 (4.60)
4.52 (4.44)
4.23 (4.80)
4.92 (4.88)
4.91 (4.82)
5.75 (5.65)
3.87 (3.24)
9.27 (8.27)
4.81 (5.35)
10.97 (11.43)
5.34 (5.26)
11.44 (10.93)
7.88 (7.45)
7.69 (7.31)
–
206
192
175
110
155
160
140
140
[(PPh3)1Ag(Tu)1]NO3
[(PPh3)2Ag(Metu)1]NO3
[(PPh3)1Ag(Metu)2]NO3
[(PPh3)2Ag(Dmtu)1]NO3
[(PPh3)1Ag(Dmtu)2]NO3
[(PPh3)1Ag(Detu)1]NO3
[(PPh3)2Ag(Detu)2]NO3
7.56 (6.30)
3.53 (4.09)
9.98 (10.47)
3.79 (4.02)
10.0 (10.01)
5.02 (5.68)
5.76 (6.69)

A.A. Isab et al. / Polyhedron 29 (2010) 1251–1256
1253
Table 2
Table 3
Summary of crystal data and details of the structure determination for 1.
Selected IR absorptions (cmꢁ1) for the free ligands and their silver(I) complexes.
Crystal data
Species
m
(C@S)
m
(NH2,NH)
m(C–N)
m(NO)3
Formula
C38H38Ag2N6O6P2S2, C38H38Ag2N4P2S2,
2(NO3)
2033.13
Tu
732
694
634
625
560
641
620
625
642
625
620
3156,3365
3180
3245,3332
3409
3197
3203
3245
3244
3215
3274
1473
1477
1488
1478
1528
1521
–
1520
1445
1478
1478
–
[(PPh3)1Ag(Tu)1] NO3
Metu
[(PPh3)2Ag(Metu)1] NO3
[(PPh3)1Ag(Metu)2] NO3
Dmtu
[(PPh3)2Ag(Dmtu)1] NO3
[(PPh3)1Ag(Dmtu)2] NO3
Detu
[(PPh3)1Ag(Detu)1] NO3
[(PPh3)2Ag(Detu)2] NO3
1375
–
1386
1354
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
Triclinic
ꢀ
P1
8.5603(5)
15.3352(10)
18.0564(11)
60.957(4)
83.279(5)
84.782(5)
2056.4(2)
1
1.642
1.184
1024
0.40 ꢃ 0.29 ꢃ 0.18
1384
1355
a
(°)
b (°)
1377
1385
c
(°)
3231
V (Å3)
Z
qcalc (g cm3)
l
(Mo K
a
) (mmꢁ1
)
Table 4
1H and 13C NMR chemical shifts of the free ligands and their Ag(I) complexes in
DMSO-d6.
F(0 0 0)
Crystal size (mm)
Data collection
Temperature (K)
Species
dN–H
dC@S
dC–N
dC-5
173(2)
Tu
6.98, 7.25
7.61, 8.05
6.99, 7.45,
7.65
7.28, 7.83,
7.99
7.35, 7.75,
7.94
7.38
183.81
180.06
181.10 29.90,
31.10
–
–
–
–
–
k Mo K
h Min–Max (°)
h limits
k limits
l limits
Reflections: total, unique data,
Rint
Observed data [I > 2
Absorption: Tmin/Tmax
a
(Å)
0.71073
[(PPh3)1Ag(Tu)1] NO3
Metu
2.29–25.09
ꢁ10:10
ꢁ18:18
[(PPh3)2Ag(Metu)1]
176.00 31.00
–
–
ꢁ21:21
NO3
24202, 7329, 0.0487
[(PPh3)1Ag(Metu)2]
177.18 30.17
NO3
r(I)]
6035
0.685/0.849
Dmtu
[(PPh3)2Ag(Dmtu)1]
182.70 30.75
177.20 29.90,
32.19
177.80 29.80,
32.19
–
–
8.14, 8.49
Refinement
Nref, Npar
NO3
7329, 505
0.0344, 0.0745, 1.033
[(PPh3)1Ag(Dmtu)2]
7.93, 8.20
–
R, wR2, S [I > 2
w = [
r(I)]
NO3
r
2(Fo2) + (0.0421P)2 + 0.4103P]ꢁ1 where P = (Fo2 + 2Fc2)/3
Detu
[(PPh3)1Ag(Detu)1]
NO3
[(PPh3)2Ag(Detu)2]
NO3
7.30
8.14, 8.22
181.38 38.21
174.49 37.85
14.54
13.60,
14.90
13.90
Min. and Max. Resd. Dens. [e Å3] ꢁ0.719, 0.869
7.70
n.o.
38.0
3. Results and discussion
n.o., not observed.
The silver nitrate, triphenylphosphine and thioureas were trea-
ted in molar ratios of 1:1:1 or 1:1:2 in methanol–acetonitrile med-
ia. The elemental analyses of the resulting products correspond to
the compositions [(Ph3P)2Ag(thione)]NO3 and [(Ph3P)Ag(thi-
one)2]NO3, respectively. The elemental analysis of the starting
Ag–PPh3 complex corresponds to the formula [Ag(PPh3)NO3]. A
similar product was also prepared for tetramethylthiourea (Tmtu)
by reacting [Ag(PPh3)NO3] with tetramethylthiourea (Tmtu) (1:1),
but it is interesting to note that the compound analyzed was found
to be a bis(phosphine) complex, [Ag(PPh3)2NO3] rather than a
mixed ligand complex.
that the ligands are coordinating to silver(I) via the thione group
(proton loss will change this to the thiolate form).
As shown in Table 4, in all the complexes the C@S resonance ap-
pears upfield compared to the free ligands, in accordance with the
data observed for other complexes of Cu(I), Ag(I) and Au(I) with
thiones [24–29,34]. The upfield shift is attributed to a lowering
of the >C@S bond order upon coordination and a shift of N ? C
electron density producing partial double bond character in the
C–N bond [24–29]. The upfield shift decreases as the number of li-
gands attached to silver(I) increases from one in [(Ph3P)2Ag(thi-
one)]NO3 to two in [(Ph3P)Ag(thione)2]NO3. This is because in the
bis(thione) complexes each thione is sharing about half a silver
atom rather than one as in the mono(thione) complexes. A small
shift of ꢂ1 ppm is observed in other carbon atoms, which shows
that the nitrogen atoms are not involved in coordination. The dif-
ference in shielding at C@S is related to the strength of the me-
tal–sulfur bond, which arises from the back donation of silver(I)
to sulfur [24]. So the Dmtu complexes with the most significant
shift in C@S are found to be the most stable.
The resonances for the triphenylphosphine ring carbons of the
complexes were observed in the region 128–134 ppm (Table 5).
The carbon atoms C(-P), C-2, C-3 and C-4 of the free triphenylphos-
phine resonate at 137.2, 133.6, 128.4 and 128.5 ppm, respectively.
In the complexes, the C–P resonance is shifted upfield, while the
other resonances remain almost unshifted. Upfield shifts of about
4–5 ppm in the C–P resonance compared to free Ph3P are consis-
tent with its coordination to a metal center [35]. The upfield shift
is attributed to the shift of electron density from the metal ion to-
3.1. Spectroscopic studies
Selected IR spectroscopic vibration bands for the free ligands
and their silver(I) complexes are given in Table 3. A low frequency
shift in the m(C@S) band and a high frequency shift in the m(N–H)
band of the complexes compared to the free ligands are indicative
of the coordination of the ligands to the metal ion. A sharp band
around 1300 cmꢁ1 for NO3ꢁ bending was observed for all theꢁcom-
plexes, indicating the presence of a non-coordinated NO3 ion
[18,19]. A characteristic peak due to m
(P–CPh) around 1090 cmꢁ1
indicated the presence of PPh3 in the complexes.
The 1H and 13C NMR chemical shifts of the complexes in DMSO-
d6 are summarized in Table 4. In the 1H NMR spectra of the com-
plexes, the N–H signal of the thiones became less intense upon
coordination and shifted downfield by 0.5–1.0 ppm from their
positions in the free ligands. The deshielding of the N–H proton
is related to an increase of the
p electron density in the C–N bond
upon complexation [24,25]. The appearance of a N–H signal shows
wards C(-P), because of the p-accepting nature of PPh3. The C(-P),

1254
A.A. Isab et al. / Polyhedron 29 (2010) 1251–1256
Table 5
Table 6
31P and 13C chemical shifts of the PPh3 part of the complexes.
Selected geometric parameters for compound 1.
Species
d(31P)
ꢁ5.5
dC-1
dC-2
dC-3
dC-4
Bond lengths (Å)
Bond
Distance
Bond
Distance
PPh3
137.20 133.60 128.40 128.60
10.20, 13.55 131.52 133.62 129.38 131.21
[Ag(PPh3)NO3]
[Ag(PPh3)2NO3]a
[(PPh3)1Ag(Tu)1] NO3
[(PPh3)2Ag(Metu)1] NO3 10.37
[(PPh3)1Ag(Metu)2] NO3 8.01
[(PPh3)2Ag(Dmtu)1]
NO3
[(PPh3)1Ag(Dmtu)2]
NO3
Ag1ꢀ ꢀ ꢀAg1a
2.9027(10)
2.5478(10)
2.4029(10)
2.6542(9)
2.519(3)
Ag2ꢀ ꢀ ꢀAg2b
2.8704(4)
2.6272(11)
2.4157(10)
2.6179(10)
9.26
9.21
131.47 133.60 129.40 131.06
132.06 133.84 129.57 131.14
131.57 133.64 129.45 131.11
132.20 133.49 129.27 130.76
131.51 133.65 129.44 131.11
Ag1–S1
Ag2–S2
Ag1–P1
Ag2–P2
Ag1–S1a
Ag1–O1
Ag2–S2b
10.42
Bond angles (°)
Bond
Angle
Bond
Angle
8.75
132.03 133.50 129.34 130.89
S1–Ag1–P1
S1–Ag1–P1a
S1–Ag1–S1a
S1–Ag1–O1
S1–Ag1–O1a
P1–Ag1–O1
120.86(3)
120.60(3)
112.18(5)
96.52(3)
91.77(7)
106.15(8)
S2–Ag2–P2
127.58(3)
118.56(3)
113.64(3)
67.80(2)
66.36(3)
S2–Ag2–P2b
S2–Ag2–S2b
Ag1–S1–Ag1a
Ag2–S2–Ag2b
[(PPh3)1Ag(Detu)1] NO3
[(PPh3)2Ag(Detu)2] NO3
10.10
7.31
131.46 133.62 129.43 131.11
132.29 133.44 129.22 130.69
a
The product is actually isolated from the reaction of [Ag(PPh3)NO3] and
tetramethylthiourea.
Symmetry codes: (a) 1 ꢁ x, 1 ꢁ y, 1 ꢁ z; (b) ꢁx, ꢁy, ꢁz.
C-2 and C-3 resonances are in the form of doublets, while C-4 ap-
pears as a singlet.
coordination environment around the silver atoms. In one of the
binuclear units, the silver atom, Ag1, is tetrahedrally coordinated
to one P atom of PPh3, two S atoms of bridging thiourea ligands
and one oxygen atom of the nitrate ion. The two S1–Ag1–P1 angles
have values of 120.60(3)° and 120.86(3)°, which are larger than the
normal tetrahedral value of 109.5°. This large angle is counter bal-
anced by the S1–Ag1–O1 bond angles of 91.77(7)° and 96.52(7)°.
This tetrahedral distortion is probably due to the steric imposition
of the bulky phosphine ligands. In the second independent mole-
cule, the silver atom, Ag2, is bound to one PPh3 and two sulfur
atoms of the bridging thiourea units in a trigonal planar environ-
ment. In the two units the Ag–P [2.4029(10)–2.4157(10) Å] and
Ag–S [2.5478(10)–2.6542(9) Å] distances are comparable to the
values reported for similar silver(I) complexes [9,17–21,36,37],
while the Ag–O bond length [2.519(3) Å] is somewhat longer than
that found in other silver–oxygen bonding complexes [38,39]. The
Ag–P distances of the tetrahedrally coordinated Ag1 atoms are
similar to those in the trigonally coordinated center, Ag2. However,
while the Ag–S bonds involving the atom Ag2 are similar
[2.6272(11) and 2.6179(19) Å], those involving atom Ag1 are con-
siderably different [2.5478(10) and 2.6542(9) Å]. The nitrate ions
in both units are strictly planar but exhibit low symmetry owing
to rather strong hydrogen bonding interactions with the NH2
groups of the thione ligands.
The 31P NMR chemical shifts are given in Table 5. In the 13P NMR
spectra of the complexes, a sharp singlet was observed for Ph3P ex-
cept for [Ag(Ph3P)NO3], where a doublet was observed. The doublet
shows that 31P–109/107Ag coupling is partially resolved for
[Ag(PPh3)NO3], with a coupling constant of 678 Hz. The P–Ag cou-
pling could not be detected for the other complexes and only sing-
lets are observed due to rapid exchange of PPh3 at various positions
in solution. The 31P resonance in the complexes is significantly
downfield shifted compared to free Ph3P. A downfield shift in the
31P resonance of the complexes is related to the donation of the
electron pair on the phosphorus to the metal, which reduces the
shielding at the phosphorus nucleus. The shifts are found to be
smaller for bis(thione) complexes than for mono(thione)
complexes.
3.2. Crystal structure description
The molecular structure of compound 1 is shown in Fig. 1, and
selected bond lengths and angles are given in Table 6. The complex
consists of two independent centrosymmetric binuclear units, each
consisting of two silver(I) ions. In each binuclear unit the two silver
centers are bridged by the sulfur atoms of two thiourea molecules
to form a four-membered Ag–S–Ag–S ring. There are two kinds of
Fig. 1. A view of the molecular structure of compound 1, with displacement ellipsoids drawn at the 50% probability level [H-atoms have been omitted for clarity; symmetry
operations (a) 1 ꢁ x, 1 ꢁ y, 1 ꢁ z; (b) ꢁx, ꢁy, ꢁz].

A.A. Isab et al. / Polyhedron 29 (2010) 1251–1256
1255
The Ag1ꢀ ꢀ ꢀAg1a and Ag2ꢀ ꢀ ꢀAg2b distances of 2.9027(10) and
2.8704(4) Å, respectively, indicate that the complex is stabilized
by significant argentophilic interactions. The Agꢀ ꢀ ꢀAg distances
are comparable to reported values [40–43]. Due the presence of
these Agꢀ ꢀ ꢀAg interactions, the Ag1–S1–Ag1a and Ag2–S2–Ag2b
bond angles [68.80(2)° and 66.36(3)°, respectively], are consider-
ably smaller than the C–S–Ag bond angles [95.75(12)–
112.59(14)° involving Ag1, and 108.20(12)–110.44(11)° involving
Ag2].
In the crystal, N–Hꢀ ꢀ ꢀO hydrogen-bonding interactions are pres-
ent. They involve all four –NH2 groups in each independent unit
and all six nitrate oxygen atoms (Table 7). This results in the for-
mation of a two-dimensional hydrogen bonded network propagat-
ing in (0 1 1), as shown in Fig. 2.
Ag(Mtu)2]NO3, exhibits the most significant activity among these
complexes, especially its activity against bacteria is remarkable.
[(PPh3)1Ag(Detu)1]NO3 is only effective against bacteria and is
inactive against all other tested microorganisms. The other com-
plexes, particularly [(PPh3)1Ag(Dmtu)2]NO3 and [(PPh3)2Ag(De-
tu)2]NO3, display a moderate activity.
The antibacterial activities of the complexes are due to a direct
interaction of the metal ions with biological ligands such as pro-
teins, enzymes and membranes [1,6,44]. The activities of the sil-
ver(I) complexes given in Table 8 may be attributed to their
tendency to undergo further ligand replacement reactions with
the biological ligands such as proteins and DNA. The poor activity
of the title complex shows that the chelate is highly stable due to
which the ligands could not be displaced easily by biological
ligands.
3.3. Antimicrobial activities
The antimicrobial activities of the silver(I) complexes (average
of three measurements) estimated by minimum inhibitory
4. Conclusion
concentrations (MIC; l
g mLꢁ1) are listed in Table 8. Table 8 shows
The present report describes that thioureas in the presence of
PPh3 react with AgNO3 to form complexes of the type
[(Ph3P)2Ag(thione)]NO3 and [(Ph3P)Ag(thione)2]NO3, in which the
thione ligands coordinate through the sulfur atom. The crystal
structure of the complex (1) presented here represents a novel sil-
ver(I) cluster that consists of two different types of binuclear mol-
ecules, with the nitrate ions present in the form of a ligand as well
as a non-coordinated counter ion. One of the complexes exhibits
significant biological activity, showing the potential for its use as
an antibacterial agent.
that the tested complexes showed a wide range of activity against
two gram-negative bacteria (E. coli, P. aeruginosa). However, the ti-
tle complex, {(PPh3)1Ag(Tu)1NO3}4, did not show activity against
any of the tested microorganisms. The Metu complex, [(PPh3)1
Table 7
Hydrogen bonding details in compound 1.
D–Hꢀ ꢀ ꢀA
D–H (Å)
Hꢀ ꢀ ꢀA (Å)
Dꢀ ꢀ ꢀA (Å)
D–Hꢀ ꢀ ꢀA (°)
N1–H1Aꢀ ꢀ ꢀO2a
N1–H1Bꢀ ꢀ ꢀO6
N2–H2Aꢀ ꢀ ꢀO2a
N2–H2Bꢀ ꢀ ꢀO1
N4–H4Aꢀ ꢀ ꢀO5b
N4–H4Bꢀ ꢀ ꢀO4c
N5–H5Aꢀ ꢀ ꢀO6b
N5–H5Bꢀ ꢀ ꢀO2d
N5–H5Bꢀ ꢀ ꢀO3d
0.88
0.88
0.88
0.88
0.88
0.88
0.88
0.88
0.88
2.16
1.97
2.09
2.06
2.31
2.07
2.3
2.940(4)
2.841(4)
2.887(5)
2.847(5)
2.975(4)
2.924(4)
2.910(5)
2.969(4)
3.159(5)
147
170
150
148
132
165
127
159
131
5. Supplementary data
CCDC 745856 contains the supplementary crystallographic data
for compound 1. 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, Cam-
bridge CB2 1EZ, UK; fax: (+44) 1223–336-033; or e-mail: deposit@
ccdc.cam.ac.uk.
2.13
2.51
Symmetry codes: (a) 2 ꢁ x, 1 ꢁ y, 1 ꢁ z; (b) x, y ꢁ 1, z; (c) 1 ꢁ x, 1 ꢁ y, ꢁz; (d) 1 ꢁ x,
ꢁy, 1 ꢁ z.
Fig. 2. View along the c-axis of the crystal packing in compound 1 showing the N–Hꢀ ꢀ ꢀO hydrogen bonds.

1256
A.A. Isab et al. / Polyhedron 29 (2010) 1251–1256
Table 8
Antimicrobial activities of the Ph3P–silver(I)–thione complexes evaluated by the minimum inhibitory concentration (MIC:
l
g mLꢁ1).
Microbial activity (in terms of MIC:
l
g mLꢁ1
)
Complexes
E. coli
P. aeruginosa
A. niger
P. citrinum
C. albicans
S. cerevisiae
[(PPh3)1Ag(Tu)1] NO3
>1000
480
50
420
180
510
170
>1000
390
40
470
220
620
210
>1000
810
210
910
390
>1000
970
320
840
410
>1000
>1000
440
>1000
720
>1000
>1000
410
930
630
[(PPh3)2Ag(Metu)1] NO3
[(PPh3)1Ag(Metu)2] NO3
[(PPh3)2Ag(Dmtu)1] NO3
[(PPh3)1Ag(Dmtu)2] NO3
[(PPh3)1Ag(Detu)1] NO3
[(PPh3)2Ag(Detu)2] NO3
>1000
570
>1000
610
>1000
630
>1000
580
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