Silver(I) complexes with heterocyclic thiones and tertiary phosphines as ligands. Part 4. Dinuclear complexes of silver(I) bromide: The crystal structure of bis[bromo-(pyrimidine-2-thione)(triphenylphosphine)silver(I)]

Article abstract of DOI:10.1016/S0020-1693(00)00286-3

Mixed-ligand complexes of the formula [Ag(PPh₃)(L)Br]₂ were obtained by treatment of various heterocyclic thiones L {L = pyridine-2-thione (py2SH), pyrimidine-2-thione (pymtH), benz-1,3-imidazoline-2-thione (bzimtH₂), benz-1,3-thiazoline-2-thione (bztztH), 1-methyl-1,3-imidazoline-2-thione (meimtH) and 5-methoxy-benz-1,3-imidazoline-2-thione (5MeObzimtH₂)} with equivalent quantities of silver(I) bromide and triphenylphosphine in dry acetone. The compounds were characterized by their IR, far-IR, UV-Vis and ¹H NMR spectroscopic data. The crystal structure of [Ag(PPh₃)(pymtH)Br]₂ was determined by single-crystal X-ray diffraction methods. The complex exhibits a planar Ag₂Br₂ moiety in which each of the doubly bromine-bridged Ag(I) centres is further bonded to one phosphine P and one thione S atom.

Full text of DOI:10.1016/S0020-1693(00)00286-3

www.elsevier.nl/locate/ica
Inorganica Chimica Acta 310 (2000) 268–272
Note
Silver(I) complexes with heterocyclic thiones and tertiary
phosphines as ligands. Part 4. Dinuclear complexes of silver(I)
bromide: the crystal structure of
bis[bromo-(pyrimidine-2-thione)(triphenylphosphine)silver(I)]
Phil J. Cox* a,1, Paraskevas Aslanidis* b,2, Petros Karagiannidis b, Sotiris Hadjikakou c
a School of Pharmacy, The Robert Gordon Uni6ersity, Schoolhill, Aberdeen, AB10 1FR, UK
b Aristotle Uni6ersity of Thessaloniki, Faculty of Chemistry, Inorganic Chemistry Laboratory, PO Box 135, GR-540 06 Thessaloniki, Greece
c Inorganic and Analytical Chemistry, Department of Chemistry, Uni6ersity of Ioannina, 45100 Ioannina, Greece
Received 3 June 2000; accepted 28 August 2000
Abstract
Mixed-ligand complexes of the formula [Ag(PPh3)(L)Br]2 were obtained by treatment of various heterocyclic thiones L
{L=pyridine-2-thione (py2SH), pyrimidine-2-thione (pymtH), benz-1,3-imidazoline-2-thione (bzimtH2), benz-1,3-thiazoline-2-
thione (bztztH), 1-methyl-1,3-imidazoline-2-thione (meimtH) and 5-methoxy-benz-1,3-imidazoline-2-thione (5MeObzimtH2)} with
equivalent quantities of silver(I) bromide and triphenylphosphine in dry acetone. The compounds were characterized by their IR,
far-IR, UV–Vis and 1H NMR spectroscopic data. The crystal structure of [Ag(PPh3)(pymtH)Br]2 was determined by single-crystal
X-ray diffraction methods. The complex exhibits a planar Ag2Br2 moiety in which each of the doubly bromine-bridged Ag(I)
centres is further bonded to one phosphine P and one thione S atom. © 2000 Elsevier Science B.V. All rights reserved.
Keywords: Crystal structures; Heterocyclic thione complexes; Photolysis; Silver(I) bromide complexes; Triphenylphosphine complexes
phosphines as bulky p-acceptor co-ligands, whereby
particular emphasis has been placed on the determina-
tion of the factors causing variations of copper(I) ge-
ometry. In doing so, several synthetic routes have been
applied that have led to an exciting variety of struc-
tures, ranging from mononuclear three- or four-coordi-
nate species with trigonal planar and tetrahedral
copper(I) respectively, to dimers with a pseudo-four-co-
ordinated geometry [2].
In view of such extraordinary flexibility of the stereo-
chemistry of copper(I) with soft ligands, we decided to
extend our investigations to the related complexes of
the other coinage metals, starting with the examination
of any possible analogies when replacing copper(I) by
silver(I). In our first attempt, monomeric complexes of
the type [Ag(PPh3)2(L)Cl] were observed as a result of
the reaction between the cubane-like [Ag(PPh3)Cl]4 and
several heterocyclic thiones [3]. This result contrasted
1. Introduction
A considerable amount of work has been performed
on the synthesis and characterization of metal com-
plexes containing heterocyclic thiones as ligands in the
past two decades [1]. The chemical interest of these
thiones is due to the fact that they are potentially
ambidentate or multi-functional donors with either the
exocyclic S or heterocyclic N (or S or O) atom available
for coordination, whereas their biological interest arises
from their structural analogy to thiolated nucleosides.
In this context, our research has been focused for some
time on coordination compounds of copper(I) with a
large range of heterocyclic thiones containing triaryl-
1 *Corresponding author
2 *Corresponding author. Tel.: +30-31-997694; fax: +30-31-
997738; aslanidi@auth.gr
0020-1693/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(00)00286-3

P.J. Cox et al. / Inorganica Chimica Acta 310 (2000) 268–272
269
with the corresponding reactions with copper(I), where
binuclear complexes of the general formula
[Cu(PPh3)(L)X]2 were realized. More recently, two dif-
ferent types of monomeric complex, [Ag(PPh3)2(L)2]-
NO3 and [Ag(PPh3)2(L)], have been obtained on the
reaction of AgNO3 with several heterocyclic thiones
and triphenylphosphine as ligands [4]. Since these unex-
pected results showed the thione-containing coordina-
tion compounds of the heavier coinage metals to be just
as structurally diverse as their copper analogues, with
the promise of further surprising results, we decided to
continue our investigations in this very interesting field
of research. Here we report the preparation and charac-
terization of several silver(I) complexes obtained by
interaction of heterocyclic thiones with silver(I) bro-
mide in the presence of triphenylphosphine as a soft,
bulky co-ligand. On the occasion of the fact that both
terminal and bridging bonding modes were observed
for bromo ligands in [Cu(PPh3)2(pymtH)Br] [5] or in
[Cu(tmtp)(pymtH)Br]2 [6] and [Cu(PPh3)(pymtH)Br]2
sample to polyethylene on a Perkin–Elmer Spectrum
GX FT-IR system. The photolyses of non-gaseous solu-
tions of the complexes and quantum yields measure-
ments were carried out in 1 cm quartz cells using a
high-pressure HBO 200W/4 Osram lamp; a 2 cm water
filter and an ‘Applied Photophysics’ monochromator
were applied. All the photochemical work was carried
out in the dark.
2.2. Preparation of the complexes
The complexes of the formula [Ag(PPh3)(L)Br]2 were
prepared according to the following general procedure.
A
solution of 0.5 mmol triphenylphosphine and
0.5 mmol of the appropriate thione in 50 ml of acetone
was added to a suspension of 0.5 mmol of AgBr in
15 ml acetone and the mixture was moderately heated
for 12 h. The resulting clear solution was allowed to
cool and slow evaporation of the solvent at room
temperature gave the microcrystalline solid, which was
filtered off and dried in vacuo. All complexes prepared
and their elemental analyses are given in Table 1.
[7] respectively,
the molecular
structure
of
[Ag(PPh3)(pymtH)Br]2 has been determined by single-
crystal X-ray diffraction methods in order to discuss
how, in this case, the bromine atom acts.
2.3. Collection and reduction of X-ray data
2. Experimental
The unit cell and intensity data were collected on a
Delft Instruments FAST diffractometer using the rou-
2.1. Materials and instruments
tines ENDEX, REFINE and MADONL in the MADNES
software [9] and processed using ABSMAD [10]; detailed
procedures are described in the literature [11]. Absence
of crystal decay in the X-ray beam was confirmed by
checking equivalent reflections at the beginning and end
of data collection, which lasted about 8 h. The structure
was solved with SIR92 [12] and refined with SHELX93
[13]. Details are given in Table 2. The silver, bromine,
sulfur, phosphorus, nitrogen and carbon atoms were
refined with anisotropic temperature factors. The hy-
drogen atoms were allowed to ride on their attached
Silver bromide (Aldrich) and triphenylphosphine
(Fluka) were used as obtained, whereas the thiones
(Merck or Aldrich) were recrystallized from hot ethanol
prior to their use. All solvents used were of reagent
grade. IR, UV, Vis and NMR spectra, conductivities,
melting points and elemental analyses of carbon, nitro-
gen and hydrogen were performed as described previ-
ously [8]. The far-IR spectra were obtained from
polyethylene discs of approximate composition 1:15
Table 1
Melting points, analytical dataa and electronic spectral datab of the complexes
Complex
M.p. (°C)
Elemental analysis (%)
UV–Vis umax (log m)
C
H
N
1.
2.
3.
4.
5.
6.
[Ag(PPh3)(py2SH)Br]2
132
124
141
218
133
221
50.02 (49.22)
47.16 (46.92)
50.04 (50.02)
49.07 (48.64)
47.06 (46.83)
49.08 (49.55)
3.87 (3.59)
3.60 (3.58)
3.54 (3.53)
3.30 (3.26)
3.76 (3.75)
3.58 (3.68)
2.58 (2.50)
5.08 (4.97)
4.53 (4.66)
2.52 (2.27)
4.81 (4.96)
4.43 (4.44)
327.5(3.90)–285.(4.52)–258(4.30)
273(3.93)–266(3.97)–242.6(3.85)
309.0(3.93)–249.0(3.86)
329.5(4.85)–244.5(4.48)
285.5(3.99)–263.5(4.27)
[Ag(PPh3)(pymtH)Br]2
[Ag(PPh3)(bzimtH2)Br]2
[Ag(PPh3)(bztztH)Br]2
[Ag(PPh3)(meimtH)Br]2
[Ag(PPh3)(5MeObzimtH2)Br]2
322(3.92)–251.5(3.87)
a Calculated percentages follow the obtained values in parentheses.
b Maxima observed in CHCl3 (log m values in parentheses).

270
P.J. Cox et al. / Inorganica Chimica Acta 310 (2000) 268–272
Table 2
3.1. Spectroscopy
Crystal data and structure refinement
The UV–Vis spectra of the complexes in chloroform
Empirical formula
Formula weight
Temperature (K)
C44H38Ag2Br2N4P2S2
1124.4
293(2)
0.710 73
Monoclinic
C2/c
solutions are dominated by two main broad bands in
the regions 240–260 and 290–320 nm, which can be
attributed to intraligand transitions of the phosphine
and thione ligands respectively.
,
Wavelength (A)
Crystal system
Space group
The main feature of the solid-state infrared spectra of
Unit cell dimensions
the compounds, recorded in the range 4000–250 cm−1
,
,
a (A)
27.284(3)
9.219(2)
18.465(2)
108.44(2)
4406.1(12)
4
,
b (A)
apart from the existence of strong phosphine bands, is
the production of the usual four ‘thioamide bands’ at
wavenumbers around 1510, 1320, 100 and 750 cm−1
[15], as well as of the characteristic NH stretching
vibrations observed in the 3050–3160 cm−1 [16] region,
suggesting, in combination with the lack of w(SH)
bands at approximately 2500–2600 cm−1 [17], the ex-
clusive S-coordination mode of the thione ligands.
New bands in the far-IR spectra can be attributed to
metal–ligand vibrations, provided that they are suffi-
ciently distinct from those generated by the thione or
phosphine ligands in the same region. In fact, a single
band lying in the 217–228 cm−1 region in most of the
complexes under investigation can be positively as-
signed to w(AgS) stretching modes. This is a strong
indication for the terminal bonding mode of the thione
ligands; consequently, the bromine atoms may act as
bridging ligands between the two metals forming an
asymmetric Ag2Br2 core. Further useful information
supporting the above conclusion could be obtained
from the halogen-sensitive bands, for which, as has
already been well demonstrated [18], a good correlation
exists between the w(AgBr) wavenumbers and the
AgꢀBr bond lengths. Given that the w(AgBr) band for
,
c (A)
i (°)
Volume (A )
Z
3
,
Density (calculated)
1.695
(Mg m−3
)
Absorption coefficient
(mm−1
F(000)
2.906
)
2224
0.35×0.21×0.21
2.33 to 25.04
Crystal size (mm)
q range for data
collection (°)
Index ranges
−305h523
−105k59
−185l521
9013
3359 (Rint=0.0537)
2854
Reflections collected
Independent reflections
Observed reflections
[I\2|(I)]
Refinement method
Number of parameters
Goodness-of-fit on F2
(S)
Full-matrix least squares on F2
254
0.95
Final R indices
[I\2|(I)]
R1=0.027, wR2= 0.063
R1=0.033, wR2= 0.069
R indices (all data)
Final weighting scheme w=1/[|2(Fo2)+(0.0352P)2] where
P=(F2o+2F2c)/3
0.41
,
[AgBr(PPh3)2] with an AgꢀBr bond length of 2.568(1) A
Residual diffraction
max. (e−
A
)
lies at 170 cm−1 [18], whereas the corresponding value
−3
,
Residual diffraction
−0.40
,
for the ‘long’ AgꢀBr bond of 2.742(1) A in
−3
min. (e−
A
)
,
[Ag2Br2(PPh3)4].2CHCl3 is decreased by 50 cm−1, two
w(AgBr) bands assigned to the two inequivalent AgꢀBr
bonds, shifted near the 120 cm−1 region and separated
by less than 50 cm−1, are expected for the complexes
under investigation. However, even this region of the
far-IR spectra is occupied, in most of the cases, by
strong thione absorptions, making a definite location of
these halogen-sensitive bands impossible.
atoms with common isotropic temperature factors for
methyl and non-methyl hydrogen atoms. An absorption
correction was made with DIFABS [14].
The prevalence of the thione tautomer in the com-
1
plexes is further confirmed by the H NMR spectra of
the compounds, which display, apart from the signals
expected for the phosphine and thione ligands, a single
resonance at l:11–13 ppm attributed to the NH
proton.
3. Results and discussion
All the complexes are solids soluble in chloroform,
methanol, ethanol, acetone and acetonitrile. Their ele-
mental analyses (given in Table 1) are in accordance
with the proposed structures. Their solutions are non-
conducting in acetone and chloroform. Room-tempera-
ture magnetic measurements confirm the diamagnetic
nature of the compounds.
3.2. Photolysis
Room-temperature irradiation of the complexes at
uexit=270–310 nm in non-degassed chloroform solu-
tions causes decomposition into two photoproducts as

P.J. Cox et al. / Inorganica Chimica Acta 310 (2000) 268–272
271
3.3. Description of the structure
can be estimated according to the method of Coleman
et al. [19]. In accordance with our earlier observations in
analogous copper(I) mixed-ligand complexes, the decom-
position occurs within seconds and can be checked by
comparison of the intensities of the bands in the UV-
spectra, since no evolution of new bands or significant
shifts could be observed during the experiment. The
constitution of the solid products, which in all cases
deposit quickly, verified by means of elemental analyses
and by their IR spectra, is in agreement with
[Ag(L)2Br]n.
Bond lengths and valence angles are given in Table 3.
The atomic arrangement in the complex is shown in Fig.
1. The basic structural unit of [Ag(PPh3)(pymtH)Br]2 is
a dimer, where the two monomers are related by inver-
sion. The double bridging Br atoms generate a strictly
planar Ag2Br2 core in which each of the Ag atoms
displays a distorted tetrahedral environment. The other
two positions of each tetrahedron are occupied by one
S atom from pymtH and one P atom from PPh3. The
nitrogen-bonded hydrogen atoms of the two trans-posi-
tioned pymtH units participate in two short intramolec-
,
ular hydrogen bonds [N···Br=3.301(3) A, H···Br=
Table 3
,
2.453(3) A and NꢀHꢀBr=168.7(3)°].
,
Selected bond distances (A) and angles (°)
,
The two AgꢀP distances, both 2.4390(7) A, are some-
what shorter than those found in other tetracoordinate
silver(I) phosphine complexes, e.g. [Ag(PPh3)2(py2SH)-
Cl] (2.482(1) and 2.476(1) A) [3] and [Ag(PPh3)2-
(boztH)2]NO3 (2.480(1) and 2.514(2) A) [20].
Ag(1)ꢀP(1)
Ag(1)ꢀS(1)
2.4390(7)
2.5548(9)
2.7350(6)
2.8241(5)
2.7349(6)
1.689(3)
1.824(3)
1.826(3)
P(1)ꢀC(11)
N(1)ꢀC(2)
N(1)ꢀC(1)
N(2)ꢀC(4)
N(2)ꢀC(1)
C(2)ꢀC(3)
C(2)ꢀC(3)
C(3)ꢀC(4)
1.825(3)
1.322(4)
1.347(4)
1.332(4)
1.357(4)
1.366(5)
1.366(5)
1.343(5)
a
,
Ag(1)ꢀBr(1)c1
Ag(1)ꢀBr(1)
,
Br(1)ꢀAg(1)c1 a
S(1)ꢀC(1)
The BrꢀAgꢀBr and AgꢀBrꢀAg angles (95.17(2) and
84.32(2)°) are remarkably similar to those found in other
double-bromo-bridged species containing silver(I) in dif-
ferent environments, e.g. in [Ag2(PPh)3)4Br2] [18] and
[Ag2Br4]2− [21] with approximately tetrahedral and trig-
onal planar silver atoms respectively. Consequently, this
arrangement in the Ag2Br2 core can be hardly considered
as a consequence of any steric repulsions between the
terminal ligands, but can more easily attributed to the
close Ag···Ag and Br···Br contacts within the Ag2Br2
core. In general, the asymmetry in the molecule under
investigation is greater than in [Ag2(PPh)3)4Br2]·2CHCl3
[18].
P(1)ꢀC(5)
P(1)ꢀC(17)
P(1)ꢀAg(1)ꢀS(1)
118.03(3)
C(5)ꢀP(1)ꢀAg(1) 114.88(9)
C(17)ꢀP(1)ꢀAg(1) 117.91(9)
C(11)ꢀP(1)ꢀAg(1) 110.76(8)
C(2)ꢀN(1)ꢀC(1) 117.7(3)
C(4)ꢀN(2)ꢀC(1) 122.2(3)
N(1)ꢀC(1)ꢀN(2) 118.6(3)
N(1)ꢀC(1)ꢀS(1)
N(2)ꢀC(1)ꢀS(2)
N(1)ꢀC(2)ꢀC(3) 125.9(3)
C(4)ꢀC(3)ꢀC(2) 115.7(3)
N(2)ꢀC(4)ꢀC(3) 120.7(4)
P(1)ꢀAg(1)ꢀBr(1)c1 a 119.30(2)
S(1)ꢀAg(1)ꢀBr(1)c1 a 102.95(3)
P(1)ꢀAg(1)ꢀBr(1)
S(1)ꢀAg(1)ꢀBr(1)
110.33(2)
108.37(3)
Br(1)c1ꢀAg(1)ꢀBr(1) a 95.17(2)
Ag(1)c1ꢀBr(1)ꢀAg(1) a 84.83(2)
120.4(2)
120.9(2)
C(1)ꢀS(1)ꢀAg(1)
C(5)ꢀP(1)ꢀC(17)
C(5)ꢀP(1)ꢀC(11)
C(17)ꢀP(1)ꢀC(11)
111.77(11)
102.96(13)
104.63(13)
104.34(13)
a Atomic coordinates transposed by 3/2−x, 1/2−y, 1−z.
4. Supplementary material
Supplementary data are available free of charge on
request from the The Director, Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge, CB2
1EZ, UK (fax: +44-1223-336033; e-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk),
quoting the deposition number CCDC 114092.
Acknowledgements
We thank the EPSRC X-ray crystallographic service
at the University of Wales, Cardiff for data collection.
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NꢀH···Br hydrogen bonds.

272
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