Structural and infrared spectroscopic studies of some novel mechanochemically accessed adducts of silver(I) oxoanion salts with thiourea

Article abstract of DOI:10.1021/ic802312j

An investigation of the silver(l) nitrate/thiourea ("tu") system, exploiting the uniquely powerful access provided by the recently developed combination of mechanochemical synthesis coupled with Vibrational Spectroscopy, has resulted in the identification

Full text of DOI:10.1021/ic802312j

Inorg. Chem. 2009, 48, 3185-3197
Structural and Infrared Spectroscopic Studies of Some Novel
Mechanochemically Accessed Adducts of Silver(I) Oxoanion Salts with
Thiourea
Graham A. Bowmaker,*,† Brian W. Skelton,‡ and Allan H. White‡
Department of Chemistry, UniVersity of Auckland, PriVate Bag 92019, Auckland, New Zealand,
and Chemistry M313, School of Biomedical, Biomolecular and Chemical Sciences, UniVersity of
Western Australia, Crawley, Western Australia 6009, Australia
Received December 2, 2008
An investigation of the silver(I) nitrate/thiourea (“tu”) system, exploiting the uniquely powerful access provided by
the recently developed combination of mechanochemical synthesis coupled with vibrational spectroscopy, has resulted
in the identification of solid adducts AgNO3/tu (x:y) for x:y ) 1:1, 1:1.5, 15:23 () 1:1.5333), and 1:3. This contrasts
with previously published claims for the existence of 1:2 and 1:4 complexes and was confirmed in the case of the
1:3 and 15:23 complexes by X-ray crystal structure determinations on samples prepared by crystallization from
aqueous solution. The 1:3 sulfate and perchlorate complexes were also prepared for comparison with the
corresponding nitrate compound. In the 1:3 nitrate complex, the one independent silver atom major component
(0.78(1)) is closely trigonal planar AgS3 (Ag-S 2.518(2)-2.592(1) Å, Σ(S-Ag-S) 359.70°); there are minor nearby
components (0.11(1)) which may be regarded as four-coordinate, forming a putative one-dimensional polymer. The
sulfate, obtained as its tetrahydrate, has a cation of the familiar binuclear form [{(tu)2Ag(µ-S-tu)}2](SO4)·4H2O,
while the perchlorate, previously also characterized with the binuclear cation in the anhydrate, has now been
isolated as the hemihydrate, having a single-stranded polymeric cation, [· · ·Ag(tu)2(µ-S-tu)· · · (∞|∞)(ClO4) · 0.5H2O,
]
similar to that observed in CuX/tu (1:3) (X ) Cl, Br, I). The remarkable 15:23 nitrate complex (shown to be distinct
14+
from the 1:1.5 complex) may be regarded as essentially ionic [Ag15(tu)23(ONO2)] (NO-3 )14 (the cation incorporating
(∞|∞)
one O-nitrate ion loosely associated) and comprising one-dimensional polymer strands made up of four-, six-, and
eight-membered Ag2nS2n rings, cross-linked by the sulfur of one of the tu ligands. The ν(CS) and νa(CN) bands in
the infrared spectra of the complete series of adducts show a monotonic wavenumber decrease and increase,
respectively, with decreasing tu content of the adduct, indicating a decrease in the C-S bond strength and a
concomitant increase in the C-N bond strength with increasing Ag-S bond strength. The increase in Ag-S bond
strength with decreasing tu content is also indicated by an increase in the wavenumbers of the bands assigned to
ν(AgS) in the 140-200 cm-1 region in the far-IR. These and the structural data for the 1:3 and 15:23 complexes
provide the basis for establishing a correlation between ν(AgS) and the Ag-S bond length d(AgS) for silver complexes
involving the tu ligand.
Introduction
compositions and structures, have been reported in the past;1
in these, the thiourea and its derivatives (x)tu behave as “soft”
ligands, capable of unidentate or diverse bridging modes.
Much of the interest in these compounds derives from the
many and varied structures that they show and the relevance
of these in areas as diverse as bioinorganic chemistry and
A considerable number of complexes of simple copper(I)
salts, formed with thiourea (“tu”; SC(NH2)2) and its simple
substituted derivatives (xtu), involving a wide variety of
*
To whom correspondence should be addressed. E-mail:
ga.bowmaker@auckland.ac.nz.
†
University of Auckland.
(1) Bowmaker, G. A.; Hanna, J. V.; Pakawatchai, C.; Skelton, B. W.;
‡
University of Western Australia.
Thanyasirikul, Y.; White, A. H. Inorg. Chem. 2009, 48, 350–368.
10.1021/ic802312j CCC: $40.75  2009 American Chemical Society
Inorganic Chemistry, Vol. 48, No. 7, 2009 3185
Published on Web 02/25/2009

Bowmaker et al.
electrochemistry.2-4 Complexes CuX/(x)tu (1:n), where X
is a coordinating or noncoordinating anion (halide, nitrate,
perchlorate, etc.), with a range of integral and nonintegral n
values are known, and the complexity of the structural types
ranges from mononuclear to infinite polymeric, with a
number of tetranuclear complexes of diverse composition
and structure being featured in the compounds reported to
date.1 In contrast to the situation for copper(I), a considerably
smaller number of silver(I) complexes of thiourea and its
derivatives have been reported, with mainly mononuclear
or binuclear structures being observed for compounds of the
form AgX/(x)tu (1:n), in the main with integral n ) 1, 2, 3,
and 4,5,6 although an infinite polymeric n ) 0.5 complex
has also been reported.7
Many of the diverse structural types that have been
reported for copper(I)/(x)tu complexes involve the parent
(unsubstituted) tu ligand together with noncoordinating nitrate
and sulfate (oxo-)counterions.1,8-13 It is therefore rather
surprising that there have been no reports of structures of
silver(I)/thiourea complexes involving these anions. In a
recent solid-state NMR study of the silver(I) nitrate/thiourea
system, it was claimed that the results demonstrated the
existence of AgNO3/tu (1:n), for n ) 1 and 4 only.14 This
contrasts with a much earlier report of the existence of a
1:3 complex.15 There appear to be no reports of the formation
and composition of Ag2SO4/tu complexes, although the
structure of a 1:6 ethylenethiourea complex is known.5 We
report here the results of studies of the synthesis, crystal
structures, and IR spectra of the AgNO3/tu, AgClO4/tu, and
Ag2SO4/tu systems, which showed unexpected and unprec-
edented degrees of complexity in a number of systems. These
compounds have provided a good basis for a study of the
relationship between the IR spectra and the composition and
structures of the complexes concerned, and the results are
reported herewith. We have recently shown that the method
of solvent-assisted mechanochemical synthesis coupled with
IR spectroscopy provides a unique and powerful window
into the systematic study of the formation of metal com-
plexes;1,16,17 the further exploitation of this technique in the
present work has been fundamental in enabling the access
of new and surprising stoichiometries and forms.
Experimental Section
Preparation of Compounds. Mechanochemical Experiments.
Reactants producing about 0.2-0.4 mmol of the silver complex
were mixed and ground using an agate mortar and pestle of the
type normally used for preparing samples for IR spectroscopy. A
small amount of solvent (2-4 drops), just sufficient to allow the
formation of a paste during grinding, was added and the mixture
further ground for a few minutes. The solvent was removed from
the resulting paste of product by allowing it to stand for a few
minutes in the air, and the IR spectra of the products were recorded
immediately by using the attenuated total reflectance (ATR) method.
The systems studied (and the solvents used) are as follows:
AgNO3:ntu; n ) 1, 1.5, 2, 3, 4 (water)
AgNO3:ntu; n ) 4 (methanol)
Ag2SO4:ntu; n ) 6 (water)
Solution-Based Syntheses. AgNO3/tu (1:3), 1. A solution of
AgNO3 (0.340 g, 2 mmol) in water (5 mL) was added rapidly with
stirring to a solution of thiourea (0.760 g, 10 mmol) in water (7
mL) at room temperature. An initial white precipitate dissolved
upon stirring. Fine colorless crystals suitable for X-ray diffraction
studies separated upon standing. The product was collected and
washed with ice-cold water. Yield: 0.423 g (53.1%). Anal. calcd
for C3H12AgN7O3S3: C, 9.05; H, 3.04; N, 24.62. Found: C, 9.1; H,
2.9; N, 24.5%. The same complex was obtained from an acetonitrile/
methanol solvent mixture: A solution of AgNO3 (0.340 g, 2 mmol)
in boiling acetonitrile (5 mL) was added rapidly with stirring to a
solution of thiourea (0.760 g, 10 mmol) in boiling methanol (5 mL).
An initial white cloudiness dissolved upon stirring. A fibrous mass
of white solid separated upon standing. The product was collected
and washed with acetonitrile/methanol (1:1 v/v). Yield: 0.318 g
(39.9%). Anal. calcd for C3H12AgN7O3S3: C, 9.05; H, 3.04; N,
24.62. Found: C, 9.3; H, 3.0; N, 24.9%. The IR spectrum of this
product is identical to that of the corresponding compound obtained
from aqueous solution.
AgNO3/tu (1:1.5), 2, and (15:23), 3. A solution of AgNO3 (0.340
g, 2 mmol) in water (10 mL) was added rapidly with stirring to a
solution of thiourea (0.228 g, 3 mmol) in water (10 mL) at room
temperature. A white flocculent precipitate formed as the last of
the AgNO3 solution was added. Heating the mixture dissolved the
precipitate but caused some decomposition, resulting in the forma-
tion of a black precipitate. The warm solution was filtered twice to
remove most of the black material, and the filtrate was allowed to
stand and cool. After about 30 min, the whole solution had become
a solid mass of interlocked colorless microcrystalline solid. This
was collected and washed with water. Yield: 0.170 g (29.9%). Anal.
calcd for the 1:1.5 complex C1.5H6AgN4O3S1.5: C, 6.34; H, 2.13;
N, 19.72. Found: C, 6.4; H, 2.4; N, 19.5%. Small colorless crystals
suitable for X-ray diffraction studies formed in the filtrate upon
standing in an open beaker in the fume cupboard to facilitate
evaporation for 4 days, and these were collected and washed with
(2) Bordas, J.; Koch, M. H. J.; Hartmann, H. J.; Weser, U. Inorg. Chim.
Acta 1983, 78, 113–120.
(3) Javet, P.; Hintermann, H. E. Electrochim. Acta 1969, 14, 527–532.
(4) Alodan, M.; Smyrl, W. Electrochim. Acta 1998, 44, 299–309.
(5) Bowmaker, G. A.; Chaichit, N.; Pakawatchai, C.; Skelton, B. W.;
White, A. H. Can. J. Chem. 2009, 87, 161–170.
(6) Bowmaker, G. A.; Pakawatchai, C.; Skelton, B. W.; Thanyasirikul,
Y.; White, A. H. Z. Anorg. Allg. Chem. 2008, 634, 2583–2588.
(7) For example: Beheshti, A.; Clegg, W.; Brooks, N. R.; Sharafi, F.
Polyhedron 2005, 24, 435–441.
(8) Griffith, E. H.; Hunt, G. W.; Amma, E. L. J. Chem. Soc., Chem. Comm.
1976, 432–433.
(9) Van Meerssche, M.; Kamara, R.; Germain, G.; Declercq, J. P. Bull.
Soc. Chim. Belg. 1982, 91, 553–564.
(10) Declercq, J. P.; Kamara, R.; Moreaux, C.; Dereppe, J. M.; Germain,
G.; Van Meerssche, M. Acta Crystallogr., Sect. B 1978, 34, 1036–
1037.
(11) Bott, R. C.; Bowmaker, G. A.; Davis, C. A.; Hope, G. A.; Jones, B. E.
Inorg. Chem. 1998, 37, 651–657.
(12) Solov’ev, L. A.; Vasil’ev, A. D.; Golovnev, N. N. Russ J. Coord.
Chem. 2002, 28, 587–592.
(13) Piro, O. E.; Piatti, R. C. V.; Bolza´n, A. E.; Salvarezza, R. C.; Arvia,
A. J. Acta Crystallogr., Sect. B 2000, 56, 993–997.
(14) Wazeer, M. I. M.; Isab, A. A.; Ahmad, S. Can J. Anal. Sci. Spectrosc.
2006, 51, 43–48.
(16) Bowmaker, G. A.; Chaichit, N.; Pakawatchai, C.; Skelton, B. W.;
White, A. H. Dalton Trans. 2008, 2926–2928.
(15) Pawelka, F. G. Z. Elektrochem. Angew. Phys. Chem. 1924, 30, 180–
186.
(17) Bowmaker, G. A.; Hanna, J. V.; Hart, R. D.; Skelton, B. W.; White,
A. H. Dalton Trans. 2008, 5290–5292.
3186 Inorganic Chemistry, Vol. 48, No. 7, 2009

NoWel Adducts of SilWer(I) Oxoanion Salts
Table 1. Crystal/Refinement Data, AgX/tu (x:y)(·nH2O)
compound X/x:y(:n)
1(NO3)/1:3
3 (NO3)/15:23
5 (SO4)/1:6:4
6 (ClO4)/2:6:1
formula
Mr (Da)
cryst syst
space group
a (Å)
C3H12AgN7O3S3
398.3
tetragonal
I4122 (No. 98)
14.2104(2)
C23H92Ag15N61O45S23
4299
C6H32Ag2N12O8S7
840.6
tetragonal
P4/n (No. 85)
21.3314(2)
C6H26Ag2Cl2N12O9S6
889.4
orthorhombic
Pna21 (No. 33)
26.3181(3)
monoclinic
P21 (No. 4)
13.2388(2)
24.6552(3)
19.1194(2)
107.293(2)
5959
2.400
2
2.91
b (Å)
c (Å)
13.1235(1)
8.3189(1)
24.5695(8)
6.2920(1)
ꢀ (deg)
V (Å3)
4961
2.133
16
2.14
2863
1.950
4
1.93
2873
2.056
4
2.04
Dcalcd (g cm-3
Z
)
µMo (mm-1
)
specimen (mm3)
Tmin/max
0.29 × 0.08 × 0.06
0.29 × 0.16 × 0.11
0.16 × 0.10 × 0.045
0.22 × 0.14 × 0.055
0.72
0.87
0.95
0.63
2θmax (deg)
Nt
N (Rint)
No (I > 2σ(I))
R1
65
35931
4487 (0.051)
3581
0.046
65
77302
37946 (0.027)
30348
0.029
62
65
34651
8253 (0.048)
6686
0.029
33760
4783 (0.040)
3542
0.034
wR2 (a(,b))
0.105 (0.042,14.8)
0.80
-0.01(4)
0.050 (0.020)
1.16
0.305(7)
0.086 (0.048)
2.1
n/a
0.069 (0.038)
1.17
0.08(6)
|∆Fmax| (e Å-3
)
xabs
Table 2. Selected Geometries, AgNO3/tu (1:3), 1a
ice-cold water. Yield: 0.159 g (28.0%). Anal. calcd for the 15:23
complex C23H92Ag15N61O45S23: C, 6.43; H, 2.16; N, 19.88. Found:
C, 6.6; H, 2.2; N, 20.1%.
atoms
parameter
atoms
parameter
AgNO3/tu (1:1), 4. A solution of thiourea (0.152 g, 2 mmol) in
water (5 mL) was added rapidly with stirring to a solution of AgNO3
(0.340 g, 2 mmol) in water (5 mL) at room temperature. A white
precipitate formed, which started to turn gray after about 1 min.
This was collected and washed with water and required overnight
drying. The particles of product had fused together to form a thin
cake on the filter. Yield: 0.455 g (92.5%). The compound turned
black upon further standing and was unsuitable for microanalysis.
The product from the same reaction carried out in a 1:1 acetonitrile/
methanol solvent mixture was more stable and gave the same IR
spectrum as the initial product from the aqueous solution reaction.
Yield: 0.492 g (100%). Anal. calcd for CH4AgN3O3S: C, 4.88; H,
1.64; N, 17.08. Found: C, 5.1; H, 1.9; N, 16.5%.
[Ag2(tu)6](SO4)·4H2O, 5. Water (5 mL) was added to a mixture
of Ag2SO4 (0.31 g, 1 mmol) and thiourea (0.61 g, 8 mmol), and
the mixture was heated. Most of the solids dissolved to give a clear
solution. A small amount of undissolved solid melted upon further
heating to give a clear oil. Futher oil separated, and colorless crystals
suitable for X-ray diffraction studies formed upon cooling. These
were collected and washed with ice-cold water. Yield: 0.83 g
(98.3%). Anal. calcd for C6H32Ag2N12O8S7: C, 8.57; H, 3.84; N,
20.00. Found: C, 8.6; H, 4.0; N, 19.7%.
[Ag2(tu)6](ClO4)2 ·H2O, 6. A solution of AgClO4 (0.79 g, 3.8
mmol) in water (2.5 mL) was added to a solution of thiourea (0.87
g, 11.4 mmol) in water (7 mL). No product separated from the
resulting clear solution upon standing in an open beaker overnight,
so it was seeded with a small amount of solid obtained by
evaporating all of the water from a 0.5 mL sample of the solution
at 70 °C for 3 h. Colorless crystals of the product suitable for X-ray
diffraction studies separated slowly from the solution upon standing
and were collected and washed with ice-cold water. Yield: 0.43 g
(25.0%). Anal. calcd for C6H26Ag2Cl2N12O9S6: C, 8.10; H, 2.95;
N, 18.90. Found: C, 8.3; H, 2.8; N, 19.1%.
Distances (Å)
Ag(1)-S(1)
2.547(2)
2.518(2)
2.592(1)
3.203(1)
2.654(2)
3.249(1)
2.61(1)
1.24(2)
0.75(1)
1.99(2)
Ag(2)-S(1)
Ag(2)-S(2)
Ag(2)-S(3)
Ag(2) · · ·S(2ii)
Ag(3)-S(1)
Ag(3)-S(2)
Ag(3)-S(3)
Ag(3) · · ·S(3i)
Ag(1) · · ·S(3i)
Ag(1) · · ·S(2ii)
2.356(6)
2.723(6)
2.872(14)
2.96(1)
2.495(8)
2.874(13)
2.563(8)
2.67(1)
Ag(1)-S(2)
Ag(1)-S(3)
Ag(1)· · ·Ag(1i)
Ag(1)· · ·Ag(3i)
Ag(1)· · ·Ag(1ii)
Ag(1)· · ·Ag(2ii)
Ag(2)· · ·Ag(3)
Ag(1)· · ·Ag(2)
Ag(2)· · ·Ag(2ii)
3.152(1)
3.533(2)
Angles (degrees)
S(1)-Ag(1)-S(2)
S(1)-Ag(1)-S(3)
S(1)-Ag(2)-S(2)
S(1)-Ag(2)-S(3)
S(1)-Ag(2)-S(2ii)
S(2)-Ag(2)-S(3)
S(2)-Ag(2)-S(2ii)
S(3)-Ag(2)-S(2ii)
124.59(5)
132.14(7)
123.8(2)
127.6(6)
102.1(4)
91.2(4)
S(2)-Ag(1)-S(3)
Σ
102.97(6)
359.70
S(1)-Ag(3)-S(2)
S(1)-Ag(3)-S(3)
S(1)-Ag(3)-S(3i)
S(2)-Ag(3)-S(3)
S(2)-Ag(3)-S(3i)
S(3)-Ag(3)-S(3i)
113.1(5)
136.4(3)
98.9(4)
94.5(4)
95.9(2)
111.6(5)
128.2(5)
76.5(1)
a Ag lies 0.080(2), 2.466(2), 2.078(4), and 2.388(4) Å out of the S3 and
three SCN2 ligand planes, respectively; the dihedral angles of the latter to
the S3 plane are 75.5(1), 65.2(1), and 65.4(1)°. Coordinate transformations
i and ii are x, 1/2 - y, 1/4 - z and 1 - y, 1 - x, jz.
were recorded on powders suspended in polythene disks using a
Perkin-Elmer Spectrum 400 FT-IR spectrometer.
Structure Determinations. Full spheres of CCD area-detector
diffractometer data were measured (monochromatic Mo KR radia-
tion, λ ) 0.71073 Å; ω-scans; T ) ca. 110 K), yielding Nt(otal)
reflections, these merging to N unique (Rint cited) after “empirical”/
multiscan absorption correction, full matrix least-squares refinement
refining anisotropic displacement parameter forms for the non-
hydrogen atoms, and hydrogen atom treatment following a riding
model. Neutral atom complex scattering factors were employed
within the context of the SHELXL 97 program;18 reflection weights
were [σ2(Fo )+ (aP)2 (+ bP)]-1 (P ) (Fo + 2Fc2)/3). Pertinent
results are given below and in Tables 1-5 and Figures 1-4, the
latter showing 50% probability amplitude displacement envelopes
2
2
Warning! Perchlorate salts are potentially explosiVe and should
be handled with care!
Infrared Spectroscopy. IR spectra were recorded on dry
powders using a Perkin-Elmer Spectrum 100 FT-IR spectrometer
equipped with a Universal ATR sampling accessory. Far-IR spectra
(18) Sheldrick, G. M. SHELXL 97; University of Go¨ttingen: Go¨ttingen,
Germany, 1997.
Inorganic Chemistry, Vol. 48, No. 7, 2009 3187

Bowmaker et al.
Table 3. Selected Geometries, Ag2SO4/tu/H2O (1:6:4), 5a
atoms parameter atoms
Table 5. Selected Bond Lengths, AgNO3/tu (15: 23), 3a
parameter
atoms
parameter
atoms
parameter
Distances (Å)
Distances (Å)
Ag-S(1)
2.5857(7) Ag-S(3)
2.5148(7) Ag-S(3i)
3.2854(4) S(3) · · ·S(3i)
2.7363(7)
2.5204(7)
4.1091(9)
Ag(1)-S(5)
2.5133(9)
2.5133(8)
2.7815(9)
2.5841(8)
2.5470(8)
2.5806(8)
2.8136(8)
2.5507(8)
2.5318(8)
2.5077(9)
2.9456(8)
2.5515(9)
2.4449(8)
2.5337(8)
2.5992(8)
2.6125(8)
2.6136(9)
2.4770(8)
2.4721(8)
2.7525(9)
2.4783(8)
2.5048(8)
2.7153(8)
2.8215(8)
2.5294(8)
3.2659(4)
3.2224(4)
3.1199(4)
3.1526(4)
2.9054(4)
2.9250(4)
3.0804(4)
Ag(2)-S(2)
2.5343(8)
2.5606(9)
2.8063(8)
2.5357(9)
2.5156(8)
2.5962(8)
2.7201(8)
2.5451(9)
2.7383(8)
2.5721(8)
2.5707(8)
2.5507(8)
2.459(3)
2.4856(8)
2.9251(9)
2.4790(8)
2.8302(8)
2.6406(8)
2.5363(8)
2.4855(8)
2.4705(8)
2.4800(8)
2.7009(8)
2.666(2)
Ag-S(2)
Ag(1)-S(7)
Ag(2)-S(9)
Ag· · ·Agi
Ag(1)-S(11)
Ag(1)-S(12)
Ag(3)-S(3)
Ag(2)-S(11)
Ag(2)-S(20)
Ag(4)-S(1)
Angles (degrees)
S(1)-Ag-S(2)
S(1)-Ag-S(3)
S(1)-Ag-S(3i)
Ag-S(3)-Agi
109.54(2)
S(2)-Ag-S(3)
S(2)-Ag-S(3i)
S(3)-Ag-S(3i)
100.81(2)
120.24(2)
102.76(2)
Ag(3)-S(6)
Ag(4)-S(6ii)
Ag(4)-S(8)
110.74(2)
111.72(2)
77.24(2)
Ag(3)-S(8i)
Ag(3)-S(13)
Ag(5)-S(4)
Ag(4)-S(20)
Ag(6)-S(11)
Ag(6)-S(12)
Ag(6)-S(17)
Ag(6)-S(19)
Ag(8)-O(31)
Ag(8)-S(1)
Hydrogen-Bonding Contacts within the Binuclear Cation (Å)
N(12),H(12B)· · ·S(2) 3.491(2), 2.6 N(32),H(32B) · · ·S(1i) 3.448(3), 2.6
N(21),H(21B)· · ·S(1) 3.591(3), 2.7
a Coordinate transformation: (i) 1 - x, 1 - y, jz. The CN2 planes of
ligands 1-3 make dihedral angles of 83.07(8), 89.95(12), and 78.25(5)°
with the central Ag2S2 plane; Ag-S-C angles are 104.15(9), 104.55(12),
and 111.59(11)/102.49(9)° for S(1-3), respectively.
Ag(5)-S(5)
Ag(5)-S(8)
Ag(5)-S(22)
Ag(7)-S(9)
Ag(7)-S(15)
Ag(7)-S(23)
Ag(9)-S(14)
Ag(9)-S(16)
Ag(9)-S(22iii)
Ag(11)-S(2)
Ag(11)-S(15)
Ag(11)-S(19)
Ag(13)-S(10)
Ag(13)-S(15)
Ag(13)-S(21)
Ag(13)-S(23)
Ag(1)· · ·Ag(6)
Ag(3)· · ·Ag(4i)
Ag(3)· · ·Ag(14)
Ag(6)· · ·Ag(15)
Ag(7)· · ·Ag(13)
Ag(9)· · ·Ag(10)
Ag(10)· · ·Ag(13)
Ag(8)-S(4)
Ag(8)-S(7)
Ag(10)-S(10)
Ag(10)-S(14)
Ag(10)-S(16)
Ag(10)-S(21)
Ag(12)-S(4iii)
Ag(12)-S(13iv)
Ag(12)-S(14)
Ag(12)-O(23iii)
Ag(14)-S(3)
Ag(14)-S(10v)
Ag(14)-S(18)
Ag(14)-O(21)
Ag(15)-S(17)
Ag(15)-S(18)
Ag(15)-S(21)
Table 4. Selected Geometries, AgClO4/tu/H2O (2:6:1), 6a
atoms
parameter
atoms
parameter
Distances (Å)
Ag(1)-S(1)
2.5070(7) Ag(2)-S(4)
2.5536(7) Ag(2)-S(5)
2.5209(10) Ag(2)-S(3)
2.7942(9) Ag(2)-S(6i)
4.1292(5) Ag(1) · · · Ag(2i)
2.5629(7)
2.5366(7)
2.7037(10)
2.5543(9)
4.1899(5)
Ag(1)-S(2)
Ag(1)-S(3)
Ag(1)-S(6)
Ag(1) · · · Ag(2)
2.4947(8)
2.5302(8)
2.4619(9)
2.666(2)
2.4919(8)
2.4603(9)
2.5675(8)
Angles (degrees)
S(1)-Ag(1)-S(2)
S(6)-Ag(1)-S(1)
S(6)-Ag(1)-S(2)
S(6)-Ag(1)-S(3)
S(3)-Ag(1)-S(1)
S(3)-Ag(1)-S(2)
Ag(1)-S(3)-Ag(2)
106.31(2)
111.89(3)
91.29(3)
103.77(3)
126.23(3)
111.85(3)
104.38(3)
S(4)-Ag(2)-S(5)
S(6i)-Ag(2)-S(4)
S(6i)-Ag(2)-S(5)
S(6i)-Ag(2)-S(3)
S(3)-Ag(2)-S(4)
S(3)-Ag(2)-S(5)
107.23(2)
118.78(3)
118.28(3)
104.41(3)
98.31(3)
a Silver atom deviations (Å) from the ligand SCN2 planes are 1/Ag(4,8)
0.350(5), 1.726(3); 2/Ag(2,11) 0.579(5), 1.856(3); 3/Ag(3,14) 1.625(4),
-1.486(4); 4/Ag(5,8,12vi) -0.770(4), 2.569(2), -1.449(4); 5/Ag(1,5)
1.895(4), -1.999(3); 6/Ag(3,4i) -1.514(8), 1.705(4); 7/Ag(1,8) 0.067(6),
2.001(3); 8/Ag(3ii,4,5) 0.367(3), 2.682(3), -0.053(1); 9/Ag(2,7) -2.505(1),
0.066(6); 10/Ag(10,13,14iv) 1.436(5), 2.338(2), -2,186(3); 11/Ag(1,2,6)
-2.349(3), 1.947(5), -1.902(4); 12/Ag(1,6) -1.892(3), 1.345(4); 13/
Ag(3,12v) 1.279(4), 1.538(4); 14/Ag(9,10,12) 0.535(5), -2.119(3), 2.476(2);
15/Ag(7,11,13) 0.566(5), 2.314(3), -2.159(3); 16/Ag(9,10) 1.346(5),
-1.549(4); 17/Ag(6,15) -2.028(3), 1.032(4); 18/Ag(14,15) -0.793(4),
0.383(4); 19/Ag(6,11) 0.882(4), 1.936(3); 20/Ag(2,4) 1.942(4), -2.107(3);
21/Ag(10,13,15) 2.322(2), 1.465(4), -2.283(2); 22/Ag(5,9vi) 2.500(2),
0.094(6); 23/Ag(7,13) -1.888(4), 0.946(5). Coordinate transformations: (i)
x, y, z + 1; (ii) x, y, z - 1; (iii) x + 1, y, z + 1; (iv) x + 1, y, z; (V) x -
1, y, z.
107.25(3)
Ag(1)-S(6ii)-Ag(2ii) 103.05(3)
Hydrogen-Bonding Contacts within the Cation (Å)
N(11),H(11B) · · · S(4) 3.424(3), 2.5 N(41),H(41B) · · · S(1) 3.336(3), 2.5
N(12),H(12B) · · · S(4ii) 3.382(3), 2.5 N(42),H(42B) · · · S(1i) 3.393(3), 2.5
N(21),H(21B) · · · S(5) 3.431(3), 2.6 N(51),H(51B) · · · S(2) 3.389(3), 2.5
N(22),H(22B) · · · S(5ii) 3.378(3), 2.5 N(52),H(52B) · · · S(2i) 3.394(3), 2.5
N(31),H(31B) · · · S(6) 3.606(3), 2.7
a Coordinate transformations: (i) x, y, z - 1; (ii) x, y, z + 1.
for the non-hydrogen atoms, the hydrogen atoms, where shown,
having arbitrary radii of 0.1 Å. Full CIF depositions (excluding
structure factor amplitudes) reside with the Cambridge Crystal-
lographic Data Centre, CCDC #696760, 696761, 706741, and
706742. Nonroutine features of the determinations of the 1:3 (Ag:
tu) nitrate and sulfate complexes are mentioned in the Results and
Discussion section.
methanol. The products were initially characterized by their
IR spectra in the range 4000-650 cm-1, which contain bands
due to the tu ligand and the nitrate ion. The wavenumbers
of selected bands in the spectra are listed in Table 6. Bands
due to the thiourea ligand lie close to those previously
reported for the uncomplexed tu molecule11 and are assigned
accordingly. Of the several tu bands observed in the spectra,
the two assigned as ν(CS) and νa(CN) (the asymmetric C-N
stretching mode)11 proved to be the most sensitive to
complex formation, and their wavenumbers are listed in
Table 6. Bands due to the ν3(E′) mode of nitrate, which
occurs at about 1380 cm-1 in the uncomplexed ion in
KNO3,19 are obscured by a strong tu ligand band at 1410
cm-1. However, the nitrate ν2(A2′′) band that occurs at 828
cm-1 in KNO3 is clearly visible in all cases, and its
wavenumber for each complex is recorded in Table 6.
Results and Discussion
Synthesis of Compounds. In a recent study of complexes
of silver(I) halides with ethylenethiourea (imidazolidine-2-
thione; etu), it was shown that the method of solvent-assisted
mechanochemical synthesis in association with IR spectros-
copy can be used to establish the composition of compounds
of this type and to obtain information about their structures.16
In view of the disagreement between different literature
reports on the composition of complexes formed between
AgNO3 and thiourea,14,15 we initially undertook a systematic
solvent-assisted mechanochemical study of the AgNO3/tu (1:
n) system for n ) 1-4. In addition, we investigated the n )
1.5 case on the basis of the previously reported existence of
a corresponding etu complex.5 The solvents used in the
solvent-assisted processes were water and (in one case)
(19) Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coor-
dination Compounds, 5th ed., part A; Wiley: New York, 1997; p 182.
3188 Inorganic Chemistry, Vol. 48, No. 7, 2009

NoWel Adducts of SilWer(I) Oxoanion Salts
Figure 1. (a) The [Ag(tu)3]+ cation in AgNO3/tu (1:3), 1, showing incipient dimer formation with the symmetry-related molecule at (x, 1/2 - y, 1/4 - z) (Ag(1)· · ·S(3′)
3.152(1) Å). (b) Projection of the disordered array of silver atom components Ag(2,3) within the sheath of ligands, showing the formation of a putative polymer
along c involving four-coordinate silver atoms. (c) Projection of the unit cell contents down c, showing the tunnels containing the disordered nitrate anions.
Inorganic Chemistry, Vol. 48, No. 7, 2009 3189

Bowmaker et al.
Figure 2. (a) The binuclear cation of Ag2SO4/tu/H2O (1:6:4), 5, [(tu-S)2Ag(µ-S-tu)2Ag(S-tu)2]2+. (b) Unit cell contents, projected down c.
These studies clearly establish the existence of AgNO3/tu
(1:3), which was confirmed by subsequent synthesis of this
compound, 1, from aqueous solution (see the Experimental
Section) and a determination of its crystal structure (see
below). This result is in agreement with an early report15
but contradicts a more recent claim, based on solid-state
NMR measurements, that only the 1:1 and 1:4 complexes
exist.14
work that the 1:3 complex is the only product obtained from
a reaction carried out in an acetonitrile/methanol mixture in
which the tu/AgNO3 ratio is as high as 5 (see the Experi-
mental Section). Also, mechanochemical treatment of a
AgNO3/tu (1:4) mixture with methanol resulted in a mixture
of the 1:3 complex and unreacted tu, as in the case of the
reaction carried out in water. These results conclusively prove
the nonexistence of a 1:4 complex.
Mechanochemical Treatment of AgNO3/tu (1:4). Me-
chanochemical treatment of a AgNO3/tu (1:4) mixture
resulted in a product that was shown by IR spectroscopy to
be a mixture of the 1:3 complex and unreacted tu. In the
previously reported solid-state NMR study that claimed the
existence of a 1:4 complex, an acetonitrile/methanol solvent
mixture was used rather than water, raising the possibility
that the compositions of complexes in this system might be
solvent-dependent. However, it was shown in the present
Mechanochemical Treatment of AgNO3/tu (1:1). Me-
chanochemical treatment of a AgNO3/tu (1:1) mixture
resulted in a product that was shown by IR spectroscopy
to be the same as that obtained from the 1:1 reaction in
solution (see the Experimental Section), with IR bands
that are clearly different from those of the 1:3 complex
(Table 6). The product of the reaction from homogeneous
aqueous solution was significantly contaminated by a black
decomposition product. This contrasts with the result of
3190 Inorganic Chemistry, Vol. 48, No. 7, 2009

NoWel Adducts of SilWer(I) Oxoanion Salts
Figure 3. (a) The single-stranded polymer (c horizontal in the page) of AgClO4/tu/H2O (2:6:1), 6. (b) Unit cell contents, projected down c.
the mechanochemical reaction, also carried out in the
presence of water, where the product showed absolutely
no sign of such decomposition. This is probably due to
the fact that, in the mechanochemical reaction, the
reactants spend very little time in solution, so that the
opportunity for side reactions is greatly reduced. This
phenomenon may be of wider applicability and can be
added to the previously noted advantages of solvent-
assisted mechanochemical synthesis.16,17
The fact that the 15:23 complex was observed in the initial
mechanochemical treatment of a 1:1.5 mixture implies that
this formed preferentially to the 1:1.5 complex, leaving a
small amount of unreacted AgNO3, which reacted upon
subsequent treatments to produce the 1:1.5 complex. Multiple
mechanochemical treatments of the pure 15:23 complex with
water resulted in no change in its IR spectrum. These
observations show that the 1:1.5 and 15:23 complexes do in
fact have distinct chemical compositions, rather than being
different polymorphs of the same composition, which could,
in principle, be interconverted by mechanochemical treat-
ment.17
Mechanochemical Treatment of AgNO3/tu (1:1.5). Me-
chanochemical treatment of a AgNO3/tu (1:1.5) mixture
resulted in a product that was shown by IR spectroscopy to
be the same as that initially obtained from the 1:1.5 reaction
in solution and established by elemental analysis to be of
1:1.5 stoichiometry (see the Experimental Section), with IR
bands that are clearly different from those of the 1:1 and
1:3 complexes (Table 6). However, this IR spectrum
developed only after three successive mechanochemical
treatments. The spectrum observed after the first mechano-
chemical treatment was the same as that observed for
AgNO3/tu (15:23 ) 1:1.5333), the second product obtained
from a AgNO3/tu (1:1.5) reaction in a homogeneous aqueous
solution, following the initial separation of a 1:1.5 complex.
The AgNO3/tu (15:23) product, 3, obtained from solution
was characterized by elemental analysis (see the Experi-
mental Section) and by X-ray crystallography (see below).
Mechanochemical Treatment of AgNO3/tu (1:2). Me-
chanochemical treatment of a AgNO3/tu (1:2) mixture
resulted in a product that was shown by IR spectroscopy
to be a mixture of the 1:3 complex and another compound,
possibly unreacted AgNO3, with ν2(A2′′ NO3-) ) 824
cm-1. The nonexistence of a 1:2 complex is in agreement
with a recent NMR study14 but does not agree with earlier
synthetic/IR studies, which claimed the existence of a
crystalline 1:2 adduct.20,21 The considerable discrepancy
between the properties (e.g., mp, ν(CS)) reported for the
1:2 compound in these two studies is consistent with our
finding that the 1:2 product is a mixture rather than a pure
compound.
Inorganic Chemistry, Vol. 48, No. 7, 2009 3191

Bowmaker et al.
Figure 4. (a) Unit cell contents of AgNO3/tu (15:23), 3, down a, showing the partitioning of the cell contents at y ) 0, 0.5. (b) Projections of the unit cell
contents down b, showing cross-linking of the polymer strands by tu(18). (c) A single strand of the cation polymer, showing the Ag,S(,O) framework only.
Within the Ag/S framework, the following rings are identified (Ag,S by number, S italicized, primed atoms related by the unit c translation): (a) four-
membered rings, a1 3, 4′, 6, 8′; a2 7, 13, 15, 23; a3 1, 6, 11, 12; a4 10, 13, 10, 21; a5 9, 10, 14, 16; (b) six-membered rings, b1 5′, 9, 12, 4′, 14, 22′; b2 3, 5′,
12, 4′, 13, 8′; b3 1, 5, 8, 4, 5, 7; b4 2, 7, 11, 2, 9, 15; b5 2, 6, 11, 2, 11, 19; (c) eight-membered rings, c1 1, 4, 5, 8, 1, 5, 7, 8; c2 1, 2, 4, 8, 1, 7, 11, 20; c3
6, 11, 13, 15, 15, 17, 19, 21; c4 3, 10, 12, 14, 3, 10, 13, 14.
3192 Inorganic Chemistry, Vol. 48, No. 7, 2009

NoWel Adducts of SilWer(I) Oxoanion Salts
Table 6. Selected Bands (cm-1) in the IR Spectra of AgNO3/tu,
Å, respectively, too close for simultaneous occupancy within
each pair. However, alternate occupancy results in a plausible
one-dimensional polymer about a crystallographic 4-axis
along c, with Ag(2,3) both having plausible four-coordinate
environments (Figure 1b; Table 2), the nitrate ions occupying
tunnels about the alternative set of 4-axes (Figure 1c). As is
usual in tu complexes, hydrogen bonds are a significant
determinant of the lattice array. Somewhat unusually, there
are no NH · · · S interactions within the primary [Ag(tu)3]+
unit. However, from every NH2 group, there is one NH · · ·S
interaction to an adjacent unit in the columnar array up c,
with the other hydrogen atom from each NH2 group directed
outward from the column, so that all disordered oxygen atom
components of the adjacent anionic nitrate column are
contacted.
AgClO4/tu, and Ag2SO4/tu Complexes
ν
(CS)
νa
(CN)
ν
ν
-
compound
(A2′′NO3
)
(AgS)
tu
729 1462
KNO3
828
815
813
819
815
AgNO3/tu (1:3), 1
AgNO3/tu (15:23), 3
AgNO3/tu (1:1.5), 2
AgNO3/tu (1:1), 4
710 1490
698 1510
700 1513
694 1532
190, 157, 146
255, 211
230, 177
213, 175
AgClO4/tu/H2O (2:6:1), 6 711 1491
Ag2SO4/tu/H2O (1:6:4), 5 711 1500, 1478
164 (broad)
186, 154, 95
In order to investigate the effect of the anion on the
structure of complexes with a given Ag/tu ratio, 1:3
complexes involving sulfate and perchlorate counterions were
also prepared.
Mechanochemical Treatment of Ag2SO4/tu (1:6). Me-
chanochemical treatment of a Ag2SO4/tu (1:6) mixture with
water produced a product that showed the same IR spectrum
(Table 6) as that of [Ag2(tu)6](SO4) · 4H2O, 5, produced in
an aqueous solution reaction (see the Experimental Section).
In the case of the latter reaction, an excess of tu was required
to obtain an analytically pure product, and the product
initially obtained was an oil, which solidified only upon
cooling, whereas the mechanochemical reaction yielded the
pure solid product directly, in one treatment. The yield of
product from the mechanochemical synthesis was greater
than the sum of the masses of the reactants, and consistent
with the formation of the tetrahydrate.
Ag2SO4/tu/H2O (1:6:4), 5. Very few (x)tu complexes have
been defined with silver(I) sulfate and none at all structurally
defined with thiourea as the ligand. Remarkably, despite the
noncoordinating nature of the anion in all three 1:3 silver(I)
oxoanion/tu complexes defined in the present work, the
resulting cations are all different, perhaps an indicator of
the extent to which, as participants in hydrogen-bonding, this
may be a determinant of the nature of the resulting lattice,
even to the detail of the cation component. In the present
complex, the cation is binuclear; one-half of the formula unit
comprises the asymmetric unit of the structure, the cation
being centrosymmetric [(tu-S)2Ag((µ-S-tu)2Ag(S-tu)2]2+, each
silver atom being four-coordinated by a pair of terminal and
a pair of bridging S-thiourea ligands (Table 3, Figure 2a).
There are two independent sulfate groups: sulfate 1 lies with
the sulfur atom disposed on a 4 axis; unlike sulfate 2, it is
nicely ordered with the one independent oxygen atom
involved in strong hydrogen bonding (Figure 2b). The sulfur
atom of sulfate 2 is similarly disposed, but the oxygen atom
is modeled as disposed over two equally populated sets of
sites, both also involved in hydrogen bonding, in a number
of situations to residues assigned and refined as water
molecule oxygen atom fragments, O(1) ordered, fully oc-
cupied, and with hydrogen atoms sensibly located, the other
disordered over a pair of equally occupied sites O(2,3). (No
associated hydrogen atoms were located for these, but they
are disposed at reasonable notionally hydrogen-bonding
distances from other oxygen atom components.) There are
also intracation hydrogen bonds of the usual type (Table 3).
The present binuclear [M2tu6]2+ cation form has a precedent,
defined in the recently reported AgNO3/etu (1:3)2 adduct;5
the dimensions in that array are similar, with the bridging
sulfur atom similarly disposed in respect to the asymmetry
in its Ag-S distances, perhaps induced by unsymmetrical
(intracation) hydrogen-bonding associations, since the ge-
ometry remains more nearly four- rather than three-
coordinate.
An attempted synthesis of the previously reported AgClO4/
22
tu (1:3)2 resulted in the isolation of a new hemihydrate
form AgClO4/tu/H2O (2:6:1), 6, with a different structure
for the cation (see below).
Single Crystal X-Ray Studies. AgNO3/tu (1:3), 1. The
results of the single-crystal X-ray study are consistent
with the present formulation, one such formula unit compris-
ing the asymmetric unit of the structure. To a first ap-
proximation, the complex may be described as ionic,
comprising a quasi-trigonal planar mononuclear [Ag(tu)3]+
cation (Table 2) and a nitrate anion; the latter is well-removed
from any interaction with the silver atom and was modeled
as disordered over two sets of sites (N · · ·N′ 0.57(1) Å), with
occupancies set at 0.5 after trial refinement. There is a long
Ag · · ·S contact (3.152(1) Å; cf. van der Waals 3.5 Å) which
may be ascribed to a weak dimer formation (Figure 1a). As
in a significant number of silver(I) coordination complexes,
there is some ambiguity concerning the silver atom location
and its coordination environment and number. A pair of
significant residues, designated Ag(2,3), are located to either
side of the primary silver atom Ag(1); refinement of the site
occupancies within a total constraint of unity results in
Ag(1,2,3) of 0.78(1), 0.11(1), 0.11(1), respectively, suggest-
ing the disorder involving the Ag(2,3) components to
possibly be concerted. Ag(2) · · · Ag(2) (1 - x, 1 - y, jz) and
Ag(3) · · · Ag(3) (x, 1/2 - y, 1/4 - z) are 1.99(2) and 2.12(2)
(20) Ahmad, S.; Isab, A. A.; Perzanowski, H. P. Trans. Met. Chem. 2002,
27, 782–785.
(21) El-Etri, M. M.; Scovell, W. M. Inorg. Chim. Acta 1991, 187, 201–
206.
(22) Udupa, M. R.; Krebs, B. Inorg. Chim. Acta 1973, 7, 271–276.
Numerous counterpart arrays for M ) Cu have been
summarized in Table 1 of ref 1.
Inorganic Chemistry, Vol. 48, No. 7, 2009 3193

Bowmaker et al.
The structure of anhydrous AgClO4/tu (1:3) has been
previously reported23 as having a similar binuclear cation,
being [Ag2(tu)6](ClO4)2. The present synthesis, following that
of ref 23, has surprised by yielding a different product of
novel form, a hemihydrate.
with AgS3O, with Ag-S ranging widely between 2.4790(8)
and 2.9456(8) Å. The other six are three-coordinate (AgS3),
Ag-S more tightly constrained between 2.4449(8) and
2.7525(9) Å. Angle sums at the latter are (Ag(7,9,11,12,14,15))
357.6, 354.14, 350.36, 353.57, 359.62, and 359.91°, indicative
of approaches, more or less effective, toward a trigonal planar
stereochemistry for these atoms. A projection of the unit cell
contents down a (Figure 4a) shows the partitioning of the
cell contents, the polymeric cation components being dis-
posed about y ) 1/4, 3/4, the (majority of the) anions about
y ) 0, 0.5. Projection down b (Figure 4b) shows the cationic
component to be primarily a one-dimensional polymer lying
across the short cell diagonal, adjacent strands linked by a
single bridging thiourea sulfur atom (S(18)) in a second
dimension. All thiourea sulfur atoms are bridging between
silver atoms; seven (S(4,8,10,11,14,15,21)) are triply bridging
(µ3), the remainder doubly (µ2), although the assignment in
a number of cases is not clear-cut, with ‘µ3’-S-Ag distances
ranging upward toward 3 Å (see above). In complexes of
the type AgX/(x)tu (x:y) in which X is (as is essentially the
case here with the one exception) a noncoordinating anion,
the structural types/motifs which have been defined are quite
limited, confined to mononuclear [Ag(µ-S-(x)tu)n]+ and
binuclear [((x)tu-S)nAg(µ-S-(x)tu))2Ag(S-(x)tu)n]2+; the sys-
tems which have been defined all have AgX/(x)tu ratios
greater than the present, being 1:2,23-25 3,22,26-29 and 4.5
With copper(I), lower ratios are found, leading to oligo-
nuclear forms, in which tetranuclear species [Cu4((x)tu)x]4+
predominate,1 and it would not surprise to find parallels
between the motifs found in species of that type and silver(I)
complexes of low AgX/(x)tu ratios such as the present. The
present polymer, the Ag/S/(O) framework of which is shown
in Figure 4c, is comprised of four-, six-, and eight-membered
(AgS)2n ringssfive four-membered (‘an’), five six-membered
rings (‘bn’), and four eight-membered (‘cn’). The four-
membered rings generally deviate appreciably from planarity,
with “fold” angles (across their S · · · S lines) of 32.13(6),
39.64(6), 31.54(6), 45.88(6), and 40.33(6)° for rings a1-a5,
respectively; the pyramidalizations of the three-coordinate
sulfur atoms and the proto-tetrahedral four-coordinate silver
atoms result in considerable folding throughout the polymer,
resulting in incipient formation of three-dimensional motifs,
none of which, however, is closed, in the manner found in
the [Cu4((x)tu)x]4+ forms.
AgClO4/tu/H2O (2:6:1), 6. The full formula unit com-
prises the asymmetric unit of the structure. Again, the
complex is ionic, but in this, the third independent cationic
form of 1:3 stoichiometry of the present paper, the form
taken is that of a single-stranded polymer,...-tu)Ag(S-tu)2(µ-
S-tu)Ag(S-..., with two crystallographically independent...(µ-
S-tu)Ag(tu)2... units alternating in the strand, and in the
asymmetric unit (Figure 3a). This is the first such example
incorporating silver(I); with copper(I), three isomorphous
examples are found, unexpectedly in the isomorphous arrays
CuX/tu (1:3) (X ) Cl, Br, I), where the anions are “softer”.1
Again, each silver atom is four-coordinated, by a pair of
terminal S-tu and a pair of bridging µ-S-tu ligands; again,
the pairs of Ag-(µ-S) distances show differences which are
comparable with those found in the preceding dimer, despite
the quite different Ag-S-Ag angles. The thiourea ligands
are all oriented quasi-parallel to the polymer axis (c) with
one exception (Figure 3b), so that five out of the six are
involved in H · · · S hydrogen bonds along the polymer,
presumably stabilizing it (Table 4). For the copper(I) arrays
(averages over Cl, Br, I), Cu-S (bridging) distances are
2.371(12) and 2.412(21) and Cu-S (terminal-tu) are 2.285(4)
and 2.349(3) Å. The Cu · · · Cu distances range between
4.379(1) and 4.4366(3) Å with concomitant divergence in
(µ-)S-Cu-(µ-)S (113.87(2)-116.24(5)°), Cu-S-Cu being
remarkably constant (<>134.44(11)°) and much larger than
the silver(I) counterpart values (Table 4).
AgNO3/tu (15:23), 3. A recent survey of structurally
defined complexes found between simple silver(I) salts, AgX,
and simple (substituted) thiourea ligands, (x)tu,5 shows a
variety of adducts of generally simpler form than their
copper(I) counterparts,1 of composition AgX/(x)tu (x:y), x
and y being simple integers overwhelmingly of the form 1:n,
n ) 1, 2, 3, 4(,0.5), with complexity rarely greater than
binuclear, except for small x:y ratios, where polymers may
be found.7 With this latter example in mind, there would be
an overwhelming temptation on the basis of analysis alone
to formulate the present material as a 1:1.5 complex.
However, the results of the single-crystal X-ray study show
the stoichiometry to be 15:23, one such formula unit
comprising the asymmetric unit of the structure; the structure
is nicely ordered and unsolvated. Selected bond lengths are
given in Table 5. The complex is essentially an ionic
polymer; interestingly, most anions have no interaction with
silver atomssthe strongest, NO3(3), has a single interaction,
Given the bridging nature of the sulfur atoms in the present
structure, it is not surprising to find that, among the 90
hydrogen bonds ascribed to the 92 hydrogen atoms, only 10
hydrogen-bond to sulfur atoms (eight of these µ2), all others
being to nitrate oxygen atoms. All of the latter (except O(31),
(24) Braun, U.; Sieler, J.; Richter, R.; Hettich, B.; Simon, A. Z. Anorg.
Allg. Chem. 1988, 557, 134–142.
(25) Jian, F.-F.; Xiao, H.-L.; Zhao, P.-S. Jiegou Huaxue 2004, 23, 486–
489.
(26) Pakawatchai, C.; Sivakumar, K.; Fun, H.-K. Acta Crystallogr., Sect.
C 1996, 52, 1954–1957.
(27) Jian, F.-F.; Sun, P.-P.; Xiao, H.-L.; Jiao, K. Wuji Huaxue Xuebao 2003,
19, 979–982. (CCDC: EXONOU).
Ag(8)-O(31) ) 2.459(3) Å, and the complex might thus
14+
be formulated as [Ag15(tu)23(ONO2)] (NO-3 )14, although
(∞|∞)
there are weaker ONO2 interactions with Ag(12,14), both at
2.666(2) Å. Nine of the silver atoms are four-coordinate,
eight with AgS4 coordination environments and one (or three)
(28) Casas, J. S.; Garcia Mart´ınez, E.; Sa´nchez, A.; Sa´nchez Gonza´lez,
A.; Sordo, J.; Casellato, U.; Graziani, R. Inorg. Chim. Acta 1996, 241,
117–123.
(23) Sola, J.; Lo´pez, A.; Coxall, R. A.; Clegg, W. Eur. J. Inorg. Chem.
2004, 487, 1–4881.
(29) Jones, P. G. CCDC private communication: BIBXIU.
3194 Inorganic Chemistry, Vol. 48, No. 7, 2009

NoWel Adducts of SilWer(I) Oxoanion Salts
Figure 5. Plot of the ν(CS) and νa(CN) wavenumbers for AgNO3/tu (1:n)
(n ) 1, 1.5, and 3; 4, 2, and 1) and uncomplexed tu (n ) ∞) as a function
of 1/n.
the most strongly coordinated to a silver atom) are involved
in at least one hydrogen bond.
Vibrational Spectroscopy. The ν(CS) and νa(CN) wave-
numbers for AgNO3/tu (1:n) (n ) 1, 1.5, 3) show a
monotonic increase and decrease, respectively, with increas-
ing n (Table 6). Plotting the wavenumbers as a function of
1/n allows a comparison of these with the values for
uncomplexed tu (n ) ∞), and this plot is shown in Figure 5.
From this, it is apparent that coordination of the tu ligand
results in a decrease in the strength of the C-S bond and an
increase in the strength of the C-N bonds, and this effect
increases with decreasing n. The latter trend is entirely as
expected, since the ability of the silver atom to coordinate
to the tu ligand is greater when the number of such ligands
is smaller with increased tendency toward the formation of
µ2- and µ3-S coordination modes. Of the tu ligand vibrational
modes, the νa(CN) mode is the most sensitive to coordination.
In the case of AgNO3/tu (1:n) (n ) 1, 1.5, 3), the band
associated with this mode is fairly sharp, but for AgNO3/tu
(15:23), this band, which shows a maximum at 1510 cm-1,
is rather broad, with shoulders at 1500 and 1530 cm-1. This
is consistent with the crystal structure (see above), which
shows a large number of different Ag/tu interactions. A larger
effect of this kind is seen in a comparison of the νa(CN)
wavenumbers for AgNO3/tu (1:3) and Ag2SO4/tu/H2O (1:6:
4); in the latter case, the νa(CN) band is split into two
components at 1500 and 1478 cm-1 (Table 6). The average
of these, 1489 cm-1, is very close to the value of 1490 cm-1
observed for AgNO3/tu (1:3; Table 6), which is appropriate
for the Ag/tu ratio 1:3 that applies to both compounds.
However, the primary structural unit in the nitrate is the
[Ag(tu)3]+ unit (see above), in which all three tu ligands are
terminally bound to the silver, which is consistent with the
presence of a single νa(CN) band in the IR. The presence of
two such bands in the sulfate might be considered to be due
to the presence of both bridging and terminal tu ligands in
the dimeric [Ag2(tu)6]2+ cation present in this compound.
However, the factor that is most likely to affect the
vibrational frequency is the strength of interaction of the tu
ligand with the Ag atom, as reflected in the Ag-S bond
length. The crystal structure (see above) shows that that there
is not a close relationship between the Ag-S bond length
Figure 6. Far-IR spectra of AgNO3/tu adducts (a) 1:3, 1; (b) 15:23, 3; (c)
1:1.5, 2; (d) 1:1, 4. Bands assigned to ν(AgS) are labeled with their
wavenumbers.
and the terminal or bridging nature of the ligand. There are
two short bonds (Ag-S(2) ) 2.5148(7) (terminal); Ag-S(3i)
) 2.5204(7) Å (bridging)) and two longer bonds (Ag-S(1)
) 2.5857(7) (terminal); Ag-S(3) ) 2.7363(7) Å (bridging);
Table 3, Figure 2a), and the presence of two νa(CN) bands
is attributed to the presence of these two groups of short
and longer Ag-S bonds. This interpretation is supported by
the fact that the perchlorate complex does not show a
resolved splitting of the νa(CN) band, despite the presence
of both terminal and bridging tu ligands in the complex
(Figure 3a). There are eight Ag-S distances from Ag-S(1)
) 2.5070(7) to Ag(1)-S(6) ) 2.7942(9) Å in this complex
(Table 4, Figure 3a), and this apparently results in a greater
number of νa(CN) frequencies for the coordinated tu, so that
only a relatively broad, unresolved band is observed with a
maximum absorbance at 1491 cm-1 (Table 6). This, however,
is exactly at the position expected for a complex of 1:3 Ag+/
tu stoichiometry (Figure 5). Similar behavior to that described
above is observed for the ν(AgS) bands in the far-IR spectra
of the sulfate and perchlorate complexes (see below).
The far-IR spectra of AgNO3/tu (1:3, 15:23, 1:1.5, and
1:1) are shown in Figure 6. The region above 400 cm-1
contains bands due to coordinated thiourea, and these can
readily be assigned in accordance with previous studies.11
The region below 300 cm-1 contains bands due to the
presence of Ag-S linkages. We have previously shown that
a good correlation exists between ν(CuS) and the Cu-S
distance d(CuS) in a number of copper(I) thiourea complexes,
and this is illustrated in Figure 7 for the complexes
Inorganic Chemistry, Vol. 48, No. 7, 2009 3195

Bowmaker et al.
for [Ag(tu)3](NO3) and AgNO3/tu (15:23) is shown in Figure
7. Also shown in Figure 7 are the fits of the ν(MS) data to
the equation
ν/cm-1 ) b(r/Å)-m
(1)
where r ) d(MS) and b ) 31 180 and 374 110 and m )
5.94 and 8.25 for M ) Cu and Ag, respectively. Similar
relationships have been recorded previously for ν(MX) (X
) Cl, Br, I) in a wide range of copper(I), silver(I), and gold(I)
halide complexes,30-32 and the above results for copper(I)/
thiourea complexes were reported previously, together with
corresponding results for copper(I)/ethylenethiourea com-
pounds.11 While the band assignments that form the basis
of the above correlation for the silver(I)/thiourea compounds
are rather less certain because of the complicated structures
of the complexes involved, comparison of the curves in
Figure 7 for the copper(I) and silver(I) complexes suggests
that these assignments are reasonable. The decrease in ν(MS)
and the increase in d(MS) from M ) Cu to Ag is entirely in
line with expectations based on the greater atomic mass and
size of Ag relative to Cu, and the relative slopes of the curves
and positions of the data points in Figure 7 are very similar
to those for copper(I) and silver(I) ethylenethiourea com-
plexes.5
Figure 7. Correlation between ν(MS) and the M-S bond length d(MS)
for AgNO3/tu (1:3), 1, abd AgNO3/tu (15:23), 3 (O) (M ) Ag; this work),
and for Cu2SO4/tu/H2O (1:5:3) and Cu2SO4/tu/H2O (1:6:1) (•) (M ) Cu;
data from ref 11).
The far-IR spectra of AgNO3/tu (1:1.5) and (1:1) (Figure
6c,d) show bands at 230 and 177 (1:1.5) and at 255 and 211
cm-1 (1:1) that can be assigned as ν(AgS). It is perhaps not
surprising that the spectrum of the 1:1.5 complex is very
similar to that of the 15:23 () 1:1.5333) compound, given
the close similarity in their composition. However, there is
a definite upward shift in the ν(AgS) wavenumbers with
decreasing AgNO3/tu ratio, implying the presence of sig-
nificantly shorter Ag-S bonds in the 1:1.5 compound. This
trend continues in the 1:1 complex, which shows two well-
resolved ν(AgS) bands at 255 and 211 cm-1.
The structure of this compound is not known, but a one-
dimensional polymeric structure involving a linear chain of
two-coordinate silver atoms with doubly bridging thiourea
ligands alternating above and below the chain has been
proposed.20 This structure would appear to be ruled out by
the far-IR data because all of the Ag-S bond lengths should
be equal in such a structure, whereas the far-IR spectrum
suggests the presence of two quite different bond lengths.
The band at 156 cm-1 is assigned to δ(AgSC) bending, the
counterpart of δ(CuSC) bands that occur at about 170 cm-1
in copper(I)/tu complexes.11 This probably contributes to
absorption on the low wavenumber side of the broad ν(AgS)
bands observed in the other AgNO3/tu compounds (Fig-
ure 6).
Figure 8. Frequency of occurrence of Ag-S bond lengths (within a 0.02
Å interval) as a function of the bond length for AgNO3/tu (15:23), 3 (data
from Table 5).
[Cu2(tu)5](SO4)·3H2O and [Cu2(tu)6](SO4)·H2O. The present
results for the AgNO3/tu complexes provide an opportunity
to investigate the possibility of a similar relationship for
silver(I) complexes. The situation is not as straightforward
as it was for the copper(I) complexes, due to the greater
complexity of the structures of the AgNO3/tu complexes.
However, it is possible to get some indication of the nature
of the relationship between ν(AgS) and d(AgS) in AgNO3/
tu (1:3) and AgNO3/tu (15:23) from the following consid-
erations. Although the structure of AgNO3/tu (1:3) shows a
degree of disorder, the predominant Ag site occupancy
(corresponding to the [Ag(tu)3]+ cationic form) is Ag(1)
(78%). This has the coordination environment shown in
Figure 1a, with Ag(1)-S(1,2,3) ) 2.547(2), 2.518(2),
2.592(1) Å respectively. Ag(1)-S(2) is the shortest Ag-S
distance in the complex, and we associate this with the band
at 190 cm-1, the highest wavenumber band in the region
below 300 cm-1 (Figure 6a). Two partially resolved shoulders
at 157 and 146 cm-1 are assigned to the Ag(1)-S(1) and
Ag(1)-S(3) bonds, respectively. The situation for AgNO3/
tu (15:23) is potentially far more complex, but the far-IR
spectrum shows a single band at 175 cm-1, with a shoulder
at 213 cm-1 (Figure 6b). The Ag-S bond lengths in this
compound cover a wide range (Table 5), but most of the
values may be considered as falling into two groups: 11 in
the range below 2.49 Å (<>2.472(12) Å) and 29 in the range
2.49-2.62 Å (<>2.55(3) Å) (see Figure 8). We therefore
assign the 213 cm-1 shoulder to the former and the 175 cm-1
band to the latter of these groups. The ν(AgS) versus d(AgS)
correlation that results from the assignments discussed above
The far-IR spectra of Ag2SO4/tu/H2O (1:6:4) and AgClO4/
tu/H2O (2:6:1) are shown in Figure 9. According to the
relationship shown in Figure 7 for the M ) Ag case, the
(30) Bowmaker, G. A.; Healy, P. C.; Kildea, J. D.; White, A. H.
Spectrochim. Acta 1988, 44A, 1219–1223.
(31) Bowmaker, G. A.; Hart, R. D.; de Silva, E. N.; Skelton, B. W.; White,
A. H. Aust. J. Chem. 1997, 50, 553–565.
(32) Bowmaker, G. A.; Brown, C. L.; Hart, R. D.; Healy, P. C.; Rickard,
C. E. F.; White, A. H. J. Chem. Soc., Dalton Trans. 1999, 881–889.
3196 Inorganic Chemistry, Vol. 48, No. 7, 2009

NoWel Adducts of SilWer(I) Oxoanion Salts
) 1:1, 1:1.5, 15:23 () 1:1.5333), and 1:3. This contrasts
with previously published claims for the existence of 1:2
and 1:4 complexes and was confirmed in the case of the 1:3
and 15:23 complexes by X-ray crystal structure determina-
tions on samples prepared by crystallization from aqueous
solution. The mechanochemical study demonstrated a previ-
ously unknown advantage of solvent-assisted mechanochem-
ical synthesis, namely, the suppression of unwanted side
reactions that lead to impure products in conventional
solution-based synthesis, and exploitation of this technique
in the present work has been fundamental in enabling the
access of new and surprising stoichiometries and forms, such
as the remarkable, essentially ionic 15:23 nitrate complex
14+
[Ag15(tu)23(ONO2)] (NO-3 )14. The ν(CS) and νa(CN) bands
(∞|∞)
Figure 9. Far-IR spectra of (a) Ag2SO4/tu/H2O (1:6:4), 5, and (b) AgClO4/
tu/H2O (2:6:1), 6. Bands assigned to ν(AgS) are labeled with their
wavenumbers.
in the infrared spectra of the complete series of adducts show
a monotonic wavenumber decrease and increase, respec-
tively, with decreasing tu content of the adduct, indicating a
decrease in the C-S bond strength and a concomitant
increase in the C-N bond strength with increasing Ag-S
bond strength. The increase in Ag-S bond strength with
decreasing tu content is also indicated by an increase in the
wavenumbers of the bands assigned to ν(AgS) in the
140-200 cm-1 region in the far-IR. These and the structural
data for the 1:3 and 15:23 complexes provide the basis for
establishing a correlation between ν(AgS) and the Ag-S
bond length d(AgS) for silver complexes involving the tu
ligand. We have defined three different cation forms for
complexes of 1:3 Ag/tu stoichiometry, with distinctive IR
spectra for each, which are of potential value in identifying
the form taken in other 1:3 complexes.
four Ag-S bond lengths in the sulfate complex correspond
to ν(AgS) ) 93, 148, 183, and 187 cm-1. This agrees well
with the observed spectrum (Figure 9a), which shows ν(AgS)
bands at 95, 154, and 186 cm-1. A corresponding analysis
for the structurally more complex perchlorate compound
yields eight ν(AgS) values in the range 80-190 cm-1, with
the most frequently occurring bond length (Ag(1)-S(2),
Ag(2)-S(6) ) 2.554 Å) corresponding to ν(AgS) ) 164
cm-1. This agrees well with the observed spectrum (Figure
9b), which shows a broad ν(AgS) band in the range 80-200
cm-1, with a peak at 164 cm-1.
Conclusion
Supporting Information Available: Expanded versions of
Tables 2-5 containing additional structural parameters (bond angles
and H-bonding distances). This material is available free of charge
via the Internet at http://pubs.acs.org.
An investigation of the silver(I) nitrate/thiourea system,
exploiting the uniquely powerful access provided by the
recently developed combination of mechanochemical syn-
thesis coupled with vibrational spectroscopy, has resulted
in the identification of solid adducts AgNO3/tu (x:y) for x:y
IC802312J
Inorganic Chemistry, Vol. 48, No. 7, 2009 3197