Substituent effects on the supramolecular aggregation of Ag I-pyrazolato trimers

Article abstract of DOI:10.1021/cg301411j

The interplay of argentophilic and dipolar (π-acid...base) interactions, on one hand, and the presence or absence of interstitial solvent molecules, on the other, determines the supramolecular organization of trinuclear silver-pyrazolato complexes in the solid state. The crystal structures of one gold and six silver metallacyclic complexes of the type [M^I(μ-pz*)]₃, where pz* are the substituted pyrazolato anions 3,5-Ph₂-pz, 3-Me-5-Ph-pz, 4-Br-3,5-Ph ₂-pz, 4-Br-3-^tBu-pz and 3-(o-Cl-C₆H ₄)-pz and M = Ag and Au, are discussed in the context of their supramolecular organization. Two silver complexes, for which the π-acid character of their Ag₃-faces is maximized by their peripheral electron-withdrawing substituents, show crystal packing dominated by short Ag₃...Br contacts, the first structural manifestation of supramolecular structure via dipolar interactions involving the tunable π-acidity of the Ag₃-face.

Full text of DOI:10.1021/cg301411j

Article
pubs.acs.org/crystal
Substituent Effects on the Supramolecular Aggregation of
AgI‑Pyrazolato Trimers
Guang Yang,# Peter Baran,§ Angel R. Martínez, and Raphael G. Raptis*
Department of Chemistry, University of Puerto Rico, San Juan, Puerto Rico 00931-3346, United States
S
* Supporting Information
ABSTRACT: The interplay of argentophilic and dipolar (π-
acid···base) interactions, on one hand, and the presence or
absence of interstitial solvent molecules, on the other,
determines the supramolecular organization of trinuclear
silver-pyrazolato complexes in the solid state. The crystal
structures of one gold and six silver metallacyclic complexes of
the type [MI(μ-pz*)]3, where pz* are the substituted
pyrazolato anions 3,5-Ph2-pz, 3-Me-5-Ph-pz, 4-Br-3,5-Ph2-pz,
4-Br-3-tBu-pz and 3-(o-Cl-C6H4)-pz and M = Ag and Au, are
discussed in the context of their supramolecular organization.
Two silver complexes, for which the π-acid character of their
Ag3-faces is maximized by their peripheral electron-with-
drawing substituents, show crystal packing dominated by short Ag3···Br contacts, the first structural manifestation of
supramolecular structure via dipolar interactions involving the tunable π-acidity of the Ag3-face.
group-11 metal complexes (including pyrazolates) has shown
that the π-acidity/basicity of their M3-faces  and con-
sequently, their supramolecular structures  depends on both
the nature of the metal and the peripheral substituents of the
bridging ligands. Silver was found, in that study, to be the most
acidic of the three metals, whose acidities increase for bridges
with electron-withdrawing substituents and decrease for
electron-releasing ones.15 This has been clearly demonstrated
experimentally in the cases of silver pyrazolates with
trifluoromethyl substituents.16,17 On the other hand, several
cyclic trinuclear gold(I) imidazolates and carbeniates display π-
basicity, forming stacks with π-acids.18−23 As supramolecular
architectures are intimately associated with the physicochemical
and biological properties of materials, such as luminescence and
bioavailability,24,25 the exploration of the possible aggregation
modes of a given motif, with a long-term view of gaining
predictive capacity over it, is a worthwhile endeavor.
We report here the synthesis and crystallographic character-
ization of five new silver pyrazolato trimers with the general
formula [Ag(μ-pz*)]3 (Scheme 1), where pz* = peripherally
substituted pyrazolato anion: pz* = 3,5-Ph2-pz (1), 3-Me-5-Ph-
pz (2), 4-Br-3,5-Ph2-pz (3), 4-Br-3-tBu-pz (4) and 3-(o-Cl-
C6H4)-pz (5). We also report the methanol solvate of 2
(2·MeOH) and the gold analogue of 3 (3-Au).
INTRODUCTION
■
Supramolecular structures depend on the interplay of a host of
weak intermolecular interactions.1 In a biological context and in
aqueous media in general, H-bonds of 4−10 kcal/mol are
typically the dominant structure determining factor. In the
absence of H-bonds, however, weaker dipolar and van der
Waals interactions in the range of 2−5 kcal/mol manifest
themselves in the three-dimensional assemblies, and metal-
lophilic interactions of comparable strength can be competitive
with the latter.2 Because of the weak forces involved in such
assemblies, more than one structure is often possible with the
same components (polymorphs), as molecules tumble from
one supramolecular arrangement to another, each one
representing a kinetically trapped local energy minimum.3
Trinuclear group-11 metal pyrazolato complexes have been a
convenient platform to study the interplay of weak
intermolecular forces in crystalline compounds.4 The crystal
packing of sterically unhindered gold pyrazolates is dictated by
aurophilic interactions.5 However, when long aliphatic
substituents were introduced to the pyrazoles, columnar gold
pyrazolate structures resulted.6 Wider structural variety is
known in silver pyrazolates, in which the argentophilic
interactions, weaker than the aurophilic ones, can be easier to
overcome by the sum of weak dipolar interactions.7,8 So,
supramolecular arrangements in which silver−silver contacts
are maximized are known, just as are ones containing a
combination of silver−silver and dipolar interactions, as well as
arrangements based solely on dipolar and van der Waals
contacts.9−12 Two independent studies have suggested that
silver pyrazolato complex aggregates can persist even in
solution.13,14 A detailed computational study of triangular
Received: September 26, 2012
Revised: November 10, 2012
© XXXX American Chemical Society
A
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Article
an off-white solid. The mixture was filtered under suction, and the
residue was washed with cold water and air-dried. To the dry residue
was added a small amount of diethyl ether, and the suspension was
filtered under suction to remove insoluble NaBr. Removal of ether
from the filtrate left a pale yellow powder of 4-bromo-3-tert-
butylpyrazole in 75% yield. mp 122−123 °C (recrystallized from
petroleum ether).
Scheme 1.
Calcd. for C7H11N2Br: C, 41.40; H, 5.46; N, 13.79%. Found: C,
1
40.67; H, 5.60; N, 13.61%. H-NMR: (CDCl3, ppm) δ = 1.40 (s, 9H,
tBu), 7.49 (s, 1H, 5-pz), 11.16 (s, br, 1H, N−H).
[Ag(μ-3,5-Ph2-pz)]3·1/4C6H14 (1·1/4C6H14). A CH2Cl2/hexane
7,8
solution of [Ag(μ-3,5-Ph2-pz)]3 was allowed to slowly evaporate at
−5 °C for several weeks, yielding colorless large blocks of 1·1/4C6H14.
Synthesis of [Ag(μ-3-Me-5-Ph-pz)]3 (2). 3-Me-5-Ph-pzH (47
mg, 0.3 mmol) and AgPhCOO (69 mg, 0.3 mmol) were mixed
together in 10 mL of dry THF. The mixture was stirred for several
hours at room temperature to give a turbid solution. The resulting
solution was filtered under suction, and the white residue was washed
with ether. The white solid was taken up in CH2Cl2, and a small
amount of PPh3 (33 mg, 0.13 mmol) was added to facilitate the
crystallization process. Slow diethylether diffusion in a vial containing
the above solution yielded colorless needles in 37% yield after several
days.
EXPERIMENTAL SECTION
■
3,5-Diphenylpyrazole and 3(5)-methyl-5(3)-phenylpyrazole, obtained
from commercial sources, were used as received, while 4-bromo-3,5-
diphenylpyrazole,26 3(5)-tert-butylpyrazole, and 3(5)-ortho-chlorophe-
nylpyrazole were prepared by literature methods.27 All solvents were
distilled and stored over molecular sieves prior to use. The H-NMR
spectra were recorded with a Bruker AVANCE DPX-300 spectrom-
eter.
Calcd. for C30H27Ag3N6: C, 45.46; H, 3.44; N, 10.61%. Found: C,
45.54; H, 3.52; N, 10.49%.
Single crystals of 2·MeOH were obtained by carefully layering
methanol over the surface of a CH2Cl2 solution of 2.
1
Synthesis of [Ag(μ-4-Br-3,5-Ph2-pz)]3 (3). To a THF solution
(10 mL) of Ag(OCOPh) (415 mg, 1.83 mmol) was added 4-Br-3,5-
Ph2-pzH (545 mg, 1.83 mmol). The clear reaction mixture was stirred
for 18 h, the solvent was reduced to approximately 1/5 of its volume,
and the product was crushed out as a white powder by addition of
Et2O. The supernatant was removed and the product was washed with
EtOH and Et2O. Yield: 70%. Single crystals of 3·1/2CH2Cl2 suitable
Synthesis of 4-Bromo-3(5)-tert-butyl-1H-pyrazole (4-Br-
5-tBu-pzH). 3(5)-tert-Butylpyrazole (0.71 g, 5.8 mmol) was dissolved
in 50 mL of CH2Cl2. Bromine (0.92 g, 5.8 mmol) was added dropwise
under stirring until the yellow color of bromine persisted in solution.
The resulting solution was refluxed for 30 min and cooled to ambient
temperature. Concentrated aqueous NaOH solution was added to the
reaction solution until it was slightly basic, resulting in precipitation of
Table 1. Crystallographic Data
1·1/4C6H14
2
2·CH3OH
3·1/2CH2Cl2
3-Au·CH2Cl2
4
5
formula
mol. wt.
C45H33Ag3N6·1/
C60H54Ag6N12
C30H27Ag3N6·CH4O
C45H30Ag3Br3N6·1/
C45H30Au3Br3N6·CH2Cl2 C21H30Ag3Br3N6
C27H18Ag3Cl3N6
4C6H14
2CH2Cl2
1024.47
triclinic
1590.37
triclinic
827.23
1260.56
1570.31
929.85
865.43
crystal
system
triclinic
monoclinic
monoclinic
triclinic
triclinic
space group
a (Å)
P1
P1
P1
P21
C2/c
P1
P1
̅
̅
̅
̅
̅
11.806(7)
13.182(8)
14.862(9)
100.076(7)
101.519(7)
107.103(7)
2098(2)
2
14.082(4)
15.035(4)
16.149(5)
115.984(6)
100.687(5)
100.292(6)
2886.4(14)
2
7.617(6)
14.224(11)
15.311(12)
108.204(9)
102.225(10)
90.820(10)
1534(2)
2
10.289(2)
27.383(6)
15.356(3)
30.132(4)
17.197(2)
17.427(2)
11.144(18)
11.983(9)
13.076(10)
113.598(10)
100.645(13)
101.305(13)
1500(3)
2
7.624(6)
14.456(12)
14.713(12)
114.799(8)
91.273(2)
94.630(10)
1464(2)
2
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
91.952(4)
98.396(2)
4324.0(16)
8933.2(19)
4
8
T (K)
298
298
298
298
1.936
298
2.335
298
298
ρcalcd. (Mg/
1.582
1.830
1.791
2.058
1.942
m3)
μ(mm−1
)
1.425
2.045
1.930
8723
4.220
12.674
19438
5.953
9676
2.288
8756
reflns
12369
12875
19280
collected
reflns unique 8687 (Rint
=
8271 (Rint
0.0604)
=
6420 (Rint = 0.0307) 12379 (Rint = 0.0730) 6427 (Rint = 0.0371)
6167 (Rint
0.0267)
=
6079 (Rint =
0.0200)
0.0266)
reflns obs/
7153/514
4158/637
4597/375
6309/844
5233/542
3733/307
3765/353
param
final R
indices
R1 = 0.0349
R1 = 0.0529
wR2 = 0.1136
R1 = 0.0440
wR2 = 0.1178
R1 = 0.0595
R1 = 0.0254
wR2 = 0.0540
R1 = 0.0526
R1 = 0.0577
wR2 = 0.1628
[I > 2σ(I)]
Flack param
S
wR2 = 0.1155
wR2 = 0.0991
0.040(15)
0.874
wR2 = 0.1324
1.055
1.000
0.908
0.805
0.977
0.653
1.048
1.308
1.107
0.839
1.030
1.522
Δρmax (e
0.760
Å−3
)
B
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Crystal Growth & Design
Article
for X-ray work were obtained by slow diffusion of Et2O into a CH2Cl2
solution of 3.
Calcd. for C45H30Ag3Br31N6: C, 44.56; H, 2.50; N, 6.93%. Found: C,
44.05; H, 2.55; N, 6.68%. H-NMR: (CD2Cl2, ppm) δ = 7.20 (t, 2H,
m-Ph), 7.32 (t, 1H, p-Ph), 7.55 (d, 2H, o-Ph).
Synthesis of [Au(μ-4-Br-3,5-Ph2-pz)]3 (3-Au). To a clear THF
solution (5 mL) of AuClTHT (0.1 mmol, 32 mg) and 4-Br-3,5-
Ph2pzH (0.1 mmol, 30 mg) was added an equivalent amount of Et3N.
The reaction mixture was stirred for 12 h, the solvent was reduced to
approximately 1/5 of its volume, and the product was crushed out as a
white powder by addition of hexane. The supernatant was removed,
and the residue was dissolved in CH2Cl2. After filtration, Et2O was
allowed to slowly diffuse into the filtrate, affording colorless prisms of
the product. Yield: 60%.
unsymmetrical one with approximate C3h and Cs point group
symmetries, respectively. For all four complexes, only the C3h
isomer was found in the solid state.
Crystal Packing Patterns. Compound 1, [Ag(3,5-Ph2-
pz)]3·1/4C6H14, is a new solvate of silver 3,5-diphenylpyr-
azolate. Two other crystalline forms for this complex, [Ag(3,5-
Ph2-pz)]3·2THF and {[Ag(3,5-Ph2-pz)]3}2, have been reported
by Fackler et al.7,8 Interestingly, 1 is isomorphous to [Cu(3,5-
Ph2-pz)]3·1/2C6H14.29 In the crystal structure of 1 (Figure 1),
Calcd. for C45H30Au3Br3N6: C, 36.36; H, 2.00; N, 5.66%. Found: C,
35.91; H, 2.09; N, 5.48%.
Synthesis of [Ag(μ-4-Br-3-tBu-pz)]3 (4). 4-Br-3-tBu-pzH (0.5
mmol, 102 mg) and AgNO3 (0.5 mmol, 85 mg) were mixed in 10 mL
of MeCN. After stirring for 10 min, a methanol solution (5 mL) of
equivalent Et3N was added dropwise. Soon afterward, white precipitate
appeared. The mixture was stirred for another 2 h at room
temperature and then filtered with suction. The white powder
obtained was washed by MeOH and then Et2O. Yield: 65%. Single
crystals of 4 suitable for X-ray work were obtained by slow diffusion of
Et2O into a CH2Cl2 solution of 4.
Calcd. for C21H30Ag3Br3N6: C, 27.13; H, 3.25; N, 9.04%. Found: C,
1
26.92; H, 3.30; N, 8.94%. H-NMR: (CDCl3, ppm) δ = 1.57 (s, 27H,
tBu), 7.40 (s, 3H, 5-pz).
Synthesis of [Ag(μ-3-(o-Cl-C6H4)-pz)]3 (5). This compound was
prepared as 3. Yield: 81%.
Calcd. for C27H18Ag3Cl3N6: C, 38.04; H, 2.13; N, 9.86%. Found: C,
1
37.91; H, 2.22; N, 9.90%. H-NMR: (CD2Cl2, ppm) δ = 6.65 (d, 3H,
4-pz), 7.28−7.42 (m, 9H), 7.45−7.60 (m, 6H).
Figure 1. A ball-and-stick diagram of [Ag(μ-3,5-Ph2-pz)]3 (1),
highlighting phenyl groups (green-colored) capping Ag3 faces.
X-ray Crystallography. Diffraction intensities were collected on a
Bruker Smart CCD 1K diffractometer with graphite-monochromated
Mo-Kα radiation (0.71073 Å). Absorption corrections were applied
using the multiscan program. The structures were solved by direct
methods and refined by least-squares techniques using the SHELXS-
97 and SHELXL-97 programs.28 All non-hydrogen atoms were refined
with anisotropic displacement parameters; hydrogen atoms were
generated geometrically. The phenyl groups of 2 have been refined as
rigid hexagons. Crystallographic data are summarized in Table 1.
[Ag(3,5-Ph2-pz)]3 exists as a single trimer; however, it is by no
means isolated in the lattice. A careful inspection reveals
extensive intermolecular and intramolecular π−π and C−H···π
interactions among the 3,5-phenyl substituents, while additional
C−H···π interactions involve pyrazole rings. In addition, one of
the phenyl rings is capping one side of an Ag3 plane of an
adjacent trimer with approximately parallel face-to-face distance
and dihedral angle being 3.55 Å and 6.9° (Figure 1). This is
indicative of a π-acid−base stack, providing structural evidence
for the π-acidity displayed by the trimeric silver pyrazolate.15
The absence of intermolecular Ag···Ag contacts in 1 confirms
the earlier observation that while quite short Ag···Ag contacts
of 2.971(1) Å are sterically allowed in the dimer-of-trimers
structure {[Ag(3,5-Ph2-pz)]3}2,8 those interactions are dis-
rupted in the presence of either weakly coordinating solvents,
as in [Ag(3,5-Ph2-pz)]3·2THF,7 or interstitial solvents enabling
the manifestation of π−π and C−H···π interactions, exemplified
by 1. The conclusion drawn here is that the packing patterns of
[Ag(μ-3,5-Ph2-pz)]3-units in the solid state are the results of a
compromise between the above interactions.
The asymmetric unit of 2 consists of two crystallographically
independent trimers, both in the C3h isomer topology (Figure
2). After an inversion operation is applied, two structurally
similar but still different “dimers-of-trimers” can be generated
via Ag···Ag contacts, in which the six Ag-atoms defining a chair
geometry (Figure 2). Close inspection reveals that these two
dimers in 2 are different not only in their inter-trimer Ag···Ag
distances but also the π−π interaction patterns. The inter-
trimer Ag···Ag distances are 3.203(2) and 3.321(2) Å for two
dimers of trimers, respectively. On the other hand, [Ag(μ-3-
RESULTS AND DISCUSSION
■
Synthesis. All the silver trimers were prepared by either
reaction of silver benzoate with pyrazole or reaction of silver
nitrate with pyrazoles in the presence of triethylamine.
Benzoate here acts in the same way as Et3N, namely, a base
required to deprotonate pyrazole.
General Description of the Structures of the Trimer.
All six silver-pyrazolato structures feature nine-membered [Ag−
N−N]3 metallacycles with Ag−N bond lengths being
2.049(15)−2.132(14) Å. All Ag-atoms are two-coordinate in
approximately linear geometry, as indicated by N−Ag−N
angles in the 169.31(9)−179.8(2)° range. The [Ag−N−N]3
metallacycles are approximately planar with smaller deviations
from ideal geometry for 2, 2·MeOH and 5 and larger ones for
1, 3 and 4: The mean deviations from the planes defined by
three Ag-atom and six pyrazole N-atoms are 0.2457 Å for 1;
0.0530 Å and 0.0523 Å for 2; 0.0259 Å for 2·MeOH; 0.1304 Å
and 0.1460 Å for 3; 0.1090 Å for 4; 0.0623 Å for 5, respectively.
For the gold-pyrazolato complex 3-Au, the corresponding value
is 0.0344 Å. Complete tables of bond lengths and angles for all
seven complexes are in the Supporting Information section
(Tables S1 and S2). For structures 2, 2·MeOH, 4 and 5,
involving unsymmetrically substituted pyrazoles, there are two
possible geometrical isomers of each: a 3-fold symmetric and an
C
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Crystal Growth & Design
Article
argentophilic interactions by the inclusion of an interstitial
solvent molecule in the lattice.
Complex 3 contains two crystallographically independent
[Ag(μ-4-Br-3,5-Ph2-pz)]3 molecules in its asymmetric unit and
shows extensive intra-trimer π-interactions including π−π
stacking and C−H···π interaction, as seen in the structures of
1,7,8 but no inter-trimer Ag···Ag contacts (Figure 3a,b).
Interestingly, three of the six Br atoms point to the centers
of neighboring trimers (Figure 3a). A close inspection reveals
that eight of the nine Ag···(μ3-Br) distances (3.208−3.722 Å)
are shorter than the sum of Bondi’s van der Waals radii of Ag
and Br atoms (1.72 + 1.85 = 3.57 Å), indicative of dipolar
Ag···Br interactions promoted by the π-acidity of 3 (Table S2).
The network of Ag···Br interactions generate two-dimensional
wavy chiral sheets stacked along the crystallographic b-axis
(Figure 3b), which are responsible for the polar space group
P21 of 3.
The crystal structure of the AuI-complex 3-Au shows isolated
planar [Au(μ-4-Br-3,5-Ph2-pz)]3 molecules arranged parallel to
each other and to the crystallographic C-face (Figure 3c). The
closest intermolecular Au···Au and Au···Br distances are
4.442(1) Å and 4.970(1) Å, respectively.
The asymmetric unit of 4 consists of only one [Ag(μ-4-Br-
3-tBu-pz)]3 molecule, related by an inversion center to its
closest neighbor. The two parallel Ag3-units are held together
by two argentophilic Ag···Ag contacts of 3.142(3) Å forming a
dimer-of-trimers (Figure 4). One of the Br atom of each trimer
points to the center of a neighboring Ag3 triangle, in a similar
fashion to that observed in 3; however, the Ag···Br distances,
3.567, 3.766, and 3.968 Å, are longer than the corresponding
values in 3, indicative of a weaker Ag···Br interaction in 4.
Figure 2. A ball-and-stick diagram of the dimer of trimers of [Ag(μ-3-
Me-5-Ph-pz)]3 (2), formed via argentophilic contacts (dashed green
lines).
Me-5-Ph-pz)]3 exists as a single trimer in the crystal structure of
its methanol solvate, 2·MeOH. The closest inter-trimer Ag···Ag
distance in 2·MeOH is only 3.419(2) Å, which is still shorter
than the sum of Bondi’s van der Waals radii for Ag atoms (2 ×
1.72 = 3.44 Å). Comparison of the intermolecular Ag···Ag
distances in 2 and 2·MeOH shows an increase from 3.203 Å
and 3.321 Å to 3.419 Å, reflecting the disruption of
Figure 3. (a) A ball-and-stick diagram of [Ag(μ-4-Br-3,5-Ph2-pz)]3 (3), showing the Ag3···Br weak interactions (dashed green lines). (b) A 2D net of
[Ag(μ-4-Br-3,5-Ph2-pz)]3 via Ag3···Br weak interactions (dashed green lines). The phenyl groups have been omitted for clarity. (c) A ball-and-stick
diagram of [Au(μ-4-Br-3,5-Ph2-pz)]3 (3-Au).
D
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Article
supramolecular interactions among the trinuclear units in the
solid state. The bulky 3,5-Ph2-pz ligands do not prevent the
close argentophilic interaction of 2.971(1) Å in the nonsolvated
complex 1.8 However, the presence of interstitial solvent
molecules, like hexane in the structure of 1·1/4C6H12 here, or
weakly coordinating THF, as in 1·2THF,7 are sufficient to
disrupt that argentophilic contact. Similar to 1, the nonsolvated
complex 2, containing the less bulky 3-Me-5-Ph-pz ligands,
forms dimer-of-trimer assemblies via weak argentophilic
contacts, which are disrupted in the structure of its methanol
solvate, 2·MeOH, the latter containing only isolated trinuclear
complexes in its crystal structure.
The situation changes when 4-Br substituents are introduced.
The electron withdrawing bromine atoms increase the π-acidity
of the Ag3-faces of the complexes and also constitute an
electron-rich donor polar terminus. Consequently, in the
structures of 3 and 4, containing the 4-Br-3,5-Ph2-pz and 4-
Br-3-tBu-pz ligands, respectively, show intermolecular inter-
actions between the Ag3-faces of the complexes and the Br-
atoms and are acid−base in character. The Ag3···Br are shorter
in 3 than in 4, consistent with the stronger π-acidity of 3,
caused by its electron-withdrawing Ph-groups, compared to the
opposite effect caused by the electron-releasing tBu-groups of 4.
The Ag3···Br are also the only intermolecular contacts in 3,
while 4 contains argentophilic contacts in addition to π-
acid···base ones. It is interesting to compare the crystal
structures of 3 and 4 with that of [Ag(4-Br-3,5-iPr2pz)]3:10
The latter exists as a dimer-of-trimers via Ag···Ag contacts, but
also contains several inter-trimer Ag···Br links of 3.513, 3.889,
and 4.898 Å for one Br atoms to its nearest Ag3 trimer, longer
than those in 3, but comparable to those in 4. Consistent with
the predicted relative π-acidity, Ag > Cu > Au, by DFT
calculations,15 the crystal structure of 3-Au, the Au-analogue of
3, contains no Au3···Br contacts; gold is less π-acidic than silver.
Halide···π acid (Cu3) interactions have also been observed in a
series of polymeric structures constructed from copper halides
and 3,5-diethyl-4-(4-pyridyl)-pyrazolate, containing [Cu(μ-
pz*)]3-units.30 Short AgI···X-aryl (X = Br, I) interactions have
been reported by Mak et al., with notable Ag···Br distances of
2.584 and 2.599 Å,31 even shorter than those found in crystal
structure of AgBr (2.88 Å). The introduction of Cl-atoms at a
site remote from the Ag-centers in 5 does not increase the π-
acidity of its Ag3-face and the presence of basic halogen atoms
in this complex is mute.
Figure 4. A ball-and-stick diagram of the dimer-of-trimers of [Ag(μ-4-
Br-3-tBu-pz)]3 (4), formed via argentophilic contacts (dashed green
lines).
The unit cell of complex 5 contains two parallel, inversion-
related [Ag(μ-3-(o-Cl-C6H4)-pz)]3 molecules, rotated by
approximately 60° with respect to each other, forming a
“head-to-tail” assembly of S6 symmetry with inter-trimer
Ag···Ag distance of 3.524(1)−4.281(1) Å, longer than the
sum of Bondi’s van der Waals radii for Ag atoms (Figure 5).
CONCLUSION
■
Although the molecular structures of monovalent group-11
pyrazolates are largely dictated by the strength and direction of
M-N dative bonds, the noncoordinative groups in 3,4,5-
positions of pyrazole rings are by no means spectators. Besides
their straightforward steric requirements, they also exert
electronic effects manifested in the varying strength of dipolar
and/or metallophilic interactions. The conclusion drawn from
the study of structures 1, 2 and 2·MeOH is that Ag···Ag
contacts and π−π interactions are comparable in strength.
Elegant computational and experimental studies have demon-
strated how the π-acid/base properties of such complexes are
tuned by the electron withdrawing or releasing properties of the
substituents.15−23 Our present work demonstrates examples in
which the increased π-acid character of complexes 3 and 4
together with the presence of basic Br-atoms bring about
dominant Ag3···Br acid−base interactions that compete with
argentophilicity to determine their supramolecular organiza-
Figure 5. Ball-and-stick diagram of a pair of [Ag(μ-3-(o-Cl-C6H4)-
pz)]3 (5) molecules.
The six phenyl groups are rotated as to position their six Cl-
atoms in the space between the two parallel Ag3 planes, with
the inter-trimer Ag···Cl distances ranging from 4.350(2) to
5.330(2) Å. Evidently, the S6 assembly is held together only by
crystal packing forces. Similar intermolecular Ag···Ag distance
of 3.516(1) Å are also found between Ag3 units in consecutive
unit cells along the crystallographic a-axis.
The π-acidity/basicity of the Ag3-faces of [Ag(μ-pz*)]3
complexes, which is tuned by the peripheral 3-, 4- and 5-
pyrazole substituents, results in variation of the pattern of
E
dx.doi.org/10.1021/cg301411j | Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design
Article
(10) Dias, H. V. R.; Diyabalanage, H. V. K. Polyhedron 2006, 25,
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tion. Clearly, for Ag3···halogen interactions to dominate, the
other substituents need to induce sufficient π-acidity to the Ag3-
core. When this is not the case, as in complex 5, no acid−base
interactions are observed.
Germane to this is the observation that in a thallium-
trispyrazolylborate system, the substitution at the pyrazole 3-
position influences the length of intermolecular Tl−Tl, closed
shell contacts.32 A detailed study of the effect of pyrazole
peripheral substitution on the strength of metallophilic
interactions is still lacking.
(11) Dias, H. V. R.; Gamage, C. S. P.; Keltner, J.; Diyabalanage, H. V.
K.; Omari, I.; Eyobo, Y.; Dias, N. R.; Roehr, N.; McKinney, L.; Poth,
T. Inorg. Chem. 2007, 46, 2979−2987.
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Chim. Acta 2010, 363, 2977−2989.
(13) Meyer, F.; Jacobi, A.; Zsolnai, L. Chem. Ber. 1997, 130, 1441−
1447.
(14) Krishantha, D. M. M.; Gamage, C. S. P.; Schelly, Z. A.; Dias, H.
V. R. Inorg. Chem. 2008, 47, 7065−7067.
(15) Tekarli, S. M.; Cundari, T. R.; Omary, M. A. J. Am. Chem. Soc.
2008, 130, 1669−1675.
ASSOCIATED CONTENT
* Supporting Information
■
(16) Dias, H. V. R.; Gamage, C. S. P. Angew. Chem., Int. Ed. 2007, 46,
2192−2194.
S
ORTEP diagrams, tables of interatomic distances and angles for
1−5 and packing diagrams for 3-Au and 5. This information is
available free of charge via the Internet at http://pubs.acs.org/.
(17) Tsupreva, V. N.; Titov, A. A.; Filippov, O. A.; Bilyachenko, A.
N.; Smol’yakov, A. F.; Dolgushin, F. M.; Agapkin, D. V.; Godovikov, I.
A.; Epstein, L. M.; Shubina, E. S. Inorg. Chem. 2011, 50, 3325−3331.
(18) Mohamed, A. A.; Rawashdeh-Omary, M. A.; Omary, M. A.;
Fackler, J. P., Jr. Dalton Trans. 2005, 2597−2602.
(19) Burini, A.; Bravi, R.; Fackler, J. P., Jr.; Galassi, R.; Grant, T. A.;
Omary, M. A.; Pietroni, B. R.; Staples, R. J. Inorg. Chem. 2000, 39,
3158−3156.
AUTHOR INFORMATION
Corresponding Author
*E-mail: Raphael@epscor.upr.edu.
■
(20) Burini, A.; Fackler, J. P., Jr.; Galassi, R.; Grant, T. A.; Omary, M.
A.; Rawashdeh-Omary, M. A.; Pietroni, B. R.; Staples, R. J. J. Am.
Chem. Soc. 2000, 122, 11264−11265.
(21) Rawashdeh-Omary, M. A.; Omary, M. A.; Fackler, J. P., Jr.;
Galassi, R.; Pietroni, B. R.; Burini, A. J. Am. Chem. Soc. 2001, 123,
9689−9691.
Present Addresses
#College of Chemistry and Molecular Engineering, Zhengzhou
University, Zhengzhou, 450001 China.
§Department of Chemistry, Juniata College, Huntingdon, PA
16652, USA.
Notes
(22) Burini, A.; Fackler, J. P.; Galassi, R.; Macchioni, A.; Omary, M.
A.; Rawashdeh-Omary, M. A.; Pietroni, B. R.; Sabatini, S.; Zuccaccia,
C. J. Am. Chem. Soc. 2002, 124, 4570−4571.
The authors declare no competing financial interest.
(23) Olmstead, M. M.; Jiang, F.; Attar, S.; Balch, A. L. J. Am. Chem.
Soc. 2001, 123, 3260−3267.
ACKNOWLEDGMENTS
■
This work has been supported by the National Aeronautics and
Space Administration (Grants NNX09AV05A and
NNX08BA48A), the National Science Foundation (HRD-
0833112), and the Institute for Functional Nanomaterials-UPR.
Y.G. acknowledges a grant from the National Science
Foundation of China (#21071126).
́
(24) Badjic, J. D.; Nelson, A.; Cantrill, S. J.; Turnbull, W. B.;
Stoddart, J. F. Acc. Chem. Res. 2005, 38, 723−732.
(25) Metrangolo, P.; Neukirch, H.; Pilati, T.; Resnati. Acc. Chem. Res.
2005, 38, 386−395.
́ ̌
(26) Zueva, E. M.; Petrova, M. M.; Herchel, R.; Travnícek, Z.; Raptis,
R. G.; Mathivathanan, L.; McGrady, J. E. Dalton Trans. 2009, 5924−
5932.
(27) Trofimenko, S.; Calabrese, J. C.; Thompson, J. S. Inorg. Chem.
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