Supramolecular Structural Variations with Changes in Anion and Solvent in Silver(I) Complexes of a Semirigid, Bitopic Tris(pyrazolyl)methane Ligand

Article abstract of DOI:10.1021/ic035207i

The bitopic ligand p-C₆H₄[CH₂OCH ₂C(pz)₃]₂ (pz = pyrazolyl ring) that contains two tris(pyrazolyl) methane units connected by a semirigid organic spacer reacts with silver(I) salts to yield {p-C₆H₄[CH ₂OCH₂C(pz)₃]₂(AgX) ₂}∞, where X = CF₃SO₃^- (1), SbF₆^- (2), PF₆^- (3), BF ₄^- (4), and NO₃^- (5). Crystallization of the first three compounds from acetone yields {p-C ₆H₄[CH₂OCH₂C(pz)₃] ₂(AgCF₃SO₃)₂}∞ (1a), {p-C ₆H₄[CH₂OCH₂C(pz)₃] ₂(AgSbF₆)₂[(CH₃)₂CO] ₂}∞ (2b), and {p-C₆H₄[CH ₂OCH₂C(pz)₃]₂AgPF ₆}∞ (3a), where the stoichiometry for the latter compound has changed from a metal:ligand ratio of 2:1 to 1:1. The structure of 1a is based on helical argentachains constructed by a κ²-κ ¹ coordination to silver of the tris(pyrazolyl)methane units. These chains are organized into a tubular 3D structure by cylindrical [(CF ₃SO₃)^6- clusters that form weak C-H...O hydrogen bonds with the bitopic ligand. The same κ²-κ ¹ coordination is present in the structure of 2a, but the structure is organized by six different tris(pyrazolyl) methane units from six ligands bonding with six silvers to form a 36-member argentamacrocycle core. The cores are organized in a tubular array by the organic spacers where each pair of macrocycles sandwich six acetone molecules and one SbF₆^- counterion. The structure of 3a is based on a κ²-κ ⁰ coordination mode of each tris(pyrazolyl)methane unit forming a helical coordination polymer, with two strands organized in a double stranded helical structure by a series of C-H...π interactions between the central arene rings. Crystallization of 2-4 from acetonitrile yields complexes of the formula {p-C₆H₄[CH₂OCH ₂C(pz)₃]₂[(AgX)₂(CH ₃CN)_n]∞ where n = 2 for X = SbF₆ ^- (2b), X = PF₆^- (3b) and n = 1 for X = BF ₄^- (4b). All three structures contain argentachains formed by a κ²-κ¹ coordination mode of the tris(pyrazolyl)methane units linked by the organic spacer and arranged in a 2D sheet structure with the anions sandwiched between the sheets. Crystallization of 5 from acetonitrile yields crystals of the formula {p-C₆H ₄[CH₂OCH₂C(pz)₃] ₂(AgNO₃)₂(CH³CN)₄}∞ , where the nitrate is bonded to the silver. The argentachains, again formed by κ²-κ¹ coordination, are arranged in W-shaped sheets that have an overall configuration very different from 2b-4b. Treating {p-C₆H₄[CH₂OCH₂C(pz) ₃]₂(AgSbF₆)₂}∞ with a saturated aqueous solution of KPF₆ or KO₃SCF₃ slowly leads to complete exchange of the anion. Crystallization of a sample that contains an approximately equal mixture of SbF₆ ^-/PF₆^- from acetonitrile yields {p-C ₆H₄[CH₂OCH₂C(pz)₃] ₂[Ag₂(PF₆)_0.78(1)(SbF ₆)_1.22(1)(CH₃CN)₂][(CH ₃CN)_0.25 (C₄H₁₀O) _0.25]}∞, a compound with a sheet structure analogous to 2b-4b. Crystallization of the same mixture from acetone yields {p-C₆H ₄[CH₂OCH₂C(pz)₃] ₂(AgSbF₆)[(CH₃)₂CO] _1.5}∞, where the metal-to-ligand ratio is 1:1 and the [C(pz)₃] units are κ²-κ⁰ bonded forming a coordination polymer. The supramolecular structures of all species are organized by a combination of C-H...π, π-π, or weak C-H-F(O) hydrogen bonding interactions.

Full text of DOI:10.1021/ic035207i

Inorg. Chem. 2004, 43, 537−554
Supramolecular Structural Variations with Changes in Anion and
Solvent in Silver(I) Complexes of a Semirigid, Bitopic
Tris(pyrazolyl)methane Ligand
Daniel L. Reger,* Radu F. Semeniuc, Vitaly Rassolov, and Mark D. Smith
Department of Chemistry and Biochemistry, UniVersity of South Carolina,
Columbia, South Carolina 29208
Received October 21, 2003
The bitopic ligand p-C H [CH OCH C(pz)3]2 (pz ) pyrazolyl ring) that contains two tris(pyrazolyl)methane units
6
4
2
2
connected by a semirigid organic spacer reacts with silver(I) salts to yield {p-C H [CH OCH C(pz)3]2(AgX)2}∞,
6
4
2
2
where X ) CF SO - (1), SbF - (2), PF - (3), BF - (4), and NO - (5). Crystallization of the first three compounds
3
3
6
6
4
3
from acetone yields {p-C H [CH OCH C(pz)3]2(AgCF SO ) }∞ (1a), {p-C H [CH OCH C(pz)3]2(AgSbF ) [(CH ) -
6
4
2
2
3
3 2
6
4
2
2
6 2
3 2
CO]2}∞ (2b), and {p-C H [CH OCH C(pz)3]2AgPF }∞ (3a), where the stoichiometry for the latter compound has
6
4
2
2
6
changed from a metal:ligand ratio of 2:1 to 1:1. The structure of 1a is based on helical argentachains constructed
by a κ2−κ1 coordination to silver of the tris(pyrazolyl)methane units. These chains are organized into a tubular 3D
structure by cylindrical [(CF SO ) ]6- clusters that form weak C−H‚‚‚O hydrogen bonds with the bitopic ligand. The
3
3 6
same κ2−κ1 coordination is present in the structure of 2a, but the structure is organized by six different tris-
(pyrazolyl)methane units from six ligands bonding with six silvers to form a 36-member argentamacrocycle core.
The cores are organized in a tubular array by the organic spacers where each pair of macrocycles sandwich six
acetone molecules and one SbF - counterion. The structure of 3a is based on a κ2−κ0 coordination mode of each
6
tris(pyrazolyl)methane unit forming a helical coordination polymer, with two strands organized in a double stranded
helical structure by a series of C−H‚‚‚π interactions between the central arene rings. Crystallization of 2−4 from
acetonitrile yields complexes of the formula {p-C H [CH OCH C(pz)3]2[(AgX)2(CH CN)n]}∞ where n ) 2 for X )
6
4
2
2
3
SbF - (2b), X ) PF - (3b) and n ) 1 for X ) BF - (4b). All three structures contain argentachains formed by
6
6
4
a κ2−κ1 coordination mode of the tris(pyrazolyl)methane units linked by the organic spacer and arranged in a 2D
sheet structure with the anions sandwiched between the sheets. Crystallization of 5 from acetonitrile yields crystals
of the formula {p-C H [CH OCH C(pz)3]2(AgNO ) (CH CN)4}∞, where the nitrate is bonded to the silver. The
6
4
2
2
3 2
3
argentachains, again formed by κ2−κ1 coordination, are arranged in W-shaped sheets that have an overall
configuration very different from 2b−4b. Treating {p-C H [CH OCH C(pz)3]2(AgSbF ) }∞ with a saturated aqueous
6
4
2
2
6 2
solution of KPF or KO SCF slowly leads to complete exchange of the anion. Crystallization of a sample that
6
3
3
contains an approximately equal mixture of SbF -/PF - from acetonitrile yields {p-C H [CH OCH C(pz)3]2[Ag2-
6
6
6
4
2
2
(PF6)0.78(1)(SbF6)1.22(1)(CH CN)2][(CH CN)0.25 (C H O)0.25]}∞, a compound with a sheet structure analogous to 2b−
3
3
4 10
4b. Crystallization of the same mixture from acetone yields {p-C H [CH OCH C(pz)3]2(AgSbF )[(CH ) CO]1.5}∞,
6
4
2
2
6
3 2
where the metal-to-ligand ratio is 1:1 and the [C(pz)3] units are κ2−κ0 bonded forming a coordination polymer. The
supramolecular structures of all species are organized by a combination of C−H‚‚‚π, π−π, or weak C−H−F(O)
hydrogen bonding interactions.
Introduction
groups, the ligand topicity (i.e., the number and position of
coordinating groups), flexibility or rigidity of the linker
groups joining the coordination sites, and the stereochemical
preferences of the coordinated metal ion.1-3 The role of
noncovalent interactions is also recognized as providing
further organization into more complex networks. A wide
The key features that determine the overall architectures
of self-assembled species are the nature of coordinating
* To whom correspondence should be addressed. E-mail: Reger@
mail.chem.sc.edu.
10.1021/ic035207i CCC: $27.50 © 2004 American Chemical Society
Published on Web 12/30/2003
Inorganic Chemistry, Vol. 43, No. 2, 2004 537

Reger et al.
variety of these interactions, some relating to the anions3a-d,4
and the solvent,2g,3b,5 have been found to impact the
organization of such compounds. Important examples are
strong5 and weak3e,7 hydrogen bonds, π-π stacking,8
X-H‚‚‚π interactions (X ) O, N, C),9 and interhalogen
interactions.10 Silver(I) is frequently used as the metal
because the flexibility of its coordination sphere can produce
sophisticated coordination architectures. This flexibility
affords an opportunity to investigate how the self-assembly
process is influenced by modifications of the ligand denticity,
the ligand-to-metal ratio, the counterions, and noncovalent
interactions.3a-d,4-10,11
Insight into the self-assembly process can be obtained by
carrying out systematic studies using a series of similar
complexes assembled from a specific ligand and the same
metallic center and imposing subtle alterations in the
environment such as changing the anions and the crystal-
lization solvent. Extensive research has been done in this
area using mostly rigid ligands because they allow a better
prediction of the overall structure, shape, and porosity of
the resulting array. Schro¨der et al., studying silver(I)
coordination polymers based on aromatic nitrogen-donor
ligands, found, besides covalent metal-ligand contacts, that
a plethora of interactions (e.g., π-π interactions, metal-
metal interactions, metal-π interactions) have an influence
on the outcome of the resulting supramolecular array.1c,d,11c
Zaworotko,12 Yaghi,13 and others14 used polycarboxylic acids
and various metal centers to construct both discrete and
infinite architectures, based on the rigid orientation and
binding mode of the ligand to the metallic centers. All these
studies gave rise to a series of principles that can be applied
in the design of new structures with a high degree of
confidence.
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538 Inorganic Chemistry, Vol. 43, No. 2, 2004

Bitopic Tris(pyrazolyl)methane Ligand
Scheme 1. The Ligand p-C6H4[CH2OCH2C(pz)3]2 (L) and Possible Noncovalent Interactions That the Ligand Can Promote To Support
Supramolecular Structuresa
a Color code: metallic center, purple; carbon, yellow; oxygen, red; nitrogen, blue.
ligands and silver(I) salts. Several other research groups16
also used flexible ligands in the construction of coordination
polymers, and useful patterns with potential application in
crystal engineering were found.15,16
The use of both types of ligands is, to some extent,
restricted because rigid ligands limit the structures of possible
products and flexible ligands have a very low degree of
prediction of the resulting structure. At the interface between
rigid and flexible ligands resides a class of ligands that
contain in their structure both rigid and flexible parts and
are designated as either “semirigid” or “semiflexible” ligands
or sometimes “flexible” only, although they have the same
features.17
We are investigating the field of coordination polymers
using a new class of semirigid ligands based on linking two
or more tris(pyrazol-1-yl)methane units in a single mol-
ecule.18 The chemistry reported here is based on the bitopic
ligand p-C6H4[CH2OCH2C(pz)3]2 (L, pz ) pyrazolyl ring),
shown in Scheme 1. Also shown are the noncovalent
interactions and/or conformations that are possible with this
ligand. The ether linkage offers the possibility of cis or trans
orientations of the sidearms, while the presence of acidic
hydrogen atoms on the pyrazolyl ring or the methylene
groups adjacent to oxygen on the sidearms can promote weak
hydrogen bonds if suitable proton acceptors are introduced
into the system.18a,b,d,h The presence of aromatic pyrazolyl
rings and linking arene ring that can act as acceptors in
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Zhang, R.-H.; Brisse, F. Inorg. Chem. 2002, 41, 3477. (g) Brandys,
M.-C.; Puddephatt, R. J. J. Am. Chem. Soc. 2002, 124, 3946. (h) Bu,
X.-H.; Chen, W.; Lu, S.-L.; Zhang, R.-H.; Liao, D.-Z.; Bu, W.-M.;
Shionoya, M.; Brisse, F.; Ribas, J. Angew. Chem., Int. Ed. 2001, 40,
3201. (i) McMorran, D. A.; Pfadenhauer, S.; Steel, P. J. Aust. J. Chem.
2002, 55, 519. (j) Tabellion, F. M.; Seidel, S. R.; Arif, A. M.; Stang,
P. J. J. Am. Chem. Soc. 2001, 123, 11982. (k) Tabellion, F. M.; Seidel,
S. R.; Arif, A. M.; Stang, P. J. J. Am. Chem. Soc. 2001, 123, 7440.
(17) (a) Kasai, K.; Aoyagi, M.; Fujita, M. J. Am. Chem. Soc. 2000, 122,
2140. (b) Seward, C.; Chan, J. L.; Song, D. T.; Wang, S. N. Inorg.
Chem. 2003, 42, 1112. (c) Sun, D. F.; Cao, R.; Sun, Y. Q.; Bi, W. H.;
Li, X. H.; Hong, M. C.; Zhao, Y. J. Eur. J. Inorg. Chem. 2003, 38.
(d) McMorran, D. A.; Pfadenhauer, S.; Steel, P. J. Inorg. Chem.
Commun. 2002, 5, 449. (e) Banfi, S.; Carlucci, L.; Caruso, E.; Ciani,
G.; Proserpio, D. M. J. Chem. Soc., Dalton Trans. 2002, 2714. (f)
Fujita, M.; Sasaki, O.; Watanabe, K.; Ogura, K.; Yamaguchi, K. New
J. Chem. 1998, 22, 189.
(18) (a) Reger, D. L.; Wright, T. D.; Semeniuc, R. F.; Grattan, T. C.; Smith,
M. D. Inorg. Chem. 2001, 40, 6212. (b) Reger, D. L.; Semeniuc, R.
F.; Smith, M. D. Inorg. Chem. 2001, 40, 6545. (c) Reger, D. L.;
Semeniuc, R. F.; Smith, M. D. Eur J. Inorg. Chem. 2002, 543. (d)
Reger, D. L.; Semeniuc, R. F.; Smith, M. D. J. Chem. Soc., Dalton
Trans. 2002, 476. (e) Reger, D. L.; Semeniuc, R. F.; Smith, M. D.
Inorg. Chem. Commun. 2002, 5, 278. (f) Reger, D. L.; Semeniuc, R.
F.; Smith, M. D. J. Organomet. Chem. 2003, 666, 87. (g) Reger, D.
L.; Semeniuc, R. F.; Smith, M. D. J. Chem. Soc., Dalton Trans. 2003,
285. (h) Reger, D. L.; Semeniuc, R. F.; Silghi-Dumitrescu, I.; Smith,
M. D. Inorg. Chem. 2003, 42, 3751.
Inorganic Chemistry, Vol. 43, No. 2, 2004 539

Reger et al.
Scheme 2. Possible Modes of Coordination of Tris(pyrazolyl)methane Units
C-H‚‚‚π interactions18f-h or participate in π-π stacking18,b,d,f,h
can lead to arene-arene, pyrazolyl-arene interactions or the
double π-π stacking/C-H‚‚‚π interaction we have named,
after a CSD database search showed that it was a general
interaction, the “quadruple pyrazolyl embrace”.19 Another
possible noncovalent interaction is cation-π interactions
between a metallic center and a pyrazolyl ring within the
ligand.20 In addition, the tris(pyrazolyl)methane units can act
in different binding modes as (a) κ3 tripodal, (b) κ2 bonded
to a single metal with the third pyrazolyl not coordinated,
and (c) κ2-κ1 bonded bridging two metals (Scheme 2). As
a means of simplifying the language related to these types
of semirigid ligands used in supramolecular chemistry, both
those developed in our group and elsewhere, we define them
as “structurally adaptive”.
Reported here are the syntheses and characterization of a
series of silver(I) coordination polymers of this versatile
ligand. We have carefully investigated the supramolecular
structural modifications influenced by several types of
noncovalent forces when the anions and crystallization
solvent are varied, with an emphasis on the solid-state
structures. The solution structure and dynamics, as deduced
from 1H NMR and, indirectly, from ESI-MS, are also
discussed. We have previously communicated the structures
of three of these compounds.18c,g
tromethane) are white solids that are air stable and show
only slight decomposition after several weeks of exposure
to daylight.
2nAgX + n{p-C6H4[CH2OCH2C(pz)3]2} THF8
{p-C6H4[CH2OCH2C(pz)3]2(AgX)2}n
X ) CF3SO3- (1), SbF6- (2), PF6- (3),
BF4- (4), and NO3- (5)
Elemental analyses of the solids correspond to a metal-
to-ligand ratio of 2:1; therefore, the complexes are formulated
as follows: {p-C6H4[CH2OCH2C(pz)3]2(AgX)2}∞, where X
-
-
-
-
-
) CF3SO3 (1), SbF6 (2), PF6 (3), BF4 (4), and NO3
(5). The same metal-to-ligand ratio was found when the
starting materials were mixed in a 1:1 reaction, with half an
equivalent of the ligand recovered from the filtrate. While
the chemical composition of the products is by no means
sufficient for making any structural predictions due to the
many different structural architectures of coordination frame-
works that can be generated from identical stoichiometries,
we established18a by molecular mechanics calculations that
the overall length and structure of the xylene based bridge
prevent simultaneous coordination of both sides of L to one
metal center.
1
The H NMR spectra of the solids in CD3CN show that
Results and Discussion
the acetonitrile completely replaces the ligand; the spectrum
of the compound in CD3CN is the same as the free ligand in
Syntheses and Characterization. The bitopic ligand L
was prepared18a in a one pot synthesis starting from R,R′-
dibromo-p-xylene, p-(BrCH2)2C6H4, and tris-2,2,2-(1-pyra-
zolyl)ethanol, HO-CH2-C(pz)3, under basic (NaH) condi-
tions. NMR and elemental analysis confirmed its chemical
composition and purity. The preparation of the complexes
was readily achieved by combining the ligand with the
respective metal salts in a 2:1 metal-to-ligand ratio. The
compounds (insoluble in halogenated solvents, water, or
alcohols but soluble in acetone, acetonitrile, and ni-
1
this solvent. However, the H spectra of the compounds in
deuterated acetone are clearly different from the free ligand,
showing the coordination of the ligand to the silver(I) in
solution. Although the X-ray structure shows that in the solid
state the pyrazolyl rings are nonequivalent (vide infra), the
NMR spectra show equivalent rings, presumably because of
fast exchange of the ligands and metals on the NMR time
scale. This fast exchange process is maintained even at low
temperatures. The spectra of metal complexes 1-5 in acetone
are essentially identical, showing the same upfield shifts
when compared to the free ligand. This result suggests that
the species present in acetone solution are identical and anion
independent. Electrospray mass spectroscopy showed peaks
corresponding to [LAg]+ and [LAg2X]+ (except for 3 that
only shows [LAg]+). Surprisingly, these spectra were very
similar when run in either acetone or acetonitrile.
(19) Reger, D. L.; Gardinier, J. R.; Semeniuc, R. F.; Smith, M. D. J. Chem.
Soc., Dalton Trans. 2003, 1712.
(20) For examples of cation-π interactions between metallic centers and
pyrazolyl rings see: (a) Craven, E.; Mutlu, E.; Lundberg, D.;
Temizdemir, S.; Dechert, S.; Brombacher, H.; Janiak, C. Polyhedron
2002, 21, 553. (b) Kisko, J. L.; Hascall, T.; Kimblin, C.; Parkin, G. J.
Chem. Soc., Dalton Trans. 1999, 1929. (c) Janiak, C.; Temizdemir,
S.; Scharmann, T. G. Z. Anorg. Allg. Chem. 1998, 624, 755.
540 Inorganic Chemistry, Vol. 43, No. 2, 2004

Bitopic Tris(pyrazolyl)methane Ligand
Figure 1. ORTEP representation of {p-C6H4[CH2OCH2C(pz)3]2(AgCF3-
SO3)2}∞ (1a) with displacement ellipsoids shown at 50% probability level.
In order to ascertain the influences of the crystallization
solvent and the counterion on the resulting “molecular” and
supramolecular structures of the compounds, we performed
crystallization procedures using acetone and acetonitrile as
solvents and diethyl ether as precipitating agent, using the
vapor phase diffusion method. All other conditions (ambient
temperature, concentration of the mother liquors) were kept
unchanged. In 7 of the 10 possible cases (1a, 2a, 3a, from
acetone, and 2b, 3b, 4b, 5‚4CH3CN, from acetonitrile)
crystals formed that were subjected to X-ray diffraction
studies.
Figure 2. (a) Two adjacent helical argentachains for {p-C6H4[CH2OCH2C-
(pz)3]2(AgCF3SO3)2}∞ (1a), showing the double π-π stacking. (b) View
of the same helical argentachains down the helical axis. Color code is the
same as in Scheme 1, with silver ) purple.
Solid-State Structures. In describing the highly organized
supramolecular structures reported here, we will use the
terminology developed by Lehn.21 The primary structure of
a supramolecular compound is created by the covalent bonds
of the individual atoms in the reacting building blocks (also
known as “tectons”22), with the secondary structure being
the arrangement of the tectons one with respect to another.
If one or more secondary structural elements impose a further
distinct and more encompassing motif on the compound as
a whole, this arrangement is the tertiary structure and
constitutes the dominant structural motif. If several separate
tertiary structural units are connected, the resulting compound
would have four levels of structural organization, with
quaternary structure required to describe the arrangement of
the “individual” tertiary structural units relative to each other.
Crystallization of the product resulting from the reaction
of AgCF3SO3 and p-C6H4[CH2OCH2C(pz)3]2 from acetone
leads to the formation of {p-C6H4[CH2OCH2C(pz)3]2(AgCF3-
SO3)2}∞ (1a), a compound with a metal/ligand ratio of 2:1.
In the primary structure (Figure 1) the ligand has a skewed
trans arrangement of the sidearms with respect to the central
arene ring. Each tris(pyrazolyl)methane unit has a κ2-κ1
coordination to silver placing three nitrogen atoms around
each metal in a distorted trigonal planar arrangement with
the sum of the N-Ag-N angles being nearly 360°. The
Ag-N bond distances and angles display no unusual features
and are provided as Supporting Information.
Figure 3. Overall structure of 1a, down the c axis. Color code is the
same as in Scheme 1, plus sulfur ) light brown and fluorine ) green.
2a), that are oriented along a crystallographic 31 screw axis.
Figure 2b shows the view down two of the chiral chains.
These helical chains are organized in a tertiary structure
by the ether-based sidearms combined with a double face-
to-face π-π stacking, involving two pyrazolyl rings sand-
wiching the central phenyl ring.8 Figure 3 shows the overall
3D arrangement of 1a. Six helical chains, connected by the
organic bridges, are arranged in cylinders around a central
core of triflate anions. Each adjacent cylinder shares a pair
of helical chains such that each of the AgNNCNN helices is
part of three overlapping cylinders. A schematic representa-
tion of the structure is illustrated in Figure 4. Every cylinder
overlaps with six other cylinders, with every helical chain
being surrounded by three helical chains of opposite chirality.
Noncovalent interactions from the triflate anions are clearly
important in this arrangement of the 3D structure into
“cylinders”. The triflate anions in 1a are not bonded to silver
as in other cases17b,23 but are arranged in circular clusters of
six, the same as the number of helices in each cylinder. As
shown in Figure 5, six S6 symmetry related triflate anions
The secondary structure consist of single stranded helical
chains constructed by this κ2-κ1 coordination generating
helical argentachains (no interactions between the silver(I)
centers are implied), with a AgNNCNN sequence (Figure
(21) Hasenknopf, B.; Lehn, J.-M.; Boumediene, N.; Dupont-Gervais, A.;
van Dorsselaer, A.; Kneisel, B.; Fenske, D. J. Am. Chem. Soc. 1997,
119, 10956.
(22) Tecton ) any molecule whose interactions are dominated by particular
associative forces that induce self-assembly of an organized network
with specific architectural or functional features. See: Simard, M.;
Su, D.; Wuest, J. D. J. Am. Chem. Soc. 1991, 113, 4696.
(23) For examples of OTf- coordinated to a silver(I) center in coordination
polymers see: (a) Ino, I.; Wu, L. P.; Munakata, M.; Maekawa, M.;
Suenaga, Y.; Kuroda-Sowa, T.; Kitamori, Y. Inorg. Chem. 2000, 39,
2146. (b) Venkataraman, D.; Lee, S.; Moore, J. S.; Zhang, P.; Hirsch,
K. A.; Gardner, G. B.; Covey, A. C.; Prentice, C. L. Chem. Mater.
1996, 8, 2030. (c) Buchholz, H. A.; Prakash, G. K. S.; Vaughan, J. F.
S.; Bau, R.; Olah, G. A.; Inorg. Chem. 1996, 35, 4076.
Inorganic Chemistry, Vol. 43, No. 2, 2004 541

Reger et al.
Figure 6. ORTEP representation of the cationic unit in {p-C6H4[CH2-
OCH2C(pz)3]2(AgSbF6)2[(CH3)2CO]2}∞ (2a) with displacement ellipsoids
shown at 40% probability level.
Figure 4. Schematic representation of 1a: orange rings are cylinders of
helical argentachains connected by the organic spacer; green rings are
circular association of the triflate anions; blue triangles are 31 helical
argentachains with “2” and “1” representing opposite handed helices.
The Hartree-Fock model does not describe van der Waals
interactions. When these are included at the MP2 level, the
energy of interaction between two adjacent fluorine atoms
becomes 1.05 kcal/mol, making the F‚‚‚F energy of interac-
tion for each [(CF3SO3)6]6- cluster 6.3 kcal/mol. This is a
surprisingly large number, given the distance between the
fluorines. We also calculated the energy of the F‚‚‚F
6-
interaction in the one other example of a similar (CF3SO3)6
reported cluster.26 In this case, the F‚‚‚F distances are much
shorter, in the range 2.7-2.9 Å. At this shorter distance, the
average energy of each interaction increases to 1.93 kcal/
6-
mol, making the energy of interaction for each (CF3SO3)6
cluster 11.6 kcal/mol.
The hexameric triflate clusters control the circular ar-
-
rangement of 2a through the six SO3 groups that are
-
oriented away from the center of the cluster. Each SO3
group makes two weak C-H‚‚‚O hydrogen bonds with the
bitopic ligand with metrical parameters that indicate both of
these interactions are substantial. The presence of the
hydrogen bonds is also supported by vibrational data of the
trifluoromethanesulfonate anion by a 24 cm-1 blue-shift of
the νas(E) stretching vibrations of the CF3 group.27
The crystallization of the product resulting from the
reaction of AgSbF6 and p-C6H4[CH2OCH2C(pz)3]2 from
acetone leads to the formation of {p-C6H4[CH2OCH2C
(pz)3]2(AgSbF6)2[(CH3)2CO]2}∞ (2b), a compound with the
same metal/ligand ratio of 2:1 as in 1a. Single crystal X-ray
analysis showed that in 2a the primary structure (Figure 6)
is similar to that of 1a, although the coordination environment
around the silver(I) is more pyramidal, with the sum of the
N-Ag-N angles being 341.71°.
However, the secondary structure of 2a is very different
from that of 1a, although the same method of construction
is used in the organization. As in 1a each tris(pyrazolyl)-
methane unit is κ2 bonded to one silver(I) atom and κ1 to
another, but this construction does not lead to the formation
of argentachains. Six κ2-κ1 [C(pz)3] units from six different
ligands together with six silver atoms to form a 36-member
argentamacrocycle core with the same AgNNCNN sequence
as in the helical chain secondary structure of 1, Figure 7.
The shortest Ag‚‚‚Ag distance is 5.54 Å indicating that there
are no interactions between the silver(I) cations.
Figure 5. (a) Two triflate clusters of 1a, view perpendicular to c axis,
showing the distances (Å) between planes formed by the carbon atoms of
triflate groups. (b) The same two triflate clusters, viewed end on.
have their fluorine atoms directed toward one another. The
cluster is formed by the circular arrangement of three triflate
anions in a plane and three others related by an S6 symmetry
operation. The distance between the planes formed by the
carbon atoms of the triflate groups within the cluster is 4.53
Å. In contrast, the distance between two adjacent planes from
two separate clusters is 7.20 Å.
Attractive interactions of the type X‚‚‚X (X ) F, Cl, Br,
I) are known to play an important role in many structures,
although the exact nature of the interaction is still unclear.10
For compound 1a, the shortest F‚‚‚F distances are 3.28 Å,
more than the sum of the van der Waals radii for fluorine at
2.94 Å.24 The energy of interaction between the fluorine
atoms of the triflate groups at 3.28 Å in the [(CF3SO3)6]6-
clusters was calculated on the MP2/aug-cc-pVDZ level of
theory, with only the valence electrons correlated. The
calculation was based on the work of Halkier et al.25 and on
the experimentally measured shortest F‚‚‚F distance. We
neglected the basis set superposition error and presume our
basis set to be sufficiently large for a qualitatively correct
estimate. The energy of interaction between two adjacent
fluorine atoms at the Hartree-Fock level is 0.34 kcal/mol.
(26) Su, C.-Y.; Kang, B.-S.; Wang, Q.-G.; Mak, T. C. W. J. Chem. Soc.,
Dalton Trans. 2000, 1831.
(27) (a) Johnston, D. H.; Shriver, D. F. Inorg. Chem. 1993, 32, 1045. (b)
Huang, W.; Wheeler, R. A.; Frech, R. Spectrochim. Acta, Part A 1994,
50A, 985. (c) Rhodes, C. P.; Frech, R. Solid State Ionics 2000, 136-
137, 1131. (d) Huang, W.; Frech, R.; Wheeler, R. A. J. Phys. Chem.
1994, 98, 100. (e) Lawrance, G. F. Chem. ReV. 1986, 86, 17.
(24) (a) Bondi, A. J. Phys. Chem. 1964, 68, 441. (b) Rowland, R. S.; Taylor,
R. J. Phys. Chem. 1996, 100, 738.
(25) Halkier, A.; Klopper, W.; Helgaker, T.; Jorgensen, P.; Taylor, P. R.
J. Chem. Phys. 1999, 111, 9157.
542 Inorganic Chemistry, Vol. 43, No. 2, 2004

Bitopic Tris(pyrazolyl)methane Ligand
Figure 9. Schematic representation of the spatial arrangement of the
argentamacrocycles showing the formation of the tubes in 2a.
Figure 7. The argentamacrocycle core of {p-C6H4[CH2OCH2C(pz)3]2-
(AgSbF6)2[(CH3)2CO]2}∞ (2a) created by the κ2-κ1 bonding mode of the
tris(pyrazolyl)methane units; hydrogen atoms omitted.
-
Figure 10. Six argentacrown cores, 24 acetone molecules, and four SbF6
anions building up two adjacent tubular metallamacrocycles in 2a and their
relative position one to another. Only essential atoms are shown, and the
-
disordered fluorine atoms of the SbF6 groups are omitted.
Figure 10 shows the arrangement of two stacks of the
argentamacrocycles that make up the tubes. Each pair of
-
macrocycles sandwich six acetone molecules and one SbF6
counterion. The acetones interact with the argentamacrocycle
cores via short C-H‚‚‚π interactions with the pyrazolyl
-
rings.9 The location of the one SbF6 anion among the
electron rich acetone double bonds and the π clouds from
-
the pyrazolyl rings seems unusual. The remaining SbF6
anions are located in the chiral, helical channels of the
spacers. Figure 10 shows that each argentamacrocycle
“looks” like a crown and each pair acts as a “host” to a SbF6
-
Figure 8. The overall structure of 2a, SbF6 anions not shown, viewed
down seven of the argentamacrocycle tubes connected by trigonally shaped
-
helical spirals.
and six acetone “guests”.
In the tertiary structure, the organic spacers that connect
two [C(pz)3] units in the ligand link the argentamacrocycles
in an extended tubular 3D structure. The ether-based sidearms
have a skewed trans arrangement with the angle formed by
the arene ring and the plane of the attached CH2OCH2 group
of 42.6°. This orientation of the spacer allows a helical
arrangement of the L-Ag-L-Ag sequence along a crystal-
lographic 31 screw axis. Also supporting this structure is a
double π-π interaction involving the central arene core and
two (symmetry related) pyrazolyl rings sandwiching the
former aromatic moiety.8b
In the 3D tertiary structure, each argentamacrocycle is
surrounded by six trigonally shaped helical spirals formed
by the organic spacers that connect them to six other
argentamacrocycles, Figure 8. A schematic representation
of this arrangement that shows the relative position of the
macrocycles is shown in Figure 9. Each helical spiral places
every fourth argentamacrocycle on top of each other forming
a tubular structure.
Crystallization from acetone of the product from the
reaction between AgPF6 and p-C6H4[CH2OCH2C(pz)3]2 leads
to the formation of {p-C6H4[CH2OCH2C(pz)3]2AgPF6}∞ (3a).
In contrast to 1a and 2a and the stoichiometry of the solid
taken into the crystallization step, the metal/ligand ratio is
1:1. The primary structure consists (Figure 11) of two tris-
(pyrazolyl)methane units bonded to silver(I) in a κ2-κ0
coordination mode. The silver atom has a tetrahedral
environment, with a distortion imposed by the restricted
“bite” angle of the chelating pyrazolyl rings (see bond
distances and angles in Supporting Information). Each tris-
(pyrazolyl)methane unit has one noncoordinated pyrazolyl
ring. In the chain structure the ligand exists in an alternating
cis and trans conformation, both pictured at the top of Figure
12. These conformers, combined with the κ2-coordination
mode, leads to a single stranded helical secondary structure,
also shown in Figure 12. The presence of the cis ligand is
critical to the helical organization of 3a. Two single stranded
helices of opposite chirality self-assemble in a tertiary
Inorganic Chemistry, Vol. 43, No. 2, 2004 543

Reger et al.
When acetone was replaced by acetonitrile in the crystal-
lization procedure for compound 2, crystals of the formula
{p-C6H4[CH2OCH2C(pz)3]2[(AgSbF6)2(CH3CN)2][(CH3CN)0.25
-
(C4H10O)0.25]}∞ (2b) were obtained. Crystallographic studies
revealed that the asymmetric unit contains two crystallo-
graphically nonequivalent Ag atoms and two independent
SbF6- anions; two ligands are situated about crystallographic
inversion centers, and therefore, only half of each ligand is
present in the asymmetric unit (Figure 14). The primary
structure is formed by the κ2-κ1 coordination mode of the
tris(pyrazolyl)methane units. All silver atoms have a distorted
tetrahedral environment, with an acetonitrile molecule oc-
cupying the fourth coordination site (Figures 14 and 15).
The secondary structure is organized in argentachains, with
the AgNNCNN sequence of construction, analogous to 1a
rather than the argentamacrocycles observed for 2a. The
chains are linked by the organic spacer (trans arrangement
of the sidearms) and arranged in a 2D sheet tertiary structure.
Figure 16 shows two such sheets oriented horizontally, down
the argentachains showing the linking organic spacers, with
Figure 11. ORTEP representation of the strand repeat unit in 3a. Individual
strands in the double helix are related to one another by pure translation
along the a axis; the double helix direction is along the a axis. Displacement
parameters for atoms refined anisotropically shown at the 40% probability
level and isotropic atoms drawn as spheres of arbitrary radii.
structure consisting of two strands wrapped one around
another, leading to a double stranded helical structure, Figure
13. The “glue” that holds the helices together in the double
stranded helix is a series of C-H‚‚‚π interactions between
the central arene rings, with the arene rings from the cis
conformers acting as acceptors and with the arene rings from
the trans conformers acting as donors. The H‚‚‚centroid
distance is 2.59 Å, with the corresponding C‚‚‚centroid
distance of 3.46 Å and the associated C-H‚‚‚centroid angle
of 153.4°. The counterions are not involved in any nonco-
valent interactions as reported in other cases for this
anion,7c,28 the crystal packing of the double stranded helices
being based solely on van der Waals forces.
It should be noted that 3a represents a rare example of a
double stranded helical organization of a coordination
polymer consisting of two separate single stranded helical
chains wrapped one around another. In most of the known
examples of discrete or infinite helical architectures, all the
strands of the helix are attached through coordinate covalent
bonds to the metal atoms that form the axis of the helix.29
In contrast, there are only a few examples of chemical species
that consist of single stranded helical independent chains
interacting through one or another only by noncovalent
interaction, with the resulting structure being a double helix.30
-
the sheets sandwiching the SbF6 anions and disordered
solvent molecules. The sheets are connected in a quaternary
-
structure by means of hydrogen bonds between the SbF6
anions and acidic hydrogen atoms from the ligands, Figure
16. The H‚‚‚F distances range from 2.24 to 2.38 Å and the
C-H‚‚‚F angles from 166.9° to 157.4°, values that suggest
strong interactions within this class of weak noncovalent
contacts.7
While the primary driving forces for this structure are the
covalent bonds between the ligand, silver, and coordinated
acetonitrile, the structure is also supported by an additional
important noncovalent interaction, a C-H‚‚‚π interaction
between a hydrogen atom from a pyrazolyl ring that chelates
the Ag(1) and the π system of the central arene ring.
Interestingly, only one of the two nonequivalent central arene
rings is involved in this interaction; the other one is not
involved in any type of noncovalent interaction. Thus, as
shown in Figure 15, every other row of central arene rings
acts as an acceptor for two H(13) hydrogen atoms that
sandwich the ring. This interaction arranges the argentachains
in a flattened zigzag orientation within the overall sheet, as
it can be seen in Figure 16.
(28) (a) Cantrill, S. J.; Preece, J. A.; Stoddart, J. F.; Wang, Z.-H.; White,
A. J. P.; Williams, D. J. Tetrahedron 2000, 56, 6675.
(29) For reviews on helical assemblies based on dative bonds see ref 1a
and 1o; for selected recent examples see: (a) Wang, X.; Vittal, J. J.
Inorg. Chem. Commun. 2003, 6, 1074. (b) Koeller, S.; Bernardinelli,
G.; Piguet, C. J. Chem. Soc., Dalton Trans. 2003, 2395. (c) Tuna, F.;
Hamblin, J.; Jackson, A.; Clarkson, G.; Alcock, N. W.; Hannon, M.
J. J. Chem. Soc., Dalton Trans. 2003, 2141. (d) Khlobystov, A. N.;
Brett, M. T.; Blake, A. J.; Champness, N. R.; Gill, P. M. W.; O’Neill,
D. P.; Teat, S. J.; Wilson, C.; Schroeder, M. J. Am. Chem. Soc. 2003,
125, 6753. (e) Floquet, S.; Ouali, N.; Bocquet, B.; Bernardinelli, G.;
Imbert, D.; Bunzli, J.-C. G.; Hopfgartner, G.; Piguet, C. Chem. Eur.
J. 2003, 9, 1860. (f) Carlucci, L.; Ciani, G.; Proserpio, D. M.; Rizzato,
S. New J. Chem. 2003, 27, 483. (g) Barboiu, M.; Vaughan, G.;
Kyritsakas, N.; Lehn, J.-M. Chem. Eur. J. 2003, 9, 763. (h) Shova,
S.; Novitchi, G.; Gdaniec, M.; Caneschi, A.; Gatteschi, D.; Korob-
chenko, L.; Voronkova, V. K.; Simonov, Y. A.; Turta, C. Eur. J. Inorg.
Chem. 2002, 3313. (i) Beauchamp, D. A.; Loeb, S. J. Chem. Commun.
2002, 2484. (j) Keegan, J.; Kruger, P. E.; Nieuwenhuyzen, M.; Martin,
N. Cryst. Growth Des. 2002, 2, 329. (k) Isola, M.; Liuzzo, V.;
Marchetti, F.; Raffaelli, A. Eur. J. Inorg. Chem. 2002, 1588. (l) Stahl,
J.; Bohling, J. C.; Bauer, E. B.; Peters, T. B.; Mohr, W.; Martin-
Alvarez, J. M.; Hampel, F.; Gladysz, J. A. Angew. Chem., Int. Ed.
2002, 41, 1871. (m) Albrecht, M.; Schneider, M. Eur. J. Inorg. Chem.
2002, 1301. (n) Guo, D.; He, C.; Duan, C.-Y.; Qian, C.-Q.; Meng,
Q.-J. New J. Chem. 2002, 26, 796.
Crystallization of 3 from acetonitrile yields crystals of the
formula {p-C6H4[CH2OCH2C(pz)3]2[(AgPF6)2(CH3CN)2][(CH3-
CN)0.25(C4H10O)0.25]}∞ (3b), a compound with a metal/ligand
ratio of 2:1, in contrast to the 1:1 ratio found in 3a. The
structure is organized in the same manner with that of 2b:
a κ2-κ1 bonding mode of the tris(pyrazolyl)methane unit with
a trans orientation of the ligand (Figure 17), leading to a
sheet structure for 3b similar to that depicted in Figures 14-
16 for 2b. However, a close analysis of the noncovalent
interactions present in 3b shows two major differences. First,
although the sheet structure is supported by C-H‚‚‚π
interactions as in 2b, in this case the central arene ring is
the proton donor and a pyrazolyl ring is the acceptor. As in
2b, every other row of central arene rings is involved in such
an interaction, pictured in Figure 18. The second difference
(30) Selected examples: (a) Jouaiti, A.; Hosseini, M. W.; Kyritsakas, N.
Chem. Commun. 2003, 472. (b) Chen, X.-M.; Liu, G.-F. Chem. Eur.
J. 2002, 8, 4811. (c) Mamula, O.; von Zelewsky, A.; Bark, T.;
Bernardinelli, G. Angew. Chem., Int. Ed. 1999, 38, 2945.
-
is that the PF6 anions are not involved in weak C-H‚‚‚F
544 Inorganic Chemistry, Vol. 43, No. 2, 2004

Bitopic Tris(pyrazolyl)methane Ligand
Figure 12. The formation of one helical single strand in {p-C6H4[CH2OCH2C(pz)3]2AgPF6}∞ (3a): (a) cis orientation of one ligand; (b) trans orientation
of another ligand; (c) their successive occurrence linked by the silver(I) centers.
Figure 13. The double stranded helical structure of 3a: (a) two intertwined strands, view perpendicular to a axis, with the C-H‚‚‚π interaction showed
as red dotted lines; (b) the same two strands viewed along the a axis; (c) space filling of 3a.
a sheet structure similar to 2b and 3b, organized by a κ2-κ1
bonding mode of the tris(pyrazolyl)methane units (Figure
19), but in contrast to the other “type b” structures it contains
two types of helical argentachains, one of which does not
contain a acetonitrile bonded to the silver(I), Figure 20. The
three-coordinate silver in this chain has a flattened trigonal
pyramid arrangement (sum of the N-Ag(1)-N bond angles
) 347°). In addition, each silver in this chain interacts with
the π cloud of a pyrazolyl ring κ2-coordinated to the next
silver(I) atom in the chain.31 The second type of silver atom
has a distorted tetrahedral arrangement with the CH3CN
molecules bonded alternatively above and below the chain.
As in other “type b” structures, there are C-H‚‚‚π interac-
tions supporting the sheet structure. The same pyrazolyl ring
that is involved in the silver-π contact acts as a hydrogen
donor, with the central arene ring acting as acceptor.
The differences in the coordination environment of silver
atoms in 4b lead to a change in symmetry when compared
to 2b and 3b. While both 2b and 3b crystallize in the triclinic
system, space group P1h, 4b crystallizes in the chiral
Figure 14. ORTEP representation of the cationic unit in {p-C6H4[CH2-
OCH2C(pz)3]2[(AgSbF6)2(CH3CN)2][(CH3CN)0.25(C4H10O)0.25]}∞ (2b) with
displacement ellipsoids shown at 40% probability level.
-
hydrogen bonds as observed for the SbF6 counterions in
the case of 2b, with all C-H‚‚‚F distances being greater than
the sum of van der Waals radii of hydrogen and fluorine.
Crystallization of 4 from acetonitrile yields crystals of the
formula {p-C6H4[CH2OCH2C(pz)3]2[(AgBF4)2(CH3CN)](C4-
H10O)}∞ (4b). This compound is a coordination polymer with
(31) (a) Mascal, M.; Kerdelhue, J. L.; Blake, A. J.; Cooke, P. A. Angew.
Chem., Int. Ed. 1999, 39, 1968. (b) Mascal, M.; Kerdelhue, J. L.; Blake,
A. J.; Cooke, P. A.; Mortimer, R. J.; Teat, S. J. Eur. J. Inorg. Chem.
2000, 485.
Inorganic Chemistry, Vol. 43, No. 2, 2004 545

Reger et al.
Figure 17. ORTEP representation of the cationic unit in {p-C6H4[CH2-
OCH2C(pz)3]2[(AgPF6)2(CH3CN)2][(CH3CN)0.25(C4H10O)0.25]}∞ (3b) with
displacement ellipsoids shown at 20% probability level.
Figure 15. One sheet of 2b, formed by three argentachains linked by the
organic spacers; the red lines represent the C-H‚‚‚π interactions between
two pyrazolyl rings sandwiching one row of central arene rings.
Figure 18. The sheet structure of {p-C6H4[CH2OCH2C(pz)3]2[(AgPF6)2(CH3-
CN)2][(CH3CN)0.25(C4H10O)0.25]}∞ (3b): (a) view perpendicular to the sheet;
(b) an end on view of the same sheet, in both the C-H‚‚‚π interactions
within the sheet are shown as red dotted lines.
identical to the length of the a axis of the unit cell, 10.282
Å, making the pitches of both helicates identical.
Figure 21 shows that the 2D network (viewed end on),
formed by the helical chains and the connecting organic
bridges, is arranged into a 3D supramolecular quaternary
structure by C-H‚‚‚F weak hydrogen bonds. One of the two
Figure 16. The crystal packing of 2b showing the C-H‚‚‚F hydrogen
bonds as blue dotted lines; also shown (red dotted lines) are the C-H‚‚‚π
interactions within the sheet structure of 2b.
-
orthorhombic space group P212121. The different coordination
environment of silver atoms, coupled with a trans orientation
of the organic spacer, leads to a helical arrangement of both
AgNNCNN argentachains. In both cases, the arrangement
of the backbone is helical, but the chirality of each is
opposite. Both helices are generated around crystallographic
21 screw axes along the a axis of the unit cell. For both, the
distance between every other silver atom is equal and
nonequivalent BF4 ions makes four hydrogen bonds with
two of the 2D sheets forming the 3D architecture.24 The
second BF4- ion makes two hydrogen bonds, one to each of
two sheets. A particularly interesting part of the structure is
that each diethyl ether molecule is bonded through one
-
terminal methyl group to the BF4 counterion that makes
four hydrogen bonds and also through the ether oxygen atom
to a coordinated acetonitrile.
546 Inorganic Chemistry, Vol. 43, No. 2, 2004

Bitopic Tris(pyrazolyl)methane Ligand
Figure 19. ORTEP representation of the cationic unit of {p-C6H4[CH2-
OCH2C(pz)3]2[(AgBF4)2(CH3CN)](C4H10O)}∞ (4b) with displacement el-
lipsoids shown at 50% probability level.
Figure 21. Two sheets in 4b held together through C-H‚‚‚F bonds
-
involving the BF4 anions, forming a 3-D quaternary architecture; ether
molecules situated between the sheets are also shown.
Figure 22. ORTEP representation of {p-C6H4[CH2OCH2C(pz)3]2-
(AgNO3)2}∞‚4CH3CN (5‚4CH3CN), at the 50% probability level with the
-
NO3 anions coordinated to silver(I) centers; acetonitrile molecules of
solvation and hydrogen atoms not shown.
Figure 20. View perpendicular to one sheet formed by the alternating
silver chains in 4b; the C-H‚‚‚π interactions are shown as red dotted lines
and the Ag-π contacts pictured with black dotted lines.
All these interactions build up a chiral network of helices
of opposite chirality. This is an example of a racemic mixture
of helices crystallizing in a chiral space group, where no
symmetry operation relates the two helices of opposite
chirality.
Crystallization of 5 from acetonitrile yields crystals of the
formula {p-C6H4[CH2OCH2C(pz)3]2(AgNO3)2(CH3CN)4}∞
(5‚4 CH3CN). The primary structure (Figure 22) is formed
again by a κ2-κ1 coordination mode of the ligand to the
silver(I) centers. In addition, the anions are also coordinated
to the silvers, a common feature for discrete silver(I)
compounds or silver(I) coordination polymers formed from
Figure 23. One argentachain of {p-C6H4[CH2OCH2C(pz)3]2(AgNO3)2}∞‚
4CH3CN (5‚4CH3CN), with the NO3- anions coordinated to silver(I) centers;
hydrogen atoms not shown.
consists of W-shaped sheets that have an overall configu-
ration very different from 2b-4b. Figure 24 shows two such
sheets down the polymeric chains. The sheets are held
together in a quaternary structure via a favorable noncovalent
interaction that we have named “quadruple pyrazolyl em-
brace” and presented in detail in Scheme 1: a concerted set
-
this counterion.1c,d,16j,17b The NO3 anion is anisobidentate
with one short (2.504(5) Å) and one long (2.761(5) Å)
oxygen-silver distance.
The secondary structure again consists of AgNNCNN
argentachains, Figure 23. However, the tertiary 2D structure
Inorganic Chemistry, Vol. 43, No. 2, 2004 547

Reger et al.
Figure 24. Two stacked sheets of 5‚CH3CN; the pyrazolyl embrace interactions are centrally pictured and marked with *.
of π-π stacking and C-H‚‚‚π interaction.19 Two closely
situated sets of pyrazolyl rings, part of adjacent sheets, within
the [C(pz)] units that chelate the silver(I) centers, are involved
in this supramolecular contact. Within these four pyrazolyl
rings, two of them are stacked and parallel displaced, and
they serve as hydrogen donors in the associated C-H‚‚‚π
interaction, where two other pyrazolyl rings act as acceptors.
The association between the sheets creates channels that
bisect the b and c axes of the unit cell creating 12 × 10 Å2
channels that are filled with acetonitrile molecules.
Anion Exchange Properties. The anion exchange proper-
ties of these compounds have been explored by treating {p-
C6H4[CH2OCH2C(pz)3]2(AgSbF6)2}∞ (2) with a saturated
aqueous solution of KPF6 and separately a solution of KO3-
SCF3. The solid was periodically collected by filtration (every
2 h) and the presence of the second anion monitored by
infrared spectroscopy following the characteristic bands of
the anions.32,33 Samples containing mixtures of anions as well
-
as ones with the SbF6 completely exchanged could be
obtained by these methods. The IR spectrum of pure 2 (red
line in Figure 25) shows a band at 664 cm-1 (marked with
-
*) that is assigned to ν3(T1u) vibration of the SbF6 anion.
-
-
The IR spectrum of a partially (SbF6 /PF6 ) exchanged
sample (after 4 h of stirring) is shown in Figure 25 as a green
line; the band at 664 cm-1 is still present, but of a weaker
intensity, an indication of a decreased quantity of this anion.
There are two new bands (both marked with b) at 841 and
550 cm-1, assigned to ν3(T1u) and ν4(T1u) vibrations of the
Figure 25. Anion exchange monitored by IR spectroscopy; red line
indicates IR spectra of 2: the band at 664 cm-1 (marked with *) is assigned
-
PF6 anion. The anions can be completely exchanged by
-
to ν3(T1u) vibration of the SbF6 anion. Green line indicates IR spectra of
-
stirring for 12 h. The IR spectrum of completely (SbF6 /
a partially (SbF6-/PF6-) exchanged sample: the bands at 841 and 550 cm-1
-
-
PF6 ) exchanged sample is pictured as a blue line; the band
(marked with b) are assigned to ν3(T1u) and ν4(T1u) vibrations of the PF6
-
anion. Blue line indicates IR spectra of a completely (SbF6-/PF6
)
/
at 664 cm-1 is no longer present, and the two strong bands
-
exchanged sample. Black line indicates IR spectra of a partially (SbF6
F3CSO3-) exchanged sample: the band at 1154 cm-1 (marked with #) is
(32) Related examples: (a) Yaghi, O. M.; Li, H. J. Am. Chem. Soc. 1996,
118, 295. (b) Khlobystov, A. N.; Champness, N. R.; Roberts, C. J.;
Tendler, S. J. B.; Thompson, C.; Schroeder, M. CrystEngComm 2002,
4, 426. (c) Noro, S.; Kitaura, R.; Kondo, M.; Kitagawa, S.; Ishii, T.;
Matsuzaka, H.; Yamashita, M. J. Am. Chem. Soc. 2002, 124, 2568.
(d) Sui, B.; Fan, J.; Okamura, T.; Sun, W.-Y.; Ueyama, N. New J.
Chem. 2001, 25, 1379. (e) Jung, O.-S.; Kim, Y. J.; Lee, Y.-A.; Chae,
H. K.; Jang, H. G.; Hong, J. Inorg. Chem. 2001, 40, 2105. (f) Min, K.
S.; Suh, M. P. J. Am. Chem. Soc. 2000, 122, 6834.
assigned to the δasCF3(E) vibration.
-
of the PF6 anion clearly present. This procedure can be
extended to other anions as well: the IR spectrum of a
-
-
partially (SbF6 /CF3SO3 ) exchanged sample is shown in
Figure 25 as a black line. The band at 664 cm-1 is still
present but again of a weaker intensity, and the band (marked
with #) at 1154 cm-1 is clearly assigned to δasCF3(E).27
(33) Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coor-
dination Compounds, 3rd ed.; Wiley-VCH: New York, 1978.
548 Inorganic Chemistry, Vol. 43, No. 2, 2004

Bitopic Tris(pyrazolyl)methane Ligand
Figure 26. ORTEP representation of the cationic unit of {p-C6H4[CH2-
OCH2C(pz)3]2[Ag2(PF6)0.78(1)(SbF6)1.22(1)(CH3CN)2][(CH3CN)0.25
-
(C4H10O)0.25]}∞ (6) with displacement ellipsoids shown at 40% probability
level.
From a sample containing a SbF6-/PF6- mixture of anions,
crystals of the formula {p-C6H4[CH2OCH2C(pz)3]2[Ag2-
(PF6)0.78(1)(SbF6)1.22(1)(CH3CN)2][(CH3CN)0.25(C4H10-
O)0.25]}∞ (6) were obtained from the same acetonitrile system
used for “b type” complexes and were subjected to X-ray
diffraction studies. The cationic unit is shown in Figure 26.
A complete structural analysis revealed the same basic 2D
sheet structure as observed for 2-4b. Two independent
Figure 27. The sheet structure of {p-C6H4[CH2OCH2C(pz)3]2[Ag2-
(PF6)0.78(1)(SbF6)1.22(1)(CH3CN)2][(CH3CN)0.25(C4H10O)0.25]}∞ (6); the red
dotted lines are the C-H‚‚‚π interactions.
-
-
(P,Sb)F6 anion positions were located; however, the PF6
-
and SbF6 anions were found to be mixed on both sites, in
the proportion P(1)/Sb(1) ) 0.314(1)/0.686(1) and P(2)/
Sb(2) ) 0.467(1)/0.543(1). Refinement of either site as fully
P or fully Sb resulted in unreasonably small (P) or large (Sb)
displacement parameters as well as higher R-values. The
fluorine atoms in both anion sites are well ordered, and
therefore, the P(Sb)-F bond lengths represent a weighted
average of the P-F and Sb-F contributions. The slightly
inflated displacement parameters for these fluorine atoms
may reflect the presence of two closely separated F6
octahedra, or simply the rotational disorder commonly
encountered in spherical anions of this type.
Figure 28. ORTEP representation of the cationic unit of {p-C6H4[CH2-
OCH2C(pz)3]2(AgSbF6)[(CH3)2CO]1.5
}
(7) with displacement ellipsoids
∞
Analysis of the covalently bonded network indicated the
presence of two types of C-H‚‚‚π interactions between the
pyrazolyl-central arene ring pairs. Interestingly, both of the
interactions in which a pyrazolyl ring acted as the hydrogen
donor and the phenyl ring as acceptor as in 2b and the inverse
situation found in 3b were found, as pictured in Figure 27.
In this case, every other row of central arene rings alterna-
tively acts as either hydrogen donor or acceptor. In other
words, both interactions found separately in alternate rows
in 2b and 3b are combined in the case of 6, in an alternating
occurrence, involving every row.
shown at 50% probability level.
-
from acetone, a new compound containing only SbF6 as
the counterion was obtained, of the formula {p-C6H4[CH2-
OCH2C(pz)3]2(AgSbF6)[(CH3)2CO]1.5}∞ (7). In contrast to its
-
other two SbF6 “homologues” 2a and 2b, where the tris-
(pyrazolyl)methane units act in the κ2-κ1 coordination mode
and the metal-to-ligand ratio is 2:1, here the [C(pz)3] unit is
κ2-κ0 bonded with a metal-to-ligand ratio of 1:1 (Figure 28).
This feature leads to a 1D secondary structure represented
in Figure 29a, where all the ligands have a trans arrangement
of the sidearms. The tertiary structure is organized by acetone
molecules that interact with a pyrazolyl ring via C-H‚‚‚π
interactions, with one of the methyl groups acting as the
hydrogen donor, Figure 29b. In addition, the oxygen atoms
within the acetones act as acceptors in weak C-H‚‚‚O
hydrogen bonds, where the hydrogen donor is a CH group
-
When the SbF6 anion was completely exchanged with
-
PF6 and a crystalline sample was subjected to crystal-
lographic studies, an identical structure with that of 3b
prepared directly from AgPF6 was obtained.
-
When the same SbF6 /PF6- mixture that was used for the
growth of the crystals for 6 from acetonitrile was crystallized
Inorganic Chemistry, Vol. 43, No. 2, 2004 549

Reger et al.
The double π-π stacking interactions in the organic linkers
are critical to the circular organization of these argentachains
(Figures 2 and 3). In the case of 2a, the acetone molecules
noncovalently connected to the covalent framework along
-
with the “trapped” SbF6 counterion appear to support the
tubular organization of the argentamacrocycles with the
helical organization of the L-Ag-L-Ag sequence also
important to this arrangement.
Among the helical systems, DNA is certainly the most
commonly known example. The DNA double helix is formed
upon self-assembly of two complementary helical strands.
The driving force for the formation of the double helical
arrangement is the establishment of hydrogen bonds between
complementary nucleic acid bases. However, in principle,
any type of attractive interaction may be used to generate
double helical architectures, as long as there are two
complementary helical strands with complementary recogni-
tion sites that will induce a recognition pattern within their
structure. In the case of 3a, the self-complementary recogni-
tion pattern is played by the central arene ring that undergoes
a C-H‚‚‚π interaction, as pictured in Figure 13.
Figure 29. (a) One chain of {p-C6H4[CH2OCH2C(pz)3]2(AgSbF6)[(CH3)2-
CO]1.5
∞ (7) showing the κ2-κ0 bonding mode of the [C(pz)3] unit and the
trans arrangement of the ligand; (b) two strands of 7 and their associated
acetone molecules (C-H‚‚‚π contacts showed as red dotted lines). The
C-H‚‚‚O hydrogen bonds responsible for organization of 7 in sheets are
shown as a blue dotted line.
}
The crystalline solids obtained from acetonitrile, “b type”,
show similar structures; two-dimensional sheets build up by
linking the AgNNCNN sequence of argentachains by the
organic spacer. Although the covalent part of the 2b-4b
networks is two-dimensional, the structures have thickness.
The views of 2b (Figure 16), 3b (Figure 18b), and 4b (Figure
21) in the same alignment of the sheets illustrate the
similarity in the width of the sheets. Also shown are
U-shaped channels formed between the silver strands by the
1,4-bis[ethoxymethyl]benzene bridge. The dimensions of the
channels are ca. 6 × 4 Å2 in all structures, as measured
between the two methylene groups directly bonded to the
phenyl ring and between these methylene groups and the
central methine carbon atoms from the tris(pyrazolyl)methane
units. Despite the similarity between the sheets, subtle
differences induced by the anions are also present (vide
supra). The differences between 2b and 3b are at the
noncovalent level only, but when 4b is compared with its
analogues a drastic change in symmetry is observed. The
asymmetric units of 2b and 3b contain two crystallographi-
cally inequivalent Ag atoms and two independent anions;
two ligands are situated about crystallographic inversion
centers, and therefore, only half of each ligand is present.
The asymmetric unit of 4b is composed also of two
crystallographically inequivalent Ag atoms and two inde-
pendent anions, but one full ligand is present. Further, the
coordinated acetonitrile molecules are bonded to only one
type of silver. These differences lead to the following
situation: in the case of 2b and 3b the inequivalent Ag atoms
are found alternatively in the same argentachain, while in
the case of 4b the inequivalent Ag atoms are found in
different chains. An additional important structural difference
is that in 4b the solvent molecules are held between the
helical layers in a very ordered fashion by weak hydrogen
bonds, a rather unusual observation for helical superstructures.1a
In 2b and 3b (where the solvent is not involved in any
from a pyrazolyl ring situated on an adjacent strand. These
interactions build up a 2D tertiary structure, arranging the
strands closely one to another in a sheetlike structure.
Comparison of “Molecular” and Supramolecular Struc-
tures. The structural behavior of the silver(I)-p-C6H4[CH2-
OCH2C(pz)3]2 system with noncoordinating counterions
shows a dual solvent-counterion dependence. The solvent
used for crystallization primarily controls the structures.
When the compounds are crystallized from the coordinating
solvent acetonitrile, similar 2-D sheet structures are observed
(“b type”), with the anions imposing small differences within
the sheets. When crystallized from the weakly coordinating
solvent acetone (“a type”), the anions impose major structural
variations of the resulting architectures.
In all “a type” structures, helical arrangements were
observed, either of the argentachains (1a), of the organic
spacer only (2a), or of the whole 1-D covalent network (3a).
Given the major differences in the secondary structures of
1a and 2a, there are surprising similarities: both compounds
crystallize in the rhombohedral space group R3h (hexagonal
setting), both with Z ) 9. In both compounds, the κ2-κ1
coordination mode of the ligand is present, and both tertiary
structures are supported by the same double π-π stacking
where two pyrazolyl rings (symmetry related) sandwich the
central arene core. In both compounds the local structure of
the ligand is almost identical: the ether-based sidearms have
a skewed trans arrangement with the angle formed by the
arene ring and the plane of the attached CH2OCH2 group
being around 42°. This orientation of the ligand is required
by the double π-π stacking in which the ligand is involved.
In the case of 1a, the F‚‚‚F interactions, coupled with the
extensive network of weak hydrogen bonds between the
triflate oxygen atoms and C-H groups on the ligands,
organize the tubular tertiary structure of helical argentachains.
550 Inorganic Chemistry, Vol. 43, No. 2, 2004

Bitopic Tris(pyrazolyl)methane Ligand
noncovalent interaction) the trapped solvent was found to
be disordered.
in the crystallization process was a compound with a ligand-
to-metal ratio of 1:2, both the final crystalline compounds
were found to have a ligand-to-metal ratio of 1:1, a
phenomenon found only in the case where PF6 was the
counterion and acetone was used as crystallization solvent.
When the structure of 5‚4 CH3CN, containing the coor-
dinating counterion nitrate, is compared with its homologues,
the differences are even more pronounced. The nitrates
coordinate to the silvers, and the acetonitrile molecules in
the crystals are simply solvents of crystallization. This
alteration imposes a change in the structure from an almost
planar sheet to a W-shaped sheet (compare Figures 16, 18b,
21, and 27b with Figure 24). Also different is the packing
of the sheets within the crystal that is controlled by the
pyrazolyl embrace in 5‚4CH3CN.
-
Conclusion
Critical for the formation of these supramolecular struc-
tures is the organization inherently built into the bitopic
ligand by its rigid parts (central arene core and [C(pz)3] units)
linked by a set of three sp3 hybridized atoms. Importantly,
it is the flexibility of the ether linkage that allows the anions
to organize the structures reported here; rigid ligands would
have to be perfectly tailored to allow such structures, and
their inherent rigidity would restrict the influence of the
anions in the final structures.
-
-
Crystallization of the partially exchanged SbF6 /PF6
mixture from both acetonitrile and acetone leads to two very
different complexes. From acetonitrile, a “b type” structure
of the mixed counterion species 6 is observed. In the presence
of both anions, both types of C-H‚‚‚π interactions are
observed that are found separately in 2b and 3b (see Figures
15, 16, 18, and 27).
Summing all the findings for this system, we observed
that all counterions impose changes in the overall structures
of the crystalline solids, but those differences are much
greater when the material is crystallized from a noncoordi-
nating solvent. The following essential patterns in the self-
assembly processes were found in these structures: (a) the
ligand displays a κ2-κ1 coordination mode of the [C(pz)3]
units in all cases, except the cases when the PF6- anion was
present and the crystallization solvent was acetone (3a and
7) where the coordination mode was κ2-κ0; (b) the ligand
was able to adjust its structure to maximize both covalent
and noncovalent interactions; (c) there are the absence of
coordinated acetone molecules in “a type” structures and the
presence of coordinated acetonitrile molecules in “b type”
-
-
Crystallization of the SbF6 /PF6 mixture from acetone
produces a complex with the formula {p-C6H4[CH2OCH2C-
(pz)3]2(AgSbF6)[(CH3)2CO]1.5}∞ (7), containing only the
-
SbF6 anion and with different stoichiometry than its two
-
-
SbF6 “homologues” 2a and 2b. The presence of the PF6
in the crystallization solution leads to precipitation of a new
-
SbF6 complex that is very different from the 2a and 2b
complexes. As observed with 2a, acetone molecules are
involved in organizing the association of the coordination
polymer into a higher level of organization (see Figure 29).
As expected from the similar stoichiometry, the κ2-κ0
behavior of the [C(pz)3] unit in 7 (Figure 29a) is the same
as in 3a (Figures 11, 12), but the ligand has only the trans
orientation. The missing cis orientation of the ligand impedes
the formation of the single and the subsequent double
stranded helical organization as in the case of 3a. Interest-
ingly, the alignment of the strands with the central arene
cores situated close one to another shows the incipient
formation of weak C-H‚‚‚π interactions somewhat analo-
gous to those observed with 3a.
The formation process for 7 is unique in this work. Using
biological systems, Lindsey34 has identified several types of
self-assembly processes, and besides the “strict” self-as-
sembly process, we mention here only a few: (a) irreversible
self-assembly (irreversible reactions kinetically channeled to
a particular pathway); (b) assisted self-assembly (where an
external species prevents the formation of unwanted inter-
mediates and does not appear in the final product); (c)
directed self-assembly (where a species directs the course
of the assembly but is not present in the final product). While
all the processes leading to the self-assembly of 1-6 (either
type a or b) are the “strict” self-assembly process, the
assembly of 7 is a “directed” self-assembly process. The
presence of the PF6- anion in solution “influences” a κ2-κ0
coordination mode of the [C(pz)3] unit as observed in the
“pure” PF6- sample, when both are crystallized from acetone.
Although in the case of 3a and 7 the bulk starting material
-
structures; (d) there are the involvement of OTf-, SbF6 ,
and BF4- anions in weak C-H‚‚‚O(F) hydrogen bonds and
-
the lack of such interactions in the PF6 case; (e) the
-
coordination of NO3 to silver(I) center contrasts to that of
OTf- anion that is also known to be sometimes a coordinat-
ing anion.
An important result of these patterns is the demonstration,
particularly with 1a and 2a, of success using a noncovalent
strategy for the assembly of covalent networks with remark-
able topologies. Although the three-dimensional structures
of both of these compounds are built on covalent bonds, the
tertiary structures observed appear to be arranged by the
noncovalent bonds. This contention is strongest for 1a where
the [(CF3SO3)6]6- clusters are held together by weak F‚‚‚F
interactions and then these clusters organize the covalent
structure through weak C-H‚‚‚O hydrogen bonds with the
bitopic ligand involving the -SO3 groups. For 2a, the six
acetone molecules and one SbF6- anion present between the
argentamacrocycles also organize the tubular structure
observed. For 3a, the covalent bonds organize the strands,
but weak C-H‚‚‚π interactions between the central arene
rings organize the double helix. Crystallization of these
systems from weakly coordinating solvents is necessary to
allow these weak forces to dominate the structures: the three-
coordinate silver centers appear to be more flexible in
accommodating particular structures than the four-coordinate
silvers in the complexes crystallized from acetonitrile. In
(34) Lindsey, J. S. New J. Chem. 1991, 15, 153.
Inorganic Chemistry, Vol. 43, No. 2, 2004 551

Reger et al.
6H, 4-H pz), 5.02 (s, 4H, OCH2C(pz)3), 4.67 (s, 4H, OCH2Ph).
Calcd for C30H30Ag2F12N12O2Sb2: C, 28.20; H, 2.37; N, 13.15.
Found: C, 28.51; H, 2.21; N, 13.17. ES+/MS: m/z 699 and 1041,
corresponding to [LAg]+ and [LAg2SbF6]+.
these cases, the coordination of the solvent influences the
system such that sheet structures are observed in all cases.
NMR and ES/MS studies show that in solution the cationic
species present are anion independent and that in solutions
of coordinating solvents a complicated series of equilibria
take place between ligand-silver(I) species, species in which
the solvent has partially or completely displaced the ligands.
The structural diversity observed in the solid state, triggered
by the anion and/or solvent, must develop in the final
crystallization step.
The structures reported here demonstrate that the bitopic
p-C6H4[CH2OCH2C(pz)3]2 ligand is structurally adaptive; that
is, it can adjust its structure to maximize all covalent and
noncovalent forces within a given system. With this ability
to adjust to changes in the system, coupled with the ability
to participate in π-π stacking and form C-H‚‚‚π and weak
hydrogen bonding interactions, the C6H6-n[CH2OCH2C(pz)3]n
class of ligands based on linking tris(pyrazolyl)methane units
with semirigid organic spacers contains ideal candidates for
studying the self-assembly process. We have also shown that
although the structures reported here are very different,
several important similarities can be found. This strategy for
the assembly of covalent networks based on semirigid ligands
completes the gap between strategies based on rigid or
completely flexible ligands.
Synthesis of {p-C6H4[CH2OCH2C(pz)3]2(AgPF6)2}∞ (3). This
compound was synthesized as above for 1 using AgPF6 (0.254 g,
1.00 mmol), to afford 0.409 g (74%) of solid identified as
1
{p-C6H2[CH2OCH2C(pz)3]4(AgPF6)2}∞. H NMR (acetone-d6): δ
7.83, 7.76 (m, m, 6,6H, 3,5-H pz), 7.08 (s, 4H, C6H4), 6.59 (m,
6H, 4-H pz), 5.01 (s, 4H, OCH2C(pz)3), 4.65 (s, 4H, OCH2Ph).
Calcd for C30H30Ag2F12N12O2P2: C, 32.87; H, 2.76; N, 15.33.
Found: C, 33.05; H, 3.15; N, 14.99. ES+/MS: m/z 699 corre-
sponding to [LAg]+.
Synthesis of {p-C6H4[CH2OCH2C(pz)3]2(AgBF4)2}∞ (4). This
compound was synthesized as above for 1 using AgBF4 (0.195 g,
1.00 mmol), to afford 0.445 g (84%) of solid identified as
{p-C6H4[CH2OCH2C(pz)3]2Ag2(BF4)2(THF)}∞. 1H NMR (acetone-
d6): δ 7.82, 7.77 (m, m, 6,6H, 3,5-H pz), 7.09 (s, 4H, C6H4), 6.57
(m 6H, 4-H pz), 5.02 (s, 2H, OCH2Ph), 4.67 (s, 2H, OCH2C(pz)3),
3.62 (m, 2H, CH2O THF), 1.92 (m, 2H, CH2 THF). Calcd for
C30H30Ag2B2F8N12O2‚C4H8O: C, 38.81; H, 3.64; N, 15.98. Found
C, 38.86; H, 3.55; N, 16.23. ES+/MS: m/z 699 and 893, corre-
sponding to [LAg]+ and [LAg2BF4]+.
Synthesis of {p-C6H4[CH2OCH2C(pz)3]2(AgNO3)2}∞ (5). This
compound was synthesized as above for 1 using AgNO3 (0.167 g,
1.00 mmol) in dry acetonitrile (15 mL) under an inert atmosphere.
The clear solution was stirred for 2 h, and 100 mL of diethyl ether
was added, resulting in the precipitation of a white compound. The
solvents were removed by cannula filtration and the white
precipitate washed with THF (2 × 10 mL) and then vacuum-dried
to afford 0.306 g (66%) of solid identified as {p-C6H2[CH2OCH2C-
(pz)3]4(AgNO3)2}∞. 1H NMR (acetone-d6): δ 7.82, 7.77 (m, m, 6,-
6H, 3,5-H pz), 7.09 (s, 4H, C6H4), 6.57 (m 6H, 4-H pz), 5.02 (s,
4H, OCH2Ph), 4.67 (s, 4H, OCH2C(pz)3). Calcd for C30H30-
Ag2N14O8: C, 38.73; H, 3.25; N, 21.08. Found: C, 38.52; H, 3.02;
N, 20.88. ES+/MS: m/z 699 and 868, corresponding to [LAg]+
and [LAg2NO3]+.
Crystallization Procedure. In a typical crystallization procedure,
a sample of about 5 mg was dissolved in ca. 3 mL of solvent
(acetone or acetonitrile). To remove any potential insoluble
materials, this solution was filtered through cotton into a small test
tube via a pipet. The open small test tube was inserted in a second,
larger one that already had ca. 20 mL of diethyl ether and was
closed with a Teflon screw cap. The test tubes were kept at room
temperature for several days, during which time colorless crystals
suitable for X-ray diffraction studies formed.
Experimental Section
General Procedure. All operations were carried out under a
nitrogen atmosphere using standard Schlenk techniques and a
Vacuum Atmospheres HE-493 drybox. All solvents were dried and
1
distilled prior to use following standard techniques. The H NMR
spectra were recorded on a Varian AM300 spectrometer using a
broad-band probe. Proton chemical shifts are reported in ppm versus
internal Me4Si. IR spectra were recorded on a Nicolet 5DXBO FTIR
spectrometer. Electrospray ionization mass spectrometry data were
obtained on a MicroMass QTOF spectrometer. Clusters assigned
to specific ions show appropriate isotopic patterns as calculated
for the atoms present. Elemental analyses were performed by
Robertson Microlit Laboratories (Madison, NJ). Tris-2,2,2-(1-
pyrazolyl)ethanol, HOCH2C(pz)3, and p-C6H4[CH2OCH2C(pz)3]2
(L) were prepared following literature methods.18a
Synthesis of {p-C6H4[CH2OCH2C(pz)3]2(AgO3SCF3)2}∞ (1).
A THF (20 mL) solution of p-C6H4[CH2OCH2C(pz)3]2, L, (0.295
g, 0.500 mmol) was added dropwise to a solution of AgO3SCF3
(0.256 g, 1.00 mmol) in dry THF (20 mL) under an inert
atmosphere. A white precipitate appeared as the mixture was stirred
for 2 h. The THF was removed by cannula filtration and the white
precipitate washed with THF (2 × 10 mL) and then vacuum-dried
to afford 0.413 g (75%) of solid identified as {p-C6H2[CH2OCH2C-
(pz)3]4(AgO3SCF3)2}∞. 1H NMR (acetone-d6): δ 7.84, 7.81, (d, d,
J ) 1.9, 2.7 Hz, 6,6H, 3,5-H pz), 7.10 (s, 4H, C6H4), 6.59 (dd, 6H,
J ) 1.9, J ) 2.7 Hz, 4-H pz), 5.03 (s, 4H, OCH2Ph), 4.68 (s, 4H,
OCH2C(pz)3). Calcd for C32H30Ag2F6N12O8S2: C, 34.80; H, 2.74;
N, 15.22. Found: C, 34.97; H, 2.69, N, 15.30. ES+/MS: 699 and
955 corresponding to [LAg]+ and [LAg2O3SCF3]+.
Anion Exchange Procedure. A 100 mg sample of 2 was
suspended in a saturated aqueous solution of KPF6 or KO3SCF3
(50 mL), stirred, filtered, washed with water (100 mL), and air-
dried. The anion exchange was monitored by IR spectroscopy (KBr
pellets). The first notable anion exchange was observed after the
sample was stirred for 0.5 h. The sample used in the crystallization
of 6 and 7 was obtained after 4 h of stirring. After 12 h of stirring,
the anion was completely exchanged.
Crystallography. All crystals were mounted on thin glass fibers
with inert oil or epoxy. After preliminary crystal quality, symmetry
and unit cell parameter determination, a full sphere (1a, 2b, 3b
3
and 6), approximately /4 of a sphere (3a), or a hemisphere (2a,
Synthesis of {p-C6H4[CH2OCH2C(pz)3]2(AgSbF6)2}∞ (2). This
compound was synthesized as above for 1 using AgSbF6 (0.343 g,
1.00 mmol), to afford 0.510 g (79%) of solid identified as
{p-C6H2[CH2OCH2C(pz)3]4(AgSbF6)2}∞. 1H NMR (acetone-d6): δ
7.82, 7.77 (m, m, 6,6H, 3,5-H pz), 7.09 (s, 4H, C6H4), 6.57 (m,
4b, 5b) of X-ray intensity data was collected at the temperatures
indicated in tables in the Supporting Information on a Bruker
SMART APEX CCD-based diffractometer (Mo KR radiation, λ )
0.71073 Å).35 Raw area detector data frame integration and Lorentz/
polarization corrections were carried out with SAINT+.35 Final unit
552 Inorganic Chemistry, Vol. 43, No. 2, 2004

Bitopic Tris(pyrazolyl)methane Ligand
cell parameters are based on the least-squares refinement of all
reflections with I > 5σ(I) from each data set. For 1a, 2a, 2b, 3b,
4b, 6, and 7, an empirical absorption correction based on the
multiple measurement of equivalent reflections was applied with
SADABS.35 Direct methods structure solution (except where noted),
difference Fourier calculations, and full-matrix least-squares refine-
ment against F2 were performed with SHELXTL for all structures.36
atoms in the structure. The asymmetric unit contains two indepen-
dent sets each of Ag atoms, organic ligands, and PF6- anions. The
refinement was hampered by major disorder affecting the -CH2-
OCH2C(pz)3 tripodal end of one of the two independent ligands.
An arduous effort to model the disorder of the pyrazolyl rings in
this region of the structure as three superimposed κ2-κ0 orientations
was unsuccessful; therefore, only the major disorder component
was included. Due to the severity of the disorder, these pyrazolyl
rings were fit to regular pentagons whose size was allowed to vary
(SHELX AFIX 59 command) and refined with isotropic displace-
ment parameters. A total of 33 restraints was employed. Disorder
Compound 1a crystallizes in the space group R3h (hexagonal
setting) with Z ) 9 for the given formula. The space group choice
was confirmed by the successful solution and refinement of the
data; higher symmetry space groups were ruled out on the basis of
systematic absences in the intensity data and by manual examination
of the completed structure, supported by the ADDSYM routine in
PLATON.37 All atoms are on positions of general crystallographic
symmetry. The central phenyl ring of the ligand is situated about
an inversion center at 0, 1/2, 0. The asymmetric unit consists of the
Ag atom, half a ligand, and the triflate anion. Non-hydrogen atoms
were refined with anisotropic displacement parameters; hydrogen
atoms were placed in geometrically idealized positions and included
as riding atoms.
-
was also observed in one of the two PF6 anions. This anion was
3
modeled as eight /4-occupied F atoms surrounding the central P.
With the exception of the ligand atoms affected by disorder, all
non-hydrogen atoms were eventually refined with anisotropic
displacement parameters. Hydrogen atoms were idealized and
included as riding atoms. The final refined value of the absolute
structure (Flack) parameter is 0.04(3), indicating the correct absolute
structure and the absence of racemic twinning.
Compounds 2b and 3b crystallize in the triclinic system. The
space group P1h was assumed and confirmed in each case by the
successful solution and refinement of the structure. The asymmetric
units contain two crystallographically inequivalent Ag atoms and
Compound 2a also crystallizes in the space group R3h (hexagonal
setting). This space group was confirmed in the same manner as
for 1a. The asymmetric unit contains one Ag atom, half a ligand,
an acetone molecule of crystallization, and two crystallographically
-
two independent SbF6 anions. Two ligands are situated about
crystallographic inversion centers, and therefore, only half of each
ligand is present in the asymmetric units. A region of disordered
solvent is also present in the crystals, which was modeled as 1/4
Et2O and 1/4 CH3CN, both disordered about an inversion center.
Eventually, all non-H and nonsolvent atoms were refined with
anisotropic displacement parameters; the solvent molecules were
refined isotropically. A total of 7 geometric restraints were used in
modeling the solvent disorder (SHELX SAME and DFIX). Hy-
drogen atoms were idealized and included as riding atoms.
For 4b the pattern of systematic absences in the intensity data
uniquely determined the orthorhombic space group P212121. All
non-hydrogen atoms were refined with anisotropic displacement
parameters; hydrogen atoms were idealized and included as riding
atoms.
Though metrically consistent with the orthorhombic crystal
system, the pattern of systematic absences in the intensity data of
5b was not consistent with any orthorhombic space group.
Processing the data in the monoclinic system (with â ) 90.000-
(4)°) gave absences uniquely consistent with the monoclinic space
group P21/c. The structure was readily solved in P21/c. After
location of all heavy atoms, the refinement “hung up” at R1 ∼
25%. Refinement of the data including a correction for pseudo-
orthorhombic twinning resulted in a reduction of R1 from ∼25%
to 6.2% and gave reasonable atomic displacement parameters and
residual electron density (+2.47/-1.68 e-/Å3, near Ag). The twin
law is (100/01h0/001h), corresponding to a 2-fold rotation around
the a axis. Such twinning is relatively common in monoclinic
crystals with â coincidentally near 90°.36 Upon successful solution
and twin refinement in P21/c, a check for missed symmetry was
performed with the ADDSYM routine in PLATON,37 which verified
the crystal system and space group choice.
-
independent SbF6 counterions. Significant positional and oc-
-
cupational disorder was encountered for both SbF6 counterions.
Sb1 was modeled as occupying a split position, Sb1A and Sb1B,
with six surrounding F atoms. Sb2, located on the origin, was
modeled with eight surrounding F atoms having suitable occupan-
cies. The central Sb of both SbF6- anions exhibited unusually large
displacement parameters when refined as fully occupied, notwith-
standing the F atom disorder. In addition, full occupancy of both
-
SbF6 positions would violate charge balance. Refinement of the
site occupation factors (sof’s) for each Sb led to a large drop in
R-values (from ca. 20% at that stage of refinement) and resulted in
ellipsoids of a reasonable magnitude. Refinement of the sof’s led
to values appropriate to maintain electroneutrality within the crystal;
subsequently, the sof’s were fixed at those values. Eventually all
non-hydrogen atoms were refined with anisotropic displacement
parameters; hydrogen atoms were idealized and included as riding
atoms. The largest residual electron density peaks (ca 1.35 e-/Å3)
-
are located in the vicinity of the disordered SbF6 anions.
In the case of 3a, systematic absences in the intensity data were
consistent with the space groups P21 or P21/m; intensity statistics
indicated P21. After initial failure to achieve a reasonable solution
in P21/m, a successful solution and refinement was achieved in P21.
Subsequently, the absence of mirror symmetry was confirmed by
manual examination of the structure, as well as by ADDSYM/
PLATON.37 To eliminate the possibility that the significant ligand
and anion disorder present in the final refined structure generated
erroneously low symmetry, ADDSYM was also performed on a
partial structural model including only the atomic positions of the
Ag and P atoms, yielding the same results. Application of Patterson
methods in the space group P21 initially located the positions of
two Ag atoms and the two P atoms of the PF6- anions. Subsequent
difference Fourier syntheses revealed the rest of the non-hydrogen
The asymmetric unit of 5b contains one Ag ion, half a ligand
situated about an inversion center, one nitrate counterion, and two
acetonitrile molecules of crystallization. All atoms reside on
positions of general crystallographic symmetry. Non-hydrogen
atoms were refined with anisotropic displacement parameters.
Hydrogen atoms were idealized and included as riding atoms.
Compound 6 crystallizes in the triclinic system. The space group
P1h was assumed and confirmed by successful solution and
(35) SMART Version 5.625, SAINT+ Version 6.22 and SADABS Version
2.05; Bruker Analytical X-ray Systems, Inc.: Madison, WI, 2001.
(36) Sheldrick, G. M. SHELXTL Version 6.1; Bruker Analytical X-ray
Systems, Inc.: Madison, WI, 2000.
(37) PLATON: (a) Spek, A. L. Acta Crystallogr., Sect. A 1990, 46, C34.
(b) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool;
Utrecht University: Utrecht, The Netherlands, 2002.
Inorganic Chemistry, Vol. 43, No. 2, 2004 553

Reger et al.
Table 1. Selected Crystal and Structure Refinement Data
1a
2a
3a
2b
3b
4b
5‚4 CH3CN
6
7
formula
C
32H30Ag2-
C36H42Ag2-
C30H30Ag-
F6N12O2P
C35.50H39.25
-
C35.50H39.25
-
C36H43Ag2-
B2F8N13O3
C38H42Ag2- C35.50H39.25
-
C34.50H39Ag-
F6N12O8S2
F12N12O4Sb2
Ag2F12N14.25
-
Ag2F12N14.25
-
N18O8
Ag2F12N14.25- F6N12O3.50Sb
O2.25Sb2
O2.25P2
O2.25P0.78
Sb1.22
-
fw, g mol-1 1104.54
cryst syst trigonal
space group R3h
a, Å
b, Å
c, Å
1394.06
trigonal
R3h
31.3014(18)
31.3014(18)
12.7921(11)
90
90
120
9
843.50
monoclinic
P21
15.3714(14) 10.4341(6)
13.5220(12) 15.4008(9)
18.0243(16) 15.8447(9)
1388.80
triclinic
P1h
1207.24
triclinic
P1h
10.3981(8)
15.1727(11)
15.9055(12)
79.326(2)
77.1400(10)
78.0300(10)
2
1095.19
1094.64
1317.99
1021.40
monoclinic
P21/c
14.8013(12)
30.058(2)
8.7987(7)
90
92.368(2)
90
4
orthorhombic monoclinic triclinic
P212121
10.2820(7)
20.2872(14)
20.5518(14)
90
90
90
4
P21/c
P1h
29.9011(10)
29.9011(10)
11.7415(6)
90
90
120
9
0.0372
0.0678
12.131(2)
19.079(4)
10.4348(11)
10.4348(11)
9.6355(19) 15.8339(16)
R, deg
â, deg
γ, deg
Z
90
77.7240(10)
77.4120(10)
78.3260(10)
2
0.0339
0.0771
90
90.000(4)
90
78.255(2)
77.464(2)
78.424(2)
2
114.519(2)
90
4
0.0694
0.1751
2
R1a
0.0591
0.1794
0.0452
0.1146
0.0388
0.0913
0.0624
0.1452
0.0389
0.0943
0.0650
0.1860
wR2b
2
2
2
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) {∑[w(Fo2 - Fc )2]/∑[w(Fo )2]}1/2 for I > 2σ(I). w ) 1/[σ2(Fo ) + (aP)2 + bP], where P is [2Fc2 + max(Fo , 0)]/3.
refinement of the structure. The asymmetric unit contains two
crystallographically inequivalent Ag atoms. Two ligands are situated
about crystallographic inversion centers; therefore, only half of each
ligand is present in the asymmetric unit. Two independent (P,Sb)F6-
anion positions were located; however, the PF6- and SbF6- anions
were found to be mixed together on both sites, in the refined
proportions P1/Sb1 ) 0.314(1)/0.686(1) and P2/Sb2 ) 0.467(1)/
0.543(1). Refinement of either site as fully P or fully Sb resulted
in unreasonably small (P) or large (Sb) displacement parameters
as well as higher R-values. The fluorine atoms in both anion sites
are reasonably ordered, and therefore, the P(Sb)-F bond lengths
represent a weighted average of the P-F and Sb-F contributions.
The slightly inflated displacement parameters for these fluorine
atoms may reflect the presence of two closely separated F6
octahedra, or simply the rotational disorder commonly encountered
in spherical anions of this type. A region of disordered solvent is
general crystallographic symmetry. The asymmetric unit contains
one Ag atom, one ligand, one SbF6 counterion, a fully ordered
-
acetone molecule of crystallization, and half of another acetone
disordered about an inversion center. Non-hydrogen atoms were
refined with anisotropic displacement parameters; hydrogen atoms
were idealized and included as riding atoms. At convergence, two
relatively large electron density peaks (ca. 4.0 and 3.6 e Å-3) located
ca. 1 Å from the Sb atom are present. The origin of these peaks is
unknown.
The metric parameters of noncovalent interactions (π-π stacking,
C-H‚‚‚π interactions, and weak hydrogen bonding) were calculated
by PLATON.37 Crystal and refinement data are provided in Table
1 and also in Supporting Information.
Acknowledgment. The authors thank the National Sci-
ence Foundation (CHE-0110493) for support. We thank Drs.
Sherine O. Obare and Latha A. Gearheart for assistance in
physical measurements.
1
also present in the crystal, which was modeled as /4Et2O and
1/4CH3CN, both disordered about an inversion center. Eventually,
all non-H and nonsolvent atoms were refined with anisotropic
displacement parameters; the solvent molecules were refined
isotropically. A total of 7 geometric restraints were used in modeling
the solvent disorder (SHELX SAME and DFIX). Hydrogen atoms
were idealized and included as riding atoms.
Supporting Information Available: X-ray crystallographic files
in CIF format, selected bond lengths and angles, and crystal and
refinement data for 1-7. This material is available free of charge
via the Internet at http://pubs.acs.org.
Systematic absences in the intensity data of 7 uniquely deter-
mined the space group P21/c. All atoms reside on positions of
IC035207I
554 Inorganic Chemistry, Vol. 43, No. 2, 2004