Manipulating self-assembly in silver(I) complexes of 1,3-Di-N- pyrazolylorganyls

Article abstract of DOI:10.1021/ic900982m

A series of ligands with two pyrazolyls (pz) linked by either a propyl (pz₂prop), a benzyl (pz₂Bn or pzBnpz*, where Bn = benzyl and pz* = 3,5-dimethylpyrazolyl), or a 1,8-naphthyl (pz ₂naphth) spacer and their silver(l) te

Full text of DOI:10.1021/ic900982m

8404 Inorg. Chem. 2009, 48, 8404–8414
DOI: 10.1021/ic900982m
Manipulating Self-Assembly in Silver(I) Complexes of 1,3-Di-N-pyrazolylorganyls
Brendan J. Liddle,† Daniel Hall,† Sergey V. Lindeman,† Mark D. Smith,‡ and James R. Gardinier*,†
†Department of Chemistry, Marquette University, Milwaukee, Wisconsin 53201-1881, and ‡Department of
Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208
Received May 19, 2009
A series of ligands with two pyrazolyls (pz) linked by either a propyl (pz2prop), a benzyl (pz2Bn or pzBnpz*, where Bn =
benzyl and pz* = 3,5-dimethylpyrazolyl), or a 1,8-naphthyl (pz2naphth) spacer and their silver(I) tetrafluoroborate
complexes have been prepared with the intent of evaluating how the conformational flexibility of the ligands would
affect the supramolecular assembly of the 1:1 [Ag(ligand)](BF4) complexes and their capacity for promoting short
Ag Ag interactions. The noncoordinating nature of the tetrafluoroborate anion ensured low coordination numbers to
3 3 3
the silver(I) centers, thereby allowing the metal ion to participate in multiple noncovalent interactions that dictate the
ligand conformations and supramolecular isomerism observed in the solid state. In the solid state, the complex
[Ag(CH3CN)(pz2prop)](BF4) forms a cyclic bimetallic cation that assembles into one-dimensional chains as a result of
Ag-π and CH F noncovalent interactions, in a manner distinct from the known nitrate derivative. With
3 3 3
[Ag(pz2Bn)](BF4), either cyclic bimetallic cations or coordination polymers can be formed depending on the solvents
used for crystallization, where acetone promotes the formation of the former while acetonitrile gives the latter. The
complex [Ag(pzBnpz*)](BF4) forms two different one-dimensional coordination polymers in the same flask during
crystallization from acetone/Et2O, where the presence or absence of the included solvent dictates the differences in the
secondary coordination sphere of (and noncovalent interactions involving) silver(I). In all the above cases, neighboring
silver atoms are separated beyond van der Waals contact. In contrast, the complex [Ag(pz2naphth)](BF4) 2CH3CN
forms discrete cyclic bimetallic cations where the rigid ligand enforces a short (3.19 A) Ag Ag contact. All
3
3 3 3
complexes are extensively dissociated in a CH3CN solution, as indicated from a combination of 1H NMR and positive-
ion electrospray ionization mass spectral data.
Introduction
Simple, multinucleating ligand scaffolds with the capacity for
enforcing discrete metal-metal interactions and extending
these (or other) interactions over multiple metal centers via
noncovalent self-assembly are enticing candidates for this
prospect. For a given multinucleating ligand, the various
structural factors influencing the controlled molecular and
supramolecular organization of metal complexes can be most
conveniently studied by an initial examination of their silver(I)
coordination chemistry.3 Appropriately designed silver(I) com-
plexes are known to participate in either intra- or intermolecular
closed-shell d10-d10 metallophilic interactions.4 Moreover, the
possibility of exploiting well-documented Agþ-π interactions5
Self-assembling “wirelike” systems are desirable to circum-
vent the highly (sometimes prohibitively) demanding synthetic
efforts required to traverse various size regimes (from the
molecular scale to the nanoscale and beyond) warranted in
emerging technological applications such as those found in the
areas of molecular electronics1 or even solar energy conversion.2
*To whom correspondence should be addressed. E-mail: james.gardinier@
marquette.edu.
(1) In Molecular Electronics; Jortner, J., Ratner, M., Eds.; Blackwell Science,
Ltd.: Malden, MA, 1997.
(2) For example, see: (a) Fukuzumi, S.; Honda, T.; Ohkubu, K.; Kojima,
T. Dalton Trans. 2009, 3880. (b) Rybtchinski, B.; Sinks, L. E.; Wasielewski, M.
R. J. Am. Chem. Soc. 2004, 126, 12268.
(4) (a) Pyykko, P. Chem. Rev. 1997, 97, 597. (b) For other leading references,
see: Rasika Dias, H. V.; 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.
(3) (a) See the special issue on silver(I) coordination polymers: Aust. J.
Chem. 2006, 59, 1. (b) Khlobystov, A. N.; Blake, A. J.; Champness, N. R.;
::
Lemenovskii, D. A.; Majouga, A. G.; Zyk, N. V.; Schroder, M. Coord. Chem.
Rev. 2001, 222, 155. (c) Kalf, I.; Braun, M.; Wang, Y.; Englert, U. CrystEng-
Comm 2006, 8, 916. (d) Feazell, R. P.; Carson, C. E.; Klausmeyer, K. K. Inorg.
Chem. 2006, 45, 935. (e) Oh, M.; Stern, C. L.; Mirkin, C. A. Inorg. Chem. 2005,
44, 2647. (f) Mann, K. L. V.; Jeffery, J. C.; McCleverty, J. A.; Ward, M. D. J.
Chem. Soc., Dalton Trans. 1998, 3029. (g) Schultheiss, N.; Powell, D. R.; Bosch,
E. Inorg. Chem. 2003, 42, 8886 and references cited therein. (h) Beloso, I.;
(5) (a) Ma, N. L. Chem. Phys. Lett. 1998, 297, 230. (b) Klippenstein, S. I.;
Dunbar, R. C. J. Phys. Chem. A 1997, 101, 3338. (c) Munakata, M.; Wu, L. P.;
Ning, G. L.; Kuroda-Sowa, T.; Maekawa, M.; Suenaga, Y.; Maeno, N. J. Am.
Chem. Soc. 1999, 121, 4968. (d) Munakata, M.; Wu, L. P.; Sugimoto, K.; Kuroda-
Sowa, T.; Maekawa, M.; Suenaga, Y.; Maeno, N.; Fujita, M. Inorg. Chem. 1999,
38, 5674. (e) Lindeman, S. V.; Rathore, R.; Kochi, J. K. Inorg. Chem. 2000, 39,
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ꢀ
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Castro, J.; Garca-Vazquez, J. A.; Perez-Lourido, P.; Romero, J.; Sousa, A. Inorg.
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r
pubs.acs.org/IC
Published on Web 08/03/2009
2009 American Chemical Society

Article
Inorganic Chemistry, Vol. 48, No. 17, 2009 8405
Figure 2. Possible supramolecular isomers of 1:1 metal complexes of
bridging multinucleating ligands (ligands are in black and metals in gray).
Left: Cyclic structures. Right: Polymeric structures.
Figure 1. Expected geometries for metals (M) binding to tethered
monodentate heterocycles with unspecified Lewis donor atoms (black
spheres) containing one-atom (left), two-atom (center), and three-atom
spacers (right).
Chart 1. Dipyrazolylorganyl Ligands Investigated in This Study
to promote supramolecular assembly may provide an alter-
native means for mediating electronic communication within
assemblies in the absence of intermolecular metallophilic inter-
actions. Other advantages of exploring silver(I) systems include
the synthetic simplicity of complex preparation, the favorable
solubility of the complexes, the ease of obtaining high-quality
crystalline products, the accessibility of desirable linear or
T-shaped metal coordination geometries that permit the metal’s
involvement in noncovalent interactions, and, finally, their
potential utility as reagents for subsequent chemistry.
in solution and the solid state when anions are noncoordinat-
ing (BF4- and PF6-) but forming linear oligomers or polymers
with nitrate anions; no short Ag Ag contacts were found
As illustrated in Figure 1, dinucleating ligands constructed of
monodentate heterocycles connected by three-atom or longer
(but structurally flexible) spacers6 can adopt desirable geome-
3 3 3
owing to the high coordination number of silver.13 The silver
nitrate complex of the simpler 1,3-dipyrazolylpropane ligand
(pz2prop) did not exhibit short intramolecular Ag Ag
tries that support short “intramolecular” Ag Ag contacts
3 3 3
3 3 3
contacts.14 Instead, a remarkable structure with two supra-
molecular isomers was found in the same crystal lattice, having
both cyclic bimetallic [Ag(μ-κ1,κ1-pz2prop)(NO3)]2 units and
polymeric sheets comprised of one-dimensional chains of
[Ag(μ-κ1,κ1-pz2prop)]þ units connected in a second dimension
(i.e., with an Ag Ag separation less than twice the van der
3 3 3
Waals radius of silver, 3.44 A);7 however, ligand scaffolds with
one- or two-atom spacers do not possess the correct geometries
for short “intramolecular” metal-metal contacts. The strategy
of using heterocycles tethered to three-atom spacers to promote
intramolecular argentophilic contacts in silver(I) complexes
has been successfully demonstrated for a number of such
ligands like 1,3-di-4-pyridyltetramethyldisiloxane,8 bis(thio-
imidazolyl)methane,9 among others.10
by μ2-NO3 anions. One aspect of the current study is to
-
determine whether replacement of the nitrate in
“[Ag(pz2prop)](NO3)” with a noncoordination anion would
promote the exclusive formation of cyclic species as in the case
of 1,10,3,30-tetrapyrazolylpropanes above and, if so, whether
the ligand conformation and/or change in the silver coordina-
Of particular relevance to this study, several silver com-
plexes of ligands with pyrazolyls spaced three atoms apart
have been structurally characterized but argentophilic inter-
actions were found in only one of these cases.11 The 1:1 silver
nitrate complex of tetrakis(pyrazolylmethyl)ethane-1,2-dia-
mine (with two C-N-C spacers) adopted a cyclic bimetallic
geometry with a short Ag-Ag distance of 3.160 A,11 while
the closely related 1:1 silver(I) nitrate complex of tetrakis-
(pyrazolylmethyl)methane was found to exist as polymeric
tion sphere would permit short Ag Ag contacts.
3 3 3
In this study, the ligands in Chart 1 each possess
N-pyrazolyl heterocycles linked through three carbon atom
chain spacers with differing degrees of rotational freedom,
consisting of a propyl group (pz2prop), a benzyl group
(pz2Bn and pzBnpz*), or a naphthyl group (pz2naphth).
These ligands were chosen or designed in an effort to
ascertain the various factors (including the relative rigidity
of organyl backbones as well as the steric demand of
pyrazolyl substituents in the case of pz2Bn versus pzBnpz*)
that might promote or hinder the formation of argentophilic
contacts and/or, by subtle changes in ligand conformations,
that could influence the relative stabilities of possible supra-
molecular isomers such as those depicted in Figure 2.
Furthermore, in this current study, only those silver(I) com-
plexes of the noncoordinating tetrafluoroborate anion15 were
chains of cyclic bimetallic [Ag(μ2,κ2,κ1-L)]2 moieties con-
2þ
nected via bridging NO3- anions, without discrete Ag Ag
3 3 3
interactions.12 Similarly, with 1,10,3,30-tetrapyrazolylpro-
panes, each end of two bridging ligands binds silver in a
μ-κ2,κ2-coordination mode, forming cyclic bimetallic species
(6) For instance, 1,2-bis(imidazolylmethyl)benzene with a four-atom
spacer between imidazolyl rings was capable of adopting a desirable
geometry for rectangular bimetallic complexes that exhibit short intracatio-
nic Ag Ag contacts. See: (a) Zhou, T.; Zhang, X.; Chen, W.; Qiu, H J.
3 3 3
Organomet. Chem. 2008, 693, 205. (b) Also see: Hartshorn, C. M.; Steel. P. J.
Inorg. Chem. Commun. 2000, 3, 476.
(13) (a) Reger, D. L.; Gardinier, J. R.; Semeniuc, R. F.; Smith, M. D.
Dalton Trans. 2003, 1712. (b) Reger, D. L.; Gardinier, J. R.; Grattan, T. C.; Smith,
M. R.; Smith, M. D. New J. Chem. 2003, 27, 1670.
(7) Bondi, A. J. Phys. Chem. 1964, 68, 441.
(8) Jung, O.-S.; Kim, Y. J.; Lee, Y.-A.; Kang, S. W.; Choi, S. N. Cryst.
Growth Des. 2004, 4, 23.
(9) Silva, R. M.; Smith, M. D.; Gardinier, J. R. Inorg. Chem. 2006, 45,
2132.
(10) (a) Awaleh, M. O.; Badia, A.; Brisse, F. Cryst. Growth Des. 2005, 5,
1897. (b) Koizumi, T.; Tanaka, K. Inorg. Chim. Acta 2004, 357, 3666. (c) Chen,
C. Y.; Zeng, J. Y.; Lee, H. M. Inorg. Chim. Acta 2007, 360, 21.
(11) Clegg, W.; Cooper, P. J.; Lockhart, J. C.; Rushton, D. J. Acta
Crystallogr., Sect. C: Cryst. Struct. Commun. 1994, C50, 383.
(12) McMorran, D. A.; Pfadenhauer, S.; Steel, P. J. Inorg. Chem.
Commun. 2002, 5, 449.
(14) McMorran, D. A.; Pfadenhauer, S.; Steel, P. J. Aust. J. Chem. 2002,
55, 519.
-
(15) The influence of BF4 and other anions on assisting to organize
ꢀ
structures has been previously addressed. See: (a) Manzano, B. R.; Jalon, F.
ꢀ
A.; Soriano, M. L.; Carrion, M. C.; Carranza, M. P.; Mereiter, K.;
ꢀ ꢀ
Rodrıguez, A. M.; de la Hoz, A.; Sanchez-Migallon, A. Inorg. Chem.
´
2008, 47, 8957. (b) Wei, K.-J.; Ni, J.; Liu, Y.; Liu, Q.-L. Eur. J. Inorg. Chem.
2007, 3868. (c) Withersby, M. A.; Blake, A. J.; Champness, N. A.; Hubberstey, P.;
Li, W.-S.; Schroder, M. Angew. Chem., Int. Ed. 1997, 36, 2327.

8406 Inorganic Chemistry, Vol. 48, No. 17, 2009
Liddle et al.
Scheme 1. Syntheses of Dipyrazolylorganyls and Their Silver(I) Complexes
examined with the intention of maintaining consistency in the
role of the anion10c,15 in determining the supramolecular
organization of the structures (potentially limiting any orga-
nizing forces to weak Ag F or CH F noncovalent
interactions). A more thorough examination of the anion
dependence on the supramolecular organization of these and
related complexes will be the subject of a future publication
by our group.
halide group of the starting haloarene, as might be
expected. Similar to 1, the silver tetrafluoroborate com-
plexes of other dipyrazolylorganyls ([Ag(pz2Bn)](BF4)
(2a), [Ag(pzBnpz*)](BF4) (2b), and [Ag(pz2naphth)]-
(BF4) (3); Scheme 1) were prepared in good yield by
mixing equimolar amounts of the desired ligand and
AgBF4 in THF, which resulted in precipitation of the
desired 1:1 complexes. For 2a and 3, 0.5 equiv of THF is
retained even upon prolonged heating under vacuum, as
indicated from mass measurements and NMR spectral
data. Elemental analyses of dried single crystals also
indicate that the solvent is tightly retained in these com-
plexes (vide infra). The complexes are soluble in Lewis
base solvents more polar than THF [acetone, CH3CN, N,
N-dimethylformamide (DMF), and dimethyl sulfoxide
(DMSO)] and are insoluble in halo- and hydrocarbon
solvents. Given the known propensity for solvents to
effect changes in the supramolecular organization of
silver(I) complexes,3 we made every attempt to crystallize
samples from the same solvent system (CH3CN/Et2O or
acetone/Et2O); however, X-ray diffraction quality crys-
tals could not be obtained for the complete series using
any one solvent system (vide infra).
3 3 3
3 3 3
Results
Syntheses. As mentioned in the Introduction, the li-
gand pz2prop and its silver nitrate complex have been
prepared previously.14 In this contribution, we prepared
[Ag(pz2prop)](BF4) (1) in a manner similar to that of the
nitrate complex by mixing solutions of the ligand and
silver salt but using tetrahydrofuran (THF) as a solvent to
afford a precipitate of 1 as a colorless powder. The
synthetic methodology to the various new ligands and
silver(I) complexes in this study is found in Scheme 1. The
key step in the syntheses of benzyl or naphthyl derivatives
was a copper-catalyzed amination reaction between the
appropriate aryl halides and pyrazole in the presence of a
::
Bronsted base by adopting modifications16 of the reac-
tion conditions first outlined by Taillefer et al.17 and
Buchwald et al.18 The potency of this approach is high-
lighted by the mild conditions in which the products are
formed and by the isolation of the relatively sterically
encumbered pz2naphth. It is noted that, regardless of the
reaction conditions (base, copper catalyst, chelating li-
gand cocatalyst, and solvent), the reaction times in-
creased and yields of the product decreased with
increasing steric bulk of the substituents proximal to the
Solid-State Structures. To facilitate the discussion of
the structural details of the complexes, it will be useful to
define two torsion angles, τN4 and τNC (Figure 3), that are
independent of the three-atom spacer connecting the two
pyrazolyls and that help to describe the conformation of
the ligands.
2
1
1
2
0
0
The first torsion angle, τN4 (N N -N N , pink lines
in Figure 3), describes the relative orientation of the
metal-binding nitrogen atoms and provides an alterna-
tive, more quantitative description of cases where these
nitrogen atoms reside on the same (syn) or opposite (anti)
faces of a given ligand. The second torsion angle, τNC
(16) Liddle, B. J.; Silva, R. M.; Morin, T. J.; Macedo, F. P.; Shukla, R.;
Lindeman, S. V.; Gardinier, J. R. J. Org. Chem. 2007, 72, 5637.
(17) (a) Taillefer, M.; Xia, N.; Ouali, A. Angew. Chem., Int. Ed. 2007, 46,
934. (b) Cristau, H.-J.; Cellier, P. P.; Spindler, J.-F.; Taillefer, M. Eur. J. Org.
Chem. 2004, 695. (c) Christau, H.-J.; Cellier, P. P.; Spindler, J.-F.; Taillefer, M.
Chem.;Eur. J. 2004, 10, 5607.
1
1
3
1
0
(N C -C N , green lines in Figure 3), enumerates
whether the 1- and 3- carbons of the three-atom spacer
are in pseudo eclipsed, staggered, or gauche conformations
(whether these atoms are actually sp3-hybridized or are
hypothetically modeled as such). An ideal conformation
(18) Antilla, J. C.; Baskin, J. M.; Barder, T. E.; Buchwald, S. L. J. Org.
Chem. 2004, 69, 5578.

Article
Inorganic Chemistry, Vol. 48, No. 17, 2009 8407
2
1
1
2
1
1
3
1
0
0
0
Figure 3. Two spacer-independent torsion angles, τN4 (N N -N N , pink) and τNC (N C -C N , green), for describing the relative conformations of
pyrazolyls using pz2Bn with coplanar pyrazolyls as an example (two views of the molecule are given for each conformation): (a) eclipsed, syn-τN4 = τNC
0ꢀ; (b) eclipsed, anti-τN4 = 125ꢀ, τNC = 0ꢀ; (c) staggered, anti-τN4 = 180ꢀ, τNC = 60ꢀ. See the text for comments on the carbon hybridization.
=
for promoting Ag Ag interactions would be eclipsed,syn
(τN4 = τNC = 0ꢀ) and with coplanar stacking of the
3 3 3
pyrazolyl rings. Such a geometry could allow Ag Ag
separations as short as 2.55 A based on the C-C separation
of the respective organic linker.
3 3 3
The solid-state structures of pz2naphth (see the Sup-
porting Information for full details) as well as solvated
and/or nonsolvated forms of the various silver(I) com-
plexes (1 CH3CN, 2a 0.5acetone, 2b, 2b acetone, and
3
3
3
3 2CH3CN) were characterized by single-crystal X-ray
3
diffraction. A summary of the data collection and struc-
ture refinements as well as additional details regarding the
structure solutions is provided in the Supporting Infor-
mation. The structures and atom labeling of cyclic dica-
tions in 1 CH3CN, 2a 0.5acetone, and 3 2CH3CN or the
3
3
3
monomeric units of coordination polymers 2a, 2b, and
2b acetone are depicted in Figure 4, while a summary of
3
the pertinent structural features of these and related
complexes is provided in Table 1.
The structure of 1 CH3CN (Figure 4A) is remarkably
3
different from its previously reported nitrate counter-
part “[Ag(pz2prop)](NO3)”14 (both being obtained by
vapor diffusion of Et2O into a CH3CN solution of the
complex), underscoring the influence of the anion on the
molecular and supramolecular architecture of silver(I)
complexes.10c,15 The new derivative 1 CH3CN consists of
3
discrete cyclic bimetallic {[Ag(CH3CN)]2(μ-pz2prop)2}2þ
dications centralized on inversion centers where two
pz2prop ligands bridge two silver(I) centers to form a
16-membered ring system. The primary coordination
geometry about silver is distorted T-shaped with a planar
(sum of angles about silver = 360ꢀ) AgN3 kernel derived
from two shorter Ag-N(pz) bonds (2.181 and 2.207 A,
with average 2.194 A) and one longer Ag-N(CH3CN)
bond (2.393 A). The ligands adopt a gauche,syn confor-
Figure 4. ORTEP diagrams (thermal ellipsoids drawn at the 50%
probability level) and atom labeling of cyclic disilver dications or mono-
meric cation units of silver coordination polymers. (A) 1 CH3CN; (B) 2a;
3
(C) 2a 0.5acetone; (D) 2b; (E) 2b acetone; (F) 3 2CH3CN.
3
3
3
addition to the planar AgN3 kernel described above, there
are two close contacts that occur between silver and
atoms of the nearby pyrazolyl groups, specifically be-
tween Ag N21 (3.237 A) and Ag C22 (2.938 A),
3 3 3
3 3 3
mation with two torsion angles, τN4 = 19.1ꢀ and τNC
=
which are nearly collinear (N21-Ag-C22 = 171ꢀ) and
are orthogonal to the AgN3 plane (red and pink dashed
lines in Figure 5B-D). These contact distances are longer
17.9ꢀ, with slipped cofacial arrangement of the pyrazolyls
[centroid (N11)-centroid (N12) distance of 3.505 A with
dihedral, slip, and tilt angles: R = 17.1ꢀ, β = 13.8ꢀ, and
than those typically found in more familiar Agþ
π
3 3 3
complexes of aromatic hydrocarbons (2.4-2.9 A),5 but
γ = 24.6ꢀ]. As such, the Ag Ag distance of 3.682 A
3 3 3
within the dication is longer than twice the van der Waals
radius (3.44 A) of silver, precluding metallophilic inter-
actions.
each is less than the sum of the van der Waals radii of the
respective elements ( vdw(Ag,N) =3.27A; vdw(Ag,C) =
P
P
3.42 A). Given the paucity of known Ag π complexes
3 3 3
of N-heterocycles,19 it remains unclear whether these long
A closer inspection of the structure reveals a number of
noncovalent interactions that support the geometry of the
dication and the overall layered supramolecular struc-
ture. A view of the extended coordination sphere around
contacts are due to very weak Ag π interactions or are
3 3 3
(19) Reger, D. L.; Semeniuc, R. F.; Radu, F.; Smith, M. D. Inorg. Chem.
2005, 44, 2995.
silver in 1 CH3CN is given in the top of Figure 5. In
3

8408 Inorganic Chemistry, Vol. 48, No. 17, 2009
Liddle et al.
Table 1. Summary of the Structural Features of Silver(I) Complexes
compound
CNa Ag-Navg (A) N-Ag-N (deg) Ag-Agb (A) τN4c (deg) τNCc (deg) conformation
form
[Ag(pz2prop)](NO3)14
3
4
3
2
2
2
2
2
2
2
3
3
2.171
2.276
2.194
2.134
2.125
2.098
2.119
2.110
2.125
2.133
2.175
2.213
161.8
111.4
152.5
169.9
176.8
174.0
177.1
174.3
166.3
168.7
152.4
147.6
5.334
5.502
3.682
5.434
3.767
75.0
11.1
19.1
59.1
20.3
51.7
20.8
51.3
173.1
165.5
4.1
133.9
123.8
17.9
60.2
145.4
53.4
145.5
52.7
52.9
50.6
0.1
gauche,syn
cyclic
staggered,anti polymer
gauche,syn cyclic
staggered,anti polymer
[Ag(pz2prop)](BF4)
[Ag(pz2Bn)](BF4)
[Ag(pz2Bn)](BF4) 0.5 acetoned
gauche,syn
cyclic
3
staggered,syn
gauche,syn
staggered,syn
staggered,anti 31 polymer
staggered,anti polymer
3.775
cyclic
[Ag(pzBnpz*)](BF4)
[Ag(pzBnpz*)](BF4) acetone
[Ag(pz2naphth)](BF4)
6.167
6.695
3.187
3
eclipsed,syn
eclipsed,syn
cyclic
2.6
5.8
a Primary coordination no. about Ag. b Closest Ag Ag distance. c See Figure 3 for the definition. d Two independent dications in the asymmetric
3 3 3
unit.
Figure 5. Supramolecular structure of 1 CH3CN. (A) Extended coordination sphere around Ag1. (B) View of the polymeric chain along the b axis,
3
supported by CH F (green dashed lines) and Ag π (red and pink dashed lines) noncovalent interactions. (C) View of the chain down the b axis. (D)
3 3 3
3 3 3
View down the b axis of a sheet in the ab plane.
simply a consequence of the numerous CH F interac-
The longer interdicationic Ag C contacts also support
the chain. The bifurcated CH F interactions involving
3 3 3
3 3 3
3 3 3
tions20 that both bolster the “intradicationic” geometry
and dictate the overall supramolecular structure. The
various weak CH F interactions involving the dication
F3 (with a pyrazolyl hydrogen, H13, of one chain and an
acetonitrile hydrogen, H2S2, of an adjacent chain) and F4
(with propyl hydrogens of adjacent chains, H1A and
H2B) serve to link the chains into sheets in the ab plane.
Although not shown, the sheets are stacked along the c
direction, with the closest contacts occurring between F3
and an acetonitrile hydrogen of a neighboring sheet,
H2S3 (C2s-H2S3 = 0.979 A, H2S3-F3 = 2.595 A,
and C2s-H2S3-F3 = 129.4ꢀ).
Two different supramolecular isomers of 2a can be
obtained by altering the solvents for crystallization.
Vapor diffusion of Et2O into an acetonitrile solution
of the complex affords a solvent-free coordination poly-
mer (Figures 4B and 6), 2a, whereas substitution of
3 3 3
hydrogen donors and the tetrafluoroborate acceptor of
1 CH3CN are summarized in Table 2. Of the fluorine
3
groups, all except F2 are involved in bifurcated hydrogen-
bonding interactions. Briefly, F1 is involved in bifurcated
hydrogen-bonding interactions with H21 of a pyrazolyl
of one dication and with H3b of the propyl backbone of
an adjacent dication (green dashed lines in Figures 5C,D).
The inversion center in the middle of the dications gives
rise to a polymeric chain that propagates along the b axis.
(20) Grepioni, F.; Cojazzi, G.; Draper, S. M.; Scully, N.; Braga, D.
Organometallics 1998, 17, 296.

Article
Inorganic Chemistry, Vol. 48, No. 17, 2009 8409
Table 2. Geometries of Various CH F Interactions in 1 CH3CN
3 3 3
3
donor (D)-H acceptor (A)
3 3 3
D-H (A)
H
A (A)
D
A (A)
D-H A (deg)
3 3 3
3 3 3
3 3 3
C1-H1a F4
0.99
0.99
0.98
0.95
0.99
0.95
2.54
3.406(3)
3.291(3)
3.209(3)
3.179(2)
3.374(2)
3.184(2)
146
135
139
165
157
133
3 3 3
C2-H2b F4
2.51
2.40
2.25
2.44
2.46
3 3 3
C2s-H2s2 F3
3 3 3
C13-H13 F3
3 3 3
C3-H3b F1
3 3 3
C21-H21 F1
3 3 3
dication are skewed with respect to each other such that
the two bound silver centers are well-separated
(Ag1 Ag2 of 3.767 A and Ag3 Ag4 of 3.775 A)
3 3 3
3 3 3
excluding any Ag-Ag interactions. In both 2a and
2a 0.5acetone, the ligand conformations are secured by
3
multiple noncovalent interactions that also organize the
overall supramolecular structures (see the Supporting
Information for complete details).
When the analytically pure sample of 2b was subject to
vapor diffusion of Et2O into an acetone solution of the
complex, two types of crystals formed in the same vial, the
majority being small bar-shaped crystals of solvent-free
2b (Figure 4D) and a few larger colorless blocks of an
Figure 6. Two views of the coordination polymer chain of 2a. Left:
Chain propagating along the b axis. Right: View of the chain down the b
axis.
acetone solvate 2b acetone (Figure 4E), where both were
coordination polymers. As indicated in Table 1, the silver
centers in each 2b and 2b acetone are nominally
3
acetonitrile for acetone affords a cyclic bimetallic species
(Figure 4C), 2a 0.5 acetone, which crystallizes with 0.5
3
3
equiv of acetone included in the lattice (but not bound to
silver). In both cases, the primary coordination geometry
around silver is nearly linear, as indicated by the short
Ag-N bonds that average 2.134 A for 2a (with N-Ag-N
of 169.9ꢀ) and 2.113 A (average of two crystallographi-
two-coordinate with short Ag-N distances and nearly
linear N-Ag-N bonds (Ag-Navg = 2.125 A, N-Ag-
N = 166.3ꢀ for 2b and Ag-Navg = 2.133 A, N-Ag-N =
168.7ꢀ for 2b acetone) where the metal centers connect
3
the arylpyrazolyl arm of one ligand to the benzylic
dimethylpyrazolyl arm of a neighboring ligand. As in-
dicated later, in 2b acetone, the acetone is very weakly
cally independent dications) for 2a 0.5 acetone (with an
3
average N-Ag-N of 175.6ꢀ). The ligand in solvent-free
2a adopts a staggered,anti conformation, indicated by the
two torsion angles τN4 = 59.1ꢀ and τNC = 60.2ꢀ, with
proximal pyrazolyl rings that deviate modestly from
coplanarity by a dihedral angle between the mean planes,
R, of 11.3ꢀ and that also have large slip angles β of 36.9ꢀ
and γ of 39.1ꢀ, giving a centroid-centroid distance of
3.88 A and an average perpendicular distance between the
mean planes of 3.00 A; these geometric features are
3
associated with silver and can only be considered as a
secondary interaction. As can be seen in Figure 8 and as
summarized in Table 1, there are relatively small but
significant differences in the staggered,anti ligand con-
formations in each 2b and 2b acetone (with τN4 = 173.1ꢀ
3
and τNC = 52.9ꢀ for the former and τN4 = 165.5ꢀ and
τNC = 50.6ꢀ for the latter) that arise, in part, by differ-
ences in the secondary coordination sphere of silver and
the noncovalent interactions organizing the supramole-
cular structures.
outside the accepted values for a normal π π stacking
3 3 3
interaction.21 As such, the bridging ligands separate silver
centers beyond any reasonable metallophilic considera-
tions (5.43 A).
The extended structure of solvent-free 2b reveals a
helical coordination polymer formed as a result of the
divergent disposition of nitrogen donors on the pz and
pz* groups and the large dihedral angle between the mean
planes of the pz and pz* rings, R, of 30ꢀ. This large
dihedral angle combined with and two large slip angles
β of 36ꢀ and γ of 31ꢀ gives a centroid-centroid distance of
3.93 A, parameters that are outside the accepted ranges
for a π π-stacking interaction.21 The Ag Ag separa-
In each of the two nearly identical crystallographically
independent cyclic dications in 2a 0.5acetone (Table 1
3
and Figure 7), two ligands span silver centers in such a
manner that one silver (Ag2 or Ag4) connects the aryl
pyrazolyl of each ligand while the other silver (Ag1 or
Ag3) connects the benzylic pyrazolyl of each ligand. The
two ligands in each cyclic dication exhibit different con-
formations (Table 1). One ligand adopts a staggered,syn
conformation (average τN4 = 51.5ꢀ and τNC = 53.1ꢀ)
with offset and fairly coplanar pyrazolyls (R = 16ꢀ, β =
31ꢀ, and γ = 26ꢀ with an average centroid-centroid
distance of 3.54 A and with a perpendicular separation
of 3.16 A), whereas the second ligand adopts a gauche,syn
conformation (average τN4 = 20.5ꢀ and τNC = 145.5ꢀ)
that places pyrazolyl rings further apart and closer to
orthogonality (the angle between the mean pyrazolyl
planes is 128ꢀ in each dication). The two ligands in each
3 3 3
3 3 3
tion of 6.17 A in 2b is substantially longer than 5.43 A
found in 2a (mainly because of the discrepancy in τN4 in
each complex, as above). In the crystal structure of 2b, the
coordination polymer adopts a right-handed 31 helical
arrangement along the crystallographic c axis (Figure 9a).
It is likely that the bulk crystalline sample contains equal
quantities of crystals from each of the enantiomorphous
space groups P31 and P32 and that it was fortuitous that
the crystal selected was from the former, composed of
right-handed helices, rather than the latter, presumably
composed of left-handed helices. In the right-handed
helix, the angle between three adjacent silvers, Ag-Ag-Ag,
(21) Janiak, C. J. Chem. Soc., Dalton Trans. 2000, 3885.

8410 Inorganic Chemistry, Vol. 48, No. 17, 2009
Liddle et al.
Figure 7. Overlay of two crystallographically independent cyclic dications in 2a 0.5acetone (left) with views of gauche,syn (center) and staggered,syn
3
(right) ligand conformations that occur within each cyclic dication.
interaction. Moreover, while the nitrogen donors of the
pz and pz* groups are divergent in each complex, the
angle between N-Ag bond vectors within the ligand is
more obtuse in 2b acetone (86ꢀ) than in 2b (70ꢀ). The
3
metrical parameters of the noncovalent interactions in
2b acetone are listed in Table 4. The coordination geo-
3
metry about silver including secondary interactions can
be described as square pyramidal with an AgN2OFC
kernel as a result of a presumably weak interaction
between silver and oxygen atoms of acetone (with a long
Figure 8. Overlay of cationic monomer units in 2b (black) and
2b acetone (green) with silver in cyan.
Ag O distance of 2.815 A; violet dashed lines in
3
3 3 3
Figure 10), κ1F coordination of tetrafluoroborate
(Ag F1 = 2.993 A; cyan dashed lines in Figure 10),
is 147ꢀ, and by the plotting of centroids between three
neighboring silver centers, which represent the loci of the
helix, the pitch and rise were found to be 17.47 and 5.825
A, respectively. Examination of the supramolecular
3 3 3
and a weak Ag π interaction with the carbon meta to
the aryl-bound pyrazolyl and ortho to the benzylic pyr-
3 3 3
azolyl (Ag C5 = 3.00 A; red dashed lines in Figure 10).
Two types of noncovalent interactions secure the one-
3 3 3
structural features shows that the extended coordination
sphere [ vdw(Ag,X) = 0.2 A] of silver is distorted
P
dimensional chain. First, a CH π interaction24 (solid
3 3 3
octahedral as a result of Ag π and Ag F interactions
3 3 3
3 3 3
pink lines in Figure 10) occurs between a methyl hydrogen
donor of the coordinated acetone and the pyrazolyl
acceptor of a neighboring ligand. Second, the tetrafluor-
oborate anion, which is anchored to silver, also partici-
(Figure 9c,d and Table 3). Specifically, silver is sand-
wiched between aryl rings with Ag1-C6 = 2.90 A and
Ag-C1 = 3.05 A where the C1-Ag-C6 angle is 121ꢀ, at
the upper end of the range found for other Ag
π
3 3 3
pates in a bifurcated CH F interaction (green dashed
3 3 3
interactions. The tetrafluoroborate is anchored to silver
in an asymmetric κ2 mode with Ag-F1 = 2.77 A and
Ag-F2 = 2.99 A.22 As such, 3-fold symmetry of various
lines in Figure 10) involving F2 and a benzylic hydrogen
[C5-H5 F2 (2.45 A, 158ꢀ)] along with an aryl hydro-
3 3 3
gen ortho to the benzylic pyrazolyl [C7-H7A F2
3 3 3
CH F interactions (green lines in Figure 9) with the
3 3 3
(2.56 A, 159ꢀ)]. Two additional CH F interactions
involving F3 and F4 organize the chains into a three-
dimensional supramolecular structure.
Diffusion of a layer of Et2O into an acetonitrile solu-
3 3 3
metrical parameters given in Table 3 gives a close-packed
arrangement of helices, completing the three-dimensional
supramolecular structure.
The subtle differences in the ligand geometry imposed
by the secondary coordination sphere of silver differenti-
ate the 31 helical chains in nonsolvated 2b in Figure 9 from
tion of 3 0.5THF resulted in a species best described by
3
the
(CH3CN)2]}(BF4)2 CH3CN (Figure 4F), which, for sim-
formula
{[Ag(CH3CN)](μ-cis-pz2naphth)2[Ag-
3
that of the nonhelical polymeric structure of 2b acetone
in Figure 10. In 2b acetone, the individual “2b acetone”
3
plicity, will be referred to as 3 2CH3CN. The complex
3
3
3
contains a discrete cyclic bimetallic dication, where both
ligands adopt desirable eclipsed,syn conformations (one
with τN4 = 4.1ꢀ and τNC = 0.1ꢀ and one with τN4 = 2.6ꢀ
and τNC = 8.5ꢀ). The ligands sandwich two silver(I)
centers in such a manner as to give a pseudochair con-
formation to the 16-membered Ag2N8C6 ring, where the
naphthyl rings of the ligands are directed in opposite
directions away from the mean N4 plane formed by the
silver-bound nitrogen atoms of the pyrazolyl groups
(N11, N21, N31, and N41). Interestingly, the primary
coordination sphere around the silver atoms is nominally
three-coordinate (slightly distorted T-shaped) as a result
of coordinating two nearly linear N(pyrazolyl) donors
moieties of the chain are related via a c-glide operation, as
can be seen in Figure 10B,C; the repeat positions of the
acetone and tetrafluoroborate groups signify that the
chain does not propagate along a 21-screw axis (the latter
symmetry operation is coincident with the b axis in
Figure 10D). As indicated earlier, the ligand conforma-
tion in 2b acetone is similar to that in 2b, but in
3
2b acetone, the pz and pz* rings are closer together and
3
more coplanar relative to those in 2b. That is, the cen-
troid-centroid distance of 3.67 A, the dihedral angle
between the mean planes, R, of 21ꢀ, and the slip angles
β of 28ꢀ and γ of 26ꢀ are all smaller in magnitude in
2b acetone than in 2b (vide supra), yet these values are
3
still outside the accepted ranges for an effective π-π
(23) Hartshorn, C. M.; Steel, P. J. Aust. J. Chem. 1997, 50, 1195.
(24) Takahashi, H.; Tsuboyama, S.; Umezawa, Y.; Honda, K.; Nishio,
M. Tetrahedron 2000, 56, 6185.
(22) Beck, W.; Suenkel, K. Chem. Rev. 1988, 88, 1405.

Article
Inorganic Chemistry, Vol. 48, No. 17, 2009 8411
Figure 9. (A) Viewof2balong the aaxis ofthe 31 helical coordinationpolymerchain. (B) Viewofthe helical chainalongthec axis. (C)Viewofthe extended
coordinationspherearoundsilver in the helicalchain emphasizingAg F (cyan dashed lines), Ag π (reddashed lines), andCH F (greendashedlines)
interactions. (D) View down the c axis of four chains assembled by CH F interactions of tetrafluoroborate anions (orange tetrahedra).
3 3 3
3 3 3
3 3 3
3 3 3
Table 3. Geometries of Various Noncovalent Interactions in 2ba
B-F
Ag interactions
B-F (A)
F
Ag (A)
B-F Ag (deg)
3 3 3
3 3 3
3 3 3
B1-F1 Ag1
1.399
1.385
2.765(4)
2.985(3)
106
96
3 3 3
B1-F2 Ag1
3 3 3
Ag π (shortest contact, X)
Ag-X (A)
Ag-Ct (A)
^ Dist (A)
β (deg)
rs (A)
3 3 3
Ag1 C6
3 3 3
2.898(4)
3.048(5)
3.201
3.568
2.875
2.987
26
33
1.408
1.952
Ag1 C1
3 3 3
donor (D)-H acceptor (A)
D-H (A)
H
A (A)
D
A (A)
D-H A (deg)
3 3 3
3 3 3
3 3 3
3 3 3
C7-H7b F2
0.99
0.95
0.95
0.95
2.52
3.485(6)
3.214(7)
3.307(5)
3.485(7)
166
173
161
171
3 3 3
C5-H5 F3
2.27
2.40
2.54
3 3 3
C22-H22 F3
3 3 3
C13-H13 F4
3 3 3
a Ct(i) = centroid of the ring-containing atom i; β = angle between the Ct(i)-Ag vector and normal to the plane containing Ct(i); rs = ring slippage;
^ = projection of a heavy atom on the least-squares mean plane of the ring and centroid.
(Ag1-Navg = 2.175 A, N11-Ag1-N31 = 152.4ꢀ and
Ag2-Navg = 2.213 A, N21-Ag2-N41 = 147.6ꢀ) and
one acetonitrile (Ag1-N71 = 2.446 A and Ag2-N81 =
2.398 A) to give a sum of angles of about Ag1 = 353.4ꢀ
and about Ag2 = 353.0ꢀ. For Ag2, there is an additional
the sum of the van der Waals radii minus 0.2 A
and is intermediate between 2.78 A found in the silver complex
of 1,2,4,5-tetrakis(pyrazol-1-ylmethyl)benzene23 and 3.37 A
found in {[Ph2P(O)CH2C(pz)3Ag]2(THF)2}(BF4)2,19
where Ag-Ag interactions were proposed (supported
by semiempirical Fenske-Hall calculations, in the latter
case). It is noted that vacuum-dried single crystals lose
acetonitrile molecules of solvation and the sample ab-
sorbs atmospheric moisture because elemental analyses
are consistent with the formula 3 3H2O 0.5CH3CN.
rather long Ag N contact for a weakly bound acetoni-
3 3 3
trile (Ag1-N71 = 2.519 A), which is probably best
described as a secondary interaction given its length10b
and the apparent sensitivity of the Ag-N(pyrazolyl)
bond distances to the metal’s primary coordination geo-
metry (two-coordinate Ag-Navg. ∼ 2.10-2.14 A, three-
coordinate 2.2-2.3 A, and four-coordinate 2.3-2.4 A). It
should be noted that the fourth acetonitrile is not asso-
ciated with any silver centers and that the overall dication
geometry may be influenced, in part, by crystal packing
forces that afford the overall three-dimensional supra-
molecular structure (see the Supporting Information).
3
3
Solution Properties. The solution and solid-state struc-
tures of ionic silver(I) coordination compounds are gen-
erally thought to be quite different from one another,
given the labile nature of the d10 metal centers in Lewis
basic solvents (in which the complexes are soluble).
As such, solution spectroscopic data can be deceptively
simple (or ambiguous), requiring a combination of
techniques such as NMR and positive-ion electrospray
ionization mass spectrometry [ESI(þ)-MS] to glean any
useful information about possible solution structures.
Nonetheless, the two metal atoms in 3 2CH3CN
3
are constrained to an Ag1-Ag2 separation of 3.19 A,
the shortest such distance of all of the new compounds
reported here. This Ag-Ag distance is less than twice
1
For example, the H NMR spectra in CD3CN for each

8412 Inorganic Chemistry, Vol. 48, No. 17, 2009
Liddle et al.
Figure 10. Molecular and supramolecular structures of 2b acetone. (A) ORTEP diagram of the asymmetric unit (thermal ellipsoids drawn at 50%
3
probability). (B) View of the polymeric chain with an extended coordination environment around the silver. (C) View of the chain along the c axis. (D) View
of three-dimensional packing along the c axis.
Table 4. Geometries of Various Noncovalent Interactions in 2b acetone
3
B-F
Ag interaction
B-F (A)
F
Ag (A)
B-F Ag (deg)
3 3 3
3 3 3
3 3 3
B1-F1 Ag1
1.360
2.9965(17)
136
3 3 3
C-O
Ag interaction
C-O (A)
O
Ag (A)
C-O Ag (deg)
3 3 3
3 3 3
3 3 3
C31-O1 Ag1
1.216
2.8120(16)
133
3 3 3
Ag π (shortest contact, X)
Ag-X (A)
Ag-Ct (A)
^ Dist (A)
2.881
A (A)
β (deg)
rs (A)
3 3 3
Ag1 C5
3 3 3
2.9996(17)
3.410
32
1.824
donor (D)-H acceptor (A)
3 3 3
D-H (A)
H
A (A)
D
D-H A (deg)
γ (deg)
3 3 3
3 3 3
3 3 3
C32-H32A [Ct(N21)]
3 3 3
0.98
0.95
0.95
0.99
0.98
2.83
157
159
158
159
142
17
C4-H4 F3
2.51
2.45
2.56
2.39
3.410(3)
3.345(3)
3.501(3)
3.221(3)
3 3 3
C5-H5 F2
3 3 3
C7H7A F2
C32-H32C F4
3 3 3
3 3 3
Ct(i) = centroid of the ring-containing atom i; β = angle between the Ct(i)-Ag vector and normal to the plane containing Ct(i); γ = angle CH-Ct(i)
and normal to plane containing Ct(i); rs = ring slippage;^ = projection of a heavy atom on the least-squares mean plane of the ring and centroid.
silver(I) complex examined here showed only a downfield
shift in resonances relative to those obtained in spectra of
the free ligands. For complexes of pz2prop, pz2Bn, and
pzBnpz*, the methylene hydrogen atoms would be in-
equivalent if the solid-state structures and ligand confor-
mations were retained in solution. As such, additional
resonances characteristic of AB splitting patterns (in
pyrazolyls), dissociative processes, or both. It was not
possible to slow any potential dynamic process occurring
in CD3CN upon cooling to -35 ꢀC so as to be distin-
guished by NMR. Clearly, ESI(þ)-MS data (vide infra)
provide more insight into the structural nature in solution
in all of the above cases.
ESI-MS data are thought to accurately reflect the
solution structures of coordination complexes and coor-
dination polymers.25 The ESI(þ)-MS data obtained from
3
addition to other J couplings for the propyl derivative)
are expected. In these cases, such splitting patterns of
resonances were not observed, indicating a stereochemi-
cally nonrigid ligand environment due to either rapid
conformational averaging (where silver remains bound to
(25) (a) Miras, H. N.; Wilson, E. F.; Cronin, L. Chem. Commun. 2009,
1297. (b) Baytekin, B.; Baytekin, H. T.; Schalley, C. A. Org. Biomol. Chem.
2006, 4, 2825.

Article
Inorganic Chemistry, Vol. 48, No. 17, 2009 8413
Figure 11. Representative ESI(þ)-MS of 3 0.5THF in acetonitrile.
3
either crystals or the as-isolated powders of the silver
complexes dissolved in CH3CN were nearly identical,
with only the relative intensities of the peaks changing
(vide infra). Taken altogether, the ESI(þ)-MS data sug-
gest that all of the present complexes are predominantly
dissociated in solution. Peaks for solvated silver ions
[Ag(CH3CN)n]þ (n = 2-4) and protonated ligands
[HL]þ were present, those of dimeric bimetallic ions such
as [Ag2L2]2þ were only sometimes observed, but those for
higher oligomers [Ag2L3]þ, [Ag3L3]2þ, etc., were never
observed. It is noteworthy that the ESI(þ)-MS spectra of
silver(I) coordination polymers of more strongly donat-
ing multitopic ligands have shown peaks for higher-order
oligomeric species.9
originates from a common impurity in the MS experi-
ments rather than from the crystals that were examined.
All of these data are indicative of substantial dissocia-
tive processes occurring in solution and, perhaps,
also of the relative efficacy for self-assembly processes
to occur during the desolvation phase of the MS experi-
ment.
Summary. Four di-N-pyrazolylorganyl ligands, one
known and three new derivatives with pyrazolyls spaced
three atoms apart by carbon backbones with differing
degrees of conformational flexibility, have been prepared
in order to delineate the ligand design factors most likely
to afford metallophilic interactions in coordination com-
plexes. The copper-catalyzed amination reactions de-
scribed by Taillefer et al. and Buchwald et al. provide
an alternative, convenient means for obtaining N-pyra-
zolylaryls with respect to nucleophilic aromatic substitu-
tion reactions that have been traditionally used to access
such derivatives. Reactions of the various ligands with
AgBF4 afforded 1:1 complexes that contain low-coordi-
nate silver(I), a requisite feature that allows the metal
center to participate in a variety of noncovalent second-
In every case reported here, the major peaks in the
ESI(þ)-MS spectrum (see the data for 3 CH3CN in
3
Figure 11 as an example) correspond to [AgL2]þ,
[AgL(CH3CN)]þ, [AgL]þ, [Ag(CH3CN)2]þ (m/z = 189),
[HL]þ, [HL-pz (or pz* for 2b)]þ, and [Ag(CH3CN)]þ
(m/z = 148), a pattern consistent with that observed for
other silver(I) complexes of poly(pyrazolyl)organyls.26
Interestingly, for 1 or 2a, peaks for dimeric bimetallic
ions such as [Ag2L2]2þ or {[Ag2L2](BF4)}þ were absent
even though the solid-state structure contained such an
ion. Surprisingly, in the case of 2b, minor peaks (ca. 1%
intensity) for dimeric bimetallic ions {[Ag2L2](X)}þ (X =
BF4-, Cl-, and formate-; the latter two anions arise from
the nature of the MS experiments) were observed, even
though the solid-state structure showed a coordination
polymer. For 3, similar peaks for {[Ag2L2](X)}þ [X = Cl-
ary [Ag-π, Ag X (X = F, N, O), and d10-d10]
3 3 3
interactions. The results presented here along with ex-
tensive work on related systems by other groups13,19,26
show that Ag-N(pyrazolyl) bond distances are sensitive
to the primary coordination number of the metal with
Ag-Navg ∼ 2.10-2.14 A for two-coordinate silver, Ag-
Navg ∼ 2.2-2.3 A for three-coordinate silver, and Ag-
Navg ∼ 2.3-2.4 A for four-coordinate silver. The striking
difference in structures between the 1:1 silver/dipyrazo-
lylpropane complexes with the coordinating nitrate and
noncoordinating tetrafluoroborate anions is noteworthy.
With the nitrate, a complicated structure with two types
of silver centers is obtained. When silver is three-coordi-
nate, a cyclic bimetallic species is formed, whereas when
silver is four-coordinate, a polymeric sheet is formed. In
both cases, the secondary coordination sphere is
-
(m/z = 771), formate- (m/z = 781), and BF4 (m/z =
823)] ions were observed. In addition, there was an
unusual peak at m/z = 517, which appears to correspond
to the [NaAgL(CH3CN)(BF4)]þ ion, where the sodium
(26) (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. Eur. J. Inorg. Chem. 2002, 543. (c) Reger, D. L.; Semeniuc, R. F.;
Smith, M. D. Inorg. Chem. Commun. 2002, 5, 278. (d) Reger, D. L.; Gardinier, J.
R.; Smith, M. D. Inorg. Chem. 2004, 43, 3825.
dominated by Ag O-NO2 contacts, and the ligand
3 3 3

8414 Inorganic Chemistry, Vol. 48, No. 17, 2009
Liddle et al.
conformations (perhaps dictated by extensive CH
O
forms. Finally, the rigid 1,8-dipyrazolylnaphthalene ligand
(pz2naphth) was successfully used to enforce a short
intracationic Ag Ag contact (3.19 A) in a cyclic bime-
3 3 3
noncovalent interactions27) are such that neighboring
silver centers are greatly separated (Ag Ag > 5.3 A).
3 3 3
3 3 3
When the noncoordinating tetrafluoroborate is employed
instead of nitrate, a simple structure with three-coordi-
nate silver is obtained (with a coordinated acetonitrile
solvent) that contains a cyclic bimetallic species with
shorter intracationic Ag-Ag separation (3.7 A), but this
distance is still outside twice the sum of the van der Waals
radii of silver. In this latter case, the silver is involved in
intra- and intercationic Ag-π secondary interactions
that assemble cations into one-dimensional chains. The
ligand conformation and supramolecular structure are
tallic [Ag2(pz2naphth)2]2þ framework. This Ag Ag con-
3 3 3
tact distance is intermediate in length compared to other
related systems that were proposed to exhibit argentophilic
interactions. In all cases, the combined NMR and ESI(þ)-
MS data indicate that the solid-state structures are not
retained in a CH3CN solution because extensive dissocia-
tion likely occurs in this solvent.
Conclusions. While the short metal-metal contacts in
the [Ag2(pz2naphth)2]2þ framework did not bestow any
unusual photophysical properties to this complex in
either the solid state or solution, the structural result is
an important first step toward the longer term goal of
discovering the design features that would promote self-
assembled, extended metallophilic contacts. In this re-
gard, it can be conjectured that more strongly donating
ligands (such as negatively charged species) built upon the
1,8-naphthyl spacer (and perhaps even the other more
flexible spacers) would be better equipped to confer
greater solution stability to the self-assembled systems.
More importantly, more electron-rich or anionic systems
may also offset any electrostatic repulsion between prox-
imal silver(I) centers (allowing shorter contacts) and
could render a closer energy separation between the
metal’s filled 4d10 and virtual 5s orbitals that may bestow
interesting photophysical properties in the resulting com-
plexes. Synthetic efforts toward these goals are currently
underway in our laboratory.
bolstered by various CH F interactions involving the
3 3 3
ligands and the tetrafluoroborate anion. With the rela-
tively more rigid pz2Bn ligand, both cyclic bimetallic
dications (Ag Ag > 5.3 A) and one-dimensional co-
3 3 3
ordination polymers (Ag Ag > 5.3 A), each with two-
3 3 3
coordinate silver, are formed, depending on the solvent of
crystallization. With the relatively less polar and less
donating solvent, acetone, the former is obtained, but
with the more polar and more strongly donating solvent,
acetonitrile, the latter is obtained; in neither case is
solvent bound to the silver center in the solid state, but
acetone fills channels available by crystal packing of the
former. Interestingly, by replacement of the benzylic
pyrazolyl in pz2Bn with a dimethylpyrazolyl, a mixture
of two different coordination polymers, each with two-
coordinate silver and with Ag-Ag separations greater
than 6.1 A, is obtained under crystallization conditions: a
solvent-free 31-helical chain and an acetone solvate with a
nonhelical chain. In these two cases, differences in the
secondary coordination sphere (the former contains two
Acknowledgment. J.R.G. thanks Marquette University
and the Petroleum Research Fund for financial support.
Ag-π and two Ag F interactions, while the latter
3 3 3
has one Ag-π, one Ag F, and one Ag O interaction)
likely dictate the ligand conformations in each of the two
Supporting Information Available: Experimental procedures,
analytical and spectral characterization data, expanded discus-
sions of structural findings, and crystallographic data in CIF
format. This material is available free of charge via the Internet
at http://pubs.acs.org.
3 3 3
3 3 3
(27) (a) Taylor, R.; Kennard, O. J. Am. Chem. Soc. 1982, 104, 5063. (b)
Steiner, T.; Saenger, F. J. Am. Chem. Soc. 1992, 114, 10146.