Crystal retro-engineering: Structural impact on silver(I) complexes with changing complexity of tris(pyrazolyl)methane ligands

Article abstract of DOI:10.1021/ic0606936

The preparation and structures of seven new silver(I) complexes involving the parent tris(pyrazolyl)methane unit, [C(pz)₃], as the donor set, {[C₆H₅CH₂OCH₂C(pz) ₃]Ag}(BF₄), {[C₆H₅CH ₂OCH₂C(pz)₃]₂Ag₃}(CF ₃SO₃)₃, {[HOCH₂-C(pz) ₃]Ag}(BF₄), {[HOCH₂C(pz)₃]Ag} (CF₃SO₃), {[HC(pz)₃]₂Ag ₂(CH₃CN)}(BF₄)₂, {[HC(pz) ₃]Ag}(PF₆), and {[HC(pz)₃]Ag}(CF ₃SO₃), are reported. This project is based on a retro-design of our multitopic C₆H_6-n[CH ₂OCH₂C(pz)₃]_n (pz = pyrazolyl ring, n = 2, 3, 4, and 6) family of ligands in such a way that each new ligand has one fewer organizational feature. The κ²-κ¹ bonding mode of the [C(pz)₃] units to two silvers, also observed with the multitopic ligands, is the dominant structural feature in all cases. Changing the counterion has important effects on the local structures and on crystal packing. When these structures are compared to similar ones based on the multitopic C₆H_6-n[CH₂OCH₂C(pz) ₃]_n ligands, it has been shown that the presence of the rigid parts (central arene core and the [C(pz)₃] units) are important in order to observe highly organized supramolecular structures. The presence of the flexible ether linkage is also crucial, allowing all noncovalent forces to manifest themselves in a cumulative and complementary manner.

Full text of DOI:10.1021/ic0606936

Inorg. Chem. 2006, 45, 7758−7769
Crystal Retro-Engineering: Structural Impact on Silver(I) Complexes
with Changing Complexity of Tris(pyrazolyl)methane Ligands
Daniel L. Reger,* Radu F. Semeniuc, Christine A. Little, and Mark D. Smith
Department of Chemistry and Biochemistry, UniVersity of South Carolina,
Columbia, South Carolina 29208
Received April 24, 2006
The preparation and structures of seven new silver(I) complexes involving the parent tris(pyrazolyl)methane unit,
[C(pz)3], as the donor set, [C6H5CH2OCH2C(pz)3]Ag (BF4), [C6H5CH2OCH2C(pz)3]2Ag3 (CF3SO3)3, [HOCH2-
C(pz)3]Ag (BF4), [HOCH2C(pz)3]Ag (CF3SO3), [HC(pz)3]2Ag2(CH3CN) (BF4)2, [HC(pz)3]Ag (PF6), and
[HC(pz)3]Ag (CF3SO3), are reported. This project is based on a retro-design of our multitopic C6H6 n[CH2OCH2C(pz)3]n
{
}
{
}
{
}
{
}
{
}
{
}
{
}
-
(pz
) pyrazolyl ring, n ) 2, 3, 4, and 6) family of ligands in such a way that each new ligand has one fewer
organizational feature. The κ2−κ1 bonding mode of the [C(pz)3] units to two silvers, also observed with the multitopic
ligands, is the dominant structural feature in all cases. Changing the counterion has important effects on the local
structures and on crystal packing. When these structures are compared to similar ones based on the multitopic
C6H6 n[CH2OCH2C(pz)3]n ligands, it has been shown that the presence of the rigid parts (central arene core and
-
the [C(pz)3] units) are important in order to observe highly organized supramolecular structures. The presence of
the flexible ether linkage is also crucial, allowing all noncovalent forces to manifest themselves in a cumulative and
complementary manner.
Introduction
manifestation of all possible noncovalent forces that can
influence the self-assembly process.3
Two important directions have emerged within chemical
research around the world: (1) a quest for new materials
with promising and useful properties by applying the
principles of supramolecular chemistry and (2) a continuous,
systematic characterization of the self-assembly processes
from a theoretical point of view. While promising results
were achieved and startling applications are being developed,
much work and effort is still needed in order to lay a
foundation for a “grand unified supramolecular theory”.1
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 while imposing subtle alterations in the
environment such as changing the anions and the crystal-
lization solvent.2 Extensive research has been done in this
area using mostly rigid ligands because they allow a good
prediction of the overall structure, shape, and porosity of
the resulting array. The use of rigid ligands is, to some extent,
restricting because they limit the structures of possible
products and also have to be perfectly tailored to support
certain structures. Further, their inherent rigidity hampers the
Another class of ligands that have been used is the so-
called “semi-flexible ligands”, where various donor sets are
connected through semi-flexible linkers.4 The control of their
organization is achieved by incorporating within the struc-
tures of the building blocks specific recognition sites that
will drive the self-assembling process toward the desired
(1) (a) DeIonno, E.; Tseng, H.-R.; Harvey, D. D.; Stoddart, J. F.; Heath,
J. R. J. Phys. Chem. B 2006, 110, 7609. (b) Moonen, N. N. P.; Flood,
A. H.; Fernandez, J. M.; Stoddart, J. F. Top. Curr. Chem. 2005, 262,
99. (c) Collin, J.-P.; Heitz, V.; Sauvage, J.-P. Top. Curr. Chem. 2005,
262, 29. (d) Balzani, V.; Credi, A.; Ferrer, B.; Silvi, S.; Venturi, M.
Top. Curr. Chem. 2005, 262, 1. (e) Balzani, V.; Clemente-Leon, M.;
Credi, A.; Ferrer, B.; Venturi, M.; Flood, A. H.; Stoddart, J. F. Proc.
Nat. Acad. Sci. 2006, 103, 1178. (f) Saha, S.; Johansson, E.; Flood,
A. H.; Tseng, H.-R.; Zink, J. I.; Stoddart, J. F. Chem. Eur. J. 2005,
11, 6846. (g) Liu, Y.; Flood, A. H.; Bonvallet, P. A.; Vignon, S. A.;
Northrop, B. H.; Tseng, H.-R.; Jeppesen, J. O.; Huang, T. J.; Brough,
B.; Baller, M.; Magonov, S.; Solares, S. D.; Goddard, W. A.; Ho,
C.-M.; Stoddart, J. F. J. Am. Chem. Soc. 2005, 127, 9745. (h) Badjic,
J. D.; Balzani, V.; Credi, A.; Silvi, S.; Stoddart, J. F. Science 2004,
303, 1845. (i) Hernandez, R.; Tseng, H.-R.; Wong, J. W.; Stoddart, J.
F.; Zink, J. I. J. Am. Chem. Soc. 2004, 126, 3370. (j) Kay, E. R.;
Leigh, D. A. Top. Curr. Chem. 2005, 262, 133. (k) Tian, H.; Wang,
Q.-C. Chem. Soc. ReV. 2006, 35, 361. (l) Yoshizawa, M.; Miyagi, S.;
Kawano, M.; Ishiguro, K.; Fujita, M. J. Am. Chem. Soc. 2004, 126,
9172. (m) Yoshizawa, M.; Takeyama, Y.; Kusukawa, T.; Fujita, M.
Angew. Chem., Int. Ed. 2002, 41, 1347. (n) Fiedler, D.; Bergman, R.
G.; Raymond, K. N. Angew. Chem., Int. Ed. 2004, 43, 6748.
* To whom correspondence should be addressed. E-mail:
Reger@mail.chem.sc.edu.
7758 Inorganic Chemistry, Vol. 45, No. 19, 2006
10.1021/ic0606936 CCC: $33.50
© 2006 American Chemical Society
Published on Web 08/16/2006

Crystal Engineering Based on Tris(pyrazolyl)methane Ligands
Chart 1. C6H6-n[CH2OCH2C(pz)3]n Family of Ligands
goal.5 Hydrogen bonding, π-π stacking, X-H‚‚‚π interac-
tions (X ) O, N, C), and inter-halogen interactions are
among the most employed noncovalent forces used to
organize a large variety of building blocks (from discrete
molecules to coordination polymers) into higher-order su-
pramolecular (not covalently linked) architectures.6 There are
numerous examples where each of these noncovalent interac-
tions was used as the only driving force for the organization
of the building blocks into supramolecular architectures. In
contrast, there are only a few examples where two or more
of the aforementioned interactions were simultaneously used
for the same purposes. A major difficulty in logically using
several noncovalent interactions in the same system is the
fact that they are not always complementary, making it
difficult in most cases to “design” specific architectures.
To study various types of intermolecular forces which may
lead to new supramolecular architectures, with the hope of
finding complementary noncovalent interactions that would
help the researcher designing new solid materials, we have
been studying the coordination chemistry of multitopic,
semirigid ligands based on poly(pyrazolyl)methane units that
contain functionalities suitable to support a variety of weak
intermolecular forces. These ligands can adjust their structure
to maximize all covalent and noncovalent forces within a
given system; they are “structurally adaptive”.7 These ligands
are ideal candidates for studying the self-assembly process
and the various factors that might have an influence over
such processes. One such class is the C6H6-n[CH2OCH2-
C(pz)3]n (n ) 2, 3, 4, and 6, pz ) pyrazolyl ring) family of
ligands, with the structural formulas shown in Chart 1. We
have designated these ligands as “third generation” poly-
(2) (a) Khlobystov, A. N.; Blake, A. J.; Champness, N. R.; Lemenovskii,
D. A.; Majouga, G.; Zyk, N. V.; Schroder, M. Coord. Chem. ReV.
2001, 222, 155. (b) Blake, A. J.; Champness, N. R.; Hubberstey, P.;
Li, W. S.; Withersby, M. A.; Schroder, M. Coord Chem. ReV. 1999,
183, 117. (c) Blake, A. J.; Baum, G.; Champness, N. R.; Chung, S. S.
M.; Cooke, P. A.; Fenske, D.; Khlobystov, A. N.; Lemenovskii, D.
A.; Li, W.-S.; Schroder, M. J. Chem. Soc., Dalton Trans. 2000, 4285.
(d) Abourahma, H.; Bodwell, G. J.; Lu, J.; Moulton, B.; Pottie, I. R.;
Bailey W. R.; Zaworotko, M. J. Cryst. Growth Design 2003, 3, 513.
(e) Bourne, S. A.; Mondal, A.; Zaworotko, M. J. Cryst. Eng. 2001, 4,
25. (f) Moulton, Brian; Zaworotko, Michael J. Chem. ReV. 2001, 101,
1629. (g) Lu, J.; Moulton, B.; Zaworotko, M. J.; Bourne, S. A. Chem.
Commun. 2001, 861.
(3) (a) Yaghi, O. M.; O’Keeffe, M.; Ockwig, N. W.; Chae, H. K.;
Eddaoudi, M.; Kim, J. Nature 2003, 423, 705. (b) Rosi, N. L.; Eckert,
J.; Eddaoudi, M.; Vodak, D. T.; Kim, J.; O’Keeffe, M.; Yaghi, O. M.
Science 2003, 300, 1127. (c) Rosi, N. L.; Eddaoudi, M.; Kim, J.;
O’Keeffe, M.; Yaghi, O. M. CrystEngComm 2002, 4, 401. (d) Rosi,
N. L.; Eddaoudi, M.; Kim, J.; O’Keeffe, M.; Yaghi, O. M. Angew.
Chem., Int. Ed. 2002, 41, 284. (e) Braun, M. E.; Steffek, C. D.; Kim,
J.; Rasmussen, P. G.; Yaghi, O. M. Chem. Commun. 2001, 2532. (f)
Eddaoudi, M.; Kim, J.; O’Keeffe, M.; Yaghi, O. M. J. Am. Chem.
Soc. 2002, 124, 376. (g) Eddaoudi, M.; Moler, D. B.; Li, H.; Chen,
B.; Reineke, T. M.; O’Keeffe, M.; Yaghi, O. M. Acc. Chem. Res.
2001, 34, 319. (h) Chen, B.; Eddaoudi, M.; Hyde, S. T.; O’Keeffe,
M.; Yaghi, O. M. Science 2001, 291 1021. (i) Chen, B.; Eddaoudi,
M.; Reineke, T. M.; Kampf, J. W.; O’Keeffe, M.; Yaghi, O. M. J.
Am. Chem. Soc. 2000, 122, 11559. (j) Wang, Y.; Cao, R.; Sun, D.;
Bi, W.; Li, X.; Li, X. J. Mol. Struct. 2003, 657, 301. (k) Zhang, L.-
P.; Mak, T. C. W. Polyhedron 2003, 22, 2787.
(4) (a) Carlucci, L.; Ciani, G.; Proserpio, D. M.; Rizzato, S. Chem. Eur.
J. 2002, 8, 1519. (b) Carlucci, L.; Ciani, G.; Moret, M.; Proserpio, D.
M.; Rizzato, S. Chem. Mater. 2002, 14, 12. (c) Carlucci, L.; Ciani,
G.; Proserpio, D. M.; Rizzato, S. Chem. Commun. 2000, 1319. (d)
Carlucci, L.; Ciani, G.; v. Gundenberg, D. W.; Proserpio, D. M. Inorg.
Chem. 1997, 36, 3812. (e) Ng, M. T.; Deivaraj, T. C.; Vittal, J. J.
Inorg. Chim. Acta 2003, 348, 173. (f) Chen, C.-L.; Su, C.-Y.; Cai,
Y.-P.; Zhang, H.-X.; Xu, A.-W.; Kang, B.-S. New Chem. 2003, 27,
790. (g) Gao, E.-Q.; Bai, S.-Q.; Wang, Z.-M.; Yan, C.-H. J. Chem.
Soc., Dalton Trans. 2003, 1759. (h) Erxleben, A. CrystEngComm 2002,
4, 472. (i) Tong, M.-L.; Wu, Y.-M.; Ru, J.; Chen, X.-M.; Chang, H.-
C.; Kitagawa, S. Inorg. Chem. 2002, 41, 4846. (j) Bu, X.-H.; Chen,
W.; Hou, W.-F.; Du, M.; Zhang, R.-H.; Brisse, F. Inorg. Chem. 2002,
41, 3477;
(5) (a) Brandys, M.-C.; Puddephatt, R. J. J. Am. Chem. Soc. 2002, 124,
3946. (b) 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. (c) McMorran, D. A.; Pfadenhauer, S.; Steel, P.
J. Aust. J. Chem. 2002, 55, 519. (d) Tabellion, F. M.; Seidel, S. R.;
Arif, A. M.; Stang, P. J. J. Am. Chem. Soc. 2001, 123, 11982. (e)
Tabellion, F. M.; Seidel, S. R.; Arif, A. M.; Stang, P. J. J. Am. Chem.
Soc. 2001, 123, 7440. (f) Kasai, K.; Aoyagi, M.; Fujita, M. J. Am.
Chem. Soc. 2000, 122, 2140. (g) Seward, C.; Chan, J. L.; Song, D.
T.; Wang, S. N. Inorg. Chem. 2003, 42, 1112. (h) 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. (i) McMorran, D. A.; Pfadenhauer, S.; Steel,
P. J. Inorg. Chem. Commun. 2002, 5, 449. (j) Fujita, M.; Sasaki, O.;
Watanabe, K.; Ogura, K.; Yamaguchi, K. New J. Chem. 1998, 22,
189.
Inorganic Chemistry, Vol. 45, No. 19, 2006 7759

Reger et al.
Scheme 1. Ligand p-C6H4[CH2OCH2C(pz)3]2 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.
(pyrazolyl)methane ligands. Second generation ligands di-
rectly influence the coordination sphere of the metal by
placing bulky substituents at the 3-position. Third generation
ligands are designed to be those specifically functionalized
at the noncoordinating, “back” position of the ligands and
can be used to introduce functionality that impacts the
supramolecular structure, as well as dictates the directional
orientation of multiple [C(pz)3] units in polytopic ligands.8
In Scheme 1 we show the noncovalent interactions and/
or conformations that have been observed with these ligands,
exemplified on the p-C6H4[CH2OCH2C(pz)3]2 ligand. The
ether linkage offers the possibility of either cis or trans
orientations of the sidearms, while the presence of acidic
hydrogen atoms on the pyrazolyl ring and methylene groups
adjacent to oxygen on the sidearms can promote weak
hydrogen bonds if suitable proton acceptors are introduced
into the system.7a,b,d,h The pyrazolyl rings and the linking
arene ring can act as acceptors in C-H‚‚‚π interactions7f,g,h
or participate in π-π stacking,7,b,d,f,h leading to arene-arene,
pyrazolyl-arene interactions or the double π-π stacking/
C-H‚‚‚π interaction that we have named, after a CSD
database search showed that it was a general interaction, the
“quadruple pyrazolyl embrace”.7k,l Another possible nonco-
valent interaction is cation-π contact between a metallic
center and a pyrazolyl ring within the ligand.9 The tris-
(pyrazolyl)methane units can also act in different covalent
binding modes as (a) κ3 tripodal, (b) κ2 bonded to a single
(7) (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.; Silaghi-Dumitrescu, I.; Smith,
M. D. Inorg. Chem. 2003, 42, 3751. (i) Reger, D. L.; Semeniuc, R.
F.; Rassolov, V.; Smith, M. D. Inorg. Chem. 2004, 43, 537. (j) Reger,
D. L.; Semeniuc, R. F.; Smith, M. D. Inorg. Chem. 2003, 42, 8137.
(k) Reger, D. L.; Gardinier, J. R.; Semeniuc, R. F.; Smith, M. D. J.
Chem. Soc., Dalton Trans., 2003, 1712. (l) Reger, D. L.; Semeniuc,
R. F.; Gardinier, J. R.; Brown, K. J.; Smith, M. D. In Functional
Nanomaterials; Geckeler, K. E., Rosenberg, E., Eds.; American
Scientific Publishers, 2005; p 411.
(8) (a) Reger, D. L.; Gardinier, J. R.; Gemmill, W. R.; Smith, M. D.;
Shahin, A. M.; Long, G. J.; Rebbouh, L.; Grandjean, F. J. Am. Chem.
Soc. 2005, 127, 2303. (b) Reger, D. L.; Gardinier, J. R.; Smith, M.
D.; Shahin, A. M.; Long, G. J.; Rebbouh, L.; Grandjean, F. Inorg.
Chem. 2005, 44, 1852. (c) Reger, D. L.; Gardinier, J. R.; Bakbak, S.;
Semeniuc, Radu F.; Bunz, U. H. F.; Smith, M. D. New J. Chem. 2005,
29, 1035-1043.
(9) 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.
(6) (a) Braga, D.; Grepioni, F. J. Chem. Soc. Dalton Trans. 1999, 1. (b)
Allen, M. T.; Burrows, A. D.; Mahon, M. F. J. Chem. Soc., Dalton
Trans. 1999, 215. (c) Ziener, U.; Breuning, E.; Lehn, J.-M.; Wegelius,
E.; Rissanen, K.; Baum, G.; Fenske, D.; Vaughan, G. Chem. Eur. J.
2000, 6, 4132. (d) Goddard, R.; Claramunt, R. M. Escolastico, C.;
Elguero, J. New. J. Chem. 1999, 23, 237. (e) Calhorda, M. J. Chem.
Commun. 2000, 801. (f) Desiraju, G. R. Acc. Chem. Res. 1996, 29,
441. (g) Grepioni, F.; Cojazzi, G.; Draper, S. M.; Scully, N.; Braga,
D. Organometallics, 1998, 17, 296 (h) Weiss, H. C.; Boese, R.; Smith,
H. L.; Haley, M. M. Chem. Commun. 1997, 2403. (i) Hunter, C. A.;
Sanders, J. K. M. J. Am. Chem. Soc. 1990, 120, 5525. (j) Janiak, C.
J. Chem. Soc., Dalton Trans., 2000, 3885 and references therein. (k)
Takahashi, H.; Tsuboyama, S.; Umezawa, Y.; Honda, K.; Nishio, M.
Tetrahedron 2000, 56, 6185. (l) Tsuzuki, S.; Honda, K.; Uchimaru,
T.; Mikami, M.; Tanabe, K. J. Am. Chem. Soc. 2000, 122, 11450.
(m) Madhavi, N. N. L.; Katz, A. K.; Carrell, H. L.; Nangia, A.;
Desiraju, G. R. Chem. Commun. 1997, 2249. (n) Nishio, M.; Hirota,
M.; Umezawa, Y. The CH/π Interaction EVidence, Nature and
Consequences; Wiley-VCH: New York, 1998. (o) Jennings, W. B.;
Farrell, B. M.; Malone, J. F. Acc. Chem. Res. 2001, 34, 885. (p) Reddy,
D. S.; Craig, D. C.; Desiraju, G. R. J. Am. Chem. Soc. 1996, 118,
4090. (q) Kowalik, J.; VanDerveer, D.; Clower, C.; Tolbert, L. M.
Chem. Commun. 1999, 2007. (r) Freytag, M.; Jones, P. G.; Ahrens,
B.; Fischer, A. K. New J. Chem. 1999, 23, 1137. (s) Thaimattam, R.;
Reddy, D. S.; Xue, F.; Mak, T. C. W.; Nangia, A.; Desiraju, G. R.
New J. Chem. 1998, 22, 143. (t) Edwards, A. J.; Burke, N. J.; Dobson,
C. M.; Prout, K.; Heyes, S. J. J. Am. Chem. Soc. 1995, 117, 4637.
7760 Inorganic Chemistry, Vol. 45, No. 19, 2006

Crystal Engineering Based on Tris(pyrazolyl)methane Ligands
Scheme 2. Possible Modes of Coordination of
Tris(pyrazolyl)methane Units
modifications influenced by several types of noncovalent
forces when the anions and crystallization solvent are varied,
with an emphasis on the solid-state structures.
Results
Syntheses and characterization. While the ligands L2
and L3 were prepared as described in the literature,10 L1
was prepared in a one-pot synthesis starting from 1-(bro-
momethyl)benzene, C6H5CH2Br, and HOCH2C(pz)3 under
basic (NaH) conditions. NMR and elemental analysis con-
firmed its chemical composition and purity. The preparation
of complexes of the general formula [LAg](counterion) was
readily achieved by combining the ligands with either AgBF4,
AgO3SCF3 (AgOTf), or AgPF6. The compounds (insoluble
in halogenated solvents, water, or alcohols but soluble in
acetone, acetonitrile, and nitromethane) are white solids that
are air stable and show only slight decomposition after
several weeks of exposure to daylight. Elemental analyses
of the solids correspond to a metal-to-ligand ratio of 1:1.
The same metal-to-ligand ratio was found when the starting
materials were mixed in different ratios, with the excess
Chart 2. Ligands Used in the Present Work
metal with the third pyrazolyl ring not coordinated, and (c)
κ2-κ1 bonded bridging two metals (Scheme 2). To date, our
most important findings about the self-assembly processes
organizing these structures are (a) the ligand usually displays
a κ2-κ1 coordination mode of the [C(pz)3] units, but the other
two coordinating modes were also found in some cases; (b)
the “molecular” and supramolecular structures were depend-
ent on the number of sidearms and ligand topology, i.e., the
position around the central arene ring of the [C(pz)3] units;
(c) the overall structures of the crystalline solids showed a
dependency on both the counterion and the solvent; and (d)
several different anions were involved in weak hydrogen
bonds with the metal-organic frameworks. Overall, remark-
ably intricate topologies have been observed with the metal
complexes of these multitopic ligands.
While these findings are clearly helpful in the design of
new architectures based on these ligands, three issues still
need to be elucidated (1) how important is the organization
inherently built into the multitopic ligands by their rigid parts
(i.e., directionality of the central arene core and the [C(pz)3]
units) for the formation of these supramolecular structures;
(2) to what extent is the flexibility of the ether linkage (a
set of three sp3 hybridized atoms) responsible for the
structurally adaptive nature; and (3) are these two opposed
structural characteristics (rigid parts vs flexible linkers) in
conflict or are they complementary?
To answer these questions, we started a project based on
a retro-design of our multitopic ligands in such a way that
each new ligand would have one less organizational feature,
as depicted in Chart 2. We have prepared the “one arm”
ligand C6H5CH2OCH2C(pz)3 (L1) to analyze what structural
changes in its silver(I) complexes, if any, will occur after
such a dramatic modification in ligand topicity and topology.
We also used the ligand tris-2,2,2-(1-pyrazoyl)ethanol, HO-
CH2C(pz)3 (L2), to assess the influence of the terminal arene
core in L1. While both of these ligands are “third genera-
tion,” the substitution is much less complex than with the
multitopic ligands. Finally, we prepared the silver(I) com-
plexes of the “first generation,” parent HC(pz)3 ligand (L3)
to evaluate the influence of the flexible, ether-type linker
and the rigid arene core in L1 and our multitopic ligands.
We have carefully investigated the supramolecular structural
1
starting material recovered from the filtrate. The H NMR
spectra of the solids in CD3CN show that the acetonitrile
completely replaces the ligands in all cases; the spectra of
the compounds in CD3CN are the same as those of the free
1
ligands in this solvent. However, the H spectra of the
compounds in deuterated acetone are clearly different from
the free ligands, showing the coordination of the ligands to
the silver(I) in solution. Although the X-ray structure shows
that the pyrazolyl rings are nonequivalent (vide infra) in the
solid state, the NMR spectra show equivalent rings in all
cases, 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 of the same ligands with different
counterions in acetone are essentially identical, showing the
same upfield shifts when compared to the free ligand. This
result suggests that the cationic species present in acetone
solution are identical and anion independent.
Solid-State Structures. Crystallization experiments were
performed for all compounds by vapor phase diffusion of
diethyl ether into an acetone (or, in one case, acetonitrile)
solution of the compound. In all but one case, the metal-to-
ligand ratio of 1:1 of the initial sample was maintained in
the crystalline form. The exception was observed for the
crystalline form of the AgOTf complex of L1, where the
metal-to-ligand ratio was 3:2.
Crystal Structure of {[C6H5CH2OCH2C(pz)3]Ag}(BF4)
(1). The asymmetric unit of (L1)Ag(BF4) consists of five
crystallographically independent silver atoms, with Ag(1) and
Ag(5) located on inversion centers, four L1 ligands, and four
-
BF4 counterions. All bond lengths and angles fall within
the normal range found for these types of compounds.7 The
silver centers in compound 1 show two different geom-
(10) Reger, D. L.; Grattan, T. C.; Brown, K. J.; Little, C. A.; Lamba, J. J.
S.; Rheingold, A. L.; Sommer, R. D. Organomet. Chem. 2000, 607,
120.
Inorganic Chemistry, Vol. 45, No. 19, 2006 7761

Reger et al.
Figure 2. Overall 1D strand of 1. Each Ag(1) is flanked by two Ag(2)
and each Ag(5) is flanked by two Ag(4) metallic centers, consistent with
their position on inversion centers.
Figure 3. View down the chain of 1. The [C(pz)3Ag]n “argentachains”
form a coordination polymer; the -CH2OCH2C6H5 portion of the ligand is
wrapped around the chains.
Figure 1. Coordination patterns of the ligand and silver environments in
{[C6H5CH2OCH2C(pz)3]Ag}(BF4) (1). Top, linear Ag(1) and tetrahedral
Ag(2) coordination; the π sandwich of the pyrazolyl rings around Ag(1) is
clearly shown in the middle of the figure. Middle, linear coordination of
Ag(3); the cation-π contacts are indicated here by the blue dotted lines.
Bottom, tetrahedral Ag(4) environment and linear Ag(5) coordination; the
cation-π contacts for Ag(5) are shown in a similar manner as for Ag(1).
The remaining pyrazolyl ring from the ligand that com-
pletes the coordination around the Ag(2) is bonded to Ag-
(3), which is the second linear silver, shown in the middle
of Figure 1. The other pyrazolyl ring needed for the
completion of the linear geometry of the Ag(3) is provided
by another ligand, which coordinates again in a κ2-κ1 mode;
one pyrazolyl ring coordinates to Ag(3), and the two other
are bonded to Ag(4). As with Ag(1), two pyrazolyl rings
(one bonded to Ag(2) and one bonded to Ag(4)) are
sandwiching the Ag(3) center, as shown in the middle of
Figure 3 by the blue dotted lines. Since Ag(3) is not situated
on an inversion center, both Ag-N and Ag-centroid
distances are not equal. The Ag-N(231) and Ag-N(331)
distances are 2.157(3) and 2.169(3) Å, respectively, with a
N(231)-Ag(3)-N(331) angle of 168.58(10)°. The Ag-π
contacts are as follows. Ag(3)-centroid distances are 3.17
and 3.08 Å, respectively, with the corresponding centroid-
Ag(3)-centroid angle of 177.6°.
etries: linear, Ag(1), Ag(3), and Ag(5) and tetrahedral, Ag-
(2) and Ag(4). All L1 ligands are κ2-κ1 coordinated to the
metallic centers. The environment around the Ag(1) and Ag-
(2) is pictured at the top of Figure 1. Ag(1) is linearly
coordinated by two pyrazolyl rings from two different
ligands, with the N(131)-Ag(1) distance being 2.104(3) Å
with a corresponding angle of 180°. The remaining four
pyrazolyl rings from the two tris(pyrazolyl)methane units κ1
bonded to Ag(1), are coordinated to Ag(2) in a κ2 manner,
with an average Ag-N distance of 2.3 Å. Furthermore, two
pyrazolyl rings coordinated to Ag(2), one from each ligand,
are oriented toward Ag(1). Each Ag(1)-centroid distance
is 3.18 Å, and the corresponding centroid-Ag(1)-centroid
angle is 180°. The pyrazolyl-silver “sandwich”, made up
by cation-π interactions, is clearly shown in the middle of
the top picture in Figure 1. These values are in good
agreement with those found for several studies on arene-
silver interactions, including statistical analyses based on the
existing structures in the Cambridge Structural Database,11
where distances falling in the range of 2.89-3.37 Å were
reported for Ag-arene interactions. Two other L1 ligands,
with two pyrazolyl rings κ2 bonded to the metallic center
complete the distorted tetrahedral coordination for the Ag-
(2) atom.
The coordination polymer is further propagated by the κ2
coordination of the remaining pyrazolyl rings from the ligand
that is κ1 bonded to Ag(3) and another κ2 bonded ligand to
the same Ag(4), as can be seen at the bottom of the Figure
1. As with Ag(2), the environment around Ag(4) is a distorted
tetrahedron due to the restricted bite angle of the ligand. The
repeating unit of the coordination polymer is completed by
the κ1 coordination of the last pyrazolyl ring from the last
ligand (κ2 bonded to Ag(4)) to the fifth independent silver
within the asymmetric unit, that is Ag(5). The environment
around Ag(5) is similar to that of Ag(1) because both of
them are situated on inversion centers. The Ag(5)-N(431)
distance and the corresponding N(431)-Ag-N(431#1) angle
(11) (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.
7762 Inorganic Chemistry, Vol. 45, No. 19, 2006

Crystal Engineering Based on Tris(pyrazolyl)methane Ligands
Figure 5. 1D chain in {[HOCH2C(pz)3]Ag}(BF4)‚0.5[(CH3)2CO] (3‚0.5
[(CH3)2CO]); the Ag‚‚‚pz contacts are shown as blue dotted lines.
environment (sum of the N-Ag(1)-N bond angles )
357.26°), with a significant distortion caused by the restricted
angle [78.12(12)°] of the κ2 bonded ligand. There are no
other contacts for this Ag(1) atom, the two pyrazolyl rings
oriented toward the Ag(1), shown at the right side of the
figure are too far away to consider a cation-π interaction
between the two moieties. The Ag(2) is coordinated by two
pyrazolyl rings from the second ligand and one triflate anion
in a nonplanar arrangement. If we consider two other Ag-O
contacts, of 2.61 and 2.75 Å, indicated by two red dotted
lines in Figure 4, the polyhedron around Ag(2) becomes a
trigonal bipyramid. The Ag(3) center is κ1 coordinated by
the remaining pyrazolyl ring from the first ligand and by all
three triflate counterions. The nitrogen atom from the
pyrazolyl ring and two oxygen atoms from two different
anions form the base of a trigonal pyramid and a third
oxygen, coming from one triflate counterion, completes the
pyramid. The silver(I) center is positioned within the base,
the sum of N-Ag-O and O-Ag-O bond angles ) 359.48°.
One pyrazolyl ring from the pair that chelates the Ag(1) atom
is oriented toward the Ag(3) atom, making a cation-π
contact, at 3.00 Å, as is indicated by the blue dotted line in
Figure 4. Considering this interaction, the geometry around
the silver(I) center becomes trigonal bipyramidal, with three
short bonds in the equatorial plane and two long bonds in
the axial plane. The repeating unit of 2 is best described as
“independent” (L1)2(Ag)3 units linked by two triflate anions
into argentachains through covalent and secondary bonds.
With no other noncovalent interactions being identified, the
remaining crystal packing of 2 is based solely on van der
Waals forces.
Crystal Structure of {[HOCH2C(pz)3]Ag}(BF4)‚0.5-
[(CH3)2CO] (3‚0.5[(CH3)2CO]). Crystallization of the white
powder from an acetone-diethyl ether system produced a
1D coordination polymer made up by the κ2-κ1 bonding
mode of the [C(pz)3] unit, as pictured in Figure 5. The
asymmetric unit contains two independent silver atoms, two
L2 ligands, two BF4- counterions, and an acetone molecule
of crystallization. Both silver(I) centers are found alterna-
tively situated within the same chain and each κ2 bonded by
one of the ligands and κ1 bonded by the second L2. Both
the Ag(1) and Ag(2) environments are trigonal planar, with
the sum of the corresponding N-Ag-N bond angles being
359.67° and 359.68°, respectively. The difference between
Ag(1) and Ag(2) is that Ag(2) is involved in a cation-π
interaction with one of the pyrazolyl rings from the pair that
is κ2 bonded to Ag(1), as shown by the blue dotted lines in
Figure 5.
Figure 4. Portion of the 1D chain in {[C6H5CH2OCH2C(pz)3]2Ag3}(OTf)3‚
0.5[(CH3)2CO].
are 2.131(3) Å and 180°, respectively. Two other pyrazolyl
rings are π-coordinated to Ag(5), one from two different
ligands. Each Ag(5)-centroid distance is 3.22 Å, and the
corresponding centroid-Ag(5)-centroid angle is 180°.
Overall, the structure of 1 is a one-dimensional polymer,
as pictured in Figure 2. Each linear Ag(1) and Ag(5) is
flanked by two tetrahedral Ag(2) and Ag(4) centers, respec-
tively, which are in turn linked by Ag(3). This κ2-κ1 bridging
coordination mode of L1 create what we call an “argen-
tachain” (no Ag‚‚‚Ag interactions implied)12 surrounded by
the CH2OCH2C6H5 coating, Figure 3. The 1D architecture
is supported by a series of intrachain C-H‚‚‚π interactions
with H-centroid distances ranging from 2.69 to 3.17 Å
(perpendicular distances from the H atoms to the ring planes
from 2.51 to 2.91 Å) and C-H-centroid angles from 127.1°
to 134.2°. The counterions are situated in close prox-
imity of the chains and are “connected” to them by weak
C-H‚‚‚F hydrogen bonds, without expanding the dimen-
sionality of the overall architecture. The C-H‚‚‚F distances
fall in the range 2.13-2.26 Å, and the corresponding
C-H-F angles are in the range 159.9-167.8°.
Crystal Structure of {[C6H5CH2OCH2C(pz)3]2Ag3}-
(OTf)3‚0.5[(CH3)2CO] (2‚0.5[(CH3)2CO]). During the crys-
tallization process of the white powder obtained from the
reaction between L1 and AgOTf, the metal-to-ligand ratio
of 1:1 (established on the basis of elemental analysis results)
changed to a 3:2 ratio. The compound crystallizes with half
a molecule of acetone per unit cell. The structure of (L1)2Ag3-
(OTf)3‚0.5[(CH3)2CO] is a 1D coordination polymer, as with
1. A portion of the chain is pictured in Figure 4. The structure
of 2 shows unique features, not encountered in other cases
where the tris(pyrazolyl)methane unit was used as a donor
set. There are two ligands, both acting in the bridging κ2-
κ1 mode and three silvers, each in different environments:
trigonal planar (Ag(1)) with coordination number (C.N.) )
3, trigonal pyramidal (Ag(2)) with C.N. ) 3 and distorted
tetrahedral (Ag(3)) with C.N. ) 4. One ligand is κ2 bonded
to Ag(1) and κ1 bonded to Ag(3). The environment around
Ag(1) is completed by the second ligand, which is κ1 bonded
to the same Ag(1). The Ag(1) atom is in a distorted planar
(12) We use the term “argentachain” to describe the -AgNNCNN-
sequence of atoms that form the coordination polymer, created by the
κ2-κ1 coordination mode of the tris(pyrazolyl)methane donor set
without claiming Ag-Ag contacts of any kind; see also ref 7g.
Inorganic Chemistry, Vol. 45, No. 19, 2006 7763

Reger et al.
Figure 8. Sheet formation in 4 shown down the argentachains pictured
in Figure 7.
nated by the remaining two pyrazolyl rings and two triflate
counterions. The sinusoidal arrangement of these strands is
supported by a “pyrazolyl embrace” interaction forming
metallocycles along the strand. This interaction is a concerted
set of noncovalent interactions between a pyrazolyl tetrad,
consisting of cooperative π-π and two C-H‚‚‚π inter-
actions.7k,l In 4, two of the pyrazolyl rings that chelate the
Ag(1) atoms are π-stacked at a perpendicular distance
between the planes of 3.6 Å, as pointed out in Figure 7 by
the blue dotted lines, with a slip angle of 22.8°. The hydrogen
atoms from the 4-position of the rings involved in the π-π
stacking interaction are oriented toward the other two
pyrazolyl rings that are coordinated to Ag(1), with a
H-centroid distance of 3.2 Å (C-centroid distance of 4.1
Å) and a C-H-centroid angle of 146.9°. Another interaction
that supports the 1D coordination polymer is an intrachain
hydrogen bond, involving the terminal OH group of the
ligand. The hydrogen atoms are oriented toward the oxygen
atoms from the triflate groups, with the H‚‚‚O distance )
2.29 Å, the O‚‚‚O distance ) 3.04 Å, and the O-H-O angle
) 150.5 °.
The chains are arranged into sheets (Figure 8) by two
C-H‚‚‚O interactions. Two hydrogen atoms H(11) and H(21)
situated at the 3-position of the pyrazolyl rings are oriented
toward two different oxygen atoms from the triflate groups.
The geometric parameters for these two interactions are as
follows. The H‚‚‚O distances are for both interactions 2.38
Å, with only the C-H-O angles and C‚‚‚O separations being
different, 169.89° and 147.41°, respectively, and 3.32 and
3.22 Å, respectively.
Figure 6. Crystal packing in 3‚0.5[(CH3)2CO] oriented down the
argentachains; the C-H‚‚‚F hydrogen bonds are shown as red dotted lines.
Figure 7. Structure of {[HOCH2C(pz)3]Ag}(OTf) (4); the π-π stacking
component of the pyrazolyl embrace interaction is shown as blue dotted
lines.
The crystal packing of 3‚0.5[(CH3)2CO] (Figure 6) is
dominated by a network of C-H‚‚‚F hydrogen bonds, shown
in Figure 6 by the red dotted lines. There are two BF4- anions
within the asymmetric unit, each with different supramo-
lecular contacts but both having the same function: con-
necting the covalent 1D cationic strands into a 3D architec-
ture. The average H‚‚‚F distance is 2.41 Å, and the average
C-H-F angle is 164.2°. The -CH2OH groups of each
ligand were both found to be disordered over two orienta-
tions, and therefore, their contribution to the crystal packing
is difficult to interpret.
Crystal Structure of {[HC(pz)3]2Ag2(CH3CN)}(BF4)2
(5). Crystals suitable for X-ray diffraction studies were
obtained from an acetonitrile-diethyl ether system (efforts
to grow crystals form the acetone-diethyl ether were
unsuccessful). Although the ligand-to-metal ratio is 1:1, the
asymmetric unit contains two chemically identical but
crystallographically inequivalent L3 ligands, two Ag centers,
Crystal Structure of {[HOCH2C(pz)3]Ag}(OTf) (4). The
-
change in counterion from BF4 to OTf-generated major
structural changes of the cationic 1D strand, pictured in
Figure 7. There are two crystallographically inequivalent Ag
cations, both having a distorted tetrahedral coordination. The
Ag(1) atoms are coordinated by two pairs of pyrazolyl rings
from two different ligands, while Ag(2) atoms are coordi-
-
one coordinated CH3CN molecule, and two BF4 counter-
7764 Inorganic Chemistry, Vol. 45, No. 19, 2006

Crystal Engineering Based on Tris(pyrazolyl)methane Ligands
Figure 9. 1D chain in {[HC(pz)3]2Ag2(CH3CN)}(BF4)2 (5); the Ag‚‚‚pz
contacts are shown as blue dotted lines.
Figure 11. 1D chain in {[HC(pz)3]Ag}(PF6)‚0.5[(CH3)2CO]; no inter- or
intrastrand contacts were observed.
Figure 10. One corrugated sheet in 5, viewed down the argentachains;
the C-H‚‚‚F hydrogen bonds are shown as red dotted lines.
ions. The covalent 1D argentachain of 5 is built up by the
same κ2-κ1 coordination mode of the ligands to both silver
centers. However, the covalent and noncovalent silver
environments within the strand are different for the two L3-
Ag pairs. As seen in Figure 9, Ag(1) is into an almost planar
environment, the sum of the corresponding N-Ag-N bond
angles being 358.58°, the metallic center being slightly out
of the plane defined by the three nitrogen atoms. In addition,
there is a cation-π interaction between the silver(I) center
and one of the pyrazolyl rings from the ligand that is κ2
bonded to Ag(2), pictured in Figure 9 by the blue dotted
line. The Ag‚‚‚centroid distance is 3.17 Å, with a perpen-
dicular distance from Ag to the pyrazolyl ring of 2.9 Å. The
Ag(2) atom is four coordinate, bonded to the three pyrazolyl
rings coming from two L3 ligands and an acetonitrile
molecule. If we consider only the pyrazolyl rings, the AgN3
core is a flattened trigonal pyramid, the sum of the corre-
sponding N-Ag-N bond angles being 353°. Together with
the acetonitrile molecule, the Ag(2) environment is a highly
distorted tetrahedron.
Figure 12. Structural characteristics of the bimetallic unit in {[HC-
(pz)3]2Ag2}(OTf)2; Ag‚‚‚oxygen contacts are shown as red dotted lines.
Figure 11. In contrast to 5, a check of the supramolecular
structure revealed no association between the 1D strands of
the coordination polymer or between the strands and the
acetone molecule of crystallization.
Crystal Structure of {[HC(pz)3]2Ag2}(OTf)2 (7). The
-
change in counterion from either BF4- or PF6- to F3CSO3
generated dramatic changes in the molecular and crystal
structure of the compound. Crystallization from an acetone-
diethyl ether system produced a discrete bimetallic com-
pound, rather than a coordination polymer, see Figure 12.
Although the ligand-to-metal ratio is still 1:1, the compound
is a dimer, built up by the two L3 ligands κ2-κ1 bonding to
the same two silvers. Each ligand chelates a different silver
using two pyrazolyl rings, while the third ring has κ1 bonding
to the silver κ2 bonded to the other ligand. The distance
between the silver atoms is 2.86 Å, considerably shorter than
the sum of silver-silver van der Waals radii (3.44 Å),13
which is indicative of a strong Ag-Ag interaction. Such
interactions have been shown to influence the outcome of
several supramolecular assemblies, and their importance has
been crystallographically and theoretically documented.14
Each silver is equatorially surrounded by three nitrogen
atoms. The sum of Ag-N angles around the silver is 358.54°,
thus placing it in a slightly distorted trigonal planar geometry.
In addition, the triflate counterions are in close proximity to
the metallic centers, with one Ag-O distance ) 2.82 Å. If
-
The BF4 counterions are situated along the chain. The
shortest Ag(1)-F and Ag(2)-F distances are 3.18 and 3.00
Å, respectively, too long to be considered Ag‚‚‚F contacts.
However, there are several (C)H‚‚‚F hydrogen bonds,
involving both anions. For the first BF4- group, the average
H‚‚‚F distance is 2.39 Å, with a corresponding average
C-H-F angle of 154.8°. The second BF4- group was found
disordered over two orientations; therefore, an accurate
analysis of its contribution to the crystal packing is precluded.
-
Considering only the interactions of the well-behaved BF4
moiety, shown as red dotted lines in Figure 10, the one-
dimensional strands are organized in corrugated sheets in
the ab plane of the unit cell.
(13) Bondi, A. J. Phys. Chem. 1964, 68, 441.
(14) (a) Sailaja, S.; Rajasekharan, M. V. Inorg. Chem. 2003, 42, 5675. (b)
Kristiansson, O. Inorg. Chem. 2001, 40, 5058. (c) Singh, K.; Long, J.
R.; Stavropoulos, P. J. Am. Chem. Soc. 1997, 119, 2942. (d) Pyykko¨,
P. Chem. ReV. 1997, 97, 597. (e) 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.
Crystal Structure of {[HC(pz)3]Ag}(PF6)‚0.5[(CH3)2CO]
-
(2‚0.5[(CH3)2CO]). Similar to 5, with PF6 as the anion,
the resulting structure is again a simple coordination polymer
built up by the same κ2-κ1 bonding mode of the ligand,
Inorganic Chemistry, Vol. 45, No. 19, 2006 7765

Reger et al.
the triflate anions and the second silver atom are considered
along with the three equatorial nitrogen atoms, the geometry
around each silver becomes trigonal bipyramidal. Other
structural characteristics of this compound will be analyzed
in a forthcoming paper, together with other compounds with
similar structures that involve Ag-Ag interactions.
One of the basic ideas behind this report is to deter-
mine if the removal of one or more “sidearms” from our
multitopic ligands will still lead to similar covalent bond-
ing and supramolecular structural trends with those observed
previously with multitopic ligands. In general, the struc-
tures reported here have similar bonding characteristics but
are much less complex, both in terms of the covalent bond-
ing and the supramolecular structures. For example, the
structure of 1 reveals a similar argentachain organiza-
tion as {m-C6H4[CH2OCH2C(pz)3]2Ag2}(BF4)2 (8) (for full
details see ref 7h) with different types of silver(I) centers in
alternating linear and tetrahedral environments. The differ-
ence is that in the structure of 8, in addition to the simple
argentachain structure of 1, the additional linkage provided
by the bitopic ligand leads to a more complex chain of 32
atom metallomacrocycles. Also, in 8 the central arene rings
were involved in π-π stacking, thus expanding the dimen-
sionality of the supramolecular structure, whereas in com-
pound 1 no such interaction exits.
The absence of multiple sidearms in 2‚0.5[(CH3)2CO],
when compared to {p-C6H4[CH2OCH2C(pz)3]2Ag2}(OTf)2
(9), also influences the structure in that 2‚0.5[(CH3)2CO]
shows unique features not encountered in other cases where
the tris(pyrazolyl)methane unit was used as a donor set. The
counterion was found coordinated to the silver(I) atom and
also bridging two “independent” (L1)2(Ag)3 units through
covalent and secondary bonds. In the complex structure of
9, the triflate anions are not bonded to the silver but organize
the supramolecular structure into a tubular 3D arrangement
(for details see ref 7i). As with 1, no noncovalent interactions
involving groups other than the triflate groups were identified
in the structure of 2‚0.5[(CH3)2CO].
Discussion
The structures described here fall within the general
structural trends found with silver(I) complexes of the
C6H6-n[CH2OCH2C(pz)3]n (n ) 2, 3, 4, and 6) family of
ligands. Specifically, the structures of compounds 1-7 are
counterion and solvent dependent, as observed in all previ-
ously described cases.7 Changing the counterion, especially
to triflate, has a greater effect on the structures than observed
previously.
The most important trend in all these structures is the
overwhelming dominance of the κ2-κ1 bonding mode of the
[C(pz)3] units in all of these ligands. In all but one of the
cases reported here, 7, this bonding mode leads to the
formation of coordination polymers that we have referred
to as argentachains, in which no direct Ag‚‚‚Ag interaction
is implied (Ag‚‚‚Ag distances in the κ2-κ1 bonding mode
range from 4.12 to 5.55 Å7). In five of the cases, the
argentachains are supported solely by the κ2-κ1 bonding
mode, whereas in {[C6H5CH2OCH2C(pz)3]2Ag3}(OTf)3‚0.5-
[(CH3)2CO], the chains are formed, in addition, by interac-
tions of the triflate counterion. In 7, the κ2-κ1 bonding mode
to the same two silvers supports isolated dimers. In designing
the C6H6-n[CH2OCH2C(pz)3]n family of ligands, we antici-
pated the formation of coordination polymers built upon the
intrinsic linking of the [C(pz)3] units in a single multitopic
ligand but did not anticipate this bridging κ2-κ1 linking
feature to be so dominant. This dominance is clearly
confirmed by the new structures in this work, including
structures of the “first generation” HC(pz)3 ligand, demon-
strating that the κ2-κ1 bonding mode, frequently leading to
argentachains, is a general feature in complexes of silver(I)
with ligands containing the [C(pz)3] unit and is not specific
to the “third generation,” multitopic ligands. This type of
bonding has also been shown to occur for [HC(pz)3Ag]-
(NO3).16 In contrast, κ3 bonding is the dominant coordination
mode of tris(pyrazolyl)borate and ring-substituted tris-
(pyrazolyl)methane ligands.15 For example, in our first silver-
(I) paper with tris(pyrazolyl)methane ligands, we used the
substituted ligands HC(3,5-Me2pz)3 and HC(3-Butpz)3.17 In
the structures of the silver(I) complexes of these ligands,
the κ3 bonding mode is observed. Clearly, substitution on
the pyrazolyl rings favors this type of bonding, whereas the
[C(pz)3] unit, at least in silver(I) chemistry, favors the κ2-
κ1 bonding mode.
With the HOCH2C(pz)3 alcohol as the ligand, the structure
of {[HOCH2C(pz)3]Ag}(BF4)‚0.5[(CH3)2CO] is also a simple
-
covalent 1D coordination polymer, but the BF4 ion orga-
nizes them in a 3D structure, as observed with complexes
of this ion using the multitopic ligands. In the latter cases,
the structures are more complex because of the linkages
provided by the ligands. As observed with 2‚0.5[(CH3)2CO],
in the case of 4, the triflate counterions are coordinated
to half of the silver centers and also organize the normal
κ2-κ1 argentachain structure into sheets.
Upon further simplifying the ligands, that is, using
HC(pz)3, two different situations were encountered. With 7,
the triflate ion coordinates to the silver centers, leading to a
discrete bimetallic compound rather than argentachains. The
two other compounds, 5 and 6‚0.5[(CH3)2CO], are simple
1D coordination polymers, built up by a κ2-κ1 bonding mode
of the tris(pyrazolyl)methane ligands, although in the struc-
-
ture of 6‚0.5[(CH3)2CO] the BF4 ion organizes the poly-
mers into corrugated sheets. In striking similarity with
{p-C6H4[CH2OCH2C(pz)3]2Ag2CH3CN}(BF4)2‚(C4H10O),7i 5
also contains two different types of silvers; one Ag atom is
four coordinate, bonded by three pyrazolyl rings with the
fourth site occupied by an acetonitrile molecule, and one
Ag atom is only three coordinate. In addition, in both
structures, the latter Ag atom makes a π-contact with a
pyrazolyl ring, as pictured in Figure 9.
(15) (a) Trofimenko, S. Scorpionates: The Coordination Chemistry of Poly-
pyrazolylborate Ligands; Imperial College Press: London, 1999. (b)
Pettinari, C.; Pettinari, R. Coord. Chem. ReV. 2005, 249, 525.
(16) Cingolani, A.; Effendy, G.; Martini, D.; Pellei, M.; Pettinari,
C.; Skelton, B. W.; White, A. H. Inorg. Chem. Acta 2002, 328,
87.
(17) Reger, D. L.; Collins, J. E.; Rheingold, A. L.; Liable-Sands; L. M.;
Yap, G. P. A. Organometallics 1997, 16, 349.
7766 Inorganic Chemistry, Vol. 45, No. 19, 2006

Crystal Engineering Based on Tris(pyrazolyl)methane Ligands
-
The PF6 counterion in 6‚0.5[(CH3)2CO] has no organi-
nitrile. We have also shown that, although the structures
reported here are different, several important patterns can
be found that can be transferred from one case to another.
Therefore, this strategy for the assembly of covalent networks
based on semirigid ligands completes the gap between
strategies based on rigid or completely flexible ligands.
zational function. Its structure is a simple 1D coordination
polymer, with no remarkable supramolecular structural
characteristics. This result is consistent with our previous
findings,7i where the PF- anion, when present, was not
involved in a supramolecular organization of the covalent
networks.
Experimental Section
On the basis of our results reported here, we can clearly
state that the presence of the rigid core of the multitopic
ligands contributes to the highly organized supramolecular
structures. Further, the presence of multiple [C(pz)3]-contain-
ing sidearms grafted onto the central arene ring is important
for this functional group to show supramolecular associations,
as well as to control the orientation around the central arene
core. For example, when comparing compound 1 with 8,
we found no π-π stacking in the former, while strong π-π
stacking interactions in the latter led to an increased
dimensionality of the crystal structure. It is well known that
substituents perturb the uniform charge distribution in
aromatic rings (which, in our case, is the central arene core),
causing partial atomic charges and a permanent dipole, which
introduce electrostatic dipole-dipole and dipole-induced
dipole forces that are responsible for the increased stability
of π-stacked species.
The flexible ether linkage role is also crucial. It is the
flexibility of the ether linkage that allows the anions to
organize the structures observed in our studies; 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. Therefore, ligands based on
tris(pyrazolyl)methane units linked with flexible organic
spacers are ideal candidates for studying the self-assembly
process in its entirety and especially the interplay between
different types of noncovalent interaction.
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 vs
internal Me4Si. Elemental analyses were performed by Robertson
Microlit Laboratories (Madison, NJ). Tris(pyrazolyl)methane, HC-
(pz)3 (L3), and tris-2,2,2-(1-pyrazoyl)ethanol, HOCH2C(pz)3 (L2),
were prepared following literature methods.10 The starting materials
benzyl bromide, silver tetrafluoroborate, silver hexafluorophosphate,
and silver triflate were obtained from commercial sources (Aldrich)
and used as received.
Synthesis of C6H5[CH2OCH2C(pz)3] (L1). Benzyl bromide
(1.71 g, 10 mmol) and tris-2,2,2-(1-pyrazoyl)ethanol, HOCH2C-
(pz)3 (2.44 g, 10 mmol), were dissolved in dry THF (75 mL). This
solution was added dropwise to a suspension of NaH (1.0 g) in
dry THF (100 mL) under an inert atmosphere. The mixture was
stirred under reflux for 12 h and then allowed to cool at room
temperature. To this solution enough water (250 mL) was added
dropwise to consume the excess NaH and dissolve the resulting
NaBr and NaOH. The THF-water mixture was extracted with ethyl
ether (4 × 100 mL), and the combined organic extracts were washed
with 100 mL of saturated NaHCO3 solution, with 100 mL of
saturated NaCl solution, and finally with 100 mL of water. The
organic layer was dried over anhydrous Na2SO4 and filtered, and
the solvent removed under vacuum to afford the desired compound
1
as a white powder (3.11 g, 93%); H NMR (acetone-d6): δ 7.60,
7.50 (d, d, J ) 1.5, 2.4 Hz, 3,3H, 3,5-H pz), 7.29 (m, 5H, C6H5),
6.35 (dd, 3H, J ) 1.5, J ) 2.4 Hz, 4-H pz), 5.13 (s, 2H, OCH2C-
(pz)3), 4.57 (s, 2H, OCH2Ph); ES+/MS for [C18H19N6O]+: Calcd
335.1620; Found 335.1621.
Conclusion
The major structural characteristic of all the complexes
that contain the [C(pz)3] unit with silver(I) as the metal is
that all of these ligands strongly favor the κ2-κ1 bonding
mode. Also important is the number of the donor units within
the ligand and their relative position with respect to each
other. The crystal packing is influenced by a combination
of noncovalent interactions. The two opposed structural
characteristics built into the C6H6-n[CH2OCH2C(pz)3]n family
of ligands (rigid groups and flexible linkers) are comple-
mentary; while the rigid groups definitely support special
organizational features within the structures, the flexible
linkers allow all these features to manifest themselves in a
cumulative and complementary manner.
The counterions also impose changes in the overall
structures of the crystalline solids; these differences are much
greater with the simple ligands reported here and when the
material is crystallized from a noncoordinating solvent. The
crystallization of these systems from weakly coordinating
solvents allows the 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 aceto-
Synthesis of {[C6H5CH2OCH2C(pz)3]Ag}(BF4) (1). A THF (20
mL) solution of L1 (0.334 g, 1 mmol) was added dropwise to a
solution of AgBF4 (0.194 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 0.492 g (93%) of solid identified as {[C6H5-
CH2OCH2C(pz)3]Ag}(BF4). Crystallization of this compound from
acetone afforded {[C6H5CH2OCH2C(pz)3]Ag}(BF4). 1H NMR
(acetone-d6): δ 7.91, 7.77 (d, d, J ) 1.5, 2.4 Hz, 3,3H, 3,5-H pz),
7.32 (m, 5H, C6H5), 6.52 (dd, 3H, J ) 1.5, J ) 2.4 Hz, 4-H pz),
5.17 (s, 2H, OCH2C(pz)3), 4.65 (s, 2H, OCH2Ph); Calcd for C18H18-
AgBF4N6O: C, 40.86; H, 3.43; N, 15.89; Found C, 40.81; H, 2.99,
N, 15.50; ES+/MS: Calcd for [C6H5CH2OCH2C(pz)3]Ag}]+ m/z
441.0593, Found 441.0584.
Synthesis of {[C6H5CH2OCH2C(pz)3]Ag}(OTf) (2). This com-
pound was synthesized as above for 1 using AgOTf (0.256 g, 1.00
mmol) to afford 0.510 g (86%) of solid identified as {[C6H5CH2-
OCH2C(pz)3]Ag}(OTf). Crystallization of this compound from
acetone afforded 2‚0.5[(CH3)2CO]. 1H NMR (acetone-d6): δ 7.90,
7.76 (d, d, J ) 1.5, 2.4 Hz, 3,3H, 3,5-H pz), 7.32 (m, 5H, C6H5),
6.52 (dd, 3H, J ) 1.5, J ) 2.4 Hz, 4-H pz), 5.17 (s, 2H, OCH2C-
Inorganic Chemistry, Vol. 45, No. 19, 2006 7767

Reger et al.
Table 1. Selected Crystal and Structure Refinement Data
1
2‚0.5[(CH3)2CO]
3‚0.5[(CH3)2CO]
4
formula
fw, g mol-1
cryst syst
space group
T (K)
a, Å
b, Å
c, Å
C18H18AgBF4N6O
529.06
triclinic
P1h
190(2)
10.8577(8)
20.0205(15)
21.8994(16)
116.6500(10)
93.116(2)
102.1530(10)
4098.6(5)
8
C40.50H39Ag3F9N12O11.50S3
C12.50H15AgBF4N6O1.50
467.98
monoclinic
P21/n
C12H12AgF3N6O4S
1468.63
monoclinic
P21/c
501.21
orthorhombic
Pnna
150(2)
13.6420(7)
13.9842(7)
17.9820(9)
90
90
90
3430.5(3)
8
293(2)
190(2)
12.2301(18)
13.1990(19)
32.933(5)
90
100.761(3)
90
9.0888(13)
22.974(3)
16.479(2)
90
92.219(3)
90
R, deg
â, deg
γ, deg
V, Å3
5222.7(13)
4
3438.2(8)
8
Z
R1 I > 2σ(I)
wR2 I > 2σ(I)
0.0412
0.0872
0.0489
0.1110
0.0468
0.1283
0.0433
0.0921
5
6‚0.5[(CH3)2CO]
7
formula
fw, g mol-1
cryst syst
space group
T (K)
C22H23Ag2B2F8N13
858.89
monoclinic
P21/c
C11.50H13AgF6N6O0.50
496.12
monoclinic
P21/c
190(2)
P
C22H20Ag2F6N12O6S2
942.36
triclinic
P1h
150(2)
150(2)
a, Å
b, Å
c, Å
10.0218(6)
12.6040(7)
23.8071(13)
90
95.0650(10)
90
11.6571(8)
13.5851(9)
10.7084(7)
90
97.6620(10)
90
8.6922(6)
9.4966(7)
10.3316(8)
71.5870(10)
68.4530(10)
81.8470(10)
752.30(10)
1
R, deg
â, deg
γ, deg
V, Å3
2995.4(3)
4
1680.67(19)
4
Z
R1 I > 2σ(I)
wR2 I > 2σ(I)
0.0330
0.0766
0.0596
0.1621
0.0247
0.0600
(pz)3), 4.65 (s, 2H, OCH2Ph); Calcd For C19H18AgF3N6O4S: C,
38.59; H, 3.07; N, 14.21; Found C, 38.51; H, 3.02, N, 14.53.
Synthesis of {[HOCH2C(pz)3]Ag}(BF4) (3). A THF (20 mL)
solution of L2 (0.244 g, 1 mmol) was added dropwise to a solution
of AgBF4 (0.194 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 0.401 g (91%) of solid identified as {[HOCH2C(pz)3]Ag}-
(BF4). Crystallization of this compound from acetone afforded
{[HOCH2C(pz)3]Ag}(BF4)‚0.5[(CH3)2CO]. 1H NMR (acetone-
d6): δ 7.91, 7.77 (d, d, J ) 1.5, 2.4 Hz, 3,3H, 3,5-H pz), 7.32 (m,
5H, C6H5), 6.52 (dd, 3H, J ) 1.5, J ) 2.4 Hz, 4-H pz), 5.17 (s,
2H, OCH2C(pz)3), 4.65 (s, 2H, OCH2Ph); Calcd for C11H12AgBF4-
N6O: C, 30.10; H, 2.76; N, 19.15; Found C, 30.57; H, 2.99, N,
19.72.
3,3H, 3,5-H pz), 6.54 (s, 3H, 4-H pz); Calcd for C10H10AgBF4N6:
C, 29.37; H, 2.47; N, 20.55; Found C, 28.98; H, 2.89, N, 19.99.
Synthesis of {[HC(pz)3]Ag}(PF6) (6). This compound was
synthesized as above, using AgPF6 (0.252 g, 1.00 mmol), to afford
0.392 g (83%) of solid identified as {[HC(pz)3]Ag}(PF6). Crystal-
lization of this compound from acetone afforded {[HC(pz)3]Ag}-
(PF6)‚0.5[(CH3)2CO]. 1H NMR (acetone-d6): δ 9.29 (s, 1H,
HC(pz)3), 8.24, 7.86 (s, s, 3,3H, 3,5-H pz), 6.54 (s, 3H, 4-H pz);
Calcd for C10H10AgF6N6P: C, 25.72; H, 2.16; Found C, 24.73; H,
2.18.
Synthesis of {[HC(pz)3]Ag}(OTf) (7). This compound was
synthesized as above, using AgOTf (0.256 g, 1.00 mmol), to afford
0.392 g (83%) of solid identified as {[HC(pz)3]Ag}(OTf). 1H NMR
(acetone-d6): δ 9.30 (s, 1H, HC(pz)3), 8.24, 7.85 (s, s, 3,3H, 3,5-H
pz), 6.54 (s, 3H, 4-H pz); Calcd for C11H10AgF3N6O3S: C, 28.04;
H, 2.14; N, 17.84; Found C, 28.12; H, 2.53, N, 17.44.
Synthesis of {[HOCH2C(pz)3]Ag}(OTf) (4). This compound
was synthesized as above, using AgOTf (0.256 g, 1.00 mmol), to
afford 0.432 g (86%) of solid identified as {[HOCH2C(pz)3]Ag}-
(OTf). 1H NMR (acetone-d6): δ 7.91, 7.77 (d, d, J ) 1.5, 2.4 Hz,
3,3H, 3,5-H pz), 7.32 (m, 5H, C6H5), 6.52 (dd, 3H, J ) 1.5, J )
2.4 Hz, 4-H pz), 5.17 (s, 2H, OCH2C(pz)3), 4.65 (s, 2H, OCH2Ph);
Calcd for C12H12AgF3N6O4S: C, 28.76; H, 2.41; N, 16.77; Found
C, 28.32; H, 2.83, N, 17.14.
Synthesis of {[HC(pz)3]Ag}(BF4) (5). A THF (20 mL) solution
of L3 (0.214 g, 1 mmol) was added dropwise to a solution of AgBF4
(0.194 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 was washed with thf (2 × 10 mL) and then vacuum-
dried to afford 0.362 g (88%) of solid identified as {[HC(pz)3]Ag}-
(BF4). Crystallization of this compound from acetonitrile afforded
5. 1H NMR (acetone-d6): δ 9.29 (s, 1H, HC(pz)3), 8.25, 7.83 (s, s,
Crystallography. All crystals were mounted on thin glass fibers
with inert oil. After preliminary crystal quality, symmetry, and unit
cell parameter determination, a full sphere (1, 5, 6‚0.5[(CH3)2CO])
or a hemisphere (2‚0.5[(CH3)2CO], 3‚0.5[(CH3)2CO], 4, 7) of
X-ray intensity data was collected on a Bruker SMART APEX
CCD-based diffractometer (Mo KR radiation, λ ) 0.71073 Å).18
Raw area detector data frame integration and Lorentz/polarization
corrections were carried out with SAINT+.18 Final unit cell
parameters are based on the least-squares refinement of all
reflections with I > 5σ(I) from each data set. Direct methods
structure solution, difference Fourier calculations, and full-matrix
least-squares refinement against F2 were performed with SHELXTL
(18) SMART Version 5.624, SAINT+ Version 6.02a, and SADABS; Bruker
Analytical X-ray Systems, Inc.: Madison, WI, 1998.
(19) Sheldrick, G. M. SHELXTL Version 5.1; Bruker Analytical X-ray
Systems, Inc.: Madison, WI, 1997.
7768 Inorganic Chemistry, Vol. 45, No. 19, 2006

Crystal Engineering Based on Tris(pyrazolyl)methane Ligands
for all structures.19 Selected crystal and structure refinement data
can be found in Table 1.
Supporting Information Available: X-ray crystallographic files
in CIF format and details of crystal structure determination for all
compounds. This material is available free of charge via the Internet
at http://pubs.acs.org.
Acknowledgment. The financial support from the Na-
tional Science Foundation (CHE-0414239) is greatly ap-
preciated.
IC0606936
Inorganic Chemistry, Vol. 45, No. 19, 2006 7769