Silver(I) complexes of fixed, polytopic bis(pyrazolyl)methane ligands: Influence of ligand geometry on the formation of discrete metallacycles and coordination polymers

Article abstract of DOI:10.1021/ic0613053

Reactions of the arene-linked bis(pyrazolyl)methane ligands m-bis[bis(1-pyrazolyl)methyl]benzene, (m-[CH(pz)₂]₂C ₆H₄, L_m), p-bis[bis(1-pyrazolyl)methyl]benzene, (p-[CH(pz)₂]₂C₆H₄, L_p), and 1,3,5-tris[bis(1-pyrazolyl)methyl]benzene (1,3,5-[CH(pz)₂] ₃C₆H₃, L³) with AgX salts (pz = 1-pyrazolyl; X = BF₄^- or PF₆^-) yield two types of molecular motifs depending on the arrangement of the ligating sites about the central arene ring. Reactions of the m-phenylene-linked L _m with AgBF₄ and AgPF₆ afford complexes consisting of discrete, metallacyclic dications: [Ag₂(μ-L _m)₂]-(BF₄)₂ (1) and [Ag ₂(μ-L_m)₂](PF₆)₂ (2). When the p-phenylene-linked L_p is treated with AgBF₄ and AgPF₆, acyclic, cationic coordination polymers are obtained: {[Ag(μ-L_p)]BF₄}_∞ (3) and {[Ag(μ-L_p)]PF₆}_∞ (4). Reaction of the ligand L³, containing three bis(pyrazolyl)methane units in a meta arrangement, with an equimolar amount of AgBF₄ again yields discrete metallacyclic dications in which one bis(pyrazolyl)methane unit on each ligand remains unbound: [Ag₂(μ-L³)₂](BF ₄)₂ (5). Treatment of L³ with an excess of AgBF₄ affords a polymer of metallacycles, {[Ag₃(μ- L³)₂]-(BF₄)₃}_∞ (6), with one of the bis(pyrazolyl)methane units on each ligand bound to a silver cation bridging two metallacycles. The supramolecular structures of the silver(I) complexes 1-6 are organized by noncovalent interactions, including weak hydrogen bonding, π-π, and anion-π interactions.

Full text of DOI:10.1021/ic0613053

Inorg. Chem. 2006, 45, 10077−10087
Silver(I) Complexes of Fixed, Polytopic Bis(pyrazolyl)methane Ligands:
Influence of Ligand Geometry on the Formation of Discrete
Metallacycles and Coordination Polymers
Daniel L. Reger,* Russell P. Watson, and Mark D. Smith
Department of Chemistry and Biochemistry, UniVersity of South Carolina,
Columbia, South Carolina 29208
Received July 14, 2006
Reactions of the arene-linked bis(pyrazolyl)methane ligands m-bis[bis(1-pyrazolyl)methyl]benzene, (m-[CH(pz)2]2C6H4,
Lm), p-bis[bis(1-pyrazolyl)methyl]benzene, (p-[CH(pz)2]2C6H4, Lp), and 1,3,5-tris[bis(1-pyrazolyl)methyl]benzene (1,3,5-
-
[CH(pz)2]3C6H3, L3) with AgX salts (pz
)
1-pyrazolyl; X
)
BF4 or PF6-) yield two types of molecular motifs
depending on the arrangement of the ligating sites about the central arene ring. Reactions of the m-phenylene-
linked Lm with AgBF4 and AgPF6 afford complexes consisting of discrete, metallacyclic dications: [Ag2( -Lm)2]-
(BF4)2 (1) and [Ag2( -Lm)2](PF6)2 (2). When the p-phenylene-linked Lp is treated with AgBF4 and AgPF6, acyclic,
cationic coordination polymers are obtained:
µ
µ
{
[Ag(µ-Lp)]BF4}∞ (3) and {[Ag(µ-Lp)]PF6}∞ (4). Reaction of the ligand
L3, containing three bis(pyrazolyl)methane units in a meta arrangement, with an equimolar amount of AgBF4 again
yields discrete metallacyclic dications in which one bis(pyrazolyl)methane unit on each ligand remains unbound:
[Ag2(µ
-L3)2](BF4)2 (5). Treatment of L3 with an excess of AgBF4 affords a polymer of metallacycles,
{
[Ag3(
µ
-L3)2]-
(BF4)3
}
(6), with one of the bis(pyrazolyl)methane units on each ligand bound to a silver cation bridging two
∞
metallacycles. The supramolecular structures of the silver(I) complexes 1−6 are organized by noncovalent interactions,
including weak hydrogen bonding, π−π, and anion−π interactions.
Introduction
(pyrazolyl)methane compounds.5 Modification of the sub-
stituents on the pyrazolyl rings of the original poly(pyrazolyl)-
methane ligands reported by Trofimenko6 has led to a rich
coordination chemistry of the resulting “second-generation”
ligands.7 We have also been interested in the possibilities
afforded by functionalization at the carbon “backbone” to
which each pyrazolyl ring is attached. These poly(pyrazolyl)-
methane compounds have been designated as “third-genera-
tion” ligands.8 Many of our third-generation ligands are
Coordination compounds of silver(I) are frequently the
subject of studies that aim to design molecular and supramo-
lecular architectures with chemical and biological applica-
tions, such as molecular recognition and catalysis.1,2 The
range of stable coordination numbers and geometries adopted
by the silver(I) cation makes it possible to test a wide variety
of ligand systems,3 and the various factors that dictate the
final molecular and supramolecular structures have been
investigated in detail by several researchers.4 To expand upon
this body of knowledge using unique ligand systems, we are
actively exploring the coordination chemistry of poly-
(3) (a) Khlobystov, A. N.; Blake, A. J.; Champness, N. R.; Lemenovskii,
D. A.; Majouga, A. G.; Zyk, N. V.; Schro¨der, M. Coord. Chem. ReV.
2001, 222, 155. (b) Cortez, S. M.; Raptis, R. G. Coord. Chem. ReV.
1998, 169, 363.
* To whom correspondence should be addressed. E-mail: reger@
mail.chem.sc.edu.
(4) See, for example: (a) Piguet, C.; Bernardinelli, G.; Hopfgartner, G.
Chem. ReV. 1997, 97, 2005. (b) Blake, A. J.; Champness, N. R.;
Hubberstey, P.; Li, W. S.; Withersby, M. A.; Schroder, M. Coord.
Chem. ReV. 1999, 183, 117. (c) Batten, S. T.; Robson, R. Angew.
Chem., Int. Ed. Engl. 1998, 37, 1461. (d) Leininger, S.; Olenyuk, B.;
Stang, P. J. Chem. ReV. 2000, 100, 853. (e) Seidel, R. S.; Stang, P. J.
Acc. Chem. Res. 2002, 35, 972. (f) Sweigers, G. F.; Malefetse, T. J.
Chem. ReV. 2000, 100, 3483. (g) Zaworotko, M. J. Chem. Commun.
2001, 1. (h) Dong, Y.-B.; Cheng, J.-Y.; Huang, R.-Q.; Smith, M. D.;
zur Loye, H.-C. Inorg. Chem. 2003, 42, 5699. (i) Albrecht, M. Chem.
ReV. 2001, 101, 3457. (j) Reger, D. L.; Semeniuc, R. F.; Rassolov,
V.; Smith, M. D. Inorg. Chem. 2004, 43, 537 and references therein.
(k) Lin, R.; Yip, J. H. K. Inorg. Chem. 2006, 45, 4423.
(1) For recent examples, see: (a) Seidel, R. S.; Stang, P. J. Acc. Chem.
Res. 2002, 35, 972. (b) Fujita, M. Chem. Soc. ReV. 1998, 27, 417. (c)
Caulder, D. L.; Raymond, K. N. Acc. Chem. Res. 1999, 32, 975. (d)
Holliday, B. J.; Mirkin, C. A. Angew. Chem., Int. Ed. 2001, 40, 2022.
(e) Winpenny, R. E. P. J. Chem. Soc., Dalton Trans. 2002, 1. (f)
Yoshizawa, M.; Takeyama, Y.; Okana, T.; Fujita, M. J. Am. Chem.
Soc. 2003, 125, 3243. (g) Kusukawa, T.; Fujita, M. J. Am. Chem.
Soc. 2002, 124, 13576. (h) Reger, D. L.; Semeniuc, R. F.; Smith, M.
D. Inorg. Chem. 2003, 42, 8137 and references therein.
(2) (a) Lehn, J.-M. Supramolecular Chemistry: Concepts and Perspec-
tiVes; VCH: Weinheim, 1995. (b) Steed, J. W.; Atwood, J. L.
Supramolecular Chemistry; John Wiley: New York, 2001.
10.1021/ic0613053 CCC: $33.50
Published on Web 10/17/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 25, 2006 10077

Reger et al.
Figure 2. Representations of metallacyclic dimers (top) and infinite
coordination polymers (bottom).5a Red spheres are metal cations. Black lines
represent ligand molecules.
bottom). In addition to building predictable molecular
structures, another feature designed into these pyrazolyl-
based ligands is the potential for organization of complex
supramolecular structures through π-π and weak hydrogen-
bonding (including CH-π) interactions9 involving the pyra-
zolyl groups as well as the counterions.
Figure 1. Alkylidene-linked5a,b (upper left) and arene-linked5c,d third-
generation bis(pyrazolyl)methane ligands.
In general, more flexible ligands, such as the ethylene-
and propylene-linked compounds in Figure 1, provide limited
control over the molecular structures formed by the self-
assembly process. Tectons containing rigid components, on
the other hand, often restrict the types of products formed.2
We were interested in whether replacing the flexible alkyli-
dene linkers with arene spacers in our bis(pyrazolyl)methane
compounds would allow for the formation of similar dimeric
metallacycles while providing greater predictive power over
the resulting molecular and supramolecular architectures. The
advantage of using arene-linked ligands is that the distance
between bis(pyrazolyl)methane ligating sites is fixed, unlike
in the ethylene- and propylene-linked ligands, and this feature
adds rigidity to the overall system. Herein, we describe the
preparation and structural characterization of silver(I) com-
plexes of the arene-linked bis(pyrazolyl)methane ligands
m-[CH(pz)2]2C6H4 (Lm),5c p-[CH(pz)2]2C6H4 (Lp),5c and 1,3,5-
[CH(pz)2]3C6H3 (L3)5d (Figure 1).
polytopic in that two or more poly(pyrazolyl)methane units
are linked through the carbon backbone by organic spacers
of varying flexibilities and geometries, providing multiple
ligating sites.
Recently, we described a series of bitopic bis(pyrazolyl)-
methane ligands linked by alkylidene spacers, [CH(pz)2]2-
(CH2)n (pz ) 1-pyrazolyl; n ) 1-3; Figure 1).5a,b Using the
coordinatively flexible silver(I) cation, we showed how these
ligands, regardless of spacer size, consistently direct the
formation of discrete metallacyclic dimers of the type
illustrated in Figure 2 (top) when weakly coordinating anions
-
-
are used (BF4 , SO3CF3 ). The more strongly coordinating
-
NO3 , however, shifts the preferred molecular arrangement
from discrete cyclic structures to acyclic species, particularly
infinite one-dimensional coordination polymers (Figure 2,
(5) (a) Reger, D. L.; Watson, R. P.; Gardinier, J. R.; Smith, M. D. Inorg.
Chem. 2004, 43, 6609. (b) Reger, D. L.; Gardinier, J. R.; Semeniuc,
R. F.; Smith, M. D. J. Chem. Soc., Dalton Trans. 2003, 1712. (c)
Reger, D. L.; Watson, R. P.; Smith, M. D.; Pellechia, P. J. Organo-
metallics 2005, 24, 1544. (d) Reger, D. L.; Watson, R. P.; Smith, M.
D.; Pellechia, P. J. Organometallics 2006, 25, 743. (e) Reger, D. L.;
Gardinier, J. R.; Grattan, T. C.; Smith, M. R.; Smith, M. D. New J.
Chem. 2003, 27, 1670. (f) Reger, D. L.; Semeniuc, R. F.; Smith, M.
D. J. Organomet. Chem. 2003, 666, 87. (g) Reger, D. L.; Brown, K.
J.; Smith, M. D. J. Organomet. Chem. 2002, 658, 50. (h) Reger, D.
L.; Wright, T. D.; Semeniuc, R. F.; Grattan, T. C.; Smith, M. D. Inorg.
Chem. 2001, 40, 6212. (i) Reger, D. L.; Brown, K. J.; Gardinier, J.
R.; Smith, M. D. Organometallics 2003, 22, 4973. (j) Reger, D. L.;
Gardinier, J. R.; Smith, M. D. Polyhedron 2004, 23, 291.
(6) (a) Trofimenko, S. Scorpionates: The Coordination Chemistry of
Polypyrazolylborate Ligands; Imperial College: London, 1999. (b)
Trofimenko, S. Chem. ReV. 1993, 93, 943. (c) Pettinari, C.; Santini,
C. ComprehensiVe Coordination Chemistry II; McCleverty, J. A.,
Meyer, T. J., Eds.; Elsevier: Oxford, 2004; Vol. 1, p 159. (d) Reger,
D. L. Comments Inorg. Chem. 1999, 21, 1. (d) Bigmore, H. R.;
Lawrence, S. C.; Mountford, P.; Tredget, C. S. Dalton Trans. 2005,
635. (e) Buyers, P. K.; Canty, A. J.; Honeyman, R. T. AdV. Organomet.
Chem. 1992, 34, 1. (f) Long, G. J.; Grandjean, F.; Reger, D. L. Top.
Curr. Chem. 2004, 233, 91.
Experimental Section
General Considerations. Air-sensitive materials were handled
under a nitrogen atmosphere using standard Schlenk techniques or
in a Vacuum Atmospheres HE-493 drybox. All solvents were dried
(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.; Bakbak, S.;
Semeniuc, R. F.; Bunz, U. H. F.; Smith, M. D. New J. Chem. 2005,
29, 1035. (c) White, D.; Faller, J. W. J. Am. Chem. Soc. 1982, 104,
1548. (d) Brock, C. P.; Das, M. K.; Minton, R. P.; Niedenzu, K. J.
Am. Chem. Soc. 1988, 110, 817. (e) Janiak, C.; Braun, L.; Girgsdies,
F. J. Chem. Soc., Dalton Trans. 1999, 3133. (f) Kisko, J. L.; Hascall,
T.; Kimblin, C.; Parkin, G. J. Chem. Soc., Dalton Trans. 1999, 1929.
(g) Hardin, N. C.; Jeffrey, J. C.; McCleverty, J. A.; Rees, L. H.; Ward,
M. A. New J. Chem. 1998, 22, 661. (h) Niedenzu, K.; Trofimenko, S.
Inorg. Chem. 1985, 24, 4222. (i) Ja¨kle, F.; Polborn, K.; Wagner, M.
Chem. Ber. 1996, 129, 603. (j) Fabrizi de Biani, F.; Ja¨kle, F.; Spiegler,
M.; Wagner, M.; Zanello, P. Inorg. Chem. 1997, 36, 2103. (k)
Herdtweck, E.; Peters, F.; Scherer, W.; Wagner, M. Polyhedron 1998,
17, 1149. (l) Guo, S. L.; Peters, F.; Fabrizi de Biani, F.; Bats, J. W.;
Herdtweck, E.; Zanello, P.; Wagner, M. Inorg. Chem. 2001, 40, 4928.
(m) Guo, S. L.; Bats, J. W.; Bolte, M.; Wagner, M. J. Chem. Soc.,
Dalton Trans. 2001, 3572. (n) Bieller, S.; Zhang, F.; Bolte, M.; Bats,
J. W.; Lerner, H.-W.; Wagner, M. Organometallics 2004, 23, 2107.
(7) (a) Pettinari, C.; Pettinari, R. Coord. Chem. ReV. 2005, 249, 525. (b)
Pettinari, C.; Pettinari, R. Coord. Chem. ReV. 2005, 249, 663. (c) Reger,
D. L.; Grattan, T. C.; Brown, K. J.; Little, C. A.; Lamba, J. J. S.;
Rheingold, A. L.; Sommer, R. D. J. Organomet. Chem. 2000, 607,
120. (d) Julia, S.; del Mazo, J. M.; Avila, L.; Elguero, J. Org. Prep.
Proc. Int. 1984, 16, 299.
10078 Inorganic Chemistry, Vol. 45, No. 25, 2006

SilWer(I) Complexes of Bis(pyrazolyl)methane Ligands
1
by conventional methods prior to use. The compounds m-[CH-
(pz)2]2C6H4,5c p-[CH(pz)2]2C6H4,5c and 1,3,5-[CH(pz)2]3C6H35d were
prepared following reported procedures. All other chemicals were
purchased from Aldrich or Fisher Scientific and used as received.
Reported melting points are uncorrected. IR spectra were obtained
on a Nicolet 5DXBO FTIR spectrometer. NMR spectra were
recorded on a Varian Mercury/VX 300 or 400 spectrometer. All
chemical shifts are in ppm. 1H NMR spectra were secondary
referenced using the signals from residual undeuterated solvents.
19F NMR spectra were externally referenced to CFCl3. Mass
spectrometric measurements were obtained on a MicroMass QTOF
spectrometer. Elemental analyses were performed on vacuum-dried
samples by Robertson Microlit Laboratories (Madison, NJ).
Syntheses of Silver Complexes. Silver complexes 1-4 were
prepared by the following general procedure: To a foil-covered,
10-mL THF solution of AgBF4 (0.070 g, 0.36 mmol) or AgPF6
(0.080 g, 0.32 mmol) was added by cannula an equimolar, 15-mL
THF solution of m-C6H4[CH(pz)2]2 (Lm) or p-C6H4[CH(pz)2]2 (Lp).
A white precipitate immediately formed. After stirring in the dark
for 3-5 h, the solvent was removed in vacuo and the remaining
white solid was washed with 5 mL of THF and dried in vacuo
overnight. Crystals for elemental analyses, grown by vapor diffusion
of Et2O into 1-mL CH3CN (acetone for 1) solutions of the solids,
were isolated by filtration, rinsed with Et2O, and dried in vacuo.
X-ray-quality crystals were grown in the same manner and taken
directly from the mother liquor.
The silver complexes 5 and 6 were prepared by dissolving a
mixture of 1,3,5-[CH(pz)2]3C6H3 (L3, 0.050 g, 0.097 mmol) and
AgBF4 (0.019 g, 0.098 mmol for 5; 0.057 g, 0.29 mmol for 6) in
a minimum amount of CH3CN and allowing Et2O to diffuse into
1-mL portions of the resulting solutions. Crystals formed within 2
days. Crystals for X-ray analysis were taken directly from the
mother liquor. All other crystals for characterization were isolated
by filtration, rinsed with Et2O, and dried in vacuo.
[Ag2(µ-m-[CH(pz)2]2C6H4)2](BF4)2 (1). Yield ) 0.15 g (65%).
Mp > 300 °C. Anal. Calcd for C40H36Ag2B2F8N16: C, 42.51; H,
3.21; N, 19.83. Found: C, 42.56; H, 2.99; N, 19.77. IR (KBr, cm-1):
3150, 3134, 2987, 1520, 1454, 1070, 825, 760, 519. 1H NMR (400
MHz, CD3CN): δ 7.81 (dd, J ) 0.6, 2.6 Hz, 4 H, 5/3-pz), 7.80 (s,
2 H, CH(pz)2), 7.55 (d, J ) 2.0 Hz, 4 H, 5/3-pz), 7.40 (t, J ) 7.8
Hz, 1 H, C6H4), 6.89 (d, J ) 7.6 Hz, 2 H, C6H4), 6.37 (t, J ) 2.2
Hz, 4 H, 4-pz), 6.23 (s, 1 H, C6H4). 19F NMR (376 MHz, CD3-
CN): δ -152. MS ESI(+) m/z (rel. % abund.) [assgn]: 1043 (10)
[Ag2(Lm)2BF4]+, 847 (30) [Ag(Lm)2]+, 479 (100) [AgLm]+, 371 (65)
[HLm]+, 303 (80) [Lm - pz]+.
3126, 3109, 1516, 1446, 1401, 1287, 1099, 1050, 796, 764. H
NMR (400 MHz, CD3CN): δ 7.82 (s, 2 H, CH(pz)2), 7.79 (d, J )
2.4 Hz, 4 H, 5/3-pz), 7.55 (d, J ) 1.6 Hz, 4 H, 5/3-pz), 6.87 (s, 4
H, C6H4), 6.38 (t, J ) 2.2 Hz, 4 H, 4-pz).19F NMR (376 MHz,
CD3CN): δ -152. MS ESI(+) m/z (rel. % abund.) [assgn]: 847
(35) [Ag(Lp)2]+, 477 (50) [AgLp]+, 371 (45) [HLp]+, 303 (100)
[Lp - pz]+.
{[Ag(µ-p-[CH(pz)2]2C6H4)]PF6}∞ (4). Yield ) 0.16 g (82%).
Mp > 300 °C. Anal. Calcd for C21H19.5AgF6N8.5P (4‚0.5CH3CN):
C, 39.18; H, 3.06; N, 18.49. Found: C, 39.17; H, 2.71; N, 18.43.
IR (KBr, cm-1): 3146, 1446, 1397, 1295, 1095, 1050, 845, 760,
559. 1H NMR (400 MHz, CD3CN): δ 7.82 (s, 2 H, CH(pz)2), 7.78
(d, J ) 2.0 Hz, 4 H, 5/3-pz), 7.56 (d, J ) 1.2 Hz, 4 H, 5/3-pz),
6.89 (s, 4 H, C6H4), 6.38 (t, J ) 2.2 Hz, 4 H, 4-pz).19F NMR (376
MHz, CD3CN): δ -73 (d, JF-P ) 706 Hz). MS ESI(+) m/z (rel.
% abund.) [assgn]: 847 (40) [Ag(Lp)2]+, 477 (80) [AgLp]+, 371
(50) [HLp]+, 303 (100) [Lp - pz]+.
[Ag2(µ-1,3,5-[CH(pz)2]3C6H3)2](BF4)2 (5). Yield ) 0.040 g
(58%). Mp > 300 °C. Anal. Calcd for C54H48Ag2B2F8N24: C, 45.59;
H, 3.40; N, 23.63. Found: C, 45.43; H, 3.49; N, 23.35. IR (KBr,
cm-1): 3142, 3121, 3109, 3011, 2983, 1520, 1462, 1442, 1393,
1058, 784, 756, 523.1H NMR (300 MHz, CD3CN): δ 7.75 (s, 3
H, CH(pz)2), 7.68 (dd, J ) 0.6, 2.7 Hz, 6 H, 5/3-pz), 7.50 (d, J )
1.5 Hz, 6 H, 5/3-pz), 6.46 (d, J ) 0.6 Hz, 3 H, C6H3), 6.32 (dd, J
) 1.8, 2.4 Hz, 6 H, 4-pz). 19F NMR (376 MHz, CD3CN): δ -152.
MS ESI(+) m/z (rel. % abund.) [assgn]: 1335 (1) [Ag2(L3)2(BF4)]+,
1139 (20) [Ag(L3)2]+, 625 (100) [AgL3]+, 517 (55) [HL3]+, 449
(40) [L3 - pz]+. HRMS: ESI(+) (m/z) calcd for C54H48Ag2BF4N24,
[Ag2(L3)2(BF4)]+ 1335.2635, found 1335.2595.
{[Ag3(µ-1,3,5-[CH(pz)2]3C6H3)2](BF4)3}∞ (6). Yield ) 0.070 g
(89%). Mp > 300 °C. Anal. Calcd for C54H48Ag3B3F12N24: C,
40.11; H, 2.99; N, 20.79. Found: C, 40.33; H, 3.03; N, 21.11. IR
(KBr, cm-1): 3126, 2974, 1524, 1401, 1303, 1074, 788, 768, 514.1H
NMR (300 MHz, CD3CN): δ 7.74 (s, 3 H, CH(pz)2), 7.71 (dd, J
) 0.6, 2.7 Hz, 6 H, 5/3-pz), 7.49 (dd, J ) 0.6, 2.1 Hz, 6 H, 5/3-
pz), 6.39 (s, 3 H, C6H3), 6.32 (dd, J ) 1.8, 2.4 Hz, 6 H, 4-pz). 19
F
NMR (376 MHz, CD3CN): δ -152. MS ESI(+) m/z (rel. %
abund.) [assgn]: 1531 (1) [Ag3(L3)2(BF4)2]+, 1335 (10) [Ag2(L3)2-
(BF4)]+, 1139 (10) [Ag(L3)2]+, 625 (100) [AgL3]+, 517 (15) [HL3]+,
449 (15) [L3 - pz]+.
Crystal Structure Determinations. X-ray intensity data from
a colorless hexagonal, rod-shaped crystal of 1‚2(CH3)2CO‚0.43H2O,
a colorless plate of 2, a colorless bar-shaped crystal of 3, a colorless
needle of 4‚0.5CH3CN, and colorless prisms of 5 and 6‚2CH3CN
were measured at 150(1) K (200(1) K for 3) on a Bruker SMART
APEX CCD-based diffractometer (Mo KR radiation, λ ) 0.71073
Å).10 Raw data frame integration and Lp corrections were performed
with SAINT+.10 Final unit cell parameters were determined by
least-squares refinement of 2905, 5652, 4331, 7064, 7531, and 8971
strong reflections for 1-6, respectively. Analyses of the data
showed negligible crystal decay during data collection. Direct
methods structure solution, difference Fourier calculations, and full-
matrix least-squares refinement against F2 were performed with
SHELXTL.11 All non-hydrogen atoms were refined with anisotropic
displacement parameters except where noted. Hydrogen atoms were
placed in geometrically idealized positions and included as riding
atoms. Details of the data collections are given in Table 1, while
[Ag2(µ-m-[CH(pz)2]2C6H4)2](PF6)2 (2). Yield ) 0.15 g (76%).
Mp > 300 °C. Anal. Calcd for C40H36Ag2F12N16P2: C, 38.54; H,
2.91; N, 17.98. Found: C, 38.83; H, 2.68; N, 18.32. IR (KBr, cm-1):
3150, 3134, 1520, 1446, 1401, 1295, 1103, 837, 760, 555. 1H NMR
(400 MHz, CD3CN): δ 7.79 (s, 2 H, CH(pz)2) 7.75 (d, J ) 2.0
Hz, 4 H, 5/3-pz), 7.54 (d, J ) 1.6 Hz, 4 H, 5/3-pz), 7.40 (t, J )
7.8 Hz, 1 H, C6H4), 6.94 (dd, J ) 2.0, 7.6 Hz, 2 H, C6H4), 6.38 (br
s, 1 H, C6H4) 6.35 (t, J ) 2.2 Hz, 4 H, 4-pz). 19F NMR (376 MHz,
CD3CN): δ -73 (d, JF-P ) 706 Hz). MS ESI(+) m/z (rel. %
abund.) [assgn]: 1101 (20) [Ag2(Lm)2PF6]+, 847 (30) [Ag(Lm)2]+,
479 (100) [AgLm]+, 371 (50) [HLm]+, 303 (60) [Lm - pz]+.
{[Ag(µ-p-[CH(pz)2]2C6H4)]BF4}∞ (3). Yield ) 0.19 g (95%).
Mp > 300 °C. Anal. Calcd for C20H18AgBF4N8: C, 42.51; H, 3.21;
N, 19.83. Found: C, 42.50; H, 2.94; N, 20.07. IR (KBr, cm-1):
(10) SMART, Version 5.630; Bruker Analytical X-ray Systems, Inc.:
Madison, WI, 2003. SAINT+, Version 6.45; Bruker Analytical X-ray
Systems, Inc.: Madison, WI, 2003.
(11) Sheldrick, G. M. SHELXTL, Version 6.1; Bruker Analytical X-ray
Systems, Inc.: Madison, WI, 2000.
(9) For examples, see: (a) Desiraju, G. R. Acc. Chem. Res. 2002, 35,
565. (b) Steiner, T. Angew. Chem., Int. Ed. 2002, 41, 48. (c) Cited
papers in reference in 4j. (d) Rowland, R. S.; Taylor, R. J. Phys. Chem.
1996, 100, 7384.
Inorganic Chemistry, Vol. 45, No. 25, 2006 10079

Reger et al.
Table 1. Crystal Data and Refinement Details for [Ag2(µ-m-[CH(pz)2]2C6H4)2](BF4)2‚2(CH3)2CO‚0.43H2O (1‚2(CH3)2CO‚0.43H2O),
[Ag2(µ-m-[CH(pz)2]2C6H4)2](PF6)2 (2), {[Ag(µ-p-[CH(pz)2]2C6H4)]BF4}∞ (3), {[Ag(µ-p-[CH(pz)2]2C6H4)2]PF6‚0.5CH3CN}∞ (4‚0.5CH3CN),
[Ag2(µ-1,3,5-[CH(pz)2]3C6H3)2](BF4)2 (5), and [Ag3(µ-1,3,5-[CH(pz)2]3C6H3)2](BF4)3‚2CH3CN (6‚2CH3CN)
1‚2(CH3)2CO‚0.43H2O
2
3
4‚0.5CH3CN
5
6‚2CH3CN
empirical formula
C46H48.85Ag2B2F8N16O2. 43 C40H36Ag2F12N16P2 C20H18AgBF4N8
C21H19.50AgF6N8.50
P
C54H48Ag2B2F8N24 C58H54Ag3B3F12 N26
fw
T (K)
cryst syst
space group
a, Å
b, Å
c, Å
1254.05
150(1)
trigonal
R3h
31.1829(7)
31.1829(7)
14.4581(7)
90
90
120
12175.2(7)
9
1246.53
150(1)
monoclinic
P21/c
10.4689(5)
13.7249(6)
16.8065(8)
90
102.5020(10)
90
565.10
200(1)
triclinic
P1h
9.1941(4)
11.7500(5)
11.8114(5)
60.5720(10)
85.6080(10)
86.0190(10)
1107.35(8)
2
643.79
150(1)
1422.52
150(1)
orthorhombic
Pbca
16.3200(8)
16.8460(8)
21.6388(10)
90
90
90
5949.1(5)
4
1699.31
150(1)
triclinic
P1h
12.2901(6)
14.7478(7)
20.6296(10)
70.6900(10)
83.0950(10)
85.5340(10)
3500.3(3)
2
monoclinic
P21/n
19.4787(9)
11.9258(6)
21.3614(10)
90
96.6930(10)
90
4928.4(4)
8
R, deg
â, deg
γ, deg
V, Å3
2357.58(19)
2
Z
D (calcd), Mg‚m-3
abs coeff, mm-1
cryst size, mm3
final R indices [I > 2σ(I)]
R1
1.539
0.806
0.46 × 0.16 × 0.10
1.756
0.997
1.695
0.970
1.735
0.958
1.588
0.744
1.612
0.922
0.18 × 0.12 × 0.04 0.20 × 0.12 × 0.08 0.46 × 0.14 × 0.10 0.34 × 0.22 × 0.14 0.44 × 0.38 × 0.35
0.0448
0.1009
0.0448
0.0757
0.0392
0.0962
0.0346
0.0757
0.0407
0.1043
0.0308
0.0863
wR2
further notes regarding the solution and refinement for all six
structures follow.
the intensity data. The asymmetric unit contains two Ag centers,
one complete p-[CH(pz)2]2C6H4 ligand and one-half each of two
additional p-[CH(pz)2]2C6H4 ligands (both on inversion centers),
two independent PF6 anions, and one acetonitrile molecule of
crystallization.
The compound 1‚2(CH3)2CO‚0.43H2O crystallizes in the trigonal/
rhombohedral crystal system. The pattern of systematic absences
in the intensity data positively ruled out a c-glide symmetry
operation; the space group R3h was eventually confirmed by the
successful solution and refinement of the data. The asymmetric unit
consists of one-half of a [Ag2(µ-m-[CH(pz)2]2C6H4)2]2+ cation
located on an inversion center, one BF4- anion, an acetone molecule
of crystallization, and two partially occupied water molecule sites.
Thorough understanding of the full crystal structure and composition
is hampered by disorder. The acetone molecule is disordered over
two orientations. Occupancies were initially refined and subse-
quently fixed near the final refined values. These atoms were
assigned a common isotropic displacement parameter. There are
two isolated electron density peaks which were modeled as water
molecules O3S and O4S. These two atoms were given a fixed
isotropic displacement parameter and their occupancies refined. No
hydrogen atoms were located or refined for these atoms. Elongated
-
Compound 5 crystallizes in the orthorhombic space group Pbca
as determined uniquely by the pattern of systematic absences in
the intensity data. The asymmetric unit contains one Ag center,
-
one ligand, and one BF4 counterion.
The compound 6‚2CH3CN crystallizes in the triclinic system.
The space group P1h was confirmed by the successful solution and
refinement of the data. The asymmetric unit contains three Ag
centers, three BF4- counterions, two complete 1,3,5-[CH(pz)2]3C6H3
ligands, two identifiable acetonitrile molecules of crystallization,
and a region of disordered solvent which could not be modeled
successfully. The contribution of the solvent was removed from
the structure factor calculations with the Squeeze program in
PLATON (165.1 Å3 solvent-accessible void volume centered at 0,
1/2, 1/2; 38 e-/cell).12 The final tabulated fw, d(calcd), and F(000)
do not include the unknown solvent species.
-
displacement ellipsoids of the fluorine atoms of the BF4 anion
indicate mild disorder of this group, which was not modeled. The
large average displacement parameters for the BF4- anion and for
the disordered species and the presence of several residual electron
density peaks in the disorder regions indicate the limitations of the
model employed.
Results
Syntheses and Characterization. Combining separate
-
-
THF solutions of AgX (X ) BF4 , PF6 ) and m-[CH-
(pz)2]2C6H4 (Lm) resulted in the precipitation of complexes
[Ag2(µ-m-[CH(pz)2]2C6H4)2](BF4)2 (1) and [Ag2(µ-m-[CH-
(pz)2]2C6H4)2](PF6)2 (2) according to eq 1. Similarly, com-
bination of THF solutions of AgX and p-[CH(pz)2]2C6H4 (Lp)
gave white precipitates of the complexes {Ag(µ-p-[CH-
(pz)2]2C6H4)]BF4}∞ (3) and {[Ag(µ-p-[CH(pz)2]2C6H4)]PF6}∞
(4) as given in eq 2. Elemental analyses of 1-4 were
consistent with the empirical formulas [AgL]X (L ) Lm or
Lp; X ) BF4 or PF6 ). X-ray crystallographic analyses,
discussed below, confirmed that complexes of Lm (1 and 2)
exist as discrete metallacyclic dimers and that complexes of
Lp (3 and 4), in contrast, form simple (acyclic) coordination
polymers.
Compound 2 crystallizes in the space group P21/c as determined
uniquely by the pattern of systematic absences in the intensity data.
The asymmetric unit contains one-half of a discrete [Ag2(µ-m-[CH-
-
(pz)2]2C6H4)2]2+ cation located on an inversion center and one PF6
anion.
Compound 3 crystallizes in the triclinic system. The space group
P1h was confirmed by the successful solution and refinement of the
structure. The asymmetric unit consists of one Ag atom, one-half
each of two independent p-[CH(pz)2]2C6H4 ligands, both located
-
-
-
on inversion centers, and a disordered BF4 anion. A reasonable
and stable disorder model involving three components was refined
for the anion. Occupancies of the three components were refined
but constrained to sum to unity. A total of 31 distance restraints
were used to maintain chemically reasonable B-F and F-F
distances. All non-hydrogen atoms were refined with anisotropic
displacement parameters except the anion atoms (isotropic).
The compound 4‚0.5CH3CN crystallizes in the space group P21/n
as determined uniquely by the pattern of systematic absences in
(12) PLATON/PLUTON: (a) Spek, A. L. Acta Crystallogr., Sect. A 1990,
46, C34. (b) Spek, A. L. PLATON, A Multipurpose Crystallographic
Tool; Utrecht University: Utrecht, The Netherlands, 1998.
10080 Inorganic Chemistry, Vol. 45, No. 25, 2006

SilWer(I) Complexes of Bis(pyrazolyl)methane Ligands
2AgX + 2Lm f [Ag2(µ-Lm)2]X2, X ) BF4- (1), PF6- (2)
(1)
AgX + Lp f {[Ag(µ-Lp)]X}∞, X ) BF4- (3), PF6- (4) (2)
Dissolving equimolar amounts of AgBF4 and 1,3,5-[CH-
(pz)2]3C6H3 (L3) together in acetonitrile and allowing ether
to slowly diffuse into these solutions yielded crystals of [Ag2-
(µ-1,3,5-[CH(pz)2]3C6H3)2](BF4)2 (5, eq 3). Analysis of
complex 5 indicated an empirical formula [AgL3]BF4 with
a one-to-one silver-to-ligand ratio. X-ray crystallographic
studies of 5 confirmed the presence of discrete metallacyclic
dications in which one bis(pyrazolyl)methane unit on each
ligand in the metallacycle is unbound. When L3 and an excess
of AgBF4 were dissolved in acetonitrile and ether was
allowed to slowly diffuse into these solutions, compound
{[Ag3(µ-1,3,5-[CH(pz)2]3C6H3)2](BF4)3}∞ (6) was obtained
(eq 4). Analysis of 6 yielded an empirical formula corre-
sponding to a three-to-two silver-to-ligand ratio, and crystal-
lographic studies revealed that 6 consists of a polymer of
metallacycles resulting from coordination of the third bis-
(pyrazolyl)methane unit on each ligand to an additional silver
cation.
Figure 3. ORTEP drawing of the cationic unit in [Ag2(µ-m-[CH-
(pz)2]2C6H4)2](BF4)2‚2(CH3)2CO‚0.43H2O (1‚2(CH3)2CO‚0.43H2O). Dis-
placement ellipsoids are drawn at the 30% probability level. The complex
[Ag2(µ-m-[CH(pz)2]2C6H4)2](PF6)2 (2) contains analogous cations. Selected
bond distances (Å) and angles (deg) for 1‚2(CH3)2CO‚0.43H2O: Ag(1)-
N(11) 2.366(4), Ag(1)-N(21) 2.247(4), Ag(1)-N(31a) 2.382(4), Ag(1)-
N(41a) 2.239(4); N(11)-Ag(1)-N(21) 85.47(14), N(11)-Ag(1)-N(31a)
111.59(13), N(11)-Ag(1)-N(41a) 112.81(14), N(21)-Ag(1)-N(31a) 106.94-
(14), N(21)-Ag(1)-N(41a) 152.27(14), N(31a)-Ag(1)-N(41a) 86.22(14).
Selected bond distances (Å) and angles (deg) for 2: Ag(1)-N(11) 2.373-
(4), Ag(1)-N(21) 2.235(3), Ag(1)-N(31a) 2.238(4), Ag(1)-N(41a) 2.424-
(4); N(11)-Ag(1)-N(21) 84.89(13), N(11)-Ag(1)-N(31a) 111.34(12),
N(11)-Ag(1)-N(41a) 102.61(12), N(21)-Ag(1)-N(31a) 158.54(13), N(21)-
Ag(1)-N(41a) 106.64(12), N(31a)-Ag(1)-N(41a) 84.11(13).
2AgBF4 + 2L3 f [Ag2(µ-L3)2](BF4)2 (5)
3AgBF4 + 2L3 f {[Ag3(µ-L3)2](BF4)3}∞ (6)
(3)
(4)
consistent with previously studied poly(pyrazolyl)methane
complexes of silver(I).4j,5a,b Infrared spectra of all six
compounds showed the expected B-F and P-F stretching
The positive-ion electrospray (ESI(+)) mass spectra of the
complexes derived from Lm, 1 and 2, contained peaks
corresponding to dimeric metallacycles associated with one
counterion, [Ag2(Lm)2(BF4)]+ or [Ag2(Lm)2(PF6)]+. A peak
corresponding to the free dication, however, was not
observed for either compound. Instead, the monocation
[AgLm]+, whose peak pattern is distinct from that of the free
dicationic dimer, gave rise to the base peak in the spectra of
both 1 and 2. As opposed to complexes of Lm, complexes
of Lp, 3 and 4, showed no peaks corresponding to dimers as
observed for 1 and 2. The remaining features of the spectra
of 3 and 4, including the presence of the peak from [AgLp]+,
were identical to those observed in the spectra of 1 and 2
with the exception that the base peaks for 3 and 4 were due
to the species formed by loss of one pyrazolyl group from
the free ligand, [Lp - pz]+, rather than the monocation
[AgLp]+. The ESI(+) mass spectrum of 5 also showed the
respective dimeric metallacycle, [Ag2(L3)2(BF4)]+, as well
as the monocation [AgL3]+. The spectrum of 6 was identical
except that it also displayed a peak resulting from association
of an additional AgBF4 equivalent, namely, [Ag3(L3)2-
(BF4)2]+. Spectra of all six compounds exhibited a peak due
to the silver cation bound to two ligands, [AgL2]+.
-
frequencies (ca. 1070 and 777 cm-1 for BF4 and ca. 865
-
cm-1 for PF6 ).13
Solid-State Structures. (a) Complexes of Bitopic
Ligands: Metallacycles. The crystalline forms of [Ag2(µ-
m-[CH(pz)2]2C6H4)2](BF4)2 (1), which crystallizes with two
molecules of acetone and trace water, and [Ag2(µ-m-[CH-
(pz)2]2C6H4)2](PF6)2 (2) exist in the solid state as discrete
metallacycles where two ligand molecules are each bridging
two silver cations. An ORTEP representation of the dicationic
macrocycle in 1‚2(CH3)2CO‚0.43H2O is shown in Figure 3.
The dication in 2 is analogous, and the cations of both 1
and 2 lie on inversion centers. The environment about the
silver ions is distorted tetrahedral with the chelate ring bite
imposing N-Ag-N angles of 85° and 86° for 1‚2(CH3)2-
CO‚0.43H2O and 84° and 85° for 2. Silver-nitrogen bond
lengths for both complexes are typical but asymmetric with
most values falling between 2.24 and 2.38 Å. Compound 2
possesses a longer Ag-N distance of 2.42 Å. The Ag‚‚‚Ag
distances across the argentacycles are 5.31 and 4.83 Å for
1‚2(CH3)2CO‚0.43H2O and 2.
-
The packing of the argentacycles and the BF4 anions in
1‚2(CH3)2CO‚0.43(H2O) is governed by CH-F hydrogen-
bonding interactions, the most prominent of which give rise
to infinite one-dimensional ribbons running along the c-axis
direction. This primary linkage involves both of the unique
Proton NMR spectra of all six complexes in acetonitrile
showed only one set of ligand signals, shifted downfield of
those of the respective free ligand. Since the complexes,
particularly those consisting of metallacycles, are expected
to show nonequivalence of ligand protons, the silver com-
plexes must be labile in solution and undergo ligand
exchange that is rapid on the NMR time scale. This result is
-
methine hydrogen atoms (H(1) and H(2)) and two BF4
anions, which are sandwiched between two argentacycles
(13) Nakamoto, K. Infrared and Raman Spectra of Inorganic Coordination
Compounds, 4th ed.; John Wiley: New York, 1986.
Inorganic Chemistry, Vol. 45, No. 25, 2006 10081

Reger et al.
Figure 6. View down the b axis of 2 showing π-π stacking (red dashed
lines) of parallel sheets of metallacycles and embedded layers of PF6- anions
participating in anion-π interactions (black dashed lines).
Figure 4. Illustrations of the extended structure of 1‚2(CH3)2CO‚0.43H2O.
(Left) View perpendicular to two adjacent 1-D ribbons (vertical). CH-F
hydrogen bonds which link the argentacycles into ribbons are shown as
black dashed bonds; those which link the individual ribbons are shown in
green. (Right) Perspective view down the c-axis direction parallel to six
1-D ribbons. Hydrogen atoms and solvent molecules are omitted, and CH-F
interactions are not indicated.
Figure 7. ORTEP drawing of the cationic coordination polymer in {[Ag-
(µ-p-[CH(pz)2]2C6H4)]BF4}∞ (3). Displacement ellipsoids are drawn at the
30% probability level. Selected bond distances (Å) and angles (deg): Ag-
(1)-N(11) 2.300(3), Ag(1)-N(21) 2.339(3), Ag(1)-N(31) 2.282(3), Ag-
(1)-N(41) 2.391(3); N(11)-Ag(1)-N(21) 81.28(11), N(11)-Ag(1)-N(31)
148.42(12), N(11)-Ag(1)-N(41) 106.03(1), N(21)-Ag(1)-N(31) 117.15-
(11), N(21)-Ag(1)-N(41) 132.36(11), N(31)-Ag(1)-N(41) 81.05(11).
Figure 5. View of a sheet in the bc plane of 2 organized by CH-π
interactions (purple dashed lines).
(CH-F distances 2.05 and 2.20 Å; Figure 4, left). Longer
CH-F (2.4-2.5 Å) interactions between pyrazolyl ring
hydrogen atoms serve to aggregate the individual ribbons
into a distinct three-dimensional honeycomb structure, one
“cell” of which is shown in Figure 4 (right). The cells caused
-
The PF6 anions in 2, which exist in layers embedded
-
between the sheets, take part in both CH-F and anion-π
interactions that support the π-π stacking shown in Figure
6 by bridging the parallel sheets of argentacycles. The CH-F
bonds (not shown) are in the range of 2.2-2.5 Å and include
hydrogen-atom acceptors from the pyrazolyl rings, methine
hydrogen atoms on the -CH(pz)2 units, and the central ligand
arene ring. Only one of the two sets of anion-π interactions
is illustrated in Figure 6. These interactions are long with
F-centroid distances of 3.31 and 3.46 Å and shortest F-ring
distances of 3.27 and 3.35 Å. In both sets of anion-π
interactions, the more π-acidic pyrazolyl rings, rather than
the linking arene rings, act as the electron-pair acceptors.
(b) Complexes of Bitopic Ligands: Coordination Poly-
mers. Both AgBF4 and AgPF6 complexes of the p-phenylene-
linked, bitopic ligand p-[CH(pz)2]2C6H4, 3 and 4, crystallize
as acyclic coordination polymers (Figures 7 and 8). The
asymmetric unit of 3 comprises one silver cation, one-half
each of two independent ligand molecules, and a disordered
by the honeycomb arrangement of argentacycles and BF4
ions are channels extending along the c-axis direction, and
they contain the disordered acetone and water molecules (not
pictured).
The structure of 2 is replete with significant noncovalent
interactions. The supramolecular three-dimensional frame-
work of 2 consists of parallel sheets of argentacycles in the
bc plane that stack along the a axis. As shown in Figure 5,
the planes of argentacycles are organized by CH-π interac-
tions between pyrazolyl hydrogen atoms at the 4-position
and pyrazolyl rings on adjacent cations (CH-centroid
distance 2.70 Å; angle 165°). Each metallacycle is participat-
ing in four of these CH-π interactions with four neighboring
metallacycles, and each contains two hydrogen-atom donors
(the 4-pyrazolyl hydrogen atoms) and two hydrogen-atom
acceptors (pyrazolyl rings). The packing of these sheets along
the a axis is directed by π-π interactions (3.64 Å; Figure
6) between ideally aligned central phenylene rings from
neighboring sheets. The interacting rings are perfectly
parallel, and their centroids are offset by 17°.
-
BF4 anion. The asymmetric unit of 4‚0.5CH3CN contains
two silver cations, one complete ligand molecule, and one-
10082 Inorganic Chemistry, Vol. 45, No. 25, 2006

SilWer(I) Complexes of Bis(pyrazolyl)methane Ligands
Figure 8. ORTEP drawing of the cationic coordination polymer in {[Ag(µ-p-[CH(pz)2]2C6H4)2]PF6‚0.5CH3CN}∞ (4‚0.5CH3CN). Displacement ellipsoids
are drawn at the 50% probability level. Hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (deg): Ag(1)-N(11) 2.304(2),
Ag(1)-N(21) 2.331(2), Ag(1)-N(31) 2.370(2), Ag(1)-N(41) 2.293(2), Ag(2)-N(51) 2.346(2), Ag(2)-N(61) 2.290(2), Ag(2)-N(71) 2.355(2), Ag(1)-
N(81) 2.306(2); N(11)-Ag(1)-N(21) 83.12(8), N(11)-Ag(1)-N(31) 136.94(9), N(11)-Ag(1)-N(41) 121.52(8), N(21)-Ag(1)-N(31) 105.74(8), N(21)-
Ag(1)-N(41) 135.93(8), N(31)-Ag(1)-N(41) 81.36(8), N(51)-Ag(2)-N(61) 84.28(8), N(51)-Ag(2)-N(71) 124.00(8), N(51)-Ag(2)-N(81) 111.17(8),
N(61)-Ag(2)-N(71) 110.45(8), N(61)-Ag(2)-N(81) 149.67(8), N(71)-Ag(2)-N(81) 83.12(8).
Figure 9. View down the chains of 3 showing two sets of quadruple
pyrazolyl embrace interactions (red or green dashed lines).
Figure 10. Parallel chains in 4‚0.5CH3CN bridged by the quadruple
pyrazolyl embrace (red dashed lines).
half each of two additional ligand molecules as well as two
PF6- counterions and an acetonitrile molecule. The geometry
about the silver is distorted tetrahedral with silver-nitrogen
bond lengths and chelate ring bite angles comparable to those
in the previous two complexes (2.28-2.39 Å and 81-84°).
The cationic chains of both 3 and 4‚0.5CH3CN are compact
because of a tortuous propagation of the coordination
polymers along the a axis in both structures.
The dominant feature of the supramolecular structures of
both 3 and 4‚0.5CH3CN is the quadruple pyrazolyl embrace,5b
a concerted set of intermolecular CH-π and π-π interac-
tions that associates the four pyrazolyl rings from two nearby
bis(pyrazolyl)methane sites. This supramolecular motif is
common in poly(pyrazolyl)methane and -borate compounds5b
and illustrated here for both 3 and 4‚0.5CH3CN (Figures 9
and 10). In the pyrazolyl embrace, two pyrazolyl rings are
aligned for π-π stacking, and these two rings also act as
hydrogen-atom donors, from their respective 4-pyrazolyl
positions, in CH-π interactions involving the remaining two
pyrazolyl rings. The structure of 3 contains two distinct sets
of pyrazolyl embrace interactions, which correspond to the
crystallographically independent ligand molecules and are
shown in Figure 9 as red and green dashed lines, respectively.
The interactions shown in red involve a centroid-centroid
distance of 3.60 Å and CH-π distances of 2.67 Å. These
interactions link the chains along the b axis. The interactions
shown in green include a centroid-centroid distance of 3.56
Å and CH-π distances of 2.64 Å, and these interactions
link the chains along the c axis. Since each set of interactions
results in two-dimensional sheets of cationic polymers, the
combined interactions produce a three-dimensional frame-
work of these polymers. Beyond the pyrazolyl embrace, no
significant noncovalent forces are evident in the crystal.
The crystal structure of 4‚0.5CH3CN displays a supramo-
lecular complexity similar to its meta counterpart, 2. The
pyrazolyl embrace, shown in Figure 10, is the most dominant
feature with a centroid-centroid distance of 3.51 Å and
CH-π distances of 2.80 and 3.00 Å. The sheets of cationic
polymers formed by the embrace are expanded into an overall
three-dimensional structure by a multitude of CH-F hydro-
gen bonds and anion-π interactions. The CH-F hydrogen
bonds include as donors the pyrazolyl rings and the methine
(-CH(pz)2) units and are in the range of 2.2-2.5 Å. As
Inorganic Chemistry, Vol. 45, No. 25, 2006 10083

Reger et al.
Figure 12. View down the b axis of 5 showing metallacycles associated
through CH-π interactions (purple dashed lines).
Figure 11. ORTEP drawing of the cationic unit in [Ag2(µ-1,3,5-[CH-
(pz)2]3C6H3)2](BF4)2 (5). Displacement ellipsoids are drawn at the 40%
probability level. Hydrogen atoms are omitted for clarity. Selected bond
distances (Å) and angles (deg): Ag(1)-N(11) 2.363(2), Ag(1)-N(21) 2.269-
(3), Ag(1)-N(31a) 2.241(2), Ag(1)-N(41a) 2.393(2); N(11)-Ag(1)-N(21)
84.03(8), N(11)-Ag(1)-N(31a) 104.25(8), N(11)-Ag(1)-N(41a) 117.79-
(7), N(21)-Ag(1)-N(31a) 164.22(9), N(21)-Ag(1)-N(41a) 102.35(7),
N(31a)-Ag(1)-N(41a) 85.85(7).
Unique to this structure, because of the noncoordinated
pyrazolyl rings, are CH-N interactions at 2.5-2.6 Å with
the donors coming from the methine and coordinated
pyrazolyl groups.
The complex {[Ag3(µ-1,3,5-[CH(pz)2]3C6H3)2](BF4)3‚2CH3-
CN}∞ (6‚2CH3CN) results from reaction of an excess of
AgBF4 with L3. It is the formal product of adding one more
equivalent of AgBF4 to bind the free bis(pyrazolyl)methane
units of two complexes of 5 discussed above. An ORTEP
drawing of 6‚2CH3CN (Figure 13) shows that the two bis-
(pyrazolyl)methane ligating sites that are unbound in 5 are
coordinated to the additional silver cations in 6‚2CH3CN to
yield a coordination polymer of metallacycles in which the
additional silver ion bridges what are discrete metallacycles
in 5. All silver cations reside in distorted tetrahedral
coordination environments similar to the other complexes
reported here. The noncovalent interactions in 6‚2CH3CN
resemble those in 5 in that CH-π interactions are the only
strong forces between the argentacycles. In 6‚2CH3CN these
multiple CH-π interactions bridge parallel chains of di-
cations (Figure 14), resulting in a three-dimensional extended
structure. This structure is also supported by various CH-F
interactions (2.1-2.5 Å, not pictured). Unlike 5, 6‚2CH3-
CN exhibits a weak anion-π interaction (F-centroid
distance 3.77 Å; shortest F-ring distance 3.59 Å) between
a fluorine atom in BF4- and a pyrazolyl ring coordinated to
a bridging silver cation, but this anion-π interaction does
not support the extended structure of 6‚2CH3CN.
observed in 2, the anion-π interactions are long (F-centroid
distances 3.59 and 3.73 Å; F-ring distances 3.28 and 3.56
Å) and involve pyrazolyl rings but not the linking phenylene
rings.
(c) Complexes of the Tritopic Ligand. Crystals of the
complex [Ag2(µ-1,3,5-[CH(pz)2]3C6H3)2](BF4)2 (5), resulting
from the equimolar combination of AgBF4 and the tritopic
ligand 1,3,5-[CH(pz)2]3C6H3 (L3), consist of discrete dimeric
argentacycles analogous to those in 1 and 2 except with a
third bis(pyrazolyl)methane site that remains unbound. An
ORTEP representation of the dicationic argentacycle in 5 is
shown in Figure 11. The dication rests on an inversion center,
and the third, unbound bis(pyrazolyl)methane units are
diametrically arranged about the metallacycle. The geometry
about the silver and bond lengths and angles in 5 are within
the same ranges as those described for the previous four
complexes.
The most notable features of the extended structure of 5
are the CH-π interactions that organize the complex ions
into two-dimensional sheets in the ac plane. Figure 12 shows
four molecules of 5 associated through CH-π interactions
(purple dashed lines) where the hydrogen-atom donors are
at the 5-position of metal-coordinated pyrazolyl groups and
at the methine carbon atom. In both interactions, pyrazolyl
rings from uncoordinated units serve as the hydrogen-atom
acceptors. The 4-fold symmetry at the center of the grouping
Discussion
Complex Structure in the Solid State. We previously
showed that alkylidene-linked, bitopic bis(pyrazolyl)methane
ligands (see Figure 1) are reliable synthons for building [L2-
Ag2]2+-type metallacyclic structures.5a,b In the presence of
weakly coordinating anions, all the alkylidene-linked ligands
prefer to form these dimeric metallacycles rather than simple
coordination polymers, regardless of the length of the spacer.
Table 2 shows the Ag‚‚‚Ag distances across the metallacycles
formed using ligands with methylene, ethylene, and pro-
pylene spacers. The table also includes the corresponding
average distances between methine carbon atoms in the
-
of ions in Figure 12 is apparent. Although the BF4 anions
are ordered in this structure, no anion-π interactions are
present, although several CH-F interactions (2.25-2.53 Å)
do contribute to the three-dimensional supramolecular struc-
ture. Whereas the hydrogen-atom donors in the CH-π
interactions do not include unbound pyrazolyl groups, the
donors in the weak CH-F hydrogen bonds include both
coordinated and uncoordinated pyrazolyl groups. Methine
hydrogen atoms also take part in these CH-F interactions.
10084 Inorganic Chemistry, Vol. 45, No. 25, 2006

SilWer(I) Complexes of Bis(pyrazolyl)methane Ligands
Table 2. Comparison of Intraargentacyclic Distances in Complexes
5a,b
with Alkylidene-Linked Ligands, [CH(pz)2](CH2)n
spacer
size, n
Ag‚‚‚Ag
distance (Å)
methine‚‚‚methine
distance (Å)
counterion
-
1
2
4.34
6.02
6.16
6.16
6.42
2.52
3.81
3.81
5.00
5.02
SO3-CF3
BF4
-
SO3-CF3
3
BF4
-
SO3CF3
Table 3. Comparison of Torsion Angles and Intraargentacyclic
Distances in Complexes with Fixed Ligands
average torsion Ag‚‚‚Ag methine‚‚‚methine
compound
angle, τ (deg) distance (Å)
distance (Å)
1‚2(CH3)2CO‚0.43H2O
69
75
89
92
99
5.31
4.83
4.73
4.24
4.10
4.95
4.93
5.04
5.07
5.03
2
5
6‚2CH3CNa
a Values given are for the two crystallographically distinct argentacycles
present in the crystal.
Figure 13. ORTEP drawing of a fragment of a chain of metallacycles in
{[Ag3(µ-1,3,5-[CH(pz)2]3C6H3)2](BF4)3‚2CH3CN}∞ (6‚2CH3CN). Displace-
ment ellipsoids are drawn at the 50% probability level. Hydrogen atoms
are omitted for clarity. Selected bond distances (Å) and angles (deg): Ag-
(1)-N(11) 2.361(2), Ag(1)-N(21) 2.289(2), Ag(1)-N(31a) 2.232(2), Ag-
(1)-N(41a) 2.5068(19), Ag(2)-N(51) 2.2963(19), Ag(2)-N(61) 2.3186-
(18), Ag(2)-N(71) 2.3832(19), Ag(2)-N(81) 2.2451(18), Ag(3)-N(91)
2.429(2), Ag(3)-N(101) 2.237(2), Ag(3)-N(111b) 2.251(2), Ag(3)-
N(121b) 2.425(2); N(11)-Ag(1)-N(21) 86.73(7), N(11)-Ag(1)-N(31a)
109.31(7), N(11)-Ag(1)-N(41a) 104.44(7), N(21)-Ag(1)-N(31a) 162.95-
(7), N(21)-Ag(1)-N(41a) 87.11(7), N(31a)-Ag(1)-N(41a) 83.35(6),
N(51)-Ag(2)-N(61) 84.83(6), N(51)-Ag(2)-N(71) 105.47(6), N(51)-
Ag(2)-N(81) 138.64(7), N(61)-Ag(2)-N(71) 132.77(7), N(61)-Ag(2)-
N(81) 116.88(7), N(71)-Ag(2)-N(81) 85.61(7), N(91)-Ag(3)-N(101)
85.16(7), N(91)-Ag(3)-N(111b) 98.23(7), N(91)-Ag(3)-N(121b) 114.55-
(7), N(101)-Ag(3)-N(111b) 167.99(8), N(101)-Ag(3)-N(121b) 104.17-
(7), N(111b)-Ag(3)-N(121b) 84.98(7).
distances, which are greater by no more than 0.4 Å, but has
a greater effect on the methine‚‚‚methine separations, which
increase by approximately 1.2 Å. These trends show the
expected flexibility of the propylene-linked ligand. The
ethylene system can also be considered flexible because it
has the freedom to alter the methine‚‚‚methine distances, but
when forming these types of metallacycles, this flexibility
is greatly reduced.
Two questions prompted the use of arene spacers in the
current work: would ligands with fixed distances between
ligating groups, and therefore a greater degree of rigidity,
also direct formation of dimeric metallacycles as in the
alkylidene system and would the decrease in flexibility result
in a greater impact of lengthening the spacer? To answer
these questions we used the meta- and para-phenylene-linked
ligands, Lm and Lp, because they represent the simplest
members of a family of arene-linked compounds comparable
to the alkylidene-linked compounds studied previously. The
tritopic ligand L3 is simply the bitopic ligand Lm with an
additional ligating site that is meta to the other two sites. In
changing from meta to para orientation about the phenylene
ring the length of the spacer is effectively increased because
the relative distances between ligating groups remain fixed
at their respective meta or para distances.
As discussed above, the ligands Lm and L3, in which the
ligating sites are oriented in a meta fashion about the arene
linker, direct formation of silver metallacycles similar to
those formed with the alkylidene ligands. The Ag‚‚‚Ag
distances in the four metallacyclic complexes, shown in Table
3, fall in the range 4.10-5.31 Å and more closely resemble
the distance in the methylene-linked complex (4.34 Å) than
they do the distances in the longer alkylidene systems (6.02-
6.42 Å). The similarities between the methylene- and arene-
linked systems support the intuitive conclusion that the
methylene-linked compound, with only a single carbon atom
spacer, is a fixed ligand as well, despite its chemical
similarities to the flexible ethylene- and propylene-linked
systems.
Figure 14. Fragments of parallel argentacyclic polymers in 6‚2CH3CN,
associated by a representative set of CH-π interactions (purple dashed
lines).
ligand molecules within the metallacycles. The increase in
Ag‚‚‚Ag distance when lengthening the carbon chain from
one to two, along with an increase in methine‚‚‚methine
distance, is expected given the natural increase in chain size
and the propensity of the bis(pyrazolyl)methane groups to
avoid steric crowding. Lengthening the spacer size from two
to three, however, has a modest impact on the Ag‚‚‚Ag
Inorganic Chemistry, Vol. 45, No. 25, 2006 10085

Reger et al.
of [L2Ag2]2+ metallacycles. Clearly, the greater rigidity built
into these arene-linked ligands results in greater control of
structure than with the alkylidene system reported earlier.
Recent work by Wagner14 also suggests that para-
phenylene-linked ligands analogous to p-[CH(pz)2]2C6H4 do
not form stable metallacyclic dimers. The related bis-
(pyrazolyl)borate ligand {p-[B(pz)2(tBu)]2C6H4}2- forms
discrete chloride- and oxide-bridged complexes of titanium
and manganese. Although two metals are coordinated in a
fashion similar to complexes 1, 2, 5, and 6, only one ligand
bridges the two metals rather than two, with the coordination
environments of the metals usually completed by smaller
ligands such as additional chloride ions, dimethylamide, or
solvent molecules.
Figure 15. Illustration of the torsion angle, τ, for a silver(I) metallacycle
(complete structure not shown).
The arene-linked ligands are best described as “fixed” but
not necessarily “rigid” because although the relative distances
between bis(pyrazolyl)methane ligating sites (the methine
carbon atoms) remain essentially constant, rotation of the
bis(pyrazolyl)methane units about the methine-arene carbon
(ipso) bond allows variation in the way the ligands bind metal
centers. For Lm and L3 this rotation can be quantified using
the torsion angle, τ, which is defined as shown in Figure 15
as the torsion angle about the ipso and methine carbon atoms
relative to the arene carbon atom that is ortho to both ipso
carbon atoms and the methine hydrogen atom. For each
metallacycle in this study, two of these torsion angles exist
for both of the bitopic ligands Lm present. Because the
coordinated metals are necessarily on the same side of the
arene ring, the two values of τ in each ligand will be opposite
in sign. The utility of τ arises from the fact that the greater
the absolute value of τ, the closer the silver cations are to
each other in the metallacycles.
Table 3 compares the average absolute values of the
torsion angles for each metallacycle along with the respective
Ag‚‚‚Ag and methine‚‚‚methine distances. The trend of
increasing τ corresponding to decreasing Ag‚‚‚Ag distance
is clear, with the longest Ag‚‚‚Ag distance (5.31 Å in 1)
being associated with the smallest torsion angle (69°) and
the shortest Ag‚‚‚Ag distance (4.10 Å in 6) corresponding
to the largest value of τ (99°). In contrast, the average
methine‚‚‚methine distance for all the complexes remains
essentially constant, varying by no more than 0.14 Å. The
distinction between “fixed” and “rigid” ligands is brought
out clearly in our previous work with complexes such as
{µ-m-[CH(pz)2]2C6H4}[Re(CO)3Br]2 where the metals are on
opposite sides of the arene linker. Such an arrangement of
the silver(I) systems reported here would lead to coordination
polymers, but we observe only metallacycles, demonstrating
the tendency to form this type of structure with the meta
ligands coordinated to metals that do not contain other
ligands.
An interesting comparison of these compounds is with the
-
those formed in similar reactions of Lm and L3 with BF4
salts of divalent iron, zinc, and cadmium.15 These reactions
also result in formation of metallacyclic dimers similar to
the ones reported here but are accompanied by fluoride
-
abstraction from one or two BF4 ions to yield the mono-
or difluoride-bridged dimeric cations [M2(µ-Lm)2(µ-F)](BF4)3
(M ) Fe, Zn), [Cd2(µ-Lm)2(µ-F)2](BF4)2, and [Zn2(µ-L3)2-
(µ-F)](BF4)3. The lower fluoride affinity of Ag+, a softer
ion than the divalent cations, and the generally lower
coordination numbers found in silver(I) complexes reduce
-
the impetus of Ag+ to abstract fluoride from BF4 .
Complex Structures in Solution. Positive-ion electro-
spray (ESI(+)) mass spectrometry provides some indication
of the solution structures of these complexes. The mass
spectra of 1 and 2, which exist as metallacycles in the solid
state, show clusters of peaks corresponding to the dimeric
metallacycles associated with one counterion, [Ag2(Lm)2X]+,
as described in the Results section. The analogous peaks are
not detected in solutions of 3 and 4, which are acyclic
polymers in the solid state. Other than the differences in base
peak identities, these [Ag2(Lm)2X]+ dimeric peaks are the
only distinction between the spectra of the metallacycles and
those of the polymers. The ESI(+) mass spectra of the
argentacycles reported here closely match the spectra from
the argentacycles formed in the alkylidene-linked systems
previously described5a,b in that the mass spectra of complexes
that show the metallacycle in the solid state also have a peak
assigned to the respective [Ag2L2X]+ ions. Detection in the
mass spectral experiments of clusters corresponding to the
metallacycles for 1 and 2, as well as for the alkylidene-linked
systems, is not direct evidence for the presence of argenta-
cycles in solution but does appear to provide a reliable
measure for distinguishing complexes that in the solid state
will form metallacycles from those forming acyclic species.
The discrete metallacycles of compound 5 and the
polymeric metallacycles of 6, both made from L3, also yield
ESI(+) mass spectra suggestive of their solid-state structures.
The spectra of 5 and 6 are identical in all but one respect.
Both show the dimeric cation [Ag2(L3)2BF4]+ as well as the
Changing from meta- to para-linked ligands has a dramatic
effect on the solid-state structure as the metallacycles formed
in complexes 1, 2, 5, and 6 are replaced by coordination
polymers in 3 and 4. Although, as just described, some
flexibility remains in these fixed systems, the greater stability
of the polymers as compared to the macrocycles in the para-
systems is attributed to the increased distance between
ligating sites in Lp relative to Lm. By increasing the distance
between the methine carbon atoms from ca. 5 Å with Lm to
5.8 Å with Lp the latter ligand no longer favors formation
(14) Bieller, S.; Bolte, M.; Lerner, H.-W.; Wagner, M. Inorg. Chem. 2005,
44, 9489.
(15) Reger, D. L.; Watson, R. P.; Gardinier, J. R.; Smith, M. D.; Pellechia,
P. J. Inorg. Chem. 2006, 45, 10088-10097.
10086 Inorganic Chemistry, Vol. 45, No. 25, 2006

SilWer(I) Complexes of Bis(pyrazolyl)methane Ligands
fragment [AgL3]+, but the spectrum of 6 also contains a
cluster corresponding to the dimer associated with an
additional AgBF4 equivalent, [Ag3(L3)2(BF4)2]+. It is pos-
sible, therefore, that in solution both compounds retain the
metallacyclic structure and that for 6 at least some extended
polymeric structure exists. In a general sense, the ESI(+)
mass spectra of silver(I) complexes of our polytopic poly-
(pyrazolyl)methane ligands appear to parallel the solid-state
structures.5
are long compared to the significant anion-π interactions
reported in the recent literature, which tend to be below 3.0
Å.17,18 All of the anion-π interactions observed here involve
the pyrazolyl rings as the π acids, and this observation is
consistent with the expected electron deficiency of the
pyrazolyl group caused by the electron-withdrawing nitrogen
atoms. The lack of a significant change in the chemical shifts
of the BF4- and PF6- fluoride signals in the 19F NMR spectra
of the complexes reported here implies that no significant
anion-π interactions exist in solution.17
Solid-State Supramolecular Structure. The supramo-
lecular structures of the silver complexes reported here
exhibit a variety of weak hydrogen bonds, largely in the form
of CH-π and CH-F interactions, as well as π-π stacking
and anion-π interactions. The quadruple pyrazolyl embrace5b
is present only in the coordination polymers 3 and 4.
Formation of the macrocycles, however, does not preclude
the pyrazolyl embrace because it is observed in the macro-
cycle-containing structures of the alkylidene-linked ligands.5a,b
Similarly, π-π stacking plays a limited role in the current
study, and it is only present in the macrocyclic compound
2, despite the intermolecular access to the central phenylene
ring in 1 as well. It is not surprising that the winding
polymers of 3 and 4 or the macrocycles of 5 and 6, whose
arene rings are partially blocked by another ligating group,
do not allow π-π interactions in the solid state.
Summary
The arene-linked ligands employed in this study form
silver(I) complexes with consistent structures: dimeric
metallacycles for ligands with a meta configuration and
simple coordination polymers for the para configuration.
These less flexible ligands in which the length of the spacer
is fixed by the arene substitution do control the formation
of metallacycles versus coordination polymers when com-
pared to the more flexible alkylidene systems we reported
earlier. Use of the tritopic ligand affords stoichiometry-
dependent complexes containing either discrete dimeric
metallacycles with equimolar amounts of silver salt and
ligand or a polymer of metallacycles in the presence of an
excess of silver salt. Weak noncovalent interactions supported
by the functionality built into the ligands play an important
role in the supramolecular structures of these complexes, and
long anion-π contacts involving the relatively π-acidic
pyrazolyl groups support the structures of some of these
complexes. The results demonstrate that the series of bis-
(pyrazolyl)methane ligands we have been investigating, both
alkylidene- and arene-based, increase the potential for the
rational design of molecular and supramolecular structures,
based on variations in cation and anion, as well as geometry
and flexibility of the ligand.
-
Full appreciation of the impact of the BF4 ions on the
structure of 3 is hindered by disorder, but several weak
CH-F hydrogen bonds are observed in the crystals of 1
(despite mild disorder in the anions), 5 and 6. Similarly, the
PF6- counterion in 2 and 4 also participates in several CH-F
hydrogen bonds. Exploitation of noncovalent anion-π
interactions in supramolecular chemistry is gaining ground
on the more developed chemistry of cation-π interactions.16
For example, Dunbar and co-workers recently published a
thorough study of noncovalent anion-π interactions in AgX
-
-
-
-
(X ) BF4 , PF6 , AsF6 , SbF6 ) complexes of the π-acidic
ligands 3,6-bis(2′-pyridyl)-1,2,4,5-tetrazine (bptz) and 3,6-
bis(2′-pyridyl)-1,2-pyridazine (bppn).17 For our silver com-
plexes reported here, anion-π contacts have been identified
in 2, 4, and 6, and the shortest F-centroid or F-ring plane
distances are in the range of 3.2-3.8 Å. These interactions
Acknowledgment. We thank Drs. James Gardinier and
Radu Semeniuc for helpful discussion and the National
Science Foundation (CHE-0414239) for financial support.
We also thank the Alfred P. Sloan Foundation for support
of R.P.W. The Bruker CCD Single Crystal Diffractometer
was purchased using funds provided by the NSF Instrumen-
tation for Materials Research Program through Grant DMR:
9975623.
(16) (a) Quin˜onero, D.; Garau, C.; Rotger, C.; Frontera, A.; Ballester, P.;
Costa, A.; Deya`, P. M. Angew. Chem., Int. Ed. 2002, 41, 3389. (b)
Campos-Ferna´ndez, C. S.; Cle´rac, R.; Dunbar, K. R. Angew. Chem.,
Int. Ed. 1999, 38, 3477. (c) Campos-Ferna´ndez, C. S.; Cle´rac, R.;
Kooman, J. M.; Russell, D. H.; Dunbar, K. R. J. Am. Chem. Soc.
2001, 123, 773. (d) Campos-Ferna´ndez, C. S.; Schottel, B. L.;
Chifotides, H. T.; Bera, J. K.; Basca, J.; Kooman, J. M.; Russell, D.
H.; Dunbar, K. R. J. Am. Chem. Soc. 2005, 127, 12909.
Supporting Information Available: X-ray crystallographic files
in CIF format for all structures. This material is available free of
charge via the Internet at http://pubs.acs.org.
IC0613053
(17) Schottel, B. L.; Chifotides, H. T.; Shatruk, M.; Chouai, A.; Pe´rez, L.
M.; Basca, J.; Dunbar, K. R. J. Am. Chem. Soc. 2006, 128, 5895.
(18) Fairchild, R. M.; Holman, K. T. J. Am. Chem. Soc. 2005, 127, 16364.
Inorganic Chemistry, Vol. 45, No. 25, 2006 10087