Tuning the coordination geometry of silver in bis(pyrazolyl)alkane complexes

Article abstract of DOI:10.1021/ic0497174

Silver(I) complexes of the bis(pyrazolyl)methane ligands Ph ₂C(pz)₂, PhCH(pz)₂, and PhCH ₂CH(pz)₂ (pz = pyrazolyl ring) have been prepared in an attempt to explore how sterically hindered poly(pyrazolyl) methane ligands influence the variable coordination geometries exhibited by silver(I) complexes, especially its ability to participate in cation...π interactions. The complex {Ag[(pz)₂CPh₂]₂}(PF₆) ·C₃H₆O adopts an unusual square planar coordination environment as indicated by the sum of the four N-Ag-N angles being 360°. The proximity of phenyl groups above and below the AgN₄ core enforces the unusual coordination geometry about the metal center. This arrangement is not a result of silver(I)...π arene interactions but rather of the constraints imposed by the steric crowding caused by (aryl)₂C(pz) ₂ ligands. In contrast, the complexes of the other two ligands, {Ag[(pz)₂CHPh]₂}(PF₆)·0.5CH ₂Cl₂ and {Ag[(pz)₂CH(CH₂Ph)] ₂}(PF₆)·CH₂Cl₂, show normal tetrahedral geometry about the silver(I), also with no indication of silver(I)...π arene interactions. All three new complexes have extended supramolecular structures supported by a combination of CH...π and CH...F interactions.

Full text of DOI:10.1021/ic0497174

Inorg. Chem. 2004, 43, 3825−3832
Tuning the Coordination Geometry of Silver in Bis(pyrazolyl)alkane
Complexes
Daniel L. Reger,* James R. Gardinier, and Mark D. Smith
Department of Chemistry and Biochemistry, UniVersity of South Carolina,
Columbia, South Carolina 29208
Received March 4, 2004
Silver(I) complexes of the bis(pyrazolyl)methane ligands Ph2C(pz)2, PhCH(pz)2, and PhCH CH(pz)2 (pz ) pyrazolyl
2
ring) have been prepared in an attempt to explore how sterically hindered poly(pyrazolyl)methane ligands influence
the variable coordination geometries exhibited by silver(I) complexes, especially its ability to participate in
cation‚‚‚π interactions. The complex {Ag[(pz)2CPh2]2}(PF )‚C H O adopts an unusual square planar coordination
6
3 6
environment as indicated by the sum of the four N−Ag−N angles being 360°. The proximity of phenyl groups
above and below the AgN core enforces the unusual coordination geometry about the metal center. This arrangement
4
is not a result of silver(I)‚‚‚π arene interactions but rather of the constraints imposed by the steric crowding caused
by (aryl)2C(pz)2 ligands. In contrast, the complexes of the other two ligands, {Ag[(pz)2CHPh]2}(PF )‚0.5CH Cl2 and
6
2
{Ag[(pz)2CH(CH Ph)]2}(PF )‚CH Cl2, show normal tetrahedral geometry about the silver(I), also with no indication
2
6
2
of silver(I)‚‚‚π arene interactions. All three new complexes have extended supramolecular structures supported by
a combination of CH‚‚‚π and CH‚‚‚F interactions.
Introduction
It is of fundamental and practical1 interests to more fully
understand what factors govern whether a cation‚‚‚π interac-
tion will take place when the components are brought into
close proximity. One common approach to preparing com-
pounds capable of becoming involved in a cation‚‚‚π
interaction is to have multiple Lewis bases tethered to a
central arene core where the donors serve to anchor the metal
cation close to the π-cloud of the ring (Figure 1). This
strategy, coupled with the use of noncoordinating anions to
render the metal centers more “electron deficient”, may
promote but does not guarantee the occurrence of a
cation‚‚‚π interaction (as typically quantified by X-ray
structural data and/or spectroscopic methods; vide infra).
Our group recently reported the structure of a silver poly-
(pyrazolyl)methane coordination polymer, {o-C6H4[CH2-
OCH2C(3-Phpz)3]2Ag2(acetone)(BF4)2}n (pz ) pyrazolyl
ring), that exhibited an η2-cation‚‚‚π interaction between the
Figure 1. Typical framework used for studying metal cation‚‚‚π com-
plexes.
metal center and a 3-phenyl group bound to a pyrazolyl ring
of an adjacent cation.2 We also recently described the
preparation of a new bitopic fixed geometry heteroscorpi-
onate, m-C6H4[C(pz)2(2-py)]2 (py ) pyridyl ring), and its
corresponding silver hexafluorophosphate complex, {Ag(κ2-
m-C6H4[C(pz)2(2-py)]2)2}(PF6).3 One striking feature about
this latter complex was a square planar arrangement of
nitrogen atoms from coordinated pyrazolyl groups about the
silver(I) center where the uncoordinated pyridyl groups
sandwiched the metal center. The compound {Ag(κ2-C6H5-
[C(pz)2(2-py)])2}(PF6)3 showed a similar square planar
arrangement of donor atoms about silver; however, phenyl
groups rather than pyridyls sandwiched the metal center. We
proposed that the atypical coordination geometry of tetra-
* Author to whom correspondence should be addressed. E-mail: reger@
mail.chem.sc.edu.
(1) For instance, in metal cation sensors: Xu, F.-B.; Li, Q.-S.; Wu, L.-
Z.; Leng, X.-B.; Li, Z.-C.; Zeng, X.-S.; Chow, Y. L.; Zhang, Z.-Z.
Organometallics 2003, 22 (4), 633. (b) de Silva, A. P.; Gunaratne, H.
Q. N.; Gunnlaugsson, T.; Huxley, A. J. M.; McCoy, C. P.; Radema-
cher, J. T.; Rice, T. E. Chem. ReV. 1997, 97 (5), 1515. Fabbrizzi, L.;
Poggi, A. Chem. Soc. ReV. 1995, 24 (3), 197.
(2) Reger, D. L.; Semeniuc, R. F.; Smith, M. D. Inorg. Chem. Commun.
2002, 5, 278.
(3) Reger, D. L.; Gardinier, J. R.; Smith, M. D. Polyhedron 2004, 23
(2-3), 291.
10.1021/ic0497174 CCC: $27.50 © 2004 American Chemical Society
Published on Web 05/22/2004
Inorganic Chemistry, Vol. 43, No. 13, 2004 3825

Reger et al.
H5-pz), 7.45-7.36 (br m, 6H, Ph), 7.05 (d, J ) 8 Hz, 4H, Ph),
6.36 (dd, J ) 2,1 Hz, 2H, H4-pz). 13C NMR (100.6 MHz, acetone-
d6): 141.8, 140.6 (C5-pz), 133.3, 130.0, 129.7 (C3-pz), 128.6, 106.1
(C4-pz), 88.3 (CR). HRMS-direct probe (m/z): [M]+, calcd for
C19H16N4 300.1375; found, 300.1367. Direct probe MS {m/z (rel
int %), [assignment]+}: 300 (35), [M]+; 233 (100), [M - pz]+;
223 (44), [M - Ph]+; 166 (21), [M - 2pz]+; 156 (13), [M - Ph
- pz]+; 77 (22), [C6H5]+.
r,r-Bis(pyrazol-1-yl)toluene, PhCH(pz)2 (L2). PhCH(pz)2 was
prepared by a modification of the known route.5 Thus, 15.2 g (0.100
mol) of PhCH(OMe)2, 13.6 g (0.200 mol) of pyrazole, and 0.203
g (1.07 mmol) of p-toluenesulfonic acid monohydrate (p-TsOH‚
H2O) were heated in a short-path distillation apparatus 12 h at
atmospheric pressure until 7.1 mL (87% expected) of methanol was
collected. The residue was partitioned between 100 mL each of
H2O and Et2O. The organic and aqueous portions were separated,
and the aqueous portion was extracted with three 100 mL portions
of Et2O. The combined organic fractions were dried over MgSO4
and filtered, and solvent was removed by vacuum distillation. The
residue was taken up with 100 mL of 1:1 (v/v) hexanes/Et2O, and
the solution was flushed through a silica gel plug to remove colored
impurities. Solvent was removed, leaving a colorless solid that was
washed with two 15 mL portions of hexanes and dried under
vacuum to give 16.9 g (75%) of PhCH(pz)2 as a colorless solid.
Figure 2. Possible cation‚‚‚π interaction in {Ag[(pz)2CHCH2Ph]2}+, where
some carbon and hydrogen atoms of two pz rings have been omitted for
clarity.
coordinate silver(I) in these complexes was due to inter-
cationic CH‚‚‚F interactions involving the arene substituents
of the ligands and the fluorines of the hexafluorophosphate
salts rather than to any intracationic Ag‚‚‚π or CH‚‚‚π
interactions. To more fully elucidate the factors that were
responsible for the unusual coordination environment about
silver in the solid state structures of the above bidentate
scorpionates and to probe the possibility of obtaining species
with short cation‚‚‚π interactions, we investigated silver
complexes of the bis(pyrazolyl)methane ligands Ph2C(pz)2
(L1), PhCH(pz)2 (L2), and PhCH2CH(pz)2 (L3). The
latter ligand was thought to be capable of promoting a
silver‚‚‚arene interaction due to the flexibility of the ligand
backbone as in Figure 2.
1
Mp: 68-69 °C (lit. mp 61-62 °C,6 62-63 °C7). H NMR (300
MHz): 7.95 (s, 1H, CH), 7.81 (d, J ) 2 Hz, 2H, H5-pz), 7.58 (d,
J ) 1 Hz, 2H, H3-pz), 7.41-7.37 (br m, 3H, Ph), 7.09-7.05 (br
m, 2H, Ph), 6.36 (dd, J ) 2,1 Hz, 2H, H4-pz). 13C NMR (75.4
MHz): 140.8 (C5-pz), 138.3 (CipsoPh), 130.8 (Cpara), 129.7 (C3-
pz), 129.3 (Cortho), 127.8 (Cmeta), 106.9 (C4-pz), 78.1 (CR). HRMS-
direct probe (m/z): [M]+ calcd for C13H12N4, 224.1062; found,
224.1060. Direct probe MS {m/z (rel int %), [assignment]+}: 224
(21), [M]+; 157 (100), [M - pz]+; 77 (16), [C6H5]+.
Experimental Section
General Considerations. Solvents for synthetic procedures and
spectroscopic studies were dried by conventional methods and
distilled under N2 atmosphere immediately prior to use. All reagents
were used as received from Aldrich Chemical Co. Silica gel
(0.040-0.063 mm, 230-400 mesh) used for chromatographic
separations was purchased from Fischer Scientific. PhCH2CH(OEt)2
(bp 85-88 °C, 1 mmHg) was prepared by an established method
from Mg°, benzylbromide, and HC(OEt)3.4 Manipulation of AgPF6
was carried out in an inert-atmosphere drybox or by using standard
Schlenk techniques. After reaction of AgPF6 with bis(pyrazolyl)-
methane ligands, no special precautions are needed to handle the
silver salts. Robertson Microlit Laboratories performed all elemental
analyses. Melting point determinations were made on samples
contained in sealed glass capillaries by using an Electrothermal 9100
apparatus and are uncorrected. Mass spectrometric measurements
recorded in ESI(+) mode were obtained on a Micromass Q-Tof
spectrometer whereas those performed by using direct probe
analyses were made on a VG 70S instrument. NMR spectra were
recorded by using either a Varian Gemini 300 or a Varian Mercury
400 instrument, as noted within the text. Chemical shifts were
referenced to solvent resonances at δH 2.05 and δC 29.8 for acetone-
d6.
Ligand Syntheses. r,r-Diphenyl-r,r-bis(pyrazol-1-yl)methane,
Ph2C(pz)2 (L1). A Schlenk flask was charged with 5.00 g (21.0
mmol) of Ph2CCl2, 6.61 g (97.1 mmol) of pyrazole, 25 mL of NEt3,
and 50 mL of toluene, and the reaction mixture was heated at reflux
for 3 d. Solvent was then removed by vacuum distillation, and the
resulting pale yellow solid was washed with four 20 mL portions
of methanol to leave 3.76 g (61% yield) of the desired ligand as a
colorless solid. Mp: 158-159 °C (lit.6b mp 153-154 °C). 1H NMR
(400 MHz): 7.65 (d, J ) 1 Hz, 2H, H3-pz), 7.49 (d, J ) 2 Hz, 2H,
r-Benzyl-r,r-bis(pyrazol-1-yl)methane, PhCH2CH(pz)2 (L3).
A mixture of 1.77 g (9.11 mmol) of PhCH2CH(OEt)2 and 1.24 g
(18.2 mmol) of pyrazole and a catalytic amount (0.023 g, 0.12
mmol, 1 mol %) of p-TsOH‚H2O were heated in a short-path
distillation apparatus for 8 h until 0.6 mL (60% of expected) of
EtOH was collected. The residue was partitioned between 100 mL
each of H2O and Et2O. The organic and aqueous portions were
separated, and the aqueous portion was extracted with three 100
mL portions of Et2O. After the organic portions were dried over
MgSO4 and filtered and solvent was removed, the resulting brown
oil was loaded onto a silica gel column; grease and two impurities
thought to be 1-(pyrazolyl)styrene and 1-(ethoxy)styrene (on the
basis of the NMR spectra of the mixture) were removed by first
eluting the column with C6H6. The column was then flushed with
Et2O to elute the desired product, which after removing solvent by
vacuum distillation afforded 0.832 g (38% yield) of PhCH2CH-
(pz)2 as a colorless solid. Mp: 105-107 °C (lit.7 mp 107-108
°C). 1H NMR (300 MHz): 7.86 (d, J ) 2 Hz, 2H, H5-pz), 7.58 (d,
J ) 1 Hz, 2H, H3-pz), 7.22-7.16 (br m, 5H, Ph), 6.79 (t, J ) 8
Hz, 1H, CH), 6.22 (dd, J ) 2,1 Hz, 2H, H4-pz), 3.91 (d, J ) 8 Hz,
2H, CH2). 13C NMR (75.4 MHz, acetone-d6): 140.2 (C5-pz), 130.0,
129.7 (C3-pz), 129.1, 127.6, 106.6 (C4-pz), 77.1 (CR), 40.4 (CH2).
(5) (a) Ballesteros, P.; Elguero, J.; Claramunt, R. M. Tetrahedron 1985,
41 (24), 5955. (b) Ballaesteros, P.; Lopez, C.; Claramunt, R. M.;
Jimenez, J. A.; Cano, M.; Heras, J. V.; Pinilla, E.; Monge, A.
Organometallics 1994, 13, 289.
(6) (a) The, K. I.; Peterson, L. K. Can. J. Chem. 1973, 51 (3), 422. (b)
The, K. I.; Peterson, L. K.; Kiehlman, E. Can. J. Chem. 1973, 51
(15), 2448.
(4) McElvain, S. M.; Clarke, R. L.; Jones, G. D. J. Am. Chem. Soc. 1942,
64, 1966.
(7) Katritzky, A. R.; Abdel-Rahman, A. E.; Leahy, D. E.; Schwarz, O.
A. Tetrahedron 1983, 39 (24), 4133.
3826 Inorganic Chemistry, Vol. 43, No. 13, 2004

Tuning the Coordination Geometry of SilWer
HRMS-direct probe (m/z): [M]+ calcd for C14H14N4, 238.1218;
found, 238.1223. Direct probe MS {m/z (rel int %), [assignment]+}:
238 (7), [M]+; 170 (34), [M - Hpz]+; 147 (100), [(pz)2CH]+;
103 (13), [CHCHPh]+; 91 (18), [H2CPh2]+.
Anal. Calcd (found) for C29H30N8F6Cl2PAg, M‚CH2Cl2: C, 42.77
(43.26); H, 3.71 (3.38); N, 13.76 (13.77).
Crystallography. X-ray Structure Determinations of {Ag-
[(pz)2CPh2]2}(PF6)‚C3H6O, 1‚Acetone, Ag[(pz)2CHPh]2}(PF6)‚
0.5CH2Cl2, 2‚0.5CH2Cl2, and Ag[(pz)2CHCH2Ph]2}(PF6)‚CH2Cl2,
3‚CH2Cl2. Colorless block crystals of 1 and 2 and a colorless plate
of 3 were each mounted onto the end of thin glass fibers using
inert oil. X-ray intensity data from 1 was measured at 190(2) K,
while those data from 2 and 3 were measured at 150(2) K on a
Bruker SMART APEX CCD-based diffractometer (Mo KR radia-
tion, λ ) 0.710 73 Å).8 The raw data frames were integrated with
SAINT+,8 which also applied corrections for Lorentz and polariza-
tion effects. Final unit cell parameters were determined by least-
squares refinement of 6659 reflections from the data set of 1, of
5066 reflections from the data set of 2, and of 8072 reflections
from the data set of 3, each with I > 5σ(I). Analysis of the data
showed negligible crystal decay during each data collection.
Empirical absorption corrections for each data set were applied with
SADABS.8
Structure Refinement of {Ag[(pz)2CPh2]2}(PF6)‚C3H6O, 1‚
Acetone. Structure solutions at 190 and 294 K (Supporting
Information) (direct methods) and full-matrix least-squares refine-
ment against F2 were carried out with SHELXTL.9 {Ag[(pz)2-
CPh2]2}(PF6)‚C3H6O crystallizes in the triclinic system. The space
group P1h was assumed and confirmed by successful solution and
refinement of the data. The Ag atom of the cation and the P atom
of the anion reside on crystallographic inversion centers. One
acetone molecule/formula unit is disordered about an inversion
center, and a restrained model incorporating two orientations was
used. All non-hydrogen atoms were refined with anisotropic
displacement parameters; hydrogen atoms were placed in idealized
positions and included as riding atoms.
Silver Complexes. {Ag[(pz)2CPh2]2}(PF6) (1). A 5 mL THF
solution of 0.38 g (1.3 mmol) of Ph2C(pz)2 was added to a 5 mL
THF solution of 0.16 g (0.63 mmol) of AgPF6 under a nitrogen
atmosphere. A colorless precipitate formed within 10 min of stirring.
The resulting suspension was stirred 4 h and then was separated
by cannula filtration. The colorless solid was washed with 5 mL
of Et2O and dried under vacuum to leave 0.40 g (74% yield) of
{Ag[(pz)2CPh2]2}(PF6) as a colorless solid. Mp: 215-218 °C (dec).
Anal. Calcd (found) for C38H32F6N8PAg: C, 53.47 (53.78); H, 3.78
1
(3.86); 13.13 (12.83). H NMR (400 MHz): 7.67 (d, J ) 2 Hz,
4H, H5-pz), 7.63-7.54 (br m, 12 H, Ph), 7.46 (d, J ) 1 Hz, 4H,
H3-pz), 6.83 (d, J ) 8 Hz, 8H, Ph), 6.49 (dd, J ) 2,1 Hz, 4H,
H4-pz). 13C NMR (100.6 MHz, acetone-d6): 143.8 (C5-pz), 139.2,
136.2, 131.3, 129.9 (C3-pz), 129.6, 106.6 (C4-pz), CR not obsd.
HRMS-ESI(+) (m/z): calcd for C38H32N8Ag [M - PF6]+, 707.1801;
found, 707.1773. ESI(+) MS {m/z (rel int %), [assignment]+}: 707
(68) [AgL1 ]+, 448 (100), [Ag(CH3CN)(L1)]+; 407 (71), [AgL1]+;
2
233, [L1]+. Crystals suitable for X-ray structural studies were grown
by layering an acetone solution with Et2O and allowing the solvents
to slowly diffuse.
{Ag[(pz)2CHPh]2}(PF6) (2). Under a nitrogen atmosphere, a
solution of 0.421 g (1.88 mmol) of PhCH(pz)2 in 10 mL of THF
was added by cannula to a solution of 0.237 g (0.938 mmol) of
AgPF6 in 10 mL of THF. A colorless precipitate formed within 10
min of stirring, and the resulting suspension was stirred 4 h. After
separation of the colorless solid from the colorless solution by
cannula filtration, the colorless solid was washed with two 5 mL
portions of Et2O and dried under vacuum to leave 0.545 g (83%
yield) of {Ag[(pz)2CHPh]2}(PF6) as a colorless solid. Mp: 245-
247 °C (dec). Anal. Calcd (found) for C26H24F6N8PAg: C, 44.53
(44.45); H, 3.45 (3.01); 15.98 (16.05). 1H NMR (300 MHz): 8.38
(d, J ) 2 Hz, 4H, H5-pz), 8.37 (s, 2H, CRH), 7.46 (br m, 6 H, Ph),
7.37 (d, J ) 1 Hz, 4H, H3-pz), 6.63 (br m, 4H, Ph), 6.53 (dd, J )
2,1 Hz, 4H, H4-pz). 13C NMR (75.4 MHz, acetone-d6): 143.7 (C5-
pz), 136.7, 134.5, 130.0, 129.7 (C3-pz), 127.3, 107.1 (C4-pz), 75.8.
HRMS-ESI(+) (m/ z): [M - PF6]+ calcd for C26H24N8Ag,
555.1175; found, 555.1174. Crystals suitable for X-ray structural
studies were grown by vapor diffusion of Et2O into a CH2Cl2
solution of the compound.
Structure Refinement of {Ag[(pz)2CHPh]2}(PF6)‚0.5CH2Cl2,
2‚0.5CH2Cl2. Systematic absences in the intensity data were
consistent with the space groups P31, P32, P3121, and P3221.
Preliminary solutions confirmed the presence of a C2 axis in the
crystal, leaving the enantiomorphous pair P3121/P3221. Solutions
were obtained in both space groups. The space group P3221 resulted
in a Flack parameter of 0.00(3). Refinement in P3121 gave a Flack
parameter of 0.9(2), confirming P3221 as the correct space group.
Final R values were also lower in P3221. The final refinement was
carried out in P3221. Structure solutions were obtained by a
combination of direct methods and difference Fourier syntheses,
and refinement was carried out by full-matrix least squares against
F2, using SHELXTL.9 The {Ag[(pz)2CHPh]2}+ complex has
{Ag[(pz)2CHCH2Ph]2}(PF6) (3). A solution of 0.111 g (0.466
mmol) of PhCH2CH(pz)2 in 10 mL of THF was added to a solution
of 0.590 g (0.233 mmol) of AgPF6 in 10 mL of THF under a
nitrogen atmosphere. The resulting amber solution was stirred 4 h,
and then solvent was removed by vacuum distillation. The colorless
solid was washed with 5 mL of Et2O and dried under vacuum to
leave 0.137 g (81% yield) of {Ag[(pz)2CHCH2Ph]2}(PF6) as a
colorless solid. Mp: 186-188 °C (dec). Anal. Calcd (found) for
C28H28N8F6PAg: C, 46.13 (46.05); H, 3.87 (3.72); N, 15.37 (15.21).
1H NMR (400 MHz): 8.10 (d, J ) 2 Hz, 4H, H5-pz), 7.87 (d, J )
1 Hz, 4H, H3-pz), 7.38 (t, J ) 8 Hz, 2H, CRH), 7.23 (br m, 10 H,
Ph), 6.44 (dd, J ) 2.1 Hz, 4H, H4-pz), 4.30 (d, J ) 8 Hz, 4H,
CH2). 13C NMR (100.6 MHz, acetone-d6): 143.8 (C5-pz), 135.7,
133.3, 130.0, 129.4 (C3-pz), 128.2, 107.2 (C4-pz), 75.9, 40.7.
HRMS-ESI(+) (m/z): [M - PF6]+ calcd for C28H28N8Ag, 583.1488;
found, 583.1473. ESI(+) MS {m/z (rel int %) [assignment]+}: 583
(43), [M - PF6]+; 345 (41), [AgL3]; 239 (100), [HL3]; 171 (20),
[HL3 - pz]. Crystals of {Ag[(pz)2CHCH2Ph]2}(PF6)‚CH2Cl2 suit-
able for X-ray structural studies were grown by layering a CH2Cl2
solution with hexanes and allowing the solvents to slowly diffuse.
-
crystallographically imposed 2-fold symmetry. The disordered PF6
anion was modeled in two positions with equal weighting. A
methylene chloride molecule is also equally disordered over two
positions. Eventually all non-hydrogen atoms were refined with
anisotropic displacement parameters; hydrogen atoms were placed
in geometrically idealized positions and included as riding atoms
with refined isotropic displacement parameters.
Structure Refinement of {Ag[(pz)2CHCH2Ph]2}(PF6)‚CH2Cl2,
3‚CH2Cl2. Systematic absences in the intensity data uniquely
determined the space group Pbca. The structure was solved by a
combination of direct methods and difference Fourier syntheses
and refined by full-matrix least squares against F2, using SHELX-
TL.9 All atoms reside on positions of general crystallographic
-
symmetry. The {Ag[(pz)2CHCH2Ph]2}+ cation, PF6 anion, and
(8) SMART Version 5.625, SAINT+ Version 6.22, and SADABS Version
2.03; Bruker Analytical X-ray Systems, Inc.: Madison, WI, 2001.
(9) Sheldrick, G. M. SHELXTL Version 6.1; Bruker Analytical X-ray
Systems, Inc.: Madison, WI, 2000.
Inorganic Chemistry, Vol. 43, No. 13, 2004 3827

Reger et al.
Scheme 1
Scheme 2
minutes of mixing THF solutions of the appropriate ligand
and silver hexafluorophosphate (in a 2:1 mol ratio) (Scheme
2). These compounds appear to be indefinitely stable as solids
toward ambient light; however, trace decomposition with the
deposition of metallic silver has been observed for acetone-
d6 and CDCl3 solutions upon prolonged (1 week) exposure
included CH2Cl2 solvent are all afflicted by disorder. The benzyl
group {C4-C66} of the cation is equally disordered over two
nearby positions. The C6 rings of both components were refined
-
as rigid hexagons. The PF6 anion is disordered over two closely
spaced positions in an approximate 60/40 ratio. A CH2Cl2 molecule
of crystallization is also disordered over two closely spaced
positions, in the ratio 80/20. A total of 29 geometric restraints were
employed to assist in the refinement of the disordered atoms. The
minor disorder component of the CH2Cl2 was refined isotropically;
all other non-hydrogen atoms were refined with anisotropic
displacement parameters. Hydrogen atoms were placed in geo-
metrically idealized positions and included as riding atoms.
1
to ambient light. The H and 13C NMR spectra show only
one set of resonances that differ from the spectra of the free
ligands by an upfield shift of the H3-pz and one of the phenyl
resonances of compounds 2 and 3, while the remainder of
the resonances in each compound exhibit downfield shifts
with respect to the free ligand. These observations are
consistent with the known lability of related silver poly-
(pyrazolyl)methane complexes and indicate that metal-arene
interactions are nonexistent in solution.12 The ESI(+) mass
spectrum of each compound showed peaks corresponding
to the [AgL2]+ cation.
Compounds 1-3 crystallize as solvates as noted in the
Experimental Section and in Table 1. The geometry of the
cations and labeling of atoms are given for each in Figures
3 and 4, while important bond distances and angles are
provided in Table 2.
As can be seen in Figure 3, the silver center in 1 adopts
an unusual square planar coordination environment as
indicated by the sum of the four N-Ag-N angles which is
360°. The square planar geometry is distorted by the N(11)-
Ag-N(21) bite angle of 74.44(6)° associated with the
chelating ring. The Ag-N bond distances (the silver atom
resides on an inversion center) of 2.356(2) and 2.367(2) Å
fall within the range of 2.28-2.50 Å found in {Ag(κ2-m-
C6H4[C(pz)2(2-py)]2)2}(PF6), {Ag(κ2-C6H5[C(pz)2(2-py)])2}-
(PF6),3 and related systems.12b,13,17
Results and Discussion
Syntheses. The synthetic methods used to prepare the
ligands L1-L3 are outlined in Scheme 1. Both PhCH(pz)2
(L2) and PhCH2CH(pz)2 (L3) were prepared in good to fair
yields (75% and 38%, respectively) by the alcohol elimina-
tion reactions between pyrazole and either benzaldehyde
dimethyl acetal or phenylacetaldehyde diethyl acetal, as
appropriate. The ease of handling the air-stable, inexpensive,
and commercially available reagents make the alcohol
elimination reactions more favorable than the literature route
to these compounds.7 In the previously known route, CH2-
(pz)2 (which must be prepared) is first reacted with butyl-
lithium and then with the appropriate electrophile to give a
product mixture that contains significant amounts of pyra-
zolyl-substituted compounds (from competing pyrazolyl
deprotonation reactions). Compound L1, on the other hand,
was prepared in good yield (74%) by the reaction between
dichlorodiphenylmethane, pyrazole, and triethylamine fol-
lowing a modification of the procedure used for the prepara-
tion of Ph2C(pz3Me)2.10 In our hands, the known alcohol
elimination route11 involving benzophenone diethyl ketal and
pyrazole provided a poor yield (<10% by NMR) of the
desired product as a mixture with the starting material and
benzophenone (hydrolysis byproduct). It should also be
mentioned that attempts to prepare compound L1 from the
Peterson rearrangement reaction6 between benzophenone, bis-
(pyrazolyl)carbonyl, and CoCl2 were unsuccessful as only
trace quantity of L1 was formed (NMR) regardless of the
heating period (1-7 days).
The proximity of phenyl groups above and below the AgN4
core enforces the unusual square planar coordination geom-
etry about the metal center. The shortest silver-carbon
(12) (a) Reger, D. L.; Gardinier, J. R.; Grattan, T. C.; Smith, M. D. New
J. Chem. 2003, 1670. (b) Reger, D. L.; Gardinier, J. R.; Semeniuc, R.
F.; Smith, M. D. J. Chem. Soc., Dalton Trans. 2003, 1712.
(13) Reger, D. L.; Brown, K. J.; Gardinier, J. R.; Smith, M. D. Organo-
metallics 2003 22, 4973.
(14) (a) Lindeman, S. V.; Rathore, R.; Kochi, J. K. Inorg. Chem. 2000,
39, 5707. (b) Munakata, M.; Wu, L. P.; Ning, G. L.; Kuroda-Sowa,
T.; Maekawa, M.; Suenaga, Y.; Maeno, N. J. Am. Chem. Soc. 1999,
121, 4968. (c) Munakata, M.; Wu, L. P.; Sugimoto, K.; Kuroda-Sowa,
T.; Maekawa, M.; Suenaga, Y.; Maeno, N.; Fujita, M. Inorg. Chem.
1999, 38, 5674.
The silver compounds 1-3 were isolated in approximately
70-80% yield as colorless solids that precipitated within
(15) Cotton, F. A.; Frenz, B. A.; Murillo, C. A. J. Am. Chem. Soc. 1975,
97 (8), 2118.
(16) Cremer, D.; Pople, J. A. J. Am. Chem. Soc. 1975, 97 (6), 1354.
(17) Lorenzotti, A.; Bonati, F.; Cingolani, A.; Lobbia, G. G.; Leonesi, D.;
Bovio, B. Inorg. Chim. Acta 1990, 170, 199.
(10) Shiu, K.-B.; Yeh, L.-Y.; Peng, S. M.; Cheng, M. C. J. Organomet.
Chem. 1993, 460, 203.
(11) Tsuji, S.; Swenson, D. C.; Jordan, R. F. Organometallics 1999, 18,
4758.
3828 Inorganic Chemistry, Vol. 43, No. 13, 2004

Tuning the Coordination Geometry of SilWer
Figure 3. (A) Molecular geometry of the cation in {Ag[(pz)2CPh2]2}(PF6)‚C3H6O, 1‚acetone, with 40% probability ellipsoids and (B) view depicting
shortest silver-arene contact (2.89 Å) and intracationic noncovalent interactions (red dashed lines).
Figure 4. Molecular geometry of the cations in (A) {Ag[(pz)2CHPh]2}(PF6)‚0.5CH2Cl2, 2‚0.5CH2Cl2, and (B) {Ag[(pz)2CH(CH2Ph)]2}(PF6)‚CH2Cl2, 3‚CH2-
Cl2.
Table 1. Crystallographic Data for {Ag[(pz)2CPh2]2}(PF6)‚C3H6O, 1‚Acetone, Ag[(pz)2CHPh]2}(PF6)‚0.5CH2Cl2, 2‚0.5CH2Cl2, and
Ag[(pz)2CHCH2Ph]2}(PF6)‚CH2Cl2, 3‚CH2Cl2
param
emp formula
1‚acetone
2‚0.5CH2Cl2
3‚CH2Cl2
C41H38AgF6N8OP
911.63
C26.5H25AgClF6N8P
743.84
C29H30AgCl2F6N8P
814.35
fw
temp (K)
space group
a (Å)
b (Å)
c (Å)
190(2)
P1h
150(2)
P3221
12.4420(4)
12.4420(4)
17.627(1)
90
90
120
2363.1(2)
3
1.568
150(2)
Pbca
26.7828(14)
9.2886(5)
27.116(1)
90
90
90
6745.8(6)
8
1.604
8.2996(6)
10.5681(7)
12.0865(8)
72.7520(10)
77.4620(10)
80.7140(10)
982.94(12)
1
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
F
calcd (g/cm3)
1.540
0.627
abs coeff (mm-1
)
0.842
0.871
final R indices [I > 2σ(I)]
R1 ) 0.0324,
wR2 ) 0.0870
R1 ) 0.0349,
wR2 ) 0.0884
R1 ) 0.0281,
wR2 ) 0.0687
R1 ) 0.0291,
wR2 ) 0.0692
R1 ) 0.0570
wR2 ) 0.1444
R1 ) 0.0618
wR2 ) 0.1480
R indices (all data)
distance of 2.892(2) Å [Ag-C(41)] is shorter than the
corresponding distance of 3.193 Å in {Ag(κ2-m-C6H4[C(pz)2-
(2-py)]2)2}(PF6) and is just at the upper limit of the 2.4-2.9
Å range found in other compounds suggested to have η1-
silver(I)‚‚‚arene π interactions.14 This silver-carbon distance
increases to 2.921(2) Å (above the Ag‚‚‚π cutoff) in the
room-temperature crystal structure (see Supporting Informa-
tion) which underscores the weakness of the interaction (if
there is one).
The geometry of the ligand L1 appears to be constant
regardless of the metal system to which it is bound as
evidenced by inspecting the structures of 1 and [Ph2C(pz)2]-
PdCl2.11 As originally pointed out by Cotton and co-
workers,15 in the related [Ph2B(pz)2]Mo(allyl)(CO)3 ligand
Inorganic Chemistry, Vol. 43, No. 13, 2004 3829

Reger et al.
Table 2. Selected Bond Lengths and Angles for Compounds 1-3
compd 3
compd 1a
compd 2
Bond Distances (Å)
2.300(2)
2.337(3)
1.351(4)
1.353(4)
1.457(4)
1.449(4)
Ag-N(11)
2.367(2)
2.356(2)
1.358(2)
1.363(2)
1.487(2)
1.479(2)
2.243(4)
2.419(5)
1.359(6)
1.354(6)
1.458(7)
1.447(7)
Ag-N(31)
Ag-N(41)
N(31)-N(32)
N(41)-N(42)
C(3)-N(32)
C(3)-N(42)
2.273(5)
2.408(5)
1.355(6)
1.359(6)
1.450(7)
1.454(7)
Ag-N(21)
N(11)-N(12)
N(21)-N(22)
C(1)-N(12)
C(1)-N(22)
Bond Angles (deg)
N(11)-Ag-N(21)
N(11)-Ag-N(21a)
N(12)-N(11)-Ag
C(13)-N(11)-Ag
C(13)-N(11)-N(12)
N(11)-N(12)-C(11)
N(11)-N(12)-C(1)
C(11)-N(12)-C(1)
N(22)-C(1)-N(12)
N(21)-N(22)-C(1)
C(21)-N(22)-C(1)
C(21)-N(22)-N(21)
N(22)-N(21)-Ag
C(23)-N(21)-N(22)
C(23)-N(21)-Ag
74.44(6)
105.56(6)
117.4(1)
133.9(1)
104.9(2)
110.53(15)
118.93(13)
130.19(15)
108.92(12)
118.78(14)
130.22(14)
110.32(15)
118.51(11)
105.39(16)
135.74(13)
83.97(9)
123.56
85.1 (2)
119.2(2)b
121.9(3)
130.2(4)
105.5(4)
110.1(5)
121.6(4)
128.3(5)
110.0(5)
121.0(4)
128.4(6)
110.5(6)
116.3(3)
105.3(5)
131.0(4)
N(31)-Ag-N(41)
N(31)-Ag-N(21)
N(32)-N(31)-Ag
C(33)-N(31)-Ag
C(33)-N(31)-N(32)
N(31)-N(32)-C(31)
N(31)-N(32)-C(3)
C(31)-N(32)-C(3)
N(42)-C(3)-N(32)
N(41)-N(42)-C(3)
C(41)-N(42)-C(3)
C(41)-N(42)-N(41)
N(42)-N(41)-Ag
C(43)-N(41)-N(42)
C(43)-N(41)-Ag
84.6(2)
122.5(2)
119.7(3)
126.9(4)
105.5(5)
110.2(5)
121.8(4)
128.0(5)
111.3(5)
121.1(4)
127.5(5)
111.3(4)
119.9(3)
105.1(4)
134.1(4)
120.9(2)
132.0(2)
104.3(2)
111.6(3)
121.4(2)
127.0(3)
111.5(3)
121.8(3)
126.4(3)
111.2(3)
119.5(2)
104.5(3)
135.0(2)
a 190 K. b N(11)-Ag-N(41).
11
system, any other arrangement of phenyl groups in the
complex (such as to promote phenyl CH-Mo agostic
interactions) is prevented by steric interactions between
aromatic hydrogens. Therefore, the steric congestion about
the quarternary carbon combined with the additional favor-
able energetics associated with intracationic noncovalent
interactions (Figure 3b and Supporting Information) in the
present system contributes to the close Ag-aryl contact as
opposed to any significant cation‚‚‚π interaction.
The nitrogen atoms bonded to silver in 2 (Figure 4a) reside
at the corners of a distorted tetrahedron with Ag-N bond
distances (the silver atom resides on an inversion center) of
2.300(2) and 2.337(3) Å. The largest distortion from
tetrahedral geometry is the N(11)-Ag-N(21) bite angle of
84.0° associated with the chelating ligand. The torsion angle
between the two mean planes defined by N(11), Ag, and
N(21) and its symmetry-related counterpart N(11a), Ag, and
N(21a) in 2 is 84.7°. A torsion angle of 90° is expected for
a perfect tetrahedron whereas a torsion angle of 0° is
expected for a square planar arrangement as found in the
case of compound 1.
uration (as shown previously with complexes of Ph2Cpz2
- 15
or (Ph2Bpz2 ) ligands), while compounds 2 and 3 adopt
conformations between a boat and half-boat geometry. These
conclusions are supported by the data in Table 3 showing
both the fold angles and Cremer-Pople ring puckering
parameters16 for compounds 1-3 and several related
derivatives.12b,13,17 By examination of either set of parameters
given in Table 3 for a number of structurally characterized
bis(pyrazolyl)methane complexes, it is evident that there is
a trend correlating the steric demands of the substituents
bound to the central methine carbon and the tendency toward
adopting a boat conformation. The more bulky aryl group
substituents bound to the central methine carbon have more
acute fold angles involving silver (as defined in Table 3)
and, as a consequence, exhibit a greater degree of boat
character than those with fewer aryls. Thus, the fold angles
decrease and a greater boat character is observed in the order
+
of 172.4/173.4° for {Ag[(pz)2CMe2]2 } < 164.1/165.4° for
{Ag[(pz)2CH(CH2Ph)]2+}(3) < 160.3° for {Ag[(pz)2CHPh]2+}
+
(2) < 136.9° for {Ag[(pz)2CPh2]2 } (1).
Supramolecular Structures. In both the 190 and 293 K
(Supporting Information) structures, the cations in 1 ag-
gregate into polymeric chains (Figure 5) along the crystal-
lographic a-axis as a result of CH‚‚‚π interactions between
the phenyl group proximal to silver of one cation which acts
as a hydrogen donor to the π clouds of the two pyrazolyl
acceptors of an adjacent cation.18,19 Interestingly, the poly-
meric supramolecular structure in 1 at 190 and 293 K is in
contrast to the 294 K structures of {Ag(κ2-C6H5[C(pz)2(2-
py)])2}(PF6) and {Ag(κ2-m-C6H4[C(pz)2(2-py)]2)2}(PF6), whose
cations were organized into quasi-inorganic-organic layered
The coordination geometry about silver in 3 is distorted
tetrahedral (Figure 4b), and contrary to the schematic
depicted in Figure 2, there is no close Ag-arene contact.
The four Ag-N bond distances in 3 show a disparity with
two short [2.243(4) and 2.273(5) Å for Ag-N(11) and Ag-
N(31)] and two long [2.419(5) and 2.408(5) Å for Ag-N(21)
and Ag-N(41)] Ag-N bonds. Of the three title compounds
1-3, compound 3 has the largest average N-Ag-N bite
angle for the chelate ring(s) at an average value of 84.8°.
The torsion angle between the two mean planes defined by
N(11)-Ag-N(21) and N(31)-Ag-N(41) is 90.2°; however,
the tetrahedron is further distorted by a 19.0° pivot of the
mean N(31)-Ag-N(41) plane toward N(21).
(18) Takahashi, H.; Tsuboyama, S.; Umezawa, Y.; Honda, K.; Nishio, M.
Tetrahedron 2000, 56, 6185.
(19) Grepioni, F.; Cojazzi, G.; Draper, S. M.; Scully, N.; Braga, D.
Organometallics 1998, 17, 296.
Analysis of the arrangements of the AgN4C chelate rings
in these three structures shows that 1 adopts a boat config-
3830 Inorganic Chemistry, Vol. 43, No. 13, 2004

Tuning the Coordination Geometry of SilWer
Table 3. Coordination Geometries and AgN4C Ring Puckering Parameters in Various Silver Di(pyrazolyl)Methane Complexes
fold
Cremer-Pople paramsc
θ (deg)
cation
coord environ
AgNNa
NNCb
Q
φ (deg)
ref
+
d
{Ag(C6H5[C(pz)2(2-py)])2
}
sq pl
sq pl
sq pl
sq pl
tet
tet
tet
tet
tet
135.4
136.4
136.9
147.7
154.0
160.3
160.4
161.9
164.1
165.4
167.6
172.4
173.4
130.4
127.9
128.6
128.6
124.5
124.8
126.9
121.8
121.4
123.0
121.1
121.4
120.9
na
na
na
3
j
{Ag[(pz)2CPh2]2+} (1)d (190 K)
1.090
1.081
0.910
0.823
0.736
0.726
0.741
0.712
0.697
0.669
0.634
0.633
101.56
101.57
96.90
88.30
87.62
87.20
84.13
82.64
83.08
79.00
72.44
73.23
184.2
184.6
181.8
178.5
180.5
172.3
189.9
171.9
184.3
178.7
174.5
186.6
{Ag[(pz)2CPh2]2+} (1)d (293 K)
+
d,g
{Ag(m-C6H4[C(pz)2(2-py)]2)2
{Fe[C5H4CH(pz)2]2Ag‚OEt2
}
3
13
j
12b
13
j
+
d,h
}
n
{Ag[(pz)2CHPh]2+} (2)d
+
d,g
{Ag2(µ-[(pz)2CH]2CH2)2
}
{Fe[C5H4CH(pz)2]2Ag+}n
d,i
{Ag[(pz)2CHCH2Ph]2+} (3)d
+
e,g
{Ag2(µ-[(pz)2CH]2CH2)2
}
tet
tet
12b
17
+
f
{Ag[(pz)2CMe2]2
}
a Fold AgNN is the angle defined by points connecting silver and the centroid between N(11) and N(21) and the centroid between N(12) and N(22), each
of which lies on a plane bisecting AgN4C chelate ring. b Fold CNN is similar but with the C atom replacing Ag as one point. c Reference 16. na: calculations
-
-
not available due to extensive ligand disorder. Ideal boat has θ ) 90 and φ ) 180/0; ideal half-boat has θ ) 54.7 and φ ) 180/0. d PF6 salt. e CF3SO3
-
salt. f ClO4 salt. g One of two independent Ag sites. h Helical form. i Nonhelical form. j This work.
CH‚‚‚F bonding interactions.19 The helical chains can be
generated by considering only the interaction between the
methine hydrogen and F(2), while the remainder of the
CH‚‚‚F interactions involving F(5), F(6), and C(34)H-
(34)‚‚‚F(3) that are below the 2.6 Å cutoff (Table 4) help
support both the helical arrangement and the overall three-
dimensional supramolecular structure which is that of a close-
packed network of helices (Figure 7). The helices are
arranged in a close-packed network by a combination of the
aforementioned CH‚‚‚F interactions and by two types of
CH‚‚‚π interactions between the phenyl and pyrazolyl
groups. In the first CH‚‚‚π interaction, the pyrazolyl group
acts as a hydrogen donor [H(13)], while the phenyl group
acts as an acceptor [C(13)H(13)‚‚‚centroid: 3.198 Å, 134.36°].
The second CH‚‚‚π interaction is a bifurcated one in which
the phenyl group acts as a hydrogen donor to the π clouds
of two pyrazolyl rings of one adjacent cation. Specifically,
H(33) of the phenyl group is directed toward the centroids
(Ct) of the pyrazolyl rings containing N(11) and N(21) of
an adjacent cation. The geometry of the interaction is such
that the C(33)H(33)‚‚‚Ct[N(11)] distance and angle of 3.12
Å and 121.1° along with the C(33)H(33)‚‚‚Ct[N(21)] distance
and angle of 2.97 Å and 134.7° are each within the typical
range for a CH‚‚‚π interaction (vide supra).18
Figure 5. Polymeric chains of cations in {Ag[(pz)2CPh2]2}(PF6)‚C3H6O,
1‚acetone, formed via CH‚‚‚π interactions (pink lines).
Table 4. Summary of Noncovalent Interactions in
{Ag[(pz)2CHPh]2}(PF6)‚0.5CH2Cl2, 2‚0.5CH2Cl2
donor (D)‚‚‚acceptor (Å)
H‚‚‚A (Å)
C(H)‚‚‚A (deg)
C(1)H(1)‚‚‚F(2)
2.36
2.44
2.43
2.50
2.48
2.50
2.45
2.40
3.20
3.12
2.97
156.6
157.1
146.1
147.8
138.5
136.7
129.7
130.3
134.4
121.1
134.7
C(1)H(1)‚‚‚F(2a)
C(1)H(1)‚‚‚F(5)
C(1)H(1)‚‚‚F(6)
C(11)H(11)‚‚‚F(2)
C(21)H(21)‚‚‚F(6)
C(22)H(22)‚‚‚F(5)
C(34)H(34)‚‚‚F(3)
C(13)H(13)‚‚‚Ct[C(33)]a
C(33)H(33)‚‚‚Ct[N(11)]
C(33)H(33)‚‚‚Ct[N(21)]
Compound 3 appears to form a layered structure (Figure
8) as a result of numerous short CH‚‚‚F interactions (<2.6
Å) and a CH‚‚‚π interaction between a phenyl group
hydrogen donor [H(42)] and a pyrazolyl group [containing
N(31)] acceptor [C(42)H(42)‚‚‚centroid 2.89 Å, 141.5°].
Unfortunately, a full examination of the supramolecular
structure of 3 is precluded as a result of the disorder of one
benzyl group (vide supra) in addition to that affecting both
a Ct refers to centroid of the arene ring that contains the element denoted
in brackets.
three-dimensional supramolecular structures by a combina-
tion of weak CH‚‚‚π18 and CH‚‚‚F interactions.19
The cations in 2 are arranged into helical chains by
CH‚‚‚F interactions as shown in Figure 6, where the
hexafluorophosphate anion serves as a bridge connecting
adjacent cations. In particular, the acidic methine hydrogen
participates in a trifurcated interaction with F(2), F(5), and
F(6) of the hexafluorophosphate anion where the geometry
of each component of this interaction is given in Table 4. It
should be noted that while the hexafluorophosphate anion
is disordered over two nearby positions, the proximity of
the methine hydrogen [CH(1)] to each disorder component
of the bridging atom F(2) is 2.36 and 2.44 Å, respectively,
which are each well below the 2.6 Å proposed limit for weak
-
the PF6 anion and the solvent of crystallization.
Conclusions
We have prepared three bis(pyrazolyl)methane ligands that
contain varying degrees of steric bulk around the central
carbon atom of the ligand. In the case of Ph2C(pz)2, L1, the
steric constraints imposed by the aryl groups enforce an
unusual square planar conformation in the silver hexafluo-
Inorganic Chemistry, Vol. 43, No. 13, 2004 3831

Reger et al.
Figure 6. Helical chains in {Ag[(pz)2CHPh]2}(PF6)‚0.5CH2Cl2, 2‚0.5CH2Cl2. Views are perpendicular to the c-axis (left) and along the c-axis (right).
The supramolecular structures of the three complexes {Ag-
[(pz)2CPh2]2}(PF6), 1‚acetone, {Ag[(pz)2CHPh]2}(PF6)‚0.5CH2-
Cl2, 2‚0.5CH2Cl2, and {Ag[(pz)2CHCH2Ph]2}(PF6)‚CH2Cl2,
3‚CH2Cl2 are assembled as a result of CH‚‚‚π interactions
and for 2‚0.5CH2Cl2 and 3‚CH2Cl2 also by CH‚‚‚F interac-
tions such that polymeric chains of cations form in the case
of compound 1, a closed-packed helical network of cations
is found for 2, and sheets of a cations are found in 3. It is
likely that the supramolecular organization has a minor
contribution to the perturbing the coordination geometry
about silver; given the large variety of supramolecular
structures observed for the known silver pyrazolylmethane
complexes, it is evident that the coordination geometry about
silver is primarily dictated by the steric demands of the
Figure 7. Close packing of helices in {Ag[(pz)2CHPh]2}(PF6)‚0.5CH2-
ligand.
Cl2, 2‚0.5CH2Cl2. Solvent (not shown) resides in channels created by helices.
Finally, given that no significant Ag‚‚‚π interactions were
observed in 1-3, {Ag(κ2-m-C6H4[C(pz)2(2-py)]2)2}(PF6), or
{Ag(C6H5[C(pz)2(2-py)])2}(PF6) but were observed in the
coordination polymer {o-C6H4[CH2OCH2C(3-Phpz)3]2Ag2-
(acetone)(BF4)2}n, it is clear that designing ligands that place
an arene group in proximity to silver(I) is not enough to
Figure 8. View of the side of a sheet in 3 (down b-axis) assembled by
CH‚‚‚F (green lines) and CH‚‚‚π interactions (red lines).
ensure a cation‚‚‚π interaction. Rather, it is also necessary
for the silver center to have an available coordination site.
rophosphate complex. This same effect was also observed
The tetracoordination of the silver(I) observed for the former
in the related bis(pyrazolyl)(2-pyridyl)methane-aryl com-
five compounds prevents cation‚‚‚π arene interactions,
plexes, {Ag(κ2-m-C6H4[C(pz)2(2-py)]2)2}(PF6) and {Ag-
whereas in the latter coordination polymer the tricoordinate
(C6H5[C(pz)2(2-py)])2}(PF6). One consequence of this ar-
silver expands its coordination sphere by η2-bonding to a
rangement is that the AgN4C chelate rings adopt boat
neighboring phenyl ring.
configurations. When the steric congestion about the methine
carbon is alleviated as in either PhCH(pz)2, L2, or PhCH2C-
Acknowledgment. We thank the National Science Foun-
(pz)2, L3, the silver(1) centers adopt the more familiar
tetrahedral coordination geometry and the AgN4C rings are
dation (Grant CHE-0110493) for support. The Bruker CCD
single-crystal diffractometer was purchased using funds
no longer in the boat conformation; rather they adopt
provided by the NSF Instrumentation for Materials Research
conformations between a full boat and half boat. Qualita-
Program through Grant DMR:9975623.
tively, the boat conformation is favored for bulky groups
bound to the methine carbon whereas the less sterically
demanding substituents favor the half-boat conformation. The
general order found by a comparison of the fold angle
involving the metal atom of the AgN4C chelate ring for a
number of different structurally characterized silver bis-
(pyrazolyl)methane complexes is (alkyl)(H)C(pz)2 > (aryl)-
(H)C(pz)2 > (aryl)2C(pz)2.
Supporting Information Available: Crystallographic informa-
Cl ,
and 3‚CH2Cl2 and full details of supramolecular interactions in 1.
This material is available free of charge via the Internet at
http://pubs.acs.org.
tion files (CIF’s) for 1‚acetone at 293 and at 190 K, 2‚0.5CH2
2
IC0497174
3832 Inorganic Chemistry, Vol. 43, No. 13, 2004