Synthesis of meta-C6H4[C(1-pyrazolyl) 2(2-pyridyl)]2, a fixed geometry bitopic heteroscorpionate and the crystal structure of its unusual square planar silver(I) complex

Article abstract of DOI:10.1016/j.poly.2003.11.018

The reaction between bis(1-pyrazolyl)sulfone (prepared in situ by the reaction between NaH, Hpz, and SOCl₂ in THF) and C₆H ₄[C(O)(2-py)]₂ in THF catalyzed by CoCl₂ yields m-C₆H₄[C(pz)₂(2-py)]₂ (1, pz= pyrazolyl, py=pyridyl) in moderate yield, along with 1-[C(pz) ₂(2-py)]-4-[C(O)(2-py)]C₆H₄. The potentially bitopic ligand 1 reacts with AgPF₆ to yield [Ag(1) ₂](PF)₆ (3), regardless of the stoichiometry of reagents used in the preparation. X-ray structural analysis of this silver complex shows that two ligands bond to a silver in a κ²-fashion via the pyrazolyls in one C(pz)₂(py) group in each ligand while the other is non-coordinated. The AgN₄C chelate rings adopt a boat conformation and the silver resides in an unusual square planar coordination environment. Non-covalent forces organize the two-dimensional structure of 3 such that it approaches a layered inorganic-organic hybrid material. Reaction of C ₆H₅[C(pz)₂(2-py)] and AgPF₆ yields {Ag(κ²-C₆H₅[C(pz)₂(2-py)]) ₂}(PF₆) (4). The structure is disordered but the ligands are bidentate, the nitrogen donor atoms are in a square planar coordination environment about the silver and the overall structure is similar to 3.

Full text of DOI:10.1016/j.poly.2003.11.018

Polyhedron 23 (2004) 291–299
www.elsevier.com/locate/poly
Synthesis of meta-C6H4[C(1-pyrazolyl)2(2-pyridyl)]2, a fixed geometry
bitopic heteroscorpionate and the crystal structure of its
unusual square planar silver(I) complex
*
Daniel L. Reger , James R. Gardinier, Mark D. Smith
Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, USA
Received 21 May 2003; accepted 12 August 2003
Abstract
The reaction between bis(1-pyrazolyl)sulfone (prepared in situ by the reaction between NaH, Hpz, and SOCl2 in THF) and
C6H4[C(O)(2-py)]2 in THF catalyzed by CoCl2 yields m-C6H4[C(pz)2(2-py)]2 (1, pz ¼ pyrazolyl, py ¼ pyridyl) in moderate yield,
along with 1-[C(pz)2(2-py)]-4-[C(O)(2-py)]C6H4. The potentially bitopic ligand 1 reacts with AgPF6 to yield [Ag(1)2](PF)6 (3), re-
gardless of the stoichiometry of reagents used in the preparation. X-ray structural analysis of this silver complex shows that two
ligands bond to a silver in a j2-fashion via the pyrazolyls in one C(pz)2(py) group in each ligand while the other is non-coordinated.
The AgN4C chelate rings adopt a boat conformation and the silver resides in an unusual square planar coordination environment.
Non-covalent forces organize the two-dimensional structure of 3 such that it approaches a layered inorganic–organic hybrid ma-
terial. Reaction of C6H5[C(pz)2(2-py)] and AgPF6 yields {Ag(j2-C6H5[C(pz)2(2-py)])2}(PF6) (4). The structure is disordered but the
ligands are bidentate, the nitrogen donor atoms are in a square planar coordination environment about the silver and the overall
structure is similar to 3.
Ó 2003 Elsevier Ltd. All rights reserved.
Keywords: Bitopic heteroscorpionate ligand; Square planar silver complex
1. Introduction
tain two bis(pyrazolyl)methane units linked by either a
flexible methylene or a semi-rigid ferrocenyl group, and
have explored their coordination chemistry with silver
[5,6]. Additionally, we have reported on the preparation
of coordination polymers that incorporate semi-rigid
organic spacers based on polytopic tris(pyrazolyl)meth-
anes of the type C6H6ꢀn[CH2OCH2C(pz)3]n (n ¼ 2, 4
[7–9]; pz ¼ pyrazolyl ring). The use of poly(pyraz-
olyl)methane ligands linked by rigid organic spacers
would be of interest toward the preparation of either
large metallacycles of predefined geometry or the devel-
opment of coordination networks with a predictable
arrangement of metal centers within the material. To this
end, we have prepared a; a; a0; a0-tetrakis(1-pyrazolyl)-
a; a0-bis(2-pyridyl)-1,3-xylene, m-C6H4[C(pz)2 (2-py)]2
(1, py ¼ pyridyl ring), a potentially bitopic heteroscor-
pionate, that can be envisioned as a 120o rigid organic
spacer. In this paper we will detail the preparation of 1
and outline our initial observations regarding its coor-
dination chemistry with silver hexafluorophosphate. For
Current interest in coordination networks is driven in
part by the desire to combine the variety in structural,
physical, and spectroelectrochemical properties of both
the inorganic and organic constituents with the practi-
cality and function of zeolite-type materials [1,2]. Recent
work published by Wenbin LinÕs group is testament to
the potential for the realization of such a goal [3,4].
Advances in the design of polytopic ligands, which serve
as organic spacers between two or more metal centers,
have been instrumental to this area of research. Over
recent years, our group has been interested in exploring
the preparation and coordination chemistry of a variety
of polytopic poly(pyrazolyl)methane ligands. We have
prepared bitopic tetra-(pyrazolyl) compounds that con-
* Corresponding author. Tel.: +1-803-777-5263; fax: +1-803-777-
9521.
E-mail address: reger@mail.chem.sc.edu (D.L. Reger).
0277-5387/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2003.11.018

292
D.L. Reger et al. / Polyhedron 23 (2004) 291–299
comparison, the related chemistry involving the mono-
topic analogue, C6H5[C(pz)2(2-py)] (2), will also be
described.
1-[C(pz)2(2-py)]-4-[C(O)(2-py)]C6H4, 1a, as a colorless
solid from the second pale yellow band (Rf ¼ 0:3 TLC
1
plate). Mp 113–115 °C. IR (cmꢀ1): mco 1669 (br, vs). H
NMR (400 MHz, CDCl3) 8.68 (d, J ¼ 4 Hz, 1H, H6-
pyCO), 8.62 (d, J ¼ 4 Hz, 1H, H6-py), 8.16 (m, 1H,
aryl), 8.00 (d, J ¼ 8 Hz, 1H, H3-pyCO), 7.98 (s, 1H,
aryl), 7.85 (ddd, J ¼ 8, 8, 2 Hz, 1H, H4-pyCO), 7.73
(ddd, J ¼ 8, 8, 2 Hz, 1H, H4-py, 7.68 (d, J ¼ 1 Hz, 2H,
H3-pz), 7.56 (d, J ¼ 2 Hz, 2H, H5-pz), 7.49 (m, 2H,
aryl), 7.45 (ddd, J ¼ 8, 4, 1 Hz, 1H, H5-pyCO), 7.32
(ddd, J ¼ 8, 4, 1 Hz, 1H, H5-py), 7.24 (d, J ¼ 8 Hz, 1H,
H3-py), 6.33 (d, J ¼ 2 Hz, 2H, H4-pz). 13C NMR
(101.62 MHz, CDCl3) 193.0 (C@O), 158.3 (C2-py),
154.9 (C2-pyCO), 148.9 (C6-pyCO), 148.6 (C6-py), 140.9
(C5-pz), 139.7 (C3-aryl), 137.2 (C4-pyCO), 137.1 (C4-
py), 136.0 (C1-aryl), 133.8 (C4-aryl), 132.6 (C3-pz), 131.9
(C2;6-aryl), 128.1 (C5-aryl), 126.4 (C3-pyCO), 124.9 (C3-
py), 124.6 (C5-pyCO), 123.9 (C5-py), 106.1 (C4-pz), 87.1
(Ca). Direct probe MS m/z (Rel. Int. %) [assgn]: 406(32)
[M]þ, 338(100) [M-Hpz]þ, 328(21) [M-py]þ, 233(29)
[C(C6H4)(pz)py]þ, 182(12) [PhC(O)py]þ, 78(37) [py]þ.
After complete elution of 1a, the column was sequen-
tially flushed with acetone, acetonitrile, acetonitrile/
methanol (1:4) which after combining these fractions
and evaporating the solvents gave 0.27 g (0.51 mmol,
34% based on C6H4[C(O)(2-py)]2) of 1 as a pale yellow
solid. Mp 223–225 °C dec. 1H NMR (400 MHz, CDCl3)
8.61 (d, J ¼ 4 Hz, 2H, H6-py), 7.69 (ddd, J ¼ 8, 8, 2 Hz,
2H, H4-py), 7.61 (d, J ¼ 1 Hz, 4H, H3-pz), 7.53 (d,
J ¼ 2 Hz, 4H, H5-pz). 7.31 (t, J ¼ 8 Hz, 1H, H5-aryl),
7.29 (ddd, J ¼ 8, 4, 2, Hz, 2H, H5-py), 7.18–7.13 (m, 4H,
aryl and H3-py ), 6.28 (d, J ¼ 2 Hz, 2H, H4-pz). 1H
NMR (400 MHz, acetone-d6) 8.57 (d, J ¼ 5 Hz, 2H, H6-
py), 7.82 (ddd, J ¼ 7, 7, 2 Hz, 2H, H4-py), 7.57 (d, J ¼ 1
Hz, 4H, H3-pz), 7.50 (d, J ¼ 2 Hz, 4H, H5-pz). 7.40
(ddd, J ¼ 7, 5, 2 Hz, 2H, H5-py), 7.33 (t, J ¼ 8 Hz, 1H,
H5-aryl), 7.25 (s, 1H, aryl), 7.13 (d, J ¼ 8 Hz, 2H, aryl),
7.09 (dd, J ¼ 7, 2 Hz, 2H, H3-py), 6.32 (dd, J ¼ 2, 1 Hz,
4H, H4-pz). 13C NMR (101.62 MHz, CDCl3) 158.3 (C2-
py), 148.6 (C6-py), 140.7 (C5-pz), 138.8 (Cipso-Ph), 136.9
(C4-py), 133.7 (aryl), 132.6 (C3-pz), 129.2 (C4=6-aryl),
128.2 (C2-aryl), 124.8 (C3-py), 123.8 (C5-py), 105.9 (C4-
pz), 87.2 (Ca). HRMS-Direct probe (m/z): Anal. Calc.
for C30H24Nþ10 524.2185. Found: 524.217. Direct probe
MS m/z (Rel. Int. %) [assgn]: 524(2) [M]þ, 456(100) [M-
Hpz]þ, 389(36) [M-2pz]þ, 378(31) [M-pz-py]þ,
322(19)[M-3pz]þ, 310(18) [M-2pz-py]þ, 78(12) [py]þ.
2. Experimental
2.1. General
Solvents for synthetic procedures, and spectroscopic
studies were dried by conventional methods and distilled
under N2 atmosphere immediately prior to use. The
compound m-C6H4[C(O)(2-py)]2 was prepared as de-
scribed previously [10]. All other 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. Sil-
ver hexafluorophosphate was stored and handled under
a purified nitrogen atmosphere in a drybox. Robertson
Microlit Laboratories performed all elemental analyses.
Melting point determinations were made on samples
contained in sealed glass capillaries by using an Elec-
trothermal 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 Mercury 400 or a
Varian Inova 500 instrument, as noted within the text.
Chemical shifts were referenced to solvent resonances at
either dH 7.27, dC 77.2 for CDCl3, or dH 2.05, dC 29.8 for
acetone-d6.
2.2. Ligand preparation
The preparation of C6H5C(pz)2(2-py) has been de-
scribed previously [11], however, in this contribution an
alternate purification step and additional characteriza-
tion data are provided. The title bitopic derivative was
prepared by using an analogous procedure. Therefore,
only the quantity of reagents, solvent, reaction time, and
the details of chromatographic separation are described
below for each.
2.3. Preparation of m-C6H4[C(pz)2(2-py)]2, a; a; a0; a0-
tetrakis(1-pyrazolyl)-a; a0-bis(2-pyridyl)-1,3-xylene, (1)
A mixture of 2.9 mmol SO(pz)2 [from 0.14 g (5.9
mmol) NaH, 0.40 g (5.9 mmol) Hpz and 0.21 ml (2.9
mmol) SOCl2], 0.43 g (1.5 mmol) C6H4[C(O)(2-py)]2,
and 60 mg (30 mol% of C6H4[C(O)(2-py)]2) CoCl2 in 80
ml THF were heated at reflux for four days. After work-
up, chromatographic separation of the product mixture
on SiO2 by using Et2O as the eluent afforded 0.16 g (0.55
mmol) C6H4[C(O)(2-py)]2 from the first pale yellow
band (Rf ¼ 0:7 on TLC plate) and 0.14 g (0.34 mmol) of
2.4. Preparation of C6H5[C(pz)2(2-py)], a; a-bis(1-
pyrazolyl)-a-(2-pyridyl)toluene (2)
A mixture of 21 mmol SO(pz)2 [from 1.0 g (42 mmol)
NaH, 2.9 g (42 mmol) Hpz, and 1.5 ml (21 mmol)
SOCl2], 3.7 g (20 mmol) 2-benzoylpyridine, and 75 mg
(3 mol% of 2-benzoylpyridine) CoCl2 in 20 ml THF
were heated at reflux for 15 h. After work-up,

D.L. Reger et al. / Polyhedron 23 (2004) 291–299
293
chromatographic separation of the product mixture on
SiO2 with 50% Et2O/hexanes afforded 2.2 g (37% based
on 2-benzoylpyridine) of 2 as a colorless solid from the
second colorless band (Rf ¼ 0:4 on TLC plate). Mp 138–
139 °C (lit. 123–125 °C [11]). 1H NMR (400 MHz,
CDCl3) 8.70 (d, J ¼ 4 Hz, 1H, H6-py), 7.73 (ddd, J ¼ 8,
8, 2 Hz, 1H, H4-py), 7.70 (d, J ¼ 1 Hz, 2H, H3-pz), 7.57
(dd, J ¼ 2, 1 Hz, 2H, H5-pz). 7.41–7.35 (m, 3H, o- and
p-H of Ph), 7.31 (ddd, J ¼ 8, 4, 1 Hz, 1H, H5-py), 7.24
(d, J ¼ 8 Hz, 1H, H3-py), 7.20 (dd, J ¼ 8, 2 Hz, 2H, m-
H of Ph), 6.33 (d, J ¼ 2 Hz, 2H, H4-pz). 13C NMR
(101.62 MHz, CDCl3) 158.7 (C2-py), 148.8 (C6-py),
140.7 (C5-pz), 139.6 (Cipso-Ph), 137.0 (C4-py), 132.6 (C3-
pz), 129.4 (o- and p- of Ph), 128.2 (m-C of Ph), 124.3
(C3-py), 123.7 (C5-py), 105.8 (C4-pz), 87.3 (Ca). Direct
probe MS m/z (Rel. Int. %) [assgn]: 301(62) [M]þ,
233(100) [M-Hpz]þ, 223(86) [M-py]þ, 167(99) [M-
2Hpz]þ, 77(28) [Ph]þ.
by layering an acetone solution with Et2O and allowing
the solvents to diffuse. Mp, 175–178 °C crystals become
opaque and shatter; 187–188 °C dec. to green–gray so-
1
lid. H NMR (400 MHz, acetone-d6) 8.59 (d, J ¼ 4 Hz,
1H, H6-py), 7.98 (ddd, J ¼ 8, 8, 2 Hz, 1H H4-py), 7.62
(d, J ¼ 1 Hz, 2H, H3-pz), 7.59–7.49 (br m, 6H, H5-pz
and aryl), 7.04 (d, J ¼ 8 Hz, H3-py), 6.85–6.83 (br m,
H5-py and aryl), 6.46 (dd, J ¼ 2, 1 Hz, H4-pz). 13C
NMR (101.62 MHz, acetone-d6) 157.5 (C2-py), 150.4
(C6-py), 142.8 (C3-pz), 139.5, 138.9, 135.0, 131.0 (C5-
pz), 129.8, 129.7, 126.1, 125.8, 106.8 (C4-pz), 88.0 (Ca).
HRMS-ESI(+) (m/z): Anal. Calc. for [M-PF6]þ,
C36H30N10Agþ: 709.1702. Found: 709.1706. ESI(+) MS
m/z (Rel. Int. %) [assgn]: 709 (100) [AgL2]þ, 449 (29)
[AgL(CH3CN)]þ, 408 (2) [AgL]þ, 302 (65) [HL]þ, 234
(60) [HL-pz]þ.
2.6. Crystallography
2.5. Silver hexafluorophosphate complexes
2.6.1. X-ray structure determinations of {Ag(j2-m-
C6H4[C(pz)2(2-py)]2)2}(PF6), (3) and {Ag(j2-C6H5
[C(pz)2(2-py)])2}(PF6)ꢁacetone (4ꢁacetone)
2.5.1. Preparation of {Ag(j2-m-C6H4[C(pz)2(2-py)]2)2}
(PF6), (3)
A colorless prism of 3 and a colorless prismatic
crystal of 4ꢁacetone were each mounted onto the end of
a thin glass fiber using inert oil. X-ray intensity data
were measured in the dark at 190(2) K in the nitrogen
cold stream of a Bruker SMART APEX CCD-based
A mixture of 0.087 g (0.17 mmol) 1 and 0.042 g (0.17
mmol) AgPF6 was dissolved in 15 ml of a 2:1 mixture of
CH3CN/acetone. After a reflux period of 6 h, trace gray
solid was observed and solvent was removed by vacuum
distillation. The resulting brown solid was washed se-
quentially with 5 ml each of Et2O and hexanes. The
insoluble residue was then extracted with 10 ml CH3CN.
The filtered extract was layered with 50 ml Et2O and
after allowing the solvents to diffuse overnight, the col-
orless crystals of {Ag(C6H4[C(pz)2(2- py)]2)2}(PF6) (3)
were isolated by filtration and were air-dried (84 mg,
78%). Mp, 205–210 °C dec. Anal. Calc. for
C60H52N20AgF6O2P, 3ꢁ2 H2O: C, 53.86 (53.98); H, 3.92
ꢀ
diffractometer system (Mo Ka radiation, k ¼ 0:71073 A
[12]. A total of 1800 raw data frames of width 0.3° in x
were collected at three different / angles, with an ex-
posure time of 15 and 20 s per frame for 3 and 4ꢁacetone,
respectively. The data collections covered the entire
sphere of reciprocal space. The first 50 frames of each
were re-collected at the end of the data set to monitor
crystal decay. The raw data frames were integrated into
reflection intensity files using SAINT+ [12], which also
applied corrections for Lorentz and polarization effects.
The final unit cell parameters are based on the least-
squares refinement of 6425 reflections with I > 5ðrÞI
from the data set for 3 and 3377 reflections with
I > 5ðrÞI from the data set for 4ꢁacetone. Analysis of the
data showed negligible crystal decay during the data
collections and no absorption corrections were applied
(see Table 1).
1
(3.53); N, 20.94 (20.81). H NMR (400 MHz, acetone-
d6) 8.60 (d, J ¼ 4:5 Hz, 2H, H6-py), 7.89 (ddd, J ¼ 8, 8,
2 Hz, 2H, H4-py). 7.64 (d, J ¼ 1 Hz, 4H, H3-pz), 7.52 (d,
J ¼ 2 Hz, 4H, H5-pz), 7.47–7.40 (m, 3H, aryl), 7.15 (dd,
J ¼ 8, 2 Hz, 2H, H5-py), 7.09 (d, J ¼ 8 Hz, 2H, H3-py),
6.95 (s, 1H, aryl), 6.38 (dd, J ¼ 2, 1 Hz, 4H, H4-pz).
2.5.2. Preparation of {Ag(j2-C6H5[C(pz)2(2-py)])2}
(PF6) (4)
A solution of 0.333 g (1.10 mmol) C6H5[C(pz)2(2-py)]
in 10 ml THF was added by cannula to a solution of
0.139 g (0.550 mmol) AgPF6 in 10 ml THF under a
nitrogen atmosphere. A colorless solid precipitated
within a few minutes of mixing and the resulting sus-
pension was stirred 4 h. The product mixture was then
separated by cannula filtration. The insoluble colorless
solid was washed with two 5 ml portions of Et2O and
dried under vacuum to leave 0.435 g (92% yield) of
{Ag(C6H5[C(pz)2(2-py)])2}(PF6) as a colorless solid.
Crystals suitable for X-ray structural studies were grown
2.6.2. Structure refinement of 3
The compound crystallized in the triclinic system; the
ꢁ
space group P1 was confirmed by successful solution
and refinement of the structure. The structure was
solved by direct methods followed by difference Fourier
synthesis, and refined by full-matrix least-squares
against F 2, using the SHELXTL software package [13].
The Ag and P atoms both lie on centers of symmetry;
all other atoms are on general positions. The asym-
metric unit is made up of the Ag ion, one C6H4[C(pz)2
(2-py)]2 ligand, and half a PFꢀ6 anion. The PF6ꢀ anion is

294
D.L. Reger et al. / Polyhedron 23 (2004) 291–299
Table 1
Experimental and crystal data for {Ag(j2-m-C6H4[C(pz)2(2-py)]2)2}(PF6), (3), and {Ag(j2-C6H5[C(pz)2(2-py)])2}(PF6) (4)
3
4ꢁacetone
C39H36AgF6N10OP
Formula
Mw
C
60H48AgF6N20
P
1302.02
triclinic
913.62
triclinic
Crystal system
Space group
ꢁ
ꢁ
P1
8.620(1)
P1
8.316(1)
ꢀ
a (A)
ꢀ
b (A)
12.427(2)
13.683(2)
105.464(2)
91.531(2)
98.713(2)
1392.8(3)
1
10.256(2)
12.191(2)
ꢀ
c (A)
a (°)
b (°)
c (°)
73.002(3)
75.898(3)
79.908(3)
958.2(3)
3
ꢀ
V (A )
Z
1
1.583
0.645
qcalc (g/cm3)
1.552
0.473
l (mmꢀ1
)
h range (°)
Index range
1.56–26.41
ꢀ10 6 h 6 10
ꢀ15 6 k 6 15
ꢀ17 6 l 6 17
12879 (5695)
1.78–26.48
ꢀ10 6 h 6 10
ꢀ12 6 h 6 12
ꢀ15 6 h 6 15
8836 (3941)
R1 ¼ 0:0439, wR2 ¼ 0:0872
R1 ¼ 0:0718, wR2 ¼ 0:0964
0.556/)0.258
Total (independent) reflections
Final R indices [I > 2rðIÞ]
R indices (all data)
R1 ¼ 0:0434, wR2 ¼ 0:0960
R1 ¼ 0:0584, wR2 ¼ 0:1012
0.617/)0.311
3
ꢀ
Largest different peak/hole (e=A )
disordered over two orientations in an 80/20 ratio. All
non-hydrogen atoms were refined with anisotropic dis-
placement parameters; hydrogen atoms were placed in
calculated positions and refined as riding atoms.
F–P–F axis in a 0.59/0.41 ratio. Finally, the acetone
molecule of crystallization is disordered about an in-
version center. To achieve a stable refinement, a total of
13 restraints (SHELX EADP and SADI) were em-
ployed. Eventually, all non-hydrogen atoms were refined
with anisotropic displacement parameters; hydrogen
atoms were placed in calculated positions and refined
using a riding model. Solution and refinement in the
space group P1 resulted in the same ligand pz/py ring
and PF6 disorder, as well as unstable ring geometries
and large correlations between inversion-related atoms.
2.6.3. Structure refinement of 4ꢁacetone
This compound crystallized in the triclinic system
ꢁ
where the space group P1 was confirmed by successful
solution and refinement of the structure. The structure
was solved by a combination of direct methods and
difference Fourier synthesis, and refined by full-matrix
least-squares against F 2, using the SHELXTL software
package [13]. The Ag and P atoms lie on a centers of
symmetry; all other atoms are on general positions. The
asymmetric unit is made up of the Ag ion, one
C6H5[C(pz)2(2-py)] ligand, half a PFꢀ6 anion, and half
an acetone molecule of crystallization. All components
of the crystal (cation, anion, solvent) are affected by
disorder. The ligand bound to Ag is disordered over all
three possible j2, j0 conformations allowed by the
combination of two pyrazolyl rings (pz) and one pyridyl
ring (py). Only the donor rings are affected; the central
methine carbon and the pendant phenyl ring behave
normally. Referring to the ring numbering scheme in
Figure 5a, the average composition of ring ‘‘1n’’ is 0.75
pz/0.25 py; that of ring ‘‘2n’’ is 0.75 pz/0.25 py, and that
of ring ‘‘3n’’ is 0.50/0.50 pz/py. These values were ar-
rived at by initially refining the pz/py composition of
each ring with a free variable constrained to sum to
unity (SHELX FVAR card), and then fixing the ring
occupation factors at reasonable values, such that the
overall composition of the ligand would be PhC(pz)2py.
The PFꢀ6 anion is rotationally disordered about one
ꢁ
Therefore, the disorder model in P1 was retained.
3. Results and discussion
3.1. Syntheses of ligands
The bitopic and monotopic aryl scorpionates 1 and 2,
respectively, were prepared by the CoCl2 catalyzed re-
arrangement reaction between bis(1-pyrazolyl)sulfone
(prepared in situ by the reaction between NaH, Hpz,
and SOCl2 in THF) and the appropriate aryl(pyr-
idyl)ketone in THF (Scheme 1). While the reaction to
produce the monotopic derivative 2 as described in the
literature proceeded smoothly (over the period of about
one day), longer reaction times were necessary in order
to obtain appreciable quantities of the corresponding
bitopic derivative 1. Even after four days at reflux, the
starting material was only 60% consumed and the re-
action produces a 1:2 mol ratio of the mono-derivatized
compound 1a and the desired bitopic compound 1.
The two products are easily separable by column

D.L. Reger et al. / Polyhedron 23 (2004) 291–299
295
Scheme 1.
chromatography since 1 is strongly retained on silica
whereas 1a is not. It should be noted that yields of either
1 or 2 were not improved by using CO(pz)2 as a re-
placement for S(O)(pz)2. The low yields and long reac-
tion times for the preparation of 1 and 2 can be
contrasted with the preparation of HC(pz)2(py) by using
similar conditions (45%, 4 h) [14]. These observations
and coordinated C(pz)2(py) groups, can be explained by
fast exchange between coordinated and non-coordinated
ends of the ligand on the NMR time scale, in accord
with the known lability of silver compounds.
The results of single crystal X-ray diffraction study of
3 reveal the monotopic nature of the potentially bitopic
ligand 1. An ORTEP diagram is given in Fig. 1 and
important bond distances and angles are provided in
Table 2. In the solid state, two ligands are bonded to one
silver in a j2-fashion via two pyrazolyl groups; the
ꢂ
are consistent with those originally made by The and
Peterson who indicated that the relative reactivity order
for CoCl2 catalyzed rearrangement of aryl carbonyls
was: PhC(O)H > PhC(O)CH3 ꢂ Ph2C(O) [15].
Regardless of the stoichiometry of reagents (mol ra-
tios of 2, 1, and 0.5 were investigated), the reactions
between silver hexafluorophosphate and either 1 or 2
always produced [Ag(1)2](PF)6 (3), and [Ag(2)2][PF6]
(4), respectively, as indicated from elemental analyses,
mass spectral data, and X-ray diffraction studies (vide
infra). The insensitivity of the productÕs metal:ligand
mol ratio on the stoichiometry of reactants is fairly
common in silver chemistry and has been reported
previously for reactions between silver salts and a series
of tris(pyrazolyl)methane ligands [16]. Compounds 3
and 4 are hygroscopic but otherwise air stable colorless
solids that can be stored for weeks without appreciable
decomposition under ambient light. Each is soluble in
acetonitrile, moderately soluble in acetone, slightly sol-
uble in methylene chloride, but insoluble in most other
common (less polar) solvents. The NMR spectra of each
compound in acetone-d6 show one set of resonances that
differ from those of the pure ligand by a downfield shift.
This result for 3, where the stoichiometry and solid state
structure (vide infra) indicate the presence of both free
Fig. 1. Two views of the structure of the cation in Ag(j2-m-
C6H4[C(pz)2(2-py)]2)2(PF6) (3). Top: ORTEP diagram with 50%
thermal ellipsoids. Bottom: ball and stick view emphasizing planar
geometry of nitrogens about silver. Hydrogen atoms have been omit-
ted for clarity in each.

296
D.L. Reger et al. / Polyhedron 23 (2004) 291–299
Table 2
Selected bond distances and angles in {Ag(j2-m-C6H4[C(pz)2(2-py)]2)2}(PF6), 3
ꢀ
Bond distances (A)
Ag–N(11)
Ag–N(21)
2.398(2)
2.279(2)
N(11)–N(12)
N(11)–N(12)
1.365(3)
1.365(3)
N(12)–C(1)
N(11)–N(12)
1.482(3)
1.365(3)
Bond angles (°)
N(11)–Ag–N(21)
N(21a)–Ag–N(11a)
Ag–N(11)–C(13)
C(11)–N(12)–C(1)
C(1)–N(22)–N(21)
Ag–N(21)–C(23)
76.95(8)
76.95(8)
N(11)–Ag–N(21a)
N(21)–Ag–N(11a)
Ag–N(11)–N(12)
N(12)–C(1)–N(22)
C(21)–N(22)–N(21)
103.05(8)
103.05(8)
121.56(18)
110.62(18)
111.60(20)
N(11)–Ag–N(11a)
N(21)–Ag–N(21a)
N(11)–N(12)–C(1)
C(31)–C(1)–C(2)
Ag–N(21)–N(22)
180.00 (0)
180.00 (0)
119.59(18)
112.89(18)
124.55(2)
132.46(18)
127.60(20)
119.25(20)
129.20(2)
Symmetry transformation: ꢀx þ 1, ꢀy þ 1, ꢀz þ 2.
pyridyl part of the bonded C(pz)2(py) group is not co-
ordinated to the silver(I). On each ligand, one of the two
C(pz)2(py) groups is not bonded to a silver(I).
One striking feature of the structure is the planar
coordination geometry of the nitrogen donor atoms
about silver. There are two short and two longer Ag–N
bonds (the silver atom resides on an inversion center) of
ꢀ
2.279 and 2.398 A involving Ag–N(21) and Ag–N(11),
Fig. 2. Comparison of the AgN4C chelate rings and coordination ge-
ometry about silver between (a) square planar compound 3 (with boat
conformation) and (b) distorted tetrahedral Ag[(pz)2CMe2]2(ClO4)
(with a half-boat conformation).
respectfully. These distances are comparable to those
found in related systems [5,6,23]. Since the sum of the
four N–Ag–N angles is 360o, the coordination geometry
about silver can best be described as distorted square
planar where the distortion occurs as an elongation
along one axis of the plane (rectangular planar coordi-
nation). An inspection of Fig. 1 would appear to sug-
gest, using the scorpionate vernacular, that the planar
arrangement is forced by the aryl group serving as a
Ônon-venomousÕ stinger. While it would be surprising to
have C- rather than N-coordination, aryl coordination
has been observed in other systems [26,27]. In the case of
3, the closest contact between silver and the pyridyl ring
is associated with the ipso carbon, C(31), (bottom of
Fig. 1) where the corresponding Ag–C(31) bond dis-
tance of 3.193 A is outside the 2.4–2.9 A range found for
g1 silver(I)-arene p complexes [17–19]. As far as we are
aware, there are only five other examples of tetracoor-
dinate silver complexes that exhibit square planar co-
ordination geometry as opposed to the more typical
tetrahedral or distorted tetrahedral geometries [20,21].
The AgN4C ring adopts a boat conformation (Fig. 2(a)).
If silver is assigned to the bow and C(1) to the stern, the
puckering parameters originally defined by Cremer and
Pople [22] are Q ¼ 0:910, h ¼ 83:1°, and / ¼ 1:78. The
latter two values may be compared to those for an ideal
boat conformation (h ¼ 90° and / ¼ 0) and for an ideal
half-boat (h ¼ 54:7° and / ¼ 0); the puckering ampli-
tude Q in these cases would depend on the bond lengths
between the ring atoms. It should be noted that the re-
lated compound {Ag[(pz)2CMe2]2}(ClO4) [23] contains
two different AgN4C six-member rings and each adopts
a slightly distorted half-boat conformation (Fig. 2(b)).
The puckering parameters Q ¼ 0:662, 0.634; h ¼ 73:2°,
72.5°; and / ¼ 6:6°, 5.5° were determined from the data
obtained from the Crystallographic Information File
extracted from the Cambridge Structural Database after
a phase adjustment for consistency in atom labeling and
normalization to allow meaningful comparison with 3
(Reference code; SIKYOA). The difference between the
boat conformation of the AgN4C ring in 3 and the half-
boat conformation in {Ag[(pz)2CMe2]2}(ClO4) is found
in the fold angles involving the respective silver atoms
(and to a lesser extent those involving the carbon at-
oms). The fold angle can be defined as being the devi-
ation from planarity created by the displacement of one
atom (at either the bow or stern) from the four (copla-
nar) atoms that would represent the deck of the boat. In
the case of 3, the fold angles are the complement to
those found in Fig. 2(a); that associated with silver is
32.3° whereas that associated with C(1) is 61.4°. The
corresponding values in {Ag[(pz)2CMe2]2}(ClO4) are
7.6° and 6.6° for those involving silver and 58.6° and
59.1° for those involving carbon.
Given that there does not to appear to be any sig-
nificant silver(I)-p interactions in 3, the unusual coor-
dination environment about silver is likely due to both
steric and electronic effects associated with the presence
of multiple arene substituents bound to the central
methane carbon. The relative orientations of the pyridyl
and pyrazolyl groups in the ligands are supported by
multiple intracationic CHꢁ ꢁ ꢁp interactions as shown in
Fig. 3. The distances and angles associated with the
CHꢁ ꢁ ꢁp interactions are given in Table 3 and are in
ꢀ
ꢀ

D.L. Reger et al. / Polyhedron 23 (2004) 291–299
297
Fig. 3. View of the cation in 3 showing the intracationic CH-p inter-
actions.
Table 3
Summary of non-covalent interactions involving {Ag(j2-m-C6H4-
[C(pz)2(2-py)]2)2}(PF6), 3
Fig. 4. Supramolecular structure of 3 emphasizing the pseudo inor-
ganic–organic layered structure. Large (green) polyhedra are disor-
dered PFꢀ6 anions whereas the small (pink) polyhedra represent
coordination sphere about silver. The red lines represent intercationic
CHꢁ ꢁ ꢁp interactions. The CHꢁ ꢁ ꢁF interactions that associate cationic
layers are highlighted and enclosed within the green polyhedra. (For
interpretation of the references to color in this figure legend, the reader
is referred to the web version of this article.)
ꢀ
ꢀ
Donor (D)ꢁ ꢁ ꢁ Acceptor (A)
Hꢁ ꢁ ꢁA (A)
C(H)ꢁ ꢁ ꢁA (°)
(a) Intramolecular CHꢁ ꢁ ꢁp interactions
C(11)H(11)ꢁ ꢁ ꢁCt[N(11)]a
C(11)H(11)ꢁ ꢁ ꢁCt[C(7)]
3.546
3.032
3.148
2.961
118.96
121.35
121.00
130.53
C(21)H(21)ꢁ ꢁ ꢁCt[C(7)]
C(7)H(7)ꢁ ꢁ ꢁCt[C(33)]
(b) Intermolecular interactions
C(64)H(64)ꢁ ꢁ ꢁCt[N(12)]
C(63)H(63)ꢁ ꢁ ꢁCt[N(12)]
C(35)H(35)ꢁ ꢁ ꢁCt[N(22)]
C(23)H(23)ꢁ ꢁ ꢁF(3b)b
C(23)H(23)ꢁ ꢁ ꢁF(2a)b
3.13
3.23
3.14
2.43
2.46
2.51
2.57
2.40
2.58
123.7
120.1
145.8
142.0
147.8
145.6
143.4
133.2
155.5
provides bond distances and angles for the non-covalent
interactions that support the pseudo-layered structure.
There are 12 CHꢁ ꢁ ꢁF distances involving a disordered
hexafluorophosphate anion and that are shorter than
C(32)H(32)ꢁ ꢁ ꢁF(1a)b
C(32)H(32)ꢁ ꢁ ꢁF(1b)b
C(33)H(33)ꢁ ꢁ ꢁF(2a)b
ꢀ
the limit of 2.6 A suggested to be indicative of weak
hydrogen bonding interactions (Table 3) [25]. The result
of these interactions is to organize the cationic sheets
along the bc-plane as in Fig. 4. In particular, within a
given cation containing two meta-linked ligands, the
hydrogens H(32) and H(33) situated meta- and para-,
respectively, to the nitrogen atom of the pyridyl ring
proximal to silver on one ligand and the hydrogen at the
3-position of the silver-bound pyrazolyl rings of the
second ligand are each involved in short CHꢁ ꢁ ꢁF
bonding interactions with the fluorines of both compo-
nents of the disordered PF6 anion. Each hydrogen in-
C(23)H(23)ꢁ ꢁ ꢁF(2b)b
a Ct refers to centroid of the arene ring that contains the element
denoted in brackets.
b An equivalent interaction is produced through inversion.
accord with accepted values [24]. Since the CHꢁ ꢁ ꢁp in-
teractions occur within each ligand rather than spanning
both ligands in the cation, the total number of CH-p
bonding interactions would not change if the AgN4C
chelate rings adopted a half-boat conformation similar
to those observed in {Ag[(pz)2CMe2]2}(ClO4). There-
fore, we attribute the unusual coordination environment
about silver to the forces that arrange 3 into its three
dimensional supramolecular structure.
The supramolecular structure of 3 approaches that of
a inorganic–organic hybrid material where the silver
centers and the hexafluourophosphate anions reside in
layers in the crystallographinc ab planes. The inorganic
layers are separated by organic ligands along the c axis
teracts with a component of the orientationally
disordered hexafluorophosphate anion such that the
ꢀ
CHꢁ ꢁ ꢁF distances are never greater than 2.6 A. The
CHꢁ ꢁ ꢁp interactions (Table 3) shown as red lines in
Fig. 4 afford connectivity in a third dimension (the a-
axis) such that the sheets depicted in Fig. 4 would stack
directly on top of one another into and out of the plane
of the paper, forming segregated anion and cation lay-
ers. The particular interactions that propagate along the
a-axis occur between the pyridyl rings proximal to silver
of one cation and the silver-bound pyrazolyl groups
with the shorter Ag–N distance [Ag–N(21) 2.279(2)].
Those interactions involving the pyridyl rings on the
Ôsilver-freeÕ side of the meta-linked ligand of one cation
and the silver-bound pyrazolyl group with the longer
Ag–N distance [Ag–N(11) 2.398(2)] of support the
overall structure (along the c-axis). The boat confor-
mation of the AgN4C rings is thought to maximize the
ꢀ
where the interlayer separation is 13.7 A as in Fig. 4.
Pyridyl rings, located above and below the AgN4 plane
also separate the cation and anions in the Ôinorganic
layersÕ. There are two types of non-covalent interactions
that assist in organizing 3 in the solid state; CHꢁ ꢁ ꢁp
interactions where both pyridyl rings of the ligand act as
hydrogen donors and the silver bound pyrazolyl rings
act as hydrogen acceptors and CHꢁ ꢁ ꢁF interactions
involving the hexafluorophosphate anion and the
acidic arene (pyrazolyl and pyridyl) hydrogens. Table 3

298
D.L. Reger et al. / Polyhedron 23 (2004) 291–299
total number of CHꢁ ꢁ ꢁF bonding and CHꢁ ꢁ ꢁp interac-
tions, thereby supporting the overall structure. A half-
boat arrangement would place the acidic hydrogens of
the pyridyl [H(32) and H(33)] and pyrazolyl groups
[H(23)] at too great a distance for PFꢀ6 bridged CHꢁ ꢁ ꢁF
interactions and would likely reduce the total number of
CHꢁ ꢁ ꢁp interactions. A future report will further address
the role of groups bound to the central methine carbon
on the intracationic and supramolecular structure of
related silver derivatives.
layered inorganic–organic hybrid material (Fig. 6) as in
3, however in the current case, the separation between
ꢀ
layers is 10.3 A. Unfortunately, detailed analysis of any
other bond distances and angles in 4 is precluded since,
with the exception of the silver atom, the phenyl ring
and the central methine carbon of the cation, disorder
affects all components of the structure (cation, anion,
and solvent).
In an effort to determine whether the structural motif
found in 3 was unique to the meta-linked ligand or was a
more common framework, an X-ray structural study of
{Ag(j2-C6H5[C(pz)2(2-py)])2}(PF6) (4), the monotopic
derivative of 3 was undertaken and the results are given
in Fig. 5. One important feature of the structure is the
nature of the disorder that afflicts the nitrogen-
containing heterocycles of the ligand (Fig. 5(a)). As
described in the experimental, the ligand bound to silver
is disordered over all three possible j2, j0 conformations
allowed by the combination of two pyrazolyl and one
pyridyl ring. Fig. 5(b) reveals one component of the
disordered structure showing that the coordination ge-
ometry about silver is square planar, as in compound 3.
The overall structure again has the form of a pseudo-
4. Conclusions
A potentially bitopic heteroscorpionate, m-C6H4
[C(pz)2(2-py)]2 (1), has been prepared by using the Pet-
erson rearrangement reaction between two equivalents
of SO(pz)2 and one equivalent of m-C6H4[C(O)(2-py)]2.
The reactions between this ligand and silver hexaflu-
orophosphate led only to a product with a 2:1 mol ratio
of ligand to metal. X-ray structural analysis of this silver
complex revealed that the ligand was bound to silver in a
j2-fashion via the pyrazolyl groups, the silver resided in
an unusual square planar coordination environment,
and the AgN4C chelate ring adopted a boat conforma-
tion. While a half-boat arrangement is more typical of
complexes with a C(pz)2Ag chelate ring, the unusual
boat conformation was proposed to be due to energetics
associated with the organization of the two-dimensional
structure, specifically, the CHꢁ ꢁ ꢁF interactions between
the hexafluorophosphate anion and hydrogen atoms of
the ligand. These non-covalent forces, coupled with
CHꢁ ꢁ ꢁp interactions, organize the two-dimensional
structure of 3 such that it approaches a layered inor-
ganic–organic hybrid material. The structure of the
monotopic derivative {Ag(j2-C6H5[C(pz)2(2-py)])2}
(PF6) (4) was highly disordered but also revealed the
bidentate nature of the C(pz)2(2-py) scorpionate moiety
towards silver and a square planar arrangement for
coordination environment about the metal.
Fig. 5. Results of single crystal X-ray analysis of Ag(j2-C6H5[C(pz)2(2-
py)])2(PF6) (4) showing (a) ligand disorder and (b) one component of
the disordered structure emphasizing the square planar geometry
about silver and boat conformation of AgN4C chelate rings.
5. Supplementary material
Crystallographic data for the structures reported in
this paper have been deposited at the Cambridge Crys-
tallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK (fax: +44-1223-336033; E-mail: de-
posit@ccdc.cam.ac.uk or www: http://www.ccdc.cam.
ac.uk), CCDC 210455 for 3 and 210456 for 4ꢁacetone.
Acknowledgements
We thank the National Science Foundation (CHE-
0110493) for support and a referee for helpful com-
ments. The Bruker CCD Single Crystal Diffractometer
Fig. 6. View of the pseudo-layered structure in the crystal of Ag(j2-
C6H5[C(pz)2(2-py)])2(PF6) (4).

D.L. Reger et al. / Polyhedron 23 (2004) 291–299
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