Supramolecular networks of silver(i) and iron(ii) complexes of the third generation tris(pyrazolyl)methane ligand Ph2(O)POCH 2C(pz)3 (pz = pyrazolyl ring)

Article abstract of DOI:10.1039/b719023a

The new ligand Ph₂(O)POCH₂C(pz)₃ (pz = pyrazolyl ring), prepared from the reaction of HOCH₂C(pz)₃ and Ph₂P(O)Cl in the presence of base, reacts with either AgBF ₄ or Fe(BF₄)₂?6H₂O in a 2/1 molar ratio to yield {[Ph₂(O)POCH₂C(pz)₃] ₂Ag}(BF₄) (1) and {[Ph₂(O)POCH ₂C(pz)₃]₂Fe}(BF₄)₂ (4), respectively. In the structure of 1, the silver is in an unusual planar geometry with each of the ligands in a κ²-κ⁰ coordination mode. Slow evaporation of a thf solution of 1 yields crystalline [Ph₂(O)POCH₂C(pz)₃Ag]₂(thf) ₂}(BF₄)₂ (2). In each cationic unit of 2, the two Ph₂(O)POCH₂C(pz)₃ ligands coordinate to the same two silver(i) centers in a κ²-κ¹ bonding mode, with a silver atom separation of 3.36 A. The supramolecular structure of both 1 and 2 is dominated by a pair of cooperative hydrogen bonding interactions between the Ph₂P(O) secondary tecton and a hydrogen atom from a methylene group situated on a neighboring building block, which arranges the cations in chains. The reaction of HC(pz)₃ and AgO ₃SCF₃ (AgOTf) yields {[HC(pz)₃] ₂Ag₂}(OTf)₂ (3). The cationic unit in 3 has a structure very similar to that of 2, but with a much shorter distance between the silver atoms at 2.86 A. The supramolecular structure of 3 is dominated by an unusual pyrazolyl embrace interaction where the acceptor ring in the C-Hπ interaction is the pyrazolyl ring κ¹-bonded to silver in the adjacent dimeric unit rather than the other ring in a κ²-bonded Cpz₂ unit. This interaction arranges the cations in chains which are further organized into sheets by the triflate anions that link the chains via combined AgO/CHO interactions. The iron in 4 is octahedral with each tris(pyrazolyl)methane unit in the κ³-tripodal coordination mode. The supramolecular structure is sheets formed by hydrogen bonding between the Ph₂P(O) oxygen and a meta-position hydrogen on one of the diphenylphosphine rings from an adjacent cation. The Royal Society of Chemistry.

Full text of DOI:10.1039/b719023a

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PAPER
www.rsc.org/dalton | Dalton Transactions
Supramolecular networks of silver(I) and iron(II) complexes of the third
generation tris(pyrazolyl)methane ligand Ph2(O)POCH2C(pz)3
(pz = pyrazolyl ring)†
Daniel L. Reger,* Radu F. Semeniuc‡ and Mark D. Smith
Received 10th December 2007, Accepted 23rd January 2008
First published as an Advance Article on the web 4th March 2008
DOI: 10.1039/b719023a
The new ligand Ph2(O)POCH2C(pz)3 (pz = pyrazolyl ring), prepared from the reaction of
HOCH2C(pz)3 and Ph2P(O)Cl in the presence of base, reacts with either AgBF4 or Fe(BF4)2·6H2O in a
2/1 molar ratio to yield {[Ph2(O)POCH2C(pz)3]2Ag}(BF4) (1) and {[Ph2(O)POCH2C(pz)3]2Fe}(BF4)2
(4), respectively. In the structure of 1, the silver is in an unusual planar geometry with each of the
ligands in a j2–j0 coordination mode. Slow evaporation of a thf solution of 1 yields crystalline
[Ph2(O)POCH2C(pz)3Ag]2(thf)2}(BF4)2 (2). In each cationic unit of 2, the two Ph2(O)POCH2C(pz)3
ligands coordinate to the same two silver(I) centers in a j2–j1 bonding mode, with a silver atom
˚
separation of 3.36 A. The supramolecular structure of both 1 and 2 is dominated by a pair of
cooperative hydrogen bonding interactions between the Ph2P(O) secondary tecton and a hydrogen atom
from a methylene group situated on a neighboring building block, which arranges the cations in chains.
The reaction of HC(pz)3 and AgO3SCF3 (AgOTf) yields {[HC(pz)3]2Ag2}(OTf)2 (3). The cationic unit
in 3 has a structure very similar to that of 2, but with a much shorter distance between the silver atoms
˚
at 2.86 A. The supramolecular structure of 3 is dominated by an unusual pyrazolyl embrace interaction
where the acceptor ring in the C–H · · · p interaction is the pyrazolyl ring j1-bonded to silver in the
adjacent dimeric unit rather than the other ring in a j2-bonded Cpz2 unit. This interaction arranges the
cations in chains which are further organized into sheets by the triflate anions that link the chains via
combined Ag · · · O/CH · · · O interactions. The iron in 4 is octahedral with each tris(pyrazolyl)methane
unit in the j3-tripodal coordination mode. The supramolecular structure is sheets formed by hydrogen
bonding between the Ph2P(O) oxygen and a meta-position hydrogen on one of the diphenylphosphine
rings from an adjacent cation.
alcohol-appended derivative HOCH2C(pz)3 that has allowed the
Introduction
preparation of the multitopic C6H6−n[CH2OCH2C(pz)3]n (n = 2, 3,
4 and 6, pz = pyrazolyl ring) family of semirigid, third generation
ligands3 as well as other types4 of systems. Metal complexes of
these ligands have remarkable topologies that maximize nonco-
valent interactions of the groups in the ligand backbone. This
family of ligands is “structurally adaptive” because they are ideal
candidates for studying the self-assembly process and the various
factors that might have an influence over such processes.3i,f ,5
We desire to expand this chemistry in order to develop new
types of metal-containing systems. Our approach to the synthesis
of such species is, among others, to replace the hydrogen atom
from tris(pyrazolyl)ethanol3l with either a secondary donor
system (SDS) or a secondary tecton (ST), as shown in Scheme 1,
that has either coordination properties very different from the
tris(pyrazolyl)methane units or has different supramolecular
interactions than the HO-group on the backbone of the ligand,
respectively.
Crystal engineering is a topic of intense research interest that
holds promise for revolutionizing materials design and synthesis.1
An essential step along the path to predicting solid structures
based on specific substituent groups in a chemical species of
interest is to more clearly elucidate the factors that govern the
noncovalent assembly of molecules or ions into their ultimate solid
state architectures. Remarkable strides have been made with both
common organic and inorganic systems, as has been the subject
of several reviews.1 Our research focuses on the syntheses and
supramolecular aspects of the metal complexes of the ubiquitous
scorpionate ligands, first introduced by Trofimenko 40 years
ago.2 We have developed synthetic routes to controllably impart
substitution at the scorpionate “backbone,” ligands we have
termed “third generation,” an advancement that is essential for
further probing the role of noncovalent forces on supramolecular
organization involving these ligands.3 Of note is the synthesis of the
Reported here is the synthesis and coordination chemistry of
Ph2(O)POCH2C(pz)3, a ligand with an imbedded bulky, secondary
tecton that is also capable of being an acceptor in hydrogen
bonding interactions. In this chemistry with silver(I), we observe
the formation of unusual dimers with Ag · · · Ag interactions when
the new compounds are crystallized in the presence of oxygen
donors. We have previously communicated some of these results.6,7
Department of Chemistry and Biochemistry, University of South Carolina,
Columbia, South Carolina, USA. E-mail: Reger@mail.chem.sc.edu
† CCDC reference numbers 272227, 625866, 670349 and 670350. For
crystallographic data in CIF or other electronic format see DOI:
10.1039/b719023a
‡ Present address: Eastern Illinois University, Department of Chemistry,
Charleston, IL 61920, USA.
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crystals formed after two days, which were filtered to yield 0.060 g
of crystalline material. 1H NMR (300 MHz, acetone-d6): 7.96, 7.85
(d, d, J = 2.7, J = 1.6 Hz, 6H, 6H, 3,5-H pz), 7.72–7.49 (m, 20 H,
Ph), 6.58 (dd, 6 H, J = 1.6, J = 2.7 Hz, 4-H pz), 5.73 (d, 4H, JPH
=
5.2 Hz, OCH2C(pz)3), 3.64–3.60 (m, 8H, CH2O, THF), 1.80–1.76
(m, 8H, CH2, THF); 31P NMR (acetone-d6): 35.07; Calcd. for
C54H58Ag2B2F8N12O6P2: C, 45.60; H, 4.11; N, 11.82; Found C,
45.95; H, 3.95; N, 12.25.
Preparation of {[HC(pz)3]2Ag2}(OTf)2 (3). A thf (20 mL)
solution of HC(pz)3, (0.214 g, 1.0 mmol) was added dropwise
to a solution of AgOTf (0.256 g, 1.0 mmol) in dry thf (20 mL)
under an inert atmosphere. A white precipitate appeared as the
mixture was stirred for 2 h. The thf was removed by cannula
filtration, the white precipitate was washed with thf (2 × 10 mL)
and then vacuum dried to afford 0.392 g (83%) of solid identified
Scheme
1 Synthetic strategy toward functionalized tris(pyrazolyl)-
methane ligands: replacement of the hydrogen atom with a secondary
donor set (SDS) or with a secondary tecton (ST).
1
as {[HC(pz)3]2Ag2}(OTf)2. H NMR (acetone-d6): d 9.30 (s, 2H,
Experimental
HC(pz)3), 8.24, 7.85 (s, s, 6H, 6H, 3,5-H pz), 6.54 (s, 6H, 4-H
pz); Calcd. For C22H20Ag2F6N12O6S2: C, 28.04; H, 2.14; N, 17.84;
Found C, 28.12; H, 2.53, N, 17.44.
General considerations
All operations were carried out under a nitrogen atmosphere
using either standard Schlenk techniques or a dry box. All
solvents were dried, degassed and distilled prior to use. AgBF4,
AgO3SCF3 (AgOTf) and Fe(BF4)2·6H2O were purchased from
Aldrich. Elemental analyses were performed by Robertson Mi-
crolit Laboratories (Madison, NJ). Tris(1-pyrazolyl)methane,
HC(pz)3, and tris-2,2,2-(1-pyrazoyl)ethanol, HOCH2C(pz)3, were
prepared following literature methods.3l
Preparation
of
{[Ph2(O)POCH2C(pz)3]2Fe}(BF4)2
(4).
Fe(BF4)2·6H2O (0.168 g, 0.50 mmol) was dissolved in thf
(20 mL). A solution of Ph2(O)POCH2C(pz)3 (0.444 g, 1.0 mmol)
in thf (20 mL) was added dropwise. A purple precipitate formed
and the solution was stirred for an additional 10 minutes. The
solvent was removed by cannula filtration, the precipitate washed
with thf (2 × 10 mL) and then vacuum dried to afford 0.532 g
1
(87%) of 4 as a purple solid. H NMR (300 MHz, acetone-d6):
Preparation of Ph2(O)POCH2C(pz)3. To a stirred solution of
tris(pyrazolyl)ethanol, HOCH2C(pz)3, (2.44 g, 0.010 mol) in dry
toluene (75 mL) was added an excess of triethylamine (5 mL) and
a solution of chlorodiphenylphosphine oxide (2.36 g, 0.010 mol)
in dry toluene (50 mL). The mixture was stirred for two hours,
the precipitate filtered, the organic layer washed with water (3 ×
100 mL) and then removed◦to afford the ligand as a white powder
(3.86 g, 87%): MP 114–116 C; 1H NMR (400 MHz, acetone-d6):
7.70–7.46 (m, 16 H, 3,5-H pz and Ph), 6.41 (dd, 3 H, J = 1.5, J =
2.1 Hz, 4-H pz), 5.49 (d, 2H, JPH = 4.5 Hz, OCH2C(pz)3); 31P
NMR (acetone-d6): 32.59; ESI+/MS: [C23H21N6O2P + H+] Calcd.
445.1542; Found 445.1534.
7.94, 7.86 (d, d, J = 2.7, J = 1.6 Hz, 6H, 6H, 3,5-H pz), 7.71–7.45
(m, 20 H, Ph), 6.60 (dd, 6 H, J = 1.6, J = 2.7 Hz, 4-H pz), 5.70 (d,
4H, JPH = 5.2 Hz, OCH2C(pz)3); 31P NMR (acetone-d6): 36.27;
Calcd. for C46H42B2F8FeN12O4P2: C, 49.40; H, 3.79; N, 15.03;
Found C, 48.99 H, 3.99; N, 15.25.
Crystallography
X-Ray intensity data for 1–4·2C3H6O were measured at 150 K
on a Bruker SMART APEX CCD-based diffractometer (Mo Ka
8
˚
radiation, k = 0.71073 A). The raw data frames were processed
with SAINT+.8 The reported unit cell parameters were determined
by least-squares refinement of >5000 reflections from the respec-
tive data sets. Analyses showed negligible crystal decay during
collections and the data were not corrected for absorption. Direct
methods structure solutions, difference Fourier calculations and
full-matrix least-squares refinements against F2 were performed
with SHELXTL.9 All non-hydrogen atoms were refined with
anisotropic displacement parameters and all hydrogen atoms were
placed in geometrically idealized positions and included as riding
atoms. Notes regarding the structure solution and refinement for
each structure are collected below and the numerical results are
given in Table 1.
Preparation of {[Ph2(O)POCH2C(pz)3]2Ag}(BF4) (1). AgBF4
(0.097 g, 0.50 mmol) was dissolved in thf (15 mL). With vigorous
stirring, a solution of Ph2(O)POCH2C(pz)3 (0.444 g, 10 mmol) in
thf (20 mL) was added dropwise via a syringe during a 10 min.
period. The solution became cloudy and the mixture was stirred
for an additional 3 h. To promote complete precipitation, hexanes
were added (150 mL) and the flask was kept at −20◦ for two hours.
The cold thf/hexanes solution was removed by cannula filtration,
the white precipitate washed with cold hexanes (2 × 10 mL) and
then vacuum dried to afford 0.487 g (93%) of 1 as a white solid. 1H
NMR (300 MHz, acetone-d6): 7.94, 7.86 (d, d, J = 2.7, J = 1.6 Hz,
6H, 6H, 3,5-H pz), 7.71–7.45 (m, 20 H, Ph), 6.60 (dd, 6 H, J =
1.6, J = 2.7 Hz, 4-H pz), 5.70 (d, 4H, JPH = 5.2 Hz, OCH2C(pz)3);
31P NMR (acetone-d6): 36.27; Calcd. for C46H42AgBF4N12O4P2: C,
50.99; H, 3.91; N, 15.51; Found C, 50.62; H, 3.95; N, 15.25.
Compound 1 crystallizes in the triclinic system. The space
¯
group P1 was assumed and confirmed by the successful solution
+
and refinement of the data. The {[Ph2PO2CH2C(pz)3]2Ag} cation
−
resides on a crystallographic inversion center. The BF4 anion is
disordered about an inversion center. Compound 2 crystallizes in
¯
Crystallization procedure for {[Ph2(O)POCH2C(pz)3Ag]2-
(THF)2} (BF4)2 (2). A 100 mg portion of 1 was dissolved in thf
(ca. 50 mL) and the beaker covered with aluminum foil. Colorless
the triclinic system. The space group P1 was assumed and con-
firmed by the successful solution and refinement of the data. The
asymmetric unit consists of half of the [(Ph2PO2CH2C(pz)3Ag]2
2254 | Dalton Trans., 2008, 2253–2260
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Table 1 Selected crystal data and structure refinement results
1
2
3
4·2C3H6O
Formula
C46H42AgBF4N12O4P2
1083.54
C54H58Ag2B2F8N12O6P2
1422.42
C22H20Ag2F6N12O6S2
942.36
C52H54B2F8FeN12O6P2
1234.48
Monoclinic
P21/n
Fw/g mol−1
Crystal system
Space group
T/K
Triclinic
Triclinic
Triclinic
¯
¯
¯
P1
P1
P1
150
150
150
150
˚
a/A
9.0846(7)
10.9600(9)
13.9140(12)
67.246(2)
73.530(2)
71.977(2)
1193.48(17)
1
10.9754(8)
11.4045(8)
12.9314(9)
109.108(1)
98.409(1)
102.747(1)
1449.22(18)
1
8.6922(6)
9.4966(7)
10.3316(8)
71.587(1)
68.453(1)
81.847(1)
752.30(10)
1
12.3175(7)
18.4056(10)
12.3750(7)
90
96.839(1)
90
2785.6(3)
2
0.0422
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
V/A
Z
3
˚
R1 I > 2r(I)
wR2 I > 2r(I)
0.0461
0.0767
0.0404
0.0993
0.0247
0.0600
0.1026
−
complex situated on an inversion center, a BF4 anion and a
Solid state structures
THF molecule. Compound 3 crystallizes in the triclinic system.
The space group P1 was confirmed by the successful solution
{[Ph2(O)POCH2C(pz)3]2Ag}(BF4) (1). Compound 1 was crys-
tallized by vapor phase diffusion of diethyl ether into a ni-
tromethane solution. Bond lengths and angles are listed in Table 2.
Two Ph2PO2CH2C(pz)3 ligands coordinate to the silver(I) center
in the j2–j◦ coordination mode, see Fig. 1. The silver atom is in
an unusual planar geometry (sum of the four N–Ag–N angles is
360◦), defined by the four coordinated pyrazolyl rings which lie
in the corners of a rectangle rather that a perfect square, with
¯
and refinement of the data. The asymmetric unit consists of half
of a centrosymmetric [l-(HC(pz)3)2Ag2]2+ cation and one triflate
anion. Compound 4·2C3H6O crystallizes in the space group P21/n
as determined uniquely by the pattern of systematic absences in
the intensity data. The asymmetric unit consists of half of the
2+
{[Ph2PO2CH2C(pz)3]2Fe} cation located on an inversion center,
one BF4− counterion and one acetone molecule of crystallization.
˚
˚
the edges of the rectangle being 3.05 A and 3.59 A, respectively.
This slight deviation is due to the restraints imposed by the bite
angle (80.63(10)◦) of the two chelating pyrazolyl rings. The non-
coordinating pyrazolyl rings are oriented with their nitrogen atoms
away from the silver atom, but with their p-clouds toward the
Results
Syntheses
As shown in eqn (1), the Ph2(O)POCH2C(pz)3 ligand is pre-
pared from previously reported HOCH2C(pz)3 by reaction with
Ph2P(O)Cl in the presence of base.
˚
silver(I) center. However, the rings are ca. 3.5 A away from the Ag(I)
atoms, a distance too long to indicate any cation–p interaction
between the two moieties.
(1)
The reaction of this new ligand with either AgBF4 or Fe-
(BF4)2·6H2O in a 2/1 molar ratio yields {[Ph2(O)POCH2-
C(pz)3]2Ag}(BF4) (1) and {[Ph2(O)POCH2C(pz)3]2Fe}(BF4)2 (4),
respectively, eqn (2). A similar reaction of HC(pz)3 and AgOTf in
either a 1/1 or 2/1 molar ratio yields {[HC(pz)3]2Ag2}(OTf)2 (3).
The compound [Ph2(O)POCH2C(pz)3Ag]2(thf)2}(BF4)2 (2) forms
when thf solutions of 1 are allowed to partially evaporate.
(2)
Fig. 1 ORTEP diagram of {[Ph2(O)POCH2C(pz)3]2Ag}(BF4) (1) with
atom labeling scheme. Displacement ellipsoids drawn at the 50% probabil-
ity level.
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◦
˚
Table 2 Selected bond distances (A) and angles ( ) for {[Ph2(O)POCH2C(pz)3]2Ag}(BF4) (1), {[Ph2(O)POCH2C(pz)3Ag]2(THF)2}(BF4)2 (2),
{[HC(pz)3]2Ag2}(OTf)2 (3) and {[Ph2(O)POCH2C(pz)3]2Fe}(BF4)2·2[(CH3)2CO] (4·2[(CH3)2CO])a
1
2
3
4·2[(CH3)2CO]
Ag(1)–N(11)
Ag(1)–N(21)
Ag(1)–N(31)
Ag(1)–O(1)
2.362(3)
2.352(3)
2.464(2)
2.257(2)
2.182(2)
2.407(2)
2.413(2)
2.237(2)
2.821(2)
2.971(2)
Ag(1)–O(2)
Ag(1)–O(3)
Ag(1)–Ag(1)*
2.795(3)
3.3690(5)
2.8664(4)
Fe(1)–N(11)
Fe(1)–N(21)
Fe(1)–N(31)
1.948(2)
1.946(2)
1.931(2)
N(11)–Ag(1)–N(21)
N(11)–Ag(1)–N(21)*
N(11)–Ag(1)–N(11)*
N(21)–Ag(1)–N(21)*
N(21)–Ag(1)–N(31)*
N(31)*–Ag(1)–N(21)*
N(11)–Ag(1)–N(31)*
N(31)–Fe(1)–N(21)
N(21)–Fe(1)–N(31)*
N(11)–Fe(1)–N(31)*
N(11)–Fe(1)–N(31)
N(11)–Fe(1)–N(21)
N(11)–Fe(1)–N(21)*
80.63(10)
99.37(10)
180
180
75.79(8)
79.22(7)
149.94(9)
134.01(8)
138.91(7)
140.42(7)
87.74(6)
92.26(6)
93.00(6)
87.00(6)
87.65(6)
92.35(6)
a Asterisk denotes a symmetry-equivalent atom.
A pair of cooperative hydrogen bonding interactions connects
these cationic building blocks into chains that run within the
bc plane of the unit cell (Fig. 2). Each oxygen atom from a
Ph2P(O) secondary tecton interacts with a hydrogen atom from
a methylene group situated on a neighboring building block, The
Ag–Ag interaction. Each silver is equatorially surrounded by
the three nitrogen atoms, two from one ligand and one from
the second. The sum of the three N–Ag–N angles around the
silver is 359.7◦. The geometry is pseudotrigonal planar, but with
a significant distortion caused by the restricted angle (75.79◦)
of the j2-bonded ligands. If the thf molecules and the second
silver atom are also considered, the geometry around each silver
becomes pseudotrigonal bipyramidal. In this compound, the
tris(pyrazolyl)methane ligand has an unprecedented coordination
mode in which two pyrazolyl rings bridge two silver atoms
using r-type orbitals on the nitrogen donor atoms and the third
pyrazolyl ring coordinates to one of the silver atoms with a p-type
orbital on the nitrogen atom, Fig. 3.7
˚
˚
H · · · O distance is 2.18 A (C · · · O distance = 3.16 A), and a C–H–
O angle of 169.4◦. Unfortunately, the disorder of the BF4 anion
−
prevents us from addressing its contribution to the crystal packing.
+
Fig. 2 Two {[Ph2(O)POCH2C(pz)3]2Ag} building blocks linked in a
chain by the hydrogen bonding pattern involving the Ph2P(O) tecton, color
code: magenta—silver, yellow—carbon; gray—hydrogen, blue—nitrogen,
red—oxygen, purple—phosphorus.
{[Ph2(O)POCH2C(pz)3Ag]2(THF)2}(BF4)2 (2). Crystalliza-
tion of compound 1 by slow evaporation of its thf solution
causes the ligand:metal ratio to change from 2:1 to 1:1 and
dramatically alters the coordination mode of the ligand (see
Table 2 for bond lengths and angles). Two Ph2(O)POCH2C(pz)3
ligands coordinate to the same two silver(I) centers in a j2–j1
bonding mode. In addition, a thf molecule makes a secondary
Fig. 3 ORTEP diagram of {[Ph2(O)POCH2C(pz)3Ag]2(THF)2}(BF4)2
(2). Displacement ellipsoids drawn at the 50% probability level.
˚
bond to each silver atom; these Ag–O bonds are long at 2.79 A.
˚
˚
The silver atom separation is 3.36 A, less that the sum of
The supramolecular structure of 2 is based on the same
cooperative hydrogen bonding pattern as shown in Fig. 2 for
10
silver–silver van der Waals radii (3.44 A), indicative of a weak
2256 | Dalton Trans., 2008, 2253–2260
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1, involving the Ph2P(O) secondary tecton and the methylene
group. Each oxygen atom interacts with a hydrogen atom from
two C–H · · · p interactions between the four pyrazolyl rings, with
two pyrazolyl rings stacked one on top of another with their
4-position hydrogen atom oriented toward the other pyrazolyl
rings, not involved in the p–p stacking motif. Fig. 5 depicts three
{[HC(pz)3]2Ag2}2+ building blocks linked by the pyrazolyl embrace
synthon, but in this case the interaction is unique. Instead of
taking place between two j2-bonded Cpz2 units, in 3 the p–p
stacking interaction comes from pyrazolyl rings in two j2-bonded
Cpz2 units and the acceptor rings in the C–H · · · p interactions are
the pyrazolyl rings j1-bonded to silver in the adjacent dimeric unit.
These chains are further associated by the triflate anions (Fig. 6,
blue lines) that link the units via a combined Ag · · · O/CH · · · O
˚
a neighboring methylene group, with a H · · · O distance of 2.22 A
◦
˚
(C · · · O distance = 3.20 A), and a C–H–O angle of 170.5 . This
interaction builds up chains that run along the body diagonal of
the unit cell.
{[HC(pz)3]2Ag2}(OTf)2 (3). Crystallization from an acetone–
diethyl ether system of this compound produced crystals of 3, a
discrete bimetallic complex, rather than a coordination polymer
as in other cases with this tris(pyrazolyl)methane ligand.3 The
ligand to metal ratio is 1 to 1, the compound is a dimer, built
up by two ligands j2–j1 bonding to the same two silvers as seen
with compound 2 (Fig. 4). Each ligand chelates a different silver
using two pyrazolyl rings, while the third ring has j1-bonding to
the silver j2-bonded to the other ligand. The distance between
˚
interaction. The Ag–O distances are 2.82 A and the H · · · O
˚
˚
distances are 2.14 A (C · · · O distance = 3.1 A), with a C–H–O
angle of 161.1◦. All these interactions build up sheets shown in
Fig. 6.
˚
the silver atoms is 2.86 A, considerably shorter than the sum
of silver–silver van der Waals radii.10 Each silver is equatorially
surrounded by three nitrogen atoms. The sum of the Ag–N angles
around the silver is 358.54◦, thus placing it in a slightly distorted
trigonal planar geometry. In addition, the triflate counterions are
in close proximity to the metallic centers, with an Ag–O secondary
˚
bonding distance of 2.821(2) A. If the triflate anions and the
second silver atom are considered along with the three equatorial
nitrogen atoms, the geometry around each silver becomes trigonal
bipyramidal.
Fig. 5 Chain formation in 3 via the pyrazolyl embrace synthon; the p–p
stacking component of the interaction in clearly shown for two pairs of
pyrazolyl rings in the middle of the figure and the red dotted lines show
the C–H · · · p interactions.
Fig. 6 The sheet like architecture of 3.
{[Ph2(O)POCH2C(pz)3]2Fe}(BF4)2·2[(CH3)2CO] (4·2[(CH3)2CO]).
Vapor phase diffusion of diethyl ether into an acetone so-
lution of the compound produced crystals suitable for X-ray
diffraction. Both tris(pyrazolyl)methane ligands shows the j3-
tripodal coordination mode, thus placing the Fe(II) center in an
octahedral environment (Fig. 7). The structural parameters of
Fig. 4 ORTEP diagram of the formula unit of {[HC(pz)3]2Ag2}(OTf)2
(3). Displacement ellipsoids drawn at the 50% probability level.
These dimeric building blocks self-assemble into chains via
the quadruple pyrazolyl embrace synthon–an interaction that
we substantiated in other papers.3k,11 In other cases involving
tris(pyrazolyl)methane donor units, the interaction consist of two
adjacent Cpz2 units involved in a cooperative p–p stacking and
2+
the {[C(pz)3]2Fe} core are similar to those reported previously
by us.12 The Fe–N bond distances that average 1.94 A clearly
˚
demonstrate that the iron(II) is in the low spin electronic state.12
=
In contrast to compounds 1 and 2 described earlier, the P O
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Fig. 9 Sheet supramolecular structure of 4·2[(CH3)2CO]; stars indicate
the locations of the C–H · · · O interactions.
cation changing to [L2Ag2]2+, two ligands j2–j1 bond two silver(I)
forming dimeric cationic units with close Ag · · · Ag distances. In
4, with the formula of the cation being L2Fe2+, changing the metal
to iron(II), which prefers octahedral coordination, leads to j3
coordination again forming monomeric cationic units. In none
of the compounds of this ligand do we observe the structural
arrangement most prevalent for the -C(pz)3 structural unit which
is the formation of j2–j1 bonding where each unit bridges different
silver(I) centers leading to a coordination polymer.3i,6,13 Compound
3 is also an exception to this rule having a structure like 2, in this
case with a very short Ag · · · Ag distance.
Fig. 7 ORTEP diagram of {[Ph2(O)POCH2C(pz)3]2Fe}(BF4)2·2[(CH3)-
2CO] (4·2[(CH3)2CO]).
oxygen atom is involved in a hydrogen bond with H(55) situated
in the meta-position on one of the diphenylphosphine rings from
˚
an adjacent cation. The O · · · H distance is 2.35 A (O · · · C distance
◦
˚
is 3.35 A), and the corresponding C–H–O angle is 166 ; a detailed
view of the interaction is shown in Fig. 8. This symmetry related
interaction builds up a sheet like overall supramolecular structure,
pictured in Fig. 9, where the blue stars show where the interaction
described in Fig. 8 takes place. The BF4− counterions are involved
in hydrogen bonds with acidic hydrogen atoms from the methylene
group; however, these interactions are intramolecular only and do
not increase the dimensionality of the supramolecular structure.
The Ph2(O)POCH2C(pz)3 ligand was designed with a secondary
tecton, P(O)Ph2, to support supramolecular structures. In both
silver(I) structures 1 and 2 the electronegative oxygen of the
Ph2P(O) secondary tectons interact in a cooperative pair of
hydrogen bonds with the methylene groups situated on the
neighboring building block so as to connect these cationic building
blocks into chains. In contrast, in octahedral 4 this oxygen is
involved in a hydrogen bond with a meta-position hydrogen on one
of the diphenyl-phosphine rings from an adjacent cation. Overall,
it appears that this secondary tecton does not influence structure
in a predictable fashion.
In addition to the structural variation in metal complexes
of L, an interesting feature of these compounds is the dimeric
nature of {[Ph2(O)POCH2C(pz)3Ag]2(THF)2}(BF4)2 (2) and
{[HC(pz)3]2Ag2}(OTf)2 (3). In both structures the two silver(I) are
bridged by j2–j1 bonding of two tris(pyrazolyl)methane ligands,
a bonding arrangement that is unique to these two compounds.
It is not clear whether this arrangement is a consequence of the
Ag · · · Ag interaction or is the reason why the bridged metals are
in such close proximity. This type of ligand bonding has been
observed in tris(pyrazolyl)borate chemistry, but with smaller, hard
metals that had no M · · · M interaction.14 The Ag · · · Ag bond
Fig. 8 Intermolecular forces that organize the supramolecular structure
of 4·2[(CH3)2CO]; arrows indicate the location of the additional C–H · · · O
interactions.
˚
distances are surprisingly different with 3 being 0.5 A shorter
than in 2. Another unusual structural feature of 3, which could
possibly account for the short Ag · · · Ag bond distance, is the
unusual pyrazolyl embrace interaction where the acceptor ring
Table 3 AgN(n1)–N(n2)C(1) torsion angles (◦)
Discussion
It is interesting to note that in the three compounds of the new
third generation Ph2(O)POCH2C(pz)3 ligand (L) reported here
there are three very different bonding arrangements. In 1, with the
formula of the cation being L2Ag+, j2–j0 coordination is observed
forming monomeric cationic units. In 2, with the formula of the
Angle
2
3
Ag(1)N(11)–N(12)C(1)
Ag(1)N(21)–N(22)C(1)
Ag(1)N(31)–N(32)C(1)
89.5(2)
42.3(3)
18.6(3)
8.1(3)
51.6(3)
56.5(2)
2258 | Dalton Trans., 2008, 2253–2260
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Table 4 Coordination geometries and AgN4C ring puckering parameters in various silver di(pyrazolyl)methane complexes
Cation
Coord. env.
Fold AgNNa
Fold CNNb
Ref.
+
{Ag(C6H5[C(pz)2(2-py)])2
}
sq. pl.
sq. pl.
sq. pl.
sq. pl.
tet.
tet.
tet.
135.4
136.4
147.7
152.3
160.3
160.4
164.1 165.4
167.6
172.4 173.4
130.4
127.9
128.6
121.8
124.8
126.9
121.4 123.0
121.1
121.4 120.9
17
16
+
{Ag[(pz)2CPh2]2 } (190 K)
{Ag(m-C6H4[C(pz)2(2-py)]2)2
+
}
17
{[Ph2(O)POCH2C(pz)3]2Ag+} (1)
c
+
{Ag[(pz)2CHPh]2
}
16
18
16
18
19
+
{Ag2(l-[(pz)2CH]2CH2)2
}
}
+
d
{Ag[(pz)2CHCH2Ph]2
{Ag2(l-[(pz)2CH]2CH2)2
}
+
tet.
tet.
+
d
{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 This work. d Two
independent Ag sites.
in the C–H · · · p interaction is the pyrazolyl ring j1-bonded to
silver in the adjacent dimeric unit rather than the other ring in a
j2-bonded Cpz2 unit.
ands with only one bulky substituents or {Ag[(pz)2CMe2]2}(ClO4),
that contains two smaller groups, bonded to the central methine
carbon atom. Compound 1, with one bulky substituent and one
smaller substituent has a fold angle between these previously
studied compounds, although more closely aligned with the
square planar complexes. Apparently the steric bulk on the
methine carbon is substantial enough to push the non-coordinated
pyrazolyl rings over the silver center, favoring the square planar
arrangement.
In both dimeric structures, secondary bonding of an oxygen
donor to the silvers is observed. In fact, 2 is formed from the
crystallization of monomeric {[Ph2(O)POCH2C(pz)3]2Ag}(BF4)
(1) from thf, so a radical change takes place in that process. In the
case of 3, although this compound forms directly in the reaction
of AgOTf, the analogous reactions with AgBF4 and AgPF6 yield
compounds that are “normal” coordination polymers in which
each tris(pyrazolyl)methane ligand is bonded j2–j1 to two silvers
6
˚
that are over 4 A apart. This secondary bonding interaction of
Acknowledgements
the oxygen donor appears to support the unusual j2–j1 bonded
We thank the National Science Foundation (CHE-0715559) for
support. The Bruker CCD Single Crystal Diffractometer was
purchased using funds provided by the NSF Instrumentation for
Materials Research Program through Grant DMR:9975623.
[Ag2L2]2+ arrangement.
Another unique feature of the bonding in both 2 and 3 involves
the orientations of the pyrazolyl rings with respect to the metal.
For maximum overlap with the lone pair on the nitrogen donor
atom, the silver would lie in the plane of each pyrazole ring. Any
deviation from this orientation can be measured by the AgN(n1)–
N(n2)C(1) torsion angle, where n denotes the ring number, an
angle that would have the value of 0◦ if the metal were in the
pyrazolyl ring plane. The torsion angles are presented in Table 3.
Large deviations down have been observed in several other cases,
especially for large metallic centers (e.g. lead(II) and thallium(I))
where for {[HC(3,5-Me2pz)3]2Tl}(PF6) the average is 49◦.15 The
deviation to 89.5◦ for one angle in 2 and 51.6 and 56.5◦ for two
of the angles in 3 indicate that the silver, a smaller metal cation, is
coordinated more by p-type orbitals from the pyrazolyl rings than
a conventional nitrogen based r-type lone pair orbital in these
cases.
Finally, the square planar structure of 1 is unusual. We have
previously reported that silver(I) bis(pyrazolyl)methane complexes
with two bulky substituents bonded to the central methine
carbon atom, such as in {Ag[(pz)2CPh2]2}(PF6) or {Ag(j2-m-
C6H4[C(pz)2(2-py)]2)2}(PF6) adopt square planar arrangements
about silver(I) and argued that the steric constraints imposed
by these aromatic groups enforce the unusual square planar
conformation.16 We also pointed out an indication that the steric
bulk of the substituents will force the square planar arrangement
is the AgN4C chelate rings in the square planar complexes
adopt a more boat-like configuration (lower fold angles, Table 4)
when compared to analogous tetrahedral complexes, such as
{Ag[(pz)2CHPh]2}(PF6), that contain bis(pyrazolyl)methane lig-
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