Supramolecular Structural Variations with Changes in Anion and Solvent in Silver(I) Complexes of a Semirigid, Bitopic Tris(pyrazolyl)methane Ligand

Inorg. Chem. 2004, 43, 537−554

Supramolecular Structural Variations with Changes in Anion and

Solvent in Silver(I) Complexes of a Semirigid, Bitopic

Tris(pyrazolyl)methane Ligand

Daniel L. Reger,* Radu F. Semeniuc, Vitaly Rassolov, and Mark D. Smith

Department of Chemistry and Biochemistry, UniVersity of South Carolina,

Columbia, South Carolina 29208

Received October 21, 2003

The bitopic ligand p-C H [CH OCH C(pz)₃]₂(pz ) pyrazolyl ring) that contains two tris(pyrazolyl)methane units

6

4

2

connected by a semirigid organic spacer reacts with silver(I) salts to yield {p-C H [CH OCH C(pz)₃]₂(AgX)₂}_∞,

6

4

2

where X ) CF SO ^-(1), SbF ^-(2), PF ^-(3), BF ^-(4), and NO ^-(5). Crystallization of the first three compounds

3

6

4

3

from acetone yields {p-C H [CH OCH C(pz)₃]₂(AgCF SO ) }_∞(1a), {p-C H [CH OCH C(pz)₃]₂(AgSbF ) [(CH ) -

6

4

2

3

3 2

6

4

2

6 2

3 2

CO]₂}_∞(2b), and {p-C H [CH OCH C(pz)₃]₂AgPF }_∞(3a), where the stoichiometry for the latter compound has

6

4

2

6

changed from a metal:ligand ratio of 2:1 to 1:1. The structure of 1a is based on helical argentachains constructed

by a κ²−κ¹coordination to silver of the tris(pyrazolyl)methane units. These chains are organized into a tubular 3D

structure by cylindrical [(CF SO ) ]^6-clusters that form weak C−H‚‚‚O hydrogen bonds with the bitopic ligand. The

3

3 6

same κ²−κ¹coordination is present in the structure of 2a, but the structure is organized by six different tris-

(pyrazolyl)methane units from six ligands bonding with six silvers to form a 36-member argentamacrocycle core.

The cores are organized in a tubular array by the organic spacers where each pair of macrocycles sandwich six

acetone molecules and one SbF ^-counterion. The structure of 3a is based on a κ²−κ⁰coordination mode of each

6

tris(pyrazolyl)methane unit forming a helical coordination polymer, with two strands organized in a double stranded

helical structure by a series of C−H‚‚‚π interactions between the central arene rings. Crystallization of 2−4 from

acetonitrile yields complexes of the formula {p-C H [CH OCH C(pz)₃]₂[(AgX)₂(CH CN)_n]}_∞where n ) 2 for X )

6

4

2

3

SbF ^-(2b), X ) PF ^-(3b) and n ) 1 for X ) BF ^-(4b). All three structures contain argentachains formed by

6

4

a κ²−κ¹coordination mode of the tris(pyrazolyl)methane units linked by the organic spacer and arranged in a 2D

sheet structure with the anions sandwiched between the sheets. Crystallization of 5 from acetonitrile yields crystals

of the formula {p-C H [CH OCH C(pz)₃]₂(AgNO ) (CH CN)₄}_∞, where the nitrate is bonded to the silver. The

6

4

2

3 2

3

argentachains, again formed by κ²−κ¹coordination, are arranged in W-shaped sheets that have an overall

configuration very different from 2b−4b. Treating {p-C H [CH OCH C(pz)₃]₂(AgSbF ) }_∞with a saturated aqueous

6

4

2

6 2

solution of KPF or KO SCF slowly leads to complete exchange of the anion. Crystallization of a sample that

6

3

contains an approximately equal mixture of SbF ^-/PF ^-from acetonitrile yields {p-C H [CH OCH C(pz)₃]₂[Ag₂-

6

4

2

(PF₆)_0.78(1)(SbF₆)_1.22(1)(CH CN)₂][(CH CN)_0.25(C H O)_0.25]}_∞, a compound with a sheet structure analogous to 2b−

3

4 10

4b. Crystallization of the same mixture from acetone yields {p-C H [CH OCH C(pz)₃]₂(AgSbF )[(CH ) CO]_1.5}_∞,

6

4

2

6

3 2

where the metal-to-ligand ratio is 1:1 and the [C(pz)₃] units are κ²−κ⁰bonded forming a coordination polymer. The

supramolecular structures of all species are organized by a combination of C−H‚‚‚π, π−π, or weak C−H−F(O)

hydrogen bonding interactions.

Introduction

groups, the ligand topicity (i.e., the number and position of

coordinating groups), flexibility or rigidity of the linker

groups joining the coordination sites, and the stereochemical

preferences of the coordinated metal ion.^1-3The role of

noncovalent interactions is also recognized as providing

further organization into more complex networks. A wide

The key features that determine the overall architectures

of self-assembled species are the nature of coordinating

* To whom correspondence should be addressed. E-mail: Reger@

mail.chem.sc.edu.

Published on Web 12/30/2003

Inorganic Chemistry, Vol. 43, No. 2, 2004 537

Reger et al.

variety of these interactions, some relating to the anions^3a-d,4

and the solvent,^2g,3b,5have been found to impact the

organization of such compounds. Important examples are

strong⁵and weak^3e,7hydrogen bonds, π-π stacking,⁸

X-H‚‚‚π interactions (X ) O, N, C),⁹and interhalogen

interactions.¹⁰Silver(I) is frequently used as the metal

because the flexibility of its coordination sphere can produce

sophisticated coordination architectures. This flexibility

affords an opportunity to investigate how the self-assembly

process is influenced by modifications of the ligand denticity,

the ligand-to-metal ratio, the counterions, and noncovalent

interactions.^3a-d,4-10,11

Insight into the self-assembly process can be obtained by

carrying out systematic studies using a series of similar

complexes assembled from a specific ligand and the same

metallic center and imposing subtle alterations in the

environment such as changing the anions and the crystal-

lization solvent. Extensive research has been done in this

area using mostly rigid ligands because they allow a better

prediction of the overall structure, shape, and porosity of

the resulting array. Schro¨der et al., studying silver(I)

coordination polymers based on aromatic nitrogen-donor

ligands, found, besides covalent metal-ligand contacts, that

a plethora of interactions (e.g., π-π interactions, metal-

metal interactions, metal-π interactions) have an influence

on the outcome of the resulting supramolecular array.^1c,d,11c

Zaworotko,¹²Yaghi,¹³and others¹⁴used polycarboxylic acids

and various metal centers to construct both discrete and

infinite architectures, based on the rigid orientation and

binding mode of the ligand to the metallic centers. All these

studies gave rise to a series of principles that can be applied

in the design of new structures with a high degree of

confidence.

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538 Inorganic Chemistry, Vol. 43, No. 2, 2004

Bitopic Tris(pyrazolyl)methane Ligand

Scheme 1. The Ligand p-C₆H₄[CH₂OCH₂C(pz)₃]₂(L) and Possible Noncovalent Interactions That the Ligand Can Promote To Support

Supramolecular Structures^a

^aColor code: metallic center, purple; carbon, yellow; oxygen, red; nitrogen, blue.

ligands and silver(I) salts. Several other research groups¹⁶

also used flexible ligands in the construction of coordination

polymers, and useful patterns with potential application in

crystal engineering were found.^15,16

The use of both types of ligands is, to some extent,

restricted because rigid ligands limit the structures of possible

products and flexible ligands have a very low degree of

prediction of the resulting structure. At the interface between

rigid and flexible ligands resides a class of ligands that

contain in their structure both rigid and flexible parts and

are designated as either “semirigid” or “semiflexible” ligands

or sometimes “flexible” only, although they have the same

features.¹⁷

We are investigating the field of coordination polymers

using a new class of semirigid ligands based on linking two

or more tris(pyrazol-1-yl)methane units in a single mol-

ecule.¹⁸The chemistry reported here is based on the bitopic

ligand p-C₆H₄[CH₂OCH₂C(pz)₃]₂(L, pz ) pyrazolyl ring),

shown in Scheme 1. Also shown are the noncovalent

interactions and/or conformations that are possible with this

ligand. The ether linkage offers the possibility of cis or trans

orientations of the sidearms, while the presence of acidic

hydrogen atoms on the pyrazolyl ring or the methylene

groups adjacent to oxygen on the sidearms can promote weak

hydrogen bonds if suitable proton acceptors are introduced

into the system.^18a,b,d,hThe presence of aromatic pyrazolyl

rings and linking arene ring that can act as acceptors in

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Inorganic Chemistry, Vol. 43, No. 2, 2004 539

Reger et al.

Scheme 2. Possible Modes of Coordination of Tris(pyrazolyl)methane Units

C-H‚‚‚π interactions^18f-hor participate in π-π stacking^18,b,d,f,h

can lead to arene-arene, pyrazolyl-arene interactions or the

double π-π stacking/C-H‚‚‚π interaction we have named,

after a CSD database search showed that it was a general

interaction, the “quadruple pyrazolyl embrace”.¹⁹Another

possible noncovalent interaction is cation-π interactions

between a metallic center and a pyrazolyl ring within the

ligand.²⁰In addition, the tris(pyrazolyl)methane units can act

in different binding modes as (a) κ³tripodal, (b) κ²bonded

to a single metal with the third pyrazolyl not coordinated,

and (c) κ²-κ¹bonded bridging two metals (Scheme 2). As

a means of simplifying the language related to these types

of semirigid ligands used in supramolecular chemistry, both

those developed in our group and elsewhere, we define them

as “structurally adaptive”.

Reported here are the syntheses and characterization of a

series of silver(I) coordination polymers of this versatile

ligand. We have carefully investigated the supramolecular

structural modifications influenced by several types of

noncovalent forces when the anions and crystallization

solvent are varied, with an emphasis on the solid-state

structures. The solution structure and dynamics, as deduced

from ¹H NMR and, indirectly, from ESI-MS, are also

discussed. We have previously communicated the structures

of three of these compounds.^18c,g

tromethane) are white solids that are air stable and show

only slight decomposition after several weeks of exposure

to daylight.

2nAgX + n{p-C₆H₄[CH₂OCH₂C(pz)₃]₂} ^THF8

{p-C₆H₄[CH₂OCH₂C(pz)₃]₂(AgX)₂}n

X ) CF₃SO₃^-(1), SbF₆^-(2), PF₆^-(3),

BF₄^-(4), and NO₃^-(5)

Elemental analyses of the solids correspond to a metal-

to-ligand ratio of 2:1; therefore, the complexes are formulated

as follows: {p-C₆H₄[CH₂OCH₂C(pz)₃]₂(AgX)₂}_∞, where X

-

) CF₃SO₃(1), SbF₆(2), PF₆(3), BF₄(4), and NO₃

(5). The same metal-to-ligand ratio was found when the

starting materials were mixed in a 1:1 reaction, with half an

equivalent of the ligand recovered from the filtrate. While

the chemical composition of the products is by no means

sufficient for making any structural predictions due to the

many different structural architectures of coordination frame-

works that can be generated from identical stoichiometries,

we established^18aby molecular mechanics calculations that

the overall length and structure of the xylene based bridge

prevent simultaneous coordination of both sides of L to one

metal center.

1

The H NMR spectra of the solids in CD₃CN show that

Results and Discussion

the acetonitrile completely replaces the ligand; the spectrum

of the compound in CD₃CN is the same as the free ligand in

Syntheses and Characterization. The bitopic ligand L

was prepared^18ain a one pot synthesis starting from R,R′-

dibromo-p-xylene, p-(BrCH₂)₂C₆H₄, and tris-2,2,2-(1-pyra-

zolyl)ethanol, HO-CH₂-C(pz)₃, under basic (NaH) condi-

tions. NMR and elemental analysis confirmed its chemical

composition and purity. The preparation of the complexes

was readily achieved by combining the ligand with the

respective metal salts in a 2:1 metal-to-ligand ratio. The

compounds (insoluble in halogenated solvents, water, or

alcohols but soluble in acetone, acetonitrile, and ni-

1

this solvent. However, the H spectra of the compounds in

deuterated acetone are clearly different from the free ligand,

showing the coordination of the ligand to the silver(I) in

solution. Although the X-ray structure shows that in the solid

state the pyrazolyl rings are nonequivalent (vide infra), the

NMR spectra show equivalent rings, presumably because of

fast exchange of the ligands and metals on the NMR time

scale. This fast exchange process is maintained even at low

temperatures. The spectra of metal complexes 1-5 in acetone

are essentially identical, showing the same upfield shifts

when compared to the free ligand. This result suggests that

the species present in acetone solution are identical and anion

independent. Electrospray mass spectroscopy showed peaks

corresponding to [LAg]⁺and [LAg₂X]⁺(except for 3 that

only shows [LAg]⁺). Surprisingly, these spectra were very

similar when run in either acetone or acetonitrile.

(19) Reger, D. L.; Gardinier, J. R.; Semeniuc, R. F.; Smith, M. D. J. Chem.

Soc., Dalton Trans. 2003, 1712.

(20) For examples of cation-π interactions between metallic centers and

pyrazolyl rings see: (a) Craven, E.; Mutlu, E.; Lundberg, D.;

Temizdemir, S.; Dechert, S.; Brombacher, H.; Janiak, C. Polyhedron

2002, 21, 553. (b) Kisko, J. L.; Hascall, T.; Kimblin, C.; Parkin, G. J.

Chem. Soc., Dalton Trans. 1999, 1929. (c) Janiak, C.; Temizdemir,

S.; Scharmann, T. G. Z. Anorg. Allg. Chem. 1998, 624, 755.

540 Inorganic Chemistry, Vol. 43, No. 2, 2004

Bitopic Tris(pyrazolyl)methane Ligand

Figure 1. ORTEP representation of {p-C₆H₄[CH₂OCH₂C(pz)₃]₂(AgCF₃-

SO₃)₂}_∞(1a) with displacement ellipsoids shown at 50% probability level.

In order to ascertain the influences of the crystallization

solvent and the counterion on the resulting “molecular” and

supramolecular structures of the compounds, we performed

crystallization procedures using acetone and acetonitrile as

solvents and diethyl ether as precipitating agent, using the

vapor phase diffusion method. All other conditions (ambient

temperature, concentration of the mother liquors) were kept

unchanged. In 7 of the 10 possible cases (1a, 2a, 3a, from

acetone, and 2b, 3b, 4b, 5‚4CH₃CN, from acetonitrile)

crystals formed that were subjected to X-ray diffraction

studies.

Figure 2. (a) Two adjacent helical argentachains for {p-C₆H₄[CH₂OCH₂C-

(pz)₃]₂(AgCF₃SO₃)₂}_∞(1a), showing the double π-π stacking. (b) View

of the same helical argentachains down the helical axis. Color code is the

same as in Scheme 1, with silver ) purple.

Solid-State Structures. In describing the highly organized

supramolecular structures reported here, we will use the

terminology developed by Lehn.²¹The primary structure of

a supramolecular compound is created by the covalent bonds

of the individual atoms in the reacting building blocks (also

known as “tectons”²²), with the secondary structure being

the arrangement of the tectons one with respect to another.

If one or more secondary structural elements impose a further

distinct and more encompassing motif on the compound as

a whole, this arrangement is the tertiary structure and

constitutes the dominant structural motif. If several separate

tertiary structural units are connected, the resulting compound

would have four levels of structural organization, with

quaternary structure required to describe the arrangement of

the “individual” tertiary structural units relative to each other.

Crystallization of the product resulting from the reaction

of AgCF₃SO₃and p-C₆H₄[CH₂OCH₂C(pz)₃]₂from acetone

leads to the formation of {p-C₆H₄[CH₂OCH₂C(pz)₃]₂(AgCF₃-

SO₃)₂}_∞(1a), a compound with a metal/ligand ratio of 2:1.

In the primary structure (Figure 1) the ligand has a skewed

trans arrangement of the sidearms with respect to the central

arene ring. Each tris(pyrazolyl)methane unit has a κ²-κ¹

coordination to silver placing three nitrogen atoms around

each metal in a distorted trigonal planar arrangement with

the sum of the N-Ag-N angles being nearly 360°. The

Ag-N bond distances and angles display no unusual features

and are provided as Supporting Information.

Figure 3. Overall structure of 1a, down the c axis. Color code is the

same as in Scheme 1, plus sulfur ) light brown and fluorine ) green.

2a), that are oriented along a crystallographic 3₁screw axis.

Figure 2b shows the view down two of the chiral chains.

These helical chains are organized in a tertiary structure

by the ether-based sidearms combined with a double face-

to-face π-π stacking, involving two pyrazolyl rings sand-

wiching the central phenyl ring.⁸Figure 3 shows the overall

3D arrangement of 1a. Six helical chains, connected by the

organic bridges, are arranged in cylinders around a central

core of triflate anions. Each adjacent cylinder shares a pair

of helical chains such that each of the AgNNCNN helices is

part of three overlapping cylinders. A schematic representa-

tion of the structure is illustrated in Figure 4. Every cylinder

overlaps with six other cylinders, with every helical chain

being surrounded by three helical chains of opposite chirality.

Noncovalent interactions from the triflate anions are clearly

important in this arrangement of the 3D structure into

“cylinders”. The triflate anions in 1a are not bonded to silver

as in other cases^17b,23but are arranged in circular clusters of

six, the same as the number of helices in each cylinder. As

shown in Figure 5, six S₆symmetry related triflate anions

The secondary structure consist of single stranded helical

chains constructed by this κ²-κ¹coordination generating

helical argentachains (no interactions between the silver(I)

centers are implied), with a AgNNCNN sequence (Figure

(21) Hasenknopf, B.; Lehn, J.-M.; Boumediene, N.; Dupont-Gervais, A.;

van Dorsselaer, A.; Kneisel, B.; Fenske, D. J. Am. Chem. Soc. 1997,

119, 10956.

(22) Tecton ) any molecule whose interactions are dominated by particular

associative forces that induce self-assembly of an organized network

with specific architectural or functional features. See: Simard, M.;

Su, D.; Wuest, J. D. J. Am. Chem. Soc. 1991, 113, 4696.

(23) For examples of OTf^-coordinated to a silver(I) center in coordination

polymers see: (a) Ino, I.; Wu, L. P.; Munakata, M.; Maekawa, M.;

Suenaga, Y.; Kuroda-Sowa, T.; Kitamori, Y. Inorg. Chem. 2000, 39,

2146. (b) Venkataraman, D.; Lee, S.; Moore, J. S.; Zhang, P.; Hirsch,

K. A.; Gardner, G. B.; Covey, A. C.; Prentice, C. L. Chem. Mater.

1996, 8, 2030. (c) Buchholz, H. A.; Prakash, G. K. S.; Vaughan, J. F.

S.; Bau, R.; Olah, G. A.; Inorg. Chem. 1996, 35, 4076.

Inorganic Chemistry, Vol. 43, No. 2, 2004 541

Reger et al.

Figure 6. ORTEP representation of the cationic unit in {p-C₆H₄[CH₂-

OCH₂C(pz)₃]₂(AgSbF₆)₂[(CH₃)₂CO]₂}_∞(2a) with displacement ellipsoids

shown at 40% probability level.

Figure 4. Schematic representation of 1a: orange rings are cylinders of

helical argentachains connected by the organic spacer; green rings are

circular association of the triflate anions; blue triangles are 3₁helical

argentachains with “2” and “1” representing opposite handed helices.

The Hartree-Fock model does not describe van der Waals

interactions. When these are included at the MP2 level, the

energy of interaction between two adjacent fluorine atoms

becomes 1.05 kcal/mol, making the F‚‚‚F energy of interac-

tion for each [(CF₃SO₃)₆]^6-cluster 6.3 kcal/mol. This is a

surprisingly large number, given the distance between the

fluorines. We also calculated the energy of the F‚‚‚F

6-

interaction in the one other example of a similar (CF₃SO₃)₆

reported cluster.²⁶In this case, the F‚‚‚F distances are much

shorter, in the range 2.7-2.9 Å. At this shorter distance, the

average energy of each interaction increases to 1.93 kcal/

6-

mol, making the energy of interaction for each (CF₃SO₃)₆

cluster 11.6 kcal/mol.

The hexameric triflate clusters control the circular ar-

-

rangement of 2a through the six SO₃groups that are

-

oriented away from the center of the cluster. Each SO₃

group makes two weak C-H‚‚‚O hydrogen bonds with the

bitopic ligand with metrical parameters that indicate both of

these interactions are substantial. The presence of the

hydrogen bonds is also supported by vibrational data of the

trifluoromethanesulfonate anion by a 24 cm^-1blue-shift of

the ν_as(E) stretching vibrations of the CF₃group.²⁷

The crystallization of the product resulting from the

reaction of AgSbF₆and p-C₆H₄[CH₂OCH₂C(pz)₃]₂from

acetone leads to the formation of {p-C₆H₄[CH₂OCH₂C

(pz)₃]₂(AgSbF₆)₂[(CH₃)₂CO]₂}_∞(2b), a compound with the

same metal/ligand ratio of 2:1 as in 1a. Single crystal X-ray

analysis showed that in 2a the primary structure (Figure 6)

is similar to that of 1a, although the coordination environment

around the silver(I) is more pyramidal, with the sum of the

N-Ag-N angles being 341.71°.

However, the secondary structure of 2a is very different

from that of 1a, although the same method of construction

is used in the organization. As in 1a each tris(pyrazolyl)-

methane unit is κ²bonded to one silver(I) atom and κ¹to

another, but this construction does not lead to the formation

of argentachains. Six κ²-κ¹[C(pz)₃] units from six different

ligands together with six silver atoms to form a 36-member

argentamacrocycle core with the same AgNNCNN sequence

as in the helical chain secondary structure of 1, Figure 7.

The shortest Ag‚‚‚Ag distance is 5.54 Å indicating that there

are no interactions between the silver(I) cations.

Figure 5. (a) Two triflate clusters of 1a, view perpendicular to c axis,

showing the distances (Å) between planes formed by the carbon atoms of

triflate groups. (b) The same two triflate clusters, viewed end on.

have their fluorine atoms directed toward one another. The

cluster is formed by the circular arrangement of three triflate

anions in a plane and three others related by an S₆symmetry

operation. The distance between the planes formed by the

carbon atoms of the triflate groups within the cluster is 4.53

Å. In contrast, the distance between two adjacent planes from

two separate clusters is 7.20 Å.

Attractive interactions of the type X‚‚‚X (X ) F, Cl, Br,

I) are known to play an important role in many structures,

although the exact nature of the interaction is still unclear.¹⁰

For compound 1a, the shortest F‚‚‚F distances are 3.28 Å,

more than the sum of the van der Waals radii for fluorine at

2.94 Å.²⁴The energy of interaction between the fluorine

atoms of the triflate groups at 3.28 Å in the [(CF₃SO₃)₆]^6-

clusters was calculated on the MP2/aug-cc-pVDZ level of

theory, with only the valence electrons correlated. The

calculation was based on the work of Halkier et al.²⁵and on

the experimentally measured shortest F‚‚‚F distance. We

neglected the basis set superposition error and presume our

basis set to be sufficiently large for a qualitatively correct

estimate. The energy of interaction between two adjacent

fluorine atoms at the Hartree-Fock level is 0.34 kcal/mol.

(26) Su, C.-Y.; Kang, B.-S.; Wang, Q.-G.; Mak, T. C. W. J. Chem. Soc.,

Dalton Trans. 2000, 1831.

(27) (a) Johnston, D. H.; Shriver, D. F. Inorg. Chem. 1993, 32, 1045. (b)

Huang, W.; Wheeler, R. A.; Frech, R. Spectrochim. Acta, Part A 1994,

50A, 985. (c) Rhodes, C. P.; Frech, R. Solid State Ionics 2000, 136-

137, 1131. (d) Huang, W.; Frech, R.; Wheeler, R. A. J. Phys. Chem.

1994, 98, 100. (e) Lawrance, G. F. Chem. ReV. 1986, 86, 17.

(24) (a) Bondi, A. J. Phys. Chem. 1964, 68, 441. (b) Rowland, R. S.; Taylor,

R. J. Phys. Chem. 1996, 100, 738.

(25) Halkier, A.; Klopper, W.; Helgaker, T.; Jorgensen, P.; Taylor, P. R.

J. Chem. Phys. 1999, 111, 9157.

542 Inorganic Chemistry, Vol. 43, No. 2, 2004

Bitopic Tris(pyrazolyl)methane Ligand

Figure 9. Schematic representation of the spatial arrangement of the

argentamacrocycles showing the formation of the tubes in 2a.

Figure 7. The argentamacrocycle core of {p-C₆H₄[CH₂OCH₂C(pz)₃]₂-

(AgSbF₆)₂[(CH₃)₂CO]₂}_∞(2a) created by the κ²-κ¹bonding mode of the

tris(pyrazolyl)methane units; hydrogen atoms omitted.

-

Figure 10. Six argentacrown cores, 24 acetone molecules, and four SbF₆

anions building up two adjacent tubular metallamacrocycles in 2a and their

relative position one to another. Only essential atoms are shown, and the

-

disordered fluorine atoms of the SbF₆groups are omitted.

Figure 10 shows the arrangement of two stacks of the

argentamacrocycles that make up the tubes. Each pair of

-

macrocycles sandwich six acetone molecules and one SbF₆

counterion. The acetones interact with the argentamacrocycle

cores via short C-H‚‚‚π interactions with the pyrazolyl

-

rings.⁹The location of the one SbF₆anion among the

electron rich acetone double bonds and the π clouds from

-

the pyrazolyl rings seems unusual. The remaining SbF₆

anions are located in the chiral, helical channels of the

spacers. Figure 10 shows that each argentamacrocycle

“looks” like a crown and each pair acts as a “host” to a SbF₆

-

Figure 8. The overall structure of 2a, SbF₆anions not shown, viewed

down seven of the argentamacrocycle tubes connected by trigonally shaped

-

helical spirals.

and six acetone “guests”.

In the tertiary structure, the organic spacers that connect

two [C(pz)₃] units in the ligand link the argentamacrocycles

in an extended tubular 3D structure. The ether-based sidearms

have a skewed trans arrangement with the angle formed by

the arene ring and the plane of the attached CH₂OCH₂group

of 42.6°. This orientation of the spacer allows a helical

arrangement of the L-Ag-L-Ag sequence along a crystal-

lographic 3₁screw axis. Also supporting this structure is a

double π-π interaction involving the central arene core and

two (symmetry related) pyrazolyl rings sandwiching the

former aromatic moiety.^8b

In the 3D tertiary structure, each argentamacrocycle is

surrounded by six trigonally shaped helical spirals formed

by the organic spacers that connect them to six other

argentamacrocycles, Figure 8. A schematic representation

of this arrangement that shows the relative position of the

macrocycles is shown in Figure 9. Each helical spiral places

every fourth argentamacrocycle on top of each other forming

a tubular structure.

Crystallization from acetone of the product from the

reaction between AgPF₆and p-C₆H₄[CH₂OCH₂C(pz)₃]₂leads

to the formation of {p-C₆H₄[CH₂OCH₂C(pz)₃]₂AgPF₆}_∞(3a).

In contrast to 1a and 2a and the stoichiometry of the solid

taken into the crystallization step, the metal/ligand ratio is

1:1. The primary structure consists (Figure 11) of two tris-

(pyrazolyl)methane units bonded to silver(I) in a κ²-κ⁰

coordination mode. The silver atom has a tetrahedral

environment, with a distortion imposed by the restricted

“bite” angle of the chelating pyrazolyl rings (see bond

distances and angles in Supporting Information). Each tris-

(pyrazolyl)methane unit has one noncoordinated pyrazolyl

ring. In the chain structure the ligand exists in an alternating

cis and trans conformation, both pictured at the top of Figure

12. These conformers, combined with the κ²-coordination

mode, leads to a single stranded helical secondary structure,

also shown in Figure 12. The presence of the cis ligand is

critical to the helical organization of 3a. Two single stranded

helices of opposite chirality self-assemble in a tertiary

Inorganic Chemistry, Vol. 43, No. 2, 2004 543

Reger et al.

When acetone was replaced by acetonitrile in the crystal-

lization procedure for compound 2, crystals of the formula

{p-C₆H₄[CH₂OCH₂C(pz)₃]₂[(AgSbF₆)₂(CH₃CN)₂][(CH₃CN)_0.25

-

(C₄H₁₀O)_0.25]}_∞(2b) were obtained. Crystallographic studies

revealed that the asymmetric unit contains two crystallo-

graphically nonequivalent Ag atoms and two independent

SbF₆^-anions; two ligands are situated about crystallographic

inversion centers, and therefore, only half of each ligand is

present in the asymmetric unit (Figure 14). The primary

structure is formed by the κ²-κ¹coordination mode of the

tris(pyrazolyl)methane units. All silver atoms have a distorted

tetrahedral environment, with an acetonitrile molecule oc-

cupying the fourth coordination site (Figures 14 and 15).

The secondary structure is organized in argentachains, with

the AgNNCNN sequence of construction, analogous to 1a

rather than the argentamacrocycles observed for 2a. The

chains are linked by the organic spacer (trans arrangement

of the sidearms) and arranged in a 2D sheet tertiary structure.

Figure 16 shows two such sheets oriented horizontally, down

the argentachains showing the linking organic spacers, with

Figure 11. ORTEP representation of the strand repeat unit in 3a. Individual

strands in the double helix are related to one another by pure translation

along the a axis; the double helix direction is along the a axis. Displacement

parameters for atoms refined anisotropically shown at the 40% probability

level and isotropic atoms drawn as spheres of arbitrary radii.

structure consisting of two strands wrapped one around

another, leading to a double stranded helical structure, Figure

13. The “glue” that holds the helices together in the double

stranded helix is a series of C-H‚‚‚π interactions between

the central arene rings, with the arene rings from the cis

conformers acting as acceptors and with the arene rings from

the trans conformers acting as donors. The H‚‚‚centroid

distance is 2.59 Å, with the corresponding C‚‚‚centroid

distance of 3.46 Å and the associated C-H‚‚‚centroid angle

of 153.4°. The counterions are not involved in any nonco-

valent interactions as reported in other cases for this

anion,^7c,28the crystal packing of the double stranded helices

being based solely on van der Waals forces.

It should be noted that 3a represents a rare example of a

double stranded helical organization of a coordination

polymer consisting of two separate single stranded helical

chains wrapped one around another. In most of the known

examples of discrete or infinite helical architectures, all the

strands of the helix are attached through coordinate covalent

bonds to the metal atoms that form the axis of the helix.²⁹

In contrast, there are only a few examples of chemical species

that consist of single stranded helical independent chains

interacting through one or another only by noncovalent

interaction, with the resulting structure being a double helix.³⁰

-

the sheets sandwiching the SbF₆anions and disordered

solvent molecules. The sheets are connected in a quaternary

-

structure by means of hydrogen bonds between the SbF₆

anions and acidic hydrogen atoms from the ligands, Figure

16. The H‚‚‚F distances range from 2.24 to 2.38 Å and the

C-H‚‚‚F angles from 166.9° to 157.4°, values that suggest

strong interactions within this class of weak noncovalent

contacts.⁷

While the primary driving forces for this structure are the

covalent bonds between the ligand, silver, and coordinated

acetonitrile, the structure is also supported by an additional

important noncovalent interaction, a C-H‚‚‚π interaction

between a hydrogen atom from a pyrazolyl ring that chelates

the Ag(1) and the π system of the central arene ring.

Interestingly, only one of the two nonequivalent central arene

rings is involved in this interaction; the other one is not

involved in any type of noncovalent interaction. Thus, as

shown in Figure 15, every other row of central arene rings

acts as an acceptor for two H(13) hydrogen atoms that

sandwich the ring. This interaction arranges the argentachains

in a flattened zigzag orientation within the overall sheet, as

it can be seen in Figure 16.

(28) (a) Cantrill, S. J.; Preece, J. A.; Stoddart, J. F.; Wang, Z.-H.; White,

A. J. P.; Williams, D. J. Tetrahedron 2000, 56, 6675.

(29) For reviews on helical assemblies based on dative bonds see ref 1a

and 1o; for selected recent examples see: (a) Wang, X.; Vittal, J. J.

Inorg. Chem. Commun. 2003, 6, 1074. (b) Koeller, S.; Bernardinelli,

G.; Piguet, C. J. Chem. Soc., Dalton Trans. 2003, 2395. (c) Tuna, F.;

Hamblin, J.; Jackson, A.; Clarkson, G.; Alcock, N. W.; Hannon, M.

J. J. Chem. Soc., Dalton Trans. 2003, 2141. (d) Khlobystov, A. N.;

Brett, M. T.; Blake, A. J.; Champness, N. R.; Gill, P. M. W.; O’Neill,

D. P.; Teat, S. J.; Wilson, C.; Schroeder, M. J. Am. Chem. Soc. 2003,

125, 6753. (e) Floquet, S.; Ouali, N.; Bocquet, B.; Bernardinelli, G.;

Imbert, D.; Bunzli, J.-C. G.; Hopfgartner, G.; Piguet, C. Chem. Eur.

J. 2003, 9, 1860. (f) Carlucci, L.; Ciani, G.; Proserpio, D. M.; Rizzato,

S. New J. Chem. 2003, 27, 483. (g) Barboiu, M.; Vaughan, G.;

Kyritsakas, N.; Lehn, J.-M. Chem. Eur. J. 2003, 9, 763. (h) Shova,

S.; Novitchi, G.; Gdaniec, M.; Caneschi, A.; Gatteschi, D.; Korob-

chenko, L.; Voronkova, V. K.; Simonov, Y. A.; Turta, C. Eur. J. Inorg.

Chem. 2002, 3313. (i) Beauchamp, D. A.; Loeb, S. J. Chem. Commun.

2002, 2484. (j) Keegan, J.; Kruger, P. E.; Nieuwenhuyzen, M.; Martin,

N. Cryst. Growth Des. 2002, 2, 329. (k) Isola, M.; Liuzzo, V.;

Marchetti, F.; Raffaelli, A. Eur. J. Inorg. Chem. 2002, 1588. (l) Stahl,

J.; Bohling, J. C.; Bauer, E. B.; Peters, T. B.; Mohr, W.; Martin-

Alvarez, J. M.; Hampel, F.; Gladysz, J. A. Angew. Chem., Int. Ed.

2002, 41, 1871. (m) Albrecht, M.; Schneider, M. Eur. J. Inorg. Chem.

2002, 1301. (n) Guo, D.; He, C.; Duan, C.-Y.; Qian, C.-Q.; Meng,

Q.-J. New J. Chem. 2002, 26, 796.

Crystallization of 3 from acetonitrile yields crystals of the

formula {p-C₆H₄[CH₂OCH₂C(pz)₃]₂[(AgPF₆)₂(CH₃CN)₂][(CH₃-

CN)_0.25(C₄H₁₀O)_0.25]}_∞(3b), a compound with a metal/ligand

ratio of 2:1, in contrast to the 1:1 ratio found in 3a. The

structure is organized in the same manner with that of 2b:

a κ²-κ¹bonding mode of the tris(pyrazolyl)methane unit with

a trans orientation of the ligand (Figure 17), leading to a

sheet structure for 3b similar to that depicted in Figures 14-

16 for 2b. However, a close analysis of the noncovalent

interactions present in 3b shows two major differences. First,

although the sheet structure is supported by C-H‚‚‚π

interactions as in 2b, in this case the central arene ring is

the proton donor and a pyrazolyl ring is the acceptor. As in

2b, every other row of central arene rings is involved in such

an interaction, pictured in Figure 18. The second difference

(30) Selected examples: (a) Jouaiti, A.; Hosseini, M. W.; Kyritsakas, N.

Chem. Commun. 2003, 472. (b) Chen, X.-M.; Liu, G.-F. Chem. Eur.

J. 2002, 8, 4811. (c) Mamula, O.; von Zelewsky, A.; Bark, T.;

Bernardinelli, G. Angew. Chem., Int. Ed. 1999, 38, 2945.

-

is that the PF₆anions are not involved in weak C-H‚‚‚F

544 Inorganic Chemistry, Vol. 43, No. 2, 2004

Bitopic Tris(pyrazolyl)methane Ligand

Figure 12. The formation of one helical single strand in {p-C₆H₄[CH₂OCH₂C(pz)₃]₂AgPF₆}_∞(3a): (a) cis orientation of one ligand; (b) trans orientation

of another ligand; (c) their successive occurrence linked by the silver(I) centers.

Figure 13. The double stranded helical structure of 3a: (a) two intertwined strands, view perpendicular to a axis, with the C-H‚‚‚π interaction showed

as red dotted lines; (b) the same two strands viewed along the a axis; (c) space filling of 3a.

a sheet structure similar to 2b and 3b, organized by a κ²-κ¹

bonding mode of the tris(pyrazolyl)methane units (Figure

19), but in contrast to the other “type b” structures it contains

two types of helical argentachains, one of which does not

contain a acetonitrile bonded to the silver(I), Figure 20. The

three-coordinate silver in this chain has a flattened trigonal

pyramid arrangement (sum of the N-Ag(1)-N bond angles

) 347°). In addition, each silver in this chain interacts with

the π cloud of a pyrazolyl ring κ²-coordinated to the next

silver(I) atom in the chain.³¹The second type of silver atom

has a distorted tetrahedral arrangement with the CH₃CN

molecules bonded alternatively above and below the chain.

As in other “type b” structures, there are C-H‚‚‚π interac-

tions supporting the sheet structure. The same pyrazolyl ring

that is involved in the silver-π contact acts as a hydrogen

donor, with the central arene ring acting as acceptor.

The differences in the coordination environment of silver

atoms in 4b lead to a change in symmetry when compared

to 2b and 3b. While both 2b and 3b crystallize in the triclinic

system, space group P1h, 4b crystallizes in the chiral

Figure 14. ORTEP representation of the cationic unit in {p-C₆H₄[CH₂-

OCH₂C(pz)₃]₂[(AgSbF₆)₂(CH₃CN)₂][(CH₃CN)_0.25(C₄H₁₀O)_0.25]}_∞(2b) with

displacement ellipsoids shown at 40% probability level.

-

hydrogen bonds as observed for the SbF₆counterions in

the case of 2b, with all C-H‚‚‚F distances being greater than

the sum of van der Waals radii of hydrogen and fluorine.

Crystallization of 4 from acetonitrile yields crystals of the

formula {p-C₆H₄[CH₂OCH₂C(pz)₃]₂[(AgBF₄)₂(CH₃CN)](C₄-

H₁₀O)}_∞(4b). This compound is a coordination polymer with

(31) (a) Mascal, M.; Kerdelhue, J. L.; Blake, A. J.; Cooke, P. A. Angew.

Chem., Int. Ed. 1999, 39, 1968. (b) Mascal, M.; Kerdelhue, J. L.; Blake,

A. J.; Cooke, P. A.; Mortimer, R. J.; Teat, S. J. Eur. J. Inorg. Chem.

2000, 485.

Inorganic Chemistry, Vol. 43, No. 2, 2004 545

Reger et al.

Figure 17. ORTEP representation of the cationic unit in {p-C₆H₄[CH₂-

OCH₂C(pz)₃]₂[(AgPF₆)₂(CH₃CN)₂][(CH₃CN)_0.25(C₄H₁₀O)_0.25]}_∞(3b) with

displacement ellipsoids shown at 20% probability level.

Figure 15. One sheet of 2b, formed by three argentachains linked by the

organic spacers; the red lines represent the C-H‚‚‚π interactions between

two pyrazolyl rings sandwiching one row of central arene rings.

Figure 18. The sheet structure of {p-C₆H₄[CH₂OCH₂C(pz)₃]₂[(AgPF₆)₂(CH₃-

CN)₂][(CH₃CN)_0.25(C₄H₁₀O)_0.25]}_∞(3b): (a) view perpendicular to the sheet;

(b) an end on view of the same sheet, in both the C-H‚‚‚π interactions

within the sheet are shown as red dotted lines.

identical to the length of the a axis of the unit cell, 10.282

Å, making the pitches of both helicates identical.

Figure 21 shows that the 2D network (viewed end on),

formed by the helical chains and the connecting organic

bridges, is arranged into a 3D supramolecular quaternary

structure by C-H‚‚‚F weak hydrogen bonds. One of the two

Figure 16. The crystal packing of 2b showing the C-H‚‚‚F hydrogen

bonds as blue dotted lines; also shown (red dotted lines) are the C-H‚‚‚π

interactions within the sheet structure of 2b.

-

orthorhombic space group P2₁2₁2₁. The different coordination

environment of silver atoms, coupled with a trans orientation

of the organic spacer, leads to a helical arrangement of both

AgNNCNN argentachains. In both cases, the arrangement

of the backbone is helical, but the chirality of each is

opposite. Both helices are generated around crystallographic

2₁screw axes along the a axis of the unit cell. For both, the

distance between every other silver atom is equal and

nonequivalent BF₄ions makes four hydrogen bonds with

two of the 2D sheets forming the 3D architecture.²⁴The

second BF₄^-ion makes two hydrogen bonds, one to each of

two sheets. A particularly interesting part of the structure is

that each diethyl ether molecule is bonded through one

-

terminal methyl group to the BF₄counterion that makes

four hydrogen bonds and also through the ether oxygen atom

to a coordinated acetonitrile.

546 Inorganic Chemistry, Vol. 43, No. 2, 2004

Bitopic Tris(pyrazolyl)methane Ligand

Figure 19. ORTEP representation of the cationic unit of {p-C₆H₄[CH₂-

OCH₂C(pz)₃]₂[(AgBF₄)₂(CH₃CN)](C₄H₁₀O)}_∞(4b) with displacement el-

lipsoids shown at 50% probability level.

Figure 21. Two sheets in 4b held together through C-H‚‚‚F bonds

-

involving the BF₄anions, forming a 3-D quaternary architecture; ether

molecules situated between the sheets are also shown.

Figure 22. ORTEP representation of {p-C₆H₄[CH₂OCH₂C(pz)₃]₂-

(AgNO₃)₂}_∞‚4CH₃CN (5‚4CH₃CN), at the 50% probability level with the

-

NO₃anions coordinated to silver(I) centers; acetonitrile molecules of

solvation and hydrogen atoms not shown.

Figure 20. View perpendicular to one sheet formed by the alternating

silver chains in 4b; the C-H‚‚‚π interactions are shown as red dotted lines

and the Ag-π contacts pictured with black dotted lines.

All these interactions build up a chiral network of helices

of opposite chirality. This is an example of a racemic mixture

of helices crystallizing in a chiral space group, where no

symmetry operation relates the two helices of opposite

chirality.

Crystallization of 5 from acetonitrile yields crystals of the

formula {p-C₆H₄[CH₂OCH₂C(pz)₃]₂(AgNO₃)₂(CH₃CN)₄}_∞

(5‚4 CH₃CN). The primary structure (Figure 22) is formed

again by a κ²-κ¹coordination mode of the ligand to the

silver(I) centers. In addition, the anions are also coordinated

to the silvers, a common feature for discrete silver(I)

compounds or silver(I) coordination polymers formed from

Figure 23. One argentachain of {p-C₆H₄[CH₂OCH₂C(pz)₃]₂(AgNO₃)₂}_∞‚

4CH₃CN (5‚4CH₃CN), with the NO₃^-anions coordinated to silver(I) centers;

hydrogen atoms not shown.

consists of W-shaped sheets that have an overall configu-

ration very different from 2b-4b. Figure 24 shows two such

sheets down the polymeric chains. The sheets are held

together in a quaternary structure via a favorable noncovalent

interaction that we have named “quadruple pyrazolyl em-

brace” and presented in detail in Scheme 1: a concerted set

-

this counterion.^1c,d,16j,17bThe NO₃anion is anisobidentate

with one short (2.504(5) Å) and one long (2.761(5) Å)

oxygen-silver distance.

The secondary structure again consists of AgNNCNN

argentachains, Figure 23. However, the tertiary 2D structure

Inorganic Chemistry, Vol. 43, No. 2, 2004 547

Reger et al.

Figure 24. Two stacked sheets of 5‚CH₃CN; the pyrazolyl embrace interactions are centrally pictured and marked with *.

of π-π stacking and C-H‚‚‚π interaction.¹⁹Two closely

situated sets of pyrazolyl rings, part of adjacent sheets, within

the [C(pz)] units that chelate the silver(I) centers, are involved

in this supramolecular contact. Within these four pyrazolyl

rings, two of them are stacked and parallel displaced, and

they serve as hydrogen donors in the associated C-H‚‚‚π

interaction, where two other pyrazolyl rings act as acceptors.

The association between the sheets creates channels that

bisect the b and c axes of the unit cell creating 12 × 10 Å²

channels that are filled with acetonitrile molecules.

Anion Exchange Properties. The anion exchange proper-

ties of these compounds have been explored by treating {p-

C₆H₄[CH₂OCH₂C(pz)₃]₂(AgSbF₆)₂}_∞(2) with a saturated

aqueous solution of KPF₆and separately a solution of KO₃-

SCF₃. The solid was periodically collected by filtration (every

2 h) and the presence of the second anion monitored by

infrared spectroscopy following the characteristic bands of

the anions.^32,33Samples containing mixtures of anions as well

-

as ones with the SbF₆completely exchanged could be

obtained by these methods. The IR spectrum of pure 2 (red

line in Figure 25) shows a band at 664 cm^-1(marked with

-

*) that is assigned to ν₃(T_1u) vibration of the SbF₆anion.

-

The IR spectrum of a partially (SbF₆/PF₆) exchanged

sample (after 4 h of stirring) is shown in Figure 25 as a green

line; the band at 664 cm^-1is still present, but of a weaker

intensity, an indication of a decreased quantity of this anion.

There are two new bands (both marked with b) at 841 and

550 cm^-1, assigned to ν3(T_1u) and ν4(T_1u) vibrations of the

Figure 25. Anion exchange monitored by IR spectroscopy; red line

indicates IR spectra of 2: the band at 664 cm^-1(marked with *) is assigned

-

PF₆anion. The anions can be completely exchanged by

-

to ν₃(T_1u) vibration of the SbF₆anion. Green line indicates IR spectra of

-

stirring for 12 h. The IR spectrum of completely (SbF₆/

a partially (SbF₆^-/PF₆^-) exchanged sample: the bands at 841 and 550 cm^-1

-

PF₆) exchanged sample is pictured as a blue line; the band

(marked with b) are assigned to ν₃(T_1u) and ν₄(T_1u) vibrations of the PF₆

-

anion. Blue line indicates IR spectra of a completely (SbF₆^-/PF₆

)

/

at 664 cm^-1is no longer present, and the two strong bands

-

exchanged sample. Black line indicates IR spectra of a partially (SbF₆

F₃CSO₃^-) exchanged sample: the band at 1154 cm^-1(marked with #) is

(32) Related examples: (a) Yaghi, O. M.; Li, H. J. Am. Chem. Soc. 1996,

118, 295. (b) Khlobystov, A. N.; Champness, N. R.; Roberts, C. J.;

Tendler, S. J. B.; Thompson, C.; Schroeder, M. CrystEngComm 2002,

4, 426. (c) Noro, S.; Kitaura, R.; Kondo, M.; Kitagawa, S.; Ishii, T.;

Matsuzaka, H.; Yamashita, M. J. Am. Chem. Soc. 2002, 124, 2568.

(d) Sui, B.; Fan, J.; Okamura, T.; Sun, W.-Y.; Ueyama, N. New J.

Chem. 2001, 25, 1379. (e) Jung, O.-S.; Kim, Y. J.; Lee, Y.-A.; Chae,

H. K.; Jang, H. G.; Hong, J. Inorg. Chem. 2001, 40, 2105. (f) Min, K.

S.; Suh, M. P. J. Am. Chem. Soc. 2000, 122, 6834.

assigned to the δ_asCF₃(E) vibration.

-

of the PF₆anion clearly present. This procedure can be

extended to other anions as well: the IR spectrum of a

-

partially (SbF₆/CF₃SO₃) exchanged sample is shown in

Figure 25 as a black line. The band at 664 cm^-1is still

present but again of a weaker intensity, and the band (marked

with #) at 1154 cm^-1is clearly assigned to δ_asCF₃(E).²⁷

(33) Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coor-

dination Compounds, 3rd ed.; Wiley-VCH: New York, 1978.

548 Inorganic Chemistry, Vol. 43, No. 2, 2004

Bitopic Tris(pyrazolyl)methane Ligand

Figure 26. ORTEP representation of the cationic unit of {p-C₆H₄[CH₂-

OCH₂C(pz)₃]₂[Ag₂(PF₆)_0.78(1)(SbF₆)_1.22(1)(CH₃CN)₂][(CH₃CN)_0.25

-

(C₄H₁₀O)_0.25]}_∞(6) with displacement ellipsoids shown at 40% probability

level.

From a sample containing a SbF₆^-/PF₆^-mixture of anions,

crystals of the formula {p-C₆H₄[CH₂OCH₂C(pz)₃]₂[Ag₂-

(PF₆)_0.78(1)(SbF₆)_1.22(1)(CH₃CN)₂][(CH₃CN)_0.25(C₄H₁₀-

O)_0.25]}_∞(6) were obtained from the same acetonitrile system

used for “b type” complexes and were subjected to X-ray

diffraction studies. The cationic unit is shown in Figure 26.

A complete structural analysis revealed the same basic 2D

sheet structure as observed for 2-4b. Two independent

Figure 27. The sheet structure of {p-C₆H₄[CH₂OCH₂C(pz)₃]₂[Ag₂-

(PF₆)_0.78(1)(SbF₆)_1.22(1)(CH₃CN)₂][(CH₃CN)_0.25(C₄H₁₀O)_0.25]}_∞(6); the red

dotted lines are the C-H‚‚‚π interactions.

-

(P,Sb)F₆anion positions were located; however, the PF₆

-

and SbF₆anions were found to be mixed on both sites, in

the proportion P(1)/Sb(1) ) 0.314(1)/0.686(1) and P(2)/

Sb(2) ) 0.467(1)/0.543(1). Refinement of either site as fully

P or fully Sb resulted in unreasonably small (P) or large (Sb)

displacement parameters as well as higher R-values. The

fluorine atoms in both anion sites are well ordered, and

therefore, the P(Sb)-F bond lengths represent a weighted

average of the P-F and Sb-F contributions. The slightly

inflated displacement parameters for these fluorine atoms

may reflect the presence of two closely separated F₆

octahedra, or simply the rotational disorder commonly

encountered in spherical anions of this type.

Figure 28. ORTEP representation of the cationic unit of {p-C₆H₄[CH₂-

OCH₂C(pz)₃]₂(AgSbF₆)[(CH₃)₂CO]_1.5

}

(7) with displacement ellipsoids

∞

Analysis of the covalently bonded network indicated the

presence of two types of C-H‚‚‚π interactions between the

pyrazolyl-central arene ring pairs. Interestingly, both of the

interactions in which a pyrazolyl ring acted as the hydrogen

donor and the phenyl ring as acceptor as in 2b and the inverse

situation found in 3b were found, as pictured in Figure 27.

In this case, every other row of central arene rings alterna-

tively acts as either hydrogen donor or acceptor. In other

words, both interactions found separately in alternate rows

in 2b and 3b are combined in the case of 6, in an alternating

occurrence, involving every row.

shown at 50% probability level.

-

from acetone, a new compound containing only SbF₆as

the counterion was obtained, of the formula {p-C₆H₄[CH₂-

OCH₂C(pz)₃]₂(AgSbF₆)[(CH₃)₂CO]_1.5}_∞(7). In contrast to its

-

other two SbF₆“homologues” 2a and 2b, where the tris-

(pyrazolyl)methane units act in the κ²-κ¹coordination mode

and the metal-to-ligand ratio is 2:1, here the [C(pz)₃] unit is

κ²-κ⁰bonded with a metal-to-ligand ratio of 1:1 (Figure 28).

This feature leads to a 1D secondary structure represented

in Figure 29a, where all the ligands have a trans arrangement

of the sidearms. The tertiary structure is organized by acetone

molecules that interact with a pyrazolyl ring via C-H‚‚‚π

interactions, with one of the methyl groups acting as the

hydrogen donor, Figure 29b. In addition, the oxygen atoms

within the acetones act as acceptors in weak C-H‚‚‚O

hydrogen bonds, where the hydrogen donor is a CH group

-

When the SbF₆anion was completely exchanged with

-

PF₆and a crystalline sample was subjected to crystal-

lographic studies, an identical structure with that of 3b

prepared directly from AgPF₆was obtained.

-

When the same SbF₆/PF₆^-mixture that was used for the

growth of the crystals for 6 from acetonitrile was crystallized

Inorganic Chemistry, Vol. 43, No. 2, 2004 549

Reger et al.

The double π-π stacking interactions in the organic linkers

are critical to the circular organization of these argentachains

(Figures 2 and 3). In the case of 2a, the acetone molecules

noncovalently connected to the covalent framework along

-

with the “trapped” SbF₆counterion appear to support the

tubular organization of the argentamacrocycles with the

helical organization of the L-Ag-L-Ag sequence also

important to this arrangement.

Among the helical systems, DNA is certainly the most

commonly known example. The DNA double helix is formed

upon self-assembly of two complementary helical strands.

The driving force for the formation of the double helical

arrangement is the establishment of hydrogen bonds between

complementary nucleic acid bases. However, in principle,

any type of attractive interaction may be used to generate

double helical architectures, as long as there are two

complementary helical strands with complementary recogni-

tion sites that will induce a recognition pattern within their

structure. In the case of 3a, the self-complementary recogni-

tion pattern is played by the central arene ring that undergoes

a C-H‚‚‚π interaction, as pictured in Figure 13.

Figure 29. (a) One chain of {p-C₆H₄[CH₂OCH₂C(pz)₃]₂(AgSbF₆)[(CH₃)₂-

CO]_1.5

_∞(7) showing the κ²-κ⁰bonding mode of the [C(pz)₃] unit and the

trans arrangement of the ligand; (b) two strands of 7 and their associated

acetone molecules (C-H‚‚‚π contacts showed as red dotted lines). The

C-H‚‚‚O hydrogen bonds responsible for organization of 7 in sheets are

shown as a blue dotted line.

}

The crystalline solids obtained from acetonitrile, “b type”,

show similar structures; two-dimensional sheets build up by

linking the AgNNCNN sequence of argentachains by the

organic spacer. Although the covalent part of the 2b-4b

networks is two-dimensional, the structures have thickness.

The views of 2b (Figure 16), 3b (Figure 18b), and 4b (Figure

21) in the same alignment of the sheets illustrate the

similarity in the width of the sheets. Also shown are

U-shaped channels formed between the silver strands by the

1,4-bis[ethoxymethyl]benzene bridge. The dimensions of the

channels are ca. 6 × 4 Å²in all structures, as measured

between the two methylene groups directly bonded to the

phenyl ring and between these methylene groups and the

central methine carbon atoms from the tris(pyrazolyl)methane

units. Despite the similarity between the sheets, subtle

differences induced by the anions are also present (vide

supra). The differences between 2b and 3b are at the

noncovalent level only, but when 4b is compared with its

analogues a drastic change in symmetry is observed. The

asymmetric units of 2b and 3b contain two crystallographi-

cally inequivalent Ag atoms and two independent anions;

two ligands are situated about crystallographic inversion

centers, and therefore, only half of each ligand is present.

The asymmetric unit of 4b is composed also of two

crystallographically inequivalent Ag atoms and two inde-

pendent anions, but one full ligand is present. Further, the

coordinated acetonitrile molecules are bonded to only one

type of silver. These differences lead to the following

situation: in the case of 2b and 3b the inequivalent Ag atoms

are found alternatively in the same argentachain, while in

the case of 4b the inequivalent Ag atoms are found in

different chains. An additional important structural difference

is that in 4b the solvent molecules are held between the

helical layers in a very ordered fashion by weak hydrogen

bonds, a rather unusual observation for helical superstructures.^1a

In 2b and 3b (where the solvent is not involved in any

from a pyrazolyl ring situated on an adjacent strand. These

interactions build up a 2D tertiary structure, arranging the

strands closely one to another in a sheetlike structure.

Comparison of “Molecular” and Supramolecular Struc-

tures. The structural behavior of the silver(I)-p-C₆H₄[CH₂-

OCH₂C(pz)₃]₂system with noncoordinating counterions

shows a dual solvent-counterion dependence. The solvent

used for crystallization primarily controls the structures.

When the compounds are crystallized from the coordinating

solvent acetonitrile, similar 2-D sheet structures are observed

(“b type”), with the anions imposing small differences within

the sheets. When crystallized from the weakly coordinating

solvent acetone (“a type”), the anions impose major structural

variations of the resulting architectures.

In all “a type” structures, helical arrangements were

observed, either of the argentachains (1a), of the organic

spacer only (2a), or of the whole 1-D covalent network (3a).

Given the major differences in the secondary structures of

1a and 2a, there are surprising similarities: both compounds

crystallize in the rhombohedral space group R3h (hexagonal

setting), both with Z ) 9. In both compounds, the κ²-κ¹

coordination mode of the ligand is present, and both tertiary

structures are supported by the same double π-π stacking

where two pyrazolyl rings (symmetry related) sandwich the

central arene core. In both compounds the local structure of

the ligand is almost identical: the ether-based sidearms have

a skewed trans arrangement with the angle formed by the

arene ring and the plane of the attached CH₂OCH₂group

being around 42°. This orientation of the ligand is required

by the double π-π stacking in which the ligand is involved.

In the case of 1a, the F‚‚‚F interactions, coupled with the

extensive network of weak hydrogen bonds between the

triflate oxygen atoms and C-H groups on the ligands,

organize the tubular tertiary structure of helical argentachains.

550 Inorganic Chemistry, Vol. 43, No. 2, 2004

Bitopic Tris(pyrazolyl)methane Ligand

noncovalent interaction) the trapped solvent was found to

be disordered.

in the crystallization process was a compound with a ligand-

to-metal ratio of 1:2, both the final crystalline compounds

were found to have a ligand-to-metal ratio of 1:1, a

phenomenon found only in the case where PF₆was the

counterion and acetone was used as crystallization solvent.

When the structure of 5‚4 CH₃CN, containing the coor-

dinating counterion nitrate, is compared with its homologues,

the differences are even more pronounced. The nitrates

coordinate to the silvers, and the acetonitrile molecules in

the crystals are simply solvents of crystallization. This

alteration imposes a change in the structure from an almost

planar sheet to a W-shaped sheet (compare Figures 16, 18b,

21, and 27b with Figure 24). Also different is the packing

of the sheets within the crystal that is controlled by the

pyrazolyl embrace in 5‚4CH₃CN.

-

Conclusion

Critical for the formation of these supramolecular struc-

tures is the organization inherently built into the bitopic

ligand by its rigid parts (central arene core and [C(pz)₃] units)

linked by a set of three sp³hybridized atoms. Importantly,

it is the flexibility of the ether linkage that allows the anions

to organize the structures reported here; rigid ligands would

have to be perfectly tailored to allow such structures, and

their inherent rigidity would restrict the influence of the

anions in the final structures.

-

Crystallization of the partially exchanged SbF₆/PF₆

mixture from both acetonitrile and acetone leads to two very

different complexes. From acetonitrile, a “b type” structure

of the mixed counterion species 6 is observed. In the presence

of both anions, both types of C-H‚‚‚π interactions are

observed that are found separately in 2b and 3b (see Figures

15, 16, 18, and 27).

Summing all the findings for this system, we observed

that all counterions impose changes in the overall structures

of the crystalline solids, but those differences are much

greater when the material is crystallized from a noncoordi-

nating solvent. The following essential patterns in the self-

assembly processes were found in these structures: (a) the

ligand displays a κ²-κ¹coordination mode of the [C(pz)₃]

units in all cases, except the cases when the PF₆^-anion was

present and the crystallization solvent was acetone (3a and

7) where the coordination mode was κ²-κ⁰; (b) the ligand

was able to adjust its structure to maximize both covalent

and noncovalent interactions; (c) there are the absence of

coordinated acetone molecules in “a type” structures and the

presence of coordinated acetonitrile molecules in “b type”

-

Crystallization of the SbF₆/PF₆mixture from acetone

produces a complex with the formula {p-C₆H₄[CH₂OCH₂C-

(pz)₃]₂(AgSbF₆)[(CH₃)₂CO]_1.5}_∞(7), containing only the

-

SbF₆anion and with different stoichiometry than its two

-

SbF₆“homologues” 2a and 2b. The presence of the PF₆

in the crystallization solution leads to precipitation of a new

-

SbF₆complex that is very different from the 2a and 2b

complexes. As observed with 2a, acetone molecules are

involved in organizing the association of the coordination

polymer into a higher level of organization (see Figure 29).

As expected from the similar stoichiometry, the κ²-κ⁰

behavior of the [C(pz)₃] unit in 7 (Figure 29a) is the same

as in 3a (Figures 11, 12), but the ligand has only the trans

orientation. The missing cis orientation of the ligand impedes

the formation of the single and the subsequent double

stranded helical organization as in the case of 3a. Interest-

ingly, the alignment of the strands with the central arene

cores situated close one to another shows the incipient

formation of weak C-H‚‚‚π interactions somewhat analo-

gous to those observed with 3a.

The formation process for 7 is unique in this work. Using

biological systems, Lindsey³⁴has identified several types of

self-assembly processes, and besides the “strict” self-as-

sembly process, we mention here only a few: (a) irreversible

self-assembly (irreversible reactions kinetically channeled to

a particular pathway); (b) assisted self-assembly (where an

external species prevents the formation of unwanted inter-

mediates and does not appear in the final product); (c)

directed self-assembly (where a species directs the course

of the assembly but is not present in the final product). While

all the processes leading to the self-assembly of 1-6 (either

type a or b) are the “strict” self-assembly process, the

assembly of 7 is a “directed” self-assembly process. The

presence of the PF₆^-anion in solution “influences” a κ²-κ⁰

coordination mode of the [C(pz)₃] unit as observed in the

“pure” PF₆^-sample, when both are crystallized from acetone.

Although in the case of 3a and 7 the bulk starting material

-

structures; (d) there are the involvement of OTf^-, SbF₆,

and BF₄^-anions in weak C-H‚‚‚O(F) hydrogen bonds and

-

the lack of such interactions in the PF₆case; (e) the

-

coordination of NO₃to silver(I) center contrasts to that of

OTf^-anion that is also known to be sometimes a coordinat-

ing anion.

An important result of these patterns is the demonstration,

particularly with 1a and 2a, of success using a noncovalent

strategy for the assembly of covalent networks with remark-

able topologies. Although the three-dimensional structures

of both of these compounds are built on covalent bonds, the

tertiary structures observed appear to be arranged by the

noncovalent bonds. This contention is strongest for 1a where

the [(CF₃SO₃)₆]^6-clusters are held together by weak F‚‚‚F

interactions and then these clusters organize the covalent

structure through weak C-H‚‚‚O hydrogen bonds with the

bitopic ligand involving the -SO₃groups. For 2a, the six

acetone molecules and one SbF₆^-anion present between the

argentamacrocycles also organize the tubular structure

observed. For 3a, the covalent bonds organize the strands,

but weak C-H‚‚‚π interactions between the central arene

rings organize the double helix. Crystallization of these

systems from weakly coordinating solvents is necessary to

allow these weak forces to dominate the structures: the three-

coordinate silver centers appear to be more flexible in

accommodating particular structures than the four-coordinate

silvers in the complexes crystallized from acetonitrile. In

(34) Lindsey, J. S. New J. Chem. 1991, 15, 153.

Inorganic Chemistry, Vol. 43, No. 2, 2004 551

Reger et al.

6H, 4-H pz), 5.02 (s, 4H, OCH₂C(pz)₃), 4.67 (s, 4H, OCH₂Ph).

Calcd for C₃₀H₃₀Ag₂F₁₂N₁₂O₂Sb₂: C, 28.20; H, 2.37; N, 13.15.

Found: C, 28.51; H, 2.21; N, 13.17. ES⁺/MS: m/z 699 and 1041,

corresponding to [LAg]⁺and [LAg₂SbF₆]⁺.

these cases, the coordination of the solvent influences the

system such that sheet structures are observed in all cases.

NMR and ES/MS studies show that in solution the cationic

species present are anion independent and that in solutions

of coordinating solvents a complicated series of equilibria

take place between ligand-silver(I) species, species in which

the solvent has partially or completely displaced the ligands.

The structural diversity observed in the solid state, triggered

by the anion and/or solvent, must develop in the final

crystallization step.

The structures reported here demonstrate that the bitopic

p-C₆H₄[CH₂OCH₂C(pz)₃]₂ligand is structurally adaptive; that

is, it can adjust its structure to maximize all covalent and

noncovalent forces within a given system. With this ability

to adjust to changes in the system, coupled with the ability

to participate in π-π stacking and form C-H‚‚‚π and weak

hydrogen bonding interactions, the C₆H_6-n[CH₂OCH₂C(pz)₃]_n

class of ligands based on linking tris(pyrazolyl)methane units

with semirigid organic spacers contains ideal candidates for

studying the self-assembly process. We have also shown that

although the structures reported here are very different,

several important similarities can be found. This strategy for

the assembly of covalent networks based on semirigid ligands

completes the gap between strategies based on rigid or

completely flexible ligands.

Synthesis of {p-C₆H₄[CH₂OCH₂C(pz)₃]₂(AgPF₆)₂}_∞(3). This

compound was synthesized as above for 1 using AgPF₆(0.254 g,

1.00 mmol), to afford 0.409 g (74%) of solid identified as

1

{p-C₆H₂[CH₂OCH₂C(pz)₃]₄(AgPF₆)₂}_∞. H NMR (acetone-d₆): δ

7.83, 7.76 (m, m, 6,6H, 3,5-H pz), 7.08 (s, 4H, C₆H₄), 6.59 (m,

6H, 4-H pz), 5.01 (s, 4H, OCH₂C(pz)₃), 4.65 (s, 4H, OCH₂Ph).

Calcd for C₃₀H₃₀Ag₂F₁₂N₁₂O₂P₂: C, 32.87; H, 2.76; N, 15.33.

Found: C, 33.05; H, 3.15; N, 14.99. ES⁺/MS: m/z 699 corre-

sponding to [LAg]⁺.

Synthesis of {p-C₆H₄[CH₂OCH₂C(pz)₃]₂(AgBF₄)₂}_∞(4). This

compound was synthesized as above for 1 using AgBF₄(0.195 g,

1.00 mmol), to afford 0.445 g (84%) of solid identified as

{p-C₆H₄[CH₂OCH₂C(pz)₃]₂Ag₂(BF₄)₂(THF)}_∞. ¹H NMR (acetone-

d₆): δ 7.82, 7.77 (m, m, 6,6H, 3,5-H pz), 7.09 (s, 4H, C₆H₄), 6.57

(m 6H, 4-H pz), 5.02 (s, 2H, OCH₂Ph), 4.67 (s, 2H, OCH₂C(pz)₃),

3.62 (m, 2H, CH₂O THF), 1.92 (m, 2H, CH₂THF). Calcd for

C₃₀H₃₀Ag₂B₂F₈N₁₂O₂‚C₄H₈O: C, 38.81; H, 3.64; N, 15.98. Found

C, 38.86; H, 3.55; N, 16.23. ES⁺/MS: m/z 699 and 893, corre-

sponding to [LAg]⁺and [LAg₂BF₄]⁺.

Synthesis of {p-C₆H₄[CH₂OCH₂C(pz)₃]₂(AgNO₃)₂}_∞(5). This

compound was synthesized as above for 1 using AgNO₃(0.167 g,

1.00 mmol) in dry acetonitrile (15 mL) under an inert atmosphere.

The clear solution was stirred for 2 h, and 100 mL of diethyl ether

was added, resulting in the precipitation of a white compound. The

solvents were removed by cannula filtration and the white

precipitate washed with THF (2 × 10 mL) and then vacuum-dried

to afford 0.306 g (66%) of solid identified as {p-C₆H₂[CH₂OCH₂C-

(pz)₃]₄(AgNO₃)₂}_∞. ¹H NMR (acetone-d₆): δ 7.82, 7.77 (m, m, 6,-

6H, 3,5-H pz), 7.09 (s, 4H, C₆H₄), 6.57 (m 6H, 4-H pz), 5.02 (s,

4H, OCH₂Ph), 4.67 (s, 4H, OCH₂C(pz)₃). Calcd for C₃₀H₃₀-

Ag₂N₁₄O₈: C, 38.73; H, 3.25; N, 21.08. Found: C, 38.52; H, 3.02;

N, 20.88. ES⁺/MS: m/z 699 and 868, corresponding to [LAg]⁺

and [LAg₂NO₃]⁺.

Crystallization Procedure. In a typical crystallization procedure,

a sample of about 5 mg was dissolved in ca. 3 mL of solvent

(acetone or acetonitrile). To remove any potential insoluble

materials, this solution was filtered through cotton into a small test

tube via a pipet. The open small test tube was inserted in a second,

larger one that already had ca. 20 mL of diethyl ether and was

closed with a Teflon screw cap. The test tubes were kept at room

temperature for several days, during which time colorless crystals

suitable for X-ray diffraction studies formed.

Experimental Section

General Procedure. All operations were carried out under a

nitrogen atmosphere using standard Schlenk techniques and a

Vacuum Atmospheres HE-493 drybox. All solvents were dried and

1

distilled prior to use following standard techniques. The H NMR

spectra were recorded on a Varian AM300 spectrometer using a

broad-band probe. Proton chemical shifts are reported in ppm versus

internal Me₄Si. IR spectra were recorded on a Nicolet 5DXBO FTIR

spectrometer. Electrospray ionization mass spectrometry data were

obtained on a MicroMass QTOF spectrometer. Clusters assigned

to specific ions show appropriate isotopic patterns as calculated

for the atoms present. Elemental analyses were performed by

Robertson Microlit Laboratories (Madison, NJ). Tris-2,2,2-(1-

pyrazolyl)ethanol, HOCH₂C(pz)₃, and p-C₆H₄[CH₂OCH₂C(pz)₃]₂

(L) were prepared following literature methods.^18a

Synthesis of {p-C₆H₄[CH₂OCH₂C(pz)₃]₂(AgO₃SCF₃)₂}_∞(1).

A THF (20 mL) solution of p-C₆H₄[CH₂OCH₂C(pz)₃]₂, L, (0.295

g, 0.500 mmol) was added dropwise to a solution of AgO₃SCF₃

(0.256 g, 1.00 mmol) in dry THF (20 mL) under an inert

atmosphere. A white precipitate appeared as the mixture was stirred

for 2 h. The THF was removed by cannula filtration and the white

precipitate washed with THF (2 × 10 mL) and then vacuum-dried

to afford 0.413 g (75%) of solid identified as {p-C₆H₂[CH₂OCH₂C-

(pz)₃]₄(AgO₃SCF₃)₂}_∞. ¹H NMR (acetone-d₆): δ 7.84, 7.81, (d, d,

J ) 1.9, 2.7 Hz, 6,6H, 3,5-H pz), 7.10 (s, 4H, C₆H₄), 6.59 (dd, 6H,

J ) 1.9, J ) 2.7 Hz, 4-H pz), 5.03 (s, 4H, OCH₂Ph), 4.68 (s, 4H,

OCH₂C(pz)₃). Calcd for C₃₂H₃₀Ag₂F₆N₁₂O₈S₂: C, 34.80; H, 2.74;

N, 15.22. Found: C, 34.97; H, 2.69, N, 15.30. ES⁺/MS: 699 and

955 corresponding to [LAg]⁺and [LAg₂O₃SCF₃]⁺.

Anion Exchange Procedure. A 100 mg sample of 2 was

suspended in a saturated aqueous solution of KPF₆or KO₃SCF₃

(50 mL), stirred, filtered, washed with water (100 mL), and air-

dried. The anion exchange was monitored by IR spectroscopy (KBr

pellets). The first notable anion exchange was observed after the

sample was stirred for 0.5 h. The sample used in the crystallization

of 6 and 7 was obtained after 4 h of stirring. After 12 h of stirring,

the anion was completely exchanged.

Crystallography. All crystals were mounted on thin glass fibers

with inert oil or epoxy. After preliminary crystal quality, symmetry

and unit cell parameter determination, a full sphere (1a, 2b, 3b

3

and 6), approximately /₄of a sphere (3a), or a hemisphere (2a,

Synthesis of {p-C₆H₄[CH₂OCH₂C(pz)₃]₂(AgSbF₆)₂}_∞(2). This

compound was synthesized as above for 1 using AgSbF₆(0.343 g,

1.00 mmol), to afford 0.510 g (79%) of solid identified as

{p-C₆H₂[CH₂OCH₂C(pz)₃]₄(AgSbF₆)₂}_∞. ¹H NMR (acetone-d₆): δ

7.82, 7.77 (m, m, 6,6H, 3,5-H pz), 7.09 (s, 4H, C₆H₄), 6.57 (m,

4b, 5b) of X-ray intensity data was collected at the temperatures

indicated in tables in the Supporting Information on a Bruker

SMART APEX CCD-based diffractometer (Mo KR radiation, λ )

0.71073 Å).³⁵Raw area detector data frame integration and Lorentz/

polarization corrections were carried out with SAINT+.³⁵Final unit

552 Inorganic Chemistry, Vol. 43, No. 2, 2004

Bitopic Tris(pyrazolyl)methane Ligand

cell parameters are based on the least-squares refinement of all

reflections with I > 5σ(I) from each data set. For 1a, 2a, 2b, 3b,

4b, 6, and 7, an empirical absorption correction based on the

multiple measurement of equivalent reflections was applied with

SADABS.³⁵Direct methods structure solution (except where noted),

difference Fourier calculations, and full-matrix least-squares refine-

ment against F²were performed with SHELXTL for all structures.³⁶

atoms in the structure. The asymmetric unit contains two indepen-

dent sets each of Ag atoms, organic ligands, and PF₆^-anions. The

refinement was hampered by major disorder affecting the -CH₂-

OCH₂C(pz)₃tripodal end of one of the two independent ligands.

An arduous effort to model the disorder of the pyrazolyl rings in

this region of the structure as three superimposed κ²-κ⁰orientations

was unsuccessful; therefore, only the major disorder component

was included. Due to the severity of the disorder, these pyrazolyl

rings were fit to regular pentagons whose size was allowed to vary

(SHELX AFIX 59 command) and refined with isotropic displace-

ment parameters. A total of 33 restraints was employed. Disorder

Compound 1a crystallizes in the space group R3h (hexagonal

setting) with Z ) 9 for the given formula. The space group choice

was confirmed by the successful solution and refinement of the

data; higher symmetry space groups were ruled out on the basis of

systematic absences in the intensity data and by manual examination

of the completed structure, supported by the ADDSYM routine in

PLATON.³⁷All atoms are on positions of general crystallographic

symmetry. The central phenyl ring of the ligand is situated about

an inversion center at 0, ¹/₂, 0. The asymmetric unit consists of the

Ag atom, half a ligand, and the triflate anion. Non-hydrogen atoms

were refined with anisotropic displacement parameters; hydrogen

atoms were placed in geometrically idealized positions and included

as riding atoms.

-

was also observed in one of the two PF₆anions. This anion was

3

modeled as eight /₄-occupied F atoms surrounding the central P.

With the exception of the ligand atoms affected by disorder, all

non-hydrogen atoms were eventually refined with anisotropic

displacement parameters. Hydrogen atoms were idealized and

included as riding atoms. The final refined value of the absolute

structure (Flack) parameter is 0.04(3), indicating the correct absolute

structure and the absence of racemic twinning.

Compounds 2b and 3b crystallize in the triclinic system. The

space group P1h was assumed and confirmed in each case by the

successful solution and refinement of the structure. The asymmetric

units contain two crystallographically inequivalent Ag atoms and

Compound 2a also crystallizes in the space group R3h (hexagonal

setting). This space group was confirmed in the same manner as

for 1a. The asymmetric unit contains one Ag atom, half a ligand,

an acetone molecule of crystallization, and two crystallographically

-

two independent SbF₆anions. Two ligands are situated about

crystallographic inversion centers, and therefore, only half of each

ligand is present in the asymmetric units. A region of disordered

solvent is also present in the crystals, which was modeled as 1/4

Et₂O and 1/4 CH₃CN, both disordered about an inversion center.

Eventually, all non-H and nonsolvent atoms were refined with

anisotropic displacement parameters; the solvent molecules were

refined isotropically. A total of 7 geometric restraints were used in

modeling the solvent disorder (SHELX SAME and DFIX). Hy-

drogen atoms were idealized and included as riding atoms.

For 4b the pattern of systematic absences in the intensity data

uniquely determined the orthorhombic space group P2₁2₁2₁. All

non-hydrogen atoms were refined with anisotropic displacement

parameters; hydrogen atoms were idealized and included as riding

atoms.

Though metrically consistent with the orthorhombic crystal

system, the pattern of systematic absences in the intensity data of

5b was not consistent with any orthorhombic space group.

Processing the data in the monoclinic system (with â ) 90.000-

(4)°) gave absences uniquely consistent with the monoclinic space

group P2₁/c. The structure was readily solved in P2₁/c. After

location of all heavy atoms, the refinement “hung up” at R1 ∼

25%. Refinement of the data including a correction for pseudo-

orthorhombic twinning resulted in a reduction of R1 from ∼25%

to 6.2% and gave reasonable atomic displacement parameters and

residual electron density (+2.47/-1.68 e^-/Å³, near Ag). The twin

law is (100/01h0/001h), corresponding to a 2-fold rotation around

the a axis. Such twinning is relatively common in monoclinic

crystals with â coincidentally near 90°.³⁶Upon successful solution

and twin refinement in P2₁/c, a check for missed symmetry was

performed with the ADDSYM routine in PLATON,³⁷which verified

the crystal system and space group choice.

-

independent SbF₆counterions. Significant positional and oc-

-

cupational disorder was encountered for both SbF₆counterions.

Sb1 was modeled as occupying a split position, Sb1A and Sb1B,

with six surrounding F atoms. Sb2, located on the origin, was

modeled with eight surrounding F atoms having suitable occupan-

cies. The central Sb of both SbF₆^-anions exhibited unusually large

displacement parameters when refined as fully occupied, notwith-

standing the F atom disorder. In addition, full occupancy of both

-

SbF₆positions would violate charge balance. Refinement of the

site occupation factors (sof’s) for each Sb led to a large drop in

R-values (from ca. 20% at that stage of refinement) and resulted in

ellipsoids of a reasonable magnitude. Refinement of the sof’s led

to values appropriate to maintain electroneutrality within the crystal;

subsequently, the sof’s were fixed at those values. Eventually all

non-hydrogen atoms were refined with anisotropic displacement

parameters; hydrogen atoms were idealized and included as riding

atoms. The largest residual electron density peaks (ca 1.35 e^-/Å³)

-

are located in the vicinity of the disordered SbF₆anions.

In the case of 3a, systematic absences in the intensity data were

consistent with the space groups P2₁or P2₁/m; intensity statistics

indicated P2₁. After initial failure to achieve a reasonable solution

in P2₁/m, a successful solution and refinement was achieved in P2₁.

Subsequently, the absence of mirror symmetry was confirmed by

manual examination of the structure, as well as by ADDSYM/

PLATON.³⁷To eliminate the possibility that the significant ligand

and anion disorder present in the final refined structure generated

erroneously low symmetry, ADDSYM was also performed on a

partial structural model including only the atomic positions of the

Ag and P atoms, yielding the same results. Application of Patterson

methods in the space group P2₁initially located the positions of

two Ag atoms and the two P atoms of the PF₆^-anions. Subsequent

difference Fourier syntheses revealed the rest of the non-hydrogen

The asymmetric unit of 5b contains one Ag ion, half a ligand

situated about an inversion center, one nitrate counterion, and two

acetonitrile molecules of crystallization. All atoms reside on

positions of general crystallographic symmetry. Non-hydrogen

atoms were refined with anisotropic displacement parameters.

Hydrogen atoms were idealized and included as riding atoms.

Compound 6 crystallizes in the triclinic system. The space group

P1h was assumed and confirmed by successful solution and

(35) SMART Version 5.625, SAINT+ Version 6.22 and SADABS Version

2.05; Bruker Analytical X-ray Systems, Inc.: Madison, WI, 2001.

(36) Sheldrick, G. M. SHELXTL Version 6.1; Bruker Analytical X-ray

Systems, Inc.: Madison, WI, 2000.

(37) PLATON: (a) Spek, A. L. Acta Crystallogr., Sect. A 1990, 46, C34.

(b) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool;

Utrecht University: Utrecht, The Netherlands, 2002.

Inorganic Chemistry, Vol. 43, No. 2, 2004 553

Reger et al.

Table 1. Selected Crystal and Structure Refinement Data

1a

2a

3a

2b

3b

4b

5‚4 CH₃CN

6

7

formula

C

₃₂H₃₀Ag₂-

C₃₆H₄₂Ag₂-

C₃₀H₃₀Ag-

F₆N₁₂O₂P

C_35.50H_39.25

-

C_35.50H_39.25

-

C₃₆H₄₃Ag₂-

B₂F₈N₁₃O₃

C₃₈H₄₂Ag₂- C_35.50H_39.25

-

C_34.50H₃₉Ag-

F₆N₁₂O₈S₂

F₁₂N₁₂O₄Sb₂

Ag₂F₁₂N_14.25

-

Ag₂F₁₂N_14.25

-

N₁₈O₈

Ag₂F₁₂N_14.25- F₆N₁₂O_3.50Sb

O_2.25Sb₂

O_2.25P₂

O_2.25P_0.78

Sb_1.22

-

fw, g mol^-11104.54

cryst syst trigonal

space group R3h

a, Å

b, Å

c, Å

1394.06

trigonal

R3h

31.3014(18)

12.7921(11)

90

120

9

843.50

monoclinic

P2₁

15.3714(14) 10.4341(6)

13.5220(12) 15.4008(9)

18.0243(16) 15.8447(9)

1388.80

triclinic

P1h

1207.24

triclinic

P1h

10.3981(8)

15.1727(11)

15.9055(12)

79.326(2)

77.1400(10)

78.0300(10)

2

1095.19

1094.64

1317.99

1021.40

monoclinic

P2₁/c

14.8013(12)

30.058(2)

8.7987(7)

90

92.368(2)

90

4

orthorhombic monoclinic triclinic

P2₁2₁2₁

10.2820(7)

20.2872(14)

20.5518(14)

90

4

P2₁/c

P1h

29.9011(10)

11.7415(6)

90

120

9

0.0372

0.0678

12.131(2)

19.079(4)

10.4348(11)

9.6355(19) 15.8339(16)

R, deg

â, deg

γ, deg

Z

90

77.7240(10)

77.4120(10)

78.3260(10)

2

0.0339

0.0771

90

90.000(4)

90

78.255(2)

77.464(2)

78.424(2)

2

114.519(2)

90

4

0.0694

0.1751

2

R1^a

0.0591

0.1794

0.0452

0.1146

0.0388

0.0913

0.0624

0.1452

0.0389

0.0943

0.0650

0.1860

wR2^b

2

^aR1 ) ∑||F_o| - |F_c||/∑|F_o|. ^bwR2 ) {∑[w(F_o²- F_c)²]/∑[w(F_o)²]}^1/2for I > 2σ(I). w ) 1/[σ²(F_o) + (aP)²+ bP], where P is [2F_c²+ max(F_o, 0)]/3.

refinement of the structure. The asymmetric unit contains two

crystallographically inequivalent Ag atoms. Two ligands are situated

about crystallographic inversion centers; therefore, only half of each

ligand is present in the asymmetric unit. Two independent (P,Sb)F₆^-

anion positions were located; however, the PF₆^-and SbF₆^-anions

were found to be mixed together on both sites, in the refined

proportions P1/Sb1 ) 0.314(1)/0.686(1) and P2/Sb2 ) 0.467(1)/

0.543(1). Refinement of either site as fully P or fully Sb resulted

in unreasonably small (P) or large (Sb) displacement parameters

as well as higher R-values. The fluorine atoms in both anion sites

are reasonably ordered, and therefore, the P(Sb)-F bond lengths

represent a weighted average of the P-F and Sb-F contributions.

The slightly inflated displacement parameters for these fluorine

atoms may reflect the presence of two closely separated F₆

octahedra, or simply the rotational disorder commonly encountered

in spherical anions of this type. A region of disordered solvent is

general crystallographic symmetry. The asymmetric unit contains

one Ag atom, one ligand, one SbF₆counterion, a fully ordered

-

acetone molecule of crystallization, and half of another acetone

disordered about an inversion center. Non-hydrogen atoms were

refined with anisotropic displacement parameters; hydrogen atoms

were idealized and included as riding atoms. At convergence, two

relatively large electron density peaks (ca. 4.0 and 3.6 e Å^-3) located

ca. 1 Å from the Sb atom are present. The origin of these peaks is

unknown.

The metric parameters of noncovalent interactions (π-π stacking,

C-H‚‚‚π interactions, and weak hydrogen bonding) were calculated

by PLATON.³⁷Crystal and refinement data are provided in Table

1 and also in Supporting Information.

Acknowledgment. The authors thank the National Sci-

ence Foundation (CHE-0110493) for support. We thank Drs.

Sherine O. Obare and Latha A. Gearheart for assistance in

physical measurements.

1

also present in the crystal, which was modeled as /₄Et₂O and

¹/₄CH₃CN, both disordered about an inversion center. Eventually,

all non-H and nonsolvent atoms were refined with anisotropic

displacement parameters; the solvent molecules were refined

isotropically. A total of 7 geometric restraints were used in modeling

the solvent disorder (SHELX SAME and DFIX). Hydrogen atoms

were idealized and included as riding atoms.

Supporting Information Available: X-ray crystallographic files

in CIF format, selected bond lengths and angles, and crystal and

refinement data for 1-7. This material is available free of charge

via the Internet at http://pubs.acs.org.

Systematic absences in the intensity data of 7 uniquely deter-

mined the space group P2₁/c. All atoms reside on positions of

IC035207I

554 Inorganic Chemistry, Vol. 43, No. 2, 2004

Article Doi

Supramolecular Structural Variations with Changes in Anion and Solvent in Silver(I) Complexes of a Semirigid, Bitopic Tris(pyrazolyl)methane Ligand

DOI: 10.1021/ic035207i

Source and publish data:

Authors:

Article abstract of DOI:10.1021/ic035207i

Full text of DOI:10.1021/ic035207i

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