Packing Principles of Thioether Derivatives of Triarylamine Silver Salts

Banglin Chen, Stephen Lee,* D. Venkataraman, Francis J. DiSalvo,. Emil Lobkovsky, and Miki Nakayama. Department of Chemistry and Chemical Biology, ...
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Packing Principles of Thioether Derivatives of Triarylamine Silver Salts Banglin Chen, Stephen Lee,* D. Venkataraman, Francis J. DiSalvo, Emil Lobkovsky, and Miki Nakayama

CRYSTAL GROWTH & DESIGN 2002 VOL. 2, NO. 2 101-105

Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301 Received November 5, 2001

ABSTRACT: Tris(4-methylthiophenyl)amine, 1, has been crystallized together with three silver salts, AgOTf (silver trifluoromethane sulfonate), AgClO4, and AgSbF6. The resulting crystal structures have been determined by singlecrystal X-ray methods. All three structures prove to have the same topological theme: their structures can be related to a double honeycomb pattern. In all cases, each silver ion is coordinated to at least three tris(4- methylthiophenyl)amine molecules. Introduction There is currently a strong current interest in triarylamines. To date, there are over 2000 patents on their use as hole transport materials in organic light emitting diodes.1-4 The interest in triarylamines extends to other fields as well. Recently explored applications range from organic reaction methodology,5 to dendrimer formation,6,7 to high spin building blocks for organic ferromagnets8,9 and to fundamental charge-transfer studies.10 As in many of these applications the actual orientation of the molecule within the solid state is important, it is potentially useful to develop methods that would allow us to rationalize and control the packing of the abovementioned molecules. Recent developments in the coordination networks and polymers show that such rationalizations of crystal topology are possible in a wide variety of chemical systems.11-57 We apply this same methodology here: we prepared three silver salts of tris(4-methylthiophenyl)amine, 1 (see Figure 1), and then subsequently developed a rational framework in which to understand their crystal structures. In this molecule 1, the triarylamine core has been derivatized with three thioether linkages in the para-position. We chose such para-thioether linkages as the metal-thioether coordination bonds have proven compatible with extended solid frameworks,58 as many of the most important electroactive materials contain sulfur, and as it is known that blockage of the para-position is essential for the reversible oxidation of triarylamines.59 Results and Discussion As outlined in the experimental section, we prepared three 1 silver salts: 1‚AgOTf, 1‚AgClO4‚THF, and (1)3‚ (AgSbF6)2. Their corresponding crystal structures are determined by single-crystal X-ray diffraction methods. All three crystal structures are related to one another. In each, the silver ions are in tetrahedral coordination and at least three of the four atoms bonded to these silver ions are the sulfur atoms of molecule 1. For the * To whom cornell.edu).

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Figure 1. Synthetic scheme for tris(4-methylthiophenyl)amine.

three crystal structures, Ag-S bonds range from 2.49 to 2.66 Å, while S-Ag-S bond angles are only approximately tetrahedral and range from 89 to 126°. In the case of 1‚AgOTf, the remaining fourth coordination bond to the silver ion is to an oxygen atom of the triflate counterion; the Ag-O bond distance is 2.442(4) Å. For 1‚AgClO4‚THF, the tetrahydrofuran oxygen atom occupies this fourth site with an Ag-O bond distance of 2.446(6) Å. For these first two crystal structures, the silver ions are coordinated to the sulfur atoms on three adjacent molecules 1, and each molecule 1 is coordinated to three silver ions. This is a well-known connectivity in the crystal design field that most frequently leads to the honeycomb (6,3) network. As we describe below, the two crystal structures are indeed related to the honeycomb pattern. For the third crystal structure, that of (1)3‚(AgSbF6)2, the situation is more complex. It turns out there are two different types of molecule 1 in this crystal structure. Some molecules 1 are coordinated to three silver atoms, while others are bonded to just two silver ions. In this paper, we refer to these molecules as being 13 and 12, respectively, with the number in the superscript denoting the number of silver ions coordinated to the molecule. With respect to this notation, (1)3‚(AgSbF6)2 can be rewritten as (13)2‚(AgSbF6)2‚12. Every silver ion is bound to three different 13 molecules but only a single 12 molecule. Furthermore, as every silver ion is bound to three 13 molecules and conversely as every 13 molecule is bound to three silver ions, one again has the possibility that the 13 molecule and the silver ions can form in a honeycomb (6,3) net. As we describe below, this structure is indeed related to the honeycomb struc-

10.1021/cg010030t CCC: $22.00 © 2002 American Chemical Society Published on Web 02/08/2002

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Figure 2. Double interpenetrated honeycomb (6,3) net. The structure is composed of two interwoven honeycomb nets (red and green).

ture. The remaining 12 molecule serves a different role in the structure. There are only half as many 12 molecules as silver ions, and each 12 molecule is linked to just two silver ions. The 12 molecules can therefore be viewed as bridging moieties. They form additional cross-links between the honeycomb net derived from the silver ions and 13 molecules. The relation between these three crystal structures and the honeycomb (6,3) net is of interest. To understand this relation, consider first the double interpenetrated (6,3) net illustrated in Figure 2. This double interpenetrated topology is well-established and was first discovered in one of the very first extended coordination solids, that of AgC(CN)3.11

Chen et al.

We represent this structure schematically in Figure 3a. In Figure 3a, we represent each organic molecule as a Y. The tips of the Y are represented as filled circles or open circles. A filled circle represents a tip that is canted so as to lie above the plane of the paper. An open circle is a tip canted to lie below the plane of the paper. As Figure 3a shows, both the filled circles and open circles come together in hexagons composed of alternating open and filled circles. If one then places in the center of each hexagon a pair of metal atoms, one above the plane and one below the plane, the above-the-plane metal ion will link together the open circle tips, while the below-the-plane metal ions will link together the filled circle tips. The result is two interpenetrated honeycomb networks. In Figure 3a, one network is shown in green, the other is shown in red. Figure 3a is therefore a schematic representation of the structure illustrated in Figure 2. As Figure 3a suggests, one can cant the organic molecules in other fashions. As long as we require that in each hexagon there are three open and three filled circles, one can still place pairs of tricoordinate metal atoms and generate extended solid structures. In Figure 3b,c, we show two alternate canting arrangements. The crystal structures of 1‚AgOTf and 1‚AgClO4‚THF can be related to the structure illustrated in Figure 3b. For example, the crystal structure of 1‚AgOTf is illustrated in Figure 4c, where for sake of clarity all solvent molecules and triflate counterions have been omitted. As Figure 4c shows, the crystal structure can be viewed as being built from two honeycomb networks, shown respectively in red and green. These individual nets are themselves displayed in Figure 4a,b. But as an examination of Figure 4 shows, the dark red mol-

Figure 3. Schematical illustration of double honeycomb patterns. Individual honeycomb patterns are shown in red and green. Organic molecules are represented either as right-side-up or up-side-down Y’s. Each tip of the Y’s is capped with a circle. Filled and open circles denote, respectively, tips raised above or lowered below the plane of the paper. All neighboring filled circles are connected to one another through coordination bonds. Open circles are similarly connected. In (a), the result is two interpenetrated honeycomb networks, in (b) one has parallel chains, and in (c) one has an noninterpenetrated two-dimensional sheet.

Figure 4. Crystal structure of 1‚AgOTf. In (a) and (b), the individual honeycomb fragments are illustrated in, respectively, red and green. In (c), the full combined structure is shown. Silver atoms are shown as light blue spheres, and nitrogen atoms are shown in black. In (c), dark-colored molecules are connected via coordination bonds to dark-colored molecules, and light-colored molecules are connected to light-colored molecules.

Thioether Derivatives of Triarylamine Silver Salts

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Figure 5. Illustration of the relation between (a) a double honeycomb pattern and (b) the crystal structure of 1‚AgClO4‚THF. In (a), the two individual honeycomb patterns are illustrated, respectively, in green and in red. In (b) (the actual crystal structure), the dark-colored molecules have been laterally shifted. Note silver ions are represented as light blue spheres, nitrogen atoms are shown in black, and dark-colored molecules are linked via coordination bonds to other dark-colored molecules.

Figure 6. The crystal structure of (13)2‚(AgSbF6)2‚12. In (a), we illustrate the (13)2‚(AgSbF6)2 sheet, composed of two honeycomb patterns, one illustrated in red, the other in green. In (b), the 12 ligands are given in black and superimposed on the double honeycomb pattern. Silver ions are represented as light blue spheres, and in (a) nitrogen atoms are shown in black.

ecules are linked to dark green molecules and similarly light red molecules are linked to light green molecules. This is indeed the topology shown in Figure 3b. In this topology, the silver ions and the organic molecules form one-dimensional chains running in the horizontal direction. The structure of 1‚AgClO4‚THF is also related to the Figure 3b topology. In Figure 5a, we give another example of the 3b topology. Chains of dark green and dark red molecules run parallel to chains of light green and light red molecules. As there are no coordination bonds linking the dark- and light-colored chains, it is facile to shift the position of these chains with respect to one another. In Figure 5b, we keep the light-colored chains fixed, but shift the dark-colored chain laterally. It is this laterally shifted structure shown in Figure 5b that is the actual structure adopted by 1‚AgClO4‚THF. Finally, we turn to the (13)2‚(AgSbF6)2‚12 structure, illustrated in Figure 6. In Figure 6a, we illustrate the 13‚AgSbF6 substructure. Again, one sees clearly the two honeycomb nets, one shown in green, the other in red. The actual topological linkage is that of Figure 3c, a twodimensional noninterpenetrated sheet. In Figure 6b, we show the full crystal structure. The 12 molecules are shown in black. It may be seen that of the three sulfur atoms in the 12 molecules, one sulfur remains uncoordinated to silver. We plan to study hole mobility in these compounds. Experimental Section General Methods. Unless otherwise indicated, all starting materials were purchased from Aldrich and used without further purification. Analytical grade solvents were obtained from commercial suppliers (Aldrich and Fisher Scientific). All atomsphere sensitive reactions were conducted under nitrogen using a Schlenk vacuum line. Tris(4-bromophenyl)amine was synthesized according to an established procedure.60 1H NMR was performed on a Bruker AM-300 instrument. Electrospray

ionization mass spectra were collected on a Micromass QUATTRO spectrometer. For the crystallization experiments, Teflonlined screw-caps were used to seal the vials. No additional precautions were employed to exclude oxygen or moisture during crystallization. For X-ray powder analysis, the crystalline samples were sealed in special 0.5-mm glass capillary tubes with small amounts of the mother liquid to prevent degradation of crystallinity. Single-crystal X-ray data were collected on a Bruker SMART diffractometer equipped with a CCD area detector using Mo KR radiation. Single crystal diffraction data were collected at 173 K. All structure solutions were obtained by direct methods and refined using full-matrix least squares with Shelxl 97. The hydrogen atoms were included in the last stage of refinement at their geometrically constrained positions. A summary of crystallographic data for the complexes is listed in Table 1. Tables of bond distances, bond angles, and anisotropic thermal factors appear in the Supporting Information. Powder X-ray diffraction data were recorded on an INEL MPD diffractometer (XRG 3000, CPS 120 detector) at 25 mA and 35 KV for CuKR1; λ ) 1.54056 Å, with external silver behenate and elemental silicon as standards. Lattice constants were fitted, and powder data were indexed with a least-squares method. Safety notes! Perchlorate salts of metal complexes with organic ligands are potentially explosive. Only small amounts of materials should be prepared, and these should be handled with great caution. Tris(4-methylthiophenyl)amine (1). Tris(4-bromophenyl)amine (1.00 g, 2.08 mmol) was added to sodium methyl sulfide (0.6 g, 8.57 mmol) in dimethylformamide (20 mL) in a 50-mL two-necked flask and allowed to react at 110 °C for 10 h. The solvent was removed under reduced pressure on a rotary evaporator. The residue was dissolved in dichloromethane (50 mL), and the solution was washed with water (3 × 50 mL). After drying the sample in anhydrous magnesium sulfate and removing the solvent, compound 1 was separated by column chromatography on silica gel (3/7, dichloromethane/ hexane, v/v) as a light yellow solid (0.25 g, 31% yield): 1H NMR (300 MHz, CDCl3) δ 7.15 (d, J ) 8.4 Hz, 2H), 6.97 (d, J ) 8.4 Hz, 2H), 2.47 (s, 3H). ESMS (acetonitrile) m/z 383 M+. 1‚AgOTf. A solution of silver(I) triflate (5.4 mg, 0.021 mmol) in benzene (5 mL) was added to a solution of 1 (8.2 mg, 0.021

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Table 1. Crystal Data and Structure Refinements for Compounds 1·AgOTf, 1·AgClO4·THF, and (1)3·(AgSbF6)2 formula mol wt T wavelength system space group a b c R β γ V Z Fcalc (g/cm3) absp coeff (mm-1) θ range limiting indices data/restraints/parameters measd reflns unique reflns absp correction GOF on F2 Rint R1 (I > 2σ(I)) wR2 (I > 2σ(I))

1‚AgOTf

1‚AgClO4‚THF

(1)3‚(AgSbF6)2

C31H33AgF3NO3S4 760.69 173(2) K 0.71073 Å triclinic P-1 10.192(1) Å 14.284(2) Å 23.164(2) Å 99.197(3)° 93.272(3)° 102.595(3)° 3234.1(6) Å3 4 1.562 0.932 1.48-26.37° -12 e h e 12 -17 e k e 17 -28 e l e 25 13078/0/840 31863 13078 SADABS 1.034 0.0390 0.0501 0.1076

C31H41AgClNO7S3 779.15 173(2) K 0.71073 Å triclinic P-1 11.033(4) Å 12.524(4) Å 13.345(4) Å 70.404(8)° 87.048(8)° 79.495(8)° 1708.0(10) Å3 2 1.515 0.897 1.88-23.25° -12 e h e 12 -13 e k e 13 -14 e l e 14 4875/0/397 11835 4875 SADABS 1.129 0.0462 0.0599 0.1423

C67.5H63Ag2Cl3F12N3S9Sb2 1998.34 173(2) K 0.71073 Å triclinic P-1 15.785(1) Å 15.856(1) Å 19.256(1) Å 96.079(1)° 105.808(1)° 118.420(1)° 3917.0(3) Å3 2 1.694 1.587 2.14-24.71° -18 e h e 18 -18 e k e 18 -22 e l e 22 13282/21/826 32810 13282 SADABS 1.122 0.0506 0.0875 0.2145

mmol) in benzene (5 mL) in a clean flask equipped with a Teflon-lined screw-cap. A white precipitate formed immediately. The sealed flask was heated to 90 °C, held at this temperature for 4 h, and then cooled to room temperature at 0.1 °C/min. Colorless plates were formed at the bottom of the flask. The X-ray powder data taken on the bulk sample indicate that the primary product of this procedure is 1‚AgOTf reported in this paper as major peaks in the powder data correspond to the peaks calculated for the solved single-crystal structure. However, additional impurity phases are also revealed by the presence of additional diffraction peaks in the bulk sample powder pattern. These additional peaks are indicated by an asterisk in Figure 1 of the Supporting Information. 1‚AgClO4‚THF. A solution of silver(I) perchlorate (5.4 mg, 0.026 mmol) in tetrahydrofuran (5 mL) was added to a solution of 1 (10 mg, 0.026 mmol) in tetrahydrofuran (5 mL) in a clean flask equipped with a Teflon-lined screw-cap. A white precipitate formed immediately. The sealed flask was heated to 90 °C, held at this temperature for 4 h, and then cooled to room temperature at 0.1 °C/min. Colorless plates were formed at the bottom of the flask. The X-ray powder diffraction pattern of the bulk sample corresponds to the pattern generated by the solved single-crystal structure of 1‚AgClO4‚THF. See Supporting Information. No second phase was detected in this diffraction pattern. (1)3‚(AgSbF6)2. A solution of AgSbF6 (13 mg, 0.039 mmol) in methanol (20 mL) was added to a solution of 1 (10 mg, 0.026 mmol) in dichloromethane (20 mL) in a 100-mL beaker and covered with aluminum foil. Colorless plates were formed at the bottom of the beaker 2 days later after evaporation. The X-ray powder diffraction pattern of the bulk sample corresponds to the pattern generated by the solved single-crystal structure of (1)3‚(AgSbF6)2. See Supporting Information. No second phase was detected in this diffraction pattern.

Acknowledgment. This work was supported by the National Science Foundation (Grants DMR-9812351 and DMR-0104267). We thank Mr. Derek Van Allen for providing us with tris(4-bromophenyl)amine. Supporting Information Available: Tables of crystal refinement data, bond distances, bond angles, anisotropic thermal factors for compounds 1‚AgOTf, 1‚AgClO4‚THF, and

(1)3‚(AgSbF6)2. Experimental and calculated powder diffraction data for the above compounds. This material is available free of charge via the Internet at http://pubs.acs.org.

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