CRYSTAL GROWTH & DESIGN
Alkynolpyridines and Their Complexes with Triphenylphosphine Oxide
2002 VOL. 2, NO. 6 619-624
Brian T. Holmes, Clifford W. Padgett, Mariusz Krawiec, and William T. Pennington* Department of Chemistry, Clemson University, Clemson, South Carolina 29634-0973, USA Received July 8, 2002;
Revised Manuscript Received August 14, 2002
ABSTRACT: 2,6-Bis(3-methyl-butyn-3-ol)pyridine (1) and 2-bromo-6-[3-methyl-butyn-3-ol]pyridine (2) form complexes with triphenylphosphine oxide, 1‚2tppo and 2‚tppo, respectively. Hydrogen bonding dominates the crystal packing in 1, but in the complexes phenyl embraces play a major role. Hydrogen bonding between the hydroxyl end groups of 1 link the molecules into infinite chains, and the chains are cross-linked through hydrogen bonding between one hydroxyl group and the pyridine nitrogen atom to form layers. In 1‚2tppo the hydroxyl groups are terminated through O-H‚‚‚OdP interactions, but the chain structure is perpetuated sextuple embraces. The loosely associated chains pack so that the pyridyl rings of one chain are inserted into cavities of the next. Replacement of one of the alkynol arms by a bromine atom in 2‚tppo results in formation of a dimer through C-H‚‚‚O interactions. Phenyl embraces coupled with C-H‚‚‚N and C-H‚‚‚Br interactions extend the structure in two dimensions, and the resulting layers stack normal to this plane. Thermal analysis of the complexes reveals that decomposition of 1‚2tppo occurs through simultaneous loss of both components, while the monoalkynol pyridine diffuses out of the complex first in 2‚tppo. Introduction Bis-alkynol “wheel and axle” host molecules (Scheme 1)1 and similar awkwardly shaped diols2 are known to form inclusion complexes with a wide variety of guests. The resulting complexes have proven useful for applications such as separations,3 enantioselective photodimerization of guest enones,4 and facilitation of liquid transport of guests from crystal to crystal.5 The inclusion properties of these hosts are tunable through incorporation of expansion groups within the dialkyne skeleton4,5 or appropriate choice of terminal R-groups. Compounds 1 and 2 were prepared as precursors to develop shape-persistent functionalized macrocyclic and acyclic pyridyl acetylene systems.6 As compound 1 is very similar to those described above, but with incorporation of an expansion group that contains additional functionality and alters the directionality of the alkynol groups, it should exhibit interesting inclusion behavior. Compound 2 is a mono-alkynol derivative of 1 containing a bromo substituent, which adds the possibility of halogen bonding7 for complex formation.
Scheme 1.
“Wheel and Axle” Host Compounds
alkynol‚‚‚tppo group has been replaced by a more weakly interacting halide group is also reported. Experimental Section Materials and Methods. All materials were used as received from commercial sources (Acrojs and Aldrich); solvents were purified and dried according to standard methods.8 Synthesis of 2,6-Bis(3-methyl-butyn-3-ol)pyridine (1). In a nitrogen flushed three-neck round-bottom flask, 10 mL of diethylamine, followed by 0.88 mL (9.16 mmol) of 2-methyl3-butyn-1-ol was added into a measured amount of 1.00 g (4.16 mmol) of 2,6-dibromopyridine, 0.073 g (2.5 mol %) of bis(triphenylphosphine)palladium(II) chloride and 0.020 g (2.5 mol %) of copper(I) iodide. After 1 h, the reaction mixture was quenched with water, extracted with diethyl ether, dried with magnesium sulfate, and filtered. The solvent was removed under reduced pressure, and the pure white solid was isolated by performing column chromatography followed by recrystallization from hexane/diethyl ether (silica gel, 1:1 hexane/ diethyl ether, Rf ) 0.27, 96% yield). δH (300 MHz, CDCl3): 7.58 (t, J ) 7.88 Hz, 1H), 7.31 (d, J ) 7.79 Hz, 2H), 2.77 (s, 2H), 1.60 (s, 12H). δC (75 MHz, CDCl3): 143.12, 136.47 (CH), 126.18 (CH), 94.77, 80.93, 65.19, 31.05 (CH). Elemental analysis calculated for C15H17NO2: C, 74.05; H, 7.04; N, 5.76. Found: C, 73.74; H, 7.12; N, 5.68.
As an initial investigation of these interesting host compounds, the crystal structures of 1 and its 1:2 complex with triphenylphosphine oxide (tppo) are reported here. These represent the extremes of pure host and a complex of 1 in which the hydrogen bonding sites have been capped with a group providing a different type of noncovalent interaction (phenyl embraces). For comparison, the crystal structure of 2‚tppo in which one 10.1021/cg0255523 CCC: $22.00 © 2002 American Chemical Society Published on Web 09/27/2002
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Synthesis of Complex 1‚2tppo. Triphenylphosphine oxide (1.64 mmol, 0.458 g) was dissolved in a solution of 2,6-bis(3methyl-butyn-3-ol)pyridine (0.822 mmol, 0.200 g) in 99% dichloromethane. Slow evaporation of solvent yielded 0.395 g of clear crystals (60% yield). Elemental analysis calculated for C51H47NO4P2: C, 76.58; H, 5.92; N, 1.75. Found: C, 77.18; H, 5.91; N, 1.77 (the slight deviation in the observed and calculated values for carbon may be due to a slight excess of tppo in the bulk sample). Synthesis of 2-Bromo-6-[3-methyl-butyn-3-ol]pyridine (2). In a nitrogen flushed three-neck round-bottom flask, 20 mL of diethylamine, followed by 0.44 mL (4.58 mmol) of 2-methyl-3-butyn-1-ol was added into a measured amount of 1.00 g (4.16 mmol) of 2,6-dibromopyridine, 0.073 g (2.5 mol %) of bis(triphenylphosphine)palladium(II) chloride and 0.020 g (2.5 mol %) of copper(I) iodide. After 3 h, the reaction mixture was quenched with water; extracted with diethyl ether, dried with magnesium sulfate and filtered. The solvent was removed under reduced pressure and the pure white solid was isolated by performing column chromatography followed by recrystallization from hexane/chloroform (silica gel, 1:1 hexane/dichloromethane, Rf ) 0.07, 47% yield). δH (300 MHz, CDCl3): 7.41 (m, 3H), 2.04 (s, 1H), 1.60 (s, 6H). δC (75 MHz, CDCl3): 143.44, 141.66, 138.28 (CH), 127.57 (CH), 125.96 (CH), 95.23, 80.43, 65.45, 31.06 (CH). Elemental Analysis Calculated for C10H10BrNO: C, 50.02; H, 4.20; N, 5.83. Found: C, 50.30; H, 4.45; N, 5.58.
Synthesis of Complex 2‚tppo. Triphenylphosphine oxide (0.833 mmol, 0.232 g) was dissolved in a solution of 2-bromo6-[3-methyl-butyn-3-ol]pyridine (0.833 mmol, 0.200 g) in 99% toluene. Slow evaporation of solvent yielded 0.359 g of clear crystals (83% yield). Elemental analysis calculated for C28H25BrNO2P: C, 64.87; H, 4.86; N, 2.70. Found: C, 65.10; H, 4.94; N, 2.69. X-ray Crystallographic Studies. X-ray powder diffraction analysis was used to verify sample purity and identity. Diffraction patterns obtained from bulk reaction products were compared to patterns calculated from single-crystal results using the program POWD12.9 Powder diffraction data were acquired on a Scintag XDS/2000 theta-theta diffractometer with Cu KR1 radiation (λ ) 1.54060 Å) and an intrinsic germanium solid-state detection system. Relevant crystallographic data for the single-crystal studies are given in Table 1. All measurements were made at room temperature (298 ( 2 K), with graphite-monochromated Mo KR radiation (λ ) 0.71073 Å) on either a Rigaku AFC8 diffractometer with Mercury CCD detector (1), a Crystal Logic modified Syntex P21 diffractometer (1‚2tppo), or Nicolet P3 diffractometer (2‚tppo). The data were corrected for Lorentz and polarization effects. An absorption correction based on azimuthal scans of several intense reflections was applied to the data for compounds 1‚2tppo and 2‚tppo and an absorption correction based on comparison of the intensities of symmetry equivalent reflections10 was applied for compound 1. The structures were solved by direct methods and refined by using full-matrix least-squares techniques. All nonhydrogen atoms were refined anisotropically; hydrogen atoms were refined with isotropic displacement parameters. Compound 1 crystallizes in monoclinic crystal system, with a β angle near 90°. As is typical for this type of crystal, 1 is twinned. The twin law is: -1 0 0, 0 1 0, 0 0 1, and the minor component contribution factor is 0.145(2). Structure solution, refinement (on F2), and the calculation of derived results were performed with the SHELXTL11
Holmes et al. Table 1. Crystal Data for 1, 1‚2tppo, and 2‚tppo 1 formula Mw crystal system space group a, Å b, Å c, Å β, (°) V, Å3 Z Dcalc, g cm-3 µ, mm-1 transmission coefficients reflections collected reflections unique (Rmerge) R1a wR2b
1‚2tppo
2‚tppo
C15H17NO2 243.30 monoclinic
C51H47NO4P2 799.84 monoclinic
C28H25NOPBr 518.37 monoclinic
P21/c (14) 9.620(3) 13.954(5) 10.877(4) 90.858(9) 1459.9(7) 4 1.11 0.073 0.78-1.00
C2/c (15) 21.152(2) 8.997(1) 23.314(2) 98.409(3) 4389.1(7) 4 1.21 0.144 0.64-1.00
P21/n (14) 9.743(2) 25.233(5) 11.336(1) 112.84(1) 2568.4(7) 4 1.34 1.69 0.74-1.00
13845
3989
5565
2902 (0.042)
3875 (0.013)
5122 (0.032)
0.0741 (0.0807) 0.0534 (0.1144) 0.0405 (0.1263) 0.1622 (0.1701) 0.1138 (0.1279) 0.0663 (0.0757)
a R ) ∑||F | - |F ||/∑|F | for observed data (I > 2σ(I)); number 1 o c o in parentheses is for all data. b wR2 ) {∑[w(Fo2 - Fc2)2]/ 2 2 1/2 ∑[w(Fo ) ]} for observed data (I > 2σ(I)); number in parentheses is for all data.
package of computer programs. Neutral atom scattering factors and the real and imaginary anomalous dispersion corrections were taken from International Tables for X-ray Crystallography, Vol. IV.12 Thermal Analysis. Thermal gravimetric analyses were performed on a Mettler-Toledo TGA (SDTA851e) instrument with the Stare software package (version 6.0). The samples had a mass of approximately 10 mg each, and all calculations were performed on data represented as percent loss of starting mass. For onset calculations, the samples were heated at a constant rate of 5 °C min-1 from 25 °C until all of the material had evaporated. Mass loss and onset calculations were performed by standard methods. Experiments were performed under nitrogen gas (50 mL/min).
Results and Discussion Selected distances and angles for the pyridine-alkynol molecules are given in Table 2. Thermal ellipsoid plots of 1, 1‚2tppo, and 2‚tppo are shown in Figure 1a-c, respectively. Crystal packing in all three is dominated by hydrogen bonding (also tabulated in Table 2), and in the case of the complexes, phenyl embraces. No evidence of halogen bonding in 2‚tppo was observed. Crystal Structure of 1. Molecules of 1 related by a 21 screw operation parallel to the b-axis are linked into infinite chains by O-H‚‚‚O hydrogen bonding involving one hydroxyl (O1) as acceptor and the other hydroxyl (O2) as donor. Chains related by a c-glide operation are cross-linked through O-H‚‚‚N hydrogen bonding from a hydroxyl group (O2) and the pyridyl nitrogen atom (N1). The resulting layer (Figure 2a.) contains large R44(38) rings13 centered at (1/2 0 0) and smaller R44(18) rings centered at (1/2 1/2 0). The layers stack in the a-direction with weak interlayer C-H‚‚‚O interactions14 involving atoms O2 and the pyridyl C-H group para to the nitrogen atom. Crystal Structure of 1‚2tppo. Upon complexation with triphenylphosphine oxide, the hydrogen-bonded chains of 1 are interrupted, as the hydroxyl groups are terminated through O-H‚‚‚OdP interactions. This complex can be thought of as a noncovalent derivative of 1
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Table 2. Selected Bond Distances (Å) and Angles (°) for 1, 1‚2tppo, and 2‚tppoa 1
1‚2tppo
2‚tppo Distances
O(1)-C(8) O(2)-C(13) N(1)-C(1) N(1)-C(5) C(1)-C(2) C(1)-C(6) C(2)-C(3) C(3)-C(4) C(4)-C(5) C(5)-C(11) C(6)-C(7) C(7)-C(8) C(8)-C(10) C(8)-C(9) C(11)-C(12) C(12)-C(13) C(13)-C(14) C(13)-C(15)
1.421(4) 1.438(3) 1.341(3) 1.353(3) 1.385(4) 1.444(4) 1.381(4) 1.370(5) 1.395(4) 1.433(4) 1.186(4) 1.472(4) 1.517(5) 1.532(6) 1.193(4) 1.477(4) 1.516(5) 1.524(5)
O(1)-C(6) N(1)-C(1) N(1)-C(1a) C(1)-C(2) C(1)-C(4) C(2)-C(3)
1.424(3) 1.342(3) 1.342(3) 1.379(4) 1.451(4) 1.367(4)
C(4)-C(5) C(5)-C(6) C(6)-C(8) C(6)-C(7)
1.184(4) 1.481(4) 1.511(4) 1.518(4)
Br(1)-C(1) O(1)-C(8)
1.918(4) 1.414(4)
N(1)-C(1) N(1)-C(5) C(1)-C(2) C(1)-C(6) C(2)-C(3) C(3)-C(4) C(4)-C(5) C(5)-C(6) C(6)-C(7) C(7)-C(8) C(8)-C(10) C(8)-C(9)
1.334(4) 1.354(4) 1.357(5) 1.444(4) 1.362(5) 1.376(5) 1.365(5) 1.452(4) 1.166(4) 1.508(5) 1.521(6) 1.541(6)
Angles C(1)-N(1)-C(5) N(1)-C(1)-C(2) N(1)-C(1)-C(6) C(2)-C(1)-C(6) C(3)-C(2)-C(1) C(4)-C(3)-C(2) C(3)-C(4)-C(5) N(1)-C(5)-C(4) N(1)-C(5)-C(11) C(4)-C(5)-C(11) C(7)-C(6)-C(1) C(6)-C(7)-C(8) O(1)-C(8)-C(7) O(1)-C(8)-C(10) C(7)-C(8)-C(10) O(1)-C(8)-C(9) C(7)-C(8)-C(9) C(10)-C(8)-C(9) C(12)-C(11)-C(5) C(11)-C(12)-C(13) O(2)-C(13)-C(12) O(2)-C(13)-C(14) C(12)-C(13)-C(14) O(2)-C(13)-C(15) C(12)-C(13)-C(15) C(14)-C(13)-C(15)
117.5(2) 123.2(2) 118.1(2) 118.7(2) 118.6(3) 119.4(3) 119.0(3) 122.3(2) 118.1(2) 119.6(2) 175.5(3) 179.2(4) 109.8(2) 107.5(3) 110.8(3) 108.7(3) 108.7(3) 111.3(4) 175.1(3) 178.7(3) 108.7(2) 110.1(3) 110.3(3) 105.5(3) 109.6(3) 112.6(3)
H(1)‚‚‚N(1b) O(1)‚‚‚N(1b) O(1)-H(1)‚‚‚N(1b) H(2)‚‚‚O(1c) O(2)‚‚‚O(1c) O(2)-H(2)‚‚‚O(1c) H(3a)‚‚‚O(2d) C(3)‚‚‚O(2d) C(3)-H(3A)‚‚‚O(2d) H(2)‚‚‚O(1c) O(2)‚‚‚O(1c) O(2)-H(2)‚‚‚O(1c) H(3a)‚‚‚O(2d) C(3)‚‚‚O(2d) C(3)-H(3A)‚‚‚O(2d)
1.87(5) 2.851(4) 166(4) 1.76(4) 2.746(3) 170(3) 2.48(4) 3.192(4) 170(3) 1.76(4) 2.746(3) 170(3) 2.48(4) 3.192(4) 170(3)
C(1)-N(1)-C(1a) N(1)-C(1)-C(2) N(1)-C(1)-C(4) C(2)-C(1)-C(4) C(3)-C(2)-C(1) C(2)-C(3)-C(2a)
117.4(3) 122.8(3) 115.2(3) 121.9(2) 118.5(3) 119.9(4)
C(5)-C(4)-C(1) C(4)-C(5)-C(6) O(1)-C(6)-C(5) O(1)-C(6)-C(8) C(5)-C(6)-C(8) O(1)-C(6)-C(7) C(5)-C(6)-C(7) C(8)-C(6)-C(7)
176.8(3) 178.3(3) 109.6(2) 110.4(3) 109.9(3) 106.2(3) 109.3(3) 111.4(3)
Hydrogen Bonding H(1)‚‚‚O(2) 1.88(3) O(1)‚‚‚O(2) 2.747(3) O(1)-H(1)‚‚‚O(2) 172(3) H(20)‚‚‚O(2e) 2.84(3) C(20)‚‚‚O(2e) 3.578(4) C(20)-H(20)‚‚‚O(2e) 134(2)
H(20)‚‚‚O(2e) C(20)‚‚‚O(2e) C(20)-H(20)‚‚‚O(2e)
2.84(3) 3.578(4) 134(2)
N(1)-C(1)-Br(1) C(2)-C(1)-Br(1) C(1)-N(1)-C(5) N(1)-C(1)-C(2)
113.2(3) 119.7(3) 115.2(3) 127.1(4)
C(1)-C(2)-C(3) C(2)-C(3)-C(4) C(5)-C(4)-C(3) N(1)-C(5)-C(4) N(1)-C(5)-C(6) C(4)-C(5)-C(6) C(7)-C(6)-C(5) C(6)-C(7)-C(8) O(1)-C(8)-C(7) O(1)-C(8)-C(10) C(7)-C(8)-C(10) O(1)-C(8)-C(9) C(7)-C(8)-C(9) C(10)-C(8)-C(9)
115.8(4) 120.4(5) 119.2(4) 122.2(4) 115.1(3) 122.7(4) 178.1(4) 176.7(4) 110.5(3) 108.0(4) 107.5(3) 110.7(3) 108.5(4) 111.6(4)
H(1)‚‚‚O(2) O(1)‚‚‚O(2) O(1)-H(1)‚‚‚O(2) H(15)‚‚‚O(2f) C(15)‚‚‚O(2f) C(15)-H(15)‚‚‚O(2f) H(13)‚‚‚Br(1f) C(13)‚‚‚Br(1f) C(13)-H(13)‚‚‚Br(1f) H(14)‚‚‚N(1f) C(14)‚‚‚N(1f) C(14)-H(14)‚‚‚N(1f) H(3)‚‚‚O(2g) C(3)‚‚‚O(2g) C(3)-H(3)‚‚‚Br(2g) 145(2)
1.83(4) 2.779(4) 178(4) 2.50(4) 3.415(5) 155(3) 3.20(4) 4.027(4) 143(3) 2.54(4) 3.383(5) 144(3) 2.52(3) 3.285(5) 145(2)
a Symmetry operators: a: -x, y, -z + 1/2; b: x, -y + 1/2, z + 1/2; c: -x + 1, y + 1/2, -z + 1/2; d: -x, 1 - y, -z; e: -x + 1/2, -y + 1/2, 1 - z; f: x + 1/2, y - 1/2, z + 1/2; g: -x + 1, -y, -z + 1.
in which the bulkiness of the endgroups has been dramatically increased. The terminal tppo groups interact with those of neighboring inversion-related molecules through sextuple embraces15 to generate loosely associated chains running parallel to the c-axis. The orientation of the tppo molecules linked to either end
of 1 form a predominately hydrophobic cavity centered about the crystallographic 2-fold rotation axis upon which the pyridyl ring is situated. The pyridyl rings of neighboring chains (generated by translation along the b-axis) fit into these hydrophobic pockets (Figure 3) to extend the structure in the b-direction.
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Figure 2. (a) Hydrogen-bonded layers of 1, viewed normal to the bc-plane. (b) Stacked layers of 1, viewed down the c-axis.
Figure 1. (a) Thermal ellipsoid plot (50% probability) of 1. (b) Thermal ellipsoid plot (50% probability) of 1‚2tppo. (c) Thermal ellipsoid plot (50% probability) of 2‚tppo.
Weak C-H‚‚‚O hydrogen bonding between tppo molecules related by an inversion center at (1/4 1/4 1/2) link the loosely associated layers shown in Figure 3 into stacks up the a-axis. Triphenylphosphine oxide provides a strong hydrogenbonding acceptor for cocrystal formation.16 Phenyl embraces play a very important role in the stability of the resulting complexes. Dance and co-workers have proven the consistency and significance of this important interaction, and have recently classified coordinated triphenylphosphine moieties (PPh3) according to the rotational conformation of the phenyl groups.17 In this classification scheme, PPh3 groups in which all three phenyl rings are twisted about the P-Cipso bond in the same sense relative to the X-P bond and have X-PCipso-C torsion angles in the range of 20-70° are considered to be in a “rotor” conformation. “Nonrotor” conformations have one or more phenyl rings in parallel
Figure 3. Chains of 1‚2tppo generated by sextuple embraces, which interact through insertion of pyridyl rings into hydrophobic cavities.
(torsion angle of 0-20°) or orthogonal (torsion angle of 70-90°) orientations. The PPh3 group in 1‚2tppo fits the criteria for a “rotor conformation, with torsion angles of -26.4(3), -43.0(3), and -50.1(3)°, and as described above takes part in a 6-fold phenyl embrace as is typical for this conformation. The P‚‚‚P separation distance of 6.987(1) Å is also within the range seen for this type of interaction. Crystal Structure of 2‚tppo. In comparison to 1‚ 2tppo, one of the alkynol arms has been replaced by a
Alkynolpyridines and Triphenylphosphine Oxide
Crystal Growth & Design, Vol. 2, No. 6, 2002 623 Table 3. Thermal Data compound 1 2 tppo 1‚2tppo 2‚tppo
onset temp (°C)
%lossexpected
%lossobs
284 183 301 284 214 303
30.4 (loss of 1) 46.3 (loss of 2) 53.7 (loss of tppo)
80.2 33.7 52.3
∆temp (°C)a
31
a Change in temperature from lowest vaporization of individual component to first onset temperature of the complex.
ponent and the first mass loss in the complex gives a crude measure of the stability of the crystal matrix. Compound 2‚tppo loses 33.4% of its mass in an event with an onset temperature slightly higher than that of pure 2, indicating that the first component lost is the more volatile alkynol. In 1‚2tppo on the other hand, mass loss is less well-defined. Initial mass loss has an onset equal to that of the dialkynol, but is much greater than that which could be attributed to this component. Apparently loss of the hydrogen-bonding donor disrupts the matrix to the extent that a significant portion of the acceptor is volatilized at the lower temperature as well. Conclusions
Figure 4. (a) C-H‚‚‚O linked dimers of 2‚tppo. (b) Crystal packing of 2‚tppo, viewed down the a-axis, showing the phenyl embraces.
bromine atom. A pair of hydrogen-bonded molecules of 2 and tppo are linked by C-H‚‚‚O interactions to form a dimer which is situated about an inversion center (1/2 0 1/2), shown in Figure 4a. Phenyl embraces between molecules related by the n-glide along with weak C-H‚‚‚N and C-H‚‚‚Br interactions extend the structure in two-dimensions parallel to the (1 0 -1) plane (Figure 4b), and the resulting layers stack normal to this plane. The PPh3 group has a “nonrotor” conformation according to the Dance criteria, with torsion angles of 14.0(3), 28.0(3), and 63.3(3)° (i.e., one ring in a parallel orientation). As has been seen with similar conformations, this PPh3 group is involved in a 6-fold phenyl interaction, but not all of these are edge-face interactions as required for a formal 6-fold embrace. Thermal Analysis. The thermal decomposition data of the reported compounds are shown in Table 3. The compounds were heated until all components were completely volatilized. The initial mass loss corresponds to the destruction of the crystal matrix and evaporation of either the alkynol (1 or 2), tppo or both. The difference between the vaporization temperature of the most volatile com-
On the basis of similar alkynol hosts, the rigid, extended shape and bulky endgroups of 1, coupled with its distinctive hydrogen bonding donor and acceptor sites and numerous sites for C-H‚‚‚X interactions, compound 1 should lead to a high potential to selectively accommodate guest molecules. Complex formation of 1 and its related mono-alkynol derivative, 2, demonstrate the ability to form cocrystals with a suitable partner. Interestingly, the complex, 1‚2tppo, represents a noncovalent derivative of 1 in which the bulkiness of the endgroups has been dramatically increased, and these new terminal groups provide an additional structure directing interaction to utilize for crystal design. Future work will focus on additional complex formation of 1 and on the formation of ternary complexes of the tppo complexes of 1 and 2 with additional guests. Acknowledgment. Financial support of the National Science Foundation for purchase of the CCDbased X-ray system used in this study (CHE-9808165), and of the NASA/Space Grant program (NCC5-575) provided by SC/EPSCoR is gratefully acknowledged. Supporting Information Available: X-ray crystallographic information files (CIF) and tables of observed and calculated powder patterns (2θ, dhkl, and Ihkl) for 1, 1‚2tppo, and 2‚tppo. This material is available free of charge via the Internet at http://publs.acs.org.
References (1) (a) Kaftory, M. Tetrahedron 1987, 43, 1503. (b) Kaftory, M.; Yagi, M.; Tanaka, K.; Toda, F. J. Org. Chem. 1988, 53, 4391. (c) Johnson, L.; Nassimbeni, L. R.; Toda, F. Acta Crystallogr. 1992, B48, 827. (2) Weber, E.; Hens, T.; Brehmer, T.; Cso¨regh, I. J. Chem. Soc., Perkin 2 2000, 235. (3) (a) Caira, M. R.; Nassimbeni, L. R.; Toda, F.; Vujovic, D. J. Chem. Soc., Perkin 2 1999, 2681. (b) Caira, M. R.; Nassimbeni, L. R.; Toda, F.; Vujovic, D. J. Am. Chem. Soc. 2000, 122, 9367.
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