J . A m . Chem. SOC.1990, 112, 9053-9058
9053
NMR and Crystallographic Studies of a p-Sulfonatocalix[41arene-Guest Complex Seiji Shinkai,**'Koji Araki,' Tsutomu Matsuda,' Nobuaki Nishiyama,2 Hirotaka Ikeda,3 Isao T a k a ~ u and , ~ Masakazu Iwamoto4 Contribution from the Department of Organic Synthesis, Faculty of Engineering, Kyushu University, Fukuoka 812, Japan, Center of Advanced Instrumental Analysis, Kyushu University, Kasuga. Fukuoka 816, Japan, Department of Physics, Faculty of Sciences, Kyushu University, Fukuoka 812, Japan, and Department of Industrial Chemistry, Faculty of Engineering, Miyazaki University, Miyazaki 889-21, Japan. Receioed June 7 , I990
"C NMR spectra of a complex formed from tetrasodium p-suIfonatocaIix[4]arene (14) and trimcthylanilinium chloride (2) in D20 showed that 2 is bound to the cavity of cone-shaped 14: in the acidic pH region (pD 0.4) the phenyl moiety resides in the cavity, whereas i n the neutral pH region (pD 7.3) both the trimethylammonium and the phenyl moiety are included nonspecifically in the cavity. The difference was accounted for by the change in the electron dcnsity in the benzene n-systems induced by the dissociation of OH groups. The complex was crystallized from acidic aqueous solution. The solid-state I3C NMR (CP-MAS) supports the inclusion of the phenyl moiety in the cavity. The X-ray crystallographic studies cstablished that (i) l 4 adopts a cone conformation. (ii) l4and 2 form a host-guest-type complex with the phenyl moiety inscrtcd into the cavity, (iii) not only the hydrophobic force but also the electrostatic force operates for guest inclusion, and (iv) the overall structure is similar to that of clays, l4 molecules being arranged into bilayers. These findings serve as a useful cross-link between solution complexes and solid-state complexes. Abstract: The 'H and
Calixarenes are cyclic oligomers made from phenol and formaldehyde which belong to the class of [ I,,]metacyclophanes. Since they have a characteristic cavity-shaped architecture, they have bccn expected to be useful as a basic skeleton in the design of new functionalizcd host m o l ~ c u l e s . ~ Solid-state -~ complexes of calixarcncs have been known for many years, the first unequivocal demonstration of their structure having been provided by the X-ray crystallographic work of Andreetti and c o - w ~ r k e r s . ~Evidence for complexation in solution, however, has been obtained more slowly. The earliest examples appeared only in the mid 1980s and involved both aqueous systems with water soluble sulfonatocalixarcncs'O*'land nonaqueous systems with calix[4]arenes and amines.'* Several additional examples have appeared more reccr~tly."-'~ Interest in this laboratory has centered mainly on water-soluble calixarcncs, resulting from our synthesis in 1984 of calixarcncs carrying sulfonate groupsI0 simultaneously with the ' ~ calixarenes ~ carrying synthcsis of Ungaro and c o - w ~ r k e r sof carboxyl groups. Aqueous systems are particularly interesting I'or complexation studies because one can expect hydrophobic forces to play an important role. ( I ) Faculty of Engineering, Kyushu University. (2) Center of Advanced Instrumental Analysis, Kyushu University. ( 3 ) Faculty of Scicnccs, Kyushu University. (4) Miyazaki University. ( 5 ) Gutsche, C. D. Acc. Chem. Res. 1983, 16, 161. (6)( a ) Gutsche. C. D. I n Synthesis oJMacrocyc1e.y: The Design oJSeIrctiue Complexing Agents; Izatt, R. M., Christensen, J. J., Eds.; John Wiley & Sons Inc.: New York. 1987; p 93. (b) Gutsche. C. D. In Calixarenes:
Royal Socicty of Chemistry: Cambridge, 1989. (7) Shinkai, S . Pure Appl. Chem. 1986, 58, 1523. ( 8 ) Shinkai, S.; Manabc, 0. Nippon Kagaku Kai.yhi 1988, 1917. (9) (a) Ungaro. R.; Pochini. A,; Andreetti, G . D.; Domiano. P. J . Chem. Soc.. Perkin Trans. 2 1985. 197. (b) Andreetti, G . D.: Ungaro, R.; Pochini, A. J . Chem. Soc.. Chem. Commun. 1979, 1005. (c) Coruzzi. M.;Andreetti. G.D.: Bocchi. V.: Pochini. A,; Ungaro, R . J . Chem. Soc.. Perkin Trans. 2 1982. 1 133. (d) I n p-( I ,1.3.3-tetramethyibutyI)calix[4]arenethe guest itiolcculc (tolucnc) is not trapped in the calixarcne cavity but in the crystal lattice: Andrcctti. G. D.; Pochini, A,; Ungaro, R. J . Chem. Soc., f r r k i n Trun.t. 2 1983. 1773. (IO) Shinkai, S.; Mori, S.;Tsubaki, T.; Sone, T.: Manabe. 0. Tetrahedron Lett. 1984. 25. 5315. (. I I ,) Shinkai. S.; Mori. S.; Korcishi. H.: Tsubaki, T.: Manabe, 0.J . Am Chiwt. Soc. 1984. 108. 2409. ( 1 2 ) Baucr and Gutsche reported inclusion of tert-butylamine in calix[4]arcnca. but the driving force for inclusion is supposed to a combination of proton transfer plus electrostatic attraction: Bauer. L. J.: Gutsche, C. D. J . . A r i l . Chrm. Soc. 1985. 107, 6063.
0002-7863/90/ I5 I2-Yo53$02.5o/O
Table 1. ' H N M R Chemical Shifts of 2 in D20' d ( w m ) of 2 pD o-H p-H m-H sample 2 2
2 2
+ l4 + Id
0.4 7.3 0.4 7.3
DO
0-H
0.4 7.3
-0.82 -0.87
1.86 7.82 7.04 6.95
7.67 7.65 6.05 6.79
7.62 1.61 5.20 6.46
N'CH, 3.67 3.64 3.42 2.54
Ad (ppm) of 2 induced by I,b 111-H n- H N'CH, -1.62 -0.86
-2.42
-0.25
-1.15
-1.10 "30 O C , 121 = (14] (when added) = 1.0 mM. I M DCI/D,O for pD 0.4, 0.1 M phosphatc buffcr for pD 7.3. Judging from the association a on st ants.'^ morc than 9892 of 2 is included in the cavity of 2 under the mcasurcmcnt conditions. bThe negative value denotes the shift to the
liighcr mngnctic field. We have recently estimated the association constants ( K ) for aqueous complexes with p-sulfonatocalix[n]arenes(I,,: n = 4.6, and 8) by the NMR m e t h ~ d . ' ~The , ' ~ purpose of this investigation wxs to determine if the calixarene cavity is capable of molecular rccognition in solution, and it has been found that l4and 1, form I : 1 complcxcb with guest molccules such as trimcthylanilinium chloridc (2) and I -adamantyltrimethylammonium chloride. whcrcas 1, forms I :2 1,-guest complexes. The association con( I 3) Uatcr-rulublc calixurcnca and ita analoguca bcaring hydrophilic groups such as SOl-. COO-, PO1'. S02N(CH2CH20H),,etc. were subsequently synthesized. (a) Arduini, A.; Reverberi, S.: Ungaro. R. J . Chem. Soc.. C h m . Commun. 1984.981, (b) Gutsche, C. D.:Alam, I . Tetrahedron 1988, 44. 4689. (c) Poh, B.-L.; Lim. C. S.; Khoo, K. S . Terrohedron Letr. 1988. 44. 4689. (d) Almi. M.; Arduini, A.; Casnati, A.; Pochini, A,; Ungaro, R. Terrohedron 1989, 45, 2177. (e) Arimura, T.; Nagasaki, T.; Shinkai, S.: Matsuda. T. J . Urg. Chem. 1989, 54, 3766. ( 0 Shinkai, S.: Kawabata. H.: Matsuda, T.; Kawaguchi, H . ; Manabc, 0. Bull. Chem. Soc. Jpn. 1990, 6 3 . 1272. Water-soluble calixarenes with cationic charges were also synthesized. (;I) Shinkai. S.: Arimura. T.; Araki, K.; Kawabata, H.; Satoh, H.; Tsubaki. T.; Manabc. 0.;Sunamoto. J . J. Chem. Soc., Perkin Trans. I 1989,2039. (b) Shinkiii. S.:Shirahama. Y.; Tsubaki. T.; Manabe, 0.J . Am. Chem. Soc. 1989. 1 1 1 . 5477. (14) Shinkai, S . ; Araki, K.; Manabe, 0. J . A m . ('hem. Soc. 1988, 110. 7214. ( I 5 ) Shinkai. S.;Araki, K.; Matsuda, T.; Manabe, 0. Bull. Chem. So( Jpti. 1989. 62. 3856.
@I I990 American Chemical Society
9054 J . A m . Chem. SOC.,Vol. 112, No. 25, 1990
H&/?J HO
pD 0.4
Shinkai et al.
-03s
OH
N+ SO:,
HO
-03s
OH
@ SO:, J
/I'
Table 111. Crystal Data
chemical formula f-w crystal systcm spacc group ccll dimensions
C ~ H T A."O.~ ~ .S A. -N ~17NC1 ~~*CIOH I&3.79 triclinic Pi
A A l', A
12.559 (4) 15.127 (3) 1 1.863 (4) 97.72 (2) 92.27 (3) 93.82 (2)
a.
b.
0- 0-
(I,
0- 0Z
pD 7.3
dcg
il. dcg Y. dcg
L
&, g cm-) -03s
h+
SO3
soy
-03s
'I' Figure 1. Complexation of l4 with 2 in acidic and neutral pD solutions. Table 11. "C N M R Chemical Shifts of 2
CI c2 c3 c 4 cs 67.32 156.85 129.84 140.77 140.77 66.65 155.39 128.3 1 138.89 138.40 56.90 146.39 b 128.28 128.38 il d (ppm) of 2 induccd by 1,' state C, C, c, c, C, D20 (PD 0.4) -0.67 -1.46 -1.53 -1.88 -2.37 didd -10.42 -10.46 b -12.39 -12.39 "30 O C , (21 = [14] (when added) = 166 mM, I M DCI/DzO. *The pcak could not bc found probably bccausc of a vigorous thermal motion. In Fact, thc general temperature factor for this carbon is much grcatcr than thosc for othcr carbons. 'Thc ncgativc value denotes thc shift to thc higher magnetic field. dThe values are compared with d for 2 in D,O. sample state 2 D20 (PD 0.4)' 2 + l4 D 2 0 (pD 0.4)@ 2 + l A solid
~
~
~~~~~
stants wcrc (5.5-56.0) X IO2 M-I. These findings support the view that calixarcncs (1,'s) are capable of molecular recognition on
1"
2
the basis of the ring size. To obtain further insights into calixarene-guest interactions we have carried out X-ray crystallographic studies of a 14-2 complex, hoping to establish a cross-link between the solution complex we previously examined and the solid-statc complcx.
Experimental Section
1.794 15.6
R. 7 Table IV. Bond Lengths Parentheses
C2-C3 C2-CI C20-Cl9 C20-CZI C24-C23 C24-CI9 C24-02 C3-C4 C3-C04 C4-C5 C4-01 CX-C7 C8-C9 Cl5-Cl6 C15-CI4 C15-CO2 CI6-CI7 C12-Cll C12-C7 CI2-03 C22-C23
1.35 (2) 1.44 (2) 1.38 (2) 1.41 (2) 1.39 (2) 1.42 (2) 1.37 (2) 1.41 (2) 1.S0 (2) 1.44 (2) 1.327 (15) 1.38 (2) 1.41 (2) 1.37 (2) 1.40 (2) 1.53 (2) 1.42 (2) 1.39 (2) 1.46 (2) 1.315 (15) 1.41 (2)
(A) with Estimated Standard Deviations in
C22-C2I C6-C5 C6-C1 C5-COI C17-CI8 C17-S4 C14-CI3 C14-04 C23-C02 CIO-CII CIO-C9 C13-CI8 C13-C03 C19-COI Cll-C03 C7-C04 C9-S3 CI-SI C21-S2
S2-021 S2-022
1.32 (2) 1.38 (2) 1.35 (2) 1.53 (2) 1.42 (2) 1.762 (15) 1.34 (2) 1.42 (2) 1.52 (2) 1.39 (2) 1.32 (2) 1.38 (2) 1.54 (2) 1.54 (2) 1.53 (2) 1.54 (2) 1.797 (14) 1.774 (14) 1.784 (15) 1.429 (14) 1.417 (14)
S2-023 S4-042 S4-041 S4-043
SI-011 SI-013 SI-012 S3-031 S3-033 S3-032 NI-C38 NI-C30 NI-C36 NI-C37 C3O-C31 C3O-C35 C31-C32 C32-C33 C33-C34 C35-C34 CI-Nal
1.433 (IS) 1.39 (2) 1.47 (2) 1.40 (2) 1.36 (2) 1.31 (2) 1.46 (2) 1.42 (2) 1.40 (2) 1.36 (2) 1.49 (2) 1.53 (2) 1.49 (2) 1.55 (2) 1.28 (3) 1.42 (3) 1.30 (3) 1.21 (4) 1.54 (4) 1.47 (4) 2.38 (3)
were measured with a Bruker PC-250. The ')C cross-polarization/magic angle spinning N M R spectra were recorded at 30 OC with a CP-MAS method: the crystalline powder sample was contained in a bullet-type rotor and spun at 3.5 kHz. Contact time was 3 ms, and repetition time chemical shifts were calibrated indirectly through was 5 s. The extcrnal TMS. Thc crystals in aqucous solution were initially quite clear and transparent, but they became cloudy in the air. Therefore, we put the solution containing these crystals into a glass capillary (diameter I mm) and scnlcd it with an adhcsivc agent. Integral intensities were collected by using graphitc-nionochromatizcdCu K n radiation by the 8-28 scan tcchniquc u p to 28 = 120'' Of the 6964 reflections measured, the numbcr of reflections observed was 3814 ( I > 3u(/), where u is the standard dcviation obscrved from the counting statics). The structure was solved by thc dircct nicrhod (MULTAN 78). Then, the structure was refined by thc full-matrix Icast-squares procedure with anisotropic thermal paramctcrs. All calculations were performed on a PDP 1 I /23 PLUS computer with thc Enraf-Nonius SDP-PLUSprogram package. The final R value (0.150) was not particularly prccisc becausc of thc background arising I'rom thc aqucous solution and the glass tube, but thc ORTEP view has sul'ficicnt prccision for the discussion of molecular recognition occurring in ;I watcr-solublc calix[4]arcnc. For a computer graphics, MODRAST-E(developed by Professor Hidehiko Nakano (Himcji lnstitutc of Technology)) was uscd.
Results and Discussion
The synthesis of l4was rcportcd previously.I6 The crystals for X-ray analysis and solid-state I'C N M R were grown from acidic aqueous so'H and I3C NMR Spectra of a 14-2 Complex. We previously lution (10 M HCI) containing l4 and 2 in a I : l molar ratio. Large. found t h a t in aqueous solution 1, adopts a "cone" conformation colorlcss crystals wcrc thus obtained, the crystal system being triclinic: irrespective of the pH of the medium.Is To clarify how compound nip > 300 OC. Anal. Calcd for (C7H504SNa)4~C4H,4NCl~12Hz0: C, 2 is bound to the cone-shaped cavity, we first examined the N M R 36.40; H. 4.79: N . 1.15. Found: C, 36.50: H. 4.60: N. 1.16. spcctra. T h c data arc summarized in T a b l e I. In the abscncc Thc ' I f nnd I3C NMR spectra in D 2 0 solution were measured w i t h or I, t h c chcmical shifts of 2 are scarcely affected by the pD of a JEOL GX-400 NMR apparatus. The solid-state "C N M R spectra the medium. In thc prcsence of 14, in contrast, the chemical shifts Shinkai. S.,Araki. K.. raubaki. T.; Arimura. l'.;Manabc, Sir1 P r r k i n Trcoi.r I 1987. 2297.
( 16) ('/witi
.
bccomc surprisingly pD-dependent: all resonance peaks move to a higher magnctic field, indicating that 2 is included in the cavity of l 4 and affected by the ring current of the aromatic components.
p-.Si~l/onntocalix/4~a~ene-Guest Complex
J . A m . Chem. SOC.,Vol. 112, No. 25, 1990 9055
Figure 2. ORTEP view from the A-axis.
Figure 3. ORTEP view from the B-axis.
Carcrul cxamination of each chemical shift reveals that in acidic uyueou.~solution thc peaks assignable to aromatic protons spccifically shift to the higher magnetic field @-H > nt-H > o-H > N+-CH,). whereas in neutral aqueous solution both ammoniomcthyl and aromatic protons shift nonspecifically to the higher
magnetic ricld. Thc results substantiate that in acidic aqueous solution the phcnyl moicty is selectively bound to the calixarene cavity, wticrcas in ncutral aqueous solution both the ammoniomethyl and the phenyl moiety are nonselectivcly bound to thc calixarene cavity (Figure I ) .
9056
J. Am. Chem. SOC.,Vol. 112. No. 25, 1990
Table V. Bond Angles (deg) with Estimated Standard c3-c2-c I 119.0 ( I ) 118.0 ( I ) 118.0 ( I ) c 2 3-c24-c 1 9 122.0 ( I ) C23-C24-02 122.0 ( I ) 116.0 ( I ) C I9-C24-02 120.0 ( I ) c2-c3-c4 120.0 ( I ) C2-C3-C04 120.0 ( I ) C4-C3-C04 c3-c4-c5 120.0 ( I ) 119.0 ( I ) c3-c4-0 1 c5-c4-0 1 121.0 ( I ) C7-C8-C9 120.0 ( I ) C 16-C 15-C I4 120.0 ( I ) C 16-C I 5-C02 119.0 ( I ) C 14-C 1 5-C02 121.0 ( I ) C l5-CI6-Cl7 117.0 ( I ) Cll-CI2-C7 119.0 ( I ) CI I-c12-03 120.0 ( I ) C7-C 12-03 121.0 ( I ) c23-c22-c21 123.0 ( I ) 120.0 ( I ) C5-C6-C I C4-C5-C6 119.0 ( I ) 042-S4-043 121.0 ( I ) 0 4 I -S4-043 112.0 ( I ) CI-SI-011 107.9 (9) c I -SI - 0 3 1 107.0 ( I ) CI-SI-012 105.0 ( I ) 01I-s14-013 121.0 (2) 01I-SI-012 100.0 ( I ) c 13-SI -012 115.0 (2) C9-S3-03 I 103.0 (8) C9-S3-033 107.9 (9) 107.0 ( I ) C9-S3-032
Shinkai rf al.
Deviations in Parentheses C4-C5-C01 119.0 ( I ) C6-C 5-CO 1 121.0 ( I ) CI 6-Cl7-Cl8 122.0 ( I ) C 16-C 17-C4 120.0 ( I ) C 18-C 17-S4 119.0 ( I ) CI 5-CI 4-CI 3 124.0 ( I ) C 1 5-C 14-04 118.0 ( I ) c 13-c 14-04 119.0(1) c24-c23-c22 116.0 ( I ) C24-C23-C02 122.0 ( I ) C22-C23-C02 122.0 ( I ) CI I-ClO-C9 120.0 ( I ) C I4-Cl3-Cl8 119.0 ( I ) C 14-C 13-C03 124.0 ( I ) C 18-C 13-C03 117.0 ( I ) C20-C 19-C24 119.0(1) C20-C 19-COI 120.0 ( I ) C24-CI 9-COI 121.0 ( I ) CI 7-CI 9-c I3 119.0 ( I ) CI2-CII-CIO 120.0 ( I ) C I2-Cl1 -C03 120.0 ( I ) CIO-CI 1-C03 120.0 ( I ) C31-S3-033 105.0 ( I ) 031-S3-032 113.0 ( I ) 033-S3-032 120.0 ( I ) 013-so3-011 llO.O(l) CI 5-C02-023 113.0 ( I ) c3-co4-c7 113.0 ( I ) c5-COI -c 19 114.0 ( I ) C38-N 1-C30 112.0 ( I ) C38-N 1-C36 107.0 ( I ) C38-N 1-C37 108.0 ( I ) C30-N 1-C36 109.0 ( I )
C8-C7-C 12 C8-C7-C04 C 1 2-C7-C04 C8-C8-C I O C8-C9-S3 C 1O-C9-S3 C2-C 1 -C6 c 2 - c 1-s I C6-C 1-S 1 c20-c2 I -c22 c20-c21-s2 c22-c21 -s2 c 2 1-s2-021 c 2 1-s2-022 C21-S2-023 0 2142-022 021-S2-023 022-S2-023 C 17-S4-042 c1744-04 1 CI 7-S4-043 04244-04 I C30-N I-C37 C36-N 1-C37 NI-C30-C31 N I-C3O-C35 c 3 1 -c30-c35 c30-c 3 1- c 3 2 c 3 1-c3 2-c3 3 c32-c33-c34 c3o-c35-c34 c33-c34-c3 5
117.0(1) 122.0 ( I ) 120.0 ( I ) 123.0 ( I )
118.0 ( I ) 119.0 ( I ) 112.0 ( I ) 118.0 ( I ) 120.0 ( I ) 122.0 ( I ) 117.0 ( I ) 121.0 ( I ) 105.2 (8) 106.6 (8) 106.5 (8) 115.0 ( I ) 115.0 ( I ) 107.8 (9) 109.0 ( I ) 106.2 (8) 104.8 (8) 103.0 ( I ) 110.0 ( I ) Ill.O(l) 127.0 (2) 116.0 (2) 116.0 (2) 128.0 (2) 123.0 (2) 119.0 (2) 119.0 (2) 112.0 (2)
of the dissociated oxyanions. According to Dougherty and coworkers,’*-” ammonium cations are bound to the cavity composed of clcctron-rich bcnzene n-systems owing to electrostatic interactions. Thus, the ammonium group in 2 can also be included at pD 7.3. This situation results in nonspecific inclusion of 2: both thc phenyl and the ammonium moiety can be bound to the cavity of l,, the driving forces being both the hydrophobic interactions and thc clcctrostatic attractions. I3C NMR spectral data are summarized in Table 11. The assignment of each peak was made on the basis of a two-dimensional NMR spectrum between ‘Hand 13C. The magnitude of thc up field shift induced by 1, in acidic aqueous solution is on thc ordcr of C5 > C, > C3 > Cz > C, (for the numbering systcm, see Table 11). This order shows good agreement with the ’HN M R data, supporting the view that the phenyl moiety is sclcctivcly included in the cavity. The crystals used for X-ray analysis, which were grown up in acidic aqucous solution, were also used for the solid-state I3C NMR mcasurcments. As summarized in Table 11, the spectrum is similar to that in acidic aqueous solution although all peaks shift to thc highcr magnetic field. In particular, the up field shift obscrvcd for C4 and C5 is greater than that observed for C, and C,. Thc result is also compatible with inclusion of the phenyl moicty. Crystal Structure of a 14-2 Complex. The X-ray crystallographic studies that have been reported have shown that in the solid statc p-t~rf-butylcalix[n]arenesand their analogues are capablc of inclusion of small molecules such as chloroform, acctonc, tolucnc, anisolc, c t ~ . ~ . ~ *In~solution, - ~ ’ . ~ on ~ the other
Figure 4. ORTEP view of the 14.2 complex
Why is such a change in a binding manner induced by changes in the pD of the medium? According to the titration data,” none or onc of thc four OH groups is dissociated at pD 0.4, whereas thrcc of thcm arc dissociated at pD 7.3. Hence, the hydrophobic forcc acts us the solc driving force for complcxation in acidic aqucous solution. In ncutral aqueous solution, on the other hand, thc bcnzcnc n-systems become considerably electron-rich because
( 1 7) Shinkai, S.; Araki, K.; Koreishi, H.; Tsubaki, T.: Manabe, 0.Chew. Letr. 1986, 1351. (18) Stauffcr, D. A,; Dougherty. D. A. Tetrahedron Lett. 1988,29,6063.
(19) Petti, M. A.; Shepodd, T. J.: Barrans, R. E., Jr.; Dougherty, D. A. J . A m . Chem. Soc. 1988, 110. 6825. (20) Shepodd. T. J.; Petti. M. A,; Dougherty, D. A. J. Am. Chem. Soc. 1986. 108, 6085. (21) McKcrvcy, M. A,; Seward, E.: Ferguson, G.;Ruhl. B. L. J . Org. Chem. 1986. S I . 3581. (22) (a) Bott, S. G.;Coleman, A . W.; Atwood. J. L. J. A m . Chem. SOC. 1986. 108, 1709. (b) Coleman, A. W.: Bott, S. G.: Atwood, J. L. J . Inclusion Phenom. 1986, 4. 247.
p-Sulfonatocalix/4/arene-Guest Complex
J . Am. Chem. SOC.,Vol. 112, No. 25, I990
9057
Table VI. Distances from N 1 in 2 to Sulfonate Oxygens
sulfonate oxygen
distance,
01 1
7.162 6.984 8.939 6.288 4.1 17 4.680
012 013 0 21 022 023
A
sulfonate oxygen 0 31 032 033 0 41 042 0 43
distance,
A
7.190 9.286 8.639 3.695 5.202 6.028
Table VII. Distances from Na' to C1- and Sulfonate Oxygens
atoms Nal-CI Na2-011 Na2-022
distance, 2.378 3.125 2.874
A
atoms Na3-012 Na3-04 1 Na4-03 1
distance, 2.126 2.570 2.362
A
hand, there are no published data in support of inclusion of these guest molecules in p-tert-butylcalix[n]arenes. Conceivably, inclusion in p-tert-butylcalix [nlarenes must compete with solvation, and, in most cases, solvation energy is greater than stabilization energy brought forth by inclusion in the calixarene cavities. The sole exception is the inclusion of tert-butylamine reported by Bauer and Gutsche.12 In contrast, compounds 1,'s form host-guest-type complexes in water owing to the hydrophobic force broadly operating on organic mo1ecules,7~8~10~11~14~1s but such complexes have never been crystallized. Therefore, there are no useful data which can provide a cross-link between the solid-state inclusion complex and the solution complex. It thus occurred to us that if the 14.2 complex could be crystallized, its crystal structure would provide important information for understanding how the complex is formed in aqueous solution. The crystal structure of l4has been reported by Atwood et al.23 According to their structure determination, l4adopts a cone c ~ n f o r m a t i o n . ~Interestingly, ~ the crystal system forms a bilayer with a 15-A repeat unit, which closely mimics the structural behavior of clays: the calix[4]arene rings form two hydrophobic layers, and the sulfonate groups form a hydrophilic layer.23 The crystal data obtained from the 14-2complex are summarized in Table I l l . The crystal system is triclinic (space group PI) and different from the monoclinic C2/c or P2,/n obtained for 14.23 Bond lengths and bond angles are reported in Tables IV and V, respectively (for the numbering system see Figure 4). The ORTEP views from the A- and B-axis are shown in Figures 2 and 3, respectively, and a 14*2complex is drawn in Figure 4. A number of interesting points can be raised about the X-ray structure. Firstly, it is seen from Figure 4 that l4adopts a cone conformation. In aqueous solution, it is known that l4favorably adopts the cone conformation because of stabilization by intramolecular hydrogen-bonding interactions among OH groups.14Js The cone structure is further stabilized by inclusion of guest molecule^.'^ Figure 4 shows that this is also the case in the crystal state. The four bond angles for the Ar-CH2-Ar linkage (Table V) are 114' for C5-COl-C19,113' for C15-CO2-C23,llO' for C13-CO3-Cl1, and 1 13' for C3-CO4-C7. This indicates that the cylinder is slightly distorted from C, symmetry. The phenyl moiety in 2 is placed exactly in the cone-shaped cavity, and C32 (facing C5-COl-Cl9) is inserted into the cavity more deeply than C34 (facing C1 l-CO3-Cl3). The bond angle for C5-COl-Cl9 is greater than that for Cll-CO3-C13. This implies that the C5-CO I-C 19 bond angle is expanded so that the cavity can allow deep insertion of the guest molecule. Secondly important is the fact that 2 is included in the cavity. As described above, calix[n]arenes can be crystallized with small organic molecules, but they are included not only in the cavity (endo-calix complexes) but also in the void of the crystal lattice (23) (a) Bott, S. G.; Coleman, A. W.; Atwood, J. L. J . Am. Chem. SOC. 1988, 110.610. (b) Coleman, A.; Bott, S. G.; Morley, S. D.; Means, C. M.;
Robinson, K. D.; Zhang, H.; Atwood, J. L. Angew. Chem., In?. Ed. Engl. 1%8,27, 1361. In these papers l4was crystallized with MeOSO, or acetone present in crystallization soluents. However, the host-guest-type inclusion properties of these small molecules were not investigated in aqueous solution.
Figure 5. Computer-graphic illustration of the 14.2 complex with van der Waals radii cut in the plane of and at right angles to the phenyl moiety of 2 (upper and lower, respectively): N (blue), 0 (red), S (yellow), Na (purple), and CI (green).
formed outside calix[n]arenes (exo-calix c o m p I e x e ~ ) . ~At *~~,~~ present, it is difficult to predict which complex will be formed in the crystal state, the "endo-calix" complex or the "endo-calix" complex. In a 14-2complex, on the other hand, we have established that it forms a host-guest-type complex in aqueous media.l43l5 The sample used for X-ray analysis was prepared from acidic aqueous solution, so that it could reflect the association mode occurring in acidic aqueous solution. As expected, 2 is bound to l4with the phenyl moiety inserting into the cavity. This suggests that the hydrophobic force is a primary driving force for complexation. The C-H bond length in benzene is 1.20 The half thickness of the benzene 7r-system is 1.70 When the aromatic protons in 2 are brought into contact with the benzene 7r-systems in 14, the distance between the aromatic carbons in 2 and those in l4should be about 2.9 A. This is the case in the 14.2 complex: the calculation from the table of positional parameters gives 2.832 8, for C6-C32, 2.867 A for C5-C32, 2.900 8, for C7-C33, and 2.908 8, for ClO-C34. These results support the view that at least three aromatic hydrogens (C32, C33, and C34) are in contact with the benzene 7r-systems in 1,. To obtain further insights into the hydrophobic interaction we used a computergraphic technique adding the van der Waals radii to a ball-andstick model in Figure 4. Two pictures in Figure 5 show cross sections of the 14.2 complex cut in the plane of and at right angles (24) In Kagaku Binran (Chemistry Data Tables); Chemical Society of
Japan, Ed.; Maruzen: Tokyo, 1966.
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J. Am. Chem. SOC.,Vol. 112, No. 25, 1990
to the phenyl moiety. I t is seen from Figure 5 that m-H’s on C32 and C34 and p-H on C33 are in contact with a-systems in calixarene phenyl rings. This supports the view that the hydrophobic force is indispensable to the complex formation. The third point is related to the question of whether the electrostatic force also operates. We calculated distances from cationic N I in 2 to anionic sulfonate oxygens. The results (Table VI) indicate that the distance to 0 4 1 in s(4)03-is shortest and those to 0 2 2 and 0 2 3 in S(2)03- are the next. This suggests that the ammonium cation is bound to an electrostatic pocket formed by s(4)03and S(2)03-. Thus, one can safely conclude that the electrostatic force also operates on the complex formation. We calculated distances from sodium cations to sulfonate oxygens. The results (Table VII) show that N a l forms an ion pair with Cl-, Na2 with S( 1)O; and/or S(2),-, Na3 with S(l)03-and/or S(4)0
