CRYSTAL GROWTH & DESIGN
Dianiline-Diphenol Molecular Complexes Based on Supraminol Recognition Vangala,†
Mondal,‡
2005 VOL. 5, NO. 1 99-104
Broder,‡
Venu R. Raju Charlotte K. Judith A. K. Howard,‡,* and Gautam R. Desiraju†,*
School of Chemistry, University of Hyderabad, Hyderabad 500 046, India (
[email protected]) and Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, U.K. Received January 16, 2004
ABSTRACT: Dianilines and diphenols form well-defined crystalline molecular complexes that arise from complementary O-H‚‚‚N and N-H‚‚‚O recognition. The crystal structures of four such 1:1 complexes 1, 2, 3 and 4 based on diphenylmethane frameworks are reported and discussed. Three supramolecular synthons are found, the N(H)O based square motif and infinite chain, already reported, and a new cyclohexane chair consisting of N(H)O, O-H‚‚‚O and N-H‚‚‚N hydrogen bridges. The replacement of a -CH2- group by an S-atom leads in two cases to little change in the crystal structure and in another to a complete change. It is possible that the dianiline component plays a more important role in molecular recognition in these complexes than does the diphenol component. Introduction Strength and directionality of noncovalent interactions contribute to structural predictability in crystal engineering.1 In recent years, efforts have been made to identify robust supramolecular synthons in order that the variety inherent in crystal packing is appropriately classified and simplified in structural analysis.2 Specificity of recognition between amino and hydroxy functionalities to give supraminol structures has been studied extensively.3 The Ermer3a and Hanessian3b,d,h,m groups have shown that hierarchic crystal structures that have a saturation of O-H‚‚‚N and N-H‚‚‚O [henceforth jointly called N(H)O] hydrogen bridges are obtained in many cases. Work in our laboratories in Hyderabad and Durham has shown that deviations from hierarchy are also not uncommon with N-H‚‚‚π bridges making their appearance on occasion.3f,n In a molecular complex, there are specific noncovalent interactions between chemically distinct molecules, and molecular complexes may accordingly be distinguished from, say solid solutions or inclusion compounds.4 According to Kitaigorodskii,5 all these two-component systems fall into the overall category of mixed crystals. Kitaigorodskii also noted that the formation of a molecular complex is one of the most sensitive ways of probing the significance of particular intermolecular interactions in a crystal structure. He stated that studies of binary crystals of organic substances are a key to the study of intermolecular interactions. Accordingly, molecular complexes are of great significance in crystal engineering. We have noted, many years ago, that the formation of a molecular complex A‚B is, in itself, an indication that interactions of the type A‚‚‚B are more significant than interactions of the type A‚‚‚A or B‚‚‚B.6 With reference to the supraminols, the formation of 1:1 amine-alcohol (or phenol) molecular complexes is favored because the resulting N(H)O hydrogen bridges are better than the O-H‚‚‚O and † ‡
University of Hyderabad. University of Durham.
Scheme 1
N-H‚‚‚N bridges in the crystal structures of the respective individual components. Ermer and Eling3a isolated the 1:1 complex between p-phenylenediamine and hydroquinone and between the phenylogous extensions of these compounds. The Hanessian group has reported many examples of helical diamine-diol complexes.3b Loehlin3c,g and Toda3e and their co-workers have also observed the formation of 1:1 amine-alcohol molecular complexes. In all these cases, saturation of N(H)O hydrogen bond forming ability is invariably observed. In this work, we have examined the 1:1 molecular complexes 1-4 formed by all possible permutations of diamines 5 and 6 with diols 7 and 8. The prototype structures for these molecular complexes are aminophenols 9, 4-(4-aminobenzyl)phenol, and 10, 4-(4-aminophenylsulfamyl)phenol. In these latter structures, which are based on that of 3-aminophenol,3f optimization of herringbone interactions is the primary structural effect and this leads to the formation of weak N-H‚‚‚π, N-H‚‚‚S and C-H‚‚‚O bridges7 rather than to a saturation of N(H)O bonds (Figure 1). Both 9 and 10 have a square motif N(H)O synthon. Replacement of the -CH2group in 9 by an isosteric S-atom in 10 leads, however, to an exchange of the N-H‚‚‚π by an N-H‚‚‚S bridge. This prompted us to investigate complexes 1 through 4. What would be the modularity or how much structural interference would one observe here?
10.1021/cg049967v CCC: $30.25 © 2005 American Chemical Society Published on Web 08/11/2004
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Figure 1. Square motif synthons in aminols 9 (a) and 10 (b).
Experimental Section General Methods. All compounds were commercially available, except for diphenol 7, 4-(4-hydroxybenzyl)phenol, which was prepared from dianiline 5 by diazotization and hydrolysis. Stoichiometric amounts of the selected components were ground well, dissolved in the appropriate solvents and recrystallized. All the melting points were determined on a Mettler Toledo DSC 822e instrument. Complex 1. Diamine 5 (24 mg, 0.125 mmol) and diphenol 7 (25 mg, 0.125 mmol) were dissolved in 1:1 hot MeOHbenzene. Colorless blocks were formed after 3 days; mp 135.5 °C. Complex 2. Diamine 5 (24 mg, 0.125 mmol) and diphenol 8 (27 mg, 0.125 mmol) were dissolved in hot EtOH. Colorless blocks were obtained after slow evaporation of the solvent; mp 132.5 °C. Complex 3. Diamine 6 (27 mg, 0.125 mmol) and diphenol 7 (25 mg, 0.125 mmol) were dissolved in 1:1 hot MeOH-xylene. Colorless cubes were obtained after a few days upon slow evaporation; mp 109.9 °C. Complex 4. Diamine 6 (27 mg, 0.125 mmol) and diphenol 8 (27 mg, 0.125 mmol) were dissolved in hot EtOH. Light yellow prisms were obtained after one week upon slow evaporation of the solvent; mp 121.8 °C. X-ray Data Collection and Crystal Structure Determinations. The X-ray data were collected on a Bruker SMART-1000 diffractometer (1, 2) or the Bruker SMART-6000 diffractometer (3, 4) using Mo KR radiation. The structure solution and refinements were carried out using the SHELXTL programs.8 In all cases, the hydroxy and amine H-atoms were located in difference Fourier maps and refined isotropically. The other H-atoms were either fixed in geometrically sensible positions (2), or located in difference Fourier maps and refined isotropically (1, 3, 4). All interatomic distance and related
calculations were carried out with PLATON2002.9 For further details see Table 1. For details of hydrogen bridge geometry, see Table 2.
Results and Discussion Complex 1. 1:1 4-(4-Aminobenzyl)aniline (5)‚4-(4Hydroxybenzyl)phenol (7). The structure of complex 1 is closely related to that of aminol 9 and is made up of square motif synthons that are linked to form chains. The minor differences between 1 and 9 lie in the internal geometry of the chains and the way in which they pack together. In 1, the square motifs are constructed by functionalities from two diamine and two diphenol molecules (Figure 2). The planes of adjacent square motifs within a chain are ∼55° to each other (parallel in 9). N-H‚‚‚π hydrogen bridges (2.62Å, 134° and 2.84Å, 135.9°) bring adjacent chains together and complete the close packed arrangement (Figure 3).11 Complex 2. 4-(4-Aminobenzyl)aniline (5)‚4-(4Hydroxyphenylsulfanyl)phenol (8). The substitution of the -CH2- group in the diphenol component of 1 by an S-atom to give complex 2 has very little effect on the crystal structure. This is a classic example of how shape and size factors are important in crystal packing,5b and we have noted such CH2/S exchange previously.3n The cell dimensions of 1 and 2 are nearly identical and 2 also consists of square synthon linked chains connected with N-H‚‚‚π hydrogen bridges. A comparison of the unit cell dimensions (Table 1) gives an isostructurality parameter (Π) of 0.0082,12 where zero indicates an exact match. The near identity of the packing of 1:1 molecular
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Table 1. Crystallographic Data and Structure Refinement Parameters Compound emp. form. form. wt. crystalsystem sp. group T [K] a [Å] b [Å] c [Å] R [deg] β [deg] γ [deg] Z V [Å3] λ [Å] Dcalc [mg/m3] F [000] µ [mm-1] 2θ /° index ranges reflections collected unique reflections observed reflections R1 [I >2σ(I)] wR2 GOF synthon C-O, C-O; C-N, C-N angle[°]a Ck* [%]b pyramidal factorc latt. energies [kcal mol-1]d van der Waals electrostatic h. bond total energy
1
2
3
4
C13H14N2‚C13H12O2 398.50 monoclinic P21/n (no. 14) 120(2) 11.401(4) 9.943(3) 19.681(6) 90 103.500(10) 90 4 2169.4(12) 0.71073 1.2201(7) 848 0.08 1.9-29.0 -15 e h e 15 -13 e k e 13 -26 e 1 e 26 24503 5700 4521 0.0437 0.1095 1.03 square motif
C13H14N2‚C12H10O2S 416.54 monoclinic P21/n (no. 14) 100(2) 11.2547(11) 10.1129(9) 19.9982(17) 90 103.654(5) 90 4 2211.8(4) 0.71073 1.2509(2) 880 0.17 1.9-27.5 -14 e h e 14 -13 e k e13 -25 e 1 e 25 15070 5052 2881 0.0571 0.1162 0.99 square motif
C12H12N2S‚ C13H12O2 416.52 monoclinic P21/n (no. 14) 120(2) 5.2528(1) 42.3571(6) 9.4214(1) 90 94.8010(10) 90 4 2088.84(5) 0.71073 1.3245(1) 880 0.18 1.9-27.5 -6 e h e 6 -54 e k e 55 -12 e 1 e 12 20890 4793 4032 0.0368 0.0923 1.03 infinite chain
121; 105 0.67 0.285, 0.298
117; 107 0.66 0.267, 0.291
114; 104 0.70 0.306, 0.330
C12H12N2S‚ C12H10O2S 434.56 orthorhombic P212121 (no. 19) 120(2) 9.9090(4) 10.2700(4) 22.0100(8) 90 90 90 4 2239.86(15) 0.71073 1.2887(1) 912 0.26 1.90-20.0 -13 e h e 13 -14 e k e 14 -30 e 1 e 30 46859 6408 5751 0.0369 0.0936 1.04 cyclohexane chair 120; 111 0.66 0.295, 0.330
-33.63 -20.93 -12.77 -67.33
-36.65 -24.53 -13.54 -74.72
-36.97 -23.09 -10.93 -70.99
-36.15 -29.36 -18.29 -83.80
a The angle between the C-O, C-O and C-N, C-N vectors in the molecular complexes have been calculated using RPluto. This gives a measure of the linearity of the molecule. b Ck*, packing coefficient calculated with PLATON. c The perpendicular distance from the basal plane to the apex of the pyramid. d Lattice Energies calculated using Cerius2 from Accelrys.10
Figure 2. Complex 1 showing the square motifs of hydrogen bridges forming chains. Notice also the C-H‚‚‚O interactions.
complexes of 1 and 2 was also quantified with NIPMAT and simulated powder X-ray plots (see Supporting Information). Complex 3. 4-(4-Aminophenylsulfanyl)aniline (6)‚ 4-(4-Hydroxybenzyl)phenol (7). Notably, CH2/S exchange does not lead to isostructurality. Replacement of the -CH2- group in the dianiline component of complex 1 by an S-atom changes the packing. The major synthon in complex 3 is a one-dimensional infinite chain of N(H)O bridges3n (Figure 5). Cross-linking of these chains is shown schematically in Figure 6. In simple aminols that have the N(H)O linear chain, the “extra” N-H group forms an N-H‚‚‚π bridge. But in complex 3, this interaction loses out and the N-H group is “free”. The electronegative S-atom seems to activate an adjacent phenyl H-atom to the extent of promoting a C-H‚‚‚S dimer3n,7 (Figure 7).
Complex 4. 4-(4-Hydroxyphenylsulfanyl)phenol (6)‚4-(4-Aminophenylsulfanyl)aniline (8). This structure (orthorhombic P212121) appears, at first glance, to be similar to that of aminol 10. For example, the “windmill” type arrangement of molecules is seen here (Figure 8). However, the N(H)O networking is not built with square synthons as in 10 but rather there is a new arrangement that could be termed as “cyclohexane chair”. In addition to the N(H)O bridges, one also sees O-H‚‚‚O and N-H‚‚‚N interactions. This is very unusual in a supraminol and has never been observed previously in this group of compounds. The anilino N-atom completes its tetrahedral coordination with an N-H‚‚‚S bridge.3n,7 Yet, the N(H)O synthon is more likely to be the primary structure stabilizing factor because the O-H‚‚‚N interaction is stronger than O-H‚‚‚O interaction (Table 2). Lattice energies calculated with Cerius2 shows that hydrogen bond stabilization for molecular complex 4 is greater than for the other binary crystals in this study. Even so, the crystal structure of 4 was not anticipated (and probably cannot be anticipated). DSC experiments revealed that there are no metastable forms for these mixed crystals. We attempted to grow crystals using different solvents and also using hydrothermal conditions but no other forms were found in the former case, and in the latter case no X-ray quality crystals were
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Figure 3. Stereoview of complex 1 to show close packing of chains. Notice the N-H‚‚‚π and C-H‚‚‚π interactions on either side of the phenyl rings. Table 2. Pertinent Hydrogen Bridges for the Molecular Complexes in This Study Compound
H-bond
d (Å)a
D (Å)
θ (deg)
1
O-H‚‚‚N O-H‚‚‚N N-H‚‚‚O N-H‚‚‚O N-H‚‚‚π N-H‚‚‚π C-H‚‚‚O C-H‚‚‚π C-H‚‚‚π C-H‚‚‚π C-H‚‚‚π C-H‚‚‚π O-H‚‚‚N O-H‚‚‚N N-H‚‚‚O N-H‚‚‚O N-H‚‚‚π N-H‚‚‚π C-H‚‚‚O C-H‚‚‚S C-H‚‚‚π C-H‚‚‚π C-H‚‚‚π O-H‚‚‚N O-H‚‚‚N N-H‚‚‚O N-H‚‚‚O C-H‚‚‚S C-H‚‚‚π C-H‚‚‚π O-H‚‚‚N O-H‚‚‚O N-H‚‚‚O N-H‚‚‚O N-H‚‚‚N N-H‚‚‚S C-H‚‚‚S C-H‚‚‚S C-H‚‚‚S C-H‚‚‚O
1.8052(13) 1.8540(13) 2.1897(12) 2.2926(13) 2.62 2.84 2.3635(12) 2.59 2.70 2.71 2.82 2.88 1.780(2) 1.850(3) 2.120(4) 2.252(2) 2.55 2.96 2.46 3.04 2.69 2.73 2.74 1.8573(14) 1.8640(12) 2.0901(11) 2.0887(11) 2.7875(4) 2.79 2.82 1.7030(13) 1.8323(11) 2.0636(12) 2.1861(11) 2.0409(14) 2.7712(4) 2.8133(4) 2.9039(4) 2.9487(4) 2.7641(13)
2.7760(18) 2.8010(18) 3.120(2) 3.1938(19) 3.397 3.638 3.294(2) 3.641 3.712 3.730 3.881 3.862 2.760(3) 2.798(3) 3.078(3) 3.167(3) 3.340 3.739 3.372(3) 3.789(3) 3.690 3.736 3.745 2.8381(17) 2.8234(16) 3.0958(18) 3.0565(17) 3.6976(15) 3.823 3.868 2.6775(18) 2.8122(16) 3.0423(19) 3.1369(18) 3.042(2) 3.7060(15) 3.7982(16) 3.9282(18) 4.0245(16) 3.637(2)
168.75(7) 160.78(7) 152.64(7) 148.07(7) 134.0 135.9 143.09(7) 161.1 154.7 156.3 166.0 150.1 174.37(14) 160.94(14) 157.88(13) 150.12(14) 135.1 134.2 141.1 126.8 153.0 155.0 155.0 175.24(8) 164.49(6) 174.41(8) 160.02(8) 141.56(7) 157.6 160.8 170.52(8) 174.29(8) 162.86(9) 156.42(9) 171.14(9) 154.24(8) 151.19(8) 157.84(10) 172.27(8) 137.52(9)
2
3
4
Figure 4. Square motif in complex 2. Compare this with Figure 2.
Figure 5. Infinite N(H)O chain in complex 3.
a O-H, N-H and C-H distances are neutron normalized to 0.983, 1.009 and 1.083 Å.
obtained. In general, we note the absence of polymorphism in the aminophenols. Why this is the case is the subject of ongoing work in our laboratories.
Figure 6. Schematic of cross-linking of molecules in complex 3. N(H)O hydrogen bridges are shown as dotted lines.
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Crystal Growth & Design, Vol. 5, No. 1, 2005 103
Figure 7. Stereoview of the packing in complex 3. Note the C-H‚‚‚S dimer synthon.
Figure 8. (a) Complex 4 to show supramolecular cyclohexane chair and N-H‚‚‚S bridge. (b) Detail of chair. Note N(H)O, O-H‚‚‚O and N-H‚‚‚N interactions.
Scheme 2.
a
Square Motif, Infinite Chain and Cyclohexane Chair Synthonsa
Note the O-H‚‚‚O and N-H‚‚‚N bonds in the cyclohexane chair.
General Discussion of Complexes 1-4. The propensity toward formation of 1:1 phenol-aniline complexes is noted in this group of compounds and confirms earlier trends. The formation of N(H)O bridges is a dominant feature in all these molecular complexes. We also note that in none of the cocrystallization experiments, were the uncomplexed substances 5-8 recovered if 1:1 stoichiometries of the dianiline and diphenol components were taken. This demonstrates the specificity of the aniline-phenol recognition. The three major supramolecular synthons observed are given in Scheme 2. The square motif and infinite chain have been observed before. A cyclohexane chair with four types of
hydrogen bridge, O-H‚‚‚N, N-H‚‚‚O, O-H‚‚‚O and N-H‚‚‚N, is seen for the first time here. While complexes 1 and 2 are isostructural and are closely related to aminol 9, complex 3 is distinct. This hints that the role of the dianiline component is more significant than that of the diphenol in the supraminol recognition bearing out Kitaigorodskii’s comment mentioned earlier.5 The divergent structure of complex 4 shows that the system has been disturbed to a sufficient extent by S-atom replacement in both diamine and diphenol components. Complex 4 is not even related to aminol 10 to the extent that complex 1 is related to aminol 9.
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Conclusions This series highlights the advantages of molecular complexation in crystal engineering and also hints at some of the difficulties of crystal structure prediction. The subtleties of crystal packing are illustrated by the variations in the structures despite the presence of the same (or similar) synthons. Hardly predictable is the fact that exchanging -CH2- groups by S-atoms may have little (molecular complex 2), moderate (complex 3) or deep seated (complex 4) structural effects. To conclude, crystal engineering with complementary multifunctional multicomponent systems requires a detailed understanding of the factors that control supramolecular organization. However, the device of molecular complexation affords an entry into this difficult problem. Acknowledgment. V.R.V. thanks the CSIR for a fellowship. R.M. thanks the ORS for funding, C.K.B. thanks the EPSRC for a studentship and J.A.K.H thanks the EPSRC for a Senior Research Fellowship. G.R.D. thanks the CSIR and DST for research support. Supporting Information Available: NIPMAT plots, simulated powder spectra, ORTEP diagrams, structure solution and refinement, atomic coordinates, bond lengths and angles, and anisotropic parameters for 1-4 1:1 molecular complexes (PDF). This material is available free of charge via the Internet at http://www.pubs.acs.org.
References (1) Selected references on crystal engineering of organic molecular solids include (a) Desiraju, G. R. Crystal Engineering. The Design of Organic Solids; Elsevier: Amsterdam, 1989. (b) Comprehensive Supramolecular Chemistry; Atwood, J. L., Davies, J. E. D., MacNicol, D. D., Vo¨gtle, F., Eds.; Pergamon: Oxford, 1996; Vols. 6, 7, 9, 10. (c) Desiraju, G. R. Science 1997, 278, 404. (d) Aakero¨y, C. B. Acta Crystallogr. 1997, B53, 569. (e) Design of Organic Solids; Weber, E., Ed.; Topics in Current Chemistry; Springer: Berlin, 1998; Vol. 198. (f) Steed, J. W.; Atwood, J. L. Supramolecular Chemistry, Wiley: Chichester, 2000, pp 389-462. (g) Sharma, C. V. K. Cryst. Growth Des. 2002, 2, 465. (h) Braga, D. Chem. Commun. 2003, 2751. (i) Biradha, K. CrystEngComm. 2003, 5, 374. (2) Desiraju, G. R. Angew. Chem., Int. Ed. Engl. 1995, 34, 2311. (3) (a) Ermer, O.; Eling, A. J. Chem. Soc., Perkin Trans. 2 1994, 925. (b) Hanessian, S.; Gomtsyan, A.; Simard, M.; Roelens, S. J. Am. Chem. Soc. 1994, 116, 4495. (c) Loehlin, J. H.; Etter, M. C.; Gendreau, C.; Cervasio, E. Chem. Mater. 1994,
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CG049967V
