"*u,,loi!":{!l:"l,triiiii - Whitesides Research Group - Harvard University
Copyright
Reprinted from the Journal of the American Chemical Society, 1992, 114. O 1992 by the American Chemical Society and reprinted by permission of the copyright
owner.
Solid-StateStructuresof *Rosette'and *CrinkledTape" Motifs Derivedfrom the CyanuricAcid-Melamine Latticer JonathanA. Zerkowski, ChristopherT. Seto. and George M. Whitesides*
,"*u,,loi!":{!l:"l,triiiii neceiuedFebruary 21,1gg2 We are using the pattern of hydrogenbondspresentin the l: I complex formed from cyanuric acid and melamine (CA.M) as the basisfor the designof self-assemblingstructures.2-s We have describeda solid-statestructure basedon a 'linear" tape motif taken from this lattice (3, Figure I ),r and we have inferred the existenceof cyclic aggregatescontaining three melamineand three isocyanuratemoieties in solution.a'5Here we report solid-state structuresof a new type of tape format (a *crinkled tape', 4) and a cyclic structure (a "rosette",5), both obtained by combination of ff Nrbis(p-substituted phenyl)melamine(l) and 5,5-diethylbarbituric acid (2). We believethat the three solid-statestructur€s 3-5 are the most plausiblestructural motifs that can be derived from the CA.M lattice: other. more collapsedtape or cyclic structures(e.9.,6 and 7, and larger cyclic structurescontaining these units) are destabilized by nonbonded steric interactions (indicated by arrows in Figure l). These two new structures, together with the structure of a linear tape (X = H) already described,3serve as paradigms for use in the design of self-assembling structures based on the CA.M lattice and provide structural parametersapplicableto evaluationof the energetics of these structures using molecular mechanics.6 Figure 2 (middle) showsthe structure of the l:l complex of la (X = COzCH3) and 2.7 This crinkled format occurs commonly: of l5 structures we have determined in the series of cocrystalsincorporating substituted diphenylmelaminesand 2, three are crinkled tapes. The complex la.2 crystallizes from
( I ) Supportedby the NationalSciene Foundation, Grant CHE-88-12709 to G.M.W., Grant DMR-89-20490 to the Harvard University Materials ResearchLaboratory,and Grant CHE 80-00670for the purchaseof the SiemensX-Ray diffractometer. (2) Whitesides, G. M.; Mathias,J. P.;Seto,C.T. Science1991,254,t312. (3) Zerkowski,J. A.;Seto,C. T.;Wierda, D. A.; Whitqsides, G. M. J. Am. Chem.Soc. 1990,I 12, 9025. (4) Seto,C. T.; Whitesides,G. M. J. Am. Chem.Soc. 1990,I I 2, 6409. ( 5 ) S e t o ,C . T . ; W h i t e s i d e sG, . M . J . A m . C h e m .S o c . 1 9 9 1 . : , 1 3 , 7 1 2 . (6) Desiraju,G. R. Crystal Engineering'. The Designof Organic Solids; Elsevier: New York, 1989. Wright, J. D. Molecular Crystals;Cambridge UniversityPress: Cambridge,1987. ( 7 ) C r y s t a l d a t af o r l a . 2 ( X = C O 2 C H 3 ) :( 9 r c H r s N e O r ) ( C s { ; 2 N 2 O 3 ) . C H 3 C H 2 O Hs: p a c eg r o u pC 2 l c : a = 2 3 . 9 5( 3 ) A , b = 1 6 . 9 5( 4 ) A , c = 1 4 . 5 9 ( l ) A , 0 = 9 4 . q( l ) o . , / = - s 9 0 5( 2 ) A r . D q r " d= 1 . 3 0 2g / c m 3 w i t h o u ta contributionfrom includedsolvent,1.405g/cm3 with the solvent;Z = 8 1.2 pairs;R = 0.14 (further refinementto modelthe disorderedsolventmolecule is underway).
S oci ety 0 0 0 2 -7 8 6l 3 @ 1992A meri canC hemi cal 9 2 l 1 5 l 4 -5 4 73S 03.00/0
Communications to the Editor
I 1 4 .N o . I 3 , 1 9 9 2
5474
2
4 crinkled tape
5 rosette
RR
.ATA
,-SAX'
7
basedon repeatingunits of structures representation Figurel. Schematic by filledtriangles,diethylbarbituric are represented of 1.2. Melamines by opentriangles,and the triad of hydrogenbonds acid is represented dottedlines. Regionsof unfaby the threeconnecting is represented areindicatedby thearrows.The structureof vorablestericinteractions onepair of R groupson a unit of 2 to showthe steric 7 superimposes strain. ethanol as a solvate.8 Figure 2 (lower) shows the structure of lb (X = C(CH:)r) and 2.e The mean planesof all the rosettes in the crystal are parallel: that is, they do not adopt a herringbone packing motif. No solvent of crystallization is included in the lattice. We hypothesizethat a competition between nonbondedsteric interactions between the X groups and a tendency for a high packing coefficientr0in the crystal is important in determining which structural motif is adopted by a l:l cocrystal of I and 2. We assumethat any structure must retain the triad pattern of hydrogen bonds. The linear tape 3 is observed for a number of groupsX that are small (F, Cl. Br, I. CHr). When X becomes larger than CFj or I,lr unfavorablelateral nonbondtnginteractions betweenX groups on adjacent melamines(Figure l) are relieved in going to the crinkled structure 4, but are replacedby unfavorable intiraciions with the ethyl groups of 2 (Figure 2, bottom).r2 The
Figure 2. Top: crystal structures of linear tape (X = CHr),3 crinkled tape (X = CO2CH3). and rosette (X = C(CH3)3) motifs. The crinkled tape crystal contains drsorderedethanol that has been deleted from this view for clarity; it is located above and below the planes of the phenyl rings. Bottom: hypotheticalspace-fillingmodel generatedby replacing the ester groups in the crinkled tape with tert-butyl groups, without changing any other nuclear positions. The arrow indicates regions of unfavorable steric interaction between the terl-butyl group and the ethyl groups of the diethylbarbituric acid.r2
crinkled structure is sufficiently loosely packed to accommodate one ethanol per dimer unit of 14.2.8 Both types of steric interstructureswe haveobserved (8) All threeof the crinkleddiphenylmelamine actions are relieved in the rosette 5. are solvates. = The structures reported here demonstratethat simple modi( C 2 3 H 3 o N 6 ) 3 ( C s H 1 2 N 2 Q 3 ) 3 ; ( X C ( C H r ) r ) : f o r l b ' 2 (a) Crystal_data fications in the molecular structuresof a self-assemblingsystem s p a c eg r o u p P l : a = 1 6 . 4 7 1( 3 ) A . D = l 9 - 9 3 0( 2 ) A , c = . 1 5 . 4 1 0( 4 ) A , a = 9 5 . 1 -(0l i ' , P = 9 9 . 7 9( 2 ) " , t = 9 7 . 0 1( l ) ' , r = 4 9 1 7( 2 ) A r . D o 6 6= 1 . 1 6 5 can lead to changesin crystalline architecture that can be rag/cm3,Z = 2 rosettes(6 1.2 pairs):R = 0.1I 2 (four of the lerl-butyl groups tionalized (at least qualitatively) using steric arguments. By with alternative the structure refine to we are continuing disordered; iie positions for the CH3 grouPs). ' (10) Kitaigorodsky,A. L Molecular Crystalsand Molecules;Academic P r e s s :N e w Y o r k , 1 9 7 3 . ( l l ) Z e r k o w s k i J, . A . ; S e t o ,C ' ljnpublishedwork.
(12) We have not examinedthesesystemsfor crystallinepolymorphism and have not excludedthe pnssibilitythat someof thesestructuresare kineticallydetermined,rather than being thermodynamicminima.
5475 varying the steric demandsof substituentsaround the periphery of our hydrogen-bondedcomponents,we expect to be able to select from among alternative geometrical isomersof hydrogen-bonded assembliesin the solid state. SupplementaryMaterial Available: Brief synthetic outline, details of X-ray data collection, tables of crystal data and atomic positional parameters,and oRTEPdrawings for both complexes (23 pages). Ordering information is given on any current masthead page.
Reprinted from the Journal of the American Chemical Society, 1992, 114. O 1992 by the American Chemical Society and reprinted by permission of the copyright
owner.
Solid-StateStructuresof *Rosette'and *CrinkledTape" Motifs Derivedfrom the CyanuricAcid-Melamine Latticer JonathanA. Zerkowski, ChristopherT. Seto. and George M. Whitesides*
,"*u,,loi!":{!l:"l,triiiii neceiuedFebruary 21,1gg2 We are using the pattern of hydrogenbondspresentin the l: I complex formed from cyanuric acid and melamine (CA.M) as the basisfor the designof self-assemblingstructures.2-s We have describeda solid-statestructure basedon a 'linear" tape motif taken from this lattice (3, Figure I ),r and we have inferred the existenceof cyclic aggregatescontaining three melamineand three isocyanuratemoieties in solution.a'5Here we report solid-state structuresof a new type of tape format (a *crinkled tape', 4) and a cyclic structure (a "rosette",5), both obtained by combination of ff Nrbis(p-substituted phenyl)melamine(l) and 5,5-diethylbarbituric acid (2). We believethat the three solid-statestructur€s 3-5 are the most plausiblestructural motifs that can be derived from the CA.M lattice: other. more collapsedtape or cyclic structures(e.9.,6 and 7, and larger cyclic structurescontaining these units) are destabilized by nonbonded steric interactions (indicated by arrows in Figure l). These two new structures, together with the structure of a linear tape (X = H) already described,3serve as paradigms for use in the design of self-assembling structures based on the CA.M lattice and provide structural parametersapplicableto evaluationof the energetics of these structures using molecular mechanics.6 Figure 2 (middle) showsthe structure of the l:l complex of la (X = COzCH3) and 2.7 This crinkled format occurs commonly: of l5 structures we have determined in the series of cocrystalsincorporating substituted diphenylmelaminesand 2, three are crinkled tapes. The complex la.2 crystallizes from
( I ) Supportedby the NationalSciene Foundation, Grant CHE-88-12709 to G.M.W., Grant DMR-89-20490 to the Harvard University Materials ResearchLaboratory,and Grant CHE 80-00670for the purchaseof the SiemensX-Ray diffractometer. (2) Whitesides, G. M.; Mathias,J. P.;Seto,C.T. Science1991,254,t312. (3) Zerkowski,J. A.;Seto,C. T.;Wierda, D. A.; Whitqsides, G. M. J. Am. Chem.Soc. 1990,I 12, 9025. (4) Seto,C. T.; Whitesides,G. M. J. Am. Chem.Soc. 1990,I I 2, 6409. ( 5 ) S e t o ,C . T . ; W h i t e s i d e sG, . M . J . A m . C h e m .S o c . 1 9 9 1 . : , 1 3 , 7 1 2 . (6) Desiraju,G. R. Crystal Engineering'. The Designof Organic Solids; Elsevier: New York, 1989. Wright, J. D. Molecular Crystals;Cambridge UniversityPress: Cambridge,1987. ( 7 ) C r y s t a l d a t af o r l a . 2 ( X = C O 2 C H 3 ) :( 9 r c H r s N e O r ) ( C s { ; 2 N 2 O 3 ) . C H 3 C H 2 O Hs: p a c eg r o u pC 2 l c : a = 2 3 . 9 5( 3 ) A , b = 1 6 . 9 5( 4 ) A , c = 1 4 . 5 9 ( l ) A , 0 = 9 4 . q( l ) o . , / = - s 9 0 5( 2 ) A r . D q r " d= 1 . 3 0 2g / c m 3 w i t h o u ta contributionfrom includedsolvent,1.405g/cm3 with the solvent;Z = 8 1.2 pairs;R = 0.14 (further refinementto modelthe disorderedsolventmolecule is underway).
S oci ety 0 0 0 2 -7 8 6l 3 @ 1992A meri canC hemi cal 9 2 l 1 5 l 4 -5 4 73S 03.00/0
Communications to the Editor
I 1 4 .N o . I 3 , 1 9 9 2
5474
2
4 crinkled tape
5 rosette
RR
.ATA
,-SAX'
7
basedon repeatingunits of structures representation Figurel. Schematic by filledtriangles,diethylbarbituric are represented of 1.2. Melamines by opentriangles,and the triad of hydrogenbonds acid is represented dottedlines. Regionsof unfaby the threeconnecting is represented areindicatedby thearrows.The structureof vorablestericinteractions onepair of R groupson a unit of 2 to showthe steric 7 superimposes strain. ethanol as a solvate.8 Figure 2 (lower) shows the structure of lb (X = C(CH:)r) and 2.e The mean planesof all the rosettes in the crystal are parallel: that is, they do not adopt a herringbone packing motif. No solvent of crystallization is included in the lattice. We hypothesizethat a competition between nonbondedsteric interactions between the X groups and a tendency for a high packing coefficientr0in the crystal is important in determining which structural motif is adopted by a l:l cocrystal of I and 2. We assumethat any structure must retain the triad pattern of hydrogen bonds. The linear tape 3 is observed for a number of groupsX that are small (F, Cl. Br, I. CHr). When X becomes larger than CFj or I,lr unfavorablelateral nonbondtnginteractions betweenX groups on adjacent melamines(Figure l) are relieved in going to the crinkled structure 4, but are replacedby unfavorable intiraciions with the ethyl groups of 2 (Figure 2, bottom).r2 The
Figure 2. Top: crystal structures of linear tape (X = CHr),3 crinkled tape (X = CO2CH3). and rosette (X = C(CH3)3) motifs. The crinkled tape crystal contains drsorderedethanol that has been deleted from this view for clarity; it is located above and below the planes of the phenyl rings. Bottom: hypotheticalspace-fillingmodel generatedby replacing the ester groups in the crinkled tape with tert-butyl groups, without changing any other nuclear positions. The arrow indicates regions of unfavorable steric interaction between the terl-butyl group and the ethyl groups of the diethylbarbituric acid.r2
crinkled structure is sufficiently loosely packed to accommodate one ethanol per dimer unit of 14.2.8 Both types of steric interstructureswe haveobserved (8) All threeof the crinkleddiphenylmelamine actions are relieved in the rosette 5. are solvates. = The structures reported here demonstratethat simple modi( C 2 3 H 3 o N 6 ) 3 ( C s H 1 2 N 2 Q 3 ) 3 ; ( X C ( C H r ) r ) : f o r l b ' 2 (a) Crystal_data fications in the molecular structuresof a self-assemblingsystem s p a c eg r o u p P l : a = 1 6 . 4 7 1( 3 ) A . D = l 9 - 9 3 0( 2 ) A , c = . 1 5 . 4 1 0( 4 ) A , a = 9 5 . 1 -(0l i ' , P = 9 9 . 7 9( 2 ) " , t = 9 7 . 0 1( l ) ' , r = 4 9 1 7( 2 ) A r . D o 6 6= 1 . 1 6 5 can lead to changesin crystalline architecture that can be rag/cm3,Z = 2 rosettes(6 1.2 pairs):R = 0.1I 2 (four of the lerl-butyl groups tionalized (at least qualitatively) using steric arguments. By with alternative the structure refine to we are continuing disordered; iie positions for the CH3 grouPs). ' (10) Kitaigorodsky,A. L Molecular Crystalsand Molecules;Academic P r e s s :N e w Y o r k , 1 9 7 3 . ( l l ) Z e r k o w s k i J, . A . ; S e t o ,C ' ljnpublishedwork.
(12) We have not examinedthesesystemsfor crystallinepolymorphism and have not excludedthe pnssibilitythat someof thesestructuresare kineticallydetermined,rather than being thermodynamicminima.
5475 varying the steric demandsof substituentsaround the periphery of our hydrogen-bondedcomponents,we expect to be able to select from among alternative geometrical isomersof hydrogen-bonded assembliesin the solid state. SupplementaryMaterial Available: Brief synthetic outline, details of X-ray data collection, tables of crystal data and atomic positional parameters,and oRTEPdrawings for both complexes (23 pages). Ordering information is given on any current masthead page.
