Strong and Weak Hydrogen-Bonding Interactions in the Structures of N,N′,N′′-Trisubstituted Guanidinium Chlorides and Bromides Farouq F. Said,*,‡ Tiow-Gan Ong,# Glenn P. A. Yap,† and Darrin Richeson*,#
CRYSTAL GROWTH & DESIGN 2005 VOL. 5, NO. 5 1881-1888
Department of Chemistry, Al al-bayt University, Mafraq, Jordan, Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware, and Department of Chemistry, University of Ottawa, Ottawa, Ontario Canada K1N 6N5 Received April 21, 2005;
Revised Manuscript Received June 22, 2005
ABSTRACT: The reaction of two trisubstituted guanidines N,N′,N′′- triisopropylguanidine (TPG) and N,N′diisopropyl-N′′-2,6-dimethylphenylguanidine (DPArG) with HX or equivalents (X ) Cl, Br) yielded the anticipated guanidinium halide salts. The structures of TPGH+X- (X ) Cl, 1), TPGH+X-‚H2O (X ) Br, 3‚H2O), and DPArGH+X(X ) Cl, 2; Br, 4) were determined by single-crystal X-ray diffraction analysis to examine the potential intermolecular interactions in these compounds and their influence on the extended structures that were observed. The formation of strong, charge-assisted hydrogen bonds, NH+‚‚‚X-, dominates the extended structures. In addition, weaker interactions between the N-substituents and between the X- anions and CH bonds of the substituents have an apparent role in the structures of these materials. While the TPGH+ cation displayed a C3 propeller-type orientation in the structures of 1 and 3‚H2O, two different isomeric forms for the less symmetric DPArGH+ cations were observed, and the identity of the anion and of the substituents both appear to be important in determining which form is obtained. Although the DPArGH+ cation exhibited different isomeric structures in 2 and 4, a common structural motif consisting of hydrogen-bonded chains was observed in their solid-state structures. Introduction Delineating the fundamental principles that control the assembly of molecular building blocks into extended structures is an exciting challenge at the forefront of supramolecular chemistry. This knowledge could have significant impact in areas as diverse as the design of new functional materials, drug development, and understanding of the structures of macromolecules. The combination of intermolecular hydrogen bonding and ionic interactions represent essential forces for the self-organization of individual charged units into robust supramolecules.1-6 For example, the hydrogen bond strength accompanied by an ionic component ranges between 10 and 45 kcal mol-1 compared to 4-15 kcal mol-1 for hydrogen bonds between neutral molecules. In addition, several studies of organic ammonium halides have demonstrated that the N-H+‚‚‚X- interactions play a significant role in influencing the structural motif adopted in the solid state.7 We chose to examine the potential of charge-enhanced hydrogen bonding in the extended structures of N-substituted guanidinium halides with the ultimate goal of employing these interactions in future crystal design. Within the realm of molecular materials, the parent guanidinium cation (C(NH2)3+) has been elegantly employed for the preparation lamellar frameworks derived from hydrogen-bonded sheets and ribbons and in three-dimensional networks.8-11 Guanidinium is isoelectronic with the carbonate dianion, the smallest C3symmetric ion. A primary reason for the success of * To whom correspondence should be addressed. E-mail: darrin@ science.uottawa.ca. ‡ Al al-bayt University. † University of Delaware. # University of Ottawa.
guanidinium as a triangular building block in crystal design can be traced to its capacity to form intermolecular contacts mediated by three pairs of directional hydrogen bonding interactions (A).
In contrast to the rich supramolecular chemistry that has been developed around the parent guanidinium cation, there are a few reports employing N,N′,N′′trisubstituted analogues.12 Recent reports of modified triaminoguanidinium species demonstrate the potential of these species.13-15 In conjunction with our exploration of new preparative routes to novel guanidines,16 we now report the preparation and extended structures of halide ion salts of N,N′,N′′-triisopropylguanidinium (TPGH+) (B) and N,N′-diisopropyl-N′′-2,6-dimethylphenylguanidinum (DPArGH+) (C). In the first case, the symmetrical substitution pattern retains the C3-symmetry in the cation, while the implementation of a symmetry-reducing aryl group in the latter case changes the steric and electronic features of the cation while preserving the
10.1021/cg050172d CCC: $30.25 © 2005 American Chemical Society Published on Web 08/19/2005
1882
Crystal Growth & Design, Vol. 5, No. 5, 2005
potential for 3-fold, hydrogen-bonding arrays. We anticipated that small spherical halide anions would represent good starting points for analyzing the hydrogen-bonding schemes offered by guanidinium cations B and C.
Experimental Section General. N,N′,N′′-Triisopropylguanidine (TPG) and N,N′diisopropyl-N′′-2,6-dimethylphenylguanidine (DPArG) were prepared according to literature methods.16 All other reagents were purchased from Aldrich Chemical Co. and used without further purification. Elemental analyses were run on a PerkinElmer PE CHN 4000 elemental analysis system. Synthesis and Crystallization of N,N′,N′′-Triisopropylguanidinium Chloride, {C(HNiPr)3}+Cl- (TPGHCl) (1). Method A. In a round-bottom flask, a combination of 0.100 g (1.87 mmol) of ammonium chloride and 0.346 g (1.87 mmol) of TPG were dissolved in 10 mL of distilled water. The reaction mixture was heated to boiling and maintained until the solution became turbid. Off-white cubic crystals of 1 were deposited upon slow cooling of the solution (0.40 g, 91.0% yield). Method B. Direct reaction of 0.100 g (0.54 mmol) of TPG with 0.60 mL of HCl (1.0 M, 0.60 mmol) in diethyl ether led to immediate precipitation of a white solid. The solid was removed by filtration, washed with diethyl ether, and dried under vacuum to give a quantitative yield of 1 (0.118 g, 0.53 mmol). Method C. X-ray quality crystals of compound 1 could also be isolated in quantitative yield when 0.100 g (0.54 mmol) of TPG was dissolved in CHCl3 and the solution was allowed to sit for approximately one week. In addition to confirming the molecular formula through elemental analysis, we examined samples of solids obtained by the three synthetic methods by single-crystal X-ray analysis and determined that they possess identical structures. Anal. Calcd for C10H24N3Cl C, 54.16; H, 10.91; N, 18.95. Found C, 54.25; H, 10.85; N, 19.29. Synthesis and Crystallization of N,N′-Diisopropyl-N′′2,6-dimethylphenylguanidinium Chloride, {C(HNiPr)2(HN2,6-Me2C6H3)}+Cl- (DPArGHCl) (2). Method A. In a round-bottom flask, 0.200 g (0.810 mmol) of (DPArG) was dissolved in 10 mL of hot distilled water. To this was added 0.0433 g (0.810 mmol) of ammonium chloride, and the resulting mixture was boiled for 15 min, cooled to room temperature, and cooled to 5 °C in a refrigerator. White crystals of TPGH+Br- (3) deposited in about 1 h (0.215 g, 93.5% yield) and were isolated by filtration. Method B. To a sample of 0.200 g (0.810 mmol) of DPArG in a round-bottom flask was added 0.90 mL of HCl (1.0 M, 0.90 mmol). The solution was initially homogeneous, and white precipitate began to form shortly after addition was complete. Solid was isolated by filtration and dissolved in thionyl chloride. This solution was cooled to 5 °C in a refrigerator. Crystals of 3 deposited the following day and were isolated by filtration (0.22 g, 95.7% yield). In addition to confirming the molecular formula through elemental analysis, samples of solids obtained by the two
Said et al. synthetic methods were examined by single-crystal X-ray analysis and determined to possess identical structures. Anal. Calcd for C15H26ClN3 C, 63.47; H, 9.23; N, 14.80. Found C, 63.86, H, 9.08, N, 15.01. Synthesis and Crystallization of N,N′,N′′-Triisopropylguanidinium Bromide, {C(HNiPr)3}+Br-‚H2O (TPGHBr‚H2O) (3‚H2O). In a round-bottom flask, 0.100 g (1.02 mmol) of ammonium bromide and 0.189 g (1.02 mmol) of TPG were dissolved in 10 mL of distilled water. The reaction mixture was boiled for 15 min, cooled to room temperature, and cooled to 5 °C in a refrigerator. The following day, a crystalline white solid 2 (0.28 g, 96.5%) was obtained by filtration. Anal. Calcd for C10H26BrN3O C, 42.26; H, 9.22; N, 14.78. Found C, 41.97, H, 9.08, N, 15.13. Synthesis and Crystallization of N,N′-Diisopropyl-N′′2,6-dimethylphenylguanidinium Bromide, {C(HNiPr)2(HN2,6-Me2C6H3)}+Br- (DPArGHBr) (4). In a round-bottom flask, 0.200 g (0.810 mmol) of DPArG was dissolved in 10 mL of hot distilled water. To this solution was added 0.080 g (0.816 mmol) of ammonium bromide, and the resulting mixture was boiled for 15 min. The reaction mixture was placed in a refrigerator (5 °C), and white crystals of 4 deposited over the next 3 h (0.256 g, 96.2% yield). Anal. Calcd for C15H26BrN3 C, 54.88; H, 7.98; N, 12.80. Found C, 54.97, H, 8.08, N, 12.69. Structural Determination for Compounds 1-4. Single crystals were mounted on thin glass fibers using viscous oil and then cooled to the data collection temperature. Crystal data and details of the measurements are summarized in Table 1. Data were collected on a Bruker AX SMART 1k CCD diffractometer using 0.3° ω-scans at 0, 90, and 180° in φ. Unitcell parameters were determined from 60 data frames collected at different sections of the Ewald sphere. Semiempirical absorption corrections based on equivalent reflections were applied. The structures were solved by direct methods, completed with difference Fourier syntheses and refined with fullmatrix least-squares procedures based on F2. The low calculated density for compound 1 prompted a void space analysis, which indicated no solvent accessible voids in the crystal lattice. Thus, the low density observed for 1 is apparently a consequence of less than optimal packing. In the case of compound 2, the structure was treated as a racemic twin with a refined distribution of 27/73. All non-hydrogen atoms were refined with anisotropic displacement parameters. All hydrogen atoms were treated as idealized contributions. All scattering factors and anomalous dispersion factors are contained in the SHELXTL 5.1 program library.
Results and Discussion The two guanidines employed in this study, TPG and DPArG, react readily and in near quantitative yields with HX equivalents as summarized in eq 1 to yield compounds 1-4. Interestingly, the basicity of TPG allowed for the efficient synthesis of compounds 1 and 3 by simply dissolving the guanidine in chloroform or bromoform, respectively.17 In all cases, a comparison of microanalytical results and single-crystal structures of the product materials confirmed the appropriate formulation.
The primary purpose of preparing compounds 1-4 was to examine their extended solid-state structures
N,N′,N′′-Trisubstituted Guanidinium Chlorides and Bromides
Crystal Growth & Design, Vol. 5, No. 5, 2005 1883
Table 1. Crystal Data and Structure Refinement for 1, 2, 3‚H2O, and 4
a
compound
1
empirical formula formula weight temperature (K) λ (Å) crystal system space group a (Å) b (Å) c (Å) β (deg) V (Å3) Z F (calc) (Mg/m3) µ (mm-1) absorption correction final R indices [I > 2σ(I)] R1a wR2b
C10H24ClN3 221.77
2 C15H26ClN3 283.84
3‚H2O
4
C10H26BrN3O 284.25
C15H26BrN3 328.30
tetragonal P41212 9.6903(12) 9.6903(12) 34.257(6)
monoclinic P21/c 7.991(4) 18.379(9) 11.456(6) 91.82(3) 1681.8(15) 4 1.297 2.437
203 0.71073 cubic P213 11.5301(16) 11.5301(16) 11.5301(16)
orthorhombic Aba2 11.978(2) A 37.836(6) 14.948(3)
1532.8(4) 4 0.961 0.226 0.0658
6775(2) 3216.8(8) 16 8 1.113 1.174 0.219 2.542 semiempirical from equivalents 0.0680 0.0585
0.1772
0.1612
0.0764
0.0587 0.0718
R1 ) ∑ ||Fo| - |Fc||/∑ |Fo|. b wR2 ) (∑ w(|Fo| - |Fc|)2/∑ w|Fo|2)1/2.
Figure 1. Molecular structure and atom numbering scheme for N,N′,N′′-triisopropylguanidinium chloride, (TPGH+Cl-) (1).
with the ultimate goal of elucidating the impact of N-substitution and guanidinium symmetry on the hy-
drogen-bonding arrays of the guanidinium cations. To focus on the effects on the guanidinium cation, we chose to concentrate our initial efforts on the bonding motifs of TPGH+ and DPArGH+ with spherical chloride and bromide anions. Compounds 1-4 were characterized by single-crystal X-ray diffraction analysis, and results of the data collections are summarized in Table 1. Compound 1 crystallized in the cubic space group P213, and a diagram of the asymmetric unit is presented in Figure 1. This compound consists of the anticipated TPGH+ cation, residing on a C3 axis of the unit cell, along with a chloride anion. The bond distances and angles within the planar cation are summarized in Table 2. The equivalent C-N bond lengths (1.332 (4) Å) and planarity of the CN3 core (∑ of angles ) 360°) suggest an electron-delocalized, Y-conjugated species.18 Two views of the hydrogen-bonding network of this solid are presented in Figure 2, and a summary of the metrical parameters of hydrogen bonding is presented in Table 4. Each of the three NH groups of the cation interacts with a different Cl- anion (N1-Cl bonds
Figure 2. Two views of the hydrogen-bonding network for compound 1. The guanidinium cation is shown in stick figure representation with the chloride anion as a green sphere. Panel (a) emphasizes the local hydrogen bonding of the cation and (b) emphasizes that of the anion.
1884
Crystal Growth & Design, Vol. 5, No. 5, 2005
Said et al.
Table 2. Selected Bond Lengths [Å] and Angles [deg] for 1 and 2 compound 1
compound 2 Distances
N(1)-C(4) N(1)-C(1)
1.332(4) 1.437(5)
N(1)-C(15) N(1)-C(6) N(2)-C(15) N(2)-C(9) N(3)-C(15) N(3)-C(12) N(4)-C(30) N(4)-C(21) N(5)-C(30) N(5)-C(24) N(6)-C(30) N(6)-C(27)
1.365(7) 1.454(7) 1.323(7) 1.481(8) 1.328(7) 1.477(7) 1.351(7) 1.436(7) 1.327(7) 1.468(9) 1.329(8) 1.480(8)
Angles C(4)-N(1)-C(1) N(1)-C(1)-C(3) N(1)-C(1)-C(2) C(3)-C(1)-C(2) N(1)-C(4)-N(1A) N(1)-C(4)-N(1B)
129.9(4) 109.0(5) 113.1(5) 116.0(6) 119.998(4) 119.998(5)
C(1)-N(1)-C(4)-N(1A) C(1)-N(1)-C(4)-N(1B)
153.1(4) -26.0(10)
C(15)-N(1)-C(6) C(15)-N(2)-C(9) C(15)-N(3)-C(12) C(30)-N(4)-C(21) C(30)-N(5)-C(24) C(30)-N(6)-C(27) N(2)-C(15)-N(3) N(2)-C(15)-N(1) N(3)-C(15)-N(1) N(6)-C(30)-N(5) N(6)-C(30)-N(4) N(5)-C(30)-N(4)
124.6(5) 128.1(5) 127.7(5) 126.3(5) 128.8(6) 126.8(5) 122.6(5) 115.1(5) 122.2(5) 121.0(6) 122.5(5) 116.5(5)
Torsion Angles C(9)-N(2)-C(15)-N(3) C(9)-N(2)-C(15)-N(1) C(12)-N(3)-C(15)-N(2) C(12)-N(3)-C(15)-N(1) C(6)-N(1)-C(15)-N(2) C(27)-N(6)-C(30)-N(5) C(24)-N(5)-C(30)-N(6) C(24)-N(5)-C(30)-N(4) C(21)-N(4)-C(30)-N(5)
4.5(9) -173.3(5) -162.4(5) 15.3(9) -143.5(5) 161.4(5) -5.2(9) 175.3(5) 142.7(5)
Table 3. Selected Bond Lengths [Å] and Angles [deg] for 3‚H2O and 4 compound 3‚H2O
compound 4 Distances
N(1)-C(10) N(2)-C(10) N(3)-C(10) N′(1)-C(10) N′(2)-C(10) N′(3)-C(10)
1.358(9) 1.280(9) 1.370(8) 1.312(9) 1.399(9) 1.371(9)
N(1)-C(15) N(1)-C(1) N(2)-C(15) N(2)-C(4) N(3)-C(15) N(3)-C(12)
1.329(5) 1.478(6) 1.330(6) 1.478(5) 1.359(5) 1.438(6)
Angles C(1)-N(1)-C(10) C(10)-N(2)-C(4) C(10)-N(3)-C(7) N(2)-C(10)-N(3) N(2)-C(10)-N(1) N(3)-C(10)-N(1) N′(2)-C(10)-N′(3) N′(2)-C(10)-N′(1) N′(3)-C(10)-N′(1) C(4)-N(2)-C(10)-N(3) C(4)-N(2)-C(10)-N(1) C(7)-N(3)-C(10)-N(2) C(7)-N(3)-C(10)-N(1) C(1)-N(1)-C(10)-N(2)
134.7(9) 136.7(8) 125.4(7) 120.1(7) 122.9(7) 116.4(6) 116.1(7) 119.7(7) 121.9(7) -179.0(8) 10.9(14) 31.9(10) -157.3(8) -154.2(9)
C(15)-N(1)-C(1) C(15)-N(2)-C(4) C(15)-N(3)-C(12) N(1)-C(1)-C(2) N(1)-C(1)-C(3) C(2)-C(1)-C(3) N(2)-C(15)-N(1) N(2)-C(15)-N(3) N(1)-C(15)-N(3)
128.8(4) 128.4(4) 123.8(4) 109.0(4) 108.2(4) 113.1(4) 118.7(4) 119.9(5) 121.4(5)
C(4)-N(2)-C(15)-N(1) C(4)-N(2)-C(15)-N(3) C(1)-N(1)-C(15)-N(2) C(1)-N(1)-C(15)-N(3) C(12)-N(3)-C(15)-N(2) C(12)-N(3)-C(15)-N(1)
154.1(5) -27.6(8) 149.3(5) -29.0(8) 153.1(5) -28.6(9)
Torsion Angles
distance ) 3.270 Å) (Figure 2a), and each of the anions is bonded to three different guanidinium cations (Figure 2b). The result is a three-dimensional extended structure with symmetrical use of all NH groups of the guanidine in hydrogen bonding to a three-coordinate Clanion. Interestingly, the reported structure of guanidinium chloride, C(NH2)3+Cl-, displays chloride anions with six
hydrogen-bonding interactions to three different guanidinium cations. Each Cl- forms hydrogen bonds with two NH groups within the same guanidinium cation (NH-Cl ) 3.303 Å) as represented by D.19 The major difference between the parent guanidinium cation, C(NH2)3+, and the TPGH+ cation is the introduction of the C3-oriented iPr substituents in the latter. This change eliminates one of the possible NH‚‚‚Cl interac-
N,N′,N′′-Trisubstituted Guanidinium Chlorides and Bromides
Crystal Growth & Design, Vol. 5, No. 5, 2005 1885 Table 4. Hydrogen Bonds and Short Contacts [Å and deg] for 1, 2, 3‚H2O, and 4a d(D‚‚‚A)
