Journal of Molecular Structure 645 (2003) 177–183 www.elsevier.com/locate/molstruc
Piperidine –CO2 –H2O molecular complex Huiming Jiang, Igor Novak* Department of Chemistry, National University of Singapore, 10 Kent Ridge Crescent, Singapore, Singapore 117543 Received 16 August 2002; accepted 11 October 2002
Abstract Piperidine forms a molecular complex with CO2 and H2O through hydrogen bonding. The formation of the complex was found to be a reversible process. The complex decomposes to the original components at room temperature. The structure of the complex obtained via X-ray diffraction is described and compared to the previously reported 4-methylpiperidine carboxylate. q 2002 Elsevier Science B.V. All rights reserved. Keywords: Piperidine; Molecular complex; Crystal structure
1. Introduction Hydrogen bonding is very important for the existence and properties of various chemical systems like ice, proteins and liquids even though the bond itself is weak when compared to covalent or ionic bonds. Hydrogen bonding is responsible e.g. for the secondary structure of DNA or for the fact that water is liquid at standard temperature and pressure. Because hydrogen bonds extend over quite long distances, their studies reveal information about long-range intermolecular forces. Piperidine is a strong base as can be expected from the secondary aliphatic amine [1]. However, the incorporation of nitrogen into the six-member ring ‘exposes’ the electron density on nitrogen and makes the molecule a good nucleophile. As a result, when the piperidine came in contact with air, its vapor reacted with carbon dioxide and moisture to * Corresponding author. Fax: þ 65-6779-1691. E-mail address:
[email protected] (I. Novak).
form a hydrogen-bonded molecular complex similar to the complex a-piperidine –carboxylic acid. The title complex was in the form of white crystals which accumulated on the walls of the glassware. The complex formation was discovered accidentally when piperidine was being tested as a possible solvent. Upon further investigation, we found that the formation of the complex was the product of the gas phase reaction i.e. piperidine vapor reacting with carbon dioxide and moisture from the air. This was confirmed by running the same reaction in the liquid phase. When carbon dioxide and water were introduced into the colorless, liquid piperidine no complex formation could be detected. The formation of the complex is a reversible process. The complex is not very stable and will decompose to the starting material piperidine at room temperature when left standing for a long time or if heated for several minutes. The hydrogen bond plays a critical role in stabilizing the molecular complex and allows it to exist in the crystalline form at room temperature for some time. Piperidine is known to
0022-2860/03/$ - see front matter q 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 2 8 6 0 ( 0 2 ) 0 0 5 4 5 - 8
178
H. Jiang, I. Novak / Journal of Molecular Structure 645 (2003) 177–183
Fig. 1. Reaction route.
form a series of molecular complexes with isobutyric acid [2] and aliphatic amine [3], while 4-methylpiperidine forms a molecular complex [4] with CO2 which is similar to our complex. Piperidine can also form a molecular complex with sulfur dioxide [5], the mechanism of whose formation is very similar to the complex described in this work. Hydrogen bonding is crucial for the formation of all of these complexes.
The title complex dissolves readily in organic solvents such as cyclohexane, acetone and chloroform, but tends to decompose in solution as could be deduced from 1H NMR, 13C NMR and UV-absorption spectra. The spectra of the complex in solution are almost the same as that of pure piperidine. This is understandable because the intermolecular collisions in the liquid will disrupt the stabilizing hydrogen bonding network. Because of its instability in
Table 1 Crystal data and structure refinement Empirical formula Formula weight Temperature Wavelength Crystal system Space group Unit cell dimensions
Volume Z Density (calculated) Absorption coefficient F(000) Crystal size Theta range for data collection Index ranges Reflections collected Independent reflections Completeness to theta ¼ 27.488 Absorption correction Max and min transmission Refinement method Data/restraints/parameters Goodness-of-fit on F 2 Final R indices [I . 2sigma(I )] R indices (all data) Largest diff. peak and hole
C11 H24 N2 O3 232.32 223(2) K ˚ 0.71073 A Triclinic P21 ˚ a ¼ 6.4596(6) A ˚ b ¼ 7.9569(8) A ˚ c ¼ 13.5086(13) A ˚3 646.37(11) A 2 1.194 Mg/m3 0.086 mm21 256 0.45 £ 0.40 £ 0.36 mm3 1.57–27.488. 28 , ¼ h , ¼ 8, 210 , ¼ k , ¼ 10, 217 , ¼ l , ¼ 17 7787 2949 [R(int) ¼ 0.0547] 98.8% Sadabs, (Sheldrick 2001) 0.9697 and 0.9623 Full-matrix least-squares on F 2 2949/0/241 0.977 R1 ¼ 0.0625, wR2 ¼ 0.1570 R1 ¼ 0.0716, wR2 ¼ 0.1636 ˚ 23 0.298 and 20.257 e A
a ¼ 96.831(2)8. b ¼ 101.832(2)8. g ¼ 104.741(2)8.
H. Jiang, I. Novak / Journal of Molecular Structure 645 (2003) 177–183
179
Table 2 Spectra of the molecular complex Spectra
Piperidine–CO2 complex
Piperidine
1
d3.01 (4H, m), 1.53 (6H, m) d44.91, 25.20, 24.11 3542.3, 2947.2, 2841.9, 2807.9, 1656.4, 1562.3, 1456.2, 1366.2, 1232.8. 224 (cyclohexane) Undetectable due to decomposition upon heating 231, 213, 158, 129, 84, 73
d2.69 (4H, m), 1.45 (6H, m) d47.18, 27.01, 25.12 3280.6, 2927.9, 2852.1, 2804.5, 1442.7, 1317.9, 1112.3. 219 (cyclohexane)
HNMR(300 MHz, acetone-d6) C NMR (75 MHz, acetone-d6) FT-IR (KBr) (cm21) 13
UV (l/nm) Melting Point EI-MS
solution, the complex could only be detected by FTIR and single crystal X-Ray diffraction.
2. Experimental section 2.1. Scheme Fig. 1. Preparation: 5 ml of colorless, pure piperidine was put inside the test-tube and after 20 min. exposure to air, white crystals appeared and aggregated on the wall of the tube.
84, 56, 44
2.2. X-Ray crystallographic analysis The single crystal of the complex was obtained as described above and X-ray diffraction measurements performed on a Bruker SMART CCD diffractometer with a Mo Ka sealed tube at 223 K. The collected frames were integrated using the preliminary cell-orientation matrix. The software used was as follows: SMART [6] for collecting frames of data, indexing reflection, and determining lattice parameters; SAINT [6] for integrating intensity of reflections and scaling; SADABS [7] for correcting for absorption; and
Fig. 2. The formation mechanism of mass peaks.
180
H. Jiang, I. Novak / Journal of Molecular Structure 645 (2003) 177–183
Fig. 3. The crystal structure of the molecular complex: piperidine–CO2 (The hydrogen bonds are shown as the dashed lines).
Fig. 4. View of the crystal packing along the x-axis. Table 3 Atomic coordinates ( £ 104) and equivalent isotropic displacement ˚ 2 £ 103) for 2091. U(eq) is defined as one third of the parameters (A trace of the orthogonalized U ij tensor
N(1) O(1) O(2) C(1) C(2) C(3) C(4) C(5) C(6) N(2) C(7) C(8) C(9) C(10) C(11) O(1S)
x
y
z
U(eq)
4152(2) 3223(2) 6517(2) 5589(3) 5734(3) 3465(3) 2043(3) 1943(2) 4645(2) 6931(2) 5140(3) 5627(3) 7854(3) 9665(3) 9145(3) 9370(3)
7456(2) 8221(1) 7792(2) 6795(2) 7627(2) 7397(2) 8079(3) 7219(2) 7827(2) 8445(2) 7231(2) 7512(2) 7268(2) 8459(3) 8211(2) 5613(2)
7092(1) 8575(1) 8634(1) 6545(1) 5598(1) 4915(1) 5537(1) 6469(1) 8145(1) 10682(1) 11012(1) 12174(1) 12622(1) 12257(1) 11096(1) 8594(1)
32(1) 35(1) 41(1) 35(1) 38(1) 41(1) 43(1) 38(1) 27(1) 32(1) 40(1) 42(1) 50(1) 47(1) 39(1) 63(1)
SHELXTL [8] for determining space group and structure, least-squares-refining on F 2, and reporting graphics and structure. A brief summary of crystallographic data is given in Table 1.
3. Results and discussion 1. The major FT-IR peaks of the complex (Table 2) are assigned according to the following scheme: 3542.3 (cm21) (broad) Mixture of N – H, O – H. [It is broad because of the hydrogen bond between N, H and O] 1656.4 (cm21) OyC–O2. Because of the resonant structure, the two oxygen atoms are identical, the CO bond order is between double and single bond. That is why it is shifted towards lower frequencies when compared with carbonyl group in carboxylic acids
H. Jiang, I. Novak / Journal of Molecular Structure 645 (2003) 177–183
(, 1700 cm21). 1562.3 (cm21)dNHþ 2: 1232.8 (cm21) (N – CO2)-str is shifted to higher frequency (CN-str in piperidine: 1112.3 cm21) due to the increased double bond character of CN bond. 2. The EI-MS peaks of the complex are assigned according to the following scheme: Fig. 2 3. Structure of the molecular complex: Piperidine – CO2 – H2O: Figs. 3 and 4 (Table 3). According to the data in Table 4, the bond length of ˚ which is shorter than the N – C(O2) is 1.371 A standard single CN bond length. For example, ˚. standard CN bond length in piperidine is 1.45 A The result shows that the N – C bond in the complex has double bond character indicating a fairly strong Table 4 ˚ ] and angles [8] Bond lengths [A N(1)–C(6) N(1)–C(5) N(1)–C(1) O(1)–C(6) O(2)–C(6) C(1)–C(2) C(2)–C(3) C(3)–C(4) C(4)–C(5) N(2)–C(7) N(2)–C(11) C(7)–C(8) C(8)–C(9) C(9)–C(10) C(10)–C(11) C(6)–N(1) –C(5) C(6)–N(1) –C(1) C(5)–N(1) –C(1) N(1)–C(1) –C(2) C(3)–C(2)–C(1) C(2)–C(3)–C(4) C(5)–C(4)–C(3) N(1)–C(5) –C(4) O(2)–C(6) –O(1) O(2)–C(6) –N(1) O(1)–C(6) –N(1) C(7)–N(2) –C(11) N(2)–C(7) –C(8) C(9)–C(8)–C(7) C(8)–C(9)–C(10) C(11)–C(10)– C(9) N(2)–C(11) –C(10)
1.3708(18) 1.4532(18) 1.4561(18) 1.2657(16) 1.2623(17) 1.518(2) 1.517(2) 1.518(2) 1.508(2) 1.488(2) 1.4918(19) 1.514(2) 1.512(3) 1.514(3) 1.513(2) 121.86(12) 121.58(11) 114.44(12) 110.57(12) 111.67(13) 110.02(13) 111.26(14) 110.67(13) 123.45(12) 118.07(12) 118.47(12) 112.60(13) 110.07(13) 110.79(15) 111.28(14) 111.52(15) 110.41(13)
181
Table 5 ˚ 2 £ 103) for 2091. The Anisotropic displacement parameters (A anisotropic displacement factor exponent takes the form: 22p 2[h 2a *2U 11 þ · · · þ 2hka* b* U 12 ]
N(1) O(1) O(2) C(1) C(2) C(3) C(4) C(5) C(6) N(2) C(7) C(8) C(9) C(10) C(11) O(1S)
U 11
U 22
U 33
U 23
U 13
U 12
28(1) 36(1) 36(1) 36(1) 40(1) 49(1) 42(1) 29(1) 31(1) 35(1) 38(1) 51(1) 73(1) 42(1) 35(1) 45(1)
43(1) 38(1) 64(1) 45(1) 46(1) 49(1) 56(1) 53(1) 26(1) 35(1) 41(1) 37(1) 47(1) 54(1) 44(1) 47(1)
26(1) 34(1) 26(1) 27(1) 30(1) 25(1) 33(1) 31(1) 27(1) 25(1) 34(1) 36(1) 31(1) 40(1) 41(1) 104(1)
4(1) 2(1) 2(1) 4(1) 4(1) 7(1) 7(1) 4(1) 4(1) 4(1) 21(1) 7(1) 11(1) 4(1) 8(1) 22(1)
7(1) 15(1) 5(1) 9(1) 13(1) 7(1) 2(1) 5(1) 10(1) 6(1) 7(1) 16(1) 8(1) 25(1) 9(1) 24(1)
16(1) 13(1) 22(1) 19(1) 11(1) 15(1) 23(1) 13(1) 9(1) 13(1) 3(1) 6(1) 23(1) 20(1) 17(1) 17(1)
Table 6 Hydrogen coordinates ( £ 104) and isotropic displacement par˚ 2 £ 103) ameters (A
H(1A) H(1B) H(2A) H(2B) H(3A) H(3B) H(4A) H(4B) H(5A) H(5B) H(21) H(22) H(7A) H(7B) H(8A) H(8B) H(9A) H(9B) H(10A) H(10B) H(11A) H(11B) H(1SA) H(1SB)
x
y
z
U(eq)
5020(30) 7000(30) 6500(30) 6630(30) 2760(30) 3620(30) 2660(30) 540(40) 1230(30) 1140(30) 6670(30) 6860(30) 3710(40) 5090(30) 5650(30) 4460(40) 8140(30) 7850(40) 9880(30) 11120(40) 9140(30) 10210(30) 10650(40) 8460(40)
5490(20) 7070(20) 8920(20) 7090(20) 6120(20) 7990(30) 9350(30) 7820(30) 5920(20) 7690(20) 8200(30) 9590(20) 7480(30) 6060(30) 8720(30) 6680(30) 7510(30) 6000(30) 9740(30) 8190(30) 7030(20) 9090(20) 6380(40) 6170(30)
6312(13) 7015(14) 5821(13) 5214(14) 4642(14) 4322(17) 5755(16) 5115(18) 6246(13) 6900(16) 9967(18) 10885(14) 10709(17) 10733(16) 12434(15) 12369(17) 13376(19) 12415(19) 12551(16) 12474(17) 10814(14) 10870(15) 8623(19) 8619(17)
38(4) 41(4) 34(4) 42(4) 39(4) 49(5) 49(5) 60(6) 37(4) 51(5) 56(6) 39(4) 57(6) 56(5) 44(5) 57(5) 62(6) 77(7) 53(5) 60(6) 36(4) 45(5) 81(8) 55(6)
182
H. Jiang, I. Novak / Journal of Molecular Structure 645 (2003) 177–183
Table 7 Hydrogen bonds with H· · ·A , (A) þ 2.000 Angstroms and ,DHA . 1108 D–H
d(D –H)
d(H· · ·A)
,DHA
d(D· · ·A)
A
N2–H21 N2–H21 N2–H22 O1S–H1SA O1S–H1SB
0.934 0.934 0.933 0.833 0.824
1.769 2.610 1.827 1.934 2.017
173.43 128.84 173.82 172.69 172.56
2.689 3.277 2.756 2.813 2.837
O2 O1 O1 [2x þ 1, 2y þ 2, 2z þ 2] O1 [x þ 1, y, z ] O2
interaction between piperidine and carbon dioxide molecules. The double bond character is due to the interaction between the nitrogen lone pair and p-electron density in carbon dioxide. The oxygen atoms of carbon dioxide are linked via two hydrogen bonds to the water molecule and another piperidine molecule thus forming a Piperidine – CO2 – H2O – Piperidine cluster. Hydrogen bonding does not affect the CO bond lengths in the CO2 part of the cluster; CO ˚ and 1.2623 A ˚ . The C –O bond lengths are 1.2657 A bond character in the complex is between single and double bond, with slightly more double bond character. This conclusion is based on the comparison with the observed CO bond lengths in pure carbon ˚ ) and methanol (1.429 A ˚ ). The dioxide (1.162 A conclusion is also supported by FT-IR data; the frequency of carbonyl group in the complex being 1656.4 cm21 which is lower than that of carboxylic acids (, 1700 cm21). It is important to note that the CO2 unit is bent (123.458) unlike free CO2 which is linear. Also, the piperidine nitrogen bound to CO2 has planar instead of pyramidal coordination. These observations reveal the double bond character of C6 – N1 bond and the reduction in bond order of CO2 moiety. The geometry parameters of our complex are similar to the complex between 4-metylpiperidine and CO2 reported earlier [4]. For example, nitrogen– carbon bond lengths in this and previous work are ˚ , respectively. The /OCO angles 1.3708 and 1.373 A are also similar being 123.45 and 124.23, respectively. The principal structural difference between our complex and the complex reported by Freytag and Jones [4] is in hydrogen bonding network. Both complexes contain four classical hydrogen bonds in their crystal packing (Tables). However, in our complex the NH groups act as proton donors only to
CO2 moieties, while in 4-methylpiperidine complex, the NH groups donate protons to both water and CO2 moieties
4. Conclusion Hydrogen bond is essential for stabilizing molecular complexes such as amine –water, alcohol – water, but in most cases the molecular complexes exist only in the liquid or gas phases. The complex described in this work exists in the crystalline state for several hours in the air and can therefore be readily studied by single crystal X-ray diffraction. The results of X-ray diffraction measurements reveal the presence of water molecules in the crystal lattice. The complex is formed in the absence of silver ions, which are thus not a necessary catalyst for the complex formation as was suggested previously [4].
5. Supporting information available Tables of spectra and crystal structure data given in Tables 1 and 2.
Acknowledgements We thank the staff of the X-ray diffraction laboratory at the National University of Singapore for help and fruitful discussions. We also thank CPEC Centre at the National University of Singapore for financial assistance.
H. Jiang, I. Novak / Journal of Molecular Structure 645 (2003) 177–183
References [1] M. Rubiralta, E. Giralt, A. Diez, Piperidine, Chapter 5, Elsevier, Amsterdam, 1991. [2] G.V. Gusakoca, G.S. Denisov, A.L. Smolyanskii, Zh. Prikl. Spektrosk. 16 (1972) 503. [3] A. Gzella, U. Wrzeciono, Acta Crystallogr. Sect. C: Cryst. Struct. Commun. 31 (1995) 484. [4] M. Freytag, P.G. Jones, Acta Crystallogr. Sect. C: Cryst. Struct. Commun. 55 (1999) 1874.
183
[5] J. Schiewe, H. Matschiner, Phosphorus Sulfur and Silicon 91 (1994) 179. [6] SMART and SAINT Software Reference Manuals, version 4.0, Analytical Instrumention, Siemens Energy and Automation, Inc, Madison, WI, 1996. [7] G.M. Sheldrick, SADABS : Software for Empirical Absorption Correction, University of Go¨ttingen, Go¨ttingen, Germany, 1996. [8] SHELXTL Reference manual, version 5.03, Analytical Instrumentation, Siemens Energy and Automation, Inc, Madison, WI, 1996.
